Regulation of vascular smooth muscle cell apoptosis. Modulation of bad by a phosphatidylinositol 3-kinase-dependent pathway.
Our objective was to define the signaling mechanisms by which mitogens such as insulin-like growth factor-I (IGF-I) regulate vascular smooth muscle cell (VSMC) apoptosis. We confirmed that IGF-I inhibits serum withdrawal-induced apoptosis of cultured VSMCs in a dose-dependent and time-dependent fashion. To test the hypothesis that the phosphatidylinositol (PI) 3-kinase signaling pathway regulates VSMC survival, we examined the relationship between PI 3-kinase activity and cell fate. PI 3-kinase was elevated in viable VSMCs maintained in serum-containing medium, declined significantly in response to serum withdrawal, and increased in response to IGF-I-induced survival. Moreover, blockade of PI 3-kinase with 2 structurally dissimilar inhibitors (wortmannin or LY294002) abolished the capacity of IGF-I to maintain VSMC viability. Similarly, transient transfection of a dominant-negative Deltap85 PI 3-kinase mutant construct abrogated the capacity of IGF-I to prevent VSMC death. Thus, PI 3-kinase is a critical antiapoptotic signal in VSMCs. To define the distal element of the antiapoptotic cascade, we tested the hypothesis that IGF-I inhibits the influence of the proapoptotic gene Bad. Indeed, IGF-I stimulates increased expression of the inactive, phosphorylated form of Bad by a PI 3-kinase-dependent pathway. Moreover, the proapoptotic effect of Bad was attenuated by the stimulation of IGF-I. Thus, growth factors appear to prevent VSMC death by activating signal transduction pathways linked to apoptotic regulatory genes.
Bai
H z
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Molecular Vascular Cell Biology Research Laboratory, Brigham and Women's Hospital, Harvard Medical School, 75 Francis St, Boston, MA, USA.
Pollman
M J
MJ
Inishi
Y
Y
Gibbons
G H
GH
D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D002352:Carrier Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism* / Q000502:physiology; D002460:Cell Line; D002478:Cells, Cultured; D004789:Enzyme Activation / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005799:Genes, Dominant / Q000235:genetics; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000378:metabolism / Q000494:pharmacology; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D009154:Mutation / Q000502:physiology; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000502:physiology*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation; D051381:Rats; D011994:Recombinant Proteins; D051025:bcl-Associated Death Protein
D002352:Carrier Proteins; D004791:Enzyme Inhibitors; D007334:Insulin-Like Growth Factor I; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011994:Recombinant Proteins; D051025:bcl-Associated Death Protein; C494819:BAD protein, human; C494821:Bad protein, rat