Mechanism of action of Hic-5/androgen receptor activator 55, a LIM domain-containing nuclear receptor coactivator.
Hic-5/androgen receptor (AR) coactivator 55 (ARA55) is a group III LIM domain protein that functions as a nuclear receptor coactivator. In the present study, we examined the mechanism by which Hic-5/ARA55 potentiates glucocorticoid receptor (GR) transactivation in the A1-2 derivative of T47D breast cancer cells. Hic-5/ARA55 is an important component of GR-coactivator complexes in A1-2 cells because ablation of Hic-5/ARA55 expression by RNA interference-mediated silencing reduced GR transactivation. As shown by chromatin immunoprecipitation (ChIP) assays, Hic-5/ARA55 is recruited to glucocorticoid-responsive promoters of the mouse mammary tumor virus, c-fos, and p21 genes in response to glucocorticoid treatment. Results from sequential ChIPs established that Hic-5/ARA55 associates with GR-containing complexes at these promoters. We also used sequential ChIPs to examine Hic-5/ARA55 interactions with other well-characterized nuclear receptor coactivators and detected transcriptional intermediary factor 2, receptor-associated coactivator 3, cAMP response element binding protein-binding protein, and p300 within Hic-5/ARA55 complexes on the mouse mammary tumor virus promoter in hormone-treated cells. Ablation of Hic-5/ARA55 expression resulted in reduction of both transcriptional intermediary factor 2 and p300 recruitment to glucocorticoid-responsive promoters. Hic-5/ARA55 is also associated with the corepressor, nuclear receptor corepressor, on glucocorticoid-responsive promoters in cells not exposed to glucocorticoids. These results suggest that Hic-5/ARA55 is required for optimal GR-mediated gene expression possibly by providing a scaffold that organizes or stabilizes coactivator complexes at some hormone-responsive promoters.
Heitzer
M D
MD
Department of Cell Biology and Physiology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261, USA.
DeFranco
D B
DB
D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism*; D047369:Chromatin Immunoprecipitation; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism; D003598:Cytoskeletal Proteins / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D016762:Genes, fos / Q000502:physiology; D005938:Glucocorticoids / Q000502:physiology; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D060588:LIM Domain Proteins; D008324:Mammary Tumor Virus, Mouse / Q000235:genetics; D008565:Membrane Proteins / Q000235:genetics; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D034741:RNA, Small Interfering / Q000235:genetics; D011965:Receptors, Glucocorticoid / Q000378:metabolism*; D011991:Receptors, Virus / Q000235:genetics; D014157:Transcription Factors / Q000378:metabolism; D015533:Transcriptional Activation; D050880:p300-CBP Transcription Factors / Q000378:metabolism
D017362:Cyclic AMP Response Element-Binding Protein; D003598:Cytoskeletal Proteins; D004268:DNA-Binding Proteins; C111417:Fam89b protein, mouse; D005938:Glucocorticoids; D047908:Intracellular Signaling Peptides and Proteins; D060588:LIM Domain Proteins; D008565:Membrane Proteins; D034741:RNA, Small Interfering; D011965:Receptors, Glucocorticoid; D011991:Receptors, Virus; C490351:TGFB1I1 protein, human; D014157:Transcription Factors; D050880:p300-CBP Transcription Factors