IQGAP1 and NWASP promote human cancer cell dissemination and metastasis by regulating β1-integrin via FAK and MRTF/SRF

Attachment of circulating tumor cells to the endothelial cells (ECs) lining blood vessels is a critical step in cancer metastatic colonization, which leads to metastatic outgrowth. Breast and prostate cancers are common malignancies in women and men, respectively. Here, we observe that β1-integrin is required for human prostate and breast cancer cell adhesion to ECs under shear-stress conditions in vitro and to lung blood vessel ECs in vivo. We identify IQGAP1 and neural Wiskott-Aldrich syndrome protein (NWASP) as regulators of β1-integrin transcription and protein expression in prostate and breast cancer cells. IQGAP1 and NWASP depletion in cancer cells decreases adhesion to ECs in vitro and retention in the lung vasculature and metastatic lung nodule formation in vivo. Mechanistically, NWASP and IQGAP1 act downstream of Cdc42 to increase β1-integrin expression both via extracellular signal-regulated kinase (ERK)/focal adhesion kinase signaling at the protein level and by myocardin-related transcription factor/serum response factor (SRF) transcriptionally. Our results identify IQGAP1 and NWASP as potential therapeutic targets to reduce early metastatic dissemination.

The Chlamydia trachomatis secreted effector TmeA hijacks the N-WASP-ARP2/3 actin remodeling axis to facilitate cellular invasion

As an obligate intracellular pathogen, host cell invasion is paramount to Chlamydia trachomatis proliferation. While the mechanistic underpinnings of this essential process remain ill-defined, it is predicted to involve delivery of prepackaged effector proteins into the host cell that trigger plasma membrane remodeling and cytoskeletal reorganization. The secreted effector proteins TmeA and TarP, have risen to prominence as putative key regulators of cellular invasion and bacterial pathogenesis. Although several studies have begun to unravel molecular details underlying the putative function of TarP, the physiological function of TmeA during host cell invasion is unknown. Here, we show that TmeA employs molecular mimicry to bind to the GTPase binding domain of N-WASP, which results in recruitment of the actin branching ARP2/3 complex to the site of chlamydial entry. Electron microscopy revealed that TmeA mutants are deficient in filopodia capture, suggesting that TmeA/N-WASP interactions ultimately modulate host cell plasma membrane remodeling events necessary for chlamydial entry. Importantly, while both TmeA and TarP are necessary for effective host cell invasion, we show that these effectors target distinct pathways that ultimately converge on activation of the ARP2/3 complex. In line with this observation, we show that a double mutant suffers from a severe entry defect nearly identical to that observed when ARP3 is chemically inhibited or knocked down. Collectively, our study highlights both TmeA and TarP as essential regulators of chlamydial invasion that modulate the ARP2/3 complex through distinct signaling platforms, resulting in plasma membrane remodeling events that are essential for pathogen uptake.

N-Wasp Regulates Oligodendrocyte Myelination

Oligodendrocyte myelination depends on actin cytoskeleton rearrangement. Neural Wiskott-Aldrich syndrome protein(N-Wasp) is an actin nucleation factor that promotes polymerization of branched actin filaments. N-Wasp activity is essential for myelin membrane wrapping by Schwann cells, but its role in oligodendrocytes and CNS myelination remains unknown. Here we report that oligodendrocytes-specific deletion of N-Wasp in mice of both sexes resulted in hypomyelination (i.e., reduced number of myelinated axons and thinner myelin profiles), as well as substantial focal hypermyelination reflected by the formation of remarkably long myelin outfolds. These myelin outfolds surrounded unmyelinated axons, neuronal cell bodies, and other myelin profiles. The latter configuration resulted in pseudo-multimyelin profiles that were often associated with axonal detachment and degeneration throughout the CNS, including in the optic nerve, corpus callosum, and the spinal cord. Furthermore, developmental analysis revealed that myelin abnormalities were already observed during the onset of myelination, suggesting that they are formed by aberrant and misguided elongation of the oligodendrocyte inner lip membrane. Our results demonstrate that N-Wasp is required for the formation of normal myelin in the CNS. They also reveal that N-Wasp plays a distinct role in oligodendrocytes compared with Schwann cells, highlighting a difference in the regulation of actin dynamics during CNS and PNS myelination.SIGNIFICANCE STATEMENT Myelin is critical for the normal function of the nervous system by facilitating fast conduction of action potentials. During the process of myelination in the CNS, oligodendrocytes undergo extensive morphological changes that involve cellular process extension and retraction, axonal ensheathment, and myelin membrane wrapping. Here we present evidence that N-Wasp, a protein regulating actin filament assembly through Arp2/3 complex-dependent actin nucleation, plays a critical role in CNS myelination, and its absence leads to several myelin abnormalities. Our data provide an important step into the understanding of the molecular mechanisms underlying CNS myelination.

N-WASP Control of LPAR1 Trafficking Establishes Response to Self-Generated LPA Gradients to Promote Pancreatic Cancer Cell Metastasis

Pancreatic ductal adenocarcinoma is one of the most invasive and metastatic cancers and has a dismal 5-year survival rate. We show that N-WASP drives pancreatic cancer metastasis, with roles in both chemotaxis and matrix remodeling. lysophosphatidic acid, a signaling lipid abundant in blood and ascites fluid, is both a mitogen and chemoattractant for cancer cells. Pancreatic cancer cells break lysophosphatidic acid down as they respond to it, setting up a self-generated gradient driving tumor egress. N-WASP-depleted cells do not recognize lysophosphatidic acid gradients, leading to altered RhoA activation, decreased contractility and traction forces, and reduced metastasis. We describe a signaling loop whereby N-WASP and the endocytic adapter SNX18 promote lysophosphatidic acid-induced RhoA-mediated contractility and force generation by controlling lysophosphatidic acid receptor recycling and preventing degradation. This chemotactic loop drives collagen remodeling, tumor invasion, and metastasis and could be an important target against pancreatic cancer spread.

Loss of N-WASP drives early progression in an Apc model of intestinal tumourigenesis

N-WASP (WASL) is a widely expressed cytoskeletal signalling and scaffold protein also implicated in regulation of Wnt signalling and homeostatic maintenance of skin epithelial architecture. N-WASP mediates invasion of cancer cells in vitro and its depletion reduces invasion and metastatic dissemination of breast cancer. Given this role in cancer invasion and universal expression in the gastrointestinal tract, we explored a role for N-WASP in the initiation and progression of colorectal cancer. While deletion of N-wasp is not detectably harmful in the murine intestinal tract, numbers of Paneth cells increased, indicating potential changes in the stem cell niche, and migration up the crypt-villus axis was enhanced. Loss of N-wasp promoted adenoma formation in an adenomatous polyposis coli (Apc) deletion model of intestinal tumourigenesis. Thus, we establish a tumour suppressive role of N-WASP in early intestinal carcinogenesis despite its later pro-invasive role in other cancers. Our study highlights that while the actin cytoskeletal machinery promotes invasion of cancer cells, it also maintains normal epithelial tissue function and thus may have tumour suppressive roles in pre-neoplastic tissues. © 2018 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

MicroRNA-214-5p Inhibits the Invasion and Migration of Hepatocellular Carcinoma Cells by Targeting Wiskott-Aldrich Syndrome Like

BACKGROUND/AIMS

This study aims to explore the effects of microRNA-214-5p (miR-214-5p) on the invasion and migration of Hepatocellular Carcinoma cells (HCC).

METHODS

Hepatocellular Carcinoma tissues and adjacent normal tissues from 44 hepatocellular carcinoma patients were prepared for this study. The HepG2 and BEL-7402 cells were transfected with miR-214-5p mimic and inhibitor. qRT-PCR was performed to detect the expressions of miR-214-5p. Transwell assays were used to detect the invasion and migration assays in HepG2 and BEL-7402 cells. A dual-luciferase reporter assay was conducted to examine the effect of miR-214-5p on Wiskott-Aldrich Syndrome Like (WASL/ N-WASP). Western blot and qRT-PCR were used to measure the expressions of the E-cadherin, N-cadherin and Vimentin proteins. Transwell chamber assays were performed to detect cell invasion and migration.

RESULTS

Compared with normal tissues, HCC tissues demonstrated significantly lower expression of miR-214-5p. Overexpression of miR-214-5p significantly inhibited the migration and invasion of HCC cells and inhibition of miR-214-5p promoted the migration and invasion. Additionally, miR-214-5p suppressed the epithelial-mesenchymal transition (EMT). Further study showed WASL was a putative target gene of miR-214-5p. Up-regulating the expression of WASL could reverse the inhibition effect of miR-214-5p on invasion and migration.

CONCLUSION

Our data suggested that miR-214-5p inhibited the invasion and migration of HepG2 and BEL-7402 by targeting WASL in Hepatocellular carcinoma.

The prognostic value of CXCR4, α-SMA and WASL in upper lip basal cell carcinomas

Lip cancers account for 10-12% of the total head and neck cancers and, although squamous cell carcinoma is by far the most common lower lip cancer, the basal cell carcinoma (BCC) seems to be more common for the upper lip. Most BCCs have a clinically indolent behavior, but there are also local aggressive and∕or metastatic cases, with the incidence of such cases being estimated at about 1-10% of all cases of BCC. Many of the molecular mechanisms underlying this aggression are still unknown, which is why our study aimed to investigate the potential prognosis of a few markers, such as C-X-C chemokine receptor type 4 (CXCR4), alpha-smooth muscle actin (α-SMA) and Wiskott-Aldrich syndrome like (WASL) in upper lip BCCs. For this purpose, 24 basocellular cancers with this localization have been investigated immunohistochemically, histopathologically belonging to the next varieties: superficial, nodular, micronodular, adenoid cystic, keratotic, sclerodermiform and mixed. Regardless of the histopathological subtype, for all invasive cases we have recorded an increased reactivity of the three markers especially in the invasion front, reactivity also present at the stroma level, especially at the stroma-parenchyma interface. The most intense immunoreactivity was obtained for the micronodular and sclerodermiform subtypes, confirming their biological behavior to be more aggressive than the rest of the investigated strains. All these results confirm the prognostic value of the CXCR4∕α-SMA∕WASL panel in assessing the biological behavior of the upper lip BCC.

Oncogenic KRas-induced Increase in Fluid-phase Endocytosis is Dependent on N-WASP and is Required for the Formation of Pancreatic Preneoplastic Lesions

Fluid-phase endocytosis is a homeostatic process with an unknown role in tumor initiation. The driver mutation in pancreatic ductal adenocarcinoma (PDAC) is constitutively active KRasG12D, which induces neoplastic transformation of acinar cells through acinar-to-ductal metaplasia (ADM). We have previously shown that KRasG12D-induced ADM is dependent on RAC1 and EGF receptor (EGFR) by a not fully clarified mechanism. Using three-dimensional mouse and human acinar tissue cultures and genetically engineered mouse models, we provide evidence that (i) KRasG12D leads to EGFR-dependent sustained fluid-phase endocytosis (FPE) during acinar metaplasia; (ii) variations in plasma membrane tension increase FPE and lead to ADM in vitro independently of EGFR; and (iii) that RAC1 regulates ADM formation partially through actin-dependent regulation of FPE. In addition, mice with a pancreas-specific deletion of the Neural-Wiskott-Aldrich syndrome protein (N-WASP), a regulator of F-actin, have reduced FPE and impaired ADM emphasizing the in vivo relevance of our findings. This work defines a new role of FPE as a tumor initiating mechanism.

The Shigella Virulence Factor IcsA Relieves N-WASP Autoinhibition by Displacing the Verprolin Homology/Cofilin/Acidic (VCA) Domain

Shigella flexneri is a bacterial pathogen that invades cells of the gastrointestinal tract, causing severe dysentery. Shigella mediates intracellular motility and spreading via actin comet tail formation. This process is dependent on the surface-exposed, membrane-embedded virulence factor IcsA, which recruits the host actin regulator N-WASP. Although it is clear that Shigella requires N-WASP for this process, the molecular details of this interaction and the mechanism of N-WASP activation remain poorly understood. Here, we show that co-expression of full-length IcsA and the Shigella membrane protease IcsP yields highly pure IcsA passenger domain (residues 53-758). We show that IcsA is monomeric and describe the solution structure of the passenger domain obtained by small-angle X-ray scattering (SAXS) analysis. The SAXS-derived models suggest that IcsA has an elongated shape but, unlike most other autotransporter proteins, possesses a central kink revealing a distinctly curved structure. Pull-down experiments show direct binding of the IcsA passenger domain to both the WASP homology 1 (WH1) domain and the GTPase binding domain (GBD) of N-WASP and no binding to the verprolin homology/cofilin/acidic (VCA) region. Using fluorescence polarization experiments, we demonstrate that IcsA binding to the GBD region displaces the VCA peptide and that this effect is synergistically enhanced upon IcsA binding to the WH1 region. Additionally, domain mapping of the IcsA interaction interface reveals that different regions of IcsA bind to the WH1 and GBD domains of N-WASP. Taken together, our data support a model where IcsA and N-WASP form a tight complex releasing the N-WASP VCA domain to recruit the host cell machinery for actin tail formation.

The cell division control protein 42-Src family kinase-neural Wiskott-Aldrich syndrome protein pathway regulates human proplatelet formation

Essentials The role of the cytoskeleton during megakaryocyte differentiation was examined. Human megakaryocytes are derived from in vitro cultured CD34+ cells. Cell division control protein 42 (CDC42) positively regulates proplatelet formation (PPF). Neural Wiskott-Aldrich syndrome protein, the main effector of CDC42 with Src positively regulates PPF.

SUMMARY

Background Cytoskeletal rearrangements are essential for platelet release. The RHO small GTPase family, as regulators of the actin cytoskeleton, play an important role in proplatelet formation (PPF). In the neuronal system, CDC42 is involved in axon formation, a process that combines elongation and branching as for PPF. Objective To analyze the role of CDC42 and its effectors of the Wiskott-Aldrich syndrome protein (WASP) family in PPF. Methods Human megakaryocytes (MKs) were obtained from CD34+ cells. Inhibition of CDC42 in MKs was performed with the chemical inhibitor CASIN or with an active or a dominant-negative form of CDC42. The knock-down of N-WASP was obtained with a small hairpin RNA strategy Results Herein, we show that CDC42 activity increased during MK differentiation. The use of the chemical inhibitor CASIN or of an active or a dominant-negative form of CDC42 demonstrated that CDC42 positively regulated PPF in vitro. We determined that N-WASP, but not WASP, regulated PPF. We found that N-WASP knockdown led to a marked decrease in PPF, owing to a defect in the demarcation membrane system (DMS). This was associated with RHOA activation, and a concomitant augmentation in the phosphorylation of mysosin light chain 2. Phosphorylation of N-WASP, creating a primed form of N-WASP, increased during MK differentiation. Phosphorylation inhibition by two Src family kinase inhibitors decreased PPF. Conclusions We conclude that N-WASP positively regulates DMS development and PPF, and that the Src family kinases in association with CDC42 regulate PPF through N-WASP.

microRNA miR-142-3p Inhibits Breast Cancer Cell Invasiveness by Synchronous Targeting of WASL, Integrin Alpha V, and Additional Cytoskeletal Elements

MicroRNAs (miRNAs, micro ribonucleic acids) are pivotal post-transcriptional regulators of gene expression. These endogenous small non-coding RNAs play significant roles in tumorigenesis and tumor progression. miR-142-3p expression is dysregulated in several breast cancer subtypes. We aimed at investigating the role of miR-142-3p in breast cancer cell invasiveness. Supported by transcriptomic Affymetrix array analysis and confirmatory investigations at the mRNA and protein level, we demonstrate that overexpression of miR-142-3p in MDA-MB-231, MDA-MB-468 and MCF-7 breast cancer cells leads to downregulation of WASL (Wiskott-Aldrich syndrome-like, protein: N-WASP), Integrin-αV, RAC1, and CFL2, molecules implicated in cytoskeletal regulation and cell motility. ROCK2, IL6ST, KLF4, PGRMC2 and ADCY9 were identified as additional targets in a subset of cell lines. Decreased Matrigel invasiveness was associated with the miR-142-3p-induced expression changes. Confocal immunofluorescence microscopy, nanoscale atomic force microscopy and digital holographic microscopy revealed a change in cell morphology as well as a reduced cell volume and size. A more cortical actin distribution and a loss of membrane protrusions were observed in cells overexpressing miR-142-3p. Luciferase activation assays confirmed direct miR-142-3p-dependent regulation of the 3’-untranslated region of ITGAV and WASL. siRNA-mediated depletion of ITGAV and WASL resulted in a significant reduction of cellular invasiveness, highlighting the contribution of these factors to the miRNA-dependent invasion phenotype. While knockdown of WASL significantly reduced the number of membrane protrusions compared to controls, knockdown of ITGAV resulted in a decreased cell volume, indicating differential contributions of these factors to the miR-142-3p-induced phenotype. Our data identify WASL, ITGAV and several additional cytoskeleton-associated molecules as novel invasion-promoting targets of miR-142-3p in breast cancer.

N-wasp is required for structural integrity of the blood-testis barrier

During spermatogenesis, the blood-testis barrier (BTB) segregates the adluminal (apical) and basal compartments in the seminiferous epithelium, thereby creating a privileged adluminal environment that allows post-meiotic spermatid development to proceed without interference of the host immune system. A key feature of the BTB is its continuous remodeling within the Sertoli cells, the major somatic component of the seminiferous epithelium. This remodeling is necessary to allow the transport of germ cells towards the seminiferous tubule interior, while maintaining intact barrier properties. Here we demonstrate that the actin nucleation promoting factor Neuronal Wiskott-Aldrich Syndrome Protein (N-WASP) provides an essential function necessary for BTB restructuring, and for maintaining spermatogenesis. Our data suggests that the N-WASP-Arp2/3 actin polymerization machinery generates branched-actin arrays at an advanced stage of BTB remodeling. These arrays are proposed to mediate the restructuring process through endocytic recycling of BTB components. Disruption of N-WASP in Sertoli cells results in major structural abnormalities to the BTB, including mis-localization of critical junctional and cytoskeletal elements, and leads to disruption of barrier function. These impairments result in a complete arrest of spermatogenesis, underscoring the critical involvement of the somatic compartment of the seminiferous tubules in germ cell maturation.

Mammalian spermatogenesis takes place within a sheltered environment, whereby somatic Sertoli cells protect and guide germ cells as they mature and differentiate. A key structure generated by the protective Sertoli cell epithelium is the blood-testis barrier (BTB), a composite of junctional and cytoskeletal elements, which prevents exposure of post-meiotic spermatids to the immune system. The BTB is a highly dynamic structure, which needs to be dismantled and rapidly rebuilt, in order to allow passage of maturing preleptotene spermatocytes, without compromising their isolation. Here we show that N-WASP, a conserved facilitator of formation of branched actin microfilament arrays, provides a function that is essential for maintenance of an intact BTB. Genetic disruption of N-WASP in mouse Sertoli cells leads to loss of BTB impermeability, resulting in a complete arrest of spermatogenesis at early and post-meiotic stages. Based on the localization patterns of key elements, we propose that branched-actin filaments participate in recycling of BTB materials to ensure the dynamic and efficient maintenance of this structure, one of a series of blood-tissue barriers that preserve privileged organ environments.

c-Src and neural Wiskott-Aldrich syndrome protein (N-WASP) promote low oxygen-induced accelerated brain invasion by gliomas

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), -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.

The antagonistic modulation of Arp2/3 activity by N-WASP, WAVE2 and PICK1 defines dynamic changes in astrocyte morphology

Astrocytes exhibit a complex, branched morphology, allowing them to functionally interact with numerous blood vessels, neighboring glial processes and neuronal elements, including synapses. They also respond to central nervous system (CNS) injury by a process known as astrogliosis, which involves morphological changes, including cell body hypertrophy and thickening of major processes. Following severe injury, astrocytes exhibit drastically reduced morphological complexity and collectively form a glial scar. The mechanistic details behind these morphological changes are unknown. Here, we investigate the regulation of the actin-nucleating Arp2/3 complex in controlling dynamic changes in astrocyte morphology. In contrast to other cell types, Arp2/3 inhibition drives the rapid expansion of astrocyte cell bodies and major processes. This intervention results in a reduced morphological complexity of astrocytes in both dissociated culture and in brain slices. We show that this expansion requires functional myosin II downstream of ROCK and RhoA. Knockdown of the Arp2/3 subunit Arp3 or the Arp2/3 activator N-WASP by siRNA also results in cell body expansion and reduced morphological complexity, whereas depleting WAVE2 specifically reduces the branching complexity of astrocyte processes. By contrast, knockdown of the Arp2/3 inhibitor PICK1 increases astrocyte branching complexity. Furthermore, astrocyte expansion induced by ischemic conditions is delayed by PICK1 knockdown or N-WASP overexpression. Our findings identify a new morphological outcome for Arp2/3 activation in restricting rather than promoting outwards movement of the plasma membrane in astrocytes. The Arp2/3 regulators PICK1, and N-WASP and WAVE2 function antagonistically to control the complexity of astrocyte branched morphology, and this mechanism underlies the morphological changes seen in astrocytes during their response to pathological insult.

Identification of Shigella flexneri IcsA residues affecting interaction with N-WASP, and evidence for IcsA-IcsA co-operative interaction

The Shigella flexneri IcsA (VirG) protein is a polarly distributed outer membrane protein that is a fundamental virulence factor which interacts with neural Wiskott-Aldrich syndrome protein (N-WASP). The activated N-WASP then activates the Arp2/3 complex which initiates de novo actin nucleation and polymerisation to form F-actin comet tails and allows bacterial cell-to-cell spreading. In a previous study, IcsA was found to have three N-WASP interacting regions (IRs): IR I (aa 185-312), IR II (aa 330-382) and IR III (aa 508-730). The aim of this study was to more clearly define N-WASP interacting regions II and III by site-directed mutagenesis of specific amino acids. Mutant IcsA proteins were expressed in both smooth lipopolysaccharide (S-LPS) and rough LPS (R-LPS) S. flexneri strains and characterised for IcsA production level, N-WASP recruitment and F-actin comet tail formation. We have successfully identified new amino acids involved in N-WASP recruitment within different N-WASP interacting regions, and report for the first time using co-expression of mutant IcsA proteins, that N-WASP activation involves interactions with different regions on different IcsA molecules as shown by Arp3 recruitment. In addition, our findings suggest that autochaperone (AC) mutant protein production was not rescued by another AC region provided in trans, differing to that reported for two other autotransporters, PrtS and BrkA autotransporters.

N-WASP coordinates the delivery and F-actin-mediated capture of MT1-MMP at invasive pseudopods

Metastasizing tumor cells use matrix metalloproteases, such as the transmembrane collagenase MT1-MMP, together with actin-based protrusions, to break through extracellular matrix barriers and migrate in dense matrix. Here we show that the actin nucleation-promoting protein N-WASP (Neural Wiskott-Aldrich syndrome protein) is up-regulated in breast cancer, and has a pivotal role in mediating the assembly of elongated pseudopodia that are instrumental in matrix degradation. Although a role for N-WASP in invadopodia was known, we now show how N-WASP regulates invasive protrusion in 3D matrices. In actively invading cells, N-WASP promoted trafficking of MT1-MMP into invasive pseudopodia, primarily from late endosomes, from which it was delivered to the plasma membrane. Upon MT1-MMP's arrival at the plasma membrane in pseudopodia, N-WASP stabilized MT1-MMP via direct tethering of its cytoplasmic tail to F-actin. Thus, N-WASP is crucial for extension of invasive pseudopods into which MT1-MMP traffics and for providing the correct cytoskeletal framework to couple matrix remodeling with protrusive invasion.

Nck and Cdc42 co-operate to recruit N-WASP to promote FcγR-mediated phagocytosis

The adaptor protein Nck has been shown to link receptor ligation to actin-based signalling in a diverse range of cellular events, such as changes in cell morphology and motility. It has also been implicated in phagocytosis. However, its molecular role in controlling actin remodelling associated with phagocytic uptake remains to be clarified. Here, we show that Nck, which is recruited to phagocytic cups, is required for Fcγ receptor (FcγR)- but not complement receptor 3 (CR3)-induced phagocytosis. Nck recruitment in response to FcγR ligation is mediated by the phosphorylation of tyrosine 282 and 298 in the ITAM motif in the cytoplasmic tail of the receptor. In the absence of FcγR phosphorylation, there is also no recruitment of N-WASP or Cdc42 to phagocytic cups. Nck promotes FcγR-mediated phagocytosis by recruiting N-WASP to phagocytic cups. Efficient phagocytosis, however, only occurs, if the CRIB domain of N-WASP can also interact with Cdc42. Our observations demonstrate that Nck and Cdc42 collaborate to stimulate N-WASP-dependent FcγR-mediated phagocytosis.

N-WASP-mediated invadopodium formation is involved in intravasation and lung metastasis of mammary tumors

Invadopodia are proteolytic membrane protrusions formed by highly invasive cancer cells, commonly observed on substrate(s) mimicking extracellular matrix. Although invadopodia are proposed to have roles in cancer invasion and metastasis, direct evidence has not been available. We previously reported that neural Wiskott-Aldrich syndrome protein (N-WASP), a member of WASP family proteins that regulate reorganization of the actin cytoskeleton, is an essential component of invadopodia. Here, we report that N-WASP-mediated invadopodium formation is essential in breast cancer invasion, intravasation and lung metastasis. We established stable cell lines based on MTLn3 rat mammary adenocarcinoma cells that either overexpressed a dominant-negative (DN) N-WASP construct or in which N-WASP expression was silenced by a pSuper N-WASP shRNA. Both the N-WASP shRNA and DN N-WASP cells showed a markedly decreased ability to form invadopodia and degrade extracellular matrix. In addition, formation of invadopodia in primary tumors and collagen I degradation were reduced in the areas of invasion (collagen-rich areas in the invasive edge of the tumor) and in the areas of intravasation (blood-vessel-rich areas). Our results suggest that tumor cells in vivo that have a decreased activity of N-WASP also have a reduced ability to form invadopodia, migrate, invade, intravasate and disseminate to lung compared with tumor cells with parental N-WASP levels.

Putative phosphorylation sites on WCA domain of HA2 is essential for Helicoverpa armigera single nucleopolyhedrovirus replication

Protein phosphorylation is one of the most common post-translational modification processes that play an essential role in regulating protein functionality. The Helicoverpa armigera single nucleopolyhedrovirus (HearNPV) orf2-encoded nucleocapsid protein HA2 participates in orchestration of virus-induced actin polymerization through its WCA domain, in which phosphorylation status are supposed to be critical in respect to actin polymerization. In the present study, two putative phosphorylation sites ((232)Thr and (250)Ser) and a highly conserved Serine ((245)Ser) on the WCA domain of HA2 were mutated, and their phenotypes were characterized by reintroducing the mutated HA2 into the HearNPV genome. Viral infectivity assays demonstrated that only the recombinant HearNPV bearing HA2 mutation at (245)Ser can produce infectious virions, both (232)Thr and (250)Ser mutations were lethal to the virus. However, actin polymerization assay demonstrated that all the three viruses bearing HA2 mutations were still capable of initiating actin polymerization in the host nucleus, which indicated the putative phosphorylation sites on HA2 may contribute to HearNPV replication through another unidentified pathway.

Neural Wiskott-Aldrich syndrome protein is required for accurate chromosome congression and segregation

The accurate distribution and segregation of replicated chromosomes through mitosis is crucial for cellular viability and development of organisms. Kinetochores are responsible for the proper congression and segregation of chromosomes. Here, we show that neural Wiskott-Aldrich syndrome protein (N-WASP) localizes to and forms a complex with kinetochores in mitotic cells. Depletion of NWASP by RNA interference causes chromosome misalignment, prolonged mitosis, and abnormal chromosomal segregation, which is associated with decreased proliferation of N-WASP-deficient cells. N-WASP-deficient cells display defects in the kinetochores recruitment of inner and outer kinetochore components, CENP-A, CENP-E, and Mad2. Live-cell imaging analysis of GFP-α-tubulin revealed that depletion of N-WASP impairs microtubule attachment to chromosomes in mitotic cells. All these results indicate that N-WASP plays a role in efficient assembly of kinetochores and attachment of microtubules to chromosomes, which is essential for accurate chromosome congression and segregation.

Bacterial actin assembly requires toca-1 to relieve N-wasp autoinhibition

Actin polymerization in the mammalian cytosol can be locally activated by mechanisms that relieve the autoinhibited state of N-WASP, an initiator of actin assembly, a process that also requires the protein Toca-1. Several pathogenic bacteria, including Shigella, exploit this host feature to infect and disseminate efficiently. The Shigella outer membrane protein IcsA recruits N-WASP, which upon activation at the bacterial surface mediates localized actin polymerization. The molecular role of Toca-1 in N-WASP activation during physiological or pathological actin assembly processes in intact mammalian cells remains unclear. We show that actin tail initiation by S. flexneri requires Toca-1 for the conversion of N-WASP from a closed inactive conformation to an open active one. While N-WASP recruitment is dependent on IcsA, Toca-1 recruitment is instead mediated by S. flexneri type III secretion effectors. Thus, S. flexneri independently hijacks two nodes of the N-WASP actin assembly pathway to initiate localized actin tail assembly.

Sorting nexin 9 interacts with dynamin 1 and N-WASP and coordinates synaptic vesicle endocytosis

Sorting nexin 9 (SNX9) is a member of the sorting nexin family of proteins, each of which contains a characteristic Phox homology domain. SNX9 is widely expressed and plays a role in clathrin-mediated endocytosis, but it is not known if it is present in neuronal cells. We report that SNX9 is expressed in the presynaptic compartment of cultured hippocampal neurons, where it binds to dynamin-1 and N-WASP. Overexpression of full-length SNX9 or a C-terminal truncated version caused severe defects in synaptic vesicle endocytosis during, as well as after, stimulation. Knockdown of SNX9 with short interfering RNA also reduced synaptic vesicle endocytosis, and the W39A mutation of SNX9 abolished the inhibitory effect of SNX9 on endocytosis. Rescue experiments showed that most of the effect of SNX9 on endocytosis results from its interaction with dynamin 1, although its interaction with N-WASP contributes in some degree. We further showed that SNX9 dimerizes through its C-terminal domain, suggesting that it may interact simultaneously with dynamin 1 and N-WASP. We propose that SNX9 interacts with dynamin-1 and N-WASP in presynaptic terminals, where it links actin dynamics and synaptic vesicle endocytosis.

Cdc42 and phosphoinositide 3-kinase drive Rac-mediated actin polymerization downstream of c-Met in distinct and common pathways

Activation of c-Met, the hepatocyte growth factor (HGF)/scatter factor receptor induces reorganization of the actin cytoskeleton, which drives epithelial cell scattering and motility and is exploited by pathogenic Listeria monocytogenes to invade nonepithelial cells. However, the precise contributions of distinct Rho-GTPases, the phosphatidylinositol 3-kinases, and actin assembly regulators to c-Met-mediated actin reorganization are still elusive. Here we report that HGF-induced membrane ruffling and Listeria invasion mediated by the bacterial c-Met ligand internalin B (InlB) were significantly impaired but not abrogated upon genetic removal of either Cdc42 or pharmacological inhibition of phosphoinositide 3-kinase (PI3-kinase). While loss of Cdc42 or PI3-kinase function correlated with reduced HGF- and InlB-triggered Rac activation, complete abolishment of actin reorganization and Rac activation required the simultaneous inactivation of both Cdc42 and PI3-kinase signaling. Moreover, Cdc42 activation was fully independent of PI3-kinase activity, whereas the latter partly depended on Cdc42. Finally, Cdc42 function did not require its interaction with the actin nucleation-promoting factor N-WASP. Instead, actin polymerization was driven by Arp2/3 complex activation through the WAVE complex downstream of Rac. Together, our data establish an intricate signaling network comprising as key molecules Cdc42 and PI3-kinase, which converge on Rac-mediated actin reorganization essential for Listeria invasion and membrane ruffling downstream of c-Met.

Mechanism of actin network attachment to moving membranes: barbed end capture by N-WASP WH2 domains

Actin filament networks exert protrusive and attachment forces on membranes and thereby drive membrane deformation and movement. Here, we show that N-WASP WH2 domains play a previously unanticipated role in vesicle movement by transiently attaching actin filament barbed ends to the membrane. To dissect the attachment mechanism, we reconstituted the propulsive motility of lipid-coated glass beads, using purified soluble proteins. N-WASP WH2 mutants assembled actin comet tails and initiated movement, but the comet tails catastrophically detached from the membrane. When presented on the surface of a lipid-coated bead, WH2 domains were sufficient to maintain comet tail attachment. In v-Src-transformed fibroblasts, N-WASP WH2 mutants were severely defective in the formation of circular podosome arrays. In addition to creating an attachment force, interactions between WH2 domains and barbed ends may locally amplify signals for dendritic actin nucleation.

Hyaluronan-CD44 Interaction with Neural Wiskott-Aldrich Syndrome Protein (N-WASP) Promotes Actin Polymerization and ErbB2 Activation Leading to β-Catenin Nuclear Translocation, Transcriptional Up-regulation, and Cell Migration in Ovarian Tumor Cells

In this study we have investigated the interaction of hyaluronan (HA) and CD44 with the neuronal Wiskott-Aldrich syndrome protein (N-WASP) in regulating actin polymerization and ErbB2/beta-catenin signaling in human ovarian tumor cells (SK-OV-3.ipl cells). Biochemical and immunological analyses indicate that N-WASP is expressed in SK-OV-3.ipl cells and that the binding of HA stimulates N-WASP association with CD44 and Arp2/Arp3 leading to filamentous actin formation and ovarian tumor cell migration. In addition, HA binding promotes CD44-N-WASP association with ErbB2 and activates ErbB2 kinase activity that in turn increases phosphorylation of the cytoskeletal protein, beta-catenin. Subsequently, phosphorylated beta-catenin is transported into the nucleus leading to beta-catenin-mediated TCF/LEF-transcriptional co-activation. Because HA-induced beta-catenin phosphorylation, nuclear translocation, and TCF/LEF transcriptional activation is effectively blocked by the ErbB2 inhibitor, AG825, we conclude that HA/CD44-N-WASP-associated ErbB2 activation is required for beta-catenin-mediated signaling events. Transfection of SK-OV-3.ipl cells with N-WASP-VCA (verpolin homology, cofilin homology, and acidic domain) fragment cDNA not only blocks HA/CD44-induced N-WASP-Arp2/3 complex formation but also inhibits actin polymerization/F-actin assembly and tumor cell migration. Overexpression of the N-WASP-VCA domain also significantly reduces HA-induced ErbB2 recruitment to CD44, diminishes beta-catenin phosphorylation/nuclear translocation, and abrogates TCF/LEF-specific transcriptional co-activation by beta-catenin. Taken together, our findings strongly suggest that N-WASP plays a pivotal role in regulating HA-mediated CD44-ErbB2 interaction, beta-catenin signaling, and actin cytoskeleton functions that are required for tumor-specific behaviors and ovarian cancer progression.

N-WASP regulates extension of filopodia and processes by oligodendrocyte progenitors, oligodendrocytes, and Schwann cells—implications for axon ensheathment at myelination

The molecular mechanisms used by oligodendrocyte precursor cells (OPCs), oligodendrocytes (OLs), and Schwann cells (SCs) to advance processes for motility in the developing nervous system and to ensheath axons at myelination are currently not well defined. Here we demonstrate that OPCs, OLs, and SCs express the major proteins involved in actin polymerization-driven protrusion; these key proteins including F-actin, the Arp2/3 complex, neural-Wiskott Aldrich Syndrome protein (N-WASP) and WAVE proteins, and the RhoGTPases Rac and Cdc42 are present at the leading edges of processes being extended by OPCs, OLs, and SCs. We reveal by real-time PCR that OLs and SCs have different dominant WAVE isoforms. Inhibition of the WASP/WAVE protein, N-WASP, with wiskostatin that prevents activation of the Arp2/3 complex, blocks process extension by OPCs and SCs. Inhibition of N-WASP also causes OPC and SC process retraction, which is preceded by retraction of filopodia. This implicates filopodia in OPC and SC process stability and also of N-WASP in OPC and SC process dynamics. We also demonstrate that p34 (a component of the Arp2/3 complex), WASP/WAVE proteins, actin, alpha-tubulin, Rac, Cdc42, vinculin, and focal adhesion kinase are detected in water-shocked myelin purified from brain. Inhibition of N-WASP with wiskostatin decreases the number of axons undergoing initial ensheathment in intact optic nerve samples and reduces the Po content of dorsal root ganglia:SC co-cultures. Our findings indicate that OPCs, OLs, and SCs extend processes using actin polymerization-driven protrusion dependent on N-WASP. We hypothesize that inner mesaxons of OLs and SCs use the same mechanism to ensheath axons at myelination.

N-WASP involvement in dorsal ruffle formation in mouse embryonic fibroblasts

The Wiskott-Aldrich syndrome protein (WASP) family activates the Arp2/3 complex leading to the formation of new actin filaments. Here, we study the involvement of Scar1, Scar2, N-WASP, and Arp2/3 complex in dorsal ruffle formation in mouse embryonic fibroblasts (MEFs). Using platelet-derived growth factor to stimulate circular dorsal ruffle assembly in primary E13 and immortalized E9 Scar1(+/+) and Scar1 null MEFs, we establish that Scar1 loss does not impair the formation of dorsal ruffles. Reduction of Scar2 protein levels via small interfering RNA (siRNA) also did not affect dorsal ruffle production. In contrast, wiskostatin, a chemical inhibitor of N-WASP, potently suppressed dorsal ruffle formation in a dose-dependent manner. Furthermore, N-WASP and Arp2 siRNA treatment significantly decreased the formation of dorsal ruffles in MEFs. In addition, the expression of an N-WASP truncation mutant that cannot bind Arp2/3 complex blocked the formation of these structures. Finally, N-WASP(-/-) fibroblast-like cells generated aberrant dorsal ruffles. These ruffles were highly unstable, severely depleted of Arp2/3 complex, and diminished in size. We hypothesize that N-WASP and Arp2/3 complex are part of a multiprotein assembly important for the generation of dorsal ruffles and that Scar1 and Scar2 are dispensable for this process.

Regulation of RNA-polymerase-II-dependent transcription by N-WASP and its nuclear-binding partners

The presence of actin in the nucleus has been well established, and several studies have implicated nuclear actin in transcriptional regulation. Neuronal Wiskott-Aldrich syndrome protein (N-WASP) is a member of the WASP family of proteins; these proteins function in the cytoplasm as key regulators of cortical actin filament. Interestingly, N-WASP has also been observed in the nucleus. However, a potential nuclear function for N-WASP has not been established. Here, we report the identification of nuclear N-WASP within a large nuclear-protein complex containing PSF-NonO (polypyrimidine-tract-binding-protein-associated splicing factor-non-Pou-domain octamer-binding protein/p54(nrb)), nuclear actin and RNA polymerase II. The PSF-NonO complex is involved in the regulation of many cellular processes, such as transcription, RNA processing, DNA unwinding and repair. We demonstrate that the interaction of N-WASP with the PSF-NonO complex can couple N-WASP with RNA polymerase II to regulate transcription. We also provide evidence that the potential function of N-WASP in promoting polymerization of nuclear actins has an important role in this process. Based on these results, we propose a nuclear function for N-WASP in transcriptional regulation.

Interaction of N-WASP with hnRNPK and its role in filopodia formation and cell spreading

N-WASP is a member of the WASP family of proteins, which play essential roles in actin dynamics during cell adhesion and migration. hnRNPK is a member of the heterogeneous nuclear ribonucleoprotein complex, which has also been implicated in the regulation of cell spreading. Here, we identify a direct interaction between N-WASP and hnRNPK. We show that this interaction is mediated by the N-terminal WH1 domain of N-WASP and the segment of hnRNPK containing its K interaction (KI) domain. Furthermore, these two proteins are co-localized at the cell periphery in the spreading initiation center during the early stage of cell spreading. We found that co-expression of hnRNPK with N-WASP reverses the stimulation of cell spreading by N-WASP, and this effect is correlated with hnRNPK binding to N-WASP. Expression of hnRNPK does not affect subcellular localization of N-WASP protein. However, co-expression of hnRNPK with N-WASP reduced filopodia formation stimulated by N-WASP in spreading cells. Together, these results identify hnRNPK as a new negative regulator of N-WASP and suggest that hnRNPK may regulate the initial stage of cell spreading by direct association with N-WASP in the spreading initiation center.

Coordination between the actin cytoskeleton and membrane deformation by a novel membrane tubulation domain of PCH proteins is involved in endocytosis

The conserved FER-CIP4 homology (FCH) domain is found in the pombe Cdc15 homology (PCH) protein family members, including formin-binding protein 17 (FBP17). However, the amino acid sequence homology extends beyond the FCH domain. We have termed this region the extended FC (EFC) domain. We found that FBP17 coordinated membrane deformation with actin cytoskeleton reorganization during endocytosis. The EFC domains of FBP17, CIP4, and other PCH protein family members show weak homology to the Bin-amphiphysin-Rvs (BAR) domain. The EFC domains bound strongly to phosphatidylserine and phosphatidylinositol 4,5-bisphosphate and deformed the plasma membrane and liposomes into narrow tubules. Most PCH proteins possess an SH3 domain that is known to bind to dynamin and that recruited and activated neural Wiskott-Aldrich syndrome protein (N-WASP) at the plasma membrane. FBP17 and/or CIP4 contributed to the formation of the protein complex, including N-WASP and dynamin-2, in the early stage of endocytosis. Furthermore, knockdown of endogenous FBP17 and CIP4 impaired endocytosis. Our data indicate that PCH protein family members couple membrane deformation to actin cytoskeleton reorganization in various cellular processes.