Src Is an Important Mediator of Extracellular Signal–Regulated Kinase 1/2–Dependent Growth Signaling by Angiotensin II in Smooth Muscle Cells From Resistance Arteries of Hypertensive Patients

Abstract

The role of c-Src in growth signaling by angiotensin (Ang) II was investigated in vascular smooth muscle cells (VSMCs) from arteries of hypertensive patients. c-Src and extracellular signal–regulated kinase 1/2 (ERK1/2) activity, proto-oncogene expression, activating protein-1 (AP-1) DNA-binding activity, and DNA and protein synthesis were studied in Ang II–stimulated VSMCs derived from small peripheral resistance arteries of normotensive subjects (NTs, n=5) and age-matched untreated hypertensive patients (HTs, n=10). Ang II type 1 (AT 1 ) and type 2 (AT 2 ) receptor status was also assessed. Ang II dose-dependently increased the synthesis of DNA and protein, with enhanced effects in VSMCs from HTs. PD 098,059, a selective inhibitor of the ERK1/2 pathway, attenuated Ang II–stimulated growth in HTs. The effects of PD 098,059 were greater in HTs than in NTs. In NTs, Ang II transiently increased ERK1/2 phosphorylation, whereas in HTs, Ang II–stimulated actions were augmented and sustained. PP2, a selective Src inhibitor, reduced ERK1/2 activity and normalized ERK1/2 responses in HTs. Ang II–induced c-Src phosphorylation was 2- to 3-fold greater in HTs than in NTs. In HTs but not NTs, kinase activation was followed by overexpression of c- fos and enhanced AP-1 DNA-binding activity. PD 098,059 and PP2 attenuated these responses. AT 1 receptor expression was similar in NTs and HTs. In HT cells transfected with c- fos antisense oligodeoxynucleotide, Ang II–stimulated growth was reduced compared with sense oligodeoxynucleotide. Our findings suggest that augmented Ang II–stimulated VSMC growth is mediated via hyperactivation of c-Src–regulated ERK1/2-dependent pathways, leading to overexpression of c- fos mRNA and enhanced AP-1 DNA-binding activity. Because AT 1 receptor expression was unaltered in HTs, increased Ang II signaling may be a postreceptor phenomenon. These data define a signal transduction pathway whereby Ang II mediates exaggerated growth in VSMCs from HTs.