FIGURE 4.

Mutant Brm or BRG1, which act as dominant negative inhibitors, inhibit calcitonin induction of 1α(OH)ase transcription. AOK-B50 cells were co-transfected with 0.3 μg mouse 1α(OH)ase promoter (–85/+22) and Brm-DN expression vectors (0.05, 0.1 μg) (A) or BRG1-DN (0.1 μg) (B). After 24 h, cells were treated with vehicle or 100 nm calcitonin (CT) for another 24 h. 1α(OH)ase promoter activity was measured by firefly luciferase activity/protein concentration and represented as -fold induction (mean ± S.E.; n = at least three observations per group) by comparison to basal levels. Similar results were obtained using the –1651/+22 promoter construct (not shown). Note that there was no effect of 0.1 μg of Brm-DN or 0.1 μg of BRG1-DN on basal levels of 1α(OH)ase transcription (open bar, Brm-DN (A); open bar, BRG1-DN (B)).