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T Maehama

Publications and source records attributed to T Maehama.

At least 19 recordsLinked to original sources
PubMed2004

The tumour suppressor PTEN: involvement of a tumour suppressor candidate protein in PTEN turnover.

The tumour suppressor PTEN (phosphatase and tensin homologue deleted on chromosome 10) plays essential roles in regulating signalling pathways involved in cell growth and apoptosis, and is inactivated in a wide variety of tumours. The role of PTEN as a tumour suppressor has been firmly established; however, the mechanism(s) by which its function and activity are regulated remains elusive. Here, we summarize recent progress in research directed towards trying to understand the molecular basis of regulatory mechanisms for PTEN. We also describe our novel finding that a tumour suppressor candidate protein binds to extreme C-terminal region of PTEN and regulates PTEN protein turnover.

Amino Acid Sequence↗
PubMed2002

Prevalence of human papillomavirus in cervical swabs in the Okinawa Islands, Japan.

Although human papillomavirus (HPV) is the main risk factor for invasive cervical cancer, the mechanisms of developing carcinoma are not entirely understood. In particular, the biology and natural history of HPV infection are still unknown. Therefore, we have investigated the incidence of human papillomavirus infection by polymerase chain reaction (PCR) in cervical swabs obtained from women who had cervical cancer screening in three separate areas of the islands of Okinawa. The prevalence of HPV in women aged between 30 and 85 years in the three local areas, Yonashiro-town, Naha-city, and Hirara-city, was consistent (9 to 10%). HPV of various oncogenic types, including HPV16, 18, 31, 33, 35, 35, and 58, were identified in HPV-positive swabs and the prevalence of these types varied in the three areas.

Adult↗
PubMed2001

The PTEN tumor suppressor protein inhibits tumor necrosis factor-induced nuclear factor kappa B activity.

Nuclear factor kappaB (NF-kappaB) transcriptionally activates genes that promote immunity and cell survival. Activation of NF-kappaB is induced by an IkappaB kinase (IKK) complex that phosphorylates and promotes dissociation of IkappaB from NF-kappaB, which then translocates into the nucleus. Activation of phosphatidylinositol (PI) 3-kinase/Akt signaling by tumor necrosis factor (TNF) activates IKK and NF-kappaB. The present study shows that PTEN, a tumor suppressor that inhibits PI 3-kinase function, impairs TNF activation of Akt and the IKK complex in 293 cells. Transient expression of PTEN suppressed IKK activation and TNF-induced NF-kappaB DNA binding and transactivation. Studies were conducted with PC-3 prostate cancer cells that do not express PTEN and DU145 prostate cancer cells that express PTEN. TNF activated Akt in PC-3 cells, but not in DU145 cells, and the ability of TNF to activate NF-kappaB was blocked by pharmacological inhibition of PI 3-kinase activity in PC-3 cells, but not in DU145 cells. Expression of PTEN in PC-3 cells to a level comparable with that endogenously present in DU145 cells inhibited TNF activation of NF-kappaB. The cell type-specific ability of PTEN to negatively regulate the PI 3-kinase/AKT/NF-kappaB pathway may be important to its tumor suppressor activity.

Cell Line↗
PubMed2001

A phosphatidylinositol 3-kinase/Akt/mTOR pathway mediates and PTEN antagonizes tumor necrosis factor inhibition of insulin signaling through insulin receptor substrate-1.

Tyrosine phosphorylation of insulin receptor substrate-1 (IRS-1) by the insulin receptor permits this docking protein to interact with signaling proteins that promote insulin action. Serine phosphorylation uncouples IRS-1 from the insulin receptor, thereby inhibiting its tyrosine phosphorylation and insulin signaling. For this reason, there is great interest in identifying serine/threonine kinases for which IRS-1 is a substrate. Tumor necrosis factor (TNF) inhibited insulin-promoted tyrosine phosphorylation of IRS-1 and activated the Akt/protein kinase B serine-threonine kinase, a downstream target for phosphatidylinositol 3-kinase (PI 3-kinase). The effect of TNF on insulin-promoted tyrosine phosphorylation of IRS-1 was blocked by inhibition of PI 3-kinase and the PTEN tumor suppressor, which dephosphorylates the lipids that mediate PI 3-kinase functions, whereas constitutively active Akt impaired insulin-promoted IRS-1 tyrosine phosphorylation. Conversely, TNF inhibition of IRS-1 tyrosine phosphorylation was blocked by kinase dead Akt. Inhibition of IRS-1 tyrosine phosphorylation by TNF was blocked by rapamycin, an inhibitor of the mammalian target of rapamycin (mTOR), a downstream target of Akt. mTOR induced the serine phosphorylation of IRS-1 (Ser-636/639), and such phosphorylation was inhibited by rapamycin. These results suggest that TNF impairs insulin signaling through IRS-1 by activation of a PI 3-kinase/Akt/mTOR pathway, which is antagonized by PTEN.

Amino Acid Sequence↗
PubMed2001

Malignant struma ovarii with thyrotoxicosis.

BACKGROUND: Malignant struma ovarii is seldom diagnosed preoperatively due to the rarity of the disease itself and the even rarer complications of thyrotoxicosis. CASE: A 48-year-old woman presented with symptoms of hyperthyroidism and a pelvic tumor raising the possibility of ovarian malignancy. Hormonal findings revealed increased thyroid function, but the thyroid gland was normal in size and texture. Thus, she was diagnosed preoperatively as having a hormone-producing malignant struma ovarii. At surgery, a FIGO stage Ia ovarian papillary adenocarcinoma of the thyroid was found. An immunohistochemical tumor stain for thyroglobulin was positive and the ovarian venous thyroglobulin level was extremely high. Findings of hyperthyroidism disappeared over several weeks. CONCLUSION: Malignant struma ovarii can be diagnosed preoperatively. Complications of thyrotoxicosis should be kept in mind when evaluating an ovarian tumor.

Adenocarcinoma, Papillary↗
PubMed2001

Detection of human papillomavirus DNA in primary and metastatic lesions of carcinoma of the cervix in women from Okinawa, Japan.

Of 351 patients with invasive cervical cancer treated at Ryukyu University Hospital, Okinawa, 293 who were tested for human papilloma virus (HPV) DNA of the primary cervical lesion before the initiation of treatment were considered for the study. The polymerase chain reaction (PCR) was performed using fresh specimens, immediately after sampling. In 250 of 293 patients (85.3%), HPV DNA was detected in cervical tumor by PCR using L1 consensus primer. The positive rate by histology was 89.9% in squamous cell carcinoma, 93.8% in adenosquamous carcinoma, and 51.4% in adenocarcinoma. The former two figures were significantly higher than the latter (p < 0.001 and p = 0.002). Concerning identification of HPV types, HPV 16 was most predominant in squamous cell carcinoma, whereas type 18 was relatively high in adenocarcinoma. However, the type distribution of HPV was different to some extent from those in other countries. During treatment, 489 nodal and other tissue samples were obtained from 113 of 250 HPV DNA-positive patients, and were submitted to an assay of HPV DNA. HPV DNA was amplified in all 55 metastatic samples and also in 12 of 434 nonmetastatic tissues (2.8%). HPV types specified in these samples were always identical with the HPV types determined in their primary tumors. In 154 samples from 29 of 43 HPV DNA-negative patients, HPV DNA was not detected, either in 14 metastatic samples or in 140 histologically benign samples. Cancer-free, but HPV DNA-positive nodal, liver, and pulmonary tissues could be interpreted to be already involved at the time of examination, by observing the clinical course of the disease over time.

Adenocarcinoma↗
PubMed2001

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.

Animals↗
PubMed2000

Myotubularin, a protein tyrosine phosphatase mutated in myotubular myopathy, dephosphorylates the lipid second messenger, phosphatidylinositol 3-phosphate.

The lipid second messenger phosphatidylinositol 3-phosphate [PI(3)P] plays a crucial role in intracellular membrane trafficking. We report here that myotubularin, a protein tyrosine phosphatase required for muscle cell differentiation, is a potent PI(3)P phosphatase. Recombinant human myotubularin specifically dephosphorylates PI(3)P in vitro. Overexpression of a catalytically inactive substrate-trapping myotubularin mutant (C375S) in human 293 cells increases PI(3)P levels relative to that of cells overexpressing the wild-type enzyme, demonstrating that PI(3)P is a substrate for myotubularin in vivo. In addition, a Saccharomyces cerevisiae strain in which the myotubularin-like gene (YJR110w) is disrupted also exhibits increased PI(3)P levels. Both the recombinant yeast enzyme and a human myotubularin-related protein (KIAA0371) are able to dephosphorylate PI(3)P in vitro, suggesting that this activity is intrinsic to all myotubularin family members. Mutations in the MTM1 gene that cause human myotubular myopathy dramatically reduce the ability of the phosphatase to dephosphorylate PI(3)P. Our findings provide evidence that myotubularin exerts its effects during myogenesis by regulating cellular levels of the inositol lipid PI(3)P.

Amino Acid Sequence↗
PubMed2000

Use of double-stranded RNA interference in Drosophila cell lines to dissect signal transduction pathways.

We demonstrate the efficacy of double-stranded RNA-mediated interference (RNAi) of gene expression in generating "knock-out" phenotypes for specific proteins in several Drosophila cell lines. We prove the applicability of this technique for studying signaling cascades by dissecting the well-characterized insulin signal transduction pathway. Specifically, we demonstrate that inhibiting the expression of the DSOR1 (mitogen-activated protein kinase kinase, MAPKK) prevents the activation of the downstream ERK-A (MAPK). In contrast, blocking ERK-A expression results in increased activation of DSOR1. We also show that Drosophila AKT (DAKT) activation depends on the insulin receptor substrate, CHICO (IRS1-4). Finally, we demonstrate that blocking the expression of Drosophila PTEN results in the activation of DAKT. In all cases, the interference of the biochemical cascade by RNAi is consistent with the known steps in the pathway. We extend this powerful technique to study two proteins, DSH3PX1 and Drosophila ACK (DACK). DSH3PX1 is an SH3, phox homology domain-containing protein, and DACK is homologous to the mammalian activated Cdc42 tyrosine kinase, ACK. Using RNAi, we demonstrate that DACK is upstream of DSH3PX1 phosphorylation, making DSH3PX1 an identified downstream target/substrate of ACK-like tyrosine kinases. These experiments highlight the usefulness of RNAi in dissecting complex biochemical signaling cascades and provide a highly effective method for determining the function of the identified genes arising from the Drosophila genome sequencing project.

Animals↗
PubMed2000

Persistence of human papillomavirus infection after therapeutic conization for CIN 3: is it an alarm for disease recurrence?

OBJECTIVE: The aims of this study were (1) to examine whether HPV DNA is persistently detected in the cervix after therapeutic conization for CIN 3 and (2) to explore whether a patient with persistence of HPV infection is at risk of developing recurrent disease. METHODS: Of 74 patients referred with CIN 3, 58 who were tested for HPV DNA in the pretreatment cervical lesions were enrolled in the study. After standard therapeutic conization, patients were followed prospectively at the outpatient clinic. Our follow-up protocol was to follow patients without therapeutic intervention as long as they developed no recurrence or recurrence of CIN 1 or 2, while patients who experienced recurrence of CIN 3 were recommended for reconization or hysterectomy. The polymerase chain reaction for detecting HPV DNA was performed using fresh cell samples from the cervix. RESULTS: In 56 of 58 patients (96.6%), HPV DNAs were detected in their primary cervical lesions prior to conization. With regard to the distribution of HPV types, HPV type 16 family (types 16, 31, and 35) was identified in 28 cases (50.0%), type 18 family (types 18, 33 and 58) in 15 (26.8%), and type X in 18 (32.1%). Up to August 1999, all of the 58 patients have been followed with a mean follow-up period of 31.8 months (range: 12 to 73 months). After treatment, HPV DNA was persistently detected in 11 (19.6%) but negative in 45 (80.4%) of 56 HPV DNA-positive patients. HPV DNA was not detected in both HPV DNA-negative patients. Five of 11 persistently HPV DNA-positive patients (45.5%) developed CIN recurrence, while none of 45 persistently HPV DNA-negative patients did. Thus, there was a significant difference between the recurrence rates of these two groups (P < 0.0001). Both patients who were initially HPV DNA-negative developed no recurrence. Accordingly, the overall recurrence following conservative treatment for CIN 3 was 5 of 58 patients (8.6%). CONCLUSIONS: Patients with persistent HPV infection after conization for CIN 3 should be especially closely followed because they are at increased risk of developing disease recurrence.

Adult↗
PubMed2000

ERBB-2 overexpression confers PI 3' kinase-dependent invasion capacity on human mammary epithelial cells.

Amplification and overexpression of ERBB-2 in human breast cancer is thought to play a significant role in the progression of the disease; however, its precise role in the aetiology of altered phenotypes associated with human breast cancer is unknown. We have previously shown that exogenous overexpression of ERBB-2 conferred growth factor independence on human mammary epithelial cells. In this study, we show that ERBB-2 overexpression also causes the cells to acquire other characteristics exhibited by human breast cancer cells, such as anchorage-independent growth and invasion capabilities. ERBB-2-induced invasion is dependent on fibronectin and correlates with the down-regulation of cell surface alpha4 integrin. In addition ERBB-2 co-immunoprecipitates with focal adhesion kinase (FAK) in these cells. We have also shown, by use of exogenously expressed PTEN and by treatment with the PI3'-kinase inhibitor LY294002, that ERBB-2-induced invasion is dependent on the PI3'-kinase pathway; however, PTEN does not dephosphorylate FAK in these cells.

Breast↗
PubMed1999

Crystal structure of the PTEN tumor suppressor: implications for its phosphoinositide phosphatase activity and membrane association.

The PTEN tumor suppressor is mutated in diverse human cancers and in hereditary cancer predisposition syndromes. PTEN is a phosphatase that can act on both polypeptide and phosphoinositide substrates in vitro. The PTEN structure reveals a phosphatase domain that is similar to protein phosphatases but has an enlarged active site important for the accommodation of the phosphoinositide substrate. The structure also reveals that PTEN has a C2 domain. The PTEN C2 domain binds phospholipid membranes in vitro, and mutation of basic residues that could mediate this reduces PTEN's membrane affinity and its ability to suppress the growth of glioblastoma tumor cells. The phosphatase and C2 domains associate across an extensive interface, suggesting that the C2 domain may serve to productively position the catalytic domain on the membrane.

Amino Acid Sequence↗
PubMed1999

PTEN: a tumour suppressor that functions as a phospholipid phosphatase.

The tumour suppressor PTEN has been implicated in a large number of human tumours and is conserved from humans to worms. Characterization of PTEN protein showed that it is a phosphatase that acts on proteins and on 3-phosphorylated phosphoinositides, including phosphatidylinositol (3,4,5)-trisphosphate, and can therefore modulate signal-transduction pathways that involve lipid second messengers. Recent results indicate that at least part of its role is to regulate the activity of the serine/threonine kinase AKT/PKB, and thus influence cell survival signalling. This article discusses the function of PTEN and how this could be linked to its activity as a tumour suppressor.

Amino Acid Sequence↗