A specific binding protein/receptor for 1alpha,25-dihydroxyvitamin D(3) is present in an intestinal caveolae membrane fraction.
The steroid hormone 1alpha,25-dihydroxyvitamin D(3) [1alpha,25(OH)(2)D(3)] produces biological responses by interaction with both a well-characterized nuclear receptor (VDR(nuc)) to regulate gene transcription and with an as-yet uncharacterized membrane-associated protein/receptor (VDR(mem)) to generate a variety of rapid, non-genotropic responses. We report for the first time that [3H]1alpha,25(OH)(2)D(3) binds with high affinity to a chick duodenal caveolae-enriched membrane fraction (CMF) isolated without the use of detergents. Caveolae are plasma membrane invaginations implicated in signal transduction and molecular transport processes. Using the CMF fraction as a possible source of VDR(mem), we found that the in vitro binding of [3H]1alpha,25(OH)(2)D(3) was ligand dependent and saturable; the K(D) and B(max) were 1.3+/-0.6nM and 29+/-11fmol 1,25(OH)(2)D(3)/mg protein (n=17), respectively. Immunoblot analysis of the CMF confirms the presence of caveolin-1, a marker protein for membranes with caveolae. Therefore, chick CMF may represent a good source for isolation and characterization of the putative VDR(mem) for 1alpha,25(OH)(2)D(3).
Norman
Anthony W
AW
Department of Biochemistry, University of California, Riverside, CA 92521, USA. Anthony.Norman@ucr.edu
Olivera
Christopher J
CJ
Barreto Silva
Fátima R M
FR
Bishop
June E
JE
D000818:Animals; D015153:Blotting, Western; D002117:Calcitriol / Q000378:metabolism*; D021941:Caveolae / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D002645:Chickens; D007413:Intestinal Mucosa / Q000378:metabolism*; D008297:Male; D011485:Protein Binding; D018167:Receptors, Calcitriol / Q000378:metabolism*
D018167:Receptors, Calcitriol; D002117:Calcitriol