One stone, two birds: circACTN4, a nexus for a coordinated activation of Hippo and Wnt/β-catenin pathways in cholangiocarcinoma

The study on circRNA profiling uncovers the regulatory function of the hsa_circ_0059665/miR-602 pathway in breast cancer

Abnormal expression of circRNAs has been observed in different types of carcinomas, and they play significant roles in the biology of these cancers. Nevertheless, the clinical relevance and functional mechanisms of the majority of circRNAs implicated in breast cancer progression remain unclear. The primary objective of our investigation is to uncover new circRNAs in breast cancer and elucidate the underlying mechanisms by which they exert their effects. The circRNA expression profile data for breast cancer and RNA-sequencing data were acquired from distinct public databases. Differentially expressed circRNAs and mRNA were identified through fold change filtering. The establishment of the competing endogenous RNAs (ceRNAs) network relied on the interplay between circular RNAs, miRNAs, and mRNAs. The hub genes were identified from the protein-protein interaction (PPI) regulatory network using the CytoHubba plugin in Cytoscape. Moreover, the expression levels and prognostic value of these hub genes in the PPI network were assessed using the GEPIA and Kaplan-Meier plotter databases. Fluorescence in situ hybridization (FISH) was used to identified the expression and intracellular localization of hsa_circ_0059665 by using the tissue microarray. Transwell analysis and CCK-8 analysis were performed to assess the invasion, migration, and proliferation abilities of breast cancer cells. Additionally, we investigated the interactions between hsa_circ_0059665 and miR-602 through various methods, including FISH, RNA-binding protein immunoprecipitation (RIP), and luciferase reporter assay. Rescue experiments were conducted to determine the potential regulatory role of hsa_circ_0059665 in breast cancer progression. A total of 252 differentially expressed circRNAs were identified. Among them, 246 circRNAs were up-regulated, while 6 circRNAs were down-regulated. Based on prediction and screening of circRNA-miRNA and miRNA-mRNA binding sites, we constructed a network consisting of circRNA-miRNA-mRNA interactions. In addition, we constructed a Protein-Protein Interaction (PPI) network and identified six hub genes. Moreover, the expression levels of these six hub genes in breast cancer tissues were found to be significantly lower. Furthermore, the survival analysis results revealed a significant correlation between low expression levels of KIT, FGF2, NTRK2, CAV1, LEP and poorer prognosis in breast cancer patients. The FISH experiment results indicated that hsa_circ_0059665 exhibits significant downregulation in breast cancer, and its decreased expression is linked to poor prognosis in breast cancer patients. Functional in vitro experiments revealed that overexpression of hsa_circ_0059665 can inhibit proliferation, migration and invasion abilities of breast cancer cells. Further molecular mechanism studies showed that hsa_circ_0059665 exerts its anticancer gene role by acting as a molecular sponge for miR-602. In our study, we constructed and analyzed a circRNA-related ceRNA regulatory network and found that hsa_circ_0059665 can act as a sponge for miR-602 and inhibit the proliferation, invasion and migration of breast cancer cells.

Circular RNAs in human diseases

Circular RNAs (circRNAs) are a unique class of RNA molecules formed through back-splicing rather than linear splicing. As an emerging field in molecular biology, circRNAs have garnered significant attention due to their distinct structure and potential functional implications. A comprehensive understanding of circRNAs' functions and potential clinical applications remains elusive despite accumulating evidence of their involvement in disease pathogenesis. Recent research highlights their significant roles in various human diseases, but comprehensive reviews on their functions and applications remain scarce. This review provides an in-depth examination of circRNAs, focusing first on their involvement in non-neoplastic diseases such as respiratory, endocrine, metabolic, musculoskeletal, cardiovascular, and renal disorders. We then explore their roles in tumors, with particular emphasis on exosomal circular RNAs, which are crucial for cancer initiation, progression, and resistance to treatment. By detailing their biogenesis, functions, and impact on disease mechanisms, this review underscores the potential of circRNAs as diagnostic biomarkers and therapeutic targets. The review not only enhances our understanding of circRNAs' roles in specific diseases and tumor types but also highlights their potential as novel diagnostic and therapeutic tools, thereby paving the way for future clinical investigations and potential therapeutic interventions.

TGFβ-induced circLTBP2 predicts a poor prognosis in intrahepatic cholangiocarcinoma and mediates gemcitabine resistance by sponging miR-338-3p

BACKGROUND & AIMS

Intrahepatic cholangiocarcinoma (iCCA) is a deadly cancer worldwide with an increasing incidence and limited therapeutic options. Therefore, there is an urgent need to open the field to new concepts for identifying clinically relevant therapeutic targets and biomarkers. Here, we explored the role and the clinical relevance of circular RNA (circRNA) circLTBP2 in iCCA.

METHODS

Transforming growth factor β (TGFβ)-regulated circRNAs were identified by dedicated microarrays in human HuCC-T1 iCCA cell line, and their clinical relevance was evaluated in independent cohorts of patients. Gain and loss of function of circLTBP2 combined with functional tests was performed in vitro and in vivo in mice. RNA pulldown, microRNA sequencing, and RNA immunoprecipitation were performed to explore the sponging activity of circLTBP2.

RESULTS

CircLTBP2 (has_circ_0032603) was identified as a novel TGFβ-induced circRNA in several cholangiocarcinoma cell lines. CircLTBP2 promotes tumour cell proliferation, migration, and resistance to gemcitabine-induced apoptosis in vitro and tumour growth in vivo. Mechanistically, circLTBP2 acts as a competitive RNA regulating notably the activity of the tumour suppressor microRNA miR-338-3p, leading to the overexpression of its pro-metastatic targets. The restoration of miR-338-3p levels in iCCA cells reversed the pro-tumourigenic effects driven by circLTBP2, including the resistance to gemcitabine-induced apoptosis. In addition, circLTBP2 expression predicted a reduced survival, as detected in not only tumour tissues but also serum extracellular vesicles isolated from patients with iCCA.

CONCLUSIONS

CircLTBP2 is a novel effector of the pro-tumourigenic arm of TGFβ and a clinically relevant biomarker easily detected from liquid biopsies in iCCA.

IMPACT AND IMPLICATIONS

Intrahepatic cholangiocarcinoma (iCCA) is an aggressive cancer with limited therapeutic options. Opening the field to new concepts is urgently needed to improve the survival of patients. Here, we evaluated the role and the clinical relevance of circular RNA. We report that TGFβ-induced circLTBP2 contributes to CCA carcinogenesis and may constitute a clinically relevant prognostic biomarker detected in liquid biopsies.

circRNF10 Regulates Tumorigenic Properties and Natural Killer Cell-Mediated Cytotoxicity against Breast Cancer through the miR-934/PTEN/PI3k-Akt Axis

Circular RNA (circRNA), a type of non-coding RNA, has received a great deal of attention with regard to the initiation and progression of tumors. However, the molecular mechanism and function of circRNAs in breast cancer (BC) remain unclear. In the current study, we discovered that hsa_circ_0028899 (also called circRNF10) was significantly reduced in BC tissues, and a higher level of circRNF10 was markedly related to a favorable prognosis. The results of CCK8, colony formation, Transwell, ELISA, and NK cell-mediated cytotoxicity assays indicated that increased circRNF10 expression could significantly repress the proliferation, invasion, and migration of BC cells and enhance the killing efficiency of NK cells against BC cells. According to these biological functions, the possible role and molecular mechanism of circRNF10 in BC cells were further investigated. We used bioinformatics prediction tools to predict circRNF10-bound miRNAs, which were verified by many experimental studies, including FISH, luciferase reporter assays, RIP, and Western blots. These data suggest that circRNF10 serves as a molecular sponge for miR-934 to further regulate PTEN expression and PI3k/Akt/MICA signaling in vitro and tumor growth in vivo. Altogether, these findings reveal that circRNF10 functions as a novel anti-oncogene in BC via sponging miR-934 and suppressing the PI3K/Akt/MICA pathway.

Circular RNAs: Biomarkers of cancer

Circular RNAs (circRNAs) are a class of single-stranded closed RNAs that are produced by the back splicing of precursor mRNAs. The formation of circRNAs mainly involves intron-pairing-driven circularization, RNA-binding protein (RBP)-driven circularization, and lariat-driven circularization. The vast majority of circRNAs are found in the cytoplasm, and some intron-containing circRNAs are localized in the nucleus. CircRNAs have been found to function as microRNA (miRNA) sponges, interact with RBPs and translate proteins, and play an important regulatory role in the development and progression of cancer. CircRNAs exhibit tissue- and developmental stage-specific expression and are stable, with longer half-lives than linear RNAs. CircRNAs have great potential as biomarkers for cancer diagnosis and prognosis, which is highlighted by their detectability in tissues, especially in fluid biopsy samples such as plasma, saliva, and urine. Here, we review the current studies on the properties and functions of circRNAs and their clinical application value.

Identification and Characterization of the Roles of circCASP9 in Gastric Cancer Based on a circRNA-miRNA-mRNA Regulatory Network

Accumulating evidence demonstrates that circular RNAs (circRNAs) have substantial effects on gastric cancer (GC) tumorigenesis and development. In this study, we performed a screen and identified two differentially expressed circRNAs (circCASP9 and circDLG5) from our circRNA microarray. We validated the expression of circCASP9 and circDLG5 in GC tissues and their normal counterparts by using qRT-PCR. Only circCASP9 was revealed to be downregulated in tumor tissues compared with adjacent normal tissues. Functionally, circCASP9 significantly inhibited the proliferation, migration, and invasion of GC cells both in vitro and in vivo. A competing endogenous RNA (ceRNA) network was constructed for the identification of candidate target genes of circCASP9. circCASP9, two miRNAs, and 55 mRNAs were selected for construction of the ceRNA network. We confirmed that circCASP9 can function as a sponge of miR-589-5p to regulate KANK1 expression, thereby controlling GC progression. Accordingly, we identified that the novel circRNA circCASP9 was differentially expressed between GC tissues and their normal counterparts. We also showed that circCASP9 can regulate the growth and metastasis of GC via the miR-589-5p/KANK1 axis. The circCASP9/miR-589-5p/KANK1 axis might provide crucial insights for investigating the occurrence and development of GC.