LncRNA MALAT1 Epigenetically Promotes Proinflammatory Cytokine Production In Hepatocellular Carcinoma Progression

Hepatocellular carcinoma(HCC)is the third leading cause of cancer-related deaths worldwide.Mechanisms underlying HCC formation and progression at transcriptional level,translational level or post-translational level have been devoted to all the time,among which long non-coding RNA(lncRNA)was the most concerned.lncRNAs,a large catalog of noncoding RNAs with the length of more than 200 nucleotides,have been demonstrated to play critical roles in the development,and even cancer.Many kinds of lncRNAs have been identified to be involved in the carinigenesis and tumor metastasis,acting as the potential biomarkers for the diagnosis of cancer patients or targets for drug design of cancer therapeutics.Among the lncRNAs identified in cancer,lncRNA MALAT1 was found to upregulated in certain kinds of cancers including lung cancer,colon cancer,breast cancer.However,the expression profile and the roles of lncRNA MALAT1 in HCC remains to be investigated.By analyzing TCGA data base,MALAT1 was indicated to be upregulated in HCC tissues.In this study,we found that MALAT1 was upregulated in HCC tumor tissues as compared to its expression in non-tumor tissues.The upregulation of MALAT1 expression suggests that MALAT1 may promote HCC progression.We went further to investigate the role of MALAT1 in HCC growth and invasion in vitro.We found that knockdown of MALAT1 suppressed cell proliferation,cell cycle and migration in HCC cell lines QGY-7701 and QGY-7703 cells in response to LPS stimulation(mimics of inflammatory factor in promoting cancer progression).Furthermore,we found that MALAT1 deficiency significantly decreased the expression of pro-inflammatory mediators IL-6 and CXCL8 in LPS-stimulated HCC cells,while overexpression MALAT1 could rescue the downregulated expression of IL-6 and CXCL8 in these HCC cells.It's well know that pro-inflammatory cytokines IL-6 and CXCL8 are all the important mediators to promote cancer growth and metastasis.Mechanistically,by mass spectrometry,we found that MALAT1 might associate SWI/SNF subunit BRG1,and we confirmed that MALAT1 could bind BRG1.Knockdown of BRG1 also decreased the expression of pro-inflammatory mediators IL-6 and CXCL8 in LPS-stimulated HCC cells,phenocoping the knockdown and deficiency of MALAT1.Finally,we found that MALAT1 recruited NF-?B and BRG1 to the promoter of IL-6 and CXCL8 in HCC cells in response to inflammatory stimulation,thus promoting the expressions of these inflammatory factors.In vivo,we knockdown MALAT1 by intratumoral administration of cholesterol-conjugated MALAT1 antisense oligonucleotide(ASO)in SMMU-LTNM HCC-bearing nude mice,which is more close to clinical progression of HCC as high level of ?-fetoprotein(AFP)could be detected in sera.MALAT1 silence suppresses tumor growth compared to negative control.Immunohistochemistry(IHC)shows that MALAT1 knochdown promotes apoptosis,suppresses cell proliferation and angiogenesis compared to negative control.Down-regulation of AFP,IL-6 and CXCL8 was also detected in MALAT1 silence groups.All these results were consistent with those in vitro.Our results have demonstrated that MALAT1,upregulated in HCC,can associate SWI/SNF subunit BRG1 to induce more pro-inflammatory mediators IL-6 and CXCL8 production in HCC via NF-?B pathway,thus contributing to the progression of HCC.The data provide the insight to the epigenetic mechanisms of HCC progression and also potential target for drug design of HCC treatment.