Formation of Apoptotic Bodies Is Associated with Internucleosomal DNA Fragmentation during Drug-Induced Apoptosis

Abstract

The onset of apoptosis is often coincident with internucleosomal DNA fragmentation or ladders which are considered a hallmark of the process. However, several studies have indicated that MOLT-4 human lymphoblastoid cells exposed to various agents, including VP16, display some apoptotic characteristics in the absence of either internucleosomal ladders or production of apoptotic bodies. The present study records that, in the presence of aurintricarboxylic acid (ATA), internucleosomal ladders were detected in DNA isolated from VP16-treated MOLT-4 cells; a paradoxical result in view of inhibition by ATA of nuclease activity in cell free preparations. The activity of ATA in mediating genomic fragmentation was dose- and time-dependent. Moreover, addition of ATA to VP16-treated MOLT-4 cells also resulted in production of apoptotic bodies, this effect being quantified by morphological examination and flow cytometry. Detection of ladders and apoptotic bodies after addition of ATA was not attributable to increased toxicity in cells exposed to the combined treatment relative to VP16 alone. A similar response, that is the appearance of both internucleosomal fragmentation and apoptotic bodies, occurred after exposure of MOLT-4 cells to the mitotic inhibitor podophyllotoxin. The consistent association between internucleosomal fragmentation of DNA and formation of apoptotic bodies exhibited during death of MOLT-4 cells, insofar as both characteristics are either present or absent following different agents, suggests interdependence.