Induction of differentiation by tumour necrosis factor in HL-60 cells is associated with the formation of large DNA fragments.

The DNA fragmentation induced by tumor necrosis factor (TNF) of differentiable human myeloid leukemic HL-60 cells has been further characterized. TNF increased the appearance of very high molecular weight DNA fragments detected by agarose gel electrophoresis. The use of pulsed-field gel electrophoresis (PFGE) revealed these fragments to be as high as 200-400 kilobase pairs. The pattern of HL-60 DNA fragmentation contrasted with that of U937 cells, which exhibited lower molecular weight, nucleosome multiple sized fragments, and greater cytotoxicity in response to TNF. The peak increase of fragments from HL-60 occurred between one and two hours of incubation, with TNF concentrations of 10 U/ml or higher, and was inhibitable by 1 mM Zn2+. Southern blotting of these fragments disclosed enrichment for c-myc related sequences compared with control probes including beta-actin and kappa and lambda light chains. Treatment of DNA with NotI or gamma-irradiation, followed by PFGE, disclosed a class of still higher molecular weight DNA, which decreased following TNF treatment, and which was apparently the precursor of the TNF-induced fragments. TNF thus rapidly increases a class of high molecular weight DNA fragments which are enriched for c-myc related sequences and may arise preferentially from higher molecular weight structures which are detectable following linearization by NotI or gamma-irradiation. Such major but non-random alterations in chromatin structure may contribute to TNF-induced monocytoid differentiation of HL-60.