Abstract
1,25-Dihydroxyvitamin D3 is believed to mediate the regulation of calcium metabolism by a steroid hormone receptor mechanism. We now demonstrate that phosphorylation of the 1,25-dihydroxyvitamin D3 receptor occurs rapidly in embryonic chick duodenal organ culture in response to 1,25-dihydroxyvitamin D3. Phosphorylation of the receptor is strongly induced within 1 h by 1,25-dihydroxyvitamin D3 and occurs prior to the initiation of calcium uptake or induction of calcium-binding protein in this system. Phosphorylation is not affected by inhibition of protein synthesis by cycloheximide. Since chick duodenal organ culture is a vitamin D-responsive system that closely parallels in vivo rachitic chicken intestine, the occurrence of receptor phosphorylation in response to 1,25-dihydroxyvitamin D3 strongly suggests that it is a physiologically relevant event. In addition, since it occurs prior to the other responses to 1,25-dihydroxyvitamin D3, it appears possible that phosphorylation may play a significant role in the 1,25-dihydroxyvitamin D3 regulation of transcription in the intestine.
Highlights
From the DeDartment of Biochemistrv. .,I Universitv I of
Ds is believed to mediate the regulation of calcium metabolism by a steroid hormone receptor mechanism
This receptor is a member of the steroid/thyroid hormone receptor gene family [2, 3] and is thought to act through a classic steroid hormone mechanism [4]
Summary
From the DeDartment of Biochemistrv. .,I Universitv I of. Wisconsin, Madison, Wkonsin 53iOS college of Agricultural and Life Sciences, Ds is believed to mediate the regulation of calcium metabolism by a steroid hormone receptor mechanism. Phosphorylation of steroid receptors is induced by their respective ligands [7], including a recent report [9] that the number of phosphates per glucocorticoid receptor is increased by agonist. Many functional roles for steroid receptor phosphorylation have been suggested, including the regulation of steroid binding, DNA binding, specificity of DNA binding, nuclear localization, association with heat shock proteins, and association with auxiliary transcription factors [7].
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