Evidence that insulin-like growth factor-1 requires protein kinase C-epsilon, PI3-kinase and mitogen-activated protein kinase pathways to protect human vascular smooth muscle cells from apoptosis.
Insulin-like growth factor (IGF)-1 has been implicated in the development of occlusive vascular lesions. Although its role in vascular smooth muscle cell (VSMC) growth and migration are fairly well characterized, anti-apoptotic signals of IGF-1 in human VSMC remain largely unknown. In this study, we examined IGF-1 signals that protect human and rat VSMC from staurosporine (STAU)- and c-myc- induced apoptosis, respectively. Treatment with STAU resulted in apoptotic DNA fragmentation, phosphatidylserine externalization and cell shrinkage, but only occasional VSMC 'blebbing'. STAU-induced death and IGF-1-mediated survival were concentration dependent, while time-lapse video microscopy showed that IGF-1 inhibited c-myc-induced apoptosis by 90%. Pretreatment with mitogen-activated protein kinase/extracellular signal regulated kinase kinase (MEK) inhibitors UO126 and PD098059, or with the phosphatidylinositol 3-kinase (PI3-K) inhibitor wortmannin, reversed IGF-1-mediated human VSMC survival by 25-27% and 66%, respectively. Translocation studies showed that IGF-1 activated protein kinase C (PKC)-epsilon, but not PKC-alpha or PKC-delta, even in the presence of STAU, while pharmacological PKC inhibition (Ro-318220 or Go6976) implicated PKC-zeta or a novel PKC isozyme in IGF-1-mediated survival. Transient expression of activated PKC-epsilon but not activated PKC-zeta decreased myc-induced apoptosis in rat VSMC. In human VSMC, antisense oligodeoxynucleotides to PKC-epsilon partially reversed IGF-1-induced survival. In addition, IGF-1 elicited a mild but sustained activation of extracellular signal regulated kinase (ERK)1/2 in human VSMC that was abolished after 1 h in the presence of STAU. PKC downregulation reversed both IGF-1- and PMA-induced ERK activity, but platelet-derived growth factor (PDGF)-induced activity was unchanged. These results indicate for the first time that IGF-1 can protect human VSMC via multiple signals, including PKC-epsilon, PI3-K and mitogen-activated protein kinase pathways.
Allen
Todd R
TR
Department of Medical Microbiology and Immunology, Creighton University School of Medicine, Omaha, Nebraska 68178, USA.
Krueger
Kristopher D
KD
Hunter
William J
WJ
Agrawal
Devendra K
DK
D017209:Apoptosis / Q000187:drug effects*; D048430:Cell Shape / Q000187:drug effects; D002478:Cells, Cultured; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D020935:MAP Kinase Signaling System / Q000187:drug effects*; D008855:Microscopy, Electron, Scanning; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects* / Q000201:enzymology / Q000648:ultrastructure; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D051744:Protein Kinase C-epsilon / Q000378:metabolism*; D019311:Staurosporine / Q000494:pharmacology
D007334:Insulin-Like Growth Factor I; D019869:Phosphatidylinositol 3-Kinases; C497255:PRKCE protein, human; D051744:Protein Kinase C-epsilon; D020929:Mitogen-Activated Protein Kinase Kinases; D019311:Staurosporine