Involvement of CREM in CYP1A1 induction through ligand-independent activation pathway of aryl hydrocarbon receptor in HepG2 cells

Using a radiation-hybrid cell, E11, produced by the fusion of Hepa-1c1c7 and X-ray irradiated HepG2 cells, we located the omeprazole (OP) responsive region on chromosome 10p. The cDNA of 12 genes expressed in E11 cells were cloned from HepG2 mRNA by RT-PCR. The cDNA was transfected into Hepa-1c1c7 cells to check the increased expression of Cyp1a1 by reporter gene (luciferase) assay. Finally, one gene (τCREM: cAMP responsive element modulator, τ-isoform) was identified as a candidate gene for the gene responsive to OP. The regulatory sequence of Cyp1a1 in response to τCREM transfection was identified in one region (−60 to −52 bp relative to the transcription start site), which was the basic transcription element (BTE). Electromobility shift assay with the BTE sequence showed an increase in the band intensity when the cells were treated with OP. Decreased level of endogenous CREM by siRNA transfection inhibited the induction of CYP1A1-mRNA in HepG2 cells by OP.