title: Signal strength dictates phosphoinositide 3-kinase contribution to Ras/extracellular signal-regulated kinase 1 and 2 activation via differential Gab1/Shp2 recruitment: consequences for resistance to epidermal growth factor receptor inhibition.
abstract: Phosphoinositide 3-kinase (PI3K) participates in extracellular signal-regulated kinase 1 and 2 (ERK1-2) activation according to signal strength, through unknown mechanisms. We report herein that Gab1/Shp2 constitutes a PI3K-dependent checkpoint of ERK1-2 activation regulated according to signal intensity. Indeed, by up- and down-regulation of signal strength in different cell lines and through different methods, we observed that Gab1/Shp2 and Ras/ERK1-2 in concert become independent of PI3K upon strong epidermal growth factor receptor (EGFR) stimulation and dependent on PI3K upon limited EGFR activation. Using Gab1 mutants, we observed that this conditional role of PI3K is dictated by the EGFR capability of recruiting Gab1 through Grb2 or through the PI3K lipid product PIP(3), according to a high or weak level of receptor stimulation, respectively. In agreement, Grb2 siRNA generates, in cells with maximal EGFR stimulation, a strong dependence on PI3K for both Gab1/Shp2 and ERK1-2 activation. Therefore, Ras/ERK1-2 depends on PI3K only when PIP(3) is required to recruit Gab1/Shp2, which occurs only under weak EGFR mobilization. Finally, we show that, in glioblastoma cells displaying residual EGFR activation, this compensatory mechanism becomes necessary to efficiently activate ERK1-2, which could probably contribute to tumor resistance to EGFR inhibitors.
authors.affiliation: INSERM U563, Dept. Lipoprotéines et Médiateurs Lipidiques, Site Purpan, BP3028, Toulouse F-31024, France.
authors.forename: Carla
authors.initials: C
authors.lastname: Sampaio
authors.forename: Marie
authors.initials: M
authors.lastname: Dance
authors.forename: Alexandra
authors.initials: A
authors.lastname: Montagner
authors.forename: Thomas
authors.initials: T
authors.lastname: Edouard
authors.forename: Nicole
authors.initials: N
authors.lastname: Malet
authors.forename: Bertrand
authors.initials: B
authors.lastname: Perret
authors.forename: Armelle
authors.initials: A
authors.lastname: Yart
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Salles
authors.forename: Patrick
authors.initials: P
authors.lastname: Raynal
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism*; D020816:Amino Acid Motifs; D000818:Animals; D002460:Cell Line; D002522:Chlorocebus aethiops; D004789:Enzyme Activation / Q000187:drug effects; D066246:ErbB Receptors / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D051380:GRB2 Adaptor Protein / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic; D006801:Humans; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D054592:Protein Tyrosine Phosphatase, Non-Receptor Type 11 / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000235:genetics; D015398:Signal Transduction / Q000187:drug effects; D018631:ras Proteins / Q000378:metabolism*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D066246:ErbB Receptors; D051380:GRB2 Adaptor Protein; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D047428:Protein Kinase Inhibitors; D054592:Protein Tyrosine Phosphatase, Non-Receptor Type 11; D034741:RNA, Small Interfering; D018631:ras Proteins; C098587:GAB1 protein, human