Identification of a specific binding protein for 1 alpha,25-dihydroxyvitamin D3 in basal-lateral membranes of chick intestinal epithelium and relationship to transcaltachia.
The steroid hormone 1 alpha,25-dihydroxyvitamin D3 (1 alpha,25-(OH)2D3) elicits biological responses by both genomic and nongenomic pathways. This report describes purification of a receptor for 1 alpha,25-(OH)2D3 (VDR) located in the basal-lateral membrane (BLM) of vitamin D-replete chick intestinal epithelium, which is implicated in the nongenomic stimulation of calcium transport (transcaltachia). The BLM-VDR exhibited saturable binding for [3H]1,25-(OH)2D3 (KD = 0.72 x 10(-9)M, Bmax = 0.24 pmol/mg of protein). A 4500-fold purification of the BLM-VDR receptor was achieved. In addition, saturable binding was observed for [3H]24R,25-(OH)2D3 at physiologically relevant levels (KD = 19 x 10(-9) M, Bmax = 2.4 pmol/mg of protein) to a component apparently distinct from the 1 alpha,25-(OH)2D3 BLM-VDR. A functional correlation between the BLM-VDR and transcaltachia was observed in three experimental situations: (i) vitamin D deficiency, which suppresses transcaltachia, resulted in reduced specific [3H]1 alpha,25-(OH)2D3 binding in the BLM-VDR, relative to corresponding fractions from vitamin D-replete chicks; (ii) the BLM-VDR exhibited down-regulation of specific [3H]1 alpha,25-(OH)2D3 binding following exposure to nonradioactive 1 alpha,25-(OH)2D3; and (iii) the relative potencies of two "6-s-cis" analogs of 1 alpha,25-(OH)2D3 to initiate transcaltachia and their ability to compete with [3H]1 alpha,25-(OH)2D3 for binding to the BLM-VDR were parallel. The combined results support the existence of a plasmalemal 1 alpha,25-(OH)2D3 receptor which is a prime candidate for signal transduction in transcaltachia.
Nemere
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Department of Biochemistry, University of California, Riverside 92521.
Dormanen
M C
MC
Hammond
M W
MW
Okamura
W H
WH
Norman
A W
AW
D000818:Animals; D001667:Binding, Competitive; D001692:Biological Transport; D002117:Calcitriol / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000737:chemistry; D016764:Cell Polarity; D002645:Chickens; D007413:Intestinal Mucosa / Q000378:metabolism*; D011485:Protein Binding; D018167:Receptors, Calcitriol / Q000302:isolation & purification* / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000302:isolation & purification* / Q000378:metabolism
D018167:Receptors, Calcitriol; D011956:Receptors, Cell Surface; D002117:Calcitriol; D002118:Calcium