Retinoic acid uses divergent mechanisms to activate or suppress mitogenesis in rat aortic smooth muscle cells.
In different experimental models, retinoid has been shown to stimulate or suppress mitogenesis in cultured cells. The mechanisms underlying this seemingly paradoxical activity remain only partially understood. We have examined the ability of all-trans retinoic acid (ATRA), as well as a number of synthetic retinoids, either alone or in the presence of a mitogenic stimulus (i.e., endothelin), to regulate DNA synthesis and cell replication in cultured rat aortic smooth muscle cells. ATRA alone stimulates [3H]thymidine incorporation (approximately twofold) and increases cell number (approximately twofold) in these cultures but suppresses [3H]thymidine incorporation and reduces cell number in cultures treated with endothelin. The reduction in endothelin-stimulated DNA synthesis correlates closely with the ability of ATRA to inhibit endothelin-stimulated extracellular signal-regulated kinase but not c-Jun NH2-terminal kinase activity. Activation of mitogenesis, seen in the presence of ATRA alone, was independent of extracellular signal-regulated kinase activation but correlated well with increased expression of cyclin D1 mRNA and protein. Concomitant activation of the cdk inhibitor p21 led to truncation of ATRA's mitogenic activity at higher doses of ligand. Collectively, these data indicate that the role of retinoids in the regulation of mitogenesis in vascular smooth muscle is complex. Under quiescent conditions they activate mitogenesis, while in the presence of growth stimulation, as is frequently seen with vasculopathic conditions, they suppress mitogenesis. It appears that independent circuitry is involved in signaling each of these effects.
Metabolic Research Unit and Department of Medicine, University of California at San Francisco, San Francisco, California 94143, USA.
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Gardner
D000818:Animals; D001011:Aorta / Q000166:cytology; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002478:Cells, Cultured; D019938:Cyclin D1 / Q000378:metabolism; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000378:metabolism; D004347:Drug Interactions; D016232:Endothelins / Q000494:pharmacology; D006131:Growth Inhibitors / Q000494:pharmacology; D007536:Isomerism; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D008934:Mitogens / Q000494:pharmacology; D008938:Mitosis / Q000187:drug effects*; D008954:Models, Biological; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects*; D051381:Rats; D012176:Retinoids / Q000494:pharmacology*; D015398:Signal Transduction; D014212:Tretinoin / Q000494:pharmacology*
C493958:Cdkn1a protein, rat; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D016232:Endothelins; D006131:Growth Inhibitors; D008934:Mitogens; D012176:Retinoids; D019938:Cyclin D1; D014212:Tretinoin; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases