FIGURE 2.

MN1 knock-out osteoblasts have diminished VDR-mediated transcriptional responses. Subconfluent WT and MN1 KO primary osteoblasts were transiently transfected with a 1.2-kb human 24-hydroxylase promoter reporter (cyp24(-1200)-luc in A) or a multicopy VDRE-driven reporter (VDRE⁴-TATA-luc in B). Cells were treated with the indicated concentration of 1,25(OH)₂D₃ for 24 h, and the normalized luciferase activity was measured as described under “Experimental Procedures.” Data represent the mean ± S.D. (n = 4 in each group). C, RNA was isolated from MN1 WT or KO cells that were treated ethanol vehicle (−) or 10 nm 1,25(OH)₂D₃ (+) for 24 h. The expression of 24-hydroxylase and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) was examined by Northern blot analysis.