title: Modulation of vitamin d receptor activity by the corepressor hairless: differential effects of hairless isoforms.
abstract: The vitamin D receptor (VDR) and its corepressor Hairless (HR) are thought to regulate key steps in the hair cycle because mutations in VDR or HR cause alopecia in humans and mice. Many mammalian cells express two major HR isoforms due to alternative splicing of exon 17. HR isoform-a encodes an 1189-amino acid protein (full-length HR), and isoform-b encodes an 1134-amino acid protein (HRDelta1072-1126). We demonstrated that both HR isoforms are expressed in primary human keratinocytes and in the human keratinocyte cell line HaCaT. In transfected COS-7 cells, the full-length HR repressed VDR-mediated transactivation. In contrast, HRDelta1072-1126 failed to suppress and even stimulated VDR-mediated transactivation. In coimmunoprecipitation, both HR isoforms interacted with the VDR, but only the full-length HR interacted with histone deacetylase 1 (HDAC1). Alanine mutagenesis of two conserved glutamic acids residues (E1100A/E1101A) encoded by exon 17 completely eliminated HR corepressor activity and interactions with HDAC1. When the two HR isoforms were coexpressed in COS-7 cells, the corepressor activity of the full-length HR was not antagonized by the HRDelta1072-1126 isoform. When transfected into HaCaT cells, the full-length HR inhibited endogenous CYP24A1 basal gene expression as well as 1,25-dihydroxyvitamin D3-stimulated CYP24A1 expression. HRDelta1072-1126 failed to suppress basal or 1,25-dihydroxyvitamin D3-stimulated CYP24A1 gene expression. In conclusion, we have demonstrated that both HR isoforms are expressed in keratinocytes and that the HRDelta1072-1126 isoform lacks corepressor activity and is unable to bind HDACs. HRDelta1072-1126 may function as a coactivator in some settings by inhibiting HDAC recruitment to the VDR transcriptional complex.
authors.affiliation: S025 Division of Endocrinology, Gerontology, and Metabolism, Stanford University School of Medicine, 300 Pasteur Drive, Stanford, California 94305-5103, USA. pjmalloy@stanford.edu
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Malloy
authors.forename: Jining
authors.initials: J
authors.lastname: Wang
authors.forename: Kristin
authors.initials: K
authors.lastname: Jensen
authors.forename: David
authors.initials: D
authors.lastname: Feldman
mesh_terms: D000505:Alopecia / Q000235:genetics / Q000378:metabolism; D000818:Animals; D019556:COS Cells; D002478:Cells, Cultured; D002522:Chlorocebus aethiops; D056284:Histone Deacetylase 1; D006655:Histone Deacetylases / Q000235:genetics / Q000378:metabolism; D006801:Humans; D015603:Keratinocytes / Q000378:metabolism; D011485:Protein Binding; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D018167:Receptors, Calcitriol / Q000235:genetics / Q000378:metabolism*; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D015533:Transcriptional Activation
chemical_list: C490267:HR protein, human; D020033:Protein Isoforms; D018167:Receptors, Calcitriol; D012097:Repressor Proteins; D014157:Transcription Factors; C110550:HDAC1 protein, human; D056284:Histone Deacetylase 1; D006655:Histone Deacetylases