Soluble adenylyl cyclase regulates tight junctions of human intestinal epithelial cells via claudin-4

Although cAMP is a major intracellular messenger, studies on modulating effects of cAMP on tight junctions in epithelial cells are very limited. In this study, we characterized a bidirectional and prominent regulation of the tight junction by soluble adenylyl cyclase (sAC) in human intestinal epithelial (Caco2Bbe1) cells. Pharmacological inhibition and knockdown of sAC substantially increased TEER, whereas overexpression of sAC reciprocally decreased TEER. Mechanistically, EPAC1 was the sole cAMP effector responsible for the regulation of TEER by sAC. Pharmacological inhibition or knockdown of sAC and inhibition of EPAC1 resulted in increased protein expression of claudin-4, and again, with a reciprocal decrease of claudin-4 protein expression upon sAC overexpression. These interventions did not affect paracellular lucifer yellow permeability. sAC inhibition also induced phosphorylated extracellular signal-regulated kinase (p-ERK) protein expression. Although the ERK inhibitor, SCH772984, decreased TEER, ERK did not seem to be involved in the regulation of claudin-4 expression via sAC. Concluding from these data, sAC activity exerts a prominent bidirectional control over the ionic permeability of tight junctions in Caco2Bbe1 monolayers by regulating claudin-4 protein expression via EPAC1. This suggests a pivotal role of sAC in modulation of tight junctions in human intestinal epithelial cells, and proposes a molecular mechanism by which cAMP modulate tight junctions.NEW & NOTEWORTHY It is established that cAMP modulates tight junctions, but little is known about the mechanism behind. Here, for the first time, soluble adenylyl cyclase (sAC) was found to exert exclusive control over the ionic paracellular permeability in Caco2Bbe1 monolayers, while sparing the paracellular permeability of larger molecules. EPAC1 and claudin-4 were shown to be involved in the mechanism. Our data also suggest that other adenylyl cyclases are of minor importance in regulating ionic paracellular permeability.