Differentiation of HL-60 cells by dimethylsulfoxide activates a Na+-dependent nucleoside transport system

Abstract

Uridine transport in undifferentiated HL-60 cells occurs primarily facilitated diffusion, but a limited Na+-dependent process can be demonstrated (K(m) = 44 ± 4.4 μM, V(max) = 0.13 ± 0.01 μM/s). This latter transport system was inhibited by adenosone and inosine (K(i) = 110 and 260 μM, respectively), whereas guanosine and thymidine were less effective (K(i) = 1600 and 1200 μM, respectively). Dimethylsulfoxide (DMSO) caused a concentration-dependent decrease in facilitated uridine transport. This change was attributable to a decrease in the number of transporter molecules as determined by the binding of [3H]nitrobenzylthioinosine to cell membranes. Morever, the Na+-dependent transport of uridine was enhanced by DMSO at a concentration of the polar solvent as low as 0.4%. When HL-60 cells were exposed to 1.0% DMSO, a marked increase in Na+-dependent uridine transport occurred within 72 hr, a time preceding maximum granulocytic differentiation. This change was attributable to an increase in transport affinity (K(m) = 1.54 ± 0.65 μM), with no change in V(max) (V(max) = 0.13 ± 0.02 μM/s). The consequence of these changes was the generation of a 3- to 4-fold increase in the intracellular concentration of relative to the medium at a physiological concentration of 5 μM uridine. Similar increases in transport affinity were observed for adenosine, inosine, guanosine and thymidine in DMSO-differentiated HL-60 cells (K(m) values of 2 to 5 μM). These results complement our previous studies with phorbol 12-myristate 13-acetate, in which differentiation to a monocytic phenotype was also associated with enhanced Na+-dependent nucleoside transport.