atypical cytochrome P450 induction profiles in glomerular mesangial cells at the mRNA and enzyme level: Evidence for CYP1A1 and CYP1B1 expression and their involvement in benzo[A]pyrene metabolism

Recent studies in this laboratory have shown that benzo[a]pyrene (BaP) modulates growth factor-related gene expression and proliferation of renal glomerular mesangial cells (GMCs) in vitro. Because many of the toxic and biochemical effects of this polycyclic aromatic hydrocarbon are mediated through oxidative metabolism, the present studies were conducted to examine the patterns of cytochrome P450IA1 (CYP1A1) and P450IB1 (CYP1B1) inducibility in mesangial cells and the molecular consequences of this response. Exposure of cultured GMCs to BaP (30 μM) or 2,3,7,8-tetrachlorodibenzo- p-dioxin (TCDD, 10 nM) for 24 hr induced CYP1 A1 mRNA levels, a response abolished by cotreatment with 10 μM cycloheximide. The pattern of hydrocarbon inducibility was atypical in that BaP was a more effective inducer of CYP1A1 gene expression than TCDD, and both hydrocarbons induced aryl hydrocarbon hydroxylase (AHH) activity, but not ethoxyresorufin-O-deethylase activity. Cotreatment with α-naphthoflavone (αNF, 1 μM) or ellipticine (ELLIP, 0.1 nM) only partially inhibited the induction of AHH activity by BaP (30 μM). BaP and TCDD also induced expression of the CYP1B1 protein and the pattern of induction was comparable to that observed for CYP1A1. Treatment of GMCs with 30 μM BaP was associated with the formation of eight DNA adducts, and their occurrence could be inhibited by pretreatment with αNF (1 μM), but not ELLIP (0.1 nM). These results demonstrate that CYP1A1 and CYP1B1-related activities are induced in GMCs by BaP and TCDD and this induction is associated with metabolism of BaP to reactive intermediates that bind covalently to DNA.