NADPH oxidase is the major source of superoxide production in cardiovascular tissues. We and others reported that PG (prostaglandin) F2alpha, 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 PGF2alpha 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 PGF2alpha- or PDGF-induced increase in NOX1 mRNA. In a luciferase reporter assay, activation of the CRE (cAMP-response element)-dependent gene transcription by PGF2alpha was attenuated by oligomycin, an inhibitor of mitochondrial F(o)F1-ATPase. Oligomycin and other mitochondrial inhibitors also suppressed PGF2alpha-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 PGF2alpha 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.