SSeCKS gene expression in vascular smooth muscle cells: Regulation by angiotensin II and a potential role in the regulation of PAI-1 gene expression

Rat aortic smooth muscle cells (RASM) express the src suppressed C-kinase substrate (SSeCKS), which is thought to be an integral regulatory component of cytoskeletal dynamics and G-protein coupled-receptor signaling modules. The specific sub-classes of growth factor receptors that regulate the genomic changes in SSeCKS expression in smooth muscle cells have not been characterized. In this study we identify SSeCKS as an angiotensin type 1 (AT₁) receptor-dependent target gene in RASM cells treated with angiotensin II (Ang II). SSeCKS mRNA levels increase up to three-fold relative to the control within 3.5 h of Ang II treatment and are followed by a slight decrease of mRNA relative to the control levels after 24 h of stimulation. SSeCKS gene expression and plasminogen activator inhibitor-1 (PAI-1) gene expression correlate in RASM cells treated with Ang IL By co-transfecting plasmids bearing recombinant-SSeCKS and a PAI-1-promoter/luciferase reporter into Cos-1 cells, we show that alternative forms of recombinant-SSeCKS protein differentially influence PAI-1 promoter activity. These data indicate a biochemical linkage between SSeCKS activity and one or more of the cytoplasmic signaling pathways that are involved in the control of PAI-1 promoter activity. Finally, we show that the alternative forms of recombinant-SSeCKS protein differentially influence cell-spreading when ectopically expressed in ras-transformed rat kidney (KNRK) fibroblasts. Taken together, our data suggest that SSeCKS interacts with intracellular signaling pathways that control cytoskeletal remodeling and extracellular matrix remodeling following Ang II stimulation of the RASM cell.