1,25-Dihydroxyvitamin D3-inducible catabolism of vitamin D metabolites in mouse intestine.
The 1,25-dihydroxyvitamin D3 [1,25(OH)2D3]-inducible C-24 oxidation pathway is a major catabolic pathway for vitamin D metabolites in target tissues. Using intestinal homogenates derived from 1,25(OH)2D3-treated mice, we examined the time course of induction, the intestinal localization and kinetics of induced enzyme activity, as well as the sensitivity of induction to transcriptional inhibitors actinomycin D and alpha-amanitin. 24-Hydroxylation of 500 nM 3H-labeled 25-hydroxyvitamin D3 [25(OH)D3] and 50 nM 3H-labeled 1,25(OH)2D3 by duodenal homogenates was detected 1 h after 1,25(OH)2D3 treatment; C-24 oxidation products of 25(OH)D3 and 1,25(OH)2D3 peaked at approximately 6 h and remained elevated for 17 h. Induced enzyme activity was localized to the mitochondrial fraction, was highest in duodenum, and was also detected in jejunum, ileum, and colon. The apparent Michaelis constant of the induced duodenal enzyme for 25(OH)D3 was 451 nM and for 1,25(OH)2D3 was 14 nM. Induction of intestinal catabolic activity was inhibited by prior treatment of 1,25(OH)2D3-injected mice with either actinomycin D or alpha-amanitin. The characteristics of the 1,25(OH)2D3-inducible C-24 oxidation pathway in the intestine resembled that of the kidney. However, the catabolic pathway was constitutively expressed only in the kidney. We conclude that 1,25(OH)2D3-inducible degradation of vitamin D metabolites occurs throughout the length of mouse intestine and can be prevented by transcriptional inhibitors, suggesting that mRNA synthesis is required for the induction process.
Tomon
M
M
Department of Pediatrics, McGill University-Montreal Children's Hospital Research Institute, Quebec, Canada.
Tenenhouse
H S
HS
Jones
G
G
D000469:Alkaline Phosphatase / Q000378:metabolism; D000546:Amanitins / Q000494:pharmacology; D000818:Animals; D002117:Calcitriol / Q000494:pharmacology*; D002762:Cholecalciferol / Q000378:metabolism*; D003577:Cytochrome P-450 Enzyme System; D003609:Dactinomycin / Q000494:pharmacology; D007413:Intestinal Mucosa / Q000187:drug effects / Q000378:metabolism*; D007421:Intestine, Small / Q000378:metabolism; D007672:Kidney Cortex / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008928:Mitochondria / Q000378:metabolism; D013250:Steroid Hydroxylases / Q000378:metabolism*; D013384:Succinate Cytochrome c Oxidoreductase / Q000378:metabolism; D065668:Vitamin D3 24-Hydroxylase
D000546:Amanitins; D002762:Cholecalciferol; D003609:Dactinomycin; D003577:Cytochrome P-450 Enzyme System; D013384:Succinate Cytochrome c Oxidoreductase; D013250:Steroid Hydroxylases; D065668:Vitamin D3 24-Hydroxylase; D000469:Alkaline Phosphatase; D002117:Calcitriol