TEX264-mediated selective autophagy in the repair of cytotoxic trapped PARP1

Thesis

Targeting genomic instability in cancer therapy has been achieved by exploiting the synthetic lethal interaction between PARP inhibitors (PARPi) and homologous recombination (HR). PARPi induce cytotoxicity in HR-deficient cancers by causing PARP1 to become tightly bound to chromatin, a phenomenon known as PARP1 trapping, resulting in irreparable replication-associated DNA damage. Despite their initial promise, resistance commonly arises in PARPi-treated cancers, highlighting a need for improved understanding of cellular PARPi response and tolerance mechanisms. Previous work demonstrated that p97 extracts trapped PARP1 from chromatin, allowing tolerance to PARPi treatment, but regulation of its function and downstream processing remain unclear. Using immunofluorescence and cell viability assays, I identified a novel role of the p97 co-factor and selective autophagy receptor TEX264 in regulation of trapped PARP1. Further biochemical and cell biological studies uncovered a mechanism of selective nucleophagy of trapped PARP1, mediated by TEX264 and p97 and regulated by ubiquitination and SUMOylation, which promotes shuttling of trapped PARP1 to the lysosome. Impairing this process resulted in increased genomic instability, replication stress and sensitivity to PARPi. This was found to be highly dependent on PARP1 trapping, with only trapped PARP1 processed this way. Strikingly, inhibition of TEX264-orchestrated nucleophagy re-sensitised PARPi resistant cells, implying a potential relevance of this pathway for improving therapy. Overall, I demonstrate a novel mechanism of trapped PARP1 clearance by selective nucleophagy mediated by dual functions of the p97 co-factor and selective autophagy receptor TEX264, which regulates tolerance of sensitive and resistant cells to PARPi.

Authors: Hoslett, G

• DOI: 10.5287/ora-gpenzyedd
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: DNA damage; breast cancer; PARP inhibitor; TEX264; autophagy