Silencing of circ_002136 sensitizes gastric cancer to paclitaxel by targeting the miR-16-5p/HMGA1 axis.

The dysregulated expression of circRNA in gastric cancer (GC) induces paclitaxel (Tax) resistance of cancer cells, which in turn affects disease progression and prognosis. Here, we sought to investigate the role and mechanism of circ_002136 in Tax-resistant GC. In this study, we found the enriched circ_002136 level and the declined miR-16-5p level in Tax-resistant GC tissues and cells. Biologically, knockdown of circ_002136 elevated the Tax sensitivity of Tax-resistant GC cells, inhibited the cell motility properties, and simultaneously drove the apoptosis. Mechanically, circ_002136 promoted the HMGA1-mediated cellular Tax resistance and cell invasion by sponging miR-16-5p. Furthermore, circ_002136 silencing impeded the growth of Tax-resistant GC tumors in vivo. Overall, our study revealed a novel signaling pathway that could be used for future clinical applications, namely the circ_002136/miR-16-5p/HMGA1 axis to regulate the Tax resistance of GC cells.

Exosome-transmitted circ_002136 promotes hepatocellular carcinoma progression by miR-19a-3p/RAB1A pathway.

BACKGROUND: Circular RNAs (circRNAs) are enriched in exosomes and are extremely stable. Exosome-mediated intercellular transfer of specific biologically active circRNA molecules can drive the transformation of the tumor microenvironment and accelerate or inhibit the local spread and multifocal growth of hepatocellular carcinoma (HCC). In this study, we explored in depth about the biological roles of HCC cell-derived exosomes and exosome-transported circRNAs on HCC in vivo and in vitro. METHODS: Exosomes extracted from HCC cells (Huh7 and HA22T) were characterized using transmission electron microscopy, nanoparticle size tracer analysis, and western blotting. Exosomes were observed for endocytosis using fluorescent labeling. The effects of HCC cell-derived exosomes and the circ_002136 they carried on cell growth, metastasis and apoptosis were determined by CCK-8 assay, transwell assay, flow cytometry analysis and TUNEL staining, respectively. The expressions of circ_002136, miR-19a-3p and RAB1A were detected by quantitative RT-PCR (qRT-PCR). Targeted binding between miR-19a-3p and circ_002136 or RAB1A was predicted and verified by bioinformatics analysis, dual-luciferase reporter and RNA pull-down experiments. The in vivo effect of circ_002136 was determined by constructing a xenograft tumor model. RESULTS: The findings revealed that Huh7 and HA22T exosomes conferred enhanced viability as well as invasive ability to recipient HCC cells. Circ_002136 was shown for the first time to be differentially upregulated in HCC tissues and cells and transferred by HCC cell-derived exosomes. More importantly, selective silencing of circ_002136 depleted the malignant biological behaviors of HCC exosome-activated Huh7 and HA22T cells. Depletion of circ_002136 in vivo effectively retarded the growth of HCC xenograft tumors. Furthermore, a well-established circ_002136 ceRNA regulatory network was constructed, namely circ_002136 blocked miR-19a-3p expression, elevated RAB1A expression activity and stimulated HCC development. Finally, high levels of circ_002136 or RAB1A, as well as low levels of miR-19a-3p, negatively affected HCC patient survival. CONCLUSION: The study on circ_002136 provides good data to support our insight into the mechanism of to-be-silenced circRNA as a therapeutic agent in the progression of HCC.

FUS/circ_002136/miR-138-5p/SOX13 feedback loop regulates angiogenesis in Glioma.

BACKGROUND: Angiogenesis plays a critical role in the progression of glioma. Previous studies have indicated that RNA-binding proteins (RBPs) interact with RNAs and participate in the regulation of the malignant behaviors of tumors. As a type of endogenous non-coding RNAs, circular RNAs (circRNAs) are abnormally expressed in various cancers and are involved in diverse tumorigeneses including angiogenesis. METHODS: The expression levels of FUS, circ_002136, miR-138-5p, SOX13, and SPON2 were determined using quantitative real-time PCR (qRT-PCR) and western blot. Transient cell transfection was performed using the Lipofectamine 3000 reagent. The RNA-binding protein immunoprecipitation (RNA-IP) and the RNA pull-down assays were used to detect the interaction between FUS and circ_002136. The dual-luciferase reporter assay system was performed to detect the binding sites of circ_002136 and miR-138-5p, miR-138-5p and SOX13. The chromatin immunoprecipitation (ChIP) assays were used to examine the interactions between transcription factor SOX13 and its target proteins . RESULTS: We demonstrated that down-regulation of FUS or circ_002136 dramatically inhibited the viability, migration and tube formation of U87 glioma-exposed endothelial cells (GECs). MiR-138-5p was down-regulated in GECs and circ_002136 functionally targeted miR-138-5p in an RNA-induced silencing complex (RISC). Inhibition of circ_002136, combined with the restoration of miR-138-5p, robustly reduced the angiogenesis of GECs. As a target gene of miR-138-5p, SOX13 was overexpressed in GECs and was proved to be involved in circ_002136 and miR-138-5p-mediated angiogenesis in gliomas. In addition, we found that SOX13 was directly associated with and activated the SPON2 promoter, thereby up-regulating the expression of SPON2 at the transcriptional level. Knockdown of SPON2 suppressed the angiogenesis in GECs. More important, SOX13 activated the FUS promoter and increased its expression, forming a feedback loop. CONCLUSION: Our data suggests that the feedback loop of FUS/circ_002136/miR-138-5p/SOX13 played a crucial role in the regulation of angiogenesis in glioma. This also provides a potential target and an alternative strategy for combined glioma therapy.