title: Proteins in the heat shock-70 family specifically bind 25-hydroxyvitamin D3 and 17beta-estradiol.
abstract: Most New World primates evolved to express a form of compensated resistance to steroid hormones from the gonads and adrenal glands as well as to the hydroxylated vitamin D3 prohormone, 25-hydroxyvitamin D3 (25OHD3), and the vitamin D hormone 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] originating from the liver and kidney, respectively. We recently demonstrated that this form of resistance is associated with the overexpression of a novel member of the 70-kDa heat shock protein (hsp-70) molecular chaperone family, which we have termed the intracellular vitamin D binding protein (IDBP). In the current report we more closely examine the ligand-binding capability of purified IDBP and two other mammalian hsp-70 family members, heat-inducible (hsp-70) and constitutively expressed (hsc-70) hsp-70 proteins. Purified IDBP, hsp-70, and hsc-70 all bound 25OHD3 with relatively high affinity; the mean Kd for 25OHD3 ranged from 0.5-2.2 nmol/L (rank order: IDBP > or = hsp-70 > or = hsc-70). By Scatchard analysis, high affinity, specific binding of 1,25-(OH)2D3 was not reproducibly observed for any of the three members of the hsp-70 family. Unlike purified IDBP, hsc-70 and hsp-70 were also competent binders of the gonadal steroid 17beta-estradiol (mean Kd for 25OHD3, 2.5 and 6.6 nmol/L by hsc-70 and hsp-70, respectively), but not of two other gonadal hormones, progesterone and testosterone. These data suggest that IDBP is relatively specific for 25OHD3 and that additional hsp-70-like binding proteins are present in unpurified New World primate cell extracts that are specific for 1-hydroxylated vitamin D metabolites as well as other gonadal steroid hormones.
authors.affiliation: Burns and Allen Research Institute and Division of Endocrinology and Metabolism, Cedars-Sinai Medical Center, University of California School of Medicine, Los Angeles 90048, USA.
authors.forename: M A
authors.initials: MA
authors.lastname: Gacad
authors.forename: J S
authors.initials: JS
authors.lastname: Adams
mesh_terms: D001667:Binding, Competitive; D002112:Calcifediol / Q000378:metabolism*; D004958:Estradiol / Q000378:metabolism*; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism*; D006801:Humans; D011485:Protein Binding; D014407:Tumor Cells, Cultured; D014809:Vitamin D-Binding Protein / Q000378:metabolism*
chemical_list: D018840:HSP70 Heat-Shock Proteins; D014809:Vitamin D-Binding Protein; D004958:Estradiol; D002112:Calcifediol