Identification of Fyn-binding proteins in MC/9 mast cells using mass spectrometry

Chronic Wound Initiation: Single-Cell RNAseq of Cutaneous Wound Tissue and Contributions of Oxidative Stress to Initiation of Chronicity

Chronic wounds (CWs) in humans affect millions of people in the US alone, cost billions of dollars, cause much suffering, and still there are no effective treatments. Patients seek medical care when wound chronicity is already established, making it impossible to investigate factors that initiate chronicity. In this study, we used a diabetic mouse model of CWs that mimics many aspects of chronicity in humans. We performed scRNAseq to compare the cell composition and function during the first 72 h post-injury and profiled 102,737 cells into clusters of all major cell types involved in healing. We found two types of fibroblasts. Fib 1 (pro-healing) was enriched in non-CWs (NCWs) whereas Fib 2 (non-healing) was in CWs. Both showed disrupted proliferation and migration, and extracellular matrix (ECM) deposition in CWs. We identified several subtypes of keratinocytes, all of which were more abundant in NCWs, except for Channel-related keratinocytes, and showed altered migration, apoptosis, and response to oxidative stress (OS) in CWs. Vascular and lymphatic endothelial cells were both less abundant in CWs and both had impaired migration affecting the development of endothelial and lymphatic microvessels. Study of immune cells showed that neutrophils and mast cells are less abundant in CWs and that NCWs contained more proinflammatory macrophages (M1) whereas CWs were enriched in anti-inflammatory macrophages (M2). Also, several genes involved in mitochondrial function were abnormally expressed in CWs, suggesting impaired mitochondrial function and/or higher OS. Heat shock proteins needed for response to OS were downregulated in CWs, potentially leading to higher cellular damage. In conclusion, the initiation of chronicity is multifactorial and involves various cell types and cellular functions, indicating that one type of treatment will not fix all problems, unless the root cause is fundamental to the cell and molecular mechanisms of healing. We propose that such a fundamental process is high OS and its association with wound infection/biofilm.

The involvement of vimentin in copper-induced regression of cardiomyocyte hypertrophy

Vimentin is critically involved in the VEGFR-1 mediated activation of the PKG-1 signaling pathway, leading to the regression of cardiomyocyte hypertrophy.

New twists to an old story: novel concepts in the pathogenesis of allergic eye disease

The prevalence of allergy is rising globally at a very significant rate, which is currently at 20-40% of individuals in westernized nations. In the eye, allergic conditions can take on the acute form such as in seasonal and perennial allergic conjunctivitis, or a more severe and debilitating chronic form such as in vernal and atopic keratoconjunctivitis. Indeed, some key aspects of allergic eye disease pathophysiology are understood, such as the role of mast cells in the acute allergic reaction, and the contribution of eosinophils in late-onset and chronic allergy. However, recent developments in animal models and clinical studies have uncovered new and important roles for previously underappreciated players, including chemokine receptors on ocular surface dendritic cells such as CCR7, the contribution of conjunctival epithelium to immunity, histamine and leukotriene receptors on conjunctival goblet cells and a role for mast cells in late-onset manifestations. Furthermore, recent work in animal models has delineated the contribution of IL-4 in the increased incidence of corneal graft rejection in hosts with allergic conjunctivitis. Recent studies such as these mean that conventional paradigms and concepts should be revisited. The aim of this review is to highlight some of the most recent advances and insights on newly appreciated players in the pathogenesis of allergic eye disease.

Cytoskeleton in mast cell signaling

Mast cell activation mediated by the high affinity receptor for IgE (FcεRI) is a key event in allergic response and inflammation. Other receptors on mast cells, as c-Kit for stem cell factor and G protein-coupled receptors (GPCRs) synergistically enhance the FcεRI-mediated release of inflammatory mediators. Activation of various signaling pathways in mast cells results in changes in cell morphology, adhesion to substrate, exocytosis, and migration. Reorganization of cytoskeleton is pivotal in all these processes. Cytoskeletal proteins also play an important role in initial stages of FcεRI and other surface receptors induced triggering. Highly dynamic microtubules formed by αβ-tubulin dimers as well as microfilaments build up from polymerized actin are affected in activated cells by kinases/phosphatases, Rho GTPases and changes in concentration of cytosolic Ca(2+). Also important are nucleation proteins; the γ-tubulin complexes in case of microtubules or Arp 2/3 complex with its nucleation promoting factors and formins in case of microfilaments. The dynamic nature of microtubules and microfilaments in activated cells depends on many associated/regulatory proteins. Changes in rigidity of activated mast cells reflect changes in intermediate filaments build up from vimentin. This review offers a critical appraisal of current knowledge on the role of cytoskeleton in mast cells signaling.

Evidence that formation of vimentin mitogen-activated protein kinase (MAPK) complex mediates mast cell activation following FcεRI/CC chemokine receptor 1 cross-talk

Accumulating evidence points to cross-talk between FcεRI and CC chemokine receptor (CCR)-mediated signaling pathways in mast cells. Here, we propose that vimentin, a protein comprising type III intermediate filament, participates in such cross-talk for CCL2/monocyte chemotactic protein 1 (MCP-1) production in mast cells, which is a mechanism for allergic inflammation. Co-stimulation via FcεRI, using IgE/antigen, and CCR1, using recombinant CCL3/macrophage inflammatory protein-1α (MIP-1α), increased expression of phosphorylated, disassembled, and soluble vimentin in rat basophilic leukemia (RBL)-2H3 cells expressing human CCR1 (RBL-CCR1 cells) and bone marrow-derived murine mast cells, both models of mucosal type mast cells. Furthermore, co-stimulation enhanced production of CCL2 as well as phosphorylation of MAPK. Treating the cells with p38 MAPK inhibitor SB203580, but not with MEK inhibitor PD98058, reduced CCL2 production, suggesting that p38 MAPK, but not ERK1/2, plays a critical role in the chemokine production. Immunoprecipitation analysis showed that vimentin interacts with phosphorylated ERK1/2 and p38 MAPKs in the co-simulated cells. Preventing disassembly of the vimentin by aggregating vimentin filaments using β,β'-iminodipropionitrile reduced the interaction of vimentin with phosphorylated MAPKs as well as CCL2 production in the cells. Taken together, disassembled vimentin interacting with phosphorylated p38 MAPK could mediate CCL2 production in mast cells upon FcεRI and CCR1 activation.

Adapters in the organization of mast cell signaling

Mast cells are pivotal in innate immunity and play an important role in amplifying adaptive immunity. Nonetheless, they have long been known to be central to the initiation of allergic disorders. This results from the dysregulation of the immune response whereby normally innocuous substances are recognized as non-self, resulting in the production of IgE antibodies to these 'allergens'. Preformed and newly synthesized inflammatory (allergic) mediators are released from the mast cell following allergen-mediated aggregation of allergen-specific IgE bound to the high-affinity receptors for IgE (FcepsilonRI). Thus, the process by which the mast cell is able to interpret the engagement of FcepsilonRI into the molecular events necessary for release of their allergic mediators is of considerable therapeutic interest. Unraveling these molecular events has led to the discovery of a functional class of proteins that are essential in organizing activated signaling molecules and in coordinating and compartmentalizing their activity. These so-called 'adapters' bind multiple signaling proteins and localize them to specific cellular compartments, such as the plasma membrane. This organization is essential for normal mast cell responses. Here, we summarize the role of adapter proteins in mast cells focusing on the most recent advances toward understanding how these molecules work upon FcepsilonRI engagement.

The tyrosine kinase network regulating mast cell activation

Mast cell mediator release represents a pivotal event in the initiation of inflammatory reactions associated with allergic disorders. These responses follow antigen-mediated aggregation of immunoglobulin E (IgE)-occupied high-affinity receptors for IgE (Fc epsilon RI) on the mast cell surface, a response which can be further enhanced following stem cell factor-induced ligation of the mast cell growth factor receptor KIT (CD117). Activation of tyrosine kinases is central to the ability of both Fc epsilon RI and KIT to transmit downstream signaling events required for the regulation of mast cell activation. Whereas KIT possesses inherent tyrosine kinase activity, Fc epsilon RI requires the recruitment of Src family tyrosine kinases and Syk to control the early receptor-proximal signaling events. The signaling pathways propagated by these tyrosine kinases can be further upregulated by the Tec kinase Bruton's tyrosine kinase and downregulated by the actions of the tyrosine Src homology 2 domain-containing phosphatase 1 (SHP-1) and SHP-2. In this review, we discuss the regulation and role of specific members of this tyrosine kinase network in KIT and Fc epsilon RI-mediated mast cell activation.

Interaction between the Yersinia Tyrosine Phosphatase YopH and Its Macrophage Substrate, Fyn-Binding Protein, Fyb

Pathogenic Yersinia species can evade phagocytosis by injecting virulence effectors that interfere with the phagocytic machinery of host cells. One of these virulence effectors is the protein tyrosine phosphatase YopH. Through its enzymatic activity, YopH interferes with the initial phagocytic process by affecting signalling for cytoskeletal rearrangements. Fyb (Fyn-binding protein), which is an immune cell-specific adaptor protein, has been identified as a substrate of YopH in macrophages. In this study, the interaction between YopH and Fyb is studied. We show that YopH binds to Fyb via different regions in both phosphotyrosine-dependent and phosphotyrosine-independent ways. The phosphotyrosine substrate binding N-terminal part (1-130) of YopH as well as the C-terminal catalytic region binds to Fyb in a phosphotyrosine-dependent manner. We also show that a central part of YopH (130-260) interacts with the Fyb C-terminus (548-783) in a phosphotyrosine-independent manner. Further, we demonstrate that the N-terminal binding region of YopH is important for YopH-mediated functions on macrophages such as dephosphorylation of Fyb, blockage of phagocytosis, and cytotoxic effects.

Fyn binding protein, Fyb, interacts with mammalian actin binding protein, mAbp1

The immune cell specific protein Fyn-T binding protein (Fyb) has been identified as a target of the Yersinia antiphagocytic effector Yersinia outer protein H (YopH), but its role in macrophages is unknown. By using Fyb domains as bait to screen a mouse lymphoma cDNA library, we identified a novel interaction partner, mammalian actin binding protein 1 (mAbp1). We show that mAbp1 binds the Fyb N-terminal via its C-terminally located src homology 3 domain. The interaction between Fyb and mAbp1 is detected in macrophage lysates and the proteins co-localize with F-actin in the leading edge. Hence, mAbp1 is likely to constitute a downstream effector of Fyb involved in F-actin dynamics.