title: The antigen-binding fragment of anti-double-stranded DNA IgG enhances F-actin formation in mesangial cells by binding to alpha-actinin-4.
abstract: Anti-double-stranded DNA (dsDNA) IgG causes renal damage in patients with lupus nephritis by cross-reacting with multiple autoantigens, including alpha-actinin-4, in mesangial cells (MCs). However, how the cross-reactions play a role in mesangial phenotypic abnormalities is not well understood. Here, we investigated the effects of the fragment antigen-binding (Fab) of anti-dsDNA IgG3 on the biochemical properties of alpha-actinin-4. Experiments revealed that anti-dsDNA Fab specifically binds to alpha-actinin-4, but not G-actin. The binding by anti-dsDNA Fab sequentially increases the positive charge of alpha-actinin-4 and inhibits the affinity of alpha-actinin-4 to calcium ions. By the low shear viscosity and a co-sedimentation assay, we found that the alpha-actinin-4-induced F-actin gelation improves when anti-dsDNA Fab is added. However, the Fab control has no such effect on F-actin gelation. Furthermore, the in vitro cultured MCs exhibit higher F-actin expression and transforming growth factor-β1 synthesis after the incubation with anti-dsDNA Fab. Therefore, our results indicated that anti-dsDNA Fab may enhance F-actin formation by the proprietary modification of alpha-actinin-4, which could partially explain the myofibroblast-like phenotype of MCs in anti-dsDNA-positive lupus nephritis.
authors.affiliation: Department of Medicine, Renmin Hospital of Wuhan University, Wuhan 430060, China.
authors.forename: Xiaoyan
authors.initials: X
authors.lastname: Zou
authors.forename: Hong
authors.initials: H
authors.lastname: Cheng
authors.forename: Yi
authors.initials: Y
authors.lastname: Zhang
authors.forename: Chunhong
authors.initials: C
authors.lastname: Fang
authors.forename: Yumin
authors.initials: Y
authors.lastname: Xia
mesh_terms: D000185:Actinin / Q000276:immunology / Q000378:metabolism*; D000199:Actins / Q000378:metabolism*; D000818:Animals; D000974:Antibodies, Antinuclear / Q000276:immunology* / Q000378:metabolism; D001324:Autoantigens / Q000276:immunology; D002460:Cell Line; D004247:DNA / Q000276:immunology*; D006801:Humans; D007140:Immunoglobulin Fab Fragments / Q000276:immunology / Q000378:metabolism; D007074:Immunoglobulin G / Q000276:immunology / Q000378:metabolism; D007668:Kidney / Q000276:immunology; D008181:Lupus Nephritis / Q000276:immunology / Q000473:pathology; D050527:Mesangial Cells / Q000378:metabolism*; D051379:Mice; D058628:Myofibroblasts; D053773:Transforming Growth Factor beta1 / Q000096:biosynthesis
chemical_list: D000199:Actins; C491752:Actn4 protein, mouse; D000974:Antibodies, Antinuclear; D001324:Autoantigens; D007140:Immunoglobulin Fab Fragments; D007074:Immunoglobulin G; D053773:Transforming Growth Factor beta1; D000185:Actinin; D004247:DNA