Downregulation of Circ_0071589 Suppresses Cisplatin Resistance in Colorectal Cancer by Regulating the MiR-526b-3p/KLF12 Axis

CircUGGT2 facilitates progression and cisplatin resistance of bladder cancer through nonhomologous end-joining pathway

The development of resistance to cisplatin (CDDP) in bladder cancer presents a notable obstacle, with indications pointing to the substantial role of circular RNAs (circRNAs) in this resistance. Nevertheless, the precise mechanisms through which circRNAs govern resistance are not yet fully understood. Our findings demonstrate that circUGGT2 is significantly upregulated in bladder cancer, facilitating cancer cell migration and invasion. Additionally, our analysis of eighty patient outcomes revealed a negative correlation between circUGGT2 expression levels and prognosis. Using circRNA pull-down assays, mass spectrometry analyses, and RNA Immunoprecipitation (RIP), it was shown that circUGGT2 interacts with the KU heterodimer, consisting of KU70 and KU80. Both KU70 and KU80 are critical components of the non-homologous end joining (NHEJ) pathway, which plays a role in CDDP resistance. Flow cytometry was utilized in this study to illustrate the impact of circUGGT2 on the sensitivity of bladder cancer cell lines to CDDP through its interaction with KU70 and KU80. Additionally, a reduction in the levels of DNA repair factors associated with the NHEJ pathway, such as KU70, KU80, DNA-PKcs, and XRCC4, was observed in chromatin of bladder cancer cells following circUGGT2 knockdown post-CDDP treatment, while the levels of DNA repair factors in total cellular proteins remained constant. Thus, the promotion of CDDP resistance by circUGGT2 is attributed to its facilitation of repair factor recruitment to DNA breaks via interaction with the KU heterodimer. Furthermore, our study demonstrated that knockdown of circUGGT2 resulted in reduced levels of γH2AX, a marker of DNA damage response, in CDDP-treated bladder cancer cells, implicating circUGGT2 in the NHEJ pathway for DNA repair.

Advanced strategies of targeting circular RNAs as therapeutic approaches in colorectal cancer drug resistance

Colorectal cancer (CRC) stands second in terms of mortality and third among the highest prevalent kinds of cancer globally. CRC prevalence is rising in moderately and poorly developed regions and is greater in economically advanced regions. Despite breakthroughs in targeted therapy, resistance to chemotherapeutics remains a significant challenge in the long-term management of CRC. Circular RNAs (circRNAs) have been involved in growing cancer therapy resistance, particularly in CRC, according to an increasing number of studies in recent years. CircRNAs are one of the novel subclasses of non-coding RNAs, previously thought of as viroid. According to studies, circRNAs have been recommended as biological markers for therapeutic targets and diagnostic and prognostic purposes. That is particularly notable given that the expression of circRNAs has been linked to the hallmarks of CRC since they are responsible for drug resistance in CRC patients; thereby, circRNAs are significant for chemotherapy failure. Moreover, knowledge concerning circRNAs remains relatively unclear despite using all these advanced techniques. Here, in this study, we will go over the most recent published work to highlight the critical roles of circRNAs in CRC development and drug resistance and highlight the main strategies to overcome drug resistance to improve clinical outcomes.

Preclinical Repurposing of Sitagliptin as a Drug Candidate for Colorectal Cancer by Targeting CD24/CTNNB1/SOX4-Centered Signaling Hub

Despite significant advances in treatment modalities, colorectal cancer (CRC) remains a poorly understood and highly lethal malignancy worldwide. Cancer stem cells (CSCs) and the tumor microenvironment (TME) have been shown to play critical roles in initiating and promoting CRC progression, metastasis, and treatment resistance. Therefore, a better understanding of the underlying mechanisms contributing to the generation and maintenance of CSCs is crucial to developing CSC-specific therapeutics and improving the current standard of care for CRC patients. To this end, we used a bioinformatics approach to identify increased CD24/SOX4 expression in CRC samples associated with poor prognosis. We also discovered a novel population of tumor-infiltrating CD24+ cancer-associated fibroblasts (CAFs), suggesting that the CD24/SOX4-centered signaling hub could be a potential therapeutic target. Pathway networking analysis revealed a connection between the CD24/SOX4-centered signaling, β-catenin, and DPP4. Emerging evidence indicates that DPP4 plays a role in CRC initiation and progression, implicating its involvement in generating CSCs. Based on these bioinformatics data, we investigated whether sitagliptin, a DPP4 inhibitor and diabetic drug, could be repurposed to inhibit colon CSCs. Using a molecular docking approach, we demonstrated that sitagliptin targeted CD24/SOX4-centered signaling molecules with high affinity. In vitro experimental data showed that sitagliptin treatment suppressed CRC tumorigenic properties and worked in synergy with 5FU and this study thus provided preclinical evidence to support the alternative use of sitagliptin for treating CRC.

Circ_0071589 contributes to growth, angiogenesis, and metastasis of colorectal cancer through regulating miR-296-5p/EN2 axis

To explore the function and regulation mechanism of circ_0071589 in colorectal cancer (CRC). The expression levels of circ_0071589, microRNA-296-5p (miR-296-5p), and Engrailed-2 (EN2) were detected by quantitative real-time polymerase chain reaction (qRT-PCR). Western blot was performed to check the protein levels of EN2 and apoptosis-related proteins. Cell colony formation and 5-Ethynyl-29-deoxyuridine (EdU) assay were used to exhibit cell proliferation. Cell apoptosis was shown by flow cytometry. Tube formation assay manifested the angiogenesis ability of CRC cells. Transwell assay demonstrated cell migration and invasion. The interaction between miR-296-5p and circ_0071589 or EN2 was identified by dual-luciferase reporter assay. The effect of circ_0071589 on tumor formation was demonstrated by in vivo tumor formation experiments. Immunohistochemical (IHC) assay was used to detect the positive cell rate of Ki67 in tumor tissue. Circ_0071589 was upregulated in CRC tissue and cells. Circ_0071589 knockdown repressed CRC cells proliferation, angiogenesis, migration, invasion, and promoted cell apoptosis. MiR-296-5p was downregulated in CRC tissue and cells. And miR-296-5p inhibitor could reverse the malignant phenotypes and angiogenesis inhibition of CRC cells caused by circ_0071589 knockdown. Additionally, miR-296-5p decreased CRC cell colony formation, EdU-positive cells, angiogenesis, and increased cell apoptosis through reducing the expression level of EN2. Finally, circ_0071589 silencing inhibited tumor formation in vivo. Circ_0071589 upregulated EN2 expression through sponging miR-296-5p, thereby promoting the malignant phenotype and angiogenesis of CRC cells, which provided a new target for the treatment of CRC.

Hsa_circ_0071589 aggravates stemness and oxaliplatin resistance in colorectal cancer through sponging miR-133b to upregulate SOX13 expression

Hsa_circ_0071589 can exacerbate the malignant behavior of colorectal cancer (CRC) cells. However, its function in stemness and oxaliplatin (OXP) resistance of CRC cells remains unclear. To assess the function of hsa_circ_0071589 in stemness and OXP resistance of CRC cells. Western blotting and qRT-PCR were applied to assess protein and mRNA levels. The association between hsa_circ_0071589, miR-133b and SOX13 was explored via a correlation analysis. Sphere formation was used to assess cell stemness. Meanwhile, the viability of CRC cells and OXP-resistant CRC cells was evaluated with the MTT assay. Cell stemness marker (CD133) levels and apoptosis of CRC cells and OXP-resistant CRC cells were tested using flow cytometry. The ALDH level was investigated using the related detection kit. In addition, the association between hsa_circ_0071589 and miR-133b and SOX13 was investigated using the RIP and dual luciferase assay. Finally, in vivo experiments were performed to detect the function of hsa_circ_0071589 in CRC, and the levels of SOX13, Ki67, and CD44 in mice were evaluated via immunohistochemistry staining. The expression of hsa_circ_0071589 and SOX13 was upregulated in CRC, whereas the expression of miR-133b was downregulated. Hsa_circ_0071589 knockdown significantly inhibited CRC stemness via the mediation of miR-133b. Moreover, hsa_circ_0071589 silencing significantly sensitized CRC cells to OXP by upregulating miR-133b. SOX13 was the direct target of miR-133b, and miR-133b could attenuate stemness and OXP resistance in CRC cells by targeting SOX13. Notably, hsa_circ_0071589 knockdown inhibited tumor growth and decreased OXP resistance in mice with CRC. Hsa_circ_0071589 aggravates stemness and OXP resistance by sponging miR-133b to indirectly target SOX13 in CRC. Thus, our study might present a novel treatment strategy against OXP-resistant CRC.

The critical role of circular RNAs in drug resistance in gastrointestinal cancers

Nowadays, drug resistance (DR) in gastrointestinal (GI) cancers, as the main reason for cancer-related mortality worldwide, has become a serious problem in the management of patients. Several mechanisms have been proposed for resistance to anticancer drugs, including altered transport and metabolism of drugs, mutation of drug targets, altered DNA repair system, inhibited apoptosis and autophagy, cancer stem cells, tumor heterogeneity, and epithelial-mesenchymal transition. Compelling evidence has revealed that genetic and epigenetic factors are strongly linked to DR. Non-coding RNA (ncRNA) interferences are the most crucial epigenetic alterations explored so far, and among these ncRNAs, circular RNAs (circRNAs) are the most emerging members known to have unique properties. Due to the absence of 5' and 3' ends in these novel RNAs, the two ends are covalently bonded together and are generated from pre-mRNA in a process known as back-splicing, which makes them more stable than other RNAs. As far as the unique structure and function of circRNAs is concerned, they are implicated in proliferation, migration, invasion, angiogenesis, metastasis, and DR. A clear understanding of the molecular mechanisms responsible for circRNAs-mediated DR in the GI cancers will open a new window to the management of GI cancers. Hence, in the present review, we will describe briefly the biogenesis, multiple features, and different biological functions of circRNAs. Then, we will summarize current mechanisms of DR, and finally, discuss molecular mechanisms through which circRNAs regulate DR development in esophageal cancer, pancreatic cancer, gastric cancer, colorectal cancer, and hepatocellular carcinoma.

Up-regulated Circular RNAs in Colorectal Cancer: New Entities for Therapy and Tools for Identification of Therapeutic Targets

Patients with disseminated colorectal cancer have a dismal prognosis with a 5-year survival rate of only 13%. In order to identify new treatment modalities and new targets, we searched the literature for up-regulated circular RNAs in colorectal cancer which induce tumor growth in corresponding preclinical in vivo models. We identified nine circular RNAs that mediate resistance against chemotherapeutic agents, seven that up-regulate transmembrane receptors, five that induce secreted factors, nine that activate signaling components, five which up-regulate enzymes, six which activate actin-related proteins, six which induce transcription factors and two which up-regulate the MUSASHI family of RNA binding proteins. All of the circular RNAs discussed in this paper induce the corresponding targets by sponging microRNAs (miRs) and can be inhibited by RNAi or shRNA in vitro and in xenograft models. We have focused on circular RNAs with demonstrated activity in preclinical in vivo models because the latter is an important milestone in drug development. All circular RNAs with in vitro activity only data are not referenced in this review. The translational impact of inhibition of these circular RNAs and of the identified targets for treatment of colorectal cancer (CRC) are discussed.

Novel strategies to reverse chemoresistance in colorectal cancer

Colorectal cancer (CRC) is a common gastrointestinal malignancy with high morbidity and fatality. Chemotherapy, as traditional therapy for CRC, has exerted well antitumor effect and greatly improved the survival of CRC patients. Nevertheless, chemoresistance is one of the major problems during chemotherapy for CRC and significantly limits the efficacy of the treatment and influences the prognosis of patients. To overcome chemoresistance in CRC, many strategies are being investigated. Here, we review the common and novel measures to combat the resistance, including drug repurposing (nonsteroidal anti-inflammatory drugs, metformin, dichloroacetate, enalapril, ivermectin, bazedoxifene, melatonin, and S-adenosylmethionine), gene therapy (ribozymes, RNAi, CRISPR/Cas9, epigenetic therapy, antisense oligonucleotides, and noncoding RNAs), protein inhibitor (EFGR inhibitor, S1PR2 inhibitor, and DNA methyltransferase inhibitor), natural herbal compounds (polyphenols, terpenoids, quinones, alkaloids, and sterols), new drug delivery system (nanocarriers, liposomes, exosomes, and hydrogels), and combination therapy. These common or novel strategies for the reversal of chemoresistance promise to improve the treatment of CRC.

CircMERTK modulates the suppressive capacity of tumor-associated macrophage via targeting IL-10 in colorectal cancer

Macrophages represent the major population in the tumor microenvironment (TME). Recent studies have demonstrated circular RNAs (circRNAs) are implicated in the development and progression of different immune responses and immune diseases. However, the role of circRNAs in the development of tumor-associated macrophages (TAM) remains unknown. Here, we used the circRNA sequencing to identify the differentially expressed circRNAs (DEcircRNAs) in TAM-like cell induced by culture medium of colorectal cancer cell lines. Of note, the expression of circMERTK was remarkably overexpressed in TAMs. The ISH assay displayed that the expressions of circMERTK were mainly overlapped with macrophages marker CD68, and the abundance of circMERTK in CRC tissues was much higher than that in matched normal tissues. Functionally, circMERTK knockdown resulted in attenuated CD8⁺ T cell apoptosis in the co-culture assay, indicating that circMERTK could have an impact on the immunosuppressive activity of TAM-like cell. Mechanically, TAM-like cell could exert immunosuppressive activity via circMERTK/miR-125a-3p/IL-10 axis. These data suggested that circMERTK could play an important role in TAM activation, and may serve as a potential therapeutic target for CRC.

Biological functions, mechanisms, and clinical significance of circular RNA in colorectal cancer

Colorectal cancer (CRC) is a leading cause of cancer-related death worldwide due to the lack of effective diagnosis and prognosis biomarkers and therapeutic targets, resulting in poor patient survival rates. Circular RNA (circRNA) is a type of endogenous non-coding RNA (ncRNA) with a closed-loop structure that plays a crucial role in physiological processes and pathological diseases. Recent studies indicate that circRNAs are involved in the diagnosis, prognosis, drug resistance, and development of tumors, particularly in CRC. Therefore, circRNA could be a potential new target for improving CRC diagnosis, prognosis, and treatment. This review focuses on the origin and biological functions of circRNA, summarizes recent research on circRNA's role in CRC, and discusses the potential use of circRNAs as clinical biomarkers for cancer diagnosis and prognosis, as well as therapeutic targets for CRC treatment.

Systematic analysis of circRNA biomarkers for diagnosis, prognosis and therapy in colorectal cancer

As the third most common cancer and the second leading cause of cancer death worldwide, colorectal cancer (CRC) poses a serious threat to people's health. In recent years, circRNA has been widely reported as a new biomarker in CRC, but a comprehensive summary and analysis is lacking. This study aims to evaluate the diagnostic, therapeutic and prognostic significance of circRNAs in CRC by systematically analysing their expression patterns, biological functions and clinical significance in CRC. The literature on circRNA in CRC was searched in the PubMed database and included for analysis after screening according to strict inclusion and exclusion criteria. The UALCAN online tool was used to obtain host gene expression data. The miRTargetLink 2.0 was used to predict target genes for miRNAs action in CRC patients. Cytoscape was used to construct circRNA-miRNA-mRNA interaction networks. From the 236 included papers, we identified 217 circRNAs and their associated 108 host genes and 145 miRNAs. Among the 145 miRNAs, 27 miRNAs had no corresponding target genes. After prediction of target genes and differential analysis, a total of 25 target genes were obtained and a circRNA-miRNA-mRNA interaction network was constructed. Among the 217 circRNAs, 74 were associated with diagnosis, 160 with treatment and 51 with prognosis. And 154 of them function as oncogenes while 58 as tumour suppressor genes. In addition, these circRNAs include 32 exosomal circRNAs, which have unique advantages as biomarkers. In total, we summarize and analyze the expression patterns, biological functions and clinical significance of circRNAs in CRC. In addition, we constructed some new circRNA-miRNA-mRNA regulatory axes based on the miRNAs sponged by circRNAs.

Circ-FAT1 Up-Regulates FOSL2 Expression by Sponging miR-619-5p to Facilitate Colorectal Cancer Progression

Circular RNA FAT atypical cadherin 1 (circ-FAT1) has been reported to play roles in colorectal cancer (CRC) development. Here, the purpose of this study was to investigate the function and mechanism of circ-FAT1 in CRC tumorigenesis and its potential value in the clinic. Levels of genes and proteins were examined by quantitative real-time polymerase chain reaction and Western blot. In vitro assays were conducted using cell counting kit-8 assay, 5-Ethynyl-2'-deoxyuridine assay, flow cytometry, transwell assay, and tube formation assay, respectively. The target relationship between miR-619-5p and circ-FAT1 or FOS-like antigen 2 (FOSL2) was verified by dual-luciferase reporter and RNA immunoprecipitation assays. In vivo assay was performed using a mouse subcutaneous xenograft model. Circ-FAT1 and FOSL2 were highly expressed in CRC tissues and cells. Functionally, knockdown of circ-FAT1 or FOSL2 suppressed CRC cell apoptosis, migration, invasion, and angiogenesis, but induced cell apoptosis in vitro. Mechanistically, circ-FAT1 acted as a sponge for miR-619-5p to up-regulate the expression of FOSL2, which was confirmed to be a target of miR-619-5p. A series of rescue experiments demonstrated that miR-619-5p inhibition or FOSL2 overexpression reversed the inhibitory action of circ-FAT1 silencing on CRC cell malignant phenotypes mentioned above. Pre-clinically, lentivirus-mediated circ-FAT1 knockdown inhibited the tumorigenesis of CRC xenografts in nude mice via regulating miR-619-5p and FOSL2. Circ-FAT1 knockdown repressed FOSL2 expression by sponging miR-619-5p to suppress CRC tumorigenesis, providing a potential approach for CRC therapeutics.

Advances in the Study of CircRNAs in Tumor Drug Resistance

Recent studies have revealed that circRNAs can affect tumor DNA damage and repair, apoptosis, proliferation, and invasion and influence the transport of intratumor substances by acting as miRNA sponges and transcriptional regulators and binding to proteins in a variety of ways. However, research on the role of circRNAs in cancer radiotherapy and chemoresistance is still in its early stages. Chemotherapy is a common approach to oncology treatment, but the development of tumor resistance limits the overall clinical efficacy of chemotherapy for cancer patients. The current study suggests that circRNAs have a facilitative or inhibitory effect on the development of resistance to conventional chemotherapy in a variety of tumors, suggesting that circRNAs may serve as a new direction for the study of antitumor drug resistance. In this review, we will briefly discuss the biological features of circRNAs and summarize the recent progression of the involvement of circRNAs in the development and pathogenesis of cancer chemoresistance.

Contribution of MicroRNAs in Chemoresistance to Cisplatin in the Top Five Deadliest Cancer: An Updated Review

Cisplatin (DDP) is a well-known anticancer drug used for the treatment of numerous human cancers in solid organs, including bladder, breast, cervical, head and neck squamous cell, ovarian, among others. Its most important mode of action is the DNA-platinum adducts formation, inducing DNA damage response, silencing or activating several genes to induce apoptosis; these mechanisms result in genetics and epigenetics modifications. The ability of DDP to induce tumor cell death is often challenged by the presence of anti-apoptotic regulators, leading to chemoresistance, wherein many patients who have or will develop DDP-resistance. Cancer cells resist the apoptotic effect of chemotherapy, being a problem that severely restricts the successful results of treatment for many human cancers. In the last 30 years, researchers have discovered there are several types of RNAs, and among the most important are non-coding RNAs (ncRNAs), a class of RNAs that are not involved in protein production, but they are implicated in gene expression regulation, and representing the 98% of the human genome non-translated. Some ncRNAs of great interest are long ncRNAs, circular RNAs, and microRNAs (miRs). Accumulating studies reveal that aberrant miRs expression can affect the development of chemotherapy drug resistance, by modulating the expression of relevant target proteins. Thus, identifying molecular mechanisms underlying chemoresistance development is fundamental for setting strategies to improve the prognosis of patients with different types of cancer. Therefore, this review aimed to identify and summarize miRs that modulate chemoresistance in DDP-resistant in the top five deadliest cancer, both in vitro and in vivo human models.

Circ_0058063 contributes to cisplatin-resistance of bladder cancer cells by upregulating B2M through acting as RNA sponges for miR-335-5p

Bladder cancer (BC) is one of the most common malignant tumors of the urinary system, and cisplatin (CDDP) is a critical chemical drug for the treatment of BC. However, CDDP-resistance seriously limits the therapeutic efficacy of this drug for clinical utilization. Thus, identification of pivotal molecule targets that regulate CDDP-resistance in BC become urgent and necessary. In this study, we firstly identified a novel BC-associated circular RNA circ_0058063 that participates in the regulation of CDDP-resistance in BC. Specifically, circ_0058063 was significantly overexpressed in CDDP-resistant tissue and cells, in contrast with the corresponding CDDP-sensitive counterparts. Further loss-of-function experiments validated that downregulation of circ_0058063 suppressed cell proliferation and tumor growth, whereas induced cell apoptosis in the CDDP-resistant BC cells in vitro and in vivo. In addition, we disclosed that circ_0058063 acts as a sponge for miR-335-5p to positively regulate B2M expression, and further rescuing experiments verified that the enhancing effects of sh-circ_0058063 on CDDP-sensitivity in the CDDP-resistant BC cells were abrogated by silencing miR-335-5p. Taken together, our results demonstrated that circ_0058063 contributed to CDDP resistance of bladder cancer cells via sponging miR-335-5p, and B2M might be the downstream effector gene. This study firstly evidenced that targeting circ_0058063 might be an effective strategy to improve CDDP-sensitivity in BC.

The optimum inhibitory effects of Alpha Interferon and Cisplatin in colon cancer, a comparative in vitro study

Cisplatin is well known as a potent anti-cancer agent against colon cancer. However, alpha interferons are also widely used for cancer suppression. This in vitro study was designed to investigate and compare the cancer suppression function of alpha interferon in colon cancer with Cisplatin. The analysis used a human SW 480 cancer cell line with RPMI-1630 culture media. Six dilutions of interferon (2.5 μg/ml, 1.25 μg/ml, 0.562 μg/ml, 0.286 μg/ml, 0.143 μg/ml, and 0.057 μg/ml) and six dilutions of cisplatin (100 μg/ml, 50 μg/ml, 25 μg/ml, 6.25 μg/ml, and 3.125) were used at 24, 48 and 72 hours along with the presence of control groups. Following this, results were observed by ELISA plate reader, and percentage inhibition was calculated using ANOVA analysis. The interferon and cisplatin percentage of inhibition was comparable with higher inhibition rates observed with alpha interferon. The statistical analysis showed that the maximum inhibition was observed at a 0.143 μg/ml interferon concentration when exposed for 48 to 72 hours. This in vitro analysis demonstrated the anti-cancer activity of alpha interferon and its advanced inhibitory activity compared to Cisplatin.

The Emerging Roles of Circular RNAs in the Chemoresistance of Gastrointestinal Cancer

Gastrointestinal (GI) cancer represents a major global health problem due to its aggressive characteristics and poor prognosis. Despite the progress achieved in the development of treatment regimens, the clinical outcomes and therapeutic responses of patients with GI cancer remain unsatisfactory. Chemoresistance arising throughout the clinical intervention is undoubtedly a critical barrier for the successful treatment of GI cancer. However, the precise mechanisms associated with chemoresistance in GI cancer remain unclear. In the past decade, accumulating evidence has indicated that circular RNAs (circRNAs) play a key role in regulating cancer progression and chemoresistance. Notably, circRNAs function as molecular sponges that sequester microRNAs (miRNAs) and/or proteins, and thus indirectly control the expression of specific genes, which eventually promote or suppress drug resistance in GI cancer. Therefore, circRNAs may represent potential therapeutic targets for overcoming drug resistance in patients with GI cancer. This review comprehensively summarizes the regulatory roles of circRNAs in the development of chemoresistance in different GI cancers, including colorectal cancer, gastric cancer and esophageal cancer, as well as deciphers the underlying mechanisms and key molecules involved. Increasing knowledge of the important functions of circRNAs underlying drug resistance will provide new opportunities for developing efficacious therapeutic strategies against GI cancer.

MiR-526b-3p Attenuates Breast Cancer Stem Cell Properties and Chemoresistance by Targeting HIF-2α/Notch Signaling

Chemoresistance is a severe clinical challenge in breast cancer. Hypoxia and cancer stem cells (CSCs) contribute to the paclitaxel (PTX) resistance, but the molecular mechanisms are still elusive. MicorRNAs (miRNA) have been considered a promising therapeutic strategy in various cancers. Here, we identified the crucial function of miR-526b-3p in regulating PTX resistance and CSC properties. Our data demonstrated that miR-526b-3p mimic repressed the cell viability of breast cancer cells. The counts of Edu-positive cells were reduced by miR-526b-3p in breast cancer cells. Meanwhile, the apoptosis of breast cancer cells was induced by miR-526b-3p. Tumorigenicity analysis in the nude mice confirmed that miR-526b-3p attenuated the breast cancer cell growth in vivo. Significantly, hypoxia could enhance IC50 value of PTX in breast cancer cells. IC50 value of PTX was induced in breast cancer mammospheres. The hypoxia-inducible factor 2α (HIF-2α) expression was enhanced, but miR-526b-3p expression was repressed under hypoxia in breast cancer cells. Also, breast cancer mammospheres presented high HIF-2α expression and low miR-526b-3p expression. The inhibition of miR-526b-3p enhanced the IC50 value of PTX in breast cancer cells. MiR-526b-3p inhibitor enhanced the colony formation counts of PTX-treated breast cancer cells. The treatment of miR-526b-3p mimic suppressed the sphere formation counts of breast cancer cells and inhibited ALDH1 and Nanog expression. MiR-526b-3p was able to target HIF-2α in the cells. The overexpression enhanced but miR-526b-3p reduced the IC50 value of PTX in breast cancer cells, in which the overexpression of HIF-2α could rescue the miR-526b-3p-inhibited IC50 value of PTX. Overexpression of HIF-2α reversed miR-526b-3p-regulated apoptosis, colony formation ability, and ALDH1 and Nanog expression in the cells. Interestingly, the overexpression of HIF-2α induced but miR-526b-3p repressed the expression of HIF-2α, Hey2, and Notch in PTX-treated breast cancer cells, while HIF-2α could reverse the effect of miR-526b-3p. In conclusion, miR-526b-3p attenuated breast cancer stem cell properties and chemoresistance by targeting HIF-2α/Notch signaling. MiR-526b-3p may be utilized in the relieving chemoresistance in breast cancer.

Research progress of circRNAs in chemotherapy resistance of digestive system neoplasms

Circular RNAs (circRNAs) are a novel class of noncoding RNA molecules with a unique closed continuous loop structure. CircRNAs are abundant in eukaryotic cells, have unique stability and tissue specificity, and can play a biological regulatory role at various levels, such as transcriptional and posttranscriptional levels. Accumulating evidence indicates that circRNAs play critical roles in tumor genesis, development, and chemotherapy. Chemotherapy is a primary type of intervention for most cancers, but its therapeutic efficacy is usually retarded by intrinsic and acquired resistance. CircRNAs regulate tumor chemoresistance through various molecular mechanisms, such as affecting apoptosis, promoting drug transportation, promoting DNA repair, promoting epithelial-mesenchymal transformation, regulating the characteristics of tumor stem cells, and affecting autophagy. This review summarizes the recent progress and mechanisms of circRNAs in cancer cell resistance to chemotherapy.

Roles of circular RNAs in colorectal cancer

Colorectal cancer (CRC) is one of the most common types of malignant cancer worldwide and poses a significant burden on both the individual and healthcare systems. Despite advances in treatment options, advanced-stage CRC has a high mortality rate due to its heterogeneity, metastatic potential and/or delay in diagnosis. In recent years, an increasing number of studies have indicated that circular RNAs (circRNAs) serve important roles in several types of cancer, including CRC. Recent studies have revealed that circRNAs are aberrantly expressed in CRC tissues and function as oncogenic or tumor suppressive regulators of CRC carcinogenesis and development. Numerous circRNAs have been associated with the clinicopathological features of patients with CRC and have been considered as potential biomarkers for the diagnosis and prognosis of CRC, as well as targets for treatment. However, a deeper understanding of their potential function is required. In the present review, the current body of knowledge on the biogenesis and functions of CRC-associated circRNAs, and their potential value in clinical applications, such as in CRC diagnosis, prognosis and treatment, is discussed and summarized.

Circular RNA circβ-catenin aggravates the malignant phenotype of non-small-cell lung cancer via encoding a peptide

Background

More and more evidences demonstrate that circular RNAs (circNRAs) can encode protein. As a circRNA with translation capabilities, outcomes of circβ‐catenin in non‐small cell lung cancer (NSCLC) still need to be explored.

Method

The research methods of circβ‐catenin in the article include qRT‐PCR, wound healing assay, CCK‐8, colony formation, and Transwell assay. Western blotting and immunofluorescence were provided to detect protein expression levels and peptide encoded by circβ‐catenin, respectively.

Results

A prominently higher circβ‐catenin expression was found in NSCLC tissues. Silencing of circβ‐catenin was able to inhibit NSCLC cell migrating, invasive, and proliferative phenotypes. Overexpression of circβ‐catenin could enhance the migrating, invasive, and proliferative phenotypes of NSCLC cells. Importantly, circβ‐catenin was found to encode a peptide in NSCLC cells. Silencing or overexpression of circβ‐catenin could reduce or increase β‐catenin protein expression via suppressing the degradation of β‐catenin.

Conclusion

Circβ‐catenin could promote NSCLC cell malignant phenotypes via peptide‐regulated β‐catenin pathway. Our study provided a new understanding for the mechanisms of NSCLC.

Circular RNA FAT atypical cadherin 1 (circFAT1)/microRNA-525-5p/spindle and kinetochore-associated complex subunit 1 (SKA1) axis regulates oxaliplatin resistance in breast cancer by activating the notch and Wnt signaling pathway

Increasing evidence has confirmed the vital roles of circular RNAs (CircRNAs) in the drug resistance of breast cancer (BC). Herein, we intended to study the effect of circular RNA FAT atypical cadherin 1 (circFAT1) on BC oxaliplatin (OX) resistance and find out the potential molecular mechanism in it. In this study, mRNA and protein levels of genes were measured by RT-qPCR and western blotting, respectively. Luciferase reporter assay confirmed the relationship between microRNA-525-5p (miR-525-5p) and circFAT1 or spindle and kinetochore-associated complex subunit 1 (SKA1). CCK-8, transwell, and flow cytometry experiments were utilized to investigate the chemosensitivity, migration, invasion, and apoptosis of BC cells. Gene Set Enrichment Analysis (GSEA) was applied to discover possible pathways related to SKA1. It was uncovered that circFAT1 was overexpressed in OX-resistant BC tissues and cells. Functional experiments showed that circFAT1 depletion reduced the level of chemoresistance-related genes. Moreover, circFAT1 knockdown remarkably facilitated apoptosis and decreased OX (half-maximal inhibitory concentration) IC₅₀ value, migration, and invasion in OX-resistant BC cells. It was identified that miR-525-5p directly targeted circFAT1 and SKA1. Besides, rescue assays exhibited that circFAT1 promoted OX resistance in BC cells via the miR-525-5p/SKA1 regulatory network. Furthermore, GSEA and western blotting identified that SKA1 activated the Notch and Wnt pathway in OX-resistant BC cells. In conclusion, our results demonstrated that circFAT1 conferred OX resistance in BC by regulating the miR-525-5p/SKA1 via the Notch and Wnt pathway, providing a potential therapeutic target for patients with OX-resistant BC.

Oncogenic Functions and Clinical Significance of Circular RNAs in Colorectal Cancer

Colorectal cancer (CRC) is ranked as the second most commonly diagnosed disease in females and the third in males worldwide. Therefore, the finding of new more reliable biomarkers for early diagnosis, for prediction of metastasis, and resistance to conventional therapies is an important challenge in overcoming the disease. The current review presents circular RNAs (circRNAs) with their unique features as potential prognostic and diagnostic biomarkers in CRC. The review highlights the mechanism of action and the role of circRNAs with oncogenic functions in the CRC as well as the association between their expression and clinicopathological characteristics of CRC patients. The comprehension of the role of oncogenic circRNAs in CRC pathogenesis is growing rapidly and the next step is using them as suitable new drug targets in the personalized treatment of CRC patients.