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The Rho family GTPases Cdc42 and Rac1 are critical regulators of the actin cytoskeleton and are essential for skin and hair function. Wiskott-Aldrich syndrome family proteins act downstream of these GTPases, controlling actin assembly and cytoskeletal reorganization, but their role in epithelial cells has not been characterized in vivo. Here, we used a conditional knockout approach to assess the role of neural Wiskott-Aldrich syndrome protein (N-WASP), the ubiquitously expressed Wiskott-Aldrich syndrome-like (WASL) protein, in mouse skin. We found that N-WASP deficiency in mouse skin led to severe alopecia, epidermal hyperproliferation, and ulceration, without obvious effects on epidermal differentiation and wound healing. Further analysis revealed that the observed alopecia was likely the result of a progressive and ultimately nearly complete block in hair follicle (HF) cycling by 5 months of age. N-WASP deficiency also led to abnormal proliferation of skin progenitor cells, resulting in their depletion over time. Furthermore, N-WASP deficiency in vitro and in vivo correlated with decreased GSK-3beta phosphorylation, decreased nuclear localization of beta-catenin in follicular keratinocytes, and decreased Wnt-dependent transcription. Our results indicate a critical role for N-WASP in skin function and HF cycling and identify a link between N-WASP and Wnt signaling. We therefore propose that N-WASP acts as a positive regulator of beta-catenin-dependent transcription, modulating differentiation of HF progenitor cells.

The actin cytoskeleton plays a critical role in the cellular morphological changes. Its organization is essential for neurite extension and synaptogenesis under the processes of neuronal development. Recently, neural Wiskott-Aldrich syndrome protein (N-WASP) and WASP family verprolin-homologous protein (WAVE) have been identified as key molecules, which specifically participate in regulation of actin cytoskeleton through small GTPases. The functions of these factors have been investigated using cultured cells; however, in vivo developmental changes in these factors are not fully understood. In this study, we examined the expression levels and distributions of N-WASP, WAVE and their related proteins in the rat cerebral cortex and hippocampus during postnatal development. Protein levels of these factors were progressively increased during development, and actin was accumulated in membranous fractions. Immunoreactivities for these factors were widely but differentially observed in entire brain. In the developing brain, N-WASP and WAVE seemed to exist in the synapse-rich areas, such as stratum radiatum of hippocampal CA1 subfield. A similar tendency in the distributions of these factors was observed in the mature brain. Taken together, N-WASP, WAVE and their related proteins may participate in normal brain development and synaptic plasticity by regulating the actin cytoskeleton.

Cortactin is an actin-associated scaffolding protein that regulates cell migration. Amplification of the human gene, EMS1, has been detected in breast, head and neck tumors, where it correlates with increased invasiveness. Cortactin can regulate actin dynamics directly via its N-terminal half, which can bind and activate the Arp2/3 complex. The C-terminal portion of cortactin, however, is thought to have limited function in its regulation of the actin polymerization machinery. In this report, we identify a role for the cortactin C-terminus in regulating cell migration and, more specifically, actin dynamics. Overexpression of either full-length cortactin or cortactin C-terminus is sufficient to enhance migration of mammary epithelial cells. In vitro, cortactin binds to and activates, via its SH3 domain, a regulator of the Arp2/3 complex, neural Wiskott Aldrich Syndrome protein (N-WASP). This in vitro activation of N-WASP is likely to be important in vivo, as cortactin-enhanced migration is dependent upon N-WASP. Thus, our results suggest that cortactin has multiple mechanisms by which it can recruit and modulate the actin machinery and ultimately regulate cell migration.

N-methyl-D-aspartate (NMDA) receptor antagonism by perinatal phencyclidine (PCP) treatment leads to neuronal damage and causes long-term behavioural alterations in rodents. It is routinely used to model pathological processes in the brain that may be present in schizophrenia, such as alterations to dendritic development, and disruptions to myelin processes. Both of these processes occur during brain development and are highly implicated in the schizophrenia pathophysiology. Changes to the polymerization and reorganization of the actin cytoskeleton can have significant effects on the morphology and dynamics of the dendrites within the brain. Actin regulation is primarily regulated by neural Wiskott-Aldrich syndrome protein (NWASP), and WASP-family verprolin homology protein-1 (WAVE1). Here we have examined the role of actin related, cytoskeletal proteins NWASP and WAVE1 in a neurodevelopmental model of schizophrenia using PCP to determine if these signaling pathways are altered in the prefrontal cortex and hippocampus throughout different stages of neurodevelopment. Male Sprague Dawley rats were injected subcutaneously with PCP (10 mg/kg) or saline at postnatal days (PN) 7, 9 and 11. Rats (n=6/group) were sacrificed at PN 12, 5 weeks or 14 weeks. Relative expression levels of protein expression were examined in the prefrontal cortex and hippocampus of the treated rats. NWASP, WAVE1 and MBP were decreased (0.001≤p≤0.032) in the prefrontal cortex of PCP treated rats at PN12. At 5 weeks of age, NWASP was reduced in the prefrontal cortex (p=0.037) and WAVE1 was reduced in the hippocampus (p=0.006). At 14 weeks, there were no significant changes in any of the tested proteins (p > 0.05). This is the first report of an alteration in NWASP and WAVE1 proteins in the rat brain, directly following NMDA receptor antagonism by PCP treatment in early development. These findings suggest that alterations in these important scaffolding related proteins may contribute to the development of deficits in myelination and cognitive performance in the brain.

Shigella, the causative agent of bacillary dysentery, is capable of directing its movement within host cells by forming an actin comet tail. The VirG (IcsA) pro-tein expressed at one pole of the bacterium recruits neural Wiskott-Aldrich syndrome protein (N-WASP), a member of the WASP family, which in turn stimulates actin-related protein (Arp) 2/3 complex-mediated actin polymerization. As all the WASP family proteins induce actin polymerization by recruiting Arp2/3 complex, we investigated their involvement in Shigella motility. Here, we show that VirG binds to N-WASP but not to the other WASP family proteins. Using a series of chimeras obtained by swapping N-WASP and WASP domains, we demonstrated that the specificity of VirG to interact with N-WASP lies in the N-terminal region containing the pleckstrin homology (PH) domain and calmodulin-binding IQ motif of N-WASP. A conformational change in N-WASP was important for the VirG-N-WASP interaction, as elimination of the C-terminal acidic region, which is responsible for the intramolecular interaction with the central basic region of N-WASP, affected the specific binding to VirG. We observed that, in haematopoietic cells such as macrophages, polymorphonuclear leucocytes (PMNs) and platelets, WASP was predominantly expressed, whereas the expression of N-WASP was greatly suppressed. Indeed, unlike Listeria, Shigella was unable to move in macrophages at all, although the movement was restored as N-WASP was expressed ectopically. Thus, our findings demonstrate that N-WASP is a specific ligand of VirG, which determines the host cell type allowing actin-based spreading of Shigella.

Neural Wiskott-Aldrich syndrome protein (N-WASP) is an actin-regulating protein that induces filopodium formation downstream of Cdc42. It has been shown that filopodia actively extend from the growth cone, a guidance apparatus located at the tip of neurites, suggesting their role in neurite extension. Here we examined the possible involvement of N-WASP in the neurite extension process. Since verprolin, cofilin homology and acidic region (VCA) of N-WASP is known to be required for the activation of Arp2/3 complex that induces actin polymerization, we prepared a mutant (Deltacof) lacking four amino acid residues in the cofilin homology region. The corresponding residues in WASP had been reported to be mutated in some Wiskott-Aldrich syndrome patients. Expression of Deltacof N-WASP suppressed neurite extension of PC12 cells. In support of this, the VCA region of Deltacof cannot activate Arp2/3 complex enough compared with wild-type VCA. Furthermore, H208D mutant, which has been shown unable to bind to Cdc42, also works as a dominant negative mutant in neurite extension assay. Interestingly, the expression of H208D-Deltacof double mutant has no significant dominant negative effect. Finally, the expression of the Deltacof mutant also severely inhibited the neurite extension of primary neurons from rat hippocampus. Thus, N-WASP is thought to be a general regulator of the actin cytoskeleton indispensable for neurite extension, which is probably caused through Cdc42 signaling and Arp2/3 complex-induced actin polymerization.

The intracellular protozoan parasite Cryptosporidium parvum accumulates host cell actin at the interface between the parasite and the host cell cytoplasm. Here we show that the actin polymerizing proteins Arp2/3, vasodilator-stimulated phosphoprotein (VASP), and neural Wiskott Aldrich syndrome protein (N-WASP) are present at this interface and that host cell actin polymerization is necessary for parasite infection.

Summary Several findings suggest that actin-mediated motility can play a role in clathrin-mediated endocytosis but it remains unclear whether and when key proteins required for this process are recruited to endocytic sites. Here we investigate this question in live Swiss 3T3 cells using two-colour evanescent field (EF) microscopy. We find that Arp3, a component of the Arp2/3 complex, appears transiently while single clathrin-coated pits internalize. There is also additional recruitment of Neural-Wiskott Aldrich Syndrome Protein (N-WASP), a known activator of the Arp2/3 complex. Both proteins appear at about the same time as actin. We suggest that N-WASP and the Arp2/3 complex trigger actin polymerization during a late step in clathrin-mediated endocytosis, and propel clathrin-coated pits or vesicles from the plasma membrane into the cytoplasm.

Rho family GTPases regulate neuronal morphology. Rnd subfamily is a new branch of Rho family GTPases. Of these GTPases, Rnd2 is specifically expressed in brain. We recently identified Rapostlin as a novel effector of Rnd2. Rapostlin induces neurite branching in response to Rnd2 in PC12 cells. During the cloning of Rapostlin, we have found two mainly expressed splicing variants of Rapostlin (renamed as RapostlinL), RapostlinM and RapostlinS, lacking 29 residues and 61 residues within the unique insert region at the center, respectively, and three minor variants, RapostlinLd, RapostlinMd, and RapostlinSd, each with the identical five-amino acid deletion from RapostlinL, RapostlinM, and RapostlinS, respectively. RapostlinL is predominantly expressed in brain, whereas RapostlinS is expressed ubiquitously. In a dot-blot assay, all splicing variants bind to Rnd2 in a GTP-dependent manner. However, RapostlinM and RapostlinS induce less neurite branching when coexpressed with Rnd2 in PC12 cells, indicating that the insert region is important for the branching activity of RapostlinL. All splicing variants bind to N-WASP in vitro and in vivo through the SH3 domain at the carboxyl terminus, and the SH3 domain is essential for branching activity of RapostlinL. In immunoprecipitation experiments, Rnd2 reduces RapostlinL-N-WASP interaction, whereas it has little effect on the interaction of RapostlinM or RapostlinS with N-WASP. Therefore, we found that functionally different splicing variants of Rapostlin have different responses to Rnd2 in association with N-WASP.

Neural Wiskott-Aldrich syndrome protein (N-WASP) is an essential regulator of actin cytoskeleton formation via its association with the actin-related protein (Arp) 2/3 complex. It is believed that the C-terminal Arp2/3 complex-activating domain (verprolin homology, cofilin homology, and acidic (VCA) or C-terminal region of WASP family proteins domain) of N-WASP is usually kept masked (autoinhibition) but is opened upon cooperative binding of upstream regulators such as Cdc42 and phosphatidylinositol 4,5-bisphosphate (PIP2). However, the mechanisms of autoinhibition and association with Arp2/3 complex are still unclear. We focused on the acidic region of N-WASP because it is thought to interact with Arp2/3 complex and may be involved in autoinhibition. Partial deletion of acidic residues from the VCA portion alone greatly reduced actin polymerization activity, demonstrating that the acidic region contributes to Arp2/3 complex-mediated actin polymerization. Surprisingly, the same partial deletion of the acidic region in full-length N-WASP led to constitutive activity comparable with the activity seen with the VCA portion. Therefore, the acidic region in full-length N-WASP plays an indispensable role in the formation of the autoinhibited structure. This mutant contains WASP-homology (WH) 1 domain with weak affinity to the Arp2/3 complex, leading to activity in the absence of part of the acidic region. Furthermore, the actin comet formed by the DeltaWH1 mutant of N-WASP was much smaller than that of wild-type N-WASP. Partial deletion of acidic residues did not affect actin comet size, indicating the importance of the WH1 domain in actin structure formation. Collectively, the acidic region of N-WASP plays an essential role in Arp2/3 complex activation as well as in the formation of the autoinhibited structure, whereas the WH1 domain complements the activation of the Arp2/3 complex achieved through the VCA portion.

International audience; Proteins of the Wiskott-Aldrich Syndrome protein (WASp) family connect signaling pathways to the actin polymerization-driven cell motility. The ubiquitous homolog of WASp, N-WASp, is a multidomain protein that interacts with the Arp2/3 complex and G-actin via its C-terminal WA domain to stimulate actin polymerization. The activity of N-WASp is enhanced by the binding of effectors like Cdc42-guanosine 5'-3-O-(thio)triphosphate, phosphatidylinositol bisphosphate, or the Shigella IcsA protein. Here we show that the SH3-SH2-SH3 adaptor Grb2 is another activator of N-WASp that stimulates actin polymerization by increasing the amount of N-WASp. Arp2/3 complex. The concentration dependence of N-WASp activity, sedimentation velocity and cross-linking experiments together suggest that N-WASp is subject to self-association, and Grb2 enhances N-WASp activity by binding preferentially to its active monomeric form. Use of peptide inhibitors, mutated Grb2, and isolated SH3 domains demonstrate that the effect of Grb2 is mediated by the interaction of its C-terminal SH3 domain with the proline-rich region of N-WASp. Cdc42 and Grb2 bind simultaneously to N-WASp and enhance actin polymerization synergistically. Grb2 shortens the delay preceding the onset of Escherichia coli (IcsA) actin-based reconstituted movement. These results suggest that Grb2 may activate Arp2/3 complex-mediated actin polymerization downstream from the receptor tyrosine kinase signaling pathway.

Syndapin I (SdpI) interacts with proteins involved in endocytosis and actin dynamics and was therefore proposed to be a molecular link between the machineries for synaptic vesicle recycling and cytoskeletal organization. We here report the identification and characterization of SdpII, a ubiquitously expressed isoform of the brain-specific SdpI. Certain splice variants of rat SdpII in other species were named FAP52 and PACSIN 2. SdpII binds dynamin I, synaptojanin, synapsin I, and the neural Wiskott-Aldrich syndrome protein (N-WASP), a stimulator of Arp2/3 induced actin filament nucleation. In neuroendocrine cells, SdpII colocalizes with dynamin, consistent with a role for syndapin in dynamin-mediated endocytic processes. The src homology 3 (SH3) domain of SdpI and -II inhibited receptor-mediated internalization of transferrin, demonstrating syndapin involvement in endocytosis in vivo. Overexpression of full-length syndapins, but not the NH2-terminal part or the SH3 domains alone, had a strong effect on cortical actin organization and induced filopodia. This syndapin overexpression phenotype appears to be mediated by the Arp2/3 complex at the cell periphery because it was completely suppressed by coexpression of a cytosolic COOH-terminal fragment of N-WASP. Consistent with a role in actin dynamics, syndapins localized to sites of high actin turnover, such as filopodia tips and lamellipodia. Our results strongly suggest that syndapins link endocytosis and actin dynamics.

Shigella, the causative agent of bacillary dysentery, is capable of directing its own movement in the cytoplasm of infected epithelial cells. The bacterial surface protein VirG recruits host components mediating actin polymerization, which is thought to serve as the propulsive force. Here, we show that neural Wiskott-Aldrich syndrome protein (N-WASP), which is a critical target for filopodium formation downstream of Cdc42, is required for assembly of the actin tail generated by intracellular S.flexneri. N-WASP accumulates at the front of the actin tail and is capable of interacting with VirG in vitro and in vivo, a phenomenon that is not observed in intracellular Listeria monocytogenes. The verprolin-homology region in N-WASP was required for binding to the glycine-rich repeats domain of VirG, an essential domain for recruitment of F-actin on intracellular S.flexneri. Overexpression of a dominant-negative N-WASP mutant greatly inhibited formation of the actin tail by intracellular S.flexneri. Furthermore, depletion of N-WASP from Xenopus egg extracts shut off Shigella actin tail assembly, and this was restored upon addition of N-WASP protein, suggesting that N-WASP is a critical host factor for the assembly of the actin tail by intracellular Shigella.

Cdc42 is a small GTPase of the Rho family which regulates the formation of actin filaments to generate filopodia1,2. Although there are several proteins such as PAK3, ACK4 and WASP (Wiskott–Aldrich syndrome protein)5 that bind Cdc42 directly, none of these can account for the filopodium formation induced by Cdc42. Here we demonstrate that before it can induce filopodium formation, Cdc42 must bind a WASP-related protein, N-WASP, that is richest in neural tissues6 but is expressed ubiquitously. N-WASP induces extremely long actin microspikes only when co-expressed with active Cdc42, whereas WASP, which is expressed in haematopoietic cells, does not, despite the structural similarities between WASP and N-WASP. In a cell-free system, addition of active Cdc42 significantly stimulates the actin-depolymerizing activity of N-WASP, creating free barbed ends from which actin polymerization can then take place. This activation seems to be caused by exposure of N-WASP's actin-depolymerizing region induced by Cdc42 binding.

Malignant gliomas remain associated with poor prognosis and high morbidity because of their ability to invade the brain; furthermore, human gliomas exhibit a phenotype of accelerated brain invasion in response to anti-angiogenic drugs. Here, we study 8 human glioblastoma cell lines; U251, U87, D54 and LN229 show accelerated motility in low ambient oxygen. Src inhibition by Dasatinib abrogates this phenotype. Molecular discovery and validation studies evaluate 46 molecules related to motility or the src pathway in U251 cells. Demanding that the molecular changes induced by low ambient oxygen are reversed by Dasatinib in U251 cells, identifies neural Wiskott-Aldrich syndrome protein (NWASP), Focal adhesion Kinase (FAK), [Formula: see text]-Catenin, and Cofilin. However, only Src-mediated NWASP phosphorylation distinguishes the four cell lines that exhibit enhanced motility in low ambient oxygen. Downregulating c-Src or NWASP by RNA interference abrogates the low-oxygen-induced enhancement in motility by in vitro assays and in organotypic brain slice cultures. The findings support the idea that c-Src and NWASP play key roles in mediating the molecular pathogenesis of low oxygen-induced accelerated brain invasion by gliomas.

We identified a novel adaptor protein that contains a Src homology (SH)3 domain, SH3 binding proline-rich sequences, and a leucine zipper-like motif and termed this protein WASP interacting SH3 protein (WISH). WISH is expressed predominantly in neural tissues and testis. It bound Ash/Grb2 through its proline-rich regions and neural Wiskott-Aldrich syndrome protein (N-WASP) through its SH3 domain. WISH strongly enhanced N-WASP–induced Arp2/3 complex activation independent of Cdc42 in vitro, resulting in rapid actin polymerization. Furthermore, coexpression of WISH and N-WASP induced marked formation of microspikes in Cos7 cells, even in the absence of stimuli. An N-WASP mutant (H208D) that cannot bind Cdc42 still induced microspike formation when coexpressed with WISH. We also examined the contribution of WISH to a rapid actin polymerization induced by brain extract in vitro. Arp2/3 complex was essential for brain extract–induced rapid actin polymerization. Addition of WISH to extracts increased actin polymerization as Cdc42 did. However, WISH unexpectedly could activate actin polymerization even in N-WASP–depleted extracts. These findings suggest that WISH activates Arp2/3 complex through N-WASP–dependent and –independent pathways without Cdc42, resulting in the rapid actin polymerization required for microspike formation.