Stimulation of intestinal calcium-binding-protein mRNA synthesis in the nucleus of vitamin D-deficient chicks by 1,25-dihydroxycholecalciferol

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Abstract
Stimulation of intestinal Ca transport by the hormone 1,25-dihydroxycholecalciferol [DHCC] appears to involve RNA transcriptions and the synthesis of new proteins. Although 1 of these proteins has been identified as Ca-binding protein, no RNA molecules specifically induced by the hormone in the nucleus have been identified. Nuclear RNA from intestine of vitamin D-deficient chicks before and at various time intervals after treatment with the hormone or cholecalciferol was tested for its ability to code for Ca-binding protein in a cell-free system. Ca-binding-protein mRNA could only just be detected in the intestinal nuclei 2 h after dosing with these steroids which is the same time that it was 1st observed in the polyribosomes. Thus DHCC induces the production of new Ca-binding protein by stimulating the formation and rapid release from the nucleus of new mRNA molecules for this protein. Polyribosomal translation of the mRNA continued only as long as it was being synthesized, and the maximum rate of synthesis following a pulse dose of 125 ng of the hormone was the same as that observed after prolonged stimulation with cholecalciferol. The possibility that other DHCC-dependent events may be occurring in the nucleus in the lag period between accumulation of the hormone in the intestine and the appearance of active Ca-binding-protein mRNA, and that these may ultimately control the synthesis of that mRNA, is discussed.

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