Fer and Fps/Fes participate in a Lyn-dependent pathway from FcepsilonRI to platelet-endothelial cell adhesion molecule 1 to limit mast cell activation

Establishing the role of the FES tyrosine kinase in the pathogenesis, pathophysiology, and severity of sepsis and its outcomes

Introduction

Sepsis is a result of initial over-activation of the immune system in response to an infection or trauma that results in reduced blood flow and life-threatening end-organ damage, followed by suppression of the immune system that prevents proper clearance of the infection or trauma. Because of this, therapies that not only limit the activation of the immune system early on, but also improve blood flow to crucial organs and reactivate the immune system in late-stage sepsis, may be effective treatments. The tyrosine kinase FES may fulfill this role. FES is present in immune cells and serves to limit immune system activation. We hypothesize that by enhancing FES in early sepsis and inhibiting its effects in late sepsis, the severity and outcome of septic illness can be improved.

Methods and analysis

In vitro and in vivo modeling will be performed to determine the degree of inflammatory signaling, cytokine production, and neutrophil extracellular trap (NET) formation that occurs in wild-type (WT) and FES knockout (FES-/- ) mice. Clinically available treatments known to enhance or inhibit FES expression (lorlatinib and decitabine, respectively), will be used to explore the impact of early vs. late FES modulation on outcomes in WT mice. Bioinformatic analysis will be performed to examine FES expression levels in RNA transcriptomic data from sepsis patient cohorts, and correlate FES expression data with clinical outcomes (diagnosis of sepsis, illness severity, hospital length-of-stay).

Ethics and dissemination

Ethics approval pending from the Queen's University Health Sciences & Affiliated Teaching Hospitals Research Ethics Board. Results will be disseminated through scientific publications and through lay summaries to patients and families.

Mast cells enhance sterile inflammation in chronic nonbacterial osteomyelitis

Chronic nonbacterial osteomyelitis (CNO) is an autoinflammatory bone disease, and patients with active or recurrent bone inflammation at multiple sites are diagnosed with chronic recurrent multifocal osteomyelitis (CRMO). The Chronic multifocal osteomyelitis (CMO) mouse model develops IL-1β-driven sterile bone lesions reminiscent of severe CRMO. The goal of this study was to evaluate the potential involvement of mast cells in CMO/CRMO. Here, we show that mast cells accumulate in inflamed tissues from CMO mice and that mast cell protease Mcpt1 can be detected in the peripheral blood. A transgenic model of connective tissue mast cell depletion (Mcpt5-Cre:Rosa26-Stop^fl/fl-DTa) was crossed with CMO mice and the resulting mice (referred to as CMO/MC^–) showed a significant delay in disease onset compared with age-matched CMO mice. At 5-6 months of age, CMO/MC^– mice had fewer bone lesions and immune infiltration in the popliteal lymph nodes that drain the affected tissues. In bone marrow-derived mast cell cultures from CMO mice, cytokine production in response to the alarmin IL-33 was elevated compared with wild-type cultures. To test the relevance of mast cells to human CRMO, we tested serum samples from a cohort of healthy controls and from CRMO patients at diagnosis. Interestingly, mast cell chymase was elevated in CRMO patients as well as in patients with oligoarticular juvenile arthritis. Tryptase-positive mast cells were also detected in bone lesions from CRMO patients and patients with bacterial osteomyelitis. Together, our results identify mast cells as cellular contributors to bone inflammation in CMO/CRMO and provide rationale for further study of mast cells as therapeutic targets.

Summary: This paper reports that mast cells promote bone loss in an autoinflammatory disease model and that mast cell mediators were detected in autoinflammatory disease patient samples.

SLAP Is a Negative Regulator of FcεRI Receptor-Mediated Signaling and Allergic Response

Binding of antigen to IgE-high affinity FcεRI complexes on mast cells and basophils results in the release of preformed mediators such as histamine and de novo synthesis of cytokines causing allergic reactions. Src-like adapter protein (SLAP) functions co-operatively with c-Cbl to negatively regulate signaling downstream of the T cell receptor, B cell receptor, and receptor tyrosine kinases (RTK). Here, we investigated the role of SLAP in FcεRI-mediated mast cell signaling, using bone marrow derived mast cells (BMMCs) from SLAP knock out (SLAP KO) mice. Mature SLAP-KO BMMCs displayed significantly enhanced antigen induced degranulation and synthesis of IL-6, TNFα, and MCP-1 compared to wild type (WT) BMMCs. In addition, SLAP KO mice displayed an enhanced passive cutaneous anaphylaxis response. In agreement with a negative regulatory role, SLAP KO BMMCs showed enhanced FcεRI-mediated signaling to downstream effector kinases, Syk, Erk, and Akt. Recombinant GST-SLAP protein binds to the FcεRIβ chain and to the Cbl-b in mast cell lysates, suggesting a role in FcεRI down regulation. In addition, the ubiquitination of FcεRIγ chain and antigen mediated down regulation of FcεRI is impaired in SLAP KO BMMCs compared to the wild type. In line with these findings, stimulation of peripheral blood human basophils with FcεRIα antibody, or a clinically relevant allergen, resulted in increased SLAP expression. Together, these results indicate that SLAP is a dynamic regulator of IgE-FcεRI signaling, limiting allergic responses.

A novel immunotherapy targeting MMP-14 limits hypoxia, immune suppression and metastasis in triple-negative breast cancer models

Matrix metalloproteinase-14 (MMP-14) is a clinically relevant target in metastatic cancers due to its role in tumor progression and metastasis. Since active MMP-14 is localized on the cell surface, it is amenable to antibody-mediated blockade in cancer, and here we describe our efforts to develop novel inhibitory anti-MMP-14 antibodies. A phage-displayed synthetic humanized Fab library was screened against the extracellular domain of MMP-14 and a panel of MMP14-specific Fabs were identified. A lead antibody that inhibits the catalytic domain of MMP-14 (Fab 3369) was identified and treatment of MDA-MB-231 breast cancer cells with Fab 3369 led to significant loss of extracellular matrix degradation and cell invasion abilities. In mammary orthotopic tumor xenograft assays, MMP-14 blockade by IgG 3369 limited tumor growth and metastasis. Analysis of tumor tissue sections revealed that MMP-14 blockade limited tumor neoangiogenesis and hypoxia. Similar effects of MMP-14 blockade in syngeneic 4T1 mammary tumors were observed, along with increased detection of cytotoxic immune cell markers. In conclusion, we show that immunotherapies targeting MMP-14 can limit immune suppression, tumor progression, and metastasis in triple-negative breast cancer.

A co-association network analysis of the genetic determination of pig conformation, growth and fatness

BACKGROUND

Several QTLs have been identified for major economically relevant traits in livestock, such as growth and meat quality, revealing the complex genetic architecture of these traits. The use of network approaches considering the interactions of multiple molecules and traits provides useful insights into the molecular underpinnings of complex traits. Here, a network based methodology, named Association Weight Matrix, was applied to study gene interactions and pathways affecting pig conformation, growth and fatness traits.

RESULTS

The co-association network analysis underpinned three transcription factors, PPARγ, ELF1, and PRDM16 involved in mesoderm tissue differentiation. Fifty-four genes in the network belonged to growth-related ontologies and 46 of them were common with a similar study for growth in cattle supporting our results. The functional analysis uncovered the lipid metabolism and the corticotrophin and gonadotrophin release hormone pathways among the most important pathways influencing these traits. Our results suggest that the genes and pathways here identified are important determining either the total body weight of the animal and the fat content. For instance, a switch in the mesoderm tissue differentiation may determinate the age-related preferred pathways being in the puberty stage those related with the miogenic and osteogenic lineages; on the contrary, in the maturity stage cells may be more prone to the adipocyte fate. Hence, our results demonstrate that an integrative genomic co-association analysis is a powerful approach for identifying new connections and interactions among genes.

CONCLUSIONS

This work provides insights about pathways and key regulators which may be important determining the animal growth, conformation and body proportions and fatness traits. Molecular information concerning genes and pathways here described may be crucial for the improvement of genetic breeding programs applied to pork meat production.

Phosphoproteomic analysis of platelets activated by pro-thrombotic oxidized phospholipids and thrombin

Specific oxidized phospholipids (oxPCCD36) promote platelet hyper-reactivity and thrombosis in hyperlipidemia via the scavenger receptor CD36, however the signaling pathway(s) induced in platelets by oxPCCD36 are not well defined. We have employed mass spectrometry-based tyrosine, serine, and threonine phosphoproteomics for the unbiased analysis of platelet signaling pathways induced by oxPCCD36 as well as by the strong physiological agonist thrombin. oxPCCD36 and thrombin induced differential phosphorylation of 115 proteins (162 phosphorylation sites) and 181 proteins (334 phosphorylation sites) respectively. Most of the phosphoproteome changes induced by either agonist have never been reported in platelets; thus they provide candidates in the study of platelet signaling. Bioinformatic analyses of protein phosphorylation dependent responses were used to categorize preferential motifs for (de)phosphorylation, predict pathways and kinase activity, and construct a phosphoproteome network regulating integrin activation. A putative signaling pathway involving Src-family kinases, SYK, and PLCγ2 was identified in platelets activated by oxPCCD36. Subsequent ex vivo studies in human platelets demonstrated that this pathway is downstream of the scavenger receptor CD36 and is critical for platelet activation by oxPCCD36. Our results provide multiple insights into the mechanism of platelet activation and specifically in platelet regulation by oxPCCD36.

Immunoreceptor tyrosine-based inhibitory motif (ITIM)-mediated inhibitory signaling is regulated by sequential phosphorylation mediated by distinct nonreceptor tyrosine kinases: a case study involving PECAM-1

The activation state of many blood and vascular cells is tightly controlled by a delicate balance between receptors that contain immunoreceptor tyrosine-based activation motifs (ITAMs) and those that contain immunoreceptor tyrosine-based inhibitory motifs (ITIMs). Precisely how the timing of cellular activation by ITAM-coupled receptors is regulated by ITIM-containing receptors is, however, poorly understood. Using platelet endothelial cell adhesion molecule 1 (PECAM-1) as a prototypical ITIM-bearing receptor, we demonstrate that initiation of inhibitory signaling occurs via a novel, sequential process in which Src family kinases phosphorylate the C-terminal ITIM, thereby enabling phosphorylation of the N-terminal ITIM of PECAM-1 by other Src homology 2 domain-containing nonreceptor tyrosine kinases (NRTKs). NRTKs capable of mediating the second phosphorylation event include C-terminal Src kinase (Csk) and Bruton's tyrosine kinase (Btk). Btk and Csk function downstream of phosphatidylinositol 3-kinase (PI3K) activation during ITAM-dependent platelet activation. In ITAM-activated platelets that were treated with a PI3K inhibitor, PECAM-1 was phosphorylated but did not bind the tandem SH2 domain-containing tyrosine phosphatase SHP-2, indicating that it was not phosphorylated on its N-terminal ITIM. Csk bound to and phosphorylated PECAM-1 more efficiently than did Btk and required its SH2 domain to perform these functions. Additionally, the phosphorylation of the N-terminal ITIM of Siglec-9 by Csk is enhanced by the prior phosphorylation of its C-terminal ITIM, providing evidence that the ITIMs of other dual ITIM-containing receptors are also sequentially phosphorylated. On the basis of these findings, we propose that sequential ITIM phosphorylation provides a general mechanism for precise temporal control over the recruitment and activation of tandem SH2 domain-containing tyrosine phosphatases that dampen ITAM-dependent signals.

A system for reconstructing B cell antigen receptor signaling in the mouse myeloma J558L cell line

B cell antigen receptor (BCR) signaling is positively and negatively regulated by various cell surface receptors such as CD19 and CD45. Functional analysis of these receptors has been performed using gene targeting technology, which is a valid approach to elucidate their functions. However, this type of analysis is restricted when multiple molecules are evaluated simultaneously. From a different perspective, synthetic biology provides a high degree of freedom for analyzing various molecules. Here we developed a system to reconstruct BCR signaling using the J558L myeloma cell line in combination with the protein-based Ca(2+) indicator YC3.60. BCR-reconstituted J558L cells harboring YC3.60 (J558Lμv11 cells) permitted monitoring of Ca(2+) mobilization. Reconstituting CD19 in J558Lμv11 cells resulted in detectable BCR-induced Ca(2+) mobilization but with kinetics different from that of CD45-expressing cells. Furthermore, we evaluated the validity of the J558L system by proteomic analysis of tyrosine-phosphorylated proteins after antigen stimulation. Identification of more than 100 BCR-induced tyrosine-phosphorylated proteins in J558Lμv11 cells revealed a similarity to that observed in B cells, and a novel member, non-receptor protein tyrosine kinase Fer, was found. Thus, this reconstruction system using J558L cells appeared to be valid for comprehensively investigating BCR signaling.

Fer kinase limits neutrophil chemotaxis toward end target chemoattractants

Neutrophil recruitment and directional movement toward chemotactic stimuli are important processes in innate immune responses. This study examines the role of Fer kinase in neutrophil recruitment and chemotaxis to various chemoattractants in vitro and in vivo. Mice targeted with a kinase-inactivating mutation (Fer(DR/DR)) or wild type (WT) were studied using time-lapse intravital microscopy to examine leukocyte recruitment and chemotaxis in vivo. In response to keratinocyte-derived cytokine, no difference in leukocyte chemotaxis was observed between WT and Fer(DR/DR) mice. However, in response to the chemotactic peptide WKYMVm, a selective agonist of the formyl peptide receptor, a 2-fold increase in leukocyte emigration was noted in Fer(DR/DR) mice (p < 0.05). To determine whether these defects were due to Fer signaling in the endothelium or other nonhematopoietic cells, bone marrow chimeras were generated. WKYMVm-induced leukocyte recruitment in chimeric mice (WT bone marrow to Fer(DR/DR) recipients or vice versa) was similar to WT mice, suggesting that Fer kinase signaling in both leukocytes and endothelial cells serves to limit chemotaxis. Purified Fer(DR/DR) neutrophils demonstrated enhanced chemotaxis toward end target chemoattractants (WKYMVm and C5a) compared with WT using an under-agarose gel chemotaxis assay. These defects were not observed in response to intermediate chemoattractants (keratinocyte-derived cytokine, MIP-2, or LTB(4)). Increased WKYMVm-induced chemotaxis of Fer(DR/DR) neutrophils correlated with sustained PI3K activity and reduced reliance on the p38 MAPK pathway compared with WT neutrophils. Together, these data identify Fer as a novel inhibitory kinase for neutrophil chemotaxis toward end target chemoattractants through modulation of PI3K activity.

An investigation of hierachical protein recruitment to the inhibitory platelet receptor, G6B-b

Platelet activation is regulated by both positive and negative signals. G6B-b is an inhibitory platelet receptor with an immunoreceptor tyrosine-based inhibitory motif (ITIM) and an immunoreceptor tyrosine-based switch motif (ITSM). The molecular basis of inhibition by G6B-b is currently unknown but thought to involve the SH2 domain-containing tyrosine phosphatase SHP-1. Here we show that G6B-b also associates with SHP-2, as well as SHP-1, in human platelets. Using a number of biochemical approaches, we found these interactions to be direct and that the tandem SH2 domains of SHP-2 demonstrated a binding affinity for G6B-b 100-fold higher than that of SHP-1. It was also observed that while SHP-1 has an absolute requirement for phosphorylation at both motifs to bind, SHP-2 can associate with G6B-b when only one motif is phosphorylated, with the N-terminal SH2 domain and the ITIM being most important for the interaction. A number of other previously unreported SH2 domain-containing proteins, including Syk and PLCγ2, also demonstrated specificity for G6B-b phosphomotifs and may serve to explain the observation that G6B-b remains inhibitory in the absence of both SHP-1 and SHP-2. In addition, the presence of dual phosphorylated G6B-b in washed human platelets can reduce the EC(50) for both CRP and collagen.

Constitutive MHC class I molecules negatively regulate TLR-triggered inflammatory responses via the Fps-SHP-2 pathway

The molecular mechanisms that fine-tune Toll-like receptor (TLR)-triggered innate inflammatory responses remain to be fully elucidated. Major histocompatibility complex (MHC) molecules can mediate reverse signaling and have nonclassical functions. Here we found that constitutively expressed membrane MHC class I molecules attenuated TLR-triggered innate inflammatory responses via reverse signaling, which protected mice from sepsis. The intracellular domain of MHC class I molecules was phosphorylated by the kinase Src after TLR activation, then the tyrosine kinase Fps was recruited via its Src homology 2 domain to phosphorylated MHC class I molecules. This led to enhanced Fps activity and recruitment of the phosphatase SHP-2, which interfered with TLR signaling mediated by the signaling molecule TRAF6. Thus, constitutive MHC class I molecules engage in crosstalk with TLR signaling via the Fps-SHP-2 pathway and control TLR-triggered innate inflammatory responses.

Kinome analysis of receptor-induced phosphorylation in human natural killer cells

BACKGROUND

Natural killer (NK) cells contribute to the defense against infected and transformed cells through the engagement of multiple germline-encoded activation receptors. Stimulation of the Fc receptor CD16 alone is sufficient for NK cell activation, whereas other receptors, such as 2B4 (CD244) and DNAM-1 (CD226), act synergistically. After receptor engagement, protein kinases play a major role in signaling networks controlling NK cell effector functions. However, it has not been characterized systematically which of all kinases encoded by the human genome (kinome) are involved in NK cell activation.

RESULTS

A kinase-selective phosphoproteome approach enabled the determination of 188 kinases expressed in human NK cells. Crosslinking of CD16 as well as 2B4 and DNAM-1 revealed a total of 313 distinct kinase phosphorylation sites on 109 different kinases. Phosphorylation sites on 21 kinases were similarly regulated after engagement of either CD16 or co-engagement of 2B4 and DNAM-1. Among those, increased phosphorylation of FYN, KCC2G (CAMK2), FES, and AAK1, as well as the reduced phosphorylation of MARK2, were reproducibly observed both after engagement of CD16 and co-engagement of 2B4 and DNAM-1. Notably, only one phosphorylation on PAK4 was differentally regulated.

CONCLUSIONS

The present study has identified a significant portion of the NK cell kinome and defined novel phosphorylation sites in primary lymphocytes. Regulated phosphorylations observed in the early phase of NK cell activation imply these kinases are involved in NK cell signaling. Taken together, this study suggests a largely shared signaling pathway downstream of distinct activation receptors and constitutes a valuable resource for further elucidating the regulation of NK cell effector responses.

CD84 negatively regulates IgE high-affinity receptor signaling in human mast cells

CD84 is a self-binding receptor from the CD150 (or signaling lymphocyte activation molecule [SLAM]) family that is broadly expressed in hematopoietic cells. It has been described that the adaptors SLAM-associated protein (SAP) and EWS-FLI1-activated transcript 2 (EAT-2) are critical for CD150 family members' signaling and function. We observed that human mast cells express CD84 but lack SAP or EAT-2, that CD84 is tyrosine phosphorylated upon FcεRI engagement, and that the release of granule contents is reduced when FcεRI is coengaged with CD84 in LAD2 and human CD34(+)-derived mast cells. In addition, we observed that the release of IL-8 and GM-CSF was also reduced in FcεRI/CD84-costimulated cells as compared with FcεRI/Ig control. To understand how CD84 downregulates FcεRI-mediated function, we analyzed signaling pathways affected by CD84 in human mast cells. Our results showed that CD84 dampens FcεRI-mediated calcium mobilization after its co-cross-linking with the receptor. Furthermore, FcεRI-mediated Syk-linker for activation of T cells-phospholipase C-γ1 axis activity is downregulated after CD84 stimulation, compared with FcεRI/Ig control. The inhibitory kinase Fes phosphorylates mainly the inhibitory motif for CD84. Moreover, Fes, which has been described to become phosphorylated after substrate binding, also gets phosphorylated when coexpressed with CD84. Consistently, Fes was observed to be more phosphorylated after CD84 and FcεRI co-cross-linking. The phosphorylation of the protein phosphatase Src homology region 2 domain-containing phosphatase-1 also increases after CD84 and FcεRI coengagement. Taken together, our results show that CD84 is highly expressed in mast cells and that it contributes to the regulation of FcεRI signaling in SAP- and EAT-2-independent and Fes- and Src homology region 2 domain-containing phosphatase-1-dependent mechanisms.

Residues within a lipid-associated segment of the PECAM-1 cytoplasmic domain are susceptible to inducible, sequential phosphorylation

Immunoreceptor tyrosine-based inhibitory motif (ITIM)-containing receptors inhibit cellular responsiveness to immunoreceptor tyrosine-based activation motif (ITAM)-linked receptors. Although tyrosine phosphorylation is central to the initiation of both inhibitory ITIM and stimulatory ITAM signaling, the events that regulate receptor phosphorylation are incompletely understood. Previous studies have shown that ITAM tyrosines engage in structure-inducing interactions with the plasma membrane that must be relieved for phosphorylation to occur. Whether ITIM phosphorylation is similarly regulated and the mechanisms responsible for release from plasma membrane interactions to enable phosphorylation, however, have not been defined. PECAM-1 is a dual ITIM-containing receptor that inhibits ITAM-dependent responses in hematopoietic cells. We found that the PECAM-1 cytoplasmic domain is unstructured in an aqueous environment but adopts an α-helical conformation within a localized region on interaction with lipid vesicles that mimic the plasma membrane. The lipid-interacting segment contains the C-terminal ITIM tyrosine and a serine residue that undergo activation-dependent phosphorylation. The N-terminal ITIM is excluded from the lipid-interacting segment, and its phosphorylation is secondary to phosphorylation of the membrane-interacting C-terminal ITIM. On the basis of these findings, we propose a novel model for regulation of inhibitory signaling by ITIM-containing receptors that relies on reversible plasma membrane interactions and sequential ITIM phosphorylation.

Lyn and PECAM-1 function as interdependent inhibitors of platelet aggregation

Inhibition of platelet responsiveness is important to control pathologic thrombus formation. Platelet-endothelial cell adhesion molecule-1 (PECAM-1) and the Src family kinase Lyn inhibit platelet activation by the glycoprotein VI (GPVI) collagen receptor; however, it is not known whether PECAM-1 and Lyn function in the same or different inhibitory pathways. In these studies, we found that, relative to wild-type platelets, platelets derived from PECAM-1-deficient, Lyn-deficient, or PECAM-1/Lyn double-deficient mice were equally hyperresponsive to stimulation with a GPVI-specific agonist, indicating that PECAM-1 and Lyn participate in the same inhibitory pathway. Lyn was required for PECAM-1 tyrosine phosphorylation and subsequent binding of the Src homology 2 domain-containing phosphatase-2, SHP-2. These results support a model in which PECAM-1/SHP-2 complexes, formed in a Lyn-dependent manner, suppress GPVI signaling.

Regulation of mast cell responses in health and disease

Mast cells are multifunctional cells that initiate not only IgE-dependent allergic diseases but also play a fundamental role in innate and adaptive immune responses to microbial infection. They are also thought to play a role in angiogenesis, tissue remodeling, wound healing, and tumor repression or growth. The broad scope of these physiologic and pathologic roles illustrates the flexible nature of mast cells, which is enabled in part by their phenotypic adaptability to different tissue microenvironments and their ability to generate and release a diverse array of bioactive mediators in response to multiple types of cell-surface and cytosolic receptors. There is increasing evidence from studies in cell cultures that release of these mediators can be selectively modulated depending on the types or groups of receptors activated. The intent of this review is to foster interest in the interplay among mast cell receptors to help understand the underlying mechanisms for each of the immunological and non-immunological functions attributed to mast cells. The second intent of this review is to assess the pathophysiologic roles of mast cells and their products in health and disease. Although mast cells have a sufficient repertoire of bioactive mediators to mount effective innate and adaptive defense mechanisms against invading microorganisms, these same mediators can adversely affect surrounding tissues in the host, resulting in autoimmune disease as well as allergic disorders.

Fes tyrosine kinase expression in the tumor niche correlates with enhanced tumor growth, angiogenesis, circulating tumor cells, metastasis, and infiltrating macrophages

Fes is a protein tyrosine kinase with cell autonomous oncogenic activities that are well established in cell culture and animal models, but its involvement in human cancer has been unclear. Abundant expression of Fes in vascular endothelial cells and myeloid cell lineages prompted us to explore roles for Fes in the tumor microenvironment. In an orthotopic mouse model of breast cancer, we found that loss of Fes in the host correlated with reductions in engrafted tumor growth rates, metastasis, and circulating tumor cells. The tumor microenvironment in Fes-deficient mice also showed reduced vascularity and fewer macrophages. In co-culture with tumor cells, Fes-deficient macrophages also poorly promoted tumor cell invasive behavior. Taken together, our observations argue that Fes inhibition might provide therapeutic benefits in breast cancer, in part by attenuating tumor-associated angiogenesis and the metastasis-promoting functions of tumor-associated macrophages.

SHP-2 phosphatase activity is required for PECAM-1-dependent cell motility

Platelet endothelial cell adhesion molecule-1 (PECAM-1) has been implicated in endothelial cell motility during angiogenesis. Although there is evidence that SHP-2 plays a role in PECAM-1-dependent cell motility, the molecular basis of the activity of SHP-2 in this process has not been defined. To investigate the requirement of SHP-2 in PECAM-1-dependent cell motility, studies were done in which various constructs of SHP-2 were expressed in cell transfectants expressing PECAM-1. We observed that the levels of PECAM-1 tyrosine phosphorylation and SHP-2 association with PECAM-1 were significantly increased in cells expressing a phosphatase-inactive SHP-2 mutant, suggesting that the level of PECAM-1 tyrosine phosphorylation, and thus SHP-2 binding are regulated in part by bound, catalytically active SHP-2. We subsequently found that expression of PECAM-1 stimulated wound-induced migration and the formation of filopodia (a morphological feature of motile cells). These activities were associated with increased mitogen-activated protein kinase (MAPK) activation and the dephosphorylation of paxillin (an event implicated in the activation of MAPK). The phosphatase-inactive SHP-2 mutant, however, suppressed these PECAM-1-dependent phenomena, whereas the activity of PECAM-1 expressing cells was not altered by expression of wild-type SHP-2 or SHP-2 in which the scaffold/adaptor function had been disabled. Pharmacological inhibition of SHP-2 phosphatase activity also suppressed PECAM-1-dependent motility. Furthermore, PECAM-1 expression also stimulates tube formation, but none of the SHP-2 constructs affected this process. These findings therefore suggest a model for the involvement of SHP-2 in PECAM-1-dependent motility in which SHP-2, recruited by its interaction with PECAM-1, targets paxillin to ultimately activate the MAPK pathway and downstream events required for cell motility.

Small interfering RNA screen for phosphatases involved in IgE-mediated mast cell degranulation

Mast cells play pivotal roles in the initiation of the allergic response. To gain an understanding of the functions played by phosphatases in IgE-mediated mast cell activation, a small interfering RNA (siRNA) library that targets all mouse phosphatase genes was screened in a mouse mast cell line, MMC-1. Of 198 targets, 10 enhanced and 7 inhibited FcepsilonRI-induced degranulation. For seven of the strongest hits, four different siRNAs per target were tested, and at least two out of the four single siRNA per target had similar effects as the pool suggesting that these were true hits. Bone marrow-derived mast cells from normal mice further validated these results for six definite positive targets. The mechanism of the reduced mast cell degranulation due to calcineurin B deficiency was investigated. Calcineurin B deficiency reduced the phosphorylation of MAPKs and the phosphorylation of protein kinase D/protein kinase Cmu and protein kinase Cdelta, which are involved in FcepsilonRI signaling. The screen, therefore, has identified several new molecules that are critical for FcepsilonRI-induced degranulation. Regulating the function of these proteins may be potential targets for the treatment of allergic inflammation. The result also indicates that the system used is efficient for searching molecules implicated in complex receptor-induced signaling.

SH2 domain-containing phosphatase-2 protein-tyrosine phosphatase promotes Fc epsilon RI-induced activation of Fyn and Erk pathways leading to TNF alpha release from bone marrow-derived mast cells

Clustering of the high affinity IgE receptor (Fc(epsilon)RI) in mast cells leads to degranulation and production of numerous cytokines and lipid mediators that promote allergic inflammation. Initiation of FFc(epsilon)RI signaling involves rapid tyrosine phosphorylation of Fc(epsilon)RI and membrane-localized adaptor proteins that recruit additional SH2 domain-containing proteins that dynamically regulate downstream signaling. SH2 domain-containing phosphatase-2 (SHP2) is a protein-tyrosine phosphatase implicated in Fc(epsilon)RI signaling, but whose function is not well defined. In this study, using a mouse model allowing temporal shp2 inactivation in bone marrow-derived mast cells (BMMCs), we provide insights into SHP2 functions in the Fc(epsilon)RI pathway. Although no overt defects in Fc(epsilon)RI-induced tyrosine phosphorylation were observed in SHP2 knock-out (KO) BMMCs, several proteins including Lyn and Syk kinases displayed extended phosphorylation kinetics compared with wild-type BMMCs. SHP2 was dispensable for Fc(epsilon)RI-induced degranulation of BMMCs, but was required for maximal activation of Erk and Jnk mitogen-activated protein kinases. SHP2 KO BMMCs displayed several phenotypes associated with reduced Fyn activity, including elevated phosphorylation of the inhibitory pY531 site in Fyn, impaired signaling to Grb2-associated binder 2, Akt/PKB, and IkappaB kinase, and decreased TNF-alpha release compared with control cells. This is likely due to elevated Lyn activity in SHP2 KO BMMCs, and the ability of Lyn to antagonize Fyn activity. Overall, our study identifies SHP2 as a positive effector of Fc(epsilon)RI-induced activation of Fyn/Grb2-associated binder 2/Akt and Ras/Erk pathways leading to TNF-alpha release from mast cells.

Kinome signaling through regulated protein-protein interactions in normal and cancer cells

The flow of molecular information through normal and oncogenic signaling pathways frequently depends on protein phosphorylation, mediated by specific kinases, and the selective binding of the resulting phosphorylation sites to interaction domains present on downstream targets. This physical and functional interplay of catalytic and interaction domains can be clearly seen in cytoplasmic tyrosine kinases such as Src, Abl, Fes, and ZAP-70. Although the kinase and SH2 domains of these proteins possess similar intrinsic properties of phosphorylating tyrosine residues or binding phosphotyrosine sites, they also undergo intramolecular interactions when linked together, in a fashion that varies from protein to protein. These cooperative interactions can have diverse effects on substrate recognition and kinase activity, and provide a variety of mechanisms to link the stimulation of catalytic activity to substrate recognition. Taken together, these data have suggested how protein kinases, and the signaling pathways in which they are embedded, can evolve complex properties through the stepwise linkage of domains within single polypeptides or multi-protein assemblies.

The absence of Hck, Fgr, and Lyn tyrosine kinases augments lung innate immune responses to Pneumocystis murina

Src family tyrosine kinases (SFKs) phosphorylate immunotyrosine activation motifs in the cytoplasmic tail of multiple immunoreceptors, leading to the initiation of cellular effector functions, such as phagocytosis, reactive oxygen species production, and cytokine production. SFKs also play important roles in regulating these responses through the activation of immunotyrosine inhibitory motif-containing inhibitory receptors. As myeloid cells preferentially express the SFKs Hck, Fgr, and Lyn, we questioned the role of these kinases in innate immune responses to Pneumocystis murina. Increased phosphorylation of Hck was readily detectable in alveolar macrophages after stimulation with P. murina. We further observed decreased phosphorylation of Lyn on its C-terminal inhibitory tyrosine in P. murina-stimulated alveolar macrophages, indicating that SFKs were activated in alveolar macrophages in response to P. murina. Mice deficient in Hck, Fgr, and Lyn exhibited augmented clearance 3 and 7 days after intratracheal administration of P. murina, which correlated with elevated levels of interleukin 1beta (IL-1beta), IL-6, CXCL1/KC, CCL2/monocyte chemoattractant protein 1, and granulocyte colony-stimulating factor in lung homogenates and a dramatic increase in macrophage and neutrophil recruitment. Augmented P. murina clearance was also observed in Lyn(-/-) mice 3 days postchallenge, although the level was less than that observed in Hck(-/-) Fgr(-/-) Lyn(-/-) mice. A correlate to augmented clearance of P. murina in Hck(-/-) Fgr(-/-) Lyn(-/-) mice was a greater ability of alveolar macrophages from these mice to kill P. murina in vitro, suggesting that SFKs regulate the alveolar macrophage effector function against P. murina. Mice deficient in paired immunoglobulin receptor B (PIR-B), an inhibitory receptor activated by SFKs, did not exhibit enhanced inflammatory responsiveness to or clearance of P. murina. Our results suggest that SFKs regulate innate lung responses to P. murina in a PIR-B-independent manner.

Contributions of F-BAR and SH2 domains of Fes protein tyrosine kinase for coupling to the FcepsilonRI pathway in mast cells

This study investigates the roles of Fer-CIP4 homology (FCH)-Bin/amphiphysin/Rvs (F-BAR) and SH2 domains of Fes protein tyrosine kinase in regulating its activation and signaling downstream of the high-affinity immunoglobulin G (IgE) receptor (FcepsilonRI) in mast cells. Homology modeling of the Fes F-BAR domain revealed conservation of some basic residues implicated in phosphoinositide binding (R113/K114). The Fes F-BAR can bind phosphoinositides and induce tubulation of liposomes in vitro. Mutation of R113/K114 to uncharged residues (RK/QQ) caused a significant reduction in phosphoinositide binding in vitro and a more diffuse cytoplasmic localization in transfected COS-7 cells. RBL-2H3 mast cells expressing full-length Fes carrying the RK/QQ mutation show defects in FcepsilonRI-induced Fes tyrosine phosphorylation and degranulation compared to cells expressing wild-type Fes. This correlated with reduced localization to Lyn kinase-containing membrane fractions for the RK/QQ mutant compared to wild-type Fes in mast cells. The Fes SH2 domain also contributes to Fes signaling in mast cells, via interactions with the phosphorylated FcepsilonRI beta chain and the actin regulatory protein HS1. We show that Fes phosphorylates C-terminal tyrosine residues in HS1 implicated in actin stabilization. Thus, coordinated actions of the F-BAR and SH2 domains of Fes allow for coupling to FcepsilonRI signaling and potential regulation the actin reorganization in mast cells.

Structural coupling of SH2-kinase domains links Fes and Abl substrate recognition and kinase activation

The SH2 domain of cytoplasmic tyrosine kinases can enhance catalytic activity and substrate recognition, but the molecular mechanisms by which this is achieved are poorly understood. We have solved the structure of the prototypic SH2-kinase unit of the human Fes tyrosine kinase, which appears specialized for positive signaling. In its active conformation, the SH2 domain tightly interacts with the kinase N-terminal lobe and positions the kinase αC helix in an active configuration through essential packing and electrostatic interactions. This interaction is stabilized by ligand binding to the SH2 domain. Our data indicate that Fes kinase activation is closely coupled to substrate recognition through cooperative SH2-kinase-substrate interactions. Similarly, we find that the SH2 domain of the active Abl kinase stimulates catalytic activity and substrate phosphorylation through a distinct SH2-kinase interface. Thus, the SH2 and catalytic domains of active Fes and Abl pro-oncogenic kinases form integrated structures essential for effective tyrosine kinase signaling.

Targeting Lyn inhibits tumor growth and metastasis in Ewing's sarcoma

Src family tyrosine kinases (SFK) play an important role in growth and metastasis of many types of human malignancies. However, their significance in Ewing's sarcoma remains to be elucidated. The purpose of this study was to evaluate the role of Lyn, one member of the SFK, in Ewing's sarcoma growth and metastasis and to determine whether a SFK inhibitor can induce Ewing's tumor regression. Lyn was expressed and activated in TC71, A4573, and SK-ES human Ewing's sarcoma cells. Lyn expression was seen in 13 of 15 patient tumor samples, 6 of which showed Lyn activation. Specific inhibition of Lyn using small interfering RNA significantly decreased primary tumor growth and lytic activity, and also reduced lung metastases in vivo. Down-regulation of Lyn resulted in decreased invasive capacity of tumor cells in vitro. AP23994, a small-molecule SFK inhibitor, decreased Lyn kinase activity and suppressed TC71 cell growth in vitro in a dose-dependent manner. Furthermore, treatment of mice bearing s.c. TC71 tumors with AP23994 or with polyethylenimine/Lyn-small interfering RNA gene therapy resulted in reduced Lyn kinase activity and significant tumor growth suppression. EWS/FLI-1, which is translocation fusion protein associated with Ewing's sarcoma, regulated Lyn gene expression and kinase activity. These data suggest that targeting Lyn may be a new therapeutic approach in treatment of Ewing's sarcoma.

Quantitative time-resolved phosphoproteomic analysis of mast cell signaling

Mast cells play a central role in type I hypersensitivity reactions and allergic disorders such as anaphylaxis and asthma. Activation of mast cells, through a cascade of phosphorylation events, leads to the release of mediators of the early phase allergic response. Understanding the molecular architecture underlying mast cell signaling may provide possibilities for therapeutic intervention in asthma and other allergic diseases. Although many details of mast cell signaling have been described previously, a systematic, quantitative analysis of the global tyrosine phosphorylation events that are triggered by activation of the mast cell receptor is lacking. In many cases, the involvement of particular proteins in mast cell signaling has been established generally, but the precise molecular mechanism of the interaction between known signaling proteins often mediated through phosphorylation is still obscure. Using recently advanced methodologies in mass spectrometry, including automation of phosphopeptide enrichments and detection, we have now substantially characterized, with temporal resolution as short as 10 s, the sites and levels of tyrosine phosphorylation across 10 min of FcepsilonRI-induced mast cell activation. These results reveal a far more extensive array of tyrosine phosphorylation events than previously known, including novel phosphorylation sites on canonical mast cell signaling molecules, as well as unexpected pathway components downstream of FcepsilonRI activation. Furthermore, our results, for the first time in mast cells, reveal the sequence of phosphorylation events for 171 modification sites across 121 proteins in the MCP5 mouse mast cell line and 179 modification sites on 117 proteins in mouse bone marrow-derived mast cells.

The Fer tyrosine kinase regulates an axon retraction response to Semaphorin 3A in dorsal root ganglion neurons

Background

Fps/Fes and Fer are the only two members of a distinct subclass of cytoplasmic protein tyrosine kinases. Fps/Fes was previously implicated in Semaphorin 3A (Sema3A)-induced growth cone collapse signaling in neurons from the dorsal root ganglion (DRG) through interaction with and phosphorylation of the Sema3A receptor component PlexinA1, and members of the collapsin response mediator protein (CRMP) family of microtubule regulators. However, the potential role of the closely related Fer kinase has not been examined.

Results

Here we provide novel biochemical and genetic evidence that Fer plays a prominent role in microtubule regulation in DRG neurons in response to Sema3A. Although Fps/Fes and Fer were both expressed in neonatal brains and isolated DRGs, Fer was expressed at higher levels; and Fer, but not Fps/Fes kinase activity was detected in vivo. Fer also showed higher in vitro kinase activity toward tubulin, as an exogenous substrate; and this activity was higher when the kinases were isolated from perinatal relative to adult brain stages. CRMP2 was a substrate for both kinases in vitro, but both CRMP2 and PlexinA1 inhibited their autophosphorylation activities. Cultured mouse DRG neurons retracted their axons upon exposure to Sema3A, and this response was significantly diminished in Fer-deficient, but only slightly attenuated in Fps/Fes-deficient DRG neurons.

Conclusion

Fps/Fes and Fer are both capable of phosphorylating tubulin and the microtubule regulator CRMP2 in vitro; and their in vitro kinase activities were both inhibited by CRMP2 or PlexinA1, suggesting a possible regulatory interaction. Furthermore, Fer plays a more prominent role than Fps/Fes in regulating the axon retraction response to Sema3A in DRG neurons. Therefore, Fps/Fes and Fer may play important roles in developmental or regenerative axon pathfinding through signaling from Sema3A to the microtubule cytoskeleton.

Anaphylaxis: lessons from mouse models

Studies with mouse models demonstrate 2 pathways of systemic anaphylaxis: a classic pathway mediated by IgE, FcepsilonRI, mast cells, histamine, and platelet-activating factor (PAF) and an alternative pathway mediated by IgG, FcgammaRIII, macrophages, and PAF. The former pathway requires much less antigen and antibody than the latter. This is modified, however, by IgG antibodies that prevent IgE-mediated anaphylaxis by intercepting antigen before it binds to mast cell-associated IgE. Consequently, IgG antibodies block systemic anaphylaxis induced by small quantities of antigen but mediate systemic anaphylaxis induced by larger quantities. The importance of the alternative pathway in human subjects is unknown, but human IgG, IgG receptors, macrophages, mediators, and mediator receptors have appropriate properties to support this pathway if sufficient IgG and antigen are present. The severity of systemic anaphylaxis is increased by nitric oxide produced by the enzyme endothelial nitric oxide synthase and by the cytokines IL-4 and IL-13 and decreased by endogenous beta-adrenergic stimulation and receptors that contain ITIM that bind tyrosine phosphatases. Anaphylaxis is also suppressed by other receptors and ion channels that function through distinct mechanisms. Unlike systemic anaphylaxis, intestinal anaphylaxis (allergic diarrhea) is almost totally IgE and mast cell dependent and is mediated predominantly by PAF and serotonin. Some potent food allergens, including peanuts and tree nuts, can directly enhance anaphylaxis by stimulating an anaphylactoid response through the innate immune system. Results of these studies suggest novel prophylactic agents, including nonstimulatory anti-IgE mAbs, IL-4 receptor antagonists, PAF antagonists, and agents that cross-link FcepsilonRI or FcgammaRIII to an ITIM-containing inhibitory receptor.

Regulation of the mast cell response to the type 1 Fc epsilon receptor

The type I Fc epsilon receptor (Fc epsilon RI) is one of the better understood members of its class and is central to the immunological activation of mast cells and basophils, the key players in immunoglobulin E (IgE)-dependent immediate hypersensitivity. This review provides background information on several distinct regulatory mechanisms controlling this receptor's stimulus-response coupling network. First, we review the current understanding of this network's operation, and then we focus on the inhibitory regulatory mechanisms. In particular, we discuss the different known cytosolic molecules (e.g. kinases, phosphatases, and adapters) as well as cell membrane proteins involved in negatively regulating the Fc epsilon RI-induced secretory responses. Knowledge of this field is developing at a fast rate, as new proteins endowed with regulatory functions are still being discovered. Our understanding of the complex networks by which these proteins exert regulation is limited. Although the scope of this review does not include addressing several important biochemical and biophysical aspects of the regulatory mechanisms, it does provide general insights into a central field in immunology.

Pombe Cdc15 homology (PCH) proteins: coordinators of membrane-cytoskeletal interactions

Cellular adhesion, motility, endocytosis, exocytosis and cytokinesis involve the coordinated reorganization of the cytoskeleton and of the plasma membrane. The 'Pombe Cdc15 homology' (PCH) family of adaptor proteins has recently been shown to coordinate the membrane and cytoskeletal dynamics involved in these processes by curving membranes, recruiting dynamin and controlling the architecture of the actin cytoskeleton. Mutations in PCH family members or proteins that interact with them are associated with autoinflammatory, neurological or neoplastic diseases. Here, we review the nature, actions and disease associations of the vertebrate PCH family members, highlighting their fundamental roles in the regulation of processes involving membrane-cytoskeletal interactions.