VASP is a CXCR2-interacting protein that regulates CXCR2-mediated polarization and chemotaxis

Cytochalasans and Their Impact on Actin Filament Remodeling

The eukaryotic actin cytoskeleton comprises the protein itself in its monomeric and filamentous forms, G- and F-actin, as well as multiple interaction partners (actin-binding proteins, ABPs). This gives rise to a temporally and spatially controlled, dynamic network, eliciting a plethora of motility-associated processes. To interfere with the complex inter- and intracellular interactions the actin cytoskeleton confers, small molecular inhibitors have been used, foremost of all to study the relevance of actin filaments and their turnover for various cellular processes. The most prominent inhibitors act by, e.g., sequestering monomers or by interfering with the polymerization of new filaments and the elongation of existing filaments. Among these inhibitors used as tool compounds are the cytochalasans, fungal secondary metabolites known for decades and exploited for their F-actin polymerization inhibitory capabilities. In spite of their application as tool compounds for decades, comprehensive data are lacking that explain (i) how the structural deviances of the more than 400 cytochalasans described to date influence their bioactivity mechanistically and (ii) how the intricate network of ABPs reacts (or adapts) to cytochalasan binding. This review thus aims to summarize the information available concerning the structural features of cytochalasans and their influence on the described activities on cell morphology and actin cytoskeleton organization in eukaryotic cells.

The double-edged role of neutrophil heterogeneity in inflammatory diseases and cancers

Neutrophils are important immune cells act as the body's first line of defense against infection and respond to diverse inflammatory cues. Many studies have demonstrated that neutrophils display plasticity in inflammatory diseases and cancers. Clarifying the role of neutrophil heterogeneity in inflammatory diseases and cancers will contribute to the development of novel treatment strategies. In this review, we have presented a review on the development of the understanding on neutrophil heterogeneity from the traditional perspective and a high-resolution viewpoint. A growing body of evidence has confirmed the double-edged role of neutrophils in inflammatory diseases and tumors. This may be due to a lack of precise understanding of the role of specific neutrophil subsets in the disease. Thus, elucidating specific neutrophil subsets involved in diseases would benefit the development of precision medicine. Thusly, we have summarized the relevance and actions of neutrophil heterogeneity in inflammatory diseases and cancers comprehensively. Meanwhile, we also discussed the potential intervention strategy for neutrophils. This review is intended to deepen our understanding of neutrophil heterogeneity in inflammatory diseases and cancers, while hold promise for precise treatment of neutrophil-related diseases.

A Nanotherapy of Octanoic Acid Ameliorates Cardiac Arrest/Cardiopulmonary Resuscitation-Induced Brain Injury via RVG29- and Neutrophil Membrane-Mediated Injury Relay Targeting

Treatment of cardiac arrest/cardiopulmonary resuscitation (CA/CPR)-induced brain injury remains a challenging issue without viable therapeutic options. Octanoic acid (OA), a lipid oil that is mainly metabolized in the astrocytes of the brain, is a promising treatment for this type of injury owing to its potential functions against oxidative stress, apoptosis, inflammation, and ability to stabilize mitochondria. However, the application of OA is strictly limited by its short half-life and low available concentration in the target organ. Herein, based on our previous research, an OA-based nanotherapy coated with a neutrophil membrane highly expressing RVG29, RVG29-H-NP_OA, was successfully constructed by computer simulation-guided supramolecular assembly of polyethylenimine and OA. The in vitro and in vivo experiments showed that RVG29-H-NP_OA could target and be distributed in the injured brain focus via the relay-targeted delivery mediated by RVG29-induced blood-brain barrier (BBB) penetration and neutrophil membrane protein-induced BBB binding and injury targeting. This results in enhancements of the antioxidant, antiapoptotic, mitochondrial stability-promoting and anti-inflammatory effects of OA and exhibited systematic alleviation of astrocyte injury, neuronal damage, and inflammatory response in the brain. Due to their systematic intervention in multiple pathological processes, RVG29-H-NP_OA significantly increased the 24 h survival rate of CA/CPR model rats from 40% to 100% and significantly improved their neurological functions. Thus, RVG29-H-NP_OA are expected to be a promising therapeutic for the treatment of CA/CPR-induced brain injury.

Neutrophil Migratory Patterns: Implications for Cardiovascular Disease

The body's inflammatory response involves a series of processes that are necessary for the immune system to mitigate threats from invading pathogens. Leukocyte migration is a crucial process in both homeostatic and inflammatory states. The mechanisms involved in immune cell recruitment to the site of inflammation are numerous and require several cascades and cues of activation. Immune cells have multiple origins and can be recruited from primary and secondary lymphoid, as well as reservoir organs within the body to generate an immune response to certain stimuli. However, no matter the origin, an important aspect of any inflammatory response is the web of networks that facilitates immune cell trafficking. The vasculature is an important organ for this trafficking, especially during an inflammatory response, mainly because it allows cells to migrate towards the source of insult/injury and serves as a reservoir for leukocytes and granulocytes under steady state conditions. One of the most active and vital leukocytes in the immune system's arsenal are neutrophils. Neutrophils exist under two forms in the vasculature: a marginated pool that is attached to the vessel walls, and a demarginated pool that freely circulates within the blood stream. In this review, we seek to present the current consensus on the mechanisms involved in leukocyte margination and demargination, with a focus on the role of neutrophil migration patterns during physio-pathological conditions, in particular diabetes and cardiovascular disease.

CXCR2 Receptor: Regulation of Expression, Signal Transduction, and Involvement in Cancer

Chemokines are a group of about 50 chemotactic cytokines crucial for the migration of immune system cells and tumor cells, as well as for metastasis. One of the 20 chemokine receptors identified to date is CXCR2, a G-protein-coupled receptor (GPCR) whose most known ligands are CXCL8 (IL-8) and CXCL1 (GRO-α). In this article we present a comprehensive review of literature concerning the role of CXCR2 in cancer. We start with regulation of its expression at the transcriptional level and how this regulation involves microRNAs. We show the mechanism of CXCR2 signal transduction, in particular the action of heterotrimeric G proteins, phosphorylation, internalization, intracellular trafficking, sequestration, recycling, and degradation of CXCR2. We discuss in detail the mechanism of the effects of activated CXCR2 on the actin cytoskeleton. Finally, we describe the involvement of CXCR2 in cancer. We focused on the importance of CXCR2 in tumor processes such as proliferation, migration, and invasion of tumor cells as well as the effects of CXCR2 activation on angiogenesis, lymphangiogenesis, and cellular senescence. We also discuss the importance of CXCR2 in cell recruitment to the tumor niche including tumor-associated neutrophils (TAN), tumor-associated macrophages (TAM), myeloid-derived suppressor cells (MDSC), and regulatory T (T_reg) cells.

How do chemokines navigate neutrophils to the target site: Dissecting the structural mechanisms and signaling pathways

Chemokines play crucial roles in combating microbial infection and initiating tissue repair by recruiting neutrophils in a timely and coordinated manner. In humans, no less than seven chemokines (CXCL1, CXCL2, CXCL3, CXCL5, CXCL6, CXCL7, and CXCL8) and two receptors (CXCR1 and CXCR2) mediate neutrophil functions but in a context dependent manner. Neutrophil-activating chemokines reversibly exist as monomers and dimers, and their receptor binding triggers conformational changes that are coupled to G-protein and β-arrestin signaling pathways. G-protein signaling activates a variety of effectors including Ca2+ channels and phospholipase C. β-arrestin serves as a multifunctional adaptor and is coupled to several signaling hubs including MAP kinase and tyrosine kinase pathways. Both G-protein and β-arrestin signaling pathways play important non-overlapping roles in neutrophil trafficking and activation. Functional studies have established many similarities but distinct differences for a given chemokine and between chemokines at the level of monomer vs. dimer, CXCR1 vs. CXCR2 activation, and G-protein vs. β-arrestin pathways. We propose that two forms of the ligand binding two receptors and activating two signaling pathways enables fine-tuned neutrophil function compared to a single form, a single receptor, or a single pathway. We summarize the current knowledge on the molecular mechanisms by which chemokine monomers/dimers activate CXCR1/CXCR2 and how these interactions trigger G-protein/β-arrestin-coupled signaling pathways. We also discuss current challenges and knowledge gaps, and likely advances in the near future that will lead to a better understanding of the relationship between the chemokine-CXCR1/CXCR2-G-protein/β-arrestin axis and neutrophil function.

Vasodilator-stimulated phosphoprotein (VASP), a novel target of miR-4455, promotes gastric cancer cell proliferation, migration, and invasion, through activating the PI3K/AKT signaling pathway

Background

MicroRNAs (miRNAs) are small non-coding RNAs which play important roles in the carcinogenesis of gastric cancer (GC). Expression profiling of miRNAs in paired gastric cancer and adjacent normal gastric tissues has demonstrated that miR-4455 is down-regulated in gastric cancer tissues, but its functional role in the carcinogenesis of GC had not previously been investigated.

Aims

The purpose of this study was to investigate the functional and biological mechanisms of miR-4455 in the progression of GC, in vitro.

Methods

Expression of miR-4455 was compared in human GC tissue samples and paired adjacent normal tissue samples. The in vitro effects of miR-4455 expression in MGC-803 cells on their proliferation, invasion, and migration were assessed by MTT assays and 5-bromo-2′-deoxyuridine staining, matrigel-invasion analysis and wound healing assays. Bioinformatics analysis (using PicTar, target scan and miRBase target) was used to identify potential targets for miR-4455, and the luciferase reporter assay, qRT-PCR and Western-blotting analyses were used to confirm VASP as the target of miR-4455. In addition, the effects of downregulation of VASP on the activation of PI3K/AKT signaling pathway were measured using Western-blot analysis.

Results

The expression of miR-4455 was markedly down-regulated in gastric cancer tissues vs. adjacent normal tissues, and miR-4455 expression inhibited the proliferation, invasion and migration of MGC-803 GC cells in vitro. Luciferase reporter assays revealed that miR-4455 inhibited VASP expression by targeting the 3′-UTR sequence of VASP. Furthermore, silencing of VASP markedly inhibited the activation of the PI3K/AKT signaling pathway.

Conclusion

Our results suggest that miR-4455 functions as a tumor suppressor in gastric cancer, by targeting VASP leading to activation of the PI3K/AKT signaling pathway and the inhibition of VASP mediated proliferation, migration and invasion of gastric cancer cells.

Electronic supplementary material

The online version of this article (10.1186/s12935-018-0573-4) contains supplementary material, which is available to authorized users.

Deconvolution of subcellular protrusion heterogeneity and the underlying actin regulator dynamics from live cell imaging

Cell protrusion is morphodynamically heterogeneous at the subcellular level. However, the mechanism of cell protrusion has been understood based on the ensemble average of actin regulator dynamics. Here, we establish a computational framework called HACKS (deconvolution of heterogeneous activity in coordination of cytoskeleton at the subcellular level) to deconvolve the subcellular heterogeneity of lamellipodial protrusion from live cell imaging. HACKS identifies distinct subcellular protrusion phenotypes based on machine-learning algorithms and reveals their underlying actin regulator dynamics at the leading edge. Using our method, we discover "accelerating protrusion", which is driven by the temporally ordered coordination of Arp2/3 and VASP activities. We validate our finding by pharmacological perturbations and further identify the fine regulation of Arp2/3 and VASP recruitment associated with accelerating protrusion. Our study suggests HACKS can identify specific subcellular protrusion phenotypes susceptible to pharmacological perturbation and reveal how actin regulator dynamics are changed by the perturbation.

VASP regulates leukocyte infiltration, polarization, and vascular repair after ischemia

In ischemic vascular diseases, leukocyte recruitment and polarization are crucial for revascularization and tissue repair. The study of Laban et al. provides evidence that VASP is a major regulator of leukocyte recruitment and polarization and vascular repair after ischemia. Mechanistically, the study supports a novel role of VASP in chemokine receptor trafficking.

In ischemic vascular diseases, leukocyte recruitment and polarization are crucial for revascularization and tissue repair. We investigated the role of vasodilator-stimulated phosphoprotein (VASP) in vascular repair. After hindlimb ischemia induction, blood flow recovery, angiogenesis, arteriogenesis, and leukocyte infiltration into ischemic muscles in VASP^−/− mice were accelerated. VASP deficiency also elevated the polarization of the macrophages through increased signal transducer and activator of transcription (STAT) signaling, which augmented the release of chemokines, cytokines, and growth factors to promote leukocyte recruitment and vascular repair. Importantly, VASP deletion in bone marrow–derived cells was sufficient to mimic the increased blood flow recovery of global VASP^−/− mice. In chemotaxis experiments, VASP^−/− neutrophils/monocytes were significantly more responsive to M1-related chemokines than wild-type controls. Mechanistically, VASP formed complexes with the chemokine receptor CCR2 and β-arrestin-2, and CCR2 receptor internalization was significantly reduced in VASP^−/− leukocytes. Our data indicate that VASP is a major regulator of leukocyte recruitment and polarization in postischemic revascularization and support a novel role of VASP in chemokine receptor trafficking.

Expression status of cytoskeleton regulatory protein Mena as a prognostic marker for human thyroid carcinoma

OBJECTIVE

In recent years, Mena (Mammalian Enabled) has been reported to be highly expressed in malignant tumors. However, data on the expression pattern and clinical relevance of Mena in thyroid carcinoma are unclear. The purpose of this study was to investigate the expression of Mena and its prognostic significance in human thyroid carcinoma.

MATERIALS AND METHODS

Mena expression at the mRNA level was examined by real-time quantitative polymerase chain reaction (RT-PCR) in 8 paired thyroid carcinoma and adjacent normal tissues. Mena protein expression in clinical samples was analyzed in paraffin-embedded papillary thyroid carcinoma samples and normal thyroid tissues by immunohistochemistry (IHC). Statistical analyses were also performed to evaluate the clinicopathological significance of Mena expression.

RESULTS

The results show that expression of Mena mRNA is higher in thyroid carcinoma than in adjacent normal tissues in 8 paired samples. In paraffin-embedded tissue samples, the expression of Mena was higher in papillary thyroid carcinoma than normal thyroid tissues. Compared with normal thyroid tissues, overexpression of Mena was detected in 47.11% (57/121) of papillary thyroid carcinoma patients. Overexpression of Mena was significantly associated with T Stage (P = 0.007), capsular invasion (P = 0.015), lymph node metastasis (P = 0.000), and clinical stage (P = 0.029).

CONCLUSION

Mena is up-regulated in thyroid carcinoma and is associated with expression of T Stage, lymph node metastasis, clinical stage and disease-free survival. Mena may serve as a prognostic indicator for patients with thyroid carcinoma.

New insights in chemokine signaling

Chemokine signaling is essential for coordinated cell migration in health and disease to specifically govern cell positioning in space and time. Typically, chemokines signal through heptahelical, G protein-coupled receptors to orchestrate cell migration. Notably, chemokine receptors are highly dynamic structures and signaling efficiency largely depends on the discrete contact with the ligand. Promiscuity of both chemokines and chemokine receptors, combined with biased signaling and allosteric modulation of receptor activation, guarantees a tightly controlled recruitment and positioning of individual cells within the local environment at a given time. Here, we discuss recent insights in understanding chemokine gradient formation by atypical chemokine receptors and how typical chemokine receptors can transmit distinct signals to translate guidance cues into coordinated cell locomotion in space and time.

Expression of the cytoskeleton regulatory protein Mena in human gastric carcinoma and its prognostic significance

The cytoskeleton regulatory protein Mena is reportedly overexpressed in breast cancer; however, data regarding its expression level and clinical significance in gastric carcinoma (GC) is limited. The aim of the present study was to investigate Mena expression levels and prognostic significance in GC. Mena mRNA expression level was determined by reverse transcription-quantitative polymerase chain reaction in 10 paired GC and adjacent normal tissues. The Mena protein expression level was analyzed in paraffin-embedded GC samples and adjacent normal tissues by immunohistochemistry. Statistical analyses were also performed to evaluate the clinicopathological significance of Mena. The results revealed that the mRNA expression level of Mena was significantly higher in G Ct issues compared with in adjacent normal tissues from10 paired samples. In the paraffin-embedded tissue samples, the protein expression level of Mena was higher in G Ct issues compared with in adjacent normal tissues. Compared with adjacent normal tissues, Mena overexpression was observed in 52.83% (56/106) of patients. The overexpression of Mena was significantly associated with the T stage (P=0.033), tumor-node-metastasis (TNM) stage (P<0.001) and decreased overall survival (P<0.001). Based on a multivariate analysis, Mena expression level was an independent prognostic factor for overall survival time. In conclusion, Mena wasoverexpressed in G C tissues and significantly associated with the T stage, TNM stage and overall survival time. Mena may therefore be suitable as a prognostic indicator for patients with GC.

Disruption of Trim9 function abrogates macrophage motility in vivo

The vertebrate immune response comprises multiple molecular and cellular components that interface to provide defense against pathogens. Because of the dynamic complexity of the immune system and its interdependent innate and adaptive functionality, an understanding of the whole-organism response to pathogen exposure remains unresolved. Zebrafish larvae provide a unique model for overcoming this obstacle, because larvae are protected against pathogens while lacking a functional adaptive immune system during the first few weeks of life. Zebrafish larvae were exposed to immune agonists for various lengths of time, and a microarray transcriptome analysis was executed. This strategy identified known immune response genes, as well as genes with unknown immune function, including the E3 ubiquitin ligase tripartite motif-9 (Trim9). Although trim9 expression was originally described as "brain specific," its expression has been reported in stimulated human Mϕs. In this study, we found elevated levels of trim9 transcripts in vivo in zebrafish Mϕs after immune stimulation. Trim9 has been implicated in axonal migration, and we therefore investigated the impact of Trim9 disruption on Mϕ motility and found that Mϕ chemotaxis and cellular architecture are subsequently impaired in vivo. These results demonstrate that Trim9 mediates cellular movement and migration in Mϕs as well as neurons.

Neutrophil migration in infection and wound repair: going forward in reverse

Neutrophil migration and its role during inflammation has been the focus of increased interest in the past decade. Advances in live imaging and the use of new model systems have helped to uncover the behaviour of neutrophils in injured and infected tissues. Although neutrophils were considered to be short-lived effector cells that undergo apoptosis in damaged tissues, recent evidence suggests that neutrophil behaviour is more complex and, in some settings, neutrophils might leave sites of tissue injury and migrate back into the vasculature. The role of reverse migration and its contribution to resolution of inflammation remains unclear. In this Review, we discuss the different cues within tissues that mediate neutrophil forward and reverse migration in response to injury or infection and the implications of these mechanisms to human disease.

CXCL1/CXCR2 signaling in pathological pain: Role in peripheral and central sensitization

Pathological pain conditions can be triggered after peripheral nerve injury and/or inflammation. It is associated with plasticity of nociceptive pathway in which pain is prolonged even after healing of the injured tissue. Generally combinations of analgesic drugs are not sufficient to achieve selective palliation from chronic pain, besides causing a greater number of side effects. In order to identify novel alternatives for more effective treatments, it is necessary to clarify the underlying mechanisms of pathological pain. It is well established that there are two main components in pathological pain development and maintenance: (i) primary sensory neuron sensitization (peripheral sensitization), and (ii) central sensitization. In both components cytokines and chemokines act as key mediators in pain modulation. CXCL1 is a chemokine that promote both nociceptor and central sensitization via its main receptor CXCR2, which is a promising target for novel analgesic drugs. Here, we reviewed and discussed the role of the CXCL1/CXCR2 signaling axis in pathological pain conditions triggered by either peripheral inflammation or nerve injury.

Ena/VASP proteins regulate activated T-cell trafficking by promoting diapedesis during transendothelial migration

Vasodilator-stimulated phosphoprotein (VASP) and Ena-VASP-like (EVL) are cytoskeletal effector proteins implicated in regulating cell morphology, adhesion, and migration in various cell types. However, the role of these proteins in T-cell motility, adhesion, and in vivo trafficking remains poorly understood. This study identifies a specific role for EVL and VASP in T-cell diapedesis and trafficking. We demonstrate that EVL and VASP are selectively required for activated T-cell trafficking but are not required for normal T-cell development or for naïve T-cell trafficking to lymph nodes and spleen. Using a model of multiple sclerosis, we show an impairment in trafficking of EVL/VASP-deficient activated T cells to the inflamed central nervous system of mice with experimental autoimmune encephalomyelitis. Additionally, we found a defect in trafficking of EVL/VASP double-knockout (dKO) T cells to the inflamed skin and secondary lymphoid organs. Deletion of EVL and VASP resulted in the impairment in α4 integrin (CD49d) expression and function. Unexpectedly, EVL/VASP dKO T cells did not exhibit alterations in shear-resistant adhesion to, or in crawling on, primary endothelial cells under physiologic shear forces. Instead, deletion of EVL and VASP impaired T-cell diapedesis. Furthermore, T-cell diapedesis became equivalent between control and EVL/VASP dKO T cells upon α4 integrin blockade. Overall, EVL and VASP selectively mediate activated T-cell trafficking by promoting the diapedesis step of transendothelial migration in a α4 integrin-dependent manner.

Decoding the chemokine network that links leukocytes with decidual cells and the trophoblast during early implantation

Chemokine network is central to the innate and adaptive immunity and entails a variety of proteins and membrane receptors that control physiological processes such as wound healing, angiogenesis, embryo growth and development. During early pregnancy, the chemokine network coordinates not only the recruitment of different leukocyte populations to generate the maternal-placental interface, but also constitutes an additional checkpoint for tissue homeostasis maintenance. The normal switch from a pro-inflammatory to an anti-inflammatory predominant microenvironment characteristic of the post-implantation stage requires redundant immune tolerance circuits triggered by key master regulators. In this review we will focus on the recruitment and conditioning of maternal immune cells to the uterus at the early implantation period with special interest on high plasticity macrophages and dendritic cells and their ability to induce regulatory T cells. We will also point to putative immunomodulatory polypeptides involved in immune homeostasis maintenance at the maternal-placental interface.

FGF23 signaling impairs neutrophil recruitment and host defense during CKD

Chronic kidney disease (CKD) has been associated with impaired host response and increased susceptibility to infections. Leukocyte recruitment during inflammation must be tightly regulated to protect the host against pathogens. FGF23 levels are increased in blood during CKD, and levels of this hormone have been associated with a variety of adverse effects in CKD patients. Here, we have shown that CKD impairs leukocyte recruitment into inflamed tissue and host defense in mice and humans. FGF23 neutralization during CKD in murine models restored leukocyte recruitment and host defense. Intravital microscopy of animals with chronic kidney failure showed that FGF23 inhibits chemokine-activated leukocyte arrest on the endothelium, and downregulation of FGF receptor 2 (FGFR2) on PMNs rescued host defense in these mice. In vitro, FGF23 inhibited PMN adhesion, arrest under flow, and transendothelial migration. Mechanistically, FGF23 binding to FGFR2 counteracted selectin- and chemokine-triggered β2 integrin activation on PMNs by activating protein kinase A (PKA) and inhibiting activation of the small GTPase Rap1. Moreover, knockdown of PKA abolished the inhibitory effect of FGF23 on integrin activation. Together, our data reveal that FGF23 acts directly on PMNs and dampens host defense by direct interference with chemokine signaling and integrin activation.

Lamellipodin promotes actin assembly by clustering Ena/VASP proteins and tethering them to actin filaments

Enabled/Vasodilator (Ena/VASP) proteins promote actin filament assembly at multiple locations, including: leading edge membranes, focal adhesions, and the surface of intracellular pathogens. One important Ena/VASP regulator is the mig-10/Lamellipodin/RIAM family of adaptors that promote lamellipod formation in fibroblasts and drive neurite outgrowth and axon guidance in neurons. To better understand how MRL proteins promote actin network formation we studied the interactions between Lamellipodin (Lpd), actin, and VASP, both in vivo and in vitro. We find that Lpd binds directly to actin filaments and that this interaction regulates its subcellular localization and enhances its effect on VASP polymerase activity. We propose that Lpd delivers Ena/VASP proteins to growing barbed ends and increases their polymerase activity by tethering them to filaments. This interaction represents one more pathway by which growing actin filaments produce positive feedback to control localization and activity of proteins that regulate their assembly.

DOI:http://dx.doi.org/10.7554/eLife.06585.001

Actin—the most abundant protein in most eukaryotic cells—assembles into a network of filaments that spans the length and breadth of the cell. Like the skeleton of an animal, this ‘actin cytoskeleton’ gives the cell its shape and strength, and enables the cell to actively move through its environment. To start moving, many cells begin assembling actin filaments next to the cell membrane. The growth of these filaments pushes the membrane forward and creates a two-dimensional structure called a ‘lamellipod’, which explores the space around the cell and steers its movement.

The actin filaments in a lamellipod are dynamic and undergo repeated cycles of assembly and disassembly. These processes are tightly regulated by a variety of other proteins. Members of the Ena/VASP protein family, for example, collect the building blocks of an actin filament and rapidly stack them in place on the fast-growing end of a filament. The activities of Ena/VASP proteins play an especially important role in creating lamellipodial actin networks and in driving cell movement.

Previous work showed that a protein called Lamellipodin binds to Ena/VASP proteins and helps recruit them to the cell membrane. However, it was unclear whether Lamellipodin could affect the activity of Ena/VASP proteins or their interaction with the actin filaments. Hansen and Mullins have now analyzed the interactions between Ena/VASP, Lamellipodin and actin. The experiments demonstrate that Lamellipodin does not simply tether Ena/VASP proteins to the membrane but also binds directly to actin filaments, via a binding site that is distinct from the site that contacts Ena/VASP. Further experiments with purified proteins revealed that Lamellipodin could interact with both actin filaments and Ena/VASP proteins at the same time. Hansen and Mullins also found that purified Lamellipodin interacted with VASP proteins to form clustered protein complexes, and that together with the tethering of actin filaments to the membrane, this clustering greatly increased VASP's ability to lengthen actin filaments.

By visualizing Lamellipodin tagged with a green fluorescent protein in living cells, Hansen and Mullins then showed that its interaction with actin filaments was sufficient to localize Lamellipodin to the cell membrane. Finally, since Lamellipodin interacts with a multitude of signaling molecules in addition to Ena/VASP proteins, the next big challenge is to understand how Lamellipodin itself is regulated. Future studies could also explore how cells harness the power of the actin cytoskeleton to carry out these essential activities.

DOI:http://dx.doi.org/10.7554/eLife.06585.002

Yersinia protein kinase A phosphorylates vasodilator-stimulated phosphoprotein to modify the host cytoskeleton

Pathogenic Yersinia species evolved a type III secretion system that injects a set of effectors into the host cell cytosol to promote infection. One of these effectors, Yersinia protein kinase A (YpkA), is a multidomain effector that harbours a Ser/Thr kinase domain and a guanine dissociation inhibitor (GDI) domain. The intercellular targets of the kinase and GDI domains of YpkA were identified to be Gαq and the small GTPases RhoA and Rac1, respectively, which synergistically induce cytotoxic effects on infected cells. In this study, we demonstrate that vasodilator-stimulated phosphoprotein (VASP), which is critical for regulation of actin assembly, cell adhesion and motility, is a direct substrate of YpkA kinase activity. Ectopic co-expression of YpkA and VASP in HEK293T cells leads to the phosphorylation of VASP at S157, and YpkA kinase activity is essential for VASP phosphorylation at this site. Moreover, YpkA directly phosphorylates VASP in in vitro kinase assay. YpkA-mediated VASP phosphorylation significantly inhibits actin polymerization and promotes the disruption of actin cytoskeleton, which inhibits the phagocytosis. Taken together, our study found a novel molecular mechanism used by YpkA to disrupt cytoskeleton dynamics, thereby promoting the anti-phagocytosis ability of pathogenic Yersiniae.

Control of CXCR2 activity through its ubiquitination on K327 residue

Background

The interleukin-8 chemokine (IL-8) G-protein coupled receptor CXCR2 governs pro-inflammatory and pro-angiogenic responses in leukocytes and endothelial cells. At a molecular standpoint, CXCR2 is widely reported to operate through calcium flux, phosphoinoisitide 3 kinase (PI3K) and mitogen-activated protein kinase (MAPK). While CXCR2 trafficking is suspected to be intertwined with its signaling, the exact mechanism is not fully elucidated.

Results

Here, we identified the lysine 327 within the CXCR2 C-terminal tail as a key residue for ubiquitination, internalization, and signaling. First, the substitution to an arginine of K327 mutation was associated with a reduction in CXCR2 poly-ubiquitination. While WT CXCR2 was rapidly internalized following IL-8 administration, K327R mutant remained at the plasma membrane. Finally, K327R mutant failed to promote the recruitment of β-arrestin2, as estimated by imagery and bioluminescence resonance transfer. As a consequence, the activation of intracellular signaling, including both early events such as ERK phosphorylation and the increase in calcium flux, and the latter activation of the AP1 and NF-κB transcription factors, was blunted.

Conclusions

Overall, our results demonstrate that CXCR2 ubiquitination on K327 residue modulates agonist-activated CXCR2 cell sorting and intracellular signaling. Thus, the inhibition of K327 ubiquitination might emerge as an effective mean to curb exacerbated CXCR2 signaling in several pathological conditions, such as inflammatory diseases and cancer.

Directed migration of mesenchymal cells: where signaling and the cytoskeleton meet

Cell migration directed by spatial cues, or taxis, is a primary mechanism for orchestrating concerted and collective cell movements during development, wound repair, and immune responses. Compared with the classic example of amoeboid chemotaxis, in which fast-moving cells such as neutrophils are directed by gradients of soluble factors, directed migration of slow-moving mesenchymal cells such as fibroblasts is poorly understood. Mesenchymal cells possess a distinctive organization of the actin cytoskeleton and associated adhesion complexes as its primary mechanical system, generating the asymmetric forces required for locomotion without strong polarization. The emerging hypothesis is that the molecular underpinnings of mesenchymal taxis involve distinct signaling pathways and diverse requirements for regulation.

Evaluation of antibody–chemokine fusion proteins for tumor-targeting applications

There is an increasing biotechnological interest in the ‘arming’ of therapeutic antibodies with bioactive payloads. While many antibody–cytokine fusion proteins have been extensively investigated in preclinical and clinical studies, there are only few reports related to antibody–chemokine fusion proteins (‘immunochemokines’). Here, we describe the cloning, expression, and characterization of 10 immunochemokines based on the monoclonal antibody F8, specific to the alternatively spliced extra domain A (EDA) of fibronectin, a marker of angiogenesis. Among the 10 murine chemokines tested in our study, only CCL19, CCL20, CCL21, and CXCL10 could be expressed and isolated at acceptable purity levels as F8-based fusion proteins. The immunochemokines retained the binding characteristics of the parental antibody, but could not be characterized by gel-filtration analysis, an analytical limitation which had previously been observed in our laboratory for the unconjugated chemokines. When radioiodinated preparations of CCL19-F8, CCL20-F8, CCL21-F8, and CXCL10-F8 were tested in quantitative biodistribution studies in tumor-bearing mice, the four fusion proteins failed to preferentially accumulate at the tumor site, while the unconjugated parental antibody displayed a tumor:blood ratio >20:1, 24 h after intravenous (i.v.) administration. The tumor-targeting ability of CCL19-F8 could be rescued only in part by preadministration of unlabeled CCL19-F8, indicating that a chemokine trapping mechanism may hinder pharmacodelivery strategies. While this article highlights expression, analytical, and biodistribution challenges associated with the antibody-based in vivo delivery of chemokines at sites of disease, it provides the first comprehensive report in this field and may facilitate future studies with immunochemokines.

Crystal structure of the NHERF1 PDZ2 domain in complex with the chemokine receptor CXCR2 reveals probable modes of PDZ2 dimerization

The formation of CXCR2-NHERF1-PLCβ2 macromolecular complex in neutrophils regulates CXCR2 signaling and plays a key role in neutrophil chemotaxis and transepithelial neutrophilic migration. However, NHERF1 by itself, with only two PDZ domains, has a limited capacity in scaffolding the multiprotein-complex formation. Here we report the crystal structure of the NHERF1 PDZ2 domain in complex with the C-terminal CXCR2 sequence. The structure reveals that the PDZ2-CXCR2 binding specificity is achieved by numerous hydrogen bonds and hydrophobic contacts with the last four CXCR2 residues contributing to specific interactions. The structure also reveals two probable modes of PDZ2 dimerization where the two canonical ligand-binding pockets are well separated and orientated in a unique parallel fashion. This study provides not only the structural basis for the PDZ-mediated NHERF1-CXCR2 interaction, but also an additional example of how PDZ domains may dimerize, which both could prove valuable in understanding NHERF1 complex-scaffolding function in neutrophils.

Chemokine receptors in epithelial ovarian cancer

Ovarian carcinoma is the deadliest gynecologic malignancy with very poor rate of survival, and it is characterized by the presence of vast incurable peritoneal metastasis. Studies of the role of chemokine receptors, a family of proteins belonging to the group of G protein-coupled receptors, in ovarian carcinoma strongly placed this family of membrane receptors as major regulators of progression of this malignancy. In this review, we will discuss the roles that chemokine-receptor interactions play to support angiogenesis, cell proliferation, migration, adhesion, invasion, metastasis, and immune evasion in progression of ovarian carcinoma. Data regarding the role that the chemokine receptors play in the disease progression accumulated insofar strongly suggest that this family of proteins could be good therapeutic targets against ovarian carcinoma.

CDC42 switches IRSp53 from inhibition of actin growth to elongation by clustering of VASP

Filopodia explore the environment, sensing soluble and mechanical cues during directional motility and tissue morphogenesis. How filopodia are initiated and spatially restricted to specific sites on the plasma membrane is still unclear. Here, we show that the membrane deforming and curvature sensing IRSp53 (Insulin Receptor Substrate of 53 kDa) protein slows down actin filament barbed end growth. This inhibition is relieved by CDC42 and counteracted by VASP, which also binds to IRSp53. The VASP:IRSp53 interaction is regulated by activated CDC42 and promotes high-density clustering of VASP, which is required for processive actin filament elongation. The interaction also mediates VASP recruitment to liposomes. In cells, IRSp53 and VASP accumulate at discrete foci at the leading edge, where filopodia are initiated. Genetic removal of IRSp53 impairs the formation of VASP foci, filopodia and chemotactic motility, while IRSp53 null mice display defective wound healing. Thus, IRSp53 dampens barbed end growth. CDC42 activation inhibits this activity and promotes IRSp53-dependent recruitment and clustering of VASP to drive actin assembly. These events result in spatial restriction of VASP filament elongation for initiation of filopodia during cell migration, invasion, and tissue repair.

Mammalian target of rapamycin and Rictor control neutrophil chemotaxis by regulating Rac/Cdc42 activity and the actin cytoskeleton

Rictor, a component of mammalian target of rapamycin complex 2 (mTORC2), controls neutrophil chemotaxis by regulating the dynamics of the actin cytoskeleton via Rac and Cdc42. This function of Rictor is independent of mTORC2 and the kinase activity of mTOR.

Chemotaxis allows neutrophils to seek out sites of infection and inflammation. The asymmetric accumulation of filamentous actin (F-actin) at the leading edge provides the driving force for protrusion and is essential for the development and maintenance of neutrophil polarity. The mechanism that governs actin cytoskeleton dynamics and assembly in neutrophils has been extensively explored and is still not fully understood. By using neutrophil-like HL-60 cells, we describe a pivotal role for Rictor, a component of mammalian target of rapamycin complex 2 (mTORC2), in regulating assembly of the actin cytoskeleton during neutrophil chemotaxis. Depletion of mTOR and Rictor, but not Raptor, impairs actin polymerization, leading-edge establishment, and directional migration in neutrophils stimulated with chemoattractants. Of interest, depletion of mSin1, an integral component of mTORC2, causes no detectable defects in neutrophil polarity and chemotaxis. In addition, experiments with chemical inhibition and kinase-dead mutants indicate that mTOR kinase activity and AKT phosphorylation are dispensable for chemotaxis. Instead, our results suggest that the small Rho GTPases Rac and Cdc42 serve as downstream effectors of Rictor to regulate actin assembly and organization in neutrophils. Together our findings reveal an mTORC2- and mTOR kinase–independent function and mechanism of Rictor in the regulation of neutrophil chemotaxis.

Arrest Functions of the MIF Ligand/Receptor Axes in Atherogenesis

Macrophage migration inhibitory factor (MIF) has been defined as an important chemokine-like function (CLF) chemokine with an essential role in monocyte recruitment and arrest. Adhesion of monocytes to the vessel wall and their transendothelial migration are critical in atherogenesis and many other inflammatory diseases. Chemokines carefully control all steps of the monocyte recruitment process. Those chemokines specialized in controlling arrest are typically immobilized on the endothelial surface, mediating the arrest of rolling monocytes by chemokine receptor-triggered pathways. The chemokine receptor CXCR2 functions as an important arrest receptor on monocytes. An arrest function has been revealed for the bona fide CXCR2 ligands CXCL1 and CXCL8, but genetic studies also suggested that additional arrest chemokines are likely to be involved in atherogenic leukocyte recruitment. While CXCR2 is known to interact with numerous CXC chemokine ligands, the CLF chemokine MIF, which structurally does not belong to the CXC chemokine sub-family, was surprisingly identified as a non-cognate ligand of CXCR2, responsible for critical arrest functions during the atherogenic process. MIF was originally identified as macrophage migration inhibitory factor (this function being eponymous), but is now known as a potent inflammatory cytokine with CLFs including chemotaxis and leukocyte arrest. This review will cover the mechanisms underlying these functions, including MIF’s effects on LFA1 integrin activity and signal transduction, and will discuss the structural similarities between MIF and the bona fide CXCR2 ligand CXCL8 while emphasizing the structural differences. As MIF also interacts with CXCR4, a chemokine receptor implicated in CXCL12-elicited lymphocyte arrest, the arrest potential of the MIF/CXCR4 axis will also be scrutinized as well as the recently identified role of pericyte MIF in attracting leukocytes exiting through venules as part of the pericyte “motility instruction program.”

The niche-derived glial cell line-derived neurotrophic factor (GDNF) induces migration of mouse spermatogonial stem/progenitor cells

In mammals, the biological activity of the stem/progenitor compartment sustains production of mature gametes through spermatogenesis. Spermatogonial stem cells and their progeny belong to the class of undifferentiated spermatogonia, a germ cell population found on the basal membrane of the seminiferous tubules. A large body of evidence has demonstrated that glial cell line-derived neurotrophic factor (GDNF), a Sertoli-derived factor, is essential for in vivo and in vitro stem cell self-renewal. However, the mechanisms underlying this activity are not completely understood. In this study, we show that GDNF induces dose-dependent directional migration of freshly selected undifferentiated spermatogonia, as well as germline stem cells in culture, using a Boyden chamber assay. GDNF-induced migration is dependent on the expression of the GDNF co-receptor GFRA1, as shown by migration assays performed on parental and GFRA1-transduced GC-1 spermatogonial cell lines. We found that the actin regulatory protein vasodilator-stimulated phosphoprotein (VASP) is specifically expressed in undifferentiated spermatogonia. VASP belongs to the ENA/VASP family of proteins implicated in actin-dependent processes, such as fibroblast migration, axon guidance, and cell adhesion. In intact seminiferous tubules and germline stem cell cultures, GDNF treatment up-regulates VASP in a dose-dependent fashion. These data identify a novel role for the niche-derived factor GDNF, and they suggest that GDNF may impinge on the stem/progenitor compartment, affecting the actin cytoskeleton and cell migration.

Technical note: proteomic approaches to fundamental questions about neutrophil biology

Proteomics is one of a group of technologies that generates high-throughput, large-scale datasets that can be used to understand cell or organ functions at a systems level. This review will focus on the application of proteomics to the understanding of neutrophil biology. The strengths and weaknesses of common proteomic methods and their application to neutrophils are reviewed, with the goal of evaluating whether the technology is ready to advance our understanding of neutrophil biology.

Tolerance induction at the early maternal-placental interface through selective cell recruitment and targeting by immune polypeptides

Pregnancy challenges immune cells and immunomodulatory circuits of the mother and the developing fetus to dynamically adapt to each other in an homeostatic and tolerant environment for fetal growth. This entails the coordination of multiple cellular processes all devoted to accommodate and nourish the fetus while protecting the mother from endogenous and exogenous threatens. From the earliest stages of pregnancy, several strategies to efficiently communicate immune and trophoblast cells within the interface or at a distance were identified and chemokines might act at on different targets through direct or indirect mechanisms. Here, we briefly review some mechanisms of T regulatory cell recruitment to the early maternal-placental interfaces to accomplish immunotolerance and homeostatic control and we discuss evidence on two locally released polypeptides, RANTES (regulated on activation, normal, T-cell expressed, and secreted) and vasoactive intestinal peptide (VIP), as novel contributors to the multiplicity of immune tolerant responses and uterine quiescence requirements.

Increased function of the TRPV1 channel in small sensory neurons after local inflammation or in vitro exposure to the pro-inflammatory cytokine GRO/KC

OBJECTIVE

Inflammation at the level of the sensory dorsal root ganglia (DRGs) leads to robust mechanical pain behavior and the local inflammation has direct excitatory effects on sensory neurons including small, primarily nociceptive, neurons. These neurons express the transient receptor potential vanilloid-1 (TRPV1) channel, which integrates multiple signals of pain and inflammation. The aim of this study was to characterize the regulation of the TRPV1 channel by local DRG inflammation and by growth-related oncogene (GRO/KC, systemic name: CXCL1), a cytokine known to be upregulated in inflamed DRGs.

METHODS

Activation of the TRPV1 receptor with capsaicin was studied with patch clamp methods in acutely isolated small-diameter rat sensory neurons in primary culture. In vivo, behavioral effects of TRPV1 and GRO/KC were examined by paw injections.

RESULTS

Neurons isolated from lumbar DRGs 3 days after local inflammation showed enhanced TRPV1 function: tachyphylaxis (the decline in response to repeated applications of capsaicin) was significantly reduced. A similar effect on tachyphylaxis was observed in neurons pre-treated for 4 h in vitro with GRO/KC. This effect was blocked by H-89, a protein kinase A inhibitor. Consistent with the in vitro results, in vivo behavioral responses to paw injection of capsaicin were enhanced and prolonged by pre-injecting the paw with GRO/KC 4 h before the capsaicin injection. GRO/KC paw injections alone did not elicit pain behaviors.

CONCLUSION

Function of the TRPV1 channel is enhanced by DRG inflammation and these effects are preserved in vitro during short-term culture. The effects (decreased tachyphylaxis) are mimicked by incubation with GRO/KC, which has previously been found to be strongly upregulated in this and other pain models.

A chemokine receptor CXCR2 macromolecular complex regulates neutrophil functions in inflammatory diseases

Inflammation plays an important role in a wide range of human diseases such as ischemia-reperfusion injury, arteriosclerosis, cystic fibrosis, inflammatory bowel disease, etc. Neutrophilic accumulation in the inflamed tissues is an essential component of normal host defense against infection, but uncontrolled neutrophilic infiltration can cause progressive damage to the tissue epithelium. The CXC chemokine receptor CXCR2 and its specific ligands have been reported to play critical roles in the pathophysiology of various inflammatory diseases. However, it is unclear how CXCR2 is coupled specifically to its downstream signaling molecules and modulates cellular functions of neutrophils. Here we show that the PDZ scaffold protein NHERF1 couples CXCR2 to its downstream effector phospholipase C (PLC)-β2, forming a macromolecular complex, through a PDZ-based interaction. We assembled a macromolecular complex of CXCR2·NHERF1·PLC-β2 in vitro, and we also detected such a complex in neutrophils by co-immunoprecipitation. We further observed that the CXCR2-containing macromolecular complex is critical for the CXCR2-mediated intracellular calcium mobilization and the resultant migration and infiltration of neutrophils, as disrupting the complex with a cell permeant CXCR2-specific peptide (containing the PDZ motif) inhibited intracellular calcium mobilization, chemotaxis, and transepithelial migration of neutrophils. Taken together, our data demonstrate a critical role of the PDZ-dependent CXCR2 macromolecular signaling complex in regulating neutrophil functions and suggest that targeting the CXCR2 multiprotein complex may represent a novel therapeutic strategy for certain inflammatory diseases.

MicroRNA-610 inhibits the migration and invasion of gastric cancer cells by suppressing the expression of vasodilator-stimulated phosphoprotein

Vasodilator-stimulated phosphoprotein (VASP) has been implicated in the establishment of cancerous phenotypes. However, the role of VASP in gastric cancer progression and metastasis remains poorly understood. Here, we demonstrated that VASP was upregulated by epidermal growth factor (EGF) and promoted the migration and invasion of gastric cancer cells. Then we explored the regulatory mechanisms responsible for high expression of VASP in gastric cancer. Based on miRNA expression profiling of the paired gastric cancer tissues and their adjacent non-tumour gastric tissues 18 miRNAs were identified including microRNA-610 (miR-610) which were down-regulated in gastric cancer. Next, we observed an inverse correlation between VASP and miR-610 expression levels in gastric cancer cells after EGF stimulation. Then we performed bioinformatics analysis, Western blot and reverse transcription polymerase chain reaction (RT-PCR) analysis and luciferase assay to establish that miR-610 directly targets VASP 3'-UTR and inhibits its expression. Functionally, we demonstrated that miR610-mediated inhibition of VASP expression resulted in a significant reduction in the migration and invasion properties of gastric cancer cells. The identification of miR-610 as a novel miRNA regulated by EGF that targets VASP in gastric cancer cells suggests that EGF-miR610-VASP axis may be exploited for therapeutic intervention to inhibit gastric cancer progression and metastasis.

IQGAP1 is a novel CXCR2-interacting protein and essential component of the "chemosynapse"

Background

Chemotaxis is essential for a number of physiological processes including leukocyte recruitment. Chemokines initiate intracellular signaling pathways necessary for chemotaxis through binding seven transmembrane G protein-couple receptors. Little is known about the proteins that interact with the intracellular domains of chemokine receptors to initiate cellular signaling upon ligand binding. CXCR2 is a major chemokine receptor expressed on several cell types, including endothelial cells and neutrophils. We hypothesize that multiple proteins interact with the intracellular domains of CXCR2 upon ligand stimulation and these interactions comprise a “chemosynapse”, and play important roles in transducing CXCR2 mediated signaling processes.

Methodology/Principal Findings

In an effort to define the complex of proteins that assemble upon CXCR2 activation to relay signals from activated chemokine receptors, a proteomics approach was employed to identify proteins that co-associate with CXCR2 with or without ligand stimulation. The components of the CXCR2 “chemosynapse” are involved in processes ranging from intracellular trafficking to cytoskeletal modification. IQ motif containing GTPase activating protein 1 (IQGAP1) was among the novel proteins identified to interact directly with CXCR2. Herein, we demonstrate that CXCR2 co-localizes with IQGAP1 at the leading edge of polarized human neutrophils and CXCR2 expressing differentiated HL-60 cells. Moreover, amino acids 1-160 of IQGAP1 directly interact with the carboxyl-terminal domain of CXCR2 and stimulation with CXCL8 enhances IQGAP1 association with Cdc42.

Conclusions

Our studies indicate that IQGAP1 is a novel essential component of the CXCR2 “chemosynapse”.

Mena invasive (Mena(INV)) and Mena11a isoforms play distinct roles in breast cancer cell cohesion and association with TMEM

Mena, an actin regulatory protein, functions at the convergence of motility pathways that drive breast cancer cell invasion and migration in vivo. The tumor microenvironment spontaneously induces both increased expression of the Mena invasive (Mena(INV)) and decreased expression of Mena11a isoforms in invasive and migratory tumor cells. Tumor cells with this Mena expression pattern participate with macrophages in migration and intravasation in mouse mammary tumors in vivo. Consistent with these findings, anatomical sites containing tumor cells with high levels of Mena expression associated with perivascular macrophages were identified in human invasive ductal breast carcinomas and called TMEM. The number of TMEM sites positively correlated with the development of distant metastasis in humans. Here we demonstrate that mouse mammary tumors generated from EGFP-Mena(INV) expressing tumor cells are significantly less cohesive and have discontinuous cell-cell contacts compared to Mena11a xenografts. Using the mouse PyMT model we show that metastatic mammary tumors express 8.7 fold more total Mena and 7.5 fold more Mena(INV) mRNA than early non-metastatic ones. Furthermore, Mena(INV) expression in fine needle aspiration biopsy (FNA) samples of human invasive ductal carcinomas correlate with TMEM score while Mena11a does not. These results suggest that Mena(INV) is the isoform associated with breast cancer cell discohesion, invasion and intravasation in mice and in humans. They also imply that Mena(INV) expression and TMEM score measure related aspects of a common tumor cell dissemination mechanism and provide new insight into metastatic risk.

Chemotaxis in cancer

Chemotaxis of tumour cells and stromal cells in the surrounding microenvironment is an essential component of tumour dissemination during progression and metastasis. This Review summarizes how chemotaxis directs the different behaviours of tumour cells and stromal cells in vivo, how molecular pathways regulate chemotaxis in tumour cells and how chemotaxis choreographs cell behaviour to shape the tumour microenvironment and to determine metastatic spread. The central importance of chemotaxis in cancer progression is highlighted by discussion of the use of chemotaxis as a prognostic marker, a treatment end point and a target of therapeutic intervention.

Chemokines, macrophage inflammatory protein-2 and stromal cell-derived factor-1α, suppress amyloid β-induced neurotoxicity

Alzheimer's disease (AD) is characterized by a progressive cognitive decline and accumulation of neurotoxic oligomeric peptides amyloid-β (Aβ). Although the molecular events are not entirely known, it has become evident that inflammation, environmental and other risk factors may play a causal, disruptive and/or protective role in the development of AD. The present study investigated the ability of the chemokines, macrophage inflammatory protein-2 (MIP-2) and stromal cell-derived factor-1α (SDF-1α), the respective ligands for chemokine receptors CXCR2 and CXCR4, to suppress Aβ-induced neurotoxicity in vitro and in vivo. Pretreatment with MIP-2 or SDF-1α significantly protected neurons from Aβ-induced dendritic regression and apoptosis in vitro through activation of Akt, ERK1/2 and maintenance of metalloproteinase ADAM17 especially with SDF-1α. Intra-cerebroventricular (ICV) injection of Aβ led to reduction in dendritic length and spine density of pyramidal neurons in the CA1 area of the hippocampus and increased oxidative damage 24h following the exposure. The Aβ-induced morphometric changes of neurons and increase in biomarkers of oxidative damage, F(2)-isoprostanes, were significantly inhibited by pretreatment with the chemokines MIP-2 or SDF-1α. Additionally, MIP-2 or SDF-1α was able to suppress the aberrant mislocalization of p21-activated kinase (PAK), one of the proteins involved in the maintenance of dendritic spines. Furthermore, MIP-2 also protected neurons against Aβ neurotoxicity in CXCR2-/- mice, potentially through observed up regulation of CXCR1 mRNA. Understanding the neuroprotective potential of chemokines is crucial in defining the role for their employment during the early stages of neurodegeneration.

The non-receptor tyrosine kinase Lyn controls neutrophil adhesion by recruiting the CrkL-C3G complex and activating Rap1 at the leading edge

Establishing new adhesions at the extended leading edges of motile cells is essential for stable polarity and persistent motility. Despite recent identification of signaling pathways that mediate polarity and chemotaxis in neutrophils, little is known about molecular mechanisms governing cell-extracellular-matrix (ECM) adhesion in these highly polarized and rapidly migrating cells. Here, we describe a signaling pathway in neutrophils that is essential for localized integrin activation, leading edge attachment and persistent migration during chemotaxis. This pathway depends upon G(i)-protein-mediated activation and leading edge recruitment of Lyn, a non-receptor tyrosine kinase belonging to the Src kinase family. We identified the small GTPase Rap1 as a major downstream effector of Lyn to regulate neutrophil adhesion during chemotaxis. Depletion of Lyn in neutrophil-like HL-60 cells prevented chemoattractant-induced Rap1 activation at the leading edge of the cell, whereas ectopic expression of Rap1 largely rescued the defects induced by Lyn depletion. Furthermore, Lyn controls spatial activation of Rap1 by recruiting the CrkL-C3G protein complex to the leading edge. Together, these results provide novel mechanistic insights into the poorly understood signaling network that controls leading edge adhesion during chemotaxis of neutrophils, and possibly other amoeboid cells.

Chemokines in health and disease

Chemokines and their receptors play a key role in development and homeostasis as well as in the pathogenesis of tumors and autoimmune diseases. Chemokines are involved in the implantation of the early conceptus, the migration of subsets of cells during embryonic development, and the overall growth of the embryo. Chemokines also have an important role in the development and maintenance of innate and adaptive immunity. In addition, they play a significant role in wound healing and angiogenesis. When the physiological role of chemokines is subverted or chronically amplified, disease often follows. Chemokines are involved in the pathobiology of chronic inflammation, tumorigenesis and metastasis, as well as autoimmune diseases. This article reviews the role of chemokines and their receptors in normal and disease processes and the potential for using chemokine antagonists for appropriate targeted therapy.

VASP is a processive actin polymerase that requires monomeric actin for barbed end association

Visualization of VASP tetramers interacting with static and growing actin filaments in vitro by TIRF microscopy leads to a new model for VASP-mediated actin filament assembly.

Ena/VASP proteins regulate the actin cytoskeleton during cell migration and morphogenesis and promote assembly of both filopodial and lamellipodial actin networks. To understand the molecular mechanisms underlying their cellular functions we used total internal reflection fluorescence microscopy to visualize VASP tetramers interacting with static and growing actin filaments in vitro. We observed multiple filament binding modes: (1) static side binding, (2) side binding with one-dimensional diffusion, and (3) processive barbed end tracking. Actin monomers antagonize side binding but promote high affinity (K_d = 9 nM) barbed end attachment. In low ionic strength buffers, VASP tetramers are weakly processive (K_off = 0.69 s⁻¹) polymerases that deliver multiple actin monomers per barbed end–binding event and effectively antagonize filament capping. In higher ionic strength buffers, VASP requires profilin for effective polymerase and anti-capping activity. Based on our observations, we propose a mechanism that accounts for all three binding modes and provides a model for how VASP promotes actin filament assembly.

Metastasis: tumor cells becoming MENAcing

During breast cancer metastasis cells emigrate from the primary tumor to the bloodstream, and this carries them to distant sites where they infiltrate and sometimes form metastases within target organs. These cells must penetrate the dense extracellular matrix comprising the basement membrane of the mammary duct/acinus and migrate toward blood and lymphatic vessels, processes that mammary tumor cells execute primarily using epidermal growth factor (EGF)-dependent protrusive and migratory activity. Here, we focus on how the actin regulatory protein Mena affects EGF-elicited movement, invasion and metastasis. Recent findings indicate that, in invasive migratory tumor cells, Mena isoforms that endow heightened sensitivity to EGF and increased protrusive and migratory abilities are upregulated, whereas other isoforms are selectively downregulated. This change in Mena isoform expression enables tumor cells to invade in response to otherwise benign EGF stimulus levels and could offer an opportunity to identify metastatic risk in patients.

LIM and SH3 protein-1 modulates CXCR2-mediated cell migration

BACKGROUND

The chemokine receptor CXCR2 plays a pivotal role in migration of neutrophils, macrophages and endothelial cells, modulating several biological responses such as angiogenesis, wound healing and acute inflammation. CXCR2 is also involved in pathogenesis of chronic inflammation, sepsis and atherosclerosis. The ability of CXCR2 to associate with a variety of proteins dynamically is responsible for its effects on directed cell migration or chemotaxis. The dynamic network of such CXCR2 binding proteins is termed as "CXCR2 chemosynapse". Proteomic analysis of proteins that co-immunoprecipitated with CXCR2 in neutrophil-like dHL-60 cells revealed a novel protein, LIM and SH3 protein 1 (LASP-1), binds CXCR2 under both basal and ligand activated conditions. LASP-1 is an actin binding cytoskeletal protein, involved in the cell migration.

METHODOLOGY/PRINCIPAL FINDINGS

We demonstrate that CXCR2 and LASP-1 co-immunoprecipitate and co-localize at the leading edge of migrating cells. The LIM domain of LASP-1 directly binds to the carboxy-terminal domain (CTD) of CXCR2. Moreover, LASP-1 also directly binds the CTD of CXCR1, CXCR3 and CXCR4. Using a site-directed and deletion mutagenesis approach, Iso323-Leu324 of the conserved LKIL motif on CXCR2-CTD was identified as the binding site for LASP-1. Interruption of the interaction between CXCR2-CTD and LIM domain of LASP-1 by dominant negative and knock down approaches inhibited CXCR2-mediated chemotaxis. Analysis for the mechanism for inhibition of CXCR2-mediated chemotaxis indicated that LASP-1/CXCR2 interaction is essential for cell motility and focal adhesion turnover involving activation of Src, paxillin, PAK1, p130CAS and ERK1/2.

CONCLUSIONS/SIGNIFICANCE

We demonstrate here for the first time that LASP-1 is a key component of the "CXCR2 chemosynapse" and LASP-1 interaction with CXCR2 is critical for CXCR2-mediated chemotaxis. Furthermore, LASP-1 also directly binds the CTD of CXCR1, CXCR3 and CXCR4, suggesting that LASP-1 is a general mediator of CXC chemokine mediated chemotaxis. Thus, LASP-1 may serve as a new link coordinating the flow of information between chemokine receptors and nascent focal adhesions, especially at the leading edge. Thus the association between the chemokine receptors and LASP-1 suggests to the presence of a CXC chemokine receptor-LASP-1 pro-migratory module in cells governing the cell migration.

Polarization of migrating monocytic cells is independent of PI 3-kinase activity

Background

Migration of mammalian cells is a complex cell type and environment specific process. Migrating hematopoietic cells assume a rapid amoeboid like movement when exposed to gradients of chemoattractants. The underlying signaling mechanisms remain controversial with respect to localization and distribution of chemotactic receptors within the plasma membrane and the role of PI 3-kinase activity in cell polarization.

Methodology/Principal Findings

We present a novel model for the investigation of human leukocyte migration. Monocytic THP-1 cells transfected with the α_2A-adrenoceptor (α_2AAR) display comparable signal transduction responses, such as calcium mobilization, MAP-kinase activation and chemotaxis, to the noradrenaline homlogue UK 14'304 as when stimulated with CCL2, which binds to the endogenous chemokine receptor CCR2. Time-lapse video microcopy reveals that chemotactic receptors remain evenly distributed over the plasma membrane and that their internalization is not required for migration. Measurements of intramolecular fluorescence resonance energy transfer (FRET) of α_2AAR-YFP/CFP suggest a uniform activation of the receptors over the entire plasma membrane. Nevertheless, PI 3-kinse activation is confined to the leading edge. When reverting the gradient of chemoattractant by moving the dispensing micropipette, polarized monocytes – in contrast to neutrophils – rapidly flip their polarization axis by developing a new leading edge at the previous posterior side. Flipping of the polarization axis is accompanied by re-localization of PI-3-kinase activity to the new leading edge. However, reversal of the polarization axis occurs in the absence of PI 3-kinase activation.

Conclusions/Significance

Accumulation and internalization of chemotactic receptors at the leading edge is dispensable for cell migration. Furthermore, uniformly distributed receptors allow the cells to rapidly reorient and adapt to changes in the attractant cue. Polarized monocytes, which display typical amoeboid like motility, can rapidly develop a new leading edge facing the highest chemoattractant concentration at any site of the plasma membrane, including the uropod. The process appears to be independent of PI 3-kinase activity.

Differential VASP phosphorylation controls remodeling of the actin cytoskeleton

Proteins of the Enabled/vasodilator-stimulated phosphoprotein (Ena/VASP) family link signal transduction pathways to actin cytoskeleton dynamics. VASP is substrate of cAMP-dependent, cGMP-dependent and AMP-activated protein kinases that primarily phosphorylate the sites S157, S239 and T278, respectively. Here, we systematically analyzed functions of VASP phosphorylation patterns for actin assembly and subcellular targeting in vivo and compared the phosphorylation effects of Ena/VASP family members. Methods used were the reconstitution of VASP-null cells with ;locked' phosphomimetic VASP mutants, actin polymerization of VASP mutants in vitro and in living cells, site-specific kinase-mediated VASP phosphorylation, and analysis of the endogenous protein with phosphorylation-status-specific antibodies. Phosphorylation at S157 influenced VASP localization, but had a minor impact on F-actin assembly. Phosphorylation of the S157-equivalent site in the Ena/VASP family members Mena and EVL had no effect on the ratio of cellular F-actin to G-actin. By contrast, VASP phosphorylation at S239 (and the equivalent site in Mena) or T278 impaired VASP-driven actin filament formation. The data show that VASP functions are precisely regulated by differential phosphorylation and provide new insights into cytoskeletal control by serine/threonine kinase-dependent signaling pathways.

Characterization of chemokine receptor CXCR2 interacting proteins using a proteomics approach to define the CXCR2 "chemosynapse"

Chemokine-receptor signaling is initiated upon ligand binding to the receptor and continues through the process of endocytic trafficking by the association of a variety of adaptor proteins with the chemokine receptor. In order to define the adaptor proteins that associate with CXCR2 before and after ligand activation, a protocol was developed using differentiated HL-60 cells transfected to express CXCR2 stimulated or not stimulated with ligand for one minute. CXCR2-associating proteins were isolated by immunoprecipitation with CXCR2 antibody and the eluted proteins were electrophoretically run into the separating gel directly without a stacking gel. The stained single band was subjected to in-gel trypsin digestion. The tryptic peptides were subjected to, LC/MS/MS proteomic analysis. Proteins identified in a minimum of three of four separate experiments with multiple peptides were then validated as CXCR2 adaptor proteins by coimmunoprecipitation, GST pull-down studies, and immunocytochemical CXCR2-colocalization experiments using dHL-60-CXCR2 cells. Subsequently, a functional analysis of the interaction between CXCR2 and CXCR2 interacting proteins was performed. This approach can be used to characterize chemokine receptor-associating proteins over time both before and after ligand stimulation, allowing definition of the dynamic spatial and temporal formation of a "chemosynapse."