Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:P43146 (tumour suppressor)
 5,935 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

PTEN is a novel tumour suppressor gene that encodes a dual-specificity phosphatase with homology to adhesion molecules tensin and auxillin. It recently has been suggested that PTEN dephosphorylates phosphatidylinositol 3,4,5-trisphosphate [PtdIns(3, 4,5)P3], which mediates growth factor-induced activation of intracellular signalling, in particular through the serine-threonine kinase Akt, a known cell survival-promoting factor. PTEN has been mapped to 10q23.3, a region disrupted in several human tumours including haematological malignancies. We have analysed PTEN in a series of primary acute leukaemias and non-Hodgkin's lymphomas (NHLs) as well as in cell lines. We have also examined whether a correlation could be found between PTEN and Akt levels in these samples. We show here that the majority of cell lines studied carries PTEN abnormalities. At the structural level, we found mutations and hemizygous deletions in 40% of these cell lines, while a smaller number of primary haematological malignancies, in particular NHLs, carries PTEN mutations. Moreover, one-third of the cell lines had low PTEN transcript levels, and 60% of these samples had low or absent PTEN protein, which could not be attributed to gene silencing by hypermethylation. In addition, we found that PTEN and phosphorylated Akt levels are inversely correlated in the large majority of the examined samples. These findings suggest that PTEN plays a role in the pathogenesis of haematological malignancies and that it might be inactivated through a wider range of mechanisms than initially considered. The finding that PTEN levels inversely correlate with phosphorylated Akt supports the hypothesis that PTEN regulates PtdIns(3,4,5)P3and suggests a role for PTEN in apoptosis.
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PMID:PTEN is inversely correlated with the cell survival factor Akt/PKB and is inactivated via multiple mechanismsin haematological malignancies. 993 26

The tumour suppressor protein PTEN (phosphatase and tensin homolog deleted on chromosome 10) is a lipid phosphatase which can antagonize the phosphoinositide 3-kinase (PI 3-kinase) signalling pathway, promoting apoptosis and inhibiting cell-cycle progression and cell motility. We show that very little cellular PTEN is associated with the plasma membrane, but that artificial membrane-targeting of PTEN enhances its inhibition of signalling to protein kinase B (PKB). Evidence for potential targeting of PTEN to the membrane through PDZ domain-mediated protein-protein interactions led us to use a PTEN enzyme with a deletion of the C-terminal PDZ-binding sequence, that retains full phosphatase activity against soluble substrates, and to analyse the efficiency of this mutant in different cellular assays. The extreme C-terminal PDZ-binding sequence was dispensable for the efficient down-regulation of cellular PtdIns(3,4,5)P3 levels and a number of PI 3-kinase-dependent signalling activities, including PKB and p70S6K. However, the PDZ-binding sequence was required for the efficient inhibition of cell spreading. The data show that a PTEN mutation, similar to those found in some tumours, affects some functions of the protein but not others, and implicate the deregulation of PTEN-dependent processes other than PKB activation in the development of some tumours. Significantly, this hypothesis is supported by data showing low levels of PKB phosphorylation in a glioblastoma sample carrying a mutation in the extreme C-terminus of PTEN compared with tumours carrying phosphatase-inactivating mutations of the enzyme. Our data show that deregulation of PKB is not a universal feature of tumours carrying PTEN mutations and implicate other processes that may be deregulated in these tumours.
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PMID:Targeting mutants of PTEN reveal distinct subsets of tumour suppressor functions. 1143 92

The tumour suppressor protein, PTEN (phosphatase and tensin homologue deleted on chromosome 10) is a member of the mixed function, serine/threonine/tyrosine phosphatase subfamily of protein phosphatases. Its physiological substrates, however, are primarily 3-phosphorylated inositol phospholipids, which are products of phosphoinositide 3-kinases. PTEN thus antagonizes PI 3-kinase-dependent signalling pathways, which explains to a large extent its tumour suppressor status. We have examined the kinetic behaviour, substrate specificity and regulation of PTEN both in vitro and in a variety of cellular models. Although PTEN can utilize both phosphatidylinositol 3,4,5-trisphosphate [PtdIns(3,4,5)P(3)] and its water-soluble headgroup, inositol 1,3,4,5-tetrakisphosphate, as substrates, it displays classical features of interfacial catalysis, which greatly favour the lipid substrate (by as much as 1000-fold as judged by K(cat)/K(m) values). Expression of PTEN in U87 cells (which lack endogenous PTEN) and measuring the levels of all known 3-phosphorylated lipids suggests that phosphatidylinositol 3,4-bisphosphate and PtdIns(3,4,5)P(3) are both substrates, but that phosphatidylinositol 3-phosphate and phosphatidylinositol 3,5-bisphosphate are not. PTEN binds to several PDZ-domain-containing proteins via a consensus sequence at its extreme C-terminus. Disruption of targeting to PDZ-domain proteins selectively blocks some PTEN functions, but not others, suggesting the existence of spatially localized, functionally dedicated pools of signalling lipids. We have also shown recently that PTEN expression is controlled at the transcriptional level and is profoundly upregulated by peroxisome proliferator activated receptor gamma agonists, thereby providing possible implications for these drugs in diabetes, inflammation and cancer.
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PMID:Antagonism of PI 3-kinase-dependent signalling pathways by the tumour suppressor protein, PTEN. 1170 86

The PTEN (phosphatase and tensin homologue deleted on chromosome 10) tumour suppressor is a phosphatidylinositol 3,4,5-trisphosphate [PtdIns(3,4,5)P(3)] 3-phosphatase that plays a critical role in regulating many cellular processes by antagonizing the phosphoinositide 3-kinase signalling pathway. We have identified and characterized two human homologues of PTEN, which differ with respect to their subcellular localization and lipid phosphatase activities. The previously cloned, but uncharacterized, TPTE (transmembrane phosphatase with tensin homology) is localized to the plasma membrane, but lacks detectable phosphoinositide 3-phosphatase activity. TPIP (TPTE and PTEN homologous inositol lipid phosphatase) is a novel phosphatase that occurs in several differentially spliced forms of which two, TPIP alpha and TPIP beta, appear to be functionally distinct. TPIP alpha displays similar phosphoinositide 3-phosphatase activity compared with PTEN against PtdIns(3,4,5)P(3), PtdIns(3,5)P(2), PtdIns(3,4)P(2) and PtdIns(3)P, has N-terminal transmembrane domains and appears to be localized on the endoplasmic reticulum. This is unusual as most signalling-lipid-metabolizing enzymes are not integral membrane proteins. TPIP beta, however, lacks detectable phosphatase activity and is cytosolic. TPIP has a wider tissue distribution than the testis-specific TPTE, with specific splice variants being expressed in testis, brain and stomach. TPTE and TPIP do not appear to be functional orthologues of the Golgi-localized and more distantly related murine PTEN2. We suggest that TPIP alpha plays a role in regulating phosphoinositide signalling on the endoplasmic reticulum, and might also represent a tumour suppressor and functional homologue of PTEN in some tissues.
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PMID:TPIP: a novel phosphoinositide 3-phosphatase. 1171 55

PtdIns(3,4,5)P3 is an established second messenger of growth-factor and insulin-induced signalling pathways. There is increasing evidence that one of the immediate breakdown products of PtdIns(3,4,5)P3, namely PtdIns(3,4)P2, whose levels are elevated by numerous extracellular agonists, might also function as a signalling molecule. Recently, we identified two related pleckstrin-homology (PH)-domain-containing proteins, termed 'tandem-PH-domain-containing protein-1' (TAPP1) and TAPP2, which interacted in vitro with high affinity with PtdIns(3,4)P2, but did not bind PtdIns(3,4,5)P3 or other phosphoinositides. In the present study we demonstrate that stimulation of Swiss 3T3 or 293 cells with agonists that stimulate PtdIns(3,4)P2 production results in the marked translocation of TAPP1 to the plasma membrane. This recruitment is dependent on a functional PtdIns(3,4)P2-binding PH domain and is inhibited by wortmannin, a phosphoinositide 3-kinase inhibitor that prevents PtdIns(3,4)P2 generation. A search for proteins that interact with TAPP1 identified the multi-PDZ-containing protein termed 'MUPP1', a protein possessing 13 PDZ domains and no other known modular or catalytic domains [PDZ is postsynaptic density protein (PSD-95)/Drosophila disc large tumour suppressor (dlg)/tight junction protein (ZO1)]. We demonstrate that immunoprecipitation of endogenously expressed TAPP1 from 293-cell lysates results in the co-immunoprecipitation of endogenous MUPP1, indicating that these proteins are likely to interact with each other physiologically. We show that TAPP1 and TAPP2 interact with the 10th and 13th PDZ domain of MUPP1 through their C-terminal amino acids. The results of the present study suggest that TAPP1 and TAPP2 could function in cells as adapter proteins to recruit MUPP1, or other proteins that they may interact with, to the plasma membrane in response to signals that elevate PtdIns(3,4)P2.
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PMID:Evidence that the tandem-pleckstrin-homology-domain-containing protein TAPP1 interacts with Ptd(3,4)P2 and the multi-PDZ-domain-containing protein MUPP1 in vivo. 1180 82

The PTEN tumour suppressor protein is a phosphoinositide 3-phosphatase that, by metabolising phosphatidylinositol 3,4,5-trisphosphate (PtdIns(3,4,5)P(3)), acts in direct antagonism to growth factor stimulated PI 3-kinases. A wealth of data has now illuminated pathways that can be controlled by PTEN through PtdIns(3,4,5)P(3), some of which, when deregulated, give a selective advantage to tumour cells. Early studies of PTEN showed that its activity was able to promote cell cycle arrest and apoptosis and inhibit cell motility, but more recent data have identified other functional consequences of PTEN action, such as effects on the regulation of angiogenesis. The structure of PTEN includes several features not seen in related protein phosphatases, which adapt the enzyme to act efficiently as a lipid phosphatase, including a C2 domain tightly associated with the phosphatase domain, and a broader and deeper active site pocket. Several pieces of data indicate that PTEN is a principal regulator of the cellular levels of PtdIns(3,4,5)P(3), but work is only just beginning to uncover mechanisms by which the cellular activity of PTEN can be controlled. There also remains the vexing question of whether any of PTEN's cellular functions reflect its evolutionary roots as a member of the protein tyrosine phosphatase superfamily.
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PMID:PTEN: The down side of PI 3-kinase signalling. 1185 36

The PTEN tumour suppressor gene is mutated frequently in many malignancies and its importance in the development of cancer is probably underestimated. As the primary phosphatase of phosphatidylinositol (3,4,5)-trisphosphate, PTEN has a central role in reigning in the phosphoinositide 3-kinase (PI 3-kinase) network to control cellular homeostasis. Cells that lack PTEN are unable to regulate the PtdIns 3-kinase programme, which stimulates a variety of cellular phenotypes that favour oncogenesis. As well as the well-known role as tumour suppressor, recent studies show that PTEN is involved in the regulation of several basic cellular functions, such as cell migration, cell size, contractility of cardiac myocytes and chemotaxis. Here, we review the roles of PTEN in normal cellular functions and disease development.
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PMID:PTEN: from pathology to biology. 1294 27

It has been postulated that PtdIns(3,4) P (2), one of the immediate breakdown products of PtdIns(3,4,5) P (3), functions as a signalling molecule in insulin- and growth-factor-stimulated pathways. To date, the t andem- P H-domain-containing p rotein- 1 (TAPP1) and related TAPP2 are still the only known PH-domain-containing proteins that interact strongly and specifically with PtdIns(3,4) P (2). In this study we demonstrate that endogenously expressed TAPP1, is constitutively associated with the protein-tyrosine-phosphatase-like protein-1 (PTPL1 also known as FAP-1). We show that PTPL1 binds to TAPP1 and TAPP2, principally though its first PDZ domain [where PDZ is postsynaptic density protein ( P SD-95)/ Drosophila disc large tumour suppressor ( d lg)/tight junction protein ( Z O1)] and show that this renders PTPL1 capable of associating with PtdIns(3,4) P (2) in vitro. Our data suggest that the binding of TAPP1 to PTPL1 does not influence PTPL1 phosphatase activity, but instead functions to maintain PTPL1 in the cytoplasm. Following stimulation of cells with hydrogen peroxide to induce PtdIns(3,4) P (2) production, PTPL1, complexed to TAPP1, translocates to the plasma membrane. This study provides the first evidence that TAPP1 and PtdIns(3,4) P (2) could function to regulate the membrane localization of PTPL1. We speculate that if PTPL1 was recruited to the plasma membrane by increasing levels of PtdIns(3,4) P (2), it could trigger a negative feedback loop in which phosphoinositide-3-kinase-dependent or other signalling pathways could be switched off by the phosphatase-catalysed dephosphorylation of receptor tyrosine kinases or tyrosine phosphorylated adaptor proteins such as IRS1 or IRS2. Consistent with this notion we observed RNA-interference-mediated knock-down of TAPP1 in HEK-293 cells, enhanced activation and phosphorylation of PKB following IGF1 stimulation.
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PMID:Interaction of the protein tyrosine phosphatase PTPL1 with the PtdIns(3,4)P2-binding adaptor protein TAPP1. 1451 76

The tumour suppressor PTEN is a PtdIns(3,4,5)P(3) phosphatase that regulates many cellular processes through direct antagonism of PI 3-kinase signalling. Here we show that oxidative stress activates PI 3-kinase-dependent signalling via the inactivation of PTEN. We use two assay systems to show that cellular PTEN phosphatase activity is inhibited by oxidative stress induced by 1 mM hydrogen peroxide. PTEN inactivation by oxidative stress also causes an increase in cellular PtdIns(3,4,5)P(3) levels and activation of the downstream PtdIns(3,4,5)P(3) target, PKB/Akt, that does not occur in cells lacking PTEN. We then show that endogenous oxidant production in RAW264.7 macrophages inactivates a fraction of the cellular PTEN, and that this is associated with an oxidant-dependent activation of downstream signalling. These results show that oxidants, including those produced by cells, can activate downstream signalling via the inactivation of PTEN. This demonstrates a novel mechanism of regulation of the activity of this important tumour suppressor and the signalling pathways it regulates. These results may have significant implications for the many cellular processes in which PtdIns(3,4,5)P(3) and oxidants are produced concurrently.
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PMID:Redox regulation of PI 3-kinase signalling via inactivation of PTEN. 1453 22

In vertebrates, the tumour suppressor PTEN (phosphatase and tensin homologue deleted on chromosome 10) regulates many cellular processes through its PtdIns(3,4,5)P3 lipid phosphatase activity, antagonizing PI3K (phosphoinositide 3-kinase) signalling. Given the important role of PI3Ks in the regulation of directed cell migration and the role of PTEN as an inhibitor of migration, it is somewhat surprising that data now indicate that PTEN is able to regulate cell migration independent of its lipid phosphatase activity. Here, we discuss the role of PTEN in the regulation of cell migration.
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PMID:The regulation of cell migration by PTEN. 1624 56


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