Department of Endocrinology and Metabolism, Punan Hospital, Pudong New District, Shanghai, 200125, China.
Department of Endocrinology and Metabolism, Gongli Hospital, Naval Medical University, 200135, Shanghai, China.
Mol Cancer. 2022 Jul 20;21(1):149. doi: 10.1186/s12943-022-01619-4.
Emerging evidence indicates that circular RNAs (circRNAs) and mA RNA methylation participate in the pathogenesis and metastasis of multiple malignancies including hepatocellular carcinoma (HCC). However, it remains undocumented how circRNAs form a feedback loop with the mA modification contributing to HCC.
A novel hsa_circ_0017114 (circGPR137B) was identified from three pairs of primary HCC and adjacent normal tissues by circRNA expression profiling. The association of circGPR137B and miR-4739 with clinicopathological parameters and prognosis in patients with HCC was analyzed by RT-qPCR, fluorescence in situ hybridization and TCGA cohorts. The role of circGPR137B in HCC was estimated in vitro and in vivo. RT-qPCR, western blot, mA dot blot, RIP, MeRIP and dual-luciferase reporter assays were used to validate the reciprocal regulation of the feedback loop among circGPR137B, miR-4739 and mA demethylase FTO. Meanwhile, the expression, function and prognosis of FTO in HCC were investigated by RT-qPCR, western blot, TCGA and rescue experiments.
We identified a new dramatically downregulated circGPR137B in HCC tissues, and found that downregulation of circGPR137B or upregulation of miR-4739 was associated with poor prognosis in patients with HCC. Ectopic expression of circGPR137B strikingly repressed the proliferation, colony formation and invasion, whereas knockdown of circGPR137B harbored the opposite effects. Moreover, restored expression of circGPR137B inhibited tumor growth and lung metastasis in vivo. Further investigations showed that circGPR137B, co-localized with miR-4739 in the cytoplasm, acted as a sponge for miR-4739 to upregulate its target FTO, which mediated mA demethylation of circGPR137B and promoted its expression. Thus, a feedback loop comprising circGPR137B/miR-4739/FTO axis was formed. FTO suppressed cell growth and indicated favorable survival in patients with HCC.
Our results demonstrate that circGPR137B inhibits HCC tumorigenesis and metastasis through the circGPR137B/miR-4739/FTO feedback loop. This positive feedback mechanism executed by functional coupling between a circRNA sponge and an mA modification event suggests a model for epigenetics.
新兴证据表明，环状 RNA（circRNA）和 mA RNA 甲基化参与了包括肝细胞癌（HCC）在内的多种恶性肿瘤的发病机制和转移。然而，circRNAs 如何与 mA 修饰形成反馈回路，从而促进 HCC 的发生，目前仍无文献记载。
通过 circRNA 表达谱分析，从三对原发性 HCC 和相邻正常组织中鉴定出一个新的 hsa_circ_0017114（circGPR137B）。通过 RT-qPCR、荧光原位杂交和 TCGA 队列分析 circGPR137B 和 miR-4739 与 HCC 患者临床病理参数和预后的关系。在体外和体内评估 circGPR137B 在 HCC 中的作用。使用 RT-qPCR、western blot、mA 点印迹、RIP、MeRIP 和双荧光素酶报告基因检测来验证 circGPR137B、miR-4739 和 mA 去甲基化酶 FTO 之间反馈回路的相互调节。同时，通过 RT-qPCR、western blot、TCGA 和挽救实验研究了 FTO 在 HCC 中的表达、功能和预后。
我们鉴定出一种在 HCC 组织中显著下调的新型 circGPR137B，并发现 circGPR137B 的下调或 miR-4739 的上调与 HCC 患者的不良预后相关。外源性表达 circGPR137B 可显著抑制增殖、集落形成和侵袭，而 circGPR137B 的敲低则产生相反的效果。此外，体内恢复 circGPR137B 的表达可抑制肿瘤生长和肺转移。进一步研究表明，circGPR137B 与 miR-4739 一起在细胞质中定位，作为 miR-4739 的海绵，上调其靶标 FTO，介导 circGPR137B 的 mA 去甲基化并促进其表达。因此，形成了一个由 circGPR137B/miR-4739/FTO 轴组成的反馈回路。FTO 抑制 HCC 细胞的生长，并提示 HCC 患者的生存预后良好。
我们的研究结果表明，circGPR137B 通过 circGPR137B/miR-4739/FTO 反馈环抑制 HCC 的肿瘤发生和转移。这种由环状 RNA 海绵和 mA 修饰事件的功能偶联执行的正反馈机制为表观遗传学提供了一个模型。
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