Gene 33 Is an Endogenous Inhibitor of Epidermal Growth Factor (EGF) Receptor Signaling and Mediates Dexamethasone-induced Suppression of EGF Function
We report a mechanism by which the adapter protein Gene 33 (also called RALT and MIG6) regulates epidermal growth factor receptor (EGFR) signaling. We find that Gene 33 inhibits EGFR autophosphorylation and specifically blunts epidermal growth factor (EGF)-induced activation and/or phosphorylation of Ras, ERK, JNK, Akt/PKB, and retinoblastoma protein. The Ack homology domain of Gene 33, which contains the previously identified EGFR binding domain, is both necessary and sufficient for this inhibition of EGFR autophosphorylation. The endogenous Gene 33 polypeptide is induced by EGF, platelet-derived growth factor, serum, and dexamethasone (Dex) in Rat 2 rat fibroblasts. Dex induces Gene 33 expression and inhibits EGFR phosphorylation and EGF signaling. RNA interference-mediated silencing of Gene 33 significantly reverses this effect. Overexpression of Gene 33 completely blocks EGF-induced protein and DNA synthesis in Rat 2 cells, whereas gene 33 RNA interference substantially enhances EGF-induced protein and DNA synthesis in Rat 2 cells. Our results indicate that Gene 33 is a physiological feedback inhibitor of the EGFR, functioning to inhibit EGFR phosphorylation and all events induced by EGFR activation. Our results also indicate a role for Gene 33 in the suppression, by Dex, of EGF signaling pathways. We propose that Gene 33 may function in the cross-talk between EGF signaling and other mitogenic and/or stress signaling pathways. We report a mechanism by which the adapter protein Gene 33 (also called RALT and MIG6) regulates epidermal growth factor receptor (EGFR) signaling. We find that Gene 33 inhibits EGFR autophosphorylation and specifically blunts epidermal growth factor (EGF)-induced activation and/or phosphorylation of Ras, ERK, JNK, Akt/PKB, and retinoblastoma protein. The Ack homology domain of Gene 33, which contains the previously identified EGFR binding domain, is both necessary and sufficient for this inhibition of EGFR autophosphorylation. The endogenous Gene 33 polypeptide is induced by EGF, platelet-derived growth factor, serum, and dexamethasone (Dex) in Rat 2 rat fibroblasts. Dex induces Gene 33 expression and inhibits EGFR phosphorylation and EGF signaling. RNA interference-mediated silencing of Gene 33 significantly reverses this effect. Overexpression of Gene 33 completely blocks EGF-induced protein and DNA synthesis in Rat 2 cells, whereas gene 33 RNA interference substantially enhances EGF-induced protein and DNA synthesis in Rat 2 cells. Our results indicate that Gene 33 is a physiological feedback inhibitor of the EGFR, functioning to inhibit EGFR phosphorylation and all events induced by EGFR activation. Our results also indicate a role for Gene 33 in the suppression, by Dex, of EGF signaling pathways. We propose that Gene 33 may function in the cross-talk between EGF signaling and other mitogenic and/or stress signaling pathways. Feedback inhibition and cross-talk among signal transduction networks are regulatory mechanisms critical to the coordination of complex biological activities. Cross-talk can be positive, in which activation of one signaling pathway activates or enhances another. For example, G protein-coupled receptor pathways can often transactivate the epidermal growth factor receptor (EGFR) 1The abbreviations used are: EGFR, epidermal growth factor receptor; AH, Ack homology; Dex, dexamethasone; EGF, epidermal growth factor; ERK, extracellular signal-regulated kinase; GST, glutathione S-transferase; HEK, human embryonic kidney; JNK, c-Jun NH2-terminal kinase; MAPK, mitogen-activated protein kinase; PDGF, platelet-derived growth factor; Rb, retinoblastoma protein; RNAi, RNA interference; siRNA, small interfering RNA; Ack, activated CDC42-associated kinase; MOI, multiplicity of infection. signaling pathway and transmit their signals through the EGFR signaling pathway (1Prenzel N. Zwick E. Daub H. Leserer M. Abraham R. Wallasch C. Ullrich A. Nature. 1999; 402: 884-888Crossref PubMed Scopus (1499) Google Scholar). Negative cross-talk occurs when the activation of one pathway suppresses the activation of another. Thus, recruitment of the nuclear factor-κB pathway represses activation of the c-Jun NH2-terminal kinase (JNK) group of mitogen-activated protein kinases (MAPKs), thereby reducing JNK-dependent apoptosis (2Reuther-Madrid J.Y. Kashatus D. Chen S. Li X. Westwick J. Davis R.J. Earp H.S. Wang C.Y. Baldwin Jr., A.S. Mol. Cell. Biol. 2002; 22: 8175-8183Crossref PubMed Scopus (78) Google Scholar). Whereas some signaling cross-talk occurs rapidly and is mediated by existing signaling elements, some signaling cross-talk occurs more slowly, requiring the production of new elements through stimulus-induced transcription/translation. Glucocorticoids signal by direct activation of the glucocorticoid receptor, which, upon activation, translocates to the nucleus and activates DNA transcription (3McEwan I.J. Wright A.P. Gustafsson J.A. BioEssays. 1997; 19: 153-160Crossref PubMed Scopus (161) Google Scholar). Non-transcriptional functions for the glucocorticoid receptor have also been observed (4Bruna A. Nicolas M. Muñoz A. Kyriakis J.M. Caelles C. EMBO J. 2003; 22: 6035-6044Crossref PubMed Scopus (104) Google Scholar). Thus, the glucocorticoid receptor can inhibit cytokine activation of JNK via a direct interaction (4Bruna A. Nicolas M. Muñoz A. Kyriakis J.M. Caelles C. EMBO J. 2003; 22: 6035-6044Crossref PubMed Scopus (104) Google Scholar). Glucocorticoids have long been known to reduce cell proliferation and/or to inhibit mitogenic signaling pathways mediated by a variety of signals, including insulin, insulin-like growth factor I, and epidermal growth factor (EGF) (5Baus E. Andris F. Dubois P.M. Urbain J. Leo O. J. Immunol. 1996; 156: 4555-4561PubMed Google Scholar, 6Buren J. Liu H.X. Jensen J. Eriksson J.W. Eur. J. Endocrinol. 2002; 146: 419-429Crossref PubMed Scopus (140) Google Scholar, 7Hulley P.A. Gordon F. Hough F.S. Endocrinology. 1998; 139: 2423-2431Crossref PubMed Google Scholar, 8Karasik A. Kahn C.R. Endocrinology. 1988; 123: 2214-2222Crossref PubMed Scopus (25) Google Scholar, 9Nagy P. Kiss A. Schnur J. Thorgeirsson S.S. Hepatology. 1998; 28: 423-429Crossref PubMed Scopus (87) Google Scholar, 10Zendegui J.G. Inman W.H. Carpenter G. J. Cell. Physiol. 1988; 136: 257-265Crossref PubMed Scopus (42) Google Scholar). However, the exact mechanisms that underlie these inhibitory effects are poorly understood. The synthetic glucocorticoid dexamethasone (Dex) has been shown to inhibit the proliferation of an osteoblast cell line by blocking MAPK activation through recruitment of protein tyrosine phosphatase (7Hulley P.A. Gordon F. Hough F.S. Endocrinology. 1998; 139: 2423-2431Crossref PubMed Google Scholar). It has also been shown that Dex inhibits tyrosine phosphorylation of the insulin and EGF receptor (8Karasik A. Kahn C.R. Endocrinology. 1988; 123: 2214-2222Crossref PubMed Scopus (25) Google Scholar). These reports suggest that regulation of growth factor signaling by Dex occurs at the level of the growth factor receptors themselves. Feedback inhibition is a second mechanism of signaling pathway regulation and is crucial in modulating the intensity and duration of signals generated by receptors (11Dikic I. Giordano S. Curr. Opin. Cell Biol. 2003; 15: 128-135Crossref PubMed Scopus (286) Google Scholar, 12Alexander W.S. Nat. Rev. Immunol. 2002; 2: 410-416Crossref PubMed Scopus (532) Google Scholar). Thus, sustained activation of the extracellular signal-regulated kinase (ERK) group of MAPKs is necessary for agonist-induced cell proliferation (13Brunet A. Roux D. Lenormand P. Dowd S. Keyse S. Pouyssegur J. EMBO J. 1999; 18: 664-674Crossref PubMed Scopus (517) Google Scholar). EGF-stimulated ERK activation is often relatively transient, and in fibroblasts, EGF is a less effective mitogen than platelet-derived growth factor (PDGF). Any of several mechanisms might account for such relatively transient EGF signaling. It has been well documented that the EGFR is subject to ligand-induced down-regulation mediated by receptor internalization and subsequent degradation by lysosome and the ubiquitin/proteasome systems (14Wiley H.S. Exp. Cell Res. 2003; 284: 78-88Crossref PubMed Scopus (300) Google Scholar, 15Sweeney C. Carraway K.L. II I Br. J. Cancer. 2004; 90: 289-293Crossref PubMed Scopus (49) Google Scholar). Another negative regulator of EGFR signaling is the activated CDC42-associated kinase (Ack), which is believed to facilitate EGFR endocytosis (16Yang W. Lo C.G. Dispenza T. Cerione R.A. J. Biol. Chem. 2001; 276: 17468-17473Abstract Full Text Full Text PDF PubMed Scopus (62) Google Scholar, 17Teo M. Tan E. J. Biol. Chem. 2001; 276: Full Text Full Text PDF PubMed Scopus Google Scholar). and are also negative of the EGFR A. S. P. C. J. PubMed Scopus Google Scholar, X. F. M. S. C. C. J. Biol. Chem. 2001; 276: Full Text Full Text PDF PubMed Scopus Google Scholar). MAPKs can the expression of MAPK that function to and MAPKs by cell receptors S.S. S. J. Mol. Cell. 2001; PubMed Scopus Google Scholar, A.S. J. Biol. Chem. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar, T. T. R. E. J. Biol. Chem. 2001; 276: Full Text Full Text PDF PubMed Scopus (140) Google Scholar). Gene 33 (also called RALT and MIG6) is a adapter protein function has to be Gene 33 is an gene of Scholar, K.L. R. J. Biol. Chem. Full Text PDF PubMed Google Scholar). It is in of Scholar, K.L. R. J. Biol. Chem. Full Text PDF PubMed Google and can be induced by a of extracellular including growth and of stress of Scholar, K.L. R. J. Biol. Chem. Full Text PDF PubMed Google Scholar, A. Chen A. T. Kyriakis J.M. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, N. P. R. J. 1999; 18: Google Scholar, Res. PubMed Scopus Google Scholar, Endocrinology. PubMed Scopus Google Scholar). Gene 33 is induced by and such of Scholar, A. Chen A. T. Kyriakis J.M. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). the of Gene 33 that functions an protein A. Chen A. T. Kyriakis J.M. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google known the biological function of Gene It has been shown that Gene 33 is in and activates JNK or ERK A. Chen A. T. Kyriakis J.M. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). Gene 33 contains an NH2-terminal interaction and binding domain through which in a the small G protein Gene 33 also the binding adapter protein A. Chen A. T. Kyriakis J.M. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). Gene 33 also to the kinase of EGFR receptor kinases and may an feedback inhibitor of signaling by receptors in the EGFR C. M. C. M. S. P. O. Mol. Cell. Biol. PubMed Scopus Google Scholar, S. M. R. G. S. M. O. 2003; 22: PubMed Scopus Google Scholar). However, the mechanism of this inhibition of EGFR signaling by Gene 33 is is these results physiological functions of Gene the used a of and RNA interference gene to the physiological functions of Gene We find that Gene 33 specifically inhibits EGFR autophosphorylation and the subsequent activation of signaling well EGF-induced protein and DNA Dex induces Gene 33 expression and inhibits EGF-induced EGFR autophosphorylation through a mechanism that in Gene These results indicate that Gene 33 is a inhibitor of EGFR signaling at the receptor level and that Gene 33 the cross-talk between Dex and EGFR signaling. and Gene 33 generated by to which a to of Gene 33 and cells. and Cell or Gene 33 or expression which an or Gene 33 generated by a previously S. J. S. A. 1998; PubMed Scopus Google Scholar). The by The human in expression by Ullrich for Cell and RNA embryonic and Rat 2 rat in by to the of Rat 2 at a multiplicity of of than can be at this EGF or for the in the of EGF or for for or a the inhibitor (1Prenzel N. Zwick E. Daub H. Leserer M. Abraham R. Wallasch C. Ullrich A. Nature. 1999; 402: 884-888Crossref PubMed Scopus (1499) Google Scholar). For dexamethasone in the dexamethasone for which EGF for the The RNA used for Gene 33 small interfering RNA to the rat and protein and Rat 2 at a of to the and and in For cell of protein and protein for 2 by to cell or and the to to RNA the RNA DNA of Gene 33, to previously D. Kyriakis J.M. J. Biol. Chem. 2003; Full Text Full Text PDF PubMed Scopus Google Scholar). of to in a the binding domain of a glutathione protein and to and in a to the binding of G and of for of to which of been of and to by to and DNA synthesis and DNA synthesis and Rat 2 in for or in the EGF for the of or the of the and the in for and and one and a in at are in which is are used to the of The level at Gene 33 to the EGFR and EGFR in 33 is a protein the of an The of Gene 33 an NH2-terminal interaction and binding domain that is by several of binding for for and domain are also Gene 33 a to the of the this Ack homology domain previously identified an EGF receptor binding C. M. C. M. S. P. O. Mol. Cell. Biol. PubMed Scopus Google Scholar, S. M. R. G. S. M. O. 2003; 22: PubMed Scopus Google Scholar). is also a of Gene 33, which a of the NH2-terminal Gene 33 has been shown to to the of of the EGF receptor C. M. C. M. S. P. O. Mol. Cell. Biol. PubMed Scopus Google Scholar, S. M. R. G. S. M. O. 2003; 22: PubMed Scopus Google Scholar). this EGFR Gene 33 in and Gene 33 shown in EGFR Gene Gene 33 and endogenous EGFR also the Gene 33 Gene 33 to to both the and EGFR and is a report which that the binding of Gene 33 to the EGFR EGFR tyrosine Gene 33 also to the EGFR, by EGFR protein in Gene 33 may be to the of Gene 33 to inhibit EGFR autophosphorylation and internalization and observed a in the autophosphorylation of EGFR upon Gene 33 Gene 33 also inhibits ligand-induced tyrosine phosphorylation of the EGFR, at Gene 33 and for EGF-induced EGFR tyrosine the of cells, to a in EGF-induced tyrosine phosphorylation upon expression of Gene 33 in the of Gene 33 that is for the inhibition of EGFR or of Gene 33 the EGFR and or to the binding of these to We also the of these EGFR autophosphorylation. shown in and the the and the Gene 33 the Ack homology domain to and EGFR and inhibit EGFR autophosphorylation. the results of and Our that the domain of Gene 33 is necessary and sufficient for inhibition of EGFR autophosphorylation by Gene Gene 33 the of of the of Gene 33 to inhibit EGF-induced EGFR autophosphorylation 2 and that Gene 33 also inhibit EGF-induced activation of signaling of the activated EGFR is the pathway F. N. Exp. Cell Res. 2003; 284: PubMed Scopus Google Scholar). We the of Gene 33 EGF-induced and ERK activation. shown in the transient expression of of Gene 33 inhibits EGF-induced activation of cell ERK in a We for and Gene 33 in and the of Gene 33 EGF-induced activation. of and upon the of to such the binding domain of in the is a of activation. shown in EGF an of of Gene 33 completely activation in to These that expression of Gene 33 is to inhibit EGF-induced activation of the Gene 33 EGF-induced of EGFR and of the EGFR in Rat 2 and inhibition of EGFR signaling is a function of Gene 33, the of Gene 33 expression EGFR signaling in a cell Rat 2 rat fibroblasts. We Gene 33 Rat 2 an Gene used shown in when in Rat 2 cells, Gene 33 to EGF-induced EGFR well ERK, JNK, and in a and EGFR signaling Gene 33 the EGFR signaling pathway 2 and and and It be that the of Gene 33 expression EGF-induced phosphorylation is in ERK activation is in These results and that Gene 33 is to inhibit EGFR activation well the signaling elements of the that Gene 33 in Rat 2 also to the EGFR protein level and the results in and the of the of Gene 33 EGFR the of Gene 33 expression signaling by other the receptor and the G protein-coupled receptor for Whereas Gene 33 significantly EGF expression of Gene 33 receptor tyrosine phosphorylation or signaling activation of ERK substantially upon expression of Gene 33 has been shown that G protein-coupled receptor such can signal by the EGF receptor, a to be mediated by of EGF, a of the EGF (1Prenzel N. Zwick E. Daub H. Leserer M. Abraham R. Wallasch C. Ullrich A. Nature. 1999; 402: 884-888Crossref PubMed Scopus (1499) Google Scholar). a inhibitor in also completely reverses activation of in upon of Rat 2 in which EGF a EGFR autophosphorylation. It is that the of is the an activation of ERK The Gene 33 by a of has been shown that the Gene 33 can be induced by a variety of of Scholar, K.L. R. J. Biol. Chem. Full Text PDF PubMed Google Scholar, A. Chen A. T. Kyriakis J.M. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, N. P. R. J. 1999; 18: Google Scholar, Res. PubMed Scopus Google Scholar, Endocrinology. PubMed Scopus Google Scholar). However, expression of Gene 33 polypeptide is poorly Rat 2 of Gene 33 and protein and Gene 33 and protein can be induced by EGF and Gene 33 protein can also be induced by PDGF, serum, and Dex in Rat 2 These results are the that the Gene 33 contains a well a glucocorticoid of Scholar, C. M. C. M. S. P. O. Mol. Cell. Biol. PubMed Scopus Google Scholar, S. M. R. G. S. M. O. 2003; 22: PubMed Scopus Google Scholar). The of Gene 33 protein upon the Gene 33 by is the growth of Gene 33 by is the the transient, to level by Gene 33 expression is more to level by EGF and Dex the of Gene 33 expression in both of EGF-stimulated through a in upon Gene have long been known to inhibit cell proliferation and tyrosine phosphorylation of the insulin and EGF receptors (5Baus E. Andris F. Dubois P.M. Urbain J. Leo O. J. Immunol. 1996; 156: 4555-4561PubMed Google Scholar, 6Buren J. Liu H.X. Jensen J. Eriksson J.W. Eur. J. Endocrinol. 2002; 146: 419-429Crossref PubMed Scopus (140) Google Scholar, 7Hulley P.A. Gordon F. Hough F.S. Endocrinology. 1998; 139: 2423-2431Crossref PubMed Google Scholar, 8Karasik A. Kahn C.R. Endocrinology. 1988; 123: 2214-2222Crossref PubMed Scopus (25) Google Scholar, 9Nagy P. Kiss A. Schnur J. Thorgeirsson S.S. Hepatology. 1998; 28: 423-429Crossref PubMed Scopus (87) Google Scholar, 10Zendegui J.G. Inman W.H. Carpenter G. J. Cell. Physiol. 1988; 136: 257-265Crossref PubMed Scopus (42) Google Scholar). The mechanisms these have been The of Gene 33 by Dex to a in which Dex, through glucocorticoid receptor activation of the glucocorticoid in the gene 33 induces expression of Gene 33, which in to inhibit EGFR thereby EGF-induced biological shown in of Rat 2 Dex for induces expression of Gene EGF-stimulated EGFR tyrosine ERK and phosphorylation of Gene 33, the of phosphorylation Gene 33 a endogenous of EGF used to gene shown in whereas Dex of Rat 2 in of Gene 33 of Gene 33 Dex of endogenous Gene to inhibition of EGF-stimulated ERK and Gene 33 substantially inhibition of EGF-stimulated ERK and Dex also the EGF-stimulated in EGFR protein an by silencing of gene 33 These results that Gene 33, at physiological expression is an inhibitor of EGFR signaling. Dex regulates EGF signaling at through of Gene Gene 33 EGF-induced Cell and has been shown that Gene 33 inhibits EGF-induced cell C. M. C. M. S. P. O. Mol. Cell. Biol. PubMed Scopus Google Scholar). However, is endogenous Gene 33 a the which such a function might We used Gene 33 or to the of Gene 33 EGF-induced Rat 2 cell We the of Gene 33 phosphorylation of blocks cell through kinase phosphorylation of at reverses this the in and of the necessary for kinase Thus, can be indicate that Gene 33 is an endogenous inhibitor of EGF activation of ERK and that Gene 33 might also EGF-stimulated phosphorylation of shown in EGF induced a phosphorylation of Rat 2 cell at well a of Gene Dex to However, when EGF for Dex for 2 phosphorylation significantly less than that of EGF expression in Rat 2 of Gene 33 in a inhibition of the phosphorylation induced by EGF These results are the that Gene 33 may function to inhibit cell in to EGF in Rat 2 cells. the role of Gene 33 in EGF-induced DNA and protein of Gene 33 an EGF-induced DNA and protein by and and or 2 and and gene 33 by in at a of EGF-induced DNA or protein synthesis and or 2 and and Dex EGF-induced Rat 2 cell DNA and protein synthesis inhibitory upon Gene 33 and or and and also and These results are the role of Gene 33 EGF signaling and suggest that Dex may effects in through of Gene Our results that Gene 33 is an endogenous inhibitor of EGF signaling and biological It has been that Gene 33 inhibits EGFR signaling via the 2 at a level of C. M. C. M. S. P. O. Mol. Cell. Biol. PubMed Scopus Google Scholar). However, indicate that Gene 33 functions an inhibitor of EGFR autophosphorylation. function may be of a feedback inhibition mechanism to EGF and other such (Dex) may their effects in by EGF signaling in a Gene The mechanism by which Gene 33 inhibits the EGFR is is known that Gene 33 to the kinase domain of of the EGFR C. M. C. M. S. P. O. Mol. Cell. Biol. PubMed Scopus Google Scholar). may direct inhibition of the kinase of the the binding of Gene 33 to the EGFR may of the kinase domain of the EGFR to domain, thereby EGFR autophosphorylation. Gene 33 and J. M. a the that the binding of Gene 33 to the EGFR kinase domain inhibits EGFR Gene 33 may also function to agonist-induced of the EGFR and thereby EGFR activation and autophosphorylation. Gene 33 also such a tyrosine which function to the These are The of Gene 33 is of an protein The domain of Gene 33, the EGFR binding is a homology a of the of Our that the domain of the Gene 33 is sufficient for inhibition of EGFR autophosphorylation that may also have a the of Ack, has been shown to inhibit EGFR signaling J. Mol. Cell. Full Text Full Text PDF PubMed Scopus Google Scholar). The mechanism of this inhibition is that the of which is to Gene is for EGFR inhibition J. Mol. Cell. Full Text Full Text PDF PubMed Scopus Google Scholar). Whereas is that may function in a to that of Gene 33 to inhibit EGFR be that the of the polypeptide to the domain of Gene 33 has less homology the domain than that of an domain is in of the Ack to inhibit EGFR signaling M. Tan E. J. Biol. Chem. 2001; 276: Full Text Full Text PDF PubMed Scopus Google may inhibit EGFR signaling by a binding and have been shown to be (16Yang W. Lo C.G. Dispenza T. Cerione R.A. J. Biol. Chem. 2001; 276: 17468-17473Abstract Full Text Full Text PDF PubMed Scopus (62) Google Scholar, 17Teo M. Tan E. J. Biol. Chem. 2001; 276: Full Text Full Text PDF PubMed Scopus Google Scholar). may receptor signaling by receptor endocytosis M. Tan E. J. Biol. Chem. 2001; 276: Full Text Full Text PDF PubMed Scopus Google Scholar, J. S. T. T. Res. 2001; 284: PubMed Scopus Google Scholar). It is to propose that Gene 33 may have a role in EGFR a of EGFR upon of and Rat 2 cell Gene 33 and and However, homology the domain of Gene 33 the binding in M. Tan E. J. Biol. Chem. 2001; 276: Full Text Full Text PDF PubMed Scopus Google The observed of EGFR is more a of EGFR tyrosine phosphorylation and recruitment of the Gene 33 has been shown to and inhibit the signaling of other of the receptor some of which ligand-induced protein down-regulation (14Wiley H.S. Exp. Cell Res. 2003; 284: 78-88Crossref PubMed Scopus (300) Google Scholar, S. M. R. G. S. M. O. 2003; 22: PubMed Scopus Google Scholar). Gene 33 has a negative EGF signaling. is mediated by inhibition of EGFR autophosphorylation. Gene 33 to in the inhibition of EGF signaling by may an for a that can inhibit cell proliferation (5Baus E. Andris F. Dubois P.M. Urbain J. Leo O. J. Immunol. 1996; 156: 4555-4561PubMed Google Scholar, 6Buren J. Liu H.X. Jensen J. Eriksson J.W. Eur. J. Endocrinol. 2002; 146: 419-429Crossref PubMed Scopus (140) Google Scholar, 7Hulley P.A. Gordon F. Hough F.S. Endocrinology. 1998; 139: 2423-2431Crossref PubMed Google Scholar, 8Karasik A. Kahn C.R. Endocrinology. 1988; 123: 2214-2222Crossref PubMed Scopus (25) Google Scholar, 9Nagy P. Kiss A. Schnur J. Thorgeirsson S.S. Hepatology. 1998; 28: 423-429Crossref PubMed Scopus (87) Google Scholar, 10Zendegui J.G. Inman W.H. Carpenter G. J. Cell. Physiol. 1988; 136: 257-265Crossref PubMed Scopus (42) Google Scholar). Glucocorticoids have been shown to inhibit EGFR tyrosine phosphorylation and ERK activation (7Hulley P.A. Gordon F. Hough F.S. Endocrinology. 1998; 139: 2423-2431Crossref PubMed Google Scholar, 8Karasik A. Kahn C.R. Endocrinology. 1988; 123: 2214-2222Crossref PubMed Scopus (25) Google Scholar). It is that these effects are a at in of Gene 33 Gene 33, which can be induced by a of and may to transmit inhibitory signals these to the EGF signaling Gene inhibition of EGFR in the of dexamethasone is Gene 33 may function to the EGF pathway via feedback regulation of the intensity and/or of EGF signaling. Gene 33 may to EGF signaling in to the in this propose a for the function of Gene 33 this Gene 33 is induced by and/or including PDGF, and EGF Gene 33, in suppresses EGFR signaling by ligand-induced EGFR autophosphorylation. Gene 33 both a feedback inhibitor of EGFR signaling and a regulator of EGFR signaling that occurs other mitogenic or stress Gene 33 has been shown to inhibit signaling by other of the is to that Gene 33 functions in a for all of the Gene 33 to signaling by the that Gene 33 may a role in signaling by other receptor or by G protein-coupled receptors that of the find that activation of ERK is by Gene G protein-coupled receptor such have been shown in some to the EGFR through the recruitment of a that EGF (1Prenzel N. Zwick E. Daub H. Leserer M. Abraham R. Wallasch C. Ullrich A. Nature. 1999; 402: 884-888Crossref PubMed Scopus (1499) Google Scholar). It be that Rat 2 cell EGFR phosphorylation in to the of activation of ERK is than that by EGF, is that phosphorylation may be We have shown that Gene 33 through interaction and binding domain, to the of Gene 33 also of Scholar). We have also observed that Gene 33 activates cell EGF activation of Rat 2 cell JNK is by Gene 33, and activation of Rat 2 cell JNK by Gene 33 and Thus, the activation of JNK by Gene 33 may be It is also that the of Gene 33 EGF signaling at a JNK activation of EGFR Gene JNK activation may be in stress such apoptosis or line this the Gene 33 has been shown to be induced in a of and Gene 33 is also induced to of Scholar, A. Chen A. T. Kyriakis J.M. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). It is that Gene 33 may a role in signaling the function of this to role in human is