Search

Alternative splicing (AS) of pre-mRNAs is an essential process that regulates gene expression and functional diversity, yet the underlying regulatory mechanisms that control this process during cancer metastasis are not clear. Here, we uncovered that a long non-coding RNA (lncRNA), MIR99AHG, mediates regulation of AS to alter chromatin remodeler function and promote invadopodia formation in colorectal cancer (CRC). We found that MIR99AHG is highly expressed in metastatic CRC cells and patient tissue samples. In vitro and in vivo assays showed that MIR99AHG potently drove CRC cell motility, invasion, and metastasis. MIR99AHG bound to and stabilized the RNA splicing factor PTBP1, which cooperatively increased cassette exon inclusion of the chromatin remodeling gene SMARCA1. Mechanistically, MIR99AHG acted as an address label for PTBP1 to fine-tune its binding pattern on SMARCA1 pre-mRNA, thereby controlling the skipping-to-inclusion splicing switch of SMARCA1 and favouring the production of a long isoform (SMARCA1-L). Canonical SMARCA1 was found to suppress cell migration and invasiveness by inhibiting invadopodia formation, but SMARCA1-L was functionally inert. Clinicaldata revealed that MIR99AHG was positively correlated with PTBP1 and SMARCA1-L in human CRC specimens and predicted patient outcome. Furthermore, we showed that the crosstalk with cancer-associated fibroblasts triggers TGF-β/SAMD signalling in CRC cells and activates MIR99AHG expression. Our findings establish a novel mechanism for a lncRNA that interacts with PTBP1 to regulate AS process, providing a potential therapeutic target and predictive biomarker of CRC.

Background The small GTPase Ran is upregulated in multiple cancers and fundamental for cancer cell survival and progression, but its significance and molecular mechanisms in colorectal cancer (CRC) remain elusive. Methods Ran expression was detected in CRC cell lines and tumour tissues. In vitro and in vivo functional assays were performed to examine the effects of Ran on cell proliferation and metastasis. The pathways and effectors regulated by Ran were explored by an unbiased screening. Bioinformatics prediction and experimental validation were used to identify the miRNA regulator for Ran. Results Ran expression was frequently increased in metastatic CRC cells and tissues, especially in metastatic tissues. The upregulation of Ran correlated with poor CRC patient prognosis. Ran silencing reduced proliferation and metastasis of CRC cells both in vitro and in vivo. Ran regulated the expression of EGFR and activation of ERK and AKT signalling pathways. miR-802 was identified as an upstream regulator of Ran and miR-802 overexpression resulted in antiproliferative and antimetastatic activities. Conclusion Our study demonstrates the oncogenic roles and underlying mechanisms of Ran in CRC and the novel miR-802/Ran/EGFR regulatory axis may provide potential biomarkers for the treatment of CRC.

Colorectal cancer (CRC) is a major leading cause of cancer mortality worldwide in which dysregulated protein synthesis plays an etiologic role. The eukaryotic elongation factor 1 A1 (eEF1A1) exerts significant effects on protein synthesis by contributing to peptide chain extension. Whereas its role in CRC remains to be investigated. In this study, we found that the mRNA and protein levels of eEF1A1 were significantly upregulated in CRC cell lines and tissues. Elevated expression of eEF1A1 was correlated with shorter overall survival in 94 CRC patients. The inhibition of proliferation and cell cycle block were observed in CRC cells after eEF1A1 downregulation. Mechanistically, weighted gene correlation network analysis and further Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis suggested that mitogen-activated protein kinases (MAPKs) signaling pathways were significantly enriched in high-eEF1A1 expression group, and the levels of phosphorylated p38/JNK/ERK MAPK were dramatically decreased after eEF1A1 downregulation. Overexpression of eEF1A1 in CRC correlated with a poor prognosis. Collectively, this study determined the oncogenic role of eEF1A1 in CRC proliferation and tumorigenesis. eEF1A1 might be a promising therapeutic target and prognostic biomarker in CRC.

Background Metastasis leads to recurrence and death in colorectal cancer (CRC) patients; however, mechanisms underlying CRC metastasis, especially in its initial stages, remain largely unknown. In this study, we aim to identify long noncoding RNAs (lncRNAs) functionally involved in CRC metastasis initiation and their regulation that could lead to targeted therapeutics. Methods We performed whole transcriptome sequencing using CRC cell lines with divergent spontaneous metastatic properties. The biological roles and mechanisms of lncRNA MIR99AHG were characterized with a series of in vitro and in vivo models and molecular analyses. Results MIR99AHG was upregulated in CRC patients and associated with tumor stage and prognosis. MIR99AHG potently drove migration, invasion and metastasis in CRC cells, and these effects were dependent on its role in promoting invadopodia formation. MIR99AHG interacted with RNA splicing factor PTBP1, which cooperatively modulated alternative splicing of chromatin remodeling gene SMARCA1. Mechanistically, MIR99AHG acted as an address label for PTBP1 to direct its binding to the 5’ splice site of SMARCA1 intron 12, thereby facilitating inclusion of the alternative exon 13 to generate a long isoform (SMARCA1-L). The canonical SMARCA1 inhibited cell migration and invasion and suppressed a core set of genes involved in invadopodia, but the SMARCA1-L was functionally inert in metastasis suppression. Clinically, SMARCA1-L levels were positively correlated with MIR99AHG and PTBP1 in patients with metastatic CRC. Conclusions This study identified that invadopodia was regulated by a splicing switch of SMARCA1 due to the interaction between MIR99AHG and PTBP1, highlighting a novel regulatory mode mediated by lncRNA in alternative splicing of chromatin remodeler during CRC metastasis.

Aberrant activation of the Wnt/β-catenin signaling pathway is implicated in most malignant cancers, especially in the initiation and progression of colorectal cancer (CRC). DKK4 is a classical inhibitory molecule of the Wnt/β-catenin pathway, but its role in CRC is ambiguous, and the molecular mechanism remains unclear. Here, we determined DKK4 expression was significantly upregulated in 23 CRC cell lines and 229 CRC tissues when analyzed by quantitative PCR and immunohistochemistry, respectively. Our analysis of tissue samples indicated the survival time of CRC patients with high DKK4 expression was longer than that of patients with medium-low DKK4 expression. We examined the effects of DKK4 on cell proliferation and metastasis by cell counting kit-8 assays, transwell assays, and subcutaneous and metastatic mouse tumor models, and we discovered that DKK4 silencing promoted the metastasis of CRC cells both in vitro and in vivo. Our RNA-seq analysis revealed that AKT2, FZD6, and JUN, which play important roles in AKT and Wnt signaling, were significantly increased after DKK4 knockdown. DKK4 represses Wnt/β-catenin signaling by repressing FZD6 and AKT2/s552 β-catenin in CRC. Further experiments revealed recombinant Wnt3a and LiCl could induce DKK4 expression. Moreover, our bioinformatics analysis and luciferase reporter assays identified posttranscriptional regulators of DKK4 in CRC cells. In summary, DKK4 is elevated in CRC and inhibits cell metastasis by a novel negative feedback mechanism of the Wnt3a/DKK4/AKT/s552 β-catenin regulatory axis to restrict overactivation of Wnt activity in CRC. Therefore, DKK4 restoration may be applied as a potential CRC therapeutic strategy.

Epithelial-to-mesenchymal transition (EMT) is a process linked to metastasis and drug resistance with non-coding RNAs (ncRNAs) playing pivotal roles. We previously showed that miR-100 and miR-125b, embedded within the third intron of the ncRNA host gene MIR100HG, confer resistance to cetuximab, an anti-epidermal growth factor receptor (EGFR) monoclonal antibody, in colorectal cancer (CRC). However, whether the MIR100HG transcript itself has a role in cetuximab resistance or EMT is unknown.The correlation between MIR100HG and EMT was analyzed by curating public CRC data repositories. The biological roles of MIR100HG in EMT, metastasis and cetuximab resistance in CRC were determined both in vitro and in vivo. The expression patterns of MIR100HG, hnRNPA2B1 and TCF7L2 in CRC specimens from patients who progressed on cetuximab and patients with metastatic disease were analyzed by RNAscope and immunohistochemical staining.The expression of MIR100HG was strongly correlated with EMT markers and acted as a positive regulator of EMT. MIR100HG sustained cetuximab resistance and facilitated invasion and metastasis in CRC cells both in vitro and in vivo. hnRNPA2B1 was identified as a binding partner of MIR100HG. Mechanistically, MIR100HG maintained mRNA stability of TCF7L2, a major transcriptional coactivator of the Wnt/β-catenin signaling, by interacting with hnRNPA2B1. hnRNPA2B1 recognized the N6-methyladenosine (mMIR100HG and hnRNPA2B1 interact to control the transcriptional activity of Wnt signaling in CRC via regulation of TCF7L2 mRNA stability. Our findings identified MIR100HG as a potent EMT inducer in CRC that may contribute to cetuximab resistance and metastasis by activation of a MIR100HG/hnRNPA2B1/TCF7L2 feedback loop.

The liver is the predominant metastatic site for several types of malignancies. Tumor-associated macrophages (TAMs) in the liver play crucial roles in the metastasis process. Shifting tumor-promoting M2-like TAMs toward the M1-like phenotype, which exerts tumor suppressor functions via phagocytosis and the secretion of inhibitory factors, may be a potential therapeutic strategy for liver cancer metastasis treatment.We first cloned NDRG2 (N-myc downstream-regulated gene 2) and verified its tumor suppressor role in multiple solid tumors, including colorectal cancer and hepatocellular carcinoma. However, its role in the tumor-associated liver microenvironment, especially in TAMs, has not been illustrated. By establishing a liver cancer metastasis model in wild-type (WT) and Ndrg2 knockout (Ndrg2−/−) mice, we found that the loss of the tumor suppressor Ndrg2 in liver microenvironment significantly suppressed the growth of liver colonies. In addition, this process was accompanied by a higher proportion of M1-like TAM infiltration in Ndrg2−/− mice. Interestingly, bone marrow (BM) transplantation revealed that BM-derived macrophages (BMDMs) rather than liver resident Kupffer cells were responsible for the inhibitory effect. We further demonstrated that loss of Ndrg2 influenced TAM polarization via the NF-κB pathway. Inhibition of IκBα phosphorylation in cancer cell-conditioned medium-stimulated BMDMs decreased M1 marker expression in Ndrg2−/− macrophages. Finally, in vitro, invasion, migration, and proliferation assays confirmed that NF-κB participated in the tumor suppressor function of Ndrg2−/− macrophages. Collectively, our findings highlight the role of NDRG2 in the regulation of TAM polarization and its function in promoting cancer liver metastasis.