Genome-wide analysis of topoisomerase removal after campothecin treatment in the context of replication and transcription

  • Karim Ashour Garrido

    Research areas

  • PhD, School of Medical Sciences


Camptothecin (CPT) and its derivatives (e.g. Irinotecan) are commonly used anticancer drugs which increase the half-life of topoisomerase I (Top1) cleavage complexes (Top1cc) during the Top1 catalytic cycle. Even in the presence of CPT Top1 will eventually remove itself by resuming its catalytic cycle. However, increasing Top1cc half-life also increases the probability of transcription and/or replication encounters with the transient Top1cc, which can lead to double-strand breaks, highly cytotoxic for the cells. Tyrosyl-DNA phosphodiesterase 1 (Tdp1) and Mre11 nuclease activity have been suggested to have a role in the removal of Top1 in the context of transcription and replication respectively. Also, Swi10ERCC1-Rad16XPF has been shown to act as a redundant pathway with Tdp1 for the repair of Top1-mediated DNA damage. To understand the interaction among Top1 removal pathways I have performed a genome-wide study of Top1cc removal from replicating and transcribing DNA in WT, mre11, tdp1 and rad16XPF mutants using the model system Schizosaccharomyces pombe. Data in this thesis reveals new insights of the specific pathways involved in Top1cc removal in the absence and presence of CPT in proliferative and quiescent cells. The role of these proteins in proliferative and quiescent cells is very different. Data in proliferating cells suggest the role of Tdp1 in Top1cc removal is associated to active transcription, Rad16XPF contributes to Top1cc removal from transcribing and replicating cells and Mre11 is rather involved in replication-associated Top1cc removal. We speculate that in quiescent cells Top1cc is firstly degraded by the action of the proteasome and subsequently removed by Tdp1. Rad16XPF acts as a redundant pathway and Mre11 only plays a minor role


Original languageEnglish
Awarding Institution
Thesis sponsors
  • Cancer Research Wales
Award date30 Jun 2015