Targeting RIPK1 ubiquitylation to promote anti-tumour immunity

Abstract

Cancer heterogeneity is a key problem of current therapies leading to resistance. The way cancer cells die can lead to anti-cancer immunity, which is frequently referred to as "immunogenic" cell death. The aim of the project is to understand how TNF (Tumour Necrosis Factor), a master pro-inflammatory cytokine can cause "immunogenic" cell death. This death is dependent on activation of Receptor Interacting Protein Kinase 1 (RIPK1). Therefore, it is pivotal to understand how this kinase is regulated by a variety of checkpoints, which ensure that TNF stimulation induces NFkB signalling, inflammation and cell survival. However, the perturbation of these checkpoints induces TNF dependent cell death. Here, I have characterised the mechanism by which the E3 ubiquitin ligase Mind-Bomb-2 (MIB2) regulates TNF-induced cell death by inactivating RIPK1 via inhibitory ubiquitylation. While depletion of MIB2 has little effect on NFkB activation, it sensitises cells to RIPK1- and caspase-8-dependent cell death. I find that MIB2 represses the cytotoxic potential of RIPK1 by ubiquitylating RIPK1 at specific lysines, thereby interfering with RIPK1's oligomerisation and RIPK1-FADD association. Together, my findings demonstrate that Mind Bomb 3 ubiquitin-ligases can function as additional checkpoints of TNF-induced cell death, selectively protecting cells from the cytotoxic effects of TNF. Furthermore, I have used a clinically relevant animal model to evaluate the therapeutic advantage of inducing RIPK1 dependent cell death. I have shown that Sma Mimetics (SM) (IAP degraders) augment the efficacy of the standard of care (SOC) treatment of extremity malignancies. Mechanistically, combination treatment with SOC/SM promotes RIPK1-mediated cell death, which significantly improves local disease control, increases infiltration/activation of CD8+ T cells and NK cells, and enhances the survival benefit of immune checkpoint blockade. My findings warrant a clinical trial to assess the survival benefit of RIPK1-induced immunogenic cell death in patients with advanced disease at limb extremities.