ACTIVITIES OF POTENTIAL TUMOR-MARKER ENZYMES DURING INDUCED-DIFFERENTIATION IN HL-60 AND U-937 CELLS

HL-60 and U-937 cells were used as models to assess the involvement of the enzymes of thymidine metabolism in differentiation. Both cell typ es showed decreased thymidine kinase and thymidylate synthase but incr eased thymidine phosphorylase activities in response to the induction of differentiation by dimethylsulfoxide and 12-O-tetradecanoylphorbol 13-acetate. This was accompanied by a greater than three-fold increase in the stimulation of superoxide production in both cell lines. Thymi dylate synthase and thymidine kinase activities were noted as potentia l markers of leukaemic cell proliferation while thymidine phosphorylas e and superoxide production correlated well with differentiated phenot ypes. Prolonged treatment of U-937 by 12-O-tetradecanoylphorbol 13-ace tate resulted in a marked de-differentiation, indicating overstimulati on of one or more of the isoforms of protein kinase C.