Considerations on diagnosis and surveillance measures of PTEN hamartoma tumor syndrome: clinical and genetic study in a series of Spanish patients.

BACKGROUND: The limited knowledge about the PTEN hamartoma tumor syndrome (PHTS) makes its diagnosis a challenging task. We aimed to define the clinical and genetic characteristics of this syndrome in the Spanish population and to identify new genes potentially associated with the disease. RESULTS: We reviewed the clinical data collected through a specific questionnaire in a series of 145 Spanish patients with a phenotypic features compatible with PHTS and performed molecular characterization through several approaches including next generation sequencing and whole exome sequencing (WES). Macrocephaly, mucocutaneous lesions, gastrointestinal polyposis and obesity are prevalent phenotypic features in PHTS and help predict the presence of a PTEN germline variant in our population. We also find that PHTS patients are at risk to develop cancer in childhood or adolescence. Furthermore, we observe a high frequency of variants in exon 1 of PTEN, which are associated with renal cancer and overexpression of KLLN and PTEN. Moreover, WES revealed variants in genes like NEDD4 that merit further research. CONCLUSIONS: This study expands previously reported findings in other PHTS population studies and makes new contributions regarding clinical and molecular aspects of PHTS, which are useful for translation to the clinic and for new research lines.

Thyroid Follicular Cell-derived Carcinomas in a Background of Multiple Adenomatous Nodules Leading to a Diagnosis of PTEN Hamartoma Tumor Syndrome in an Adult Patient With a Novel RECQL4 Mutation.

BACKGROUND: Phosphatase and tensin homolog (PTEN) hamartoma tumor syndrome (PHTS) is a complex disorder. Carriers develop hamartomatous tumors, with an increased risk for developing malignant tumors in multiple organs. Surveillance to facilitate the early detection and treatment of malignancies is extremely important. CASE REPORT: A 31-year-old male presented with a 10 cm left lobe thyroid gland mass. After fine needle aspiration a left hemithyroidectomy was performed, which demonstrated a minimally invasive follicular thyroid carcinoma (FTC, stage pT3a) and microscopic classical papillary thyroid carcinoma (PTC) in the background of about 50 separate adenomatous nodules (0.2-5 mm). Immunostaining showed loss of PTEN protein in the minimally invasive FTC and in all of the nodules tested, with uninvolved parenchyma serving as an internal control. Kaiser Permanente Northern California (KPNC) Hereditary Cancer Panel, testing for 62 genes, was performed and showed germline mutations in PTEN and RecQ like helicase 4 (RECQL4) genes. Completion thyroidectomy subsequently performed demonstrated about 60 follicular cell-derived adenomatous nodules (0.3-10 mm). Genetic counseling and evaluation documented Cowden syndrome (CS) in the family. Thus, PHTS was confirmed. CONCLUSION: This report documents synchronous FTC and PTC in a background of multiple follicular adenomatous nodules with a novel RECQL4 mutation in an adult patient with PHTS. As such, documented the loss of PTEN protein in a thyroid gland affected by multiple adenomatous nodules aided in diagnosing PHTS.

Novel Germline PTEN Mutation Associated with Cowden Syndrome and Osteosarcoma.

BACKGROUND: Cowden syndrome (CS) is a rare autosomal-dominant inherited disorder characterized by multiple hamartomas. While the hamartomas are benign, patients with CS have increased risk of osteosarcoma and of breast, thyroid, endometrial, soft-tissue and colonic neoplasms. Germline mutations of phosphatase and tensin homolog (PTEN) are implicated in CS and in the development of osteosarcoma. We report a patient with CS who presented with osteosarcoma, ganglioneuromatosis and a benign breast mass. Osteosarcoma, as presentation of CS, is rare (only one report in the English literature). Genomic DNA from the patient's peripheral blood was quantified by spectrophotometry, then underwent sequence enrichment, polymerase chain reaction and next-generation sequencing. Molecular analysis revealed a non-synonymous c.17_18delAA frameshift mutation in exon 1 of PTEN and a c.116G>T (p.R39L) missense mutation of serine/threonine kinase 11 (STK11) of unknown significance. CONCLUSION: We report a patient with CS presenting with ganglioneuromatosis, benign breast mass and osteosarcoma, harboring a novel molecular alteration in PTEN which to our knowledge has not been previously reported.

A retrospective chart review of the features of PTEN hamartoma tumour syndrome in children.

OBJECTIVE: It is recognised that 5% - 10 % of children with macrocephaly and autism spectrum disorder (ASD) and/or intellectual disability (ID) have a heterozygous pathogenic mutation in the PTEN tumour suppressor gene that is associated with PTEN hamartoma tumour syndrome. However, the clinical features and course in children with a pathogenic PTEN mutation are unclear and have not been well documented. STUDY OBJECTIVES: We undertook a retrospective chart review of children (< 18 years) with pathogenic PTEN mutations to ascertain clinical findings, clinical course and possible outcomes. RESULTS: Clinical and molecular data were collected and analysed for 47 patients with PTEN mutation from 38 eligible families. Macrocephaly (average head circumference of + 5.7 SD) with developmental delay, ID and/or ASD were the most common presenting signs/symptoms (66 %). Clinical features included dermatological findings (66 %), gastrointestinal (GI) symptoms (34 %), ASD diagnosis (50 %), abnormal brain imaging (53 % of those examined) and abnormal thyroid imaging (26 %). CONCLUSIONS: This is the largest survey of clinical features in children with PTEN pathogenic mutations to date. It confirms earlier reports of increased rates of neurodevelopmental disorders. Dermatological, GI and thyroid abnormalities are age dependent and may not be present at the time of diagnosis, requiring regular monitoring and medical surveillance. Early paediatric diagnosis is important for institution of medical and developmental surveillance as well as for testing other at- risk family members.

Inherited PTEN mutations and the prediction of phenotype.

PTEN has been heavily studied due to its role as a tumour suppressor and as a core inhibitory component of the phosphoinositide 3-kinase (PI3K) signalling network. It is a broadly expressed phosphatase which displays complexity and diversity in both its functions and regulation and accordingly, in the laboratory numerous classes of functionally distinct mutations have been generated. Inherited loss of function mutations in the PTEN gene were originally identified in sufferers of Cowden disease, but later shown to associate with more diverse human pathologies, mostly relating to cell and tissue overgrowth, leading to the use of the broader term, PTEN Hamartoma Tumour Syndrome. Recent phenotypic analysis of clinical cohorts of PTEN mutation carriers, combined with laboratory studies of the consequences of these mutations implies that stable catalytically inactive PTEN mutants may lead to the most severe phenotypes, and conversely, that mutants retaining partial function associate more frequently with a milder phenotype, with autism spectrum disorder often being diagnosed. Future work will be needed to confirm and to refine these genotype-phenotype relationships and convert this developing knowledge into improved patient management and potentially treatment with emerging drugs which target the PI3K pathway.

Tumor-to-tumor metastases in Cowden's disease: an autopsy case report and review of the literature.

Tumor-to-tumor metastasis is a rare phenomenon, but it has been suggested to be more frequent in patients with hereditary cancer syndrome. We report an autopsy case of tumor-to-tumor metastasis in a 75-year-old male. At 6 months before his death, the patient complained of hoarseness and dysphagia, and clinical whole-body examinations revealed advanced lung adenocarcinoma (T4N2M1b, Stage IV), multiple skin verrucas, gastrointestinal polyposis, goiters, and cerebellar dysplastic gangliocytoma (Lhermitte-Duclos disease), while PTEN gene mutation was detected in his serum. An mTOR inhibitor had been used to treat his lung adenocarcinoma, but he developed aspiration pneumonia and died of respiratory failure. Autopsy revealed that the lung adenocarcinoma had metastasized to cavernous hemangiomas of the right atrial appendage and liver, to cerebellar dysplastic gangliocytoma and to multiple organs such as the liver, kidney, adrenal glands and spine. This is the first reported case of Cowden's disease with multiple tumor-to-tumor metastases.

Functionally distinct groups of inherited PTEN mutations in autism and tumour syndromes.

BACKGROUND: Germline mutations in the phosphatase PTEN are associated with diverse human pathologies, including tumour susceptibility, developmental abnormalities and autism, but any genotype-phenotype relationships are poorly understood. METHODS: We have studied the functional consequences of seven PTEN mutations identified in patients diagnosed with autism and macrocephaly and five mutations from severe tumour bearing sufferers of PTEN hamartoma tumour syndrome (PHTS). RESULTS: All seven autism-associated PTEN mutants investigated retained the ability to suppress cellular AKT signalling, although five were highly unstable. Observed effects on AKT also correlated with the ability to suppress soma size and the length and density of dendritic spines in primary neurons. Conversely, all five PTEN mutations from severe cases of PHTS appeared to directly and strongly disrupt the ability to inhibit AKT signalling. CONCLUSIONS: Our work implies that alleles causing incomplete loss of PTEN function are more commonly linked to autism than to severe PHTS cases.

Second malignant neoplasms in patients with Cowden syndrome with underlying germline PTEN mutations.

PURPOSE: Patients with Cowden syndrome (CS) with underlying germline PTEN mutations are at increased risk of breast, thyroid, endometrial, and renal cancers. To our knowledge, risk of subsequent cancers in these patients has not been previously explored or quantified. PATIENTS AND METHODS: We conducted a 7-year multicenter prospective study (2005 to 2012) of patients with CS or CS-like disease, all of whom underwent comprehensive PTEN mutational analysis. Second malignant neoplasms (SMNs) were ascertained by medical records and confirmed by pathology reports. Standardized incidence ratios (SIRs) for all SMNs combined and for breast, thyroid, endometrial, and renal cancers were calculated. RESULTS: Of the 2,912 adult patients included in our analysis, 2,024 had an invasive cancer history. Germline pathogenic PTEN mutations (PTEN mutation positive) were identified in 114 patients (5.6%). Of these 114 patients, 46 (40%) had an SMN. Median age of SMN diagnosis was 50 years (range, 21 to 71 years). Median interval between primary cancer and SMN was 5 years (range, <1 to 35 years). Of the 51 PTEN mutation-positive patients who presented with primary breast cancer, 11 (22%) had a subsequent new primary breast cancer and 10-year second breast cancer cumulative risk of 29% (95% CI, 15.3 to 43.7). Risk of SMNs compared with that of the general population was significantly elevated for all cancers (SIR, 7.74; 95% CI, 5.84 to 10.07), specifically for breast (SIR, 8.92; 95% CI, 5.85 to 13.07), thyroid (SIR, 5.83; 95% CI, 3.01 to 10.18), and endometrial SMNs (SIR, 14.08.07; 95% CI, 7.10 to 27.21). CONCLUSION: Patients with CS with germline PTEN mutations are at higher risk for SMNs compared with the general population. Prophylactic mastectomy should be considered on an individual basis given the significant risk of subsequent breast cancer.

A novel deleterious PTEN mutation in a patient with early-onset bilateral breast cancer.

BACKGROUND: An early age at Breast Cancer (BC) onset may be a hallmark of inherited predisposition, but BRCA1/2 mutations are only found in a minority of younger BC patients. Among the others, a fraction may carry mutations in rarer BC genes, such as TP53, STK11, CDH1 and PTEN. As the identification of women harboring such mutations allows for targeted risk-management, the knowledge of associated manifestations and an accurate clinical and family history evaluation are warranted. CASE PRESENTATION: We describe the case of a woman who developed an infiltrating ductal carcinoma of the right breast at the age of 32, a contralateral BC at age 36 and another BC of the right breast at 40. When she was 39 years-old, during a dermatological examination, mucocutaneous features suggestive of Cowden Syndrome, a disorder associated to germ-line PTEN mutations, were noticed. PTEN genetic testing revealed the novel c.71A > T (p.Asp24Val) mutation, whose deleterious effect, suggested by conservation data and in silico tools, was definitely demonstrated by the incapacity of mutant PTEN to inhibit Akt phosphorylation when used to complement PTEN-null cells. In BC tissue, despite the absence of LOH or somatic mutations of PTEN, Akt phosphorylation was markedly increased in comparison to normal tissue, thus implying additional somatic events into the deregulation of the PI3K/Akt/mTOR pathway and, presumably, into carcinogenesis. Hence, known oncogenic mutations in PIK3CA (exons 10 and 21) and AKT1 (exon 2) were screened in tumor DNA with negative results, which suggests that the responsible somatic event(s) is a different, uncommon one. CONCLUSION: This case stresses the importance of clinical/genetic assessment of early-onset BC patients in order to identify mutation carriers, who are at high risk of new events, so requiring tailored management. Moreover, it revealed a novel PTEN mutation with pathogenic effect, pointing out, however, the need for further efforts to elucidate the molecular steps of PTEN-associated carcinogenesis.

Phosphatase and tensin homolog immunohistochemical staining and clinical criteria for Cowden syndrome in patients with trichilemmoma or associated lesions.

Trichilemmomas and mucocutaneous papillomatous papules are associated with Cowden syndrome (CS). Germline Phosphatase and tensin homolog (PTEN) mutations have been identified in 34% to 80% of those meeting clinical criteria for CS. PTEN expression has not been well evaluated in large numbers of trichilemmoma. We investigated clinical criteria for CS in trichilemmoma patients and studied PTEN staining to determine how often patients with trichilemmoma have CS and whether PTEN staining is useful. About 102 cases of trichilemmoma or associated lesions from 95 patients were collected. Clinical histories were reviewed to investigate the incidence of CS using International Cowden Consortium operational criteria for diagnosis of CS, version 2000. PTEN staining was performed and graded for intensity and percentage. Although 1 patient had 3 trichilemmoma or associated lesions, and 5 had 2 trichilemmoma or associated lesions, none of 95 patients met clinical criteria for a diagnosis of CS. Twelve of the 89 cases available for staining (13.5%) showed decreased PTEN. Of these, the demographic, clinical, and pathological features were not significantly different compared with PTEN intact cases. None of the cases from the 6 patients with more than 1 trichilemmoma or associated lesions showed decreased PTEN staining. We thus conclude that the likelihood of a clinical diagnosis of CS among patients with a solitary or only a few trichilemmoma is extremely low. PTEN expression is decreased in some sporadic trichilemmomas or associated lesions. This is the largest study investigating clinical history and PTEN staining in patients with trichilemmoma or associated lesions. Because none of our patients met clinical diagnostic criteria for CS, the direct correlation of PTEN in CS and sporadic trichilemmoma remains unclear.

Proliferative retinopathy in Cowden syndrome.

Cowden syndrome is a multiple hamartoma syndrome with a high risk of breast and thyroid tumours, both benign and malignant. The authors report a 24-year-old female patient who presented with reduced vision in both eyes. Ocular examination showed vitreous haemorrhage secondary to retinal new vessels in both eyes. There was no evidence of diabetes mellitus, and she had a wide range of normal investigations. She was labelled as idiopathic retinal neovascularisation. Fifteen years later, she presented with a lump in her left breast and a previous history of excision of a benign lump from her right breast. She also reported multiple tumours in her family. Clinical diagnosis of Cowden syndrome was made and genetic testing confirmed mutation of the PTEN gene.

Trichilemmomas show loss of PTEN in Cowden syndrome but only rarely in sporadic tumors.

BACKGROUND: Trichilemmoma (TL) can occur as a solitary sporadic lesion usually on the face or as multiple facial lesions almost invariably associated with Cowden syndrome (CS). CS is a multisystem disorder caused by a germline inactivating mutation in PTEN (10q23.31), a tumor suppressor gene. We sought to identify PTEN loss by immunohistochemistry (IHC) in sporadic and CS-associated TL to determine whether IHC is a useful tool to assess an individual for CS. METHODS: Six TL biopsies associated with CS and 33 biopsies without CS were retrieved. IHC for PTEN was performed. RESULTS were scored as positive (reactivity in TL cells) or negative (no reactivity in TL cells); normal squamous epithelium and vascular endothelium served as internal positive controls. RESULTS: Complete PTEN loss was noted in 5/6 (83%) CS-associated TL and 1/33 (3%) sporadic (non-CS) TL. CONCLUSION: Demonstration of complete PTEN loss in TL by IHC is strongly suggestive of association with CS, but retention of PTEN staining does not entirely exclude CS. Therefore, PTEN IHC in TLs may be helpful in screening TL for association with CS, but should be used in context with other established clinical criteria, and possibly germline PTEN genotyping to confirm a diagnosis of CS.

A comprehensive functional analysis of PTEN mutations: implications in tumor- and autism-related syndromes.

The PTEN (phosphatase and tensin homolog) phosphatase is unique in mammals in terms of its tumor suppressor activity, exerted by dephosphorylation of the lipid second messenger PIP(3) (phosphatidylinositol 3,4,5-trisphosphate), which activates the phosphoinositide 3-kinase/Akt/mTOR (mammalian target of rapamycin) oncogenic pathway. Loss-of-function mutations in the PTEN gene are frequent in human cancer and in the germline of patients with PTEN hamartoma tumor-related syndromes (PHTSs). In addition, PTEN is mutated in patients with autism spectrum disorders (ASDs), although no functional information on these mutations is available. Here, we report a comprehensive in vivo functional analysis of human PTEN using a heterologous yeast reconstitution system. Ala-scanning mutagenesis at the catalytic loops of PTEN outlined the critical role of residues within the P-catalytic loop for PIP(3) phosphatase activity in vivo. PTEN mutations that mimic the P-catalytic loop of mammalian PTEN-like proteins (TPTE, TPIP, tensins and auxilins) affected PTEN function variably, whereas tumor- or PHTS-associated mutations targeting the PTEN P-loop produced complete loss of function. Conversely, Ala-substitutions, as well as tumor-related mutations at the WPD- and TI-catalytic loops, displayed partial activity in many cases. Interestingly, a tumor-related D92N mutation was partially active, supporting the notion that the PTEN Asp92 residue might not function as the catalytic general acid. The analysis of a panel of ASD-associated hereditary PTEN mutations revealed that most of them did not substantially abrogate PTEN activity in vivo, whereas most of PHTS-associated mutations did. Our findings reveal distinctive functional patterns among PTEN mutations found in tumors and in the germline of PHTS and ASD patients, which could be relevant for therapy.

Predicting PTEN mutations: an evaluation of Cowden syndrome and Bannayan-Riley-Ruvalcaba syndrome clinical features.

BACKGROUND: Cowden syndrome (CS) is associated with benign hamartomatous lesions and risks for thyroid, breast and endometrial cancers. Bannayan-Riley-Ruvalcaba syndrome is an allelic disorder characterised by macrocephaly, intestinal polyps, lipomas, and pigmented penile macules. Diagnostic criteria for CS are based on the presence of a range of clinical features. However, prior data on the component clinical features have been based primarily on compilations of cases reported before development of consensus diagnostic criteria. OBJECTIVE: This study sought to determine the clinical features most predictive of a mutation in the largest single cohort of patients with clinical testing for PTEN mutations reported to date. METHODS: Molecular and clinical data were reviewed on 802 patients referred for PTEN analysis by a single laboratory. RESULTS: Deleterious mutations were found in 172 (21.4%) subjects. Among mutation carriers significant differences from previous reports were found for the frequencies of several clinical features, including macrocephaly, uterine fibroids, benign breast disease, and endometrial cancer. Logistic regression analyses indicated that female mutation carriers were best identified by the presence of macrocephaly, endometrial cancer, trichilemmomas, papillomatous papules, breast cancer, benign thyroid disease, and benign gastrointestinal (GI) lesions. For males, the most discriminating features were macrocephaly, lipomas, papillomatous papules, penile freckling, benign GI lesions, and benign thyroid disease. Age related differences were also identified. CONCLUSION: The mutation frequency in patients meeting CS diagnostic criteria (34%) was significantly lower than previously reported, suggesting a need for reevaluation of these criteria. A mutation prediction model has been developed which can help identify patients appropriate for PTEN testing in clinical practice.

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.

[Cowden syndrome, or multiple hamartomatous tumor syndrome, in clinical endocrinology]. / Le syndrome de Cowden ou syndrome des hamartomes multiples en endocrinologie clinique.

Cowden syndrome (CS) is the prototypic PTEN hamartoma tumor syndromes (PHTS), rare clinical syndromes characterized by germline mutations of the tumor suppressor PTEN. CS is characterized by association of macrocephaly, facial trichilemmomas, acral keratoses, papillomatous papules, with increased risk for breast, thyroid and endometrial cancer. PTEN, which is located on chromosome 10q23, regulates negatively the prosurvival PI3K/Akt/mTOR pathway through a lipid phosphatase activity. Loss of PTEN activates this pathway and leads to increased cellular growth, migration, proliferation, and survival. CS diagnosis is clinical, based on the association of pathognomonic, major and minor criteria. The association in a patient with thyroid cancer, rarely with multinodular goiter, of typical dermatological manifestations, easily identifiable by clinical examination (papillomatous papules, acral keratoses, trichilemmomas), with a history of breast, endometrial, or renal cancer, or hamartomatous tumors presence, should alert the clinician. Clinical management of patients with CS is multidisciplinary, to include early and frequent screening, surveillance, and preventive care for associated malignancies. The development of antineoplastic agents targeting PI3K/Akt/mTOR pathway, such as rapamycin, may be the opportunity of treatment in PHTS and CS patients, for whom no specific medical treatment exist.

First report of ovarian dysgerminoma in Cowden syndrome with germline PTEN mutation and PTEN-related 10q loss of tumor heterozygosity.

We present the first report of ovarian dysgerminoma in Cowden syndrome, presenting in a 7-year-old girl. In her second decade, a hamartomatous soft tissue extremity mass and diffuse gastrointestinal hamartomatous polyposis with pathologic features suggestive of either juvenile, Peutz-Jeghers, or Cowden polyps were identified, along with diffuse esophageal glycogenic acanthosis and skin manifestations. During regular thyroid cancer surveillance under the provisional diagnosis of Cowden syndrome, papillary thyroid carcinoma and benign follicular nodules were diagnosed at age 23. PTEN mutational analysis revealed a novel germline nonsense point mutation of Q219X. Loss of PTEN heterozygosity was also present in the ovarian dysgerminoma. Parental mutation testing and phenotype screening were negative. The correct classification of Cowden syndrome is difficult because of its protean manifestations and overlapping phenotypes with other genetic and noninherited pathologies, particularly regarding various gastrointestinal polyposis syndromes. Despite the challenges, correct classification is critical to patient care because of the associated cancer predispositions and necessary surveillance programs. This is the first report of Cowden syndrome presenting with ovarian dysgerminoma, which implicates PTEN in the molecular pathogenesis of dysgerminoma and adds it to the phenotypic manifestations of Cowden syndrome.

PTEN catalysis of phospholipid dephosphorylation reaction follows a two-step mechanism in which the conserved aspartate-92 does not function as the general acid--mechanistic analysis of a familial Cowden disease-associated PTEN mutation.

PTEN exerts its tumour suppressor function by dephosphorylating the phospholipid second messenger phosphatidylinositol-3,4,5-trisphosphate (PIP(3)). Herein, we demonstrate that the PTEN-catalysed PIP(3) dephosphorylation reaction involves two-steps: (i) formation of a phosphoenzyme intermediate (PE) in which Cys-124 in the active site is thiophosphorylated, and (ii) hydrolysis of PE. For protein tyrosine- and dual-specificity phosphatases, catalysis requires the participation of a conserved active site aspartate as the general acid in Step 1. Its mutation to alanine severely limits PE formation. However, mutation of the homologous Asp-92 in PTEN does not significantly limit PE formation, indicating that Asp-92 does not act as the general acid. G129E is a common germline PTEN mutations found in Cowden syndrome patients. Mechanistic analysis reveals that this mutation inactivates PTEN by both significantly slowing down Step 1 and abolishing the ability to catalyse Step 2. Taken together, our results highlight the mechanistic similarities and differences between PTEN and the conventional protein phosphatases and reveal how a disease-associated mutation inactivates PTEN.

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.