The rapid nongenomic actions of 1 alpha,25-dihydroxyvitamin D3 modulate the hormone-induced increments in osteocalcin gene transcription in osteoblast-like cells.
We have previously shown that one of the rapid nongenomic actions of 1 alpha,25-dihydroxyvitamin D3 (1 alpha,25-(OH)2D3), the increase in intracellular calcium (Ca2+), accompanies the increased osteocalcin (OC) mRNA steady-state levels in rat osteosarcoma cells. To determine the functional significance of the nongenomic actions, we have measured changes in intracellular Ca2+ as an indicator of the rapid effects and have assessed the effect of inhibition of the rapid increase in cellular Ca2+ by the inactive epimer, 1 beta, 25-dihydroxyvitamin D3 (1 beta,25-(OH)2D3), on OC mRNA steady-state levels and transcription. 1 beta,25-dihydroxyvitamin D3 inhibited 1 alpha,25-(OH)2D3 induced increases in intracellular Ca2+ and OC mRNA transcription at 1 hr and OC mRNA steady state levels at 3 hr. 1 beta,25-Dihydroxyvitamin D3 did not alter the binding of the vitamin D receptor complex to the vitamin D responsive element of the OC gene. The results demonstrate the functional importance of the rapid, nongenomic actions of 1 alpha,25-(OH)2D3 in the genomic activation of the OC gene by the hormone in rat osteoblast-like cells, perhaps by modifying subtle structural and/or functional properties of the vitamin D-receptor DNA complex or by affecting other protein DNA interactions that support OC gene transcription.
Baran
D T
DT
Department of Medicine, University of Massachusetts Medical Center, Worcester 01655.
Sorensen
A M
AM
Shalhoub
V
V
Owen
T
T
Stein
G
G
Lian
J
J
D000818:Animals; D015152:Blotting, Northern; D002117:Calcitriol / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D002413:Cations, Divalent; D006728:Hormones / Q000378:metabolism*; D010006:Osteoblasts / Q000378:metabolism*; D015675:Osteocalcin / Q000235:genetics*; D012516:Osteosarcoma; D012333:RNA, Messenger; D051381:Rats; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured
D002413:Cations, Divalent; D006728:Hormones; D012333:RNA, Messenger; D015675:Osteocalcin; D002117:Calcitriol; D002118:Calcium