UBL3 Modification Reduces Nuclear POLE Levels to Potentiate Antitumor Immunity in Aero-upper Digestive Squamous Cell Carcinomas.

While immune checkpoint inhibitors (ICIs) have revolutionized treatment of the patients with aero-upper digestive squamous cell carcinomas (SCCs), including esophageal squamous cell carcinoma (ESCC) and lung squamous cell carcinoma (LUSC), only a subset of patients benefit from ICIs, therefore entailing exploration of the mechanisms to regulate treatment responsiveness. POLE, as a subunit of DNA polymerase ε, possesses 3'-5' proofreading activity, and its mutations have been associated with favourable response to ICIs in several solid tumors. However, post-translational modification (PTM) of POLE and its impact on the therapeutic efficacy of ICIs are unknown. Here, this study demonstrates that ubiquitin-like protein 3 (Ubl3), whose expression is markedly downregulated in SCCs, covalently binds to Pole, reduces nuclear Pole levels, triggers DNA damage, and activates cGAS-STING signaling pathway. Notably, Ubl3 modification of Pole significantly primes the local immune microenvironment to mitigate the growth of murine aero-upper digestive SCC cells and boost the efficacy of αPD-1 treatment in vivo. Single-cell RNA sequencing (scRNA-seq) analysis further revealed that UBL3 expression is positively correlated with better clinical outcomes in a cohort of ESCC patients receiving neoadjuvant chemotherapy combined with αPD-1. Together, our findings unravel UBL3 modification as a novel PTM mechanism governing subcellular location of POLE and its influence on immunotherapy responsiveness, thus making UBL3 modification as a promising immunomodulatory approach to enhance immunotherapy efficacy in patients with aero-upper digestive SCCs.