title: Redundancy of radioresistant signaling pathways originating from insulin-like growth factor I receptor.
abstract: The insulin-like growth factor I receptor (IGF-IR) has the ability to confer clonogenic radioresistance following ionizing irradiation. We attempted to determine the downstream pathways involved in IGF-IR-mediated radioresistance and used mouse embryo fibroblasts deficient in endogenous IGF-IR (R-) as recipients for a number of mutant IGF-IRs. Mutational analysis revealed that the tyrosine at residue 950 (Tyr-950) of IGF-IR, as well as the C-terminal domain, are required for radioresistance and that both domains must be mutated to abrogate the phenotype. Furthermore, the contribution of downstream pathways was analyzed by combining the use of wild-type or Tyr-950 and C-terminal mutants with specific inhibitors of phosphatidylinositol 3'-kinase (PI3-K) or mitogen-activated protein extracellular signal-regulated kinase (ERK) kinase (MEK). Radioresistance could be induced by IGF-IR as long as the ability of the receptor to stimulate the MEK/ERK pathway was retained. This was confirmed by the expression of constitutively active MEK in R- cells. The ability to stimulate the PI3-K pathway alone was not sufficient, but PI3-K activation coupled with MEK/ERK pathway-independent signals from the C terminus was able to induce radioresistance. Taken together, these results indicate that the IGF-IR-mediated radioresistant signaling mechanism progresses through redundant downstream pathways.
authors.affiliation: Molecular Diagnosis and Therapeutics, Department of Oral Restitution, Graduate School, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8549, Japan.
authors.forename: Dong
authors.initials: D
authors.lastname: Yu
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Watanabe
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Shibuya
authors.forename: Masahiko
authors.initials: M
authors.lastname: Miura
mesh_terms: D000818:Animals; D001665:Binding Sites; D015153:Blotting, Western; D002460:Cell Line; D002478:Cells, Cultured; D003593:Cytoplasm / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004307:Dose-Response Relationship, Radiation; D004591:Electrophoresis, Polyacrylamide Gel; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005347:Fibroblasts / Q000378:metabolism; D005720:Gamma Rays; D006801:Humans; D048728:MAP Kinase Kinase Kinase 1; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009154:Mutation; D010641:Phenotype; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010957:Plasmids / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D017434:Protein Structure, Tertiary; D017526:Receptor, IGF Type 1 / Q000378:metabolism*; D015398:Signal Transduction / Q000528:radiation effects; D013997:Time Factors; D014162:Transfection; D014443:Tyrosine / Q000737:chemistry
chemical_list: D004791:Enzyme Inhibitors; D048728:MAP Kinase Kinase Kinase 1; D020928:Mitogen-Activated Protein Kinases; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D017526:Receptor, IGF Type 1; D014443:Tyrosine; C482576:MAP3K1 protein, human; C482578:Map3k1 protein, mouse