c-Ha-ras(EJ) transfection in vascular smooth muscle cells circumvents PKC requirement during mitogenic signaling

In view of the prominent role of protein kinase C (PKC) in the regulation of vascular smooth muscle cell (VSMC) growth and differentiation, the present studies were conducted to assess the impact of c-Ha-ras(EJ) transfection on PKC-dependent growth programming. PKC activity was elevated in the cytosolic and particulate compartments of c-Ha-ras(EJ) VSMC, relative to naive or pSV2neo vector controls. Constitutive and 12-O-tetradecanoyl phorbol 13-acetate (TPA)-inducible binding to a TPA-responsive element (TRE) was also enhanced in c-Ha-ras(EJ) VSMC. Fetal bovine serum (FBS) did not increase TRE-binding activity in serum-starved c-Ha-ras(EJ) VSMC but increased TRE-binding activity in pSV2neo VSMC. FBS-mediated TRE-binding activity was dramatically decreased in serum-starved pSV2neo VSMC pretreated with 100 ng/ml TPA for 24 h to downregulate PKC activity. c-Ha-ras(EJ) VSMC exhibited a marked proliferative advantage over controls under both restrictive and growth-permissive serum conditions. PKC downregulation did not influence the mitogenic response to serum in c-Ha-ras(EJ) VSMC but ablated [³H]thymidine incorporation into DNA in naive or pSV2neo vector counterparts. Western blot analysis demonstrated increased expression of extracellular signal-regulated kinase 2 (ERK2), but not ERK1, in c-Ha- ras(EJ) VSMC, relative to pSV2neo control. Immunoblots of serum-starved and PKC-depleted c-Ha-ras(EJ) VSMC demonstrated a dramatic increase in the phosphorylated form of ERK2, relative to pSV2neo controls. These data suggest that oncogenic c-Ha-ras(EJ) circumvents a requirement for a TPA-responsive PKC isoform(s) during mitogenic stimulation of VSMC.