title: Rho-dependent and -independent activation mechanisms of ezrin/radixin/moesin proteins: an essential role for polyphosphoinositides in vivo.
abstract: Ezrin/radixin/moesin (ERM) proteins crosslink actin filaments to plasma membranes and are involved in the organization of the cortical cytoskeleton, especially in the formation of microvilli. ERM proteins are reported to be activated as crosslinkers in a Rho-dependent manner and are stabilized when phosphorylated at their C-terminal threonine residue to create C-terminal threonine-phosphorylated ERM proteins (CPERMs). Using a CPERM-specific mAb, we have shown, in vivo, that treatment with C3 transferase (a Rho inactivator) or staurosporine (a protein kinase inhibitor) leads to the dephosphorylation of CPERMs, the translocation of ERM proteins from plasma membranes to the cytoplasm and microvillar breakdown. We further elucidated that ERM protein activation does not require C-terminal phosphorylation in A431 cells stimulated with epidermal growth factor. In certain types of kidney-derived cells such as MDCK cells, however, ERM proteins appear to be activated in the absence of Rho activation and remain active without C-terminal phosphorylation. Interestingly, microinjection of an aminoglycoside antibiotic, neomycin, which binds to polyphosphoinositides, such as phosphatidylinositol (4,5)-bisphosphate [PtdIns(4,5)P(2)], affected the activation of ERM proteins regardless of cell type. These findings not only indicate the existence of a Rho-independent activation mechanism of ERM proteins but also suggest that both Rho-dependent and -independent activation of ERM proteins require a local elevation of PtdIns(4,5)P(2) concentration in vivo.
authors.affiliation: Department of Cell Biology, Faculty of Medicine, Kyoto University, Sakyo-ku, Japan. yonemura@cdb.riken.go.jp
authors.forename: Shigenobu
authors.initials: S
authors.lastname: Yonemura
authors.forename: Takeshi
authors.initials: T
authors.lastname: Matsui
authors.forename: Shoichiro
authors.initials: S
authors.lastname: Tsukita
authors.forename: Sachiko
authors.initials: S
authors.lastname: Tsukita
mesh_terms: D016475:3T3 Cells; D036002:ADP Ribose Transferases / Q000494:pharmacology; D000818:Animals; D001798:Blood Proteins / Q000378:metabolism*; D001905:Botulinum Toxins / Q000494:pharmacology; D016466:CHO Cells; D002462:Cell Membrane / Q000378:metabolism / Q000648:ultrastructure; D006224:Cricetinae; D003598:Cytoskeletal Proteins / Q000378:metabolism*; D003599:Cytoskeleton / Q000378:metabolism* / Q000648:ultrastructure; D004815:Epidermal Growth Factor / Q000494:pharmacology; D005057:Eukaryotic Cells / Q000378:metabolism / Q000648:ultrastructure; D005455:Fluorescent Antibody Technique; D006367:HeLa Cells; D006801:Humans; D008565:Membrane Proteins / Q000378:metabolism*; D051379:Mice; D008840:Microfilament Proteins / Q000378:metabolism*; D008854:Microscopy, Electron; D008871:Microvilli / Q000378:metabolism* / Q000648:ultrastructure; D010716:Phosphatidylinositols / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism*; D017434:Protein Structure, Tertiary / Q000187:drug effects / Q000502:physiology; D021381:Protein Transport / Q000187:drug effects / Q000502:physiology; D020741:rho GTP-Binding Proteins / Q000378:metabolism*; D000099149:Ezrin
chemical_list: D036002:ADP Ribose Transferases; D001798:Blood Proteins; D001905:Botulinum Toxins; D003598:Cytoskeletal Proteins; D004815:Epidermal Growth Factor; D008565:Membrane Proteins; D008840:Microfilament Proteins; D010716:Phosphatidylinositols; D010750:Phosphoproteins; D020741:rho GTP-Binding Proteins; D000099149:Ezrin; C071058:moesin; C071776:radixin; C063007:exoenzyme C3, Clostridium botulinum