Involvement of promoter methylation in the regulation of Pregnane X receptor in colon cancer cells

Abstract

BackgroundPregnane X receptor (PXR) is a key transcription factor that regulates drug metabolizing enzymes such as cytochrome P450 (CYP) 3A4, and plays important roles in intestinal first-pass metabolism. Although there is a large inter-individual heterogeneity with intestinal CYP3A4 expression and activity, the mechanism driving these differences is not sufficiently explained by genetic variability of PXR or CYP3A4. We examined whether epigenetic mechanisms are involved in the regulation of PXR/CYP3A4 pathways in colon cancer cells.MethodsmRNA levels of PXR, CYP3A4 and vitamin D receptor (VDR) were evaluated by quantitative real-time PCR on 6 colon cancer cell lines (Caco-2, HT29, HCT116, SW48, LS180, and LoVo). DNA methylation status was also examined by bisulfite sequencing of the 6 cell lines and 18 colorectal cancer tissue samples. DNA methylation was reversed by the treatment of these cell lines with 5-aza-2'-deoxycytidine (5-aza-dC).ResultsThe 6 colon cancer cell lines were classified into two groups (high or low expression cells) based on the basal level of PXR/CYP3A4 mRNA. DNA methylation of the CpG-rich sequence of the PXR promoter was more densely detected in the low expression cells (Caco-2, HT29, HCT116, and SW48) than in the high expression cells (LS180 and LoVo). This methylation was reversed by treatment with 5-aza-dC, in association with re-expression of PXR and CYP3A4 mRNA, but not VDR mRNA. Therefore, PXR transcription was silenced by promoter methylation in the low expression cells, which most likely led to downregulation of CYP3A4 transactivation. Moreover, a lower level of PXR promoter methylation was observed in colorectal cancer tissues compared with adjacent normal mucosa, suggesting upregulation of the PXR/CYP3A4 mRNAs during carcinogenesis.ConclusionsPXR promoter methylation is involved in the regulation of intestinal PXR and CYP3A4 mRNA expression and might be associated with the inter-individual variability of the drug responses of colon cancer cells.

Pregnane X receptor activation induces FGF19-dependent tumor aggressiveness in humans and mice

“…Our data are consistent with previous observations that PXR is antiapoptotic in colon (e.g., upregulates antiapoptotic BAG3, BIRC2, and MCL-1, while downregulating proapoptotic BAK1 and p53) (15,54) and ovarian cancer (20,55) and generally support the notion that PXR is associated with protection from xenobiotic damage (e.g., cellular drug resistance) (54,(56)(57)(58)(59). However our observations are in stark contrast to recent observations that PXR induces apoptosis in colon (60) and breast cancer (18) and predicts for significantly improved survival in esophageal cancer (61).…”

Expression Profiles of Cytochrome P450s Following Swimming Exercise in Aging Rats

“…42 PXR plays an important role in the regulation of CYP3A4, a major DME in humans. 43 In a previous study, swimming exercise for 8 weeks was found to increase mRNA and protein expression of PPAR in elderly mice, and the expression of 3-hydroxyacyl CoA dehydrogenase and carnitine palmitoyl transferase-I, target genes of PPAR, was also increased in the heart. 44 Thus, our findings support that exercise may prevent the increased drug toxicity observed in elderly individuals.…”

Pregnane X Receptor in Drug Development

“…Silencing of PXR through the hypermethylation of its CpG-rich promoter regions is associated with aggressive neuroblastoma (Misawa et al 2005), while a decrease in methylation of PXR promoter is correlated with colorectal cancer (Habano et al 2011). The restoration of PXR expression in neuroblastoma cells results in growth suppression of the cells, suggesting a tumor suppressive property of PXR (Misawa et al 2005).…”