Metastasis causes the vast majority of colorectal carcinoma (CRC)-related deaths. However, little is known about the specific traits and underlying mechanisms of metastasis-initiating cells in primary CRC. And whether or not circular RNAs (circRNAs) take part in this particular event remain not adequately stated yet. A screening method based on Transwell assay was first applied to build CRC subgroups with different metastatic potential. High throughput RNA sequencing was used to find out novel metastatic drivers in CRC metastasis-initiating step. A series of in vitro and in vivo assays were further applied to elucidate the functions and underlying molecular mechanisms of circRNAs in CRC metastasis. A circRNA consisting of exon 8–11 of LONP2, termed as circLONP2, was upregulated in metastasis-initiating CRC subgroups. Aberrant higher expression of circLONP2 was observed in primary CRC tissues with established metastasis, and along the invasive margin in metastatic site. High expression of circLONP2 predicted unfavorable overall survival. Functional studies revealed that circLONP2 could enhance the invasiveness of CRC cells in vitro, and targeting circLONP2 through anti-sense oligonucleotide (ASO) dramatically reduced the penetrance of metastasis to foreign organs in vivo. Mechanically, circLONP2 directly interacted with and promoted the processing of primary microRNA-17 (pri-miR-17), through recruiting DiGeorge syndrome critical region gene 8 (DGCR8) and Drosha complex in DDX1-dependent manner. Meanwhile, upregulated mature miR-17-5p could be assembled into exosomes and internalized by neighboring cells to enhance their aggressiveness. Our data indicate that circLONP2 acts as key metastasis-initiating molecule during CRC progression through modulating the intracellular maturation and intercellular transfer of miR-17, resulting in dissemination of metastasis-initiating ability in primary site and acceleration of metastasis formation in foreign organs. circLONP2 could serve as an effective prognostic predictor and/or novel anti-metastasis therapeutic target in CRC treatment.

中文翻译：

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CircLONP2通过调节microRNA-17的成熟和外泌体传播增强结直肠癌的侵袭和转移

转移导致绝大多数结直肠癌 (CRC) 相关的死亡。然而，关于原发性 CRC 中转移起始细胞的特定特征和潜在机制知之甚少。环状RNA（circRNA）是否参与这一特定事件仍未得到充分说明。首次应用基于 Transwell 检测的筛选方法构建具有不同转移潜能的 CRC 亚组。高通量 RNA 测序用于在 CRC 转移起始步骤中找出新的转移驱动因素。进一步应用一系列体外和体内检测来阐明 circRNA 在 CRC 转移中的功能和潜在分子机制。由 LONP2 的外显子 8-11 组成的 circRNA，称为 circLONP2，在引发转移的 CRC 亚组中上调。在具有确定转移的原发性 CRC 组织中以及沿转移部位的侵袭性边缘观察到 circLONP2 的异常高表达。circLONP2 的高表达预示着不利的总生存期。功能研究表明，circLONP2可以在体外增强CRC细胞的侵袭性，并且通过反义寡核苷酸（ASO）靶向circLONP2在体内显着降低了转移到外来器官的外显率。在机械上，circLONP2通过以DDX1依赖性方式招募DiGeorge综合征关键区基因8（DGCR8）和Drosha复合物，直接与初级microRNA-17（pri-miR-17）相互作用并促进其加工。同时，上调的成熟 miR-17-5p 可以组装成外泌体并被邻近细胞内化以增强其侵袭性。我们的数据表明，circLONP2 通过调节 miR-17 的细胞内成熟和细胞间转移，在 CRC 进展过程中充当关键的转移起始分子，导致原发部位转移起始能力的传播和外源器官转移形成的加速。circLONP2可以作为CRC治疗中有效的预后预测因子和/或新的抗转移治疗靶点。