Vitamin D receptor interacts with DnaK heat shock protein 70: Identification of DnaK interaction site on vitamin D receptor

Vitamin D receptor (VDR) regulates the expression of vitamin D-dependent ge nes upon binding to its cognate ligand, 1 alpha,25-dihydroxyvitamin D-3 (1, 25(OH)(2)D-3). This process represents a complex interaction of ligand-boun d VDR with nuclear proteins like retinoid X receptor, nuclear accessory fac tors, and regulatory elements of the target gene. Expression of full-length VDR in Escherichia coli revealed that VDR binds DnaK, a member of heat-sho ck protein (Hsp) family, with high affinity. By systematic N-terminal trunc ation of VDR, the interaction site of DnaK on VDR was localized within a 17 -amino-acid segment (105-122) representing the "hinge region" between the D NA-binding and hormone-binding domains of VDR. The putative DnaK-binding si te was further localized between residues 105 to 100 of VDR by using bindin g-energy-minimization studies. The interaction of DnaK with VDR did not inf luence the binding of 1,25(OH)(2)D-3 or nuclear accessory factor(s) to VDR. Furthermore, bovine brain Hsp 70, similar to DnaK, interacted with VDR-lig and-binding domain (105-427). These results suggest that DnaK/Hsp 70 may in teract with VDR prior to the activation of the latter by 1,25(OH)(2)D-3-bin ding. (C) 1999 Academic Press.