REGULATION OF MURINE OSTEOBLAST MACROPHAGE-COLONY-STIMULATING FACTOR PRODUCTION BY 1,25(OH)(2)D-3

Macrophage colony stimulating factor (MCSF) is important for formation of osteoclasts. We investigated the ability of 1,25(OH)(2)D-3 to regu late osteoblast production of MCSF. Mouse calvarial osteoblasts were c ultured for 2 days +/- 1,25(OH)(2)D-3. Since 1,25(OH)(2)D-3 decreased osteoblast proliferation by 17.6 +/- 1% at 10 nM and 11 +/- 4% at 1 nM , the effect of growth rate on MCSF secretion was examined. Limiting c ell proliferation by serum did not affect MCSF production. 1,25(OH)(2) D-3 (1 nM) increased MCSF production (U/10(5) cells) maximally by 68 /- 33% (n = 3) with an ED(50) for 1,25(OH)(2)D-3 of 5 x 10(-11) M. To investigate effects of 1,25(OH)(2)D-3 on MCSF gene regulation, RT-PCR primers were designed to identify the mRNA coding for the membrane-bou nd isoform of MCSF. Simultaneous RT-PCR of glyceraldehyde-phosphate de hydrogenase (GAP) allowed semiquantitative assessment of MCSF mRNA bet ween treatment groups expressed as the MCSF/GAP RT-PCR product ratio b oth MCSF and GAP (+) primers were labeled with P-32-ATP for phosphorim age quantitation. The membrane-bound MCSF/GAP PCR product ratio was no t affected by proliferative rate when growth was limited by [serum]. T he MCSF/GAP RT-PCR product ratio was dose dependently increased by 1,2 5(OH)(2)D-3, maximally at 1 nM at 2.2 +/- 0.2 = fold (n = 10). 1,25(OH )(2)D-3, also increased the expression of an RT-PCR MCSF/GAP product r atio which represented the secreted isoform of MCSF. The ability of 1, 25(OH)(2)D-3 to pretranslationally regulate expression of membrane-bou nd osteoblast MCSF may be important in osteoblast:osteoclast interacti ons.