Human papillomavirus 16 E7 oncoprotein alters the expression profiles of circular RNAs in Caski cells

FOXA1 co-activates circODC1 and ODC1 in HPV-positive cervical cancer cell growth

As demonstrated in previous research, hsa_circ_0052602 (circODC1) is dynamically expressed in HPV-positive cervical cancer (CC). CircODC1 expression was quantified using qRT-PCR, and its role in CC cell growth was assessed via loss-of-function assays. Interactions between miR-607 and circODC1 or ODC1 were confirmed using bioinformatics and mechanistic assays. The association of FOXA1 with the circODC1 promoter was validated through ChIP and luciferase reporter assays. CircODC1 was highly expressed in HPV-positive CC cell lines, and its depletion significantly impeded malignant processes such as proliferation, migration, and invasion. We found that ODC1 also played an oncogenic role in HPV-positive CC cells. CircODC1 was shown to positively regulate ODC1 as a ceRNA, competitively binding to miR-607 to counteract its suppression of ODC1. HPV-associated FOXA1 was identified as a potential transcription factor of circODC1. Restoration experiments showed that overexpression of circODC1 could counterbalance the inhibitory effect of FOXA1 knockdown. These findings offer new insights into therapeutic strategies for HPV-positive CC patients.

Riddle of the Sphinx: Emerging role of circular RNAs in cervical cancer

Cervical cancer is a prominent cause of cancer-related mortality among women, with recent attention directed toward exploring the involvement of circular RNAs (circRNAs) in this particular cancer. CircRNAs, characterized by a covalently closed loop structure, belong to a class of single-stranded non-coding RNA (ncRNA) molecules that play crucial roles in cancer development and progression through diverse mechanisms. The abnormal expression of circRNAs in vivo is significantly associated with the development of cervical cancer. Notably, circRNAs actively interact with miRNAs in cervical cancer, leading to the regulation of diverse signaling pathways, and they can contribute to cancer hallmarks such as self-sufficiency in growth signals, insensitivity to antigrowth signals, limitless proliferation, evading apoptosis, tissue invasion and metastasis, and sustained angiogenesis. Moreover, the distinctive biomedical attributes exhibited by circRNAs, including their abundance, conservation, and stability in body fluids, position them as promising biomarkers for various cancers. In this review, we elucidate the tremendous potential of circRNAs as diagnostic markers or therapeutic targets in cervical cancer by expounding upon their biogenesis, characteristics, functions, and databases, highlighting the novel advances in the signaling pathways associated with circRNAs in cervical cancer.

The potential role and mechanism of circRNAs in Ferroptosis: A comprehensive review

Cell death encompasses various mechanisms, including necrosis and apoptosis. Ferroptosis, a unique form of regulated cell death, emerged as a non-apoptotic process reliant on iron and reactive oxygen species (ROS). Distinguishing itself from other forms of cell death, ferroptosis exhibits distinct morphological, biochemical, and genetic features. Circular RNAs (circRNAs), a novel class of RNA molecules, play crucial regulatory roles in ferroptosis-mediated pathways and cellular processes. With their circular structure and stability, circRNAs function as microRNA sponges and participate in protein regulation, offering diverse mechanisms for cellular control. Accumulating evidence indicates that circRNAs are key players in diseases associated with ferroptosis, presenting opportunities for diagnostic and therapeutic applications. This study explores the regulatory roles of circRNAs in ferroptosis and their potential in diseases such as cancer, neurological disorders, and cardiovascular diseases. By investigating the relationship between circRNAs and ferroptosis, this research provides new insights into the diagnosis, treatment, and prognosis of ferroptosis-related diseases. Furthermore, the therapeutic implications of targeting circRNAs in cancer treatment and the modulation of ferroptosis pathways demonstrate the potential of circRNAs as diagnostic markers and therapeutic targets. Overall, understanding the involvement of circRNAs in regulating ferroptosis opens up new avenues for advancements in disease management.

Virus-Encoded Circular RNAs: Role and Significance in Viral Infections

Circular RNAs (circRNAs) have been the focus of intense scientific research to understand their biogenesis, mechanisms of action and regulatory functions. CircRNAs are single stranded, covalently closed RNA molecules lacking the 5'-terminal cap and the 3'-terminal polyadenine chain, characteristics that make them very stable and resistant. Synthesised by both cells and viruses, in the past circRNAs were considered to have no precise function. Today, increasing evidence shows that circRNAs are ubiquitous, some of them are tissue- and cell-specific, and critical in multiple regulatory processes (i.e., infections, inflammation, oncogenesis, gene expression). Moreover, circRNAs are emerging as important biomarkers of viral infection and disease progression. In this review, we provided an updated overview of current understanding of virus-encoded and cellular-encoded circRNAs and their involvement in cellular pathways during viral infection.

MicroRNAs, long non-coding RNAs, and circular RNAs and gynecological cancers: focus on metastasis

Gynecologic cancer is a significant cause of death in women worldwide, with cervical cancer, ovarian cancer, and endometrial cancer being among the most well-known types. The initiation and progression of gynecologic cancers involve a variety of biological functions, including angiogenesis and metastasis-given that death mostly occurs from metastatic tumors that have invaded the surrounding tissues. Therefore, understanding the molecular pathways underlying gynecologic cancer metastasis is critical for enhancing patient survival and outcomes. Recent research has revealed the contribution of numerous non-coding RNAs (ncRNAs) to metastasis and invasion of gynecologic cancer by affecting specific cellular pathways. This review focuses on three types of gynecologic cancer (ovarian, endometrial, and cervical) and three kinds of ncRNAs (long non-coding RNAs, microRNAs, and circular RNAs). We summarize the detailed role of non-coding RNAs in the different pathways and molecular interactions involved in the invasion and metastasis of these cancers.

Functional Involvement of circRNAs in the Innate Immune Responses to Viral Infection

Effective viral clearance requires fine-tuned immune responses to minimize undesirable inflammatory responses. Circular RNAs (circRNAs) are a class of non-coding RNAs that are abundant and highly stable, formed by backsplicing pre-mRNAs, and expressed ubiquitously in eukaryotic cells, emerging as critical regulators of a plethora of signaling pathways. Recent progress in high-throughput sequencing has enabled a better understanding of the physiological and pathophysiological functions of circRNAs, overcoming the obstacle of the sequence overlap between circRNAs and their linear cognate mRNAs. Some viruses also encode circRNAs implicated in viral replication or disease progression. There is increasing evidence that viral infections dysregulate circRNA expression and that the altered expression of circRNAs is critical in regulating viral infection and replication. circRNAs were shown to regulate gene expression via microRNA and protein sponging or via encoding small polypeptides. Recent studies have also highlighted the potential role of circRNAs as promising diagnostic and prognostic biomarkers, RNA vaccines and antiviral therapy candidates due to their higher stability and lower immunogenicity. This review presents an up-to-date summary of the mechanistic involvement of circRNAs in innate immunity against viral infections, the current understanding of their regulatory roles, and the suggested applications.

Oncogenic viruses and host lipid metabolism: a new perspective

As noncellular organisms, viruses do not have their own metabolism and rely on the metabolism of host cells to provide energy and metabolic substances for their life cycles. Increasing evidence suggests that host cells infected with oncogenic viruses have dramatically altered metabolic requirements and that oncogenic viruses produce substances used for viral replication and virion production by altering host cell metabolism. We focused on the processes by which oncogenic viruses manipulate host lipid metabolism and the lipid metabolism disorders that occur in oncogenic virus-associated diseases. A deeper understanding of viral infections that cause changes in host lipid metabolism could help with the development of new antiviral agents as well as potential new therapeutic targets.

Circular RNA ARHGAP5 inhibits cisplatin resistance in cervical squamous cell carcinoma by interacting with AUF1

Cervical squamous cell carcinoma (CSCC) is one of the leading causes of cancer death in women worldwide. Patients with advanced cervical carcinoma always have a poor prognosis once resistant to cisplatin due to the lack of effective treatment. It is urgent to investigate the molecular mechanisms of cisplatin resistance. Circular RNAs (circRNAs) are known to exert their regulatory functions in a series of malignancies. However, their effects on CSCC remain to be elucidated. Here, we found that cytoplasmic circARHGAP5, derived from second and third exons of the ARHGAP5 gene, was downregulated in cisplatin-resistant tissues compared with normal cervix tissues and untreated cervical cancer tissues. In addition, experiments from overexpression/knockdown cell lines revealed that circARHGAP5 could inhibit cisplatin-mediated cell apoptosis in CSCC cells both in vitro and in vivo. Mechanistically, circARHGAP5 interacted with AU-rich element RNA-binding protein (AUF1) directly. Overexpression of AUF1 could also inhibit cell apoptosis mediated by cisplatin. Furthermore, we detected the potential targets of AUF1 related to the apoptotic pathway and found that bcl-2-like protein 11 (BIM) was not only negatively regulated by AUF1 but positively regulated by circARHGAP5, which indicated that BIM mRNA might be degraded by AUF1 and thereby inhibited tumor cell apoptosis. Collectively, our data indicated that circARHGAP5 directly bound to AUF1 and prevented AUF1 from interacting with BIM mRNA, thereby playing a pivotal role in cisplatin resistance in CSCC. Our study provides insights into overcoming cancer resistance to cisplatin treatment.

SARS-CoV-2, SARS-CoV, and MERS-CoV encode circular RNAs of spliceosome-independent origin

Circular RNAs (circRNAs) are a newly recognized component of the transcriptome with critical roles in autoimmune diseases and viral pathogenesis. To address the importance of circRNA in RNA viral transcriptome, we systematically identified and characterized circRNAs encoded by the RNA genomes of betacoronaviruses using both bioinformatical and experimental approaches. We predicted 351, 224, and 2764 circRNAs derived from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), SARS-CoV, and Middle East respiratory syndrome coronavirus, respectively. We experimentally identified 75 potential SARS-CoV-2 circRNAs from RNA samples extracted from SARS-CoV-2-infected Vero E6 cells. A systematic comparison of viral and host circRNA features, including abundance, strand preference, length distribution, circular exon numbers, and breakpoint sequences, demonstrated that coronavirus-derived circRNAs had a spliceosome-independent origin. We further showed that back-splice junctions (BSJs) captured by inverse reverse-transcription polymerase chain reaction have different level of resistance to RNase R. Through northern blotting with a BSJ-spanning probe targeting N gene, we identified three RNase R-resistant bands that represent SARS-CoV-2 circRNAs that are detected cytoplasmic by single-molecule and amplified fluorescence in situ hybridization assays. Lastly, analyses of 169 sequenced BSJs showed that both back-splice and forward-splice junctions were flanked by homologous and reverse complementary sequences, including but not limited to the canonical transcriptional regulatory sequences. Our findings highlight circRNAs as an important component of the coronavirus transcriptome, offer important evaluation of bioinformatic tools in the analysis of circRNAs from an RNA genome, and shed light on the mechanism of discontinuous RNA synthesis.

Circular RNAs Represent a Novel Class of Human Cytomegalovirus Transcripts

Human cytomegalovirus (HCMV) infects a large portion of the human population globally. Several HCMV-derived noncoding RNAs are involved in the regulation of viral gene expression and the virus life cycle. Here, we reported that circRNAs are a new class of HCMV transcripts. We bioinformatically predict 704 candidate circRNAs encoded by the TB40/E strain and 230 encoded by the HAN strain. We also systematically compare circRNA features, including the breakpoint sequence consensus, strand preference, length distribution, and exon numbers between host genome-encoded circRNAs and viral circRNAs, and showed that the unique characteristics of viral circRNAs are correlated with their genome types. Furthermore, we experimentally confirmed 324 back-splice junctions (BSJs) from three HCMV strains, Towne, TB40/E, and Toledo, and identified 4 representative HCMV circRNAs by RNase R treatment. Interestingly, we also showed that HCMV contains alternative back-splicing circRNAs. We developed a new amplified FISH method that allowed us to visualize circRNAs and quantify the number of circRNA molecules in the infected cells. The competitive endogenous RNA network analysis suggests that HCMV circRNAs play important roles in viral DNA synthesis via circRNA-miRNA-mRNA networks. Our findings highlight that circRNAs are an important component of the HCMV transcriptome that may contribute to viral replication and pathogenesis. IMPORTANCE HCMV infects 40% to 100% of the human population globally and may be a life-threatening pathogen in immunocompromised individuals. CircRNA is a family of unique RNA that is the most newly found and remains unknown in many aspects. Our current studies computationally identified HCMV-encoded circRNAs and confirmed the existence of the HCMV circRNAs in the infected cells. We systematically compared the features between host and different viral circRNAs and found that the unique characteristics of circRNAs were correlated with their genome types. We also first reported that HCMV contained alternative back-splicing circRNAs. More importantly, we developed a new amplified FISH method which allowed us for the first time not only to visualize circRNAs but also to quantify the number of circRNA molecules in the infected cells. This work describes a novel component of HCMV transcriptome bringing a new understanding of HCMV biology and disease.

Circular RNA circLMO1 Suppresses Cervical Cancer Growth and Metastasis by Triggering miR-4291/ACSL4-Mediated Ferroptosis

Background

A number of studies have demonstrated that circular RNA (circRNA) plays a critical role in tumorigenesis and tumor progression. However, the biological effects of most circRNAs on cervical cancer remain unclear. Hsa_circ_0021087 (thereafter named circLMO1) is a circRNA generated from the circularization of exon 2 and exon 3 of LIM Domain Only 1 (LMO1) and first identified as a tumor suppressor in gastric cancer. We aimed to identify the role of circLMO1 in cervical cancer progression.

Methods

CircLMO1 was verified through qPCR and Sanger sequencing. The biological role of circLMO1 in regulating cervical cancer growth and metastasis was investigated both in vitro and in the nude mouse xenograft tumor model. The dual luciferase reporter assay and rescue experiment were conducted to evaluate the interactions among circLMO1, microRNA (miR)-4291, and acyl-CoA synthetase long chain family member 4 (ACSL4). The role of circLMO1 in regulating ferroptosis was assessed by analyzing lipid reactive oxygen species (ROS), and malonyl dialdehyde (MDA), and glutathione (GSH) content.

Results

The level of circLMO1 was down-regulated in cervical cancer tissues and was associated with the International Federation of Gynecology and Obstetrics (FIGO) staging. Functionally, circLMO1 overexpression inhibited cervical cancer growth and metastasis both in vitro and in vivo, whereas circLMO1 depletion promoted cervical cancer cell proliferation and invasion. Mechanistically, circLMO1 acted as a competing endogenous RNA (ceRNA) by sponging miR-4192 to repress target gene ACSL4. CircLMO1 promoted cervical cancer cell ferroptosis through up-regulating ACSL4 expression. Overexpression of miR-4291 or knockdown of ACSL4 reversed the effect of circLMO1 on facilitating ferroptosis and repressing cervical cancer cell proliferation and invasion.

Conclusion

CircLMO1 acted as a tumor suppressor of cervical cancer by regulating miR-4291/ACSL4-mediated ferroptosis, and could be a promising biomarker for the clinical management of cervical cancer.

Metabolic reprogramming in cervical cancer and metabolomics perspectives

Cumulative studies have shown that metabolic reprogramming is a hallmark of malignant tumors. The emergence of technological advances, such as omics studies, has strongly contributed to the knowledge of cancer metabolism. Cervical cancer is among the most common cancers in women worldwide. Because cervical cancer is a virus-associated cancer and can exist in a precancerous state for years, investigations targeting the metabolic phenotypes of cervical cancer will enhance our understanding of the interference of viruses on host cells and the progression of cervical carcinogenesis. The purpose of this review was to illustrate metabolic perturbations in cervical cancer, the role that human papillomavirus (HPV) plays in remodeling cervical cell metabolism and recent approaches toward application of metabolomics in cervical disease research. Cervical cancer displays typical cancer metabolic profiles, including glycolytic switching, high lactate levels, lipid accumulation and abnormal kynurenine/tryptophan levels. HPV, at least in part, contributes to these alterations. Furthermore, emerging metabolomics data provide global information on the metabolic traits of cervical diseases and may aid in the discovery of biomarkers for diagnosis and therapy.

The profile analysis of circular RNAs in cervical cancer

Cervical cancer (CC) is the third most common cancer among women and has a high mortality rate at the advanced stage. The mechanisms underlying the development and progression of CC are still elusive. Circular RNAs (circRNAs) play an important role in various physiological and pathological processes. The aim of this study was to identify the circRNAs significantly associated with cervical squamous cell carcinoma (CSCC), in order to discover novel diagnostic markers and elucidate their mechanistic basis.The circRNA expression profiles of CSCC and paired para-cancerous cervical tissues was downloaded from the Gene Expression Omnibus. Bioinformatics analysis were used to screen for the differentially expressed circRNAs (DECRs). The expression levels of hsa_circ_0000745, hsa_circ_0084927, hsa_circ_0002762, hsa_circ_0075341, hsa_circ_0007905, hsa_circ_0031027, hsa_circ_0065898, hsa_circ_0070190, and hsa_circ_0078383 were verified in CC and normal cervical tissues by quantitative real-time PCR.A total of 197 DECRs were identified between the CSCC and normal tissues, including 87 upregulated and 110 downregulated circRNAs. In addition, 37 miRNAs were predicted for the upregulated circRNAs and 39 for the downregulated circRNAs. Functional analysis showed that the DECRs were associated with positive regulation of substrate adhesion-dependent cell spreading, metabolism, positive regulation of GTPase activity, protein regulation, and intercellular adhesion. The MAPK signaling pathway that plays a significant role in the progression of CC, was also enriched. Consistent with the in-silico analysis, hsa_circ_0000745, hsa_circ_0084927, hsa_circ_0002762, hsa_circ_0007905 were upregulated and hsa_circ_0078383 was downregulated in CC tissues (P < .001), whereas hsa_circ_0075341 (P < .001) and hsa_circ_0031027 (P = .001) showed opposite trends.We identified novel diagnostic and therapeutic biomarkers of CSCC along with the mechanistic basis.

Circular RNA circEGFR regulates tumor progression via the miR-106a-5p/DDX5 axis in colorectal cancer

Recently, an increasing number of studies have reported that dysregulation of circular RNA (circRNA) expression plays critical roles in the progression of several cancers, including colorectal cancer (CRC). However, the detailed molecular mechanisms of circRNAs involvement in CRC remain largely unknown. Here, we confirmed that the level of circEGFR was significantly increased in CRC tissues compared to matched adjacent non-tumor tissues, and a high level of circEGFR was correlated with poor clinicopathological characteristics and poor prognosis in patients with CRC. Moreover, increased circEGFR expression promoted CRC cell proliferation, migration, and invasion in vitro. Mechanistically, circEGFR acted as a ceRNA for miR-106a-5p to relieve the repressive effect of miR-106a-5p on DDX5 mRNA. Moreover, circEGFR enhanced DDX5 expression, thereby upregulating p-AKT levels. Together, these findings showed that circEGFR promoted CRC cell proliferation, migration, and invasion through the miR-106a-5p/DDX5/AKT axis, and may serve as a promising diagnostic marker and therapeutic target for CRC patients.

A Comprehensive Overview of circRNAs: Emerging Biomarkers and Potential Therapeutics in Gynecological Cancers

Circular RNA (circRNA) is a highly conserved, stable and abundant non-coding RNA (ncRNA). Also, some circRNAs play an essential part in the progression of human cancers. CircRNA is different from traditional linear RNA. CircRNA has a closed circular structure, so it is resistant to exonuclease-mediated degradation and is more stable than linear RNA. Numerous studies have found that many circRNAs can act as a microRNA (miRNA) sponge, interact with RNA-binding proteins, regulate gene transcription, affect alternative splicing and be translated into proteins. Recently, some studies have also indicated that circRNA participates in the progression of gynecological cancers. In addition, circRNA can act as a promising biomarker for the diagnosis of gynecological tumors. Additionally, they can also play a key role in the prognosis of gynecological tumors. Furthermore, to our delight, circRNA may be a potential therapeutic target in gynecological cancers and widely used in clinical practice. This article reviews the functions and related molecular mechanisms of circRNAs in gynecological tumors, and discusses their potential as biomarkers for diagnostic and prognostic and therapeutic targets for gynecological cancers.

Emerging important roles of circRNAs in human cancer and other diseases

CircRNAs are a large class of endogenous single-stranded RNA that is different from other linear RNA, which are produced by back-splicing and fusion of either exons, introns, or both exon-intron into covalently closed loops. CircRNAs are found in almost all living organisms and have emerged as potentially important players effecting on all life activities. It was characterized by stable structure, resistant to RNA degradation, highly abundance and conservation and tissue-specific expression. Early circRNAs were ignored as a by-product of meaningless abnormally cut RNA and had little biological function. Currently, circRNAs have become a research hotspot due to its special characteristics. CircRNAs could function as miRNA sponges, interfere with splicing and bind to protein to regulate the expression of parental genes and so on. In recent years, an increasing number of studies have revealed that circRNAs are closely related to a series of physiological and pathological processes. Additionally, circRNAs play an important role in the occurrence and development of a variety of diseases, suggesting circRNAs may be as novel indicators or biomarkers for cancer and other diseases with which they are associated. In this article, we review the biogenesis, biological functions of circRNAs and recent advances in circRNAs research in human diseases. Results will provide new insights on the roles and new ideas of circRNAs for the diagnosis and treatment of diseases and possible directions and approach for future circRNA applications.

Investigating the Underlying Mechanisms of Circular RNAs and Their Application in Clinical Research of Cervical Cancer

Circular RNAs (circRNAs) are non-coding RNA molecules, and these are differentially expressed in various diseases, including cancer, suggesting that circRNAs can regulate certain diseases. CircRNAs can act as miRNAs sponges, RNA-binding protein (RBP) sponges, and translation regulators, and they can become an important part of the regulation of gene expression. Furthermore, because of their biomedical features in body fluids, such as high abundance, conservation, and stability, circRNAs are seen as potential biomarkers for various cancers. Cervical cancer (CC) is one of the main causes of cancer-related death in women, and there have been a large number of studies that analyze circRNAs as a new object to be evaluated in CC. Therefore, this review, by understanding the role of circRNAs in CC, may create innovative strategies in the future clinical diagnosis, treatment, and prognosis of CC and promote the development of personalized and highly accurate cancer therapy.

The Role of circRNAs in Human Papillomavirus (HPV)-Associated Cancers

Circular RNAs (circRNAs) are a new class of "non-coding RNAs" that originate from non-sequential back-splicing of exons and/or introns of precursor messenger RNAs (pre-mRNAs). These molecules are generally produced at low levels in a cell-type-specific manner in mammalian tissues, but due to their circular conformation they are unaffected by the cell mRNA decay machinery. circRNAs can sponge multiple microRNAs or RNA-binding proteins and play a crucial role in the regulation of gene expression and protein translation. Many circRNAs have been shown to be aberrantly expressed in several cancer types, and to sustain specific oncogenic processes. Particularly, in virus-associated malignancies such as human papillomavirus (HPV)-associated anogenital carcinoma and oropharyngeal and oral cancers, circRNAs have been shown to be involved in tumorigenesis and cancer progression, as well as in drug resistance, and some are useful diagnostic and prognostic markers. HPV-derived circRNAs, encompassing the HPV E7 oncogene, have been shown to be expressed and to serve as transcript for synthesis of the E7 oncoprotein, thus reinforcing the virus oncogenic activity in HPV-associated cancers. In this review, we summarize research advances in the biogenesis of cell and viral circRNAs, their features and functions in the pathophysiology of HPV-associated tumors, and their importance as diagnostic, prognostic, and therapeutic targets in anogenital and oropharyngeal and oral cancers.

The human papillomavirus oncoproteins: a review of the host pathways targeted on the road to transformation

Persistent infection with high-risk human papillomaviruses (HR-HPVs) is the causal factor in over 99 % of cervical cancer cases, and a significant proportion of oropharyngeal and anogenital cancers. The key drivers of HPV-mediated transformation are the oncoproteins E5, E6 and E7. Together, they act to prolong cell-cycle progression, delay differentiation and inhibit apoptosis in the host keratinocyte cell in order to generate an environment permissive for viral replication. The oncoproteins also have key roles in mediating evasion of the host immune response, enabling infection to persist. Moreover, prolonged infection within the cellular environment established by the HR-HPV oncoproteins can lead to the acquisition of host genetic mutations, eventually culminating in transformation to malignancy. In this review, we outline the many ways in which the HR-HPV oncoproteins manipulate the host cellular environment, focusing on how these activities can contribute to carcinogenesis.

CircRNA in cancer: Fundamental mechanism and clinical potential

Circular RNAs (CircRNAs) are a class of single-stranded noncoding RNAs that are formed in a circular conformation via non-canonical splicing or back-splicing events. Aberrant expressions of many circRNAs are observed in diverse cancers, indicating their crucial roles in tumorigenesis and tumor development. Recently, several pieces of evidence have revealed that many circRNAs are involved in the promotion or suppression of cancers to varying degrees via different molecular mechanisms. Here in this review, we present a summary of the characteristics, types, biogenesis, and functions of circRNAs, and outline a series of the most recently studied circRNAs and their functional mechanisms in multiple cancer types with future perspectives. With great advances in nucleic acid-based therapeutic tools, circRNAs could be further explored as targetable molecules in future cancer treatments.0.

Circ SMARCA5 Inhibited Tumor Metastasis by Interacting with SND1 and Downregulating the YWHAB Gene in Cervical Cancer

Cervical cancer is one of the diseases that seriously endanger women's health. Circular RNA plays an important role in regulating the occurrence and development of cervical cancer. Here, we investigated the mechanisms of circ SMARCA5 in the development of cervical cancer. Quantitative reverse transcriptase polymerase chain reaction (RT-qPCR) results showed that the expression of SMARCA5 was downregulated in cervical cancer tissues and cell lines. Then we found that overexpression of SMARCA5 inhibited proliferation and invasion, but promoted apoptosis in cervical cancer cells. These were detected by Cell Counting Kit-8, Transwell, and Annexin V-fluorescein isothiocyanate/propidium iodide detection kit, respectively, and the expression of the apoptosis-related proteins was determined by western blotting. Then we predicted that SMARCA5 combined with Staphylococcal nuclease domain-containing 1 (SND1) by starBase, and verified by RNA pull-down assay. To further reveal the molecular mechanisms of SMARCA5 in the progression of cervical cancer, the interaction protein of SND1 was predicted by STRING, and the interaction was verified by co-immunoprecipitation assay. Then, the effects of SND1 or YWHAB on the development of cervical cancer were detected by the gain and loss function test, and we found that knockdown of SND1 or YWHAB reversed the effects of SMARCA5 short interfering RNA on proliferation, invasion, and apoptosis of cervical cancer cells. Overexpression of SMARCA5 inhibited cervical cancer metastasis in vivo. Our results showed that overexpression of circ SMARCA5 inhibits the binding of SND1 to YWHAB, and inhibits the proliferation and invasion, but promotes apoptosis in cervical cancer cells, thus inhibiting the metastasis of cervical cancer.

Circular RNA RSF1 promotes inflammatory and fibrotic phenotypes of irradiated hepatic stellate cell by modulating miR-146a-5p

The role of circular RNA (circRNA) in radiation-induced liver disease (RILD) remains largely unknown. In this study, Ras-related C3 botulinum toxin substrate 1 (RAC1) was elevated in irradiated human hepatic stellate cell (HSC) line LX2, the important effector cell mediating RILD. Overexpression of RAC1 promotes cell proliferation, proinflammatory cytokines production, and α-smooth muscle actin expression, which were blocked by microRNA (miR)-146a-5p mimics. CircRNA RSF1 (circRSF1) was upregulated in irradiated LX2 cells and predicted to harbor binding site for miR-146a-5p. Biotinylated-RNA pull down and dual-luciferase reporter detection confirmed the direct interaction of circRSF1 and miR-146a-5p. Enforced expression of circRSF1 increased RAC1 expression by acting as miR-146a-5p sponge to inhibit miR-146a-5p activity, and thus enhanced the cell viability, and promoted inflammatory and fibrotic phenotype of irradiated LX2 cells. These findings indicate a functional regulatory axis composing of circRSF1, miR-146a-5p, and RAC1 in irradiated HSC, which may provide attractive therapeutic targets for RILD.

Circular RNAs: Novel biomarkers for cervical, ovarian and endometrial cancer (Review)

Cervical, ovarian and endometrial cancer are the three most common types of malignant tumor and the leading causes of cancer-associated death in women. Tumor debulking surgery followed by platinum and paclitaxel chemotherapy is the current treatment regime of choice. However, as a result of late diagnosis and chemoresistance, the survival rates of patients with advanced gynecological cancers remains unsatisfactory. Circular RNAs (circRNAs) are stable noncoding RNAs that are present in a wide variety of tissue and cell types. With the enhancement of RNA sequencing methods, increasing numbers of circRNAs have been identified, and their functions are gradually being revealed. In recent years, circRNAs have received increasing attention for their regulatory roles in cervical, ovarian and endometrial cancer. The aim of the present review was to summarize the possible mechanisms of recently identified circRNAs; we hypothesize that a novel diagnostic and therapeutic biomarker may be identified to prolong the survival time of patients with gynecological malignancies.

Circular RNAs: New Epigenetic Signatures in Viral Infections

Covalent closed circular RNAs (circRNAs) can act as a bridge between non-coding RNAs and coding messenger RNAs. CircRNAs are generated by a back-splicing mechanism during post-transcriptional processing and are abundantly expressed in eukaryotic cells. CircRNAs can act via the modulation of RNA transcription and protein production, and by the sponging of microRNAs (miRNAs). CircRNAs are now thought to be involved in many different biological and pathological processes. Some studies have suggested that the expression of host circRNAs is dysregulated in several types of virus-infected cells, compared to control cells. It is highly likely that viruses can use these molecules for their own purposes. In addition, some viral genes are able to produce viral circRNAs (VcircRNA) by a back-splicing mechanism. However, the viral genes that encode VcircRNAs, and their functions, are poorly studied. In this review, we highlight some new findings about the interaction of host circRNAs and viral infection. Moreover, the potential of VcircRNAs derived from the virus itself, to act as biomarkers and therapeutic targets is summarized.

Crosstalk between noncoding RNAs and ferroptosis: new dawn for overcoming cancer progression

Cancer progression including proliferation, metastasis, and chemoresistance has become a serious hindrance to cancer therapy. This phenomenon mainly derives from the innate insensitive or acquired resistance of cancer cells to apoptosis. Ferroptosis is a newly discovered mechanism of programmed cell death characterized by peroxidation of the lipid membrane induced by reactive oxygen species. Ferroptosis has been confirmed to eliminate cancer cells in an apoptosis-independent manner, however, the specific regulatory mechanism of ferroptosis is still unknown. The use of ferroptosis for overcoming cancer progression is limited. Noncoding RNAs have been found to play an important roles in cancer. They regulate gene expression to affect biological processes of cancer cells such as proliferation, cell cycle, and cell death. Thus far, the functions of ncRNAs in ferroptosis of cancer cells have been examined, and the specific mechanisms by which noncoding RNAs regulate ferroptosis have been partially discovered. However, there is no summary of ferroptosis associated noncoding RNAs and their functions in different cancer types. In this review, we discuss the roles of ferroptosis-associated noncoding RNAs in detail. Moreover, future work regarding the interaction between noncoding RNAs and ferroptosis is proposed, the possible obstacles are predicted and associated solutions are put forward. This review will deepen our understanding of the relationship between noncoding RNAs and ferroptosis, and provide new insights in targeting noncoding RNAs in ferroptosis associated therapeutic strategies.

The Regulatory Role of circRNA_101308 in Cervical Cancer and the Prediction of Its Mechanism

Purpose

Accumulating evidence indicates that circular RNAs (circRNAs) are closely involved in canceration and cancer progression. However, the role of circRNAs in cervical cancer (CC) is largely unknown. Here, we characterized the role of circRNA_101308 in CC.

Materials and Methods

The expression of circRNA_101308 in CC tissues was measured by quantitative reverse transcription-polymerase chain reaction (qRT-PCR). Then, circRNA_101308 was overexpressed in CC cells to detect its function by proliferation and apoptosis assays, Transwell assays and animal experiments. The potential mechanism of circRNA_101308 in CC was explored by RNA pull-down, Gene Ontology (GO) and pathway analyses.

Results

CircRNA_101308 was significantly downregulated in CC tissues. The level of circRNA_101308 was much lower in CC patients with lymph node metastasis or deep myometrial invasion compared to those patients without lymph node metastasis and superficial myometrial invasion. CircRNA_101308 overexpression inhibited CC cell proliferation, invasion and migration. MiR-26a-5p, miR-196a-5p, miR-196b-5p, miR-335-3p, and miR-1307-3p were found to be sponged by circRNA_101308 in CC cells. Further, GO and pathway analyses predicted the potential functional processes and pathways of circRNA_101308 in CC.

Conclusion

CircRNA_101308 is downregulated and acts as a tumor suppressor in CC. CircRNA_101308 can participate in many different processes by sponging different miRNAs in CC cells. This exploration of circRNA_101308 provides new directions for research on cancer development and the clinical treatment of CC.

The Expression, Functions and Mechanisms of Circular RNAs in Gynecological Cancers

Circular RNAs (circRNAs) are covalently closed, endogenous non-coding RNAs and certain circRNAs are linked to human tumors. Owing to their circular form, circRNAs are protected from degradation by exonucleases, and therefore, they are more stable than linear RNAs. Many circRNAs have been shown to sponge microRNAs, interact with RNA-binding proteins, regulate gene transcription, and be translated into proteins. Mounting evidence suggests that circRNAs are dysregulated in cancer tissues and can mediate various signaling pathways, thus affecting tumorigenesis, metastasis, and remodeling of the tumor microenvironment. First, we review the characteristics, biogenesis, and biological functions of circRNAs, and describe various mechanistic models of circRNAs. Then, we provide a systematic overview of the functional roles of circRNAs in gynecological cancers. Finally, we describe the potential future applications of circRNAs as biomarkers for prognostic stratification and as therapeutic targets in gynecological cancers. Although the function of most circRNAs remains elusive, some individual circRNAs have biologically relevant functions in cervical cancer, ovarian cancer, and endometrial cancer. Certain circRNAs have the potential to serve as biomarkers and therapeutic targets in gynecological cancers.

Beyond MicroRNAs: Emerging Role of Other Non-Coding RNAs in HPV-Driven Cancers

Persistent infection with high-risk Human Papilloma Virus (HPV) leads to the development of several tumors, including cervical, oropharyngeal, and anogenital squamous cell carcinoma. In the last years, the use of high-throughput sequencing technologies has revealed a number of non-coding RNA (ncRNAs), distinct from micro RNAs (miRNAs), that are deregulated in HPV-driven cancers, thus suggesting that HPV infection may affect their expression. However, since the knowledge of ncRNAs is still limited, a better understanding of ncRNAs biology, biogenesis, and function may be challenging for improving the diagnosis of HPV infection or progression, and for monitoring the response to therapy of patients affected by HPV-driven tumors. In addition, to establish a ncRNAs expression profile may be instrumental for developing more effective therapeutic strategies for the treatment of HPV-associated lesions and cancers. Therefore, this review will address novel classes of ncRNAs that have recently started to draw increasing attention in HPV-driven tumors, with a particular focus on ncRNAs that have been identified as a direct target of HPV oncoproteins.

Recent Advances on the Molecular Mechanism of Cervical Carcinogenesis Based on Systems Biology Technologies

Cervical cancer is one of the common malignancies in women worldwide. Exploration of pathogenesis and molecular mechanism of cervical cancer is pivotal for development of effective treatment for this disease. Recently, systems biology approaches based on high-throughput technologies have been carried out to investigate the expression of some genes and proteins in genomics, transcriptomics, proteomics, and metabonomics of cervical cancer. Compared with traditional methods，systems biology technology has been shown to provide large of information regarding prognostic biomarkers and therapeutic targets for cervical cancer. These molecular signatures from system biology technology could be useful to understand the molecular mechanisms of cervical cancer development and progression, and help physicians to design targeted therapeutic strategies for patients with cervical cancer.