Mechanistic studies to evaluate the enhanced antiproliferation of human keratinocytes by 1alpha,25-dihydroxyvitamin D(3)-3-bromoacetate, a covalent modifier of vitamin D receptor, compared to 1alpha,25-dihydroxyvitamin D(3).
1alpha,25-Dihydroxyvitamin D(3)-3-bromoacetate (1, 25(OH)(2)D(3)-3-BE), an affinity labeling analog of 1alpha, 25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)), displayed stronger antiproliferative activities than 1,25(OH)(2)D(3) at 10(-10)-10(-6) M dose levels in cultured human keratinocytes (CHK). Additionally, preincubation of the cells with 10(-6) M 1,25(OH)(2)D(3), followed by treatment with various doses of 1,25(OH)(2)D(3)-3-BE, resulted in a significantly stronger antiproliferative activity by the mixture than individual reagents at every dose level. To search for a mechanism of this observation, we determined that [(14)C]1, 25(OH)(2)D(3)-3-BE covalently labeled human recombinant 1alpha, 25-dihydroxyvitamin D(3) receptor (reVDR) swiftly (<1 min) with a 1:1 stoichiometry and induced conformational changes (in VDR) that are different from 1,25(OH)(2)D(3), by limited tryptic digestion. Furthermore, a protein band, corresponding to reVDR, was specifically labeled by [(14)C]1,25(OH)(2)D(3)-3-BE in CHK extract, indicating that VDR is the main target of [(14)C]1, 25(OH)(2)D(3)-3-BE. The above-mentioned observations suggest that a rapid covalent labeling of VDR in CHK might alter the interaction between the holo-VDR and 1,25(OH)(2)D(3)-controlled genes. Furthermore, we observed that 1,25(OH)(2)D(3)-3-BE significantly decreased the binding of VDR to human osteocalcin vitamin D responsive element (hOCVDRE), as well as the dissociation rate of VDR from hOCVDRE, compared with 1,25(OH)(2)D(3) in COS-1 cells, transiently transfected with a VDR construct. Additionally, 1, 25(OH)(2)D(3)-3-BE was found to be more potent in inducing 1alpha, 25-dihydroxyvitamin D(3)-24-hydroxylase (24-OHase) promoter activity and mRNA expression in keratinocytes. The accumulation of 24-OHase message was also prolonged by the analog. Collectively these results indicated that rapid covalent labeling of VDR in keratinocytes (by 1, 25(OH)(2)D(3)-3-BE) might result in the conversion of apo-VDR to a holo-form, with a conformation that is different from that of the 1, 25(OH)(2)D(3)-VDR complex. This resulted in an enhanced stability of the 1,25(OH)(2)D(3)-3-BE/VDR-VDRE complex and contributed to the amplified antiproliferative effect of 1,25(OH)(2)D(3)-3-BE in keratinocytes.
Chen
M L
ML
Endocrine Section, Boston University School of Medicine, Boston, Massachusetts, 02118, USA.
Ray
S
S
Swamy
N
N
Holick
M F
MF
Ray
R
R
D016475:3T3 Cells; D000818:Animals; D019556:COS Cells; D002117:Calcitriol / Q000031:analogs & derivatives* / Q000494:pharmacology*; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D006801:Humans; D015603:Keratinocytes / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D007700:Kinetics; D051379:Mice; D011401:Promoter Regions, Genetic; D018167:Receptors, Calcitriol / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D011994:Recombinant Proteins / Q000187:drug effects / Q000378:metabolism; D013250:Steroid Hydroxylases / Q000235:genetics; D014158:Transcription, Genetic / Q000187:drug effects; D014162:Transfection; D065668:Vitamin D3 24-Hydroxylase
C104313:1,25-dihydroxyvitamin D3-3-bromoacetate; D018167:Receptors, Calcitriol; D011994:Recombinant Proteins; D003577:Cytochrome P-450 Enzyme System; D013250:Steroid Hydroxylases; D065668:Vitamin D3 24-Hydroxylase; D002117:Calcitriol