Circular RNA CRIM1 functions as a ceRNA to promote nasopharyngeal carcinoma metastasis and docetaxel chemoresistance through upregulating FOXQ1

Insight into LncRNA- and CircRNA-Mediated CeRNAs: Regulatory Network and Implications in Nasopharyngeal Carcinoma—A Narrative Literature Review

Nasopharyngeal carcinoma (NPC) is a kind of head-and-neck malignant tumor, and distant metastasis treatment resistance is the leading cause of patient death. In-depth understanding of NPC progression and treatment failure remains to be explored. Long noncoding RNAs (lncRNAs) and circular RNAs (circRNAs) are noncoding RNAs that play key regulatory role in shaping tumor cell activities. Recent studies have revealed that lncRNA and circRNA function as competitive endogenous RNAs (ceRNAs) by regulating the posttranscriptional expression of genes as miRNA baits. The imbalanced ceRNA networks derived from lncRNA/circRNA-miRNA-mRNA interaction are widely found to contribute to NPC development. Herein, we summarize typical examples of lncRNA/circRNA-associated ceRNAs in recent years, which involved the potential molecular mechanisms in the regulation of proliferation, apoptosis, treatment resistance and metastasis of NPC, and discuss their potential clinical significance in the prognosis and treatment of NPC. Interpreting the involvement of ceRNAs networks will provide new insight into the pathogenesis and treatment strategies of NPC. However, ceRNA regulatory mechanism has some limitations currently. Screening the most effective ceRNA targets and the clinical application of ceRNA still has many challenges.

The emerging roles of circular RNA-mediated autophagy in tumorigenesis and cancer progression

Circular RNA (circRNA) is characterized by a specific covalently closed ring structure. The back-splicing of precursor mRNA is the main way of circRNA generation, and various cis/trans-acting elements are involved in regulating the process. circRNAs exhibit multiple biological functions, including serving as sponges of microRNAs, interacting with proteins to regulate their stabilities and abilities, and acting as templates for protein translation. Autophagy participates in many physiological and pathological processes, especially it plays a vital role in tumorigenesis and carcinoma progression. Increasing numbers of evidences have revealed that circRNAs are implicated in regulating autophagy during tumor development. Until now, the roles of autophagy-associated circRNAs in carcinoma progression and their molecular mechanisms remain unclear. Here, the emerging regulatory roles and mechanisms of circRNAs in autophagy were summarized. Furtherly, the effects of autophagy-associated circRNAs on cancer development were described. We also prospected the potential of autophagy-associated circRNAs as novel therapeutic targets of tumors and as biomarkers for cancer diagnosis and prognosis.

Ferroptosis regulators related scoring system by Gaussian finite mixture model to predict prognosis and immunotherapy efficacy in nasopharyngeal carcinoma

The role of ferroptosis in tumor progression and metastasis has been demonstrated. Nonetheless, potential biological function of ferroptosis regulatory pattern in nasopharyngeal carcinoma (NPC) remains unknown. Ferroptosis regulatory patterns of nasopharyngeal carcinoma samples were evaluated based on 113 ferroptosis regulators and three distinct ferroptosis subtypes were determined by unsupervised clustering. The ferroptosis score (FEP score) was identified to quantify ferroptosis patterns within individual tumors by Gaussian finite mixture model and systematically correlated with representative tumor characteristics. Subtype 1 and subtype 3 were consistent with immune activated phenotype, while subtype 2 was consistent with immune suppressed phenotype. High ferroptosis score, characterized by immune activation and suppression of mRNA based stemness index (mRNAsi) and Epstein-Barr virus (EBV) genes, indicated an immune activated tumor microenvironment (TME) phenotype, with better progression free survival (PFS) and lower risk of recurrence and metastasis. Low ferroptosis score, characterized by activation of Wnt and NF-κB signaling pathways and lack of effective immune infiltration, indicated an immune suppressed tumor microenvironment phenotype and poorer survival. High ferroptosis score was also correlated to enhanced response to immunotherapy, and was confirmed to correlate with therapeutic advantages and clinical benefits in an anti-programmed cell death 1 ligand 1 (PD-L1) immunotherapy cohort. As ferroptosis played a crucial role in the tumor microenvironment’s diversity, assessing the ferroptosis pattern within individual tumor with ferroptosis score could enhance our understanding of tumor microenvironment infiltration characterization and help develop more effective immunotherapy.

Epstein-Barr virus-encoded microRNA BART22 serves as novel biomarkers and drives malignant transformation of nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is an epithelial malignancy ubiquitously associated with Epstein-Barr virus (EBV). EBV generates various viral microRNAs (miRNAs) by processing the BHRF1 and BamHI A rightward (BART) transcripts. These BART miRNAs are abundantly expressed in NPC, but their functions and molecular mechanisms remain largely unknown. Our study found that the EBV-encoded microRNA BART-22 was significantly upregulated in NPC tissues and positively correlated with tumor progression. Furthermore, we found that EBV-miR-BART-22 was a significant predictor of poor prognosis in NPC. A reliable nomogram model to predict the preoperative overall survival (OS) of NPC patients was established. The area under the receiver operating characteristic (ROC) curve value for 5-year survival was 0.91. Elevated levels of EBV-miR-BART-22 significantly promoted the epithelial-mesenchymal transition (EMT) and metastasis of NPC cells in vivo and in vitro. We found that EBV-miR-BART-22 directly targets the 3'-UTR of MOSPD2 mRNA to promote the EMT and metastasis of NPC cells by activating the Wnt/β-catenin signaling pathway. Our findings provide a potential prognostic biomarker and new insight into the molecular mechanisms of NPC metastasis.

Epithelial-Mesenchymal Transition-Mediated Tumor Therapeutic Resistance

Cancer is one of the world’s most burdensome diseases, with increasing prevalence and a high mortality rate threat. Tumor recurrence and metastasis due to treatment resistance are two of the primary reasons that cancers have been so difficult to treat. The epithelial–mesenchymal transition (EMT) is essential for tumor drug resistance. EMT causes tumor cells to produce mesenchymal stem cells and quickly adapt to various injuries, showing a treatment-resistant phenotype. In addition, multiple signaling pathways and regulatory mechanisms are involved in the EMT, resulting in resistance to treatment and hard eradication of the tumors. The purpose of this study is to review the link between EMT, therapeutic resistance, and the molecular process, and to offer a theoretical framework for EMT-based tumor-sensitization therapy.

Exosomal circWDR62 promotes temozolomide resistance and malignant progression through regulation of the miR-370-3p/MGMT axis in glioma

Exosome-mediated delivery of circular RNAs (circRNAs) is implicated in cancer progression. However, the role of exosomal circRNAs in the chemotherapy resistance of tumours remains poorly understood. Here we identified a novel circRNA, circWDR62. It was found that circWDR62 expression was upregulated in TMZ-resistant glioma cells and TMZ-resistant glioma cell-derived exosomes compared with their controls by using high-throughput microarray analysis and quantitative real-time polymerase chain reaction, and high circWDR62 expression was associated with poor prognosis of glioma. Functionally, downregulation of circWDR62 expression could significantly inhibit the TMZ resistance and malignant progression of glioma. Further mechanistic studies showed that circWDR62 plays a role by sponging miR-370-3p as a competing endogenous RNA. Rescue experiments confirmed that MGMT is the downstream target of the circWDR62/miR-370-3p axis in glioma. In addition, circWDR62 could be transported between TMZ-resistant and TMZ-sensitive glioma cells via exosomes. Exosomal circWDR62 from TMZ-resistant cells conferred TMZ resistance in recipient sensitive cells while also enhancing the proliferation, migration and invasion of these cells. A series of clinical and in vivo trials corroborated that exosomal circWDR62 could promote TMZ chemoresistance and malignant progression of glioma. Our results demonstrate for the first time that exosome-mediated delivery of circWDR62 can promote TMZ resistance and malignant progression via targeting of the miR-370-3p/MGMT axis in vitro and in vivo in glioma, providing a new therapeutic strategy. Moreover, exosomal circWDR62 in human serum may serve as a promising therapeutic target and prognostic marker for glioma therapy.

circEXOC6B interacting with RRAGB, an mTORC1 activator, inhibits the progression of colorectal cancer by antagonizing the HIF1A-RRAGB-mTORC1 positive feedback loop

Background

In recent years, an increasing number of studies have indicated that circular RNA plays crucial roles in regulating tumor development and chemoresistance. Using two high-throughput RNA sequence datasets, we previously found that circEXOC6B was downregulated in colon cancer. However, its role and mechanism in colorectal cancer (CRC) remained unknown.

Methods

Real-time quantitative PCR was used to examine the expression of circEXOC6B in CRC tissues. In vivo and in vitro functional experiments were performed to determine the suppressor role of circEXOC6B in CRC progression. RNA pull-down, mass spectrometry, RNA-binding protein immunoprecipitation, co-immunoprecipitation, fluorescence in situ hybridization, and immunofluorescence were applied to investigate the possible mechanisms connecting circEXOC6B to CRC growth and 5-fluorouracil-induced apoptosis. Chromatin immunoprecipitation, dual-luciferase assay, western blot, and immunohistochemistry were used to explore the mechanisms underlying the HIF1A regulation of RRAGB transcription.

Results

circEXOC6B was downregulated in CRC tissues, and its lower expression was associated with poor prognosis of patients. Functional experiments showed that circEXOC6B inhibited growth and increased the 5-fluorouracil-induced apoptosis of CRC cells in vitro and in vivo. Mechanistically, circEXOC6B inhibited the heterodimer formation of RRAGB by binding to it, thereby suppressing the mTORC1 pathway and HIF1A level. In addition, HIF1A upregulated the transcription of RRAGB by binding to its promoter region. Altogether, the results demonstrated that a HIF1A-RRAGB-mTORC1 positive feedback loop drives tumor progression in CRC, which could be interrupted by circEXOC6B.

Conclusions

circEXOC6B inhibits the progression of CRC and enhances the chemosensitivity of CRC cells to 5-fluorouracil by antagonizing the HIF1A-RRAGB-mTORC1 positive feedback loop. circEXOC6B is a possible therapeutic target for CRC treatment.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12943-022-01600-1.

CircNRIP1 acts as a sponge of miR-1200 to suppress osteosarcoma progression via upregulation of MIA2

Circular RNAs (circRNAs), a class of non-coding RNAs, play an essential role in embryo development and carcinogenesis, circNRIP1 was recently identified to promote development of multiple human cancers. This study investigated the role of circNRIP1 in osteosarcoma (OS) cells and the potential mechanisms relating to the sponging miRNAs and their target genes. OS cell lines and normal human osteoblasts were grown for qRT-PCR analysis of circNRIP1 expression and functions of circNRIP1 expression in OS cell proliferation, migration, and invasion in vitro. Bioinformatics analysis was then performed to predict the sponge miRNA of circNRIP1 and the target gene, which was confirmed by using the dual-luciferase reporter assay. The in vivo functions of circNRIP1 was evaluated in OS cell xenograft models, while levels of relevant marker genes were examined using immunohistochemistry. CircNRIP1 was mainly localized in OS cell cytoplasm and significantly lower in OS cell lines than in normal human osteoblasts. CircNRIP1 overexpression significantly inhibited OS cell proliferation, migration, and invasion in vitro. miR-1200 was predicted as the sponge miRNA of circNRIP1 and directly interacted with circNRIP1 confirmed by the dual-luciferase reporter assay. Moreover, miR-1200 overexpression significantly alleviated the inhibitory effect of circNRIP1 on OS cells. A protein-coding gene MIA2 was identified as the miR-1200 targeting gene and reversely associated with miR-1200 expression in OS cells. Increase in MIA2 expression in a murine OS cell xenograft model was associated with circNRIP1 expression in inhibition of OS cell xenograft growth in vivo. These data support the circNRIP1 OS-suppressive role by sponge of miR-1200 expression and in turn to upregulate MIA2 expression.

EIF4A3-induced circFIP1L1 represses miR-1253 and promotes radiosensitivity of nasopharyngeal carcinoma

BACKGROUND

Radiation is currently used to be a mainstay of salvage therapy for nasopharyngeal carcinoma (NPC), however, development of radioresistance largely limits the radiation efficacy. Circular RNAs (circRNAs) have been shown to affect NPC progression, but its role in radioresistance remain unclear.

METHODS

The circular structure of circFIP1L1(circ_0069740) was verified by RNA-sequencing, RT-PCR based on gDNA or cDNA, RNase R treatment, and actinomycin D treatment. Cellular localization of circFIP1L1 and miR-1253 was detected by nucleoplasmic separation and/or fluorescence in situ hybridization. Expression of non-coding RNAs and mRNAs was detected by qRT-PCR, protein expression was detected by Western blot. Functionally, EdU, CCK-8, and colony formation experiments were employed to assess cell proliferation, flow cytometry was adopted to estimate cell cycle and apoptosis. Xenograft tumor growth was performed to detect the role of circFIP1L1 in vivo. Mechanistically, we examined the interplay between miR-1253 and circFIP1L1 or EIF4A3 through dual-luciferase reporter assay. The potential regulatory impacts of EIF4A3 on circFIP1L1 or PTEN was examined by RNA immunoprecipitation and RNA pull-down assays.

RESULTS

CircFIP1L1 overexpression and miR-1253 knockdown repressed NPC cell proliferation, facilitated NPC cell apoptosis, and enhanced NPC radiosensitivity. Mechanistically, circFIP1L1 was revealed to repress miR-1253 by binding to it, and EIF4A3 is a target gene of miR-1253. CircFIP1L1 regulated NPC proliferation, apoptosis, and radiosensitivity through miR-1253/EIF4A3. Moreover, we found that EIF4A3 bound to FIP1L1 mRNA transcript and induced circFIP1L1 formation, and thus stabilizing PTEN mRNA.

CONCLUSION

Our findings suggested that EIF4A3-induced circFIP1L1 repressed NPC cell proliferation, facilitated NPC cell apoptosis, and enhanced NPC radiosensitivity by miR-1253.

circRNA CRIM1 regulates the migration and invasion of bladder cancer by targeting miR182/Foxo3a axis

PURPOSE

To explore the molecular mechanism of circRNA CRIM1 in the regulation of bladder cancer by targeting the miR182/Foxo3a axis.

METHODS

50 pairs of cancer tissues and para-cancerous tissues of patients with bladder cancer were collected. RT-PCR method was used to detect the expression of CRIM1 and miR-182. The association between circRNA CRIM1 and clinical data was analyzed. qPCR was used to measure the expression of circRNA CRIM1 and miR-182 in bladder cancer cell UMUC3 and endothelial cell line HUVEC. CRIM1 genes and miR-182 in UMUC3 cell lines were overexpressed and silenced, respectively, to investigate their effects on invasion and migration of bladder cancer, and to detect the changes of miR182/Foxo3a expression. The association between circRNA CRIM1 and miR182/Foxo3a was determined by bioinformatics analysis.

RESULTS

The results showed that there was a significant association between the expression of circRNA CRIM1 and distal migration. The expression of CRIM1 in adjacent tissues was significantly down-regulated and negatively correlated with distal migration. The overexpression of circRNA CRIM1 reduced migration and invasion processes in bladder cancer cells. After circRNA CRIM1 was overexpressed, the miR-182 was significantly down-regulated. The expression levels of Foxo3a mRNA and proteins were up-regulated after miR-182 silencing of bladder cancer cell line UMUC3. miR-182 silencing inhibited invasion and migration of cancer cells to some extent. In bladder cancer cells and tissues, CRIM1 and Foxo3a were significantly down-regulated, miR-182 was significantly up-regulated.

CONCLUSION

circRNA CRIM1 regulated the migration and invasion of bladder cancer by targeting the miR182/Foxo3a axis.

CircKIAA0368 Promotes Proliferation, Migration, and Invasion by Upregulating HOXA10 in Nasopharyngeal Carcinoma

BACKGROUND

Nasopharyngeal carcinoma (NPC) represents a head and neck cancer caused by cancerization of nasal epithelial cells. HOXA10 has been identified to promote proliferation and invasion of NPC cells, but its regulatory mechanism has not been well discussed. Published research work has also pointed out that circular RNAs (circRNAs) could regulate mRNAs to affect NPC tumorigenesis and development.

AIM

To explore the roles of HOXA10 and its specific regulatory mechanism regarding circRNAs in NPC.

METHODS

Reverse transcription polymerase chain reaction and western blot were applied to test gene expression. Functional assays were used to evaluate changes in NPC cell phenotypes. Mechanism assays were done to verify RNA-RNA or RNA-protein interaction.

RESULTS

HOXA10 was highly expressed in NPC tissues and cell lines. Moreover, HOXA10 knockdown could restrict NPC cell proliferation, invasion, migration, and epithelial-mesenchymal transition. CircKIAA0368 was upregulated in NPC cells and could elevate HOXA10 expression by sponging miR-6838-5p. Furthermore, circKIAA0368 was unveiled to competitively bind to p300/CREB-binding protein-associated factor (PCAF) to repress acetylation and degradation of HOXA10 protein.

CONCLUSION

CircKIAA0368 upregulates HOXA10 expression via miR-6838-5p and PCAF, consequently promoting NPCcell and tumor growth.

Diagnostic and prognostic value of circRNAs expression in head and neck squamous cell carcinoma: A meta-analysis

Background

Circular RNAs (circRNAs) have been found to have potential biological applications against tumors in humans. This study aimed to evaluate the diagnostic, prognostic, and clinicopathological value of circRNAs in head and neck squamous cell carcinoma (HNSCC).

Methods

The PubMed, Web of Science, EMBASE, and the Cochrane Library were comprehensively searched for the relevant studies before October 20, 2021. Statistical analysis was performed based on STATA 15.0, Meta‐DiSc 1.4, and RevMan 5.3 software.

Results

A total of 55 reports regarding 56 kinds of circRNA were studied in this meta‐analysis, including 23, 38, and 26 articles on diagnosis, prognosis, and clinicopathological features, respectively. The pooled sensitivity, specificity, and area under the curve (AUC) of the summary receiver‐operating characteristic curve (SROC) were 0.78, 0.84, and 0.87, respectively. Besides, the upregulation of oncogenic circRNAs was significantly associated with poorer overall survival (OS) (HR=2.25, p < 0.05) and disease‐free interval (DFS) (HR=1.92, p < 0.05). In contrast, the elevated expression of tumor suppressor circRNAs was associated with a favorable prognosis (HR=0.50, p < 0.05). In addition, the high expression of oncogenic circRNAs was associated with the tumor size (OR=3.59, p < 0.05), degree of differentiation (OR=1.89, p < 0.05), TNM stage (OR=2.35, p < 0.05), lymph node metastasis (OR=1.85, p < 0.05), and distant metastasis (OR=3.42, p < 0.05). Moreover, the expression of tumor suppressor circRNAs was associated with improved clinicopathological features (lymph node metastasis: OR=0.25, p < 0.05).

Conclusions

CircRNAs could serve as potential predictive indicators and be useful for the diagnosis, prognosis, and identification of clinicopathological features in HNSCC.

Hsa_circ_0000345 inhibits cell proliferation, migration and invasion of nasopharyngeal carcinoma cells via miR-513a-3p/PTEN axis

BACKGROUND

Hsa_circ_0000345 has been reported to be down-regulated in nasopharyngeal carcinoma (NPC). Whether hsa_circ_0000345 can exert antitumor effect in NPC remains unclear. This study aimed to investigate the possible biological role of hsa_cic_0000345 in suppressing the progression of NPC.

METHODS

Hsa_circ_0000345 expression was detected in normal nasopharynx epithelial cells (NP69) and NPC cell lines (SUNE1, HONE1, 6-10B and HNE1). The influence of hsa_circ_0000345 on cell proliferation, migration and invasion of NPC cells was evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and transwell assays. Quantitative real-time PCR and western blot were performed to examine gene and protein expression, respectively. Luciferase reporter assay was carried out to verify the relationship among hsa_circ_0000345, miR-513a-3p and phosphatase and tensin homolog deleted on chromosome 10 (PTEN).

RESULTS

Compared with NP69 cells, hsa_circ_0000345 was down-regulated in NPC cells. Moreover, hsa_circ_0000345 overexpression repressed cell proliferation, migration and invasion of SUNE1 cells, whereas hsa_circ_0000345 knockdown promoted cell proliferation, migration and invasion of 6-10B cells. Furthermore, hsa_circ_0000345 promoted PTEN expression by sponging miR-513a-3p. Both miR-513a-3p overexpression and PTEN knockdown promoted cell proliferation, migration and invasion of SUNE1 cells, which were effectively abolished by hsa_circ_0000345 up-regulation.

CONCLUSION

Hsa_circ_0000345 inhibits cell proliferation, migration and invasion of NPC cells via miR-513a-3p/PTEN axis, thereby suppressing the progression of NPC. Thus, this work suggests that hsa_circ_0000345 may be a potential biomarker for diagnosis and treatment of NPC.

Advances in the Study of CircRNAs in Tumor Drug Resistance

Recent studies have revealed that circRNAs can affect tumor DNA damage and repair, apoptosis, proliferation, and invasion and influence the transport of intratumor substances by acting as miRNA sponges and transcriptional regulators and binding to proteins in a variety of ways. However, research on the role of circRNAs in cancer radiotherapy and chemoresistance is still in its early stages. Chemotherapy is a common approach to oncology treatment, but the development of tumor resistance limits the overall clinical efficacy of chemotherapy for cancer patients. The current study suggests that circRNAs have a facilitative or inhibitory effect on the development of resistance to conventional chemotherapy in a variety of tumors, suggesting that circRNAs may serve as a new direction for the study of antitumor drug resistance. In this review, we will briefly discuss the biological features of circRNAs and summarize the recent progression of the involvement of circRNAs in the development and pathogenesis of cancer chemoresistance.

Low CRIM1 Levels Predict Poor Prognosis in Breast Cancer Patients

Background

CRIM1 is involved in the development and preservation of the nervous system, capillary development, and vascular maintenance. Although CRIM1 was reported to involve in multiple cancers, its role in breast cancer is unclear.

Methods

We investigated CRIM1 expression levels using Oncomine, HPA, and immunohistochemistry analyses. BC-GenExMiner was employed to evaluate the relationship of CRIM1 expression with the clinicopathological characteristics of breast cancer. Its association with breast cancer prognosis was assessed by Kaplan-Meier analysis and PrognoScan. The correlation of the expression of CRIM1 with tumor immune infiltration was explored via TIMER. Gene set enrichment analysis (GSEA) was utilized to determine the cascades that are linked to CRIM1 in breast cancer. Finally, we explored CRIM1 and its co-expressed genes using R (3.6.3).

Results

Here, we find that CRIM1 expression was downregulated in various subtypes of breast cancer, and it was lowest in triple-negative breast cancers. ER and PR status were positively correlated with CRIM1 expression, while HER-2 expression was negatively correlated with CRIM1 expression. But in our immunohistochemical results in breast cancer specimens collected from our laboratory, HER-2 expression was positively correlated with CRIM1 expression. The expression of CRIM1 was correlated with menopause status, T stage, pathologic stage, histological type, and P53 status but not with age, N-stage, M-stage, Radiation therapy, and BRCA1/2 status. Survival analysis found that low CRIM1 expression was correlated with poorer DMFS, RFS and OS. Notably, CRIM1 expression was positively linked to the level of infiltration by CD8+ T-cells, endothelial cells, and neutrophils, and negatively linked to NK, B-cells, CD4+ T-cells, tumor purity, macrophage M1, and Tregs. Besides, DIXDC1 and PFDN6 were correlated to CRIM1 possibly.

Conclusion

Our findings demonstrated that low CRIM1 expression predict poor prognosis of breast cancer and CRIM1 might be used as a possible treatment target or prognostic marker in breast cancer. More researches are needed to better understand the prognostic value of CRIM1 in breast cancer.

CircCRIM1 promotes nasopharyngeal carcinoma progression via the miR-34c-5p/FOSL1 axis

BACKGROUND

Nasopharyngeal carcinoma (NPC) is a rare malignancy with multiple risk factors (Epstein-Barr virus, etc.) that seriously threatens the health of people. CircRNAs are known to regulate the tumorigenesis of malignant tumours, including NPC. Moreover, circCRIM1 expression is reported to be upregulated in NPC. Nevertheless, the impact of circCRIM1 on NPC progression is not clear.

METHODS

An MTT assay was performed to assess cell viability. In addition, cell invasion and migration were assessed by the transwell assay. Dual luciferase assays were performed to assess the association among circCRIM1, miR-34c-5p and FOSL1. Moreover, RT-qPCR was applied to assess mRNA levels, and protein levels were determined by Western blot.

RESULTS

CircCRIM1 and FOSL1 were upregulated in NPC cells, while miR-34c-5p was downregulated. Knockdown of circCRIM1 significantly decreased the invasion, viability and migration of NPC cells. The miR-34c-5p inhibitor notably promoted the malignant behaviour of NPC cells, while miR-34c-5p mimics exerted the opposite effect. Moreover, circCRIM1 could bind with miR-34c-5p, and FOSL1 was identified to be downstream of miR-34c-5p. Furthermore, circCRIM1 downregulation notably inhibited the proliferation and invasion of NPC cells, while this phenomenon was significantly reversed by FOSL1 overexpression.

CONCLUSION

Silencing circCRIM1 inhibited the tumorigenesis of NPC. Thus, circCRIM1 might be a novel target for NPC.

Downregulation of Circ-CEP128 Enhances the Paclitaxel Sensitivity of Cervical Cancer Through Regulating miR-432-5p/MCL1

Chemoresistance is a common problem in cancer treatment, and circular RNA (circRNA) has been found to be associated with the progression of chemoresistance in cancer. However, the role and mechanism of circRNA centrosomal protein 128 (circ-CEP128) in the chemoresistance of cervical cancer (CC) are still unclear. The expression of circ-CEP128, microRNA (miR)-432-5p, and myeloid cell leukemia-1 (MCL1) was measured by quantitative real-time PCR. The paclitaxel resistance of cells was assessed using MTT assay. Cell proliferation, apoptosis, migration, and invasion were determined using MTT assay, colony formation assay, flow cytometry, and transwell assay. The protein levels of metastasis markers and MCL1 were examined using western blot analysis. Mice xenograft models were constructed to assess the effect of circ-CEP128 silencing on CC tumor growth and paclitaxel sensitivity. The interaction between miR-432-5p and circ-CEP128 or MCL1 was confirmed by dual-luciferase reporter assay and RIP assay. Circ-CEP128 had highly expression in CC tumor tissues and cells. Silencing of circ-CEP128 could enhance the paclitaxel sensitivity of CC cells by decreasing cell growth, migration, and invasion. Also, knockdown of circ-CEP123 reduced CC tumor growth and promoted the paclitaxel sensitivity of CC tumors. MiR-432-5p was found to be sponged by circ-CEP128, and its inhibitor could reverse the promoting function of circ-CEP128 silencing on the paclitaxel sensitivity of CC cells. Additionally, MCL1 was a target of miR-432-5p, and circ-CEP128 could sponge miR-432-5p to regulate MCL1. Besides, overexpressed MCL1 also could reverse the enhancing effect of miR-432-5p on the paclitaxel sensitivity of CC cells. In conclusion, the present study showed that circ-CEP128 silencing could increase the paclitaxel sensitivity of CC by regulating the miR-432-5p/MCL1 axis.

CircTMTC1 contributes to nasopharyngeal carcinoma progression through targeting miR-495-MET-eIF4G1 translational regulation axis

Nasopharyngeal carcinoma (NPC) is the most common primary malignancy arising from the epithelial cells of nasopharynx. CircTMTC1 is upregulated in NPC patients, but its role and molecular mechanism in NPC are unknown. Normal nasopharyngeal epithelium and tumor tissues were collected. The expression of circTMTC1, miR-495, MET/eIF4G1 pathway-related molecules were examined. Colony formation and transwell assays were used to assess cell proliferation, migration, and invasion. Cell apoptosis was analyzed by annexin V and propidium iodide (PI) staining. Gene interaction was examined by RNA immunoprecipitation (RIP) and luciferase activity assays. Subcutaneous and intravenous xenograft mouse models were established to analyze NPC growth and metastasis in vivo. CircTMTC1 was highly expressed and miR-495 was downregulated in NPC, which were associated with poor prognosis of NPC. Both circTMTC1 knockdown and miR-495 overexpression inhibited NPC cell proliferation, migration, invasion, and epithelial–mesenchymal transition (EMT) and promoted cell apoptosis. CircTMTC1 directly targeted miR-495 to promote the expression of its downstream target gene MET. miR-495 knockdown enhanced the expression of c-Myc, Cyclin D1, and survivin and accelerated NPC cell proliferation, migration, invasion, and EMT through targeting MET and activating the MET-eIF4G1 axis. CircTMTC1 silence inhibited NPC growth and lung metastasis by targeting the miR-495-MET-eIF4G1 translational regulation axis in vivo. CircTMTC1 accelerates NPC progression through targeting miR-495 and consequently activating the MET-eIF4G1 translational regulation axis, suggesting potential therapeutic targets for NPC treatment.

The emerging roles of circRNAs in cancer and oncology

Over the past decade, circular RNAs (circRNAs) have emerged as a large class of primarily non-coding RNA molecules, many of which have key roles in cancer development and progression through diverse mechanisms of action. CircRNAs often have tissue-restricted and cancer-specific expression patterns, and accumulating data suggest that these molecules are of potential clinical relevance and utility. In particular, circRNAs have strong potential as diagnostic, prognostic and predictive biomarkers, which is underscored by their detectability in liquid biopsy samples such as in plasma, saliva and urine. However, technical issues in the detection and assessment of circRNAs as well as biological knowledge gaps need to be addressed to move this relatively young field of research forward and bring circRNAs to the forefront of clinical practice. Herein, we review the current knowledge regarding circRNA biogenesis, regulation and functions in cancer as well as their clinical potential as biomarkers, therapeutic agents and drug targets.

m6A Regulators Mediated Methylation Modification Patterns and Tumor Microenvironment Infiltration Characterization In Nasopharyngeal Carcinoma

Background

The role of RNA N6-methyladenosine (m6A) modification in tumor progression and metastasis has been demonstrated. Nonetheless, potential biological function of m6A modification patterns in nasopharyngeal carcinoma (NPC) remains unknown.

Methods

The m6A modification patterns were comprehensively evaluated based on 26 m6A regulators in NPC, and m6A subtype and also m6A score were identified and systematically correlated with representative tumor characteristics.

Results

Two distinct m6A subtypes were determined and were highly consistent with immune activated and immune suppressed phenotypes, respectively. More representative m6A scores of individual tumors could predict tumor microenvironment (TME) infiltration, mRNA based stemness index (mRNAsi), EBV gene expression, genetic variation, and prognosis of NPC patients. Low m6A score, characterized by activation of immunity and suppression of mRNAsi and EBV gene, indicated an activated TME phenotype and better PFS and also lower risk of recurrence and metastasis. High m6A score, characterized by activation of Wnt and NF-κB signaling pathway and lack of effective immune infiltration, indicated an immune suppressed TME phenotype and poorer survival. Low m6A score was also correlated with increased tumor mutation burden (TMB) and better response to immunotherapy, and vice versa. A significant therapeutic advantage in patients with low m6A score was confirmed with an anti-PDL1 immunotherapy cohort.

Conclusions

m6A patterns played an important role in the diversity and complexity of TME. m6A score could be used to evaluate the m6A pattern of individual tumor to enhance our understanding of TME infiltration and guide more effective immunotherapy strategies.

Long noncoding RNA LUCAT1 enhances the survival and therapeutic effects of mesenchymal stromal cells post-myocardial infarction

Mesenchymal stromal cell (MSC) transplantation has been a promising therapeutic strategy for repairing heart tissues post-myocardial infarction (MI). Nevertheless, its therapeutic efficacy remains low, which is mainly ascribed to the low viability of transplanted MSCs. Recently, long noncoding RNAs (lncRNAs) have been reported to participate in diverse physiological and pathological processes, but little is known about their role in MSC survival. Using unbiased transcriptome profiling of hypoxia-preconditioned MSCs (HP-MSCs) and normoxic MSCs (N-MSCs), we identified a lncRNA named lung cancer-associated transcript 1 (LUCAT1) under hypoxia. LUCAT1 knockdown reduced the survival of engrafted MSCs and decreased the MSC-based therapeutic potency, as shown by impaired cardiac function, reduced cardiomyocyte survival, and increased fibrosis post-MI. Conversely, LUCAT1 overexpression had the opposite results. Mechanistically, LUCAT1 bound with and recruited jumonji domain-containing 6 (JMJD6) to the promoter of forkhead box Q1 (FOXQ1), which demethylated FOXQ1 at H4R3me^2(s) and H3R2me^2(a), thus downregulating Bax expression and upregulating Bcl-2 expression to attenuate MSC apoptosis. Therefore, our findings revealed the protective effects of LUCAT1 on MSC apoptosis and demonstrated that the LUCAT1-mediated JMJD6-FOXQ1 pathway might represent a novel target to potentiate the therapeutic effect of MSC-based therapy for ischemic cardiovascular diseases.

Splicing factor derived circular RNA circCAMSAP1 accelerates nasopharyngeal carcinoma tumorigenesis via a SERPINH1/c-Myc positive feedback loop

Background

Circular RNAs play an important role in tumor genesis and progression, but they have not been sufficiently studied in patients with nasopharyngeal carcinoma (NPC).

Methods

The circular RNA, circCAMSAP1, was screened in NPC cells by RNA sequencing analysis. The expression of circCAMSAP1 in NPC tissues was examined by real-time quantitative polymerase chain reaction (RT-qPCR) and in situ hybridization. Wound-healing, transwell, MTT and flow cytometry assays, and nude mouse tumor models were used to explore the effect of circCAMSAP1 on proliferation and metastasis of NPC in vitro or in vivo. The downstream proteins regulated by circCAMSAP1 were screened using mass spectrometry. The interaction between circCAMSAP1 and the SERPINH1 mRNA was identified using the circular RNA immunoprecipitation method and the luciferase reporter assay. The interaction between SERPINH1 and transcription factor c-Myc was verified through Co-immunoprecipitation (Co-IP) and immunofluorescence. The effect of c-Myc on the generation of circCAMSAP1 was examined through RT-qPCR and chromatin immunoprecipitation. Finally, the splicing factors that promote the production of circCAMSAP1 were explored by RT-qPCR and RNA immunoprecipitation (RIP).

Results

We found that circCAMSAP1 was highly expressed in NPC tissues and promoted NPC proliferation and metastasis. Additionally, circCAMSAP1 promoted SERPINH1 expression through improved SERPINH1 mRNA stability by binding to the 3′-untranslated region (3’UTR) of SERPINH1. Highly expressed SERPINH1 reduced the ubiquitination-degradation rate of c-Myc, causing increased tumorigenesis. Meanwhile, c-Myc, cooperating with splicing factor 10 (SRSF10), could also promote CAMSAP1 pre-mRNA transcription and back-splicing, forming a positive feedback of circCAMSAP1 production, resulting in the proliferation and metastasis of NPC.

Conclusions

Our findings revealed that circCAMSAP1 promotes NPC proliferation and metastasis by binding to the 3’UTR of SERPINH1, suggesting that the positive feedback of circCAMSAP1-SERPINH1-c-Myc may serve as a prognostic biomarker or therapeutic target in patients with NPC.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12943-022-01502-2.

N7-methylguanosine tRNA modification promotes tumorigenesis and chemoresistance through WNT/β-catenin pathway in nasopharyngeal carcinoma

Treatment selections are very limited for patients with advanced nasopharyngeal carcinoma (NPC) experiencing disease progression. Uncovering mechanisms underlying NPC progression is crucial for the development of novel treatments. Here we show that N⁷-methylguanosine (m⁷G) tRNA modification enzyme METTL1 and its partner WDR4 are significantly elevated in NPC and are associated with poor prognosis. Loss-of-function and gain-of-function assays demonstrated that METTL1/WDR4 promotes NPC growth and metastasis in vitro and in vivo. Mechanistically, ARNT was identified as an upstream transcription factor regulating METTL1 expression in NPC. METTL1 depletion resulted in decreased m⁷G tRNA modification and expression, which led to impaired codon recognition during mRNA translation, therefore reducing the translation efficiencies of mRNAs with higher m⁷G codons. METTL1 upregulated the WNT/β-catenin signaling pathway and promoted NPC cell epithelial-mesenchymal transition (EMT) and chemoresistance to cisplatin and docetaxel in vitro and in vivo. Overexpression of WNT3A bypassed the requirement of METTL1 for EMT and chemoresistance. This work uncovers novel insights into tRNA modification-mediated mRNA translation regulation and highlights the critical function of tRNA modification in cancer progression.

Circ-PKD2 promotes Atg13-mediated autophagy by inhibiting miR-646 to increase the sensitivity of cisplatin in oral squamous cell carcinomas

Autophagy is an evolutionally conserved catabolic process that degrades cells to maintain homeostasis. Cisplatin-activated autophagy promotes the expression of circ-PKD2, which plays a role as a tumor suppressor gene in the proliferation, migration, and invasion in oral squamous cell carcinoma (OSCC). However, the role of circ-PKD2 in regulating the sensitivity of OSCC patients to cisplatin remains to be elucidated. Overexpression of circ-PKD2 increased the formation of autophagosomes in OSCC cells and activation of proteins, such as LC3 II/I. Its activation effect on autophagy was, however, alleviated by 3-MA. Bioinformatics analyses and double luciferases reporter assays conducted in this study confirmed the existence of targeted relationships between circ-PKD2 and miR-646 and miR-646 and Atg13. Functional experiments further revealed that miR-646 reversed the autophagy and apoptosis effects of circ-PKD2 in OSCC cells treated with cisplatin. In addition, circ-PKD2 promoted the expression of ATG13 by adsorption of miR-646. Its interference with Atg13 alleviated the activation effects of circ-PKD2 on autophagy and apoptosis of miR-646. Notably, the in vivo animal experiments also confirmed that circ-PKD2 inhibited tumor proliferation and activated autophagy in OSCC cells. This study provides a theoretical basis for using circ-PKD2 as a target to regulate the sensitivity of OSCC patients to cisplatin, thus increasing its chemotherapeutic effects.

Circular RNA SET domain protein 3 promotes nasopharyngeal carcinoma proliferation, cisplatin resistance, and protein kinase B / mammalian target of rapamycin pathway activation by modulating microRNA-147a expression

Circular RNA (circRNA) plays a crucial role in the establishment and progression of nasopharyngeal carcinoma (NPC). Understanding the role of circRNA in NPC is helpful to find new therapeutic targets for NPC. The purpose of this study was to explore the effects of circRNA SET domain protein 3 (circSETD3) on protein kinase B (Akt)/ mammalian target of rapamycin (mTOR) signaling pathway and cisplatin (DDP) resistance to NPC and explore its downstream mechanism. The results showed that circSETD3 was upregulated in NPC tissues and was related to DDP resistance to NPC. Functional experiments revealed that circSETD3 knockdown inhibited NPC proliferation and increased DDP sensitivity and apoptosis rate. The promotion effect of circSETD3 overexpression on NPC proliferation and DDP resistance and inhibition effect on apoptosis was reversed by elevated miR-147a. CircSETD3 knockdown or miR-147a overexpression prevented Akt/mTOR pathway's activation. In terms of the mechanism, circSETD3 acted as a sponge for miR-147a. Xenotransplantation experiments showed that knockdown circSETD3 or DDP treatment could restrain tumor growth, and the effect of DDP was enhanced by knockdown of circSETD3. In conclusion, the results of this study confirm that circSETD3 promotes NPC proliferation and DDP resistance by regulating miR-147a, and circSETD3/miR-147a axis may serve as a potential therapeutic target for NPC in the future.

FOXQ1-mediated SIRT1 upregulation enhances stemness and radio-resistance of colorectal cancer cells and restores intestinal microbiota function by promoting β-catenin nuclear translocation

Background

Resistance of colorectal cancer (CRC) cells to radiotherapy considerably contributes to poor clinical outcomes of CRC patients. Microarray profiling in this study revealed the differentially expressed forkhead box Q1 (FOXQ1) in CRC, and thus we aimed to illustrate the role of FOXQ1 in CRC by modulating stemness and radio-resistance of CRC cells.

Methods

CRC and adjacent normal tissues were collected from CRC patients, and the correlation between FOXQ1 expression and CRC prognosis was analyzed. Subsequently, we determined the expression of FOXQ1, sirtuin 1 (SIRT1) and β-catenin in CRC tissues and cell lines. The binding affinity between FOXQ1 and SIRT1 and that between SIRT1 and β-catenin were validated with luciferase reporter gene, Co-IP and ChIP assays. Following a metagenomics analysis of CRC intestinal microbiota, the effects of the FOXQ1/SIRT1/β-catenin axis on CRC stem cell phenotypes and radio-resistance was evaluated in vitro and in vivo through manipulation of gene expression. Besides, mouse feces were collected to examine changes in intestinal microbiota.

Results

FOXQ1 was highly expressed in CRC tissues and cells and positively correlated with poor prognosis of CRC patients. FOXQ1 overexpression contributed to resistance of CRC cells to radiation. Knockdown of FOXQ1 inhibited the stemness of CRC cells and reversed their radio-resistance. FOXQ1 enhanced the transcriptional expression of SIRT1, and SIRT1 enhanced the expression and nuclear translocation of β-catenin. Knockdown of FOXQ1 repressed SIRT1 expression, thus reducing the stemness and radio-resistance of CRC cells. Moreover, FOXQ1 knockdown suppressed CRC xenograft formation in xenograft-bearing nude mice through inhibiting SIRT1 and β-catenin to reduce the content of pathological bacteria that were up-regulated in CRC.

Conclusion

FOXQ1-mediated SIRT1 upregulation augments expression and nuclear translocation of β-catenin and benefits CRC-related intestinal pathological bacterial, thereby enhancing the stemness and radio-resistance of CRC cells.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13046-021-02239-4.

Circular RNAs and Drug Resistance in Genitourinary Cancers: A Literature Review

Simple Summary

Drug resistance to systematic treatment in genitourinary tumors severely aggravated the burden on patients and society. Multiple mechanisms were involved in drug resistance. As typical non-coding RNAs, circRNAs play a critical role in the onset and development of cancers and several studies implied their function in the regulation of drug resistance. Here, we reviewed the investigations of circRNAs’ behavior in drug resistance of genitourinary cancers and summarized the underlying mechanisms. This review emphasized the essential role of circRNAs in drug resistance development and also pointed out the potential topics that need further investigations in the future.

Abstract

In recent years, systematic treatment has made great progress in genitourinary tumors. However, some patients develop resistance to the treatments, resulting in an increase in mortality. Circular RNAs (circRNAs) form a class of non-coding RNAs with high stability and significant clinical relevance. Accumulating evidence indicates that circRNAs play a vital role in cancer development and tumor chemotherapy resistance. This review summarizes the molecular and cellular mechanisms of drug resistance mediated by circRNAs to common drugs used in the treatment of genitourinary tumors. Several circRNAs were identified to regulate the responsiveness to systemic treatments in genitourinary tumors, including chemotherapies such as cisplatin and targeted therapies such as enzalutamide. Canonically, cicrRNAs participate in the competing endogenous RNA (ceRNA) network, or in some cases directly interact with proteins, regulate downstream pathways, and even some circRNAs have the potential to produce proteins or polypeptides. Several cellular mechanisms were involved in circRNA-dependent drug resistance, including autophagy, cancer stem cells, epithelial-mesenchymal transition, and exosomes. The potential clinical prospect of circRNAs in regulating tumor drug resistance was also discussed.

Exosomal circ_PTPRA inhibits tumorigenesis and promotes radiosensitivity in colorectal cancer by enriching the level of SMAD4 via competitively binding to miR-671-5p

Accumulating evidence supports that exosomal RNAs are crucial in tumor microenvironment and may be used as diagnostic biomarkers for cancers. This study aimed to determine the role of exosomal circular RNA_protein tyrosine phosphatase receptor type A (circ_PTPRA) in colorectal cancer (CRC). The morphology of exosomes was identified by transmission electron microscopy (TEM), and several exosome-specific proteins were quantified by western blot. The expression of circ_PTPRA, miR-671-5p and SMAD family member 4 (SMAD4) was detected using quantitative polymerase chain reaction (qPCR). Cell cycle was assessed using flow cytometry assay. Cell proliferation was assessed by MTT assay. Radiosensitivity was observed according to colony growth and cell apoptosis rate by colony formation assay and flow cytometry assay. The protein levels of proliferation- and apoptosis-related markers and SMAD4 were measured by western blot. The predicted relationship between miR-671-5p and circ_PTPRA or SMAD4 was verified by dual-luciferase reporter assay. Animal study was performed to investigate the role of exosomal circ_PTPRA in vivo. Circ_PTPRA expression was declined in serumal exosomes from CRC patients and CRC cell lines. Exosomal circ_PTPRA induced CRC cell cycle arrest and inhibited cell proliferation. Besides, exosomal circ_PTPRA promoted radiosensitivity of CRC cells, leading to inhibitory colony formation and increased apoptotic rate. In mechanism, circ_PTPRA functioned as a competing endogenous RNA (ceRNA) to increasing SMAD4 level by binding to miR-671-5p. Rescue experiments concluded that circ_PTPRA inhibited CRC growth and radioresistance by decreasing miR-671-5p expression, and miR-671-5p inhibition also inhibited CRC growth and radioresistance by enriching SMAD4 expression. Moreover, exosomal circ_PTPRA blocked tumor growth in vivo. Exosomal circ_PTPRA enhanced CRC cell radiosensitivity and inhibited CRC malignant development partially by regulating the miR-671-5p/SMAD4 pathway, hinting that exosomal circ_PTPRA might be used as a potential predicted and therapeutic target for CRC.

SNHG8 promotes cell proliferation, migration, and invasion of nasopharyngeal carcinoma cells as an oncogene through miR-588/HMGA2 axis

Nasopharyngeal carcinoma (NC) poses a threat to the life of patients. Long non-coding RNA (LncRNA) is a novel kind of non-coding RNA, which plays a pivotal role through sponge microRNA (miRNA). Abnormal expression of small nucleolar RNA host gene 8 (SNHG8) is involved in various tumors; however, the role of SNHG8 in NC remains unknown. Quantitative real-time PCR (qRT-PCR) and Western blotting was employed to detect the expression levels of SNHG8, miR-588, and high mobility group A2 (HMGA2). Cell proliferation, migration, and invasion were analyzed by CCK-8 and transwell assays. miR-588 binding sites in SNHG8 were predicted by LncBase analysis. Luciferase reporter and RNA pull-down assay were used to confirm the interaction of SNHG8 and miR-588. SNHG8 was highly expressed in NC cells. The prognosis of the patients with NC in the high expression levels of SNHG8 was poorer than that in the low expression levels. The expression of SNHG8 was closely related to tumor size, TNM stage, and distal metastasis. Knockdown of SNHG8 inhibited cell proliferation, migration, and invasion of NC. SNHG8 targeted miR-588. Inhibition of miR-588 could partially reverse the knockdown of SNHG8 in NC cells, and miR-588 targeted HMGA2. In conclusion, SNHG8 promotes proliferation, migration, and invasion of NC cells through miR-588/HMGA2 in NC as an oncogene.

Emerging Role and Mechanism of circRNAs in Pediatric Malignant Solid Tumors

Circular RNAs (circRNAs) are non-coding RNAs with covalent closed-loop structures and are widely distributed in eukaryotes, conserved and stable as well as tissue-specific. Malignant solid tumors pose a serious health risk to children and are one of the leading causes of pediatric mortality. Studies have shown that circRNAs play an important regulatory role in the development of childhood malignant solid tumors, hence are potential biomarkers and therapeutic targets for tumors. This paper reviews the biological characteristics and functions of circRNAs as well as the research progress related to childhood malignant solid tumors.

Exosomal MIF Derived From Nasopharyngeal Carcinoma Promotes Metastasis by Repressing Ferroptosis of Macrophages

Nasopharyngeal carcinoma (NPC) is the most common malignant tumor of the head and neck cancer (HNC). Metastasis is the main cause of treatment failure. However, the molecular mechanism for NPC metastasis is still unclear. As one of the most common host immune cells in the tumor microenvironment, macrophages have been proven to regulate metastasis. Besides, exosomes are the important bridge connecting various cells in TME. Currently, the role of NPC-exos on macrophages and their impact on metastasis remains to be unexplored. In this study, we found that MIF was highly expressed in NPC cells, and the exosomes secreted by NPC cells could be taken up by macrophages, thereby, inhibiting the ferroptosis of macrophages and then promoting the metastasis of NPC. Targeting MIF may be a potential treatment to reduce the rate of metastasis.

CircRNA circ_0006156 inhibits the metastasis of prostate cancer by blocking the ubiquitination of S100A9

Circular RNAs (circRNAs) have been demonstrated to play vital roles in cancer development and progression. However, studies on the association between circRNAs and prostate cancer (PCa) are still lacking. CircRNA sequencing of two pairs of PCa tissues and adjacent normal tissues was conducted in the present study, and qRT-PCR was performed to verify the results. Functional experiments were performed to investigate cellular functions after specific changes. Mass spectrometry analysis after RNA pull-down experiments and Co-IP assays were further conducted. Downstream target proteins were predicted via online databases and detected in vitro by Western blot analysis and in vivo by immunohistochemistry. Hsa_circ_0006156 (subsequently named circ_0006156) expresses at low levels in both PCa tissues and cells, and it significantly inhibits the migration and invasion of PCa cells. Circ_0006156 binds to and blocks the ubiquitination of S100A9. Moreover, functional assays revealed that circ_0006156 represses the malignant progression of PCa by binding to S100A9. Finally, in vivo experiments showed that circ_0006156 suppresses PCa migration and invasion by increasing S100A9, revealing circ_0006156 as a potential novel effective target for PCa treatment.

Circular RNA CircPVT1 Inhibits 5-Fluorouracil Chemosensitivity by Regulating Ferroptosis Through MiR-30a-5p/FZD3 Axis in Esophageal Cancer Cells

Background

CircPVT1 is demonstrated to promote cancer progression in esophageal squamous cell carcinoma (ESCC). However, the role and potential functional mechanisms of circPVT1 in regulating 5-fluorouracil (5-FU) chemosensitivity remain largely unknown.

Methods

ESCC cells resistant to 5-FU were induced with continuous increasing concentrations of 5-FU step-wisely. A cell counting kit-8 assay was used to analyze the viability of ESCC cells. LDH release assay kit was used to evaluate the cytotoxicity. RT-qPCR was used to assess the expression level of non-coding RNAs and cDNAs. Luciferase was used to confirm the interaction between non-coding RNAs and targets. Western blotting was used to detect the expression of downstream signaling proteins. Flow cytometry and ferroptosis detection assay kit were utilized to measure the ferroptosis of ESCC cells.

Results

CircPVT1 was significantly upregulated in ESCC cells resistant to 5-FU. Knockdown of circPVT1 enhanced the 5-FU chemosensitivity of ESCC cells resistant to 5-FU by increasing cytotoxicity and downregulating multidrug-resistant associated proteins, including P-gp and MRP1. Luciferase assay showed that circPVT1 acted as a sponge of miR-30a-5p, and Frizzled3 (FZD3) was a downstream target of miR-30a-5p. The enhanced 5-FU chemosensitivity by circPVT1 knockdown was reversed with miR-30a-5p inhibitor. Besides, the increased 5-FU chemosensitivity by miR-30a-5p mimics was reversed with FZD3 overexpression. Furthermore, knockdown of circPVT1 increased ferroptosis through downregulating p-β-catenin, GPX4, and SLC7A11 while miR-30a-5p inhibition and FZD3 overexpression reversed the phenotype by upregulating p-β-catenin, GPX4, and SLC7A11.

Conclusions

These results suggested a key role for circPVT1 in ESCC 5-FU-chemosensitivity in regulating the Wnt/β-catenin pathway and ferroptosis via miR-30a-5p/FZD3 axis, which might be a potential target in ESCC therapy.

Circular RNAs: Functions and mechanisms in nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is a malignant epithelial tumor of the nasopharyngeal mucosa with a high incidence rate in southern China and Southeast Asia and an evident ethnic and geographical distribution. Circular RNAs (circRNAs) are single-stranded noncoding RNAs with covalent, closed-loop structures. They are characterized by high stability and abundance, are evolutionarily conserved, and exhibit tissue/developmental stage specificity. Previous studies have shown that circRNAs are associated with the occurrence and development of various malignant tumors. However, the expression patterns and clinical significance of circRNAs in NPC remain ambiguous. Hence, the present review focuses on the biogenesis and regulation of circRNAs, and the functional roles of abnormally expressed circRNAs in NPC. In addition, the current review discusses the possibility of utilizing circRNAs as potential clinical biomarkers for the diagnosis and prognosis of NPC.

CircCRIM1 Promotes Hepatocellular Carcinoma Proliferation and Angiogenesis by Sponging miR-378a-3p and Regulating SKP2 Expression

Mounting evidence has demonstrated that circular RNAs have an important function in tumorigenesis and cancer evolvement. CircCRIM1 has been shown to be a poor prognostic element in multiple human malignancies. However, the clinical significance and mechanism of circCRIM1 in hepatocellular carcinoma (HCC) is still unclear. The present study confirmed the expression level of circCRIM1 using quantitative real-time PCR. In addition, circCRIM1 siRNA and overexpression vectors were used for transfection into LM3 or Huh7 cells to down- or up-regulate the expression of circCRIM1. In vitro and in vivo experiments were performed to explore the function of circCRIM1 in HCC. RNA pull-down, RNA immunoprecipitation, fluorescent in situ hybridization, and luciferase reporter assays were conducted to confirm the relationship between miR-378a-3p and circCRIM1 or S-phase kinase-associated protein 2 (SKP2) in HCC. Then, circCRIM1 was up-regulated in HCC and its expression level was significantly associated with poor prognosis and clinicopathologic characteristics. CircCRIM1 enhanced the proliferation and angiogenesis of HCC cells in vitro and promoted xenograft growth in vivo. Moreover, circCRIM1 upregulated the expression of SKP2 by functioning as a sponge for miR-378a-3p. These findings suggest that circCRIM1 boosts the HCC progression via the miR-378-3p/SKP2 axis and may act as a crucial epigenetic therapeutic molecule target in HCC.

Circ_0000215 Exerts Oncogenic Function in Nasopharyngeal Carcinoma by Targeting miR-512-5p

Background: Increasing circular RNAs (circRNAs) are reported to participate in cancer progression. Nonetheless, the role of circRNAs in nasopharyngeal carcinoma (NPC) has not been fully clarified. This work is aimed to probe the role of circ_0000215 in NPC.

Methods: Circ_0000215 expression in NPC tissues and cell lines was examined by quantitative real-time polymerase chain reaction (qRT-PCR). Cell counting kit-8 (CCK-8) assay, 5-bromo-2′-deoxyuridine (BrdU) assay, scratch healing assay and Transwell experiment were executed to investigate the regulatory function of circ_0000215 on the proliferation, migration and invasion of NPC cells. RNA immunoprecipitation (RIP), pull-down and dual-luciferase reporter experiments were utilized to determine the binding relationship between circ_0000215 and miR-512-5p, and between miR-512-5p and phosphoinositide-3-kinase regulatory subunit 1 (PIK3R1) 3′UTR. The effects of circ_0000215 on NPC growth and metastasis in vivo were examined with nude mice model. Western blot was applied to detect the regulatory effects of circ_0000215 and miR-512-5p on PIK3R1 expression.

Results: Circ_0000215 was overexpressed in NPC tissues and cell lines. The functional experiments confirmed that knockdown of circ_0000215 impeded the growth and metastasis of NPC cells in vitro and in vivo. Additionally, circ_0000215 could also work as a molecular sponge to repress miR-512-5p expression. PIK3R1 was validated as a target gene of miR-512-5p, and circ_0000215 could increase the expression level of PIK3R1 in NPC cells via suppressing miR-512-5p.

Conclusion: Circ_0000215 is overexpressed in NPC and exerts oncogenic effects in NPC through regulating miR-512-5p/PIK3R1 axis.

ceRNAs in Cancer: Mechanism and Functions in a Comprehensive Regulatory Network

Noncoding RNAs have been shown with powerful ability in post-transcriptional regulation, enabling intertwined RNA crosstalk and global molecular interaction in a large amount of dysfunctional conditions including cancer. Competing endogenous RNAs (ceRNAs) are those competitively binding with shared microRNAs (miRNAs), freeing their counterparts from miRNA-induced degradation, thus actively influencing and connecting with each other. Constantly updated analytical approaches boost outstanding advancement achieved in this burgeoning hotspot in multilayered intracellular communication, providing new insights into pathogenesis and clinical treatment. Here, we summarize the mechanisms and correlated factors under this RNA interplay and deregulated transcription profile in neoplasm and tumor progression, underscoring the great significance of ceRNAs for diagnostic values, monitoring biomarkers, and prognosis evaluation in cancer.

The novel circSLC6A6/miR-1265/C2CD4A axis promotes colorectal cancer growth by suppressing p53 signaling pathway

Background

Colorectal cancer (CRC) is one of the most frequent malignancy and a leading cause of cancer-related deaths. Therefore, further researches are required to identify novel and more effective diagnoses and to identify molecular targets in treatment of CRC.

Methods

C2CD4A expression in CRC tissues and cell lines was detected by qRT-PCR and western blot. The biological functions of C2CD4A were performed both in vitro and in vivo. Western blot, cDNA array, IP-MS, Co-immunoprecipitation assay, and Ubiquitination assay were used to analyze the interaction between C2CD4A and p53. Bioinformatics analysis, FISH, RNA sequencing, luciferase reporter assay, RNA immunoprecipitation, RNA pull-down and rescue experiments, were deployed to detect upstream regulation mechanism of C2CD4A.

Results

C2CD4A was elevated in CRC tissues compared with adjacent normal colorectal tissues. C2CD4A knockdown significantly promoted cell apoptosis and with inhibited proliferation in vitro, and tumorigenicity in vivo, whereas C2CD4A overexpression led to opposite effects. Moreover, circSLC6A6 was upregulated and shown to positively regulate C2CD4A expression via sponging miR-1265. Fundamentally, C2CD4A inhibited p53 signaling pathway through interacting with p53 and increasing its ubiquitination and degradation.

Conclusion

Our results identified that circSLC6A6/miR-1265/C2CD4A axis, which was involved in CRC via the p53 signaling pathway, may serve as a therapeutic target for CRC.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13046-021-02126-y.

CircFAM114A2 Promotes Cisplatin Sensitivity via miR-222-3p/P27 and miR-146a-5p/P21 Cascades in Urothelial Carcinoma

INTRODUCTION

Circular RNAs (circRNAs) are non-coding RNAs that have the structure of a covalently closed loop. Increasing data have proven that circRNAs can influence the progression and chemotherapy sensitivity of tumors. Therefore, the underlying function and mechanisms of more circRNAs in progression and chemotherapy resistance are important.

METHODS

We conducted RNA sequencing on five pairs of urothelial carcinoma samples and screened for circRNAs. CircFAM114A2 was found to be low expressed in urothelial carcinoma. The functions of circFAM114A2 in urothelial carcinoma were explored by cell cycle assay, IC50 determination assay, cell proliferation assay, apoptosis assay, and tumorigenesis assay.

RESULTS

We discovered that the levels of circFAM114A2 were decreased in urothelial carcinoma cell lines and tissues. According to follow-up data, urothelial carcinoma patients with higher circFAM114A2 expression had better survival. Importantly, the levels of circFAM114A2 were associated with the histological grade of urothelial carcinoma. CircFAM114A2 could inhibit cell proliferation and block more urothelial carcinoma cells in the G1 phase and then increase the sensitivity of urothelial carcinoma to cisplatin chemotherapy. Mechanistically, circFAM114A2 directly sponged miR-222-3p/miR-146a-5p and subsequently influenced the expressions of the downstream target genes P27/P21, which, in turn, inhibited the progression of urothelial carcinoma and increased the sensitivity of cancer cells to cisplatin chemotherapy.

CONCLUSION

CircFAM114A2 could inhibit progression and promote cisplatin sensitivity in urothelial carcinoma through novel circFAM114A2/miR-222-3p/P27 and circFAM114A2/miR-146a-5p/P21 pathways. CircFAM1142 has therefore great potential as a prognostic biomarker and therapeutic target for urothelial carcinoma.

Identification of Circular RNAs Associated With Chemoresistance in Colorectal Cancer

Chemoresistance is a major clinical obstacle for the treatment of colorectal cancer (CRC). Circular RNAs (circRNAs) are a new type of non-coding RNA that participated in the development of chemoresistance. However, the profiles and effects of circRNAs in 5-fluorouracil (5-Fu) and cisplatin resistance of CRC are still unclear and need to be elucidated. In the present study, the profiles of circRNAs in CRC chemoresistant (HCT8/5-Fu and HCT8/DDP) and chemosensitive (HCT8) cell lines were identified via RNA-sequencing. In total, 48 and 90 differentially expressed (DE)-circRNAs were detected in HCT8/5-Fu and HCT8/DDP cell lines, respectively. Gene Ontology enrichment and Kyoto Encyclopedia of Genes and Genomes pathway analysis were conducted on the host genes of DE-circRNAs; the results showed that the most significant enrichment pathways in HCT8/5-Fu and HCT8/DDP cell lines were base excision repair and Hippo signaling pathway, respectively. In addition, 11 common DE-circRNAs in the two drug-resistant cell lines (two are upregulated and nine are downregulated) were screened and verified by quantitative real-time PCR; hsacirc_023607 and hsacirc_007420 were found to be the circRNAs with the highest upregulation and downregulation fold changes. However, functional studies showed hsacirc_023607 has no effect on CRC chemoresistance. Therefore, the regulatory networks of targeted miRNAs related to 5-Fu or cisplatin resistance were predicted and constructed, in which hsacirc_002482 was identified as a hub gene, and its overexpression could suppress HCT8/5-Fu and HCT8/DDP cell proliferation and promote cell apoptosis, and enhance cell chemosensitivity. Taken together, these results of the study suggested that hsacirc_002482 may play important roles in chemoresistance of CRC.

Circular RNAs' cap-independent translation protein and its roles in carcinomas

Circular RNAs a kind of covalently closed RNA and widely expressed in eukaryotes. CircRNAs are involved in a variety of physiological and pathological processes, but their regulatory mechanisms are not fully understood. Given the development of the RNA deep-sequencing technology and the improvement of algorithms, some CircRNAs are discovered to encode proteins through the cap-independent mechanism and participate in the important process of tumorigenesis and development. Based on an overview of CircRNAs, this paper summarizes its translation mechanism and research methods, and reviews the research progress of CircRNAs translation in the field of oncology in recent years. Moreover, this paper aims to provide new ideas for tumor diagnosis and treatment through CircRNAs translation.

The Emerging Role of Non-coding RNAs in Drug Resistance of Ovarian Cancer

Ovarian cancer is one of the most common gynecological malignancies with highest mortality rate among all gynecological malignant tumors. Advanced ovarian cancer patients can obtain a survival benefit from chemotherapy, including platinum drugs and paclitaxel. In more recent years, the administration of poly-ADP ribose polymerase inhibitor to patients with BRCA mutations has significantly improved the progression-free survival of ovarian cancer patients. Nevertheless, primary drug resistance or the acquisition of drug resistance eventually leads to treatment failure and poor outcomes for ovarian cancer patients. The mechanism underlying drug resistance in ovarian cancer is complex and has not been fully elucidated. Interestingly, different non-coding RNAs (ncRNAs), such as circular RNAs, long non-coding RNAs and microRNAs, play a critical role in the development of ovarian cancer. Accumulating evidence has indicated that ncRNAs have important regulatory roles in ovarian cancer resistance to chemotherapy reagents and targeted therapy drugs. In this review, we systematically highlight the emerging roles and the regulatory mechanisms by which ncRNAs affect ovarian cancer chemoresistance. Additionally, we suggest that ncRNAs can be considered as potential diagnostic and prognostic biomarkers as well as novel therapeutic targets for ovarian cancer.

The circular RNA circCRIM1 inhibits osteosarcoma progression through sponging miR-513

Numerous studies have suggested that the abnormal expression of circular RNAs plays an essential role in the pathological progression of numerous tumors. Nonetheless, the functions and underlying mechanisms of the circular RNA circCRIM1 in osteosarcoma (OS) are still not fully understood. In this study, 47 classes of OS tissues and adjoining normal tissues were obtained from patients. Real-time PCR was employed to measure circCRIM1 expression levels in both OS tissues and cell lines. The proliferation, migration, and invasion ability in OS cell lines were measured by MTT assays, EDU assays, transwell migration experiments, and transwell invasion assays. The results demonstrated that the expression of circCRIM1 was notably decreased both in OS tissues and cell lines. Depressed circCRIM1 expression was correlated with lymph node metastasis, advanced FIGO stage, and low overall survival of OS patients. In addition, the results indicated that circCRIM1 could decrease the migration, invasion, and growth of OS cells. Further mechanistic studies indicated that circCRIM1 served as a competing endogenous RNA (ceRNA) of miR-513, leading to decreases in the proliferation, migration, and invasion of OS cells. Taken together, our data uncovered a significant role of the circCRIM1/miR-513 pathway in the proliferation, migration, and invasion of OS cell lines and suggested that circCRIM1 may serve as a possible therapeutic target for OS treatment.

Circular RNA circRNF13 inhibits proliferation and metastasis of nasopharyngeal carcinoma via SUMO2

BACKGROUND

Circular RNAs (circRNAs) are widely expressed in human cells and are closely associated with cancer development. However, they have rarely been investigated in the context of nasopharyngeal carcinoma (NPC).

METHODS

We screened a new circRNA, circRNF13, in NPC cells using next-generation sequencing of mRNA. Reverse transcription polymerase chain reaction and RNA fluorescence in situ hybridization were used to detect circRNF13 expression in 12 non-tumor nasopharyngeal epithelial (NPE) tissues and 36 NPC samples. Cell proliferation was detected using MTT and flow cytometry assays, and colony formation capability was detected using colony formation assays. Cell migration and invasion were analyzed using wound-healing and Transwell assays, respectively. Cell glycolysis was analyzed using the Seahorse glycolytic stress test. Glucose transporter type 1 (GLUT1) ubiquitination and SUMOylation modifications were analyzed using co-immunoprecipitation and western blotting. CircRNF13 and Small Ubiquitin-like Modifier 2 (SUMO2) interactions were analyzed using RNA pull-down and luciferase reporter assays. Finally, to test whether circRNF13 inhibited NPC proliferation and metastasis in vivo, we used a xenograft nude mouse model generated by means of subcutaneous or tail vein injection.

RESULTS

We found that circRNF13 was stably expressed at low levels in NPC clinical tissues and NPC cells. In vitro and in vivo experiments showed that circRNF13 inhibited NPC proliferation and metastasis. Moreover, circRNF13 activated the SUMO2 protein by binding to the 3'- Untranslated Region (3'-UTR) of the SUMO2 gene and prolonging the half-life of SUMO2 mRNA. Upregulation of SUMO2 promotes GLUT1 degradation through SUMOylation and ubiquitination of GLUT1, which regulates the AMPK-mTOR pathway by inhibiting glycolysis, ultimately resulting in the proliferation and metastasis of NPC.

CONCLUSIONS

Our results revealed that a novel circRNF13 plays an important role in the development of NPC through the circRNF13-SUMO2-GLUT1 axis. This study implies that circRNF13 mediates glycolysis in NPC by binding to SUMO2 and provides an important theoretical basis for further elucidating the pathogenesis of NPC and targeted therapy.

CircRNAs and their regulatory roles in cancers

Circular RNAs (circRNAs), a novel type of non-coding RNAs (ncRNAs), have a covalently closed circular structure resulting from pre-mRNA back splicing via spliceosome and ribozymes. They can be classified differently in accordance with different criteria. As circRNAs are abundant, conserved, and stable, they can be used as diagnostic markers in various diseases and targets to develop new therapies. There are various functions of circRNAs, including sponge for miR/proteins, role of scaffolds, templates for translation, and regulators of mRNA translation and stability. Without m7G cap and poly-A tail, circRNAs can still be degraded in several ways, including RNase L, Ago-dependent, and Ago-independent degradation. Increasing evidence indicates that circRNAs can be modified by N-6 methylation (m6A) in many aspects such as biogenesis, nuclear export, translation, and degradation. In addition, they have been proved to play a regulatory role in the progression of various cancers. Recently, methods of detecting circRNAs with high sensitivity and specificity have also been reported. This review presents a detailed overview of circRNAs regarding biogenesis, biomarker, functions, degradation, and dynamic modification as well as their regulatory roles in various cancers. It’s particularly summarized in detail in the biogenesis of circRNAs, regulation of circRNAs by m6A modification and mechanisms by which circRNAs affect tumor progression respectively. Moreover, existing circRNA detection methods and their characteristics are also mentioned.

New insight towards development of paclitaxel and docetaxel resistance in cancer cells: EMT as a novel molecular mechanism and therapeutic possibilities

Epithelial-to-mesenchymal transition (EMT) mechanism is responsible for metastasis and migration of cancer cells to neighboring cells and tissues. Morphologically, epithelial cells are transformed to mesenchymal cells, and at molecular level, E-cadherin undergoes down-regulation, while an increase occurs in N-cadherin and vimentin levels. Increasing evidence demonstrates role of EMT in mediating drug resistance of cancer cells. On the other hand, paclitaxel (PTX) and docetaxel (DTX) are two chemotherapeutic agents belonging to taxene family, capable of inducing cell cycle arrest in cancer cells via preventing microtubule depolymerization. Aggressive behavior of cancer cells resulted from EMT-mediated metastasis can lead to PTX and DTX resistance. Upstream mediators of EMT such as ZEB1/2, TGF-β, microRNAs, and so on are involved in regulating response of cancer cells to PTX and DTX. Tumor-suppressing factors inhibit EMT to promote PTX and DTX sensitivity of cancer cells. Furthermore, three different strategies including using anti-tumor compounds, gene therapy and delivery systems have been developed for suppressing EMT, and enhancing cytotoxicity of PTX and DTX against cancer cells that are mechanistically discussed in the current review.

Circ3823 contributes to growth, metastasis and angiogenesis of colorectal cancer: involvement of miR-30c-5p/TCF7 axis

Background

Colorectal cancer (CRC) is one of the most common malignant tumours. The recurrence and metastasis of CRC seriously affect the survival rate of patients. Angiogenesis is an extremely important cause of tumour growth and metastasis. Circular RNAs (circRNAs) have been emerged as vital regulators for tumour progression. However, the regulatory role, clinical significance and underlying mechanisms still remain largely unknown.

Methods

High-throughput sequencing was used to analyse differential circRNAs expression in tumour and non-tumour tissues of CRC. In situ hybridization (ISH) and qRT-PCR were used to determine the level of circ3823 in CRC tissues and serum samples. Then, functional experiments in vitro and in vivo were performed to investigate the effects of circ3823 on tumour growth, metastasis and angiogenesis in CRC. Sanger sequencing, RNase R and Actinomycin D assay were used to verify the ring structure of circ3823. Mechanistically, dual luciferase reporter assay, fluorescent in situ hybridization (FISH), RNA immunoprecipitation (RIP) and RNA pull-down experiments were performed to confirm the underlying mechanisms of circ3823.

Results

Circ3823 was evidently highly expressed in CRC and high circ3823 expression predicted a worse prognosis of CRC patients. Receiver operating characteristic curves (ROCs) indicated that the expression of circ3823 in serum showed high sensitivity and specificity for detecting CRC which means circ3823 have the potential to be used as diagnostic biomarkers. Functional experiments in vitro and in vivo indicated that circ3823 promote CRC cell proliferation, metastasis and angiogenesis. Mechanism analysis showed that circ3823 act as a competing endogenous RNA of miR-30c-5p to relieve the repressive effect of miR-30c-5p on its target TCF7 which upregulates MYC and CCND1, and finally facilitates CRC progression. In addition, we found that N6-methyladenosine (m6A) modification exists on circ3823. And the m6A modification is involved in regulating the degradation of circ3823.

Conclusions

Our findings suggest that circ3823 promotes CRC growth, metastasis and angiogenesis through circ3823/miR-30c-5p/TCF7 axis and it may serve as a new diagnostic marker or target for treatment of CRC patients. In addition, m6A modification is involved in regulating the degradation of circ3823.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12943-021-01372-0.

Blocking circ_0014130 suppressed drug resistance and malignant behaviors of docetaxel resistance-acquired NSCLC cells via regulating miR-545-3p-YAP1 axis

Recent evidences have claimed that circular RNAs are deregulated in docetaxel (DTX) resistance in malignant tumors, including non-small-cell lung cancer (NSCLC). Hsa_circ_0014130 (circ_0014130) is a new biomarker in NSCLC. However, its role in DTX-resistant NSCLC remained to be annotated. In this study, real-time PCR was used to measure expression of circ_0014130, and circ_0014130 was upregulated in NSCLC tumors and DTX-resistant NSCLC cells (NCI-H1299/DTX and A549/DTX). MTT assay analyzed the half inhibitory concentration (IC50) of DTX, and it was lowered by circ_0014130 interference in DTX-resistant NSCLC cells. Moreover, colony formation assay, flow cytometry, transwell assays, and xenograft tumor model revealed that silencing circ_0014130 facilitated apoptosis rate of DTX-resistant NSCLC cells, suppressed the colony formation, migration and invasion, and retarded xenograft tumor growth in nude mice. Dual-luciferase reporter assay and RNA immunoprecipitation confirmed that circ_0014130 was one competing endogenous RNA (ceRNA) for miRNA (miR)-545-3p, and circ_0014130 modulated expression of yes-associated protein 1 (YAP1), a target gene for miR-545-3p. YAP1 upregulation and miR-545-3p downregulation were allied with circ_0014130 upregulation in NSCLC tumors and DTX-resistant NSCLC cells. Functionally, downregulating miR-545-3p could abate the effects of circ_0014130 knockdown in DTX-resistant NSCLC cells in vitro, whereas its overexpression exerted similar effects of circ_0014130 knockdown. Either, restoring YAP1 partially reversed miR-545-3p effects in DTX-resistant NSCLC cells. Collectively, there might be a novel circ_0014130-miR-545-3p-YAP1 ceRNA pathway in regulation of chemoresistance and malignant behaviors of DTX-resistant NSCLC cells, suggesting a potential therapeutic approach for DTX resistance.

Overexpressed circRANBP17 acts as an oncogene to facilitate nasopharyngeal carcinoma via the miR-635/RUNX2 axis

Circular RNAs (circRNAs) are implicated in the initiation and progress of several diseases, including cancer. However, the precise role of circRNAs in human nasopharyngeal carcinoma (NPC) remains unclear. In this research, we found a new circRNA hsa_circ_0001554 (circRANBP17), which was derived from the RAN binding protein 17 (RANBP17). Our qRT-PCR data found that circRANBP17 expression was up-regulated in NPC tissue and cells. Functional silencing studies revealed that circRANBP17 inhibited NPC cell proliferation and invasion in vitro, and circRANBP17 down-regulation also reduced tumor growth in nude mice. MiR-635 was demonstrated as a direct target of circRANBP17; circRANBP17 up-regulated RUNX2 expression levels by sponging miR-635, thereby promoting NPC proliferation and invasion. Thus, our data provide the evidence for the first time that circRANBP17 is a new onco-circRNA via miR-635/RUNX2 axis regulation, and may function as a novel therapeutic target for NPC treatment.

MicroRNAs in Metastasis and the Tumour Microenvironment

Metastasis is the process whereby cancer cells migrate from the primary tumour site to colonise the surrounding or distant tissue or organ. Metastasis is the primary cause of cancer-related mortality and approximately half of all cancer patients present at diagnosis with some form of metastasis. Consequently, there is a clear need to better understand metastasis in order to develop new tools to combat this process. MicroRNAs (miRNAs) regulate gene expression and play an important role in cancer development and progression including in the metastatic process. Particularly important are the roles that miRNAs play in the interaction between tumour cells and non-tumoral cells of the tumour microenvironment (TME), a process mediated largely by circulating miRNAs contained primarily in extracellular vesicles (EVs). In this review, we outline the accumulating evidence for the importance of miRNAs in the communication between tumour cells and the cells of the TME in the context of the pre-metastatic and metastatic niche.