Abstract
Approximately 30% of patients with Epstein-Barr virus (EBV)-positive advanced nasopharyngeal carcinoma (NPC) display chemoresistance to cisplatin-based regimens, but the underlying mechanisms are unclear. The Epstein-Barr virus (EBV)-encoded latent membrane protein 1 (LMP1), a functional homologue of the tumor necrosis factor receptor family, contributes substantially to the oncogenic potential of EBV through the activation of multiple signaling pathways, and it is closely associated with a poorer prognosis for NPC. Recent studies show that EBV infection can induce the expression of many cellular miRNAs, including microRNA-21, a biomarker for chemoresistance. However, neither a link between LMP1 expression and miR-21 upregulation nor their cross talk in affecting chemoresistance to cisplatin have been reported. Here, we observed that stable LMP1-transformed NPC cells were less sensitive to cisplatin treatment based on their proliferation, colony formation, the IC50 value of cisplatin and the apoptosis index. Higher levels of miR-21 were found in EBV-carrying and LMP1-positive cell lines, suggesting that LMP1 may be linked to miR-21 upregulation. These data were confirmed by our results that exogenous LMP1 increased miR-21 in both transiently and stably LMP1-transfected cells, and the knock down of miR-21 substantially reversed the resistance of the NPC cells to cisplatin treatment. Moreover, the proapoptotic factors programmed cell death 4 (PDCD4) and Fas ligand (Fas-L), which were negatively regulated by miR-21, were found to play an important role in the program of LMP1-dependent cisplatin resistance. Finally, we demonstrated that LMP1 induced miR-21 expression primarily by modulating the PI3K/AKT/FOXO3a signaling pathway. Taken together, we revealed for the first time that viral LMP1 triggers the PI3K/Akt/FOXO3a pathway to induce human miR-21 expression, which subsequently decreases the expression of PDCD4 and Fas-L, and results in chemoresistance in NPC cells.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Apoptosis / drug effects*
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Apoptosis Regulatory Proteins / antagonists & inhibitors
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Apoptosis Regulatory Proteins / genetics
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Blotting, Western
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Carcinoma
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Cell Line
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Cisplatin / pharmacology
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Cisplatin / therapeutic use*
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Colony-Forming Units Assay
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Drug Resistance, Neoplasm / genetics*
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Fas Ligand Protein / antagonists & inhibitors
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Fas Ligand Protein / genetics
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Fluorescent Antibody Technique
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Forkhead Box Protein O3
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Forkhead Transcription Factors / metabolism
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Gene Expression Regulation, Neoplastic / drug effects*
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Humans
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Inhibitory Concentration 50
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Luciferases
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MicroRNAs / genetics
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MicroRNAs / metabolism*
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Nasopharyngeal Carcinoma
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Nasopharyngeal Neoplasms / drug therapy*
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Nasopharyngeal Neoplasms / virology
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RNA-Binding Proteins / antagonists & inhibitors
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RNA-Binding Proteins / genetics
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Real-Time Polymerase Chain Reaction
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Reverse Transcriptase Polymerase Chain Reaction
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Signal Transduction / drug effects
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Tetrazolium Salts
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Thiazoles
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Viral Matrix Proteins / metabolism*
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Viral Matrix Proteins / pharmacology
Substances
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Apoptosis Regulatory Proteins
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EBV-associated membrane antigen, Epstein-Barr virus
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FASLG protein, human
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FOXO3 protein, human
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Fas Ligand Protein
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Forkhead Box Protein O3
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Forkhead Transcription Factors
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MIRN21 microRNA, human
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MicroRNAs
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PDCD4 protein, human
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RNA-Binding Proteins
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Tetrazolium Salts
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Thiazoles
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Viral Matrix Proteins
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Luciferases
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thiazolyl blue
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Cisplatin
Grants and funding
This work was supported by grants from the Chinese National Natural Science Foundation project (grant no. 30770108, 31170151, 81071822 and 81030043), the National Basic Research Program of China (973 Program No.2012CB519003), the Guangdong Provincial Key Program of Science and Technology (grant no. 2009A030331005), the Natural Science Foundation of Guangdong (grant no. 06021203) and the Guangzhou Key Program of Science and Technology (grant no. 2012Y2-00026). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.