Silencing CDR1as enhances the sensitivity of breast cancer cells to drug resistance by acting as a miR-7 sponge to down-regulate REGγ

Circular RNAs as a novel molecular mechanism in diagnosis, prognosis, therapeutic target, and inhibiting chemoresistance in breast cancer

Breast cancer (BC) is the most common cancer among women, characterized by significant heterogeneity. Diagnosis of the disease in the early stages and appropriate treatment plays a crucial role for these patients. Despite the available treatments, many patients due to drug resistance do not receive proper treatments. Recently, circular RNAs (circRNAs), a type of non-coding RNAs (ncRNAs), have been discovered to be involved in the progression and resistance to drugs in BC. CircRNAs can promote or inhibit malignant cells by their function. Numerous circRNAs have been discovered to be involved in the proliferation, invasion, and migration of tumor cells, as well as the progression, pathogenesis, tumor metastasis, and drug resistance of BC. Circular RNAs can also serve as a biomarker for diagnosing, predicting prognosis, and targeting therapy. In this review, we present an outline of the variations in circRNAs expression in various BCs, the functional pathways, their impact on the condition, and their uses in clinical applications.

Value of CDR1-AS as a predictive and prognostic biomarker for patients with breast cancer receiving neoadjuvant chemotherapy in a prospective Chinese cohort

BACKGROUND

Neoadjuvant chemotherapy (NAC) is an effective treatment for locally advanced breast cancer (BC). However, there are no effective biomarkers for evaluating its efficacy. CDR1-AS, well known for its important role in tumorigenesis, is a famous circular RNA involved in the chemosensitivity of cancers other than BC. However, the predictive role of CDR1-AS in the efficacy and prognosis of NAC for BC has not been fully elucidated. We herein aimed to clarify this role.

METHODS

The present study included patients treated with paclitaxel-cisplatin-based NAC. The expression of CDR1-AS was detected by real-time quantitative reverse transcription polymerase chain reaction testing. The predictive value of CDR1-AS expression was examined in pathological complete response (pCR) after NAC using logistic regression analysis. The relationship between CDR1-AS expression and survival was demonstrated using the Kaplan-Meier method, and tested by log-rank test and Cox proportional hazards regression model.

RESULTS

The present study enrolled 106 patients with BC. Multivariate logistic regression analysis revealed that CDR1-AS expression was an independent predictive factor for pCR (odds ratio [OR] = 0.244; 95% confidence interval [CI] 0.081-0.732; p = 0.012). Furthermore, pCR benefits with low CDR1-AS expression were observed across all subgroups. The Kaplan-Meier curves and log-rank test suggested that the CDR1-AS high-expression group showed significantly better disease-free survival (DFS; log-rank p = 0.022) and relapse-free survival (RFS; log-rank p = 0.012) than the CDR1-AS low-expression group. Multivariate analysis revealed that CDR1-AS expression was an independent prognostic factor for DFS (adjusted HR = 0.177; 95% CI 0.034-0.928, p = 0.041), RFS (adjusted HR = 0.061; 95% CI 0.006-0.643, p = 0.020), and distant disease-free survival (adjusted HR = 0.061; 95% CI 0.006-0.972, p = 0.047).

CONCLUSIONS

CDR1-AS may be a potential novel predictive biomarker of pCR and survival benefit in patients with locally advanced BC receiving NAC. This may help identify specific chemosensitive individuals and build personalized treatment strategies.

LGCDA: Predicting CircRNA-Disease Association Based on Fusion of Local and Global Features

CircRNA has been shown to be involved in the occurrence of many diseases. Several computational frameworks have been proposed to identify circRNA-disease associations. Despite the existing computational methods have obtained considerable successes, these methods still require to be improved as their performance may degrade due to the sparsity of the data and the problem of memory overflow. We develop a novel computational framework called LGCDA to predict circRNA-disease associations by fusing local and global features to solve the above mentioned problems. First, we construct closed local subgraphs by using k-hop closed subgraph and label the subgraphs to obtain rich graph pattern information. Then, the local features are extracted by using graph neural network (GNN). In addition, we fuse Gaussian interaction profile (GIP) kernel and cosine similarity to obtain global features. Finally, the score of circRNA-disease associations is predicted by using the multilayer perceptron (MLP) based on local and global features. We perform five-fold cross validation on five datasets for model evaluation and our model surpasses other advanced methods.

Dual effects of circRNA in thyroid and breast cancer

CircRNA, the latest research hotspot in the field of RNA, is a special non-coding RNA molecule, which is unable to encode proteins and bind polyribosomes. As a regulatory molecule, circRNA participates in cancer cell generation and progression mainly through the mechanism of competitive endogenous RNA. In numerous regulated cancer organs, the thyroid and breast are both endocrine organs, and both are regulated by the hypothalamic pituitary gland axis. Thyroid cancer (TC) and breast cancer (BC) are both sexually prevalent in women and both are affected by hormones, thus they are intrinsically linked. In addition, recent epidemiological surveys have found that, early metastasis and recurrence of breast cancer remain the main cause of survival in breast cancer patients. Although at home and abroad, studies have shown that new targeted anti-tumor drugs with numerous tumor markers are gradually being used in the clinic, evidence for potential molecular mechanisms affecting its prognosis lacks clinical studies. Therefore, we search the relevant literature, and based on the latest domestic and international consensus, review the molecular mechanisms and regulation relevance of circRNA, compare the difference of the same circRNA in two tumors, to more deeply understand and lay the foundation for future clinical diagnostic, therapeutic and prognostic studies in large samples.

The role of CDR1as/ciRS-7 in cardio-cerebrovascular diseases

Cerebellar degeneration-related protein 1 antisense RNA (CDR1as), also known as ciRS-7, is a circular natural antisense transcript of CDR1. It is a widely studied and powerful representative of circular RNAs. Based on its widely reported role in cancer, CDR1as is considered one of the most promising biomarkers for diagnosing and treating tumours. However, some recent studies have extensively focused on its regulatory role in cardio-cerebrovascular diseases instead of in tumours. Studies have shown that CDR1as plays a unique role in the occurrence of cardio-cerebrovascular diseases; thus, it may be a potential target for preventing and treating cardio-cerebrovascular diseases. Furthermore, CDR1as has also been found to be related to signal transduction pathways related to inflammatory response, oxidative stress, etc., which may reveal its potential mechanism in cardio-cerebrovascular diseases. However, there is no literature to summarize the role and possible mechanism of CDR1as in cardio-cerebrovascular diseases. Therefore, in the present review, we have comprehensively summarised the latest progress in the biological characteristics, development processes, regulatory mechanisms, and roles of CDR1as in cardio-cerebrovascular diseases, aiming to provide a reference and guidance for future studies.

Interplay between LncRNAs and microRNAs in Breast Cancer

(1) Although long noncoding RNAs (lncRNAs) are known to be precursors of microRNAs (miRNAs), they frequently act as competing endogoneous RNAs (ceRNAs), yet still their interplay with miRNA is not well known. However, their interaction with miRNAs may result in the modulation of miRNA action. (2) To determine the contribution of these RNA molecules in tumor resistance to chemotherapeutic drugs, it is essential to consider not only the oncogenic and tumor suppressive function of miRNAs but also the impact of lncRNAs on miRNAs. Therefore, we performed an extensive search in different databases including PubMed. (3) The present study concerns the interplay between lncRNAs and miRNAs in the regulatory post-transcriptional network and their impact on drugs used in the treatment of breast cancer. (4) Consideration of this interplay may improve the search for new drugs to circumvent chemoresistance.

TGF-β signaling promotes cervical cancer metastasis via CDR1as

BACKGROUND

Due to the lack of effective treatment, metastasis is the main cause of cancer related deaths. TGF-β pathway has been reported related to cervical cancer metastasis. However, mechanism is still unclear.

METHODS

After agonist of TGF-β treatment, RNA sequencing revealed the expression profiles of circRNA in cervical cancer. In situ hybridization was used to analysis relationship between CDR1as and prognosis. Real-time PCR, Western blot, RNA interference, Transwell assay, Wound healing assay, RNA pulldown assay and RIP assays were performed in vitro. And in vivo cervical cancer model (including foot pad model and subcutaneous tumor formation) was also performed.

RESULTS

CDR1as was found upregulated obviously following TGF-β activation. In situ hybridization showed CDR1as was positively correlated with lymph node metastasis and shortened survival length. Simultaneously, overexpression of CDR1as promoted cervical cancer metastasis in vitro and in vivo. It was also found that CDR1as could facilitate the orchestration of IGF2BP1 on the mRNA of SLUG and stabilize it from degradation. Silencing IGF2BP1 hampers CDR1as related metastasis in cervical cancer. Additionally, effective CDR1as has been proven to activate TGF-β signaling factors known to promote EMT, including P-Smad2 and P-Smad3.

CONCLUSIONS

Our study proved TGF-β signaling may promote cervical cancer metastasis via CDR1as.

Current evidence on circRNAs as potential theranostic markers for detecting chemoresistance in breast cancer: a systematic review and meta‑analysis

This study assessed the value of circRNAs (circular RNAs) as prognostic markers in BC (breast cancer). We searched pertinent studies on the PubMed, Embase, and Web of Science online databases published according to PRISMA guidelines. A random-effects model for meta-analysis was used to assess the combined effect size of the HRs (hazard ratios) of the included studies. The heterogeneity test used Cochran's Q-test and I² statistics. Thirty of the 520 trials retrieved were included in the systematic review. A total of 11 chemotherapeutic agents were used in the included studies. A total of 30 studies on 30 circRNAs were included in the systematic review. Of the 30 relevant circRNAs, 28 were upregulated and two were downregulated in breast cancer versus normal samples, and both were associated with increased drug resistance. Nine of 30 studies were used for the meta-analysis. The results of the meta-analysis showed that the groups with circRNA upregulation and circRNA downregulation showed the same prognostic risk (HR = 1.37, 95% Cl: 0.80-2.36, I² = 63.7%). The results of subgroup analysis showed that both upregulated circRNAs (HR = 2.24, 95% Cl: 1.34-3.75, I² = 0%) and downregulated circRNAs (HR = 0.61, 95% Cl: 0.45-0.83, I² = 0%) were associated with poor BC prognosis. Collectively, the results of all relevant articles collected indicated that circRNAs showed good potential as possible clinical biomarkers of chemoresistance in BC patients.

Analyses of circRNA Expression throughout the Light-Dark Cycle Reveal a Strong Regulation of Cdr1as, Associated with Light Entrainment in the SCN

Circular RNAs (circRNAs) are a large class of relatively stable RNA molecules that are highly expressed in animal brains. Many circRNAs have been associated with CNS disorders accompanied by an aberrant wake-sleep cycle. However, the regulation of circRNAs in brain homeostasis over daily light-dark (LD) cycles has not been characterized. Here, we aim to quantify the daily expression changes of circRNAs in physiological conditions in healthy adult animals. Using newly generated and public RNA-Seq data, we monitored circRNA expression throughout the 12:12 h LD cycle in various mouse brain regions. We identified that Cdr1as, a conserved circRNA that regulates synaptic transmission, is highly expressed in the suprachiasmatic nucleus (SCN), the master circadian pacemaker. Despite its high stability, Cdr1as has a very dynamic expression in the SCN throughout the LD cycle, as well as a significant regulation in the hippocampus following the entry into the dark phase. Computational integration of different public datasets predicted that Cdr1as is important for regulating light entrainment in the SCN. We hypothesize that the expression changes of Cdr1as in the SCN, particularly during the dark phase, are associated with light-induced phase shifts. Importantly, our work revises the current beliefs about natural circRNA stability and suggests that the time component must be considered when studying circRNA regulation.

Regulation of Life & Death by REGγ

REGγ, a proteasome activator belonging to the 11S (otherwise known as REG, PA28, or PSME) proteasome activator family, is widely present in many eukaryotes. By binding to the 20S catalytic core particle, REGγ acts as a molecular sieve to selectively target proteins for degradation in an ATP- and ubiquitin-independent manner. This non-canonical proteasome pathway directly regulates seemingly unrelated cellular processes including cell growth and proliferation, apoptosis, DNA damage response, immune response, and metabolism. By affecting different pathways, REGγ plays a vital role in the regulation of cellular life and death through the maintenance of protein homeostasis. As a promoter of cellular growth and a key regulator of several tumor suppressors, many recent studies have linked REGγ overexpression with tumor formation and suggested the REGγ-proteasome as a potential target of new cancer-drug development. This review will present an overview of the major functions of REGγ as it relates to the regulation of cellular life and death, along with new mechanistic insights into the regulation of REGγ.

miRNAs as therapeutic predictors and prognostic biomarkers of neoadjuvant chemotherapy in breast cancer: a systematic review and meta-analysis

PURPOSE

Accumulating evidence has shown that microRNAs (miRNAs) are promising biomarkers of neoadjuvant chemotherapy (NAC) response in breast cancer (BC). However, their predictive roles remain controversial. Thus, this systematic review and meta-analysis aimed to describe the role of miRNA expression in NAC response and prognosis in BC to increase statistical power and improve translation.

METHODS

A systematic review of electronic databases for relevant studies was conducted following PRISMA guidelines. Data were extracted, collated, and combined by odds ratio (OR) and hazard ratio (HR) with 95% confidence intervals (CIs) to estimate the strength of the associations.

RESULTS

Of the 560 articles screened, 59 studies were included in our systematic review, and 5 studies were included in the subsequent meta-analysis. Sixty of 123 miRNAs were found to be related with NAC response and an elevated baseline miR-7 level in tissues was associated with a higher pathological complete response rate (OR 5.63; 95% CI 2.15-14.79; P = 0.0004). The prognostic value of 39 miRNAs was also studied. Of them, 26 miRNAs were found to be associated with survival. Pooled HRs indicated that patients with increased levels of serum miR-21 from baseline to the end of the second NAC cycle and from baseline to the end of NAC had a worse disease-free survival than those with decreased levels.

CONCLUSION

Our results highlight that a large number of miRNAs have possible associations with NAC response and prognosis in BC patients. Further well-designed studies are needed to elucidate the molecular mechanisms underlying these associations.

Circ_CDR1as: A circular RNA with roles in the carcinogenesis

Circular RNAs are a group of ancient but recently appreciated transcripts that affect carcinogenesis. An example of cancer-related circular RNAs is circ_CDR1as. It is mostly regarded as an oncogenic circular RNA, yet in bladder cancer and glioma it has the opposite effect. In gastric and ovarian cancer, both roles have been reported for this circular RNA. Circ_CDR1as has regulatory effects on miR-1270/AFP, miR-1287/Raf1, miR-7-5p/KLF4, miR-641/HOXA9, miR-219a-5p/SOX5, miR-7/HOXB13 and miR-876-5p/MAGE-A molecular axes. miR-7 is the most appreciated interacting miRNA with circ_CDR1as, since its interaction with circ_CDR1as has been validated in liver cancer, lung cancer, colorectal cancer, esophageal carcinoma, gastric cancer, pancreatic cancer, thyroid cancer, oral squamous cell carcinoma, nasopharyngeal carcinoma and osteosarcoma. The present article aims at summarization of the role of circ_CDR1as in neoplasms and its application as a biomarker in human cancers.

Curcumol enhances cisplatin sensitivity of gastric cancer: involvement of microRNA-7 and the nuclear factor-kappa B/snail family transcriptional repressor 1 axis

Cisplatin is a primary chemotherapeutic drug for gastric cancer (GC) patients, but the drug resistance remains the leading cause of treatment failure and high mortality. Curcumol is a bioactive sesquiterpenoid that has reportedly been linked to cisplatin sensitivity in GC. This study focuses on the exact functions of curcumol in the cisplatin sensitivity of GC cells and the molecules of action. The curcumol treatment reduced the viability and migration and enhanced cisplatin sensitivity of GC cells in a dose-dependent manner. Microarray analysis suggested that microRNA-7 (miR-7) was the most upregulated miRNA in GC cells after curcumol treatment. The Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis showed that the curcumol-affected genes, including the target genes of miR-7, were enriched in the nuclear factor-kappa B (NF-κB) pathway, whose activity was suppressed after curcumol treatment. miR-7 was found to target and suppress RELA proto-oncogene (RELA, also known as p65), a NF-κB subunit. Downregulation of miR-7 blocked the sensitizing effects of curcumol on cells to cisplatin and led to increased expression of NF-κB p65 and snail family transcriptional repressor 1 (SNAIL). Further downregulation of RELA enhanced, whereas upregulation of SNAIL suppressed the sensitivity again. In summary, this study suggests that curcumol sensitizes GC cells to cisplatin via miR-7 and the suppression of the NF-κB/SNAIL axis. The findings may offer new thoughts that curcumol in combination with cisplatin might be a useful strategy for GC management.

Hsa_circRNA_0088036 acts as a ceRNA to promote bladder cancer progression by sponging miR-140-3p

Circular RNAs (circRNAs) are a class of non-coding RNAs that play vital roles in cancer biology. However, the potential role of hsa_circRNA_0088036 in bladder cancer (BCa) remains unknown. Hsa_circRNA_0088036 was identified by microarray analysis and validated by quantitative real-time polymerase chain reaction. Functional assays were conducted to confirm the effects of hsa_circRNA_0088036 on the growth, migration, invasion, tumorigenesis, and metastasis of BCa cells. The luciferase reporter assay and RNA pull down assay were performed to investigate the interactions between hsa_circRNA_0088036, miR-140-3p, and forkhead box protein Q1 (FOXQ1). Upregulated expression of hsa_circRNA_0088036 in BCa tissues and cell lines was positively correlated with overall survival and clinicopathologic characteristics. Knockdown of hsa_circRNA_0088036 inhibited the growth, migration, and invasion of BCa cells both in vivo and in vitro. Mechanistically, hsa_circRNA_0088036 could directly interact with miR-140-3p and act as a miRNA sponge to modulate FOXQ1 expression. Knockdown of hsa_circRNA_0088036 inhibited the proliferation, migration, and metastasis of BCa cells via miR-140-3p/FOXQ1 signaling, suggesting that hsa_circRNA_0088036 is a potential biomarker and therapeutic target for BCa.

CircRNA CDR1as promotes cardiomyocyte apoptosis through activating hippo signaling pathway in diabetic cardiomyopathy

Diabetic cardiomyopathy (DCM), as a major complication of diabetic patients, can cause myocardial metabolic remodeling and lead to severe and irreversible cardiac dysfunction. Previously, we found that the circular RNA cerebellar degeneration-related protein 1 antisense (Circ-CDR1as) independently predicted acute myocardial infarction (AMI) and might be a new indicator marker for this. However, CDR1as was not clearly described in diabetic cardiomyopathy. Therefore, our purpose was to deeply explore the function of CDR1as in DCM. In this study, we found that CDR1as was upregulated in DCM, and knockdown of CDR1as could improve the apoptosis caused by DCM. Mechanistically, CDR1as activates the Hippo signaling pathway by significantly inhibiting Mammalian sterile 20-like kinase 1 (MST1) ubiquitination level. Furthermore, as a transcriptional factor of CDR1as, Forkhead box group O3a (FOXO3) was identified to activate the Hippo signaling pathway. Notably, the total m6A level was downregulated in the cardiac tissue of DCM. Alk B homolog 5 (ALKBH5), a m6A demethylation enzyme, was upregulated in the cardiomyocytes of DCM mice and posttranscriptionally activated FOXO3 by m6A demethylation in an m6A-YTHDF2-dependent manner. Hence, our work reveals the key function of the ALKBH5-FOXO3-CDR1as/Hippo signaling pathway in DCM and provides insight into the critical roles of m6A methylation in DCM.

Circular RNAs as Potential Biomarkers in Breast Cancer

Due to the high heterogeneity and initially asymptomatic nature of breast cancer (BC), the management of this disease depends on imaging together with immunohistochemical and molecular evaluations. These tests allow early detection of BC and patient stratification as they guide clinicians in prognostication and treatment decision-making. Circular RNAs (circRNAs) represent a class of newly identified long non-coding RNAs. These molecules have been described as key regulators of breast carcinogenesis and progression. Moreover, circRNAs play a role in drug resistance and are associated with clinicopathological features in BC. Accumulating evidence reveals a clinical interest in deregulated circRNAs as diagnostic, prognostic and predictive biomarkers. Furthermore, due to their covalently closed structure, circRNAs are highly stable and easily detectable in body fluids, making them ideal candidates for use as non-invasive biomarkers. Herein, we provide an overview of the biogenesis and pleiotropic functions of circRNAs, and report on their clinical relevance in BC.

circKL inhibits the growth and metastasis of kidney cancer by sponging miR‑182‑5p and upregulating FBXW7

Circular RNAs (circRNAs) are a type of non-coding RNA with important roles in the regulation of various biological processes involved in malignant progression. However, the potential molecular mechanisms and roles of circRNAs in kidney cancer have remained to be fully elucidated. In a previous study by our group, high-throughput microarray sequencing data were analyzed to determine the differentially expressed circRNAs in kidney cancer. In this analysis, a novel circRNA (hsa_circ_0100312, named circKL) was identified as a frequently downregulated circRNA in kidney cancer cells and tissues by reverse transcription-quantitative PCR. In the present study, Cell Counting Kit-8, colony formation, Transwell, wound-healing and mouse xenograft assays as well as a lung metastasis experiment were performed to confirm the functions of circKL. The experiments confirmed that circKL overexpression significantly inhibited the proliferation, migration, tumor growth and metastasis of kidney cancer both in vitro and in vivo. The potential molecular mechanisms of circKL were investigated by performing dual-luciferase and RNA immunoprecipitation assays. Western blot assays confirmed that overexpression of circKL significantly increased the protein level of F-box and WD repeat domain containing 7 (FBXW7). All results suggested that circKL suppressed the growth and migration of kidney cancer by sponging microRNA (miR)-182-5p and upregulating FBXW7 expression. Overall, the circKL/miR-182-5p/FBXW7 axis was indicated to have a key role in the growth and metastasis of kidney cancer and may be targeted as a novel therapeutic strategy.

CiRS-7/CDR1as; An oncogenic circular RNA as a potential cancer biomarker

Circular RNAs (circRNAs) as a new class of non-coding RNAs (ncRNAs) play role in gene regulation in multicellular organisms via various interactions with nucleic acids, proteins and particularly microRNAs. They have been found to be involved in a number of biological functions particularly in regulation of cell cycle, and extracellular interactions. Thus, dysregulation of circRNAs is found to be associated with several human diseases and especially numerous types of cancers. ciRS-7 is an example of circRNAs which have been studied in a number of human diseases like neurological diseases, diabetes mellitus, and importantly different malignancies. It has been found to regulate cell proliferation and malignant features in cancer cells. CiRS-7 is upregulated in several cancers and its overexpression promoted malignant phenotype of cancer cells via enhancing cell proliferation, migration, and invasion in vitro and in vivo. As a competing endogenous RNA (ceRNA), ciRS-7 is found to sponge miR-7 as the most common miRNA target in interaction together. Functional analyses show role of ciRS-7 in downregulation of miR-7 and involvement of a series of signaling pathways in turn through them it is believed that ciRS-7 regulates malignant behaviors of cancer cells. Clinical studies demonstrate upregulation of ciRS-7 in cancer tissues compared to their non-cancerous adjacent tissues, correlation with worse clinicopathological features in cancerous patients and an independent prognostic factor. In this review, we have an overview to the role of ciRS-7 in development and progression of cancer and also assess its potentials as a diagnostic and prognostic biomarker in human cancers.

CircMMP1 promotes colorectal cancer growth and metastasis by sponging miR-1238 and upregulating MMP family expression

Background

Circular RNAs (circRNAs) are a type of non-coding RNA which play an important role in the regulation of biological processes of various malignant tumors. However, the potential molecular mechanisms and roles of circRNAs in colorectal cancer (CRC) remain unelucidated.

Methods

In the current study, we analyzed the data of high-throughput microarray sequencing to screen differentially expressed circRNAs in CRC. Cell counting kit-8 (CCK-8), colony-formation, transwell, mouse xenograft models and immunohistochemistry assays were used to explore the function of circRNAs. TargetScan database, quantitative real-time polymerase chain reaction (qRT-PCR), double luciferase and RNA immunoprecipitation (RIP) were used to explore the molecular mechanism.

Results

We identified circMMP1 (hsa_circ_0024109) as a frequently upregulated circRNA in both CRC tissues and cells. Both in vitro and in vivo experiments demonstrated that circMMP1 knockdown significantly inhibited the proliferation and metastasis of CRC. The results demonstrated that circMMP1 promoted the growth and metastasis of CRC by sponging miR-1238 and upregulating the expression of matrix metalloproteinase 1 (MMP1), MMP2, and MMP9 expression.

Conclusions

In conclusion, our study identified the biological role of the circMMP1-miR-1238-MMP1/MMP2/MMP9 axis in the growth and metastasis of CRC, which is crucial for the monitoring and treatment of CRC. Further research on circMMP1 may provide a theoretical basis for diagnostic biomarkers of early CRC screening.

Upregulated circRAD18 promotes tumor progression by reprogramming glucose metabolism in papillary thyroid cancer

Background

By regulating complex functional processes, circRNAs are crucial in the development of different cancers. Nevertheless, most circRNAs in papillary thyroid cancer metabolic reprogramming remain unknown.

Methods

The expression of circRNA was assessed by qRT-PCR in papillary thyroid cancer tissues and cell lines. Cell proliferation and glucose intake experiments were performed by certain kit. Transwell assays and wound healing assays were performed to investigate the function of circRNA in metastasis. In addition, a serious of molecular experiments were conducted to determine the exact mechanism of circRAD18. Luciferase reporter and RNA immunoprecipitation assay were conducted to determine the molecular interaction between circRNA and miRNA.

Results

We characterized circRAD18 as a significantly upregulated circRNA in papillary thyroid tissues and cell lines and found its downregulation could inhibit the growth and metastasis ability of papillary thyroid cancer. Interestingly, we found that circRAD18 was involved in glucose metabolism reprogramming of papillary thyroid cancer, and its silence could remarkably inhibit cell glucose uptake and lactate production in papillary thyroid cancer cells. Inhibition of circRAD18 could decrease the expression level of PDK1 protein by sponging miR-516b.

Conclusions

This study verified the novel function of the circRAD18-miR-516b-PDK1 axis in papillary thyroid cancer metabolic reprogramming progression, which has potential to be a novel therapeutic target.

The Use of circRNAs as Biomarkers of Cancer

CircRNAs are a subclass of lncRNAs that have been found to be abundantly present in a wide range of species, including humans. CircRNAs are generally produced by a noncanonical splicing event called backsplicing that is dependent on the canonical splicing machinery, giving rise to circRNAs classified into three main categories: exonic circRNA, circular intronic RNA, and exon-intron circular RNA. Notably, circRNAs possess functional importance and display their functions through different mechanisms of action including sponging miRNAs, or even being translated into functional proteins. In addition, circRNAs also have great potential as biomarkers, particularly in cancer, thanks to their high stability, tissue type and developmental stage specificity, and their presence in biological fluids, which make them promising candidates as noninvasive biomarkers. In this chapter, we describe the most commonly used techniques for the study of circRNAs as cancer biomarkers, including high-throughput techniques such as RNA-Seq and microarrays, and other methods to analyze the presence of specific circRNAs in patient samples.

Characteristics of circRNA and its approach as diagnostic tool in melanoma

One of the most common types of cancer in the world is skin cancer, which has been divided into two groups: non-melanoma and melanoma skin cancer. Different external and internal agents are considered as risk factors for melanoma skin cancer pathogenesis but the exact mechanisms are not yet confirmed. Genetic and epigenetic changes, UV exposure, arsenic compounds, and chemical substances are contributory factors to the development of melanoma. A correlation has emerged between new therapies and the discovery of a basic molecular pattern for skin cancer patients. Circular RNAs (circRNAs) are described as a unique group of extensively expressed endogenous regulatory RNAs with closed-loop structure bonds connecting the 5' and 3' ends, which are commonly expressed in mammalian cells. In this review, we describe the biogenesis of circular RNAs and its function in cancerous conditions focusing on the crosstalk between different circRNAs and melanoma. Increasing evidence suggests that circRNAs appears to be relative to the origin and development of skin-related diseases like malignant melanoma. Different circular RNAs like hsa_circ_0025039, hsa_circRNA006612, circRNA005537, and circANRIL, by targeting different cellular and molecular targets (e.g., CDK4, DAB2IP, ZEB1, miR-889, and let-7 c-3p), can participate in melanoma cancer progression.

Circular RNA circKIF4A facilitates the malignant progression and suppresses ferroptosis by sponging miR-1231 and upregulating GPX4 in papillary thyroid cancer

Circular RNAs (circRNAs) are one type of non-coding RNA. They act as important role in regulating various biological processes in the malignant progression. But we don't clearly know the specific mechanism of the majority circRNAs in papillary thyroid tumor progression. In the current study, we explored circKIF4A and the result showed that it had high expression in papillary thyroid cancer. The functions of circKIF4A were explored by CCK-8, transwell, and mouse xenograft experiments. Knockdown of circKIF4A could suppress papillary thyroid cell growth and migration. In addition, RIP assays and dual luciferase vector reporter assays were further conducted. Our consequence showed circKIF4A facilitated the malignant progress of papillary thyroid tumor by sponging miR-1231 and upregulating GPX4 expression. In conclusion, our study proved that circKIF4A-miR-1231-GPX4 axis played a vital role in cancer proliferation and ferroptosis by competing endogenous RNAs. Therefore, targeting circKIF4A is very likely to be a potential method for treatment of papillary thyroid cancer in the future.

Design BH3 domain fusion protein as targeting pro-apoptotic self-assembling nanoparticles

Cancer is a serious global health issue, and apoptosis is a logical and practical cancer therapeutic strategy. Apoptosis responses to internal and external signals. Both BH3 domain in the pro-apoptotic proteins and truncated BH3 domain can stimulate cell apoptosis. However, the faults of peptides in systemic administration restrict the applications of truncated BH3 domain. Ferritin, as an attractive nanoparticle with the capacity of self-assemble to unique hollow spherical structure, could display truncated BH3 domain an N-terminal. Thus, in this study, we designed a pro-apoptosis self-assembling protein nanoparticle by BH3 domain fusion at N-terminal of ferritin. We evaluated the size, cytotoxicity and pro-apoptosis effect of these nanoparticles. The results showed that RGD-BH3-HFn, BH3-HFn and HFn had uniformly spherical structure with sizes at 26.08 ± 0.11 nm, 22.07 ± 0.67 nm, and 16.81 ± 0.88 nm, respectively; RGD-BH3-HFn has stronger cytotoxicity against tumor cells than BH3-HFn and HFn. The total apoptosis ratios (including necrosis) of C6 cells induced by RGD-BH3-HFn, BH3-HFn, and HFn proteins were 15.24%, 10.13% and 2.14%, respectively; those of bEnd.3 cells were 15.47%, 7.33% and 1.70%, respectively; while the total apoptosis rate (including necrosis) of MCF-7 cells were 3.24%, 4.9% and - 1.68%, respectively. The results suggested self-assembling RGD-BH3-HFn could target to C6 cells and bEnd.3 cells, and enhance tumor cells apoptosis, its apoptosis effect against C6 cells was 7.11-fold that of HFn, and apoptosis effect against bEnd.3 cells was 9.08-fold that of HFn. These results indicated BH3 domain can be designed as targeting pro-apoptotic nanoparticles.

Circular RNA hsa_circ_0005046 and hsa_circ_0001791 May Become Diagnostic Biomarkers for Breast Cancer Early Detection

Breast cancer (BC) is one of the most common lethal diseases in women worldwide. Recent evidence has shown that covalently closed Circular RNA (circRNA) deregulation is observed in different human malignancies and cancers. Lately, circRNAs are being considered as a new diagnostic biomarker; however, the mechanism and the correlation of action between circRNAs and BC are still unclear. In the present study, we try to investigate the expression level of hsa_circ_0005046 and hsa_circ_0001791 in BC. By using quantitative real-time polymerase chain reaction (qRT-PCR), expression profiles of candidate circRNAs were detected in 60 BC tissue and paired adjacent normal tissues. Furthermore, the clinicopathological relation and diagnostic value were estimated. Our results showed the higher expression levels of hsa_circ_0005046 and hsa_circ_0001791 in BC tissues compared to paired adjacent normal tissues with P value (P < 0.0001) for both circRNAs, and the area under the receiver operating characteristic (ROC) curve was 0.857 and 1.0, respectively; in addition, a total 10 miRNAs that can be targeted by each candidate circRNAs was predicted base on bioinformatics databases. Taken together, for the first time, the results of our study presented high expression levels of hsa_circ_0005046 and hsa_circ_00017916 in BC; although there was no direct correlation between the high expression level of both circRNAs with clinic pathological factors, except hsa_circ_0001791 association with estrogen receptors (ER), high ROC curve in expressed samples indicated that both circRNAs could be used as a new diagnostic biomarker for BC. Moreover, miRNAs selection tools predicted that miR-215 and mir-383-5p which have a tumor suppressor role in BC can be targeted by our candidate circRNAs to affect the PI3K/AKT pathway; in conclusion, further studies are required to validate the oncogene role of our candidate circRNAs through the PI3k pathway.

Cancer-Associated circRNA-miRNA-mRNA Regulatory Networks: A Meta-Analysis

Recent advances in sequencing technologies and the discovery of non-coding RNAs (ncRNAs) have provided new insights in the molecular pathogenesis of cancers. Several studies have implicated the role of ncRNAs, including microRNAs (miRNAs), long non-coding RNAs (lncRNAs), and recently discovered circular RNAs (circRNAs) in tumorigenesis and metastasis. Unlike linear RNAs, circRNAs are highly stable and closed-loop RNA molecules. It has been established that circRNAs regulate gene expression by controlling the functions of miRNAs and RNA-binding protein (RBP) or by translating into proteins. The circRNA-miRNA-mRNA regulatory axis is associated with human diseases, such as cancers, Alzheimer's disease, and diabetes. In this study, we explored the interaction among circRNAs, miRNAs, and their target genes in various cancers using state-of-the-art bioinformatics tools. We identified differentially expressed circRNAs, miRNAs, and mRNAs on multiple cancers from publicly available data. Furthermore, we identified many crucial drivers and tumor suppressor genes in the circRNA-miRNA-mRNA regulatory axis in various cancers. Together, this study data provide a deeper understanding of the circRNA-miRNA-mRNA regulatory mechanisms in cancers.

LNC00115 Mediates Cisplatin Resistance by Regulating the miR-7/ERK Signalling Pathway in Ovarian Cancer

Background

Ovarian cancer has one of the highest mortality rates among all gynaecological malignancies, and increasing evidence suggests that lncRNAs are widely involved in the development of ovarian tumours. This study aimed to investigate the mechanism of the LNC00115/miR-7/ERK axis in the cisplatin resistance of ovarian cancer cells.

Methods

The expression of miR-7 and LNC00115 in ovarian cancer cell lines and tissues was detected by qRT-PCR. The ovarian cancer cell lines were constructed by overexpressing or knocking down the expression of LNC00115 or miR-7. CCK-8, transwell invasion, Western blot, immunohistochemistry, and luciferase reporter assays were carried out to identify the targets of LNC00115 and explore its roles and mechanisms in ovarian cancer. A nude mouse model was established, and the expression of LNC00115, miR-7 and ERK was detected. The changes in the tumours and body weights of the nude mice were measured.

Results

LNC00115 was upregulated in ovarian cancer tissues and cisplatin-resistant ovarian cancer cells. Moreover, LNC00115 promoted the cisplatin resistance, invasion and migration of ovarian cancer cells. LNC00115 was shown to directly target miR-7, and miR-7 was downregulated in ovarian cancer tissues and cisplatin-resistant ovarian cancer cells. miR-7 inhibited the cisplatin resistance, invasion and migration of ovarian cancer cells and directly targeted ERK. ERK was overexpressed in cisplatin-resistant ovarian cancer cells and ovarian cancer tissues. In animal experiments, overexpression of LNC00115 enhanced the cisplatin resistance of ovarian cancer cells, while miR-7 had the opposite effect. Mechanistically, LNC00115 sponged miR-7 to increase the expression of ERK, which in turn enhanced the cisplatin resistance of ovarian cancer.

Conclusion

Our data clarify the mechanism by which the LNC00115/miR-7/ERK axis promotes cisplatin resistance and provide a new clinical strategy for combating cisplatin resistance in ovarian cancer.

Downregulation of TAF9B by miR-7-5p Inhibits the Progression of Osteosarcoma

Background

Osteosarcoma (OS) is a malignant bone tumor with high metastatic potential. As a regulatory factor of apoptosis, TATA-box binding protein (TBP) associated factor 9B (TAF9B) is rarely studied in tumors.

Methods

We investigated the role and mechanism of TAF9B in OS cells by overexpression and knockdown. CCK8, colony formation, transwell, and flow cytometry analysis were performed to detect proliferation, migration, invasion, and apoptosis.

Results

TAF9B overexpression promotes the proliferation, migration, and invasion of OS cells, while TAF9B knockdown gives the opposite result. TAF9B inhibits apoptosis by upregulating Bcl-2 and downregulating Bax and Cleaved-caspase-3. Through starBase analysis, it was found that miR-7-5p can bind to the 3ʹUTR region of TAF9B, which is further confirmed by the dual luciferase reporter system assay. MiR-7-5p downregulates the expression of TAF9B in MG63 and U2OS cells. The proliferation and invasion of OS cells are inhibited after miR-7-5p mimics transfection and are promoted after miR-7-5p inhibitor transfection. TAF9B rescues the inhibitory effect of miR-7-5p on OS cells. TAF9B also activates the AKT/mTOR signaling pathway.

Conclusion

According to our results, miR-7-5p inhibits the translation of TAF9B and then suppresses growth and metastasis through the AKT/mTOR signaling pathway in OS cells, thereby indicating the potential value of miR-7-5p and TAF9B as therapeutic targets for human OS.

Effect of the circCDR1as/miR-641/XIAP regulatory axis on the proliferation and invasion of the prostate cancer PC-3 cell line

Prostate cancer is one of the most common malignant tumors in men. Patients with local infiltration and distant metastasis often have a poor prognosis. The present study aimed to investigate the expression and regulatory mechanism of the circular RNA cerebellar degeneration-related protein 1, anti-sense (circCDR1as) in prostate cancer cell lines. MicroRNAs (miRNAs) regulated by circCDR1as and target genes regulated by miRNAs were predicted using bioinformatics software. Prostate cancer cell lines (LNCaP, 22Rv1 and PC-3), a normal prostate epithelial cell line (RWPE-1) and a human embryonic kidney cell line (293T) were cultured. Relative gene expression was detected using reverse transcription PCR. Small interfering RNAs (siRNAs) targeting circCDR1as and X-linked inhibitor of apoptosis protein (XIAP) and miRNA mimics were designed and transfected into the cell lines using Lipofectamine^® 3000. Cell invasion was determined using a Transwell assay, the cell proliferation rate was detected using an MTT assay and cell migration was examined using a scratch assay. Relative protein expression was detected using western blotting. Double fluorescent reporter gene vectors and an anti-Ago2 RNA-binding protein immunoprecipitation assay were used to verify binding. Bioinformatics analyses indicated that there was a binding site between miR-641 and circCDR1as and between miR-641 and XIAP. The expression of circCDR1as and XIAP was higher and the expression of miR-641 was lower in the prostate cancer cell lines compared with the normal prostate epithelial cell line. After effectively reducing the expression of circCDR1as and XIAP and increasing the expression of miR-641 in PC-3 cells, the proliferation, invasion and migration of PC-3 cells were effectively inhibited. circCDR1as could bind to miR-641, which targeted the 3′-untranslated region of XIAP. Reducing the expression of circCDR1 promoted the expression of miR-641 and inhibited the expression of XIAP. Overall, the circCDR1as/miR-641/XIAP regulatory axis plays a role in the invasion and migration of the prostate cancer PC-3 cell line.

Hydrogen gas represses the progression of lung cancer via down-regulating CD47

Hydrogen gas (H₂) has been identified to play an anti-tumor role in several kinds of cancers, but the molecular mechanisms remain largely unknown. In our previous study, our project group found that H₂ could decrease the expression of CD47 in lung cancer A549 cells via the next-generation sequencing, indicating that CD47 might be involved in H₂-mediated lung cancer repression. Therefore, the present study aimed to explore the effects of CD47 on H₂-induced lung cancer repression. Western blotting and real-time PCR (RT-PCR) assays were used to detect the levels of proteins and mRNAs, respectively. Cell proliferation, invasion, migration and apoptosis were detected by using the cell counting kit-8 (CCK-8), Transwell chambers, wound healing and flow cytometry assays, respectively. The results showed that H₂ treatment caused decreases in the expression levels of CD47 and cell division control protein 42 (CDC42) in a dose-dependent manner. Up-regulation of CD47 abolished H₂ roles in promoting lung cancer cell apoptosis and repressing cell growth, invasion and migration in both A549 and H1975 cell lines. However, knockdown of CD47 enhanced H₂ role in lung cancer inhibition. Moreover, we also observed that H₂ treatment induced obvious inhibitions in the expression levels of CDC42 and CD47 in mice tumor tissues, as well as reinforced macrophage-mediated phagocytosis in A549 and H1975 cells. In conclusion, the current study reveals that H₂ inhibits the progression of lung cancer via down-regulating CD47, which might be a potent method for lung cancer treatment.

The Role of miRNA-7 in the Biology of Cancer and Modulation of Drug Resistance

MicroRNAs (miRNAs, miRs) are small non-coding RNA (ncRNA) molecules capable of regulating post-transcriptional gene expression. Imbalances in the miRNA network have been associated with the development of many pathological conditions and diseases, including cancer. Recently, miRNAs have also been linked to the phenomenon of multidrug resistance (MDR). MiR-7 is one of the extensively studied miRNAs and its role in cancer progression and MDR modulation has been highlighted. MiR-7 is engaged in multiple cellular pathways and acts as a tumor suppressor in the majority of human neoplasia. Its depletion limits the effectiveness of anti-cancer therapies, while its restoration sensitizes cells to the administered drugs. Therefore, miR-7 might be considered as a potential adjuvant agent, which can increase the efficiency of standard chemotherapeutics.

CircRNA ciRS-7: a Novel Oncogene in Multiple Cancers

circular RNA ciRS-7 (ciRS-7) is a type of endogenous circular RNA (circRNA) with a closed circular structure. Since Hansen first demonstrated that ciRS-7 could serve as a microRNA sponge in 2013, researchers have paid increased attention to this circRNA. ciRS-7 plays a crucial role in regulating RNA transcription, downstream gene expression, and protein production. Moreover, ciRS-7 acts as an oncogene and promotes tumor progression through competitively inhibiting miR-7 in various types of cancers. ciRS-7 has been identified to be closely associated with breast cancer, nasopharyngeal carcinoma, lung cancer, hepatocellular carcinoma, cervical cancer, osteosarcoma, melanoma, colorectal cancer, esophageal squamous cell carcinoma, gastric cancer, pancreatic cancer, laryngeal squamous cell carcinoma, and cholangiocarcinoma. In this review, we summarize the biological characteristics, molecular mechanisms, and future challenges of ciRS-7 in multiple tumors.

Association study of hsa_circ_0001946, hsa-miR-7-5p and PARP1 in coronary atherosclerotic heart disease

BACKGROUND

Our previous work identified an aberrant expression of hsa_circ_0001946 in coronary atherosclerotic heart disease (CHD). Here we aimed to verify the role of hsa_circ_0001946 as a biomarker for CHD, and explore the clues of its downstream regulation.

METHODS

The hsa_circ_0001946 expression in CHD patients (n = 120) and controls (n = 120) were confirmed with qRT-PCR. CircBank and miRDB were used for target analysis in silico. Spearman correlation test was performed to infer potential interrelationships among the nucleic acid molecular biomarkers, and their predictive abilities were examined using receiver operating characteristic (ROC) curves.

RESULTS

Hsa_circ_0001946 was validated to be significantly up-regulated in the peripheral blood mononuclear cells of CHD patients, and revealed as an independent indicator of increased CHD risk (odds ratio: 2.364; 95% confidence interval [CI]: 1.765-3.165) after adjusting for confounding factors. Hsa-miR-7-5p was found to own the largest number of binding sites in has_circ_0001946 sequence, and among its targets predicted, the poly ADP-ribose polymerase 1 (PARP1) has been implicated in the pathophysiology of CHD. Spearman analysis indicated negative correlations of hsa-miR-7-5p with hsa_circ_0001946 and PARP1, respectively; while hsa_circ_0001946 was positively correlated with PARP1. The prediction accuracy of hsa_circ_0001946 in CHD was evaluated, showing an area under the ROC curve of 0.897 (95% CI: 0.791-0.961), which could further increase to 0.957 (95% CI: 0.870-0.992) upon a combination of hsa-miR-7-5p and PARP1.

CONCLUSION

The present work demonstrated the predictive power of hsa_circ_0001946, hsa-miR-7-5p and PARP1 as combined biomarkers for CHD, and suggests a regulatory axis they consisted might contribute to the CHD development.

The Emerging Picture of the Roles of CircRNA-CDR1as in Cancer

Circular RNAs (circRNAs) are covalently closed circular structures without 5′ caps and 3′ tails, which are mainly formed from precursor mRNAs (pre-mRNAs) via back-splicing of exons. With the development of RNA sequencing and bioinformatic analysis, circRNAs were recently rediscovered and found to be widely expressed in the tree of life. Cerebellar degeneration-related protein 1 antisense RNA (CDR1as) is recognized as one of the most well-identified circRNAs. It contains over 70 miR-7 binding sites and can regulate gene activity by sponging miR-7. Increasing numbers of studies have recently demonstrated that CDR1as is abnormally expressed in many types of tumors, such as colorectal cancer, cholangiocarcinoma and osteosarcoma, and plays a vital role in the development of cancer. However, there are few reviews focusing on CDR1as and cancer. Hence, it is important to review and discuss the role of CDR1as in cancer. Here, we first review the main biological features of CDR1as. We then focus on the expression and roles of CDR1as in cancer. Finally, we summarize what is known on the role of CDR1as in cancer and discuss future prospects in this area of research.

The role of circular RNAs in therapy resistance of patients with solid tumors

Circular RNAs (circRNAs) are a type of single-stranded RNA molecules forming a covalently closed, continuous structure, lacking 5'-3' polarity and polyadenylated tails. Recent advances in high-throughput sequencing technologies have revealed that these molecules are abundant, resistant to degradation and often expressed in a tissue- or developmental stage-specific manner. circRNAs are produced by back-splicing circularization of primary transcripts and exhibit a variety of functions, including regulation of transcription, translation and cellular localization. This review focuses on differentially expressed circRNAs conferring therapy resistance or sensitivity of solid tumors, such as carcinomas, sarcomas and lymphomas. Deregulated circRNAs can participate in the development of resistance to treatment by modulating regulatory pathways and cellular processes, including the mitogen-activated protein kinase pathway, epithelial-mesenchymal transition, apoptosis and autophagy.

circSMARCA5 Promoted Osteosarcoma Cell Proliferation, Adhesion, Migration, and Invasion through a Competing Endogenous RNA Network

Osteosarcoma (OS) is a widely common sort among bone cancer in children, and its overall survival ratio is low. The hidden mechanism of tumor genesis, progression, and metastasis regarding osteosarcoma needed to be further investigated. Emerging studies concentrated on exploring the functional roles of circular RNAs (circRNAs) in human cancers. The present study conducted a loss-of-function experiments to explore the circSMARCA5-induced influence on OS proliferation, cell cycle, and metastasis. Moreover, our manuscript unearthed the potential mechanisms of circSMARCA5 in regulating OS progression by in silico analysis. Our findings would provide new evidence to support that circSMARCA5 could be indicated as a biomarker for OS.

Circular RNAs and cancer: Opportunities and challenges

Circular RNAs (circRNAs) are covalently circularized RNA moieties that despite being relatively abundant were only recently identified and have only begun to be investigated within the last couple of years. Even though there are many thousands of genes that appear capable of producing circRNAs, and the fact that many circRNAs appear to be highly evolutionarily conserved, the function of all but a few remain to be fully explored. What has been determined, however, is that circRNAs play key regulatory roles in many aspects of biology with focus being given to their function in cancer. Most of the studies to date have found that circRNAs act as master regulator of gene expression most often than not acting to regulate levels though sequestration or "sponging" of other gene expression regulators, particularly miRNAs. They can also function directly modulating transcription, or by interfering with splicing mechanisms. Some circRNAs can also be translated into functional proteins or peptides. A combination of tissue and developmental stage specific expression along with an innate resistance to RNAse activity means that circRNAs show perhaps their greatest potential as novel biomarkers of cancer. In this chapter we consider the current state of knowledge regarding these molecules, their synthesis, function, and association with cancer. We also consider some of the challenges that remain to be overcome to allow this emerging class of RNAs to fulfill their potential in clinical practice.

Spatial expression analyses of the putative oncogene ciRS-7 in cancer reshape the microRNA sponge theory

Circular RNAs (circRNAs) have recently gained substantial attention in the cancer research field where most, including the putative oncogene ciRS-7 (CDR1as), have been proposed to function as competitive endogenous RNAs (ceRNAs) by sponging specific microRNAs. Here, we report the first spatially resolved cellular expression patterns of ciRS-7 in colon cancer and show that ciRS-7 is completely absent in the cancer cells, but highly expressed in stromal cells within the tumor microenvironment. Additionally, our data suggest that this generally apply to classical oncogene-driven adenocarcinomas, but not to other cancers, including malignant melanoma. Moreover, we find that correlations between circRNA and mRNA expression, which are commonly interpreted as evidence of a ceRNA function, can be explained by different cancer-to-stromal cell ratios among the studied tumor specimens. Together, these results have wide implications for future circRNA studies and highlight the importance of spatially resolving expression patterns of circRNAs proposed to function as ceRNAs.

Role of microRNA-7 in liver diseases: a comprehensive review of the mechanisms and therapeutic applications

MicroRNA-7 (miR-7) is a small non-coding RNA, which plays critical roles in regulating gene expression of multiple key cellular processes. MiR-7 exhibits a tissue-specific pattern of expression, with abundant levels found in the brain, spleen, and pancreas. Although it is expressed at lower levels in other tissues, including the liver, miR-7 is involved in both the development of organs and biological functions of cells. In this review, we focus on the mechanisms by which miR-7 controls cell growth, proliferation, invasion, metastasis, metabolism, and inflammation. We also summarize the specific roles of miR-7 in liver diseases. MiR-7 is considered as a tumor suppressor miRNA in hepatocellular carcinoma and is involved in the pathogenesis of hepatic steatosis and hepatitis. Future studies to further define miR-7 functions and its mechanism in association with other types of liver diseases should be explored. An improved understanding from these studies will provide us a useful perspective leading to mechanism-based intervention by targeting miR-7 for the treatment of liver diseases.

Role of oncogenic REGγ in cancer

Cancer is a critical global health-care problem with limited therapeutic options. Since cancers are life-threatening illnesses, the identification of a promising oncotarget and its clinical correlates are relevant. Mounting evidence has emerged indicating that REG gamma (REGγ), a member of the 11S proteasome activators, plays a pivotal role in the development of multiple human cancers. However, an elaborate summary on the association between REGγ and cancer is still lacking. In this Review, we discuss how REGγ, through its ATP- and ubiquitin-independent manners, represents a promising cancer biomarker and therapeutic oncotarget for multiple human cancers. Aberrant REGγ expression closely associated with tumorigenesis attributes to its biological functions for controlling and regulating cell cycle, proliferation, migration, invasion, angiogenesis, and metastasis of the cancer cells by degrading proteins of cytosol and nucleus in the eukaryotic cells. REGγ serves as a molecular switch to activate multifarious oncogenic signaling pathways, such as MAPK/p38, TGF-β/Smad, and Wnt/β-catenin. The review describes that targeting REGγ may provide new diagnostic and therapeutic applications in cancer.

Circular RNA: A novel potential biomarker for skin diseases

Circular RNA (circRNA) has been classified as noncoding RNA with a covalent closed continuous loop, the 3'and 5' ends of which are normally joined together to increase its own stability. More recently, circRNA has been shown to encode proteins and may be involved in the regulation of gene transcription. This provides more evidence for the involvement of circRNA in disease progression. Accumulating investigations have found that the expression of many circRNAs is abnormal in plenty of skin diseases such as malignant melanoma, psoriasis, and abnormal wound healing. Herein, in addition to the summary of recent studies on the nuclear export, N⁶-methyladenosine (m⁶A) modification, degradation, and other biogenesis and properties of circRNA, we highlight the importance of circRNAin skin diseases. Although their exact roles and mechanisms in most skin disease remain preliminary, circRNAs have potential applications as diagnostic biomarkers and novel therapeutic targets for skin diseases due to its structural and functional properties (stability, specificity and sensitivity), which is worthy of deeper exploration and greater research efforts.

Functions and mechanisms of circular RNAs in cancer radiotherapy and chemotherapy resistance

Circular RNAs (circRNAs), one type of non-coding RNA, were initially misinterpreted as nonfunctional products of pre-mRNA mis-splicing. Currently, circRNAs have been proven to manipulate the functions of diverse molecules, including non-coding RNAs, mRNAs, DNAs and proteins, to regulate cell activities in physiology and pathology. Accumulating evidence indicates that circRNAs play critical roles in tumor genesis, development, and sensitivity to radiation and chemotherapy. Radiotherapy and chemotherapy are two primary types of intervention for most cancers, but their therapeutic efficacies are usually retarded by intrinsic and acquired resistance. Thus, it is urgent to develop new strategies to improve therapeutic responses. To achieve this, clarification of the underlying mechanisms affecting therapeutic responses in cancer is needed. This review summarizes recent progress and mechanisms of circRNAs in cancer resistance to radiation and chemotherapy, and it discusses the limitations of available knowledge and potential future directions.

Co-delivery system of chemotherapy drugs and active ingredients from natural plants: a brief overview of preclinical research for cancer treatment

Introduction: Many active ingredients from natural plants (AINPs) have been revealed to possess remarkable anticancer properties. Combination chemotherapy of chemo-drugs and AINPs has also proven to be more advantageous than individual chemo-drug treatment with respect to enhancing efficiency, alleviating toxicity, and controlling the development of multidrug resistance (MDR). Co-delivery is considered a promising method to effectively achieve and manage combination chemotherapy of chemo-drugs and AINPs, and various distinctive and functional co-delivery systems have been designed for these purposes to date.Areas covered: This review focuses on recent preclinical investigations of co-delivery systems for chemo-drugs and AINPs as new cancer treatment modalities. We particularly emphasize the apparent treatment advantages of these approaches, including augmenting efficiency, reducing toxicity, and controlling MDR.Expert opinion: There has already been notable progress in the application of combination chemotherapy with co-delivery systems loaded with chemo-drugs and AINPs based on results with cellular and animal models. The main challenge is to translate these successes into new anticancer compound preparations and promote their clinical application in practice. Nevertheless, continuous efforts with new designs of co-delivery systems remain essential, providing a foundation for future clinical research and development of new anticancer drugs.

CircRNA CDR1as knockdown inhibits progression of non-small-cell lung cancer by regulating miR-219a-5p/SOX5 axis

BACKGROUND

Circular RNAs (circRNAs) participate in the development of human cancers by regulating multiple cell processes. CircRNA antisense to the cerebellar degeneration-related protein 1 transcript (circCDR1as) expression is dysregulated in many cancers, including non-small-cell lung cancer (NSCLC). However, the mechanism by which circCDR1as mediates the development of NSCLC remains unknown.

METHODS

A total of 30 paired cancer and normal tissues were collected from patients with NSCLC. The expression levels of circCDR1as, microRNA (miR)-219a-5p and Sex determining region Y-box protein 5 (SOX5) were measured in tissues or cells by quantitative real-time polymerase chain reaction or western blot. Cell viability, apoptosis, migration and invasion were detected by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide, colony formation, flow cytometry and transwell assays, respectively. The target relationship between miR-219a-5p and circCDR1as or SOX5 was validated by dual-luciferase reporter assay.

RESULTS

CircCDR1as expression was elevated in NSCLC tissues and cells in comparison to the matched controls. Interference of circCDR1as led to obvious inhibition of cell viability, migration and invasion and increase of apoptosis in NSCLC cells. MiR-219a-5p acted as a target of circCDR1as and miR-219a-5p downregulation attenuated the regulatory effect of circCDR1as silencing on NSCLC progression. Moreover, miR-219a-5p targeted SOX5 to repress the progression of NSCLC in vitro. Besides, circCDR1as knockdown reduced the expression of SOX5 by increasing miR-219a-5p level.

CONCLUSION

Knockdown of circCDR1as inhibited the progression of NSCLC by decreasing cell viability, migration and invasion and increasing apoptosis by upregulating miR-219a-5p and downregulating SOX5.

miR-7 Reverses Breast Cancer Resistance To Chemotherapy By Targeting MRP1 And BCL2

Background

MicroRNAs (miRNAs) are a class of non‐coding RNAs that have been linked with breast cancer chemoresistance, which is a major clinical problem causing disease relapse and poor prognosis. miR-7 exerts several tumor suppressive activities.

Purpose

This study was designed to clarify whether and how miR-7 regulates breast cancer chemoresistance.

Methods

miR-7 level in breast cancer was determined by qRT-PCR analysis. Cell viability was assessed by MTS assay to quantify the IC₅₀ value of paclitaxel and carboplatin. The targets of miR-7 were confirmed by luciferase reporter assay.

Results

Higher miR-7 expression predicts better pathological complete response (pCR) of breast cancer patients receiving paclitaxel/carboplatin chemotherapy. In vitro, miR-7 sensitizes breast cancer cell lines (MCF-7 and MDA-MB-231) to paclitaxel and carboplatin, alone and in combination. In addition, we reveal that both the multidrug resistance-associated protein 1 (MRP1) and anti-apoptotic B cell lymphoma 2 (BCL2) are targets of miR-7 in breast cancer cells. Furthermore, miR-7-induced sensitization of breast cancer to paclitaxel/carboplatin is markedly reversed by restoration of MRP1 and BCL2.

Conclusion

These findings show that miR-7 reverses breast cancer chemoresistance through suppressing MRP1 and BCL2, and also suggest that miR-7 may possess a predictive value and represent a therapeutic target in breast cancer chemotherapy.

Downregulation of CircRNA CDR1as specifically triggered low-dose Diosbulbin-B induced gastric cancer cell death by regulating miR-7-5p/REGγ axis

Diosbulbin-B (DB) was the main compound of Dioscorea bulbifera L, which was widely used for cancer treatment in Asia. However, the hepatotoxicity induced by high-dose DB seriously limited its possibility using for gastric cancer (GC) treatment in clinic. In this study, we found that DB inhibited GC cells and hepatocytes cell viability in a dose- and time-dependent manner. Specifically, high-dose DB (50μM) significantly inhibited cell proliferation and promoted cell apoptosis, while low dose DB (12.5μM) had little effects on cell viability. Besides, high-dose DB (50μM) significantly decreased CircRNA CDR1as levels in gastric cancer cells instead of hepatocytes. Notably, knock-down of CircRNA CDR1as triggered low-dose DB (12.5μM) induced GC cell death, but had little effects on hepatocytes proliferation and apoptosis. Further results showed that CircRNA CDR1as increased REGγ expressions in GC cells by sponging miR-7-5p, and high-dose DB (50μM) increased miR-7-5p levels and inhibited REGγ expressions in GC cells instead of hepatocytes. In addition, either downregulated miR-7-5p or overexpressed REGγ reversed the promoting effects of downregulated CircRNA CDR1as on low-dose DB-induced GC cell death. Taken together, we concluded that knock-down of CircRNA CDR1as specifically promoted the cytotoxic effects of low-dose DB on GC cells instead of hepatocytes by regulating miR-7-5p/REGγ axis.

Silencing CDR1as enhances the sensitivity of breast cancer cells to drug resistance by acting as a miR-7 sponge to down-regulate REGγ

In our study, we aimed to investigate the role of CDR1as during competitive inhibition of miR‐7 in the regulation of cisplatin chemosensitivity in breast cancer via regulating REGγ. RT‐qPCR was applied to detect the expression of CDR1as and miR‐7 in breast cancer tissues, breast cancer cell lines and corresponding drug‐resistant cell lines. The correlation between CDR1as and miR‐7 and between miR‐7 and REGγ was evaluated. MCF‐7‐R and MDA‐MB‐231‐R cells were selected followed by transfection of a series of mimics, inhibitors or siRNA. The effect of CDR1as on the half maximal inhibitor concentration (IC50), cisplatin sensitivity and cell apoptosis was also analysed. Furthermore, a subcutaneous xenograft nude mouse model was established to further confirm the effect of CDR1as on the chemosensitivity of breast cancer to cisplatin in vivo. Immunohistochemical staining was conducted to test the Ki‐67 expression in nude mice. A positive correlation was found between the drug resistance and CDR1as expression in breast cancer. CDR1as could increase the resistance of breast cancer cells to cisplatin. miR‐7 expression was low, while REGγ was highly expressed in MCF‐7‐R and MDA‐MB‐231‐R cells. CDR1as competitively inhibited miR‐7 and up‐regulated REGγ. Overexpression of miR‐7 could reverse the enhanced sensitivity of silenced CDR1as to drug‐resistant breast cancer cells. Additionally, in vivo experiments demonstrated that CDR1as mediated breast cancer occurrence and its sensitivity to cisplatin. Silencing CDR1as decreased Ki‐67 expression. Silencing CDR1as may inhibit the expression of REGγ by removing the competitive inhibitory effect on miR‐7 and thus enhancing the sensitivity of drug‐resistant breast cancer cells.