Circular RNA circ_0000615 knockdown suppresses the development of nasopharyngeal cancer through regulating the miR-338-3p/FGF2 axis

Plasma Circular RNAs as Biomarkers for Breast Cancer

Breast cancer (BC) is currently the most common neoplasm, the second leading cause of cancer death in women worldwide, and is a major health problem. The discovery of new biomarkers is crucial to improve our knowledge of breast cancer and strengthen our clinical approaches to diagnosis, prognosis, and follow-up. In recent decades, there has been increasing interest in circulating RNA (circRNA) as modulators of gene expression involved in tumor development and progression. The study of circulating circRNAs (ccircRNAs) in plasma may provide new non-invasive diagnostic, prognostic, and predictive biomarkers for BC. This review describes the latest findings on BC-associated ccircRNAs in plasma and their clinical utility. Several ccircRNAs in plasma have shown great potential as BC biomarkers, especially from a diagnostic point of view. Mechanistically, most of the reported BC-associated ccircRNAs are involved in the regulation of cell survival, proliferation, and invasion, mainly via MAPK/AKT signaling pathways. However, the study of circRNAs is a relatively new area of research, and a larger number of studies will be crucial to confirm their potential as plasma biomarkers and to understand their involvement in BC.

Emerging roles of circular RNAs in the invasion and metastasis of head and neck cancer: Possible functions and mechanisms

Head and neck cancer (HNC) is the seventh most prevalent malignancy worldwide in 2020. Cancer metastasis is the main cause of poor prognosis in HNC patients. Recently, circular RNAs (circRNAs), initially thought to have no biological function, are attracting increasing attention, and their crucial roles in mediating HNC metastasis are being extensively investigated. Existing studies have shown that circRNAs primarily function through miRNA sponges, transcriptional regulation, interacting with RNA-binding proteins (RBPs) and as translation templates. Among these functions, the function of miRNA sponge is the most prominent. In this review, we summarized the reported circRNAs involved in HNC metastasis, aiming to elucidate the regulatory relationship between circRNAs and HNC metastasis. Furthermore, we summarized the latest advances in the epidemiological information of HNC metastasis and the tumor metastasis theories, the biogenesis, characterization and functional mechanisms of circRNAs, and their potential clinical applications. Although the research on circRNAs is still in its infancy, circRNAs are expected to serve as prognostic markers and effective therapeutic targets to inhibit HNC metastasis and significantly improve the prognosis of HNC patients.

Exosomal Circ_FMN2 Derived from the Serum of Colorectal Cancer Patients Promotes Cancer Progression by miR-338-3p/MSI1 Axis

BACKGROUND

Colorectal cancer (CRC) is a common malignancy of the gastrointestinal tract with high incidence and mortality. Exosomal circular RNA (circRNA) has been shown to be associated with the malignant progression of cancers, including CRC. Circ_0005100 (named as circ_FMN2) has been shown to promote CRC cell proliferation and migration. However, whether exosomal circ_FMN2 participated in CRC progression remains unclear.

METHODS

Exosomes were isolated from the serum of CRC patients and then identified using transmission electron microscope. Western blot assay was used to test the protein levels of exosome markers, proliferation-related marker, metastasis-related markers and musashi-1 (MSI1). The expression levels of circ_FMN2, microRNA (miR)-338-3p and MSI1 were detected by qPCR. Flow cytometry, colony formation assay, MTT assay, and transwell assay were employed to measure cell cycle, apoptosis, colony formation ability, viability, migration and invasion. Dual-luciferase reporter assay was performed to assess the interaction between miR-338-3p and circ_FMN2 or MSI1. BALB/c nude mice was used to conduct animal experiments.

RESULTS

Circ_FMN2 was overexpressed in the exosomes of CRC patient's serums and CRC cells. Overexpressed exosomal circ_FMN2 could promote CRC cell proliferation, metastasis, and suppress apoptosis. Circ_FMN2 acted as miR-338-3p sponge. MiR-338-3p overexpression reversed the promotion effect of circ_FMN2 on CRC progression. MSI1 was found to be a target of miR-338-3p, and its overexpression revoked the inhibitory effect of miR-338-3p on CRC progression. Furthermore, exosomal circ_FMN2 overexpression also could facilitate CRC tumor growth in vivo.

CONCLUSION

Exosomal circ_FMN2 accelerated CRC progression through miR-338-3p/MSI1 axis, revealing that exosomal circ_FMN2 might be a target for CRC treatment.

Identification of the regulatory role of the circ_0004788/miR-515-5p/FGF2 network in nasopharyngeal carcinoma development

BACKGROUND

CircularRNAs (circRNAs) played vital roles in nasopharyngeal carcinoma (NPC). However, the impacts of circ_0004788 on the development of NPC have not been explored.

METHODS

Cell counting kit-8 (CCK-8), 5-Ethynyl-2'-deoxyuridine (EdU) and colony formation assays were applied to determine cell proliferation. Wound healing, transwell invasion assay, tube formation assay, and flow cytometry were employed for the detection of cell migration, invasion, angiogenesis, and apoptosis, respectively. Xenograft tumor experiment was used to explore the biological role of circ_0004788 in NPC in vivo.

RESULTS

Circ_0004788 and fibroblast growth factor 2 (FGF2) were significantly elevated, and microRNA-515-5p (miR-515-5p) was dramatically decreased in NPC tissues and cells. The impacts of circ_0004788 knockdown on cell progression in NPC cells were reversed by miR-515-5p inhibitor, and FGF2 overexpression could block the suppressive effect of miR-515-5p on cell progression in NPC cells.

CONCLUSION

Circ_0004788 knockdown restrained the progression of NPC via the miR-515-5p/FGF2 axis.

Circular RNA circ_0065378 upregulates tumor suppressor candidate 1 by competitively binding with miR-4701-5p to alleviate colorectal cancer progression

BACKGROUND AND AIM

Colorectal cancer (CRC), the third most lethal human cancer worldwide, seriously threatens human health and life. Numerous circular RNAs (circRNAs) including circ_PLXNB1 (hsa_circ_0065378) have been confirmed to be dysregulated in CRC by RNA-seq analysis. We aimed to explore the functional role of circ_PLXNB1 in CRC malignant behaviors and clarify its potential molecular mechanism.

METHODS

Gene expression levels of circ_PLXNB1 and miR-4701-5p were determined by quantitative real-time polymerase chain reaction analysis. MTT and Transwell assays were conducted to measure cell proliferation, invasion, and migration. Protein expression of tumor suppressor candidate 1 (TUSC1), E-cadherin and N-cadherin was determined by western blot analysis. Mouse xenograft models were used to investigate the role of circ_PLXNB1 in tumor growth.

RESULTS

The results showed that gene expression of circ_PLXNB1 in CRC tissues was significantly downregulated. Overexpression of circ_PLXNB1 inhibited the malignant behaviors of CRC cells, as manifested by the decrease in cell proliferation, cell invasion, migration, and EMT. Mechanistically, circ_PLXNB1 exerted its functional effects by binding with miR-4701-5p. Moreover, TUSC1 siRNA partially abolished the suppressive effect of the miR-4701-5p inhibitor or circ_PLXNB1 on CRC cell malignant behaviors.

CONCLUSIONS

Circ_PLXNB1 attenuated CRC progression by binding with miR-4701-5p to overexpress TUSC1, indicating that the circ_PLXNB1/miR-4701-5p/TUSC1 axis might be a potential novel molecular target in CRC diagnosis and therapy.

The Diagnostic Value of Serum Exosomal Has_circ_0000615 for Breast Cancer Patients

Background

To explore the expression level of has_circ_0000615 in peripheral blood samples and evaluate its diagnostic value for breast cancer patients.

Methods

The peripheral blood samples of 95 breast cancer patients who underwent curative surgical resection and 95 age-matched healthy volunteers in our institutions from September 2019 to November 2020 were systematically collected. The expression level of has_circ_0000615 in the plasma was amplified and detected by qRT-PCR, and its correlation to clinicopathological characteristics of breast cancer patients were analyzed.

Results

Breast cancer patients had a significantly higher expression level of has_circ_0000615 in the plasma than healthy controls (P < 0.01), and its high expression was closely associated with advanced tumor stage (P=0.010), lymph node metastasis (P = 0.001) and high grade of recurrence risk (P=0.012). The receiver operator characteristic (ROC) curves showed that the area under curve (AUC) value, sensitivity and specificity of has_circ_0000615 for the diagnosis of non-metastatic breast cancer was 0.904 (95% CI: 0.863–0.944), 76.8% and 88.4%, respectively. Serum has_circ_0000615 expression had a better diagnostic efficiency than routine tumor biomarkers such as CA153, CA125 and CEA for distinguishing breast cancer patients from healthy individuals. TEM revealed that isolated exosomes from the culture medium of breast cancer cells had a disk-like appearance with a diameter of 80–200 nm vesicles, and the expression of exosome markers CD9 and CD81 was markedly increased. More importantly, the expression of has_circ_0000615 was detected in the exosomes and its expression level was markedly upregulated in breast cancer cell lines compared with normal ductal epithelial cells. The stability assay showed that there was no difference between RNA extraction at 0 hour and 24 hours in terms of the expression of has_circ_0000615 (P =0.327). Has_circ_0000615 might as exosomes be secreted into the circulating blood of breast cancer patients, resulting in a high expression level in plasma samples.

Conclusion

The detection of has_circ_0000615 might be a promising diagnostic method for breast cancer.

Circ_0000615 promotes high glucose-induced human retinal pigment epithelium cell apoptosis, inflammation and oxidative stress via miR-646/YAP1 axis in diabetic retinopathy

BACKGROUND

Diabetic retinopathy (DR), a common complication of diabetes mellitus, is the major cause of visual impairment and blindness. Circ_0000615 was found to be elevated in retina samples of diabetic patients. Hence, the detailed effects and molecular mechanisms of circ_0000615 in DN progression were explored.

METHODS

The levels of circ_0000615, microRNA (miR)-646 and YAP1 (yes-associated protein 1) were detected using quantitative real-time polymerase chain reaction and Western blot assays. Cell viability, apoptosis, inflammation and reactive oxygen species (ROS) generation were determined using cell counting kit-8 assay, flow cytometry, caspase3 activity analysis, Western blot, enzyme-linked immunosorbent assay (ELISA) and Dichlorofluorescein diacetate (DCFH-DA) assay, respectively. The binding interaction between miR-646 and circ_0000615 or YAP1 was determined using dual-luciferase reporter, RNA immunoprecipitation (RIP), and RNA pull-down assays.

RESULTS

Circ_0000615 was elevated in high glucose (HG)-induced human retinal pigment epithelium (HRPE) cells. Knockdown of circ_0000615 attenuated HG-triggered HRPE cell apoptosis, inflammation, and ROS generation. Mechanistically, miR-646 was confirmed to be a target of circ_0000615, inhibition of miR-646 reversed the protective effects of circ_0000615 knockdown on HG-evoked HRPE cell dysfunction. MiR-646 was verified to target YAP1, overexpression of YAP1 abolished the impairment induced by miR-646 on HG-induced HRPE cell damage. Besides that, we confirmed that circ_0000615 could regulate YAP1 expression via miR-646.

CONCLUSION

Circ_0000615 contributed to HG-induced HRPE cell dysfunction via miR-646/YAP1 axis, suggesting a novel insight into the pathogenesis of DR and a potential candidate for DR treatment.

A minor review of microRNA-338 exploring the insights of its function in tumorigenesis

MicroRNAs(miRNAs) are small non-coding RNAs which have a critical role in various biological processes via direct binding and post-transcriptionally regulating targeted genes expression. More than one-half of human genes were regulated by miRNAs and their aberrant expression was detected in various human diseases, including cancers. miRNA-338 is a new identified miRNA and increasing evidence show that miRNA-338 participates in the progression of lots of cancers, such as lung cancer, hepatocellular cancer, breast cancer, glioma, and so on. Although a range of targets and signaling pathways such as MACC1 and Wnt/β-catenin signaling pathway were illustrated to be regulated by miRNA-338, which functions in tumor progression are still ambiguous and the underlying molecular mechanisms are also unclear. Herein, we reviewed the latest studies in miRNA-338 and summarized its roles in different type of human tumors, which might provide us new idea for further investigations and potential targeted therapy.

hsa_circ_0001018 promotes papillary thyroid cancer by facilitating cell survival, invasion, G1/S cell cycle progression, and repressing cell apoptosis via crosstalk with miR-338-3p and SOX4

We identified a novel interactome, circ_0001018/miR-338-3p/SOX4, in papillary thyroid cancer (PTC), and we intended to confirm the regulatory relationship between the three and to study the effects of the three in PTC. The bioinformatics method was used to screen out the circular RNA and mRNA of interest. A cellular fractionation assay and fluorescence in situ hybridization (FISH) assay were conducted to prove that circ_0001018 and CCT4 (the host gene of circ_0001018) mRNA primarily localized in the cytoplasm of PTC cell lines. By qRT-PCR analysis, the expression of circ_0001018 and SOX4 mRNA was found upregulated while the expression of miR-338-3p was found downregulated in PTC tissues and cells. circ_0001018 silence significantly inhibited the tumor growth in xenografted nude mice. A series of cytological experiments such as a Cell Counting Kit-8 (CCK-8) assay, a 5-ethynyl-2′-deoxyuridine (EdU) assay, cell cycle profiling, wound healing, a transwell assay, and cell apoptosis were conducted and showed that circ_0001018 and SOX4 promoted cell proliferation, migration, and invasion, inhibited cell apoptosis, and reduced the cell cycle arrest at the G₁ phase in PTC cells. Compared with circ_0001018 and SOX4, miR-338-3p held the opposite function. The regulatory relationship between circ_0001018 and miR-338-3p, and between miR-338-3p and SOX4 mRNA, was validated using a luciferase reporter gene assay and/or RNA immunoprecipitation (RIP assay). Our findings showed that circ_0001018 acted as the tumor promoter via sponging miR-338-3p to elevate SOX4 expression level in PTC. Importantly, this novel circ_0001018/miR-338-3p/SOX4 axis has the potential to be considered as a therapy target for PTC.

The role of microRNA-338-3p in cancer: growth, invasion, chemoresistance, and mediators

Cancer still remains as one of the leading causes of death worldwide. Metastasis and proliferation are abnormally increased in cancer cells that subsequently, mediate resistance of cancer cells to different therapies such as radio-, chemo- and immune-therapy. MicroRNAs (miRNAs) are endogenous short non-coding RNAs that can regulate expression of target genes at post-transcriptional level and capable of interaction with mRNA-coding genes. Vital biological mechanisms including apoptosis, migration and differentiation are modulated by these small molecules. MiRNAs are key players in regulating cancer proliferation and metastasis as well as cancer therapy response. MiRNAs can function as both tumor-suppressing and tumor-promoting factors. In the present review, regulatory impact of miRNA-338-3p on cancer growth and migration is discussed. This new emerging miRNA can regulate response of cancer cells to chemotherapy and radiotherapy. It seems that miRNA-338-3p has dual role in cancer chemotherapy, acting as tumor-promoting or tumor-suppressor factor. Experiments reveal anti-tumor activity of miRNA-338-3p in cancer. Hence, increasing miRNA-338-3p expression is of importance in effective cancer therapy. Long non-coding RNAs, circular RNAs and hypoxia are potential upstream mediators of miRNA-338-3p in cancer. Anti-tumor agents including baicalin and arbutin can promote expression of miRNA-338-3p in suppressing cancer progression. These topics are discussed to shed some light on function of miRNA-338-3p in cancer cells.