Depending on their genetic background (p53(wt) versus p53(null)),
carcinoma cells are more or less sensitive to
drug-induced cell cycle arrest and/or apoptosis. Among the members of the p53 family, p63 is characterized by two N-terminal
isoforms, TAp63 and ΔNp63. TAp63
isoform has p53-like functions, while ΔNp63 acts as a dominant negative inhibitor of p53. We have previously published that TAp63 is involved in poly(ADP-ribose)polymerase-1 (PARP-1) signaling of DNA damage deriving from
DNA topoisomerase I (TOP I) inhibition in
carcinoma cells. In the present study, we treated MCF7
breast carcinoma cells (p53(+)/ΔNp63(-)) or SCC022 (p53(-)/ΔNp63(+))
squamous carcinoma cells with the TOP I inhibitor
topotecan (
TPT) and the
PJ34 PARP inhibitor, to compare their effects in the two different cell contexts. In MCF7 cells, we found that
PJ34 addition reverts
TPT-dependent PARP-1 auto-modification and triggers
caspase-dependent PARP-1 proteolysis. Moreover,
TPT as single agent stimulates p53(ser15) phosphorylation, p53 PARylation and occupancy of the p21WAF promoter by p53 resulting in an increase of p21WAF expression. Interestingly,
PJ34 in combination with
TPT enhances p53 occupancy at the BAX promoter and is associated with increased
BAX protein level. In SCC022 cells, instead, TPT+PJ34 combined treatment reduces the level of the anti-apoptotic ΔNp63α
protein without inducing apoptosis. Remarkably, in such cells, either exogenous p53 or TAp63 can rescue the apoptotic program in response to the treatment. All together our results suggest that in
cancer cells
PARP inhibitor(s) can operate in the choice between growth arrest and apoptosis by modulating p53 family-dependent signal.