CircLDLRAD3 inhibits Oral squamous cell carcinoma progression by regulating miR-558/Smad4/TGF-ß.

Oral squamous cell carcinoma (OSCC) is a malignant neoplasm with high mortality and morbidity. The role of circRNA and its molecular mechanism in OSCC remains largely unknown. The study aims to explore the role of a novel circular RNA (circLDLRAD3) in OSCC and its underlying mechanism. PCR and fluorescence in situ hybridization were used to explore the expression features of circLDLRAD3 in OSCC. The effects of circLDLRAD3 on the behaviour of OSCC were investigated using CCK-8, colony formation assay, transwell and animal experiments. Bioinformatics analysis along with dual luciferase reporter assay and RIP assay were used to reveal the interaction between circLDLRAD3, miR-558 and Smad4. It was revealed that circLDLRAD3 exhibited low expression status in OSCC. CircLDLRAD3 inhibits proliferation, migration, and invasion of OSCC cells both in vitro and in vivo. Mechanistically, circLDLRAD3 could bind with miR-558 to positively regulate its target gene Smad4 expression. Rescue experiments further confirmed both miR-558 overexpression and Smad4 knockdown could reverse the influence of circLDLRAD3 on OSCC phenotypes. Moreover, circLDLRAD3 regulate the TGF-ß signalling pathways to influence EMT through miR-558/Smad4 axis. Our study found that circLDLRAD3 is downregulated in OSCC and verified its tumour suppressor function and mechanism in OSCC through sponging miR-558 to regulate miR-558/Smad4/TGF-ß axis. The characterization of such regulating network uncovers an important mechanism underlying OSCC progression, which could provide promising targets targeted therapy strategies for OSCC in the future.

CircTENM3 inhibites tumor progression via the miR-558/RUNX3 axis in prostate cancer.

BACKGROUND: Prostate cancer (PCa) is currently acknowledged as the second most widespread cancer among men worldwide. Yet, the lack of dependable diagnostic biomarkers and therapeutic targets has presented considerable hurdles to the progression of prostate cancer treatment. Circular RNAs are implicated in the pathogenesis of numerous diseases, positioning them as promising biomarkers for diverse medical conditions. This study aims to uncover a specific circRNA that could serve as a diagnostic and therapeutic target for detecting and treating PCa. METHODS: The change of circTENM3 expression levels in PCa was detected by qPCR. CCK8 assays, EdU assays, Scratch assay and Transwell migration assay conducted to detect the role of circTENM3 in PCa cells in vitro. RIP assay, RNA-pull down and luciferase reporter assay were performed to explore the mechanism of circTENM3. Gain-of-function analysis was performed to reveal the function of circTENM3 in PCa in vivo. RESULTS: The results revealed that the expression level of circTENM3 was significantly down-regulated in PCa. CircTENM3 overexpression alleviated the progression of PCa in vitro. Mechanistically, circTENM3 enhanced RUNX3 levels via miR-558 sponge. Gain-of-function analysis determined that circTENM3 overexpression could inhibit PCa progression in vitro. CONCLUSIONS: Our research offers profound insights into the protective role played by circTENM3 in PCa. CircTENM3 operates as a sponge for miR-558, thereby triggering the elevation of RUNX3 expression, which subsequently curbs the progression of PCa.

Circ_0007611 stimulates IL-1 receptor accessory protein to inhibit trophoblast cell proliferation and induce cell apoptosis.

Preeclampsia (PE) is a common pregnancy disorder, and mounting evidence has revealed that circular RNA participates in PE development. However, the detailed molecular mechanism of circ_0007611 in PE progression remains unknown. RNA expressions of circ_0007611, microRNA-558 (miR-558), and IL-1 receptor accessory protein (IL1RAP) were detected by quantitative real-time polymerase chain reaction. Cell proliferation was investigated by clonogenicity, 5-Ethynyl-29-deoxyuridine, and DNA content quantitation assays. Cell apoptotic rate and angiogenesis were analyzed by cell apoptosis and tube formation assays, respectively. Protein expression was detected by western blot. The binding relationship between miR-558 and circ_0007611 or IL1RAP was identified by a dual-luciferase reporter or RNA immunoprecipitation assay. Circ_0007611 and IL1RAP expressions were significantly upregulated, while miR-558 was downregulated in the placental tissues of PE women in comparison with normal placental tissues. Functionally, circ_0007611 overexpression inhibited trophoblast cell proliferation and angiogenesis and induced cell apoptosis; however, circ_0007611 downregulation showed the opposite effects. Mechanistically, circ_0007611 acted as a miR-558 sponge, and miR-558 bound to IL1RAP. Besides, miR-558 overexpression or IL1RAP absence relieved circ_0007611-induced trophoblast cell dysfunction. Moreover, miR-558 contributed to cell proliferation and tube formation and inhibited cell apoptosis by reducing IL1RAP expression in trophoblast cells. Circ_0007611 aggravated trophoblast cell disorders by the miR-558/IL1RAP pathway in PE.

Re-expression of circ_0043610 contributes to trophoblast dysfunction through the miR-558/RYBP pathway in preeclampsia.

An increasing number of data have shown the pathogenesis of preeclampsia (PE) involves circular RNA (circRNA). The study aims to investigate the function and the potential mechanism of circ_0043610 in PE. The study was performed on two human placental trophoblastic cell lines (JEG-3 and HTR-8/SVneo). The expression of circ_0043610, microRNA-558 (miR-558), and RING1 and YY1 binding protein (RYBP) was detected by quantitative real-time polymerase chain reaction. The protein levels of N-cadherin, E-cadherin, and RYBP were assessed by Western blotting. Cell viability, proliferation, apoptosis, invasion, and migration were evaluated by cell counting kit-8, 5-Ethynyl-29-deoxyuridine, flow cytometry analysis, transwell invasion assay, and wound-healing assay, respectively. Dual-luciferase reporter assay, RNA immunoprecipitation assay, and RNA pull-down assay were performed to identify the associations among circ_0043610, miR-558, and RYBP. Compared with normal placental controls, the increased expression of circ_0043610 and RYBP and the decreased miR-558 expression were detected in PE placental tissues. The overexpression of circ_0043610 led to decreased trophoblast cell proliferation, invasion, and migration but increased cell apoptosis. Mechanistically, circ_0043610 acted as a miR-558 sponge, and miR-558 bound to RYBP. Besides, miR-558 introduction remitted circ_0043610-mediated effects in JEG-3 and HTR-8/SVneo cells. Moreover, RYBP participated in the regulation of miR-558 on trophoblast cell behaviors. Further, the ectopic expression of circ_0043610 led to RYBP upregulation through miR-558. Circ_0043610 induced RYBP production to promote trophoblast dysfunction by binding to miR-558 in PE.

Circ-OPHN1 suppresses the proliferation, migration, and invasion of trophoblast cells through mediating miR-558/THBS2 axis.

Preeclampsia (PE) is one of the most serious diseases during pregnancy. Circular RNAs (circRNAs) are strongly related to the occurrence of preeclampsia. Herein, we aimed to explore the potential role and mechanism of circRNA oligophrenin 1 (circ-OPHN1; hsa_circ_0007445) in PE. Quantitative real-time polymerase chain reaction (qPCR) and western blot were utilized to detect gene expression levels. The biological behaviors of trophoblast cells were determined by 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide (MTT), flow cytometry, transwell, and wound healing methods. The binding relationship between microRNA-558 (miR-558) and circ-OPHN1 or thrombospondin 2 (THBS2) was validated via dual-luciferase reporter assay. Circ-OPHN1 and THBS2 levels were enhanced, while miR-558 level was declined in PE placental tissues. Circ-OPHN1 or THBS2 overexpression hindered the proliferation, migration, and invasion of trophoblast cells. In addition, circ-OPHN1 sequestered miR-558 to regulate THBS2 expression, thereby repressing the growth and mobility of trophoblast cells. Circ-OPHN1 inhibited trophoblast cell proliferation, migration, and invasion through mediating miR-558/THBS2 axis, providing a novel pathway for PE pathogenesis.

A circRNA derived from linear HIPK3 relieves the neuronal cell apoptosis in spinal cord injury via ceRNA pattern.

Spinal cord injury (SCI) is a severe disable symptom and has posed a great health threat to many people. Circ-HIPK3 has been reported to modulate the biological behavior of neuronal cells. Thence, in this study, we explored the mechanism of circ-HIPK3 in affecting functions of neuronal cell in SCI. SCI rat model was constructed to evaluate the apoptosis condition of spinal cord tissue. Meanwhile, 100 µM of CoCl2 was used to treat AGE1.HN and PC12 cells to induce in vitro SCI model. Functional assays were implemented to investigate the apoptosis of AGE1.HN and PC12 cells. RNase R and Act D treatment were both conducted to verify the circular character of circ-HIPK3. In this study, circ-HIPK3 was found lowly expressed in SCI rat models and AGE1.HN and PC12 cells induced by 100uM of CoCl2. Meanwhile, inhibited circ-HIPK3 or overexpressed circ-HIPK3 could separately elevate or reduce the apoptosis of AGE1.HN and PC12 cells. Moreover, circ-HIPK3 was identified as the ceRNA against miR-558 to up-regulate DPYSL5. Circ-HIPK3/miR-558/DPYSL5 axis modulated the apoptosis of AGE1.HN and PC12 cells in SCI. In conclusion, circ-HIPK3 relieves the neuronal cell apoptosis through regulating miR-588/DPYSL5 axis in SCI.

LncRNA MALAT1 protects cardiomyocytes from isoproterenol-induced apoptosis through sponging miR-558 to enhance ULK1-mediated protective autophagy.

Investigating the molecular mechanisms of myocardial infarction (MI) and subsequent heart failure have gained considerable attention worldwide. Long noncoding RNA (lncRNA) metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) has been previously demonstrated to regulate the proliferation and metastasis of several tumors. However, little is known about the effects of MALAT1 in MI and in regulating the cell date after MI. In our study, first, it was shown that the expression levels of MALAT1 were increased in the MI samples compared with normal tissues using quantitative reverse-transcription polymerase chain reaction. Then, MALAT1 knockdown could significantly decrease the cell viability and increase the apoptotic rates in isoproterenol (ISO)-treated H9C2 cells. In addition, we screened the possible target and found that miR-558 is its direct target using dual luciferase reporter assay, indicating that MALAT1 functioned as decoys sponging miR-558. Transfection of miR-558 mimic decreased the cell viability and enhanced the apoptosis. Furthermore, we revealed that miR-558 could downregulate ULK1 expression and suppressed ISO-induced protective autophagy. Activation of MALAT1/miR-558/ULK1 pathway protected H9C2 cells from ISO-induced mitochondria-dependent apoptosis. Finally, we used MALAT1-knockout mice to further demonstrated that MALAT1 protected cardiomyocytes from apoptosis and partially improved the cardiac functions upon ISO treatment. In conclusion, we elucidated that lncRNA MALAT1 protected cardiomyocytes from ISO-induced apoptosis by sponging miR-558 thus promoting ULK1-dependent autophagy. Targeting lncRNA MALAT1 might become a potential strategy in protecting cardiomyocytes during MI.

Upregulated long noncoding RNA Linc00261 in pre-eclampsia and its effect on trophoblast invasion and migration via regulating miR-558/TIMP4 signaling pathway.

Pre-eclampsia (PE) is a leading cause of maternal and perinatal morbidity and mortality but the exact underlying mechanisms of PE pathogenesis remain elusive. Accumulated data suggested that the long noncoding RNAs (lncRNAs) play important roles in the pathogenesis of PE. The present study identified the changes of lncRNA Linc00261 in PE and its effects on trophoblasts invasion and migration. Our results showed that the expression of Linc00261 was upregulated in placental tissues of PE women compared with those of healthy pregnant women. Overexpression of Linc00261 suppressed cell invasion and migration, induced cell apoptosis, and caused cell-cycle arrest at G0 /G1 phase of HTR-8/SVneo cells; while knockdown of Linc00261 had the opposite effects on the HTR-8/SVneo cells. Mechanistic studies showed Linc00261 functioned as a competing endogenous RNA for miR-558 in HTR-8/SVneo cells, and miR-558 was negatively regulated by Linc00261. The expression level of miR-558 in the PE group was significantly lower than the control group, and the expression level of Linc00261 was negatively correlated with the expression level of miR-558 in the placental tissues of women with PE. Furthermore, miR-558 was found to negatively regulate the expression of TIMP metallopeptidase inhibitor 4 (TIMP4) via targeting the 3' untranslated region in the HTR-8/SVneo cells. Overexpression of miR-558 increased HTR-8/SVneo cell invasion and migration, which was attenuated by TIMP4 overexpression. More importantly, both overexpression of miR-558 and knockdown of TIMP4 partially reversed the suppressive effects of Linc00261 overexpression on cell invasion and migration of HTR-8/SVneo cells. Collectively, our results for the first time showed the upregulation of Linc00261 in the placental tissues of severe PE patients. The mechanistic results indicated that Linc00261 exerted the suppressive effects on the trophoblast invasion and migration via targeting miR-558/TIMP4 axis, which may involve in the pathogenesis of PE.

CircHIPK3 sponges miR-558 to suppress heparanase expression in bladder cancer cells.

Increasing evidences suggest that circular RNAs (circRNAs) exert crucial functions in regulating gene expression. In this study, we perform RNA-seq and identify 6,154 distinct circRNAs from human bladder cancer and normal bladder tissues. We find that hundreds of circRNAs are significantly dysregulated in human bladder cancer tissues. We further show that circHIPK3, also named bladder cancer-related circular RNA-2 (BCRC-2), is significantly down-regulated in bladder cancer tissues and cell lines, and negatively correlates with bladder cancer grade, invasion as well as lymph node metastasis, respectively. Over-expression of circHIPK3 effectively inhibits migration, invasion, and angiogenesis of bladder cancer cells in vitro and suppresses bladder cancer growth and metastasis in vivo Mechanistic studies reveal that circHIPK3 contains two critical binding sites for the microRNA miR-558 and can abundantly sponge miR-558 to suppress the expression of heparanase (HPSE). Taken together, our findings provide evidence that circRNAs act as "microRNA sponges", and suggest a new therapeutic target for the treatment of bladder cancer.

In Vitro and In Vivo Analyses Reveal Tumor-Derived Exosome miR-558 Promotes Angiogenesis in Tongue Squamous Cell Carcinoma by Targeting Heparinase.

This study aimed to investigate the role of miR-558 in tumor angiogenesis by targeting heparinase (HPSE) in tongue squamous cell carcinoma (TSCC)-derived exosomes. In the present study, the role of exosome miR-558 in angiogenesis in vitro and in vivo was investigated by cell proliferation, migration, tube formation, subcutaneous tumor formation in mice, and in vivo Matrigel plug assay. The target genes of miR-558 were detected by means of dual luciferase assay. It was found that TSCC cells secrete miR-558 into the extracellular environment, with exosome as the carrier. Human umbilical vein endothelial cells (HUVEC) ingested exosomes, which not only increased the expression level of miR-558, but also enhanced their proliferation, migration, and tube formation functions. In vivo Matrigel plug assay demonstrated that TSCC cell-derived exosome miR-558 promoted neovascularization in vivo. Compared with negative control cells, TSCC cells overexpressing miR-558 formed subcutaneous tumors in nude mice, with larger volume, heavier mass, and more vascularization. Dual luciferase assay confirmed that HPSE was the direct target gene regulated by miR-558. HPSE promoted the proliferation, migration, and tube formation of HUVECs, and the knockout of HPSE could downregulate the pro-angiogenic effect of miR-558. In summary, miR-558 in TSCC exosomes promotes the proliferation, migration, and tube formation of HUVECs by targeting HPSE, and enhancing tumor angiogenesis.

Hsa_circ_0007482 Promotes Proliferation and Differentiation of Chondrocytes in Knee Osteoarthritis.

OBJECTIVE: Knee osteoarthritis (KOA) is a complex degenerative joint disease and a major cause of joint dysfunction. This study aimed to explore the function of hsa_circ_0007482 on inflammation, proliferation, differentiation, and apoptosis in KOA. DESIGN: Real-time quantitative polymerase chain reaction (PCR) was performed to detect the expression of circ_0007482, inflammatory factors, and differentiation-related molecules in KOA chondrocytes and interleukin (IL)-1ß-stimulated chondrocytes. The correlation between the circ_0007482 expression and inflammatory factors was analyzed by the Pearson method. KOA cell model was established using IL-1ß for 24 hours. The proliferation activity of chondrocytes was evaluated by CCK-8 assay, and cell apoptosis rate was assessed by flow cytometry. The downstream miRNA of circ_0007482 was validated using dual-luciferase reporter assay. RESULTS: The circ_0007482 expression was elevated in both KOA cartilage tissues and IL-1ß-treated chondrocytes and positively correlated with inflammatory factors expression. In comparison to the control group, IL-1ß treatment diminished chondrocyte proliferation abilities and increased cell apoptosis and inflammatory factors IL-6, IL-8, and tumor necrosis factor (TNF)-α mRNA expression. Inhibition of circ_0007482 partially improved IL-1ß-induced inflammatory reaction. Circ_0007482 could negatively regulate the expression of miR-558. CONCLUSIONS: Interfering of circ_0007482 might partially promote cell proliferation and differentiation, while inhibit cell apoptosis to improve joint injury by regulating miR-558 in IL-1ß-treated chondrocyte cell model.

CircTBX5 knockdown modulates the miR-558/MyD88 axis to alleviate IL-1ß-induced inflammation, apoptosis and extracellular matrix degradation in chondrocytes via inactivating the NF-κB signaling.

BACKGROUND: It has been widely shared that the dysregulation of circular RNA (circRNA) may contribute to the progression of osteoarthritis (OA). OA is characterized by persistent chondrocyte injury. We aimed to clarify the role of circTBX5 in IL-1ß-induced chondrocyte injury. METHODS: The expression of circTBX5, miR-558 and MyD88 mRNA was measured using quantitative real-time PCR (qPCR). Cell viability, proliferation and apoptosis were assessed by CCK-8, EdU or flow cytometry assay. The protein levels of extracellular matrix (ECM)-associated markers, MyD88, IkBα, p65 and phosphorylated IkBα were measured by western blot. The release of inflammatory factors was assessed by ELISA. The targets of circTBX5 were screened by RIP and pull-down assay. The putative binding between miR-558 and circTBX5 or MyD88 was validated by dual-luciferase reporter assay. RESULTS: CircTBX5 and MyD88 were enhanced, while miR-558 was downregulated in OA cartilage tissues and IL-1ß-treated C28/I2 cells. IL-1ß induced C28/I2 cell injury by impairing cell viability and proliferation and promoting cell apoptosis, ECM degradation and inflammatory response, while circTBX5 knockdown alleviated IL-1ß induced injury. CircTBX5 bound to miR-558 to regulate IL-1ß induced cell injury. In addition, MyD88 was a target of miR-558, and circTBX5 targeted miR-558 to positively regulate MyD88 expression. MiR-558 enrichment attenuated IL-1ß induced injury by sequestering MyD88 expression. Moreover, circTBX5 knockdown weakened the activity of NF-κB signaling, while miR-558 inhibition or MyD88 overexpression recovered the activity of NF-κB signaling. CONCLUSION: CircTBX5 knockdown modulated the miR-558/MyD88 axis to alleviate IL-1ß induced chondrocyte apoptosis, ECM degradation and inflammation via inactivating the NF-кB signaling pathway.

Circular RNA hsa_circ_0083756 promotes intervertebral disc degeneration by sponging miR-558 and regulating TREM1 expression.

OBJECTIVES: Intervertebral disc degeneration (IVDD) is a leading cause of low back pain. Circular RNAs (circRNAs) have been demonstrated to exert vital functions in IVDD. However, the role and mechanism of hsa_circ_0083756 in the development of IVDD remain unclear. MATERIALS AND METHODS: RT-qPCR was performed to detect expressions of hsa_circ_0083756, miR-558 and TREM1 in nucleus pulposus (NP) tissues and cells. CCK8 assay, flow cytometry, TUNEL assay, RT-qPCR and WB were used to clarify the roles of hsa_circ_0083756 in NP cells proliferation and extracellular matrix (ECM) formation. Bioinformatics analyses, dual-luciferase reporter gene experiment, RNA immunoprecipitation (RIP) assay and FISH assay were performed to predict and verify the targeting relationship between hsa_circ_0083756 and miR-558, as well as that between miR-558 and TREM1. Ultimately, the effect of hsa_circ_0083756 on IVDD was tested through anterior disc-puncture IVDD animal model in rats. RESULTS: hsa_circ_0083756 was upregulated in degenerative NP tissues and cells. In vitro loss-of-function and gain-of-function studies suggested that hsa_circ_0083756 knockdown promoted, whereas hsa_circ_0083756 overexpression inhibited NP cells proliferation and ECM formation. Mechanistically, hsa_circ_0083756 acted as a sponge of miR-558 and subsequently promoted the expression of TREM1. Furthermore, in vivo study indicated that silencing of hsa_circ_0083756 could alleviate IVDD in rats. CONCLUSIONS: hsa_circ_0083756 promoted IVDD via targeting the miR-558/TREM1 axis, and hsa_circ_0083756 may serve as a potential therapeutic target for the treatment of IVDD.

Hsa_circ_0001326 regulates proliferation, migration, invasion, and EMT of HTR-8/SVneo cells via increasing IL16 expression.

BACKGROUND: Preeclampsia (PE) is a serious pregnancy complication. It has been shown that insufficient infiltration of extravillous trophoblasts (EVTs) is related to the pathogenesis of PE. Circular hsa_circ_0001326 (circ_0001326) has been uncovered to be upregulated in PE. However, the influence of circ_0001326 on the infiltration of trophoblasts is indistinct. METHODS: 48 pregnant women (25 PE patients and 23 healthy controls) were recruited for this study. Human trophoblasts HTR-8/Svneo were used for function analysis. Expression of circ_0001326 was evaluated by real-time quantitative polymerase chain reaction (RT-qPCR). The diagnostic value of circ_0001326 was analyzed by receiver operating characteristic (ROC) curve. Cell proliferation, migration, and invasion of HTR-8/Svneo cells were determined using 3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide (MTT), 5-ethynyl-2'-deoxyuridine (EdU), wound-healing, and transwell assays. Protein levels were detected using Western blotting. The regulation mechanism of circ_0001326 was surveyed by bioinformatics analysis and dual-luciferase reporter assay. RESULTS: Circ_0001326 was highly expressed in plasma samples and placental tissues of PE patients. Moreover, plasma circ_0001326 could distinguish PE patients from healthy controls (area under the curve (AUC) =0.793). Functionally, circ_0001326 overexpression repressed HTR-8/Svneo cell proliferation, epithelial-mesenchymal transition (EMT), migration, and invasion, but circ_0001326 silencing had the opposing impact. Mechanically, circ_0001326 regulated interleukin-16 (IL16) expression via sponging microRNA (miR)-558. MiR-558 mimic or IL16 knockdown overturned the inhibiting effect of circ_0001326 overexpression on HTR-8/Svneo cell proliferation, EMT, migration, and invasion. CONCLUSION: Circ_0001326 elevated IL16 expression via sponging miR-558, thus curbing HTR-8/Svneo cell proliferation, EMT, migration, and invasion, suggesting that circ_0001326 might be involved in the pathogenesis of PE.

Circ0001320 inhibits lung cancer cell growth and invasion by regulating TNFAIP1 and TPM1 expression through sponging miR-558.

Lung cancer is the most affected malignant tumor in the world, and its specific pathogenesis is still unclear. It has been confirmed that circ0001320 is down-regulated in lung cancer, but its mechanism has not been reported. Further study found that circ0001320 was down-regulated in lung cancer cells, localized in the cytoplasm, and had multiple miR-558 binding sites. Dual-luciferase reporter gene assay, RNA-pull-down, and immunoprecipitation experiments all confirmed that circ0001320 directly bound to miR-558, and then inhibit the expression of miR-558. MiR-558 was up-regulated in lung cancer cells, and bound the downstream target genes TNFAIP1 and TPM1 to inhibit their expression. Western blot showed that circ0001320 significantly up-regulated the protein levels of TNFAIP1 and TPM1, while miR-558 blocked this effect of circ0001320. Circ0001320, TNFAIP1, and TPM1 all inhibited the proliferation and invasion of lung cancer cells and promoted apoptosis, while miR-558 had the opposite effects. After transfection with circ0001320 overexpression vector, miR-558 up-regulation or down-regulation of TNFAIP1, or TPM1 expression significantly reversed the inhibition of cell growth and invasion by circ0001320. Similarly, the expression of TNFAIP1 or TPM1 was down-regulated, while miR-558 expression was inhibited, and the levels of cell proliferation, apoptosis, and invasion did not change significantly. Therefore, these fully show that circ0001320 inhibits the growth and invasion of lung cancer cells through miR-558/TNFAIP1 and TPM1 pathways, which may be closely related markers and therapeutic targets of lung cancer.

A novel circular RNA, hsa_circ_0030998 suppresses lung cancer tumorigenesis and Taxol resistance by sponging miR-558.

Circular RNAs (circRNAs) are single-stranded RNAs which form a covalently closed continuous loop. Although originally shown to be non-protein-coding, some circRNAs can give rise to micropeptides. circRNAs have also been shown to play essential regulatory roles in a variety of developmental and disease processes. In a previous study, hsa_circ_0030998 was identified as a circRNA downregulated in lung cancer, but its potential implications and mechanisms in lung cancer were not addressed. Here, we showed that overexpressing circ_0030998 decreased proliferation, migration, and invasion of lung cancer cells, while also dampening resistance to Taxol, a classical antitumor drug. Depleting circ_0030998 reversed these phenotypic effects. A high circ_0030998 expression was correlated with a high survival rate in lung cancer patients. Additionally, we found circ_0030998 could downregulate miR-558 expression, serving as a microRNA sponge. In conclusion, our data support that hsa_circ_0030998 can slow down the progression of lung cancer by targeting miR-558 and suppress malignant phenotypes such as proliferation, migration, and invasion progression of lung cancer cells. Therefore, we highlight that circ_0030998 could be a novel tumor suppressor of lung cancer.

Circular RNA circREPS2 Acts as a Sponge of miR-558 to Suppress Gastric Cancer Progression by Regulating RUNX3/ß-catenin Signaling.

Circular RNAs (circRNAs) play an essential regulatory role in multiple cancers. However, the role of a large number of circRNAs in gastric cancer (GC) is still unknown. Here, hsa_circ_0139996 (circREPS2), a novel circRNA that was significantly downregulated in GC, was selected for further investigation. circREPS2 was validated and analyzed by DNA sequencing and quantitative real-time PCR. The roles of circREPS2 in GC cells were verified by gain- and loss-of-function experiments. Bioinformatics analysis, luciferase reporter, RNA pull-down, and RNA immunoprecipitation assays were performed to evaluate the functional mechanism of circREPS2 on microRNA-558 (miR-558)/RUNX3/ß-catenin axis in GC cells. In the present study, we found that circREPS2 was downregulated in GC tissues and cell lines. Low expression of circREPS2 was associated with a higher tumor-node-metastasis (TNM) stage, poor tumor differentiation, and larger tumor size in GC patients. Functionally, circREPS2 significantly inhibited GC cell proliferation, migration, invasion, and epithelial-mesenchymal transformation (EMT) in vitro and tumorigenesis in vivo. Furthermore, our data demonstrated that circREPS2 acted as a miR-558 sponge and upregulated RUNX3 expression to inactivate ß-catenin signaling in GC cells. In conclusion, circREPS2 suppresses the progression of GC via miR-558/RUNX3/ß-catenin signaling and is a novel promising biomarker and target for GC treatment.