IL-1β-induced increase in intestinal epithelial tight junction permeability is mediated by MEKK-1 activation of canonical NF-κB pathway

IL-1β is a proinflammatory cytokine that plays a central role in the inflammatory process of the gut. IL-1β causes an increase in intestinal epithelial tight junction (TJ) permeability, but the intracellular pathways that mediate intestinal TJ permeability remain unclear. The major aims of this study were to delineate the protein kinases that regulate the IL-1β modulation of intestinal TJ barrier function and to determine the intracellular mechanisms involved, using filtergrown Caco-2 monolayers as the in vitro model system. Our results showed that IL-1β caused a rapid activation of MEKK-1 and NIK. The knockdown of MEKK-1, but not NIK, inhibited the IL-1β increase in Caco-2 TJ permeability. IL-1β caused an activation of both canonical and noncanonical NF-κB pathways; MEKK-1 regulated the activation of the canonical pathway, while NIK regulated the activation of the noncanonical pathway. Inhibition of MEKK-1 activation of the canonical pathway prevented the IL-1β increase in TJ permeability. Our data also indicated that inhibitory κB kinase was the catalytic subunit primarily involved in canonical pathway activation and TJ barrier opening. MEKK-1 also played an essential role in myosin light chain kinase gene activation. In conclusion, our data show for the first time that MEKK-1 plays an integral role in IL-1β modulation of Caco-2 TJ barrier function by regulating the activation of the canonical NF-κB pathway and the MLCK gene.