Abstract
We have examined the 5' flanking region of the mouse calbindin-D28k gene and identified a 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3]-responsive element by deletion mutant analysis of the native promoter as well as by studies with a heterologous thymidine kinase (TK) promoter. The segment between residues -200 and -169 was found to confer a dose-dependent 1,25-(OH)2D3 responsiveness through the TK promoter in Ros 17/2.8 cells as well as in CV-1 cells cotransfected with pAV-hVDR (human vitamin D receptor expression vector). This region contains sequences homologous to the rat osteocalcin vitamin D response element (VDRE). Incubation of this element with nuclear extracts from 1,25-(OH)2D3-treated Ros 17/2.8 cells or from 1,25-(OH)2D3-treated COS cells that had been transfected with pAV-hVDR resulted in a specific protein-DNA interaction. In addition to 1,25-(OH)2D3, sodium butyrate, a differentiating agent, has also been found to modulate expression of calbindin-D28k. Deletion analysis of the mouse calbindin-D28k promoter as well as studies with a heterologous TK promoter resulted in identification of a butyrate-responsive element between -180 and -150 that was found to bind specifically to nuclear factors from butyrate-treated Ros 17/2.8 cells. This butyrate-responsive element may represent a genetic element acted upon by enhancer binding proteins. In summary, the 5' flanking region of the mouse calbindin-D28k gene contains responsive elements that interact with nuclear factors and may mediate, at least in part, the enhanced expression of this gene by 1,25-(OH)2D3 and butyrate.