Down-regulated Circ_0000190 promotes cervical cancer by facilitating the activity of proto-oncogene protein EIF4E

Circular RNAs (circRNAs), a new class of non-coding RNAs, have been recently confirmed to regulate cell development, functions and certain types of pathological responses. In addition, it has been proved that circ_0000190 can serve as a tumor suppressor in several cancers. However, the underlying mechanism and biological functions of it in cervical cancer (CC) remain to be revealed. In our study, relative expression of indicated molecules was detected by RT-qPCR analysis. Loss-of-function and gain-of-function experiments were conducted to detect cell functions. Mechanism experiments including RIP assay, luciferase reporter assay and pull down assay were applied to verify the interaction among the indicated molecules. Overexpressed circ_0000190 attenuated CC progression <i>in vitro</i> and <i>in vivo</i>. Circ_0000190 functioned through the modulation of miR-1252-5p/EIF4EBP2 axis. Rescue experiments found that miR-1252-5p overexpression or EIF4EBP2 knockdown could reverse the influence on CC cells caused by circ_0000190 overexpression. Interestingly, it was found that EIF4EBP2 could bind to proto-oncogene eIF4E and prevent eIF4E from forming into complex and functioning. Circ_0000190 served as a tumor suppressor in CC and down-regulated circ_0000190 expression could weaken the binding ability of EIF4EBP2 to eIF4E thus leading to CC tumorigenesis. In our investigation, a novel tumor suppressive gene circ_0000190 was recognized, which could be treated as a promising biomarker for the diagnosis of CC.

环状RNA（circular RNAs, circRNAs）是一类新型非编码RNA，现已被证实可调控细胞发育、细胞功能及部分病理应答过程。此外，已有研究证实circ_0000190在多种癌症中发挥肿瘤抑制因子的作用。然而，其在宫颈癌（cervical cancer, CC）中的具体分子机制与生物学功能仍有待阐明。本研究通过实时定量荧光PCR（reverse transcription quantitative polymerase chain reaction, RT-qPCR）检测目标分子的相对表达水平，开展功能缺失与功能获得实验以检测细胞功能表型，并采用RNA结合蛋白免疫沉淀（RNA Immunoprecipitation, RIP）实验、荧光素酶报告基因实验（luciferase reporter assay）及下拉实验（pull down assay）验证目标分子间的相互作用。过表达circ_0000190可在体外（in vitro）与体内（in vivo）环境中抑制宫颈癌进展。circ_0000190通过调控miR-1252-5p/EIF4EBP2信号轴发挥抑癌功能。挽救实验（rescue experiment）结果显示，过表达miR-1252-5p或敲低EIF4EBP2可逆转circ_0000190过表达对宫颈癌细胞造成的功能影响。值得注意的是，本研究发现EIF4EBP2可与原癌基因（proto-oncogene）eIF4E结合，阻碍eIF4E复合物的形成及其功能发挥。circ_0000190在宫颈癌中发挥肿瘤抑制因子的作用，而下调circ_0000190的表达会削弱EIF4EBP2与eIF4E的结合能力，进而促进宫颈癌的发生发展。本研究证实了新型抑癌基因circ_0000190的存在，其可作为宫颈癌诊断的潜在生物标志物。