TRIM27‐USP7 complex promotes tumour progression via STAT3 activation in human hepatocellular carcinoma

Abstract Background & Aims TRIM27 is stabilized by binding to USP7 and mediates tumour progression in several cancers; however, the roles of TRIM27‐USP7 complex on STAT3 activation in HCC are unknown. Methods Regulations and functions of TRIM27 for activating STAT3 in HCC were assessed using 207 HCC samples or HCC cells. Results TRIM27 expression was increased in some cases of HCC. High TRIM27 expression was an independent predictor for poor prognosis in HCC after surgery. It was correlated with the expression of EpCAM, vimentin, MMP‐9, and activation of STAT3 in HCC. TRIM27 expression was correlated with USP7 expression, and HCC with high TRIM27 expression together with high USP7 expression showed enhanced STAT3 activation, resulting in poorer prognosis. p‐JAK1 expression was correlated with STAT3 activation in HCC with high TRIM27 expression. In vitro, USP7 knockdown decreased TRIM27 expression, suggesting that USP7 was essential for TRIM27 stabilization. Knocking down of TRIM27 or USP7 suppressed STAT3 activation and overexpression of TRIM27 accelerated STAT3 activation; therefore, the formation of TRIM27‐USP7 complex was needed for STAT3 activation, which led to aggressive tumour proliferation and invasion by enhancing EMT and CSC‐like property. Binding of JAK1 to TRIM27‐USP7 complex was confirmed in vitro. Deletion of TRIM27‐USP7 complex by USP7 inhibitor significantly inhibited tumour cell invasion by suppressing STAT3 activation. Conclusions TRIM27 is stabilized by binding to USP7 and is related to aggressive tumour progression in HCC via STAT3 activation, resulting in poor prognosis after operation. Therefore, TRIM27‐USP7 complex is a useful prognostic predictor and a promising therapeutic target for HCC.