CHARACTERISTICS OF NAF-INDUCED DIFFERENTIATION OF HL-60 CELLS

Sodium fluoride (NaF) is known to stimulate osteoblastic bone formatio n, but little attention has been given to the possibility that NaF als o affects bone resorption and the differentiation of osteoclastic prog enitor cells, Wen human promyelocytic HL-60 cells were treated with Na F (0.5 mM, 0-4 days), cell proliferation was inhibited, and the additi on of 1,25-dihydroxyvitamin D-3 (1,25(OH)(2)D-3) (10 nM, 0-4 days) aug mented this antiproliferative effect. NaF increased cel)dar reduction of nitroblue tetrazolium (NET), and this effect was strongly augmented by 1,25(OH)(2)D-3. In addition, NaF produced marked changes in cellul ar morphology, increased cellular adhesion to plastic, reduced the nuc lear/cytoplasmic ratio, and increased cellular expression of chloroace tate esterase, but failed to alter cellular nonspecific esterase activ ity. Furthermore, NaF increased expression of CD11b and CD66b, and thi s stimulation was enhanced by adding 1,25(OH)(2)D-3. The sum of these changes in classical promyelocytic cellular indices suggest: (1) that NaF stimulates the early stages of HL-60 differentiation toward a gran ulocyte-like cell and (2) that 1,25(OH)(2)D-3 promotes these actions o f NaF. Additional experiments aimed at further understanding the NaF-i nduced conversion of HL-60 cells identified further changes. NaF also increased cellular production of prostaglandin E(2) (PGE(2)) and nitri c oxide (NO) and induced expression of inducible nitric oxide synthase (iNOS); 1,25(OH)(2)D-3 once again augmented these NaF-induced effects . Similarly, NaF stimulated the production of interleukin 1 alpha (IL- 1 alpha). IL-6, and tumor necrosis factor-alpha and 1,25(OH)(2)D-3 aga in strongly enhanced these effects. Indomethacin completely blocked st imulation of NET reduction, NO production, and iNOS expression induced by NaF plus 1,25(OH)(2)D-3; adding exogenous PGE(2) (0.1-10 ng/ml) to these indomethacin-blocked cultures dose-dependently restored NO prod uction. These additional findings together with the observed slow onse t (24-18 h) of NaF and 1,25(OH)(2)D-3 interaction strongly suggest tha t 1,25(OH)(2)D-3 acts as a cofactor with NaF primarily through interac tion with an endogenous NaF-induced cyclo-oxygenase product(s), quite possibly PGE(2) itself. Such a mechanism for NaF and 125(OPI)(2)D-3 in teraction would be strongly analogous to the interaction we have recen tly demonstrated between 1,25(OH)(2)D-3 and PGE(1) on the differentiat ion of HL-60 cells.