Bile Acid (BA) Stimulation of Cl ‐ Secretion Involves Intricate Crosstalk Cascades in Human Colonic T84 Cells

Abstract

We recently showed that the BA chenodeoxycholate (CDCA) stimulates CFTR-mediated Cl- secretion in T84 cells via protein kinase A (PKA; AJP 305:C447-56, '13). We now demonstrate that CDCA signaling is far more complex, involving additional pathways. It is unlikely that BA specific receptors, TGR5 and FXR, are involved since their specific agonists do not increase Cl- secretion as measured by short circuit current (ΔISc, µA/cm2; TGR5: 20µM Ciprofloxacin: -3.4±4.8; FXR: 5µM GW4064: 1.5±1.5; n蠅3). However, the EGF receptor (EGFR) inhibitor AG1478 attenuates CDCA's increase in ISc (FASEB 28:908.4,'14) and decreases CDCA-induced EGFR phosphorylation by 50%. Although EGFR activation is necessary, EGF alone does not stimulate Cl- secretion (n=3). Downstream of EGFR, while CDCA increases p38 MAPK and ERK phosphorylation, their respective inhibitors alone or in combination do not alter CDCA-stimulated ISc (n蠅3). In contrast, inhibition of PI3K decreases CDCA's effect on ISc (CDCA: 14.5±2.8; + 0.5µM Wortmannin: 6.3±1.7; n蠅4; p<0.05) independent of AKT (CDCA: 14.3±1.7; + 1µM MK2206: 13.1±3; n蠅3). CDCA significantly increases IP3 production (µmoles/well: DMSO: 0.94±0.1; CDCA: 1.67±0.1; n蠅3) and the IP3 receptor inhibitor decreases CDCA-induced Isc (CDCA: 15.5±2.9; + 50µM 2-APB: 6.3±0.4; n=3). Also, Ca2+ chelation inhibits CDCA action (CDCA: 15.7±2.6; + 20µM BAPTA: 3.3±0.2; n=4). We conclude that CDCA-stimulated Cl- secretion does not involve TGR5, FXR, EGF, p38, ERK, or AKT but utilizes an EGFR-PI3K mechanism and involves intracellular Ca2+. How PKA is involved in this crosstalk remains to be determined.