Inhibition of Src-like Kinases Reveals Akt-dependent and -independent Pathways in Insulin-like Growth Factor I-mediated Oligodendrocyte Progenitor Survival*
- Departments of ‡Pharmacology and Therapeutics and ¶Psychiatry, McGill University, Montreal, Quebec H3G 1Y6, Canada
- ∥ To whom correspondence should be addressed: Dept. of Pharmacology and Therapeutics, Rm. 1321, McGill University, 3655 Promenade Sir-William-Osler, Montreal, Quebec H3G 1Y6, Canada. Tel.: 514-398-6222; Fax: 514-398-6690; E-mail: guillermina.almazan{at}mcgill.ca.
Abstract
Insulin-like growth factor I (IGF-I) has been previously shown to promote survival of oligodendrocyte progenitors; however, the underlying mechanisms are not fully understood. Our aim was to investigate the involvement of phosphatidylinositol 3-kinase (PI3K), MEK1, and Src family tyrosine kinases in IGF-I-mediated oligodendrocyte progenitor survival. In agreement with previous studies, IGF-I promoted cell survival. We show that IGF-I prevented apoptosis induced by growth factor deprivation in a PI3K-dependent and MEK/ERK-independent manner. In addition, IGF-I activated Akt while inhibiting caspase-3 activation, and these effects were reversed by the PI3K inhibitors LY 294002 and wortmannin, but not by the MEK1 inhibitor PD 98059. Interestingly, PP2, a specific Src-like kinase inhibitor, blocked the tyrosine phosphorylation of Src, Fyn, and Lyn and IGF-I-stimulated Akt activation, yet had no significant effects on caspase-3 activation or progenitor survival. To further determine whether Akt is required for IGF-I-mediated survival, oligodendrocyte progenitors were transduced with defective Akt mutants or treated with an Akt inhibitor. Although the Akt mutants and inhibitor decreased Akt activity and reduced basal cell survival, IGF-I could partially rescue oligodendrocyte progenitors by decreasing caspase-3 activation. These results suggest that 1) PI3K is essential for IGF-I-promoted cell survival, 2) downstream activation of Akt-dependent and -independent pathways is involved, and 3) Src-like tyrosine kinases participate in IGF-I-induced Akt activation. Therefore, an unidentified effector(s) of PI3K appears to be involved in conferring complete IGF-I-mediated protection of oligodendrocyte progenitors.
Footnotes
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↵1 The abbreviations used are: IGF-I, insulin-like growth factor I; IGF-IR, insulin-like growth factor I receptor; PI3K, phosphatidylinositol 3-kinase; MEK, mitogen-activated protein kinase/extracellular signal-regulated kinase kinase; ERK, extracellular signal-regulated kinase; PDK, 3-phosphoinositide-dependent kinase; GSK3β, glycogen synthase kinase-3β; RSK, ribosomal S6 kinase; DMEM, Dulbecco's modified Eagle's medium; MTT, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide; TUNEL, terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling; SFM, serum-free medium; HA, hemagglutinin; kdAkt, kinase-dead Akt; dnAkt, dominant-negative Akt; siRNA, small interfering RNA.
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↵* This work was supported in part by operating grants from the Multiple Sclerosis Society of Canada and the Canadian Institutes of Health Research (to G. A.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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The on-line version of this article (available at http://www.jbc.org) contains supplemental Figs. S1–S5.
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↵§ Supported by a studentship from the Multiple Sclerosis Society.
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- Received December 20, 2004.
- The American Society for Biochemistry and Molecular Biology, Inc.
