The PCPH oncoprotein antagonizes the proapoptotic role of the mammalian target of rapamycin in the response of normal fibroblasts to ionizing radiation.
Exposure of normal mouse fibroblasts (MEF3T3) to ionizing radiation (IR) resulted in a dose-dependent increase of mTOR mRNA and protein levels and the shuttling of the mTOR protein from its normal, predominantly mitochondrial location to the cell nucleus. The same IR doses that activated mTOR induced the phosphorylation of p53 on Ser(18) (mouse equivalent to human Ser(15)) and the subsequent transcriptional activation of PUMA, a known proapoptotic p53-target gene, and promoted apoptosis involving increased overall caspase activity, caspase-3 activation, cleavage of poly(ADP-ribose) polymerase (PARP) and classic protein kinase C (PKC) isoforms, and DNA fragmentation. The proapoptotic role of mTOR in this process was demonstrated by the fact that rapamycin, a mTOR inhibitor, blocked p53 Ser(18) phosphorylation, the induction of PUMA, and all other apoptosis events. Furthermore, the proapoptotic function of mTOR was also antagonized by the expression in MEF3T3 cells of the PCPH oncoprotein, known to enhance cell survival by causing partial ATP depletion. Tetracyclin (Tet)-regulated expression of oncogenic PCPH, or overexpression of normal PCPH, blocked both phosphorylation and nuclear shuttling of mTOR in response to IR. These results indicate that alterations in PCPH expression may render tumor cells resistant to IR, and perhaps other DNA-damaging agents, by preventing mTOR activation and signaling.
Tirado
Oscar M
OM
Laboratory of Experimental Carcinogenesis, Department of Radiation Medicine, Georgetown University Medical Center, 3970 Reservoir Road NW, Washington, DC 20057-1482, USA.
Mateo-Lozano
Silvia
S
Sanders
Sean
S
Dettin
Luis E
LE
Notario
Vicente
V
D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects*; D002467:Cell Nucleus / Q000378:metabolism / Q000528:radiation effects; D004249:DNA Damage / Q000502:physiology; D004307:Dose-Response Relationship, Radiation; D005347:Fibroblasts / Q000166:cytology / Q000528:radiation effects*; D051379:Mice; D008928:Mitochondria / Q000378:metabolism / Q000528:radiation effects; D015513:Oncogene Proteins / Q000096:biosynthesis / Q000502:physiology*; D010766:Phosphorylation / Q000528:radiation effects; D047428:Protein Kinase Inhibitors; D011494:Protein Kinases / Q000096:biosynthesis / Q000378:metabolism / Q000502:physiology; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D011836:Radiation Tolerance / Q000187:drug effects / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology / Q000528:radiation effects; D020123:Sirolimus / Q000494:pharmacology; D041701:Swiss 3T3 Cells; D058570:TOR Serine-Threonine Kinases; D015533:Transcriptional Activation / Q000528:radiation effects; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism
D015513:Oncogene Proteins; C485537:Pcph protein, mouse; D047428:Protein Kinase Inhibitors; D012333:RNA, Messenger; D016159:Tumor Suppressor Protein p53; D011494:Protein Kinases; C546842:MTOR protein, human; C546843:mTOR protein, mouse; D058570:TOR Serine-Threonine Kinases; D020123:Sirolimus