In recent years, an increasing number of studies have indicated that circular RNA plays crucial roles in regulating tumor development and chemoresistance. Using two high-throughput RNA sequence datasets, we previously found that circEXOC6B was downregulated in colon cancer. However, its role and mechanism in colorectal cancer (CRC) remained unknown. Real-time quantitative PCR was used to examine the expression of circEXOC6B in CRC tissues. In vivo and in vitro functional experiments were performed to determine the suppressor role of circEXOC6B in CRC progression. RNA pull-down, mass spectrometry, RNA-binding protein immunoprecipitation, co-immunoprecipitation, fluorescence in situ hybridization, and immunofluorescence were applied to investigate the possible mechanisms connecting circEXOC6B to CRC growth and 5-fluorouracil-induced apoptosis. Chromatin immunoprecipitation, dual-luciferase assay, western blot, and immunohistochemistry were used to explore the mechanisms underlying the HIF1A regulation of RRAGB transcription. circEXOC6B was downregulated in CRC tissues, and its lower expression was associated with poor prognosis of patients. Functional experiments showed that circEXOC6B inhibited growth and increased the 5-fluorouracil-induced apoptosis of CRC cells in vitro and in vivo. Mechanistically, circEXOC6B inhibited the heterodimer formation of RRAGB by binding to it, thereby suppressing the mTORC1 pathway and HIF1A level. In addition, HIF1A upregulated the transcription of RRAGB by binding to its promoter region. Altogether, the results demonstrated that a HIF1A-RRAGB-mTORC1 positive feedback loop drives tumor progression in CRC, which could be interrupted by circEXOC6B. circEXOC6B inhibits the progression of CRC and enhances the chemosensitivity of CRC cells to 5-fluorouracil by antagonizing the HIF1A-RRAGB-mTORC1 positive feedback loop. circEXOC6B is a possible therapeutic target for CRC treatment.

中文翻译：

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circEXOC6B 与 mTORC1 激活剂 RRAGB 相互作用，通过拮抗 HIF1A-RRAGB-mTORC1 正反馈回路来抑制结直肠癌的进展

近年来，越来越多的研究表明环状RNA在调节肿瘤发展和化疗耐药中发挥着至关重要的作用。使用两个高通量 RNA 序列数据集，我们之前发现 circEXOC6B 在结肠癌中下调。然而，其在结直肠癌（CRC）中的作用和机制仍然未知。实时定量PCR用于检测CRC组织中circEXOC6B的表达。进行了体内和体外功能实验，以确定 circEXOC6B 在 CRC 进展中的抑制作用。应用 RNA pull-down、质谱、RNA 结合蛋白免疫沉淀、共免疫沉淀、荧光原位杂交和免疫荧光来研究 circEXOC6B 与 CRC 生长和 5-氟尿嘧啶诱导的细胞凋亡相关的可能机制。染色质免疫沉淀、双荧光素酶测定、蛋白质印迹和免疫组织化学用于探索 HIF1A 调节 RRAGB 转录的机制。circEXOC6B在结直肠癌组织中下调，其低表达与患者预后不良有关。功能实验表明，circEXOC6B 在体外和体内抑制生长并增加 5-氟尿嘧啶诱导的 CRC 细胞凋亡。从机制上讲，circEXOC6B 通过与 RRAGB 的异源二聚体结合来抑制其形成，从而抑制 mTORC1 通路和 HIF1A 水平。此外，HIF1A 通过与其启动子区域结合上调 RRAGB 的转录。总之，结果表明 HIF1A-RRAGB-mTORC1 正反馈回路驱动 CRC 中的肿瘤进展，这可能被 circEXOC6B 中断。circEXOC6B 通过拮抗 HIF1A-RRAGB-mTORC1 正反馈回路来抑制 CRC 的进展并增强 CRC 细胞对 5-氟尿嘧啶的化学敏感性。circEXOC6B 是 CRC 治疗的一个可能的治疗靶点。