APPEARANCE OF 1-2-MPB GIANT DNA FRAGMENTS AS AN EARLY COMMON RESPONSELEADING TO CELL-DEATH INDUCED BY VARIOUS SUBSTANCES THAT CAUSE OXIDATIVE STRESS

The effects of oxidative stress on double strand DNA breakage were exa mined in T-24 human bladder tumor cells using various active oxygen pr oducing agents such as hydrogen peroxide (H2O2), bleomycin (BLM), neoc arzinostatin (NCS), and x-ray irradiation. Analysis of the DNA by puls ed-field gel electrophoresis (PFGE) revealed that discrete giant DNA f ragments of 1-2 Mbp and 200-800 kbp had accumulated in the nuclei of t he treated cells. The 1-2 Mbp giant DNA fragments were first observed 2 h after the T-24 cells were exposed to the active oxygen producing a gents, or irradiated with x-ray. The appearance and the amounts of 1-2 Mbp and 200-800 kbp giant DNA fragments seemed to depend on the conce ntration and the type of reagents used or the dose of x-ray. Following the accumulation of giant DNA fragments, another type of DNA fragment ation was detected and DNA fragments smaller than 100 kbp accumulated in the nuclei of the cells irradiated with x-ray or treated with NCS. In addition, DNA ladder formation, which is characteristic of apoptosi s, was observed. The giant DNA fragments appeared to arise as a conseq uence of double-stranded DNA breakage, which occurred earlier than cel l lysis, as assessed by Cr-51 release. These findings indicate that th e formation of giant DNA fragments is a specific characteristic of cel ls responding to oxidative stress, and it may be an initial event that leads to cell death. (C) 1997 Elsevier Science Inc.