Chenodeoxycholic Acid Requires Activation of EGFR, EPAC and Ca to Stimulate CFTR-

48 49 Bile acids are known to initiate intricate signaling events in a variety of tissues, primarily in the 50 liver and gastrointestinal tract. Of the known bile acids, only the dihydroxy species, deoxycholic 51 acid and chenodeoxycholic acid (CDCA), and their conjugates, activate processes that stimulate 52 epithelial Cl secretion. We have previously published that CDCA acts in a rapid manner to 53 stimulate colonic ion secretion via protein kinase A (PKA)-mediated activation of the dominant 54 Cl channel, the cystic fibrosis transmembrane conductance regulator (CFTR) (AJP 305:C44755 56, 2013); however, PKA signaling did not account for the entire CDCA response. Here we 56 show that in human colonic T84 cells, CDCA’s induction of CFTR activity, measured as changes 57 in short-circuit current (Isc), is dependent on epidermal growth factor receptor (EGFR) activation, 58 and does not involve the bile acid receptors TGR5 or FXR. CDCA activation of Cl secretion 59 does not require Src, mitogen activated protein kinases, or phosphoinositide-3 kinase 60 downstream of EGFR, but does require an increase in cytosolic Ca. In addition to PKA 61 signaling, we found that the CDCA response requires a novel involvement of the exchange 62 protein directly activated by cAMP (EPAC). EPAC is a known hub for cAMP and Ca cross talk. 63 Downstream of EPAC, CDCA activates Rap2, and changes in [Ca]i were dependent on both 64 EPAC and EGFR activation. This study establishes the complexity of CDCA signaling in the 65 colonic epithelium, and shows the contribution of EGFR, EPAC and Ca in CDCA-induced 66 activation of CFTR-dependent Cl secretion. 67 68 69