FGFR3 <sub>△7-9</sub> Promotes Tumor Progression <i>via</i> the Phosphorylation and Destabilization of Ten-Eleven Translocation-2 in Human Hepatocellular Carcinoma

Abstract

Background: Our previous study has shown that FGFR3∆7-9, a novel splicing mutation of FGFR3, contributes significantly to hepatocellular carcinoma (HCC) malignancy. However, the functional roles of oncogenic FGFR3∆7-9 are far more clear. In this study, we aimed to understanding regulatory mechanism, signaling, and clinical role of FGFR3∆7-9 in HCC carcinogenesis. Methods: Mass spectrometry and co-immunoprecipitation were employed to identify the interactors with FGFR3∆7-9. The expression and biological functions of DNA demethylase Ten-Eleven Translocation-2 (TET2) were detected in vivo and in vitro. The binding and tyrosine phosphorylation sites of TET2 to FGFR3∆7-9 were pinpointed structurally and functionally. Mechanism of TET2 in modulating PTEN expression was examined by chromatin immunoprecipitationassays and Methylation-Sensitive qPCR. Findings: It is the amount of TET2 rather than mutation functions more importantly in carcinogenesis. Downregulation of TET2 positively correlated with the poorer prognosis of HCC. TET2 could directly interact with FGFR3∆7-9 and phosphorylated at Y1902, which was the solo tyrosine phosphorylation site in the key binding fragment to FGFR3∆7-9. Phospho-deficient mutant TET2 (Y1902F) significantly reduced the tumorigenesis potential of FGFR3∆7-9 in vitro and in vivo. Through the ubiquitination and proteosomal degradation of TET2, FGFR3∆7-9 reduced PTEN expression, and then rescued the level of p-AKT to trigger the HCC cell growth advantage. Interpretation: The novel link between FGFR3∆7-9 and TET2 revealed the important functional roles of oncogenic FGFR3∆7-9 in HCC. FGFR3△7-9 promotes HCC progression via the phosphorylation and destabilization of TET2. Targeting the FGFR3△7-9/TET2-PTEN-AKT signaling axis may contribute to develop new therapeutic strategies for HCC treatment. Funding Statement: This work was supported by the following grants: National Natural Science Foundation of China (NSFC: 81772558), Shanghai Charity Research Foundation of Cancer Research, China Scholarship Council (201906230139), Ph.D. Innovation Fund of Shanghai Jiaotong University School of Medicine (BXJ201709), and “Visiting Programs for Graduate Students of Shanghai Jiaotong University School of Medicine” for this study. Declaration of Interests: The authors declare that they have no competing interests. Ethics Approval Statement: Written informed consent was obtained and the research was approved by the local Ethics Committee and the Institutional Review Board. All patients were fully informed of the experimental procedures and were made aware of the potential risks and complications of the proposed treatment scheme. All animal studies were approved by the Ethics Committee of Ruijin Hospital, Shanghai Jiao Tong University School of Medicine.