Reactive changes in free intracellular zinc cation concentration ([Zn2+]i) were monitored, using the fluorescent probe Zinquin, in human lymphoma cells exposed to the DNA-damaging agent VP-16. Two-photon excitation microscopy showed that Zinquin-Zn2+ forms complexes in cytoplasmic vesicles. [Zn2+]iincreased in both p53wt (wild type) and p53mut(mutant) cells after exposure to low drug doses. In p53mutcells noncompetent for DNA damage-induced apoptosis, elevated [Zn2+]i was maintained at higher drug doses, unlike competent p53wt cells that showed a collapse of the transient before apoptosis. In p53wt cells, the [Zn2+]i rise paralleled an increase in p53 and bax-to-bcl-2 ratio but preceded an increase in p21WAF1, active cell cycle arrest in G2, or nuclear fragmentation. Reducing [Zn2+]i, using N, N, N′, N′-tetrakis(2-pyridylmethyl)ethylenediamine, caused rapid apoptosis in both p53wt and p53mut cells, although cotreatment with VP-16 exacerbated apoptosis only in p53wt cells. This may reflect changed thresholds for proapoptotic caspase-3 activation in competent cells. We conclude that the DNA damage-induced transient is p53-independent up to a damage threshold, beyond which competent cells reduce [Zn2+]i before apoptosis. Early stress responses in p53wt cells take place in an environment of enhanced Zn2+ availability.
The p27–Skp2 axis mediates glucocorticoid-induced cell cycle arrest in T-lymphoma cells
