Circular RNA circLDB2 functions as a competing endogenous RNA to suppress development and promote cisplatin sensitivity in non-squamous non-small cell lung cancer

Circular RNAs in lung cancer: implications for preventing therapeutic resistance

LC is one of the most common malignant tumours that often presents with no distinct symptoms in the early stages, leading to late diagnoses when patients are at an advanced stage and no longer suitable for surgical treatment. Although adjuvant treatments are available, patients frequently develop tolerance to these treatments over time, resulting in poor prognoses for patients with advanced LC. Recently, circular RNAs (circRNAs), a type of non-coding RNA, have gained significant attention in LC research. Owing to their unique circular structure, circRNAs are highly stable within cells. This review systematically summarises the expression, characteristics, biological functions, and molecular regulatory mechanisms of circRNAs involved in therapy resistance as well as the potential applications in early diagnosis and gene targeting therapy in LC.

Circ_0102231 inactivates the PI3K/AKT signaling pathway by regulating the miR-635/NOVA2 pathway to promote the progression of non-small cell lung cancer

BACKGROUND

Circular RNAs (circRNAs) are involved in the malignant development of tumors. However, the mechanism of circ_0102231 in non-small cell lung cancer (NSCLC) has rarely been discussed and reported.

METHODS

Quantitative real-time polymerase chain reaction (qRT-PCR) was used to measure the expression of circ_0102231, miR-635 and NOVA alternative splicing regulator 2 (NOVA2) in NSCLC tissues and cells. Western blot was applied to detect the protein expression. Cell proliferation was monitored by cell counting kit-8 (CCK8) and 5-ethynyl-2'-deoxyuridine (EdU) experiments. The angiogenesis ability of cells was tested by angiogenesis assay. Flow cytometry was used to analyze cell apoptosis. The relationship between circ_0102231 and NOVA2 or miR-635 was analyzed by dual-luciferase reporter assay and RNA immunoprecipitation (RIP) assay. An in vivo transplanted tumor model was established to confirm the effect of circ_0102231 on tumor formation.

RESULTS

Circ_0102231 was abnormally upregulated in NSCLC tissues and correlated with clinical stage. Silencing of circ_0102231 inhibited cell proliferation and angiogenesis but significantly promoted the apoptosis of NSCLC cells. There were target binding sites between circ_0102231 and miR-635, miR-635 and NOVA2. Importantly, circ_0102231 acted as a sponge for miR-635, increased the expression of NOVA2, and activated the PI3K/AKT signaling pathway. Finally, silencing of circ_0102231 also had obvious antitumor effects in vivo.

CONCLUSION

Circ_0102231 increased the expression of NOVA2 by interacting with miR-635 to promote the malignant progression of NSCLC.

Circular RNAs: Emerging roles and new insights in human cancers

Circular RNAs (circRNAs) are single-stranded, covalently closed RNA molecules formed by mRNA exon back-splicing. Although the circRNA functions remain largely unknown, their currently known biological activities include: acting as competing endogenous RNA (ceRNA) to adsorb microRNA (miRNA), binding proteins, regulating transcription or splicing, and ability to be translated into proteins or peptides. A growing number of studies have found that many circRNAs are abnormally expressed in various cancers, and their dysregulation is highly correlated with tumor progression. Therefore, diagnosis and treatment using circRNAs as biomarkers and therapeutic targets, respectively, has gradually become an attractive research topic. In this review, we introduced the canonical biogenesis pathways and degradation mechanisms of circRNAs. In addition, we examined the biological functions of circRNAs in vivo. Finally, we discussed the current clinical applications and challenges faced by circRNA, and proposed future directions for this promising research field.

Circular RNAs in chemotherapy resistance of lung cancer and their potential therapeutic application

Lung cancer is one of the high malignancy-related incidence and mortality worldwide, accounting for about 13% of total cancer diagnoses. Currently, the use of anti-cancer agents is still the main therapeutic method for lung cancer. However, cancer cells will gradually show resistance to these drugs with the progress of treatment. And the molecular mechanisms underlying chemotherapy agents resistance remain unclear. circRNAs are newly identified noncoding RNAs molecules with covalently closed circular structures. Previous studies have shown that circRNAs are associated with tumorigenesis and progression of various cancers, including lung cancer. Recently, growing reports have suggested that circRNAs could contribute to drug resistance of lung cancer cell through different mechanisms. Therefore, in this review, we summarized the functions and underlying mechanisms of circRNAs in regulating chemoresistance of lung cancer and discussed their potential applications for diagnosis, prognosis, and treatment of lung cancer.

Role of circular RNAs in the diagnosis, regulation of drug resistance and prognosis of lung cancer (Review)

Lung cancer is one of the most common malignant tumors in China and is the highest cause of mortality among male and female patients, both in urban and rural areas. A subset of patients with lung cancer only display chest tightness without any other obvious symptoms. This is because most symptoms do not manifest during the early stages of disease development. Consequently, most patients with lung cancer are diagnosed when the disease is in the advanced stages, when they are already unfit for surgical treatment. Furthermore, the prognosis of patients with lung cancer is poor. The 5-year survival rate of patients with stage IA lung cancer is 85%, compared with 6% in those with stage IV. This requires the development of strategies for early diagnosis, treatment and prognosis to improve the management of lung cancer. Circular RNAs (circRNAs) belong to a class of closed circular non-coding RNAs formed by reverse splicing of a precursor mRNA. These RNAs are highly stable, ubiquitously expressed, conserved, and show high specificity. CircRNAs regulate biological processes, such as the proliferation, differentiation and invasion of lung cancer cells. Therefore, they can be used as biomarkers for the early diagnosis and prognosis prediction of lung cancer, as well as novel targets for therapy design. In the present review, the biological characteristics and functions of circRNAs, as well as their application in the diagnosis, control of drug resistance and effect on the prognosis of patients with lung cancer, will be discussed.

Construction of circRNA-miRNA-mRNA network and identification of novel potential biomarkers for non-small cell lung cancer

Background

The underlying circular RNAs (circRNAs)-related competitive endogenous RNA (ceRNA) mechanisms of pathogenesis and prognosis in non-small cell lung cancer (NSCLC) remain unclear.

Methods

Differentially expressed circRNAs (DECs) in two Gene Expression Omnibus datasets (GSE101684 and GSE112214) were identified by utilizing R package (Limma). Circinteractome and StarBase databases were used to predict circRNA associated-miRNAs and mRNAs, respectively. Then, protein–protein interaction (PPI) network of hub genes and ceRNA network were constructed by STRING and Cytoscape. Also, analyses of functional enrichment, genomic mutation and diagnostic ROC were performed. TIMER database was used to analyze the association between immune infiltration and target genes. Kaplan–Meier analysis, cox regression and the nomogram prediction model were used to evaluate the prognostic value of target genes. Finally, the expression of potential circRNAs and target genes was validated in cell lines and tissues by quantitative real-time PCR (qRT-PCR) and Human Protein Atlas (HPA) database.

Results

In this study, 15 DECs were identified between NSCLC tissues and adjacent-normal tissues in two GEO datasets. Following the qRT-PCR corroboration, 7 DECs (hsa_circ_0002017, hsa_circ_0069244, hsa_circ_026337, hsa_circ_0002346, hsa_circ_0007386, hsa_circ_0008234, hsa_circ_0006857) were dramatically downregulated in A549 and SK-MES-1 compared with HFL-1 cells. Then, 12 circRNA-sponged miRNAs were screened by Circinteractome and StarBase, especially, hsa-miR-767-3p and hsa-miR-767-5p were significantly up-regulated and relevant to the prognosis. Utilizing the miRDB and Cytoscape, 12 miRNA-target genes were found. Functional enrichment, genomic mutation and diagnostic analyses were also performed. Among them, FNBP1, AKT3, HERC1, COL4A1, TOLLIP, ARRB1, FZD4 and PIK3R1 were related to the immune infiltration via TIMER database. The expression of ARRB1, FNBP1, FZD4, and HERC1 was correlated with poor overall survival (OS) in NSCLC patients by cox regression and nomogram. Furthermore, the hub-mRNAs were validated in cell lines and tissues.

Conclusion

We constructed the circRNA-miRNA-mRNA network that might provide novel insights into the pathogenesis of NSCLC and reveal promising immune infiltration and prognostic biomarkers.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12935-021-02278-z.

Circular RNA circLDB2 functions as a competing endogenous RNA to suppress development and promote cisplatin sensitivity in non-squamous non-small cell lung cancer

Background

Circular RNAs (circRNAs) are covalently closed RNAs and are implicated in the development of non‐small cell lung cancer (NSCLC). Here, we identified the precise actions of circRNA LIM domain binding 2 (circLDB2, hsa_circ_0069244) in non‐squamous NSCLC development and drug sensitivity.

Methods

CircLDB2, microRNA (miR)‐346, and LIM and calponin‐homology domains 1 (LIMCH1) were quantified by quantitative real‐time polymerase chain reaction (qRT‐PCR) or western blot. Ribonuclease R (RNase R), actinomycin D, and subcellular localization assays were used to characterize circLDB2. Cell proliferation and viability, colony formation, apoptosis, migration, and invasion were gauged by Cell Counting Kit‐8 (CCK‐8), colony formation, flow cytometry, wound‐healing, and transwell assays, respectively. RNA immunoprecipitation (RIP), RNA pull‐down, and dual‐luciferase reporter assays were used to verify the direct relationship between miR‐346 and circLDB2 or LIMCH1. Animal studies were performed to evaluate the impact of circLDB2 in vivo.

Results

CircLDB2 was underexpressed in non‐squamous NSCLC and was identified as a bona fide circular transcript. Overexpression of circLDB2 impeded cell proliferation, migration, invasion, and enhanced apoptosis and cisplatin sensitivity in vitro, as well as promoted the antitumor effect of cisplatin in vivo. CircLDB2 regulated cell functional behaviors and cisplatin sensitivity by sponging miR‐346. LIMCH1 was a direct and functional target of miR‐346. Furthermore, circLDB2 acted as a competing endogenous RNA (ceRNA) for miR‐346 to induce LIMCH1 expression.

Conclusion

Our findings demonstrated that circLDB2 impeded non‐squamous NSCLC development and enhanced cisplatin sensitivity partially by acting as a ceRNA, highlighting circLDB2 as a promising candidate for the development of novel antitumor therapies.