Sustained activation of p53 in confluent nucleotide excision repair-deficient cells resistant to ultraviolet-induced apoptosis.
P53 activation is one of the main signals after DNA damage, controlling cell cycle arrest, DNA repair and apoptosis. We have previously shown that confluent nucleotide excision repair (NER)-deficient cells are more resistant to apoptosis induced by ultraviolet irradiation (UV). Here, we further investigated the effect of cell confluence on UV-induced apoptosis in normal and NER-deficient (XP-A and XP-C) cells, as well as the effects of treatments with the ATM/ATR inhibitor caffeine, and the patterns of p53 activation. Strong p53 activation was observed in either proliferating or confluent cells. Caffeine increased apoptosis levels and inhibited p53 activation in proliferating cells, suggesting a protective role for p53. However, in confluent NER-deficient cells no effect of caffeine was observed. Transcription recovery measurements showed decreased recovery in proliferating XPA-deficient cells, but no recovery was observed in confluent cells. The levels of the cyclin/Cdk inhibitor, p21(Waf1/Cip1), correlated well with p53 activation in proliferating cells. Surprisingly, confluent cells also showed similar activation of p21(Waf1/Cip1). These results indicate that reduced apoptosis in confluent cells is associated with the deficiency in DNA damage removal, since this effect is not clearly observed in NER-proficient cells. Moreover, the strong activation of p53 in confluent cells, which barely respond to apoptosis, suggests that this protein, under these conditions, is not linked to UV-induced cell death signaling.
Carvalho
Helotonio
H
Departament of Microbiology, Institute of Biomedical Sciences, University of São Paulo, São Paulo, SP 05508-900, Brazil. helotonio.carvalho@gmail.com <helotonio.carvalho@gmail.com>
Ortolan
Tatiana G
TG
dePaula
Tomás
T
Leite
Ricardo A
RA
Weinlich
Ricardo
R
Amarante-Mendes
Gustavo P
GP
Menck
Carlos Frederico Martins
CF
D017209:Apoptosis / Q000528:radiation effects*; D015153:Blotting, Western; D049109:Cell Proliferation; D002478:Cells, Cultured; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism; D004260:DNA Repair; D004261:DNA Replication; D006801:Humans; D014158:Transcription, Genetic; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*; D014466:Ultraviolet Rays
C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016159:Tumor Suppressor Protein p53