Chromatin cleavage in apoptosis: Association with condensed chromatin morphology and dependence on macromolecular synthesis

TLDR

Apoptosis in glucocorticoid‑treated rat thymocytes and murine lymphoid cell lines L5178 and S49 is morphologically linked to chromatin cleavage. Chromatin cleavage occurs at internucleosomal sites via an endogenous endonuclease, requires macromolecular synthesis, and is inhibited by cycloheximide and actinomycin D while being induced by the calcium‑magnesium ionophore A23187. Glucocorticoid‑resistant cell variants show no apoptosis or chromatin cleavage and lack steroid receptors, confirming that apoptotic condensed chromatin consists of endogenously digested fragments and that apoptosis can depend on macromolecular synthesis.

Abstract

In glucocorticoid-treated rat thymocytes and the murine lymphoid cell lines L5178 and S49 the morphology of apoptosis is associated with chromatin cleavage. The cleavage is at internucleosomal sites, apparently through activation of an endogenous endonuclease. In variants of the cell lines selected for resistance to glucocorticoid, neither apoptosis nor chromatin cleavage were observed after steroid treatment, and steroid receptors were undetectable. In thymocytes, both the morphological changes of apoptosis and chromatin cleavage were inhibited by cycloheximide and actinomycin D. The calcium-magnesium ionophore A23187 induced apoptosis and chromatin cleavage in thymocytes, and these effects were also inhibited by cycloheximide. The data confirm that the condensed chromatin which characterizes apoptosis morphologically consists of endogenously digested chromatin fragments. They also provide support for the view that at least some cells enter apoptosis by a process dependent upon macromolecular synthesis.