DNA methylation determines the regulation of pregnane X receptor on CYP3A4 expression.

The expression and activity of CYP3A4 vary among individuals. With the development of epigenetics, it is now possible to elucidate interindividual differences in drug-metabolizing enzymes. Here, we aimed to explore the potential relationship between DNA methylation and CYP3A4 expression. We analyzed the effect of a DNA methylation inhibitor, 5-aza-2-deoxycytidine, on pregnane X receptor (PXR) and CYP3A4 expression in HepG2 cells. In addition, pCpGL-CYP3A4-promoter and pCpGL-CYP3A4-enhancer plus promoter plasmids were constructed, methylated, and transfected. We found that treatment with 5-aza-2-deoxycytidine significantly increased the expression of PXR and CYP3A4 in a concentration- and time-dependent manner. In addition, CYP3A4 expression was significantly enhanced by overexpressing PXR via transfection of pSG5-PXR plasmids. Methylation of CYP3A4 enhancer inhibited CYP3A4 transcriptional activity mediated through PXR and inhibited the binding of PXR and CYP3A4 promoter. We also observed that when the promoter and enhancer of CYP3A4 were methylated, CYP3A4 expression did not increase after treatment with rifampicin. In conclusion, the investigation demonstrates that DNA methylation of CYP3A4 enhancer significantly inhibits CYP3A4 expression, mediated through PXR, which is not influenced by rifampicin.