The Biogenesis and Functions of circRNAs and Their Roles in Breast Cancer

CircRNA and lncRNA-encoded peptide in diseases, an update review

Non-coding RNAs (ncRNAs), including circular RNAs (circRNAs) and long non-coding RNAs (lncRNAs), are unique RNA molecules widely identified in the eukaryotic genome. Their dysregulation has been discovered and played key roles in the pathogenesis of numerous diseases, including various cancers. Previously considered devoid of protein-coding ability, recent research has revealed that a small number of open reading frames (ORFs) within these ncRNAs endow them with the potential for protein coding. These ncRNAs-derived peptides or proteins have been proven to regulate various physiological and pathological processes through diverse mechanisms. Their emerging roles in disease diagnosis and targeted therapy underscore their potential utility in clinical settings. This comprehensive review aims to provide a systematic overview of proteins or peptides encoded by lncRNAs and circRNAs, elucidate their production and functional mechanisms, and explore their promising applications in cancer diagnosis, disease prediction, and targeted therapy.

Hsa_circ_0137652 Regulates miR-1205/CCNB1 Axis to Accelerate the Malignancy of Breast Cancer

CircRNAs have become a hotspot in tumor research owing to their high stability and specific functions. We investigated the function of hsa_circ_0137652 in the onset and progression of breast cancer (BC). The expression of circ_0137652, miR-1205, and CCNB1 in BC tissues and cell lines were detected using RT-qPCR and/or western blotting. Dual-luciferase reporter and RNA immunoprecipitation chip assays were used to confirm any potential connections between circ_0137652, miR-1205, and CCNB1. CCK-8 and clone formation assays (CFA) were used to measure the proliferation of BC cells. The Transwell assay was used to investigate the migration of BC cells, and the impact of circ_0137652 on BC tumor formation in vivo was validated using animal experiments. RT-qPCR results showed that circ_0137652 and CCNB1 in breast cancer tissues were notably upregulated in normal tissues, whereas miR-1205 was prominently downregulated. After silencing circ_0137652, the growth and migration of BC cells were reduced. Animal experiments showed that circ_0137652 hampers the tumorigenesis of BC cells in vivo. Additionally, we found that circ_0137652 functions as a sponge for miR-1205. Moreover, the miR-1205 inhibitor notably facilitated cell proliferation and migration and attenuated the action of circ_0137652 knockdown. Furthermore, miR-1205 inhibits BC progression by targeting CCNB1. Circ_0137652 controls the miR-1205/CCNB1 axis to induce increased breast cancer malignancy. Our findings suggest that circ_0137652 may be a novel target for BC therapy.

EIF4A3-mediated circ_0042881 activates the RAS pathway via miR-217/SOS1 axis to facilitate breast cancer progression

Breast cancer (BC) is one of the most frequent cancer-related deaths in women worldwide. Studies have shown the potential impact of circRNAs in multiple human tumorigeneses. Research on the vital signaling pathways and therapeutic targets of circRNAs is indispensable. Here, we aimed to investigate the clinical implications and underlying mechanisms of circ_0042881 in BC. RT-qPCR validated circ_0042881 was notably elevated in BC tissues and plasma, and closely associated with BC clinicopathological features. Functionally, circ_0042881 significantly accelerated the proliferation, migration, and invasion of BC cells in vitro and tumor growth and metastasis in vivo. Mechanistically, circ_0042881 promoted BC progression by sponging miR-217 to relieve its inhibition effect in son of sevenless 1 (SOS1), which further activated RAS protein and initiated downstream signaling cascades, including MEK/ERK pathway and PI3K/AKT pathway. We also demonstrated that treatment of BAY-293, an inhibitor of SOS1 and RAS interaction, attenuated BC progression induced by circ_0042881 overexpression. Furthermore, Eukaryotic initiation factor 4A-III (EIF4A3) could facilitate circ_0042881 circularization. Altogether, we proposed a novel signaling network in which circ_0042881, induced by EIF4A3, influences the process of BC tumorigenesis and metastasis by miR-217/SOS1 axis.

Regulatory miRNAs, circRNAs and lncRNAs in cell cycle progression of breast cancer

Breast cancer is a complex and heterogeneous disease that poses a significant public health concern worldwide, and it remains a major challenge despite advances in treatment options. One of the main properties of cancer cells is the increased proliferative activity that has lost regulation. Dysregulation of various positive and negative modulators in the cell cycle has been identified as one of the driving factors of breast cancer. In recent years, non-coding RNAs have garnered much attention in the regulation of cell cycle progression, with microRNAs (miRNAs), circular RNAs (circRNAs), and long non-coding RNAs (lncRNAs) being of particular interest. MiRNAs are a class of highly conserved and regulatory small non-coding RNAs that play a crucial role in the modulation of various cellular and biological processes, including cell cycle regulation. CircRNAs are a novel form of non-coding RNAs that are highly stable and capable of modulating gene expression at posttranscriptional and transcriptional levels. LncRNAs have also attracted considerable attention because of their prominent roles in tumor development, including cell cycle progression. Emerging evidence suggests that miRNAs, circRNAs and lncRNAs play important roles in the regulation of cell cycle progression in breast cancer. Herein, we summarized the latest related literatures in breast cancer that emphasize the regulatory roles of miRNAs, circRNAs and lncRNAs in cell cycle progress of breast cancer. Further understanding of the precise roles and mechanisms of non-coding RNAs in breast cancer cell cycle regulation could lead to the development of new diagnostic and therapeutic strategies for breast cancer.

Hsa_circ_0060467 promotes breast cancer liver metastasis by complexing with eIF4A3 and sponging miR-1205

Breast cancer (BC) is the most common cancer and the top cause of female mortality worldwide. The prognosis for patients with breast cancer liver metastasis (BCLM) remains poor. Emerging studies suggest that circular RNAs (circRNAs) are associated with the progression of BC. Exploration of circRNAs presents a promising avenue for identifying metastasis-targeting agents and improving the prognosis of patients with BCLM. Microarray and bioinformatic analyses were used to analyze differentially expressed circRNAs between three pairs of BCLM and primary BC. The roles of hsa_circ_0060467 (circMYBL2) and its target gene E2F1 in BC cells were explored by multiple functional experiments. And xenograft mouse models and hepatic metastases of BC hemi-spleen models were used to illustrate the function of circMYBL2 in vivo. The intrinsic molecular mechanism involving circMYBL2 was confirmed by bioinformatics analyses, RIP assays, CHIRP assays, luciferase reporter assays, and rescue experiments. CircMYBL2 was overexpressed in BCLM tissues and BC cells. Functionally, circMYBL2 can facilitate the proliferation and liver metastasis of BC. Mechanistically, circMYBL2 upregulated the transcription factor E2F1 by sponging miR-1205 and complexing with eukaryotic translation initiation factor 4A3 (eIF4A3) and then facilitated the epithelial-mesenchymal transition (EMT) process in BC cells. Our findings showed that circMYBL2 promoted the tumorigenesis and aggressiveness of BC through the circMYBL2/miR-1205/E2F1 and circMYBL2/eIF4A3/E2F1 axes, which may provide a novel targeted therapy for patients with BCLM.

Circular RNA hsa_circ_0012673 Promotes Breast Cancer Progression via miR-576-3p/SOX4 Axis

Circular RNAs (circRNAs) have been reported to exert critical roles in human cancers. In this study, we investigated the role and molecular mechanism of hsa_circ_0012673 in breast cancer. Herein, we found that the expression of hsa_circ_0012673 was upregulated in breast cancer tissues and cell lines. Knockdown of hsa_circ_0012673 using RNA interference technique suppressed the proliferation, migration, and invasion of breast cancer cells. Mechanistically, hsa_circ_0012673 sponged miR-576-3p to stabilize SRY-box transcription factor 4 (SOX4), and thereby facilitating breast cancer cell proliferation, migration and invasion. Collectively, our study identified the oncogenic properties of hsa_circ_0012673/miR-576-3p/SOX4 axis in breast cancer, providing potential and exploitable diagnostic and therapeutic molecules for breast cancer.

Upregulation of circ_0008812 and circ_0001583 predicts poor prognosis and promotes breast cancer proliferation

Background: Accumulating evidence suggests that circular RNAs (circRNAs) are highly correlated with tumor progression and pathogenesis in breast cancer. Whereas, their regulatory roles and corresponding mechanisms in breast cancer are still not exhaustive. Thus, we intended to establish circRNA-mediated competive endogenous RNA (ceRNA) network to uncover the possible roles and clinical implications of circRNAs in breast cancer.

Methods: Microarray and RNA-sequencing (RNA-seq) data were download from GEO and TCGA database to screen for differentially expressed RNAs (DEcircRNAs, DEmiRNAs, DEmRNAs) in breast cancer. By implementing online databases, we established ceRNA networks, performed gene set enrichment analysis, constructed protein-protein interaction (PPI) networks, and assessed the expression levels and prognostic significance of hub genes. Subsequently, we explored the functions of prognosis-related genes and constructed gene-drug interaction networks. Finally, the functional roles of DEcircRNAs in breast cancer were revealed via MTT and colony formation assay.

Results: Based on the identified 8 DEcircRNAs, 25 miRNAs and 216 mRNAs, a ceRNA regulatory network was established. Further analysis revealed that prominent enrichments were transcription factor binding, transforming growth factor-beta (TGF-β) and Apelin signaling pathway etc. PPI network and survival curves analysis showed that elevated levels of hub genes (RACGAP1 and KPNA2) were associated with poorer prognosis. They were found to be positively relevant to cell cycle and proliferation. Then a prognostic sub-network of ceRNA was constructed, consisting of 2 circRNAs, 4 miRNAs and 2 mRNAs. The gene-drug interaction network showed that numerous drugs could regulate the expression of these two prognosis-related genes. Functional experiments showed that depletion of circ_0008812 and circ_0001583 could significantly inhibit the proliferation of MCF-7 cells.

Conclusion: Our study constructed 4 prognostic regulatory axes that are significantly correlated with tumor prognosis in breast cancer patients, and uncover the roles of circ_0008812 and circ_0001583 in breast cancer, providing a new perspective into the molecular mechanisms of breast cancer pathogenesis.

CircEPSTI1 Promotes the Proliferation of HER2-Positive Breast Cancer Cells via circEPSTI1/miR-145/ERBB3 Axis

Breast cancer is the most common type of cancer worldwide. There are great challenges in the prevention and treatment of breast cancer. In this study, we explored the molecular and biological mechanisms of circular RNA circEPSTI1 (has_circ_0000479) in the regulation of HER2-positive breast cancer cells. The expression of CircEPSTI1, microRNA miR-145, and ERBB3 in HER2-positive breast cancer cells was evaluated by qRT-PCR and western blot assays. Cell proliferation was assessed by CCK-8. Wound-healing and transwell migration assays were performed to evaluate cell migration. A transwell invasion assay was performed to detect cell invasion. The interaction of miR-145, circEPSTI1, and ERBB3 was confirmed bydual-luciferase reporter and RIP assays. CircEPSTI1 was upregulated in the HER2-positive breast cancer tissues and cells. Knockdown of circEPSTI1 inhibited SKBR3 and BT474 cell proliferation, migration, and invasion. Mechanistically, circEPSTI1 directly targeted miR-145, and miR-145 was a downstream mediator of circEPSTI1 in modulating the proliferation, migration, and invasion of SKBR3 and BT474 cells. ERBB3 was identified as a direct and functional target of miR-145 in HER2-positive breast cancer cells. Our findings demonstrate that circEPSTI1, an overexpressed circRNA in HER2-positive breast cancer, promotes the proliferation, migration, and invasion of SKBR3 and BT474 cells through the miR-145/ERBB3 axis.

The value of exosome-derived noncoding RNAs in colorectal cancer proliferation, metastasis, and clinical applications

Colorectal cancer (CRC) is the third most common cancer in the world today, and its incidence and mortality rates are increasing every year. The ease of proliferation and metastasis of CRC has long been an important reason for its high mortality rate. Exosomes serve as key mediators that mediate communication between tumor cells and various other cells. Non-coding RNAs (ncRNAs) have been shown to play a key role in apoptosis, immunosuppression and proliferation metastasis in cancer. ncRNAs are loaded on exosomes and initiate the onset of metastasis by promoting epithelial-mesenchymal transition (EMT) at the primary site of the tumor. Meanwhile, exosome-derived ncRNAs construct a pre-metastatic niche (PMN) for CRC metastasis by forming an inflammatory microenvironment in distant organs, immunosuppression, and promoting angiogenesis and remodeling of the extracellular matrix. Here, we summarize the specific mechanisms associated with exosome-derived ncRNAs promoting local invasion and metastasis in CRC. Finally, we focus on their value for clinical application in future CRC diagnosis and treatment.

Small biomarkers with massive impacts: PI3K/AKT/mTOR signalling and microRNA crosstalk regulate nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is one of the most common malignant tumours of the head and neck in Southeast Asia and southern China. The Phosphatidylinositol 3-kinase/protein kinase B (AKT)/mammalian target of rapamycin (mTOR) signalling pathway is involved in processes related to tumour initiation/progression, such as proliferation, apoptosis, metastasis, and drug resistance, and is closely related to the clinicopathological features of NPC. In addition, key genes involved in the PI3K/AKT/mTOR signalling pathway undergo many changes in NPC. More interestingly, a growing body of evidence suggests an interaction between this signalling pathway and microRNAs (miRNAs), a class of small noncoding RNAs. Therefore, in this review, we discuss the interactions between key components of the PI3K/AKT/mTOR signalling pathway and various miRNAs and their importance in NPC pathology and explore potential diagnostic biomarkers and therapeutic targets.

Circ_0005714/miR-223-3p/ADAM9 regulatory axis affects proliferation, migration, invasion, and angiopoiesis in trophoblast cells

BACKGROUND

Circular RNAs (circRNAs) have critical roles in various types of diseases, including preeclampsia (PE). Circ_0005714 function in PE was explored in this study.

METHODS

Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) was performed for level analysis of circ_0005714, micoRNA-223-3p (miR-223-3p), and a disintegrin and metalloproteinase 9 (ADAM9). Cell Counting Kit-8 (CCK-8) and colony formation assays were used for cell viability and colony formation detection. Cell proliferation was determined by EdU assay. The determination of migration and invasion was conducted by wound healing assay and transwell assay. Tube formation assay was applied to assess angiopoiesis. Target binding analysis was performed by dual-luciferase reporter assay and RNA immunoprecipitation (RIP) assay. Western blot was used for protein examination.

RESULTS

Circ_0005714 was highly expressed in PE placenta tissues. The expression promotion of circ_0005714 reduced proliferation, migration, invasion, and angiopoiesis in trophoblast cells. Furthermore, circ_0005714 acted as a molecular sponge for miR-223-3p and the effects of circ_0005714 on trophoblast cells were achieved by sponging miR-223-3p. Moreover, miR-223-3p could target ADAM9 and knockdown of ADAM9 reversed cell progression inhibition induced by miR-223-3p inhibitor. In addition, circ_0005714 upregulated the ADAM9 expression and inactivated the Wnt/β-catenin pathway through targeting miR-223-3p.

CONCLUSIONS

All results manifested that circ_0005714 retarded the progression of PE by mediating the miR-223-3p/ADAM9 signal network.

EIF4A3-mediated circPRKCI expression promotes triple-negative breast cancer progression by regulating WBP2 and PI3K/AKT signaling pathway

Triple-negative breast cancer (TNBC) is known as a highly aggressive subtype of BC due to high rate of recurrence and metastasis, poor prognosis and lacking of effective targeted therapies. Circular RNAs (circRNAs) have been reported to participate in the progression of TNBC. In this study, we demonstrated that circPRKCI, derived from the PRKCI gene, was elevated in BC tissues and cell lines, especially in TNBC. The functional investigation showed that circPRKCI could significantly promote the proliferation and migration of TNBC in vivo and in vitro. In addition, circPRKCI regulated WBP2 and the phosphorylation of AKT via serving as miR-545-3p sponge. Of note, EIF4A3 could induce circPRKCI expression and nuclear export in TNBC cells. Taken together, EIF4A3-mediated circPRKCI could promote TNBC progression by regulating WBP2 and PI3K/AKT signaling pathway, providing a new avenue of therapy for TNBC.

CircRNAs as potent biomarkers in ovarian cancer: a systematic scoping review

More powerful prognostic and diagnostic tools are urgently needed for identifying and treating ovarian cancer (OC), which is the most fatal malignancy in women in developed countries. Circular RNAs (circRNAs) are conservative and stable looped molecules that can regulate gene expression by competing with other endogenous microRNA sponges. This discovery provided new insight into novel methods for regulating genes that are involved in many disorders and cancers. This review focuses on the dysregulated expression of circRNAs as well as their diagnostic and prognostic values in OC. We found that studies have identified twenty-one downregulated circRNAs and fifty-seven upregulated ones. The results of these studies confirm that circRNAs might be potent biomarkers with diagnostic, prognostic and therapeutic target value for OC. We also consider the connection between circRNAs and OC cell proliferation, apoptosis, metastasis, and chemotherapy resistance and sensitivity.