The adaptor molecule Nck localizes the WAVE complex to promote actin polymerization during CEACAM3-mediated phagocytosis of bacteria

Fibrosis-related transcriptome unveils a distinctive remodeling matrix pattern in penetrating ileal Crohn's disease

BACKGROUND AND AIMS

Stricturing (B2) and penetrating (B3) ileal Crohn's disease have been reported to present similar levels of histopathological transmural fibrosis. This study aimed to compare the fibrosis-related transcriptomic profiles of penetrating and stricturing ileal Crohn's disease.

METHODS

Using Nanostring technology and comparative bioinformatics, we analyzed the expression of 787 fibrosis-related genes in 36 ileal surgical specimens, 12 B2 and 24 B3, the latter including 12 cases with associated stricture(s) (B3s) and 12 without (B3o). Quality control of extracted RNA was performed according to Nanostring parameters and principal component analysis for the distribution analysis. For the selection of the differentially expressed genes a p-adjusted <0.05 and Fold Change ≤-1.5 or ≥ 1.5 was adopted. qPCR and immunohistochemistry analyses were used to validate selected differentially expressed genes.

RESULTS

We included 34 patients with B2 and B3 phenotypes, balanced for age at diagnosis, age at surgery, gender, Crohn's disease localization, perianal disease and therapy. Inflammation and fibrosis histopathological scoring were similar in all cases. B2 and B3 groups showed a very good clustering regarding 30 significantly differentially expressed genes, all being remarkably upregulated in B3. More than half of these genes were involved in Crohn's disease fibrogenesis, while eight differentially expressed genes were so in other organs. The most significantly active biologic processes and pathways in penetrating disease were response to TGFβand matrix organization and degradation, as validated by immunohistochemistry.

CONCLUSIONS

Despite the histopathological similarities in fibrosis between stricturing and penetrating ileal Crohn's disease, their fibrosis-related transcriptomic profiles are distinct. Penetrating disease exhibits a distinctive transcriptomic landscape related to enhanced matrix remodeling.

Controling the cytoskeleton during CEACAM3-mediated phagocytosis

Phagocytosis, an innate defense mechanism of multicellular animals, is initiated by specialized surface receptors. A phagocytic receptor expressed by human polymorphonuclear granulocytes, the major professional phagocytes in our body, is one of the fastest evolving human proteins implying a special role in human biology. This receptor, CEACAM3, is a member of the CarcinoEmbryonic Antigen-related Cell Adhesion Molecule (CEACAM) family and dedicated to the immediate recognition and rapid internalization of human-restricted pathogens. In this focused contribution, we will review the special adaptations of this protein, which co-evolves with different species of mucosa-colonizing bacteria. While the extracellular Immunoglobulin-variable (IgV)-like domain recognizes various bacterial adhesins, an Immunoreceptor Tyrosine-based Activation Motif (ITAM)-like sequence in the cytoplasmic tail of CEACAM3 constitutes the central signaling hub to trigger actin rearrangements needed for efficient phagocytosis. A major emphasis of this review will be placed on recent findings, which have revealed the multi-level control of this powerful phagocytic device. As tyrosine phosphorylation and small GTPase activity are central for CEACAM3-mediated phagocytosis, the counterregulation of CEACAM3 activity involves the receptor-type protein tyrosine phosphatase J (PTPRJ) as well as the Rac-GTP scavenging protein Cyri-B. Interference with such negative regulatory circuits has revealed that CEACAM3-mediated phagocytosis can be strongly enhanced. In principle, the knowledge gained by studying CEACAM3 can be applied to other phagocytic systems and opens the door to treatments, which boost the phagocytic capacity of professional phagocytes.

Cortactin: A universal host cytoskeletal target of Gram-negative and Gram-positive bacterial pathogens

Pathogenic bacteria possess a great potential of causing infectious diseases and represent a serious threat to human and animal health. Understanding the molecular basis of infection development can provide new valuable strategies for disease prevention and better control. In host-pathogen interactions, actin-cytoskeletal dynamics play a crucial role in the successful adherence, invasion, and intracellular motility of many intruding microbial pathogens. Cortactin, a major cellular factor that promotes actin polymerization and other functions, appears as a central regulator of host-pathogen interactions and different human diseases including cancer development. Various important microbes have been reported to hijack cortactin signaling during infection. The primary regulation of cortactin appears to proceed via serine and/or tyrosine phosphorylation events by upstream kinases, acetylation, and interaction with various other host proteins, including the Arp2/3 complex, filamentous actin, the actin nucleation promoting factor N-WASP, focal adhesion kinase FAK, the large GTPase dynamin-2, the guanine nucleotide exchange factor Vav2, and the actin-stabilizing protein CD2AP. Given that many signaling factors can affect cortactin activities, several microbes target certain unique pathways, while also sharing some common features. Here we review our current knowledge of the hallmarks of cortactin as a major target for eminent Gram-negative and Gram-positive bacterial pathogens in humans.

Phagocytosis mediated by the human granulocyte receptor CEACAM3 is limited by the receptor-type protein tyrosine phosphatase PTPRJ

Carcinoembryonic Antigen-related Cell Adhesion Molecule 3 (CEACAM3) is a human granulocyte receptor mediating the efficient phagocytosis of a subset of human-restricted bacterial pathogens. Its function depends on phosphorylation of a tyrosine-based sequence motif, but the enzyme(s) responsible for reversing this modification are unclear. Here, we identify the receptor-type protein tyrosine phosphatase PTPRJ as a negative regulator of CEACAM3-mediated phagocytosis. We show depletion of PTPRJ results in a gain-of-function phenotype, while overexpression of a constitutively active PTPRJ phosphatase strongly reduces bacterial uptake via CEACAM3. We also determined that recombinant PTPRJ directly dephosphorylates the cytoplasmic tyrosine residues of purified full-length CEACAM3 and recognizes synthetic CEACAM3-derived phospho-peptides as substrates. Dephosphorylation of CEACAM3 by PTPRJ is also observed in intact cells, thereby limiting receptor-initiated cytoskeletal re-arrangements, lamellipodia formation, and bacterial uptake. Finally, we show that human phagocytes deficient for PTPRJ exhibit exaggerated lamellipodia formation and enhanced opsonin-independent phagocytosis of CEACAM3-binding bacteria. Taken together, our results highlight PTPRJ as a bona fide negative regulator of CEACAM3-initiated phagocyte functions, revealing a potential molecular target to limit CEACAM3-driven inflammatory responses.

PINCH1 Promotes Fibroblast Migration in Extracellular Matrices and Influences Their Mechanophenotype

Cell migration performs a critical function in numerous physiological processes, including tissue homeostasis or wound healing after tissue injury, as well as pathological processes that include malignant progression of cancer. The efficiency of cell migration and invasion appears to be based on the mechano-phenotype of the cytoskeleton. The properties of the cytoskeleton depend on internal cytoskeletal and external environmental factors. A reason for this are connections between the cell and its local matrix microenvironment, which are established by cell-matrix adhesion receptors. Upon activation, focal adhesion proteins such as PINCH1 are recruited to sites where focal adhesions form. PINCH1 specifically couples through interactions with ILK, which binds to cell matrix receptors and the actomyosin cytoskeleton. However, the role of PINCH1 in cell mechanics regulating cellular motility in 3D collagen matrices is still unclear. PINCH1 is thought to facilitate 3D motility by regulating cellular mechanical properties, such as stiffness. In this study, PINCH1 wild-type and knock-out cells were examined for their ability to migrate in dense extracellular 3D matrices. Indeed, PINCH1 wild-type cells migrated more numerously and deeper in 3D matrices, compared to knock-out cells. Moreover, cellular deformability was determined, e.g., elastic modulus (stiffness). PINCH1 knock-out cells are more deformable (compliable) than PINCH1 wild-type cells. Migration of both PINCH1−/− cells and PINCH1fl/fl cells was decreased by Latrunculin A inhibition of actin polymerization, suggesting that actin cytoskeletal differences are not responsible for the discrepancy in invasiveness of the two cell types. However, the mechanical phenotype of PINCH1−/− cells may be reflected by Latrunculin A treatment of PINCH1fl/fl cells, as they exhibit resembling deformability to untreated PINCH1−/− cells. Moreover, an apparent mismatch exists between the elongation of the long axis and the contraction of the short axis between PINCH1fl/fl cells and PINCH1−/− cells following Latrunculin A treatment. There is evidence of this indicating a shift in the proxy values for Poisson’s ratio in PINCH1−/− cells compared with PINCH1fl/fl cells. This is probably attributable to modifications in cytoskeletal architecture. The non-muscle myosin II inhibitor Blebbistatin also reduced the cell invasiveness in 3D extracellular matrices but instead caused a stiffening of the cells. Finally, PINCH1 is apparently essential for providing cellular mechanical stiffness through the actin cytoskeleton, which regulates 3D motility.

Antibody ligation of CEACAM1, CEACAM3, and CEACAM6, differentially enhance the cytokine release of human neutrophils in responses to Candida albicans

Invasive candidiasis is a healthcare-associated fungal infection with a high mortality rate. Neutrophils, the first line of defense during fungal infections, express the immunoregulatory Candida albicans receptors CEACAM1, CEACAM3, and CEACAM6. We analyzed the effects of specific antibodies on C. albicans-induced neutrophil responses. CEACAM6 ligation by 1H7-4B and to some extent CEACAM1 ligation by B3-17, but not CEACAM3 ligation by 308/3-3, resulted in the immediate release of stored CXCL8 and altered transcriptional responses of the C. albicans-stimulated neutrophils. Integrated network analyses and dynamic simulations of signaling cascades predicted alterations in apoptosis and cytokine secretion. We verified that CEACAM6 ligation enhanced Candida-induced neutrophil apoptosis and increased long-term IL-1β/IL-6 release in responses to C. albicans. CEACAM3 ligation, but not CEACAM1 ligation, increased the long-term release of pro-inflammatory IL-1β/IL-6. Taken together, we demonstrated for the first time that ligation of CEACAM receptors differentially affects the regulation of C. albicans-induced immune functions in human neutrophils.

Nck adaptors at a glance

The non-catalytic region of tyrosine kinase (Nck) family of adaptors, consisting of Nck1 and Nck2, contributes to selectivity and specificity in the flow of cellular information by recruiting components of signaling networks. Known to play key roles in cytoskeletal remodeling, Nck adaptors modulate host cell-pathogen interactions, immune cell receptor activation, cell adhesion and motility, and intercellular junctions in kidney podocytes. Genetic inactivation of both members of the Nck family results in embryonic lethality; however, viability of mice lacking either one of these adaptors suggests partial functional redundancy. In this Cell Science at a Glance and the accompanying poster, we highlight the molecular organization and functions of the Nck family, focusing on key interactions and pathways, regulation of cellular processes, development, homeostasis and pathogenesis, as well as emerging and non-redundant functions of Nck1 compared to those of Nck2. This article thus aims to provide a timely perspective on the biology of Nck adaptors and their potential as therapeutic targets.

CEACAM3-A Prim(at)e Invention for Opsonin-Independent Phagocytosis of Bacteria

Phagocytosis is one of the key innate defense mechanisms executed by specialized cells in multicellular animals. Recent evidence suggests that a particular phagocytic receptor expressed by human polymorphonuclear granulocytes, the carcinoembryonic antigen-related cell adhesion molecule 3 (CEACAM3), is one of the fastest-evolving human proteins. In this focused review, we will try to resolve the conundrum why a conserved process such as phagocytosis is conducted by a rapidly changing receptor. Therefore, we will first summarize the biochemical and structural details of this immunoglobulin-related glycoprotein in the context of the human CEACAM family. The function of CEACAM3 for the efficient, opsonin-independent detection and phagocytosis of highly specialized, host-restricted bacteria will be further elaborated. Taking into account the decisive role of CEACAM3 in the interaction with pathogenic bacteria, we will discuss the evolutionary trajectory of the CEACAM3 gene within the primate lineage and highlight the consequences of CEACAM3 polymorphisms in human populations. From a synopsis of these studies, CEACAM3 emerges as an important component of human innate immunity and a prominent example of a dedicated receptor for professional phagocytosis.

WASP Restricts Active Rac to Maintain Cells' Front-Rear Polarization

Efficient motility requires polarized cells, with pseudopods at the front and a retracting rear. Polarization is maintained by restricting the pseudopod catalyst, active Rac, to the front. Here, we show that the actin nucleation-promoting factor Wiskott-Aldrich syndrome protein (WASP) contributes to maintenance of front-rear polarity by controlling localization and cellular levels of active Rac. Dictyostelium cells lacking WASP inappropriately activate Rac at the rear, which affects their polarity and speed. WASP's Cdc42 and Rac interacting binding ("CRIB") motif has been thought to be essential for its activation. However, we show that the CRIB motif's biological role is unexpectedly complex. WASP CRIB mutants are no longer able to restrict Rac activity to the front, and cannot generate new pseudopods when SCAR/WAVE is absent. Overall levels of Rac activity also increase when WASP is unable to bind to Rac. However, WASP without a functional CRIB domain localizes normally at clathrin pits during endocytosis, and activates Arp2/3 complex. Similarly, chemical inhibition of Rac does not affect WASP localization or activation at sites of endocytosis. Thus, the interaction between small GTPases and WASP is more complex than previously thought-Rac regulates a subset of WASP functions, but WASP reciprocally restricts active Rac through its CRIB motif.

Selective recruitment of Nck and Syk contribute to distinct leukocyte immune-type receptor-initiated target interactions

The ability of phagocytes to recognize, immobilize, and engulf extracellular targets are fundamental immune cell processes that allow for the destruction of a variety of microbial intruders. The phagocytic process depends onsignalling events that initiate dynamic changes in the plasma membrane architecture that are required to accommodate the internalization of large particulate targets. To better understand fundamental molecular mechanisms responsible for facilitating phagocytic receptor-mediated regulation of cytoskeletal networks, our research has focused on investigating representative immunoregulatory proteins from the channel catfish (Ictalurus punctatus) leukocyte immune-type receptor family (IpLITRs). Specifically, we have shown that a specific IpLITR-type can regulate the constitutive deployment of filopodial-like structures to actively capture and secure targets to the phagocyte surface, which is followed by F-actin mediated membrane dynamics that are associated with the formation of phagocytic cup-like structures that precede target engulfment. In the present study, we use confocal imaging to examine the recruitment of mediators of the F-actin cytoskeleton during IpLITR-mediated regulation of membrane dynamics. Our results provide novel details regarding the dynamic recruitment of the signaling effectors Nck and Syk during classical as well as atypical IpLITR-induced phagocytic processes.

Myosin XVI Regulates Actin Cytoskeleton Dynamics in Dendritic Spines of Purkinje Cells and Affects Presynaptic Organization

The actin cytoskeleton is crucial for function and morphology of neuronal synapses. Moreover, altered regulation of the neuronal actin cytoskeleton has been implicated in neuropsychiatric diseases such as autism spectrum disorder (ASD). Myosin XVI is a neuronally expressed unconventional myosin known to bind the WAVE regulatory complex (WRC), a regulator of filamentous actin (F-actin) polymerization. Notably, the gene encoding the myosin’s heavy chain (MYO16) shows genetic association with neuropsychiatric disorders including ASD. Here, we investigated whether myosin XVI plays a role for actin cytoskeleton regulation in the dendritic spines of cerebellar Purkinje cells (PCs), a neuronal cell type crucial for motor learning, social cognition and vocalization. We provide evidence that both myosin XVI and the WRC component WAVE1 localize to PC spines. Fluorescence recovery after photobleaching (FRAP) analysis of GFP-actin in cultured PCs shows that Myo16 knockout as well as PC-specific Myo16 knockdown, lead to faster F-actin turnover in the dendritic spines of PCs. We also detect accelerated F-actin turnover upon interference with the WRC, and upon inhibition of Arp2/3 that drives formation of branched F-actin downstream of the WRC. In contrast, inhibition of formins that are responsible for polymerization of linear actin filaments does not cause faster F-actin turnover. Together, our data establish myosin XVI as a regulator of the postsynaptic actin cytoskeleton and suggest that it is an upstream activator of the WRC-Arp2/3 pathway in PC spines. Furthermore, ultra-structural and electrophysiological analyses of Myo16 knockout cerebellum reveals the presence of reduced numbers of synaptic vesicles at presynaptic terminals in the absence of the myosin. Therefore, we here define myosin XVI as an F-actin regulator important for presynaptic organization in the cerebellum.

Adaptation to Host-Specific Bacterial Pathogens Drives Rapid Evolution of a Human Innate Immune Receptor

The selective pressure by infectious agents is a major driving force in the evolution of humans and other mammals. Members of the carcinoembryonic antigen-related cell adhesion molecule (CEACAM) family serve as receptors for bacterial pathogens of the genera Haemophilus, Helicobacter, Neisseria, and Moraxella, which engage CEACAMs via distinct surface adhesins. While microbial attachment to epithelial CEACAMs facilitates host colonization, recognition by CEACAM3, a phagocytic receptor expressed by granulocytes, eliminates CEACAM-binding bacteria. Sequence analysis of primate CEACAM3 orthologs reveals that this innate immune receptor is one of the most rapidly evolving human proteins. In particular, the pathogen-binding extracellular domain of CEACAM3 shows a high degree of non-synonymous versus synonymous nucleotide exchanges, indicating an exceptionally strong positive selection. Using CEACAM3 domains derived from different primates, we find that the amino acid alterations found in CEACAM3 translate into characteristic binding patterns for bacterial adhesins. One such amino acid residue is F62 in human and chimp CEACAM3, which is not present in other primates and which is critical for binding the OMP P1 adhesin of Haemophilus aegyptius. Incorporation of the F62-containing motif into gorilla CEACAM3 results in a gain-of-function phenotype with regard to phagocytosis of H. aegyptius. Moreover, CEACAM3 polymorphisms found in human subpopulations widen the spectrum of recognized bacterial adhesins, suggesting an ongoing multivariate selection acting on this innate immune receptor. The species-specific detection of diverse bacterial adhesins helps to explain the exceptionally fast evolution of CEACAM3 within the primate lineage and provides an example of Red Queen dynamics in the human genome.

Selective Regulation of Cytoskeletal Dynamics and Filopodia Formation by Teleost Leukocyte Immune-Type Receptors Differentially Contributes to Target Capture During the Phagocytic Process

Phagocytosis evolved from a fundamental nutrient acquisition mechanism in primitive unicellular amoeboids, into a dynamic and complex component of innate immunity in multicellular organisms. To better understand the cellular mechanisms contributing to phagocytic processes across vertebrates, our research has focused on characterizing the involvement of innate immune proteins originally identified in channel catfish (Ictalurus punctatus) called leukocyte immune-type receptors (IpLITRs). These unique teleost proteins share basic structural as well as distant phylogenetic relationships with several immunoregulatory proteins within the mammalian immunoglobulin superfamily. In the present study, we use a combination of live-cell confocal imaging and high-resolution scanning electron microscopy to further examine the classical immunoreceptor tyrosine-based activation motif (ITAM)-dependent phagocytic pathway mediated by the chimeric construct IpLITR 2.6b/IpFcRγ-L and the functionally diverse immunoreceptor tyrosine-based inhibitory motif-containing receptor IpLITR 1.1b. Results demonstrate that IpLITR 1.1b-expressing cells can uniquely generate actin-dense filopodia-like protrusions during the early stages of extracellular target interactions. In addition, we observed that these structures retract after contacting extracellular targets to secure captured microspheres on the cell surface. This activity was often followed by the generation of robust secondary waves of actin polymerization leading to the formation of stabilized phagocytic cups. At depressed temperatures of 27°C, IpLITR 2.6b/IpFcRγ-L-mediated phagocytosis was completely blocked, whereas IpLITR 1.1b-expressing cells continued to generate dynamic actin-dense filopodia at this lower temperature. Overall, these results provide new support for the hypothesis that IpLITR 1.1b, but not IpLITR 2.6b/IpFcRγ-L, directly triggers filopodia formation when expressed in representative myeloid cells. This also offers new information regarding the directed ability of immunoregulatory receptor-types to initiate dynamic membrane structures and provides insights into an alternative ITAM-independent target capture pathway that is functionally distinct from the classical phagocytic pathways.

Tyrosine-phosphorylation of the scaffold protein ADAP and its role in T cell signaling

INTRODUCTION

The Adhesion and Degranulation promoting Adaptor Protein (ADAP) is phosphorylated upon T cell activation and acts as a scaffold for the formation of a signaling complex that integrates molecular interactions between T cell or chemokine receptors, the actin cytoskeleton, and integrin-mediated cellular adhesion and migration.

AREAS COVERED

This article reviews current knowledge of the functions of the adapter protein ADAP in T cell signaling with a focus on the role of individual phosphotyrosine (pY) motifs for SH2 domain mediated interactions. The data presented was obtained from literature searches (PubMed) as well as the authors own research on the topic. Expert commentary: ADAP can be regarded as a paradigmatic example of how tyrosine phosphorylation sites serve as dynamic interaction hubs. Molecular crowding at unstructured and redundant sites (pY595, pY651) is contrasted by more specific interactions enabled by the three-dimensional environment of a particular phosphotyrosine motif (pY571).

Imaging flow cytometry and GST pulldown assays provide new insights into channel catfish leukocyte immune-type receptor-mediated phagocytic pathways

Channel catfish (Ictalurus punctatus) leukocyte immune-type receptors (IpLITRs) control various innate immune cell effector responses including the phagocytic process. This large immunoregulatory receptor family also consists of multiple receptor-types with variable signaling abilities that is dependent on their inherent or acquired tyrosine-containing cytoplasmic tail (CYT) regions. For example, IpLITR 2.6b associates with the immunoreceptor tyrosine-based activation motif (ITAM)-containing adaptor molecule IpFcRγ-L, and when expressed in mammalian cells it activates phagocytosis using a similar profile of intracellular signaling mediators that also regulate the prototypical mammalian Fc receptor (FcR) phagocytic pathway. Alternatively, IpLITR 1.1b contains a long tyrosine-containing CYT with multifunctional capabilities including both inhibitory and stimulatory actions. Recently, we demonstrated that IpLITR 1.1b activates a unique phagocytic pathway involving the generation of multiple plasma membrane extensions that rapidly capture extracellular targets and secure them on the cell surface in phagocytic cup-like structures. Occasionally, these captured targets are completely engulfed albeit at a significantly lower rate than what was observed for IpLITR 2.6b. While this novel IpLITR 1.1b phagocytic activity is insensitive to classical blockers of phagocytosis, its distinct target capture and engulfment actions depend on the engagement of the actin polymerization machinery. However, it is not known how this protein translates target recognition into intracellular signaling events during this atypical mode of phagocytosis. Using imaging flow cytometry and GST pulldown assays, the aims of this study were to specifically examine what regions of the IpLITR 1.1b CYT trigger phagocytosis and to establish what profile of intracellular signaling molecules likely participate in its actions. Our results show that in stably transfected AD293 cells, the membrane proximal and distal CYT segments of IpLITR 1.1b independently regulate its phagocytic activities. These CYT regions were also shown to differentially recruit various SH2 domain-containing intracellular mediators, which provides new information about the dynamic immunoregulatory abilities of IpLITR 1.1b. Overall, this work further advances our understanding of how certain immunoregulatory receptor-types link extracellular target binding events to the actin polymerization machinery during a non-classical mode of phagocytosis.

Inhibition of WAVE Regulatory Complex Activation by a Bacterial Virulence Effector Counteracts Pathogen Phagocytosis

To establish pathogenicity, bacteria must evade phagocytosis directed by remodeling of the actin cytoskeleton. We show that macrophages facilitate pathogen phagocytosis through actin polymerization mediated by the WAVE regulatory complex (WRC), small GTPases Arf and Rac1, and the Arf1 activator ARNO. To establish extracellular infections, enteropathogenic (EPEC) and enterohaemorrhagic (EHEC) Escherichia coli hijack the actin cytoskeleton by injecting virulence effectors into the host cell. Here, we find that the virulence effector EspG counteracts WRC-dependent phagocytosis, enabling EPEC and EHEC to remain extracellular. By reconstituting membrane-associated actin polymerization, we find that EspG disabled WRC activation through two mechanisms: EspG interaction with Arf6 blocked signaling to ARNO while EspG binding of Arf1 impeded collaboration with Rac1, thereby inhibiting WRC recruitment and activation. Investigating the mode of EspG interference revealed sites in Arf1 required for WRC activation and a mechanism facilitating pathogen evasion of innate host defenses.

The WASF3-NCKAP1-CYFIP1 Complex Is Essential for Breast Cancer Metastasis

Inactivation of the WASF3 gene suppresses invasion and metastasis of breast cancer cells. WASF3 function is regulated through a protein complex that includes the NCKAP1 and CYFIP1 proteins. Here, we report that silencing NCKAP1 destabilizes the WASF3 complex, resulting in a suppression of the invasive capacity of breast, prostate, and colon cancer cells. In an in vivo model of spontaneous metastasis in immunocompromized mice, loss of NCKAP1 also suppresses metastasis. Activation of the WASF protein complex occurs through interaction with RAC1, and inactivation of NCKAP1 prevents the association of RAC1 with the WASF3 complex. Thus, WASF3 depends on NCKAP1 to promote invasion and metastasis. Here, we show that stapled peptides targeting the interface between NCKAP1 and CYFIP1 destabilize the WASF3 complex and suppress RAC1 binding, thereby suppressing invasion. Using a complex-disrupting compound identified in this study termed WANT3, our results offer a mechanistic proof of concept to target this interaction as a novel approach to inhibit breast cancer metastasis. Cancer Res; 76(17); 5133-42. ©2016 AACR.

Moraxella catarrhalis induces CEACAM3-Syk-CARD9-dependent activation of human granulocytes

The human restricted pathogen Moraxella catarrhalis is an important causal agent for exacerbations in chronic obstructive lung disease in adults. In such patients, increased numbers of granulocytes are present in the airways, which correlate with bacteria-induced exacerbations and severity of the disease. Our study investigated whether the interaction of M. catarrhalis with the human granulocyte-specific carcinoembryonic antigen-related cell adhesion molecule (CEACAM)-3 is linked to NF-κB activation, resulting in chemokine production. Granulocytes from healthy donors and NB4 cells were infected with M. catarrhalis in the presence of different inhibitors, blocking antibodies and siRNA. The supernatants were analysed by enzyme-linked immunosorbent assay for chemokines. NF-κB activation was determined using a luciferase reporter gene assay and chromatin-immunoprecipitation. We found evidence that the specific engagement of CEACAM3 by M. catarrhalis ubiquitous surface protein A1 (UspA1) results in the activation of pro-inflammatory events, such as degranulation of neutrophils, ROS production and chemokine secretion. The interaction of UspA1 with CEACAM3 induced the activation of the NF-κB pathway via Syk and the CARD9 pathway and was dependent on the phosphorylation of the CEACAM3 ITAM-like motif. These findings suggest that the CEACAM3 signalling in neutrophils is able to specifically modulate airway inflammation caused by infection with M. catarrhalis.

Biochemical and Functional Insights into the Integrated Regulation of Innate Immune Cell Responses by Teleost Leukocyte Immune-Type Receptors

Across vertebrates, innate immunity consists of a complex assortment of highly specialized cells capable of unleashing potent effector responses designed to destroy or mitigate foreign pathogens. The execution of various innate cellular behaviors such as phagocytosis, degranulation, or cell-mediated cytotoxicity are functionally indistinguishable when being performed by immune cells isolated from humans or teleost fishes; vertebrates that diverged from one another more than 450 million years ago. This suggests that vital components of the vertebrate innate defense machinery are conserved and investigating such processes in a range of model systems provides an important opportunity to identify fundamental features of vertebrate immunity. One characteristic that is highly conserved across vertebrate systems is that cellular immune responses are dependent on specialized immunoregulatory receptors that sense environmental stimuli and initiate intracellular cascades that can elicit appropriate effector responses. A wide variety of immunoregulatory receptor families have been extensively studied in mammals, and many have been identified as cell- and function-specific regulators of a range of innate responses. Although much less is known in fish, the growing database of genomic information has recently allowed for the identification of several immunoregulatory receptor gene families in teleosts. Many of these putative immunoregulatory receptors have yet to be assigned any specific role(s), and much of what is known has been based solely on structural and/or phylogenetic relationships with mammalian receptor families. As an attempt to address some of these shortcomings, this review will focus on our growing understanding of the functional roles played by specific members of the channel catfish (Ictalurus punctatus) leukocyte immune-type receptors (IpLITRs), which appear to be important regulators of several innate cellular responses via classical as well as unique biochemical signaling networks.

Outer membrane protein P1 is the CEACAM-binding adhesin of Haemophilus influenzae

Haemophilus influenzae is a Gram-negative pathogen colonizing the upper respiratory tract mucosa. H. influenzae is one of several human-restricted bacteria, which bind to carcinoembryonic antigen-related cell adhesion molecules (CEACAMs) on the epithelium leading to bacterial uptake by the eukaryotic cells. Adhesion to CEACAMs is thought to be mediated by the H. influenzae outer membrane protein (OMP) P5. However, CEACAMs still bound to H. influenzae lacking OMP P5 expression, and soluble CEACAM receptor ectodomains failed to bind to OMP P5, when heterologously expressed in Escherichia coli. Screening of a panel of H. influenzae OMP mutants revealed that lack of OMP P1 completely abrogated CEACAM binding and supressed CEACAM-mediated engulfment of H. influenzae by epithelial cells. Moreover, ectopic expression of OMP P1 in E. coli was sufficient to induce CEACAM binding and to promote attachment to and internalization into CEACAM-expressing cells. Interestingly, OMP P1 selectively recognizes human CEACAMs, but not homologs from other mammals and this binding preference is preserved upon expression in E. coli. Together, our data identify OMP P1 as the bona fide CEACAM-binding invasin of H. influenzae. This is the first report providing evidence for an involvement of the major OMP P1 of H. influenzae in pathogenesis.

MiR-146a activates WAVE2 expression and enhances phagocytosis in lipopolysaccharide-stimulated RAW264.7 macrophages

MiR-146a has been shown to play a critical role in cell immunity and phagocytosis, processes that require rearrangement of the cytoskeleton. However, the detailed mechanism by which miR-146a regulates these events remains elusive. Here, we used luciferase reporter and protein assays to show that the cytoskeleton-regulatingprotein verprolin-homologous protein 2 (WAVE2), is a direct target of miR-146a. MiR-146a overexpression resulted in a decrease in WAVE2 protein expression under endotoxin-free culture conditions. Unexpectedly, however, miR-146a activated rather than repressed the expression of WAVE2 in macrophage RAW264.7 cells when cultured continuously in the presence of endotoxin. Furthermore, we demonstrated that miR-146a induced WAVE2 expression and enhanced phagocytosis in lipopolysaccharide-stimulated RAW264.7 macrophages. Our study suggests that lipopolysaccharide- induced miR146a indirectly activates WAVE2 expression; thus, facilitating cytoskeletal reorganization and phagocytosis in lipopolysaccharide-stimulated macrophages.

Rho GTPases as pathogen targets: Focus on curable sexually transmitted infections

Pathogens have evolved highly specialized mechanisms to infect hosts. Several microorganisms modulate the eukaryotic cell surface to facilitate their engulfment. Once internalized, they hijack the molecular machinery of the infected cell for their own benefit. At different stages of phagocytosis, particularly during invasion, certain pathogens manipulate pathways governed by small GTPases. In this review, we focus on the role of Rho proteins on curable, sexually transmitted infections caused by Chlamydia trachomatis, Neisseria gonorrhoeae, Trichomonas vaginalis and Treponema pallidum. Despite the high, worldwide frequencies of these sexually-transmitted diseases, very little is known about the strategies developed by these microorganisms to usurp key eukaryotic proteins that control intracellular signaling and actin dynamics. Improved knowledge of these molecular mechanisms will contribute to the elucidation of how these clinically important pathogens manipulate intracellular processes and parasitize their hosts.

The granulocyte orphan receptor CEACAM4 is able to trigger phagocytosis of bacteria

Human granulocytes express several glycoproteins of the CEACAM family. One family member, CEACAM3, operates as a single-chain phagocytic receptor, initiating the detection, internalization, and destruction of a limited set of gram-negative bacteria. In contrast, the function of CEACAM4, a closely related protein, is completely unknown. This is mainly a result of a lack of a specific ligand for CEACAM4. By generating chimeric proteins containing the extracellular bacteria-binding domain of CEACAM3 and the transmembrane and cytoplasmic part of CEACAM4 (CEACAM3/4) we demonstrate that this chimeric receptor can trigger efficient phagocytosis of attached particles. Uptake of CEACAM3/4-bound bacteria requires the intact ITAM of CEACAM4, and this motif is phosphorylated by Src family PTKs upon receptor clustering. Furthermore, SH2 domains derived from Src PTKs, PI3K, and the adapter molecule Nck are recruited and associate directly with the phosphorylated CEACAM4 ITAM. Deletion of this sequence motif or inhibition of Src PTKs blocks CEACAM4-mediated uptake. Together, our results suggest that this orphan receptor of the CEACAM family has phagocytic function and prompt efforts to identify CEACAM4 ligands.

Signaling by epithelial members of the CEACAM family - mucosal docking sites for pathogenic bacteria

Carcinoembryonic antigen-related cell adhesion molecules (CEACAMs) comprise a group of immunoglobulin-related vertebrate glycoproteins. Several family members, including CEACAM1, CEA, and CEACAM6, are found on epithelial tissues throughout the human body. As they modulate diverse cellular functions, their signaling capacity is in the focus of current research. In this review we will summarize the knowledge about common signaling processes initiated by epithelial CEACAMs and suggest a model of signal transduction by CEACAM family members lacking significant cytoplasmic domains. As pathogenic and non-pathogenic bacteria exploit these receptors during mucosal colonization, we try to highlight the connection between CEACAMs, microbes, and cellular responses. Special emphasis in this context is placed on the functional interplay between CEACAMs and integrins that influences matrix adhesion of epithelial cells. The cooperation between these two receptor families provides an intriguing example of the fine tuning of cellular responses and their manipulation by specialized microorganisms.

Integration of signaling and cytoskeletal remodeling by Nck in directional cell migration

Planar and apical-basal cellular polarization of epithelia and endothelia are crucial during morphogenesis. The establishment of these distinct polarity states and their transitions are regulated by signaling networks that include polarity complexes, Rho GTPases, and phosphoinositides. The spatiotemporal coordination of signaling by these molecules modulates cytoskeletal remodeling and vesicle trafficking to specify membrane domains, a prerequisite for the organization of tissues and organs. Here we present an overview of how activation of the WASp/Arp2/3 pathway of actin remodeling by Nck coordinates directional cell migration and speculate on its role as a signaling integrator in the coordination of cellular processes involved in endothelial cell polarity and vascular lumen formation.

mRNA encoding WAVE-Arp2/3-associated proteins is co-localized with foci of active protein synthesis at the leading edge of MRC5 fibroblasts during cell migration

During cell spreading, mammalian cells migrate using lamellipodia formed from a large dense branched actin network which produces the protrusive force required for leading edge advancement. The formation of lamellipodia is a dynamic process and is dependent on a variety of protein cofactors that mediate their local regulation, structural characteristics and dynamics. In the present study, we show that mRNAs encoding some structural and regulatory components of the WAVE [WASP (Wiskott-Aldrich syndrome protein) verprolin homologous] complex are localized to the leading edge of the cell and associated with sites of active translation. Furthermore, we demonstrate that steady-state levels of ArpC2 and Rac1 proteins increase at the leading edge during cell spreading, suggesting that localized protein synthesis has a pivotal role in controlling cell spreading and migration.

Innate recognition by neutrophil granulocytes differs between Neisseria gonorrhoeae strains causing local or disseminating infections

Members of the carcinoembryonic antigen-related cell adhesion molecule (CEACAM) family serve as cellular receptors for Neisseria gonorrhoeae. More specifically, neisserial colony opacity (OpaCEA)) proteins bind to epithelial CEACAMs (CEACAM1, CEA, CEACAM6) to promote bacterial colonization of the mucosa. In contrast, recognition by CEACAM3, expressed by human granulocytes, results in uptake and destruction of Opa(CEA)-expressing bacteria. Therefore, CEACAM3-mediated uptake might limit the spread of gonococci. However, some strains can cause disseminating gonococcal infections (DGIs), and it is currently unknown how these strains escape detection by granulocyte CEACAM3. Therefore, the opa gene loci from N. gonorrhoeae strain VP1, which was derived from a patient with disseminated gonococcal disease, were cloned and constitutively expressed in Escherichia coli. Similar to Opa proteins of the nondisseminating strain MS11, the majority of Opa proteins from strain VP1 bound epithelial CEACAMs and promoted CEACAM-initiated responses by epithelial cells. In sharp contrast to the Opa proteins of strain MS11, the Opa proteins of strain VP1 failed to interact with the human granulocyte receptor CEACAM3. Accordingly, bacteria expressing VP1 Opa proteins were not taken up by primary human granulocytes and did not trigger a strong oxidative burst. Analysis of Opa variants from four additional clinical DGI isolates again demonstrated a lack of CEACAM3 binding. In summary, our results reveal that particular N. gonorrhoeae strains express an Opa protein repertoire allowing engagement of epithelial CEACAMs for successful mucosal colonization, while avoiding recognition and elimination via CEACAM3-mediated phagocytosis. A failure of CEACAM3-mediated innate immune detection might be linked to the ability of gonococci to cause disseminated infections.

WASPs and WAVEs: from molecular function to physiology in hematopoietic cells

The actin cytoskeleton is critically involved in a variety of cell functions. The Arp2/3 complex mediates branching of filamentous actin. The members of the Wiskott-Aldrich syndrome protein (WASP) family are major regulators of the complex. As such, the family proteins are also involved in numerous aspects of cell biology. In this short review, we first define the expanding WASP family. Next, we compare the domain structure of the members, and explain the known or proposed functions of each domain or region. Finally, we demonstrate the well-characterized roles of the proteins in specific cellular functions.

Nck enables directional cell migration through the coordination of polarized membrane protrusion with adhesion dynamics

Directional migration requires the coordination of cytoskeletal changes essential for cell polarization and adhesion turnover. Extracellular signals that alter tyrosine phosphorylation drive directional migration by inducing reorganization of the actin cytoskeleton. It is recognized that Nck is an important link between tyrosine phosphorylation and actin dynamics, however, the role of Nck in cytoskeletal remodeling during directional migration and the underlying molecular mechanisms remain largely undetermined. In this study, a combination of molecular genetics and quantitative live cell microscopy was used to show that Nck is essential in the establishment of front-back polarity and directional migration of endothelial cells. Time-lapse differential interference contrast and total internal reflection fluorescence microscopy showed that Nck couples the formation of polarized membrane protrusions with their stabilization through the assembly and maturation of cell-substratum adhesions. Measurements by atomic force microscopy showed that Nck also modulates integrin α5β1-fibronectin adhesion force and cell stiffness. Fluorescence resonance energy transfer imaging revealed that Nck depletion results in delocalized and increased activity of Cdc42 and Rac. In contrast, the activity of RhoA and myosin II phosphorylation were reduced by Nck knockdown. Thus, this study identifies Nck as a key coordinator of cytoskeletal changes that enable cell polarization and directional migration which are critical processes in development and disease.

Grb14 is a negative regulator of CEACAM3-mediated phagocytosis of pathogenic bacteria

Carcinoembryonic antigen-related cell adhesion molecule 3 (CEACAM3) is a phagocytic receptor on human granulocytes, which mediates the opsonin-independent recognition and internalization of a restricted set of Gram-negative bacteria such as Neisseria gonorrhoeae. In an unbiased screen using a SH2 domain microarray we identified the SH2 domain of growth factor receptor-bound protein 14 (Grb14) as a novel binding partner of CEACAM3. Biochemical assays and microscopic studies demonstrated that the Grb14 SH2 domain promoted the rapid recruitment of this adaptor protein to the immunoreceptor-based activation motif (ITAM)-like sequence within the cytoplasmic domain of CEACAM3. Furthermore, FRET-FLIM analyses confirmed the direct association of Grb14 and CEACAM3 in intact cells at the sites of bacteria-host cell contact. Knockdown of endogenous Grb14 by RNA interference as well as Grb14 overexpression indicate an inhibitory role for this adapter protein in CEACAM3-mediated phagocytosis. Therefore, Grb14 is the first negative regulator of CEACAM3-initiated bacterial phagocytosis and might help to focus granulocyte responses to the subcellular sites of pathogen-host cell contact.

Extracellular IgC2 constant domains of CEACAMs mediate PI3K sensitivity during uptake of pathogens

Background

Several pathogenic bacteria utilize receptors of the CEACAM family to attach to human cells. Binding to different members of this receptor family can result in uptake of the bacteria. Uptake of Neisseria gonorrhoeae, a Gram-negative human pathogen, via CEACAMs found on epithelial cells, such as CEACAM1, CEA or CEACAM6, differs mechanistically from phagocytosis mediated by CEACAM3, a CEACAM family member expressed selectively by human granulocytes.

Principal Findings

We find that CEACAM1- as well as CEACAM3-mediated bacterial internalization are accompanied by a rapid increase in phosphatidylinositol-3,4,5 phosphate (PI(3,4,5)P) at the site of bacterial entry. However, pharmacological inhibition of phosphatidylinositol-3′ kinase (PI3K) selectively affects CEACAM1-mediated uptake of Neisseria gonorrhoeae. Accordingly, overexpression of the PI(3,4,5)P phosphatase SHIP diminishes and expression of a constitutive active PI3K increases CEACAM1-mediated internalization of gonococci, without influencing uptake by CEACAM3. Furthermore, bacterial uptake by GPI-linked members of the CEACAM family (CEA and CEACAM6) and CEACAM1-mediated internalization of N. meningitidis by endothelial cells require PI3K activity. Sensitivity of CEACAM1-mediated uptake toward PI3K inhibition is independent of receptor localization in cholesterol-rich membrane microdomains and does not require the cytoplasmic or the transmembrane domain of CEACAM1. However, PI3K inhibitor sensitivity requires the Ig_C2-like domains of CEACAM1, which are also present in CEA and CEACAM6, but which are absent from CEACAM3. Accordingly, overexpression of CEACAM1 Ig_C2 domains blocks CEACAM1-mediated internalization.

Conclusions

Our results provide novel mechanistic insight into CEACAM1-mediated endocytosis and suggest that epithelial CEACAMs associate in cis with other membrane receptor(s) via their extracellular domains to trigger bacterial uptake in a PI3K-dependent manner.