LifeAct-GFP, a fluorescent reporter for actin filaments, is used to uncover the dynamics of actin cytoskeleton remodeling in real time during TGF-β–induced EMT. Efficient actin filament remodeling and complete transition to a mesenchymal phenotype depend on an increase in expression of the ERM protein moesin.

Changes in intracellular pH regulate many cell behaviors, including proliferation, migration, and transformation. However, our understanding of how physiological changes in pH affect protein conformations and macromolecular assemblies is limited. We present design principles, current modeling predictions, and examples of pH sensors or proteins that have activities or ligand-binding affinities that are regulated by changes in intracellular pH.

The mammalian Ste20-like Nck-interacting kinase (NIK) and its orthologs Misshapen in Drosophila and Mig-15 in Caenorhabditis elegans have a conserved function in regulating cell morphology, although through poorly understood mechanisms. We report two previously unrecognized actions of NIK: regulation of lamellipodium formation by growth factors and phosphorylation of the ERM proteins ezrin, radixin, and moesin. ERM proteins regulate cell morphology and plasma membrane dynamics by reversibly anchoring actin filaments to integral plasma membrane proteins. In vitro assays show that NIK interacts directly with ERM proteins, binding their N termini and phosphorylating a conserved C-terminal threonine. In cells, NIK and phosphorylated ERM proteins localize at the distal margins of lamellipodia, and NIK activity is necessary for phosphorylation of ERM proteins induced by EGF and PDGF, but not by thrombin. Lamellipodium extension in response to growth factors is inhibited in cells expressing a kinase-inactive NIK, suppressed for NIK expression with siRNA oligonucleotides, or expressing ezrin T567A that cannot be phosphorylated. These data suggest that direct phosphorylation of ERM proteins by NIK constitutes a signaling mechanism controlling growth factor-induced membrane protrusion and cell morphology.ezrin ͉ moesin ͉ ste20 kinase ͉ membrane protrusion T he Nck-interacting kinase (NIK) is a member of the germinal center kinase subfamily of Ste20͞MAP4K serine͞threonine kinases (1). Closely related to NIK are the mammalian kinases TNIK (2), MINK (3), and NRK͞NESK (4) and orthologs Misshapen (Msn) in Drosophila (5) and MIG-15 in Caenorhabditis elegans (6). NIK and its orthologs share a common function in regulating cell shape and migration. In mice, homozygous knockout of NIK results in early embryonic lethality with defects in mesoderm migration (7), and expression of kinase-inactive NIK attenuates epithelial cell invasion (8). Msn functions in determining epithelial polarity, dorsal closure. and neuronal targeting (5, 9, 10), and MIG-15 controls axonal navigation (6). NIK (1) and Msn (5) also share a conserved activation of the JNK pathway. NIK, however, does not directly phosphorylate JNK, nor do NIK nullizygous embryos precisely phenocopy mice lacking JNK1 or JNK2 (7). Additionally, activation of JNK is not associated with dynamic changes in cell morphology. Hence, NIK substrates that control cell morphogenesis have not been identified.We now report that the ERM proteins ezrin, radixin, and moesin are substrates for NIK. ERM proteins regulate cell morphology by cross-linking actin filaments to the plasma membrane. The N-terminal FERM (4.1 ERM) domain of ERM proteins binds to integral plasma membrane proteins and the C terminus binds F-actin (11). ERM proteins control cell shape primarily by regulating membrane protrusions and cell-substrate adhesion. In epithelial cells ERM proteins are necessary for the formation of apical microvilli (12)(13)(14). In fibroblasts ERM proteins regulate the assembly of focal adhesions (...

Mitogen Activated Protein Kinase (MAPK) pathways form the backbone of signal transduction within the mammalian cell. Here, we apply a systematic experimental and computational approach to map 2,269 interactions between human MAPK-related proteins and other cellular machinery and to assemble these data into functional modules. A core network of 641 interactions is supported by multiple lines of evidence including conservation with yeast. Using siRNA knockdowns, we reveal that a significant number of novel interactors can modulate MAPK mediated signaling. We uncover the Na-H exchanger NHE1 as a scaffold for a novel set of MAPKs, link HSP90 chaperones to MAPK pathways, and identify MUC12 as the human analogue to the yeast signaling mucin Msb2. This study makes available a large resource of MAPK interactions along with the accompanying clone libraries. It illustrates a methodology for probing signaling networks based on functional refinement of experimentally-derived protein interaction maps.

Background: Staphylococcal nuclease domain-containing 1 (SND1) is overexpressed in human hepatocellular carcinoma (HCC). Results: SND1 augments tumor angiogenesis by activating NF-B, resulting in the induction of miR-221, which subsequently induces angiogenin and CXCL16. Conclusion: A novel pathway activated by SND1 is identified as contributing to tumor angiogenesis. Significance: SND1 promotes hepatocarcinogenesis by multiple ways indicating that small molecule inhibitors of SND1 might be effective therapies for HCC.