Flow cytometric correlation of the c-myc oncoprotein and cell cycle kinetics of HL60 leukaemia during induced maturation with cytosine arabinoside and dimethylsulphoxide

The c-myc oncogene codes for a DNA binding protein that functions in a cell cycle-related manner. A useful model for studying the relationship of c-myc expression with cell cycle kinetics is the HL60 cell line. HL60 cells constitutively express high levels of c-myc mRNA; however, the level can be down-regulated as the cells are induced to differentiate. We have developed a flow cytometric assay for correlating c-myc oncoprotein levels with DNA content. C-myc oncoprotein levels were additionally correlated with c-myc mRNA levels as determined by slot blot hybridization. Dimethylsulphoxide (DMSO) and cytosine arabinoside were used to induce granulocytic and monocytic maturation respectively. Treatment of HL60 cells with DMSO leads to an increase in the per cent of cells in G1/G0 and a decrease in mean c-myc mRNA and oncoprotein levels. The cells with G1 DNA content show the greatest decrease in c-myc protein. ARA-c treatment of HL60 cells leads to a slowing and an accumulation of cells in S phase with a moderate decrease in mean mRNA and only a slight decrease in mean c-myc protein levels. These data support the hypothesis that c-myc is involved in the switch from G1 to G0.