Benzo(a)pyrene activates L1Md retrotransposon and inhibits DNA repair in vascular smooth muscle cells

Benzo(a)pyrene (BaP) modulates vascular smooth muscle cells (vSMCs) from a quiescent to proliferative phenotype, a shift associated with activation of L1Md retrotransposon [K.P. Lu, K.S. Ramos, Biochem. Biophys. Res. Commun. 253 (1998) 828-833]. The present studies were conducted to evaluate L1Md ac tivation profiles in murine vSMCs treated with BaP or its oxidative metabol ites, and to screen for possible insertional mutations into p53 and retinob lastoma (RB) genes. We also sought to examine the profile of DNA damage and repair in BaP-treated vSMCs. Northern analysis revealed that BaP (0.03-3 m uM), and its major reactive 7,8-diol metabolite (0.03-3 muM), activate L1Md gene in a concentration-dependent manner. Two other metabolites, 3-OH BaP and 3,6-BaP quinone (0.03-3 muM), as well as hydrogen peroxide (25-75 muM) also activated L1Md. No insertional mutations into either p53 or RE genes w ere observed in vSMCs treated with BaP in vitro, although a slight elevatio n of p53 mRNA was observed as early as 4 h after chemical challenge. Treatm ent of vSMCs with 3 or 30 muM BaP for 4 h increased unscheduled DNA synthes is (UDS) 1.4- and 2.5-fold, respectively. Challenge with 0.3 muM BaP for 24 h inhibited DNA repair capacity in vSMCs for up to 48 h. These results dem onstrate that BaP and its oxidative metabolites activate L1Md retrotranspos on in vSMCs, which coupled to DNA damage and inhibition of DNA repair are p art of the atherogenic response elicited by BaP and related hydrocarbons. ( C) 2000 Elsevier Science B.V. All rights reserved.