Molecular Dissection Of Ezrin Plasticity In Cellular Dynamic Functions

In regular organisms, different biological functions are based on functionally organized network comprised of diversity of proteins. The protein function depends on the dynamic regulation of its activity. Generally, due to the molecular plasticity of the protein, the activity will be dynamically regulated by the protein structural change induced by specific post translational modification.Different specific site modification of a same protein may result in different plastically change of the molecule, consequently regulate different cellular function.Ezrin is a typical plasma membrane-cytoskeleton linker protein. It plays important role in membrane-cytoskeleton dynamic regulation. Our previous study revealed that its function was regulated by different site phosphorylation. In gastric parietal cells, Ezrin was localized to the apical membrane. It controls gastric acid secretion by phosphrylation of PKA on its 66 serine. In research of membrane-cytoskeleton dynamic regulation, we idetified a novel Arf6 specific GAP--ACAP4, and proved that a typical function complex comprized of Ezrin-ACAP4-Arf6 play an important role in membrane-cytoskeleton remodeling. Thus, we use gastric parietal cells as our model system, to study that upon the phosphorylation of PKA on 66 serine of Ezrin, the structural change of Ezrin rearranged the interaction between Ezrin and ACAP4.This rearrangement translocated ACAP4 to the specific area on apical membrane,and induced a subsequently membrane-cytoskeleton remoduling. As a result, the gastric acid secretion was avitvated. Undoubtedly, Ezrin-ACAP4-Arf6 complex function importantly on this secretion process. And the molecular plasticity may play the most important role.Also, we have revealed that the function of Ezrin was activated by its 567 threonine phosphorylation. Our previous study showed that this site phosphorylation will open the close form of Ezrin which is in dormant stage, and is the most important step on its activation. And our heptocellular carcinoma research inferred that 567 threonine phosphorylation by Rho kinase of Ezrin is critical for tumor cell metastasis. Using a phospho-amino acid specific antibody, the western blotting analysis showed that Thr567 hyperphosphorylation is correlated with the invasive phenotype of hepatocellular carcinoma and poorclinical outcome. Using phospho-mimicking mutants, it was demonstrated that the phosphorylation of ezrin at Thr567 promotes HepG2 cell invasion.Meanwhile, our correlated AFM data showed that the Thr567 phosphorylation made Ezrin change from the close form of N-C interaction to an open form, and expose the multiple functional sites in order to activate different cellular function. And Ser66 phosphorylation function after Thr567 phosphorylation and can open the close form of the N-terminal head of Ezrin. In all, the molecular plasticity insures the highly dynamic regulation of Ezrin's function.