ABSTRACT
Actin-associated nonmuscle myosin II (NM2) motor proteins play critical roles in a myriad of cellular functions, including endocytosis and organelle transport pathways. Cell type-specific expression and unique subcellular localization of the NM2 proteins, encoded by the Myh9 and Myh10 genes, in the mouse kidney tubules led us to hypothesize that these proteins have specialized functional roles within the renal epithelium. Inducible conditional knockout (cKO) of Myh9 and Myh10 in the renal tubules of adult mice resulted in progressive kidney disease. Prior to overt renal tubular injury, we observed intracellular accumulation of the glycosylphosphatidylinositol-anchored protein uromodulin (UMOD) and gradual loss of Na+ K+ 2Cl- cotransporter from the apical membrane of the thick ascending limb epithelia. The UMOD accumulation coincided with expansion of endoplasmic reticulum (ER) tubules and activation of ER stress and unfolded protein response pathways in Myh9&10-cKO kidneys. We conclude that NM2 proteins are required for localization and transport of UMOD and loss of function results in accumulation of UMOD and ER stress-mediated progressive renal tubulointerstitial disease. These observations establish cell type-specific role(s) for NM2 proteins in regulation of specialized renal epithelial transport pathways and reveal the possibility that human kidney disease associated with MYH9 mutations could be of renal epithelial origin.
Subject(s)
Endoplasmic Reticulum Stress , Epithelium/pathology , Kidney Diseases/pathology , Kidney Tubules/pathology , Myosin Heavy Chains/physiology , Nonmuscle Myosin Type IIB/physiology , Animals , Epithelium/metabolism , Female , Kidney Diseases/etiology , Kidney Diseases/metabolism , Kidney Tubules/metabolism , Male , Mice , Mice, Inbred C57BL , Mice, Knockout , Myosin Type II/genetics , Myosin Type II/metabolism , Podocytes/metabolism , Podocytes/pathology , Solute Carrier Family 12, Member 1/genetics , Solute Carrier Family 12, Member 1/metabolism , Unfolded Protein Response , Uromodulin/genetics , Uromodulin/metabolismABSTRACT
Cell nuclei rupture following exposure to mechanical force and/or upon weakening of nuclear integrity, but nuclear ruptures are repairable. Barrier-to-autointegration factor (BAF), a small DNA-binding protein, rapidly localizes to nuclear ruptures; however, its role at these rupture sites is unknown. Here, we show that it is predominantly a nonphosphorylated cytoplasmic population of BAF that binds nuclear DNA to rapidly and transiently localize to the sites of nuclear rupture, resulting in BAF accumulation in the nucleus. BAF subsequently recruits transmembrane LEM-domain proteins, causing their accumulation at rupture sites. Loss of BAF impairs recruitment of LEM-domain proteins and nuclear envelope membranes to nuclear rupture sites and prevents nuclear envelope barrier function restoration. Simultaneous depletion of multiple LEM-domain proteins similarly inhibits rupture repair. LEMD2 is required for recruitment of the ESCRT-III membrane repair machinery to ruptures; however, neither LEMD2 nor ESCRT-III is required to repair ruptures. These results reveal a new role for BAF in the response to and repair of nuclear ruptures.
