Characterisation of Topoisomerase 1-cleavage complex repair

Thesis

Topoisomerase 1 (TOP1) resolves DNA topological stress ahead of DNA replication and transcription. As part of its enzymatic activity, TOP1 covalently binds to DNA, creating an intermediate known as TOP1 cleavage complex (TOP1cc) and a single strand DNA break which allows DNA to unwind. If not quickly repaired, TOP1cc hinders the progression of DNA replication and transcription, fostering genomic instability. Thus, stabilising TOP1cc with TOP1 poisons, such as Camptothecin or its analogue, is highly effective and widely used in cancer therapy. However, efficient removal of TOP1cc drives cancer resistance. The proteolysis of TOP1cc by the proteasome is described at excessively high doses of CPT that are not relevant in a clinical setting, calling into question the relevance of the proteasome role in TOP1cc repair for cancer therapy and patient response.

Here, I described that TOP1cc repair induced by clinically relevant doses of CPT depends on selective autophagy. In human cancer cells, proteomics, sequencing, biochemistry techniques, and live imaging all demonstrate TOP1cc lysosomal uptake after induction of replication stress. The crosstalk between stalled replication forks and lysosomes could be explained by the transient and restricted reshaping of the nuclear envelope undergoes observed in my study. My work demonstrates the direct involvement of selective autophagy in the processing of nuclear material in the context of replication stress. I identified TEX264 as the first autophagy receptor capable of targeting DNA damage for clearance while sustaining cellular proliferation in human cells. This new mechanism and its regulation are highly relevant to our understanding of genome stability and response to cancer therapy.

Authors: Lascaux, P

• Alternative title: TEX264 drives selective autophagy of DNA lesions to promote DNA repair and cell survival
• DOI: 10.5287/ora-y0vjk1qag
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: camptothecin; TEX264; replication stress; TOP1cc; cancer; autophagy; DNA damage; Topoisomerase 1
• Subjects: DNA repair, Oncology, Autophagy