Transient G2M arrest and subsequent release of apoptotic and mitotic cells in vanadyl(4)-prepulsed human Chang liver cells

Abstract

The relationship between cell cycling and apoptosis/programmed cell death has been perceived as either checkpoint arrests or mitotic aberration where common pathways between mitosis and apoptosis seem suggested. We show here evidence implicating both perceptions of cell cycle involvement. The process was initiated by hydroxyl free radicals (OH*) generated intracellularly from internalized vanadyl(4). Intranuclear sequestration of vanadyl(4) was verified by nuclear microscopy. Resultant high oxidative reactivity in the nucleus was shown by the redox indicator methylene blue, suggesting direct oxidative damage to genomic DNA. Oxidative stress was further enhanced by depletion of glutathione which is the main cellular reducing agent. Genomic degradation and fragmentation was confirmed by flow cytometric evaluation of terminal deoxynucleotidyl transferase (TdT)-mediated 3'OH end-labelling (TUNEL) of DNA nicks, and cell cycle DNA profiling demonstrating sub-G1 (sub-2N) accumulation. With DNA degradation, there was a G2M transient with hyperdiploid right-shifting, consistent with G2 arrest. G2 arrest was subsequently 'released' with abolition of G2M and all other cell cycle phases except for a solitary sub-G1 (apoptotic) peak. The cytological profile of this 'release' phenomenon was initially marked by the appearance of clusters of mitotic and apoptotic cells. At later stages, the cell population was composed exclusively of nuclear ghosts, apoptotic cells, mitotic cells, and mitotic cells with both chromosomes and apoptotic condensations. Concurrent and conjoint expression of cell death and cell division as the exclusive process of an entire cell population refuted the notion of mutual exclusivity between life and death. Zn2+, an endonuclease inhibitor, abolished all observed cytological and DNA profile changes.