CBX8 is the core component of the PCG family protein PRC1 complex. It is overexpressed in many solid tumors and plays an important role in the prognosis and biological behaviors of tumors such as occurrence, development, invasion, and metastasis. However, exploration of the role and molecular mechanism of CBX8 in tumors is still in its infancy. Our study found that the down-regulation of CBX8 expression by RNA interference induced differential expression of several microRNAs in human colon cancer cells. The 5 most differentially expressed miRNA precursors (pre-miRNA) (hsa-miR-363-3p, hsa-miR-378a-3p, hsa-miR-371b-3p, hsa-miR-361-3p, and hsa-miR-576-3p) share a common motif sequence: ARAAAKUGCMC. We selected miR-378a-3p and further revealed that the negative regulation of miRNA expression by CBX8 mainly occurs in the processing of pre-miRNA to mature miRNA. CBX8 uses its own RNA-binding domain to interact with pre-miRNA, and is dependent on its own nuclear localization characteristics to limit nucleoplasmic transport of pre-miRNA. Changing the characteristic sequence of pre-miRNA or mutating the RNA-binding domain and nuclear localization signal of CBX8 can effectively weaken the regulation of miR-378a-3p expression by CBX8. However, our experimental results showed that miR-378a-3p inhibited the malignant expression of human colon cancer cells by targeting PDIA4, resulting in increased activity of caspases-3 and -7. In summary, our study suggests that CBX8 acts as an independent RNA-binding protein to regulate miRNA expression. Simultaneously, this study shows the correlation between the CBX8/miR-378a-3p/PDIA4 pathway and the malignant biological properties of colorectal cancer, suggesting this proposed pathway as a possible therapeutic target for human cancers.

CBX8 是 PCG 家族蛋白 PRC1 复合物的核心成分。它在许多实体瘤中过表达，在肿瘤的发生、发展、侵袭和转移等预后和生物学行为中起着重要作用。然而，对CBX8在肿瘤中的作用和分子机制的探索仍处于起步阶段。我们的研究发现，通过 RNA 干扰下调 CBX8 表达会诱导人结肠癌细胞中几种 microRNA 的差异表达。5 个差异最大的 miRNA 前体（pre-miRNA）（hsa-miR-363-3p、hsa-miR-378a-3p、hsa-miR-371b-3p、hsa-miR-361-3p 和 hsa-miR- 576-3p) 共享一个共同的基序序列：ARAAAKUGCMC。我们选择了 miR-378a-3p，进一步揭示了 CBX8 对 miRNA 表达的负调控主要发生在 pre-miRNA 到成熟 miRNA 的加工过程中。CBX8 使用其自身的 RNA 结合域与 pre-miRNA 相互作用，并依赖其自身的核定位特征来限制 pre-miRNA 的核质转运。改变pre-miRNA的特征序列或突变CBX8的RNA结合域和核定位信号，可以有效减弱CBX8对miR-378a-3p表达的调控。然而，我们的实验结果表明，miR-378a-3p 通过靶向 PDIA4 抑制人结肠癌细胞的恶性表达，导致 caspase-3 和 -7 的活性增加。总之，我们的研究表明 CBX8 作为一种独立的 RNA 结合蛋白来调节 miRNA 的表达。