The Mouse Vitamin D Receptor Is Mainly Expressed through an Sp1-Driven Promoter in Vivo

The availability of the mouse vitamin D receptor (mVDR) gene has allowed a characterization of a TATA-less promoter containing a cluster of four Sp1 sites named Sp1-1, Sp1-2, Sp1-3, and Sp1-4 (F. Jehan and H. F. DeLuca, 1997, Proc. Natl. Acad. Sci. USA 94, 10138–10143). By means of primer extension analysis, S1 nuclease mapping and ribonuclease protection assay, the start site has been deduced, as has the existence of other minor transcription start sites. Initiation of transcription at the major site is located 4 bp upstream of the 5′ end of the mVDR cDNA sequence and very close to the putative Sp1 sites. A second minor promoter might exist between exon 1 and exon 2 of the mVDR gene. The nucleotide sequence of the Sp1 region is well conserved between the mouse, the human, and the chicken VDR genes, suggesting an important role for these Sp1 sites. Gel shift analysis of the four Sp1 sites of the mVDR promoter has confirmed specific binding complexes to Sp1-1, Sp1-2, and Sp1-4 (Sp1-3 rather binds an unknown complex that is unable to bind the canonical Sp1 GGGGCGGGGC). Deletion or mutation of all the Sp1 sites eliminates promoter activity. However, mutation or deletion of individual Sp1 sites did not dramatically change the promoter activity, except for mutation of Sp1-3 that increases promoter activity. We, therefore, conclude that the mVDR promoter is controlled by the Sp1 sites and is the main VDR promoter in intestine and kidney.