Allelic imbalance, including deletion of PTEN/MMACI, at the Cowden disease locus on 10q22-23, in hamartomas from patients with Cowden syndrome and germline PTEN mutation

Linear ubiquitination of PTEN impairs its function to promote prostate cancer progression

PTEN is frequently mutated in human cancers, which leads to the excessive activation of PI3K/AKT signaling and thus promotes tumorigenesis and drug resistance. Met¹-linked ubiquitination (M1-Ubi) is also involved in cancer progression, but the mechanism is poorly defined. Here we find that HOIP, one important component of linear ubiquitin chain assembly complex (LUBAC), promotes prostate cancer (PCa) progression by enhancing AKT signaling in a PTEN-dependent manner. Mechanistically, PTEN is modified by M1-Ubi at two sites K144 and K197, which significantly inhibits PTEN phosphatase activity and thus accelerates PCa progression. More importantly, we identify that the high-frequency mutants PTEN^R173H and PTEN^R173C in PCa patients showed the enhanced level of M1-Ubi, which impairs PTEN function in inhibition of AKT phosphorylation and cell growth. We also find that HOIP depletion sensitizes PCa cells to therapeutic agents BKM120 and Enzalutamide. Furthermore, the clinical data analyses confirm that HOIP is upregulated and positively correlated with AKT activation in PCa patient specimen, which may promote PCa progression and increase the risk of PCa biochemical relapse. Together, our study reveals a key role of PTEN M1-Ubi in regulation of AKT activation and PCa progression, which may propose a new strategy for PCa therapy.

Cowden Disease: A Review

ABSTRACT

PTEN hamartoma tumor syndrome (PTHS) includes diseases with germline pathogenic variants in the PTEN gene. Cowden syndrome is included in this syndrome . PTEN (phosphatase and tensin homolog) is a tumor suppressor gene located on chromosome 10q22-23; nearly 60%-90% of pathogenic variants are inherited. Cowden syndrome is a rare autosomic dominant condition, affecting approximately 1/200,000 people worldwide. Patients present benign and, malignant neoplasms in multiple organs, mostly breast and thyroid. The skin is the organ affected most consistently by Cowden disease. It is an autosomal dominant condition, characterized clinically by the presence of innumerable verrucous lesions on the skin. Interpretations of histopathologic findings in the cutaneous and mucosal lesions continue to be a matter of debate.

Pancreatic adenocarcinoma with a germline PTEN p.Arg234Gln mutation

A minor fraction of pancreatic ductal adenocarcinoma (PDAC) develops in association with germline mutations of the genes responsible for inherited cancer syndromes. However, the PDAC that has a germline PTEN mutation has not received much attention. Genome-wide whole exome sequencing was performed on germline and somatic DNA from an 82-year-old woman who had developed a solid pancreatic cancer but did not show characteristic findings of PTEN hamartoma tumor syndromes (PHTS). Histology of the resected pancreatic tumor showed unique PDAC findings of primarily dendriform structures and dense fibrous tissue, accompanied by multiple pancreatic intraepithelial neoplasias in the vicinity. The tumor immunohistochemistry revealed a loss of PTEN expression and overexpression of TP53. Exome sequencing revealed a K-ras mutation (p.Gly12Val). Germline exome sequencing revealed a missense mutation of PTEN (p.Arg234Gln), a rare variant with a reported association with cancer development but not with other PHTS phenotypes. To our knowledge, this is the first report of PDAC associated with a germline PTEN mutation, particularly a rare variant (p.Arg234Gln) with cancer risks.

Enhanced Cell Growth Inhibition following PTEN Nonviral Gene Transfer Using Polyethylenimine and Photochemical Internalization in Endometrial Cancer Cells

PTEN is a tumor suppressor gene mapped on chromosome 10q23.3 and encodes a dual specificity phosphatase. PTEN has major implication in PI3 kinase (PI3K) signal transduction pathway and negatively controls PI3 phosphorylation. It has been reported to be implicated in cell cycle progression and cell death control through inhibition of PI3K-Akt signal transduction pathway and in the control of cell migration and spreading through its interaction with focal adhesion kinase. Somatic mutations of PTEN are frequently detected in several cancer types including brain, prostate and endometrium with more than 30% of tumor tissue specimens bearing PTEN mutations and/or deletions. Because of its high frequency of mutations and its important function as tumor suppressor gene, PTEN is a good candidate for gene therapy. Inducible expression of PTEN has been also reported. In cancer cells bearing PTEN abnormalities, the reversion of PTEN function by external gene transfer becomes more and more investigated in cancer treatment research. Several technologies including the photochemical internalization (PCI) and aiming at improving the transfection efficiency have been reported. PCI is an innovative procedure based on light-induced delivery of macromolecules such as DNA, proteins and other therapeutic molecules from endocytic vesicles to the cytosol of target cells. PCI has been reported to enhance the gene delivery potential of viral and nonviral vectors. The present study was designed to evaluate the influence of photochemical internalization on polyethylenimine (PEI)-mediated PTEN gene transfer and its effects on the cellular viability in Ishikawa endometrial cancer cells bearing PTEN abnormalities. PCI was found to significantly (P < 0.01) enhance PTEN mRNA expression (4.2 fold increase). Subsequently, following PEI-mediated PTEN gene transfer, the restoration of the PTEN protein expression was observed. As a consequence, significant cell growth inhibition (44%) was observed in Ishikawa endometrial cells. Using PCI for PEI-mediated PTEN gene transfer was found to further enhance PTEN mRNA and protein expression as well as PTEN-related cell growth inhibition reaching 89%.

Neuroendocrine Tumor of the Pancreas as a Manifestation of Cowden Syndrome: A Case Report

CONTEXT

Germline mutations in the phosphatase and tensin homolog (PTEN) tumor suppressor gene are found in the majority of patients with Cowden syndrome (CS), who have an increased risk of breast, thyroid, and endometrial cancer. According to our current understanding of genetic changes in the PTEN gene and the resultant phenotypic features of CS, pancreatic neuroendocrine tumors (NETs) are not considered part of the clinical spectrum of CS.

CASE DESCRIPTION

We report a unique case of an advanced NET of the pancreas in a patient with CS. The germline DNA sequencing confirmed the clinical diagnosis of CS and revealed a PTEN mutation c.697C→T (p.R233*) causing a premature stop codon in exon 7. The tumor DNA sequencing showed no loss of heterozygosity or any copy number changes and no other deleterious genetic alterations, including those commonly mutated in sporadic pancreatic NETs: MEN1, ATRX, DAXX, TP53, and genes involved in the mammalian target of rapamycin pathway. In addition, the high-throughput transcriptome analyzed by RNA-seq did not reveal any missed genetic alterations, aberrant splicing variants, gene fusions, or gene expression alterations. The immunohistochemical staining of the tumor for PTEN revealed an abnormal, uniformly strong cytoplasmic staining of tumor cells with virtually absent nuclear staining.

CONCLUSION

The results from genetic testing and histopathological techniques used to confirm CS diagnosis and characterize this unusual tumor tempted us to believe that in this case, the pancreatic NET was not a sporadic malignancy that occurred by coincidence, but rather represented a new entity in the spectrum of malignancies associated with CS.

The expression of tumour suppressors and proto-oncogenes in tissues susceptible to their hereditary cancers

BACKGROUND

Studies of familial cancers have found that only a small subset of tissues are affected by inherited mutations in a given tumour suppressor gene (TSG) or proto-oncogene (POG), even though the mutation is present in all tissues. Previous tests have shown that tissue specificity is not due to the presence vs absence of gene expression, as TSGs and POGs are expressed in nearly every type of normal human tissue. Using published microarray expression data we tested the related hypothesis that tissue-specific expression of a TSG or POG is highest in tissue where it is of oncogenic importance.

METHODS

We tested this hypothesis by examining whether individual TSGs and POGs had higher expression in the normal (noncancerous) tissues where they are implicated in familial cancers relative to those tissues where they are not. We examined data for 15 TSGs and 8 POGs implicated in familial cancer across 12 human tissue types.

RESULTS

We found a significant difference between expression levels in susceptible vs nonsusceptible tissues. It was found that 9 (60%, P<0.001) of the TSGs and 5 (63%, P<0.001) of the POGs had their highest expression level in the tissue type susceptible to their oncogenic effect.

CONCLUSIONS

This highly significant association supports the hypothesis that mutation of a specific TSG or POG is likely to be most oncogenic in the tissue where the gene has its highest level of expression. This suggests that high expression in normal tissues is a potential marker for linking cancer-related genes with their susceptible tissues.

PTEN function: the long and the short of it

Phosphatase and tensin homolog deleted on chromosome ten (PTEN) is a phosphatase that is frequently altered in cancer. PTEN has phosphatase-dependent and -independent roles, and genetic alterations in PTEN lead to deregulation of protein synthesis, the cell cycle, migration, growth, DNA repair, and survival signaling. PTEN localization, stability, conformation, and phosphatase activity are controlled by an array of protein-protein interactions and post-translational modifications. Thus, PTEN-interacting and -modifying proteins have profound effects on the tumor suppressive functions of PTEN. Moreover, recent studies identified mechanisms by which PTEN can exit cells, via either exosomal export or secretion, and act on neighboring cells. This review focuses on modes of PTEN protein regulation and ways in which perturbations in this regulation may lead to disease.

Where Birt-Hogg-Dubé meets Cowden syndrome: mirrored genetic defects in two cases of syndromic oncocytic tumours

Birt-Hogg-Dubè (BHD) is an autosomal dominant syndrome characterised by skin fibrofolliculomas, lung cysts, spontaneous pneumothorax and renal cancer. The association of benign cutaneous lesions and increased cancer risk is also a feature of Cowden Syndrome (CS), an autosomal dominant disease caused by PTEN mutations. BHD and CS patients may develop oncocytomas, rare neoplasias that are phenotypically characterised by a prominent mitochondrial hyperplasia. We here describe the genetic analysis of a parotid and a thyroid oncocytoma, developed by a BHD and a CS patient, respectively. The BHD lesion was shown to maintain the wild-type allele of FLCN, while losing one PTEN allele. On the other hand, a double heterozygosity for the same two genes was found to be the only detectable tumorigenic hit in the CS oncocytoma. Both conditions occurred in a context of high chromosomal stability, as highlighted by comparative genomic hybridisation analysis. We conclude that, similarly to PTEN, FLCN may not always follow the classical Two Hits model of tumorigenesis and may hence belong to a class of non-canonical tumour suppressor genes. We hence introduce a role of PTEN/FLCN double heterozygosity in syndromic oncocytic tumorigenesis, suggesting this to be an alternative determinant to pathogenic mitochondrial DNA mutations, which are instead the genetic hallmark of sporadic oncocytic tumours.

Utility of PTEN protein dosage in predicting for underlying germline PTEN mutations among patients presenting with thyroid cancer and Cowden-like phenotypes

CONTEXT

Thyroid cancer is a major component of Cowden syndrome (CS). CS patients with an underlying PTEN mutation (PTEN(mut+)) have a 70-fold increased risk of developing epithelial thyroid cancer. In contrast, less than 1% of sporadic epithelial thyroid cancer patients carry a germline PTEN mutation. Cost-efficient markers capable of shortlisting thyroid cancers for CS genetic testing would be clinically useful.

OBJECTIVE

Our objective was to analyze the utility of patient blood phosphate and tensin homolog deleted on chromosome 10 (PTEN) protein levels in predicting germline PTEN mutations.

DESIGN, SETTING, AND PATIENTS

We conducted a 5-yr, multicenter prospective study of 2792 CS and CS-like patients, all of whom had comprehensive PTEN analysis. Analysis of PTEN and downstream proteins by immunoblotting was performed on total protein lysates from patient-derived lymphoblast lines. We compared blood PTEN protein levels between PTEN(mut+) patients and those with variants of unknown significance or wild-type PTEN (PTEN(wt/vus)).

MAIN OUTCOME MEASURES

We assessed the utility of PTEN protein levels in predicting germline PTEN mutations.

RESULTS

Of 2792 CS/CS-like patients, 721 patients had thyroid cancer; 582 of them (81%) had blood PTEN protein analyzed. PTEN germline pathogenic mutations were present in 27 of 582 patients (4.6%). Ninety-six percent (26 of 27) of PTEN(mut+) patients had blood PTEN protein levels in the lowest quartile as compared with 25% (139 of 555) of PTEN(wt/vus) patients (P < 0.001). Low blood PTEN levels predicted for PTEN(mut+) cases with a 99.76% negative predictive value (95% confidence interval = 98.67-99.96) and a positive test likelihood ratio of 3.84 (95% confidence interval = 3.27-4.52).

CONCLUSIONS

Our study shows that low blood PTEN protein expression could serve as a screening molecular correlate to predict for germline PTEN mutation in CS and CS-like presentations of thyroid cancer.

Acinic cell carcinoma of the retromolar trigone region: expanding the tumor phenotype in Cowden syndrome?

Cowden syndrome (CS) is a cancer predisposition syndrome caused by germline mutations in the PTEN tumor suppressor gene. It is associated with an increased risk of thyroid, breast and endometrial cancer but many manifestations can be found in the head and neck region, some of which are pathognomonic. Here we report a 35-year-old male referred by his dentist for evaluation of a lesion located near the retromolar trigone. Comprehensive clinical examination revealed papillomatous skin lesions, macrocephaly and gingival hypertrophy. Histopathological examination of the lesion showed an acinic cell carcinoma (ACC) of minor salivary gland origin. Analysis of the PTEN gene identified a germline R130Q mutation in exon 5, confirming the diagnosis of CS, but no loss of heterozygosity was seen in DNA extracted from tumor tissue. This is to our knowledge the first case describing an association of ACC of the minor salivary gland with a PTEN-gene related disorder. It emphasizes the importance of head and neck examination in these patients.

Haplo-insufficiency: a driving force in cancer

It was originally proposed that tumour suppressor genes (TSGs) act in a recessive manner. Instead, numerous TSGs, including p53 and PTEN, exhibit haplo-insufficiency as a consequence of the dose-dependency of TSG function. Due to the challenges of identifying haplo-insufficient TSGs by human genetics analysis alone, mouse models play a pivotal role in firmly establishing the haplo-insufficiency of a gene, as in the recent identification of DOK2 as a haplo-insufficient lung TSG. In many cases, TSGs exhibit conditional or compound haplo-insufficiency, in which loss of one TSG allele is functionally important only in certain settings or after compound loss of other genes. The 5q deletion syndrome (5q(-) ) is a paradigm of compound haplo-insufficiency and demonstrates the importance of combinatorial interactions to elicit specific phenotypes. These concepts must be integrated into basic science studies to avoid delay in the identification of important TSGs. In the clinical realm, the challenges for molecular pathologists are the development of quantitative measures that can accurately and systematically ascertain the status of haplo-insufficient genes in tumour biopsies, and the use of this information to accurately predict prognosis and response to therapy.

Naturally occurring germline and tumor-associated mutations within the ATP-binding motifs of PTEN lead to oxidative damage of DNA associated with decreased nuclear p53

Somatic and germline mutations in PTEN (phosphatase and tensin homolog deleted on chromosome 10) are found in sporadic cancers and Cowden syndrome patients, respectively. Recent identification of naturally occurring cancer and germline mutations within the ATP-binding motifs of PTEN (heretofore referred to as PTEN ATP-binding mutations) has revealed that these mutations disrupted the subcellular localization and tumor-suppressor activity of PTEN. However, very little is known about the underlying mechanisms of PTEN ATP-binding mutations in tumorigenesis. Here we show that these mutations impair PTEN's function both qualitatively and quantitatively. On the one hand, PTEN ATP-binding mutants lose their phosphatase activity and the effect of downregulation of cyclin D1. On the other, the mislocalized mutant PTEN results in a significantly decreased nuclear p53 protein level and transcriptional activity, enhanced production of reactive oxygen species, induction of Cu/Zn superoxide dismutase as well as dramatically increased DNA double-strand breaks (DSBs). When compared with wild-type PTEN, the ATP-binding mutant PTEN has reduced half-life in vitro and decreased protein expression levels in vivo. Our data, thus, reveal a novel mechanism of tumorigenesis in patients with germline or somatic mutations affecting PTEN ATP-binding motifs, i.e. qualitative and quantitative impairment of PTEN due to the loss of its phosphatase activity, and nuclear mislocalization, resulting in rapid PTEN protein degradation, suppression of p53-mediated transcriptional activity, loss of protection against oxidative stress as well as accumulation of spontaneous DNA DSBs.

Age dependence of radiation-induced renal cell carcinomas in an Eker rat model

Exposure to carcinogens early in life may contribute to cancer development later in life. The amount of radiation exposure children experience during medical procedures has been increasing, so it is important to evaluate the radiation risk of cancer in developing organs. Toward this goal, we assessed the risk of developing renal cell carcinoma using Eker rats as a kidney tumor model. F1 hybrids of male Eker (Tsc2 mutant) and female F344 rats were irradiated with 0.5 or 2 Gy gamma radiation on gestation days 15 and 19, and on postnatal days 5, 20, and 49. At 27 weeks of age, kidneys were examined for proliferative lesions. Preneoplastic lesions such as phenotypically altered tubules increased after postnatal irradiation as a function of age-at-irradiation, and hyperplasia were greatly increased after perinatal and postnatal irradiation. In contrast, development of adenoma and adenocarcinoma were evident in animals irradiated at perinatal ages, being maximal at gestational day 19. The frequency of LOH at the Tsc2 locus was unexpectedly low - 0% (0 of 4) for the unirradiated control, and 17% (6 of 35) for the irradiated group. Irrespective of LOH, the mTOR (mammalian target of rapamycin) pathway, which is negatively regulated by the Tsc1/2 complex, was activated in both benign and malignant lesions, as evidenced by phosphorylation of S6 ribosomal protein and 4E-BP1. This suggests that the wild-type Tsc2 allele may be functionally inactivated. In conclusion, actively growing kidneys in perinatal-aged (F344 x Eker) F1 rats (Tsc2(+/-)) are at risk for radiation-induced malignant transformation of the renal epithelium associated with mTOR activation.

Molecular pathology of thyroid cancer: diagnostic and clinical implications

There is now a reasonably good understanding of the key oncogenic events involved in the initiation and progression of thyroid cancer. Many of these are characteristic of certain tumor types, and their presence conveys diagnostic and prognostic information. It is not yet clear how this information will be applied to clinical practice. Based on preclinical evidence, mutations of genes encoding certain kinases may also predict response to specific tyrosine kinase inhibitors, although this has not yet been explored systematically in clinical trials.

Phosphatase activity of nuclear PTEN is required for CDX2-mediated intestinal differentiation of gastric carcinoma

The PTEN tumor suppressor localizes predominantly to the cytoplasm, where it negatively regulates the phosphatidylinositol 3-kinase-AKT signaling pathway; however, the biological significance of nuclear PTEN in gastric carcinoma (GC) remains unknown. In this study, transduction of recombinant PTEN into GC-derived TMK-1 cells promoted PTEN nuclear localization with increased mRNA levels of CDX2 and intestinal claudins (CLDN3 and CLDN4), whereas the G129E phosphatase 'dead' mutant had no effect. In GC tissue samples, tumors with nuclear PTEN expression frequently demonstrated the intestinal-type claudin phenotype. Our results suggested that nuclear localization of PTEN is important for determining intestinal differentiation of GCs.

Tenets of PTEN tumor suppression

Since its discovery as the elusive tumor suppressor gene at the frequently mutated 10q23 locus, PTEN has been identified as lost or mutated in several sporadic and heritable tumor types. A decade of work has established that PTEN is a nonredundant phosphatase that is essential for regulating the highly oncogenic prosurvival PI3K/AKT signaling pathway. This review discusses emerging modes of PTEN function and regulation, and speculates about how manipulation of PTEN function could be used for cancer therapy.

Hitting the mark in hamartoma syndromes

The missed mark or hamartia underlying each hamartoma syndrome is a mutation in a tumor suppressor gene. This sets the stage for the development of frequent and early tumors in multiple organs. Loss of function of the tumor suppressor in neoplastic cells leads to dysregulation of signaling pathways and tumor growth. The convergence of these signaling pathways to the mTOR pathway suggests that rapamycin or rapamycin-like drugs have potential for treatment, perhaps in combination with drugs targeting other signaling pathways. Haploinsufficient cells also play significant roles in tumor formation. Disrupting interactions between neoplastic cells and surrounding haploinsufficient cells using antiangiogenesis therapies represent an additional approach for treatment. It is hoped that the debilitating effects of these syndromes soon will be alleviated or even reversed though targeted therapies.

Mapping geographic zones of cancer risk with epigenetic biomarkers in normal breast tissue

PURPOSE

Genetic alterations were previously identified in normal epithelia adjacent to invasive cancers. The aim of this study was to determine DNA methylation in histologically normal tissues from multiple geographic zones adjacent to primary breast tumors.

EXPERIMENTAL DESIGN

First, methylation status of a 4-kb region of RASSF1A promoter was interrogated using oligonucleotide-based microarray in 144 samples (primary tumors, 47; adjacent normals, 69; reduction mammoplasty tissues, 28). Second, allelic imbalance (AI)/loss of heterozygosity (LOH) surrounding RASSF1A promoter were analyzed in 30 samples (tumors, 8; adjacent normals, 22). Third, global methylation screening of 49 samples (tumors, 12; adjacent normals, 25; reduction mammoplasty, 12) was done by differential methylation hybridization. Real-time quantitative methylation-specific PCR was used to validate the microarray findings.

RESULTS

DNA methylation in the core RASSF1A promoter was low in reduction mammoplasty tissues (P=0.0001) when compared with primary tumors. The adjacent normals had an intermediate level of methylation. The regions surrounding the core were highly methylated in all sample types. Microsatellite markers showed AI/LOH in tumors and some of the adjacent normals. Concurrent AI/LOH and DNA methylation in RASSF1A promoter occurred in two of six tumors. Global methylation screening uncovered genes more methylated in adjacent normals than in reduction mammoplasty tissues. The methylation status of four genes was confirmed by quantitative methylation-specific PCR.

CONCLUSIONS

Our findings suggest a field of methylation changes extending as far as 4 cm from primary tumors. These frequent alterations may explain why normal tissues are at risk for local recurrence and are useful in disease prognostication.

Pten Loss in the Mouse Thyroid Causes Goiter and Follicular Adenomas: Insights into Thyroid Function and Cowden Disease Pathogenesis

Inactivation and silencing of the tumor suppressor PTEN are found in many different epithelial tumors, including thyroid neoplasia. Cowden Disease patients, who harbor germ-line PTEN mutations, often display thyroid abnormalities, including multinodular goiter and follicular adenomas, and are at increased risk of thyroid cancer. To gain insights into the role PTEN plays in thyroid function and disease, we have generated a mouse strain, in which Cre-mediated recombination is used to specifically delete Pten in the thyrocytes. We found that Pten mutant mice develop diffuse goiter characterized by extremely enlarged follicles, in the presence of normal thyroid-stimulating hormone and T4 hormone levels. Loss of Pten resulted in a significant increase in the thyrocyte proliferative index, which was more prominent in the female mice, and in increased cell density in the female thyroid glands. Surprisingly, goitrogen treatment did not cause a substantial increase of the mutant thyroid size and increased only to some extent the proliferation index of the female thyrocytes, suggesting that a relevant part of the thyroid-stimulating hormone-induced proliferation signals are funneled through the phosphatidylinositol-3-kinase (PI3K)/Akt cascade. Although complete loss of Pten was not sufficient to cause invasive tumors, over two thirds of the mutant females developed follicular adenomas by 10 months of age, showing that loss of Pten renders the thyroid highly susceptible to neoplastic transformation through mechanisms that include increased thyrocyte proliferation. Our findings show that constitutive activation of the PI3K/Akt cascade is sufficient to stimulate continuous autonomous growth and provide novel clues to the pathogenesis of Cowden Disease and sporadic nontoxic goiter.

Hyperphosphorylation of tau and neurofilaments and activation of CDK5 and ERK1/2 in PTEN-deficient cerebella

Inherited mutations to the tumor suppressor PTEN sporadically lead to cerebellar gangliocytoma characterized by migration defects. This has been modeled by CNS-specific PTEN ablation in mice, but the underlying mechanism cannot be explained by the known role of PTEN in Akt/PKB inactivation. Here we show that the loss of PTEN in mouse cerebellar neurons causes neurodegeneration by hyperphosphorylation of tau and neurofilaments, and activation of Cdk5 and pERK1/2, suggesting that dysregulation of the PTEN/pAkt pathway can mediate neurodegeneration.

GSK3 beta mediates suppression of cyclin D2 expression by tumor suppressor PTEN

PTEN, encoding a lipid phosphatase, is a tumor suppressor gene and is mutated in various types of cancers. It is reported to regulate G1 to S phase transition of the cell cycle by influencing the expression, protein stability and subcellular location of cyclin D1. Here, we provide evidence that PTEN modulates the transcription and protein stability of cyclin D2. Targeted deletion of Pten in mouse embryonic fibroblasts (MEFs) endowed cells with greater potential to overcome G1 arrest than wild-type MEFs and led to the elevated expression of cyclin D2, which was suppressed by the introduction of PTEN. We further defined a pathway involving GSK3beta and beta-catenin/TCF in PTEN-mediated suppression of cyclin D2 transcription. LiCl, an inhibitor of GSK3beta, abolished inhibitory effect of PTEN on cyclin D2 expression, and TCF members could directly bind to the promoter of cyclin D2 and regulate its transcription in a CREB-dependent manner. Our results indicate that the downregulation of cyclin D2 expression by PTEN is mediated by the GSK3beta/beta-catenin/TCF pathway in cooperation with CREB, and suggest a convergence from the PI-3 kinase/PTEN pathway and the Wnt pathway in modulation of cyclin D2 expression.

p53 Down-Regulates Phosphatase and Tensin Homologue Deleted on Chromosome 10 Protein Stability Partially through Caspase-Mediated Degradation in Cells with Proteasome Dysfunction

There has been intense investigation regarding the interaction between the phosphatase and tensin homologue deleted on chromosome 10 (PTEN) and p53 tumor suppressors. p53 has been shown to up-regulate PTEN expression as a transcriptional activator. However, clinical observations by immunohistochemistry studies indicate that significant increases in p53 protein levels coexist with reduced or absent expression of PTEN protein in a variety of neoplasias. In this study, we propose a mechanism that begins to explain how p53 can both up-regulate and down-regulate PTEN. We have found that PTEN protein is down-regulated under proteasome dysfunction induced by proteasome inhibitor MG132 in both human lymphoblast cells and MCF7 cells. The reduction of PTEN is coincident with elevated p53 protein levels and the association between PTEN and p53 but independent of its phosphatase activities. Quantitative reverse transcription-PCR indicates that proteasome inhibition does not reduce PTEN message levels but affects PTEN protein stability. The p53 inhibitor, pifithrin-alpha, is able to attenuate the effect of proteasome inhibition. Using ectopic expression studies in p53-null mouse embryonic fibroblasts and p53/PTEN-null PC3 cells, we show that PTEN is more stable in p53-null cells compared with p53-expressing cells. Inhibition of caspases, the downstream targets of p53, particularly caspase-3, can partially restore the stability of PTEN. This study provides the first evidence that p53 is able to down-regulate PTEN protein stability in stressed cells. Our study sheds some light on the mechanisms that regulate PTEN protein stability, which is important to fully elucidate to comprehend the broad neoplastic manifestations of Cowden syndrome/Bannayan-Riley-Ruvalcaba and sporadic cancers.

Contiguous gene deletion within chromosome arm 10q is associated with juvenile polyposis of infancy, reflecting cooperation between the BMPR1A and PTEN tumor-suppressor genes

We describe four unrelated children who were referred to two tertiary referral medical genetics units between 1991 and 2005 and who are affected with juvenile polyposis of infancy. We show that these children are heterozygous for a germline deletion encompassing two contiguous genes, PTEN and BMPR1A. We hypothesize that juvenile polyposis of infancy is caused by the deletion of these two genes and that the severity of the disease reflects cooperation between these two tumor-suppressor genes.

Depletion of GAK/auxilin 2 inhibits receptor-mediated endocytosis and recruitment of both clathrin and clathrin adaptors

Cyclin G-associated kinase (GAK/auxilin 2), the ubiquitous form of the neuronal-specific protein auxilin 1, is an essential cofactor for the Hsc70-dependent uncoating of clathrin-coated vesicles. We have now investigated the effect of knocking down GAK in HeLa cells by vector-based small hairpin RNA. Functionally, depletion of GAK caused a marked decrease in internalization of both transferrin and epidermal growth factor and altered mannose 6-phosphate receptor trafficking, but had little effect on the recycling of transferrin receptor back to the plasma membrane. Structurally, depletion of GAK caused a marked reduction in perinuclear clathrin associated with the trans-Golgi network and in the number of clathrin-coated pits on the plasma membrane, and reduced clathrin exchange on the few clathrin-coated pits that remained. Surprisingly, while clathrin depletion does not prevent adaptors from assembling on the membrane, depletion of GAK caused a dramatic reduction in AP2 and epsin on the plasma membrane and AP1 and GGA at the trans-Golgi network. A similar effect was caused by expression of a dominant negative Hsp70 mutant. These results suggest that GAK, in conjunction with Hsc70, not only uncoats clathrin-coated vesicles and induces clathrin exchange on clathrin-coated pits, but also mediates binding of clathrin and adaptors to the plasma membrane and the trans-Golgi network.

Cowden disease and Lhermitte-Duclos disease: an update. Case report and review of the literature

OBJECT

Cowden disease is a rare autosomal-dominant phacomatosis and cancer syndrome that is associated with Lhermitte-Duclos disease (LDD), also called dysplastic cerebellar gangliocytoma.

METHODS

In this review the authors summarize the additions to the literature during the past 5 years, with emphasis on new case reports and advances in imaging and molecular biology. Adult-onset LDD is now considered pathognomonic for Cowden disease. Approximately 220 cases of LDD have been reported. Magnetic resonance imaging in patients with LDD is often diagnostic, and imaging studies have facilitated accurate diagnosis and contributed to the improved outcome in affected patients. Cowden disease and other rare, related disorders, such as Bannayan-Riley-Ruvalcaba, Proteus, and Proteus- like syndromes, are often caused by mutations of the PTEN gene.

CONCLUSIONS

Because of the high incidence of systemic cancer in patients with Cowden disease, it is important for neurosurgeons to recognize the association between this disease and LDD and to refer affected patients for appropriate cancer screenings and interventions.

High frequency of submicroscopic hemizygous deletion is a major mechanism of loss of expression of PTEN in uveal melanoma

PURPOSE

Although cytogenetic aberrations at 10q have been reported in up to 27% of uveal melanomas, the role of PTEN in the pathogenesis of uveal melanoma is largely unknown. Our aim was to determine the frequency and clinical significance of PTEN alterations in uveal melanomas.

PATIENTS AND METHODS

We examined PTEN expression using immunohistochemistry in 75 sporadic uveal melanomas, with an average follow-up of 89 months. Molecular cytogenetic alterations were studied using comparative genomic hybridization (CGH). Genotyping was carried out using an intragenic PTEN marker and two flanking markers. Mutational analysis of PTEN was also carried out.

RESULTS

Of the 75 tumors, 12 (16%) showed no PTEN immunostaining, 32 (42.7%) showed weak to moderate staining and the remaining 31 (38.2%) showed staining similar to the normal internal controls. Using CGH, only two (15.4%) of 13 samples showed any loss of 10q. However, in the 38 tumors with informative genotyping, we found that 29 (76.3%) had loss of heterozygosity (LOH) of at least one PTEN marker, and 15 (39.5%) showed LOH of at least two markers. Mutations in the coding region of PTEN were identified in four (11.4%) of 35 tumors. Further, loss of cytoplasmic PTEN expression by immunohistochemistry was associated with shortened disease-free survival (P = .029).

CONCLUSION

This is the first demonstration that PTEN is a tumor suppressor involved in uveal melanoma pathogenesis and may be associated with clinical outcome. Our data also suggest that submicroscopic deletion, but not large deletions, is the major mechanism of loss of PTEN expression in uveal melanomas.

High incidence of malformation syndromes in a series of 1,073 children with cancer

Constitutional molecular defects are known to play a role in oncogenesis, as shown by the increased incidence of embryonic cancers in children with Beckwith-Wiedemann syndrome (BWS) or of leukemia in children with Down syndrome. To establish the incidence and spectrum of malformation syndromes associated with childhood cancer we performed a clinical morphological examination on a series of 1,073 children with cancer. We diagnosed a syndrome in 42 patients (3.9%) and suspected the presence of a syndrome in another 35 patients (3.3%), for a total of 7.2%. This incidence of patients with a proven or suspected syndrome is high, and points to a possible association. We describe new syndrome-tumor associations in several entities: cleidocranial dysostosis (Wilms tumor), Bardet-Biedl syndrome (BBS) (acute lymphoblastic leukemia), Kabuki syndrome (neuroblastoma), LEOPARD syndrome (neuroblastoma), Poland anomaly (osteosarcoma; Hodgkin disease), and blepharophimosis epicanthus inversus syndrome (Burkitt lymphoma). Twenty of the 42 syndrome diagnoses were not recognized in the patients prior to this study, indicating that these diagnoses are commonly missed. We propose that all children with a malignancy should be examined by a clinical geneticist or a pediatrician skilled in clinical morphology to determine if the patients have a malformation syndrome.

De novo t(7;10)(q33;q23) translocation and closely juxtaposed microdeletion in a patient with macrocephaly and developmental delay

We have applied FISH with fully integrated BACs and BAC subfragments assessed in the human genome sequence to a de novo t(7;10)(q33;q23) translocation in a patient with developmental delay and macrocephaly. The translocation breakpoints disrupt the SEC8L1 gene on chromosome 7 and the PTEN gene on chromosome 10. RT-PCR demonstrated chimeric transcripts containing the first 11 exons of SEC8L1 fused to exon 3 of PTEN. In addition to the balanced translocation, we found a 7-Mb deletion in the translocated part of chromosome 7 at 4-Mb distance of the translocation breakpoint. This microdeletion, which disrupts the PTN and TPK1 genes and deletes 29 bonafide genes and the T-cell receptor beta locus, arose in the paternal germline. The patient's phenotype may be caused by a dominant-negative effect of the SEC8L1-PTEN fusion protein and/or haploinsufficiency of the disrupted or deleted genes. Our study demonstrates that de novo translocations can be associated with microdeletions outside the breakpoint region(s), rendering the study and risk estimation of such breakpoints more complicated than previously assumed.

Silencing of the maternally imprinted tumor suppressor ARHI contributes to follicular thyroid carcinogenesis

The two most common subtypes of thyroid cancer, follicular thyroid carcinoma (FTC) and papillary thyroid carcinoma, have been extensively studied, but our fundamental understanding of the molecular events in thyroid epithelial oncogenesis is still limited. Unreported data from our previous published global gene expression analysis revealed that the tumor suppressor gene aplysia ras homolog I (ARHI) is frequently underexpressed in FTCs. In this study, we elucidated the frequency and mechanism of ARHI silencing in benign and malignant thyroid neoplasia. We demonstrated that underexpression of ARHI occurs principally in FTCs (P = 0.0018), including its oncocytic variant (11 of 13), even at minimally invasive stage but not classic papillary thyroid carcinoma (two of seven) or follicular adenoma (FA) (three of 14). FTCs show strong allelic imbalance with reduction in copy number/loss of heterozygosity (LOH) in 69%, compared with less than 10% for FAs. In combination with our LOH data, bisulfite sequencing in a subset of samples revealed that FA displays a symmetric methylation pattern, likely representing one unmethylated allele and one presumptively imprinted allele, whereas FTC shows a virtually complete methylation pattern, representing LOH of the nonimprinted allele with only the hypermethylated allele remaining. Furthermore, we showed that pharmacologic inhibition of histone deacetylation but not demethylation could reactivate ARHI expression in the FTC133 FTC cell line. Therefore, our data suggest that silencing of the putative maternally imprinted tumor suppressor gene ARHI, primarily by large genomic deletion in conjunction with hypermethylation of the genomically imprinted allele, serves as a key early event in follicular thyroid carcinogenesis.

Hereditary cancer syndromes of the skin

Hereditary cancer syndromes are a group of disorders characterized by a genetic susceptibility to the development of malignant tumors. Multiple cancers in the family or an abnormally early onset for the given cancer may suggest an underlying inherited predisposition. Awareness of their associated dermatologic manifestations can facilitate early detection of risk for neoplasms. This article provides an update on the clinical features, diagnostic criteria, and the use of genetic analysis in the detection of causative mutations of those hereditary cancer syndromes with cutaneous manifestations.

Frequent inactivation of PTEN by promoter hypermethylation in microsatellite instability-high sporadic colorectal cancers

Loss of PTEN tumor suppressor function is observed in tumors of breast, prostate, thyroid, and endometrial origin. Allelic losses in the proximity of the PTEN locus (10q23) also occur in sporadic colorectal cancers (CRCs), but biallelic inactivation of this site has not been frequently demonstrated. We hypothesized that alternative mechanisms of PTEN allelic inactivation, such as promoter hypermethylation, might be operative in CRC and that PTEN inactivation may be related to recognized forms of genomic instability. We characterized a cohort of 273 sporadic CRCs by determining their microsatellite instability (MSI) status. Of these, 146 cancers were examined for PTEN promoter methylation by methylation-specific PCR. Mutations at the poly(A)6 repeat sequences in PTEN exons 7 and 8 and deletions at the 10q23 locus were also identified using microsatellite analysis. The presence of PTEN protein was determined by immunostaining, and the results were correlated with the promoter methylation status. We observed that PTEN promoter hypermethylation was a frequent occurrence in MSI-high (MSI-H) tumors (19.1% of MSI-H versus 2.2% of MSI-low/microsatellite stable tumors; P = 0.002). A PTEN mutation or a deletion event was present in 60% of the tumors with promoter region hypermethylation. Hypermethylation of the PTEN promoter correlated significantly with either decreased or complete loss of PTEN protein expression (P = 0.004). This is the first demonstration of PTEN inactivation as a result of promoter hypermethylation in MSI-H sporadic CRCs. These data suggest that this silencing mechanism plays a major role in PTEN inactivation and, in colon cancer, may be more important than either allelic losses or inactivating mutations. The significant correlation of PTEN hypermethylation with MSI-H tumors further suggests that PTEN is an additional important "target" of methylation along with the hMLH1 gene in the evolution of MSI-H CRCs and also confers the "second hit" in the biallelic inactivation mechanism for some proportion of tumors.

Cowden's disease: clinical and molecular genetic findings in a patient with a novel PTEN germline mutation

We report a 54-year-old woman with Cowden's disease (CD) who was found to carry a novel germline mutation in the PTEN gene. The mutation (c.334C-->G) introduced a splice donor site within exon 5 that caused the expression of an aberrant transcript lacking 159 nucleotides corresponding to codons 112-164. Clinically, the patient showed multiple benign hamartomatous lesions of the skin, papillomatosis of the lips and oral mucosa, polyposis coli and bilateral fibrocystic disease of the breast. In addition, she developed different types of malignant neoplasms, including bilateral carcinomas of the breast and malignant melanomas of the skin. Molecular genetic analysis of a benign skin hamartoma and an invasive ductal breast carcinoma revealed loss of heterozygosity (LOH) at microsatellite markers on chromosome 10 in the carcinoma but not in the hamartoma. The breast carcinoma additionally carried a somatic TP53 point mutation (c.466C-->G; R156G) that was associated with LOH on 17p and nuclear p53 protein accumulation. Taken together, our findings indicate that benign hamartomas in CD may develop without loss of the second (wild-type) PTEN allele, whereas the pathogenesis of malignant tumours, such as breast carcinomas, appears to require the complete inactivation of Pten as well as further alterations such as the loss of p53-dependent growth control.

Frequent monoallelic deletion of PTEN and its reciprocal associatioin with PIK3CA amplification in gastric carcinoma

Mutational alterations of PTEN and PIK3CA, which negatively and positively regulate PI3-kinase activity, respectively, have been observed in many types of human cancer. To explore the implication of PTEN and PIK3CA mutations in gastric tumorigenesis, we characterized the expression and mutation status of the genes in 126 gastric tissues and 15 cell lines. Expression of PTEN transcript was abnormally low in 5 of 15 (33%) cell lines and 20 of 55 (36%) primary carcinomas, whereas 0 of 71 noncancerous tissues including 16 benign tumors showed altered expression. Allelotyping analysis using an intragenic polymorphism (IVS4+109) revealed that 14 of 30 (47%) informative cases carried LOH of the gene, which is closely linked to low expression. The LOH rate was significantly higher in advanced tumors [12 of 19 (63%)] compared to early-stage tumors [2 of 11 (18%)] and more frequent in poorly differentiated tumors [9 of 13 (69%)] than well- or moderately differentiated tumors [5 of 17 (29%)]. Interestingly, however, none of the LOH tumors carried mutational disruption of the remaining allele, suggesting haploinsufficiency of PTEN in gastric tumorigenesis. Methylation studies revealed that PTEN pseudogene, but not PTEN, is methylated in cell lines and primary tumors, indicating that PTEN is not a target of epigenetic silencing in gastric cancers and that the pseudogene should be considered more carefully in methylation analysis of the PTEN promoter. Genomic amplification of PIK3CA was found in 9 of 15 (60%) cell lines and 20 of 55 (36.4%) primary tumors but in no noncancerous tissues. Furthermore, PIK3CA amplification was predominantly detected in tumors with no PTEN alterations, suggesting that mutations of PTEN and PIK3CA are mutually exclusive events in gastric tumorigenesis. Amplification of PIK3CA was strongly associated with increased expression of PIK3CA transcript and elevated levels of phospho-AKT. Collectively, our data reveal that 13 of 15 (87%) gastric cell lines and 31 of 55 (56%) primary carcinomas harbored either amplification of PIK3CA or abnormal reduction of PTEN. Mutually exclusive alterations of PTEN and PIK3CA also suggest that mutations of either gene could activate the PI3-kinase/AKT signaling pathway, which is directly linked to the malignant progression of gastric tumor cells.

PTEN tumor suppressor regulates p53 protein levels and activity through phosphatase-dependent and -independent mechanisms

We show in this study that PTEN regulates p53 protein levels and transcriptional activity through both phosphatase-dependent and -independent mechanisms. The onset of tumor development in p53(+/-);Pten(+/-) mice is similar to p53(-/-) animals, and p53 protein levels are dramatically reduced in Pten(-/-) cells and tissues. Reintroducing wild-type or phosphatase-dead PTEN mutants leads to a significant increase in p53 stability. PTEN also physically associates with endogenous p53. Finally, PTEN regulates the transcriptional activity of p53 by modulating its DNA binding activity. This study provides a novel mechanism by which the loss of PTEN can functionally control "two" hits in the course of tumor development by concurrently modulating p53 activity.

Recurrent allelic imbalance at the rat Pten locus in DMBA-induced fibrosarcomas

The tumor-suppressor gene PTEN (phosphatase and tensin homolog) is frequently inactivated in different types of human tumors. Less is known about the involvement of the homologous gene Pten in animal model systems of cancer. By sequencing one of the introns of rat Pten, we found an informative intragenic PCR marker suitable for genetic studies. Through use of this marker, the position of Pten in the genetic linkage map was localized to the distal part of rat chromosome 1 (RNO1) by analysis of F2 progeny from an intercross between inbred strains BN and LE. Subsequently, 22 markers from this region (including the intragenic Pten marker) were used to study the occurrence of allelic imbalance in distal RNO1 in fibrosarcomas that had been induced by DMBA in F1(BNxLE) rats. The analysis revealed that allelic imbalance was common in the vicinity of Pten, and there was loss or reduction of one of the Pten alleles in more than 60% of the fibrosarcomas. DNA sequencing was preformed to investigate whether the Pten allele remaining in the tumors was inactivated by mutation. However, no mutations were detected in the genomic sequence of Pten exons 5 to 9 in any of the fibrosarcomas, and normal mRNA transcripts were expressed in all tumors. Thus, based on the targeted selection for loss of Pten observed in some of these tumors and the absence of inactivation of the remaining allele, we suggest that haploinsufficiency of Pten may be an important factor in rat DMBA-induced fibrosarcomas.

Direct identification of PTEN phosphorylation sites

The PTEN tumor suppressor gene encodes a phosphatidylinositol 3'-phosphatase that is inactivated in a high percentage of human tumors, particularly glioblastoma, melanoma, and prostate and endometrial carcinoma. Previous studies showed that PTEN is a seryl phosphoprotein and a substrate of protein kinase CK2 (CK2). However, the sites in PTEN that are phosphorylated in vivo have not been identified directly, nor has the effect of phosphorylation on PTEN catalytic activity been reported. We used mass spectrometric methods to identify Ser(370) and Ser(385) as in vivo phosphorylation sites of PTEN. These sites also are phosphorylated by CK2 in vitro, and phosphorylation inhibits PTEN activity towards its substrate, PIP3. We also identify a novel in vivo phosphorylation site, Thr(366). Following transient over-expression, a fraction of CK2 and PTEN co-immunoprecipitate. Moreover, pharmacological inhibition of CK2 activity leads to decreased Akt activation in PTEN+/+ but not PTEN-/- fibroblasts. Our results contrast with previous assignments of PTEN phosphorylation sites based solely on mutagenesis approaches, suggest that CK2 is a physiologically relevant PTEN kinase, and raise the possibility that CK2-mediated inhibition of PTEN plays a role in oncogenesis.

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.

Activation of a cryptic splice site of PTEN and loss of heterozygosity in benign skin lesions in Cowden disease

Cowden disease is an autosomal dominant syndrome characterized by facial trichilemmomas, acral keratoses, papillomatous papules, mucosal lesions, and an increased risk for breast and nonmedullary thyroid cancer. Here, we describe a novel PTEN splicing site mutation in a family with classical Cowden disease and we studied benign skin lesions typical for Cowden disease for loss of heterozygosity. We found a PTEN IVS2 + 1G > Alpha 5'-splicing acceptor mutation resulting in activation of a cryptic splice site. Activation of this cryptic splice site is predicted to result in a frameshift with a premature stop codon, thus disrupting the phosphatase core motif of PTEN. Loss of heterozygosity analysis of two trichilemmomas, one fibroma, and three acanthomas of the index patient demonstrated loss of heterozygosity at the PTEN locus in four of these lesions. In conclusion, our data demonstrate that a PTEN splicing site mutation causes activation of a cryptic splice site, which results in aberrant transcripts.

Germline mutations in BMPR1A/ALK3 cause a subset of cases of juvenile polyposis syndrome and of Cowden and Bannayan-Riley-Ruvalcaba syndromes

Juvenile polyposis syndrome (JPS) is an inherited hamartomatous-polyposis syndrome with a risk for colon cancer. JPS is a clinical diagnosis by exclusion, and, before susceptibility genes were identified, JPS could easily be confused with other inherited hamartoma syndromes, such as Bannayan-Riley-Ruvalcaba syndrome (BRRS) and Cowden syndrome (CS). Germline mutations of MADH4 (SMAD4) have been described in a variable number of probands with JPS. A series of familial and isolated European probands without MADH4 mutations were analyzed for germline mutations in BMPR1A, a member of the transforming growth-factor beta-receptor superfamily, upstream from the SMAD pathway. Overall, 10 (38%) probands were found to have germline BMPR1A mutations, 8 of which resulted in truncated receptors and 2 of which resulted in missense alterations (C124R and C376Y). Almost all available component tumors from mutation-positive cases showed loss of heterozygosity (LOH) in the BMPR1A region, whereas those from mutation-negative cases did not. One proband with CS/CS-like phenotype was also found to have a germline BMPR1A missense mutation (A338D). Thus, germline BMPR1A mutations cause a significant proportion of cases of JPS and might define a small subset of cases of CS/BRRS with specific colonic phenotype.

Survey of somatic mutations in tuberous sclerosis complex (TSC) hamartomas suggests different genetic mechanisms for pathogenesis of TSC lesions

Tuberous sclerosis complex (TSC), an autosomal dominant disease caused by mutations in either TSC1 or TSC2, is characterized by the development of hamartomas in a variety of organs. Concordant with the tumor-suppressor model, loss of heterozygosity (LOH) is known to occur in these hamartomas at loci of both TSC1 and TSC2. LOH has been documented in renal angiomyolipomas (AMLs), but loss of the wild-type allele in cortical tubers appears to be very uncommon. Analysis of second, somatic events in tumors for which the status of both TSC1 and TSC2 is known is essential for exploration of the pathogenesis of TSC-lesion development. We analyzed 24 hamartomas from 10 patients for second-hit mutations, by several methods, including LOH, scanning of all exons of both TSC1 and TSC2, promoter methylation of TSC2, and clonality analysis. Our results document loss of the wild-type allele in six of seven AMLs, without evidence of the inactivation of the second allele in many of the other lesions, including tumors that appear to be clonally derived. Laser-capture microdissection further demonstrated loss of the second allele in all three cellular components of an AML. This study thus provides evidence that, in both TSC1 and TSC2, somatic mutations resulting in the loss of wild-type alleles may not be necessary in some tumor types-and that other mechanisms may contribute to tumorigenesis in this setting.

Frequent loss of PTEN expression is linked to elevated phosphorylated Akt levels, but not associated with p27 and cyclin D1 expression, in primary epithelial ovarian carcinomas

PTEN (MMAC1/TEP1), a tumor suppressor gene on chromosome subband 10q23.3, is variably mutated and/or deleted in a variety of human cancers. Germline mutations in PTEN, which encode a dual-specificity phosphatase, have been implicated in at least two hamartoma tumor syndromes that exhibit some clinical overlap, Cowden syndrome and Bannayan-Riley-Ruvalcaba syndrome. Among several series of ovarian cancers, the frequency of loss of heterozygosity (LOH) of markers flanking and within PTEN, is approximately 30 to 50%, and the somatic intragenic PTEN mutation frequency is <10%. In this study, we screened primary adenocarcinomas of the ovary for LOH of polymorphic markers within and flanking the PTEN gene and for intragenic mutations of the PTEN gene and compared them to PTEN expression using immunohistochemistry. Furthermore, we sought to detect the expression of the presumed downstream targets of PTEN, such as P-Akt, p27, and cyclin D1 by immunohistochemistry. LOH at 10q23 was observed in 29 of 64 (45%) cases. Of the 117 samples, 6 somatic intragenic PTEN mutations, 1 germline mutation, and 1 novel polymorphism were found in 7 (6%) patients. Immunostaining of 49 ovarian cancer samples revealed that 13 (27%) were PTEN immunostain-negative, 25 (51%) had reduced staining, and the rest (22%) were PTEN expression-positive. Among the 44 informative tumors assessed for 10q23 LOH and PTEN immunostaining, there was an association between 10q23 LOH and decreased or absent staining (P = 0.0317). Of note, there were five (11%) tumors with neither mutation nor deletion that exhibited no PTEN expression and 10 (25%) others without mutation or deletion but had decreased PTEN expression. Among the 49 tumors available for immunohistochemistry, 28 (57%) showed P-Akt-positive staining, 24 (49%) had decreased p27 staining, and cyclin D1 was overexpressed in 35 (79%) cases. In general, P-Akt expression was inversely correlated with PTEN expression (P = 0.0083). These data suggest that disruption of PTEN by several mechanisms, allelic loss, intragenic mutation, or epigenetic silencing, all contribute to epithelial ovarian carcinogenesis, and that epigenetic silencing is a significant mechanism. The Akt pathway is prominently involved, but clearly not in all cases. Surprisingly, despite in vitro demonstration that p27 and cyclin D1 lies downstream of PTEN and Akt, there was no correlation between p27 and cyclin D1 expression and PTEN or P-Akt status. Thus, in vivo, although PTEN and Akt play a prominent role in ovarian carcinogenesis, p27 and cyclin D1 might not be the primary downstream targets. Alternatively, these observations could also suggest that pathways involving other than Akt, p27 and cyclin D1 that lie downstream of PTEN play roles in ovarian carcinogenesis.

PTEN: life as a tumor suppressor

PTEN, a tumor suppressor located at chromosome 10q23, is mutated in a variety of sporadic cancers and in two autosomal dominant hamartoma syndromes. PTEN is a phosphatase which dephosphorylates phosphatidylinositol (3,4,5)-triphosphate (PtdIns-3,4,5-P3), an important intracellular second messenger, lowering its level within the cell. By dephosphorylating PtdIns-3,4,5-P3, PTEN acts in opposition to phosphatidylinositol 3-kinase (PI3K), which has a pivotal role in the creation of PtdIns-3,4,5-P3. PtdIns-3,4,5-P3 is necessary for the activation of Akt, a serine/threonine kinase involved in cell growth and survival. By blocking the activation of Akt, PTEN regulates cellular processes such as cell cycling, translation, and apoptosis. In this review, we will discuss the identification of PTEN, its mutational status in cancer, its role as a regulator of PI3K, and its domain structure.

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.

Pathogenesis of colorectal cancer

The development of colorectal cancer has been viewed as an ordered process in which three main phases can be identified: initiation, promotion and progression. There is definite proof that stable alterations of the structure or sequence of DNA (mutations) represent the initiating event; these are followed by an uncontrolled expansion of the neoplastic clones which characterizes tumoural growth. Several classes of genes have been identified foncogenes, tumour suppressor genes and "mutator" genes) the alterations of which are important in the initiation as well as in the promotion and progression of tumours. Colorectal cancer, therefore, results from a series of genetic changes which lead to the progressive and irreversible loss of normal control of cell growth and differentiation. Available evidence is consistent with the hypothesis that there are several molecular pathways underlying the passage from normal mucosa to colorectal carcinoma, thus explaining the existence of intestinal tumours with a different biological nature, which may represent specific targets for prevention and cure. Well-defined molecular pathways have been identified for: A) sporadic colorectal cancer ("Loss of heterozygosity pathway"); B) familial adenomatous polyposis and related polyposis syndromes; C) hereditary non-polyposis colorectal cancer ("mutator genes/microsatellite instability pathway"); D) cancer developing in inflammatory bowel diseases; E) familial colorectal cancer. Thus, there is consistent and considerable evidence suggesting the existence of several biological pathways leading to the same phenotypical expression (i.e., colorectal cancer), and it is likely that additional pathways will be clarified in the future. From a practical point of view, tumours with a diverse biology might offer different and more effective preventive and curative approaches.

Effects of ligand activation of peroxisome proliferator-activated receptor gamma in human prostate cancer

Peroxisome proliferator-activated receptor gamma (PPARgamma) is a nuclear hormone receptor that plays a key role in the differentiation of adipocytes. Activation of this receptor in liposarcomas and breast and colon cancer cells also induces cell growth inhibition and differentiation. In the present study, we show that PPARgamma is expressed in human prostate adenocarcinomas and cell lines derived from these tumors. Activation of this receptor with specific ligands exerts an inhibitory effect on the growth of prostate cancer cell lines. Further, we show that prostate cancer and cell lines do not have intragenic mutations in the PPARgamma gene, although 40% of the informative tumors have hemizygous deletions of this gene. Based on our preclinical data, we conducted a phase II clinical study in patients with advanced prostate cancer using troglitazone, a PPARgamma ligand used for the treatment of type 2 diabetes. Forty-one men with histologically confirmed prostate cancer and no symptomatic metastatic disease were treated orally with troglitazone. An unexpectedly high incidence of prolonged stabilization of prostate-specific antigen was seen in patients treated with troglitazone. In addition, one patient had a dramatic decrease in serum prostate-specific antigen to nearly undetectable levels. These data suggest that PPARgamma may serve as a biological modifier in human prostate cancer and its therapeutic potential in this disease should be further investigated.

Pediatric skin tumors

This article summarizes several malignant childhood neoplasms and benign tumors that can mimic malignancies. Because malignant skin tumors are rare in children, parents and physicians often are not sufficiently suspicious to ensure that an early diagnosis can be made. Many malignant skin tumors have features that suggest a vascular or hemangioma-like lesion. Because hemangiomas occur in 10% of infants, it is often considered prudent to adopt a wait-and-see attitude; however, if the lesion is too firm to be a hemangioma or its growth pattern does not follow that of a typical hemangioma, additional options should be considered. To manage childhood skin malignancies, one needs expert consultation, early biopsy, and correct histopathologic interpretation.