title: Insulin-like growth factor I-mediated protection from rapamycin-induced apoptosis is independent of Ras-Erk1-Erk2 and phosphatidylinositol 3'-kinase-Akt signaling pathways.
abstract: The mTOR inhibitor rapamycin induces G1 cell cycle accumulation and p53-independent apoptosis of the human rhabdomyosarcoma cell line Rh1. Insulin-like growth factor I (IGF-I) and insulin, but not epidermal growth factor or platelet-derived growth factor, completely prevented apoptosis of this cell line. Because the Ras-Erk1-Erk2 and phosphatidylinositol 3'-kinase (PI3K)-Akt pathways are implicated in the survival of various cancer cells, we determined whether protection from rapamycin-induced apoptosis by IGF-I requires one or both of these pathways. Despite the blocking of Ras-Erk signaling by the addition of PD 98059 (a MEK1 inhibitor) or by the overexpression of dominant-negative RasN17, IGF-I completely prevented rapamycin-induced death. Inhibition of Ras signaling did not prevent Akt activation by IGF-I. To determine the role of the PI3K-Akt pathway in rescuing cells from apoptosis caused by rapamycin, cells expressing dominant-negative Akt were tested. This mutant protein inhibited IGF-I-induced phosphorylation of Akt and blocked phosphorylation of glycogen synthase kinase 3. The prevention of rapamycin-induced apoptosis by IGF-I was not inhibited by expression of dominant-negative Akt either alone or under conditions in which LY 294002 inhibited PI3K signaling. Furthermore, IGF-I prevented rapamycin-induced apoptosis when the Ras-Erk1-Erk2 and PI3K-Akt pathways were blocked simultaneously. Similar experiments in a second rhabdomyosarcoma cell line, Rh30, using pharmacological inhibitors of PI3K or MEK1, alone or in combination, failed to block IGF-I rescue from rapamycin-induced apoptosis. Therefore, we conclude that a novel pathway(s) is responsible for the IGF-I-mediated protection against rapamycin-induced apoptosis in these rhabdomyosarcoma cells.
authors.affiliation: Department of Molecular Pharmacology, St. Jude Children's Research Hospital, Memphis, Tennessee 38105-2794, USA.
authors.forename: Kuntebommanahalli N
authors.initials: KN
authors.lastname: Thimmaiah
authors.forename: John
authors.initials: J
authors.lastname: Easton
authors.forename: Shile
authors.initials: S
authors.lastname: Huang
authors.forename: Karen A
authors.initials: KA
authors.lastname: Veverka
authors.forename: Glen S
authors.initials: GS
authors.lastname: Germain
authors.forename: Franklin C
authors.initials: FC
authors.lastname: Harwood
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Houghton
mesh_terms: D000903:Antibiotics, Antineoplastic / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology; D002867:Chromones / Q000494:pharmacology; D004347:Drug Interactions; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004815:Epidermal Growth Factor / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000502:physiology*; D019950:Mitogen-Activated Protein Kinase 1 / Q000037:antagonists & inhibitors / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D009025:Morpholines / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation / Q000187:drug effects; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D012208:Rhabdomyosarcoma / Q000201:enzymology / Q000473:pathology; D015398:Signal Transduction / Q000187:drug effects; D020123:Sirolimus / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D018631:ras Proteins / Q000378:metabolism
chemical_list: D000903:Antibiotics, Antineoplastic; D002867:Chromones; D004791:Enzyme Inhibitors; D004815:Epidermal Growth Factor; D005419:Flavonoids; D007334:Insulin-Like Growth Factor I; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D009025:Morpholines; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010982:Platelet-Derived Growth Factor; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D020123:Sirolimus; D018631:ras Proteins; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C494918:AKT1 protein, human; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one