Dexamethasone-induced apoptosis involves cleavage of DNA to large fragments prior to internucleosomal fragmentation.

D.G Brown,X.M Sun,G.M Cohen

doi:10.1016/s0021-9258(18)53654-1

Abstract

Apoptosis is a major form of cell death, characterized morphologically by chromatin condensation and biochemically by endonuclease cleavage of DNA into oligonucleosomal fragments. Recently, we reported that zinc arrested dexamethasone-induced apoptosis in thymocytes at an early stage, as characterized morphologically by condensation of heterochromatin into clumps abutting the nuclear membrane. In this study, we show that zinc completely inhibits endonuclease cleavage of DNA into oligonucleosomal fragments but does not prevent the cleavage of DNA into high molecular weight fragments. These results indicate that the formation of these high molecular weight fragments, which correlates with the very early morphological features of apoptosis, is a critical event in glucocorticoid-induced apoptosis. The formation of these high molecular weight fragments, despite the inhibition by zinc of the endonuclease cleavage of DNA, suggests that key enzyme(s), other than the Ca2+/Mg(2+)-dependent endonuclease, are involved at the earliest stages of induction of apoptosis.

Highlights

From the Medical Research Council Toxicology Unit, Woodmansterne Road, Carshalton, Surrey SM5 4EF, United Kingdom dexamethasone in thepresence of zinc is cleaved initially into high molecular weight fragments, but without any endonuclease cleavageinto oligonucleosomalfragments
We reported that Thymocyte Incubations-Thymocytes were isolated from male zinc arrested dexamethasone-inducedapoptosis in thy- Fischer 344 rats (4-5 weeks old)as describedpreviously [11] and mocytes at an early stage,as characterized morphologically by condensation of heterochromatin into clumps abutting the nuclear membrane.In this study,we show that zinc completely inhibits endonuclease cleavage of DNA into oligonucleosomal fragments but does not prevent the cleavage of DNA into high molecular weight fragments
These results indicate that the formation of these high molecular weight fragments, which correlates with the very early morphological diluted with RPMI1640 containing 10% fetal bovine serum to give a final suspension of 2 X lo' cells/ml

Summary

Introduction

From the Medical Research Council Toxicology Unit, Woodmansterne Road, Carshalton, Surrey SM5 4EF, United Kingdom dexamethasone in thepresence of zinc is cleaved initially into high molecular weight fragments, but without any endonuclease cleavageinto oligonucleosomalfragments. Morphologically by chromatin condensation and biochemically by endonuclease cleavage of DNA into oligonucleosomal fragments. We reported that Thymocyte Incubations-Thymocytes were isolated from male zinc arrested dexamethasone-inducedapoptosis in thy- Fischer 344 rats (4-5 weeks old)as describedpreviously [11] and mocytes at an early stage,as characterized morphologically by condensation of heterochromatin into clumps abutting the nuclear membrane.In this study,we show that zinc completely inhibits endonuclease cleavage of DNA into oligonucleosomal fragments but does not prevent the cleavage of DNA into high molecular weight fragments.

Results

Conclusion