Apoptotic nuclear morphological change without DNA fragmentation

Apoptosis is characterized morphologically by condensation and fragmentatio n of nuclei and cells and biochemically by fragmentation of chromosomal DNA into nucleosomal units [1]. CAD, also known as CPAN or DFF-40, is a DNase that can be activated by caspases [2-6]. CAD is complexed with its inhibito r, ICAD, in growing, non-apoptotic cells [2,7]. Caspases that are activated by apoptotic stimuli [8] cleave ICAD. CAD, thus released from ICAD, digest s chromosomal DNA into nucleosomal units [2,3]. Here, we examine whether nu clear morphological changes induced by apoptotic stimuli are caused by the degradation of chromosomal DNA. Human T-cell lymphoma Jurkat cells, as well as their transformants expressing caspase-resistant ICAD, were treated wit h staurosporine. The chromosomal DNA in Jurkat cells underwent fragmentatio n into nucleosomal units, which was preceded by large-scale chromatin fragm entation (50-200 kb). The chromosomal DNA in cells expressing caspase-resis tant ICAD remained intact after treatment with staurosporine but their chro matin condensed as found in parental Jurkat cells. These results indicate t hat large-scale chromatin fragmentation and nucleosomal DNA fragmentation a re caused by an ICAD-inhibitable DNase, most probably CAD, whereas chromati n condensation during apoptosis is controlled, at least in part, independen tly from the degradation of chromosomal DNA. (C) Elsevier Science Ltd ISSN 0960-9822.