Topoisomerase II-Mediated DNA Damage Is Differently Repaired during the Cell Cycle by Non-Homologous End Joining and Homologous Recombination

Topoisomerase II (Top2) is a nuclear enzyme involved in several metabolic processes of DNA. Chemotherapy agents that poison Top2 are known to induce persistent protein-mediated DNA double strand breaks (DSB). In this report, by using knock down experiments, we demonstrated that Top2α was largely responsible for the induction of γH2AX and cytotoxicity by the Top2 poisons idarubicin and etoposide in normal human cells. As DSB resulting from Top2 poisons-mediated damage may be repaired by non-homologous end joining (NHEJ) or homologous recombination (HR), we aimed to analyze both DNA repair pathways. We found that DNA-PKcs was rapidly activated in human cells, as evidenced by autophosphorylation at serine 2056, following Top2-mediated DNA damage. The chemical inhibition of DNA-PKcs by wortmannin and vanillin resulted in an increased accumulation of DNA DSB, as evaluated by the comet assay. This was supported by a hypersensitive phenotype to Top2 poisons of Ku80- and DNA-PKcs- defective Chinese hamster cell lines. We also showed that Rad51 protein levels, Rad51 foci formation and sister chromatid exchanges were increased in human cells following Top2-mediated DNA damage. In support, BRCA2- and Rad51C- defective Chinese hamster cells displayed hypersensitivity to Top2 poisons. The analysis by immunofluorescence of the DNA DSB repair response in synchronized human cell cultures revealed activation of DNA-PKcs throughout the cell cycle and Rad51 foci formation in S and late S/G2 cells. Additionally, we found an increase of DNA-PKcs-mediated residual repair events, but not Rad51 residual foci, into micronucleated and apoptotic cells. Therefore, we conclude that in human cells both NHEJ and HR are required, with cell cycle stage specificity, for the repair of Top2-mediated reversible DNA damage. Moreover, NHEJ-mediated residual repair events are more frequently associated to irreversibly damaged cells

Cytogenetic and Molecular Predictors of Outcome in Acute Lymphocytic Leukemia: Recent Developments

During the last decade a tremendous technologic progress based on genome-wide profiling of genetic aberrations, structural DNA alterations, and sequence variations has allowed a better understanding of the molecular basis of pediatric and adult B/T- acute lymphoblastic leukemia (ALL), contributing to a better recognition of the biological heterogeneity of ALL and to a more precise definition of risk factors. Importantly, these advances identified novel potential targets for therapeutic intervention. This review will be focused on the cytogenetic/molecular advances in pediatric and adult ALL based on recently published articles

IBD: Infliximab dose optimization in IBD-proactive or reactive?

no abstract availabl

Endoscopic approach to resection of polypoid and non-polypoid dysplasia in IBD

The endoscopic management of dysplasia in inflammatory bowel disease (IBD) patients has many similarities with the management of complex colorectal neoplasia in non-IBD patients. There is a need for a skilled operator, experienced nursing team, and surgical backup; however, the context of IBD leads to additional challenges for the endoscopist where the patient must be considered as a whole and over the lifetime of their disease. Major considerations include: proof of a curative resection, multifocal or non-circumscribed dysplasia, and consequences of surgery including stoma. A multi-disciplinary working group is critical. The endoscopic resection technique should be chosen after careful considerations of its risks and benefits. Endoscopic dysplasia resection in IBD represents one of the greatest challenges to the therapeutic endoscopist both in terms of skill and judgement. This chapter highlights some of the pitfalls and offers potential solutions

Endoscopic approach to resection of polypoid and non-polypoid dysplasia in IBD

The endoscopic management of dysplasia in inflammatory bowel disease (IBD) patients has many similarities with the management of complex colorectal neoplasia in non-IBD patients. There is a need for a skilled operator, experienced nursing team, and surgical backup; however, the context of IBD leads to additional challenges for the endoscopist where the patient must be considered as a whole and over the lifetime of their disease. Major considerations include: proof of a curative resection, multifocal or non-circumscribed dysplasia, and consequences of surgery including stoma. A multi-disciplinary working group is critical. The endoscopic resection technique should be chosen after careful considerations of its risks and benefits. Endoscopic dysplasia resection in IBD represents one of the greatest challenges to the therapeutic endoscopist both in terms of skill and judgement. This chapter highlights some of the pitfalls and offers potential solutions