Mounting evidences indicate that circular RNAs (circRNAs) have a vital role in human diseases, especially cancers. More recently, circHIPK3, a particularly abundant circRNA, was proposed to be involved in tumorigenesis. However, its role in colorectal cancer (CRC) has not been explored. In this study, we found circHIPK3 was significantly upregulated in CRC tissues and cell lines, at least in part, due to c-Myb overexpression and positively correlated with metastasis and advanced clinical stage. Moreover, Cox multivariate survival analysis showed that high-level expression of circHIPK3 was an independent prognostic factor of poor overall survival (OS) in CRC (hazard ratio [HR] = 2.75, 95% confidence interval [CI] 1.74–6.51, p = 0.009). Functionally, knockdown of circHIPK3 markedly inhibited CRC cells proliferation, migration, invasion, and induced apoptosis in vitro and suppressed CRC growth and metastasis in vivo. Mechanistically, by using biotinylated-circHIPK3 probe to perform RNA pull-down assay in CRC cells, we identified miR-7 was the only one microRNA that was abundantly pulled down by circHIPK3 in both HCT116 and HT29 cells and these interactions were also confirmed by biotinylated miR-7 pull-down and dual-luciferase reporter assays. Overexpression of miR-7 mimicked the effect of circHIPK3 knockdown on CRC cells proliferation, migration, invasion, and apoptosis. Furthermore, ectopic expression of circHIPK3 effectively reversed miR-7-induced attenuation of malignant phenotypes of CRC cells by increasing the expression levels of miR-7 targeting proto-oncogenes (FAK, IGF1R, EGFR, YY1). Remarkably, the combination of circHIPK3 silencing and miR-7 overexpression gave a better effect on tumor suppression both in vitro and in vivo than did circHIPK3 knockdown or miR-7 overexpression alone. Taken together, our data indicate that circHIPK3 may have considerable potential as a prognostic biomarker in CRC, and support the notion that therapeutic targeting of the c-Myb/circHIPK3/miR-7 axis may be a promising treatment approach for CRC patients.

BackgroundRecent studies indicate that circular RNA (circRNA) plays a pivotal role in cancer progression. Here, we sought to investigate its role in breast cancer.MethodsCircANKS1B (a circRNA originated from exons 5 to 8 of the ANKS1B gene, hsa_circ_0007294) was identified by RNA-sequencing and validated by qRT-PCR and Sanger sequencing. Clinical breast cancer samples were used to evaluate the expression of circANKS1B and its associations with clinicopathological features and prognosis. Gain- and loss-of-function experiments in cell lines and mouse xenograft models were performed to support clinical findings and elucidate the function and underlying mechanisms of circANKS1B in breast cancer.ResultsCircANKS1B was significantly up-regulated in triple-negative breast cancer (TNBC) compared with non-TNBC tissues and cell lines. Increased circANKS1B expression was closely associated with lymph node metastasis and advanced clinical stage and served as an independent risk factor for overall survival of breast cancer patients. Functional studies revealed that circANKS1B promoted breast cancer invasion and metastasis both in vitro and in vivo by inducing epithelial-to-mesenchymal transition (EMT), while had no effect on breast cancer growth. Mechanistically, circANKS1B abundantly sponged miR-148a-3p and miR-152-3p to increase the expression of transcription factor USF1, which could transcriptionally up-regulate TGF-β1 expression, resulting in activating TGF-β1/Smad signaling to promote EMT. Moreover, we found that circANKS1B biogenesis in breast cancer was promoted by splicing factor ESRP1, whose expression was also regulated by USF1.ConclusionsOur data uncover an essential role of the novel circular RNA circANKS1B in the metastasis of breast cancer, which demonstrate that therapeutic targeting of circANKS1B may better prevent breast cancer metastasis.Electronic supplementary materialThe online version of this article (10.1186/s12943-018-0914-x) contains supplementary material, which is available to authorized users.

BackgroundMounting evidence demonstrates that long noncoding RNAs (lncRNAs) have critical roles during the initiation and progression of cancers. In this study, we report that the small nucleolar RNA host gene 1 (SNHG1) is involved in colorectal cancer progression.MethodsWe analyzed RNA sequencing data to explore abnormally expressed lncRNAs in colorectal cancer. The effects of SNHG1 on colorectal cancer were investigated through in vitro and in vivo assays (i.e., CCK-8 assay, colony formation assay, flow cytometry assay, EdU assay, xenograft model, immunohistochemistry, and western blot). The mechanism of SNHG1 action was explored through bioinformatics, RNA fluorescence in situ hybridization, luciferase reporter assay, RNA pull-down assay, chromatin immunoprecipitation assay and RNA immunoprecipitation assay.ResultsOur analysis revealed that SNHG1 was upregulated in human colorectal cancer tissues, and high SNHG1 expression was associated with reduced patient survival. We also found that high SNHG1 expression was partly induced by SP1. Moreover, SNHG1 knockdown significantly repressed colorectal cancer cells growth both in vitro and in vivo. Mechanistic investigations demonstrated that SNHG1 could directly interact with Polycomb Repressive Complex 2 (PRC2) and modulate the histone methylation of promoter of Kruppel like factor 2 (KLF2) and Cyclin dependent kinase inhibitor 2B (CDKN2B) in the nucleus. In the cytoplasm, SNHG1 acted as a sponge for miR-154-5p, reducing its ability to repress Cyclin D2 (CCND2) expression.ConclusionsTaken together, the results of our studies illuminate how SNHG1 formed a regulatory network to confer an oncogenic function in colorectal cancer and suggest that SNHG1 may serve as a potential target for colorectal cancer diagnosis and treatment.Electronic supplementary materialThe online version of this article (10.1186/s12943-018-0894-x) contains supplementary material, which is available to authorized users.

Background Colorectal cancer (CRC) is one of the leading causes of tumor-related death worldwide, and its main cause of death is distant metastasis. Methyltransferase-like 14(METTL14), a major RNA N6-adenosine methyltransferase, is involved in tumor progression via regulating RNA function. The goal of the study is to uncover the biological function and molecular mechanism of METTL14 in CRC. Methods Quantitative real-time PCR (qRT-PCR), western blot and immunohistochemical (IHC) assays were employed to detect METTL14 and SOX4 in CRC cell lines and tissues. The biological functions of METTL14 were demonstrated using in vitro and in vivo experiments. Chromatin immunoprecipitation (ChIP), Transcrptomic RNA sequencing (RNA-Seq), m6A-RNA immunoprecipitation sequencing (MeRIP-Seq), RNA immunoprecipitation and luciferase reporter assays were used to explore the mechanism of METTL14 action. Results METTL14 expression was significantly downregulated in CRC and decreased METTL14 was associated with poor overall survival (OS). Both the univariate and multivariate Cox regression analysis indicated that METTL14 was an independent prognostic factor in CRC. Moreover, lysine-specific histone demethylase 5C(KDM5C)-mediated demethylation of histone H3 lysine 4 tri-methylation(H3K4me3) in the promoter of METTL14 inhibited METTL14 transcription. Functionally, we verified that METTL14 inhibited CRC cells migration, invasion and metastasis through in vitro and in vivo assays, respectively. Furthermore, we identified SRY-related high-mobility-group box 4(SOX4) as a target of METTL14-mediated m6A modification. Knockdown of METTL14 markedly abolished SOX4 mRNA m6A modification and elevated SOX4 mRNA expression. We also revealed that METTL14-mediated SOX4 mRNA degradation relied on the YTHDF2-dependent pathway. Lastly, we demonstrated that METTL14 might inhibit CRC malignant process partly through SOX4-mediated EMT process and PI3K/Akt signals. Conclusions Decreased METTL14 facilitates tumor metastasis in CRC, suggesting that METTL14 might be a potential prognostic biomarker and effective therapeutic target for CRC. Graphical abstract

Background Emerging studies suggest that long non-coding RNAs (lncRNAs) play crucial roles in colorectal cancer (CRC). Here, we report a lncRNA, SATB2-AS1, which is specifically expressed in colorectal tissue and is significantly reduced in CRC. We systematically elucidated its functions and possible molecular mechanisms in CRC. Methods LncRNA expression in CRC was analyzed by RNA-sequencing and RNA microarrays. The expression level of SATB2-AS1 in tissues was determined by quantitative reverse transcription polymerase chain reaction (qRT-PCR) and in situ hybridization (ISH). The functional role of SATB2-AS1 in CRC was investigated by a series of in vivo and in vitro assays. RNA pull-down, RNA immunoprecipitation (RIP), chromatin immunoprecipitation (ChIP), chromatin isolation by RNA purification (ChIRP), Bisulfite Sequencing PCR (BSP) and bioinformatics analysis were utilized to explore the potential mechanisms of SATB2-AS1. Results SATB2-AS1 is specifically expressed in colorectal tissues and downregulated in CRC. Survival analysis indicates that decreased SATB2-AS1 expression is associated with poor survival. Functional experiments and bioinformatics analysis revealed that SATB2-AS1 inhibits CRC cell metastasis and regulates TH1-type chemokines expression and immune cell density in CRC. Mechanistically, SATB2-AS1 directly binds to WDR5 and GADD45A, cis -activating SATB2 (Special AT-rich binding protein 2) transcription via mediating histone H3 lysine 4 tri-methylation (H3K4me3) deposition and DNA demethylation of the promoter region of SATB2. Conclusions This study reveals the functions of SATB2-AS1 in CRC tumorigenesis and progression, suggesting new biomarkers and therapeutic targets in CRC. Electronic supplementary material The online version of this article (10.1186/s12943-019-1063-6) contains supplementary material, which is available to authorized users.

The TGF-␤ superfamily of secreted signaling molecules represents a group of evolutionarily-conserved proteins that control multiple cellular processes in a range of organisms (for reviews, see Massagué 1998;. The cellular responses to TGF-␤ ligands are mediated by a highly conserved signal transduction pathway involving a family of transmembrane receptor serine/threonine kinases and cytoplasmic signal transducers, the Smad proteins. The activated receptors phosphorylate the receptor-regulated Smads that form complexes with the co-Smads, translocate to the nucleus, and regulate the expression of target genes by direct interaction with DNA or other transcription factors (for reviews, see Massagué and Wotton 2000; ten Dijke 2000).There are several TGF-␤ family members in Drosophila, among which Dpp is the best-studied (for review, see Podos and Ferguson 1999). The Dpp signal is transduced to the nucleus by Smad complexes containing the receptor-regulated Mad protein and the co-Smad Medea (for review, see Raftery and Sutherland 1999). Mad and Medea have been shown to bind DNA and activate several Dpp target genes. For example, Mad and Medea bind to specific sites in the Dpp response element of the tinman (tin) gene, the tin-D enhancer (Xu et al. 1998), and these sites were shown to be essential for normal tin expression in the embryonic visceral mesoderm. Direct Mad-DNA contact also plays a role in the transcriptional activation of the Ubx gene in the developing midgut (Eresh et al. 1997) and the vestigial (vg) gene in the imaginal wing disc (Kim et al. 1996(Kim et al. , 1997.Mad/Medea binding sites contain repeats of the degenerate sequence GNCN, which is consistent with the sequence of the Smad binding element (SBE) GTCT found in the response regions of TGF-␤ and activin target genes (for review, see ten Dijke 2000). However, the low complexity of the recognition sites and their low affinity for Smad binding (Shi et al. 1998) cannot explain the highly specific target gene responses to TGF-␤ signaling. It was therefore proposed that in many cases Smad proteins achieve specific interactions with cognate DNA by interacting with DNA-binding partners (for review, see ten Dijke 2000).One interesting feature of Dpp and other members of the TGF-␤ family, such as activin and the bone morphogenic proteins (BMPs), is that they can function as morphogens (for review, see Podos and Ferguson 1999). Mor-

BackgroundAbnormal expression of long non-coding RNAs (lncRNAs) has been found in almost all human tumors, providing numerous potential diagnostic biomarkers, prognostic biomarkers, and therapeutic targets.MethodsWe analyzed RNA sequencing data to explore abnormally expressed lncRNAs in colorectal cancer (CRC). The functions of small nucleolar RNA host gene 6 (SNHG6) were investigated through in vitro and in vivo assays (CCK-8 assay, colony formation assay, flow cytometry assay, EdU assay, wound healing assay, transwell assay, and xenograft model). The mechanism of action of SNHG6 was explored through bioinformatics, RNA fluorescence in situ hybridization, luciferase reporter assay, RNA pull-down assay, chromatin immunoprecipitation assay, and RNA immunoprecipitation assay.ResultsWe identified aberrantly expressed lncRNAs in CRC. We found that elevated SNHG6 expression was associated with poor prognosis and CRC progression. We also demonstrated that the high SNHG6 expression was partly due to DNA copy number gains and SP1 induction. Functional studies showed that SNHG6 promoted CRC cell growth, migration, and invasion both in vitro and in vivo. Mechanistically, we found that SNHG6 expressed predominantly in the cytoplasm. SNHG6 could interact with miR-26a, miR-26b, and miR-214 and regulate their common target EZH2.ConclusionsOur study elucidated that SNHG6 acted as an oncogene in CRC, which might serve as a novel target for CRC diagnosis and therapy.Electronic supplementary materialThe online version of this article (10.1186/s13045-018-0690-5) contains supplementary material, which is available to authorized users.

Epigenetic alterations contributed to human carcinogenesis immensely. N6-methyladenosine (m6A) is one of the most preventive and abundant modifications on RNA molecules present in eukaryotes. However, the biological function of m6A methylation in colorectal cancer (CRC) remains largely unclear. Here, we found that METTL14 was downregulated in CRC tissues and cell lines, and closely correlated with overall survival (OS). METTL14 knockdown significantly reduced m6A levels in total RNAs and promoted CRC cell growth and metastasis, whereas METTL14 overexpression markedly increased m6A levels in total RNA and inhibited CRC cell growth and metastasis. Furthermore, we demonstrated that miR-375 was a downstream target of METTL14. We also verified that METTL14 suppressed CRC cell growth via the miR-375/Yes-associated protein 1 (YAP1) pathway, as well as inhibited CRC cell migration and invasion through the miR-375/SP1 pathway. Taken together, our studies showed an important role for METTL14 in CRC progression and provided novel insight into m6A modification in CRC progression.