Involvement of the mismatch repair system in temozolomide-induced apoptosis.
Postreplicative mismatch repair plays a major role in mediating the cytotoxicity of agents generating O6-methylguanine in DNA. We previously showed that a methylating antitumor triazene compound, temozolomide, induces apoptosis and that the persistence of O6-methylguanine in DNA is required to trigger the process. We wanted to test whether the latter apoptotic signal is dependent on a functional mismatch repair system. To this end, we used two human lymphoblastoid cell lines (i.e., the mismatch repair-proficient TK6 line and its mismatch repair-deficient subline MT1) that are both deficient in O6-methylguanine repair. Temozolomide treatment of TK6 cells brought about efficient cell growth inhibition, G2/M arrest, and apoptosis, as indicated by the results of cytofluorimetric analysis of 5-bromo-2'-deoxyuridine incorporation and DNA content and evaluation of DNA fragmentation. The drug treatment resulted also in the induction of p53 and p21/waf-1 protein expression. In contrast, MT1 cells were highly resistant to the drug and no p53 and p21/waf-1 induction was observed. Importantly, we could show that MT1 cells are not deficient in the p53-dependent apoptosis pathway; treatment with etoposide, a topoisomerase II inhibitor, resulted in p53 and p21/waf-1 protein expression and apoptosis in both cell lines. In conclusion, we demonstrate the existence of a link between a functional mismatch repair system and the trigger of apoptosis in cells exposed to clinically relevant concentrations of temozolomide. The results also suggest that p53 induction in response to O6-guanine methylation involves the mismatch repair system.
Istituto Dermopatico Dell'Immacolata, Rome, Italy. s.datri@idi.it
S
S
D'Atri
L
L
Tentori
P M
PM
Lacal
G
G
Graziani
E
E
Pagani
E
E
Benincasa
G
G
Zambruno
E
E
Bonmassar
J
J
Jiricny
D018906:Antineoplastic Agents, Alkylating / Q000494:pharmacology*; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects*; D002453:Cell Cycle / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000187:drug effects / Q000378:metabolism; D004260:DNA Repair; D003606:Dacarbazine / Q000031:analogs & derivatives* / Q000494:pharmacology; D005047:Etoposide / Q000494:pharmacology; D006801:Humans; D009692:Nucleic Acid Heteroduplexes; D000077204:Temozolomide; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000187:drug effects / Q000378:metabolism
D018906:Antineoplastic Agents, Alkylating; D000972:Antineoplastic Agents, Phytogenic; C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D009692:Nucleic Acid Heteroduplexes; D016159:Tumor Suppressor Protein p53; D005047:Etoposide; D003606:Dacarbazine; D000077204:Temozolomide