C-MYC DOWN-REGULATION IN SURAMIN-TREATED HL-60 CELLS PRECEDES GROWTH-INHIBITION BUT DOES NOT TRIGGER DIFFERENTIATION

Down-regulation of c-myc mRNA expression is linked to growth arrest an d the state of differentiation of hematopoietic cells. We showed that treatment of HL60 cells with suramin results in a rapid reduction of c -myc expression followed by an inhibition of cell growth. Both c-myc m RNA and protein levels decreased by day 1 of treatment, and, by day 4, only 10% of control c-myc protein levels were detected. In contrast t o retinoic acid, dimethyl sulfoxide, and 12-O-tetradecanoylphorbol-13- acetate treatment, however, exposure of HL60 cells to suramin did not result in the induction of differentiation. These results demonstrate that suramin modulates c-myc levels in HL60 cells and that the down-re gulation of c-myc is not sufficient to trigger differentiation toward either granulocytic or monocytic lineages.