title: Adenosine 5'-triphosphate-dependent vitamin D sterol binding to heat shock protein-70 chaperones.
abstract: Chaperone proteins in the heat shock protein-70 family possess endogenous ATP binding and ATPase activity and interact with intracellular protein substrates in an ATP-dependent manner; the hydrolysis of ATP to ADP results in an increase in the affinity of the chaperone for protein substrates. Heat shock protein-70s can also specifically interact with 25-hydroxylated vitamin D metabolites. Using constitutively expressed heat shock protein-70 (hsc70) as chaperone, here we demonstrate that vitamin D metabolite binding to hsc70 is also ATP dependent. Transient overexpression of an hsc70-green fluorescent protein chimeric construct in primate kidney cells resulted in a 6-fold increase in specific, extractable 25-hydroxyvitamin D(3) binding. When ATPase capability of hsc70 was disabled, this increase was completely blocked. In solution, the binding of 25-hydroxylated vitamin D metabolites to hsc70 was significantly increased (P < 0.01) in the presence of ATP and a nonmetabolizable ATP analog. The ATP-directed increase in specific binding resulted from an increase in the abundance of relatively high-affinity hormone-binding sites (K(d), approximately 0.24 nM). These results suggest that ATP hydrolysis to ADP would favor the release of vitamin D from a donor hsc70 molecule at a time when an hsc70-bound acceptor protein substrate is anchored to the chaperone with relative avidity. We theorize that the endogenous ATPase activity of hsc70 promotes the transfer of vitamin D sterols to other intracellular vitamin D binding proteins, such as the vitamin D receptor and vitamin D hydroxylases, to which hsc70 is known to bind.
authors.affiliation: Burns and Allen Research Institute and Division of Endocrinology, Diabetes, and Metabolism, Cedars-Sinai Medical Center, David Geffen School of Medicine at University of California, Los Angeles, 90048, USA.
authors.forename: Rene
authors.initials: R
authors.lastname: Chun
authors.forename: Mercedes A
authors.initials: MA
authors.lastname: Gacad
authors.forename: Martin
authors.initials: M
authors.lastname: Hewison
authors.forename: John S
authors.initials: JS
authors.lastname: Adams
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism* / Q000494:pharmacology; D000818:Animals; D002460:Cell Line; D049452:Green Fluorescent Proteins / Q000235:genetics; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D008024:Ligands; D018832:Molecular Chaperones / Q000378:metabolism*; D011323:Primates; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D013261:Sterols / Q000378:metabolism*; D014807:Vitamin D / Q000378:metabolism*
chemical_list: D018840:HSP70 Heat-Shock Proteins; D008024:Ligands; D018832:Molecular Chaperones; D011993:Recombinant Fusion Proteins; D013261:Sterols; D014807:Vitamin D; D049452:Green Fluorescent Proteins; D000255:Adenosine Triphosphate