MIP-1 induces stromal cell RANK ligand expression and osteoclastogenesis.

(A) MIP-1 induction of RANK ligand mRNA expression by a mouse marrow stromal cell line, ST-2. ST-2 cells were cultured with or without recombinant mouse (rm) MIP-1α or MIP-1β at 10 ng/mL in the presence or absence of a suboptimal concentration (0.1 nM) of 1α,25-dihydroxyvitamin D₃. RANK ligand mRNA expression was determined by RNase protection assay as described in “Materials and methods.” The lower panel shows β-actin mRNA expression as a loading control. (B) MIP-1 induction of osteoclast differentiation of C7 in cocultures with ST-2 cells. A mouse preosteoclast cell line, C7, was cocultured with ST-2 cells with or without rmMIP-1α at 10 ng/mL in the presence or absence of 0.1 nM 1α,25-dihydroxyvitamin D₃. Osteoclast differentiation was examined by counting the number of TRAP⁺ MNCs after 8 days of culture as described in “Materials and methods.” Results represent a mean of 5 samples with an error bar of SD. * indicates significantly different from the control culture without treatment (P < .05, ANOVA with Scheffe post hoc tests).