Domingue Jada C, Ao Mei, Sarathy Jayashree, Rao Mrinalini C
Department of Physiology and Biophysics, University of Illinois at Chicago, Chicago, Illinois.
Department of Biology, Benedictine University, Lisle, Illinois.
Am J Physiol Cell Physiol. 2016 Nov 1;311(5):C777-C792. doi: 10.1152/ajpcell.00168.2016. Epub 2016 Aug 24.
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 (I), 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 Ca 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 Ca cross talk. Downstream of EPAC, CDCA activates Rap2, and changes in free cytosolic Ca 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 Ca in CDCA-induced activation of CFTR-dependent Cl secretion.
已知胆汁酸可在多种组织中引发复杂的信号事件，主要是在肝脏和胃肠道。在已知的胆汁酸中，只有7α - 二羟基胆汁酸、脱氧胆酸和鹅去氧胆酸（CDCA）及其共轭物能激活刺激上皮细胞氯离子分泌的过程。我们之前发表过，CDCA通过蛋白激酶A（PKA）介导的对主要氯离子通道——囊性纤维化跨膜电导调节因子（CFTR）的激活，快速刺激结肠离子分泌（Ao M，Sarathy J，Domingue J，Alrefai WA，以及Rao MC。《美国生理学杂志：细胞生理学》305：C447 - C456，2013）；然而，PKA信号传导并不能解释CDCA的全部反应。在此我们表明，在人结肠T84细胞中，以短路电流（I）变化衡量的CDCA对CFTR活性的诱导依赖于表皮生长因子受体（EGFR）的激活，且不涉及胆汁酸受体TGR5或法尼酯X受体。CDCA对氯离子分泌的激活在EGFR下游不需要Src、丝裂原活化蛋白激酶或磷脂酰肌醇3激酶，但确实需要胞质钙增加。除了PKA信号传导外，我们发现CDCA反应还需要由cAMP直接激活的交换蛋白（EPAC）的新参与。EPAC是已知的cAMP和钙信号交叉的枢纽。在EPAC下游，CDCA激活Rap2，游离胞质钙的变化依赖于EPAC和EGFR的激活。本研究确定了CDCA在结肠上皮细胞信号传导中的复杂性，并显示了EGFR、EPAC和钙在CDCA诱导的依赖CFTR激活的氯离子分泌中的作用。
