The Docking Molecule Gab2 Is Induced by Lymphocyte Activation and Is Involved in Signaling by Interleukin-2 and Interleukin-15 but Not Other Common γ Chain-using Cytokines

Abstract

Interleukin (IL)-2, a critical cytokine with indispensable functions in regulating lymphoid homeostasis, induces the activation of several biochemical pathways. Precisely how these pathways are linked and how they relate to the biological action of IL-2 is incompletely understood. We previously identified SHP-2 (Src homology 2 domain containing phosphatase 2) as an important intermediate in IL-2-dependent MAPK activation and showed its association with a 98-kDa phosphoprotein in response to IL-2. Here, we demonstrate that Gab2, a recently identified adapter molecule, is the major SHP-2 and phosphatidylinositol 3′-kinase-associated 98-kDa protein in normal, IL-2-activated lymphocytes. We further demonstrate that phosphorylation of both Gab2 and SHP-2 is largely dependent upon tyrosine 338 of the IL-2 receptor β chain. Gab2 can be a substrate of all the three major classes of non-receptor tyrosine kinases associated with the IL-2R, but in terms of IL-2 signaling, JAK3 but not Lck or Syk is essential for Gab2 phosphorylation. We also demonstrate that only IL-2 and IL-15, but not other γc cytokines induce Gab2 phosphorylation; the ability to phosphorylate Gab2 correlates with Shc phosphorylation and ERK1/ERK2 activation. Finally, we also show that Gab2 levels are regulated by T cell activation, and resting T cells express little Gab2. Therefore, up-regulation and activation of Gab2 may be important in linking the IL-2 receptor to activation of MAPK and may be an important means of achieving specificity in cytokine signaling. Interleukin (IL)-2, a critical cytokine with indispensable functions in regulating lymphoid homeostasis, induces the activation of several biochemical pathways. Precisely how these pathways are linked and how they relate to the biological action of IL-2 is incompletely understood. We previously identified SHP-2 (Src homology 2 domain containing phosphatase 2) as an important intermediate in IL-2-dependent MAPK activation and showed its association with a 98-kDa phosphoprotein in response to IL-2. Here, we demonstrate that Gab2, a recently identified adapter molecule, is the major SHP-2 and phosphatidylinositol 3′-kinase-associated 98-kDa protein in normal, IL-2-activated lymphocytes. We further demonstrate that phosphorylation of both Gab2 and SHP-2 is largely dependent upon tyrosine 338 of the IL-2 receptor β chain. Gab2 can be a substrate of all the three major classes of non-receptor tyrosine kinases associated with the IL-2R, but in terms of IL-2 signaling, JAK3 but not Lck or Syk is essential for Gab2 phosphorylation. We also demonstrate that only IL-2 and IL-15, but not other γc cytokines induce Gab2 phosphorylation; the ability to phosphorylate Gab2 correlates with Shc phosphorylation and ERK1/ERK2 activation. Finally, we also show that Gab2 levels are regulated by T cell activation, and resting T cells express little Gab2. Therefore, up-regulation and activation of Gab2 may be important in linking the IL-2 receptor to activation of MAPK and may be an important means of achieving specificity in cytokine signaling. interleukin- IL-2 receptor extracellular signal-regulated kinase IL-four receptor interactingprotein common γ chain interferon insulin receptor substrate Janus kinase mitogen-activated protein kinase natural killer Src homology 2 SH2 domain containing phosphatase 2 phosphatidylinositol 3′-kinase signal transducer and activator of transcription international unit phytohemagglutinin Interleukin-2 (IL-2),1 a potent T cell mitogen, plays a critical role in the regulation of lymphoid proliferation and homeostasis (1Nelson B.H. Willerford D.M. Adv. Immunol. 1998; 70: 1-81Crossref PubMed Google Scholar). The IL-2 receptor comprises a heterotrimeric complex consisting of α, β, and γ subunits. The latter is shared by other cytokines including IL-4, IL-7, IL-9, and IL-15 and hence is called common γ chain (γc) (2Leonard W.J. O'Shea J.J. Annu. Rev. Immunol. 1998; 16: 293-322Crossref PubMed Scopus (1479) Google Scholar). All of these cytokines signal through common Janus kinases, namely JAK1 and JAK3 (3Johnston J.A. Kawamura M. Kirken R.A. Chen Y.Q. Blake T.B. Shibuya K. Ortaldo J.R. McVicar D.W. O'Shea J.J. Nature. 1994; 370: 151-153Crossref PubMed Scopus (507) Google Scholar). The current paradigm is that activated JAKs phosphorylate receptor subunits and subsequently proteins with Src homology 2 (SH2) or phosphotyrosine binding domains bind the phosphorylated receptors allowing signal propagation. IL-2 stimulation can lead to the activation of signal transducers and activators of transcription (STATs) as well as the phosphatidylinositol 3′-kinase (PI 3′-kinase) (4Merida I. Diez E. Gaulton G.N. J. Immunol. 1991; 147: 2202-2207PubMed Google Scholar, 5Karnitz L.M. Burns L.A. Sutor S.L. Blenis J. Abraham R.T. Mol. Cell. Biol. 1995; 15: 3049-3057Crossref PubMed Scopus (149) Google Scholar) and the Ras/mitogen-activated protein kinase (MAPK) pathways (6Burns L.A. Karnitz L.M. Sutor S.L. Abraham R.T. J. Biol. Chem. 1993; 268: 17659-17661Abstract Full Text PDF PubMed Google Scholar,7Ravichandran K.S. Burakoff S.J. J. Biol. Chem. 1994; 269: 1599-1602Abstract Full Text PDF PubMed Google Scholar). The mechanism by which STATs become phosphorylated and activated appears to be relatively straightforward. In contrast, exactly how the latter two pathways are linked to the proximal steps is less clear. For transmembrane receptor tyrosine kinases, like the platelet-derived growth factor receptor, SHP-2 (SH2 domain containing tyrosine phosphatase), binds the receptor together with the Grb2-SOS complex (8Li W. Nishimura R. Kashishian A. Batzer A.G. Kim W.J. Cooper J.A. Schlessinger J. Mol. Cell. Biol. 1994; 14: 509-517Crossref PubMed Google Scholar,9Bennett A.M. Tang T.L. Sugimoto S. Walsh C.T. Neel B.G. Proc. Natl. Acad. Sci. U. S. A. 1994; 91: 7335-7339Crossref PubMed Scopus (347) Google Scholar). Recently, it has also been shown that SHP-2 is phosphorylated in response to IL-2 (10Adachi M. Ishino M. Torigoe T. Minami Y. Matozaki T. Miyazaki T. Taniguchi T. Hinoda Y. Imai K. Oncogene. 1997; 14: 1629-1633Crossref PubMed Scopus (35) Google Scholar, 11Nelson B.H. McIntosh B.C. Rosencrans L.L. Greenberg P.D. Proc. Natl. Acad. Sci. U. S. A. 1997; 94: 1878-1883Crossref PubMed Scopus (46) Google Scholar, 12Gadina M. Stancato L.M. Bacon C.M. Larner A.C. O'Shea J.J. J. Immunol. 1998; 160: 4657-4661PubMed Google Scholar). Moreover, we have shown that SHP-2 is critical for IL-2-dependent MAPK activation, because catalytically inactive SHP-2 blocked the IL-2-induced activation of MAPK (12Gadina M. Stancato L.M. Bacon C.M. Larner A.C. O'Shea J.J. J. Immunol. 1998; 160: 4657-4661PubMed Google Scholar). Thus, as with growth factor receptors, SHP-2 appears to be important in coupling cytokines receptors to MAPK activation (13Neel B.G. Curr. Opin. Immunol. 1997; 9: 405-420Crossref PubMed Scopus (140) Google Scholar). The mechanism by which this occurs, however, is unknown, as SHP-2 has not been found to bind directly to the IL-2R. To address this question, we searched for SHP-2-associated proteins that became phosphorylated in response to IL-2 stimulation. Recently, we and others described a phosphoprotein of 98 kDa that associates with SHP-2 in response to IL-2 (14Gadina M. Sudarshan C. O'Shea J.J. J. Immunol. 1999; 162: 2081-2086PubMed Google Scholar, 15Gesbert F. Guenzi C. Bertoglio J. J. Biol. Chem. 1998; 273: 18273-18281Abstract Full Text Full Text PDF PubMed Scopus (44) Google Scholar). Interestingly we found this polypeptide to associate with SHP-2, PI 3′-kinase, and Grb2 in response to IL-2 but not to γc or other immunoregulatory cytokines. Here, we demonstrate that this SHP-2, PI 3′-kinase and Grb2-associated molecule is Gab2 (16Gu H. Pratt J.C. Burakoff S.J. Neel B.G. Mol. Cell. 1998; 2: 729-740Abstract Full Text Full Text PDF PubMed Scopus (282) Google Scholar, 17Nishida K. Yoshida Y. Itoh M. Fukada T. Ohtani T. Shirogane T. Atsumi T. Takahashi-Tezuka M. Ishihara K. Hibi M. Hirano T. Blood. 1999; 93: 1809-1816Crossref PubMed Google Scholar). Furthermore, we show that Gab2 is phosphorylated in response to IL-2 and IL-15 stimulation and its phosphorylation is greatly diminished by mutation of the site in the IL-2R β chain (Y338F) that recruits Shc. A critical issue in cytokine signal transduction is the understanding of specificity in signaling. Consequently, defining substrates that are specific for some receptors and not others is of considerable interest. We found that among the γc-utilizing cytokines, the ability to induce Gab2/SHP-2 phosphorylation was remarkably limited. Indeed, only IL-2 and IL-15 induced Gab2/SHP-2 phosphorylation in and this ability with Shc phosphorylation and activation. Moreover, we found that Gab2 as well as Shc levels induced upon T cell activation. these that Gab2 may be a substrate in IL-2 and IL-15 that to a of cytokines receptors to MAPK activation. Thus, Gab2 may be molecule by which cytokines can IL-2 and by C. IL-7, and IL-15 and was The and 3′-kinase, and and was as described previously (16Gu H. Pratt J.C. Burakoff S.J. Neel B.G. Mol. Cell. 1998; 2: 729-740Abstract Full Text Full Text PDF PubMed Scopus (282) Google Scholar). T cells as described previously C.M. McVicar D.W. Ortaldo J.R. O'Shea J.J. J.A. J. 1995; PubMed Scopus Google Scholar). The cell was by J. and as described previously C.M. McVicar D.W. Ortaldo J.R. O'Shea J.J. J.A. J. 1995; PubMed Scopus Google Scholar). cells in and for in with cells in with For cells in 2 cells with of β or the and of or the the containing the was and with containing the was with containing and cells for To the of or IL-2R β cells with with with or for three with and a cells in of T and with cytokines for the and as described previously (3Johnston J.A. Kawamura M. Kirken R.A. Chen Y.Q. Blake T.B. Shibuya K. Ortaldo J.R. McVicar D.W. O'Shea J.J. Nature. 1994; 370: 151-153Crossref PubMed Scopus (507) Google Scholar). For kinase cell by for and the The Lck three with and with and and in of kinase and containing of The in kinase for in the or of the Src kinase or as and by the of of containing by to and to a or with We and others have previously described a phosphoprotein of 98 kDa in T cells and natural killer cells that associate with PI 3′-kinase, and SHP-2 in response to IL-2 (14Gadina M. Sudarshan C. O'Shea J.J. J. Immunol. 1999; 162: 2081-2086PubMed Google Scholar, 15Gesbert F. Guenzi C. Bertoglio J. J. Biol. Chem. 1998; 273: 18273-18281Abstract Full Text Full Text PDF PubMed Scopus (44) Google Scholar). for as signal protein and adapter like We because was not to (14Gadina M. Sudarshan C. O'Shea J.J. J. Immunol. 1999; 162: 2081-2086PubMed Google Scholar). The adapter was also however, it was because of its in cells not Gab2, a recently homology protein phosphorylated in response to several cytokines (16Gu H. Pratt J.C. Burakoff S.J. Neel B.G. Mol. Cell. 1998; 2: 729-740Abstract Full Text Full Text PDF PubMed Scopus (282) Google Scholar, 17Nishida K. Yoshida Y. Itoh M. Fukada T. Ohtani T. Shirogane T. Atsumi T. Takahashi-Tezuka M. Ishihara K. Hibi M. Hirano T. Blood. 1999; 93: 1809-1816Crossref PubMed Google was a for this 98-kDa T cell these that IL-2 induced Gab2 phosphorylation. the ability to phosphorylate substrates can cell and we to IL-2 was to induce Gab2 phosphorylation in T We also to Gab2 was a substrate shared by all γc cytokines or IL-2 induced Gab2 phosphorylation. IL-2 and IL-15 of the phosphorylation of Gab2, IL-4, IL-7, and other immunoregulatory cytokines and to To these cytokines we JAK3 which with all γc cytokines. All of the cytokines to induce JAK3 tyrosine phosphorylation and induce the phosphorylation of Bacon C.M. Sudarshan C. R. O'Shea J.J. J. Immunol. Google we phosphorylation of this molecule to the of these two immunoregulatory and the kinases, other tyrosine phosphorylated substrates have not been and in of phosphorylation in an cell shown in only IL-2 but not IL-4, or was to induce the phosphorylation of Gab2 in To that of Gab2 the was with Gab2 The specificity of the was by with a among the γc cytokines, only IL-2 and IL-15 induced Gab2 it be that other cytokines induce Gab2 phosphorylation. the specific phosphorylation among γc cytokines is found that Gab2 was a IL-2-dependent we to in it was the major 98-kDa associated with PI 3′-kinase and cells and with PI 3′-kinase by with Gab2 or PI 3′-kinase Gab2 was the two of of In we also to that the and Grb2-associated was Gab2 by the of not Moreover, the phosphorylated 98-kDa protein in the SHP-2 was by in The was in T cells with not The specific phosphorylation of Gab2 by IL-2 and IL-15 that the IL-2R β which is shared by the two cytokine receptors, be important for the phosphorylation of this has been shown previously that the IL-2R β chain is important in IL-2-induced MAPK activation J.A. W. R. Abraham R.T. O'Shea J.J. J. Biol. Chem. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar, W.J. Proc. Natl. Acad. Sci. U. S. A. 93: PubMed Scopus Google Shc and SHP-2 phosphorylation (10Adachi M. Ishino M. Torigoe T. Minami Y. Matozaki T. Miyazaki T. Taniguchi T. Hinoda Y. Imai K. Oncogene. 1997; 14: 1629-1633Crossref PubMed Scopus (35) Google Scholar). Moreover, we and others have shown that tyrosine 338 is important for Shc MAPK activation, and proliferation J.A. W. R. Abraham R.T. O'Shea J.J. J. Biol. Chem. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar, W.J. Proc. Natl. Acad. Sci. U. S. A. 93: PubMed Scopus Google Scholar). In contrast, the for SHP-2 phosphorylation not been We the of a SHP-2, and Gab2 phosphorylation with MAPK activation by cytokines in both T and shown in T cells with cytokines, and by with IL-2 2) and IL-15 to induce the phosphorylation of cells and T cells also for Shc phosphorylation. IL-2 and IL-15 the only two cytokines among that to induce Shc phosphorylation 2 and and of phosphorylation of Gab2, SHP-2, and Shc that these through a common in the IL-2R. We to is important for both Gab2 and SHP-2 phosphorylation. shown in cells with the IL-2R including or IL-2R β, and Gab2. In cells with IL-2R, Gab2 was phosphorylated in response to IL-2 the cells with the IL-2R β, Gab2 phosphorylation was a of Gab2 phosphorylation was the of means of Gab2 phosphorylation. the of the IL-2R β and this has been shown to be important for IL-2-induced SHP-2 phosphorylation (10Adachi M. Ishino M. Torigoe T. Minami Y. Matozaki T. Miyazaki T. Taniguchi T. Hinoda Y. Imai K. Oncogene. 1997; 14: 1629-1633Crossref PubMed Scopus (35) Google Scholar). Gab2 phosphorylation we also was important for SHP-2 phosphorylation. cells as with SHP-2 we that was the critical for SHP-2 phosphorylation with and with a W.J. Proc. Natl. Acad. Sci. U. S. A. 93: PubMed Scopus Google IL-2R β chain phosphorylation in response to IL-2 was diminished in the 2 with of receptor and levels of of β chain the as by however, to demonstrate binding of SHP-2 or Gab2 to the IL-2R β only Shc associates directly not of the IL-2 are upon T cell activation. IL-2R and to a the IL-2R β chain are The of Gab2 and Shc in IL-2 in T cells to these proteins or in resting lymphocytes. We Gab2 in shown in Gab2 was relatively levels in cells cells activated with the up-regulation of the Gab2 protein was of stimulation. by the cells with not T cell activation are dependent upon and are to like the IL-2R chain and are We the of Gab2 upon this shown in A not Gab2 To that the in cells not a cell we the lymphoid cells shown in Gab2 was in cells but in activated cells In with the shown in A not Gab2 up-regulation Gab2 phosphorylation with Shc we the levels of Shc be by the of activation of the shown in the was with two other that have been shown to in IL-2 signaling, Shc and Grb2 we an up-regulation of Shc levels to that for Gab2, the levels of the adapter Grb2 not upon activation. IL-2 the activation of non-receptor tyrosine kinases (1Nelson B.H. Willerford D.M. Adv. Immunol. 1998; 70: 1-81Crossref PubMed Google T. Miyazaki T. Minami Y. A. H. Y. M. Y. Acad. Sci. 1995; PubMed Scopus Google Scholar). In an to the kinase or kinases for Gab2 phosphorylation in response to IL-2 cell with Gab2 and of the Lck or shown in with the of Lck all of the kinases induce the phosphorylation of Gab2. a ability to induce phosphorylation was also as these kinases can phosphorylate K.S. M. D.M. J. F. O'Shea J.J. Mol. Cell. Biol. PubMed Scopus Google Syk less the others JAK1 was a relatively of Gab2 phosphorylation all of the kinases to be associated with the IL-2R the to Gab2 as a we which critical for Gab2 phosphorylation. We upon because it to be an kinase for Gab2 phosphorylation. To this we the Src J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar) IL-2-induced Gab2 phosphorylation. cells with or of for and subsequently with IL-2. the Gab2 phosphorylation the of the was to Lck kinase as by a Lck and a the of phosphorylation was also we not of phosphorylation K.S. M. D.M. J. F. O'Shea J.J. Mol. Cell. Biol. PubMed Scopus Google Scholar). The of a specific for Syk not to it as a IL-2-dependent however, we the IL-2R complex in which not express we to induce Gab2 as well as other substrate phosphorylation. Indeed, with the IL-2R complex only JAK3 was to Gab2 phosphorylation. the of JAK1 not induce Gab2 phosphorylation cells with IL-2 these a role for JAK3 in IL-2-dependent Gab2 in with in which we showed the of phosphorylation in cells with the IL-2R complex (14Gadina M. Sudarshan C. O'Shea J.J. J. Immunol. 1999; 162: 2081-2086PubMed Google Scholar). We and others previously described a phosphoprotein of 98 kDa that associates with SHP-2, PI 3′-kinase, and Grb2 in response to IL-2 (14Gadina M. Sudarshan C. O'Shea J.J. J. Immunol. 1999; 162: 2081-2086PubMed Google Scholar, 15Gesbert F. Guenzi C. Bertoglio J. J. Biol. Chem. 1998; 273: 18273-18281Abstract Full Text Full Text PDF PubMed Scopus (44) Google Scholar). Here, we demonstrate that Gab2 (16Gu H. Pratt J.C. Burakoff S.J. Neel B.G. Mol. Cell. 1998; 2: 729-740Abstract Full Text Full Text PDF PubMed Scopus (282) Google Scholar, 17Nishida K. Yoshida Y. Itoh M. Fukada T. Ohtani T. Shirogane T. Atsumi T. Takahashi-Tezuka M. Ishihara K. Hibi M. Hirano T. Blood. 1999; 93: 1809-1816Crossref PubMed Google Scholar) is the major 98-kDa phosphoprotein associated with SHP-2, PI 3′-kinase, and Grb2 in lymphocytes. We also show that IL-2 and IL-15 induce the phosphorylation of Gab2, other immunoregulatory cytokines, including γc cytokines as and that a receptor and other in and not induce Gab2 phosphorylation. Gab2 phosphorylation only IL-2 and IL-15 stimulation and not stimulation with other γc-utilizing cytokines, we that its phosphorylation was dependent the IL-2R β chain. Indeed, receptor with β chain or a to this site as critical for Gab2 and SHP-2 phosphorylation. and the that IL-2-induced phosphorylation of SHP-2 is dependent the of the IL-2R β chain (10Adachi M. Ishino M. Torigoe T. Minami Y. Matozaki T. Miyazaki T. Taniguchi T. Hinoda Y. Imai K. Oncogene. 1997; 14: 1629-1633Crossref PubMed Scopus (35) Google Scholar). Moreover, tyrosine 338 in the IL-2R β chain has been to be essential for the phosphorylation and binding of the adapter molecule Shc and IL-2-induced proliferation J.A. W. R. Abraham R.T. O'Shea J.J. J. Biol. Chem. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar, W.J. Proc. Natl. Acad. Sci. U. S. A. 93: PubMed Scopus Google Scholar). In in we found a in the ability of IL-2 and IL-15 but not other γc cytokines to Gab2, SHP-2, and we also show that the levels of Shc and Gab2 are not but are regulated by T cell activation. Finally, all of the kinases associated with the IL-2R β chain the to phosphorylate Gab2, only JAK3 was for IL-2-dependent phosphorylation. To a or all cytokines a that can be by shared receptor subunits and shared in pathways. they also have as by of in W. S. J. E. Y. Acad. Sci. 1998; PubMed Scopus Google Scholar). can be by the of receptor subunits and by the of specific the of the and is of The specific phosphorylation and the activation of of is of the by which cytokines that receptor subunits and other can that Gab2 is a substrate phosphorylated by IL-2 and IL-15 but not by a of immunoregulatory cytokines. a of other cytokines including and factor have been to induce the phosphorylation of Gab2 (16Gu H. Pratt J.C. Burakoff S.J. Neel B.G. Mol. Cell. 1998; 2: 729-740Abstract Full Text Full Text PDF PubMed Scopus (282) Google Scholar, 17Nishida K. Yoshida Y. Itoh M. Fukada T. Ohtani T. Shirogane T. Atsumi T. Takahashi-Tezuka M. Ishihara K. Hibi M. Hirano T. Blood. 1999; 93: 1809-1816Crossref PubMed Google Scholar). in the of a Gab2, and MAPK phosphorylation also and mutation of the Shc binding tyrosine in the common β SHP-2 and Gab2 phosphorylation T. A. S. A. T. K. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). J. J. and Mol. in be important to and the biological of these cytokines with IL-2 and IL-15 cytokines that not this and IL-2 has been shown to non-receptor tyrosine kinases three of kinases (1Nelson B.H. Willerford D.M. Adv. Immunol. 1998; 70: 1-81Crossref PubMed Google Scholar, T. Miyazaki T. Minami Y. A. H. Y. M. Y. Acad. Sci. 1995; PubMed Scopus Google Scholar). it appears that all three classes can induce Gab2 phosphorylation. the of a specific Src kinase not induce in Gab2 and because we to a IL-2 response in cells Syk kinases, we that the JAKs are the major kinases for IL-2-induced phosphorylation. of levels of JAK3 can induce Gab2 phosphorylation in a In contrast, of JAK3 phosphorylation of Gab2 IL-2 stimulation but not in the of be however, that Gab2 is also phosphorylated in response to T cell receptor (16Gu H. Pratt J.C. Burakoff S.J. Neel B.G. Mol. Cell. 1998; 2: 729-740Abstract Full Text Full Text PDF PubMed Scopus (282) Google Scholar, 17Nishida K. Yoshida Y. Itoh M. Fukada T. Ohtani T. Shirogane T. Atsumi T. Takahashi-Tezuka M. Ishihara K. Hibi M. Hirano T. Blood. 1999; 93: 1809-1816Crossref PubMed Google Scholar). be of to of the Src or Syk of protein tyrosine kinases are for Gab2 phosphorylation in this In IL-2 and IL-15 are to be potent of MAPK (6Burns L.A. Karnitz L.M. Sutor S.L. Abraham R.T. J. Biol. Chem. 1993; 268: 17659-17661Abstract Full Text PDF PubMed Google Scholar, K.S. Burakoff S.J. Proc. Natl. Acad. Sci. U. S. A. 93: PubMed Scopus Google Scholar, J. J. Biol. Chem. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar, K. Blood. 1997; PubMed Google Scholar). contrast, and have been to be activators of MAPK T. M. A. Y. Proc. Natl. Acad. Sci. U. S. A. 1991; PubMed Scopus Google Scholar, J. Biol. Chem. 1994; 269: Full Text PDF PubMed Google Scholar, J. J. Immunol. PubMed Scopus Google Scholar). have been to MAPK M. C. R. Larner A.C. 1995; 269: PubMed Scopus Google but it is that in lymphoid cells they are activators to IL-2 mechanism by which the can be activated is the phosphorylation of the receptor and of through the Grb2 and the activation of J. Sci. 1993; Full Text PDF PubMed Scopus Google Scholar). is that IL-4, IL-7, and not induce Shc phosphorylation. In however, the phosphatase SHP-2 may also be an important of this as a SHP-2 MAPK activation (12Gadina M. Stancato L.M. Bacon C.M. Larner A.C. O'Shea J.J. J. Immunol. 1998; 160: 4657-4661PubMed Google Scholar, H. Pratt J.C. Burakoff S.J. Neel B.G. Mol. Cell. 1998; 2: 729-740Abstract Full Text Full Text PDF PubMed Scopus (282) Google Scholar, K. T. R. J. 1997; PubMed Scopus Google Scholar). The that Gab2 activation (16Gu H. Pratt J.C. Burakoff S.J. Neel B.G. Mol. Cell. 1998; 2: 729-740Abstract Full Text Full Text PDF PubMed Scopus (282) Google K. Yoshida Y. Itoh M. Fukada T. Ohtani T. Shirogane T. Atsumi T. Takahashi-Tezuka M. Ishihara K. Hibi M. Hirano T. Blood. 1999; 93: 1809-1816Crossref PubMed Google Scholar) that Gab2 may be an important molecule for coupling cytokine receptors to activation of activation in appears to be important for the ability of some cytokines like IL-2 to induce proliferation W.J. Proc. Natl. Acad. Sci. U. S. A. 93: PubMed Scopus Google Scholar). the mechanism by which activation is linked to this receptor is not IL-2R β chain is important for both Shc and Gab2/SHP-2 but it not bind Gab2 or SHP-2 The of Gab2 to bind the receptor chain is with its Gab2 SH2 and phosphotyrosine binding domains and not have that it to bind directly to the this is in with and with the K. M. L.M. Cell. 1994; Full Text PDF PubMed Scopus Google Scholar). SHP-2 bind the IL-2R by of its SH2 however, we have found of an Moreover, we demonstrate that is important for SHP-2 this site is a Shc phosphotyrosine binding site J. T. M. H. H. T. R. S. R.A. Mol. Cell. Biol. 1994; 14: PubMed Scopus Google but not a SHP-2 binding Shc binding to the IL-2R β chain can be but we not a Gab2/SHP-2 and the IL-2R β chain. Therefore, it be important to Shc is of the Gab2/SHP-2 we like other of the IL-2 as IL-2R α, and to a the IL-2R β Gab2 and Shc are upon T cell activation. Moreover, the in was not to A the as the mechanism through which Gab2 and Shc is is homology adapter molecule that is phosphorylated in response to both IL-2 and and that associates with In to Gab2, MAPK phosphorylation K. J. 1998; 9: Full Text Full Text PDF PubMed Scopus Google Scholar). Thus, it is that the levels of Gab2 may be important in regulating the ability of IL-2 and IL-15 to The of to induce Gab2 phosphorylation phosphorylation may the of ability of to it may MAPK activation. that both Gab2 and Shc are upon T cell activation are of in of the that is In levels of T cell receptor E. Thus, the ability to the cytokine receptor with the MAPK may be that IL-2 has been to PI 3′-kinase, but the mechanism by which this is (4Merida I. Diez E. Gaulton G.N. J. Immunol. 1991; 147: 2202-2207PubMed Google Scholar). Moreover, for PI 3′-kinase is also to to MAPK activation L.M. Burns L.A. Sutor S.L. Blenis J. Abraham R.T. Mol. Cell. Biol. 1995; 15: 3049-3057Crossref PubMed Scopus (149) Google Scholar). The of PI 3′-kinase has been found to associate with and this association has been to be means by which PI 3′-kinase become activated S. M. W.J. Mol. Cell. Biol. 1998; PubMed Scopus Google Scholar). We also that IL-2 induces the phosphorylation of the proteins substrates and 2 J.A. L.M. O'Shea J.J. J. Biol. Chem. 1995; Full Text Full Text PDF PubMed Scopus Google but the role of in IL-2 is We show that IL-2 induces the phosphorylation of Gab2 and of the of PI 3′-kinase to a complex that also comprises which of these is the important for IL-2-induced PI 3′-kinase activation to be be however, that not induce Gab2 phosphorylation and hence PI 3′-kinase this an mechanism is for the of PI Gab2 recruits PI 3′-kinase, it be important to how this to IL-2-induced MAPK activation and to it is dependent the Gab2/SHP-2 In we Gab2 as an important in IL-2 that associates to a of PI 3′-kinase, also be important to the of Gab2 and other like and in by the γc cytokines and to role in the regulation of specific pathways. We J. for IL-2R α, IL-2R β, and IL-2R γ chain and and for the