Glypican 3 (GPC3)‐CD81 axis regulates Ezrin mediated Hippo pathway via cross talking with HGF/c‐Met axis in hepatocytes and hepatocellular carcinoma (HCC)

Abstract

The experiments that integrate different pathways in normal and abnormal circumstances will help us to develop optimum targeted therapies because of multiple pathways involved in the solid tumor carcinogenesis. We have shown that activation of CD81 is associated with phosphorylation of Ezrin, which is overexpressed in many types of solid tumors and has been identified as metastasis related protein for many years. We have also shown that GPC3 binds to the membrane tetraspanin CD81, which is one of the portals of entry of hepatitis C virus (HCV). Previous studies have shown that GPC3 is associated with inhibition of hepatocyte growth and liver regeneration by inhibiting CD81‐mediated p‐Ezrin/Hippo/Yap pathway. It also has been shown that HGF/Met axis which promotes growth in HCC can phosphorylate Ezrin as well by different kinases. Since we have demonstrated the predominant GPC+++/CD81− pattern in HCC, the purpose of this study is to explore the regulation of expression and phosphorylation of Ezrin in HCC. We have found that CD81 expression could be detected in membrane and organelle fraction in human hepatoma cell lines HepG2, Huh7 and Hep3B, but immunoprecipitation experiment suggests that CD81 from latter two human hepatoma cell lines has lost association with GPC3. Human hepatoma cell lines have dramatically up regulated Ezrin expression and Yap activity. We found that treatment of primary rat hepatocytes with CD81 agonist antibody or HGF led to higher levels of phosphorylated Ezrin and lower Hippo activity. Mice overexpressing GPC3 had decreased p‐Ezrin but increased Hippo activity. In mice with post‐natal Met knock out there was less Yap expression at baseline level. Rat hepatoma cell lines JM1 and JM2 had dramatically down regulated CD81 expression and Hippo activity, and up regulated p‐Ezrin. Treatment with 20 umol of Ezrin inhibitor led to significant cell death selectively in JM2 cells in vitro.ConclusionsBoth HGF/Met and CD81 mediate p‐Ezrin activity and enhance nuclear Yap levels. These pathways in normal hepatocytes are inhibited by GPC3 and low HGF/Met activity. In human hepatocytes, GPC3 inhibits the CD81‐mediated p‐Ezrin effect on Hippo pathway and cause a decrease in nuclear Yap. The different distribution pattern of HGF/Met and GPC3/CD81 between normal hepatocytes and HCC cells provides the chance to develop precise anti‐HCC therapies. And Ezrin is a promising target of anti‐HCC therapies including primary lesion and metastasis.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.