title: Chenodeoxycholic acid requires activation of EGFR, EPAC, and Ca2+ to stimulate CFTR-dependent Cl- secretion in human colonic T84 cells.
abstract: Bile acids are known to initiate intricate signaling events in a variety of tissues, primarily in the liver and gastrointestinal tract. Of the known bile acids, only the 7α-dihydroxy species, deoxycholic acid and chenodeoxycholic acid (CDCA), and their conjugates, activate processes that stimulate epithelial Cl-secretion. We have previously published that CDCA acts in a rapid manner to stimulate colonic ion secretion via protein kinase A (PKA)-mediated activation of the dominant Cl-channel, the cystic fibrosis transmembrane conductance regulator (CFTR) (Ao M, Sarathy J, Domingue J, Alrefai WA, and Rao MC. Am J Physiol Cell Physiol 305: C447-C456, 2013); however, PKA signaling did not account for the entire CDCA response. Here we show that in human colonic T84 cells, CDCA's induction of CFTR activity, measured as changes in short-circuit current (Isc), is dependent on epidermal growth factor receptor (EGFR) activation and does not involve the bile acid receptors TGR5 or farnesoid X receptor. CDCA activation of Cl-secretion does not require Src, mitogen-activated protein kinases, or phosphoinositide 3-kinase downstream of EGFR but does require an increase in cytosolic Ca2+In addition to PKA signaling, we found that the CDCA response requires the novel involvement of the exchange protein directly activated by cAMP (EPAC). EPAC is a known hub for cAMP and Ca2+cross talk. Downstream of EPAC, CDCA activates Rap2, and changes in free cytosolic Ca2+were dependent on both EPAC and EGFR activation. This study establishes the complexity of CDCA signaling in the colonic epithelium and shows the contribution of EGFR, EPAC, and Ca2+in CDCA-induced activation of CFTR-dependent Cl-secretion.
authors: Department of Physiology and Biophysics, University of Illinois at Chicago, Chicago, Illinois.
authors: Jada C
authors: JC
authors: Domingue
authors: Department of Physiology and Biophysics, University of Illinois at Chicago, Chicago, Illinois.
authors: Mei
authors: M
authors: Ao
authors: Department of Physiology and Biophysics, University of Illinois at Chicago, Chicago, Illinois.|Department of Biology, Benedictine University, Lisle, Illinois.
authors: Jayashree
authors: J
authors: Sarathy
authors: Department of Physiology and Biophysics, University of Illinois at Chicago, Chicago, Illinois; meenarao@uic.edu.|Department of Medicine, University of Illinois at Chicago, Chicago, Illinois; and.
authors: Mrinalini C
authors: MC
authors: Rao
mesh_terms: D002118:Calcium / Q000378:metabolism*; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000378:metabolism; D002635:Chenodeoxycholic Acid / Q000378:metabolism*; D018118:Chloride Channels / Q000378:metabolism; D002712:Chlorides / Q000378:metabolism*; D003106:Colon / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000378:metabolism*; D004847:Epithelial Cells / Q000378:metabolism; D066246:ErbB Receptors / Q000378:metabolism*; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism*; D006801:Humans; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology
chemical_list: C505032:CFTR protein, human; D018118:Chloride Channels; D002712:Chlorides; D020662:Guanine Nucleotide Exchange Factors; C116122:RAPGEF3 protein, human; D002635:Chenodeoxycholic Acid; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D000242:Cyclic AMP; D019869:Phosphatidylinositol 3-Kinases; C512478:EGFR protein, human; D066246:ErbB Receptors; D002118:Calcium
keywords: calcium ion; chenodeoxycholic acid; cystic fibrosis transmembrane conductance regulator; epidermal growth factor receptor; exchange protein directly activated by adenosine 3′,5′-cyclic monophosphate