Redox factor-1 contributes to the regulation of progression from G₀/G₁ to S by PDGF in vascular smooth muscle cells

Redox factor-1 (Ref-1/APE), a multifunctional DNA base excision repair and redox regulation enzyme, plays an important role in oxidative signaling, transcription factor regulation, and cell cycle control. We hypothesized that Ref-1 plays a regulatory role in smooth muscle cell (SMC) proliferation induced by PDGF. Ref-1 antisense oligodeoxynucleotides (AODN), which diminished the level of Ref-1 protein in SMCs by ∼50%, inhibited PDGF-BB (composed of the homodimer of B-polypeptide chain)-induced [³H]thymidine incorporation compared with control oligodeoxynucleotides. Ref-1 AODN inhibited PDGF-BB-induced S phase entry by ∼63%, which was overcome by overexpression of Ref-1 by adenoviral-mediated gene transfer. Overexpression of Ref-1 alone without PDGF enhanced SMC entry into the S phase. Furthermore, decreasing Ref-1 protein by treatment of SMCs with Ref-1 AODN, or by immunodepletion of Ref-1 from nuclear extracts, inhibited PDGF-BB-induced activator protein-1 (AP-1) DNA binding activity. Chemical reduction restored the AP-1 DNA binding in Ref-1-depleted nuclear extracts. These results suggest that Ref-1 contributes to the regulation of PDGF-BB-stimulated cell cycle progression from G₀/G₁ to S in SMCs, with one of the possible steps being redox-regulation of AP-1 by Ref-1 protein.