1,25-DIHYDROXYVITAMIN D3 AND PHORBOL-MYRISTATE ACETATE PRODUCE DIVERGENT PHENOTYPES IN A MONOMYELOCYTIC CELL-LINE

The human monomyelocytic HL-60 cell line differentiates along a monocytic lineage when cultured in the presence of phorbol myristate acetate (PMA) or 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3]. The protooncogene c-fms, coding for the macrophage colony-stimulating factor (M-CSF) receptor, is characteristically expressed in cells of monocytic lineage, but is not present in HL-60 cells. Since M-CSF has an undefined role in osteoclast development, we wished to examine the effect of 1,25-(OH)2D3, a strong promoter of osteoclast development, on the induction of M-CSF receptor. Treatment of HL-60 cells with 10-50 ng/ml PMA for 3 days stimulated expression of c-fms, as measured by steady state mRNA levels. Treatment with 10 nm 1,25-(OH)2D3 for 4-72 h did not promote c-fms expression. In fact, 1,25-(OH)2D3 attenuated PMA-stimulated c-fms expression in a dose-dependent manner (ED50, 1 nM). Along with attenuation of c-fms expression, 1,25-(OH)2D3 induced expression of mRNA for the osteoclastic enzyme carbonic anhydrase-II (CA II) almost 2-fold over the level expressed in untreated HL-60 cells. The addition of PMA to the culture diminished the basal expression of CA II mRNA, but did not affect 1,25-(OH)2D3-stimulated stimulated CA II induction. PMA and 1,25-(OH)2D3, thus, promote divergent phenotype development in the HL-60 cell. Induction of c-fms mRNA by PMA should ensure further macrophage development. The effect Of 1,25-(OH)2D3 to attenuate expression of c-fms mRNA and stimulate CA II mRNA suggests that 1,25-(OH)2D3 activates osteoclast, rather than macrophage, development. 1,25-(OH)2D3-induced phenotypic changes may, therefore, involve modulation of the M-CSF effect.