Up-regulation of CYP expression in hepatoma cells stably transfected by chimeric nuclear receptors

Most hepatoma cell lines lack proper expression and induction of cytochrome P450 (CYP) enzymes and this deficiency hampers their use as in vitro models for drug and xenobiotic metabolism. According to previous studies, the poor expression of CYP enzymes may be due to decreases in CYP gene transcription. Two nuclear receptors (NRs), the pregnane X receptor (PXR) and the constitutive androstane receptor (CAR), are known to regulate many genes involved in xenobiotic metabolism and disposition. Here, we studied the expression of different CYP, NR and NR co-regulator genes in hepatoma cell lines. Next, we created “chimeric NR” constructs by cloning the strong activation domain from the p65 subunit of transcription factor NF-κB and appending it to either N- or C-termini of the human CAR or PXR. We established that these chimeric NRs displayed enhanced trans-activation potential as compared to the unmodified NRs, and showed that transient transfection of a single chimeric NR increased the expression of several CYPs simultaneously. Finally, stable cell lines expressing a chimeric NR had elevated levels of CYP3A4, CYP2B6 and CYP2C9 mRNAs and CYP3A4-mediated metabolism when compared to the wild-type hepatoma cells. These findings establish a proof of principle how improved metabolic cell models could be designed.