CHARACTERIZATION OF THE RELEASE OF DNA BY A HUMAN LEUKEMIA-CELL LINE HL-60

Release of DNA fragments into the culture supernatant of human promyel ocytic cell line HL-60 was investigated. The released DNA has previous ly been shown to have a strong immunosuppressive effect on the prolife ration of mitogen-stimulated human peripheral lymphocytes and some can cer cell lines. In this study, HL-60 cells were cultured for four days in serum-free medium and the amount of extracellular nucleic acid was monitored daily. Nucleic acids were isolated by phenol/chloroform ext ractions, followed by ethanol precipitations. A similar amount of DNA was identified in the HL-60 culture supernatant regardless of whether the cells were incubated for one day or up to four days. Also, the sam e amount of DNA was isolated from culture supernatants after washing t he cells daily and reincubating into the fresh medium. During the firs t 8 hours of incubation no DNA material was detected in the culture su pernatant, whereas at 24 h the concentration of the extracellular DNA reached a plateau. The data suggest the extracellular DNA is not accou nted for totally by DNA from dying cells, and a regulatory mechanism m ay be involved which controls the release of DNA into the medium.