Recurrence and chemoresistance constitute the leading cause of death in colorectal cancer (CRC). Thus, it is of great significance to clarify the underlying mechanisms and identify predictors for tailoring adjuvant chemotherapy to improve the outcome of CRC. By screening differentially expressed genes (DEGs), constructing random forest classification and ranking the importance of DEGs, we identified membrane associated guanylate kinase, WW and PDZ domain containing 3 (MAGI3) as an important gene in CRC recurrence. Immunohistochemical and western blot assays were employed to further detect MAGI3 expression in CRC tissues and cell lines. Cell counting kit-8, plate colony formation, flow cytometry, sub-cutaneous injection and azoxymethane plus dextran sulfate sodium induced mice CRC assays were employed to explore the effects of MAGI3 on proliferation, growth, cell cycle, apoptosis, xenograft formation and chemotherapy resistance of CRC. The underlying molecular mechanisms were further investigated through gene set enrichment analysis, quantitative real-time PCR, western blot, co-immunoprecipitation, ubiquitination, GST fusion protein pull-down and immunohistochemical staining assays. Our results showed that dysregulated low level of MAGI3 was correlated with recurrence and poor prognosis of CRC. MAGI3 was identified as a novel substrate-binding subunit of SKP1-Cullin E3 ligase to recognize c-Myc, and process c-Myc ubiquitination and degradation. Expression of MAGI3 in CRC cells inhibited cell growth, promoted apoptosis and chemosensitivity to fluoropyrimidine-based chemotherapy by suppressing activation of c-Myc in vitro and in vivo. In clinic, the stage II/III CRC patients with MAGI3-high had a significantly good recurrence-free survival (~ 80%, 5-year), and were not necessary for further adjuvant chemotherapy. The patients with MAGI3-medium had a robustly good response rate or recurrence-free survival with fluoropyrimidine-based chemotherapy, and were recommended to undergo fluoropyrimidine-based adjuvant chemotherapy. MAGI3 is a novel E3 ubiquitin ligase by degradation of c-Myc to regulate CRC development and may act as a potential predictor of adjuvant chemotherapy for CRC patients.

中文翻译：

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E3泛素连接酶MAGI3降解c-Myc并作为结肠直肠癌化疗反应的预测因子

复发和化疗耐药是导致结直肠癌 (CRC) 死亡的主要原因。因此，阐明潜在机制并确定预测因子以定制辅助化疗以改善CRC结果具有重要意义。通过筛选差异表达基因（DEGs），构建随机森林分类并排序DEGs的重要性，我们确定膜相关鸟苷酸激酶，WW和PDZ结构域包含3（MAGI3）是CRC复发的重要基因。免疫组织化学和蛋白质印迹分析用于进一步检测 CRC 组织和细胞系中的 MAGI3 表达。细胞计数试剂盒-8，平板集落形成，流式细胞仪，采用皮下注射和偶氮甲烷加葡聚糖硫酸钠诱导小鼠结直肠癌试验，探讨MAGI3对结直肠癌增殖、生长、细胞周期、凋亡、异种移植物形成和化疗耐药性的影响。通过基因集富集分析、定量实时 PCR、蛋白质印迹、免疫共沉淀、泛素化、GST 融合蛋白下拉和免疫组织化学染色测定进一步研究了潜在的分子机制。我们的研究结果表明，失调的低水平 MAGI3 与 CRC 的复发和预后不良相关。MAGI3 被鉴定为 SKP1-Cullin E3 连接酶的新型底物结合亚基，可识别 c-Myc，并处理 c-Myc 泛素化和降解。CRC细胞中MAGI3的表达抑制细胞生长，通过在体外和体内抑制 c-Myc 的激活来促进细胞凋亡和对基于氟嘧啶的化学疗法的化学敏感性。在临床上，MAGI3-high 的 II/III 期 CRC 患者具有显着良好的无复发生存率（~80%，5 年），并且不需要进一步的辅助化疗。MAGI3-medium 的患者在以氟嘧啶为基础的化疗中具有良好的反应率或无复发生存率，并被推荐接受以氟嘧啶为基础的辅助化疗。MAGI3 是一种新型的 E3 泛素连接酶，通过降解 c-Myc 来调节 CRC 的发展，并可能作为 CRC 患者辅助化疗的潜在预测因子。MAGI3 高的 II/III 期 CRC 患者的无复发生存率（~80%，5 年）显着良好，不需要进一步的辅助化疗。MAGI3-medium 的患者在以氟嘧啶为基础的化疗中具有良好的反应率或无复发生存率，并被推荐接受以氟嘧啶为基础的辅助化疗。MAGI3 是一种新型的 E3 泛素连接酶，通过降解 c-Myc 来调节 CRC 的发展，并可能作为 CRC 患者辅助化疗的潜在预测因子。MAGI3 高的 II/III 期 CRC 患者的无复发生存率（~80%，5 年）显着良好，不需要进一步的辅助化疗。MAGI3-medium 的患者在以氟嘧啶为基础的化疗中具有良好的反应率或无复发生存率，并被推荐接受以氟嘧啶为基础的辅助化疗。MAGI3 是一种新型的 E3 泛素连接酶，通过降解 c-Myc 来调节 CRC 的发展，并可能作为 CRC 患者辅助化疗的潜在预测因子。并被推荐接受以氟嘧啶为基础的辅助化疗。MAGI3 是一种新型的 E3 泛素连接酶，通过降解 c-Myc 来调节 CRC 的发展，并可能作为 CRC 患者辅助化疗的潜在预测因子。并被推荐接受以氟嘧啶为基础的辅助化疗。MAGI3 是一种新型的 E3 泛素连接酶，通过降解 c-Myc 来调节 CRC 的发展，并可能作为 CRC 患者辅助化疗的潜在预测因子。