title: Novel N-terminal variant of human VDR.
abstract: The importance of N-terminal regions of nuclear hormone receptors in transcriptional regulation is increasingly recognized. As variant VDR gene transcripts indicated possible N-terminally extended receptors, we investigated their natural occurrence, transactivation capacity, and subcellular localization. A novel 54-kDa VDRB1 protein, in addition to the previously recognized 48-kDa VDRA form, was detected in human kidney tissue as well as in osteoblastic (MG63), intestinal (Int-407, DLD-1, and COLO 206F), and kidney epithelial (786) human cell lines by Western blots using isoform-specific and nonselective anti-VDR antibodies. VDRB1 was present at approximately one-third the level of VDRA. Isoform-specific VDRB1 expression constructs produced lower ligand-dependent transactivation than VDRA when transiently transfected with a vitamin D-responsive promoter into cell lines with low endogenous VDR. Intracellular localization patterns of the green fluorescent protein-tagged VDR isoforms differed. VDRB1 appeared as discrete intranuclear foci in the absence of 1,25-dihydroxyvitamin D3, whereas VDRA produced diffuse nuclear fluorescence. After 1,25-dihydroxyvitamin D3 treatment, both VDR isoforms exhibited similar diffuse nuclear signal. In the absence of 1,25-dihydroxyvitamin D3, the VDRB1 foci partially colocalized with SC-35 speckles and a subset of promyelocytic leukemia nuclear bodies. These data provide the first evidence of VDRB1, a novel N-terminally variant human VDR that is expressed at a level comparable to VDRA in human tissue and cell lines. It is characterized by reduced transactivation activity and a ligand-responsive speckled intranuclear localization. The intranuclear compartmentalization and altered functional activity of VDRB1 may mediate a specialized physiological role for this receptor isoform.
authors.affiliation: Bone and Mineral Research Program, Garvan Institute of Medical Research, Sydney, New South Wales, 2010 Australia.
authors.forename: K L
authors.initials: KL
authors.lastname: Sunn
authors.forename: T A
authors.initials: TA
authors.lastname: Cock
authors.forename: L A
authors.initials: LA
authors.lastname: Crofts
authors.forename: J A
authors.initials: JA
authors.lastname: Eisman
authors.forename: E M
authors.initials: EM
authors.lastname: Gardiner
mesh_terms: D002460:Cell Line; D017930:Genes, Reporter; D006801:Humans; D008856:Microscopy, Fluorescence; D009363:Neoplasm Proteins / Q000378:metabolism; D009687:Nuclear Proteins / Q000378:metabolism; D000071156:Promyelocytic Leukemia Protein; D020033:Protein Isoforms / Q000378:metabolism; D018167:Receptors, Calcitriol / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012261:Ribonucleoproteins; D000068103:Serine-Arginine Splicing Factors; D015534:Trans-Activators / Q000235:genetics; D014157:Transcription Factors / Q000378:metabolism; D014158:Transcription, Genetic; D025521:Tumor Suppressor Proteins
chemical_list: D009363:Neoplasm Proteins; D009687:Nuclear Proteins; D000071156:Promyelocytic Leukemia Protein; D020033:Protein Isoforms; D018167:Receptors, Calcitriol; D011993:Recombinant Fusion Proteins; D012261:Ribonucleoproteins; D015534:Trans-Activators; D014157:Transcription Factors; D025521:Tumor Suppressor Proteins; C068921:p80-coilin; C070576:PML protein, human; C073288:SRSF2 protein, human; D000068103:Serine-Arginine Splicing Factors