Abstract
A stable human cell line, termed HPL-A3, has newly established by co-transfection of a human pregnane X receptor (hPXR) expression vector and a reporter plasmid (p3A4-hPXRE-Luc) containing a luciferase gene and a promoter/enhancer region of the human CYP3A4 gene into a human hepatoma-derived cell line, HepG2. Then, the usefulness of HPL-A3 for chemically activated luciferase expression (CALUX) assay for the screening of human CYP3A inducers was assessed. The induction of CALUX in APL-A3 cell line was observed by hPXR activators, including rifampicin, but not by rat/mouse PXR activators, such as pregnenolone-16α-carbonitrile and dexamethasone. The hPXR activator-mediated induction of CYP3As, including CYP3A4, was also observed at both levels of mRNA and enzyme activity. There were positive correlations between chemical-mediated inductions of CALUX and CYP3A4 mRNA. Interestingly, expression levels of not only hPXR but also vitamin D receptor (VDR), one of positive transcription factors for CYP3A subfamily genes, in HPL-A3 cells were significantly increased as compared with those in a parent cell line HepG2, and consequently, VDR ligand (1,25-dihydroxyvitamin D3)-mediated inductions of CALUX and CYP3A4 mRNA were observed in the cells. These findings verified the usefulness of HPL-A3 for the screening of the CYP3A inducers, which can activate the hPXR and/or hVDR.
