Epstein–Barr virus (EBV), aetiologically linked to nasopharyngeal carcinoma (NPC), is the first human virus found to encode many miRNAs. However, how these viral miRNAs precisely regulate the tumour metastasis in NPC remains obscure. Here we report that EBV-miR-BART1 is highly expressed in NPC and closely associated with pathological and advanced clinical stages of NPC. Alteration of EBV-miR-BART1 expression results in an increase in migration and invasion of NPC cells in vitro and causes tumour metastasis in vivo. Mechanistically, EBV-miR-BART1 directly targets the cellular tumour suppressor PTEN. Reduction of PTEN dosage by EBV-miR-BART1 activates PTEN-dependent pathways including PI3K-Akt, FAK-p130Cas and Shc-MAPK/ERK1/2 signalling, drives EMT, and consequently increases migration, invasion and metastasis of NPC cells. Reconstitution of PTEN rescues all phenotypes generated by EBV-miR-BART1, highlighting the role of PTEN in EBV-miR-BART-driven metastasis in NPC. Our findings provide new insights into the metastasis of NPC regulated by EBV and advocate for developing clinical intervention strategies against NPC.
Aberrant Wnt signaling pathway is associated with a wide array of tumor types and plays an important role in the drug resistance of cancer stem cells (CSCs). To explore the effects and mechanism of WNT signaling pathway inhibitor XAV939 on drug resistance in colon cancer cells, the colon cancer cells SW480 and SW620 were treated with 5-fluorouracil (5-FU)/cisplatin (DDP) alone or combined with XAV939. Cell cycle distribution, apoptosis level and the percentage of CD133+ cells were detected by flow cytometry. The protein expression of Axin, β-catenin, EpCAM, TERT and DCAMKL-1 was detected by western blotting. XAV939 upregulated Axin, decreased the total and nuclei of β-catenin in SW480 and SW620 cells. Furthermore, XAV939 significantly downregulated the CSC markers EpCAM, TERT and DCAMKL-1 in SW480 cells, as well as EpCAM in SW620 cells. No significant difference was found in the apoptosis of SW480 and SW620 cells with XAV939 treatment, but XAV939 significantly increased apoptosis induced by 5-FU/DDP in SW480 cells, whereas, the effects were slight in SW620 cells. Collectively, we show for the first time that the WNT signaling pathway inhibitor XAV939 was able to significantly increase the apoptosis induced by 5-FU/DDP, accompanied by the protein expression level alternation of β-catenin, Axin and CSC markers in colon cancer cells. Axin, an important component of Wnt/β-catenin signaling pathway could be a potential molecular target for reversing multidrug resistance in colon cancer.
Epstein-Barr virus (EBV) infection is a major etiological factor for nasopharyngeal carcinoma (NPC). Several EBV-encoded BART miRNAs have been associated with viral latency, immune escape, cell survival, cell proliferation and apoptosis. Here, we report that EBV-miR-BART7-3p, an EBV-encoded BART miRNA highly expressed in NPC, was correlated with cell-cycle progression in vitro and increased tumor formation in vivo. This viral miRNA stimulated the PTEN/PI3K/Akt pathway and induced c-Myc and c-Jun. Knockdown of PTEN mimicked EBV-miR-BART7-3p-induced tumorigenic phenotype. Based on these results, we conducted a therapeutic experiment by using gold nano-particles (AuNPs) carrying anti-EBV-miR-BART7-3p. Silencing of EBV-miR-BART7-3p reduced tumor growth in animal model. We conclude that EBV-miR-BART7-3p favors carcinogenesis, representing a potential target for miRNA-based therapy.
Uncontrolled Wnt signaling causes leukemia. Inactivation of Wnt antagonists could play an important role in leukemia progression by activating the Wnt/β-catenin pathway. Wnt inhibitory factor-1 (WIF1) is one of the important Wnt antagonists. Few miRNAs have been reported to directly target this gene in hematopoiesis. Here, we observed that miR-181a-5p expression was markedly overexpressed in several leukemia cell lines and acute lymphoblastic leukemia (ALL) samples compared with that noted in normal peripheral blood mononuclear cells. MTT assays, soft agar colony formation assays and flow cytometry analysis collectively showed that ectopic expression of miR-181a-5p induced ALL cell growth and proliferation. Furthermore, a mechanistic study disclosed that miR-181a-5p directly downregulated WIF1 expression by binding to its 3'-UTR, and further activated Wnt/β‑catenin signaling. These findings provide a novel mechanistic insight into the role of miR-181a-5p in ALL cell growth and proliferation and implicate miR-181a-5p as an attractive candidate for ALL therapy.
Phosphatase and tensin homolog (PTEN) is a major tumor suppressor and usually silenced via the deletion, insertion and mutation. We previously discovered its inactivation via aberrant CpG island methylation. Here, we provide further evidence that EBV latent membrane protein 1(LMP1) can induce a higher intensity of DNA methylation at PTEN CpG islands, inactivating PTEN at the cellular and molecular level. Initially, increased methylation intensity of PTEN CpG islands was observed in EBV-infected nasopharyngeal carcinoma (NPC) cells, accompanied by decreased PTEN expression. In NPC tissue samples showing the methylation at PTEN promoter, LMP1 was highly expressed in higher methylation intensity group relative to lower intensity group, and DNA methyltransferase 3b (DNMT3b) expression was positively correlated with LMP1 expression. Moreover, transfection of LMP1 gene into EBV-negative NPC cells demonstrated that LMP1 up-regulated DNMT3b expression, leading to a higher intensity of PTEN CpG island methylation. Mechanistically, computational prediction and luciferase reporter assay identified a functional NF-κB binding site on DNMT3b promoter and the mutated NF-κB binding site abolished LMP1-mediated DNMT3b activation. Chromatin immunoprecipitation displayed that NF-κB p65 subunit constitutively bound to DNMT3b promoter, supporting the activation of DNMT3b by EBV LMP1 via NF-κB signaling. Furthermore, the expression level of DNMT3b was observed to be increased in the nuclei of LMP1-expressing NPC cells, and a NF-κB inhibitor, PDTC, counteracted LMP1-mediated DNMT3b overexpression. Thus, this study first reports that LMP1-mediated NF-κB can up-regulate DNMT3b transcription, thereby leading to relatively higher methylation intensity at PTEN CpG islands, and ultimately silencing major tumor suppressor PTEN.
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