title: α-Actinin 4 potentiates nuclear factor κ-light-chain-enhancer of activated B-cell (NF-κB) activity in podocytes independent of its cytoplasmic actin binding function.
abstract: Glomerular podocytes are highly specialized terminally differentiated cells that act as a filtration barrier in the kidney. Mutations in the actin-binding protein, α-actinin 4 (ACTN4), are linked to focal segmental glomerulosclerosis (FSGS), a chronic kidney disease characterized by proteinuria. Aberrant activation of NF-κB pathway in podocytes is implicated in glomerular diseases including proteinuria. We demonstrate here that stable knockdown of ACTN4 in podocytes significantly reduces TNFα-mediated induction of NF-κB target genes, including IL-1β and NPHS1, and activation of an NF-κB-driven reporter without interfering with p65 nuclear translocation. Overexpression of ACTN4 and an actin binding-defective variant increases the reporter activity. In contrast, an FSGS-linked ACTN4 mutant, K255E, which has increased actin binding activity and is predominantly cytoplasmic, fails to potentiate NF-κB activity. Mechanistically, IκBα blocks the association of ACTN4 and p65 in the cytosol. In response to TNFα, both NF-κB subunits p65 and p50 translocate to the nucleus, where they bind and recruit ACTN4 to their targeted promoters, IL-1β and IL-8. Taken together, our data identify ACTN4 as a novel coactivator for NF-κB transcription factors in podocytes. Importantly, this nuclear function of ACTN4 is independent of its actin binding activity in the cytoplasm.
authors.affiliation: From the Department of Biochemistry.
authors.forename: Xuan
authors.initials: X
authors.lastname: Zhao
authors.affiliation: From the Department of Biochemistry.
authors.forename: Kuo-Sheng
authors.initials: KS
authors.lastname: Hsu
authors.affiliation: From the Department of Biochemistry.
authors.forename: Jun Hee
authors.initials: JH
authors.lastname: Lim
authors.affiliation: Rammelkamp Center for Education and Research and Department of Medicine, MetroHealth Medical Center, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106.
authors.forename: Leslie A
authors.initials: LA
authors.lastname: Bruggeman
authors.affiliation: From the Department of Biochemistry, Case Comprehensive Cancer Center, and hxk43@cwru.edu.
authors.forename: Hung-Ying
authors.initials: HY
authors.lastname: Kao
mesh_terms: D000185:Actinin / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism; D000199:Actins / Q000235:genetics / Q000378:metabolism; D000818:Animals; D002461:Cell Line, Transformed; D005786:Gene Expression Regulation; D057809:HEK293 Cells; D006367:HeLa Cells; D006801:Humans; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D016328:NF-kappa B / Q000235:genetics* / Q000378:metabolism; D050199:Podocytes / Q000166:cytology / Q000378:metabolism*; D011485:Protein Binding; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D014158:Transcription, Genetic
chemical_list: C111453:ACTN4 protein, human; D000199:Actins; D016328:NF-kappa B; D034741:RNA, Small Interfering; D000185:Actinin
keywords: ACTN4; Alpha-Actinin 4; FSGS; Focal Segmental Glomerulosclerosis; Glomerulopathies; Glucocorticoid Receptor; NF-kappa B (NF-KB); Podocyte; Transcription Regulation; Transcriptional Coactivator