title: Effects of 1,25-dihydroxyvitamin D3 and phorbol ester on 25-hydroxyvitamin D3 24-hydroxylase cytochrome P450 messenger ribonucleic acid levels in primary cultures of rat renal cells.
abstract: The renal 25-hydroxyvitamin D3 24-hydroxylase enzyme, which may be the starting point in the catabolic pathway for vitamin D metabolism, is markedly induced by 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3], the hormonal form of vitamin D. The purpose of this study was to investigate the regulation of the cytochrome P450 component of this enzyme (P450cc24) by 1,25-(OH)2D3 and phorbol 12-myristate 13-acetate (TPA). P450cc24 messenger RNA (mRNA) levels were measured using the full-length rat complementary DNA probe (p108). In primary cultures of rat renal tubular cells, 1,25-(OH)2D3 produced a 26-fold increase in P450cc24 mRNA which was detectable at 4 h, maximal at 24 h, and returned almost to baseline by 48 h. The induction was inhibited by actinomycin D, 5,6-dichloro-1-b-D-ribofuranosyl benzimidazole (DRB), and cycloheximide, and it was specific for vitamin D compounds containing a 1-hydroxyl group. TPA alone had no effect, but TPA in the presence of 1,25-(OH)2D3 produced an increase in P450cc24 mRNA within 30 min, and this increase peaked at 2 h. TPA also shifted the dose-response curve of 1,25-(OH)2D3 to the left, so that 1,25-(OH)2D3 was effective at a concentration as low as 1 nM. In the same experiments, TPA increased c-fos mRNA levels, and this increase was accelerated by 1,25-(OH)2D3. These studies suggest that the induction of P450cc24 mRNA by 1,25-(OH)2D3 is a receptor-mediated genomic event and that this induction may account for the stimulation of 24-hydroxylase enzyme activity by 1,25-(OH)2D3. In addition, TPA accelerates the effect of 1,25-(OH)2D3 by a mechanism which may involve protein kinase C.
authors.affiliation: Geriatric Research, Education, and Clinical Center, Veterans Affairs Medical Center, St. Louis, Missouri 63125.
authors.forename: M L
authors.initials: ML
authors.lastname: Chen
authors.forename: M A
authors.initials: MA
authors.lastname: Boltz
authors.forename: H J
authors.initials: HJ
authors.lastname: Armbrecht
mesh_terms: D000818:Animals; D002117:Calcitriol / Q000494:pharmacology*; D002478:Cells, Cultured; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics*; D004305:Dose-Response Relationship, Drug; D007684:Kidney Tubules / Q000166:cytology / Q000378:metabolism*; D008297:Male; D012313:RNA / Q000378:metabolism*; D051381:Rats; D013250:Steroid Hydroxylases / Q000235:genetics*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D013997:Time Factors; D065668:Vitamin D3 24-Hydroxylase
chemical_list: D012313:RNA; D003577:Cytochrome P-450 Enzyme System; D013250:Steroid Hydroxylases; D065668:Vitamin D3 24-Hydroxylase; D002117:Calcitriol; D013755:Tetradecanoylphorbol Acetate