RESUMO
Poly(ADP-ribose) polymerase 1 (PARP1) interacts genetically with the DNA-dependent protein kinase catalytic subunit (DNA-PKcs) to suppress early-onset T-lineage lymphomas in the mouse, but the underlying mechanisms have remained unknown. To address this question, we analyzed a series of lymphomas arising in PARP1(-/-)/DNA-PKcs(-/-) (P1(-/-)/D(-/-)) mice. We found that, despite defective V(D)J recombination, P1(-/-)/D(-/-) lymphomas lacked clonal reciprocal translocations involving antigen-receptor loci. Instead, tumor cells were characterized by aneuploidy driven by two main mechanisms: p53 inactivation and abnormal chromosome disjunction due to telomere fusions (TFs). Aberrant accumulation of p53 was observed in 13/19 (68.4%) lymphomas. Sequence analysis revealed five p53 mutations: three missense point mutations (one transition in exon 8 and two transversions in exons 5 and 8, respectively), one in-frame 5-11 microindel in exon 7 and a 410-bp deletion encompassing exons 5-8, resulting in a truncated protein. Analysis of tumor metaphases using sequential telomere fluorescent in-situ hybridization and spectral karyotyping revealed that nine out of nine lymphomas contained TFs. Mutant but not wild-type p53 status was associated with frequent clonal and nonclonal TFs, suggesting that p53 normally limits the extent of telomere dysfunction during transformation. Chromosomes involved in TFs were more likely to be aneuploid than chromosomes not involved in TFs in the same metaphases, regardless of the p53 status, indicating that TFs promote aneuploidy via a mechanism that is distinct from p53 loss. Finally, analysis of radiation responses in P1(-/-)/D(-/-), and control primary cells and tissues indicates that loss of PARP1 increases in vivo radiosensitivity and genomic instability in DNA-PKcs-deficient mice without impairing p53 stabilization and effector functions, suggesting a more severe defect in double-strand break (DSB) repair in double mutants. Together, our findings uncover defective DSB repair leading to tumor suppressor inactivation and abnormal segregation of fused chromosomes as two novel mechanisms promoting tumorigenesis in thymocytes lacking PARP1 and DNA-PKcs.
Assuntos
Transformação Celular Neoplásica/patologia , Proteína Quinase Ativada por DNA/fisiologia , Proteínas de Ligação a DNA/fisiologia , Linfoma/etiologia , Mutação/genética , Proteínas Nucleares/fisiologia , Poli(ADP-Ribose) Polimerases/fisiologia , Telômero/fisiologia , Proteína Supressora de Tumor p53/genética , Animais , Apoptose , Western Blotting , Proliferação de Células , Radioisótopos de Césio , Aberrações Cromossômicas , DNA/genética , Feminino , Instabilidade Genômica , Técnicas Imunoenzimáticas , Hibridização in Situ Fluorescente , Linfoma/metabolismo , Linfoma/patologia , Masculino , Camundongos , Camundongos Knockout , Poli(ADP-Ribose) Polimerase-1 , Tolerância a Radiação/genética , Reação em Cadeia da Polimerase em Tempo Real , Timócitos/metabolismo , Timócitos/patologia , Translocação Genética , Células Tumorais CultivadasRESUMO
Oxidative DNA base damage produced primarily by reactive oxygen species is assumed to be the most important endogenous damage. Lack of its repair may contribute to mutagenesis, carcinogenesis and aging. It is supposed that most oxidative DNA base damage is removed by the base excision repair pathway; although it was shown recently that other DNA repair pathways could be involved. This review is focused on the role of nucleotide excision repair (NER) and transcription-coupled repair (TCR) in the removal of oxidative DNA base damage in mammalian cells.
