p38 mitogen-activated protein kinase inhibits calcium-dependent chloride secretion in T84colonic epithelial cells

Abstract

We have previously shown that Ca²⁺-dependent Cl⁻secretion across intestinal epithelial cells is limited by a signaling pathway involving transactivation of the epidermal growth factor receptor (EGFR) and activation of ERK mitogen-activated protein kinase (MAPK). Here, we have investigated a possible role for p38 MAPK in regulation of Ca²⁺-dependent Cl⁻secretion. Western blot analysis of T₈₄colonic epithelial cells revealed that the muscarinic agonist carbachol (CCh; 100 μM) stimulated phosphorylation and activation of p38 MAPK. The p38 inhibitor SB-203580 (10 μM) potentiated and prolonged short-circuit current ( I_sc) responses to CCh across voltage-clamped T₈₄cells to 157.4 ± 6.9% of those in control cells ( n = 21; P < 0.001). CCh-induced p38 phosphorylation was attenuated by the EGFR inhibitor tyrphostin AG-1478 (0.1 nM–10 μM) and by the Src family kinase inhibitor PP2 (20 nM–2 μM). The effects of CCh on p38 phosphorylation were mimicked by thapsigargin (TG; 2 μM), which specifically elevates intracellular Ca²⁺, and were abolished by the Ca²⁺chelator BAPTA-AM (20 μM), implying a role for intracellular Ca²⁺in mediating p38 activation. SB-203580 (10 μM) potentiated I_scresponses to TG to 172.4 ± 18.1% of those in control cells ( n= 18; P < 0.001). When cells were pretreated with SB-203580 and PD-98059 to simultaneously inhibit p38 and ERK MAPKs, respectively, I_scresponses to TG and CCh were significantly greater than those observed with either inhibitor alone. We conclude that Ca²⁺-dependent agonists stimulate p38 MAPK in T₈₄cells by a mechanism involving intracellular Ca²⁺, Src family kinases, and the EGFR. CCh-stimulated p38 activation constitutes a similar, but distinct and complementary, antisecretory signaling pathway to that of ERK MAPK.