Angiotensin II (ATII)-inducible platelet-derived growth factor A-chain gene expression is p42/44 extracellular signal-regulated kinase-1/2 and Egr-1-dependent and mediated via the ATII type 1 but not type 2 receptor - Induction by ATII antagonized by nitric oxide

Angiotensin II (ATII) and platelet-derived growth factor (PDGF) are two vas oconstrictors implicated in the maintenance of normal vascular homeostasis. PDGF A-chain levels increase in cultured vascular smooth muscle cells (SMC s) exposed to ATII. The molecular mechanisms underlying this induction are not known. We used transient transfection analysis to show that ATII can in crease reporter gene activity driven by fragments of the PDGF-A promoter be aring recognition elements for the transcription factor, Egr-1. Nuclear run -off experiments indicate that ATII induces Egr-1 expression at the level o f transcription. Gel shift and supershift studies show that Egr-1 protein a ccumulates in the nuclei of SMCs exposed to ATII and binds to the proximal region of the PDGF-A promoter in a specific, time-dependent manner. ATII in duced extracellular-signal regulated kinase (p42/44 ERK) activity as did ph orbol 12-myristate 13-acetate. The specific MEK1/2 inhibitor, PD98059, supp ressed both PDGF-A and Egr-1 endogenous and promoter-dependent expression i nducible by ATII. The ATII type 1 receptor (AT1) antagonist, Losartan, inhi bited ATII-induction of p42/44 ERK as well as Egr-1 and PDGF-A, whereas nei ther PD123319, an AT2 receptor antagonist, nor wortmannin, an inhibitor of phosphatidylinositol S-kinase and c-Jun N-terminal kinase, had any effect. ATII-induction of Egr-1 and PDGF-A was blocked by SIN-1, a NO donor. In add ition, this pathway was blocked by overexpression of NO synthase. Collectiv ely, these findings demonstrate that ATII activation of the PDGF-A promoter is mediated via the MEK/ERK/Egr-1 pathway and AT1 receptor and that this p rocess is antagonized by NO.