Endoplasmic reticulum resident oxidase ERO1-Lalpha promotes hepatocellular carcinoma metastasis and angiogenesis through the S1PR1/STAT3/VEGF-A pathway

Mounting evidence demonstrates that expression of ERO1 alpha, an endoplasmic reticulum (ER)-resident oxidase, is a poor prognosis factor in a variety of human cancers. However, the clinical relevance of ERO1 alpha and its molecular mechanisms underlying tumor progression have not been determined for hepatocellular carcinoma (HCC). ERO1 alpha expression levels in HCC tissues and cells were detected by quantitative real-time PCR and western blotting. ERO1 alpha shRNAs and overexpression vector were transfected into HCC cells to downregulate or upregulate ERO1 alpha expression. In vitro and in vivo assays were performed to investigate the function of ERO1 alpha in invasion, metastasis, and angiogenesis of HCC. We found high ERO1 alpha expression in HCC tissues and cells that was significantly associated with metastasis and poor clinicopathologic features of vascular invasion, advanced Edmondson Grade, and TNM stage. Loss-of-function and gain-of-function studies showed that ERO1 alpha prompted migration, invasion, epithelial-mesenchymal transition (EMT), and angiogenesis of HCC cells both in vitro and in vivo. Further studies verified a positive correlation between ERO1 alpha and S1PR1, upregulated in metastatic HCC tissues compared with HCC tissues without metastasis. S1PR1 knockdown markedly diminished the effects of ERO1 alpha on HCC cell migration, invasion and vascular endothelial growth factor (VEGF) expression. Most importantly, ERO1 alpha knockdown significantly repressed the death of HCC xenograft mouse models by reducing tumor distant metastasis, and host angiogenesis by suppressing the expression of S1PR1, p-STAT3, and VEGF-A in HCC cells. Our findings suggest that ERO1 alpha is significantly correlated with reduced survival and poor prognosis, and promotes HCC metastasis and angiogenesis by triggering the S1PR1/STAT3/VEGF-A signaling pathway. ERO1 alpha might be a novel candidate in HCC prognosis and therapy.