Vesicle amine transport-1 regulates hepatocellular carcinoma progression by EGF-induced STAT3 signalling

Abstract

Abstract Vesicle amine transport-1 (VAT-1) was implicated in regulation of vesicular transport, mitochondrial fusion, axonal growth, phospholipid transport and cell migration. However, the role of VAT-1 in tumour biology and disease progression of hepatocellular carcinoma (HCC) remains unknown. Here, we first investigated the expression of VAT-1 in clinical HCC samples by immunohistochemistry and in various transcriptomic datasets by bioinformatics. The biological functions of VAT-1 in HCC were then explored by using a variety of techniques including in vitro cell-based assays, in vivo xenograft models, high throughput mRNA-Seq, KEGG pathway enrichment, flow-cytometry analysis, immunoassays and bioinformatics. Underlying mechanisms were further verified in clinical tumour specimens. We demonstrated that VAT-1 is significantly upregulated in tumour tissues and associated with tumour size, invasion, clinical stage and overall survival of patients. Multivariate Cox analysis indicated VAT-1 is an independent unfavourable prognostic factor. VAT-1 downregulation significantly inhibited cell growth and colony formation in vitro and xenograft growth by decreasing proliferation and increasing apoptosis. Mechanistic studies revealed VAT-1 downregulation inhibits tumour growth through induction of the cell cycle arrest at G1-G0 by regulating the expression of cyclin D1, cyclin D3, CDK6, c-Myc and MCL-1. Strikingly, VAT-1 regulates STAT3 phosphorylation at Y705, nuclear translocation of pSTAT3-Y705, EGF-induced STAT3 signalling and consequently the expression of downstream c-Myc and cyclin D1. In both established HCC cell lines and clinical tumour samples, VAT-1 regulates numerous pathways including cell cycle, ErbB pathway, EGFR tyrosine kinase inhibitor resistance and JAK-STAT pathway; VAT-1 expression is significantly correlated with core components of EGF-EGFR-STAT3-cell cycle axis, highlighting the role of VAT-1 in regulation of EGF-STAT3-c-Myc-cyclin D/CDK6 signalling. Our results provide new insights into the carcinogenesis and disease progression of HCC and rationales for the development of novel intervention strategies against HCC. VAT-1 could serve as an independent prognostic biomarker for predicting clinical outcome of HCC patients.