FIGURE 5.

C/EBPα overexpression does not modulate actin ring formation but stimulates bone resorption by OCs. A, MBM cells were first treated with M-CSF (10 ng/ml) and RANKL (10 ng/ml) for 2 days (d) before infection with a retrovirus encoding the GFP control (GFP) or FLAG-C/EBPα (C/EBPα) for 1 day. The treatments were then continued for 2 more days. Gene expression was examined by Western blotting using β-actin as a loading control. B, the same set of assays as in A was repeated, and some cells were stained with Alexa Fluor 488-phalloidin (Phalloidin Staining) for actin ring analysis, and others were submitted to AO staining (AO Staining) for analysis of extracellular acidification in three independent experiments. Scale bars = 200 μm. C, the same set of experiments as in A was carried out with cells seeded on bone slices, but after infection, the cells were cultured for 5 more days before SEM analysis of the bone resorption pits. D, quantification for the bone resorption assays shown in C from three independent experiments. The numbers in parentheses show concentration in nanograms per milliliter. Error bars show mean ± S.D. *, p < 0.05.