Application of Proteomics and Machine Learning Methods to Study the Pathogenesis of Diabetic Nephropathy and Screen Urinary Biomarkers.

Diabetic nephropathy (DN) has become the main cause of end-stage renal disease worldwide, causing significant health problems. Early diagnosis of the disease is quite inadequate. To screen urine biomarkers of DN and explore its potential mechanism, this study collected urine from 87 patients with type 2 diabetes mellitus (which will be classified into normal albuminuria, microalbuminuria, and macroalbuminuria groups) and 38 healthy subjects. Twelve individuals from each group were then randomly selected as the screening cohort for proteomics analysis and the rest as the validation cohort. The results showed that humoral immune response, complement activation, complement and coagulation cascades, renin-angiotensin system, and cell adhesion molecules were closely related to the progression of DN. Five overlapping proteins (KLK1, CSPG4, PLAU, SERPINA3, and ALB) were identified as potential biomarkers by machine learning methods. Among them, KLK1 and CSPG4 were positively correlated with the urinary albumin to creatinine ratio (UACR), and SERPINA3 was negatively correlated with the UACR, which were validated by enzyme-linked immunosorbent assay (ELISA). This study provides new insights into disease mechanisms and biomarkers for early diagnosis of DN.

Investigating metabolic dysregulation in serum of triple transgenic Alzheimer's disease male mice: implications for pathogenesis and potential biomarkers.

Alzheimer's disease (AD) is a multifactorial neurodegenerative disease that lacks convenient and accessible peripheral blood diagnostic markers and effective drugs. Metabolic dysfunction is one of AD risk factors, which leaded to alterations of various metabolites in the body. Pathological changes of the brain can be reflected in blood metabolites that are expected to explain the disease mechanisms or be candidate biomarkers. The aim of this study was to investigate the changes of targeted metabolites within peripheral blood of AD mouse model, with the purpose of exploring the disease mechanism and potential biomarkers. Targeted metabolomics was used to quantify 256 metabolites in serum of triple transgenic AD (3 × Tg-AD) male mice. Compared with controls, 49 differential metabolites represented dysregulation in purine, pyrimidine, tryptophan, cysteine and methionine and glycerophospholipid metabolism. Among them, adenosine, serotonin, N-acetyl-5-hydroxytryptamine, and acetylcholine play a key role in regulating neural transmitter network. The alteration of S-adenosine-L-homocysteine, S-adenosine-L-methionine, and trimethylamine-N-oxide in AD mice serum can served as indicator of AD risk. The results revealed the changes of metabolites in serum, suggesting that metabolic dysregulation in periphery in AD mice may be related to the disturbances in neuroinhibition, the serotonergic system, sleep function, the cholinergic system, and the gut microbiota. This study provides novel insights into the dysregulation of several key metabolites and metabolic pathways in AD, presenting potential avenues for future research and the development of peripheral biomarkers.

A novel selective ERK1/2 inhibitor, Laxiflorin B, targets EGFR mutation subtypes in non-small-cell lung cancer.

Extracellular regulated protein kinases 1/2 (ERK1/2) are key members of multiple signaling pathways, including the ErbB axis. Ectopic ERK1/2 activation contributes to various types of cancer, especially drug resistance to inhibitors of RTK, RAF and MEK, and specific ERK1/2 inhibitors are scarce. In this study, we identified a potential novel covalent ERK inhibitor, Laxiflorin B, which is a herbal compound with anticancer activity. However, Laxiflorin B is present at low levels in herbs; therefore, we adopted a semi-synthetic process for the efficient production of Laxiflorin B to improve the yield. Laxiflorin B induced mitochondria-mediated apoptosis via BAD activation in non-small-cell lung cancer (NSCLC) cells, especially in EGFR mutant subtypes. Transcriptomic analysis suggested that Laxiflorin B inhibits amphiregulin (AREG) and epiregulin (EREG) expression through ERK inhibition, and suppressed the activation of their receptors, ErbBs, via a positive feedback loop. Moreover, mass spectrometry analysis combined with computer simulation revealed that Laxiflorin B binds covalently to Cys-183 in the ATP-binding pocket of ERK1 via the D-ring, and Cys-178 of ERK1 through non-inhibitory binding of the A-ring. In a NSCLC tumor xenograft model in nude mice, Laxiflorin B also exhibited strong tumor suppressive effects with low toxicity and AREG and EREG were identified as biomarkers of Laxiflorin B efficacy. Finally, Laxiflorin B-4, a C-6 analog of Laxiflorin B, exhibited higher binding affinity for ERK1/2 and stronger tumor suppression. These findings provide a new approach to tumor inhibition using natural anticancer compounds.

The Moonlighting Function of Soybean Disordered Methyl-CpG-Binding Domain 10c Protein.

Intrinsically disordered proteins (IDPs) are multifunctional due to their ability to adopt different structures depending on the local conditions. The intrinsically disordered regions of methyl-CpG-binding domain (MBD) proteins play important roles in regulating growth and development by interpreting DNA methylation patterns. However, whether MBDs have a stress-protective function is far from clear. In this paper, soybean GmMBD10c protein, which contains an MBD and is conserved in Leguminosae, was predicted to be located in the nucleus. It was found to be partially disordered by bioinformatic prediction, circular dichroism and a nuclear magnetic resonance spectral analysis. The enzyme activity assay and SDS-PAGE results showed that GmMBD10c can protect lactate dehydrogenase and a broad range of other proteins from misfolding and aggregation induced by the freeze-thaw process and heat stress, respectively. Furthermore, overexpression of GmMBD10c enhanced the salt tolerance of Escherichia coli. These data validate that GmMBD10c is a moonlighting protein with multiple functions.

The N-Terminal Region of Soybean PM1 Protein Protects Liposomes during Freeze-Thaw.

Late embryogenesis abundant (LEA) group 1 (LEA_1) proteins are intrinsically disordered proteins (IDPs) that play important roles in protecting plants from abiotic stress. Their protective function, at a molecular level, has not yet been fully elucidated, but several studies suggest their involvement in membrane stabilization under stress conditions. In this paper, the soybean LEA_1 protein PM1 and its truncated forms (PM1-N: N-terminal half; PM1-C: C-terminal half) were tested for the ability to protect liposomes against damage induced by freeze-thaw stress. Turbidity measurement and light microscopy showed that full-length PM1 and PM1-N, but not PM1-C, can prevent freeze-thaw-induced aggregation of POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine) liposomes and native thylakoid membranes, isolated from spinach leaves (Spinacia oleracea). Particle size distribution analysis by dynamic light scattering (DLS) further confirmed that PM1 and PM1-N can prevent liposome aggregation during freeze-thaw. Furthermore, PM1 or PM1-N could significantly inhibit membrane fusion of liposomes, but not reduce the leakage of their contents following freezing stress. The results of proteolytic digestion and circular dichroism experiments suggest that PM1 and PM1-N proteins bind mainly on the surface of the POPC liposome. We propose that, through its N-terminal region, PM1 functions as a membrane-stabilizing protein during abiotic stress, and might inhibit membrane fusion and aggregation of vesicles or other endomembrane structures within the plant cell.

Glutaminyl cyclase inhibitor contributes to the regulation of HSP70, HSP90, actin, and ribosome on gene and protein levels in vitro.

Because of the crucial roles of upregulated glutaminyl cyclase (QC) in the initiation and development of Alzheimer's disease (AD), QC inhibitors are supposed as disease-modifying agents for the treatment of AD. And reported compounds encourage this hypothesis greatly based on the remarkable anti-AD effects in vivo. To illustrate the mechanism in detail, the actions of a selected QC inhibitor (23) were assessed firstly in a cell system here. It was demonstrated that QC activities and the generation of pyroglutamate-modified ß-amyloids in PC12 cells were both inhibited obviously after the treatment of 23. A total of 13 and 15 genes were up- and downregulated significantly in treated cells by RNA-sequencing analysis. Quantitative real-time polymerase chain reaction, enzyme-linked immunosorbent assay, WB, and immunofluorescence analysis supported the effects of 23 on the transcriptome of PC12 cells consequently. The expressions of chaperones, heat shock proteins (HSP) 70, and 90, were upreglutated, while gene expression of actin and the level of encoded protein were reduced significantly in PC12 cells with the treatment. Furthermore, the regulations of ribosome were observed after the treatment. These results indicate the potency of 23 to improve the translation, expression and folding regulation of proteins and affect the multivalent cross-linking of cytoskeletal protein and other proteins subsequently in the cell system and might contribute to the understanding of the mechanism of QC inhibitor as potential anti-AD agents.

RXXPEG motif of MERIT40 is required to maintain spindle structure and function through its interaction with Tankyrase1.

Deubiquitinase BRISC complex plays important role in the maintenance of spindle structure and function; however, the underlying mechanism remains largely undefined. Here we demonstrated that MERIT40, a core component of BRISC complex, directly interacts with the RXXPEG motif in the ARC-V domain of Tankyrase1(TNKS1). Mutation of the RXXPEG motif in the MERIT40 (R28A) disrupted its interaction with TNKS1. Consistent with these data, R28A mutant cells displayed multiple mitotic defects including aberrant spindle assembly and chromosome misalignment. These results support a critical role of RXXPEG motif of MERIT40 in BRISC-mediated regulation of TNKS1 function during spindle assembly.

Novel Bioactive Peptides from Meretrix meretrix Protect Caenorhabditis elegans against Free Radical-Induced Oxidative Stress through the Stress Response Factor DAF-16/FOXO.

The hard clam Meretrix meretrix, which has been traditionally used as medicine and seafood, was used in this study to isolate antioxidant peptides. First, a peptide-rich extract was tested for its protective effect against paraquat-induced oxidative stress using the nematode model Caenorhabditis elegans. Then, three novel antioxidant peptides; MmP4 (LSDRLEETGGASS), MmP11 (KEGCREPETEKGHR) and MmP19 (IVTNWDDMEK), were identified and were found to increase the resistance of nematodes against paraquat. Circular dichroism spectroscopy revealed that MmP4 was predominantly in beta-sheet conformation, while MmP11 and MmP19 were primarily in random coil conformation. Using transgenic nematode models, the peptides were shown to promote nuclear translocation of the DAF-16/FOXO transcription factor, a pivotal regulator of stress response and lifespan, and induce the expression of superoxide dismutase 3 (SOD-3), an antioxidant enzyme. Analysis of DAF-16 target genes by real-time PCR reveals that sod-3 was up-regulated by MmP4, MmP11 and MmP19 while ctl-1 and ctl-2 were also up-regulated by MmP4. Further examination of daf-16 using RNA interference suggests that the peptide-increased resistance of C. elegans to oxidative stress was DAF-16 dependent. Taken together, these data demonstrate the antioxidant activity of M. meretrix peptides, which are associated with activation of the stress response factor DAF-16 and regulation of the antioxidant enzyme genes.

Fatty acid and metabolomic profiling approaches differentiate heterotrophic and mixotrophic culture conditions in a microalgal food supplement 'Euglena'.

BACKGROUND: Microalgae have been recognized as a good food source of natural biologically active ingredients. Among them, the green microalga Euglena is a very promising food and nutritional supplements, providing high value-added poly-unsaturated fatty acids, paramylon and proteins. Different culture conditions could affect the chemical composition and food quality of microalgal cells. However, little information is available for distinguishing the different cellular changes especially the active ingredients including poly-saturated fatty acids and other metabolites under different culture conditions, such as light and dark. RESULTS: In this study, together with fatty acid profiling, we applied a gas chromatography-mass spectrometry (GC-MS)-based metabolomics to differentiate hetrotrophic and mixotrophic culture conditions. CONCLUSIONS: This study suggests metabolomics can shed light on understanding metabolomic changes under different culture conditions and provides a theoretical basis for industrial applications of microalgae, as food with better high-quality active ingredients.

Inhibitory effect of flavonoids on human glutaminyl cyclase.

Glutaminyl cyclase (QC) plays an important role in the pathogenesis of Alzheimer's disease (AD) and can be a potential target for the development of novel anti-AD agents. However, the study of QC inhibitors are still less. Here, phenol-4' (R1-), C5-OH (R2-) and C7-OH (R3-) modified apigenin derivatives were synthesized as a new class of human QC (hQC) inhibitors. The efficacy investigation of these compounds was performed by spectrophotometric assessment and the structure-activity relationship (SAR) was evaluated. Molecular docking was also carried out to analyze the binding mode of the synthesized flavonoid to the active site of hQC.

MicroRNA-1205 promotes breast cancer cell metastasis by regulating epithelial-to-mesenchymal transition via targeting of CDK3.

Metastasis poses a huge obstacle to the survival of breast cancer patients. The microRNA miR-1205 acts as a tumor suppressor in various cancers, but its roles in breast cancer and metastasis remain unclear. To elucidate its function in breast cancer progression, we analyzed miR-1205 expression in human tumor samples and carried out a series of functional studies in in vitro and in vivo. miR-1205 was expressed more highly in metastatic breast tumor samples than in non-metastatic samples and was associated with lymph node metastasis, clinical stage, and poor prognosis. Moreover, miR-1205 promoted breast cancer cell invasiveness in vitro and metastasis in mice by directly targeting CDK3 and reducing CDK3 protein levels. We also showed that CDK3 interacts with Snail protein, inducing Snail degradation via the ubiquitin-proteasome system and potentially affecting epithelial-to-mesenchymal transition. Furthermore, analysis of clinical tissue samples indicated that CDK3 and miR-1205 levels were inversely correlated in lymph node metastasis-positive primary tumors. This study demonstrated the pro-metastatic role of miR-1205 in breast cancer, mediated via a novel miR-1205/CDK3/Snail axis. Moreover, we identified miR-1205 and CDK3 as potential markers of invasion and progression in breast cancer.

Physicochemical characterization and cosmetic application of kelp blanching water polysaccharides.

Seaweeds account for half of global mariculture and have become a key player in bio-based industries. Seaweed process typically starts with hot water blanching that helps reduce postharvest quality deterioration but also generates large amounts of hydrothermal waste. This study aims to explore the feasibility of isolating water-soluble biopolymers from seaweed hydrothermal waste and their potential applications. Using Saccharina japonica (formerly Laminaria japonica) blanching water as example, 2.9 g/L of polymeric substances were efficiently isolated by ultrafiltration, implying biopolymer coproduction potential of ~5.8 kt from blanching wastewater of current kelp industry. Physicochemical characterizations revealed polysaccharidic nature of the biopolymers, with high contents of fucose, uronic acids and sulfate, showing distinct but also overlapping structural features with hot water-extracted kelp polysaccharides. The main fraction of the blanching water polymers after anion exchange chromatography was acidic polysaccharide, the major backbone residues of which were (1-4) linked mannopyranose, (1-4) linked gulopyranose and (1-2) linked fucopyranose while the branched residues were primarily 1,3,4-, 1,2,4- and 1,4,6-linked hexoses but also 1,3,4-fucopyranose. Furthermore, the polysaccharides were found to have a good compatibility in cosmetic creams with added cohesiveness and freshness, demonstrating the application potential of such natural biopolymers from currently underexplored seaweed blanching water.

Dezocine induces apoptosis in human cervical carcinoma Hela cells via the endoplasmic reticulum stress pathway.

Dezocine, a dual agonist and antagonist of the µ-opioid receptor and κ-opioid receptor, is widely used as an analgesic in China. At present, there are few studies on anti-tumor effects of dezocine, most of which are used to treat cancer pain. However, it has recently been reported that dezocine can induce apoptosis of triple negative breast cancer cells. Dezocine may have some anti-tumor activity, but the effect and potential mechanism of dezocine in the treatment of other types of cancer remain to be fully studied. The purpose of the present study was to investigate the effect of dezocine on human Hela cervical carcinoma cells, and to elucidate the underlying molecular mechanisms. We performed CCK-8 assays, clone formation assays, xenograft, flow cytometry analysis, western blot and RNA-seq analysis to evaluate the effects of dezocine on Hela cells. In addition, the role of endoplasmic reticulum (ER) stress in dezocine-induced apoptosis was investigated using qPCR and western blot analysis. Dezocine inhibited Hela cell viability in dose-dependent and time-dependent manners, and notably did not achieve this effect by targeting the opioid receptors. Further mechanistic studies demonstrated that dezocine activated ER stress by upregulating the expression of GRP78, IRE1 and p-JNK, and that dezocine-induced apoptosis was attenuated when the ER stress pathway was blocked. Our results provide a foundation to support the redefinition of dezocine as a novel, adjuvant treatment for patients with cervical cancer, although further research will be required to support its application in clinical practice.

Polyproline II structure is critical for the enzyme protective function of soybean Em (LEA1) conserved domains.

Group 1 late embryogenesis-abundant (LEA1) proteins protect enzyme activity from dehydration and are structurally conserved with three different 20 amino acid motifs in the N-terminal, middle and C-terminal domains. Three soybean Em (LEA1) domain peptides (Em-N, Em-2M and Em-C) covering these respective motifs were constructed and had differential protective ability on lactate dehydrogenase against freeze-thaw: Em-C > Em-2M > Em-N. CD spectroscopy revealed that Em-2M and Em-C contained both polyproline II (PII) helical structure and α-helix, while Em-N had a high potential to form α-helix but did not contain PII structure. The PII helical structure between the third and fifth glycine in the middle motif was shown, through site mutation, to be critical for the enzyme protective function of soybean Em (LEA1) conserved domain under freezing stress.

Current research advances in microRNA-mediated regulation of Krüppel-like factor 4 in cancer: a narrative review.

OBJECTIVE: The purpose of this study was to investigate the miRNAs and related mechanisms that regulates KLF4 in different cancers. Furthermore, we summarized the potential targets of miRNAs regulating the KLF4 pathway in cancer research. BACKGROUND: MiRNAs are single-stranded, endogenous non-coding small RNAs, some of which are related to human cancers. miRNAs carry out post-transcriptional gene regulation through translation inhibition and degradation of target messenger RNAs (mRNAs) via complementarily pairing with their 3' untranslated regions. KLF4 is an important transcription factor with complex involvement in cancer. Increasing evidence shows that miRNAs are dysregulated in cancer and can regulate cancer-related signaling pathways, thereby affecting tumor progression. METHODS: Systematic scientific literature searches were undertaken on PubMed using the following terms: "miRNAs and KLF4", "KLF4 and cancer", "miRNAs and cancer", and "miRNAs, KLF4 and cancer". Relevant papers were retrieved and further results were found by reviewing related papers and the references of the retrieved papers. We then conducted a narrative overview of the literature to summarize the results of the papers. CONCLUSIONS: The role of KLF4 in cancer varies in a context-dependent manner. KLF4-regulating miRNAs in different tumors include miR-124, miR-9-5p, miR-10b, miR-18a, miR-25-3p, miR-10b, miR-92a, miR-103, miR-155, miR-135b-5p, miR-32-5p, miR-148-3p, miR-152-3p, miR-10b, miR-25, miR-3120-5p, miR-7, miR-1233-3p, miR-10b, miR-145, miR-139-5p, miR-16, miR-152, miR-375, and miR-145.

Dezocine, An Opioid Analgesic, Exerts Antitumor Effects in Triple-Negative Breast Cancer by Targeting Nicotinamide Phosphoribosyltransferase.

Opioids are a potential adjuvant treatment for certain cancers; while they are primarily used to relieve chronic pain, these drugs may also affect cancer progression and recurrence. Dezocine is one opioid commonly used in China, but its effects on cancer cells are unknown. Here, we demonstrated the inhibitory effect of dezocine on triple-negative breast cancer (TNBC) cells, and determined the underlying molecular mechanism. We found that dezocine suppressed cell proliferation, migration and invasion, and induced apoptosis in TNBC cells. Xenograft models demonstrated the inhibitory effects of dezocine treatment on TNBC tumor growth in vivo. The anticancer effects of dezocine were independent of opioid receptors, which are not highly expressed by normal breast or breast cancer tissues. A pull-down assay and LC-MS/MS analysis indicated that dezocine directly targets NAMPT: computer modeling verified that the free energy of dezocine kinetically bound into the pocket of NAMPT was -17.4 kcal/mol. Consequently, dezocine treatment inhibited NAMPT enzyme activity, resulting in cellular NAD abolishment. We confirmed the dezocine-induced inhibition of cell proliferation by both NAMPT knockdown and upon treatment with the inhibitor FK866. Our results suggest that both dezocine and NAMPT might represent novel therapeutic targets for TNBC.

Tacrolimus and ascomycin inhibit melanoma cell growth, migration and invasion via targeting nuclear factor of activated T-cell 3.

Melanoma is the most malignant form of skin cancer with high metastatic potential. Nuclear factor of activated T-cells (NFATs) are discovered as transcription factors that regulate the expression of proinflammatory cytokines and other genes during the immune response. Among five NFAT members, NFAT3 is exclusively not expressed in immune cells and its role in progression of different types of cancer remains controversial. Our previous study showed that NFAT3 was highly expressed in skin cancer compared with normal skin tissues and critical for melanoma cell survival and tumor growth. Here, we reported that knockdown of NFAT3 expression, as well as treatment with the calcineurin (CaN) inhibitors, tacrolimus (FK506) or ascomycin (FK520) inhibits melanoma cell migration and invasion, and also proliferation and colony formation. Mechanistic studies revealed that FK506 or FK520 blocked the nuclear translocation and reduced the transcriptional activity of NFAT3. These data support that the antimelanoma effect of FK506 and FK520 is partially mediated by inhibiting the oncogenic factor NFAT3, suggesting that therapeutics based on NFAT3 inhibition may be effective in clinical melanoma treatment.

Therapeutic potential of targeting MKK3-p38 axis with Capsaicin for Nasopharyngeal Carcinoma.

Background: Capsaicin is an active compound found in plants of the Capsicum genus; it has a range of therapeutic benefits, including anti-tumor effects. Here we aimed to delineate the inhibitory effects of capsaicin on nasopharyngeal carcinoma (NPC). Methods: The anti-cancer effects of capsaicin were confirmed in NPC cell lines and xenograft mouse models, using CCK-8, clonogenic, wound-healing, transwell migration and invasion assays. Co-immunoprecipitation, western blotting and pull-down assays were used to determine the effects of capsaicin on the MKK3-p38 axis. Cell proliferation and EMT marker expression were monitored in MKK3 knockdown (KD) or over-expression NPC cell lines treated with or without capsaicin. Finally, immunohistochemistry was performed on NPC specimens from NPC patients (n = 132) and the clinical relevance was analyzed. Results: Capsaicin inhibited cell proliferation, mobility and promoted apoptosis in NPC cells. Then we found that capsaicin directly targets p38 for dephosphorylation. As such, MKK3-induced p38 activation was inhibited by capsaicin. Furthermore, we found that capsaicin-induced inhibition of cell motility was mediated by fucokinase. Xenograft models demonstrated the inhibitory effects of capsaicin treatment on NPC tumor growth in vivo, and analysis of clinical NPC samples confirmed that MKK3 phosphorylation was associated with NPC tumor growth and lymphoid node metastasis. Conclusions: The MKK3-p38 axis represents a potential therapeutic target for capsaicin. MKK3 phosphorylation might serve as a biomarker to identify NPC patients most likely to benefit from adjunctive capsaicin treatment.

Glutaminyl cyclase inhibitor exhibits anti-inflammatory effects in both AD and LPS-induced inflammatory model mice.

Up-regulated glutaminyl cyclase (QC) plays crucial roles in the initiation of Alzheimer's disease (AD) and kinds of chronic diseases mediated by inflammation. QC is supposed as a novel target for the therapeutics of these diseases. Here, we explored the anti-inflammation effects of diphenyl conjugated imidazole (DPCI) derivatives which were previously designed, synthesized and evaluated as novel QC inhibitors for AD treatment in our lab. Behavioral tests, QC activity assay, histology and ELISA analysis were conducted on both AD and lipopolysaccharides (LPS)-induced inflammatory model mice. It was shown that behavioral and cognitive performance in AD mice treated with the selected compound DPCI-23 were enhanced notably. QC activity, the formation of pE-Aß and Aß plaques and the activation of astrocytes and microglia cells in AD mice brains were inhibited, and the levels of inflammatory factors such as IL-6, IL-1ß and TNF-α in serum were reduced remarkably. Furthermore, elevated QC activity in inflammatory mice brains was also inhibited, and levels of IL-1ß, IL-1ra, TNF-α and CCL2 in serum, kidneys and brains together with the activated astrocytes and microglia cells in brains were all repressed significantly after the treatment of DPCI-23. These findings observed in this research demonstrated the anti-inflammation potency of DPCI-23 in modal of AD and inflammation by inhibiting QC activity, and may contribute to the employment of QC inhibitors for the prevention and treatment of AD and other inflammatory diseases.

Recent progress in circular RNAs in human cancers.

Circular RNAs (circRNAs) are a large class of endogenous RNAs, formed by exon skipping or back-splicing events as covalently closed loops, which are expressed abundantly in mammalian cells. Although their biological functions remain largely unknown, recent studies show that circRNAs have three main functions in mammalian cells. First, circRNAs can regulate transcription and RNA splicing. Second, circRNAs function as microRNA (miRNA) sponges. Third, they can be translated into protein driven by N6-methyladenosine modification. Taking advantage of RNA sequencing (RNA-seq) technology, the expressions of circRNAs were found to be dysregulated in all types of cancer cell lines, tumor tissues, and even plasma samples from patients, which correlated with certain clinical characteristics, suggesting the potential roles of circRNAs in tumor progression. Considering their conserved sequences and stable structures, circRNAs were deemed to be promising biomarkers for the early diagnosis and prognosis prediction of cancer. In this review, we describe briefly the formation and properties of circRNAs, and focus mainly on recent progress in research into their function, regulation, and clinical relevance in different cancers.