Involvement of membrane-type bile acid receptor M-BAR/TGR5 in bile acid-induced activation of epidermal growth factor receptor and mitogen-activated protein kinases in gastric carcinoma cells

Bile acids, which have been implicated in gastrointestinal-tract cell carcinogenesis, share properties with tumor promoters in that both affect signal transduction pathways responsible for cell proliferation and apoptosis. In the present study, we demonstrate that EGFR–ERK1/2 is activated following treatment of AGS human gastric carcinoma cells with bile acids. EGFR phosphoactivation is ligand-dependent, since treatment of cells with HB–EGF antisera or CM197 (a selective inhibitor of HB–EGF) markedly inhibits deoxycholate (DC)-promoted activation. Membrane-type bile acid receptor (M-BAR)/TGR5 is a recently identified G-protein-coupled receptor (GPCR). In AGS cells, siRNAs that target M-BAR suppress DC-induced phosphorylation of EGFR. Furthermore, introduction of siRNAs targeting ADAM17 transcripts resulted in suppression of DC-induced activation of EGFR and ERK1/2. These results suggest that in AGS cells, DC transactivates EGFR through M-BAR- and ADAM/HB–EGF-dependent mechanisms.