A hexanucleotide repeat expansion represents the most common genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia, though the mechanisms by which the expansion cause neurodegeneration are poorly understood. We report elevated levels of DNA/RNA hybrids (R-loops) and double-strand breaks (DSBs) in rodent neurons, human cells, and in C9orf72-ALS patient spinal cord tissues. Accumulation of endogenous DNA damage is concomitant with defective ATM-mediated DNA repair signalling and accumulation of protein-linked DNA breaks. We further reveal that defective ATM-mediated DNA repair is a consequence of p62 accumulation, which impairs H2A ubiquitylation and perturbs ATM signalling. Adeno-associated virus-mediated expression of C9orf72-related RNA and dipeptide repeats in the murine central nervous system causes elevated DSBs, ATM defects, and triggers neurodegeneration. These findings identify R-Loops, DSBs, and defective ATM-mediated repair as pathological consequences of C9orf72 expansions, and suggest that C9orf72-linked neurodegeneration is driven, at least in part, by genomic instability.

Highlights d NK cells drive broad inflammatory remodeling characteristic of T-cell-inflamed tumors d PGE2 acting on EP2 and EP4 on NK cells prevents the TME switch enabling immune escape d Opposing inflammatory profiles found in many human cancer types have prognostic value d A signature capturing pro-and anti-tumor factors predicts response to immunotherapy

Identifying strategies to improve the efficacy of immune checkpoint blockade (ICB) remains a major clinical need. Here, we show that therapeutically targeting the COX-2/PGE 2 /EP2-4 pathway with widely used non-steroidal and steroidal antiinflammatory drugs synergized with ICB in mouse cancer models. We exploited a bilateral surgery model to distinguish responders from non-responders shortly following treatment and identified acute IFN-γ-driven transcriptional remodeling in responder mice, which was also associated with patient benefit to ICB. Monotherapy with COX-2 inhibitors or EP2-4 PGE 2 receptor antagonists rapidly induced this response program and, in combination with ICB, increased the intratumoral accumulation of effector T cells. Treatment of patient-derived tumor fragments from multiple cancer types revealed a similar shift in the tumor inflammatory environment to favor T cell activation. Our findings establish the COX-2/PGE 2 /EP2-4 axis as an independent immune checkpoint and a readily translatable strategy to rapidly switch the tumor inflammatory profile from cold to hot.