[3H]Ouabain binding and 86 rubidium uptake during the dimethyl sulfoxide-induced differentiation of human promyelocytic leukemia HL-60 cells

The differentiating agent, retinoic acid, causes an early inhibition of inositol lipid-specific phospholipase C activity in HL-60 cells

Retinoic acid, a derivative of vitamin A, is shown to inhibit the levels of inositol phosphates and diacylglycerol by 25-30% when added to intact HL-60 cells at concentrations which induce differentiation. The onset of inhibition occurs after 10 min and reaches a maximum at 45 min. To study the mechanism and the site of action of retinoic acid, the activity of the phosphatidylinositol bisphosphate-specific phospholipase C was studied in cells permeabilized with streptolysin O and in membrane preparations. Phospholipase C activity was stimulated either via the guanine nucleotide regulatory protein (G-protein) or directly by Ca2+. Retinoic acid treatment, in a time- and concentration-dependent manner, led to a decrease in phospholipase C activity when stimulated with either GTP gamma S or NaF, both of which activate the enzyme via the G-protein. By contrast, it had no effect on the enzyme activity when stimulated with Ca2+ alone. This indicates that retinoic acid interferes with the coupling of the G-protein and phospholipase C. A relationship between the inhibition of phospholipase C activity and the induction of differentiation by retinoic acid was investigated. Only a small inhibition of GTP gamma S-stimulated phospholipase C activity was observed when an analogue of retinoic acid, etretine or Ro10-1670, with low differentiating activity, was used. Moreover, no inhibition of the GTP gamma S-stimulated phospholipase C activity was observed in an HL-60 sub-line resistant to retinoic acid. These results suggest that phospholipase C inhibition is an important step in the induction of differentiation.

Expression of multiple Na+,K+-adenosine triphosphatase isoform genes in human hematopoietic cells. Behavior of the novel A3 isoform during induced maturation of HL60 cells

Multiple isoenzymes of the Na+,K+-ATPase (alpha, alpha+, and alpha 3) have been identified by molecular cloning (Shull, G. E., J. Greeb, and J. B. Lingrel. 1986. Biochemistry. 25:8125-8132; and Schneider, J. W., R. W. Mercer, and E. J. Benz, Jr. 1987. Clin. Res. 35:585A. [Abstr.]). At least one of these, the alpha 3 chain, represents a novel form for which protein products and enzymatic activities are just beginning to be defined in rodents. We have recently demonstrated that expression of alpha 3 is largely confined to neuromuscular tissues of fetal and adult rats (Schneider, J. W., R. W. Mercer, M. Gilmore-Hebert, M. F. Utset, C. Lai, A. Greene, and E. J. Benz, Jr. 1988. Proc. Natl. Acad. Sci. USA. 85:284-288). We now report that certain human leukemia cell lines including HL60, HEL, and Molt 4 express mRNA for both alpha and alpha 3 isoforms of Na+,K+-ATPase; mRNA was not detected in several other cell lines, including K562 and U937; no cell lines expressed alpha+ mRNA. In uninduced HL60 cells, alpha 3 mRNA comprised 20-30% of total Na+,K+-ATPase mRNA. Furthermore, in HL60 and HEL cells, both alpha and alpha 3 mRNA declined after induction of maturation by DMSO, retinoic acid, or hemin. However, the reduction in alpha 3 mRNA was far more dramatic. alpha 3 mRNA virtually disappeared, but alpha mRNA declined by only approximately 50%. In contrast, when maturation of HL60 cells along the monocyte/macrophage lineage was induced by exposure to phorbol esters, alpha 3 mRNA remained abundant. Moreover, mRNA for the beta subunit of the Na+,K+-ATPase increased dramatically. Our results demonstrate that the alpha 3 isoform, formerly thought to be confined to neuromuscular tissues, is expressed in restricted lineages of hematopoietic origin. These leukemia cell lines should provide a useful model for analyzing regulation of the alpha 3 isoform gene and characterization of alpha 3 isoform activities.

Differentiation-associated changes of cation-transport activities in myeloid leukemic cell lines

Induction of differentiation in HL-60 and U-937 leukemic cell lines, resulted in 1.5-10-fold increase in 45Ca2+ uptake. The increased 45Ca2+ uptake in the differentiating cells was inhibited by verapamil, cromolyn and amiloride. Elevation in Ca2+ uptake in differentiating cells was also demonstrated using the fluorescent probe, fura-2 acetoxymethyl ester. The increased 45Ca2+ uptake was accompanied by a decrease in ouabain-insensitive and -sensitive 86Rb+ uptake. Furthermore, correlation between the changes in these activities was observed. Modulation of extracellular pH affected differentiation: higher pH increased the extent of differentiation.

(3H)ouabain binding to leukaemic cells and intralymphocytic sodium content in chronic lymphocytic leukaemia; no evidence for alterations of the Na+/K+-pump

The number of specific (3H)ouabain binding sites and dissociation constants (Kd) were determined by Scatchard analysis of values for leucocytes from patients with B-cell chronic lymphocytic leukaemia (CLL), chronic myeloid leukaemia (CML), acute blastic leukaemia (AL) and healthy subjects. CLL lymphocytes and normal B-cells bound significantly less (3H)ouabain than did normal T-lymphocytes. CML granulocytes showed the same binding characteristics as normal granulocytes, while blast cells from AL patients bound significantly more (3H)ouabain than did normal granulocytes or B-cells. The increased binding capacity in blast cells might, at least partly, reflect their larger cell size. A decrease in Kd values was only found in CLL lymphocytes, as compared with normal B-cells. Intralymphocytic sodium content in CLL lymphocytes was significantly increased, as compared with that in T-cell-enriched normal lymphocytes. (3H)ouabain binding did not show any relationship to different prognostic variables in CLL. The present data mainly argue against altered Na+/K+-ATPase enzyme activity as an indicator of malignancy.

Retinoic-acid-induced differentiation of HL-60 cells is associated with biphasic activation of the Na+-K+ pump

The human promyelocytic leukemia cell line, HL-60, can be induced to differentiate into granulocyte-like cells when cultured in the presence of 10(-6) M retinoic acid (RA) for several days. Following the addition of RA two kinds of changes occur. First, there are early changes that comprise an increase in the intracellular concentration of sodium ions [Na]i, which reaches its maximum after 6 h, and an increase in the activity of the Na+-pump, which is reflected by an ouabain-sensitive K+ influx that peaks at 8 h (170% of the control value) and that occurs without any change in the number of pump molecules, as measured by the binding of 3H-ouabain. Second, beginning after 12 h of culture with RA, a decrease in the number of ouabain-binding sites occurs, this being accompanied by an increase in the number of K+ ions actively transported by each site. The effect of modulation of Na+-pump activity on the RA-induced differentiation of HL-60 cells was studied using low, noncytotoxic concentrations of ouabain which, although alone having no differentiating effect, accelerated and potentiated the effect of RA on differentiation. When added in combination, these drugs induced rapid stimulation of the Na+-pump, which reached its peak after 2 h. These results indicate that a concomitant increase in the level of [Na+]i and in the activity of the Na+-pump constitute primary events in the interaction between RA and HL-60 cells, and that cation fluxes may play a role in the initiation of the process of differentiation.