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The Role of the Actin‐binding Protein, Alpha Actinin 4, in Transcriptional Regulation by Glucocorticoid Receptors in Glomerular Podocytes
Author(s) -
Zhao Xuan,
Khurana Simran,
Bruggeman Leslie,
Kao Hungying
Publication year - 2016
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.30.1_supplement.1055.2
Subject(s) - glucocorticoid receptor , podocyte , transactivation , gene knockdown , microbiology and biotechnology , nuclear receptor , receptor , nephrotic syndrome , chemistry , biology , transcription factor , endocrinology , kidney , gene , proteinuria , biochemistry
Glomerular podocytes are highly specialized terminally differentiated cells that function as a filtration barrier in the kidney. Loss or damage to podocytes is associated with nephrotic syndromes, including focal segmental glomerulosclerosis (FSGS), a chronicle kidney disease characterized by proteinuria. Mutations in the actin‐crosslinking protein alpha actinin 4 (ACTN4) are associated with familial forms of FSGS. ACTNs are better known for their ability to bind actin filaments and modulate cytoskeletal organization. However, we have previously demonstrated that a fraction of ACTN4 is found in the nucleus and functions as a transcriptional co‐activator of some nuclear receptors and that ACTN4 coactivates NF‐κB transcription activity and is recruited to NF‐κB targeted promoters in cultured human podocytes (HPCs). Glucocorticoid therapy is a mainstay treatment option for many forms of nephrotic syndrome, although little is known about the mechanism by which the glucocorticoids ameliorate proteinuria and glomerular disease. Our data indicate that, similar to its action in most cell types, glucocorticoids induce nuclear translocation of glucocorticoid receptor (GR) and regulate target gene expression through transactivation and transrepression. In this study, we show that ACTN4 harbors a LXXLL nuclear receptor interacting motif and is capable of enhancing transcription activity by GR. ACTN4 interacts with GR in the nucleus of HPCs. Disruption of the receptor interacting motif, LXXLL significantly reduces its ability to potentiate transcriptional activity by GR. Stable knockdown of ACTN4 by shRNA in HPCs does not affect glucocorticoid‐induced nuclear translocation of GR, while it significantly reduces dexamethasone (Dex)‐mediated induction of GR target genes and the activity of a Glucocorticoid receptor element (GRE)‐driven reporter construct. Furthermore, loss of ACTN4 partially ablates transrepression of NF‐κB target genes in a gene‐dependent manner. Lastly, we demonstrate that FSGS‐linked ACTN4 mutants lose their ability to bind liganded GR and transcription potentiation activity. Taken together, our data suggest a role of ACTN4 in transcriptional regulation mediated by GR. We are currently dissecting the molecular basis of the interaction of ACTN4 and GR and investigating the mechanism by which ACTN4 works as a transcription co‐activator of GR.