Cellular zinc homeostasis is a regulator in monocyte differentiation of HL-60 cells by

It was reported previously that zinc-deficient mice show impaired lymphopoiesis. At the same time, mono-cyte numbers in these animals are increased, indicating a negative impact of zinc on monocyte development. Here, we investigate the role of zinc homeostasis in the differentiation of myeloid precursors into monocytes. Reduced gene expression of several zinc transporters, predominantly from the Zip family, was observed during 1, 25-dihydroxyvitamin D3 (1,25D3)-induced differentia-tion of HL-60 cells. This was accompanied by a reduc-tion of intracellular-free zinc, measured by FluoZin-3. Amplifying this reduction with the zinc chelator TPEN or zinc-depleted cell-culture medium enhanced 1,25D3-induced expression of monocytic surface markers CD11b and CD14 on HL-60, THP-1, and NB4 cells. In contrast, differentiation of NB4 cells to granulocytes was not zinc-sensitive, pointing toward a specific effect of zinc on monocyte differentiation. Further, monocyte functions, such as TNF- secretion, phagocytosis, and oxidative burst, were also augmented by differentiation in the presence of TPEN. The second messenger cAMP promotes monocyte differentiation. We could show that zinc inhibits the cAMP-synthesizing enzyme adenylate cyclase, and chelation of zinc by TPEN increases cAMP generation after stimulation with the adenylate cyclase activator forskolin. Based on our in vitro results and the in vivo observations from the literature, we suggest a model in which the intracellular-free zinc concentration limits AC activity, and the decrease of zinc after 1,25D3 treatment promotes differentiation by relieving AC inhi-bition. Thus, cellular zinc homeostasis acts as an en-dogenous modulator of monocyte differentiation. J. Leukoc. Biol. 87: 000–000; 2010