Leukemia Research Vol. 15, No. 8, pp. 727-732, 1991. 0145-2126/91 $3.00 + .00 Printed in Great Britain. Pergamon Press plc THE EFFECTS OF LITHIUM ON THE GROWTH AND PHORBOL ESTER (TPA) INDUCED DIFFERENTIATION OF TWO HL-60 SUBLINES AGATHA M. MASEMOLA, ROLF W. BECKER and ERROL M. TYOBEKA Department of Biochemistry, University of the North, Private Bag Xl106, Sovenga, 0727, South Africa (Received 5 December 1990. Accepted 18 January 1991) Abstract--Two sublines of a human promyelocytic cell line, HL-60, were used to study the effect of lithium on TPA (12-o-tetradecanoylphorbol-13-acetate) induced macrophage-like differentiation. Although these sublines, HL-60 M and HL-60 JE, had different growth rates, both showed enhanced proliferation when treated with 5 mM lithium (128 -4-- 2 and 141 -+ 1% in comparison to controls after 5 days of incubation, respectively). Treatment of the sublines with TPA for 72 h resulted in macro- phage-like differentiation (assessed by cell adhesion) of about 90% at 10 nM TPA in HL-60 JE, whereas a maximum of 50% at 100 nM TPA was obtained in HL-60 M. Differentiation was also confirmed by non-specific esterase activity. However, incubation of both sublines with TPA and 5 mM lithium revealed that lithium has little or no effect on the macrophage-like differentiation of the HL- 60 cell line. Key words: HL-60 leukemic cells, lithium, cell growth, TPA, differentiation. INTRODUCTION THE CHARACTERISTIC of HL-60, a human promy- elocytic leukemia cell line, that has attracted a lot of interest is the ability of these cells to differentiate along different myelocytic lineages, depending on the inducing agent used. Treatment with dimethyl sulf- oxide (DMSO) and retinoic acid causes maturation along the granulocytic pathway [1], whereas vitamin D 3 and TPA induce monocytic and macrophage-like differentiation, respectively [1, 2]. Furthermore, ex- posure of HL-60 cells to an alkaline medium induces eosinophilic differentiation [1]. The precise mech- anisms involved in these processes are not well under- stood, but in the case of TPA induced differentiation, protein phosphorylation [3], alteration in lipid metab- olism, and loss of transferrin receptors from the cell surface [4], are some of the biochemical changes that have been described. In addition, the onset of TPA induced differentiation seems tightly coupled to the cessation of cell growth. There is also evidence that treatment of HL-60 cells with TPA is followed by a rapid decrease in the levels of inositol phosphates and diacylglycerol [5]. However, if cells are exposed to TPA for longer Correspondence to: E. M. Tyobeka Ph.D., Department of Biochemistry, University of the North, Private Bag Xl106, Sovenga, 0727, South Africa. periods (up to 24 h), a gradual increase in the level of diacylglycerol is observed [6]. These changes in phosphatidylinositol derived second messengers seem to suggest their importance in the regulation of cell growth as well as the pathways leading to cellular differentiation. Lithium, on the other hand, is a drug used exten- sively for the management of depressive mania [7, 8]. One of the early observations in patients receiving lithium treatment was that they developed neu- trophilia as a side effect [9]. Later it was demon- strated that lithium stimulated hematopoiesis both in vivo and in vitro [10]. The exact mechanism by which lithium exerts its effects remains obscure. None the less, it is known to inhibit the glycolytic pathway [11], as well as adenylate cyclase [12] and inositol-1- phosphatase activities [13]. Since lithium and TPA exert opposing effects on the growth of HL-60 cells, and furthermore, both agents affect the inositol phosphate pathway dif- ferently, it was of interest to establish whether treat- ment of HL-60 cells with both TPA and lithium would affect macrophage-like differentiation. 727 MATERIALS AND METHODS RPMI-1640, TPA, antibiotics and the non-specific esterase kit were purchased from Sigma Chemical Co., St. Louis, fetal bovine serum from Delta Bioproducts,