Abstract
We investigated the role of a Ca(2+) channel and intracellular calcium concentration ([Ca(2+)](i)) in osmotic stress-induced JNK activation and tight junction disruption in Caco-2 cell monolayers. Osmotic stress-induced tight junction disruption was attenuated by 1,2-bis(2-aminophenoxyl)ethane-N,N,N',N'-tetraacetic acid (BAPTA)-mediated intracellular Ca(2+) depletion. Depletion of extracellular Ca(2+) at the apical surface, but not basolateral surface, also prevented tight junction disruption. Similarly, thapsigargin-mediated endoplasmic reticulum (ER) Ca(2+) depletion attenuated tight junction disruption. Thapsigargin or extracellular Ca(2+) depletion partially reduced osmotic stress-induced rise in [Ca(2+)](i), whereas thapsigargin and extracellular Ca(2+) depletion together resulted in almost complete loss of rise in [Ca(2+)](i). L-type Ca(2+) channel blockers (isradipine and diltiazem) or knockdown of the Ca(V)1.3 channel abrogated [Ca(2+)](i) rise and disruption of tight junction. Osmotic stress-induced JNK2 activation was abolished by BAPTA and isradipine, and partially reduced by extracellular Ca(2+) depletion, thapsigargin, or Ca(V)1.3 knockdown. Osmotic stress rapidly induced c-Src activation, which was significantly attenuated by BAPTA, isradipine, or extracellular Ca(2+) depletion. Tight junction disruption by osmotic stress was blocked by tyrosine kinase inhibitors (genistein and PP2) or siRNA-mediated knockdown of c-Src. Osmotic stress induced a robust increase in tyrosine phosphorylation of occludin, which was attenuated by BAPTA, SP600125 (JNK inhibitor), or PP2. These results demonstrate that Ca(V)1.3 and rise in [Ca(2+)](i) play a role in the mechanism of osmotic stress-induced tight junction disruption in an intestinal epithelial monolayer. [Ca(2+)](i) mediate osmotic stress-induced JNK activation and subsequent c-Src activation and tyrosine phosphorylation of tight junction proteins. Additionally, inositol 1,4,5-trisphosphate receptor-mediated release of ER Ca(2+) also contributes to osmotic stress-induced tight junction disruption.