title: Survival and death strategies in glioma cells: autophagy, senescence and apoptosis triggered by a single type of temozolomide-induced DNA damage.
abstract: Apoptosis, autophagy, necrosis and cellular senescence are key responses of cells that were exposed to genotoxicants. The types of DNA damage triggering these responses and their interrelationship are largely unknown. Here we studied these responses in glioma cells treated with the methylating agent temozolomide (TMZ), which is a first-line chemotherapeutic for this malignancy. We show that upon TMZ treatment cells undergo autophagy, senescence and apoptosis in a specific time-dependent manner. Necrosis was only marginally induced. All these effects were completely abrogated in isogenic glioma cells expressing O(6)-methylguanine-DNA methyltransferase (MGMT), indicating that a single type of DNA lesion, O(6)-methylguanine (O(6)MeG), is able to trigger all these responses. Studies with mismatch repair mutants and MSH6, Rad51 and ATM knockdowns revealed that autophagy induced by O(6)MeG requires mismatch repair and ATM, and is counteracted by homologous recombination. We further show that autophagy, which precedes apoptosis, is a survival mechanism as its inhibition greatly ameliorated the level of apoptosis following TMZ at therapeutically relevant doses (<100 µM). Cellular senescence increases with post-exposure time and, similar to autophagy, precedes apoptosis. If autophagy was abrogated, TMZ-induced senescence was reduced. Therefore, we propose that autophagy triggered by O(6)MeG adducts is a survival mechanism that stimulates cells to undergo senescence rather than apoptosis. Overall, the data revealed that a specific DNA adduct, O(6)MeG, has the capability of triggering autophagy, senescence and apoptosis and that the decision between survival and death is determined by the balance of players involved. The data also suggests that inhibition of autophagy may ameliorate the therapeutic outcome of TMZ-based cancer therapy.
authors: Department of Toxicology, Medical University Center, Mainz, Germany.
authors: Anna V
authors: AV
authors: Knizhnik
authors: Wynand P
authors: WP
authors: Roos
authors: Teodora
authors: T
authors: Nikolova
authors: Steve
authors: S
authors: Quiros
authors: Karl-Heinz
authors: KH
authors: Tomaszowski
authors: Markus
authors: M
authors: Christmann
authors: Bernd
authors: B
authors: Kaina
mesh_terms: D018906:Antineoplastic Agents, Alkylating / Q000633:toxicity*; D017209:Apoptosis / Q000187:drug effects / Q000235:genetics; D064007:Ataxia Telangiectasia Mutated Proteins; D001343:Autophagy / Q000187:drug effects / Q000235:genetics; D018797:Cell Cycle Proteins / Q000378:metabolism; D016923:Cell Death / Q000187:drug effects / Q000235:genetics; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects / Q000235:genetics; D016922:Cellular Senescence / Q000235:genetics; D004249:DNA Damage / Q000187:drug effects*; D053843:DNA Mismatch Repair; D015254:DNA Modification Methylases / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D003606:Dacarbazine / Q000031:analogs & derivatives* / Q000633:toxicity; D005910:Glioma / Q000235:genetics* / Q000378:metabolism; D006147:Guanine / Q000031:analogs & derivatives / Q000378:metabolism; D059765:Homologous Recombination; D006801:Humans; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D000077204:Temozolomide; D025521:Tumor Suppressor Proteins / Q000378:metabolism
chemical_list: D018906:Antineoplastic Agents, Alkylating; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D025521:Tumor Suppressor Proteins; D006147:Guanine; D003606:Dacarbazine; C008449:O-(6)-methylguanine; D015254:DNA Modification Methylases; C576324:ATM protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; D017346:Protein Serine-Threonine Kinases; D000077204:Temozolomide
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