RNF31 inhibition sensitizes tumors to bystander killing by innate and adaptive immune cells
Tumor escape mechanisms for immunotherapy include deficiencies in antigen presentation, diminishing adaptive CD8+ T cell antitumor activity. Although innate NK cells are triggered by loss of MHC class I, their response is often inadequate. To increase tumor susceptibility to both innate and adaptive immune elimination, we performed parallel genome-wide CRISPR-Cas9 knockout screens under NK and CD8+ T cell pressure. We identified all components, RNF31, RBCK1, and SHARPIN, of the linear ubiquitination chain assembly complex (LUBAC). Genetic and pharmacologic ablation of RNF31, an E3 ubiquitin ligase, strongly sensitized melanoma, breast and colorectal cancer cells to both NK and CD8+ T cell killing. This occurred in a TNF-dependent manner, causing loss of A20 and non-canonical IKK complexes from TNF Receptor Complex I. Corroborating this preclinically, a small molecule RNF31 inhibitor sensitized human colon carcinoma organoids to TNF and greatly enhanced immune bystander killing of antigen-loss and antigen presentation machinery-deficient tumor cells. These results merit exploration of RNF31 inhibition as a clinical pharmacological opportunity for immunotherapy-refractory cancers.