Noviello, Anna (2025) Loss of autophagy impairs DNA damage response via defective TIP60-ATM signaling. [Tesi di dottorato]

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Abstract

Resistance to chemotherapy remains a major obstacle in cancer treatment. Autophagy, often activated in response to anticancer agents, plays a context-dependent role by promoting either cell survival or cell death. Although its cytoprotective function under genotoxic stress is well established, the molecular determinants that dictate whether autophagy enhances or impairs the DNA damage response (DDR) remain unclear.Here, we examined how autophagy modulates the DDR in ARPE19 cells engineered with an inducible AsiSI-ER system that generates ~150 site-specific double-strand breaks (DSBs) across the genome. Genetic ablation of ATG7 impaired autophagy and resulted in defective ATM activation, reduced BRCA1 phosphorylation, and diminished RAD51 foci formation. Moreover, aberrant recruitment patterns of BRCA1 and 53BP1 during cell-cycle progression indicate compromised DSB repair pathway choice in autophagy-deficient cells.Mechanistically, loss of autophagy led to hypoactivation and destabilization of the histone acetyltransferase TIP60, accompanied by reduced H4K16 acetylation. Notably, pharmacological proteasome inhibition restored TIP60 levels and fully rescued the observed DDR defects, demonstrating that TIP60 instability is the primary driver of the phenotype. Collectively, these findings refine the current understanding of the autophagy–DDR interplay by uncovering an unrecognized regulatory axis in which ATG7-dependent autophagy safeguards genomic stability by stabilizing TIP60 and enabling proper ATM activation. This framework not only provides mechanistic insight into the epigenetic regulation of DDR by autophagy but also lays the groundwork for translational applications, including genome-wide analyses of autophagy deficiency and optimization of combinatorial therapeutic strategies in cancer treatment.

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