Induction of Smooth Muscle α-Actin in Vascular Smooth Muscle Cells by Arginine Vasopressin Is Mediated by c-Jun Amino-terminal Kinases and p38 Mitogen-activated Protein Kinase

Exposure of vascular smooth muscle cells to arginine vasopressin (AVP) increases smooth muscle α-actin (SM-α-actin) expression through activation of the SM- α-actin promoter. The goal of this study was to determine the role of the mitogen-activated protein kinase (MAP kinase) family in regulation of SM-α-actin expression. AVP activated all three MAP kinase family members: ERKs, JNKs, and p38 MAP kinase. Inhibition of JNKs or p38 decreased AVP-stimulated SM-α-actin promoter activity, whereas inhibition of ERKs had no effect. A 150-base pair region of the promoter containing two CArG boxes was sufficient to mediate regulation by vasoconstrictors. Mutations in either CArG box decreased AVP-stimulated promoter activity. Electrophoretic mobility shift assays using oligonucleotides corresponding to either CArG box resulted in a complex of similar mobility whose intensity was increased by AVP. Antibodies against serum response factor (SRF) completely super-shifted this complex, indicating that SRF binds to both CArG boxes. Overexpression of SRF increased basal promoter activity, but activity was still stimulated by AVP. AVP stimulation rapidly increased SRF phosphorylation. These data indicate that both JNKs and p38 participate in regulation of SM- α-actin expression. SRF, which binds to two critical CArG boxes in the promoter, represents a potential target of these kinases.