SET facilitates immune escape of microsatellite stability colorectal cancer by inhibiting c-Myc degradation.

Abstract

Microsatellite stability (MSS) colorectal cancer (CRC) exhibits a low mutation load and poor immunogenicity, contributing to immune escape of tumor cells and less benefit from immune checkpoint blockade (ICB) treatment. The mechanisms underlying immunotherapeutic resistance in MSS CRC remain to be elucidated. Here, we identified that nuclear proto-oncogene SET is significantly higher expressed in MSS CRC compared to microsatellite instability (MSI) CRC and facilitates immune escape of MSS CRC. Mechanistically, SET represses the expression of C-C motif chemokine ligand 5 (CCL5) and upregulates mismatch repair (MMR) proteins expression in a c-Myc-dependent manner, which inhibits infiltration and migration of CD8⁺ T cells to tumor tissues and results in low immunogenicity in MSS CRC. In addition, we found that SET impairs ubiquitination and proteasomal degradation of c-Myc by disrupting the interaction between E3 ligase FBXW7 and c-Myc. Moreover, SET inhibition enhances the response to immunotherapy in MSS CRC in vivo. Overall, this study reveals the critical roles and posttranslational regulatory mechanism of SET in immune escape and highlights the SET/c-Myc axis as a potential target for immunotherapy of MSS CRC that have implications for targeting a unique aspect of this disease.