Abstract Cytochrome P4501A (CYP1A) enzymes play important roles in the activation of PAHs such as 3-methylcholanthrene (MC) to carcinogenic DNA-binding metabolites. We reported earlier that MC causes persistent induction of hepatic and pulmonary CYP1A1 in mice for several weeks after MC withdrawal, and that the phenomenon of sustained hepatic CYP1A1 induction is lost in Cyp1a2-null mice. In this study, we tested the hypothesis that MC elicits induction of persistent CYP1A1 induction in hepa-1 cells, and that CYP1A2 contributes mechanistically to this phenomenon. Hepa-1 cells were treated with the MC (2.5 μM), or dimethylsulfoxide (DMSO) as control, and at selected time points, CYP1A1 promoter activity, CYP1A1 enzyme activities, contents, and CYP1A1 mRNA levels were studied. A 24 h treatment induced the CYP1A1 promoter activity, CYP1A1 mRNA, and ethoxyresorufin O-deethylase (EROD) activity by 2-, 1000-, and 15-fold, respectively. The induction was sustained for 4-5 days. MC persistently induced CYP1A1 apoprotein level as well. Electrophoretic mobility shift assay indicated that MC induced a nuclear protein that bound to aryl hydrocarbon response elements in the CYP1A1 promoter region. Transfection of CYP1A2 siRNA resulted in knockdown of CYP1A2 mRNA by 70%, but a statistically significant increase of basal CYP1A1 mRNA by 35-40%. The induction of CYP1A1 promoter activity, CYP1A1 mRNA, CYP1A1 protein, and EROD activity by MC were not affected by CYP1A2 siRNA at the 24 h time point, but was significantly attenuated by CYP1A2 siRNA on day 5. These results suggest that CYP1A2, possibly via a metabolite, contributes to the sustained induction of CYP1A1 by MC in hepa-I cells. Further investigations into the mechanisms of persistent induction of CYP1A1 by MC could lead to novel preventative/therapeutic strategies against PAH-mediated carcinogenesis in humans. Citation Format: Sudha Kondraganti, Chun Chu, Bhagavatula Moorthy. Role of cytochrome P450 (CYP)1A2 in the molecular regulation of CYP1A1 by the carcinogen, 3-methylcholanthrene (MC) in mouse heptoma cells (hepa-1). [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4068.