Genome-wide screens identify FBOX11-CCNC axis as a suppressor of CD155 mediated cancer immune evasion

The CD155/TIGIT axis plays a crucial role in the suppression of anti-tumor responses. The clinical benefit for patients with diverse types of advanced cancers that has been observed upon blockade of the interaction between CD155 and TIGIT has highlighted the need to study the mechanisms by which CD155 is regulated. Here we identify Cyclin C (CCNC) as a novel modulator of CD155 by using a genome-wide CRISPR-Cas9 screen. Notably, CCNC depletion increases the CD155 expression at the transcriptional level in a broad range of cancer cells. We further found that CCNC suppresses the CD155 expression by inhibiting the transcriptional activity of FOSL2. We further found that the stability of CCNC is negatively regulated by the E3 ubiquitin ligase complex component FBXO11. Functionally, CCNC depletion significantly suppresses the anti-tumor activity of natural killer (NK) and T cells both in vitro and in vivo. Clinically, the expression level of CCNC is negatively correlated with CD155 in cancer patient tissues. Together, our findings provide insights into the biology of CD155 regulation, identify a previously unrecognized master regulator of this critical immune checkpoint and highlight a combination immunotherapy (TIGIT/PD-1 co-blockade) as a promising anti-cancer therapeutic strategy to overcome immune evasion by CCNC-deficient tumor cells. Overall design: We generated CCNC knockout T24 cells and performed total mRNA sequencing to determine how the gene expression is altered in both parental and CCNC-KO cells.

CD155/TIGIT轴在抗肿瘤免疫应答的抑制过程中发挥关键作用。针对多种晚期癌症患者，阻断CD155与TIGIT的相互作用已被证实可带来临床获益，这一发现凸显了研究CD155调控机制的必要性。本研究通过全基因组CRISPR-Cas9筛选，鉴定出细胞周期蛋白C（Cyclin C, CCNC）作为CD155的新型调控因子。值得注意的是，敲除CCNC可在广泛的癌细胞系中于转录水平上调CD155的表达。进一步研究发现，CCNC通过抑制FOSL2的转录活性来负调控CD155的表达。此外，本研究还证实E3泛素连接酶复合物组分FBXO11对CCNC的稳定性具有负调控作用。功能实验结果表明，敲除CCNC可在体外及体内显著抑制自然杀伤细胞（natural killer, NK）和T细胞的抗肿瘤活性。临床数据分析显示，癌症患者组织中CCNC的表达水平与CD155呈负相关。综上，本研究揭示了CD155调控的生物学机制，鉴定出该关键免疫检查点此前未被认知的核心调控因子，并提出TIGIT/PD-1联合阻断免疫疗法作为极具潜力的抗癌治疗策略，以克服CCNC缺陷型肿瘤细胞的免疫逃逸。整体实验设计：我们构建了CCNC敲除的T24细胞，并对亲本细胞与CCNC敲除细胞进行全转录组测序，以明确基因表达的变化情况。