Reversible Inactivation of the Tumor Suppressor PTEN by H2O2

The tumor suppressor PTEN regulates cell migration, growth, and survival by removing the 3′-phosphate of phosphoinositides. Exposure of purified PTEN or of cells to H2O2 resulted in inactivation of PTEN in a time- and H2O2concentration-dependent manner. Analysis of various cysteine mutants, including mass spectrometry of tryptic peptides, indicated that the essential Cys124 residue in the active site of PTEN specifically forms a disulfide with Cys71during oxidation by H2O2. The reduction of H2O2-oxidized PTEN in cells appears to be mediated predominantly by thioredoxin. Thus, thioredoxin was more efficient than glutaredoxin, glutathione, or a 14-kDa thioredoxin-like protein with regard to the reduction of oxidized PTEN in vitro. Thioredoxin co-immunoprecipitated with PTEN from cell lysates; and incubation of cells with 2, 4-dinitro-1-chlorobenzene (an inhibitor of thioredoxin reductase) delayed the reduction of oxidized PTEN, whereas incubation with buthioninesulfoximine (an inhibitor of glutathione biosynthesis) did not. These results suggest that the reversible inactivation of PTEN by H2O2might be important for the accumulation of 3′-phosphorylated phosphoinositides and that the uncontrolled generation of H2O2 associated with certain pathological conditions might contribute to cell proliferation by inhibiting PTEN function. The tumor suppressor PTEN regulates cell migration, growth, and survival by removing the 3′-phosphate of phosphoinositides. Exposure of purified PTEN or of cells to H2O2 resulted in inactivation of PTEN in a time- and H2O2concentration-dependent manner. Analysis of various cysteine mutants, including mass spectrometry of tryptic peptides, indicated that the essential Cys124 residue in the active site of PTEN specifically forms a disulfide with Cys71during oxidation by H2O2. The reduction of H2O2-oxidized PTEN in cells appears to be mediated predominantly by thioredoxin. Thus, thioredoxin was more efficient than glutaredoxin, glutathione, or a 14-kDa thioredoxin-like protein with regard to the reduction of oxidized PTEN in vitro. Thioredoxin co-immunoprecipitated with PTEN from cell lysates; and incubation of cells with 2, 4-dinitro-1-chlorobenzene (an inhibitor of thioredoxin reductase) delayed the reduction of oxidized PTEN, whereas incubation with buthioninesulfoximine (an inhibitor of glutathione biosynthesis) did not. These results suggest that the reversible inactivation of PTEN by H2O2might be important for the accumulation of 3′-phosphorylated phosphoinositides and that the uncontrolled generation of H2O2 associated with certain pathological conditions might contribute to cell proliferation by inhibiting PTEN function. Hydrogen peroxide (H2O2) is produced by all mammalian cells as a by-product of normal metabolism, including the oxidative phosphorylation of ADP and the conversion of arachidonic acid to leukotrienes, as well as by phagocytic cells in the host defense response to noxious stimuli. In addition, ultraviolet and γ irradiation of cells results in the production of H2O2. A substantial increase in the intracellular concentration of H2O2 is generally associated with deleterious effects, including cell death by apoptosis or necrosis, in pathophysiological conditions such as inflammation and ischemia-reperfusion. The generation of H2O2 also appears to be required, however, for many normal cellular functions, including propagation of receptor signaling (1Rhee, S. G. , Bae, Y. S. , Lee, S. -R. , and Kwon, J. (2000) Science stke (www. stke. org/cgi/contentfull/OCₛigtrans;2000/53/pe1) Google Scholar, 2Finkel T. Curr. Opin. Cell Biol. 1998; 10: 248-253Crossref PubMed Scopus (1019) Google Scholar). Ligands that induce an increase in the intracellular concentration of H2O2 include peptide growth factors such as platelet-derived growth factor (PDGF) 1The abbreviations used are: PDGFplatelet-derived growth factorDTTdithiothreitolTrxthioredoxinTrxRthioredoxin reductaseDMEMDulbecco's modified Eagle's mediumHAhemagglutininGrxglutaredoxinNEMN-ethylmaleimidePI (34, 5) P3, phosphatidylinositol 3, 4, 5-trisphosphateHPLChigh-performance liquid chromatographyDNCB2, 4-dinitro-1-chlorobenzeneBSObuthioninesulfoximineGSHreduced glutathioneMALDI-TOFmatrix-assisted laser desorption ionization time-of-flightPI (45) P2, phosphatidylinositol 4, 5-biphosphatePI (34) P2, phosphatidylinositol 3, 4-biphosphate and epidermal growth factor, cytokines such as transforming growth factor β1 and tumor necrosis factor α, and agonists of heterotrimeric GTP-binding protein (G protein) -coupled receptors such as N-formyl-methionyl-leucyl-phenylalanine (fMLP) and angiotensin II (1Rhee, S. G. , Bae, Y. S. , Lee, S. -R. , and Kwon, J. (2000) Science stke (www. stke. org/cgi/contentfull/OCₛigtrans;2000/53/pe1) Google Scholar, 2Finkel T. Curr. Opin. Cell Biol. 1998; 10: 248-253Crossref PubMed Scopus (1019) Google Scholar). The essential role of H2O2 production in intracellular signaling triggered by PDGF (3Sundaresan M. Yu Z. X. Ferrans V. J. Irani K. Finkel T. Science. 1995; 270: 296-299Crossref PubMed Scopus (2342) Google Scholar, 4Brar S. S. Kennedy T. P. Whorton A. R. Murphy T. M. Chitano P. Hoidal J. R. J. Biol. Chem. 1999; 274: 20017-20026Abstract Full Text Full Text PDF PubMed Scopus (87) Google Scholar), epidermal growth factor (5Bae Y. S. Kang S. W. Seo M. S. Baines I. C. Tekle E. Chock P. B. Rhee S. G. J. Biol. Chem. 1997; 272: 217-221Abstract Full Text Full Text PDF PubMed Scopus (1109) Google Scholar), angiotensin II (6Ushio-Fukai M. Alexander R. W. Akers M. Yin Q. Fujio Y. Walsh K. Griendling K. K. J. Biol. Chem. 1999; 274: 22699-22704Abstract Full Text Full Text PDF PubMed Scopus (501) Google Scholar), and cell-cell contact (7Pani G. Colavitti R. Bedogni B. Anzevino R. Borrello S. Galeotti T. J. Biol. Chem. 2000; 275: 38891-38899Abstract Full Text Full Text PDF PubMed Scopus (131) Google Scholar) has been demonstrated by the observation that corresponding receptor-mediated events are abrogated by blocking the accumulation of H2O2 with enzymes such as catalase or small molecules such as N-acetylcysteine. platelet-derived growth factor dithiothreitol thioredoxin thioredoxin reductase Dulbecco's modified Eagle's medium hemagglutinin glutaredoxin N-ethylmaleimide 4, 5) P3, phosphatidylinositol 3, 4, 5-trisphosphate high-performance liquid chromatography 2, 4-dinitro-1-chlorobenzene buthioninesulfoximine reduced glutathione matrix-assisted laser desorption ionization time-of-flight 5) P2, phosphatidylinositol 4, 5-biphosphate 4) P2, phosphatidylinositol 3, 4-biphosphate The addition of exogenous H2O2 or the intracellular production of this metabolite in response to receptor stimulation affects the function of a variety of proteins including transcription factors, protein kinases and phosphatases, phospholipases, ion channels, and G proteins (1Rhee, S. G. , Bae, Y. S. , Lee, S. -R. , and Kwon, J. (2000) Science stke (www. stke. org/cgi/contentfull/OCₛigtrans;2000/53/pe1) Google Scholar, 2Finkel T. Curr. Opin. Cell Biol. 1998; 10: 248-253Crossref PubMed Scopus (1019) Google Scholar). However, the mechanisms by which H2O2 achieves these effects remain unknown. It is unlikely that H2O2specifically binds proteins and thereby affects their functions. On the other hand, H2O2 is a mild oxidant that is able to oxidize cysteine residues in proteins to cysteine sulfenic acid or to disulfide, both of which are readily reduced back to cysteine by various cellular reductants. Because the p Ka (where Ka is the acid constant) of the sulfhydryl group (Cys–SH) of most cysteine residues is ∼8. 5 (8Besse D. Siedler F. Diercks T. Kessler H. Moroder L. Angew. Chem. Int. Ed. Engl. 1997; 36: 883-885Crossref Scopus (118) Google Scholar) and because this group is less readily oxidized by H2O2 than the cysteine thiolate anion (Cys–S–), few proteins might be expected to possess a Cys–SH that is vulnerable to oxidation by H2O2 in cells. However, certain protein cysteine residues do exist as thiolate anions at neutral pH as a result of the lowering of their p Ka values by charge interactions between the negatively charged thiolate and nearby positively charged amino acid residues (9Kim J. R. Yoon H. W. Kwon K. S. Lee S. R. Rhee S. G. Anal. Biochem. 2000; 283: 214-221Crossref PubMed Scopus (249) Google Scholar). Proteins with low p Ka cysteine residues include protein tyrosine phosphatases (10Jia Z. Barford D. Flint A. J. Tonks N. K. Science. 1995; 268: 1754-1758Crossref PubMed Scopus (566) Google Scholar, 11Denu J. M. Dixon J. E. Curr. Opin. Chem. Biol. 1998; 2: 633-641Crossref PubMed Scopus (340) Google Scholar, 12Lee S. R. Kwon K. S. Kim S. R. Rhee S. G. J. Biol. Chem. 1998; 273: 15366-15372Abstract Full Text Full Text PDF PubMed Scopus (848) Google Scholar). All protein tyrosine phosphatases contain an essential cysteine residue (p Ka, 4. 7–5. 4) in the signature active site motif, HC XXG XXRS/T (where X is any amino acid residue), that exists as a thiolate anion at neutral pH (11Denu J. M. Dixon J. E. Curr. Opin. Chem. Biol. 1998; 2: 633-641Crossref PubMed Scopus (340) Google Scholar). This thiolate anion contributes to formation of a thiol-phosphate intermediate in the catalytic mechanism of protein tyrosine phosphatases. The active site cysteine is the target of specific oxidation by various oxidants, including H2O2, and this modification is reversed by incubation with thiol compounds such as dithiothreitol (DTT) and reduced glutathione (GSH). The ability of intracellularly produced H2O2 to inhibit protein tyrosine phosphatase activity was demonstrated by the observation that stimulation of A431 cells with epidermal growth factor resulted in a selective reduction in the extent of subsequent labeling of the active site cysteine residue of protein tyrosine phosphatase 1B by 3Hiodoacetic acid in cell lysates (12Lee S. R. Kwon K. S. Kim S. R. Rhee S. G. J. Biol. Chem. 1998; 273: 15366-15372Abstract Full Text Full Text PDF PubMed Scopus (848) Google Scholar). PTEN is a member of the protein tyrosine phosphatase family and reverses the action of phosphoinositide 3-kinase by catalyzing the removal of the phosphate attached to the 3′-hydroxyl group of the phosphoinositide inositol ring (13Maehama T. Dixon J. E. J. Biol. Chem. 1998; 273: 13375-13378Abstract Full Text Full Text PDF PubMed Scopus (2646) Google Scholar, 14Maehama T. Dixon J. E. Trends Cell Biol. 1999; 9: 125-128Abstract Full Text Full Text PDF PubMed Scopus (513) Google Scholar, 15Maehama T. Taylor G. E. Dixon J. E. Annu. Rev. Biochem. 2001; 70: 247-279Crossref PubMed Scopus (411) Google Scholar). By negatively modulating the phosphoinositide 3-kinase-Akt signaling pathway, PTEN functions as an important tumor suppressor (15Maehama T. Taylor G. E. Dixon J. E. Annu. Rev. Biochem. 2001; 70: 247-279Crossref PubMed Scopus (411) Google Scholar, 16Furnari F. B. Lin H. Huang H. S. Cavenee W. K. Proc. Natl. Acad. Sci. U. S. A. 1997; 94: 12479-12484Crossref PubMed Scopus (386) Google Scholar, 17Stambolic V. Suzuki A. de la Pompa J. L. Brothers G. M. Mirtsos C. Sasaki T. Ruland J. Penninger J. M. Siderovski D. P. Mak T. W. Cell. 1998; 95: 29-39Abstract Full Text Full Text PDF PubMed Scopus (2146) Google Scholar, 18Myers M. P. Pass I. Batty I. H. Van der Kaay J. Stolarov J. P. Hemmings B. A. Wigler M. H. Downes C. P. Tonks N. K. Proc. Natl. Acad. Sci. U. S. A. 1998; 95: 13513-13518Crossref PubMed Scopus (1023) Google Scholar, 19Li D. M. Sun H. Proc. Natl. Acad. Sci. U. S. A. 1998; 95: 15406-15411Crossref PubMed Scopus (441) Google Scholar, 20Cantley L. C. Neel B. G. Proc. Natl. Acad. Sci. U. S. A. 1999; 96: 4240-4245Crossref PubMed Scopus (1768) Google Scholar). We now show that H2O2 induces reversible inactivation of PTEN through oxidation of the essential Cys124 and the formation by this residue of a disulfide with Cys71 and that the PTEN disulfide is reduced by thioredoxin (Trx). Given that stimulation of various receptors induces H2O2 production, we propose that the receptor-mediated activation of phosphoinositide 3-kinase may not be sufficient for the accumulation of 3′-phosphorylated phosphoinositides; the concomitant inactivation of PTEN by H2O2produced in response to receptor stimulation might also be necessary for this effect. Dulbecco's modified Eagle's medium (DMEM), fetal bovine serum, penicillin, and streptomycin were from Invitrogen. Both PDGF-BB and rabbit polyclonal antibodies to PTEN were obtained from and antibodies to PTEN and to the hemagglutinin were from antibodies to or rabbit G were from and glutaredoxin were as (12Lee S. R. Kwon K. S. Kim S. R. Rhee S. G. J. Biol. Chem. 1998; 273: 15366-15372Abstract Full Text Full Text PDF PubMed Scopus (848) Google Scholar). Thioredoxin reductase was as S. R. S. Kwon J. Rhee S. G. Proc. Natl. Acad. Sci. U. S. A. 2000; PubMed Scopus Google Scholar). and N-ethylmaleimide were from and catalase were from and was from A of H2O2 was from PTEN in the for of the protein with a at the was by K. M. of The the PTEN and were by and by The and proteins were in to and purified with the of an The purified proteins were and and at The phosphatase activity of PTEN was phosphatidylinositol 3, 4, 5-trisphosphate as (13Maehama T. Dixon J. E. J. Biol. Chem. 1998; 273: 13375-13378Abstract Full Text Full Text PDF PubMed Scopus (2646) Google Scholar). and cells were at an of in with fetal bovine The PTEN or the at their with were the M. Cell. Full Text PDF PubMed Scopus Google Scholar), and the were cells by with the of cells cells in of were of acid and to The cell were and at for The were and the were with and in of and of the were to and the proteins were to a The was to with rabbit antibodies to PTEN or a to were with antibodies and or The of PTEN was with an PTEN was obtained by the purified protein for at in a of and the was by the addition of of The protein was with in and the cysteine residues were by incubation for with in an PTEN was at with in The were by a with a of in acid at a of A that at was or not to for and by mass PTEN was by H2O2 in a PTEN was also incubation with and the of which results in the generation of anions that are to H2O2 The inactivation of PTEN by the was by to by catalase that PTEN oxidation was mediated predominantly by H2O2 than by PTEN that been with H2O2 conditions than did the protein This observation that H2O2 induces the oxidation of sulfhydryl of PTEN to a disulfide, a that generally results in a more protein The PTEN protein amino with the catalytic in the and a in the H. A. T. Y. Dixon J. E. P. Cell. 1999; Full Text Full Text PDF PubMed Scopus Google Scholar). The catalytic of PTEN at and (15Maehama T. Taylor G. E. Dixon J. E. Annu. Rev. Biochem. 2001; 70: 247-279Crossref PubMed Scopus (411) Google Scholar). the cysteine residues that a disulfide, we of these in the catalytic to thereby the and The proteins were with H2O2 and by the the and to H2O2, whereas the of the and was not by H2O2 These results oxidation with H2O2, the Cys124 residue in the active site of PTEN forms a disulfide with the formation of a disulfide between Cys71 and Cys124 of PTEN, we the protein to conditions with and to with the The were by A that at not by mass including of mass this is to the of mass for a of PTEN in which a peptide and a peptide are by a disulfide the that at was with by mass mass corresponding to the was of and mass to the values of and mass for the peptide and the were These results that Cys71 and Cys124 of PTEN a disulfide to H2O2. This is with the of PTEN, which the other cysteine residues in the catalytic Cys71 is of to Cys124 to a disulfide with this residue H. A. T. Y. Dixon J. E. P. Cell. 1999; Full Text Full Text PDF PubMed Scopus Google Scholar). We PTEN is oxidized in cells to H2O2. cells were for with various of H2O2, which cell were to to and to with antibodies to Exposure of cells to H2O2 at as low as resulted in the of the of PTEN, and the of this as the concentration of H2O2 The of the oxidized of PTEN also with of incubation of cells with H2O2, a at and The of the reduced of the protein as the of the oxidized and that PTEN was by H2O2 and by cellular as the concentration of H2O2 from cells with H2O2 were with the PTEN was A and with the that the of the protein a that Cys124 contributes to the disulfide for the increase in PTEN we cells with the of PTEN with or the Exposure of the cells to that the not the reversible oxidation that Cys124 forms the disulfide for the of The reversible inactivation of PTEN was also in cells to H2O2 cells were in a medium in which H2O2 was produced as a result of the of to H2O2 with from the also in the the oxidized of PTEN for protein reduction are and A. 2000; 2: PubMed Scopus Google Scholar). proteins or through the of with oxidized is reduced by with the of by PTEN that been by to and was with and the extent of reduction was the of the in The most reduction was with the The and of and was as efficient as the of was not was less than the and the of in addition to did not increase the of the results were obtained PTEN reduction was the of activity not We also the of PTEN in the of various of was at that was co-immunoprecipitated with PTEN from cell of the of PTEN and in the by of the with of protein a of PTEN to of cells contain a 14-kDa which is to in amino acid This a motif, which is the of the that and protein disulfide The reduction of and are and oxidized and were reduced with by and S. G. we oxidized PTEN in the of and was as as the of molecules the of and with regard to of PTEN in we cells with 2, 4-dinitro-1-chlorobenzene which of by inhibiting activity J. L. A. J. Biol. Chem. 1998; 273: Full Text Full Text PDF PubMed Scopus Google Scholar), or buthioninesulfoximine which A. J. Biol. Chem. Full Text PDF PubMed Google Scholar), to H2O2. of cells with for resulted in the accumulation of of in oxidized and with for resulted in the of by not did not the reduction of H2O2-oxidized PTEN, a in PTEN reduction that the reduction of PTEN in cells is mediated predominantly by is to be and induce cell death incubation for A. Y. T. Y. 1999; PubMed Scopus Google Scholar). of cells with for however, did not any cell death as by the and of cell death were incubation for not A variety of cellular induce the activation of phosphoinositide in the conversion of to L. C. Annu. Rev. Biochem. 1998; PubMed Scopus Google Scholar, B. K. J. R. R. Annu. Rev. Biochem. 2001; 70: PubMed Scopus Google Scholar). The is back to by PTEN (13Maehama T. Dixon J. E. J. Biol. Chem. 1998; 273: 13375-13378Abstract Full Text Full Text PDF PubMed Scopus (2646) Google Scholar) or to by such as J. Biol. Chem. 1999; 274: Full Text Full Text PDF PubMed Scopus Google Scholar). are at mammalian M. P. J. Biol. Chem. 2000; 275: Full Text Full Text PDF PubMed Scopus (118) Google Scholar), and the catalytic of all of contain signature active site and these the active site of the PTEN, do not possess a cysteine The 3′-phosphorylated phosphoinositides and proteins that a variety of cellular functions (15Maehama T. Taylor G. E. Dixon J. E. Annu. Rev. Biochem. 2001; 70: 247-279Crossref PubMed Scopus (411) Google Scholar, B. K. J. R. R. Annu. Rev. Biochem. 2001; 70: PubMed Scopus Google Scholar). of the of and is the protein Both and L. C. Neel B. G. Proc. Natl. Acad. Sci. U. S. A. 1999; 96: 4240-4245Crossref PubMed Scopus (1768) Google Scholar), their to this in L. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). cell survival by the factors and and thereby inhibiting their functions S. R. H. S. , H. Y. Cell. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar, M. H. E. S. Science. 1998; PubMed Scopus Google Scholar). activation of may to tumor formation V. Suzuki A. de la Pompa J. L. Brothers G. M. Mirtsos C. Sasaki T. Ruland J. Penninger J. M. Siderovski D. P. Mak T. W. Cell. 1998; 95: 29-39Abstract Full Text Full Text PDF PubMed Scopus (2146) Google Scholar, K. M. S. Proc. Natl. Acad. Sci. U. S. A. 1998; 95: PubMed Scopus Google Scholar). PTEN this proliferation signaling by the cellular of and and blocking activation V. Suzuki A. de la Pompa J. L. Brothers G. M. Mirtsos C. Sasaki T. Ruland J. Penninger J. M. Siderovski D. P. Mak T. W. Cell. 1998; 95: 29-39Abstract Full Text Full Text PDF PubMed Scopus (2146) Google Scholar, K. M. S. Proc. Natl. Acad. Sci. U. S. A. 1998; 95: PubMed Scopus Google Scholar). H2O2 induces the activation of (6Ushio-Fukai M. Alexander R. W. Akers M. Yin Q. Fujio Y. Walsh K. Griendling K. K. J. Biol. Chem. 1999; 274: 22699-22704Abstract Full Text Full Text PDF PubMed Scopus (501) Google Scholar, H. H. M. Y. S. Y. U. 1997; PubMed Scopus Google Scholar, J. Biol. Chem. 2000; 275: Full Text Full Text PDF PubMed Scopus Google Scholar). However, the 3′-phosphorylated phosphoinositide that in response to H2O2 is than A. 2000; 2: PubMed Scopus Google Scholar, der Kaay J. M. A. Downes C. P. J. Biol. Chem. 1999; 274: Full Text Full Text PDF PubMed Scopus Google Scholar). Given that H2O2 protein tyrosine kinases such as the PDGF receptor and the epidermal growth factor receptor J. Biol. Chem. 2000; 275: Full Text Full Text PDF PubMed Scopus Google Scholar, A. A. P. J. PubMed Scopus Google Scholar, T. K. V. R. J. C. C. J. Cell Biol. 1998; PubMed Scopus Google Scholar), also phosphoinositide in the production of In of this activation of is by the phosphoinositide 3-kinase inhibitor (6Ushio-Fukai M. Alexander R. W. Akers M. Yin Q. Fujio Y. Walsh K. Griendling K. K. J. Biol. Chem. 1999; 274: 22699-22704Abstract Full Text Full Text PDF PubMed Scopus (501) Google Scholar, J. Biol. Chem. 2000; 275: Full Text Full Text PDF PubMed Scopus Google S. K. Biochem. 2001; PubMed Scopus Google Scholar). We now that PTEN is by H2O2. This with the that PTEN, not an cysteine residue at active that in cells to H2O2, by phosphoinositide 3-kinase activity is by that are to H2O2, whereas at the is as a result of inactivation of PTEN by H2O2. The of the phosphatase activity of the tumor suppressor PTEN that H2O2 produced pathological such as might contribute to of to and to tumor many normal cells to proliferation and Biol. 1995; PubMed Scopus Google Scholar, K. M. K. H. S. T. J. Biochem. PubMed Scopus Google Scholar, R. E. E. PubMed Scopus Google Scholar). that tumor cells of H2O2 T. P. Google Scholar, K. Y. J. L. M. Finkel T. Science. 1997; 275: PubMed Scopus Google Scholar), this metabolite might also tumor cell the activity of has been in of the activity of the from A variety of cell receptor induce the production of H2O2, which is necessary for receptor-mediated cellular events such as and cell (3Sundaresan M. Yu Z. X. Ferrans V. J. Irani K. Finkel T. Science. 1995; 270: 296-299Crossref PubMed Scopus (2342) Google Scholar, J. Y. S. J. Cell Biol. 2000; PubMed Scopus Google Scholar). exogenous H2O2, the H2O2 also PTEN inactivation and contributes to the accumulation of 3′-phosphorylated phosphoinositides. Thus, the receptor-mediated activation of phosphoinositide 3-kinase may not be sufficient for the accumulation of 3′-phosphorylated and the concomitant inactivation of PTEN by H2O2 might also be necessary for this effect. the of PTEN in cell growth, and migration, the mechanisms by which the activity of this protein is (15Maehama T. Taylor G. E. Dixon J. E. Annu. Rev. Biochem. 2001; 70: 247-279Crossref PubMed Scopus (411) Google Scholar). PTEN phosphatase and which an H. A. T. Y. Dixon J. E. P. Cell. 1999; Full Text Full Text PDF PubMed Scopus Google Scholar). The phosphatase substantial to protein tyrosine phosphatases, an active site with residues that are important for the of the inositol PTEN also a at this T. T. H. Proc. Natl. Acad. Sci. U. S. A. 1999; 96: PubMed Scopus Google Scholar, T. 2000; PubMed Scopus Google Scholar, A. Pass I. Downes C. P. Biochem. J. 2000; PubMed Scopus Google Scholar), the and the been to the of PTEN from the to to H. A. T. Y. Dixon J. E. P. Cell. 1999; Full Text Full Text PDF PubMed Scopus Google Scholar, K. S. , D. J. C. Proc. Natl. Acad. Sci. U. S. A. 2000; PubMed Scopus Google Scholar, Y. D. S. R. Lee Q. J. Biol. Chem. 2000; 275: Full Text Full Text PDF PubMed Scopus Google Scholar, Huang L. R. 2000; Google Scholar). of PTEN by II has also been to increase the of the protein to J. R. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar). these of might be by the activation of cell however, is not in of phosphatase activity suggest that PTEN might be mechanism for has been (15Maehama T. Taylor G. E. Dixon J. E. Annu. Rev. Biochem. 2001; 70: 247-279Crossref PubMed Scopus (411) Google Scholar). activity of PTEN is to accumulation of and of proliferation in cells. The oxidative inactivation of PTEN in response to H2O2 generation might be an important of the and of the production of this important by receptor PTEN is back to the reduced by intracellular that the reversible oxidation and reduction of the active site cysteine residue is an important mechanism for the of The for the intracellular is that oxidized PTEN was reduced more by than by or in vitro. of reduced not of reduced the of of oxidized PTEN in cells. The of with PTEN by the of these proteins that the reduction might be by a specific between oxidized PTEN and reduced thioredoxin. a specific is also by the observation that a 14-kDa protein was not able to oxidized PTEN the that a motif, which is of the and that and and We K. for PTEN in the