1,25-Dihydroxyvitamin D3 and phorbol myristate acetate synergistically increase carbonic anhydrase-II expression in a human myelomonocytic cell line.

Expression of carbonic anhydrase-II (CA-II), an enzyme important to osteoclast function, distinguishes osteoclasts from other cells of monocytic lineage. A cell's selection of terminal osteoclast phenotype is controlled by many different factors, which are not well understood and which may also control the expression of CA-II. We studied the control of CA-II expression in the human HL-60 cell to better understand the signal transduction systems involved in progression to the osteoclast phenotype. Both 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3; 10 nM] and phorbol myristate acetate (10 ng/ml), doses that cause monocytic differentiation of the HL-60 cell, induced small increases in CA-II mRNA and CA-II protein, as measured by Northern analysis and Western immunoblotting, respectively. The maximal response was seen at 3 days. Treatment of HL-60 cells with both agents resulted in synergistic increases in CA-II mRNA (80-fold) and protein. The large increase in CA-II mRNA allowed assessment of the dose dependence of both agents, with ED50 values of 1 nM for 1,25-(OH)2D3 and 1 ng/ml for phorbol myristate acetate. In addition, we have shown that this synergistic response was completely inhibited by a potent inhibitor of protein kinase-C activity, staurosporine (0.1 microM), which has not previously been demonstrated in other cell systems. Staurosporine did not inhibit 1,25-(OH)2D3 induction of nonspecific esterase. Thus, 1,25-(OH)2D3 synergistically interacts with protein kinase-C-activated systems to cause a myelomonocytic precursor to express CA-II a marker of the osteoclast phenotype.