VAV proteins as signal integrators for multi-subunit immune-recognition receptors

Immune Response of Silver Pomfret (Pampus argenteus) CC Chemokine Ligand Gene Family to Photobacterium damselae Subsp. Damselae and Nocardia seriolae Infections

Chemokines play a crucial role in immune responses by facilitating the migration of cells expressing corresponding chemokine receptors along concentration gradients. Photobacterium damselae subsp. Damselae (PDD) and Nocardia seriolae (NS) are known to induce substantial mortality in silver pomfret populations, yet there exists a dearth of research regarding the immune response of CCLs in PDD- or NS-infected silver pomfret. In our investigation, we identified 10 PaCCLs, which include one fish-specific CCL (PaCCL44). Phylogenetic analysis revealed considerable diversity in CCL types and copy numbers among various teleost fishes. Notably, silver pomfret lacks specific CCL genes, with most PaCCLs exhibiting heightened expression levels in immune-related organs such as the spleen and kidney, and some being expressed in mucosal immune-related organs like the skin and gills. Transcriptome analysis conducted on silver pomfret infected with NS and PDD elucidated that the expression changes of PaCCLs primarily manifested in the spleen during the initial stages of NS infection, shifting to the kidney in later stages. Conversely, the expression changes of PaCCLs following PDD infection predominantly occurred in the kidney. In vitro studies using silver pomfret spleen cell lines demonstrated an early peak in PaCCLs expression during infection, followed by gradual decline with NS treatment and rapid diminishment with PDD treatment. These findings suggest that PaCCLs primarily support the innate immunity of silver pomfret, potentially exhibiting chemotactic effects in the early infection stages, such as the synergistic action of PaCCL4 and PaCCL25, and later serving as direct antibacterial agents. NS invasion is characterised by a chronic infection affecting multiple organs, whereas PDD primarily inflicts severe damage to the kidney. PaCCL19a and PaCCL19b are specific to PDD, and their expression levels may decrease in the later stages of infection due to PDD immune escape. These data offer initial insights into understanding the mechanism underlying the innate immune response of the CCL gene family in silver pomfret and provide theoretical underpinnings for fish culture practices.

The survival grip-how cell adhesion promotes tumor maintenance within the microenvironment

Cell adhesion is warranted by proteins that are crucial for the maintenance of tissue integrity and homeostasis. Most of these proteins behave as receptors to link adhesion to the control of cell survival and their expression or regulation are often altered in cancers. B-cell malignancies do not evade this principle as they are sustained in relapsed niches by interacting with the microenvironment that includes cells and their secreted factors. Focusing on chronic lymphocytic leukemia and mantle cell lymphoma, this Review delves with the molecules involved in the dialog between the adhesion platforms and signaling pathways known to regulate both cell adhesion and survival. Current therapeutic strategies disrupt adhesive structures and compromise the microenvironment support to tumor cells, rendering them sensitive to immune recognition. The development of organ-on-chip and 3D culture systems, such as spheroids, have revealed the importance of mechanical cues in regulating signaling pathways to organize cell adhesion and survival. All these elements contribute to the elaboration of the crosstalk of lymphoma cells with the microenvironment and the education processes that allow the establishment of the supportive niche.

NADPH oxidase 1/4 dual inhibitor setanaxib suppresses platelet activation and thrombus formation

AIMS

The production of reactive oxygen species (ROS) by NADPH oxidase (NOX) is able to induce platelet activation, making NOX a promising target for antiplatelet therapy. In this study, we examined the effects of setanaxib, a dual NOX1/4 inhibitor, on human platelet function and ROS-related signaling pathways.

MATERIALS AND METHODS

In collagen-stimulated human platelets, aggregometry, assessment of ROS and Ca2+, immunoblotting, ELISA, flow cytometry, platelet adhesion assay, and assessment of mouse arterial thrombosis were performed in this study.

KEY FINDINGS

Setanaxib inhibited both intracellular and extracellular ROS production in collagen-activated platelets. Additionally, setanaxib significantly inhibited collagen-induced platelet aggregation, P-selectin exposure from α-granule release, and ATP release from dense granules. Setanaxib blocked the specific tyrosine phosphorylation-mediated activation of Syk, LAT, Vav1, and Btk within collagen receptor signaling pathways, leading to reduced activation of PLCγ2, PKC, and Ca2+ mobilization. Setanaxib also inhibited collagen-induced activation of integrin αIIbβ3, which is linked to increased cGMP levels and VASP phosphorylation. Furthermore, setanaxib suppressed collagen-induced p38 MAPK activation, resulting in decreased phosphorylation of cytosolic PLA2 and reduced TXA2 generation. Setanaxib also inhibited ERK5 activation, affecting the exposure of procoagulant phosphatidylserine. Setanaxib reduced thrombus formation under shear conditions by preventing platelet adhesion to collagen. Finally, in vivo administration of setanaxib in animal models led to the inhibition of arterial thrombosis.

SIGNIFICANCE

This study is the first to show that setanaxib suppresses ROS generation, platelet activation, and collagen-induced thrombus formation, suggesting its potential use in treating thrombotic or cardiovascular diseases.

Multi-modal analysis of human hepatic stellate cells identifies novel therapeutic targets for metabolic dysfunction-associated steatotic liver disease

BACKGROUND & AIMS

Metabolic dysfunction-associated steatotic liver disease ranges from metabolic dysfunction-associated steatotic liver (MASL) to metabolic dysfunction-associated steatohepatitis (MASH) with fibrosis. Transdifferentiation of hepatic stellate cells (HSCs) into fibrogenic myofibroblasts plays a critical role in the pathogenesis of MASH liver fibrosis. We compared transcriptome and chromatin accessibility of human HSCs from NORMAL, MASL, and MASH livers at single-cell resolution. We aimed to identify genes that are upregulated in activated HSCs and to determine which of these genes are key in the pathogenesis of MASH fibrosis.

METHODS

Eighteen human livers were profiled using single-nucleus (sn)RNA-seq and snATAC-seq. High priority targets were identified, then tested in 2D human HSC cultures, 3D human liver spheroids, and HSC-specific gene knockout mice.

RESULTS

MASH-enriched activated HSC subclusters are the major source of extracellular matrix proteins. We identified a set of concurrently upregulated and more accessible core genes (GAS7, SPON1, SERPINE1, LTBP2, KLF9, EFEMP1) that drive activation of HSCs. Expression of these genes was regulated via crosstalk between lineage-specific (JUNB/AP1), cluster-specific (RUNX1/2) and signal-specific (FOXA1/2) transcription factors. The pathological relevance of the selected targets, such as SERPINE1 (PAI-1), was demonstrated using dsiRNA-based HSC-specific gene knockdown or pharmacological inhibition of PAI-1 in 3D human MASH liver spheroids, and HSC-specific Serpine1 knockout mice.

CONCLUSION

This study identified novel gene targets and regulatory mechanisms underlying activation of MASH fibrogenic HSCs and demonstrated that genetic or pharmacological inhibition of select genes suppressed liver fibrosis.

IMPACT AND IMPLICATIONS

Herein, we present the results of a multi-modal sequencing analysis of human hepatic stellate cells (HSCs) from NORMAL, MASL (metabolic dysfunction-associated steatotic liver), and metabolic dysfunction-associated steatohepatitis (MASH) livers. We identified additional subclusters that were not detected by previous studies and characterized the mechanism by which HSCs are activated in MASH livers, including the transcriptional machinery that induces the transdifferentiation of HSCs into myofibroblasts. For the first time, we described the pathogenic role of activated HSC-derived PAI-1 (a product of the SERPINE1 gene) in the development of MASH liver fibrosis. Targeting the RUNX1/2-SERPINE1 axis could be a novel strategy for the treatment of liver fibrosis in patients.

Proteomic Analysis of Prehypertensive and Hypertensive Patients: Exploring the Role of the Actin Cytoskeleton

Hypertension is a pervasive and widespread health condition that poses a significant risk factor for cardiovascular disease, which includes conditions such as heart attack, stroke, and heart failure. Despite its widespread occurrence, the exact cause of hypertension remains unknown, and the mechanisms underlying the progression from prehypertension to hypertension require further investigation. Recent proteomic studies have shown promising results in uncovering potential biomarkers related to disease development. In this study, serum proteomic data collected from Qatar Biobank were analyzed to identify altered protein expression between individuals with normal blood pressure, prehypertension, and hypertension and to elucidate the biological pathways contributing to this disease. The results revealed a cluster of proteins, including the SRC family, CAMK2B, CAMK2D, TEC, GSK3, VAV, and RAC, which were markedly upregulated in patients with hypertension compared to those with prehypertension (fold change ≥ 1.6 or ≤-1.6, area under the curve ≥ 0.8, and q-value < 0.05). Pathway analysis showed that the majority of these proteins play a role in actin cytoskeleton remodeling. Actin cytoskeleton reorganization affects various biological processes that contribute to the maintenance of blood pressure, including vascular tone, endothelial function, cellular signaling, inflammation, fibrosis, and mechanosensing. Therefore, the findings of this study suggest a potential novel role of actin cytoskeleton-related proteins in the progression from prehypertension to hypertension. The present study sheds light on the underlying pathological mechanisms involved in hypertension and could pave the way for new diagnostic and therapeutic approaches for the treatment of this disease.

Positive regulation of Vav1 by Themis controls CD4 T cell pathogenicity in a mouse model of central nervous system inflammation

The susceptibility to autoimmune diseases is conditioned by the association of modest genetic alterations which altogether weaken self-tolerance. The mechanism whereby these genetic interactions modulate T-cell pathogenicity remains largely uncovered. Here, we investigated the epistatic interaction of two interacting proteins involved in T Cell Receptor signaling and which were previously associated with the development of Multiple Sclerosis. To this aim, we used mice expressing an hypomorphic variant of Vav1 (Vav1R63W), combined with a T cell-conditional deletion of Themis. We show that the combined mutations in Vav1 and Themis induce a strong attenuation of the severity of Experimental Autoimmune Encephalomyelitis (EAE), contrasting with the moderate effect of the single mutation in each of those two proteins. This genotype-dependent gradual decrease of EAE severity correlates with decreased quantity of phosphorylated Vav1 in CD4 T cells, establishing that Themis promotes the development of encephalitogenic Tconv response by enhancing Vav1 activity. We also show that the cooperative effect of Themis and Vav1 on EAE severity is independent of regulatory T cells and unrelated to the impact of Themis on thymic selection. Rather, it results from decreased production of pro-inflammatory cytokines (IFN-γ, IL-17, TNF and GM-CSF) and reduced T cell infiltration in the CNS. Together, our results provide a rationale to study combination of related genes, in addition to single gene association, to better understand the genetic bases of human diseases.

A personalized network framework reveals predictive axis of anti-TNF response across diseases

Personalized treatment of complex diseases has been mostly predicated on biomarker identification of one drug-disease combination at a time. Here, we use a computational approach termed Disruption Networks to generate a data type, contextualized by cell-centered individual-level networks, that captures biology otherwise overlooked when performing standard statistics. This data type extends beyond the "feature level space", to the "relations space", by quantifying individual-level breaking or rewiring of cross-feature relations. Applying Disruption Networks to dissect high-dimensional blood data, we discover and validate that the RAC1-PAK1 axis is predictive of anti-TNF response in inflammatory bowel disease. Intermediate monocytes, which correlate with the inflammatory state, play a key role in the RAC1-PAK1 responses, supporting their modulation as a therapeutic target. This axis also predicts response in rheumatoid arthritis, validated in three public cohorts. Our findings support blood-based drug response diagnostics across immune-mediated diseases, implicating common mechanisms of non-response.

Vav proteins do not influence dengue virus replication but are associated with induction of phospho-ERK, IL-6, and viperin mRNA following DENV infection in vitro

IMPORTANCE

Dengue disease is characterized by an inflammatory-mediated immunopathology, with elevated levels of circulating factors including TNF-α and IL-6. If the damaging inflammatory pathways could be blocked without loss of antiviral responses or exacerbating viral replication, then this would be of potential therapeutic benefit. The study here has investigated the Vav guanine exchange factors as a potential alternative signaling pathway that may drive dengue virus (DENV)-induced inflammatory responses, with a focus on Vav1 and 2. While Vav proteins were positively associated with mRNA for inflammatory cytokines, blocking Vav signaling didn't affect DENV replication but prevented DENV-induction of p-ERK and enhanced IL-6 (inflammatory) and viperin (antiviral) mRNA. These initial data suggest that Vav proteins could be a target that does not compromise control of viral replication and should be investigated further for broader impact on host inflammatory responses, in settings such as antibody-dependent enhancement of infection and in different cell types.

The Amyloid-Beta Clearance: From Molecular Targets to Glial and Neural Cells

The deposition of amyloid-beta (Aβ) plaques in the brain is one of the primary pathological characteristics of Alzheimer's disease (AD). It can take place 20-30 years before the onset of clinical symptoms. The imbalance between the production and the clearance of Aβ is one of the major causes of AD. Enhancing Aβ clearance at an early stage is an attractive preventive and therapeutic strategy of AD. Direct inhibition of Aβ production and aggregation using small molecules, peptides, and monoclonal antibody drugs has not yielded satisfactory efficacy in clinical trials for decades. Novel approaches are required to understand and combat Aβ deposition. Neurological dysfunction is a complex process that integrates the functions of different types of cells in the brain. The role of non-neurons in AD has not been fully elucidated. An in-depth understanding of the interactions between neurons and non-neurons can contribute to the elucidation of Aβ formation and the identification of effective drug targets. AD patient-derived pluripotent stem cells (PSCs) contain complete disease background information and have the potential to differentiate into various types of neurons and non-neurons in vitro, which may bring new insight into the treatment of AD. Here, we systematically review the latest studies on Aβ clearance and clarify the roles of cell interactions among microglia, astroglia and neurons in response to Aβ plaques, which will be beneficial to explore methods for reconstructing AD disease models using inducible PSCs (iPSCs) through cell differentiation techniques and validating the applications of models in understanding the formation of Aβ plaques. This review may provide the most promising directions of finding the clues for preventing and delaying the development of AD.

Syk Activation in Circulating and Tissue Innate Immune Cells in Antineutrophil Cytoplasmic Antibody-Associated Vasculitis

OBJECTIVE

Syk is a cytoplasmic protein tyrosine kinase that plays a role in signaling via B cell and Fc receptors (FcR). FcR engagement and signaling via Syk is thought to be important in antineutrophil cytoplasm antibody (ANCA) IgG-mediated neutrophil activation. This study was undertaken to investigate the role of Syk in ANCA-induced myeloid cell activation and vasculitis pathogenesis.

METHODS

Phosphorylation of Syk in myeloid cells from healthy controls and ANCA-associated vasculitis (AAV) patients was analyzed using flow cytometry. The effect of Syk inhibition on myeloperoxidase (MPO)-ANCA IgG activation of cells was investigated using functional assays (interleukin-8 and reactive oxygen species production) and targeted gene analysis with NanoString. Total and phosphorylated Syk at sites of tissue inflammation in patients with AAV was assessed using immunohistochemistry and RNAscope in situ hybridization.

RESULTS

We identified increased phosphorylated Syk at critical activatory tyrosine residues in blood neutrophils and monocytes from patients with active AAV compared to patients with disease in remission or healthy controls. Syk was phosphorylated in vitro following MPO-ANCA IgG stimulation, and Syk inhibition was able to prevent ANCA-mediated cellular responses. Using targeted gene expression analysis, we identified up-regulation of FcR- and Syk-dependent signaling pathways following MPO-ANCA IgG stimulation. Finally, we showed that Syk is expressed and phosphorylated in tissue leukocytes at sites of organ inflammation in AAV.

CONCLUSION

These findings indicate that Syk plays a critical role in MPO-ANCA IgG-induced myeloid cell responses and that Syk is activated in circulating immune cells and tissue immune cells in AAV; therefore, Syk inhibition may be a potential therapeutic option.

The guanine nucleotide exchange factor Vav3 intervenes in the migration pathway of oligodendrocyte precursor cells on tenascin-C

Oligodendrocyte precursor cells (OPCs) are the exclusive source of myelination in the central nervous system (CNS). Prior to myelination, OPCs migrate to target areas and mature into myelinating oligodendrocytes. This process is underpinned by drastic changes of the cytoskeleton and partially driven by pathways involving small GTPases of the Rho subfamily. In general, the myelination process requires migration, proliferation and differentiation of OPCs. Presently, these processes are only partially understood. In this study, we analyzed the impact of the guanine nucleotide exchange factor (GEF) Vav3 on the migration behavior of OPCs. Vav3 is known to regulate RhoA, Rac1 and RhoG activity and is therefore a promising candidate with regard to a regulatory role concerning the rearrangement of the cytoskeleton. Our study focused on the Vav3 knockout mouse and revealed an enhanced migration capacity of Vav3 -/- OPCs on the extracellular matrix (ECM) glycoprotein tenascin-C (TnC). The migration behavior of individual OPCs on further ECM molecules such as laminin-1 (Ln1), laminin-2 (Ln2) and tenascin-R (TnR) was not affected by the elimination of Vav3. The migration process was further investigated with regard to intracellular signal transmission by pharmacological blockade of downstream pathways of specific Rho GTPases. Our data suggest that activation of RhoA GTPase signaling compromises migration, as inhibition of RhoA-signaling promoted migration behavior. This study provides novel insights into the control of OPC migration, which could be useful for further understanding of the complex differentiation and myelination process.

CD16+ fibroblasts foster a trastuzumab-refractory microenvironment that is reversed by VAV2 inhibition

The leukocyte Fcγ receptor (FcγR)-mediated response is important for the efficacy of therapeutic antibodies; however, little is known about the role of FcγRs in other cell types. Here we identify a subset of fibroblasts in human breast cancer that express CD16 (FcγRIII). An abundance of these cells in HER2⁺ breast cancer patients is associated with poor prognosis and response to trastuzumab. Functionally, upon trastuzumab stimulation, CD16⁺ fibroblasts reduce drug delivery by enhancing extracellular matrix stiffness. Interaction between trastuzumab and CD16 activates the intracellular SYK-VAV2-RhoA-ROCK-MLC2-MRTF-A pathway, leading to elevated contractile force and matrix production. Targeting of a Rho family guanine nucleotide exchange factor, VAV2, which is indispensable for the function of CD16 in fibroblasts rather than leukocytes, reverses desmoplasia provoked by CD16⁺ fibroblasts. Collectively, our study reveals a role for the fibroblast FcγR in drug resistance, and suggests that VAV2 is an attractive target to augment the effects of antibody treatments.

Tetrabromobisphenol A effects on differentiating mouse embryonic stem cells reveals unexpected impact on immune system

Tetrabromobisphenol A (TBBPA) is a potent flame retardant used in numerous appliances and a major pollutant in households and ecosystems. In vertebrates, it was shown to affect neurodevelopment, the hypothalamic-pituitary-gonadal axis and thyroid signaling, but its toxicity and modes of actions are still a matter of debate. The molecular phenotype resulting from exposure to TBBPA is only poorly described, especially at the level of transcriptome reprogramming, which further limits our understanding of its molecular toxicity. In this work, we combined functional genomics and system biology to provide a system-wide description of the transcriptomic alterations induced by TBBPA acting on differentiating mESCs, and provide potential new toxicity markers. We found that TBBPA-induced transcriptome reprogramming affect a large collection of genes loosely connected within the network of biological pathways, indicating widespread interferences on biological processes. We also found two hotspots of action: at the level of neuronal differentiation markers, and surprisingly, at the level of immune system functions, which has been largely overlooked until now. This effect is particularly strong, as terminal differentiation markers of both myeloid and lymphoid lineages are strongly reduced: the membrane T cell receptor (Cd79a, Cd79b), interleukin seven receptor (Il7r), macrophages cytokine receptor (Csf1r), monocyte chemokine receptor (Ccr2). Also, the high affinity IgE receptor (Fcer1g), a key mediator of allergic reactions, is strongly induced. Thus, the molecular imbalance induce by TBBPA may be stronger than initially realized.

Hematopoietic Cells Influence Vascular Development in the Retina

Hematopoietic cells play a crucial role in the adult retina in health and disease. Monocytes, macrophages, microglia and myeloid angiogenic cells (MACs) have all been implicated in retinal pathology. However, the role that hematopoietic cells play in retinal development is understudied. The temporal changes in recruitment of hematopoietic cells into the developing retina and the phenotype of the recruited cells are not well understood. In this study, we used the hematopoietic cell-specific protein Vav1 to track and investigate hematopoietic cells in the developing retina. By flow cytometry and immunohistochemistry, we show that hematopoietic cells are present in the retina as early as P0, and include microglia, monocytes and MACs. Even before the formation of retinal blood vessels, hematopoietic cells localize to the inner retina where they eventually form networks that intimately associate with the developing vasculature. Loss of Vav1 lead to a reduction in the density of medium-sized vessels and an increased inflammatory response in retinal astrocytes. When pups were subjected to oxygen-induced retinopathy, hematopoietic cells maintained a close association with the vasculature and occasionally formed 'frameworks' for the generation of new vessels. Our study provides further evidence for the underappreciated role of hematopoietic cells in retinal vasculogenesis and the formation of a healthy retina.

Characterization of the spectrum of trivalent VAV1-mutation-driven tumors using a gene-edited mouse model

Mutations in the VAV1 guanine nucleotide exchange factor 1 have been recently found in peripheral T cell lymphoma and nonsmall‐cell lung cancer (NSCLC). To understand their pathogenic potential, we generated a gene‐edited mouse model that expresses a VAV1 mutant protein that recapitulates the signalling alterations present in the VAV1 mutant subclass most frequently found in tumours. We could not detect any overt tumourigenic process in those mice. However, the concurrent elimination of the Trp53 tumour suppressor gene in them drives T cell lymphomagenesis. This process represents an exacerbation of the normal functions that wild‐type VAV1 plays in follicular helper T cells. We also found that, in combination with the Kras oncogene, the VAV1 mutant version favours progression of NSCLC. These data indicate that VAV1 mutations play critical, although highly cell‐type‐specific, roles in tumourigenesis. They also indicate that such functions are contingent on the mutational landscape of the tumours involved.

Differential Requirement of Vav Proteins for Btk-dependent and –Independent Signaling During B Cell Development

Btk and Vav proteins are all components of the signalosome that builds upon B cell receptor (BCR) activation. However, the role of Vav proteins within the signalosome is quite complex and not yet fully understood. Until now, studies of these have focused predominantly on a deficiency of Vav proteins alone or in combination with other Vav protein family members. Since a physical association of Btk with Vav was shown previously, we asked whether these molecules lie in the same or independent signaling pathways. By analyzing Vav1 and Vav3 single knock-out mice and generating double-knock-out animals deficient for either Vav1 or Vav3 and Btk, we observed, in line with previous publications, no severe B cell developmental defects when either Vav1 or Vav3 alone are not expressed. However, a simultaneous deficiency of Btk together with either Vav1 or Vav3 leads to a severe reduction of splenic B cells, which exhibit an immature phenotype. B cell developmental defects of Btk/Vav1-double deficient mice in the periphery were more severe than those observed in Btk-single-deficient animals. Additionally, morphological changes in splenic microarchitecture were observed in double- but also in single-knock-out mutants. These observations were accompanied by reduced BCR-induced Ca²⁺ mobilization, proliferation, germinal center formation and immunoglobulin secretion. Although deletion of Btk alone impaired Ca²⁺ mobilization upon BCR activation, the defect was even more severe when Vav1 or Vav3 were also mutated, indicating that Btk and the Vav proteins act in separate pathways that converge on Ca2+ signaling. In vitro ASC differentiation suggests that both B and T cells contribute to the observed phenotype of a Btk/Vav-double deficiency. Our results show that Vav proteins and Btk are both components of the BCR-activated signalosome but control separate signaling pathways important for B cell development.

Vav Proteins in Development of the Brain: A Potential Relationship to the Pathogenesis of Congenital Zika Syndrome?

Zika virus (ZIKV) infection during pregnancy can result in a significant impact on the brain and eye of the developing fetus, termed congenital zika syndrome (CZS). At a morphological level, the main serious presentations of CZS are microcephaly and retinal scarring. At a cellular level, many cell types of the brain may be involved, but primarily neuronal progenitor cells (NPC) and developing neurons. Vav proteins have guanine exchange activity in converting GDP to GTP on proteins such as Rac1, Cdc42 and RhoA to stimulate intracellular signaling pathways. These signaling pathways are known to play important roles in maintaining the polarity and self-renewal of NPC pools by coordinating the formation of adherens junctions with cytoskeletal rearrangements. In developing neurons, these same pathways are adopted to control the formation and growth of neurites and mediate axonal guidance and targeting in the brain and retina. This review describes the role of Vavs in these processes and highlights the points of potential ZIKV interaction, such as (i) the binding and entry of ZIKV in cells via TAM receptors, which may activate Vav/Rac/RhoA signaling; (ii) the functional convergence of ZIKV NS2A with Vav in modulating adherens junctions; (iii) ZIKV NS4A/4B protein effects on PI3K/AKT in a regulatory loop via PPI3 to influence Vav/Rac1 signaling in neurite outgrowth; and (iv) the induction of SOCS1 and USP9X following ZIKV infection to regulate Vav protein degradation or activation, respectively, and impact Vav/Rac/RhoA signaling in NPC and neurons. Experiments to define these interactions will further our understanding of the molecular basis of CZS and potentially other developmental disorders stemming from in utero infections. Additionally, Vav/Rac/RhoA signaling pathways may present tractable targets for therapeutic intervention or molecular rationale for disease severity in CZS.

Vav3-Deficient Astrocytes Enhance the Dendritic Development of Hippocampal Neurons in an Indirect Co-culture System

Vav proteins belong to the class of guanine nucleotide exchange factors (GEFs) that catalyze the exchange of guanosine diphosphate (GDP) by guanosine triphosphate (GTP) on their target proteins. Here, especially the members of the small GTPase family, Ras homolog family member A (RhoA), Ras-related C3 botulinum toxin substrate 1 (Rac1) and cell division control protein 42 homolog (Cdc42) can be brought into an activated state by the catalytic activity of Vav-GEFs. In the central nervous system (CNS) of rodents Vav3 shows the strongest expression pattern in comparison to Vav2 and Vav1, which is restricted to the hematopoietic system. Several studies revealed an important role of Vav3 for the elongation and branching of neurites. However, little is known about the function of Vav3 for other cell types of the CNS, like astrocytes. Therefore, the following study analyzed the effects of a Vav3 knockout on several astrocytic parameters as well as the influence of Vav3-deficient astrocytes on the dendritic development of cultured neurons. For this purpose, an indirect co-culture system of native hippocampal neurons and Vav3-deficient cortical astrocytes was used. Interestingly, neurons cultured in an indirect contact with Vav3-deficient astrocytes showed a significant increase in the dendritic complexity and length after 12 and 17 days in vitro (DIV). Furthermore, Vav3-deficient astrocytes showed an enhanced regeneration in the scratch wound heal assay as well as an altered profile of released cytokines with a complete lack of CXCL11, reduced levels of IL-6 and an increased release of CCL5. Based on these observations, we suppose that Vav3 plays an important role for the development of dendrites by regulating the expression and the release of neurotrophic factors and cytokines in astrocytes.

T cell receptor (TCR) signaling in health and disease

Interaction of the T cell receptor (TCR) with an MHC-antigenic peptide complex results in changes at the molecular and cellular levels in T cells. The outside environmental cues are translated into various signal transduction pathways within the cell, which mediate the activation of various genes with the help of specific transcription factors. These signaling networks propagate with the help of various effector enzymes, such as kinases, phosphatases, and phospholipases. Integration of these disparate signal transduction pathways is done with the help of adaptor proteins that are non-enzymatic in function and that serve as a scaffold for various protein-protein interactions. This process aids in connecting the proximal to distal signaling pathways, thereby contributing to the full activation of T cells. This review provides a comprehensive snapshot of the various molecules involved in regulating T cell receptor signaling, covering both enzymes and adaptors, and will discuss their role in human disease.

Ezh2 harnesses the intranuclear actin cytoskeleton to remodel chromatin in differentiating Th cells

Following their first interaction with the antigen, quiescent naive T-helper (Th; CD4⁺) cells enlarge, differentiate, and proliferate; these processes are accompanied by substantial epigenetic alterations. We showed previously that the epigenetic regulators the polycomb-group (PcG) proteins have a dual function as both positive and negative transcriptional regulators; however, the underlying mechanisms remain poorly understood. Here, we demonstrate that during Th cell differentiation the methyltransferase activity of the PcG protein Ezh2 regulates post-transcriptionally inducible assembly of intranuclear actin filaments. These filaments are colocalized with the actin regulators Vav1 and WASp, vertically oriented to the T cell receptor, and intermingle with the chromatin fibers. Ezh2 and Vav1 are observed together at chromatin-actin intersections. Furthermore, the inducible assembly of nuclear actin filaments is required for chromatin spreading and nuclear growth. Altogether these findings delineate a model in which the epigenetic machinery orchestrates the dynamic mechanical force of the intranuclear cytoskeleton to reorganize chromatin during differentiation.

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Ezh2 regulates post-transcriptionally the inducible assembly of intranuclear F-actin

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F-actin is oriented toward the TCR and intermingled with the chromatin fibers

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F-actin is required for chromatin spreading and nuclear growth

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The epigenetic machinery harnesses intranuclear cytoskeleton to reorganize chromatin

Vav2 is required for Netrin-1 receptor-class-specific spinal motor axon guidance

BACKGROUND

Proper guidance of neuronal axons to their targets is required to assemble neural circuits during the development of the nervous system. However, the mechanism by which the guidance of axonal growth cones is regulated by specific intermediaries activated by receptor signaling pathways to mediate cytoskeleton dynamics is unclear. Vav protein members have been proposed to mediate this process, prompting us to investigate their role in the limb selection of the axon trajectory of spinal lateral motor column (LMC) neurons.

RESULTS

We found Vav2 and Vav3 expression in LMC neurons when motor axons grew into the limb. Vav2, but not Vav3, loss-of-function perturbed LMC pathfinding, while Vav2 gain-of-function exhibited the opposite effects, demonstrating that Vav2 plays an important role in motor axon growth. Vav2 knockdown also attenuated the redirectional phenotype of LMC axons induced by Dcc, but not EphA4, in vivo and lateral LMC neurite growth preference to Netrin-1 in vitro. This study showed that Vav2 knockdown and ectopic nonphosphorylable Vav2 mutant expression abolished the Src-induced stronger growth preference of lateral LMC neurites to Netrin-1, suggesting that Vav2 is downstream of Src in this context.

CONCLUSIONS

Vav2 is essential for Netrin-1-regulated LMC motor axon pathfinding through Src interaction.

Rho Family GTPases and Rho GEFs in Glucose Homeostasis

Dysregulation of glucose homeostasis leading to metabolic syndrome and type 2 diabetes is the cause of an increasing world health crisis. New intriguing roles have emerged for Rho family GTPases and their Rho guanine nucleotide exchange factor (GEF) activators in the regulation of glucose homeostasis. This review summates the current knowledge, focusing in particular on the roles of Rho GEFs in the processes of glucose-stimulated insulin secretion by pancreatic β cells and insulin-stimulated glucose uptake into skeletal muscle and adipose tissues. We discuss the ten Rho GEFs that are known so far to regulate glucose homeostasis, nine of which are in mammals, and one is in yeast. Among the mammalian Rho GEFs, P-Rex1, Vav2, Vav3, Tiam1, Kalirin and Plekhg4 were shown to mediate the insulin-stimulated translocation of the glucose transporter GLUT4 to the plasma membrane and/or insulin-stimulated glucose uptake in skeletal muscle or adipose tissue. The Rho GEFs P-Rex1, Vav2, Tiam1 and β-PIX were found to control the glucose-stimulated release of insulin by pancreatic β cells. In vivo studies demonstrated the involvement of the Rho GEFs P-Rex2, Vav2, Vav3 and PDZ-RhoGEF in glucose tolerance and/or insulin sensitivity, with deletion of these GEFs either contributing to the development of metabolic syndrome or protecting from it. This research is in its infancy. Considering that over 80 Rho GEFs exist, it is likely that future research will identify more roles for Rho GEFs in glucose homeostasis.

Adult astrocytes from reptiles are resistant to proinflammatory activation via sustaining Vav1 expression

Adult mammalian astrocytes are sensitive to inflammatory stimuli in the context of neuropathology or mechanical injury, thereby affecting functional outcomes of the central nervous system (CNS). In contrast, glial cells residing in the spinal cord of regenerative vertebrates exhibit a weak astroglial reaction similar to those of mammals in embryonic stages. Macrophage migration inhibitory factor (MIF) participates in multiple neurological disorders by activation of glial and immune cells. However, the mechanism of astrocytes from regenerative species, such as gecko astrocytes (gAS), in resistance to MIF-mediated inflammation in the severed cords remains unclear. Here, we compared neural stem cell markers among gAS, as well as adult (rAS) and embryonic (eAS) rat astrocytes. We observed that gAS retained an immature phenotype resembling rat eAS. Proinflammatory activation of gAS with gecko (gMIF) or rat (rMIF) recombinant protein was unable to induce the production of inflammatory cytokines, despite its interaction with membrane CD74 receptor. Using cross-species screening of inflammation-related mediators from models of gMIF- and rMIF-induced gAS and rAS, we identified Vav1 as a key regulator in suppressing the inflammatory activation of gAS. The gAS with Vav1 deficiency displayed significantly restored sensitivity to inflammatory stimuli. Meanwhile, gMIF acts to promote the migration of gAS through regulation of CXCL8 following cord lesion. Taken together, our results suggest that Vav1 contributes to the regulation of astrocyte-mediated inflammation, which might be beneficial for the therapeutic development of neurological diseases.

Biochemical and NMR characterization of the interactions of Vav2-SH2 domain with lipids and the EphA2 juxtamembrane region on membrane

Vav2 is a ubiquitous guanine nucleotide exchange factor (GEF) for Rho family GTPases that is involved in regulating a wide range of biological processes. It interacts with several tyrosine-phosphorylated cell surface receptors, including the Eph family receptors, through its SH2 domain. The interaction of Vav2 with EphA2 is crucial for EphA2-mediated tumor angiogenesis. Here we show that Vav2-SH2 domain is a lipid-binding module that can recognize PI(4,5)P2 and PI(3,4,5)P3 lipids weakly but specifically. The specific lipid-binding site in Vav2-SH2 domain was identified by NMR chemical shift perturbation experiments using the head groups of PI(4,5)P2 and PI(3,4,5)P3, both of which bind to Vav2-SH2 with millimolar binding affinities. In addition, the interaction between Vav2-SH2 and the phosphorylated juxtamembrane region (JM) of EphA2 (Y594 phosphorylated) was investigated using NMR techniques. Furthermore, by using a nickel-lipid containing peptide-based nanodiscs system, we studied the binding of Vav2-SH2 to the phosphorylated JM region of EphA2 on lipid membrane and uncovered a role of membrane environment in modulating this protein-protein recognition.

Invadopodia: A potential target for pancreatic cancer therapy

Dissemination of cancer cells is an intricate multistep process that represents the most deadly aspect of cancer. Cancer cells form F-actin-rich protrusions known as invadopodia to invade surrounding tissues, blood vessels and lymphatics. A number of studies have demonstrated the significant roles of invadopodia in cancer. Therefore, the specific cells and molecules involved in invadopodia activity can provide as therapeutic targets. In this review, we included a thorough overview of studies in invadopodia and discussed their functions in cancer metastasis. We then presented the specific cells and molecules involved in invadopodia activity in pancreatic cancer and analyzed their suitability to be effective therapeutic targets. Currently, drugs targeting invadopodia and relevant clinical trials are negligible. Here, we highlighted the significance of potential drugs and discussed future obstacles in implementing clinical trials. This review presents a new perspective on invadopodia-induced pancreatic cancer metastasis and may prosper the development of targeted therapeutics against pancreatic cancer.

No Easy Way Out for EZH2: Its Pleiotropic, Noncanonical Effects on Gene Regulation and Cellular Function

Enhancer of zeste homolog 2 (EZH2) plays critical roles in a range of biological processes including organ development and homeostasis, epigenomic and transcriptomic regulation, gene repression and imprinting, and DNA damage repair. A widely known function of EZH2 is to serve as an enzymatic subunit of Polycomb repressive complex 2 (PRC2) and catalyze trimethylation of histone H3 lysine 27 (H3K27me3) for repressing target gene expression. However, an increasing body of evidence demonstrates that EZH2 has many "non-conventional" functions that go beyond H3K27 methylation as a Polycomb factor. First, EZH2 can methylate a number of nonhistone proteins, thereby regulating cellular processes in an H3K27me3-independent fashion. Furthermore, EZH2 relies on both methyltransferase-dependent and methyltransferase-independent mechanisms for modulating gene-expression programs and/or epigenomic patterns of cells. Importantly, independent of PRC2, EZH2 also forms physical interactions with a number of DNA-binding factors and transcriptional coactivators to context-dependently influence gene expression. The purpose of this review is to detail the complex, noncanonical roles of EZH2, which are generally less appreciated in gene and (epi)genome regulation. Because EZH2 deregulation is prevalent in human diseases such as cancer, there is increased dependency on its noncanonical function, which shall have important implications in developing more effective therapeutics.

A biophysical and structural analysis of the interaction of BLNK with 14-3-3 proteins

B-cell linker protein (BLNK) is an adaptor protein that orchestrates signalling downstream of B-cell receptors. It has been reported to undergo proteasomal degradation upon binding to 14-3-3 proteins. Here, we report the first biophysical and structural study of this protein-protein interaction (PPI). Specifically, we investigated the binding of mono- and di- phosphorylated BLNK peptides to 14-3-3 using fluorescent polarization (FP) and isothermal titration calorimetry assays (ITC). Our results suggest that BLNK interacts with 14-3-3 according to the gatekeeper model, where HPK1 mediated phosphorylation of Thr152 (pT152) allows BLNK anchoring to 14-3-3, and an additional phosphorylation of Ser285 (pS285) by AKT, then further improves the affinity. Finally, we have also solved a crystal structure of the BLNKpT152 peptide bound to 14-3-3σ. These findings could serve as important tool for compound discovery programs aiming to modulate this interaction with 14-3-3.

Genetic Basis of Response of Ghanaian Local Chickens to Infection With a Lentogenic Newcastle Disease Virus

Newcastle disease (ND) is a global threat to domestic poultry, especially in rural areas of Africa and Asia, where the loss of entire backyard local chicken flocks often threatens household food security and income. To investigate the genetics of Ghanaian local chicken ecotypes to Newcastle disease virus (NDV), in this study, three popular Ghanaian chicken ecotypes (regional populations) were challenged with a lentogenic NDV strain at 28 days of age. This study was conducted in parallel with a similar study that used three popular Tanzanian local chicken ecotypes and after two companion studies in the United States, using Hy-line Brown commercial laying birds. In addition to growth rate, NDV response traits were measured following infection, including anti-NDV antibody levels [pre-infection and 10 days post-infection (dpi)], and viral load (2 and 6 dpi). Genetic parameters were estimated, and two genome-wide association study analysis methods were used on data from 1,440 Ghanaian chickens that were genotyped on a chicken 600K Single Nucleotide Polymorphism (SNP) chip. Both Ghana and Tanzania NDV challenge studies revealed moderate to high (0.18 – 0.55) estimates of heritability for all traits, except viral clearance where the heritability estimate was not different from zero for the Tanzanian ecotypes. For the Ghana study, 12 quantitative trait loci (QTL) for growth and/or response to NDV from single-SNP analyses and 20 genomic regions that explained more than 1% of genetic variance using the Bayes B method were identified. Seven of these windows were also identified as having at least one significant SNP in the single SNP analyses for growth rate, anti-NDV antibody levels, and viral load at 2 and 6 dpi. An important gene for growth during stress, CHORDC1 associated with post-infection growth rate was identified as a positional candidate gene, as well as other immune related genes, including VAV2, IL12B, DUSP1, and IL17B. The QTL identified in the Ghana study did not overlap with those identified in the Tanzania study. However, both studies revealed QTL with genes vital for growth and immune response during NDV challenge. The Tanzania parallel study revealed an overlapping QTL on chromosome 24 for viral load at 6 dpi with the US NDV study in which birds were challenged with NDV under heat stress. This QTL region includes genes related to immune response, including TIRAP, ETS1, and KIRREL3. The moderate to high estimates of heritability and the identified QTL suggest that host response to NDV of local African chicken ecotypes can be improved through selective breeding to enhance increased NDV resistance and vaccine efficacy.

Identification of Gene Modules and Hub Genes Involved in Mastitis Development Using a Systems Biology Approach

Objective

Mastitis is defined as the inflammation of the mammary gland, which impact directly on the production performance and welfare of dairy cattle. Since, mastitis is a multifactorial complex disease and the molecular pathways underlying this disorder have not been clearly understood yet, a system biology approach was used in this study to a better understanding of the molecular mechanisms behind mastitis.

Methods

Publicly available RNA-Seq data containing samples from milk of five infected and five healthy Holstein cows at five time points were retrieved. Gene Co-expression network analysis (WGCNA) approach and functional enrichment analysis were then applied with the aim to find the non-preserved module of genes that their connectivity were altered under infected condition. Hub genes were identified in the non-preserved modules and were subjected to protein-protein interactions (PPI) network construction.

Results

Among the 25 modules identified, eight modules were non-preserved and were also biologically associated with inflammation, immune response and mastitis development. Interestingly most of the hub genes in the eight modules were also densely connected in the PPI network. Of the hub genes, 250 genes were hubs in both co-expression and PPI networks and most of them were reported to play important roles in immune response or inflammatory pathways. The blue module was highly enriched in inflammatory responses and STAT1 was suggested to play an important role in mastitis development by regulating the immune related genes in this module. Moreover, a set of highly connected genes were identified such as BIRC3, PSMA6, FYN, F11R, NFKBIZ, NFKBIA, GRO1, PHB, CD3E, IL16, GSN, SOCS2, HCK, VAV1 and TLR6, which have been established to be critical for mastitis pathogenesis.

Conclusion

This study improved the understanding of the mechanisms underlying bovine mastitis and suggested eight non-preserved modules along with several most important genes with promising potential in etiology of mastitis.

Vav1 is Essential for HIF-1α Activation via a Lysosomal VEGFR1-Mediated Degradation Mechanism in Endothelial Cells

The vascular response to hypoxia and ischemia is essential for maintaining homeostasis during stressful conditions and is particularly critical for vital organs such as the heart. Hypoxia-inducible factor-1 (HIF-1) is a central regulator of the response to hypoxia by activating transcription of numerous target genes, including vascular endothelial growth factor (VEGF). Here we identify the guanine nucleotide exchange factor (GEF) Vav1, a regulator of the small Rho-GTPase and cell signaling in endothelial cells, as a key vascular regulator of hypoxia. We show that Vav1 is present in the vascular endothelium and is essential for HIF-1 activation under hypoxia. So, we hypothesized that Vav1 could be a key regulator of HIF-1 signaling. In our findings, Vav1 regulates HIF-1α stabilization through the p38/Siah2/PHD3 pathway. In normoxia, Vav1 binds to vascular endothelial growth factor receptor 1 (VEGFR1), which directs Vav1 to lysosomes for degradation. In contrast, hypoxia upregulates Vav1 protein levels by inhibiting lysosomal degradation, which is analogous to HIF-1α regulation by hypoxia: both proteins are constitutively produced and degraded in normoxia allowing for a rapid response when stress occurs. Consequently, hypoxia rapidly stabilizes Vav1, which is required for HIF-1α accumulation. This shows that Vav1 is the key mediator controlling the stabilization of HIF1α in hypoxic conditions. With this finding, we report a novel pathway to stabilize HIF-1, which shows a possible reason why clinical trials targeting HIF-1 has not been effective. Targeting Vav1 can be the new approach to overcome hypoxic tumors.

Stearic acid methyl ester ​promotes migration of mesenchymal stem cells and accelerates cartilage defect repair

Background

Mesenchymal stem cells (MSCs) can be easily expanded without losing the ability of multilineage differentiation, including oesteogenic, chondrogenic and adipogenic differentiation. These characters make MSCs a promising cell resource for cartilage defect repair. MSCs could be recruited by inflammatory stimulation, then home to the injury tissues. However, its capacity of homing is extremely limited. Thus, it has become extremely necessary to develop an agent or a method, which can be used to enhance the efficiency of MSCs homing. This study investigates the effect of stearic acid methyl ester (SAME) on MSCs mobilisation and cartilage regeneration.

Methods

MSCs were isolated from femurs of Sprague-Dawley (SD) rats. MTT assay was used to detect effect of SAME on viability of MSCs. Transwell assay and wound healing assay were used to detect effect of SAME on migration of MSCs. RNA-seq, quantitative real-time PCR and western blot were performed to analyze the expression of RNAs and proteins. Colony forming assay and flow cytometry were used to evaluate the effect of SAME on MSCs mobilisation in vivo. A rat cartilage defect model was created to evaluate the effect of SAME on cartilage regeneration.

Results

We found that SAME could promote the migration of MSCs. Interestingly, we found SAME significantly increased the expression levels of Vav1 in MSCs. On the other hand, the enhanced migration ability of MSCs induced by SAME was retarded by Vav1 small interfering RNA (siRNA) and Rho-associated protein kinase 2 (ROCK2) inhibitor. In addition, we also checked the effect of SAME on mobilisation of MSCs in vivo. The results showed that SAME increased the number of MSCs in peripheral blood and enhanced the capacity of colony formation. Finally, using a cartilage defect model in rats, we found SAME could improve cartilage repair.

Conclusion

Our study demonstrates that SAME can enhance MSCs migration ability mainly through the Vav1/ROCK2 signaling pathway, which could contribute to the accelerated cartilage regeneration.

The translational potential of this article

These findings provide evidence that SAME could be used as a therapeutic reagent for MSCs mobilisation and cartilage regeneration.

Vav1 inhibits RANKL-induced osteoclast differentiation and bone resorption

Vav1 is a Rho/Rac guanine nucleotide exchange factor primarily expressed in hematopoietic cells. In this study, we investigated the potential role of Vav1 in osteoclast (OC) differentiation by comparing the ability of bone marrow mononuclear cells (BMMCs) obtained from Vav1-deficient (Vav1-/-) and wild-type (WT) mice to differentiate into mature OCs upon stimulation with macrophage colony stimulating factor and receptor activator of nuclear kappa B ligand in vitro. Our results suggested that Vav1 deficiency promoted the differentiation of BMMCs into OCs, as indicated by the increased expression of tartrate-resistant acid phosphatase, cathepsin K, and calcitonin receptor. Therefore, Vav1 may play a negative role in OC differentiation. This hypothesis was supported by the observation of more OCs in the femurs of Vav1-/- mice than in WT mice. Furthermore, the bone status of Vav1-/- mice was analyzed in situ and the femurs of Vav1-/- mice appeared abnormal, with poor bone density and fewer number of trabeculae. In addition, Vav1-deficient OCs showed stronger adhesion to vitronectin, an αvβ3 integrin ligand important in bone resorption. Thus, Vav1 may inhibit OC differentiation and protect against bone resorption. [BMB Reports 2019; 52(11): 659-664].

Vav2 lacks Ca2+ entry-promoting scaffolding functions unique to Vav1 and inhibits T cell activation via Cdc42

Vav family guanine nucleotide exchange factors (GEFs) are essential regulators of immune function. Despite their structural similarity, Vav1 promotes and Vav2 opposes T cell receptor (TCR)-induced Ca2+ entry. By using a Vav1-deficient Jurkat T cell line, we find that Vav1 facilitates Ca2+ entry via non-catalytic scaffolding functions that are encoded by the catalytic core of Vav1 and flanking linker regions. We implicate, in this scaffolding function, a previously undescribed polybasic motif that is strictly conserved in Vav1 and absent from Vav2 in tetrapods. Conversely, the catalytic activity of Vav2 contributes to the suppression of TCR-mediated Ca2+ entry. By performing an in vivo 'GEF trapping' assay in intact cells, we demonstrate that Cdc42 interacts with the catalytic surface of Vav2 but not Vav1, and that Vav1 discriminates Cdc42 from Rac1 via F56 (W56 in Rac1). Finally, the Cdc42-specific inhibitor ZCL278 and the shRNA-mediated suppression of Cdc42 each prevent the inhibition of TCR-induced Ca2+ entry by Vav2. These findings define stark differences in the functions of Vav1 and Vav2, and provide an explanation for the differential usage of these Vav isoforms by immune subpopulations.

Lysine Acetylation Reshapes the Downstream Signaling Landscape of Vav1 in Lymphocytes

Vav1 works both as a catalytic Rho GTPase activator and an adaptor molecule. These functions, which are critical for T cell development and antigenic responses, are tyrosine phosphorylation-dependent. However, it is not known whether other posttranslational modifications can contribute to the regulation of the biological activity of this protein. Here, we show that Vav1 becomes acetylated on lysine residues in a stimulation- and SH2 domain-dependent manner. Using a collection of both acetylation- and deacetylation-mimicking mutants, we show that the acetylation of four lysine residues (Lys²²², Lys²⁵², Lys⁵⁸⁷, and Lys⁷¹⁶) leads to the downmodulation of the adaptor function of Vav1 that triggers the stimulation of the nuclear factor of activated T cells (NFAT). These sites belong to two functional subclasses according to mechanistic criteria. We have also unveiled additional acetylation sites potentially involved in either the stimulation (Lys⁷⁸²) or the downmodulation (Lys³³⁵, Lys³⁷⁴) of specific Vav1-dependent downstream responses. Collectively, these results indicate that Nε-lysine acetylation can play variegated roles in the regulation of Vav1 signaling. Unlike the case of the tyrosine phosphorylation step, this new regulatory layer is not conserved in other Vav family paralogs.

The Rho/Rac Guanine Nucleotide Exchange Factor Vav1 Regulates Hif-1α and Glut-1 Expression and Glucose Uptake in the Brain

Vav1 is a Rho/Rac (Ras-related C3 botulinum toxin substrate) guanine nucleotide exchange factor expressed in hematopoietic and endothelial cells that are involved in a wide range of cellular functions. It is also stabilized under hypoxic conditions when it regulates the accumulation of the transcription factor HIF (Hypoxia Inducible Factor)-1α, which activates the transcription of target genes to orchestrate a cellular response to low oxygen. One of the genes induced by HIF-1α is GLUT (Glucose Transporter)-1, which is the major glucose transporter expressed in vessels that supply energy to the brain. Here, we identify a role for Vav1 in providing glucose to the brain. We found that Vav1 deficiency downregulates HIF-1α and GLUT-1 levels in endothelial cells, including blood-brain barrier cells. This downregulation of GLUT-1, in turn, reduced glucose uptake to endothelial cells both in vitro and in vivo, and reduced glucose levels in the brain. Furthermore, endothelial cell-specific Vav1 knock-out in mice, which caused glucose uptake deficiency, also led to a learning delay in fear conditioning experiments. Our results suggest that Vav1 promotes learning by activating HIF-1α and GLUT-1 and thereby distributing glucose to the brain. We further demonstrate the importance of glucose transport by endothelial cells in brain functioning and reveal a potential new axis for targeting GLUT-1 deficiency syndromes and other related brain diseases.

Deletion of the Nucleotide Exchange Factor Vav3 Enhances Axonal Complexity and Synapse Formation but Tampers Activity of Hippocampal Neuronal Networks In Vitro

Vav proteins activate GTPases of the RhoA subfamily that regulate the cytoskeleton and are involved in adhesion, migration, differentiation, polarity and the cell cycle. While the importance of RhoA GTPases for neuronal morphology is undisputed, their regulation is less well understood. In this perspective, we studied the consequences of the deletion of Vav2, Vav3 and Vav2 and 3 (Vav2^-/-, Vav3^-/-, Vav2^-/-/3^-/-) for the development of embryonic hippocampal neurons in vitro. Using an indirect co-culture system of hippocampal neurons with primary wild-type (WT) cortical astrocytes, we analysed axonal and dendritic parameters, structural synapse numbers and the spontaneous network activity via immunocytochemistry and multielectrode array analysis (MEA). Here, we observed a higher process complexity in Vav3^-/-, but not in Vav2^-/- neurons after three and five days in vitro (DIV). Furthermore, an enhanced synapse formation was observed in Vav3^-/- after 14 days in culture. Remarkably, Vav2^-/-/3^-/- double knockout neurons did not display synergistic effects. Interestingly, these differences were transient and compensated after a cultivation period of 21 days. Network analysis revealed a diminished number of spontaneously occurring action potentials in Vav3^-/- neurons after 21 DIV. Based on these results, it appears that Vav3 participates in key events of neuronal differentiation.

Resveratrol suppresses neutrophil activation via inhibition of Src family kinases to attenuate lung injury

The natural stilbenoid, Resveratrol (RSV; 3,5,4'-trihydroxystilbene) has been shown to have beneficial effects on inflammatory diseases as well as cancer, neurodegenerative diseases, and cardiovascular disorders. The underlying mechanism by which RSV affects neutrophil activation has yet to be fully elucidated. In this study, we tested the hypothesis that RSV modulates the inflammatory activities of formyl-Met-Leu-Phe-stimulated human neutrophils. We employed a well-established isolated-neutrophil model to investigate the effects of RSV on neutrophil functions and the underlying mechanism of signaling transduction. The lipopolysaccharide-induced ALI murine model was employed to evaluate the therapeutic effects of RSV. Experiment results demonstrate that RSV reduces respiratory burst, degranulation, integrin expression, and cell adhesion in activated neutrophils in dose-dependent manners. RSV inhibited phosphorylation of Src family kinases (SFKs) and reduced their enzymatic activities. Moreover, RSV and a selective inhibitor of SFKs (PP2) reduced the phosphorylation of Bruton's tyrosine kinase and Vav. There results indicated that the inhibitory effects of RSV are mediated through the inhibition of the SFKs-Btk-Vav pathway. This study also revealed that RSV attenuates endotoxin-induced lung injury. We surmise that the therapeutic effects of RSV on ALI may derive from its anti-neutrophilic inflammation function and free radical-scavenging effects.

The Vav GEF Family: An Evolutionary and Functional Perspective

Vav proteins play roles as guanosine nucleotide exchange factors for Rho GTPases and signaling adaptors downstream of protein tyrosine kinases. The recent sequencing of the genomes of many species has revealed that this protein family originated in choanozoans, a group of unicellular organisms from which animal metazoans are believed to have originated from. Since then, the Vav family underwent expansions and reductions in its members during the evolutionary transitions that originated the agnates, chondrichthyes, some teleost fish, and some neoaves. Exotic members of the family harboring atypical structural domains can be also found in some invertebrate species. In this review, we will provide a phylogenetic perspective of the evolution of the Vav family. We will also pay attention to the structure, signaling properties, regulatory layers, and functions of Vav proteins in both invertebrate and vertebrate species.

Human B Cells Engage the NCK/PI3K/RAC1 Axis to Internalize Large Particles via the IgM-BCR

Growing evidence indicate that large antigen-containing particles induce potent T cell-dependent high-affinity antibody responses. These responses require large particle internalization after recognition by the B cell receptor (BCR) on B cells. However, the molecular mechanisms governing BCR-mediated internalization remain unclear. Here we use a high-throughput quantitative image analysis approach to discriminate between B cell particle binding and internalization. We systematically show, using small molecule inhibitors, that human B cells require a SYK-dependent IgM-BCR signaling transduction via PI3K to efficiently internalize large anti-IgM-coated particles. IgM-BCR-mediated activation of PI3K involves both the adaptor protein NCK and the co-receptor CD19. Interestingly, we here reveal a strong NCK-dependence without profound requirement of the co-receptor CD19 in B cell responses to large particles. Furthermore, we demonstrate that the IgM-BCR/NCK signaling event facilitates RAC1 activation to promote actin cytoskeleton remodeling necessary for particle engulfment. Thus, we establish NCK/PI3K/RAC1 as an attractive IgM-BCR signaling axis for biological intervention to prevent undesired antibody responses to large particles.

A molecular assembly phase transition and kinetic proofreading modulate Ras activation by SOS

The guanine nucleotide exchange factor (GEF) Son of Sevenless (SOS) is a key Ras activator that is autoinhibited in the cytosol and activates upon membrane recruitment. Autoinhibition release involves structural rearrangements of the protein at the membrane and thus introduces a delay between initial recruitment and activation. In this study, we designed a single-molecule assay to resolve the time between initial receptor-mediated membrane recruitment and the initiation of GEF activity of individual SOS molecules on microarrays of Ras-functionalized supported membranes. The rise-and-fall shape of the measured SOS activation time distribution and the long mean time scale to activation (~50 seconds) establish a basis for kinetic proofreading in the receptor-mediated activation of Ras. We further demonstrate that this kinetic proofreading is modulated by the LAT (linker for activation of T cells)-Grb2-SOS phosphotyrosine-driven phase transition at the membrane.

Vav1 mutations identified in human cancers give rise to different oncogenic phenotypes

Vav1 is physiologically active as a GDP/GTP nucleotide exchange factor (GEF) in the hematopoietic system. Overexpression of Vav1 in multiple tumor types is known to enhance oncogenicity, yet whether or not Vav1 is a bona fide oncogene is still a matter of debate. Although mutations in Vav1 were recently identified in human cancers of various origins, the functional activities of these mutants are not known. We tested the transforming potential of three mutations identified in human lung adenocarcinoma: E59K, D517E, and L801P. Results from several assays indicative of transforming activities such as rate of proliferation, growth in agar, and generation of tumors in NOD/SCID mice clearly indicated that E59K and D517E are highly transforming but L801P at the SH3 domain is not. The acquired oncogenic activity of these mutants can be attributed to their enhanced activity as GEFs for Rho/Rac GTPases. Deciphering of the mechanisms leading to overactivity of the tested mutants revealed that the E59K mutation facilitates cleavage of a truncated protein that is uncontrollably active as a GEF, while D517E generates a highly stable overexpressed protein that is also more active as a GEF than wild-type Vav1. These findings support the classification of Vav1 as a bona fide oncogene in human cancer.

Prioritizing candidate genes post-GWAS using multiple sources of data for mastitis resistance in dairy cattle

Background

Improving resistance to mastitis, one of the costliest diseases in dairy production, has become an important objective in dairy cattle breeding. However, mastitis resistance is influenced by many genes involved in multiple processes, including the response to infection, inflammation, and post-infection healing. Low genetic heritability, environmental variations, and farm management differences further complicate the identification of links between genetic variants and mastitis resistance. Consequently, studies of the genetics of variation in mastitis resistance in dairy cattle lack agreement about the responsible genes.

Results

We associated 15,552,968 imputed whole-genome sequencing markers for 5147 Nordic Holstein cattle with mastitis resistance in a genome-wide association study (GWAS). Next, we augmented P-values for markers in genes in the associated regions using Gene Ontology terms, Kyoto Encyclopedia of Genes and Genomes pathway analysis, and mammalian phenotype database. To confirm results of gene-based analyses, we used gene expression data from E. coli-challenged cow udders. We identified 22 independent quantitative trait loci (QTL) that collectively explained 14% of the variance in breeding values for resistance to clinical mastitis (CM). Using association test statistics with multiple pieces of independent information on gene function and differential expression during bacterial infection, we suggested putative causal genes with biological relevance for 12 QTL affecting resistance to CM in dairy cattle.

Conclusion

Combining information on the nearest positional genes, gene-based analyses, and differential gene expression data from RNA-seq, we identified putative causal genes (candidate genes with biological evidence) in QTL for mastitis resistance in Nordic Holstein cattle. The same strategy can be applied for other traits.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-5050-x) contains supplementary material, which is available to authorized users.

Rho guanosine nucleotide exchange factors are not such bad guys after all in cancera

Rho GDP/GTP exchange factors (GEFs), the enzymes that trigger the stimulation of Rho GTPases during cell signaling, are widely deemed as potential therapeutic targets owing to their protumorigenic functions. However, the sparse use of animal models has precluded a full understanding of their pathophysiological roles at the organismal level. In a recent article in Cancer Cell, we have reported that the Vav1 GEF unexpectedly acts as a tumor suppressor by mediating the noncatalytic nucleation of cytoplasmic complexes between the E3 ubiquitin ligase Cbl-b and the active Notch1 intracellular domain (ICN1). These complexes favor the ubiquitinylation-mediated degradation of ICN1 in the proteosome and, therefore, the dampening of ICN1 signals in cells. The elimination of Vav1 in mice exacerbates ICN1 signaling in specific thymocyte subpopulations and, in collaboration with ancillary mutations, prompts the development of ICN1-driven T cell acute lymphoblastic leukemia (T-ALL). This new Vav1-dependent pathway antagonizes the fitness of T-ALL of the TLX⁺ clinical subtype in humans. As a result, VAV1 is found recurrently silenced in both TLX⁺ T-ALL cell lines and patients. These results call for an overall reevaluation of Rho GEF function in cancer.

A Novel Vav3 Homolog Identified in Lamprey, Lampetra japonica, with Roles in Lipopolysaccharide-Mediated Immune Response

Vav guanine nucleotide exchange factor 3 (Vav3), a Rho family GTPase, regulates multiple cell signaling pathways including those of T- and B-cell receptors in vertebrates through mediating the activities of the Rho family members. Whether the lamprey possesses Vav3 homolog and what role it plays in immune response remain unknown. Gene cloning, recombinant expression, antibody production and expression pattern analyses were performed to characterize the lamprey Vav3 in the current study. The lamprey Vav3 is closer to jawed vertebrates' Vav3 molecules (about 53% identities in general) than to Vav2 molecules of jawless and jawed vertebrates (about 51% identities in general) in sequence similarity. Conserved motif analysis showed that the most distinguished parts between Vav3 and Vav2 proteins are their two Src-homology 3 domains. The relative expression levels of lamprey vav3 mRNA and protein were significantly up-regulated in lamprey lymphocytes and supraneural myeloid bodies after mixed-antigens stimulation, respectively. In addition, lamprey Vav3 were up-regulated drastically in lymphocytes and supraneural myeloid bodies after lipopolysaccharide (LPS) rather than phytohemagglutinin (PHA) stimulation. Lamprey Vav3 distributed in the cytoplasm of variable lymphocyte receptor B positive (VLRB⁺) lymphocytes, and the number of plasmacytes (VLRB and lamprey Vav3 double positive) in blood lymphocytes also increased after LPS stimulation. Our results proved that lamprey Vav3 was involved in the LPS-mediated immune reaction of lamprey and provided a clue for the further study of the precise role lamprey Vav3 played in the signaling pathway of lamprey VLRB⁺ lymphocytes.

A PLC-γ1 Feedback Pathway Regulates Lck Substrate Phosphorylation at the T-Cell Receptor and SLP-76 Complex

Phospholipase C gamma 1 (PLC-γ1) occupies a critically important position in the T-cell signaling pathway. While its functions as a regulator of both Ca²⁺ signaling and PKC-family kinases are well characterized, PLC-γ1's role in the regulation of early T-cell receptor signaling events is incompletely understood. Activation of the T-cell receptor leads to the formation of a signalosome complex between SLP-76, LAT, PLC-γ1, Itk, and Vav1. Recent studies have revealed the existence of both positive and negative feedback pathways from SLP-76 to the apical kinase in the pathway, Lck. To determine if PLC-γ1 contributes to the regulation of these feedback networks, we performed a quantitative phosphoproteomic analysis of PLC-γ1-deficient T cells. These data revealed a previously unappreciated role for PLC-γ1 in the positive regulation of Zap-70 and T-cell receptor tyrosine phosphorylation. Conversely, PLC-γ1 negatively regulated the phosphorylation of SLP-76-associated proteins, including previously established Lck substrate phosphorylation sites within this complex. While the positive and negative regulatory phosphorylation sites on Lck were largely unchanged, Tyr¹⁹² phosphorylation was elevated in Jgamma1. The data supports a model wherein Lck's targeting, but not its kinase activity, is altered by PLC-γ1, possibly through Lck Tyr¹⁹² phosphorylation and increased association of the kinase with protein scaffolds SLP-76 and TSAd.

Involvement of the guanine nucleotide exchange factor Vav3 in central nervous system development and plasticity

Small GTP-hydrolyzing enzymes (GTPases) of the RhoA family play manifold roles in cell biology and are regulated by upstream guanine nucleotide exchange factors (GEFs). Herein, we focus on the GEFs of the Vav subfamily. Vav1 was originally described as a proto-oncogene of the hematopoietic lineage. The GEFs Vav2 and Vav3 are more broadly expressed in various tissues. In particular, the GEF Vav3 may play important roles in the developing nervous system during the differentiation of neural stem cells into the major lineages, namely neurons, oligodendrocytes and astrocytes. We discuss its putative regulatory roles for progenitor differentiation in the developing retina, polarization of neurons and formation of synapses, migration of oligodendrocyte progenitors and establishment of myelin sheaths. We propose that Vav3 mediates the response of various neural cell types to environmental cues.

Association of VAV2 and VAV3 polymorphisms with cardiovascular risk factors

Hypertension, diabetes and obesity are cardiovascular risk factors closely associated to the development of renal and cardiovascular target organ damage. VAV2 and VAV3, members of the VAV family proto-oncogenes, are guanosine nucleotide exchange factors for the Rho and Rac GTPase family, which is related with cardiovascular homeostasis. We have analyzed the relationship between the presence of VAV2 rs602990 and VAV3 rs7528153 polymorphisms with cardiovascular risk factors and target organ damage (heart, vessels and kidney) in 411 subjects. Our results show that being carrier of the T allele in VAV2 rs602990 polymorphism is associated with an increased risk of obesity, reduced levels of ankle-brachial index and diastolic blood pressure and reduced retinal artery caliber. In addition, being carrier of T allele is associated with increased risk of target organ damage in males. On the other hand, being carrier of the T allele in VAV3 rs7528153 polymorphism is associated with a decreased susceptibility of developing a pathologic state composed by the presence of hypertension, diabetes, obesity or cardiovascular damage, and with an increased risk of developing altered basal glycaemia. This is the first report showing an association between VAV2 and VAV3 polymorphisms with cardiovascular risk factors and target organ damage.

Ligand-Receptor Interaction Modulates the Energy Landscape of Enzyme-Instructed Self-Assembly of Small Molecules

The concurrence of enzymatic reaction and ligand-receptor interactions is common for proteins, but rare for small molecules and has yet to be explored. Here we show that ligand-receptor interaction modulates the morphology of molecular assemblies formed by enzyme-instructed assembly of small molecules. While the absence of ligand-receptor interaction allows enzymatic dephosphorylation of a precursor to generate the hydrogelator that self-assembles to form long nanofibers, the presence of the ligand-receptor interaction biases the pathway to form precipitous aggregates containing short nanofibers. While the hydrogelators self-assemble to form nanofibers or nanoribbons that are unable to bind with the ligand (i.e., vancomycin), the addition of surfactant breaks up the assemblies to restore the ligand-receptor interaction. In addition, an excess amount of the ligands can disrupt the nanofibers and result in the precipitates. As the first example of the use of ligand-receptor interaction to modulate the kinetics of enzymatic self-assembly, this work not only provides a solution to evaluate the interaction between aggregates and target molecules but also offers new insight for understanding the emergent behavior of sophisticated molecular systems having multiple and parallel processes.

The IQGAP1 N-Terminus Forms Dimers, and the Dimer Interface Is Required for Binding F-Actin and Calcium-Bound Calmodulin

IQGAP1 is a multidomain scaffold protein involved in many cellular processes. We have determined the crystal structure of an N-terminal fragment spanning residues 1-191 (CHDF hereafter) that contains the entire calponin homology domain. The structure of the CHDF is very similar to those of other type 3 calponin homology domains like those from calponin, Vav, and the yeast IQGAP1 ortholog Rng2. However, in the crystal, two CHDF molecules form a "head-to-head" or parallel dimer through mostly hydrophobic interactions. Binding experiments indicate that the CHDF binds to both F-actin and Ca²⁺/calmodulin, but binding is mutually exclusive. On the basis of the structure, two dimer interface substitutions were introduced. While CHDFL157D disrupts the dimer in gel filtration experiments, oxidized CHDFK161C stabilizes the dimer. These results imply that the CHDF forms the same dimer in solution that is seen in the crystal structure. The disulfide-stabilized dimer displays a reduced level of F-actin binding in sedimentation assays and shows no binding to Ca²⁺/calmodulin in isothermal titration calorimetry (ITC) experiments, indicating that interface residues are utilized for both binding events. The Calmodulin Target Database predicts that residues ⁹³KK⁹⁴ are important for CaM binding, and indeed, the ⁹³EE⁹⁴ double mutation displays a reduced level of binding to Ca²⁺/calmodulin in ITC experiments. Our results indicate that the CHDF dimer interface is used for both F-actin and Ca²⁺/calmodulin binding, and the ⁹³KK⁹⁴ pair, near the interface, is also used for Ca²⁺/calmodulin binding. These results are also consistent with full-length IQGAP1 forming a parallel homodimer.