Essential role of ATF-1 in induction of NOX1, a catalytic subunit of NADPH oxidase: involvement of mitochondrial respiratory chain

NADPH oxidase is the major source of superoxide production in cardiovascular tissues. We and others reported that PG (prostaglandin) F, PDGF (platelet-derived growth factor) and angiotensin II cause hypertrophy of vascular smooth muscle cells by induction of NOX1 (NADPH oxidase 1), a catalytic subunit of NADPH oxidase. We found DPI (diphenylene iodonium), an inhibitor of flavoproteins, including NADPH oxidase itself, almost completely suppressed induction of NOX1 mRNA by PGF(2 alpha) or PDGF in a rat vascular smooth muscle cell line, A7r5. Exploration into the site of action of DPI using various inhibitors suggested the involvement of mitochondrial oxidative phosphorylation in PGF(2 alpha)- or PDGF-induced increase in NOX1 mRNA. In a luciferase reporter assay, activation of the CRE (cAMP-response element) -dependent gene transcription by PGF(2 alpha) was attenuated by oligomycin, an inhibitor of mitochondrial F0F1-ATPase. Oligomycin and other mitochondrial inhibitors also suppressed PGF(2 alpha)-induced phosphorylation of ATF (activating transcription factor)-1, a transcription factor of the CREB (CRE-binding protein)/ ATF family. Silencing of the ATF-1 gene by RNA interference significantly reduced the induction of NOX1 by PGF(2 alpha) or PDGF, while overexpression of ATF-1 recovered NOX1 induction suppressed by oligomycin. Taken together, ATF-1 may play a pivotal role in the up-regulation of NOX1 in rat vascular smooth muscle cells.