PROTEIN-KINASE-C DEPENDENT INDUCTION OF (PP)125(FAK) IN MONOCYTES BY COLONY-STIMULATING FACTOR-GM - EVIDENCE FOR A SYNERGISTIC EFFECT BY THE CYTOKINE AND 1,25-DIHYDROXYVITAMIN D-3

The differentiation of monocytes into osteoclasts has been recently ac hieved in vitro in a suitable milieu containing morphogens that includ es 1,25 dihydroxyvitamin D-3, colony stimulating factors, interleukins and the presence of cells of osteoblastic lineage. However, the preci se role of these factors in the osteoclastic differentiation process h as not yet been examined. Since our previous studies have shown that o steoclasts express a much higher level of focal adhesion kinase ((pp)1 25(FAK)) than cells of macrophage/monocytic lineage, the present study was carried out to ascertain which morphogens are involved in increas ing the expression of the kinase during the differentiation of monocyt es to osteoclasts. We demonstrate that a marked increase in the expres sion of (pp)125(FAK) occurs only after prolonged exposure to hCSF-GM a nd combination of hCSF-GM and 1,25 (OH)(2) D-3. The hCSF-GM was found to be a more potent stimulator of (pp)125(FAK) induction than 1,25 (OH )(2) D-3; interestingly, the presence of both hCSF-GM and 1,25 (OH)2 D g showed co-operative effect. Furthermore, the presence of a protein k inase C inhibitor, bisindolylmaleimide (GF 109203X), blocked hCSF-GM-m ediated induction of focal adhesion kinase, implicating an important r ole for protein kinase C in the induction of (pp)125(FAK).