The effect of 5-azacytidine (5-aza-CR) and its analogue on cell differentiation and DNA methylation of HL-60 cells.

The effect of 5-aza-CR and 5-aza-2'-deoxycytidine (5-aza-CdR) on cell differentiation and DNA methylation of HL-60 cells was studied. The differentiation index of HL-60 cells was measured after being treated with drugs by using the NBT stain method. DNA methylase activities of HL-60 cells treated with the drugs were assayed by using 3H-methyl-S-adenosylmethionine (3H-SAM) as a methyl donor. The DNA methylation level of HL-60 cells treated with the drugs was measured by HPLC. The results showed that the HL-60 cell differentiation index was increased after being treated with 5-aza-CR or 5-aza-CdR at a certain concentration for 4 days. But, at the same time, DNA methylase activity and the DNA methylation level were decreased. And all these changes were related to the concentration of the drugs. 5-Aza-CdR was more efficient than 5-aza-CR. We also assayed the E. coli RNA polymerase activity in vitro by using different DNA templets different in DNA methylation level. We found that the transcriptional activity of RNA polymerase was increased with the decrease of the DNA methylation level of HL-60 cells.