Biopolymers and cell. 1995; 11 (3-4): 66 - 72

THE FORMATION OF HIGH MOLECULAR WEIGHT DNA FRAGMENTS: THE HALLMARK OF APOPTOSIS OR EARLY GENOMIC EVENTS IN STRESS RESPONSE?

V. T. Solov'yan, I. O. Andreev

We studied the peculiarities of nuclear DNA fragmentation in primary culture of ma¬rine thymocytes and in human lymphoblastoid cell culture (line CEM) induced to apop-tosis by various influences. We showed that in apoptotic cells the ordered high molecular weight DNA cleavage, recognizable as DNA fragment release of 50—100 and 250—300 kb in length, preceded to typical nuclear DNA fragmentation at the internucleosomal re¬gions. Comparative study of the high molecular weight and internucleosomal DNA fragmentation demonstrated that these show different sensitivity to Zn2+ ions, actino-mycin D and cycloheximide. In addition, the formation of large molecular weight frag¬ments in contrast to oligonucleosomal ones may be reverted in conditions promoting to topoisomerase 11 mediated rejoining of cleaved DNA. These finding suggest that the high molecular weight and internucleosomal fragmentation may follow two different program¬mes of DNA cleavage during apoplosis mediated, presumably, by diverse enzymes. We showed that similar processes of ordered high molecular weight DNA cleavage occur in apoptotic cells and in those subjected to the stress challenges. The formation of high molecular weight DNA fragments was demonstrated to proceed promptly, show no correlation with cell death and occassionally may be of transient nature. The data obtained allow to interpret the formation of high molecular weight fragments as a component of cell response to stress rather that an early step of DNA fragmentation du¬ring apoptosis.