THE CLEAVAGE OF NUCLEAR-DNA INTO HIGH-MOLECULAR-WEIGHT DNA FRAGMENTS OCCURS NOT ONLY DURING APOPTOSIS BUT ALSO ACCOMPANIES CHANGES IN FUNCTIONAL-ACTIVITY OF THE NONAPOPTOTIC CELLS

In this paper we demonstrate that apoptosis in primary culture of muri ne thymocytes and in continuously growing human cells is associated wi th the progressive disintegration of nuclear DNA into high molecular w eight (HMW)-DNA fragments of about 50-150 kb. We also show that the fo rmation of similarly sized HMW-DNA fragments takes place in the same c ells in the absence of apoptotic inducers. Unlike an apoptotic fragmen tation of nuclear DNA, the formation of HMW-DNA fragments in nonapopto tic cells is rapidly induced, has no correlation with the cell death, and is not associated with the development of oligonucleosomal ''ladde r'' or apoptotic changes in nuclear morphology. The disintegration of DNA into HMW-fragments is also observed in nuclei isolated from health y, nonapoptosizing tissues of various eukaryotes. We show that the for mation of HMW-DNA fragments in the absence of apoptotic inducers is st rongly dependent on the ionic detergents, is responsive to the topoiso merase II-specific poison, teniposide, and is completely reversible un der conditions that favor topoisomerase II-dependent rejoining reactio n, Also, we demonstrate that the formation of HMW-DNA fragments in con tinuously growing cell lines caused either by serum deprivation or mon olayer establishment is of a transient nature and rapidly reverses to the control level following serum addition or dilution of monolayer, T he results suggest that the cleavage of nuclear DNA into HMW-DNA fragm ents is associated not only with apoptosis but also accompanies change s in functional activity of nonapoptotic cells. (C) 1997 Academic Pres s.