Regulation of vitamin D-responsive gene expression by fluorinated analogs of calcitriol in rat osteoblastic ROB-C26 cells.
We compared the activation of vitamin D-responsive genes by 24,24-difluorocalcitriol [F2-1 alpha,25(OH)2D3] and 26,26,26,27,27,27-hexafluorocalcitriol [F6-1 alpha,25(OH)2D3] with that by calcitriol [1 alpha,25(OH)2D3] in rat osteoblastic ROB-C26 cells. F2-1 alpha,25(OH)2D3 and F6-1 alpha, 25(OH)2D3 were ten times more potent than 1 alpha,25(OH)2D3 in inducing the expression of 1 alpha, 25(OH)2D3-24-hydroxylase (24-OHase) mRNA 6 h after adding vitamin D compounds. The lower affinity of these two fluorinated analogs compared with that of 1 alpha,25(OH)2D3 for vitamin D binding protein in serum (serum DBP) seemed to be partly involved in their increased ability to activate the 24-OHase gene. A time course study revealed that the expression of the 24-OHase and osteopontin mRNAs in the cells incubated with 1 alpha, 25(OH)2D3 and F2-1 alpha,25(OH)2D3 attained maximal levels at 6 h for 24-OHase mRNA and 18 h for osteopontin mRNA, the both decreased thereafter. On the contrary, F6-1 alpha,25(OH)2D3 increased the expression of 24-OHase and osteopontin exponentially until 72 h. While F2-1 alpha,25(OH)2[1 beta-3H]D3 was catabolized quickly by ROB-C26 cells, F6-1 alpha,25(OH)2[1 beta-3H]D3 was slowly and quantitatively converted into putative 26,26,26,27,27,27-hexafluoro-23S-hydroxy[1 beta-3H]calcitriol (F6-1 alpha,23S,25(OH)3[1 beta-3H]D3). This may explain why the time-course profiles of the accumulation of mRNAs for 24-OHase and osteopontin differed in the cells exposed to the fluorinated analogs. In addition to the longer retention, unknown up-regulating mechanisms appeared to be involved in the exponential activation of the 24-OHase and osteopontin genes induced by F6-1 alpha,25(OH)2D3.
Miyamoto
Y
Y
Department of Biochemistry, Showa University, Tokyo.
Shinki
T
T
Ohyama
Y
Y
Kasama
T
T
Iwasaki
H
H
D000818:Animals; D002117:Calcitriol / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology; D002460:Cell Line; D003577:Cytochrome P-450 Enzyme System; D005786:Gene Expression Regulation / Q000187:drug effects*; D010006:Osteoblasts / Q000187:drug effects* / Q000378:metabolism; D051381:Rats; D018167:Receptors, Calcitriol / Q000378:metabolism; D013250:Steroid Hydroxylases / Q000235:genetics; D014158:Transcription, Genetic / Q000187:drug effects*; D014809:Vitamin D-Binding Protein / Q000097:blood; D065668:Vitamin D3 24-Hydroxylase; D005466:Fluorocarbons
D002117:Calcitriol; D003577:Cytochrome P-450 Enzyme System; D018167:Receptors, Calcitriol; D013250:Steroid Hydroxylases; D014809:Vitamin D-Binding Protein; D065668:Vitamin D3 24-Hydroxylase; C023370:24,24-difluoro-1,25-dihydroxyvitamin D3; C040488:26,26,26,27,27,27-hexafluoro-1,25-dihydroxyvitamin D3; D005466:Fluorocarbons