A Myosin Chaperon, UNC‐45A, Is a Key Regulator of Intestinal Epithelial Apical Junctions

Abstract

Epithelial adherens junctions (AJs) and tight junctions (TJs) play critical roles in regulating the integrity and permeability of epithelial barriers. Proper assembly and functioning of AJs and TJs depend on their associations with underlying actin filaments and the actin motor protein, nonmuscle myosin II (NM II). Our previous studies demonstrated the roles of NM II in controlling assembly and permeability of intestinal epithelial apical junctions in vitro and in vivo. However, the molecular mechanisms that regulate NM IIA functions in intestinal epithelium remain poorly understood. UNC‐45A is a highly conserved member of the UNC‐45/CRO1/She4p family proteins, which acts as a NM II chaperone and controls a proper folding and activity of myosin heavy chains. In the present study, we investigated the roles of UNC‐45A in the regulation of apical junctions in model intestinal epithelial cell monolayers.UNC‐45A protein was abundantly expressed in several commonly‐used human intestinal epithelial cell lines. Furthermore, its expression in T84 and HT‐29 cells was significantly downregulated by proinflammatory cytokines, IFN‐γ and TNF‐α, in parallel to cytokine induced TJ disassembly and barrier disruption. Consistently, UNC‐45A and NM IIA expression was downregulated in colonic epithelial cells isolated from tissue samples of ulcerative colitis patients. CRISPR/Cas9 mediated knock‐out of UNC‐45A in SK‐CO15 and HT‐29 human colonic epithelial cells resulted in multiple defects of apical junctions. These defects include the decreased transepithelial electrical resistance, increased transepithelial dextran flux, impaired steady‐state structure of AJs and TJs, and attenuated junctional reassembly during calcium switch. Together, our findings revealed a novel cytoskeleton‐dependent mechanism that regulates structure and functions of normal intestinal epithelial barrier and may contribute to barrier disruption during mucosal inflammation.Support or Funding InformationThis work was supported by NIH grant R01DK108278.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.