PTEN mutation spectrum and genotype-phenotype correlations in Bannayan-Riley-Ruvalcaba syndrome suggest a single entity with Cowden syndrome

Allelic loss of 10q23, the PTEN tumour suppressor gene locus, in Barrett's oesophagus-associated adenocarcinoma

PTEN is a putative tumour suppressor gene located on chromosome band 10q23. Mutations in PTEN have been identified in numerous human malignancies, including cancers of the brain, endometrium, ovary, and prostate. In this study, we screened 80 Barrett's oesophagus-associated adenocarcinomas (BOAd) for loss of heterozygosity (LOH) at 10q23, using the microsatellite markers D10S541, D10S219, and D10S551. Tumours demonstrating LOH were then screened for the presence or absence of PTEN mutations. LOH at one or more loci was identified in 17/80 (21%) cases. In none of these cases did we detect mutations in PTEN. The presence of LOH did not correlate with patient age, tumour stage, degree of differentiation, presence of perineural or vascular invasion, or overall survival. We conclude that LOH at chromosome 10q23 is uncommon in BOAd, is not associated with mutations in the PTEN tumour suppressor gene, and does not correlate with the clinical or pathologic features of these tumours. It is possible that PTEN is inactivated through other mechanisms in BOAd.

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.

Identification of a PTEN mutation in a family with Cowden syndrome and Bannayan-Zonana syndrome

Cowden syndrome (CS) and Bannayan-Zonana syndrome (BZS) are two inherited hamartoma syndromes characterized by distinct phenotypic features. Mutations in the PTEN gene have been identified in patients with CS and BZS, suggesting the presence of a common genetic basis. We describe a single kindred with individuals manifesting both CS and BZS phenotypes (CS/BZS overlap family) in which we have identified a novel mutation in PTEN by DNA sequencing. We have confirmed these results by means of restriction enzyme analysis. The presence of individuals with CS and BZS within the same family, and moreover the identification of identical PTEN gene mutations in these individuals, suggest that these two syndromes represent different phenotypic expressions of one disease. Furthermore, these findings imply that, like patients with CS, individuals with BZS should be monitored for the onset of malignancy.

Epigenetic PTEN silencing in malignant melanomas without PTEN mutation

A tumor suppressor gene at 10q 23.3, designated PTEN, encoding a dual specificity phosphatase with lipid and protein phosphatase activity, has been shown to play an important role in the pathogenesis of a variety of human cancers. Germline mutations in PTEN cause Cowden syndrome (CS), which is characterized by multiple hamartomas and a high risk of breast and thyroid cancers. Frequent loss of heterozygosity at 10q is found in both early and advanced-stage sporadic melanomas; however, mutations or deletions in PTEN are detected mainly in melanoma cell lines. In this study, we examined PTEN expression in 34 unselected sporadic melanomas (4 primary melanomas, 30 metastases) using immunohistochemistry and correlated this with the results of structural studies of this gene. Immunostaining of 34 melanoma samples revealed no PTEN expression in 5 (15%) and low PTEN expression in 17 (50%), whereas the rest of the tumors (35%) had high levels of expression. Hemizygous deletion was found in 32% of the tumors but neither intragenic PTEN mutation nor biallelic deletion was found in any of the samples. Of the 5 melanomas showing no PTEN expression, 4 had no mutation or deletion of PTEN. Of the 13 tumors having weak PTEN immunoreactivity and informative loss of heterozygosity results, 6 had evidence of hemizygous allelic loss of PTEN while the remaining 7 had intact PTEN. These results strongly support PTEN as a major tumor suppressor on 10q involved in melanoma tumorigenesis and suggest an epigenetic mechanism of biallelic functional inactivation not previously observed in other cancers where PTEN might be involved.

Mutation and expression analyses reveal differential subcellular compartmentalization of PTEN in endocrine pancreatic tumors compared to normal islet cells

The pathogenesis of sporadic endocrine pancreatic tumors (EPTs) is still primarily unknown. Comparative genomic hybridization studies revealed loss of 10q in a significant number (nine of 31) of EPTs. The tumor suppressor gene PTEN lies on 10q23, and so, is a candidate to play some role in EPT pathogenesis. Germline PTEN mutations are found in Cowden and Bannayan-Riley-Ruvalcaba syndromes, whereas somatic mutations and deletions are found in a variety of sporadic cancers. The mutation and expression status of PTEN in EPTs has not yet been examined. Mutation analysis of the entire coding region of PTEN including splice sites was performed in 33 tumors, revealing one tumor with somatic L182F (exon 6). Loss of heterozygosity of the 10q23 region was detected in eight of 15 informative malignant (53%) and in none of seven benign EPTs. PTEN expression was assessed in 24 available EPTs by immunohistochemistry using a monoclonal anti-PTEN antibody. Of these 24, 23 tumors showed strong immunoreactivity for PTEN. Only the EPTs with PTEN mutation lacked PTEN protein expression. Although normal islet cells always exhibited predominantly nuclear PTEN immunostaining, 19 of 23 EPTs had a predominantly cytoplasmic PTEN expression pattern. Exocrine pancreatic tissue was PTEN-negative throughout. PTEN mutation is a rare event in malignant EPTs and PTEN protein is expressed in most (23 of 24) EPTs. Thus, intragenic mutation or another means of physical loss of PTEN is rarely involved in the pathogenesis of EPTs. Instead, either an impaired transport system of PTEN to the nucleus or some other means of differential compartmentalization could account for impaired PTEN function. Loss of heterozygosity of the 10q23 region is a frequent event in malignant EPTs and might suggest several hypotheses: a different tumor suppressor gene in the vicinity of PTEN might be principally involved in EPT formation; alternatively, 10q loss, including PTEN, seems to be associated with malignant transformation, but the first step toward neoplasia might involve altered subcellular localization of PTEN.

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.

Hereditary colorectal cancer: risk assessment and management

There are at least nine major cancer susceptibility syndromes that infer an increased risk for colorectal cancer and/or colorectal polyposis; hereditary nonpolyposis colorectal cancer syndrome, Muir-Torre syndrome, Turcot syndrome, the I1307K polymorphism of the APC gene, familial adenomatous polyposis, attenuated familial adenomatous polyposis, Peutz Jeghers syndrome, juvenile polyposis, and the PTEN hamartoma tumor syndrome. As a result, the differential diagnosis of hereditary colorectal cancer can be complex. In addition, there has been a dramatic increase in the knowledge available regarding risk assessment and management of hereditary colorectal cancer syndromes. The literature was reviewed to develop this concise review of the hereditary colorectal cancer syndromes to facilitate the accurate diagnosis of each syndrome and the appropriate medical care for individuals with these diagnoses. Referral to a qualified Clinical Cancer Genetics program is appropriate if any of these syndromes is suspected and they will ensure the most up-to-date information is available to the patient, their family, and their health care professionals.

Molecular genetics in pediatric dermatology

The field of pediatric dermatology continues to be enriched by the insights offered through molecular genetics. For some genetic skin disorders, including neurofibromatosis, tuberous sclerosis complex, and several forms of epidermolysis bullosa, genetic research has resulted in an evolving understanding of the relationship between genotype and phenotype, with the ability to predict some of the features of these disorders on the basis of the genetic defect. However, widespread use of molecular genetics for diagnostic testing of these disorders has not been possible because of genetic heterogeneity, limited availability, and reduced sensitivity. The appropriate use of genetic services is emphasized in this, the molecular era.

Phosphorylation of the PTEN tail regulates protein stability and function

The PTEN gene is a tumor suppressor localized in the frequently altered chromosomal region 10q23. The tumor suppressor function of the PTEN protein (PTEN) has been linked to its ability to dephosphorylate the lipid second-messenger phosphatidylinositol 3,4, 5-trisphosphate and phosphatidylinositol 3,4-bisphosphate and, by doing so, to antagonize the phosphoinositide 3-kinase pathway. The PTEN protein consists of an amino-terminal phosphatase domain, a lipid binding C2 domain, and a 50-amino-acid C-terminal domain (the "tail") of unknown function. A number of studies have shown that the tail is dispensable for both phosphatase activity and blocking cell growth. Here, we show that the PTEN tail is necessary for maintaining protein stability and that it also acts to inhibit PTEN function. Thus, removing the tail results in a loss of stability but does not result in a loss of function because the resultant protein is more active. Furthermore, tail-dependent regulation of stability and activity is linked to the phosphorylation of three residues (S380, T382, and T383) within the tail. Therefore, the tail is likely to mediate the regulation of PTEN function through phosphorylation.