p-Ezrin (Thr567) regulates Hippo pathway and Yap in liver.

Previous studies have shown that activation of CD81, (the portal of entry of Hepatitis C virus) by agonistic antibody results in phosphorylation of Ezrin via Syk kinase. We have previously that his is associated with inactivation of the Hippo pathway and increase in YAP. The opposite occurs when Glypican-3 (GPC3) or E2 protein of HCV bind to CD81. Hepatocyte-specific GPC3 transgenic mice have decreased p-Ezrin(Thr567) and Yap, increased Hippo activity and suppressed liver regeneration. The role of Ezrin in these processes has been speculated, but not proven. We now provide evidence for a direct role of Ezrin in regulation of Hippo pathway and Yap. Forced expression of plasmids expressing mutant Ezrin (T567D) (mimicking p-Ezrin(Thr567)) suppressed Hippo activity and activated Yap signaling in hepatocytes in vivo, and enhanced activation of pathways of beta catenin and LGR4 and LGR5 receptors. Hepatoma cell lines JM1 and JM2 have decreased CD81 expression and Hippo activity, and up regulated pEzrin(T567). NSC668394, a p-Ezrin(Thr567) antagonist, caused significant decrease in hepatoma cell proliferation. We additionally present evidence that pEzrin(T567) is controlled by EGFR and MET. CONCLUSIONS: Ezrin phosphorylation, mediated by CD81-associated Syk kinase, is directly involved in regulation of Hippo pathway, Yap levels and growth of normal and neoplastic hepatocytes. The finding has mechanistic and potentially therapeutic applications in hepatocytes growth biology and HCC and HCV pathogenesis.