MUC17 expression is differently regulated by TLRs interaction with their ligands

Abstract

MUC17 is a membrane‐bound mucin highly expressed on the apical surface of intestinal epithelia. We have shown that MUC17 promotes epithelial restitution, is anti‐apoptotic, protects intestinal cells against gut pathogens, and that live probiotics protect against enteropathogens, in part, by promoting MUC17 levels upon activation of TLR 2, 4. We hypothesized that TLRs and their ligands may affect MUC17 and other mucins, MUC1, MUC2 and MUC3, in an interdependent manner. MUC17 scrambled (sc) and siRNA (si) Caco2 and HT29 cells were exposed to LPS, PGNs, Pam2CSK4, LTAs, MPLAs, FLAs and ODNs to stimulate TLR 2, 4, 5, 9. TLRs antagonists and inhibitors of kinases were used to test mechanisms regulating MUC17. Mucins levels were assayed in both sc and si MUC17 cells. Protein, and nucleic acid analysis, and confocal microscopy were performed by standard methods. TLRs stimulation resulted in diverse levels of induction of mucins RNA and protein. This effect was dependent on type and dose of ligand tested. However, in MUC17 si cells, expression of MUC1, MUC2, and MUC3 were significantly altered after TLRs ligands treatment compared to MUC17 sc cells (MUC1 increased x2; MUC2 and MUC3 decreased x1.5 and x2, respectively). Inhibition of MAPK, IKK, PI3K reversed these effects. Our data suggest that MUC17 expression is significantly regulated by TLRs interaction with their ligands, and that levels of gut mucins show some degree of cross‐regulation. We conclude that the intestinal mucin barrier is more complexly regulated than previously thought, and that modulation of TLRs may reverse, in part, altered mucin expression observed in diseases of the gut. Funding: UCSD‐DDRDC; Research Service‐Dept Veterans Affairs