The Function And Mechanism Ot SF3B4 In Hepatocellular Carcinoma

Background and Aim:Hepatocellular carcinoma(HCC)is the second most common cause of cancer-related death worldwide and the incidence and mortality of HCC have been steadily increasing during the last two decades.China is a large country with HCC.Every year,there are about 400,000 new diagnosed HCC cases and more than 340,000 liver cancer patients die,which is accounted for more than 50%of the global total incidence and mortality of HCC.Most of the HCC patients in China are in the advanced or late stage when diagnosed,and the prognosis is poor.Therefore,investigating the mechanism of HCC development is the key for early diagnosis and treatment in HCC research field.Tumorigenesis is a complicated process,involving various mutations of tumor genes and epigenetic modifications.In eukaryotes,alternative splicing(AS)is a common gene regulation mechanism,which plays an important role in the diversity of gene expression and biological development of species.Splicing factor 3b subunit 4(SF3B4)is a member of splicing factor and previous studies found that the expression level of SF3B4 is significantly increased in HCC patients.,compared with normal people,indicating that it may play a critical role in HCC development.However,the specific function of SF3B4 in HCC and its related molecular mechanism are still unclear.The main purpose of this study is to determine the role of SF3B4 in HCC and the underlying mechanism.Methods:For the purpose of this research,the following research methods are adopted:1.The expression levels of SF3B4 and miRNA-133b in HCC tissues and normal liver tissues were explored by using public databases and clinical tissue samples,and the prognosis of HCC patients was analyzed.2.The correlation between SF3B4 and miRNA-133b was predicted by TargetScan database,and the relationship between SF3B4 and miRNA-133b was determined by dual luciferase reporter assay,qPCR and western-blot.3.Constructing SF3B4 overexpression vector to overexpress SF3B4.Small interfering RNA and lentivirus were used to knockdown SF3B4 in HCC cells.Meanwhile,mimic and inhibitor of miRNA-133b were used to promote and inhibit miRNA-133b expression respectively.4.The functions of SF3B4 and miRNA-133b was investigated by CCK8,EdU,transwell and wound healing scratch assays in vitro.The tumor xenografted mice model and metastasis model were constructed to examine the function of SF3B4 in vivo.Results:SF3B4 expression was increased in HCC tissues and cell lines,and the high level of SF3B4 in HCC patients suggested poor prognosis.In HCC cell lines,high expression of SF3B4 acts as an oncogene,SF3B4 knockout can effectively inhibit the proliferation and invasion of HCC cells.Through bioinformatics analysis,we found that there was a stable binding site between SF3B4 and miRNA-133b,then we confirmed that miRNA-133b could bind to SF3B4 via dual luciferase reporter assay.The expression level of miRNA-133b is decreased in HCC tissues,which is negatively correlated with the expression level of SF3B4.miRNA-133b inhibitor can effectively inhibit the expression of miRNA-133b and promote the progression of HCC cells.However,overexpression miRNA-133b inhibits the expression of SF3B4 and impaires the oncogene effect of SF3B4 in liver cancer.miRNA-133b can also affect SF3B4-related signaling pathway.Overexpression miRNA-133b can promote the downstream KLF4 and KIP1 expression of SF3B4 and inhibit SNAI2.Conclusions:In this study,we found that the expression level of SF3B4 is increased in HCC tissues,while miRNA-133b is decreased,showing a negative correlation.Both SF3B4 and miRNA-133b play an important role in HCC tumorigenesis.Meanwhile,miRNA-133b can regulate the splicing effect of SF3B4 and affect its downstream signaling pathway,then impaire the tumorigenesis of HCC cells.Our study suggested that the miRNA-133b/SF3B4 regulatory pathway may be served as a new therapeutic target for HCC treatment.