STX5 Inhibits Hepatocellular Carcinoma Adhesion and Promotes Metastasis by Regulating the PI3K/mTOR Pathway

Background and Aims:Syntaxin 5(STX5)is a member of the syntaxin or target-soluble SNAP receptor(t-SNARE)fam-ily and plays a critical role in autophagy.However,its function and molecular mechanism in tumor cell migration are still un-known.The role of STX5 in influencing hepatocellular carci-noma(HCC)is an important topic in our research.Methods:By using quantitative reverse transcription polymerase chain reaction(qPCR),western blotting,and immunohistochemical analysis of RNA and protein in tissues,we comprehensively evaluated data sets from public databases and clinical patient cohorts for STX5.The correlation of STX5 expression with the clinicopathological characteristics of HCC patients were assessed.In addition,we predicted signal pathways from dif-ferentially expressed genes(DEGs)and the Cancer Genome Atlas(TCGA)databases,and confirmed the prediction using integrated transcriptome and RNA-seq.We further investi-gated the underlying mechanisms of STX5 in the migration and adhesion of HCC cells both in vitro and in vivo.Results:In the TCGA dataset and our patient cohort,STX5 levels were significantly higher in HCC tissues than in adjacent normal liver tissues.At the same time,high expression of STX5 pre-dicted worse prognosis in patients with liver cancer.High ex-pression of STX5 indicates the decrease of adhesion and the increase of migration of HCC cells,and the conversion of epi-thelial-mesenchymal transition(EMT)in vitro via PI3K/mTOR pathway activation.Conversely,when Sirolimus,a phospho-inositide 3-kinase(PI3K)/AKT/mechanistic target of rapa-mycin(mTOR)inhibitor acts on cells simultaneously,STX5 overexpression-mediated enhancement of HCC metastasis is reversed.Double-negative regulation of STX5 and mTOR further enhanced the inhibitory effect of STX5 on HCC me-tastasis.In vivo,STX5 knockdown inhibited the metastasis of HCC cells.Conclusions:Our study demonstrates a novel research result that STX5 promotes HCC metastasis through PI3K/mTOR pathway.We believe that combined inhibition of STX5 and mTOR is a potential treatment for effectively pro-longing patient survival and inhibiting HCC metastasis.