A novel defect in mitochondrial p53 accumulation following DNA damage confers apoptosis resistance in Ataxia Telangiectasia and Nijmegen Breakage Syndrome T-cells.
We have previously shown that whereas T-cells from normal individuals undergo accumulation of p53 and apoptosis when treated with the genotoxic agent Actinomycin D (ActD), those from Ataxia Telangiectasia (AT) and Nijmegen Breakage Syndrome (NBS) patients resist ActD-induced apoptosis [1]. We have now found similar resistance by the p53-null Jurkat T-cell line and by siRNA p53-knockdown normal T-cells. This evidence that ActD initiates a p53-dependent apoptotic responce prompted us to look for defective p53 accumulation by AT and NBS T-cells. Surprisingly the total p53 level was only slightly reduced compared to normal T cells but its intracellular localization was highly defective: p53 was poorly accumulated in the cytosol and nearly undetectable in mitochondria. In accordance with the dependence of ActD-induced apoptosis on a mitochondrial p53 function, in control T-cells specific inhibition of mitochondrial p53 translocation with μ pifithrin reduced apoptosis by 86%, whereas treatment with α pifithrin, which blocks p53-mediated transcription, had no effect. We also showed that nuclear export is not required for mitochondrial p53 translocation. Observation of an altered p53 ubiquitination pattern and Mdm2 accumulation in ActD-treated AT and NBS T-cells provided a mechanistic link to their defective extranuclear p53 localization. Our results disclose an undescribed defect in mitochondrial p53 accumulation in AT and NBS T-cells that makes them resistant to apoptosis following unrepairable DNA damage.
Department of Clinical and Biological Sciences, University of Turin, Orbassano, Italy.
Valentina
V
Turinetto
Paola
P
Porcedda
Valentina
V
Minieri
Luca
L
Orlando
Erica
E
Lantelme
Lisa
L
Accomasso
Antonio
A
Amoroso
Mario
M
De Marchi
Laura
L
Zannini
Domenico
D
Delia
Claudia
C
Giachino
D017209:Apoptosis / Q000187:drug effects; D001260:Ataxia Telangiectasia / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism; D003593:Cytoplasm / Q000187:drug effects / Q000378:metabolism; D004249:DNA Damage; D003609:Dactinomycin / Q000633:toxicity; D006801:Humans; D019169:Jurkat Cells; D008928:Mitochondria / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D049932:Nijmegen Breakage Syndrome / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D051736:Proto-Oncogene Proteins c-mdm2 / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D013601:T-Lymphocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*; D054875:Ubiquitination / Q000187:drug effects; D051028:bcl-2-Associated X Protein / Q000378:metabolism
D016159:Tumor Suppressor Protein p53; D051028:bcl-2-Associated X Protein; D003609:Dactinomycin; D051736:Proto-Oncogene Proteins c-mdm2