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

It has been shown that up regulation activity of CD81(TAPA-1, the portal of entry of Hepatitis C virus) by agonistic antibody results in phosphorylation of Ezrin. We have previously shown that in liver, Ezrin phosphorylation occurs via Syk kinase, causing suppression of hippo intensity, therefore increases sequential Yap activity. The opposite occurs when Glypican-3 (GPC3) or E2 protein of HCV bind to CD81. Mice over-expressing GPC3 in hepatocytes 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 dynamic picture of Ezrin regulates Hippo pathway and Yap. Forced expression of plasmids expressing mutant Ezrin (T567D) (which mimics p-Ezrin(Thr567)) suppressed Hippo activity and activated Yap signaling. And this mutant Ezrin drive more cell proliferation to cell division through up regulated Yap activity in vitro and in vivo. CD81 loses expression, while p-Ezrin(Thr567) increases in JM1 and JM2 hepatocellular carcinoma (HCC) cells. Administration with compound NSC668394, a characterized p-Ezrin(Thr567) antagonist, caused significant decrease in HCC cell proliferation. We additionally present evidence that pEzrin(T567) is also 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 rates of normal and neoplastic hepatocytes. The finding has mechanistic and potentially therapeutic applications in understanding and regulating growth of hepatocytes and HCC and HCV pathogenesis.

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Xue Y, Bhushan B, Mars WM, Bowen W, Tao J, Orr A, Stoops J, Yu Y, Luo J, Duncan AW, Michalopoulos GK