Inhibition of DNA-dependent protein kinase induces accelerated senescence in irradiated human cancer cells.
DNA-dependent protein kinase (DNA-PK) plays a pivotal role in the repair of DNA double-strand breaks (DSB) and is centrally involved in regulating cellular radiosensitivity. Here, we identify DNA-PK as a key therapeutic target for augmenting accelerated senescence in irradiated human cancer cells. We find that BEZ235, a novel inhibitor of DNA-PK and phosphoinositide 3-kinase (PI3K)/mTOR, abrogates radiation-induced DSB repair resulting in cellular radiosensitization and growth delay of irradiated tumor xenografts. Importantly, radiation enhancement by BEZ235 coincides with a prominent p53-dependent accelerated senescence phenotype characterized by positive β-galactosidase staining, G(2)-M cell-cycle arrest, enlarged and flattened cellular morphology, and increased p21 expression and senescence-associated cytokine secretion. Because this senescence response to BEZ235 is accompanied by unrepaired DNA DSBs, we examined whether selective targeting of DNA-PK also induces accelerated senescence in irradiated cells. Significantly, we show that specific pharmacologic inhibition of DNA-PK, but not PI3K or mTORC1, delays DSB repair leading to accelerated senescence after radiation. We additionally show that PRKDC knockdown using siRNA promotes a striking accelerated senescence phenotype in irradiated cells comparable with that of BEZ235. Thus, in the context of radiation treatment, our data indicate that inhibition of DNA-PK is sufficient for the induction of accelerated senescence. These results validate DNA-PK as an important therapeutic target in irradiated cancer cells and establish accelerated senescence as a novel mechanism of radiosensitization induced by DNA-PK blockade.
Division of Cancer Research, Peter MacCallum Cancer Centre, East Melbourne, Victoria, Australia.
Arun
A
Azad
Susan
S
Jackson
Carleen
C
Cullinane
Anthony
A
Natoli
Paul M
PM
Neilsen
David F
DF
Callen
Sauveur-Michel
SM
Maira
Wolfgang
W
Hackl
Grant A
GA
McArthur
Benjamin
B
Solomon
D000818:Animals; D059447:Cell Cycle Checkpoints / Q000187:drug effects; D045744:Cell Line, Tumor; D016922:Cellular Senescence / Q000187:drug effects / Q000235:genetics*; D053903:DNA Breaks, Double-Stranded / Q000528:radiation effects; D004260:DNA Repair / Q000187:drug effects; D051747:DNA-Activated Protein Kinase / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism*; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D055785:Gene Knockdown Techniques; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology*; D000076222:Mechanistic Target of Rapamycin Complex 1; D051379:Mice; D008819:Mice, Nude; D046912:Multiprotein Complexes; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D047428:Protein Kinase Inhibitors / Q000494:pharmacology*; D011506:Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D011804:Quinolines / Q000494:pharmacology*; D034741:RNA, Small Interfering / Q000235:genetics; D011836:Radiation Tolerance / Q000187:drug effects*; D058570:TOR Serine-Threonine Kinases; D014183:Transplantation, Heterologous; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism; D020741:rho GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism
D051747:DNA-Activated Protein Kinase; D007093:Imidazoles; D000076222:Mechanistic Target of Rapamycin Complex 1; D046912:Multiprotein Complexes; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D047428:Protein Kinase Inhibitors; D011506:Proteins; D011804:Quinolines; D034741:RNA, Small Interfering; D058570:TOR Serine-Threonine Kinases; D016159:Tumor Suppressor Protein p53; D020741:rho GTP-Binding Proteins; C531198:dactolisib