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Adherens junctions (AJs), which are organized by adhesion proteins and the underlying actin cytoskeleton, probably sense pulling forces from adjacent cells and modulate opposing forces to maintain tissue integrity, but the regulatory mechanism remains unknown at the molecular level. Although the possibility that alpha-catenin acts as a direct linker between the membrane and the actin cytoskeleton for AJ formation and function has been minimized, here we show that alpha-catenin recruits vinculin, another main actin-binding protein of AJs, through force-dependent changes in alpha-catenin conformation. We identified regions in the alpha-catenin molecule that are required for its force-dependent binding of vinculin by introducing mutant alpha-catenin into cells and using in vitro binding assays. Fluorescence recovery after photobleaching analysis for alpha-catenin mobility and the existence of an antibody recognizing alpha-catenin in a force-dependent manner further supported the notion that alpha-catenin is a tension transducer that translates mechanical stimuli into a chemical response, resulting in AJ development.

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.

Adherens junctions (AJs), which are organized by adhesion proteins and the underlying actin cytoskeleton, probably sense pulling forces from adjacent cells and modulate opposing forces to maintain tissue integrity, but the regulatory mechanism remains unknown at the molecular level. Although the possibility that α-catenin acts as a direct linker between the membrane and the actin cytoskeleton for AJ formation and function has been minimized, here we show that α-catenin recruits vinculin, another main actin-binding protein of AJs, through force-dependent changes in α-catenin conformation. We identified regions in the α-catenin molecule that are required for its force-dependent binding of vinculin by introducing mutant α-catenin into cells and using in vitro binding assays. Fluorescence recovery after photobleaching analysis for α-catenin mobility and the existence of an antibody recognizing α-catenin in a force-dependent manner further supported the notion that α-catenin is a tension transducer that translates mechanical stimuli into a chemical response, resulting in AJ development. [ABSTRACT FROM AUTHOR]

Transient receptor potential vanilloid 4 (TRPV4) channel is a physiological sensor for hypo-osmolarity, mechanical deformation, and warm temperature. The channel activation leads to various cellular effects involving Ca2+ dynamics. We found that TRPV4 interacts with β-catenin, a crucial component linking adherens junctions and the actin cytoskeleton, thereby enhancing cell-cell junction development and formation of the tight barrier between skin keratinocytes. TRPV4-deficient mice displayed impairment of the intercellular junction-dependent barrier function in the skin. In TRPV4-deficient keratinocytes, extracellular Ca2+-induced actin rearrangement and stratification were delayed following significant reduction in cytosolic Ca2+ increase and small GTPase Rho activation. TRPV4 protein located where the cell-cell junctions are formed, and the channel deficiency caused abnormal cell-cell junction structures, resulting in higher intercellular permeability in vitro. Our results suggest a novel role for TRPV4 in the development and maturation of cell-cell junctions in epithelia of the skin. [ABSTRACT FROM AUTHOR]

Summary: IKK-related kinases are key regulators of innate immunity and oncogenesis. While their effects on transcription are well characterized, their cytoplasmic functions remain poorly understood. Drosophila IKK-related kinase, IKKɛ, regulates cytoskeletal organization and cell elongation. Here, we demonstrate that IKKɛ is activated locally at the tip of growing mechanosensory bristles and regulates the rapid shuttling of recycling endosomes, independent of its roles in F-actin organization and caspase signaling. IKKɛ regulates the localization of recycling endosome regulators Rab11 and Dynein and phosphorylates their adaptor molecule, Nuclear fallout (Nuf). Nuf''s negative regulation by IKKɛ suggests that local activation of IKKɛ inhibits Dynein on incoming recycling endosomes, converting them for outward transport. Mammalian IKK-related kinases also regulate the recycling endosomes'' distribution by phosphorylating the Nuf homolog Rab11-FIP3. Our results establish an evolutionarily conserved function of IKK-related kinases in regulating recycling endosome dynamics and point to a key role of endosome dynamics in cell morphogenesis. [Copyright &y& Elsevier]