Mutations of the human PTEN gene

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

PTEN: one gene,many syndromes

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

Germline and germline mosaic PTEN mutations associated with a Proteus-like syndrome of hemihypertrophy, lower limb asymmetry, arteriovenous malformations and lipomatosis

Germline PTEN mutations cause Cowden syndrome (CS) and Bannayan-Riley-Ruvalcaba syndrome (BRR), two hamartoma-tumour syndromes, and somatic PTEN alterations have been shown to participate, to a greater or lesser extent, in a wide variety of sporadic neoplasia. PTEN is a tumour suppressor and dual-specificity phosphatase which affects apoptosis via its lipid phosphatase activity in the phosphoinositol-3-kinase and AKT pathway as well as inhibiting cell spreading via the focal adhesion kinase pathway. CS and BRR share some features, such as hamartomas and lipomatosis. To determine whether other syndromes characterized by overgrowth and lipomas are part of the PTEN syndrome spectrum, we ascertained six individuals with overgrowth and lipomas but who did not meet the diagnostic criteria for CS or BRR. Five had Proteus syndrome and one, a Proteus-like syndrome. When germline DNA and DNA from at least one involved tissue per case were examined for PTEN mutations, only the Proteus-like patient was found to harbour a germline R335X mutation. Interestingly, a lipomatous mass, an epidermoid naevus and arteriovenous malformation tissue, all of which were sampled from physically distinct sites, were all found to carry a second hit R130X mutation on the allele opposite the germline R335X. Both mutations have been described in CS and BRR. We postulate that the second hit, R130X, occurred early in embryonic development and may even represent germline mosaicism. Thus, PTEN may be involved in Proteus-like syndrome with its implications for cancer development in the future.     

Mutation of the PTEN gene in a human hepatic angiosarcoma

The phosphatase and tensin homolog (mutated in multiple advanced cancers 1) gene, or PTEN, encodes a lipid phosphatase that contains a PTPase domain and a C2 domain and plays a role as a tumor suppressor that negatively regulates the cell-survival signaling pathway initiated by phosphatidylinositol 3-kinase (PI3K). The PTEN protein inhibits angiogenesis, and somatic mutations of the PTEN gene are involved in canine hemangiosarcoma. We screened for mutations of the PTEN gene in two patients with human hepatic angiosarcoma to determine whether PTEN is involved in the pathogenesis of human hepatic angiosarcoma. In one patient, who suffered from breast cancer, pharyngeal cancer, and hepatic angiosarcoma, we found a single base substitution in exon 7 (640C>T) of the PTEN gene in both the hepatic angiosarcoma and normal tissues. This transition results in a germline nonsense mutation (Q214X). These findings indicate that analysis of PTEN gene mutations may be useful for characterization of the molecular event in hepatic angiosarcoma and cancer predisposition.     

Germline PTEN mutations in Cowden syndrome-like families.

Cowden syndrome (CS) or multiple hamartoma syndrome (MIM 158350) is an autosomal dominant disorder with an increased risk for breast and thyroid carcinoma. The diagnosis of CS, as operationally defined by the International Cowden Consortium, is made when a patient, or family, has a combination of pathognomonic major and/or minor criteria. The CS gene has recently been identified as PTEN, which maps at 10q23.3 and encodes a dual specificity phosphatase. PTEN appears to function as a tumour suppressor in CS, with between 13-80% of CS families harbouring germline nonsense, missense, and frameshift mutations predicted to disrupt normal PTEN function. To date, only a small number of tumour suppressor genes, including BRCA1, BRCA2, and p53, have been associated with familial breast or breast/ovarian cancer families. Given the involvement of PTEN in CS, we postulated that PTEN was a likely candidate to play a role in families with a "CS-like" phenotype, but not classical CS. To answer these questions, we gathered a series of patients from families who had features reminiscent of CS but did not meet the Consortium Criteria. Using a combination of denaturing gradient gel electrophoresis (DGGE), temporal temperature gel electrophoresis (TTGE), and sequence analysis, we screened 64 unrelated CS-like subjects for germline mutations in PTEN. A single male with follicular thyroid carcinoma from one of these 64 (2%) CS-like families harboured a germline point mutation, c.209T-->C. This mutation occurred at the last nucleotide of exon 3 and within a region homologous to the cytoskeletal proteins tensin and auxilin. We conclude that germline PTEN mutations play a relatively minor role in CS-like families. In addition, our data would suggest that, for the most part, the strict International Cowden Consortium operational diagnostic criteria for CS are quite robust and should remain in place.     

Novel PTEN mutations in neurodevelopmental disorders and macrocephaly

Somatic mutations of the phosphatase and tensin ( PTEN ) gene have been frequently detected in many types of human cancer. However, germline mutations can determine multiple hamartoma syndromes and, as more recently ascertained, syndromes clinically characterized by autism associated with macrocephaly. To determine whether germline mutations of PTEN may lead to different phenotypes, we screened all the nine exons of the PTEN gene in 40 patients with neurodevelopmental disorders, with or without features of autism spectrum disorder, associated with macrocephaly. Three novel de novo missense mutations were found (p.H118P, p.Y176C, p.N276S) in two severely mentally retarded patients with autism and in a subject with neurodevelopmental disorders without autistic features. Our results provide evidence that PTEN germline mutations may sustain a more wide phenotypical spectrum than previously suggested.     

PTEN hamartoma tumor syndromes

The PTEN hamartoma tumor syndromes (PHTS) are a collection of rare clinical syndromes characterized by germline mutations of the tumor suppressor PTEN. These syndromes are driven by cellular overgrowth, leading to benign hamartomas in virtually any organ. Cowden syndrome (CS), the prototypic PHTS syndrome, is associated with increased susceptibility to breast, thyroid, and endometrial cancer. PTEN is located on chromosome 10q22-23 and negatively regulates the prosurvival PI3K/Akt/mTOR pathway through its lipid phosphatase activity. Loss of PTEN activates this pathway and leads to increased cellular growth, migration, proliferation, and survival. Clinical management of patients with PHTS, particularly those with CS, should include early and frequent screening, surveillance, and preventive care for associated malignancies. Concomitant with improved understanding of the biology of PTEN and the PI3K/Akt/mTOR pathway, inhibitors of this pathway are being developed as anticancer agents. These medications could have applications for patients with PHTS, for whom no medical options currently exist.     

PTEN as a Unique Promising Therapeutic Target for Occupational Asthma

The tumor suppressor phosphatase and tensin homologue deleted on chromosome ten (PTEN) dephophorylates phosphatidylinositol 3,4,5-triphosphate (PIP3) and is a key negative regulator of phosphoinositide kinase-3 (PI3K) signaling pathway. PTEN also suppresses cellular motility through mechanisms that may be partially independent of phosphatase activity. PTEN is one of the most commonly lost tumor suppressors in human cancers, and its down-regulation is also implicated in several other diseases including airway inflammatory diseases. There is increasing evidence regarding the protective effects of PTEN on the bronchial asthma which is induced by complex signaling networks. Very recently, as for the occupational asthma (OA) with considerable controversy for its pathobiologic mechanisms, PTEN has been considered as a key molecule which is capable of protecting toluene diisocyanate (TDI)-induced asthma, suggesting that PTEN is located at switching point of various molecular signals in OA. Knowledge of the mechanisms of PTEN regulation/function could direct to the pharmacological manipulation of PTEN. This article reviews the latest knowledge and studies on the roles and mechanisms of PTEN in OA.     

Biallelic inactivating mutations and an occult germline mutation of PTEN in primary cervical carcinomas

A tumor suppressor gene on chromosome sub-band 10q23.3, PTEN, is frequently mutated or deleted in a variety of human cancers. Germline mutations in PTEN, that encodes a dual-specificity phosphatase, have been implicated in two hamartoma-tumor syndromes that exhibit some clinical overlap, Cowden syndrome and Bannayan-Zonana syndrome. Although cervical cancer is not a known component of these two syndromes, loss of heterozygosity (LOH) of markers on chromosome arm 10q is frequently observed in cervical cancers. To determine the potential role that PTEN mutation may play in cervical tumorigenesis, we screened 20 primary cervical cancers for LOH of polymorphic markers within and flanking the PTEN gene, and for intragenic mutations in the entire coding region and exon-intron boundaries of the PTEN gene. LOH was observed in 7 of 19 (36.8%) cases. Further, one sample may have homozygous deletion. Three (15%) intragenic mutations were found: two were somatic missense mutations in exon 5, that encodes the phosphatase motif, and an occult germline intronic sequence variant in intron 7, that we show to be associated with aberrant splicing. All three samples with the mutations also had LOH of the wild-type allele. These data indicate that disruption of PTEN by allelic loss or mutation may contribute to tumorigenesis in cervical cancers. In cervical cancer, unlike some other human primary carcinomas, e.g., those of the breast and thyroid, biallelic structural PTEN defects seem necessary for carcinogenesis. Further, one in 20 unselected cervical carcinomas was found to have a germline PTEN mutation; it is unclear whether the patient with this mutation had Cowden disease or a related syndrome.     

Mutation spectrum and genotype-phenotype analyses in Cowden disease and Bannayan-Zonana syndrome, two hamartoma syndromes with germline PTEN mutation

The tumour suppressor gene PTEN , which maps to 10q23.3 and encodes a 403 amino acid dual specificity phosphatase (protein tyrosine phosphatase; PTPase), was shown recently to play a broad role in human malignancy. Somatic PTEN deletions and mutations were observed in sporadic breast, brain, prostate and kidney cancer cell lines and in several primary tumours such as endometrial carcinomas, malignant melanoma and thyroid tumours. In addition, PTEN was identified as the susceptibility gene for two hamartoma syndromes: Cowden disease (CD; MIM 158350) and Bannayan-Zonana (BZS) or Ruvalcaba-Riley-Smith syndrome (MIM 153480). Constitutive DNA from 37 CD families and seven BZS families was screened for germline PTEN mutations. PTEN mutations were identified in 30 of 37 (81%) CD families, including missense and nonsense point mutations, deletions, insertions, a deletion/insertion and splice site mutations. These mutations were scattered over the entire length of PTEN , with the exception of the first, fourth and last exons. A 'hot spot' for PTEN mutation in CD was identified in exon 5 that contains the PTPase core motif, with 13 of 30 (43%) CD mutations identified in this exon. Seven of 30 (23%) were within the core motif, the majority (five of seven) of which were missense mutations, possibly pointing to the functional significance of this region. Germline PTEN mutations were identified in four of seven (57%) BZS families studied. Interestingly, none of these mutations was observed in the PTPase core motif. It is also worthy of note that a single nonsense point mutation, R233X, was observed in the germline DNA from two unrelated CD families and one BZS family. Genotype-phenotype studies were not performed on this small group of BZS families. However, genotype-phenotype analysis inthe group of CD families revealed two possible associations worthy of follow-up in independent analyses. The first was an association noted in the group of CD families with breast disease. A correlation was observed between the presence/absence of a PTEN mutation and the type of breast involvement (unaffected versus benign versus malignant). Specifically and more directly, an association was also observed between the presence of a PTEN mutation and malignant breast disease. Secondly, there appeared to be an interdependent association between mutations upstream and within the PTPase core motif, the core motif containing the majority of missense mutations, and the involvement of all major organ systems (central nervous system, thyroid, breast, skin and gastrointestinal tract). However, these observations would need to be confirmed by studying a larger number of CD families.      

Drosophila tumor suppressor PTEN controls cell size and number by antagonizing the Chico/PI3-kinase signaling pathway

The human tumor suppressor gene PTEN encodes a putative cytoskeleton-associated molecule with both protein phosphatase and phosphatidylinositol 3,4,5-trisphosphate (PIP3) 3-phosphatase activities. In cell culture, the lipid phosphatase activity of this protein is involved in regulating cell proliferation and survival, but the mechanism by which PTEN inhibits tumorigenesis in vivo is not fully established. Here we show that the highly evolutionarily conserved Drosophila PTEN homolog, DPTEN, suppresses hyperplastic growth in flies by reducing cell size and number. We demonstrate that DPTEN modulates tissue mass by acting antagonistically to the Drosophila Class I phosphatidylinositol 3-kinase, Dp110, and its upstream activator Chico, an insulin receptor substrate homolog. Surprisingly, although DPTEN does not generally affect cell fate determination, it does appear to regulate the subcellular organization of the actin cytoskeleton in multiple cell types. From these data, we propose that DPTEN has a complex role in regulating tissue and body size. It acts in opposition to Dp110 to control cell number and growth, while coordinately influencing events at the cell periphery via its effects on the actin cytoskeleton.     

PTEN as a unique promising therapeutic target for occupational asthma

The tumor suppressor phosphatase and tensin homologue deleted on chromosome ten (PTEN) dephophorylates phosphatidylinositol 3,4,5-triphosphate (PIP3) and is a key negative regulator of phosphoinositide kinase-3 (PI3K) signaling pathway. PTEN also suppresses cellular motility through mechanisms that may be partially independent of phosphatase activity. PTEN is one of the most commonly lost tumor suppressors in human cancers, and its down-regulation is also implicated in several other diseases including airway inflammatory diseases. There is increasing evidence regarding the protective effects of PTEN on the bronchial asthma which is induced by complex signaling networks. Very recently, as for the occupational asthma (OA) with considerable controversy for its pathobiologic mechanisms, PTEN has been considered as a key molecule which is capable of protecting toluene diisocyanate (TDI)-induced asthma, suggesting that PTEN is located at switching point of various molecular signals in OA. Knowledge of the mechanisms of PTEN regulation/function could direct to the pharmacological manipulation of PTEN. This article reviews the latest knowledge and studies on the roles and mechanisms of PTEN in OA.     

ERK5对体外血小板活化及在体血栓的影响

目的:探讨细胞外信号调节激酶5(ERK5)对体外血小板聚集及在体血栓的影响及机制。方法:采用Western blot对人血小板中ERK5的表达及其在血小板活化后的磷酸化水平进行检测;采用血小板聚集仪检测ERK5特异性抑制剂XMD8-92对血小板聚集及致密颗粒释放的影响;采用Fe Cl3颈动脉血栓模型检测ERK5对在体血栓的影响;采用Western blot检测XMD8-92对蛋白激酶B(Akt)和人第10号染色体缺失的磷酸酶及张力蛋白同源蛋白(PTEN)磷酸化的影响。结果:人血小板中存在ERK5的稳定表达,其磷酸化水平在血小板活化后显著升高(P0.05)。XMD8-92可抑制多种血小板激活剂引起的血小板聚集和致密颗粒释放(P0.05)。Western blot结果表明,XMD8-92可通过下调PTEN Ser370位点磷酸化而增强PTEN的活性,从而抑制Akt的磷酸化,这种抑制效果也通过血小板特异PTEN基因敲除小鼠得到了验证。在体血栓研究表明,XMD8-92经尾静脉给药,可显著延长小鼠第一次颈动脉血栓的形成时间。结论:ERK5可通过影响PTEN的磷酸化调节Akt的活化,进而影响到体外血小板的聚集和在体血栓的形成。     

PI3KCA mutations and/or PTEN loss in Her2-positive breast carcinomas treated with trastuzumab are not related to resistance to anti-Her2 therapy

The purpose of this study is to evaluate whether activating mutations of the p110α catalytic subunit of class A phosphoinositide 3-kinases (PI3KCA) or complete loss of phosphatase and tensin homolog (PTEN) is associated with response to anti-human epidermal growth factor receptor 2 (Her2) treatment in breast cancer (BC). We analysed PI3KCA hot-spot mutations and PTEN immunohistochemical expression in 129 Her2-positive infiltrating BC treated with trastuzumab, including 26 cases treated with neoadjuvant therapy, 48 metastatic infiltrating breast cancer (IBC; MBC) and 55 early-stage IBC, with complete clinical information (mean follow-up 37, 66 and 32?months, respectively). PI3KCA hot-spot mutations were observed in 25 cases (19?%): 12 (9?%) in exon 9 and 13 (10?%) in exon 20. No correlations were observed between mutations and pathological and biological parameters. In patients treated with neoadjuvant therapy and in MBC, we did not observe any relationship with response to trastuzumab-based therapy. PTEN loss was observed in 24 out of 86 informative cases (28?%), 3 (13?%) of which were also mutated for PI3KCA. PI3K pathway activation, defined as PI3KCA mutation and/or PTEN loss, was not associated with response to treatment or clinical outcome in MBC. PI3KCA mutation and/or PTEN loss should not exclude patients from potentially beneficial anti-Her2 therapy.     

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

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