title: Insulin-like growth factor-I induces the phosphorylation and nuclear exclusion of forkhead transcription factors in human neuroblastoma cells.
abstract: Akt-mediated phosphorylation of forkhead transcription factors is linked to growth factor-stimulated cell survival. We investigated whether the survival activity of insulin-like growth factor-I (IGF-I) in SH-SY5Y human neuroblastoma (NBL) cells is associated with phosphorylation and/or localization changes in forkhead proteins. IGF-I induced phosphorylation of Erks (p42/p44), FKHR (FOXO1a) (Ser 253), FKHRL1 (FOXO3a) (Ser 256), and Akt (Ser 473). PI3-K inhibitor, LY294002, reduced IGF-I-stimulated phosphorylation of FKHR, FKHRL1, and Akt, but did not affect Erk phosphorylation. Using a GFP-FKHR construct, FKHR imported into the nucleus during growth factor withdrawal-induced apoptosis. In addition, IGF-I rescue from serum withdrawal-induced apoptosis is associated with a rapid export of GFP-FKHR into the cytoplasm. Leptomycin B, an inhibitor of Crm1-mediated nuclear export, decreased the level of FKHRL1 phosphorylation in the presence of IGF-I in vector and FKHR overexpressing cells, but had no effect on the phosphorylation status of FKHR. In addition, leptomycin B prevented IGF-I stimulated nuclear export of GFP-FKHR. These studies show IGF-I phosphorylation of FKHR and FKHRL1 via a PI3-K-dependent pathway in NBL cells.
authors.affiliation: Department of Neurology, University of Michigan, 4414 Kresge III, 200 Zina Pitcher Place, Ann Arbor, MI 48109, USA.
authors.forename: T S
authors.initials: TS
authors.lastname: Schwab
authors.forename: B B
authors.initials: BB
authors.lastname: Madison
authors.forename: A R
authors.initials: AR
authors.lastname: Grauman
authors.forename: E L
authors.initials: EL
authors.lastname: Feldman
mesh_terms: D017209:Apoptosis / Q000187:drug effects; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000187:drug effects* / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D000071161:Forkhead Box Protein O1; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors / Q000235:genetics / Q000378:metabolism*; D015870:Gene Expression / Q000187:drug effects; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D009447:Neuroblastoma / Q000201:enzymology / Q000378:metabolism* / Q000473:pathology*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D021381:Protein Transport / Q000187:drug effects; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D013347:Subcellular Fractions / Q000187:drug effects
chemical_list: C085126:FOXO1 protein, human; C499517:FOXO3 protein, human; D000071161:Forkhead Box Protein O1; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors; D011993:Recombinant Fusion Proteins; D007334:Insulin-Like Growth Factor I; D019869:Phosphatidylinositol 3-Kinases