Low protein expression of LZTR1 in hepatocellular carcinoma triggers tumorigenesis via activating the RAS/RAF/MEK/ERK signaling

Abstract LZTR1 is a substrate specific adaptor for E3 ligase involved in ubiquitination and degradation of RAS GTPases, which inhibits the RAS/RAF/MEK/ERK signaling to suppress tumor progression. However, it’s still unknown whether LZTR1 destabilizes RAS GTPases to suppress HCC progression by inhibiting such signaling pathway. Lenvatinib is the first-line drug for the treatment of advanced HCC, which has faced serious problem of drug resistance. To explore the roles of LZTR1 in HCC progression and the potential mechanisms of lenvatinib resistance, techniques such as bioinformatics analysis, immunohistochemical staining, RT-qPCR, western blot, cell functional experiments, small interfering RNA transfection and cycloheximide chase assay were applied in our study. Among these, bioinformatics analysis and immunohistochemical staining results indicated that LZTR1 protein was aberrantly low expressed in HCC tissues and low protein expression of LZTR1 was associated with poor prognosis of HCC patients. In vitro experiments confirmed that LZTR1 knockdown promoted HCC cell proliferation and migration, and western blot and cycloheximide chase assay further demonstrated that LZTR1 induced KRAS ubiquitination and degradation, thereby inhibiting the RAS/RAF/MEK/ERK signaling. In lenvatinib resistance inducible experiment, upregulation of LZTR1 protein as well as downregulation of KRAS protein were detected in HCC cells exposed to gradient concentrations of lenvatinib for 48 h. Transwell assay found that both LZTR1 knockdown and KRAS knockdown can induce lenvatinib resistance in HCC cells. In conclusion, our study revealed that LZTR1 knockdown promoted HCC cell proliferation/migration and induced lenvatinib resistance via activating the RAS/RAF/MEK/ERK signaling, which may provide new ideas and hope for the precision therapy of HCC.