REGULATION OF SMOOTH-MUSCLE ALPHA-ACTIN PROMOTER BY VASOPRESSIN AND PLATELET-DERIVED GROWTH-FACTOR IN RAT AORTIC VASCULAR SMOOTH-MUSCLE CELLS

Vasoconstrictors such as arginine vasopressin (AVP) and angiotensin II (Ang II) have been shown to increase protein and mRNA levels of smoot h muscle alpha-actin (SM-alpha-actin) in vascular smooth muscle cells. In the same cells, platelet-derived growth factor (PDGF) decreased SM -alpha-actin protein and mRNA. The rat SM-alpha-actin promoter that ha s recently been isolated contains two E-boxes and three CC(A/T)(6)GG ( CArG) elements. To examine regulation of the SM-alpha-actin promoter, a 765-bp region of the rat SM-alpha-actin gene was ligated into chlora mphenicol acetyltransferase (CAT)-containing vectors and transfected i nto rat aortic vascular smooth muscle cells. Stimulation of cells with either AVP or Ang II increased CAT activity 5- to 10-fold. PDGF was a ble to completely block the AVP-induced increase in CAT activity. To i dentify regions of the promoter responsible for both the AVP stimulati on and PDGF inhibition of promoter activity, a series of truncation mu tants were prepared and transfected into vascular smooth muscle cells. Truncation of both E-boxes and the most distal CArG element did not q ualitatively alter either AVP-induced stimulation of CAT activity or P DGF inhibition. However, removal of the middle CArG element resulted i n a loss of AVP stimulation. These studies indicate that the AVP-induc ed elevation and PDGF-induced inhibition of SM-alpha-actin levels in v ascular smooth muscle cells are mediated at least in part through regu lation of the SM-alpha-actin promoter. The critical region of the prom oter mediating this effect involves at a minimum one of the CArG eleme nts.