ID3 Enhances PD-L1 Expression by Restructuring MYC and  Promotes Colorectal Cancer Immune Evasion [RNA-seq]
The inhibitor of DNA-binding protein ID3 is a vital component of immune cells and has been associated with the progression of colorectal cancer (CRC). Despite its significance, its specific role in the immune evasion strategies utilized by CRC remains unclear. RNA-seq analysis revealed that ID3 is associated with the PD-L1 immune checkpoint. We further demonstrated that ID3 modulates PD-L1 expression, suppresses the infiltration and activation of CD8+ T cells, and facilitates the immune escape of CRC cells. Additionally, we found that the knockdown of ID3 significantly enhanced the effectiveness of PD-L1 antibody treatment in combating CRC, reduced the upregulation of PD-L1 induced by the antibody, and altered the immune microenvironment within CRC. Mechanistically, our biological and structural analyses demonstrated that ID3 reconstructed the four-dimensional structure of MYC, thereby enhancing its binding affinity to the PD-L1 promoter and augmenting PD-L1 transcriptional activity. By integrating analysis of ChIP-seq, RNA-seq, and ImmPort gene sets, we found that ID3's DNA-assisted binding function was widespread and could either enhance or suppress gene transcription, not only affecting tumor immune escape through immune checkpoints, but also regulating various cytokines and immune cells involved in tumor immunity. In conclusion, our study uncovered a new mechanism by which ID3 promotes immune evasion in CRC and targeting ID3 may improve the efficacy of anti-PD-1/PD-L1 immunotherapy. Overall design: To investigate the role of the inhibitor of DNA-binding protein ID3 in immune escape of colorectal cancer, we established ID3-knockout colorectal cancer cell line HCT116 using CRISPR/Cas9 technology to study the gene expression regulated by ID3. We then performed gene expression profiling analysis using data obtained from RNA-seq of sgID3 and sgCtrl. Comparative gene expression profiling of RNA-seq data is sgID3_1, sgID3_2, sgCtrl_1 and sgCtrl_2.