CLONING AND CHARACTERIZATION OF THE MOUSE VITAMIN-D-RECEPTOR PROMOTER

The gene encoding the mouse vitamin D receptor has been cloned. A new exon 1 has been found that changes the numbering established for the h uman VDR gene, Exons 2 and 3 in the human VDR gene (coding for the zin c fingers 1 and 2, respectively) are named exons 3 and 4 in the mouse vitamin D receptor. The 1.5-kb 5'-flanking region of the new exon 1 wa s analyzed and revealed the presence of putative cis-acting elements. Despite the absence of a TATA box, this 5'-flanking region contains se veral characteristics of a GC-rich promoter including four Sp1 sites p resent in tandem and two CCAAT boxes. Interestingly, the Sp1 site that is the most proximal to the new exon 1 overlaps a perfect site for Kr ox-20/24. Krox-20 is a transcription factor involved in brain developm ent, and also in bone remodeling, In luciferase reporter gene expressi on assays, we showed that sequences from this 5'-flanking region elici t high transactivation activity, Furthermore, in the NIH 3T3 cell line , a 3- to 5-fold increase in response to forskolin treatment (an activ ator of adenylate cyclase and in turn of protein kinase A pathway) was observed.