Bile acids induce cdx2 expression through the farnesoid x receptor in gastric epithelial cells

Abstract

Clinical and experimental studies showed that the reflux of bile into the stomach contributes to the induction of intestinal metaplasia of the stomach and gastric carcinogenesis. Caudal-type homeobox 2 (Cdx2) plays a key role in the exhibition of intestinal phenotypes by regulating the expression of intestine-specific genes such as goblet-specific gene mucin 2 (MUC2). We investigated the involvement of the farnesoid X receptor (FXR), a nuclear receptor for bile acids, in the chenodeoxycholic acid (CDCA)-induced expression of Cdx2 and MUC2 in normal rat gastric epithelial cells (RGM-1 cells). RGM-1 cells were treated with CDCA or GW4064, an FXR agonist, in the presence or absence of guggulsterone, an FXR antagonist. CDCA induced dose-dependent expression of Cdx2 and MUC2 at both the mRNA and protein levels. The maximum stimulation of Cdx2 and MUC2 mRNA induced by CDCA was observed at 3 h and by 6 h, respectively. GW4064 also induced expression of these molecules. The effects of CDCA and GW4064 on expression of Cdx2 and MUC2 were abolished by guggulsterone. These findings suggest that bile acids may induce gastric intestinal metaplasia and carcinogenesis through the FXR.

Keywords: Cdx2; FXR; bile acid; intestinal metaplasia.

Fig. 1

Effect of CDCA on the expression of Cdx2 and MUC2 in RGM-1 cells. RGM-1 cells treated with CDCA at doses ranging from 0 to 50 µM for 3 h or 6 h were subjected to measurement of expression level of mRNA for Cdx2 (A) or MUC2 (B) by real-time RT-PCR, respectively. n = 3, * p<0.01 compared with controls (vehicle-treated group). (C and D) Western blot analysis of Cdx2 (C) and MUC2 (D) in RGM-1 cells treated CDCA at doses ranging from 0 to 50 µM.

Fig. 2

Time-course of Cdx2 and MUC2 mRNA expression in RGM-1 cells stimulated with CDCA. RGM-1 cells were treated with 50 µM CDCA for 24 h, and the expression levels of Cdx2 (A) and MUC2 (B) mRNA were evaluated by real-time RT-PCR. n = 3. * p<0.05, ** p<0.01 compared with controls (vehicle-treated group).

Fig. 3

Effect of DCA on the expression of Cdx2 in RGM-1 cells. RGM-1 cells were treated with 100 µM DCA and were subjected to measurement of expression levels of Cdx2 by real-time RT-PCR (A) and Western blot analysis (B). n = 3. * p<0.05 compared with controls (vehicle-treated group).

Fig. 4

Expression of the FXR in RGM-1 cells. The expression of the FXR was assessed by immunofluorescence.

Fig. 5

Effect of FXR agonists on the expression of Cdx2 and MUC2 in the presence or absence of guggulsterone, an FXR antagonist. RGM-1 cells were treated with FXR agonists (50 µM CDCA and GW4064) in the presence or absence of guggulsterone, an FXR antagonist, for 3 h or 6 h and the levels of Cdx2 (A and C) or MUC2 (B and D) were examined. n = 3. * p<0.05 compared with controls (vehicle-treated group), ^# p<0.01 compared with CDCA group (A and B) or GW4064 group (C and D).