A myosin chaperone, UNC‐45A, is a novel regulator of intestinal epithelial barrier integrity and repair

The actomyosin cytoskeleton serves as a key regulator of the integrity and remodeling of epithelial barriers by controlling assembly and functions of intercellular junctions and cell‐matrix adhesions. Although biochemical mechanisms that regulate the activity of non‐muscle myosin II (NM‐II) in epithelial cells have been extensively investigated, little is known about assembly of the contractile myosin structures at the epithelial adhesion sites. UNC‐45A is a cytoskeletal chaperone that is essential for proper folding of NM‐II heavy chains and myofilament assembly. We found abundant expression of UNC‐45A in human intestinal epithelial cell (IEC) lines and in the epithelial layer of the normal human colon. Interestingly, protein level of UNC‐45A was decreased in colonic epithelium of patients with ulcerative colitis. CRISPR/Cas9‐mediated knock‐out of UNC‐45A in HT‐29cf8 and SK‐CO15 IEC disrupted epithelial barrier integrity, impaired assembly of epithelial adherence and tight junctions and attenuated cell migration. Consistently, decreased UNC‐45 expression increased permeability of the Drosophila gut in vivo. The mechanisms underlying barrier disruptive and anti‐migratory effects of UNC‐45A depletion involved disorganization of the actomyosin bundles at epithelial junctions and the migrating cell edge. Loss of UNC‐45A also decreased contractile forces at apical junctions and matrix adhesions. Expression of deletion mutants revealed roles for the myosin binding domain of UNC‐45A in controlling IEC junctions and motility. Our findings uncover a novel mechanism that regulates integrity and restitution of the intestinal epithelial barrier, which may be impaired during mucosal inflammation.