The 25-hydroxyvitamin D3 1α-hydroxylase, also referred to as CYP27B1, is a mitochondrial cytochrome P450 enzyme that catalyzes the biosynthesis of 1α, 25-dihydroxyvitamin D3 (1α,25(OH)2D3) from 25-hydroxyvitamin D3 in renal proximal tubular cells. Recently, human, mouse, and rat CYP27B1 cDNA have been cloned, however the gene regulation has not been fully elucidated. In the present study, porcine CYP27B1 cDNA was cloned, and the effects of cAMP and vitamin D3 on the regulation of CYP27B1 mRNA expression in LLC- PK1 cells were examined. PCR cloning revealed that porcine CYP27B1 cDNA consisted of 2316 bp, encoding a protein of 504 amino acids. The deduced amino acid sequence showed over 80% identity to the human, mouse, and rat enzyme. LLC-PK1 cells were incubated with humoral factors, and expression of CYP27B1 mRNA was measured by a quantitative reverse transcription-PCR. At the completion of 3-, 6-, 12-, and 24-h incubations, 500 μmol/L 8-bromo-cAMP had significantly increased CYP27B1 mRNA expression (260 to 340%). The adenylate cyclase activator forskolin at 50 μmol/L also had a stimulatory effect at 6 h. (190%). Moreover, the protein kinase A inhibitor H-89 reduced the cAMP effect. On the other hand, 1α,25(OH)2D3 had no effect on CYP27B1 mRNA expression at 10 and 100 nmol/L, whereas expression of 25-hydroxyvitamin D3 24-hydroxylase (CYP24) mRNA was markedly increased by 1α,25(OH)2D3. These findings suggest that LLC-PK1 cells express CYP27B1 mRNA, and that cAMP is an upregulating factor of the CYP27B1 gene in vitro.
|Number of pages||8|
|Journal||Journal of the American Society of Nephrology|
|Publication status||Published - 1999 May|
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