Regulation of Vitamin D-Responsive Gene Expression by Fluorinated Analogs of Calcitriol in Rat Osteoblastic ROB-C26 Cells

• Published in: Journal of biochemistry (Tokyo) Vol. 118; no. 5; pp. 1068 - 1076
• Main Authors: Miyamoto, Yoichi, Shinki, Toshimasa, Ohyama, Yoshihiko, Kasama, Toshio, Iwasaki, Hiroshi, Hosotani, Ryuzo, Sato, Tadashi, Suda, Tatsuo
• Format: Journal Article
• Language: English
• Published: England Oxford University Press 01.11.1995
• Subjects: 24-difluorocalcitriol; 27-hexafluorocalcitriol; Animals; calcitriol; Calcitriol - analogs & derivatives; Calcitriol - metabolism; Calcitriol - pharmacology; calcitriol-24-hydroxylase; Cell Line; Cytochrome P-450 Enzyme System; Gene Expression Regulation - drug effects; Osteoblasts - drug effects; Osteoblasts - metabolism; Rats; Receptors, Calcitriol - metabolism; Steroid Hydroxylases - genetics; Transcription, Genetic - drug effects; Vitamin D-Binding Protein - blood; vitamin D-responsive genes; Vitamin D3 24-Hydroxylase
• ISSN: 0021-924X; 1756-2651
• DOI: 10.1093/jb/118.5.1068

We compared the activation of vitamin D-responsive genes by 24, 24-difluorocalcitriol [F2-1α, 25(OH)2D3] and 26, 26, 26, 27, 27, 27-hexafluorocalcitriol [F6-1α, 25(OH)2D3] with that by calcitriol [1α, 25(OH)2D3] in rat osteoblastic ROB-C26 cells, F2-1α, 25(OH)2D3 and F6-1α, 25(OH)3D3 were ten times more potent than 1α, 25(OH)2D3 in inducing the expression of 1α, 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 1α, 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 1α, 25(OH)2D3 and F2-1α, 25(OH)2D3 attained maximal levels at 6 h for 24-OHase mRNA and 18 h for osteopontin mRNA, the both decreased therafter. On the contrary, F6-1α, 25(OH)2D3 increased the expression of 24-OHase and osteopontin exponentially until 72 h. While F2-1α, 25(OH)2[1β-3H]D3 was estabolized quickly by ROB-C26 cells, F6-1α, 25(OH)2[1β-3H]D3 was slowly and quantitatively converted into putative 26, 26, 26, 27, 27, 27-hexafluoro-23S-hydroxy[1β-3H]calcitriol {F6-1α, 23S, 25(OH)3[1β-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 osteopontion genes induced by F6-1α, 25(OH)2D3.