title: Phosphatidylinositol 3-kinase (PI3K) activity bound to insulin-like growth factor-I (IGF-I) receptor, which is continuously sustained by IGF-I stimulation, is required for IGF-I-induced cell proliferation.
abstract: Continuous stimulation of cells with insulin-like growth factors (IGFs) in G(1) phase is a well established requirement for IGF-induced cell proliferation; however, the molecular components of this prolonged signaling pathway that is essential for cell cycle progression from G(1) to S phase are unclear. IGF-I activates IGF-I receptor (IGF-IR) tyrosine kinase, followed by phosphorylation of substrates such as insulin receptor substrates (IRS) leading to binding of signaling molecules containing SH2 domains, including phosphatidylinositol 3-kinase (PI3K) to IRS and activation of the downstream signaling pathways. In this study, we found prolonged (>9 h) association of PI3K with IGF-IR induced by IGF-I stimulation. PI3K activity was present in this complex in thyrocytes and fibroblasts, although tyrosine phosphorylation of IRS was not yet evident after 9 h of IGF-I stimulation. IGF-I withdrawal in mid-G(1) phase impaired the association of PI3K with IGF-IR and suppressed DNA synthesis the same as when PI3K inhibitor was added. Furthermore, we demonstrated that Tyr(1316)-X-X-Met of IGF-IR functioned as a PI3K binding sequence when this tyrosine is phosphorylated. We then analyzed IGF signaling and proliferation of IGF-IR(-/-) fibroblasts expressing exogenous mutant IGF-IR in which Tyr(1316) was substituted with Phe (Y1316F). In these cells, IGF-I stimulation induced tyrosine phosphorylation of IGF-IR and IRS-1/2, but mutated IGF-IR failed to bind PI3K and to induce maximal phosphorylation of GSK3β and cell proliferation in response to IGF-I. Based on these results, we concluded that PI3K activity bound to IGF-IR, which is continuously sustained by IGF-I stimulation, is required for IGF-I-induced cell proliferation.
authors: Department of Animal Sciences, Graduate School of Agriculture and Life Sciences, The University of Tokyo, Tokyo 113-8657, Japan.
authors: Toshiaki
authors: T
authors: Fukushima
authors: Yusaku
authors: Y
authors: Nakamura
authors: Daisuke
authors: D
authors: Yamanaka
authors: Takashi
authors: T
authors: Shibano
authors: Kazuhiro
authors: K
authors: Chida
authors: Shiro
authors: S
authors: Minami
authors: Tomoichiro
authors: T
authors: Asano
authors: Fumihiko
authors: F
authors: Hakuno
authors: Shin-Ichiro
authors: S
authors: Takahashi
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D045744:Cell Line, Tumor; D004247:DNA / Q000096:biosynthesis / Q000235:genetics; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism; D016193:G1 Phase / Q000502:physiology*; D038362:Glycogen Synthase Kinase 3 / Q000235:genetics / Q000378:metabolism; D000071679:Glycogen Synthase Kinase 3 beta; D006801:Humans; D055504:Insulin Receptor Substrate Proteins / Q000235:genetics / Q000378:metabolism; D007334:Insulin-Like Growth Factor I / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D020125:Mutation, Missense; D041681:NIH 3T3 Cells; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation / Q000502:physiology; D017526:Receptor, IGF Type 1 / Q000235:genetics / Q000378:metabolism*; D016196:S Phase / Q000502:physiology*; D014443:Tyrosine / Q000235:genetics / Q000378:metabolism
chemical_list: C526292:IRS1 protein, human; C526297:IRS2 protein, human; D055504:Insulin Receptor Substrate Proteins; C526295:Irs1 protein, mouse; C526298:Irs2 protein, mouse; C519530:insulin-like growth factor-1, mouse; D014443:Tyrosine; D007334:Insulin-Like Growth Factor I; D004247:DNA; D019869:Phosphatidylinositol 3-Kinases; D017526:Receptor, IGF Type 1; C000605506:GSK3B protein, human; D000071679:Glycogen Synthase Kinase 3 beta; C000605507:Gsk3b protein, mouse; D038362:Glycogen Synthase Kinase 3