Tumorigenic role of YAP in hepatocellular carcinogenesis is involved in SHP2 whose function is different in vitro and in vivo

Yes-associated protein (YAP) is a nuclear effector of the cell-density sensing Hippo pathway and interacts with Src homology phosphotyrosine phosphatase 2 (SHP2), which controls cell proliferation and survival. The tumor promoting/suppressing activities of YAP and SHP2 during liver tumorigenesis remain controversial. This study aimed to investigate the tumorigenic roles of YAP and SHP2 in hepatocellular carcinogenesis. Cell density associated subcellular distributions of YAP and SHP2 in normal human hepatocytes (THLE-2) and hepatocellular carcinoma (HCC) cells (SK-Hep1, SNU-182) were investigated by Western blotting and cell block immunohistochemistry. The effects of YAP knockdown on proliferation, migration and invasion were studied using YAP-specific siRNAs. The prognostic significance of YAP and SHP2 expressions was investigated immunohistochemically using a tissue microarray (TMA) from 50 HCC cases. High-cell density decreased the nuclear expression of YAP and SHP2 in normal hepatocytes as compared with low-cell density. However, in HCC cells, nuclear YAP and SHP2 were observed regardless of cell density. Nuclear YAP influenced SHP2 expression and cell proliferation. In particular, YAP knockdown impacted nuclear levels of SHP2 protein in SK-Hep1 cells. In HCC tissues, nuclear YAP expression was elevated and cytoplasmic SHP2 expression was diminished as compared with adjacent non-tumor tissues. Notably, these expressions were found to be significantly associated with poor recurrence-free and overall survival rate in patients with HCC. Consequently, the tumor promoting role of YAP is involved in SHP2 which functions as a tumor promoter in vitro but as a tumor suppressor in vivo. YAP and SHP2 can be unfavorable prognostic markers in HCC.