High MUC2 Production in Goblet Cells Induces ER Stress and Exhibit Increase Susceptibility to Apoptosis

Abstract

MUC2 is a large glycoprotein produced by goblet cells (GC) that form the protective mucus blanket overlying the intestinal epithelium. During pathological conditions such as IBD or colonic cancers, MUC2 biosynthesis and secretion are accelerated. Little information is known on how MUC2 production is regulated and whether GC undergoes endoplasmic reticulum (ER) stress following high MUC2 biosynthesis. We studied the role of MUC2 in GC stress using a high MUC2 producing GC line, HT29‐H, and a clone of HT29‐H (HT29‐L) in which MUC2 was stably silenced using lentivirus shRNA. Cells were treated with the ER stressor, tunicamycin (TUN) and markers for ER stress (GRP78, ATF4, CHOP, sXBP1) and apoptosis (caspase 3 and PARP cleavage) quantified by western blotting and RT‐qPCR. Compared to HT29‐L, HT29‐H cells showed significant increase in ER stress and apoptosis in response to TUN. Over expressing MUC2 in non‐MUC2‐producing SKCO15 cells also increased ER stress and apoptosis confirming specificity of MUC2. Pre‐treatment of cells with reactive oxygen species (ROS) inhibitor, diphenyleneiodonium, abrogated basal stress levels, TUN‐induced ER stress and apoptosis. HT29‐H constitutively produced significantly more ROS than HT29‐L cells indicating that high MUC2 production specifically increases ROS production that drives ER stress and apoptosis. These findings were corroborated in isolated colonic epithelial cells and colonic tissues from Wt and Muc2‐/‐ mice that showed significant increase in ER stress in Wt as compared to Muc2‐/‐ mice. We conclude that high MUC2 production by GC induces ER stress and apoptosis that could subsequently lead to diminished mucus barrier function in disease pathogenesis.Grant: CIHR