Circular RNAs: The crucial regulatory molecules in colorectal cancer

Circular RNAs in the KRAS pathway: Emerging players in cancer progression

Circular RNAs (circRNAs) have been recognized as key components in the intricate regulatory network of the KRAS pathway across various cancers. The KRAS pathway, a central signalling cascade crucial in tumorigenesis, has gained substantial emphasis as a possible therapeutic target. CircRNAs, a subgroup of non-coding RNAs known for their closed circular arrangement, play diverse roles in gene regulation, contributing to the intricate landscape of cancer biology. This review consolidates existing knowledge on circRNAs within the framework of the KRAS pathway, emphasizing their multifaceted functions in cancer progression. Notable circRNAs, such as Circ_GLG1 and circITGA7, have been identified as pivotal regulators in colorectal cancer (CRC), influencing KRAS expression and the Ras signaling pathway. Aside from their significance in gene regulation, circRNAs contribute to immune evasion, apoptosis, and drug tolerance within KRAS-driven cancers, adding complexity to the intricate interplay. While our comprehension of circRNAs in the KRAS pathway is evolving, challenges such as the diverse landscape of KRAS mutant tumors and the necessity for synergistic combination therapies persist. Integrating cutting-edge technologies, including deep learning-based prediction methods, holds the potential for unveiling disease-associated circRNAs and identifying novel therapeutic targets. Sustained research efforts are crucial to comprehensively unravel the molecular mechanisms governing the intricate interplay between circRNAs and the KRAS pathway, offering insights that could potentially revolutionize cancer diagnostics and treatment strategies.

Hsa_circ_0020134 promotes liver metastasis of colorectal cancer through the miR-183-5p-PFN2-TGF-β/Smad axis

Circular RNAs (circRNAs) are a distinct class of non-coding RNAs that play regulatory roles in the initiation and progression of tumors. With advancements in transcriptome sequencing technology, numerous circRNAs that play significant roles in tumor-related genes have been identified. In this study, we used transcriptome sequencing to analyze the expression levels of circRNAs in normal adjacent tissues, primary colorectal cancer (CRC) tissues, and CRC tissues with liver metastasis. We successfully identified the circRNA hsa_circ_0020134 (circ0020134), which exhibited significantly elevated expression specifically in CRC with liver metastasis. Importantly, high levels of circ0020134 were associated with a poor prognosis among patients. Functional experiments demonstrated that circ0020134 promotes the proliferation and metastasis of CRC cells both in vitro and in vivo. Mechanistically, upregulation of circ0020134 was induced by the transcription factor, PAX5, while miR-183-5p acted as a sponge for circ0020134, leading to partial upregulation of PFN2 mRNA and protein levels, thereby further activating the downstream TGF-β/Smad pathway. Additionally, downregulation of circ0020134 inhibited epithelial-mesenchymal transition (EMT) in CRC cells, which could be reversed by miR-183-5p inhibitor treatment. Collectively, our findings confirm that the circ0020134-miR-183-5p-PFN2-TGF-β/Smad axis induces EMT transformation within tumor cells, promoting CRC proliferation and metastasis, thus highlighting its potential as a therapeutic target for patients with CRC liver metastasis.

Colon cancer transcriptome

Over the last four decades, methodological innovations have continuously changed transcriptome profiling. It is now feasible to sequence and quantify the transcriptional outputs of individual cells or thousands of samples using RNA sequencing (RNA-seq). These transcriptomes serve as a connection between cellular behaviors and their underlying molecular mechanisms, such as mutations. This relationship, in the context of cancer, provides a chance to unravel tumor complexity and heterogeneity and uncover novel biomarkers or treatment options. Since colon cancer is one of the most frequent malignancies, its prognosis and diagnosis seem to be critical. The transcriptome technology is developing for an earlier and more accurate diagnosis of cancer which can provide better protectivity and prognostic utility to medical teams and patients. A transcriptome is a whole set of expressed coding and non-coding RNAs in an individual or cell population. The cancer transcriptome includes RNA-based changes. The combined genome and transcriptome of a patient may provide a comprehensive picture of their cancer, and this information is beginning to affect treatment decision-making in real-time. A full assessment of the transcriptome of colon (colorectal) cancer has been assessed in this review paper based on risk factors such as age, obesity, gender, alcohol use, race, and also different stages of cancer, as well as non-coding RNAs like circRNAs, miRNAs, lncRNAs, and siRNAs. Similarly, they have been examined independently in the transcriptome study of colon cancer.

Circ_0060967 contributes to colorectal cancer progression by sponging miR-1184 to up-regulate SRC proto-oncogene

BACKGROUND AND STUDY AIMS

Circular RNAs (circRNAs) are closely associated with cancer pathogenesis. The purpose of our current study was to explore the role and mechanism of circ_0060967 in colorectal cancer (CRC) development.

PATIENTS AND METHODS

Human CRC specimens and paired healthy tissues were used to examine variable expression. The expression of circ_0060967 and microRNA (miR)-1184 was examined by quantitative reverse transcription-PCR. The protein levels of proliferating cell nuclear antigen, BCL2-associated X, apoptosis regulator (Bax), proto-oncogene nonreceptor tyrosine kinase Src (SRC), nuclear factor-κB inhibitor alpha (IκBα), phosphorylated-IκBα (p-IκBα), RELA proto-oncogene, nuclear factor-κB subunit (p65), and phosphorylated-p65 (p-p65) were determined by western blot. Proliferation and motility of HCT-116 and SW480 CRC cells were assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) and transwell assays, respectively. Dual-luciferase reporter assay and RNA immunoprecipitation assay were used to determine the binding relation between miR-1184 and circ_0060967 or SRC. Animal studies were used to detect the role of circ_0060967 in CRC cell tumorigenicity.

RESULTS

Circ_0060967 abundance was enhanced in human CRC tissue samples versus paired normal colorectal tissues and in HCT-116 and SW480 CRC cells versus normal HCO cells. Decreased expression of circ_0060967 could suppress cell growth, motility, and invasiveness of CRC cells in vitro and tumor growth in vivo. Circ_0060967 sponged miR-1184, and miR-1184 targeted SRC. Furthermore, we also found circ_0060967 affected cell growth by modulating miR-1184/SRC axis in CRC.

CONCLUSION

This study demonstrates a novel circ_0060967/miR-1184/SRC regulatory cascade in affecting CRC cell malignant behaviors, which can have a broad effect on the field of molecularly targeted therapeutics.

Circ_0004585 Facilitates Tumorigenesis of Colorectal Cancer Via Modulating the miR-338-3p/ZFX Axis and Activating the MEK/ERK Pathway

Background

Colorectal cancer (CRC) is a common malignant tumor in the digestive tract. Circular RNAs (circRNAs) have been identified as crucial regulators of tumorigenesis. However, the role and potential mechanism of circ_0004585 in CRC are poorly understood.

Methods

The expression of circ_0004585, microRNA-338-3p (miR-338-3p), and zinc finger protein X-linked (ZFX) was detected by quantitative real-time PCR and Western blot. Cell proliferation, cell cycle arrest, apoptosis, and angiogenesis were evaluated by 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide (MTT), 5-Ethynyl-2'-deoxyuridine (EdU), flow cytometry and tube formation assays. Western blot assay was applied to detect the expression of epithelial-mesenchymal transition (EMT)-related proteins and MEK/ERK signaling pathway-related proteins. A xenograft model was used to analyze tumor growth in vivo. The targeted relationship between miR-338-3p and circ_0004585/ZFX was verified by a dual-luciferase reporter assay.

Results

Circ_0004585 and ZFX were up-regulated, while miR-338-3p was down-regulated in CRC tissues and cells. Silencing of circ_0004585 inhibited proliferation, angiogenesis, and EMT and triggered apoptosis in CRC cells. Consistently, circ_0004585 depletion blocked tumor growth in vivo. Circ_0004585 contributed to CRC cell development via sequestering miR-338-3p. Also, miR-338-3p hindered the malignant progression of CRC cells by targeting ZFX. Circ_0004585 activated MEK/ERK pathway via regulating ZFX.

Conclusion

Circ_0004585 facilitated CRC progression through modulating miR-338-3p/ZFX/MEK/ERK pathway, which might provide a potential therapeutic target for CRC.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12195-022-00756-6.

Hsa_circ_0003602 Contributes to the Progression of Colorectal Cancer by Mediating the miR-149-5p/SLC38A1 Axis

Background/Aims

We aimed to investigate the role and working mechanism of Homo sapiens circular RNA_0003602 (hsa_circ_0003602) in colorectal cancer (CRC) development.

Methods

The expression of circ_0003602, miR-149-5p, and solute carrier family 38 member 1 (SLC38A1) was detected by quantitative real-time polymerase chain reaction. RNase R assays were conducted to determine the characteristics of circ_0003602. CCK-8 assays, flow cytometry analysis, transwell invasion assays, wound healing assays and tube formation assays were employed to evaluate cell viability, apoptosis, invasion, migration, and angiogenesis. All protein levels were examined by Western blot or immunohistochemistry assay. The glutamine metabolism was monitored by corresponding glutamine, α-ketoglutarate and glutamate assay kits. Dual-luciferase reporter assay was utilized to confirm the targeted combination between miR-149-5p and circ_0003602 or SLC38A1. A xenograft tumor model was established to analyze the role of circ_0003602 in CRC tumor growth in vivo.

Results

Circ_0003602 was upregulated in CRC tissues and cell lines. Circ_0003602 silencing suppressed CRC cell viability, migration, invasion, angiogenesis, and glutaminolysis; induced cell apoptosis in vitro; and blocked tumor growth in vivo. Moreover, circ_0003602 directly interacted with miR-149-5p to negatively regulate its expression, and circ_0003602 knockdown suppressed the malignant behaviors of CRC cells largely by upregulating miR-149-5p. MiR-149-5p directly bound to the 3' untranslated region of SLC38A1 to induce its degradation, and miR-149-5p overexpression reduced the malignant potential of CRC cells largely by downregulating SLC38A1. Circ_0003602 positively regulated SLC38A1 expression by sponging miR-149-5p in CRC cells.

Conclusions

Circ_0003602 knockdown impedes CRC development by targeting the miR-149-5p/SLC38A1 axis, which provides a novel theoretical basis and new insights for CRC treatment.

CircEIF4G2 promotes proliferation, migration, and invasion of colon cancer LoVo cells by targeting miR-144-3p

BACKGROUND

Many circular RNAs (circRNAs) are abnormally expressed in colorectal cancer, and they can regulate the expression of their target genes by acting as a miRNA sponge molecule, thereby regulating the biological behavior of colorectal cancer cells; however, the role of circEIF4G2/miR-144-3p in the occurrence and development of colorectal cancer and the underlying mechanism are not yet clear.

AIM

To investigate the effect of circEIF4G2/miR-144-3p on the proliferation, migration, and invasion of colorectal cancer LoVo cells.

METHODS

Reverse transcription-quantitative polymerase chain reaction was used to detect the expression of circEIF4G2 and miR-144-3p in colorectal cancer tissues. LoVo cells were divided into four groups and transfected with si-NC, si-circEIF4G2, si-circEIF4G2 + anti-miR-NC, and si-circEIF4G2 + anti-miR-144-3p, respectively. Dual luciferase reporter assay was performed to analyze the targeting relationship between circEIF4G2 and miR-144-3p. CCK-8 assay and clone formation assay were utilized to monitor the proliferation inhibition rate and clone formation in the four groups, respectively. Transwell assay was used to detect cell migration and invasion, and Western blot analysis was performed to determine E-cadherin and N-cadherin protein expression.

RESULTS

The expression of circEIF4G2 in 51 cases of colorectal cancer tissues increased by ~2.38 times compared with tumor adjacent tissues, and the expression of miR-144-3p decreased by about 0.54 times compared with tumor adjacent tissues (P < 0.05 for both). CircEIF4G2 targets and regulates the expression of miR-144-3p. The proliferation inhibition rate and E-cadherin protein expression in the si-circEIF4G2 group increased compared with those in the si-NC group, while the number of clones, migration, invasion, and the expression level of N-cadherin protein were lower than those of the si-NC group (P < 0.05 for all). The proliferation inhibition rate and E-cadherin protein expression in the si-circEIF4G2 + anti-miR-144-3p group were lower than those of the si-circEIF4G2 + anti-miR-NC group, while the number of clones, migration, invasion, and the expression of N-cadherin protein were higher than those of the si-circEIF4G2+anti-miR-NC group (P < 0.05 for all).

CONCLUSION

Knockdown of circEIF4G2 inhibits cell proliferation, migration, and invasion by targeting miR-144-3p in colorectal cancer LoVo cells.

Circ_0082182 upregulates the NFIB level via sponging miR-326 to promote oxaliplatin resistance and malignant progression of colorectal cancer cells

Circular RNAs (circRNAs) are key regulators in tumor metastasis and drug resistance. This study was designed to investigate circ_0082182 function and mechanism in oxaliplatin (OXA) resistance and cancer progression of colorectal cancer (CRC). The circ_0082182, microRNA-326 (miR-326), and nuclear factor I B (NFIB) levels were quantified by reverse transcription-quantitative polymerase chain reaction (RT-qPCR). Cell sensitization was analyzed by Cell Counting Kit-8 assay. The proliferation ability was determined via EdU assay, and apoptosis was measured by flow cytometry. Transwell assay and wound healing assay were performed to assess cell invasion and migration. The protein level was examined through Western blot. The binding interaction was conducted via dual-luciferase reporter assay. Xenograft tumor assay was used to explore the circ_0082182 function in vivo. The circ_0082182 level was upregulated in OXA-resistant CRC samples and cells. Downregulation of circ_0082182 suppressed OXA resistance, proliferation, invasion, and migration but promoted apoptosis of OXA-resistant CRC cells. Circ_0082182 acted as a sponge for miR-326. The regulatory role of circ_0082182 was ascribed to the miR-326 sponging function. MiR-326 directly targeted NFIB to impede OXA resistance and cancer progression in CRC cells. NFIB level was regulated by circ_0082182 via sponging miR-326. Circ_0082182 promoted tumor growth in OXA-resistant xenograft tumor model through mediating the miR-326/NFIB axis. These data suggested that circ_0082182 elevated the NFIB expression to regulate OXA resistance and CRC progression by absorbing miR-326.

Circ_0000467 Exerts an Oncogenic Role in Colorectal Cancer via miR-330-5p-Dependent Regulation of TYRO3

Colorectal cancer (CRC) remains one of the most frequent neoplasms of digestive tract worldwide. Circular RNAs (circRNAs) have been identified to serve crucial regulatory roles in the pathogenesis of human cancers. However, the role and regulatory mechanism of circ_0000467 in the progression of CRC are still unclear. The expression levels of circ_0000467, microRNA-330-5p (miR-330-5p), and tyrosine receptor kinase 3 (TYRO3) were measured by quantitative real-time polymerase chain reaction (qRT-PCR). The interaction between miR-330-5p and circ_0000467 or TYRO3 was validated by dual-luciferase reporter assay and RNA immunoprecipitation (RIP) assay. Xenograft tumor assay and Immunohistochemistry (IHC) assay were implemented to analyze CRC tumor growth in vivo. Circ_0000467 was a stable circRNA and was highly expressed in CRC tumor tissues and cells. Silencing of circ_0000467 could inhibit the proliferation, migration, invasion, and glycolysis and accelerated the apoptosis of CRC cells in vitro and hindered tumor growth in vivo. Mechanistically, circ_0000467 directly interacted with miR-330-5p and circ_0000467 depletion inhibited CRC cell malignant progression by regulating miR-330-5p. Furthermore, TYRO3 was a target of miR-330-5p and circ_0000467 upregulated TYRO3 expression by sponging miR-330-5p. Moreover, TYRO3 overexpression counteracted the inhibitory effect of miR-330-5p overexpression or circ_0000467 knockdown on CRC cell progression. Altogether, circ_0000467 knockdown suppressed CRC cell malignant development through modulating the miR-330-5p/TYRO3 network, providing a novel molecular target of CRC therapy.

Circ_0044556 Promotes the Progression of Colorectal Cancer via the miR-665-Dependent Expression Regulation of Diaphanous Homolog 1

BACKGROUND

Cancer progression can be regulated by noncoding circular RNAs. A recent study has indicated that circ_0044556 facilitated the progression of colorectal cancer.

AIM

This research was performed to explore the regulatory mechanism of circ_0044556 in CRC.

METHODS

Circ_0044556, miR-665 and Diaphanous Homolog 1 levels were detected by the quantitative real-time polymerase chain reaction. Cell proliferation analysis was performed by cell counting kit-8 assay and Edu assay. Cell cycle progression was assessed using flow cytometry. The protein examination was conducted using western blot. Transwell assay was used to analyze cell migration and invasion. Dual-luciferase reporter assay was performed to validate the interaction between targets. In vivo research was implemented by xenograft tumor assay.

RESULTS

Circ_0044556 was upregulated in colorectal cancer samples and cells. Silencing circ_0044556 inhibited cell proliferation, cell cycle progression, migration, invasion, and epithelial-mesenchymal transition in CRC cells. Circ_0044556 could directly target miR-665 and the function of circ_0044556 was associated with the regulation of miR-665. In addition, Diaphanous Homolog 1 was a target gene for miR-665 and the anti-tumor role of miR-665 in colorectal cancer was dependent on the downregulation of Diaphanous Homolog 1. Diaphanous Homolog 1 level was regulated by circ_0044556 via sponging miR-665 in CRC cells. In vivo assay suggested that circ_0044556 promoted CRC tumor growth by regulating the miR-665 and Diaphanous Homolog 1 levels.

CONCLUSION

Our findings manifested that circ_0044556 functioned as an oncogenic circRNA in colorectal cancer by mediating the miR-665/Diaphanous Homolog 1 axis, elucidating the molecular mechanism of circ_0044556 in CRC progression.

Hsa_circ_0001550 facilitates colorectal cancer progression through mediating microRNA-4262/nuclear casein kinase and cyclin-dependent kinase substrate 1 cascade

Background

Circular RNAs (circRNAs) play important roles in various malignancies, such as colorectal cancer (CRC). However, the function of hsa_circ_0001550 in CRC remains to be elucidated.

Methods

The expression levels of hsa_circ_0001550, microRNA (miR)‐4262, and nuclear casein kinase and cyclin‐dependent kinase substrate 1 (NUCKS1) were determined by real‐time qPCR. Cell biological behaviors were evaluated via colony formation assay, transwell assay, flow cytometry, and sphere formation assays. The target relationship was validated via dual‐luciferase reporter and RNA pull‐down assays. Protein expression was analyzed by western blot. Xenograft tumor model was adopted to evaluate hsa_circ_0001550 function in vivo.

Results

Hsa_circ_0001550 enrichment was enhanced in CRC tissue specimens and cell lines. Hsa_circ_0001550 absence hindered CRC cell proliferation, metastasis, stemness, and caused apoptosis. Hsa_circ_0001550 targeted miR‐4262, and hsa_circ_0001550 absence‐caused impacts were diminished by anti‐miR‐4262. MiR‐4262 targeted NUCKS1. Hsa_circ_0001550 had positive regulation on NUCKS1 expression. NUCKS1 overexpression overturned the influences of hsa_circ_0001550 silencingon CRC cell progression. Hsa_circ_0001550 interference notably blocked in vivo xenograft tumor growth.

Conclusion

Hsa_circ_0001550 facilitated CRC progression by binding to miR‐4262 to positively regulate NUCKS1 abundance.

The functional roles of the circRNA/Wnt axis in cancer

CircRNAs, covalently closed noncoding RNAs, are widely expressed in a wide range of species ranging from viruses to plants to mammals. CircRNAs were enriched in the Wnt pathway. Aberrant Wnt pathway activation is involved in the development of various types of cancers. Accumulating evidence indicates that the circRNA/Wnt axis modulates the expression of cancer-associated genes and then regulates cancer progression. Wnt pathway-related circRNA expression is obviously associated with many clinical characteristics. CircRNAs could regulate cell biological functions by interacting with the Wnt pathway. Moreover, Wnt pathway-related circRNAs are promising potential biomarkers for cancer diagnosis, prognosis evaluation, and treatment. In our review, we summarized the recent research progress on the role and clinical application of Wnt pathway-related circRNAs in tumorigenesis and progression.

Circ_VANGL1 affects proliferation, migration, and invasion of colorectal cancer cells by regulating miR-493-5p/FXR1 axis

BACKGROUND

CircRNAs are abnormally expressed in colorectal cancer (CRC) tissues, cell lines, and plasma, and are closely related to the clinical malignant characteristics of CRC. However, the expression and functional mechanism of circ_VANGL1 in CRC are still unclear. We hypothesized that circ_VANGL1 affects the proliferation, migration, and invasion of CRC cells by regulating the miR-493-5p/fragile X-related gene 1 (FXR1) axis.

AIM

To investigate the effect of circ_VANGL1 on the prolife-ration, migration, and invasion of CRC cells and the possible mechanism involved.

METHODS

Western blot was used to detect the expression of FXR1 in CRC tissues and adjacent tissues. RT-qPCR was performed to detect the expression of circ_VANGL1 and miR-493-5p. CRC cells Caco-2 were cultured in vitro and divided into si-circ_VANGL1 group, si-NC group, miR-NC group, miR-493-5p mimic group, and si-circ_VANGL1 + miR-493-5p inhibitor group. CCK-8 and clone formation assays were performed to evaluate the proliferation ability of Caco-2 cells. Transwell assay was employed to evaluate the migration and invasion ability of Caco-2 cells. Dual luciferase reporter assay was used to detect the interaction between RNAs (circ_VANGL1 and miR-493-5p, miR-493-5p, and FXR1).

RESULTS

Compared with tumor adjacent tissues, the relative expression levels of circ_VANGL1 and FXR1 protein in CRC tissue were significantly increased (P < 0.05), but the relative level of miR-493-5p was significantly decreased (P < 0.05). Compared with the si-NC group, the inhibition rate of Caco-2 cells and the relative level of miR-493-5p in the si-circ_VANGL1 group were significantly increased (P < 0.05), but the expression of FXR1 protein, the number of colonies formed, and the migration and invasion ability were significantly reduced (P < 0.05). Compared with the miR-NC group, the inhibition rate of Caco-2 cells in the miR-493-5p mimic group was significantly increased (P < 0.05), but the expression of FXR1 protein, the number of colonies formed, and the migration and invasion ability were significantly reduced (P < 0.05). Circ_VANGL1 directly bound to miR-493-5p. Compared with the si-circ_VANGL1 group, the inhibition rate of Caco-2 cells in the si-circ_VANGL1 + miR-493-5p inhibitor group was significantly reduced (P < 0.05), but the expression of FXR1 protein, the number of colonies formed, and the migration and invasion ability were significantly increased (P < 0.05).

CONCLUSION

Silencing circ_VANGL1 inhibits the proliferation, migration, and invasion of CRC cells by regulating the miR-493-5p/FXR1 axis.

Non-Coding RNAs Regulate the Resistance to Anti-EGFR Therapy in Colorectal Cancer

Colorectal cancer (CRC) is the third prevalent cancer worldwide, the morbidity and mortality of which have been increasing in recent years. As molecular targeting agents, anti-epidermal growth factor receptor (EGFR) monoclonal antibodies (McAbs) have significantly increased the progression-free survival (PFS) and overall survival (OS) of metastatic CRC (mCRC) patients. Nevertheless, most patients are eventually resistant to anti-EGFR McAbs. With the intensive study of the mechanism of anti-EGFR drug resistance, a variety of biomarkers and pathways have been found to participate in CRC resistance to anti-EGFR therapy. More and more studies have implicated non-coding RNAs (ncRNAs) primarily including microRNAs (miRNAs), long non-coding RNAs (lncRNAs), and circular RNAs (circRNAs), are widely involved in tumorigenesis and tumor progression. They function as essential regulators controlling the expression and function of oncogenes. Increasing data have shown ncRNAs affect the resistance of molecular targeted drugs in CRC including anti-EGFR McAbs. In this paper, we have reviewed the advance in mechanisms of ncRNAs in regulating anti-EGFR McAbs therapy resistance in CRC. It provides insight into exploring ncRNAs as new molecular targets and prognostic markers for CRC.

Circular RNA: A promising new star for the diagnosis and treatment of colorectal cancer

Background

Colorectal cancer (CRC) is one of the most common malignant tumors of the digestive tract. According to the research of circular RNAs in the CRC field, compared with linear RNAs, circular RNAs are a special type of noncoding RNA that are covalently closed circular structures, which have no 5' cap structure and 3' polyA tail and are not affected by RNA exonuclease and actinomycin D.

Biological functions

Notably, circular RNAs have a high degree of stability and potential effect on gene regulation. Meanwhile, circular RNAs are involved in the sponge action of microRNAs and mediate protein translation and direct binding, alternative splicing, and histone modification.

Relationships with CRC

Studies have shown that circular RNAs are related to the proliferation, invasion, recurrence, metastasis, ferroptosis, apoptosis, and chemotherapy resistance of CRC.

Conclusions

This article provides a brief review based on the source, structural characteristics, mechanisms, biological functions of circular RNAs, and the relationships between CRC.

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.

Hsa_circRNA_002144 promotes growth and metastasis of colorectal cancer through regulating miR-615-5p/LARP1/mTOR pathway

CircRNAs (circular RNAs), recently identified as a critical regulator in tumorigenesis, participate in CRC (colorectal cancer) growth. However, the role of hsa_circRNA_002144 in CRC was poorly understood. Firstly, hsa_circRNA_002144 showed significantly elevation in both of CRC tissues and cell lines, and suggested closely associated with poor prognosis in patients. Secondly, data from functional assays revealed that silence of hsa_circRNA_002144 inhibited CRC progression with reduced cell viability, proliferation, migration and invasion, while enhanced cell apoptosis. In addition, in vivo CRC growth and metastasis were also suppressed by knockdown of hsa_circRNA_002144. However, CRC progression was promoted with over-expression of hsa_circRNA_002144. Thirdly, hsa_circRNA_002144 colocalized with miR-615-5p in the cytoplasm of CRC cells, and decreased miR-615-5p expression. Moreover, miR-615-5p could target LARP1 (La ribonucleoprotein 1, translational regulator). Lastly, the suppressive effects of hsa_circRNA_002144 knockdown on CRC progression were reversed by LARP1 over-expression. In conclusion, hsa_circRNA_002144 could sponge miR-615-5p to promote CRC progression through the regulation of LARP1, providing a therapeutic target for cancer intervention.

Circular RNA profiling identifies circ102049 as a key regulator of colorectal liver metastasis

Circular RNA (circRNA) plays an essential role in the development and progression of various cancers. However, the functions and mechanisms of circRNA in colorectal liver metastasis have not been fully elucidated. We performed circRNA microarray analysis to screen differentially expressed circRNA in the pathology of colorectal liver metastasis. Quantitative real-time PCR was used to detect the expression of hsa_circ_102049 (circ102049) in colorectal cancer (CRC) samples. CRC cells were transfected with circ102049 overexpression vector or small interfering (si)RNA to assess the effects of circ102049 in vitro. Bioinformatics analysis, fluorescence in situ hybridization, RNA immunoprecipitation, RNA pull-down and luciferase reporter assays were conducted to confirm the relationship of circ102049, miR-761, miR-192-3p and FRAS1. The mechanism by which circ102049 recruits and distributes DGCR8 protein in the cytoplasm was also investigated. We found that circ102049 was highly expressed in primary CRC tumors with liver metastasis and closely correlated with the prognosis of patients with CRC. Circ102049 significantly enhanced the adhesion, migration and invasion abilities of CRC cells, and promoted CRC progression via a micro (mi)R-761/miR-192-3p-FRAS1-dependent mechanism. Notably, due to the distribution of DGCR8 protein, circ102049 may also indirectly reduce the levels of mature miR-761 and miR-192-3p in the cytoplasm. In addition, the role of circ102049 in promoting colorectal liver metastasis was confirmed in vivo. Our findings provide new evidence that circ102049 may be a potential prognostic factor in CRC, and that the circ102049-miR-761/miR-192-3p-FRAS1 axis may be an anti-metastatic target for CRC patients.