title: Intracellular vitamin D binding proteins: novel facilitators of vitamin D-directed transactivation.
abstract: Previously recognized intracellular proteins with an affinity for vitamin D metabolites include the vitamin D receptor and the cytochrome P-450-based vitamin D metabolizing mixed-function oxidases. We recently characterized a third set of high-capacity, intracellular vitamin D binding proteins (IDBPs) in the inducible heat shock protein-70 (hsp-70) family. Here we report the cloning and expression of cDNAs coding for two IDBPs. The full-length cDNAs for IDBP-1 and IDBP-2 demonstrated 95% and 94% nucleotide homology, respectively, with the cDNAs for human constitutively expressed heat shock protein 70 (hsc-70) and hsp-70. Transient expression of the IDBP cDNAs in a vitamin D-responsive primate cell line increased extractable 25-hydroxylated vitamin D metabolite-IDBP-binding 25-fold. Transfection experiments also demonstrated that the majority of the constitutively expressed 25-hydroxylated vitamin D metabolite binding activity was attributable to expression of the hsc-70-related IDBP-1 and that metabolite binding activity sublocalized to the highly conserved ATP-binding/ATPase domain of hsp-70s. Stable overexpression of IDBP-1 in wild-type cells enhanced vitamin D-directed responsiveness of endogenous vitamin D-24-hydroxylase, osteopontin, and osteocalcin genes by several-fold over that observed in cells transfected with an empty vector. These results suggest that IDBP-1 facilitates the intracellular localization of active vitamin D metabolites and vitamin D receptor-mediated transactivation.
authors.affiliation: Burns and Allen Research Institute and Division of Endocrinology, Diabetes and Metabolism, Cedars-Sinai Medical Center, University of California Los Angeles School of Medicine, 90048, USA.
authors.forename: S
authors.initials: S
authors.lastname: Wu
authors.forename: S
authors.initials: S
authors.lastname: Ren
authors.forename: H
authors.initials: H
authors.lastname: Chen
authors.forename: R F
authors.initials: RF
authors.lastname: Chun
authors.forename: M A
authors.initials: MA
authors.lastname: Gacad
authors.forename: J S
authors.initials: JS
authors.lastname: Adams
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D019556:COS Cells; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D002460:Cell Line; D002522:Chlorocebus aethiops; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics; D050883:HSC70 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins / Q000737:chemistry / Q000235:genetics; D006801:Humans; D008969:Molecular Sequence Data; D015675:Osteocalcin / Q000235:genetics; D053495:Osteopontin; D011994:Recombinant Proteins / Q000096:biosynthesis; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D012689:Sequence Homology, Nucleic Acid; D012795:Sialoglycoproteins / Q000235:genetics; D013250:Steroid Hydroxylases / Q000235:genetics; D015533:Transcriptional Activation / Q000187:drug effects; D014162:Transfection; D014807:Vitamin D / Q000494:pharmacology*; D014809:Vitamin D-Binding Protein / Q000235:genetics* / Q000378:metabolism*; D065668:Vitamin D3 24-Hydroxylase
chemical_list: D002352:Carrier Proteins; D050883:HSC70 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; C494371:HSPA8 protein, human; D011994:Recombinant Proteins; C506895:SPP1 protein, human; D012795:Sialoglycoproteins; D014809:Vitamin D-Binding Protein; C417526:vitamin D binding protein 1, primate; C417527:vitamin D binding protein 2, primate; D015675:Osteocalcin; D053495:Osteopontin; D014807:Vitamin D; D003577:Cytochrome P-450 Enzyme System; D013250:Steroid Hydroxylases; D065668:Vitamin D3 24-Hydroxylase