The role of MMAC1 mutations in early-onset breast cancer: causative in association with Cowden syndrome and excluded in BRCA1-negative cases

Interaction between S4 and the phosphatase domain mediates electrochemical coupling in voltage-sensing phosphatase (VSP)

Voltage-sensing phosphatase (VSP) consists of a voltage sensor domain (VSD) and a cytoplasmic catalytic region (CCR), which is similar to phosphatase and tensin homolog (PTEN). How the VSD regulates the innate enzyme component of VSP remains unclear. Here, we took a combined approach that entailed the use of electrophysiology, fluorometry, and structural modeling to study the electrochemical coupling in Ciona intestinalis VSP. We found that two hydrophobic residues at the lowest part of S4 play an essential role in the later transition of VSD-CCR coupling. Voltage clamp fluorometry and disulfide bond locking indicated that S4 and its neighboring linker move as one helix (S4-linker helix) and approach the hydrophobic spine in the CCR, a structure located near the cell membrane and also conserved in PTEN. We propose that the hydrophobic spine operates as a hub for translating an electrical signal into a chemical one in VSP.

Hamartomatous polyposis syndrome associated malignancies: Risk, pathogenesis and endoscopic surveillance

Hamartomatous polyposis syndromes (HPS) are a heterogeneous spectrum of diseases that are characterized by diffuse hamartomatous polyps lining the gastrointestinal (GI) tract together with extra-GI manifestations. Classical HPS includes juvenile polyposis syndrome, Peutz-Jeghers syndrome, PTEN hamartoma tumor syndrome and hereditary mixed polyposis syndrome. Patients with HPS have a higher risk of GI and extra-GI malignancies than the general population, although the underlying mechanisms remain unclear and are obviously different from the carcinogenesis of classical adenocarcinoma and colitis-associated malignancy. In this review we aimed to clarify the risks, possible mechanism and endoscopic surveillance of HPS-associated GI malignancies.

Genetic basis of Cowden syndrome and its implications for clinical practice and risk management

Cowden syndrome (CS) is an often difficult to recognize hereditary cancer predisposition syndrome caused by mutations in phosphatase and tensin homolog deleted on chromosome 10 (PTEN). In addition to conferring increased cancer risks, CS also predisposes individuals to developing hamartomatous growths in many areas of the body. Due to the rarity of CS, estimates vary on the penetrance of certain phenotypic features, such as macrocephaly and skin findings (trichilemmomas, mucocutaneous papules), as well as the conferred lifetime cancer risks. To address this variability, separate clinical diagnostic criteria and PTEN testing guidelines have been created to assist clinicians in the diagnosis of CS. As knowledge of CS increases, making larger studies of affected patients possible, these criteria continue to be refined. Similarly, the management guidelines for cancer screening and risk reduction in patients with CS continue to be updated. This review will summarize the current literature on CS to assist clinicians in staying abreast of recent advances in CS knowledge, diagnostic approaches, and management.

Characterization of a novel PTEN mutation in MDA-MB-453 breast carcinoma cell line

Background

Cowden Syndrome (CS) patients with germ line point mutations in the PTEN gene are at high risk for developing breast cancer. It is believed that cells harboring these mutant PTEN alleles are predisposed to malignant conversion. This article will characterize the biochemical and biological properties of a mutant PTEN protein found in a commonly used metastatic breast cancer cell line.

Methods

The expression of PTEN in human breast carcinoma cell lines was evaluated by Western blotting analysis. Cell line MDA-MB-453 was selected for further analysis. Mutation analysis of the PTEN gene was carried out using DNA isolated from MDA-MB-453. Site-directed mutagenesis was used to generate a PTEN E307K mutant cDNA and ectopic expressed in PC3, U87MG, MCF7 and Pten^-/- mouse embryo fibroblasts (MEFS). Histidine (His)-tagged PTEN fusion protein was generated in Sf9 baculovirus expression system. Lipid phosphatase and ubiquitination assays were carried out to characterize the biochemical properties of PTEN E307K mutant. The intracellular localization of PTEN E307K was determined by subcellular fractionation experiments. The ability of PTEN E307K to alter cell growth, migration and apoptosis was analyzed in multiple PTEN-null cell lines.

Results

We found a mutation in the PTEN gene at codon 307 in MDA-MB-453 cell line. The glutamate (E) to lysine (K) substitution rendered the mutant protein to migrate with a faster mobility on SDS-PAGE gels. Biochemically, the PTEN E307K mutant displayed similar lipid phosphatase and growth suppressing activities when compared to wild-type (WT) protein. However, the PTEN E307K mutant was present at higher levels in the membrane fraction and suppressed Akt activation to a greater extent than the WT protein. Additionally, the PTEN E307K mutant was polyubiquitinated to a greater extent by NEDD4-1 and displayed reduced nuclear localization. Finally, the PTEN E307K mutant failed to confer chemosensitivity to cisplatinum when re-expressed in Pten^-/- MEFS.

Conclusions

Mutation at codon 307 in PTEN C2 loop alters its subcellular distribution with greater membrane localization while being excluded from the cell nucleus. This mutation may predispose breast epithelial cells to malignant transformation. Also, tumor cells harboring this mutation may be less susceptible to the cytotoxic effects of chemotherapeutics.

Inferring gene-phenotype associations via global protein complex network propagation

Background

Phenotypically similar diseases have been found to be caused by functionally related genes, suggesting a modular organization of the genetic landscape of human diseases that mirrors the modularity observed in biological interaction networks. Protein complexes, as molecular machines that integrate multiple gene products to perform biological functions, express the underlying modular organization of protein-protein interaction networks. As such, protein complexes can be useful for interrogating the networks of phenome and interactome to elucidate gene-phenotype associations of diseases.

Methodology/Principal Findings

We proposed a technique called RWPCN (Random Walker on Protein Complex Network) for predicting and prioritizing disease genes. The basis of RWPCN is a protein complex network constructed using existing human protein complexes and protein interaction network. To prioritize candidate disease genes for the query disease phenotypes, we compute the associations between the protein complexes and the query phenotypes in their respective protein complex and phenotype networks. We tested RWPCN on predicting gene-phenotype associations using leave-one-out cross-validation; our method was observed to outperform existing approaches. We also applied RWPCN to predict novel disease genes for two representative diseases, namely, Breast Cancer and Diabetes.

Conclusions/Significance

Guilt-by-association prediction and prioritization of disease genes can be enhanced by fully exploiting the underlying modular organizations of both the disease phenome and the protein interactome. Our RWPCN uses a novel protein complex network as a basis for interrogating the human phenome-interactome network. As the protein complex network can capture the underlying modularity in the biological interaction networks better than simple protein interaction networks, RWPCN was found to be able to detect and prioritize disease genes better than traditional approaches that used only protein-phenotype associations.

Clinical management of hereditary breast cancer syndromes

Over the past 15 years there has been substantial improvement in the understanding of hereditary breast cancer. Germline genetic testing for mutations in BRCA1, BRCA2, PTEN and TP53 allows for the identification of individuals at increased risk for breast, ovarian and other cancers. Advances in screening, prevention and treatment have led to improved clinical management which is best defined for BRCA1 and BRCA2 mutation carriers. The addition of screening techniques such as breast magnetic resonance imaging has been shown to lead to earlier detection. Risk-reducing salpingo-oophorectomy leads to a reduction in the risk of both ovarian cancer and breast cancer and also is associated with an improvement in overall survival. BRCA1/2 mutation status may be applicable to systemic therapy decisions. Preclinical and early clinical research suggests that specific classes of chemotherapy may be more effective in mutation carriers. Finally, PARP inhibitors represent a novel therapeutic strategy that exploits the weaknesses of BRCA1/2-associated malignancies.

Absence of CHEK2*1100delC mutation in families with hereditary breast cancer in North America

The CHEK2*1100delC mutation has been reported to confer a twofold increased risk of breast cancer among carriers. The frequency of the mutation varies among populations. The highest frequency has been described in Northern and Eastern European countries; the frequency may be much lower in North America. In this study, our aim was to determine the frequency of CHEK2*1100delC in members of breast cancer families who tested negative for a deleterious mutation in BRCA1/2 at the University of Michigan Comprehensive Cancer Center. We genotyped 102 members from 90 families for CHEK2*1100delC. Most of these families had several cases of breast cancer or ovarian cancer (or both), as well as multiple members with other cancer types in a single lineage. No CHEK2*1100delC mutations were detected in any of the 102 individuals, including 51 women diagnosed with breast cancer at an early age (<45 years), 8 women with bilateral breast cancer, 3 men with breast cancer, and 8 women with ovarian cancer. Our data are consistent with the reported very low frequency of CHEK2*1100delC mutations in North American populations (compared with Northern Europe), rendering CHEK2*1100delC such an unlikely culprit in BRCA1/2 negative families that routine testing of these families appears unwarranted.

Cowden syndrome

Cowden syndrome (CS) is a rare inherited condition characterised by multiple hamartomas in a variety of tissues from all three embryonic layers. It is a cancer predisposition syndrome with an increased risk of developing malignancy in many tissues but especially breast, thyroid and endometrium. It is inherited in an autosomal dominant manner with ∼80% of patients having a germ-line mutation of the PTEN tumour suppressor gene. Presenting signs and symptoms are highly non-specific. Nevertheless clinicians should be able to recognise this syndrome so that patients may be screened for cancerous growths and afforded the opportunity to have genetic testing to assist them and their family members in making medical management decisions. We present a review of this unusual but important condition with particular emphasis on the diagnostic criteria, clinical features, genetics, management and surveillance.

Genetic testing for hereditary colorectal cancer

This article focuses on genetic testing for hereditary colorectal cancer syndromes. Genetic testing is now available in North America for all of the known hereditary colorectal cancer genes. In addition, most of these tests have improved significantly in the past few years with the inclusion of techniques to detect large rearrangements. As a result, clinicians are in a better position than ever to help families with these syndromes to identify the underlying genetic cause. This identification will ensure that they receive appropriate management, and will enable their relatives to determine their precise risks and to tailor their cancer surveillance.

PI3K/PTEN signaling in angiogenesis and tumorigenesis

Phosphatidylinositol 3-kinase (PI3K) and phosphatase and tensin homolog deleted on chromosome 10 (PTEN) signaling pathway play an important role in multiple cellular functions such as cell metabolism, proliferation, cell-cycle progression, and survival. PI3K is activated by growth factors and angiogenesis inducers such as vascular endothelial growth factor (VEGF) and angiopoietins. The amplification and mutations of PI3K and the loss of the tumor suppressor PTEN are common in various kinds of human solid tumors. The genetic alterations of upstream and downstream of PI3K signaling molecules such as receptor tyrosine kinases and AKT, respectively, are also frequently altered in human cancer. PI3K signaling regulates tumor growth and angiogenesis by activating AKT and other targets, and by inducing HIF-1 and VEGF expression. Angiogenesis is required for tumor growth and metastasis. In this review, we highlight the recent studies on the roles and mechanisms of PI3K and PTEN in regulating tumorigenesis and angiogenesis, and the roles of the downstream targets of PI3K for transmitting the signals. We also discuss the crosstalk of these signaling molecules and cellular events during tumor growth, metastasis, and tumor angiogenesis. Finally, we summarize the potential applications of PI3K, AKT, and mTOR inhibitors and their outcome in clinical trials for cancer treatment.

Selecting a BRCA risk assessment model for use in a familial cancer clinic

Background

Risk models are used to calculate the likelihood of carrying a BRCA1 or BRCA2 mutation. We evaluated the performances of currently-used risk models among patients from a large familial program using the criteria of high sensitivity, simple data collection and entry and BRCA score reporting.

Methods

Risk calculations were performed by applying the BRCAPRO, Manchester, Penn II, Myriad II, FHAT, IBIS and BOADICEA models to 200 non-BRCA carriers and 100 BRCA carriers, consecutively tested between August 1995 and March 2006. Areas under the receiver operating characteristic curves (AUCs) were determined and sensitivity and specificity were calculated at the conventional testing thresholds. In addition, subset analyses were performed for low and high risk probands.

Results

The BRCAPRO, Penn II, Myriad II, FHAT and BOADICEA models all have similar AUCs of approximately 0.75 for BRCA status. The Manchester and IBIS models have lower AUCs (0. and 0.47 respectively). At the conventional testing thresholds, the sensitivities and specificities for a BRCA mutation were, respectively, as follows: BRCAPRO (0.75, 0.62), Manchester (0.58,0.71), Penn II (0.93,0.31), Myriad II (0.71,0.63), FHAT (0.70,0.63), IBIS (0.20,0.74), BOADICEA (0.70, 0.65).

Conclusion

The Penn II model most closely met the criteria we established and this supports the use of this model for identifying individuals appropriate for genetic testing at our facility. These data are applicable to other familial clinics provided that variations in sample populations are taken into consideration.

Cowden syndrome: a critical review of the clinical literature

Cowden syndrome (CS) is a multi-system disease involving hamartomatous overgrowth of tissues of all three embryonic origins and increased risks for thyroid, breast and possibly other cancers. Benign breast, thyroid, uterine and skin lesions are also common. Approximately 80% of patients with CS have an identifiable germline mutation in the PTEN gene. The majority of the existing data on the frequencies of component clinical features have been obtained from compilations of case reports in the literature, many of which predate the establishment in 1996 of consensus diagnostic criteria. Many of these reports also suffer from ascertainment bias which emphasized the dermatologic features of the disease. This paper presents an overview of Cowden syndrome focusing on a critical evaluation of the major literature on the component cancers, benign features, and molecular findings in CS, noting the limitations of the published data.

Cowden syndrome: a critical review of the clinical literature

Cowden syndrome (CS) is a multi-system disease involving hamartomatous overgrowth of tissues of all three embryonic origins and increased risks for thyroid, breast and possibly other cancers. Benign breast, thyroid, uterine and skin lesions are also common. Approximately 80% of patients with CS have an identifiable germline mutation in the PTEN gene. The majority of the existing data on the frequencies of component clinical features have been obtained from compilations of case reports in the literature, many of which predate the establishment in 1996 of consensus diagnostic criteria. Many of these reports also suffer from ascertainment bias which emphasized the dermatologic features of the disease. This paper presents an overview of Cowden syndrome focusing on a critical evaluation of the major literature on the component cancers, benign features, and molecular findings in CS, noting the limitations of the published data.

Genetic and phenotypic heterogeneity in the PTEN hamartoma tumour syndrome

Germline PTEN (Phosphatase and TENsin homologue deleted on chromosome TEN) mutations predispose to phenotypically diverse disorders that share several overlapping clinical features: Cowden syndrome, Bannayan-Riley-Ruvalcaba syndrome, Proteus syndrome and Proteus-like syndrome, collectively classified as PTEN hamartoma tumour syndrome (PHTS). The meticulous acquisition and documentation of PHTS phenotypic data at different levels and the profiling of the plethora of genetic changes in PTEN and other genes within the same or related pathways are important in resolving the challenge of discriminating heritable cancers from sporadic PHTS-mimicking clinical features. The characterization of PTEN and PTEN-related pathways from a multidisciplinary perspective underscores the importance of incorporating data from different -omics, which is crucial for the advancement of personalized medicine.

A novel mutation of the PTEN gene in a Japanese patient with Cowden syndrome and bilateral breast cancer

Cowden syndrome (CS), also known as multiple hamartoma syndrome, is an autosomal dominant cancer syndrome associated with a high risk of breast and thyroid cancers. The phosphatase and tensin homolog gene (PTEN) encodes a lipid phosphatase that contains a PTPase domain and a C2 domain and plays a role as a tumor suppressor that negatively regulates the cell-survival signaling pathway initiated by phosphatidylinositol 3-kinase (PI3K). PTEN inhibits angiogenesis, and germline mutations of the PTEN gene are associated with CS. We screened for mutations in the PTEN gene in two unrelated Japanese patients with CS. In one patient, who suffered from bilateral breast cancer, thyroid adenoma, and gastric malignant lymphoma, we found a single-base substitution in exon 2 (115G>C) of the PTEN gene. This transversion results in a germline missense mutation (A39P). To date, nine different mutations have been identified in exon 2 of the PTEN gene in patients with CS and variant CS; however, the A39P missense mutation has not been reported previously. We also detected a previously reported nonsense mutation, 697C>T, resulting in R233X.

Suppression of PTEN function increases breast cancer chemotherapeutic drug resistance while conferring sensitivity to mTOR inhibitors

Ectopic expression of mutant forms of phosphatase and tensin homologue deleted on chromosome 10 (PTEN) lacking lipid (G129E) or lipid and protein (C124S) phosphatase activity decreased sensitivity of MCF-7 breast cancer cells, which have wild-type PTEN, to doxorubicin and increased sensitivity to the mammalian target of rapamycin (mTOR) inhibitor rapamycin. Cells transfected with a mutant PTEN gene lacking both lipid and protein phosphatase activities were more resistant to doxorubicin than cells transfected with the PTEN mutant lacking lipid phosphatase activity indicating that the protein phosphatase activity of PTEN was also important in controlling the sensitivity to doxorubicin, while no difference was observed between the lipid (G129E) and lipid and protein (C124S) phosphatase PTEN mutants in terms of sensitivity to rapamycin. A synergistic inhibitory interaction was observed when doxorubicin was combined with rapamycin in the phosphatase-deficient PTEN-transfected cells. Interference with the lipid phosphatase activity of PTEN was sufficient to activate Akt/mTOR/p70S6K signaling. These studies indicate that disruption of the normal activity of the PTEN phosphatase can have dramatic effects on the therapeutic sensitivity of breast cancer cells. Mutations in the key residues which control PTEN lipid and protein phosphatase may act as dominant-negative mutants to suppress endogenous PTEN and alter the sensitivity of breast cancer patients to chemo- and targeted therapies.

New insights into breast cancer genetics and impact on patient management

OPINION STATEMENT

The combined observation that 20-30% of all patients with breast cancer have a family history of the disease and the results from twin studies showing that 25% of breast cancer cases are heritable, indicate that this malignancy is one of the most commonly inherited cancers. Discovery of the BRCA1 and BRCA2 genes more than a decade ago has had a tremendous impact on patient care allowing for early detection and prevention of breast cancer. However, deleterious mutations within the BRCA1 and BRCA2 genes cause at most 3-8% of all breast cancer cases. New data indicate that genomic rearrangements within the same genes may occasionally identify additional carriers of nonfunctional BRCA1 and BRCA2 genes. Such genomic rearrangements are missed by conventional sequencing. The remainder of the unexplained familial risk is presumably due to other yet unidentified high penetrance genes, but polygenic mechanisms and high frequency low penetrance tumor susceptibility genes are likely to account for a greater proportion of familial breast cancers. In this regard, there is growing evidence that a common variant of the type I TGF-ss receptor, TGFBR1*6A, may account for approximately 5% of all breast cancer cases, a fraction similar to that attributable to BRCA1 and BRCA2. Such genes may also modify the penetrance of the BRCA1 and BRCA2 genes. In the next decade, screening for combinations of high and low penetrance genes will likely permit the identification of a large fraction of inherited breast cancer cases and will further reduce the burden of familial breast cancer.

Cowden syndrome and Bannayan Riley Ruvalcaba syndrome represent one condition with variable expression and age-related penetrance: results of a clinical study of PTEN mutation carriers

BACKGROUND

The most commonly reported phenotypes described in patients with PTEN mutations are Bannayan-Riley-Ruvalcaba syndrome (BRRS), with childhood onset, macrocephaly, lipomas and developmental delay, and Cowden Syndrome (CS), an adult-onset condition recognised by mucocutaneous signs, with a risk of cancers, in particular those of the thyroid and breast. It has been suggested that BRRS and CS are the same condition, but the literature continues to separate them and seek a genotype-phenotype correlation.

OBJECTIVE

To study the clinical features of patients with known PTEN mutations and observe any genotype-phenotype correlation.

METHODS

In total, 42 people (25 probands and 17 non-probands) from 26 families of all ages with PTEN mutations were recruited through the UK clinical genetics services. A full clinical history and examination were undertaken.

RESULTS

We were unable to demonstrate a genotype-phenotype correlation. Furthermore, our findings in a 31-year-old woman with CS and an exon 1 deletion refutes previous reports that whole exon deletions are only found in patients with a BRRS phenotype.

CONCLUSION

Careful phenotyping gives further support for the suggestion that BRRS and CS are actually one condition, presenting variably at different ages, as in other tumour-suppressor disorders such as neurofibromatosis type 1. This has important counselling implications, such as advice about cancer surveillance, for children diagnosed with BRRS.

A novel mutation of PTEN gene in a patient with Cowden syndrome with excessive papillomatosis of the lips, discrete cutaneous lesions, and gastrointestinal polyposis

Cowden syndrome is an inherited disease characterized by mucocutaneous lesions, gastrointestinal hamartomatous polyposis and an increased risk of breast, thyroid and endometrial carcinomas. Despite well described phenotypic expression of this disease, it is not easy to determine correct clinical diagnosis. In this case report we present a clinical history of a patient with Cowden syndrome. When he was 22 years old, he was found to have polyposis of gastrointestinal tract. The diagnosis of Peutz-Jeghers syndrome was established. Owing to intensive belly spasms, as a 36-year-old he was sent to another gastroenterological department where the thorough gastrointestinal tract examination was performed. We found glycogenic acanthosis of the esophagus; diffuse polyposis with large polyps within the stomach, and polyposis with small polyps in duodenum, colon, and rectum. We also noted the presence of excessive mucocutaneous papillomatosis of the lips and subtle skin lesions. Possible Cowden syndrome diagnosis was suggested. The same year he underwent plastic operation of the lips. During surgery, diffuse nodularity of the trachea was also noted. After plastic operation and assessment of Cowden syndrome as a possible diagnosis, he was recommended for a genetic examination. Diagnosis of Cowden syndrome was confirmed by sequencing analysis of the PTEN gene (phosphatase and tensin homolog deleted on chromosome 10). We found 'c.825_840delAAATACATTCTTCATA' deletion. This case affirmed that, for establishment of a correct diagnosis, especially for rare clinically overlapping syndromes, molecular testing is usually the only reliable method.

PTEN regulates phospholipase D and phospholipase C

PTEN is an ubiquitously expressed tumor suppressor which plays a prominent role in the pathogenesis of many types of sporadic solid tumors, including breast cancer, as well as hematologic malignancies. Germline PTEN mutations cause 85% of Cowden syndrome (CS), characterized by a high risk of breast and thyroid cancers, and 65% of Bannayan-Riley-Ruvalcaba syndrome (BRRS), characterized by lipomatosis, hemangiomas and speckled penis. Historically, PTEN's role in tumor suppression has been linked to the down-regulation of the PI3K/AKT pathway by PTEN's lipid phosphatase activity. Beyond the AKT pathway, however, there has been minimal examination of PTEN's responsibility in lipid-derived cellular signaling. As phospholipids have been shown to be critical components in signal transduction and cellular proliferation and PTEN controls cellular phospholipid levels, we hypothesized that PTEN functions as a regulator of lipid signaling and homeostasis. Increased PTEN expression in unstimulated MCF-7 breast cancer cells results in a 51% increase in phosphatidic acid, with a decrease in phosphatidylcholine, suggesting that PTEN may regulate phospholipase D (PLD). PTEN overexpression results in a 30% increase in basal PLD activity. As phospholipase C (PLC) is both involved in PLD activation and is regulated by PIP2/3 levels, we investigated the role of PTEN on PLC activation. Our data suggest that PTEN modulates PLC:PLD activation pathways and indicate that the pathogenesis of CS/BRRS has a more complex biochemical basis beyond simply activating the PI3K pathway. This provides alternative routes for PTEN's tumor suppressor action that may be beneficial in the creation of novel targets for cancer therapy and prevention.

Cowden disease: a review

Cowden disease is a genetically inherited disorder presenting with multiple hamartomatous and neoplastic lesions in various organs and tissues. We present a review of the diagnostic criteria, clinical presentation, genetics, and management of this condition.

Inhibition of ILK in PTEN-mutant human glioblastomas inhibits PKB/Akt activation, induces apoptosis, and delays tumor growth

The tumor suppressor gene phosphatase and tensin homologue (PTEN) regulates the phosphatidylinositol-3'-kinase (PI3K) signaling pathway and has been shown to correlate with poor prognosis in high-grade astrocytomas when mutational inactivation or loss of the PTEN gene occurs. PTEN mutation leads to constitutive activation of protein kinase B (PKB)/Akt with phosphorylation at the PKB/Akt sites Thr-308 and Ser-473. Integrin-linked kinase (ILK) has been shown to regulate PKB/Akt activity with the loss of PTEN in prostate cancer. We now demonstrate that ILK activity regulates PKB/Akt activity in glioblastoma cells. The activity of ILK is constitutively elevated in a serum-independent manner in PTEN mutant cells, and transfection of wild-type PTEN under the control of an inducible promoter into mutant PTEN cells inhibits ILK activity. Transfection of ILK antisense (ILKAS) or exposure to a small-molecule ILK inhibitor suppresses the constitutive phosphorylation of PKB/Akt on Ser-473 in PTEN-mutant glioblastoma cell lines. In addition, the delivery of ILKAS to PTEN-negative glioblastoma cells resulted in apoptosis. Rag-2M mice bearing established ( approximately 100 mg) human U87MG glioblastoma tumors, treated QD x 5 for 3 consecutive weeks with ILKAS (i.p. 5 mg/kg), exhibited stable disease with < or =7% increase in tumor volume over the 3-week course of treatment. In contrast, animals treated with an oligonucleotide control or saline exhibited a >100% increase in tumor volume over the same time period. Our initial results indicate that therapeutic strategies targeting ILK may be beneficial in the treatment of glioblastomas.

Constipation, polyps, or cancer? letPTEN predict your future

The inherited hamartoma polyposis syndromes encompass several distinct clinical syndromes with different genetic bases, Cowden syndrome (CS), Bannayan-Riley-Ruvalcaba syndrome (BRRS), juvenile polyposis syndrome (JPS), and Peutz-Jeghers syndrome (PJS). Germline mutations in PTEN, encoding a tumor suppressor phosphatase on 10q23.3, is associated with 80% of CS and 60% of BRRS. JPS is caused by mutations in MADH4 and BMPR1A, encoding two members of the TGFB superfamily. Germline mutations in LKB1 (STK11) are associated with a subset of PJS. The number, distribution, and histologic type of polyps differ amongst these syndromes as do component cancer risks. While rare, usually asymptomatic, hamartomatous polyps are felt to be component to CS. Hamartomatous polyposis is usually prominent and symptomatic in BRRS. Polyposis, which can be quite symptomatic, is a cardinal component feature of PJS and JPS. Interestingly, glycogenic acanthosis of the esophagus is highly predictive of CS and the presence of PTEN mutation. PTEN mutation positive CS have been shown to be at increased risk of breast, thyroid, and endometrial cancer. PTEN mutation positive BRRS are at increased risk of at least breast cancer, possibly that of the thyroid as well. In contrast, JPS and PJS have increased risk of gastrointestinal cancers in particular. Thus, molecular-based diagnoses to differentiate each of these syndromes are important for medical management.

PTEN: one gene, many syndromes

PTEN, on 10q23.3, encodes a major lipid phosphatase which signals down the phosphoinositol-3-kinase/Akt pathway and effects G1 cell cycle arrest and apoptosis. Germline PTEN mutations have been found to occur in 80% of classic Cowden syndrome (CS), 60% of Bannayan-Riley-Ruvalcaba syndrome (BRRS), up to 20% of Proteus syndrome (PS), and approximately 50% of a Proteus-like syndrome (PSL). CS is a heritable multiple hamartoma syndrome with a high risk of breast, thyroid, and endometrial carcinomas. BRRS is a congenital autosomal dominant disorder characterized by megencephaly, developmental delay, lipomatosis, and speckled penis. PS and PSL had never been associated with risk of malignancy. Finding germline PTEN mutations in patients with BRRS, PS, and PSL suggests equivalent risks of developing malignancy as in CS with implications for medical management. The mutational spectra of CS and BRRS overlap, with many of the mutations occurring in exons 5, 7, and 8. Genotype-phenotype association analyses have revealed that the presence of germline PTEN mutations is associated with breast tumor development, and that mutations occurring within and 5' of the phosphatase motif were associated with multi-organ involvement. Pooled analysis of PTEN mutation series of CS and BRRS occurring in the last five years reveals that 65% of CS-associated mutations occur in the first five exons encoding the phosphatase domain and the promoter region, while 60% of BRRS-associated mutations occur in the 3' four exons encoding mainly the C2 domain. Somatic PTEN mutations occur with a wide distribution of frequencies in sporadic primary tumors, with the highest frequencies in endometrial carcinomas and glioblastoma multiform. Several mechanisms of PTEN inactivation occur in primary malignancies derived from different tissues, but a favored mechanism appears to occur in a tissue-specific manner. Inappropriate subcellular compartmentalization and increased/decreased proteosome degradation may be two novel mechanisms of PTEN inactivation. Further functional work could reveal more effective means of molecular-directed therapy and prevention.

Germline mutations in the PTEN gene in Israeli patients with Bannayan-Riley-Ruvalcaba syndrome and women with familial breast cancer

Germline mutations in BRCA1 or BRCA2 account for the majority of inherited breast cancer cases. Yet, in up to 40% of familial breast cancer cases, no mutations can be detected in either gene. Germline mutations in PTEN underlie two inherited syndromes: Cowden disease (CD) and Bannayan-Riley-Ruvalcaba syndrome (BRRS). The known association of CD with breast cancer risk made it plausible that germline mutations within PTEN may play a role in inherited predisposition to breast cancer. The nine coding exons of the PTEN gene were screened for harboring germline mutations using denaturing gradient gel electrophoresis (DGGE) complemented by sequencing, in two subsets of Israeli patients: 12 patients clinically diagnosed with BRRS, and 89 women with an apparent inherited predisposition to breast cancer, some with salient features of CD. Two of three familial BRRS patients exhibited novel germline mutations in PTEN: a missense mutation changing methionine to arginine at codon 134, and insertion of two nucleotides (CA) at cDNA position 1215 resulting in a frameshift at codon 61 and a premature stop at codon 99. Among 89 high-risk women, two missense mutations were detected in exon 4: A to C change at cDNA position 1279 resulting in a change of aspargine to threonine at codon 82 (N82T), and a G to an A alteration in 1269 which alters threonine to alanine at codon 78 (T78A), a non-conservative missense mutation. This study suggests that PTEN does not play a major role in predisposing to hereditary breast cancer in Israeli women, and that detection of PTEN mutations in BRRS patients is more likely in familial cases.

Considerations in genetic counseling for inherited breast cancer predisposition

Of the 190000 women estimated to have been diagnosed with breast cancer in 2001, between 5% and 10% of them are likely to have developed their disease as the result of an inherited susceptibility. Although breast cancer is a component tumor of several familial cancer predisposition syndromes, mutations in BRCA1 and BRCA2 are the most commonly identified germline changes. Recognition of hereditary breast cancer is critical to allow the implementation of appropriate treatment, screening, and prevention strategies for the affected woman and her family members. Genetic testing may play an important role in refining risk assessment, identifying individuals at risk before cancer has developed, and relieving anxiety in family members who have not inherited the predisposition.

Role of PTEN, a lipid phosphatase upstream effector of protein kinase B, in epithelial thyroid carcinogenesis

Both benign and malignant thyroid disease are well-established components of Cowden syndrome (CS), an autosomal dominant disorder characterized by multiple hamartomas and breast cancer that may be considered a phakomatosis. The susceptibility gene for CS is PTEN, a tumor suppressor gene on 10q23.3 that encodes a lipid phosphatase that lies upstream of protein kinase B (Akt). Interestingly, Carney complex is also a phakomatosis where multiple endocrine neoplasias are prominent and thyroid cancer might be a rare component. One of its susceptibility genes is the regulatory subunit of protein kinase A. Over the course of the last four years, investigators have found the increasing clinical spectrum of syndromes characterized by germline loss-of-function PTEN mutation. In addition to CS, subsets of such disparate syndromes as Bannayan-Riley-Ruvalcaba syndrome, Proteus syndrome, and possibly VATER with hydrocephalus and megencephaly with autistic features have been found to have germline PTEN mutations. Paradoxically, somatic intragenic PTEN mutations were rare in uncultured primary epithelial thyroid tumors, although hemizygous deletion occurred in 10-20% of thyroid adenomas and carcinomas. However, with subsequent study, it was discovered that epigenetic silencing of PTEN and perhaps inappropriate subcellular compartmentalization were two novel mechanisms of PTEN inactivation pertinent in thyroid carcinogenesis. Ectopic expression studies in vitro have borne out the importance of PTEN in the pathogenesis of epithelial thyroid neoplasias.

Nuclear PTEN expression and clinicopathologic features in a population-based series of primary cutaneous melanoma

Germline mutations of the PTEN tumor-suppressor gene, on 10q23, cause Cowden syndrome, an inherited hamartoma syndrome with a high risk of breast, thyroid and endometrial carcinomas and, some suggest, melanoma. To date, most studies which strongly implicate PTEN in the etiology of sporadic melanomas have depended on cell lines, short-term tumor cultures and noncultured metastatic melanomas. The only study which reports PTEN protein expression in melanoma focuses on cytoplasmic expression, mainly in metastatic samples. To determine how PTEN contributes to the etiology or the progression of primary cutaneous melanoma, we examined cytoplasmic and nuclear PTEN expression against clinical and pathologic features in a population-based sample of 150 individuals with incident primary cutaneous melanoma. Among 92 evaluable samples, 30 had no or decreased cytoplasmic PTEN protein expression and the remaining 62 had normal PTEN expression. In contrast, 84 tumors had no or decreased nuclear expression and 8 had normal nuclear PTEN expression. None of the clinical features studied, such as Clark's level and Breslow thickness or sun exposure, were associated with cytoplasmic PTEN expressional levels. An association with loss of nuclear PTEN expression was indicated for anatomical site (p = 0.06) and mitotic index (p = 0.02). There was also an association for melanomas to either not express nuclear PTEN or to express p53 alone, rather than both simultaneously (p = 0.02). In contrast with metastatic melanoma, where we have shown previously that almost two-thirds of tumors have some PTEN inactivation, only one-third of primary melanomas had PTEN silencing. This suggests that PTEN inactivation is a late event likely related to melanoma progression rather than initiation. Taken together with our previous observations in thyroid and islet cell tumors, our data suggest that nuclear-cytoplasmic partitioning of PTEN might also play a role in melanoma progression.

Protean PTEN: form and function

Germline mutations distributed across the PTEN tumor-suppressor gene have been found to result in a wide spectrum of phenotypic features. Originally shown to be a major susceptibility gene for both Cowden syndrome (CS), which is characterized by multiple hamartomas and an increased risk of breast, thyroid, and endometrial cancers, and Bannayan-Riley-Ruvalcaba syndrome, which is characterized by lipomatosis, macrocephaly, and speckled penis, the PTEN hamartoma tumor syndrome spectrum has broadened to include Proteus syndrome and Proteus-like syndromes. Exon 5, which encodes the core motif, is a hotspot for mutations likely due to the biology of the protein. PTEN is a major lipid 3-phosphatase, which signals down the PI3 kinase/AKT pro-apoptotic pathway. Furthermore, PTEN is a protein phosphatase, with the ability to dephosphorylate both serine and threonine residues. The protein-phosphatase activity has also been shown to regulate various cell-survival pathways, such as the mitogen-activated kinase (MAPK) pathway. Although it is well established that PTEN's lipid-phosphatase activity, via the PI3K/AKT pathway, mediates growth suppression, there is accumulating evidence that the protein-phosphatase/MAPK pathway is equally important in the mediation of growth arrest and other crucial cellular functions.

Genes other than BRCA1 and BRCA2 involved in breast cancer susceptibility

This review focuses on genes other than the high penetrance genes BRCA1 and BRCA2 that are involved in breast cancer susceptibility. The goal of this review is the discovery of polymorphisms that are either associated with breast cancer or that are in strong linkage disequilibrium with breast cancer causing variants. An association with breast cancer at a 5% significance level was found for 13 polymorphisms in 10 genes described in more than one breast cancer study. Our data will help focus on the further analysis of genetic polymorphisms in populations of appropriate size, and especially on the combinations of such polymorphisms. This will facilitate determination of population attributable risks, understanding of gene-gene interactions, and improving estimates of genetic cancer risks.

PTEN and myotubularin: novel phosphoinositide phosphatases

Protein tyrosine phosphatases (PTPs) are a diverse group of enzymes that contain a highly conserved active site motif, Cys-x5-Arg (Cx5R). The PTP superfamily enzymes, which include tyrosine-specific, dual specificity, low-molecular-weight, and Cdc25 phosphatases, are key mediators of a wide variety of cellular processes, including growth, metabolism, differentiation, motility, and programmed cell death. The PTEN/MMAC1/TEP1 gene was originally identified as a candidate tumor suppressor gene located on human chromosome 10q23; it encodes a protein with sequence similarity to PTPs and tensin. Recent studies have demonstrated that PTEN plays an essential role in regulating signaling pathways involved in cell growth and apoptosis, and mutations in the PTEN gene are now known to cause tumorigenesis in a number of human tissues. In addition, germ line mutations in the PTEN gene also play a major role in the development of Cowden and Bannayan-Zonana syndromes, in which patients often suffer from increased risk of breast and thyroid cancers. Biochemical studies of the PTEN phosphatase have revealed a molecular mechanism by which tumorigenesis may be caused in individuals with PTEN mutations. Unlike most members of the PTP superfamily, PTEN utilizes the phosphoinositide second messenger, phosphatidylinositol 3,4,5-trisphosphate (PIP3), as its physiologic substrate. This inositol lipid is an important regulator of cell growth and survival signaling through the Ser/Thr protein kinases PDK1 and Akt. By specifically dephosphorylating the D3 position of PIP3, the PTEN tumor suppressor functions as a negative regulator of signaling processes downstream of this lipid second messenger. Mutations that impair PTEN function result in a marked increase in cellular levels of PIP3 and constitutive activation of Akt survival signaling pathways, leading to inhibition of apoptosis, hyperplasia, and tumor formation. Certain structural features of PTEN contribute to its specificity for PIP3, as well as its role(s) in regulating cellular proliferation and apoptosis. Recently, myotubularin, a second PTP superfamily enzyme associated with human disease, has also been shown to utilize a phosphoinositide as its physiologic substrate.

Rapid mutation scanning of genes associated with familial cancer syndromes using denaturing high-performance liquid chromatography

Germline mutations in tumor suppressor genes, or less frequently oncogenes, have been identified in up to 19 familial cancer syndromes including Li-Fraumeni syndrome, familial paraganglioma, familial adenomatous polyposis coli and breast and ovarian cancers. Multiple genes have been associated with some syndromes as approximately 26 genes have been linked to the development of these familial cancers. With this increased knowledge of the molecular determinants of familial cancer comes an equal expectation for efficient genetic screening programs. We have trialled denaturing high-performance liquid chromatography (dHPLC) as a tool for rapid germline mutation scanning of genes implicated in three familial cancer syndromes -- Cowden syndrome (PTEN mutation), multiple endocrine neoplasia type 2 (RET mutation) and von Hippel-Lindau disease (VHL mutation). Thirty-two mutations, including 21 in PTEN, 9 in RET plus a polymorphism, and 2 in VHL, were analyzed using the WAVE DNA fragment analysis system with 100% detection efficiency. In the case of the tumor suppressor gene PTEN, mutations were scattered along most of the gene. However, mutations in the RET proto-oncogene associated with multiple endocrine neoplasia type 2 were limited to specific clusters or "hot spots." The use of GC-clamped primers to scan for mutations scattered along PTEN exons was shown to greatly enhance the sensitivity of detection of mutant hetero- and homoduplex peaks at a single denaturation temperature compared to fragments generated using non--GC-clamped primers. Thus, when scanning tumor suppressor genes for germline mutation using dHPLC, the incorporation of appropriate GC-clamped primers will likely increase the efficiency of mutation detection.

Male breast cancer in Cowden syndrome patients with germline PTEN mutations

Cowden syndrome (CS) (OMIM 158350) is a multiple hamartoma syndrome associated with germline mutations in the PTEN tumour suppressor gene. While CS is characterised most commonly by non-cancerous lesions (mucocutaneous trichilemmomas, acral and palmoplantar keratoses, and papillomatous papules), it is also associated with an increased susceptibility to breast cancer (in females) and thyroid cancer, as well as non-cancerous conditions of the breast and thyroid. Here we report two cases of male breast cancer occurring in patients with classical CS phenotypes and germline PTEN mutations. The first subject was diagnosed with CS indicated primarily by mucocutaneous papillomatosis, facial trichilemmomas, and macrocephaly with frontal bossing at the age of 31 years. He developed breast cancer at 41 years and subsequently died of the disease. A PTEN mutation, c.802delG, was identified in this subject, yet none of his family members showed evidence of a CS phenotype, suggesting that this PTEN mutation may be a de novo occurrence. The second subject had a CS phenotype including multiple trichilemmomas and thyroid adenoma, developed male breast cancer at 43 years, and died of the disease at 57 years. He was a carrier of a PTEN mutation c.347-351delACAAT that cosegregated with the CS phenotype in affected family members. These two cases of male breast cancer associated with germline PTEN mutations and the CS phenotype suggest that CS may be associated with an increased risk of early onset male as well as female breast cancer.

Capillary and Microchip Electrophoresis for Rapid Detection of Known Mutations by Combining Allele-specific DNA Amplification with Heteroduplex Analysis

Background: Detection of mutations by gel electrophoresis and allele-specific amplification by PCR (AS-PCR) is not easily scaled to accommodate a large number of samples. Alternative electrophoretic formats, such as capillary electrophoresis (CE) and microchip electrophoresis, may provide powerful platforms for simple, fast, automated, and high-throughput mutation detection after allele-specific amplification.

Methods: DNA samples heterozygous for four mutations (185delAG, 5382insC, 3867G→T, and 6174delT) in BRCA1 and BRCA2, and homozygous for one mutation (5382insC) in BRCA1 and two mutations (16delAA and 822delG) in PTEN were chosen as the model system to evaluate the capillary and microchip electrophoresis methods. To detect each mutation, three primers, of which one was labeled with the fluorescent dye 6-carboxyfluorescein and one was the allele-specific primer (mutation-specific primer), were used to amplify the DNA fragments in the range of 130–320 bp. AS-PCR was combined with heteroduplex (HD) analysis, where the DNA fragments obtained by AS-PCR were analyzed with the conditions developed for CE-based HD analysis (using a fluorocarbon-coated capillary and hydroxyethylcellulose). The CE conditions were transferred into the microchip electrophoresis format.

Results: Three genotypes, homozygous wild type, homozygous mutant, and heterozygous mutant, could be identified by CE-based AS-PCR-HD analysis after 10–25 min of analysis time. Using the conditions optimized with CE, we translated the AS-PCR-HD analysis mutation detection method to the microchip electrophoresis format. The detection of three heterozygous mutations (insertion, deletion, and substitution) in BRCA1 could be accomplished in 180 s or less.

Conclusions: It is possible to develop a CE-based method that exploits both AS-PCR and HD analysis for detecting specific mutations. Fast separation and the capacity for automated operation create the potential for developing a powerful electrophoresis-based mutation detection system. Fabrication of multichannel microchip platforms may enable mutation detection with high throughput.

Mutations of the human PTEN gene

PTEN (phosphatase and tensin homolog deleted on chromosome ten), a recently discovered tumor suppressor gene, appears to negatively control the phosphoinositide 3-kinase signaling pathway for regulation of cell proliferation and cell survival by dephosphorylating the phosphatidylinositol 3,4,5-triphosphate. To date, 110 germline PTEN mutations have been reported in patients affected with two tumor predisposing syndromes, each having overlapping clinical features: Cowden disease and Bannayan-Riley-Ruvalcaba syndrome. These germline mutations are scattered along the length of the gene, with the exception of exon 9 (no mutation reported) and exon 1 (only two mutations reported). A mutational hot spot is found in exon 5, which encodes the phosphatase catalytic core motif, and recurrent mutations are also found at CpG dinucleotides suggesting deamination-induced mutations. PTEN has also been found to be defective in a large number of sporadic human tumors. In this article, 332 somatic point mutations of PTEN, occurring in primary tumors or metastasis, have been reviewed. Somatic PTEN mutations are more particularly involved in two types of human cancers: endometrial carcinomas and glioblastomas. In most cases, these somatic mutations result in protein inactivation and, as with germline mutations, recurrent somatic mutations are found in CpG dinucleotides. A mutagenesis by insertion-deletion in repetitive elements is however specifically observed in endometrial carcinomas.

Identification of PTEN mutations in metastatic melanoma specimens

CONTEXT

PTEN, a tumour suppressor gene located on chromosome 10q23, develops somatic mutations in various tumours and tumour cell lines including brain, endometrium, prostate, breast, kidney, thyroid, liver, and melanoma.

OBJECTIVES

To investigate the mutational profile of this gene further, as well as its role in tumour progression in melanoma. DESIGN, SETTINGS: We examined 21 metastatic melanoma samples for 10q23 allelic losses and PTEN sequence alterations. Additionally, we screened these samples for mutations in CDKN2A, a gene in which alterations are well documented in primary melanoma as well as in the germline of familial melanoma.

RESULTS

Loss of heterozygosity (LOH) at 10q23 was observed in 33% (7/21) of the samples tested. We identified four sequence alterations in PTEN (19%) and two in CDKN2A (9.5%). Of interest, only one case showed mutations in both genes.

CONCLUSIONS

These data support the notion that PTEN alterations occur in some metastatic melanomas, and that mutation of this gene plays a role in the progression of some forms of melanoma.

Hereditary breast cancer: a review

Breast cancer is the most common female malignancy and a major cause of death in middle-aged women. A positive family history of breast cancer is one of the strongest risk factors for the disease. In addition, many afflicted breast cancer families are characterized by early onset and bilateral tumors, and also, in some cases, associated malignancies, most commonly ovarian cancer. It is estimated that 5-10% of all breast cancer cases are due to autosomal dominant genes segregating with the disease. Mutations in the BRCA1 and BRCA2 genes are known to predispose to breast and ovarian cancer in many families. Other genes are only involved in very rare syndromes, and additional genes remain to be disclosed.

Mutation analysis of the PTEN / MMAC1 gene in Japanese patients with Cowden disease

Cowden disease (CD), also known as multiple hamartoma syndrome, is an autosomal dominant cancer syndrome associated with high risk of breast and thyroid cancer. Recently, germline mutations in PTEN / MMAC1, which has nine exons encoding a dual specificity phosphatase with homology to tensin and auxilin, have been identified on chromosome 10q23 in some 40 to 80% of CD patients. Our polymerase chain reaction amplification and sequence analysis of all coding regions identified five different mutations including four novel germline mutations among 5 of 12 unrelated Japanese CD patients. The novel findings included a missense mutation (G --> T) at nucleotide 1004 in exon 8 resulting in an arginine-to-leucine change at codon 335 (R335L), two novel splice-site mutations (209 + 1delGT and 209 + 1delGTAA) in intron 3, and insertion of G at nucleotide 632 in exon 6 (632insG). We also detected a nonsense mutation (C --> T) at nucleotide 697 producing R233X in exon 7, which has been reported previously. From reported phenotypic data concerning CD patients from five different families who had the R233X mutation, it may be suggested that R233X mutation correlates with macrocephaly. Although previous reports have implicated exon 5 as a "hot spot," we found no mutation in exon 5.

A novel PTEN mutation in a Japanese patient with Cowden disease

Cowden disease (CD) is an autosomal dominant syndrome characterized by multiple hamartomatous lesions and an increased risk for malignancies. Recent evidence has indicated that the PTEN gene, encoding a protein tyrosine phosphatase, is the CD susceptibility gene. However, another line of evidence has suggested that CD might be genetically heterogeneous. Clinical features of CD are variable, and there are interfamilial differences in the expression of skin lesions. Therefore, information on PTEN mutations in CD patients should be accumulated to clarify the genotype-phenotype correlation. In the present study, we found heterozygous germline mutations of PTEN in all of three Japanese patients with CD examined, indicating no genetic heterogeneity among our patients. The mutations included two non-sense mutations of R335X and R130X, and a mis-sense mutation of C136R. To the best of our knowledge, the C136R mutation has not previously been reported in CD patients. This novel mutation was located outside the core motif of the phosphatase domain of PTEN protein, where most of the missense mutations previously reported in CD patients were clustered. Mucocutaneous manifestations were far fewer in the patient with this mutation than in the patients with nonsense mutations. Whether the phenotypic difference in mucocutaneous features was due to the different mutations remains unclear.