Specific binding to vitamin D response elements of chicken intestinal DNA-binding activity is not related to the vitamin D receptor.

In this report we confirm that the putative vitamin D response element (VDRE), located between -320 and -306 in the chicken calbindin-D28K gene, is not a binding site for the vitamin D3 receptor (VDR). In examining the ability of chicken intestinal nuclear extracts (CINE) to bind known VDREs, we observed a specific VDRE-binding activity, which is distinct from VDR. In fact, VDR-depleted CINE retains the ability to bind the rat osteocalcin VDRE. The VDRE-binding activity binds DNA with high affinity and contacts it at the same guanine residues as VDR. Its specificity in binding structural variants of the AGGTCA repeat is broader than that of VDR, as direct repeats spaced by 3, 4, and 5 base pairs are almost equally effective competitors when added to the probe in molar excess. Palindromic arrangements of the same motif are lower affinity competitors. The retinoid-X receptor is involved in the binding complex, as incubation of CINE with antibody to retinoid-X receptor results in a quantitative supershift. Antibodies to retinoic acid receptors (RAR alpha and -beta), T3 receptor, or chicken ovalbumin up-stream promoter-transcription factor had no apparent effect. These data suggest that species specificity is a relevant aspect of VDR/VDRE recognition, and that a novel factor(s), different from VDR, might be involved in the effect of vitamin D on gene expression.