Monday, September 10, 2012

VHL gene

(Image from: )

Von Hippel-Lindau (VHL) disease is a cancer syndrome that is hereditary and affects 1 in 35,000 people. VHL disease is characterized by central nervous system, retinal, kidney, and adrenal gland tumors. Conducting research on VHL disease can be a complicated process; the gene for VHL is expressed in organs throughout the body, not only in those organs affected by the disease.


Patients with VHL are heterozygotes and carry one wild-type and one inactivated VHL allele. VHL gene mutations can be difficult to identify, but more recent diagnostic techniques, such as direct DNA sequencing, Southern blotting, and fluorescence in situ hybridization (FISH), have improved VHL mutation detection. Twenty to 37% of patients with VHL have germline delections, while approximately 23 to 27% have frameshift or nonsense mutations and 30 to 38% have missense mutations. More than 150 germline mutations of the VHL gene have been identified and linked to VHL disease.


Genotype-phenotype correlations have also been identified in VHL disease research. Type 1 VHL families have an absence of adrenal gland tumors and frequently have VHL deletions or truncation mutations. Type 2 VHL families have adrenal gland tumors and frequently have VHL missense mutations. Scientists believe that the genotype-phenotype correlations illustrate the VHL gene product’s alteration by various VHL mutations.
VHL is also associated with an increased risk or renal, or kidney, cell carcinoma. Familial pheochromocytoma is another feature of the VHL disease, and has also been determined to be associated with germline inactivating mutations. Somatic VHL mutations and hypertmethylation appears in approximately 50% and 10-20% of sporadic clear-cell renal carcinomas, respectively. However, VHL germline mutations rarely appear in patients with sporadic clear-cell renal carcinomas.

VHL mRNA encodes a protein, pVHL, which travels between the nucleus and cytoplasm. Researchers have discovered that pVHL lacking cells overproduce hypoxia-inducible RNAS. Vascular endothelial growth factor (VEGF) mRNA is a hypoxia-inducible RNA and is often overproduced by tumors associated with VHL inactivation.

Many genes that are regulated by hypoxia, including VEGF, are controlled by hypoxia-inducible factor (HIF), a transcription factor. It has been shown that pVHL lacking cells do not degrade HIF subunits in the presence of oxygen. Scientists thereby determined that pVHL is a ubiquitin ligase that controls the degradation of HIF subunits in the presence of oxygen. The pVHL and HIF interaction is mediated by a conserved family of Egl-nine (EGLN) enzymes that cause a post-translational hydroxylation of HIF when oxygen is present.

Without pVHL present, HIF is stabilized and can induce gene expression; many of HIF’s target genes are critical to the human body and regulate functions such as angiogenesis, cell growth, and cell survival. Researchers also hypothesize that overexpression of HIF target genes, such as platelet derived growth factor (PDGF) and VEGF, are responsible for the hypervascularity of tumors.


Additional preliminary data suggest that HIF maintains a role in the formation of pVHL defective tumors. Thus, HIF is a viable target for therapeutic research. Testing inhibitors of HIF controlled growth factors could develop potential treatments for renal cell carcinomas and central nervous system tumors.

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Sunday, September 9, 2012

MLH1 gene

(Image from: Familial endometrial cancer)

Throughout the world, endometrial cancer is the fifth most commonly diagnosed cancer in women. Approximately 34,000 new cases of endometrial cancer appear each year and it is the most commonly diagnosed gynecological cancer. However, not much is known about the genetics of endometrial cancer. Researchers have shown that PTEN, TPS3 and KRAS2 gene mutations are the most common mutations in endometrial cancer, but approximately 20% of uterine endometrium cancer exhibit MSI, also known as microsatellite instability. MSI is the instability of sequence repeats throughout an entire genome and is correlated with defective repair of DNA mismatches. MSI is commonly found in patients’ tumors with hereditary non-polyposis colorectal cancer (HNPCC) and is found in higher frequency in endometrial cancer than any other common type of cancer.


Most patients with hereditary non-polyposis colorectal cancer have mutations in their MLH1 or MSH2 mismatch repair genes. However, mismatch repair gene mutations are not commonly found in sporadic cancer. Other researchers have demonstrated a correlation between MSI-positive cancer and a lack of detectable levels of MLH1 and/or MSH2 mismatch repair genes. Another group of scientists has demonstrated that MLH1 promoter methylation to be associated with MSI with primary cancer. In primary colon cancer, the methylation of the MLH1 promoter and the presence of MSI were correlated with the absence of MLH1 expression.


Sally Simpkins and other scientists at Washington University School of Medicine and Thomas Jefferson University have also found a strong correlation between MSI-positive endometrial cancer tumors and MLH1 methylation. In their research study, the MLH1 promoter was methylated in 77% of the MSI-positive endometrial tumors. Out of the 11 MSI-negative tumors, 10 tumors exhibited MLH1 unmethylation. The correlation between the MSI-positive endometrial tumors and methylation was found to be statistically significant. Researchers also found all of the MSI-negative tumors to express MLH1 and MSH2 and all of the MSI-positive tumors failed to express either MLH1 or MSH2. While methylation was correlated to the presence of MSI, 86% of MSI-positive tumors also exhibited abnormal MLH1 expression.


Simpkins and colleagues suggest that the correlation found between MSI, MLH1 expression, and MLH1 promoter methylation shows that MLH1 plays an important role in the development of endometrial tumors. However, this research is in direct contrast to some other studies. The scientists do agree, however, that epigenetic gene silencing is most likely responsible for the defective repair of DNA mismatches reported in most endometrial cancer. Another interesting conclusion from Simpkins’s research study is that inherited cases of endometrial cancer may be correlated with the lack of MLH1 methylation and MSH2 expression. Based on the results, it appears that MSH2 appears to affect inherited endometrial cancer and MLH1 defects account for sporadic endometrial cancers. However, more research needs to be conducted on the role of genetics in inherited endometrial cancer suspectibility.


The correlations found between MSI-positive tumors and MLH1 expression, MLH1 promoter methylation, and MSH2 expression provides a potential target for cancer therapy research. Scientists could possibly design a product that could affect the expression of MLH1 or MSH2, or unmethylate MLH1. The difference found in sporadic and hereditary endometrial cancer from the two mismatch repair genes, MLH1 and MSH2, is also critical to future research in cancer therapy. This suggests that tailored therapy would need to be implemented, and that one therapy might work for one patient with sporadic cancer, but not for another patient with hereditary endometrial cancer.

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Wednesday, August 29, 2012

LOX & LOXL2

(Image from: Hypoxia)


Hypoxia, which reduces oxygen tension, is important for maintaining homeostasis in the human body. While cellular responses to hypoxia are important for maintaining normal homeostasis, it has also been shown to promote tumor growth, as a stress factor and signal, and can lead to resistance of the tumor to therapies. Hypoxia-induced transcription factor (HIF) is the mechanism of response to low oxygen content in cells. HIF consists of α and β subunits, but the hydroxylation of HIFα subunits is what mainly controls the regulation of HIF, which thereby affects transcriptional activity and stability of proteins. There are two isoforms of HIFα, HIF-1α and HIF-2α. HIF is required for glycolysis activation in tumor cells and some research studies have shown that HIF promotes growth in tumors.


Based on experimental data, scientists believe that hypoxia causes dedifferentiation of tumor cells that can lead to increased cell invasion and tumor growth. This dedifferentiation can also lead to the epithelial to mesechymal cell transition (EMT), which is a complex dedifferentiation program. The down regulation of E-cadherin expression is a hallmark feature of EMT and invasive and metastatic cell phenotypes. Researchers have indicated that HIF may be capable of regulating E-cadherin, and as an indirect result, affecting EMT.

Additionally, the HIF target gene, lysl oxidase (LOX), has shown to be involved in the regulation of E-cadherin. HIF-1, which is required for hypoxia induced tumor growth, directly targets LOX. The lysl oxidase family is a collection of amine oxidases that catalyze crosslinking of collagen and elastin side chains. This crosslinking stabilizes proteins in the extracellular matrix. LOX and the LOX-like protein, LOXL2, are highly expressed in numerous types of human cancer.


Researchers at the University of Erlangen-Nuremberg and the University of Oxford have demonstrated that lysl oxidase activation is required for the repression of E-cadherin by hypoxia. The experiments also proved that hypoxia and HIF regulate both LOX and LOXL2. This was the first research study to show that HIF-1 directly targets LOXL2 and that LOXL2 can directly repress E-cadherin on its own. The lysl oxidases utilize both inhibition and overexpression mechanisms in order to repress E-cadherin. However, the detailed molecular mechanisms of E-cadherin repression are still unknown.


The scientists also found that LOX activated Src kinases and the focal adhesion kinases, which are two proteins that enable cell migration. A previous research study has shown that hypoxia activates LOX gene expression, but maintaining enzymatic activity requires continuing reoxygenation. This reoxygenation causes activation of both the Src kinase and the focal adhesion kinase. Other research groups have also found that LOX was overexpressed in a variety of cancerous tumors and LOXL2 promotes breast cancer cell migration. All of this research demonstrates the importance of hypoxia in cancerous tumor growth, and lysl oxidases are at least one signaling pathway that influences hypoxia.


While both LOX and LOXL2 have been found to have similar functions, their gene regulation may differ. However, both lysl oxidase proteins exhibit a significant impact on tumorigenesis and the progression of cancer. LOX and LOXL2 have the potential to be therapeutic research targets. Researchers could design an anti-tumor therapy that inhibits the lysl oxidases, which would also result in a reduction of hypoxia, a lack of E-cadherin repression, and possibly a reduction of tumor cell growth.

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Wednesday, August 22, 2012

How BRCA1 and BRCA2 Genes Relate To Breast and Ovarian Cancers

(Image form: The BRCA1 network)

Breast cancer research has led to the identification of two genes that, when functioning properly, regulate cellular growth and prevent the runaway metastasis of mammary tissue which leads to breast tumors and ultimately cancer. These genes are, with typical scientific economy, called BRCA1 and BRCA2. Because of the unusually repetitive nature of these genes, speculation that they function as "regulator" genes seems well-founded, and the link between abnormalities in these genes and breast cancer has already been established. The mystifying part is understanding why these genes malfunction, and if so, what can be done about it to prevent at-risk or genetically predisposed women from developing breast cancer.


One question researchers at Oxford pose is why these genes, which seem to be universally expressed, seem to be so intrinsically tied to breast and ovarian cancer? Cancer researchers believe that finding the answer to this question may lead to new, non-invasive therapies and perhaps even prophylactic treatments for women whose genetic code reveals a predisposition toward these types of cancers. If they can work out how the breakdown of these genes relates to specific types of cancer, the ramifications for diagnosis and treatment of other forms of cancer are potentially unlimited.

A second question is whether the "masking" of these gene expression in the human body may be a contributing factor in leading to cancer, or if genetic derangement or disarray might be the culprit. Until the mechanisms by which these genes govern cellular development are understood, this remains the more daunting question, as it is the basis for everything discussed in the first. Without a clear understanding of how these genes regulate cellular activity and what specific mutations or anomalies within them cause them to cease working properly, a solution to the myriad riddles cancer poses becomes impractical at best and science fiction at worst.

What is known about BRCA1 and BRCA2 is that the anomalous functions, also known as mutations, which appear to be the proximal cause of breast and ovarian cancer are hereditary. Both of these genes, when present in their mutated states in women who are susceptible to breast cancer as a result of heredity, give a lifetime risk of breast cancer approaching eighty percent. The difference is that in BRCA1-mutated women, the disease appears to have an earlier lifetime onset than in BRCA2-mutated women.


It should be borne in mind that males also carry these genes, and male breast cancer, while rarer than female breast cancer, is still certainly possible. In males carrying mutated BRCA1 genes, the risk of prostate cancer appears to be vastly elevated, whereas the BRCA2 gene can be at least theoretically linked to pancreatic, prostate or ovarian, stomach, and skin cancer in both men and women. By understanding the mechanics and mechanisms of these genes, how they express themselves in regulating cellular growth, and what mechanisms cause them to stop working, it is entirely possible that these two genes may help us unlock the secret of one of modern man's greatest threats to life and longevity.


In laboratory experiments, scientists have determined that BRCA1 plays a critical role in repairing damage to double-strand DNA at the sub-genomic level, beginning to interact with and repair the damaged portions of the DNA within minutes of the initial damage. This makes BRCA1 first on the scene by a matter of hours before other proteins and genes begin their own work. Scientists theorize this cellular healing mechanism works by altering the chromatin structure of the cellular nucleus to allow other repair proteins into the nucleotides.

While this exciting discovery is not a cure in itself, it does offer hope that we are finally making strides toward understanding the role that BRCA1 and BRCA2 play in hereditary cancer and perhaps finding new ways of treating various cancers. Since the roles of BRCA1 and BRCA2 in cellular healing are so evident, it stands to reason that these genes may lack an "off switch" in their mutated form. By studying and understanding the mechanics of these genes, it is possible we will be able to determine how to both predict and preempt the onslaught of numerous types of cancer. If so, this discovery offers hope we might finally eradicate cancer altogether.

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Monday, August 6, 2012

The relationship between p53 and Mdm2

The p53 and Mdm2 relationship is one of the most researched areas of signaling and has taught scientists many important signaling concepts. p53 is a specific transcription factor that functions as a tumor suppressor and causes damage to DNA. When there is no stress or DNA damage, p53 activity is not activated. When stress affects the body in some way, the p53 protein is activated due to phosphorylation. Depending on the stress or DNA damage, the p53 protein can activate a variety of genes that have the potential to cause inhibition of cell growth, DNA repair, apoptosis, or changes in cell differentiation.

(Image from: P53 Tumour Suppression)

The phosphorylation of p53 is quite complex and varies in the progression of the cell cycle of normal growing cells. This complexity affects its ability to associate with its regulatory proteins, such as Mdm2. The variety of p53 phosphorylation can be seen when one analyzes signaling in tumors. p53 phosphorylation is different in tumors and an increase in the degree of phosphorylation can be seen, as compared to normal cells and tissues. This increase in p53 phosphorylation indicates a failure of the p53 phosphatases to stop signaling.

Additionally, approximately 50% of all tumor types carry a p53 mutation. These mutations are typically seen in the DNA binding domain, which affects transcriptional activity and its overall cellular activities. The elevated expression of p53 leads to greater stability, which also induces the regulatory protein Mdm2. Mdm2 is a proto-oncogene that is amplified in approximately 7% of cancers and is frequently seen in soft tissue tumors. A proto-oncogene is a gene that becomes an oncogene, a gene that has the potential to cause cancer, through mutations or an increase in expression. The combination of a p53 mutation with overexpression of Mdm2 results in a worse prognosis for a patient, as compared to a patient with only the mutation or the overexpression.


Mdm2 protein has the activity of an ubiquitin ligase, which allows for the targeted degradation of its substrates, including p53. In addition to marking p53 for degradation, Mdm2 also binds to p53 and transports it out of the nucleus into the cytoplasm for degradation. The phosphorylation of p53 affects Mdm2’s ability to target p53 for degradation. When stress or DNA damage occurs in the body and the phosphorylation of p53 occurs on multiple sites, Mdm2 does not associate with p53. Researchers have recently discovered Mdm2 in human tumors and these scientists hypothesize that Mdm2 plays a role in tumorigenesis, with or without p53.


The relationship between p53 and Mdm2 has been shown to be vital to the normal functioning of the human cell, and also has other implications in cancer. Additionally, scientists have found that this relationship is an important part of a number of complex cellular signaling cascade pathways, including Ras, β-catenin, myc, Rb, and many more. The complexity of the p53-Mdm2 link illustrates the importance of this signaling pathway and indicates it is a viable therapeutic target. Researchers are studying this signaling relationship in order to design targeted drugs and therapies for cancer, as well as many other diseases.

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Thursday, August 2, 2012

Role of Chemokines in Cancer

Prostate cancer is a serious medical issue in men; this type of cancer is the second deadliest type of cancer and the most frequently diagnosed cancer in males. Scientists have suspected that chemokines are involved in prostate cancer progression, and are now being researched extensively. Chemokines are a type of cytokines that are involved in inflammation and stimulate chemotaxis, also known as movement, of leukocytes, a type of white blood cells.

There are 45 types of chemokines in the human body and they interact with a type of receptor known as a G protein coupled receptor. Many of these chemokines are redundant; multiple chemokines interact with one receptor or multiple receptors interact with one chemokine. After the chemokines interact with a receptor, the receptor induces a signaling cascade that can control a number of different responses in the body.

(Image from: Role of Chemokines in Cancer)

Researchers believe the chemokines play a role in prostate cancer because research has shown that the expression of chemokines changes when the prostate changes from normal to benign prostatic hyperplasia (BPH) and finally, to prostate cancer itself. Most of the research being conducted on chemokines has been on CXCL8, CXCL12, and CCL2. Recent studies have shown that CXCL8 levels are higher in patients with BPH than in patients with a normal prostate. Additionally, the CXCL8 RNA levels increased in patients with an increased severity of prostate tumors. In patients with recurring prostate cancer, CXCL8 has been found in benign areas near the cancerous tumors, but it has not been found in benign areas in patients without cancer recurrence.


The chemokine, CXCL12, and its receptor, CXCR4, have also exhibited correlations with prostate cancer. Both CXCL12 and CXCR4 were higher in patients’ tissue with prostate cancer compared to patients’ tissue with BPH. Also, patients with a higher number of CXCR4 receptors expressed in tumors demonstrated a lower survival expectation than patients with a lower number of receptors.


In addition to affecting the cancer itself, chemokines have an impact on the incidence of prostate cancer. African American men with prostate cancer have higher levels of CCL5, CCRT, and CXCR4 in their cancerous tumors, as compared to European American men with prostate cancer. Correspondingly, African American men have a higher incidence of prostate overall, as compared to other male racial populations. As physicians and many patients are aware of, age also plays a important factor in the development of prostate cancer. Older prostate stromal fibroblasts, common cells present in all patients’ prostates, exhibit higher levels of CXCLR, when compared to younger prostate fibroblasts.


While there still remains much research to be done, scientists now know that chemokines are involved somehow in the progression of . These chemokines and their receptors regulate the invasion and infiltration of cells, such leukocytes, and the growth of cancerous cells and blood vessels. However, the actual signals and regulation of the chemokines in prostate cancer are not well understood. Additionally, not all of the chemokines have been studied in prostate cancer, and many chemokines are most likely involved in the disease progression. Based on the existing research, it is clear that these chemokines exist as prostate cancer markers and may serve as potential therapeutic targets for cancer treatments.

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Friday, July 27, 2012

PTEN

There have been many studies conducted related to the PTEN gene. These studies found that this gene plays a crucial role in normal cell functioning. However, mutation or lacking PTEN can lead to serious health conditions in the human body. Stem cell loss, deregulation and some forms of cancer are found to be caused by major changes in the PTEN gene. The PTEN gene belongs to the protein tyrosine phosphatase gene family.

Other Names


PTEN has other names aside from phosphatase and tensin homolog. It is also called PTEN1, PTEN_HUMAN, PTEN-MMAC1 protein, BZS, TEP1, TEP1 phosphatase, MHAM, MMAC1 and mutated in multiple advanced cancers 1.

(Image from: PTEN)

PTEN Functions


Phosphatase and tensin homolog is a protein encoded by the PTEN gene in humans. PTEN mutation can lead to the development of many types of cancer. The PTEN gene provides the instructions for enzyme production in all body tissues. This enzyme is a tumor suppressor. It ensures that cells divide and grow at a normal rate. Additionally, it removes the phosphate groups that consist of one phosphorus and three oxygen atoms. As a result, it modifies lipids and other proteins. In this mechanism of action, the PTEN enzyme is a phosphatase.


The PTEN gene plays a key role in chemical pathways during cell division and destruction. A good functioning gene signals the cells to divide and self-destruct. Moreover, PTEN has also been found to control cell migration or movement, the formation of new blood vessels and cell adhesion to surrounding tissues. Many studies found that PTEN has something to do with stabilizing cell genetic formation. Altogether, these functions effectively stop the uncontrolled cell growth that can otherwise lead to tumor formation.

The Clinical Significance of PTEN


Cancer stems from abnormal cell growth. A functioning PTEN gene can stop this cell mutation. In some types of cancer, the PTEN gene is either lost or dysfunctional. This means cell proliferation is increased, and cell death is reduced. PTEN has often been found to be inactive in cases of prostate cancer, endometrial cancer and glioblastoma. In fact, about 70 percent of men with prostate cancer have at least one missing PTEN gene at the time of diagnosis. Meanwhile, reduced PTEN expression is found in both lung and breast cancer. The PTEN mutation may also cause an inherited predisposition to cancer.

There are also certain non-cancerous conditions found to be caused by PTEN mutations. This includes Cowden syndrome. People with this condition have over 70 mutations in their PTEN gene. These mutations include missing base pairs. This stimulates the PTEN gene to produce proteins that are not functioning properly or not working at all. These dysfunctional proteins will not be able to control cell division and instruct abnormal cells to self-destruct. This condition often leads to tumor growth in the thyroid, breast and uterus.

Non-cancerous tumors like hamartomas are also caused by PTEN gene mutations. These tumors cause disorders like Proteus-like syndrome and Bannayan-Riley-Ruvalcaba syndrome. These disorders are called PTEN hamartoma tumor syndromes.


Recent studies have also shown that PTEN has a key role in the developmental disorder autism. PTEN mutation and abnormal changes were found in 3 out of 18 people with autism. This includes classical autism called Rett Syndrome and other similar conditions. Additionally, PTEN mutation is also evident in people who have an unusually large head circumference. This is known as macrocephaly. However, these findings still need to be verified. It is yet unclear as to how PTEN mutation leads to the development of these disorders.

People with PTEN mutations should be given extra care. They should get genetic counseling and testing for PTEN mutations. This is particularly true for people with Cowden syndrome and other disorders with manifesting PTEN abnormalities. With this, there is a high possibility that they can prevent the development of these disorders.


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Thursday, July 12, 2012

Wilms Tumor Is Rare and Treatable

(Image from: Wilms tumor is a cancerous tumor of the kidney that occurs in children)


Wilms tumor is a kind of cancer of the kidney, also known as nephroblastoma, that mostly affects children. Some cases do appear in adults. Of all kidney cancers, Wilms tumors are the most common type occurring in children. Nonetheless, there are only about 500 cases diagnosed each year in the United States and the incidence is about one in one million for people under the age of 15.

About 75 percent of children who are diagnosed with Wilms tumor are otherwise healthy. Symptoms of the disease include a palpable mass in the abdomen that is often first detected during a doctor’s visit, or by a parent. Often, there is no pain and the child appears healthy in other ways. Pain in the abdomen can occur in some cases, along with blood in the urine, unexplained fever, high blood pressure and constipation.

In about 25 percent of cases, Wilms tumor is associated with a group of genetic disorders known as WAGR. These result from abnormalities to a specific gene, WT1. This gene is associated with WAGR and Denys-Drash syndrome and is located on chromosome 11p13. Denys-Drash syndrome is a very rare form of kidney dis-function separate from the symptoms of Wilms.


A second gene, WT2, is associated with the Beckwith-Wiedemann syndrome and is located on chromosome 11p15. Beckwith-Wiedemann sufferers have enlarged organs, tongue and head and are at greater risk of Wilms tumor kidney cancer.

Several other genes have been identified which appear connected to inherited Wilms tumor. Gene FWT1, which is located on chromosome 17q, and FWT2, located on chromosome 19q are also implicated in genetic cases of Wilms tumor.


Other conditions associated with WAGR syndrome include aniridia in which the iris in the eye is missing. Problems with the urinary tract that are present at birth, and varying degrees of mental retardation, are also associated with WAGR, as well as hemihypertrophy which results in enlargement of one side of the body over the other.

Most cases of WAGR and Wilms tumor are diagnosed in children under the age of five. Children over the age of eight are rarely diagnosed. It is a form of cancer that responds well to treatment and 90 percent of patients live for five years or more. Complete recovery often occurs. Wilms tumor is diagnosed using ultrasound followed by CT and MRI scans. Ninety five percent of the time it only affects one kidney and remains contained.


Wilms tumor is first treated by assessing the stage of the tumor. The exact course of treatment will depend on the stage of the tumor’s development. Removing the kidney, if only one is affected, is often part of the treatment. If both kidneys are affected, the diseased tissue is removed leaving the healthy part of the kidney intact.

Chemotherapy is often prescribed as a follow up treatment and sometimes radiation therapy is also used. If the tumor is detected and treated in its early stages, Wilms tumor has a high rate of survival and recovery. Prognosis is worse if the cancer has spread to lungs, brain or other organs.

People of African descent are at a somewhat higher risk of acquiring Wilms tumor than other ethnic groups. It is also somewhat more common in siblings and twins, strengthening the possibility of a genetic basis. However, a complete understanding of the heritability of Wilms tumors is still ongoing. Clinical trials involving new drugs for treatment of Wilms tumors are underway and the genetic factors that contribute to the disease continue to be unraveled.

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Wednesday, July 11, 2012

p53

p53 is a 44 kilodalton protein encoded by the TP53 gene. It is a tumor suppressor with crucial roles in both the induction of apoptosis and the arrest of cell cycle. Consequently, at least half of all proliferating tumor cells contain one or two mutated copies of TP53. While the protein has a mass of 44 kilodaltons, the presence of numerous proline residues impairs linearization of the protein during SDS-PAGE, so p53 migrates more slowly than expected and has an apparent mass of 53 kilodaltons in western blots. Isoforms of p53 are found in nearly all mammalian tissues.


The expression and localization of p53 within a cell can be visualized through immunofluorescence using a polyclonal or site-specific monoclonal p53 antibody. While p53 is primarily localized in the nucleus when active, it is transported into the cytoplasm by the binding protein, MDM2, and may be faintly visible there when inactive. In some forms of cancer, including breast cancers and neuroblastomas, p53 aggregates in small cytoplasmic puncta, where it is "sequestered" from both degradation and its normal regulatory role within the nucleus.


When it is allowed to aggregate within the nucleus, p53 acts as a potent mediator of cell cycle, apoptosis, and DNA repair. A central DNA-binding domain is positively-charged with a zinc moiety and several arginine residues. This allows for the upregulation of repair genes and the suppresson of oncogenes such as LMO3. Over 200 genes are transcriptionally regulated by p53, and numerous nongenomic sites contain the p53 consensus sequence. During times of cellular stress, p53 arrests the cell cycle in the G1 phase until the cell's DNA has been repaired or the source of stress has been relieved. p53 halts the cell cycle by interacting with members of the E2F family of proteins and preventing progression through G1-S phase "checkpoints". If p53 is not inactivated, the cell becomes functionally senescent.

(Image from: The p53 response)


The role of p53 in apoptotic signaling primarily involves interaction with members of the ASPP protein family. The introduction of DNA damage or oncogene upregulation to a cell results in ASPP1 and ASPP2 expression. In humans the C-terminals of these proteins bind to p53. This activates the mitochondrial apoptotic pathway by activating PUMA (p53 upregulated modulator of apoptosis) and inhibiting activity of the antiapoptotic Bcl-2 protein. Conversely, expression of the iASPP (inhibitory ASPP) competes with and prevents ASPP1 and ASPP2 binding to p53 and is therefore antiapoptotic.


Perhaps the most well-researched aspect of p53 activity is its role as a tumor suppressor. This suppression is largely through p53's ability to halt cell division and induce apoptosis in cells (as in the case of E2F and ASPP proteins, respectively). p53 also interacts with YB1 (Y-box binding protein 1), which facilitates proliferation and inhibits apoptosis by downregulating p53 expression. Mutated forms of p53, including the forms seen in many cancer types, alter the interaction with YB1, causing YB1 to build up in the nucleus and inhibit p53 activity indefinitely, leading to proliferation and tumorigenesis. Thus, p53 is a potent tumor suppressor and its inactivation facilitates the development of tumors. Indeed, the anti-tumor effects of p53 are essential for long-term survival. The inactivation of a single parental copy of TP53 causes Li-Fraumeni syndrome, an autosomal dominant disorder characterized by the early onset of multiple forms of malignant cancer, especially sarcomas.


p53 expression is primarily regulated through the activity of the protein MDM2, which binds to the trans-activation domain at the N-terminal of the p53 protein. In normal cells, p53 has a half-life of under thirty minutes due to MDM2 binding, which exports p53 from the nucleus and marks it for ubiquitination and eventual proteolysis. However, during times of cell stress the MDM2 mechanism becomes dysregulated, leading to an increase in p53 protein levels. For instance, DNA damage activates DNA-damage kinases that lead to both auto-deregulation of MDM2 and the phosphorylation of p53, which disrupts MDM2 binding.


In cancer cells, p53 is often suppressed through the activation of cyclooxygenase-2 (COX-2), which inhibits apoptosis in these cells by phosphorylating MDM2 at ser166 to stimulate its degration of p53. COX inhibitors can enhance chemotherapy-induced apoptosis by downregulating MDM2. This results in slower p53 degradation and a gradual buildup of nuclear p53 levels, which enhances both the cell cycle arrest and apoptotic signaling mediated by the protein. Similarly, MDM2 antagonists such as Nutlin-3a increase the effectiveness of chemotherapeutic drugs by disinhibiting endogenous p53 activity.


Many types of cellular stress alter the localization of p53. This includes the administration of ionizing radiation, oxidative stress, hypoxia, and oncogene expression. These forms of stress cause a rapid upregulation and transnucleation of the p53 protein that can be visualized using a p53 antibody. Similarly, the myriad interactions of p53 with its DNA binding sites have been identified through chromatin immunoprecipitation using p53 antibodies on the homogenates of lightly-fixed tissue. Recent research indicates that p53 contains multiple isoforms created from splice variants of the TP53 gene that have varying affinities for MDM2 and can be identified through western blotting (in instances where the splice has a different protein length) or using a monoclonal antibody (where the epitope is absent in one of the isoforms). The presence of such isoforms may be indicative of certain forms of cancer.

References:

Braithwaite AW, Del Sal G, Lu X. Some p53-binding proteins that can function as arbiters of life and death. Cell Death Differ. 2006 Jun;13(6):984-93. Review.

Camus S, Ménendez S, Fernandes K, Kua N, Liu G, Xirodimas DP, Lane DP, Bourdon JC. The p53 isoforms are differentially modified by Mdm2. Cell Cycle. 2012 Apr 15;11(8):1646-55.

Lasham A, Moloney S, Hale T, Homer C, Zhang YF, Murison JG, Braithwaite AW, Watson J. The Y-box-binding protein, YB1, is a potential negative regulator of the p53 tumor suppressor. J Biol Chem. 2003 Sep 12;278(37):35516-23.

Lau L, Hansford LM, Cheng LS, Hang M, Baruchel S, Kaplan DR, Irwin MS. Cyclooxygenase inhibitors modulate the p53/HDM2 pathway and enhance chemotherapy-induced apoptosis in neuroblastoma. Oncogene. 2007 Mar 22;26(13):1920-31.

Menendez D, Inga A, Resnick MA. Potentiating the p53 network. Discov Med. 2010 Jul;10(50):94-100. Review.

Ohnstad HO, Paulsen EB, Noordhuis P, Berg M, Lothe RA, Vassilev LT, Myklebost O. MDM2 antagonist Nutlin-3a potentiates antitumour activity of cytotoxic drugs in sarcoma cell lines. BMC Cancer. 2011 May 30;11:211:1-11

Ostermeyer AG, Runko E, Winkfield B, Ahn B, Moll UM. Cytoplasmically sequestered wild-type p53 protein in neuroblastoma is relocated to the nucleus by a C-terminal peptide. Proc Natl Acad Sci U S A. 1996 Dec 24;93(26):15190-4.

Stommel JM, Wahl GM. Accelerated MDM2 auto-degradation induced by DNA-damage kinases is required for p53 activation. EMBO J. 2004 Apr 7;23(7):1547-56.

Varley JM. Germline TP53 mutations and Li-Fraumeni syndrome. Hum Mutat. 2003 Mar;21(3):313-20. Review.

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Wednesday, July 4, 2012

Von Hippel-Lindau (VHL) Disease

Introduction


Von Hippel-Lindau (VHL) disease is characterized by tumors or growths in multiple body systems. Typically, these growths or lesions begin as blood vessel hypertrophy in the central nervous system (CNS) and eyes. These VHL lesions can cause symptoms such as headaches, nausea or balance issues. The VHL disease can progress into other body systems such as the renal system where cysts form as a potential precursor to renal cancer. VHL also affects the body's adrenal glands and pancreas, causing cysts to form within the gland that prevent proper functioning. Approximately one in 36,000 individuals is affected by VHL, making it a relatively rare disease.

Symptoms and Diagnosis


Diagnosis of VHL often occurs only after the patient begins to exhibit symptoms, which can be latent and present until well into adulthood. Symptoms include dizziness, ataxia, and tinnitus, hearing loss, vision disturbances and hypertension. Because these symptoms can also be attributed to other causes, the patient's course of treatment can be compromised. Treatment and excision of the VHL tumors should begin as expediently as possible. Diagnosis can be definitively made upon the revelation of one's genotype, for those with VHL often have a genetic mutation.

VHL and Genetics


VHL disease follows an autosomal dominant inheritance pattern where the VHL genetic mutation must be present on only one set of chromosomes from either parent. The VHL gene resides on chromosome 3's short arm. In individuals who do not have a VHL mutation, the VHL gene codes for a specific messenger RNA (mRNA) sequence that creates Von Hippel-Lindau proteins (pVHL) that the cell then uses for a variety of cellular functions, including tumor suppression. A mutation in the VHL gene changes the individual's genetic blueprint to mutate mRNA so that pVHL is suppressed or defective. The manner by which the suppression of pVHL affects the body systems allows the disease to be made manifest.

Pathophysiology of VHL Disease


While it might seem that the suppression of pVHL would not seriously affect the mechanism of action within the cell, pVHL is a potent protein that regulates a cell's activity in numerous ways. First, the suppression of pVHL cells' cytoplasm causes marked changes in the cells' recycling program. Essentially, pVHL pairs with other proteins and begins to ubiquitinate other materials, which marks them to be deconstructed. The marker indicates which materials are no longer crucial to the cell's actions, thereby preventing the cell from engaging in unrestricted growth.

(Image from: HIF Biology)


Defective pVHL allows the cell to continue its growth without restraint


A major cytoplasmic constituent that is targeted for destruction includes a factor that should degrade in the presence of oxygen. These factors, hypoxia-inducible factors 1 (HIF1) and hypoxia-inducible factors 2 (HIF2), play an enormous role in how the cell chooses to differentiate its growth. In low-oxygen environments, HIF encourages the cell to create more blood vessels in order to relieve the cell or tissue of hypoxia. If the HIF does not become targets for recycling by the pVHL, then the HIF continues to signal to the cell that it needs to create blood vessels even if the cell is properly oxygenated. These blood vessels form the tumors that are the foundation of the VHL disease state.

Genetic testing for VHL can greatly improve an affected individual's prognosis. Because VHL can be present for years before symptoms become tiresome enough to go to the physician, genetic testing and subsequent counseling can prove to be life-saving. Proper medical imaging and surgical options can not only reduce the severity of bothersome symptoms, they can also slow the progression of VHL into deadly carcinomas.


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Monday, July 2, 2012

Tumor Suppressors

(Image from: Tumor Suppressor Genes)


Our understanding of cancer and its triggers is still in its infancy. However, recent research offers new insights to better understand what causes cancer cells to proliferate. Of particular interest is tumor suppressor genes that help stop the uncontrolled cell division and growth that permit cancer-causing mutations. Moreover, these important cells also promote cell death, a necessary component in the life cycle of healthy cells. Of critical importance, these tumor suppressor genes also play a role in DNA repair, preventing the accumulation of mutations that may lead to the development of cancer. Considering the importance of these genes in preventing cancer, any disturbance in the functioning of these tumor suppressor genes can cause irreparable damage that might ultimately lead to cancer.

The Two-Hit Hypothesis


All genes, including cancer suppressor genes, are subjected to a number of mutations. Fortunately, in the case of cancer suppressor genes, the mutations that interfere with normal functioning are typically recessive. That is, for the mutation to lead to cancer, both tumor suppressor genes in a given cell must have the same mutation. In the early 1970s, Alfred Knudson coined the term “two-hit hypothesis” to describe this phenomenon.

Case Study: Retinoblastoma

Knudson, a geneticist, discovered this important concept while studying a rare type of cancer that strikes children. Known as retinoblastoma (Rb ), this cancer affects the retina, the part of the eye that detects light. Normally, retinoblasts, or immature cells in the retina, have stopped growing and dividing by the time an embryo has developed. At this point, retinoblasts typically become differentiated, resulting in distinct photoreceptor and nerve cells within the retina. In children with retinoblastoma, however, differentiation does not occur. Rather, the retinoblasts continue to divide, leading to the development of retinal tumors. Detection and treatment is essential because, as with other cancers, untreated retinoblastoma can metastasize and affect other parts of the body.

In order to better understand this ailment, Knudson conducted a 25-year study starting in the mid-1940s. In particular, Knudson wished to understand how parents diagnosed with retinoblastoma could have children free of the malady, but whose own children were later diagnosed with retinoblastoma. The geneticist took a closer look at two groups of patients. The first group was made up of 23 patients with bilateral hereditary retinoblastoma. In bilateral hereditary retinoblastoma, cancer is detected in both eyes there is a history of retinoblastoma in the family. The second group consisted of 25 patients with unilateral nonhereditary retinoblastoma.

Age at diagnosis became particularly important at this point because of the time necessary for mutations to occur and accumulate. If the cancer were the result of mutations in a single gene, then both copies would have to mutate at the same rate for the cancer to occur. Thus, patients who inherited one mutated gene allele would only need to accumulate one mutation on the other gene allele for the cancer to occur. Those who did not inherit the mutation would need to accumulate a mutation on both alleles, a process that would take considerably more time. He noted that for his patients, bilateral hereditary retinoblastoma was diagnosed earlier than the unilateral nonhereditary variety, supporting his hypothesis that two mutations were required. Originally dubbed the two-mutation hypothesis, this phenomenon is now known as the two-hit hypothesis.

Tumor Suppressor Gene Inactivation


The two-hit hypothesis is essential to understanding the process by which tumor suppressor genes become inactive or non-functioning. During a process known as loss of heterozygosity, or dissimilarity, the second copy of a tumor suppressor gene becomes inactive when the gene is “hit” again. That is, the functioning copy undergoes a mutation, making the pair homozygous, or similar, in terms of the mutated gene. With this double mutation, the tumor suppressor gene becomes unable to fulfill its normal function.

Advances in Understanding Tumor Suppressor Genes


Once scientists were able to map the human genome, they were able to identify the particular gene (Rb1) responsible for suppressing retinoblastoma tumor growth. Researchers then used mice to examine how the Rb1 gene works and what happens when two “hits” affect this gene. They have since identified a number of other tumor suppressor genes. Future research will focus on using this growing knowledge base to better diagnose and treat a variety of cancers.


Other tumor suppressor genes: p53, VHL, WT1, BRCA1, MLH1, PTEN

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Wednesday, June 27, 2012

Lynch Syndrome

Introduction


Lynch Syndrome is a genetic disease characterized by an increased risk of cancer of the lower digestive tract including the colon and rectum. Individuals who have Lynch syndrome are also predisposed to certain types of other cancers such as stomach, liver, pancreas, small intestine, urinary tract and brain. Women who have Lynch syndrome are at an increased risk of the ovaries and endometrium. Often referred to as hereditary nonpolyposis colorectal cancer (HNPCC), experts estimate that Lynch syndrome might be responsible for between two and seven percent of all colorectal cancers.

(Image from: Colon)


Lynch Syndrome often does not present with any clear symptoms until the individual is diagnosed with colorectal cancer at a young age (younger than 50 years old). Some individuals have a strong familial history of early onset colorectal cancers and might be directed by their primary care providers to a genetic counselor for confirmation of Lynch Syndrome. While literature previously indicated that those with Lynch Syndrome do not have colorectal polyps, more recent investigations indicate that not only do individuals with Lynch Syndrome have polyps; their polyps are more likely to develop into cancerous growths.

Knowing one's status regarding Lynch Syndrome and acting accordingly remains the leading method of prevention of colorectal cancer caused by heredity. Having Lynch Syndrome is not a confirmative diagnosis of cancer; it merely predisposes one to certain cancers, and early detection and removal of polyps is the best means of preventing a devastating cancer diagnosis.

Lynch Syndrome's Genetic Basis


Lynch Syndrome is a genetic condition that follows an autosomal dominant inheritance pattern, which means that only one of the affected individual's parents must pass the mutated allele on to the individual. While there are several potential gene mutations that indicate that the individual might have Lynch Syndrome, all the markers are mutations of the body's mismatch repair (MMR) genes. MMR genes protect the body from making mistakes in the DNA replication sequence.

In Lynch Syndrome, affected individuals have mutated MMR genes. The following four genes can be affected in individuals with Lynch Syndrome: MLH1, MSH2, MSH6 and PMS2. Genetic counseling can identify the MMR gene mutations, and while this will not prevent one from getting Lynch Syndrome, it can lead to early detection and life-saving excision of polyps or tumors.

The Role of MLH1


In particular, the expression of the MLH1 gene affects one's chances of developing cancers associated with Lynch Syndrome because of the unique role MLH1 plays in the process of DNA replication at the cellular level. When DNA replicates, the process ideally creates identical copies of itself. Sometimes, however, the DNA polymerase makes mistakes in the process that results in a mutated gene or genes in the DNA strand. DNA polymerase is responsible for arranging the base pairs at the replication fork of a DNA molecule. Typically these mistakes involve arranging bases in non-complementary pairings.

When DNA polymerase makes mistakes, the body's MLH1 genes are responsible for the repair of such mistakes. MLH1 in combination with other genes, codes for certain protein complexes that control the body's response to the mismatched base pairings. MLH1, therefore, is responsible for recognizing the mistakes that have been made in the replicated strand. This mismatch can be corrected by excising the incorrect part and replacing it with the correct part. MMR genes perform this task quickly, so that the mutated genes do not become expressed in the replicated cells.

When MLH1 becomes mutated, as can be seen in Lynch Syndrome, the body cannot recognize nor repair the damage to the mismatched base pairings quickly enough before cellular replication occurs. The cells with mutated DNA continue to grow and replicate themselves, mutations intact. This can lead to the proliferation of cells that contain irreversibly mutated DNA, which can lead to malignant tumors in the affected areas of the body.

Fortunately, genetic screenings can test individuals for the presence of the MMR gene mutations. Knowing that one has the genetic mutation, and knowing more specifically which gene is mutated, can greatly improve the prognosis for individuals with Lynch Syndrome. Armed with the knowledge that Lynch Syndrome is hereditary can also improve care provided to any offspring or family members who might also have Lynch Syndrome.

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Sunday, June 24, 2012

Hereditary Breast and Ovarian Cancer

Breast and ovarian cancers are among the most common cancers for women. Indeed, more than 12% of women will be affected by breast cancer during their lifespan. Breast cancer can be an invasive cancer; ovarian cancer has one of the highest mortality rates. Both breast cancer and ovarian cancer can occur more frequently in individuals who have an inherited genetic mutation. If an individual has a mutation in his or her BRCA1 or BRCA2 gene, her chance of getting breast cancer increases to 60%. This astonishing five-fold increase is due to the way the mutation changes the body’s responses.


(Image from: The roles of BRCA1 and BRCA2 in DNA repair )



Mutated BRCA1 and BRCA2 do not only affect the breast, nor does BRCA1 or BRCA2 only affect women. Men who have BRCA2 are considerably more likely to develop male breast cancer, pancreatic cancer and prostate cancer at an early age. Indeed, families who have the BRCA1 or BRCA2 mutation have a much greater risk of many types of cancer including uterine, cervical, pancreatic, testicular and other cancers.

Breast and ovarian cancers devastate families and are the subjects of worldwide research studies to determine the link between the BRCA1/BRCA2 mutation and the incidence of early-onset cancers. Studies have found that breast and ovarian cancer as a result of BRCA1 or BRCA2 mutations occur most common in families who have a history of many incidences of breast and ovarian cancer, or in families who have a history of cancer that appears in more than just one site in the body. BRCA1 and BRCA2 mutations also occur more frequently in families from a Central/ Eastern European Jewish background.

With treatment, breast and ovarian cancers can be treatable. While tests to determine whether or not one has the BRCA1/BRCA2 gene mutation are costly, the information they yield can be invaluable to the individual. With proper preventative screenings and tests, one can help identify potentially deadly cancers early enough for intervention.

Function of the BRCA1 Gene


Located on chromosome 17, BRCA1 serves a vital purpose in the body: it suppresses tumor growth by providing the code for a protein that repairs DNA. DNA is arranged in a tight double-helix formation that uses supportive bridges to maintain its shape. When these bridges are removed as happens during replication, the DNA strand can become damaged and requires repair. Other means by which DNA may become damaged includes exposures to environmental toxins and radiation. Damaged DNA causes cells to improperly use their safeguards, and as a result, the cellular differentiation can proliferate out of control, creating tumors.

Healthy BRCA1 works to curb this wild growth because it mends the damage in DNA double helices. In the nucleus of the cell, BRCA1 works with other proteins such as those created by the genes RAD51 and BARD1 to determine the types of breaks and then repair them. Damaged DNA sometimes becomes damaged when DNA is damaged, it responds with the potential for hypertrophy in cells and tissues. This uncontrolled growth creates tumors, and in some cases malignancies. BRCA1’s protein, therefore, protects the integrity of the cell’s blueprint by repairing damage to the structure of the DNA. When BRCA1 becomes mutated, DNA can no longer be repaired, resulting in cancerous growths.
When an individual has a mutated BRCA1, its structural differences create limitations in the gene’s functional ability to create the protein that helps to repair the DNA damage. This leaves the cell prone to dysplasia and hyperplasia, which can eventually lead to tumor growth and a diagnosis of cancer in the affected area of the body. With BRCA1, the tumors are typically associated with the breasts and ovaries.

Mutations in Other Genes


In addition to BRCA1 and BRCA2, mutations in other genes may play a part in inherited predispositions to breast and ovarian cancers. These genes include CHD1, TP53, PTEN, STK11 and others. While these genes might also play an important role in the tendency toward breast cancer, the vast majority of hereditary breast cancers can be traced to a mutation in BRCA1 or BRCA2. These deadly mutations can be identified in 10 to 15 percent of all diagnoses of ovarian cancer and in 5 to 10 percent of all diagnoses of breast cancer. Because of the invasive and potentially fatal effects of mutations in BRCA1 and BRCA2, scientists center their studies on BRCA1 and BRCA2.


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Wednesday, June 20, 2012

Hypoxia


(Image from: Hypoxia)



Hypoxia is a pathological condition in which either the whole body (generalized hypoxia) or a region of the body (tissue hypoxia ) is deprived of oxygen. Tissue hypoxia commonly occurs in cancerous tumors when rapid growth causes the tumor to outgrow its blood supply resulting in regions with significantly lower oxygen concentrations. It is a negative prognostic and predictive factor, as it contributes to chemoresistance, radioresistance, angiogenesis, vasculogenesis, invasiveness, metastasis, altered metabolism and genomic instability.


The effects of tissue hypoxia are mediated through the HIF (hypoxia inducible factor) signaling cascade. Under normoxic conditions, the alpha subunits of HIF are hydroxylated by HIF prolyl-hydroxylases, which leads to ubiquitination by the VHL E3 ubiquitin ligase and subsequent degradation of HIF by proteasomes. Under hypoxic conditions, a buildup of succinate combined with a lack of oxygen results in the inhibition of HIF prolyl-hydroxylase. HIF subsequently accumulates and translocates to the nucleus where it dimerizes with the beta isoform of HIF. This dimer interacts with cofactors such as ARNT, CBP/p300 and the Pol II complex to activate the HRE (hypoxic response element), which initiates the transcription of various genes including VEGFA, Glut1 and CA9.


Hypoxia in tumors is closely associated with tumor aggressiveness and resistance to radio- and chemotherapeutic treatment. Therefore, reliable markers for hypoxia represent both valuable diagnostic markers and potential targets for investigation. CAIX (carbonic anhydrase IX) has recently been identified as a hypoxia and tumor biomarker. CAIX is a transmembrane protein that belongs to the 15 member carbonic anhydrase enzyme family and is involved in regulating cellular pH. CAIX expression is restricted to very few normal tissues, in particular the membranes of gastric mucosal epithelial cells. Under hypoxic conditions, the transcription factor HIF-1 transactivates the CA9 gene, resulting in expression of the CAIX protein in the hypoxic cells. Due to its stability, cell surface transmembrane localization and rapid increase in protein level in response to HIF-1 alpha accumulation, CAIX is an excellent biomarker of hypoxic regions in many solid tumors. CAIX has been considered one of the best cellular biomarkers of hypoxia, and recent studies have suggested that CAIX expression may be a valuable prognostic indicator for overall survival.


Tumor hypoxia has recently been proposed as a target for cancer therapy. The strategies for this type of therapy include developing drugs that are activated under hypoxic conditions and taking advantage of the selective induction of HIF under hypoxic conditions to develop gene therapies. Treatments that can exploit the unique features of hypoxic tumors may one day change this negative prognostic indicator into one that is advantageous for targeted treatments.


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Monday, June 18, 2012

Hepatic Adenoma

Hepatic adenoma, sometimes referred to as heptatocellular adenoma, is non-cancerous liver tumors. Hepatic adenoma occurs most frequently in young women and is related to the prolonged use of oral contraceptives. While the notion of tumors or lesions in the liver seems to be cause for immediate alarm, doctors discover many of these tumors during ultrasound scans for other reasons. Emergency rooms also discover the presence of hepatic adenoma in individuals who present at the emergency room for severe abdominal pain and internal bleeding from the ruptured adenoma.

Hepatic adenoma that does not cause physical symptoms, referred to as asymptomatic hepatic adenoma, require little more than watchful waiting and diagnostic testing such as imaging studies to rule out the progression of the adenoma. These imaging studies will monitor any growth or changes of the adenoma to rule out its progression. If the hepatic adenoma has ruptured and is causing liver bleeding, then a surgeon might excise the tumor from the liver to prevent further problems.

While a hepatic adenoma does not cause disease, physicians recognize that there is some risk of benign adenoma undergoing changes that might result in a malignancy in the liver. These malignancies, called hepatocellular carcinoma (HCC), are a deadly form of cancer that can necessitate extreme medical measures to prevent the spread of disease. Not all hepatic adenoma will undergo this transformation, however, and physicians feel it would be inappropriate to treat all adenoma patients with an aggressive hand. To identify which hepatic adenoma may transform into HCC, doctors now use an innovative genetic grading system to determine risk.


(Image from: Pathogenesis of human hepatocellular carcinoma)


Genetic Basis of Hepatic Adenoma


Doctors use genetic testing to determine the risk of hepatic adenoma transforming into HCC in one of two ways. First, the adenoma is genetically tested to see if it cells’ nuclei have a certain protein in them that causes other types of liver cancers: HCC and hepatoblastoma. The beta-catenin gene, also called CTNNB1, makes the protein called beta-catenin, which is an important part of normal body function. Inside some hepatic adenoma, however, beta-catenin can move into the nucleus of the cells and cause excessive DNA replication to occur leading to abnormal growth and potentially HCC. The presence of beta-catenin in the hepatic adenoma’s nucleus indicates that it may be shifting into a malignancy.

The second approach to genetic testing as a means to determine whether or not hepatic adenoma is likely to transform is to test the entire individual’s genome for any mutated genes. Specifically, individuals whose genome contains a mutation at the hepatocyte nuclear factor-1a gene (HNF1a) and/or the TCF1 gene can sometimes have transformation of the benign adenoma into carcinoma. These genes are responsible for how liver cells divide. If they are mutated, liver cancer can result. Up to 50% of individuals with a mutated TCF1 gene have hepatic adenoma that will undergo transformation into hepatocellular carcinoma.


Using Genetic Screening to Diagnose


With the advent of new genetic testing for individuals with hepatic adenoma, doctors are able to more readily predict if a patient’s benign adenoma is likely to develop into HCC. This allows the physician to tailor his or her approach with delicacy and only pursue aggressive treatment for those individuals likely to have their adenoma progress into HCC. Genetic testing for individuals with hepatic adenoma is a remarkable new approach to identification and treatment and has the potential to save many lives. As genetic testing becomes more commonplace, barriers to providing this testing will be reduced and more physicians will likely use this technology to help their patients better understand their course of disease.


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Wednesday, June 13, 2012

Smooth Muscle

● What is smooth muscle?

Smooth muscle is muscle that is involuntary and that is not striated. There are two subgroups of smooth muscle: single unit, and multi unit. Single unit smooth muscle, which is also known as unitary smooth muscle, is innervated at the single cell level by the autonomic nervous system. The single cells are located within bundles or sheets of muscle tissue.

The action potential from the nervous system moves to accompanying cells through gap junctions in a way that leads to the contraction of the entire sheet or bundle. This whole sheet contraction is known as a syncytium, which is a cytoplasm mass with many nuclei that does not have separation into individual cells.

Smooth muscle tissues in the multi unit groupings also have nerve penetrations at the individual cell level. As a result, gradual responses can occur, including those responsible for fine motor control, similar to the way motor units control fine movements through skeletal muscles.

Smooth muscle is located in a variety of regions within the human body, including inside the blood vessel walls, where it is known as vascular smooth muscle. It is also found in the tunica media part of small and large arteries, veins, and arterioles.

Smooth muscle is also located in the urinary bladder, the lymphatic vessels, the uterus, where it is known as uterine smooth muscle, the respiratory and gastrointestinal tracts, the female and male reproductive tracts, the iris of the eye, and the ciliary muscle.

Smooth muscle cells are essentially structured and work the same way regardless of which organs they inhabit, but the stimuli required to trigger them vary considerably, which is why they can perform unique actions within the body at different times. The kidney glomeruli also host cells that resemble smooth muscle cells; these are known as mesangial cells.



(Image from: Actin myosin filaments)


● What is the molecular structure of smooth muscle tissue?

Much of what makes up smooth muscle cell cytoplasm is composed of actin and myosin molecules. Together, actin and myosin can contract. There are several tensile structures linked in a chain that allow the full smooth muscle tissue to contract with myosin and actin.


● An introduction to smooth muscle myosin

Myosin is predominantly composed of class ii when found in smooth muscle. Class ii myosin involves a pair of heavy chains that make up the head and tail areas. The heavy chains include N terminal head domains and C terminals are arranged in coiled coils that keep the two heavy chains linked. As a result, two heads are present in myosin ii.

There are also 4 light chains in myosin ii, with 2 chains in each head. These light chains keep the heavy chains together between the tail and the head. Hundreds of kinds of myosin structures can be made from different light and heavy chain combinations.


● An introduction to smooth muscle actin

The contractile machinery is made up of thin filaments that are primarily made from a and y actin. Alpha actin, or a actin in smooth muscle, is the isoform of smooth muscle that is most common. B actin is also quite prevalent, but it does not affect muscle contraction. B actin forms a polymer beneath the plasma membrane when a contracting stimulant is present, which means it might help in generating or sustaining mechanical tension.

Alpha actin also has unique isoforms at a genetic level, which means that there are specific isoforms in skeletal muscle, smooth muscle, and cardiac muscle with alpha actin. There is between 2 and 10 times as much myosin as actin in smooth muscle, while the ratio of myosin to actin is 6 to 1 in skeletal muscle and 4 to 1 in muscles within the heart.


● What is a smooth muscle actin antibody?

A smooth muscle actin antibody helps tag myoepithelial cells, myofibroblasts, and ordinary smooth muscle cells. The actin antibody can prove helpful for helping physicians identify a variety of muscular cancers and neoplasms, including pleomorphic adenomas, leiomyosarcomas, and leiomyomas.

The antibody is sensitive to the alpha actin form of smooth muscles. The antibody tends to specifically react with this actin when immunoblotting assays are performed. The antibody helps label the cells in smooth muscle in tissue sections that are embedded in paraffin, fixed in formalin, or frozen.


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Sunday, June 10, 2012

Genetic and Biochemical Markers in Detection of Cancer

Cancer may be defined as the unregulated proliferation of abnormal cells of a particular type. Cancer cells are said to be of a particular “cell line” and a group of such cells represents a tumor. The original site of the tumor is known as the primary site or, simply, “the primary”. Some of these abnormal cells will eventually detach from their original site and are carried to other areas of the body where they establish themselves by forming a new blood supply (angiogenesis) and continue to replicate themselves. This breaking away and re-establishment at a different location is called metastasis, and these growths are called metastatic, or secondary tumors.


(Image from: Models of the metastatic process)


Physicians have long been aware that the presence and number of metastases is a direct predictor or both short and long term mortality in cancer patients. Since the presence or absence of metastasis is thus the most important factor in predicting the “treatability” of any form of cancer, it is of great importance that cancer be diagnosed before metastasis has occurred. The early diagnosis of cancer, which is to say prior to metastasis, is desirable for three reasons:

1. To increase the probability of diagnosis prior to spread.

When cancer is detected prior to the development of metastasis, surgical removal or other such direct procedures as cryotherapy will result in a “cure rate” of 100%. However, the detection of metastatic disease by visual inspection alone is known to be inadequate. This fact has led to intensive research in the use of “markers,” such as genetic analysis and biochemical testing, to detect both metastasis and the potential of primary tumors to produce metastatic lesions.


2. To decrease the amount of therapy required, and

The number of cancerous cells present is called the “tumor load.” Obviously, the greater the tumor load, a greater the amount of a particular therapeutic agent (e.g. chemotherapy or radiation therapy) will be required to destroy the cancer cells. Unfortunately, all such anti-cancer therapies will have the potential to affect other, healthy cells as well. Since these undesirable effects are usually “dose-dependent,” it is desirable to administer the minimum amount of a particular agent that is sufficient to destroy the cancer cells yet minimize damage to healthy non-cancerous cells.


3. To decrease the likelihood that therapy-resistant cell lines will develop.

Everyone is probably familiar with the fact that bacteria and other pathogens have a propensity to develop a resistance, or decreased susceptibility, to a number of antibiotics. In a similar vein, tumor cells that are less sensitive to chemotherapeutic drugs will live slightly longer than their more-susceptible counterparts. When these less-sensitive cells divide, their “daughter” cells will inherit that resistance and, over time, a new therapy-resistant cell line will emerge. These new cell lines are a major factor in the failure of many anti-cancer regimens.


As noted previously, there is a great deal of interest regarding the use of genetic and biochemical markers in the early detection of both primary tumors and metastatic disease. The most familiar genetic marker currently in clinical use are related to breast cancer and mutations of the BRCA1 and BRCA2 genes, while the more familiar biochemical markers of cancer are the Prostate-Specific Antigen (PSA) in prostate cancer and the Carcinoembryonic antigen (CEA) , which may be detected in the blood of those with colorectal cancer.

The BRCA1 genes and BRCA2 genes provide the genetic code that produces certain proteins that either repair or destroy defective DNA during cell division. Clinically-detectable mutations in these genes are known to carry an increased risk of breast cancer and the amount of their associated proteins present in the bloodstream are under active investigation in the potential detection and therapeutic management of that condition.

At this time, the use of biochemical markers in cancer is hampered by issues of non-specificity and non-sensitivity. As an example, the Prostate-Specific Antigen is elevated in prostate cancer. However, it is also elevated in both acute and prostatitis as well, making it a poor indicator of the presence or absence of prostate cancer. By the same token, the absence of an elevated blood level of the Carcinoembryonic antigen does not preclude the presence of colon cancer and this marker may be elevated in cases of colitis and thus yield a false-positive result when used as a cancer screening examination.

In conclusion, this brief essay has reviewed the importance of early detection of both cancer and its metastatic component. Although at this time the use of genetic and biochemical markers in diagnostic and therapeutic strategies is still evolving, these areas exhibit considerable potential for future refinement.

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Wednesday, June 6, 2012

Proto-Oncogenes

● What are Proto-Oncogenes

Proto-oncogenes are a subgroup of genes that, when mutated, are directly involved in the development of cancer. The mutation of proto-oncogenes causes normal cells to mutate into cancerous cells. A mutation of a proto-oncogene is a dominant type of mutation, and once the proto-oncogene becomes mutated it is classified as an oncogene. Before a proto-oncogene becomes affected it is often responsible for encoding protein function related to cell division as well as inhibition of cell differentiation and cellular apoptosis. These are functions that are pivotal for normal physiologic function and the mutation feeds off of this relationship. When the oncogene takes over, it typically ramps up these functions and thus increases the overall rate of cancer cell development without an inhibitory control present to halt the production of the cancerous cells. Given this fact, oncogenes are the main target in anti-cancer drug design.


● Transformation From Proto-Oncogenes to Oncogenes

As it is known today, there are over 40 different proto-oncogenes within the human genome. The transformation from a proto-oncogene to an oncogene is a very specific mutation. Oncogenes are a byproduct of mutations that increase the expression level of a proto-oncogene because these are the type of mutations that are going to lead to the greatest form of cancer cell proliferation. There are a number of genetic mechanisms that are correlated with proto-oncogene mutations,
such as:

  1. Point mutation, deletion, or insertion resulting in hyperactive gene product.
  2. Point mutation, deletion, or insertion within a promoter region of proto-oncogene that regulates transcription.
  3. Gene amplification leading to extra chromosomal copies of the mutated gene.
  4. Translocation events that move the proto-oncogene to a new locus leading to higher expression.
  5. Chromosomal translocations leading to proto-oncogene fusion and a secondary gene, resulting in a fusion protein with oncogenic activity.


(Image from: Cancer Genetics - Oncogenes)



● Oncogenic Examples

One place where proto-oncogenes have a large role is the coding of cell surface receptors, which act as a communication conduit between the extracellular environment and the intracellular environment. These receptors are composed of three separate parts that function simultaneously in order to provide optimal signaling. The extracellular region is similar to an antenna in that it collects an outside signal from the environment. The transmembrane region spans the length of the plasma membrane. The intracellular region possesses its own enzymatic activity and interacts with other proteins found within the cell.
A cell responds to signals outside from the extracellular environment in order to participate in proper growth and division. This occurs through ligand binding to the extracellular component of the transmembrane receptors. Ligands often take the form of growth factors to stimulate growth or angiogenic factors, which stimulate vascularization. Comformational changes occur with the binding of the ligand, which leads to the activation of intracellular domain resulting in a cascade effect affecting cell growth, proliferation, vascularization, or apoptosis. A specific example of this includes epidermal growth factor and epidermal growth factor receptor, which are responsible for growth factor mediation.

Proto-oncogenes are also responsible for coding proteins that may have a downstream effect resulting in stimulation of cell growth and division. A specific example of this is the RAS gene family, HRAS and KRAS. Along the same lines, there are some proto-oncogenes that are responsible for continuing cells through the cell cycle when specific signals are received by receptors. When these proto-oncogenes are overly expressed or expression is turned on at the wrong time, cancer cells begin to appear.

Oncogenes can also be expressed through translocation events occurring at the chromosome level. The best example of this is the Philadelphia chromosome. In this example, a crossover event occurs between chromosome 9 and chromosome 22. This results in interaction between the BCR gene found on chromosome 22 with the ABL1 gene found on chromosome 9. The fusion of these genes results in the production of the protein with high protein tyrosine kinase activity. If this expression goes about unregulated, there are a number of other proteins involved in cell cycle regulation that are activated to stimulate cell division. This is the gene that is often associated with numerous forms of leukemia.

Proto-oncogenes are important to understand in the development and treatment of cancer and through further research, cancer treatment can continue to progress.


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Sunday, June 3, 2012

E-cadherin is a classic cadherin that acts as an adhesion molecule and a cellular regulator



E-cadherin (epithelial cadherin) is a member of the cadherin superfamily of proteins, a group of 80 glycoproteins that are broadly involved in cell to cell adhesion via calcium-mediated homotypic interactions. It is considered to be a tumor suppressor gene because its interactions strongly bind cells together, limiting migration. E-cadherin is a type I "classic cadherin" along with neural (N) and placental (P) cadherins and is coded by the CDH1 gene. All classic cadherins contain a highly conserved transmembrane domain with a cytoplasmic tail that binds to the actin cytoskeleton via an alpha- and beta- catenin "bridge" that binds to the C-terminus. Type I and II cadherins contain an extracellular domain consisting of five identical 110 amino acid repeats, which form the basis for their role as adhesion molecules.

E-cadherin is important during early development, expressing throughout the cells soon after the first mitotic division and initiating compaction by the 8-cell stage. Soon afterwards, its expression is restricted to areas in contact with neighboring cells. In addition to its role as an adhesion molecule, E-cadherin has broad signaling properties that influence the fate of cells, especially during early differentiation. When E-cadherin is disrupted, embryonic cells lose their pluripotency and prematurely differentiate. The pattern of E-cadherin expression can be assessed via either a transgenic fluorophore tag (primarily for in vivo work) or an E-cadherin antibody for immunohistochemistry. An analysis of this expression indicates that E-cadherin is important in the establishment of left-right symmetry during morphogenesis.

The viral-mediated overexpression of E-cadherin has been used to "reprogram" embryonic cells, whereas its deletion inhibits reprogramming. Interestingly, E-cadherin is often downregulated in many cancers. It is unknown whether this has any influence over the undifferentiation often seen in metastatic tumors.

After embryonic differentiation, E-cadherin is seen largely in the epithelial cells of the gut and lungs but is also present in the kidney, skin, and liver to some extent. In these tissues, cadherin is responsible for binding cells together, often forming "belt desmosomes", which circumscribe the cell's soma. This allows the cell to both maintain its position relative to neighboring cells and, by forming a cellular seal across the entire epithelial layer, carefully control the transport of nutrient and waste particles across the membrane.

When binding to beta-catenin is disrupted (such as via dephosphorylation at the beta-catenin binding site), the E-cadherin molecule is no longer anchored to the cytoskeleton. This results in destabilization and rapid turnover, decreasing the number of cadherin-cadherin interactions at the intercellular junction, consequently reducing its strength and integrity. Similarly, the prevention of calcium binding at the extracellular domain results in a conformational change that disrupts E-cadherin's homotypic interactions.

The assessment of E-cadherin is often of clinical significance, as it is dysregulated in several forms of cancer. A good E-cadherin antibody can be used to visualize the level and pattern of protein expression via immunofluorescence or similar techniques. During metastasis, many cancers of the breast, skin, and gut substantially downregulate their E-cadherin expression. The effects of this downregulation are twofold: first, the cell to cell adhesion of the tumor cells is reduced, which lets the cancer cells spread and metastasize distant tissues; furthermore, the loosened cancer cells create holes in the basement membrane, which allows the egress of tumor cells from the lumen.


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