title: α Actinin 4 (ACTN4) Regulates Glucocorticoid Receptor-mediated Transactivation and Transrepression in Podocytes.
abstract: Glucocorticoids are a general class of steroids that possess renoprotective activity in glomeruli through their interaction with the glucocorticoid receptor. However, the mechanisms by which glucocorticoids ameliorate proteinuria and glomerular disease are not well understood. In this study, we demonstrated that α actinin 4 (ACTN4), an actin-cross-linking protein known to coordinate cytoskeletal organization, interacts with the glucocorticoid receptor (GR) in the nucleus of human podocytes (HPCs), a key cell type in the glomerulus critical for kidney filtration function. The GR-ACTN4 complex enhances glucocorticoid response element (GRE)-driven reporter activity. Stable knockdown of ACTN4 by shRNA in HPCs significantly reduces dexamethasone-mediated induction of GR target genes and GRE-driven reporter activity without disrupting dexamethasone-induced nuclear translocation of GR. Synonymous mutations or protein expression losses in ACTN4 are associated with kidney diseases, including focal segmental glomerulosclerosis, characterized by proteinuria and podocyte injury. We found that focal segmental glomerulosclerosis-linked ACTN4 mutants lose their ability to bind liganded GR and support GRE-mediated transcriptional activity. Mechanistically, GR and ACTN4 interact in the nucleus of HPCs. Furthermore, disruption of the LXXLL nuclear receptor-interacting motif present in ACTN4 results in reduced GR interaction and dexamethasone-mediated transactivation of a GRE reporter while still maintaining its actin-binding activity. In contrast, an ACTN4 isoform, ACTN4 (Iso), that loses its actin-binding domain is still capable of potentiating a GRE reporter. Dexamethasone induces the recruitment of ACTN4 and GR to putative GREs in dexamethasone-transactivated promoters, SERPINE1, ANGPLT4, CCL20, and SAA1 as well as the NF-κB (p65) binding sites on GR-transrepressed promoters such as IL-1β, IL-6, and IL-8 Taken together, our data establish ACTN4 as a transcriptional co-regulator that modulates both dexamethasone-transactivated and -transrepressed genes in podocytes.
authors.affiliation: From the Department of Biochemistry, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106.
authors.forename: Xuan
authors.initials: X
authors.lastname: Zhao
authors.affiliation: From the Department of Biochemistry, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106.
authors.forename: Simran
authors.initials: S
authors.lastname: Khurana
authors.affiliation: From the Department of Biochemistry, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106.
authors.forename: Sharmistha
authors.initials: S
authors.lastname: Charkraborty
authors.affiliation: From the Department of Biochemistry, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106.
authors.forename: Yuqian
authors.initials: Y
authors.lastname: Tian
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: John R
authors.initials: JR
authors.lastname: Sedor
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: Bruggman
authors.affiliation: From the Department of Biochemistry, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106; Case Comprehensive Cancer Center, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106. Electronic address: hxk43@cwru.edu.
authors.forename: Hung-Ying
authors.initials: HY
authors.lastname: Kao
mesh_terms: D000185:Actinin / Q000096:biosynthesis* / Q000235:genetics; D016207:Cytokines / Q000096:biosynthesis / Q000235:genetics; D003907:Dexamethasone / Q000494:pharmacology*; D057809:HEK293 Cells; D006367:HeLa Cells; D006801:Humans; D050199:Podocytes / Q000166:cytology / Q000378:metabolism*; D020033:Protein Isoforms / Q000096:biosynthesis / Q000235:genetics; D011965:Receptors, Glucocorticoid / Q000819:agonists / Q000235:genetics / Q000378:metabolism*; D020218:Response Elements / Q000502:physiology*; D015533:Transcriptional Activation / Q000187:drug effects*
chemical_list: C111453:ACTN4 protein, human; D016207:Cytokines; D020033:Protein Isoforms; D011965:Receptors, Glucocorticoid; D000185:Actinin; D003907:Dexamethasone
keywords: Glucocorticoid receptor; podocyte; transactivation; transcription coactivator; transcription corepressor; translation control; transrepression; α actinin 4