Enhanced endotoxin sensitivity in fps/fes-null mice with minimal defects in hematopoietic homeostasis

Cell atlas of the Atlantic salmon spleen reveals immune cell heterogeneity and cell-specific responses to bacterial infection

The spleen is a conserved secondary lymphoid organ that emerged in parallel to adaptive immunity in early jawed vertebrates. Recent studies have applied single cell transcriptomics to reveal the cellular composition of spleen in several species, cataloguing diverse immune cell types and subpopulations. In this study, 51,119 spleen nuclei transcriptomes were comprehensively investigated in the commercially important teleost Atlantic salmon (Salmo salar L.), contrasting control animals with those challenged with the bacterial pathogen Aeromonas salmonicida. We identified clusters of nuclei representing the expected major cell types, namely T cells, B cells, natural killer-like cells, granulocytes, mononuclear phagocytes, endothelial cells, mesenchymal cells, erythrocytes and thrombocytes. We discovered heterogeneity within several immune lineages, providing evidence for resident macrophages and melanomacrophages, infiltrating monocytes, several candidate dendritic cell subpopulations, and B cells at distinct stages of differentiation, including plasma cells and an igt + subset. We provide evidence for twelve candidate T cell subsets, including cd4+ T helper and regulatory T cells, one cd8+ subset, three γδT subsets, and populations double negative for cd4 and cd8. The number of genes showing differential expression during the early stages of Aeromonas infection was highly variable across immune cell types, with the largest changes observed in macrophages and infiltrating monocytes, followed by resting mature B cells. Our analysis provides evidence for a local inflammatory response to infection alongside B cell maturation in the spleen, and upregulation of ccr9 genes in igt + B cells, T helper and cd8+ cells, and monocytes, consistent with the recruitment of immune cell populations to the gut to deal with Aeromonas infection. Overall, this study provides a new cell-resolved perspective of the immune actions of Atlantic salmon spleen, highlighting extensive heterogeneity hidden to bulk transcriptomics. We further provide a large catalogue of cell-specific marker genes that can be leveraged to further explore the function and structural organization of the salmonid immune system.

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.

FES null mice demonstrate a reduction in neutrophil dependent pancreatic cancer metastatic burden

Patients with pancreatic ductal adenocarcinoma (PDAC) have a dismal 5-year survival rate of less than 10%, predominantly due to delayed diagnosis and a lack of effective treatment options. In the PDAC tumor microenvironment (TME), neutrophils are among the immune cell types that are most prevalent and are linked to a poor clinical prognosis. However, treatments that target tumor-associated neutrophils are limited despite recent developments in our understanding of neutrophil function in cancer. The feline sarcoma oncogene (FES) is a nonreceptor tyrosine kinase previously associated with leukemia and hematopoietic homeostasis. Here we describe a newly derived FES null mouse with no distinct phenotype and no defects in hematopoietic homeostasis including neutrophil viability. The immune cell composition and neutrophil population were analyzed with flow cytometry, colony-forming unit (CFU) assay, and a neutrophil viability assay, while the response to PDAC was examined with an in vivo cancer model. In an experimental metastasis model, the FES null model displayed a reduced PDAC hepatic metastatic burden and a reduction in neutrophils granulocytes. Accordingly, our results indicate FES as a potential target for PDAC TME modulation.

The FES Gene at the 15q26 Coronary-Artery-Disease Locus Inhibits Atherosclerosis

BACKGROUND

Genome-wide association studies have discovered a link between genetic variants on human chromosome 15q26.1 and increased coronary artery disease (CAD) susceptibility; however, the underlying pathobiological mechanism is unclear. This genetic locus contains the FES (FES proto-oncogene, tyrosine kinase) gene encoding a cytoplasmic protein-tyrosine kinase involved in the regulation of cell behavior. We investigated the effect of the 15q26.1 variants on FES expression and whether FES plays a role in atherosclerosis.

METHODS AND RESULTS

Analyses of isogenic monocytic cell lines generated by CRISPR (clustered regularly interspaced short palindromic repeats)-mediated genome editing showed that monocytes with an engineered 15q26.1 CAD risk genotype had reduced FES expression. Small-interfering-RNA-mediated knockdown of FES promoted migration of monocytes and vascular smooth muscle cells. A phosphoproteomics analysis showed that FES knockdown altered phosphorylation of a number of proteins known to regulate cell migration. Single-cell RNA-sequencing revealed that in human atherosclerotic plaques, cells that expressed FES were predominately monocytes/macrophages, although several other cell types including smooth muscle cells also expressed FES. There was an association between the 15q26.1 CAD risk genotype and greater numbers of monocytes/macrophage in human atherosclerotic plaques. An animal model study demonstrated that Fes knockout increased atherosclerotic plaque size and within-plaque content of monocytes/macrophages and smooth muscle cells, in apolipoprotein E-deficient mice fed a high fat diet.

CONCLUSIONS

We provide substantial evidence that the CAD risk variants at the 15q26.1 locus reduce FES expression in monocytes and that FES depletion results in larger atherosclerotic plaques with more monocytes/macrophages and smooth muscle cells. This study is the first demonstration that FES plays a protective role against atherosclerosis and suggests that enhancing FES activity could be a potentially novel therapeutic approach for CAD intervention.

Analysis of 200,000 Exome-Sequenced UK Biobank Subjects Implicates Genes Involved in Increased and Decreased Risk of Hypertension

BACKGROUND

Previous analyses have identified common variants along with some specific genes and rare variants which are associated with risk of hypertension, but much remains to be discovered.

METHODS AND RESULTS

Exome-sequenced UK Biobank participants were phenotyped based on having a diagnosis of hypertension or taking anti-hypertensive medication to produce a sample of 66,123 cases and 134,504 controls. Variants with minor allele frequency (MAF) <0.01 were subjected to a gene-wise weighted burden analysis, with higher weights assigned to variants which are rarer and/or predicted to have more severe effects. Of 20,384 genes analysed, 2 genes were exome-wide significant, DNMT3A and FES. Also strongly implicated were GUCY1A1 and GUCY1B1, which code for the subunits of soluble guanylate cyclase. There was further support for the previously reported effects of variants in NPR1 and protective effects of variants in DBH. An inframe deletion in CACNA1D with MAF = 0.005, rs72556363, is associated with modestly increased risk of hypertension. Other biologically plausible genes highlighted consist of CSK, AGTR1, ZYX, and PREP. All variants implicated were rare, and cumulatively they are not predicted to make a large contribution to the population risk of hypertension.

CONCLUSIONS

This approach confirms and clarifies previously reported findings and also offers novel insights into biological processes influencing hypertension risk, potentially facilitating the development of improved therapeutic interventions. This research has been conducted using the UK Biobank Resource.

The Seminiferous Epithelial Cycle of Spermatogenesis: Role of Non-receptor Tyrosine Kinases

Non-receptor tyrosine kinases (NRTKs) are implicated in various biological processes including cell proliferation, differentiation, survival, and apoptosis, as well as cell adhesion and movement. NRTKs are expressed in all mammals and in different cell types, with extraordinarily high expression in the testis. Their association with the plasma membrane and dynamic subcellular localization are crucial parameters in their activation and function. Many NRTKs are found in endosomal protein trafficking pathways, which suggests a novel mechanism to regulate the timely junction restructuring in the mammalian testis to facilitate spermiation and germ cell transport across the seminiferous epithelium.

Chemical genetics strategy to profile kinase target engagement reveals role of FES in neutrophil phagocytosis

Chemical tools to monitor drug-target engagement of endogenously expressed protein kinases are highly desirable for preclinical target validation in drug discovery. Here, we describe a chemical genetics strategy to selectively study target engagement of endogenous kinases. By substituting a serine residue into cysteine at the DFG-1 position in the ATP-binding pocket, we sensitize the non-receptor tyrosine kinase FES towards covalent labeling by a complementary fluorescent chemical probe. This mutation is introduced in the endogenous FES gene of HL-60 cells using CRISPR/Cas9 gene editing. Leveraging the temporal and acute control offered by our strategy, we show that FES activity is dispensable for differentiation of HL-60 cells towards macrophages. Instead, FES plays a key role in neutrophil phagocytosis via SYK kinase activation. This chemical genetics strategy holds promise as a target validation method for kinases.

Electroporation-mediated delivery of FER gene enhances innate immune response and improves survival in a murine model of pneumonia

Previously, we reported that electroporation-mediated (EP) delivery of the FER gene improved survival in a combined trauma-pneumonia model. The mechanism of this protective effect is unknown. In this paper, we performed a pneumonia model in C57/BL6 mice with 500 CFU of Klebsiella pneumoniae. After inoculation, a plasmid encoding human FER was delivered by EP into the lung (PNA/pFER-EP). Survival of FER-treated vs. controls (PNA; PNA/EP-pcDNA) was recorded. In parallel cohorts, bronchial alveolar lavage (BAL) and lung were harvested at 24 and 72 h with markers of infection measured. FER-EP-treated animals reduced bacterial counts and had better 5-day survival compared to controls (80 vs. 20 vs. 25%; p < 0.05). Pre-treatment resulted in 100% survival. With FER, inflammatory monocytes were quickly recruited into BAL. These cells had increased surface expression for Toll-receptor 2 and 4, and increased phagocytic and myeloperoxidase activity at 24 h. Samples from FER electroporated animals had increased phosphorylation of STAT transcription factors, varied gene expression of IL1β, TNFα, Nrf2, Nlrp3, Cxcl2, HSP90 and increased cytokine production of TNF-α, CCL-2, KC, IFN-γ, and IL-1RA. In a follow-up experiment, using Methicillin-resistant Staphylococcus aureus (MRSA) similar bacterial reduction effects were obtained with FER gene delivery. We conclude that FER overexpression improves survival through STAT activation enhancing innate immunity and accelerating bacterial clearance in the lung. This constitutes a novel mechanism of inflammatory regulation with therapeutic potential in the setting of hospital-acquired pneumonia.

Comparative oncogenomics identifies tyrosine kinase FES as a tumor suppressor in melanoma

Identification and functional validation of oncogenic drivers are essential steps toward advancing cancer precision medicine. Here, we have presented a comprehensive analysis of the somatic genomic landscape of the widely used BRAFV600E- and NRASQ61K-driven mouse models of melanoma. By integrating the data with publically available genomic, epigenomic, and transcriptomic information from human clinical samples, we confirmed the importance of several genes and pathways previously implicated in human melanoma, including the tumor-suppressor genes phosphatase and tensin homolog (PTEN), cyclin dependent kinase inhibitor 2A (CDKN2A), LKB1, and others. Importantly, this approach also identified additional putative melanoma drivers with prognostic and therapeutic relevance. Surprisingly, one of these genes encodes the tyrosine kinase FES. Whereas FES is highly expressed in normal human melanocytes, FES expression is strongly decreased in over 30% of human melanomas. This downregulation correlates with poor overall survival. Correspondingly, engineered deletion of Fes accelerated tumor progression in a BRAFV600E-driven mouse model of melanoma. Together, these data implicate FES as a driver of melanoma progression and demonstrate the potential of cross-species oncogenomic approaches combined with mouse modeling to uncover impactful mutations and oncogenic driver alleles with clinical importance in the treatment of human cancer.

Electroporation-mediated delivery of the FER gene in the resolution of trauma-related fatal pneumonia

Injured patients with lung contusion (LC) are at risk of developing bacterial pneumonia (PNA) followed by sepsis and death. A recent genome-wide association study (GWAS) showed FER gene expression positively correlating with survival rates among individuals with above conditions. We sought to determine whether electroporation (EP)-mediated delivery of FER gene could indeed improve survival, in a lethal model of combined LC and PNA. C57BL/6 mice sustained unilateral LC, which preceded a 500 Klebsiella colony forming unit (CFU) inoculation by 6 h. In-between these insults, human FER plasmid (pFER) was introduced into the lungs followed by eight EP pulses applied externally (10 ms at 200 V cm^-1). Control groups included EP of empty vector (pcDNA3) or Na⁺/K⁺-ATPase genes (pPump) and no treatment (LC+PNA). We recorded survival, histology, lung mechanics, bronchial alveolar lavage (BAL) fluid, FER and inflammatory gene expression and bacteriology. The data show that 7-day survival was significantly improved by pFER compared with control groups. pFER increased BAL monocytes and activated antibacterial response genes (nitric oxide synthase (NOS), Fizz). pFER treatment showed decreased lung and blood Klebsiella counts reaching, in some cases, complete sterilization. In conclusion, FER gene delivery promoted survival in LC+PNA mice via recruitment of activated immune cells, improving efficiency of bacterial clearance within contused lung.

Effect of erythropoietin on primed leucocyte expression profile

Resistance to erythropoietin (EPO) affects a significant number of anaemic patients with end-stage renal disease. Previous reports suggest that inflammation is one of the major independent predictors of EPO resistance, and the effects of EPO treatment on inflammatory mediators are not well established. The aim of this study was to investigate EPO-induced modification to gene expression in primary cultured leucocytes. Microarray experiments were performed on primed ex vivo peripheral blood mononuclear cells (PBMCs) and treated with human EPO-α. Data suggested that EPO-α modulated genes involved in cell movement and interaction in primed PBMCs. Of note, EPO-α exerts anti-inflammatory effects inhibiting the expression of pro-inflammatory cytokine IL-8 and its receptor CXCR2; by contrast, EPO-α increases expression of genes relating to promotion of inflammation encoding for IL-1β and CCL8, and induces de novo synthesis of IL-1α, CXCL1 and CXCL5 in primed cells. The reduction in MAPK p38-α activity is involved in modulating both IL-1β and IL-8 expression. Unlike the induction of MAPK, Erk1/2 activity leads to upregulation of IL-1β, but does not affect IL-8 expression and release. Furthermore, EPO-α treatment of primed cells induces the activation of caspase-1 upstream higher secretion of IL-1β, and this process is not dependent on caspase-8 activation. In conclusion, our findings highlight new potential molecules involved in EPO resistance and confirm the anti-inflammatory role for EPO, but also suggest a plausible in vivo scenario in which the positive correlation found between EPO resistance and elevated levels of some pro-inflammatory mediators is due to treatment with EPO itself.

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.

Pathological significance and predictive value for biochemical recurrence of c-Fes expression in prostate cancer

BACKGROUND

c-Fes is a proto-oncogene encoded non-receptor protein-tyrosine kinase (PTK). However, genetic studies have indicated that it has anti-tumorigenic effects in certain cancers. The pathological and clinical significance of c-Fes in prostate cancer are unknown.

METHODS

Expression of c-Fes was evaluated in normal glands, prostatic intraepithelial neoplasia (PIN), cancer cells in tissues of knock-in mouse adenocarcinoma prostate (KIMAP) model, and prostate cancer patients free of metastasis. Expression of c-Fes was analyzed by immunohistochemistry, and quantified by using the immunoreactivity score (IRS) (staining intensity × percentage of positive cells). Relationships between c-Fes expression and pT stage, Gleason's score (GS), and biochemical recurrence in patients who underwent radical surgery were also investigated.

RESULTS

In KIMAP, the percentage in normal glands, PIN and cancer cells positive for c-Fes expression were 0 (0/7), 25.0 (2/8), and 100% (7/7), respectively. In human tissues, c-Fes expression was also significantly higher in cancer cells than in normal cells and PIN, and it correlated with pT stage (P < 0.001) and GS (P = 0.047). Multivariate analysis showed that c-Fes expression was an independent predictor of poor outcome poor prognosis (hazard ratio = 3.21, 95% confidence interval = 1.11-9.37, P = 0.032).

CONCLUSION

The results suggested that c-Fes expression is a useful predictor of biochemical recurrence after radical surgery. The results also suggested that c-Fes is a potentially useful therapeutic target in prostate cancer and a predictor of biochemical recurrence after radical prostatectomy.

Quantitative trait loci analysis for peripheral blood parameters in a (BALB/cW × C57BL/6J-Mpl (hlb219)/J) F(2) mice

The genetic basis of the peripheral blood cell parameters is not fully elucidated. Thus, it is essential to research the correlation between blood cell counts levels and the genome in laboratory animals and subsequently in humans. In the present study, we examined 288 F(2) mice from a cross between BALB/cW and C57BL/6J-Mpl(hlb219)/J. The C57BL/6J-Mpl (hlb219)/J strain is a mouse model of thrombocytopenia. We found very strong correlations for PLT counts and revealed some highly significant correlations for RBC counts. On the basis of the obtained results, we presume that genetic control of erythrocyte parameters is divided into two pathways: first, the morphological determinants responsible for the red blood cell count (RBC), hematocrit (HCT), and mean corpuscular volume (MCV), and second, the functional pathway determining the hemoglobin content (HGB). The locus on Chromosome 4 is the only detected quantitative trait locus (QTL) influencing the analyzed platelets parameters. We also detected highly significant correlations for erythrocyte parameters on Chromosome 1 (RBC, MCV, MCH), Chr 7 (HGB), Chr 9 (MCHC), Chr 11 (RBC), and Chr 17 (MCH). Finally, with regards to the given correlations, using the Mouse Genome Database resource, we proposed candidate genes with possible meaning for the level of these parameters: cytokine receptor genes (e.g., Mpl), transcription factor genes (e.g., Xbp1, Ikzf1), hemoglobin chain genes (e.g., Hbb-b1, Hbb-ar), and many others localized in the confidence intervals of found QTLs.

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.

FES kinase participates in KIT-ligand induced chemotaxis

FES is a cytoplasmic tyrosine kinase activated by several membrane receptors, originally identified as a viral oncogene product. We have recently identified FES as a crucial effector of oncogenic KIT mutant receptor. However, FES implication in wild-type KIT receptor function was not addressed. We report here that FES interacts with KIT and is phosphorylated following activation by its ligand SCF. Unlike in the context of oncogenic KIT mutant, FES is not involved in wild-type KIT proliferation signal, or in cell adhesion. Instead, FES is required for SCF-induced chemotaxis. In conclusion, FES kinase is a mediator of wild-type KIT signalling implicated in cell migration.

fps/fes knockout mice display a lactation defect and the fps/fes tyrosine kinase is a component of E-cadherin-based adherens junctions in breast epithelial cells during lactation

The fps/fes proto-oncogene encodes a cytoplasmic protein-tyrosine kinase implicated in vesicular trafficking and cytokine and growth factor signaling in hematopoietic, neuronal, vascular endothelial and epithelial lineages. Genetic evidence has suggested a tumor suppressor role for Fps/Fes in breast and colon. Here we used fps/fes knockout mice to investigate potential roles for this kinase in development and function of the mammary gland. Fps/Fes expression was induced during pregnancy and lactation, and its kinase activity was dramatically enhanced. Milk protein and fat composition from nursing fps/fes-null mothers was normal; however, pups reared by them gained weight more slowly than pups reared by wild-type mothers. Fps/Fes displayed a predominantly dispersed punctate intracellular distribution which was consistent with vesicles within the luminal epithelial cells of lactating breast, while a small fraction co-localized with beta-catenin and E-cadherin on their basolateral surfaces. Fps/Fes was found to be a component of the E-cadherin adherens junction (AJ) complex; however, the phosphotyrosine status of beta-catenin and core AJ components in fps/fes-null breast tissue was unaltered, and epithelial cell AJs and gland morphology were intact. We conclude that Fps/Fes is not essential for the maintenance of epithelial cell AJs in the lactating breast but may instead play important roles in vesicular trafficking and milk secretion.

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.

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.

The tyrosine kinase FES is an essential effector of KITD816V proliferation signal

KIT is a tyrosine kinase receptor that is aberrantly activated in several neoplasms. In human pathologies, the most frequent mutation of KIT occurs at codon 816. The resulting KIT mutant protein is activated in the absence of ligand and is resistant to the clinically available inhibitors of KIT. In this report, we provide evidence for an essential function of the cytoplasmic tyrosine kinase FES downstream of KITD816V. FES is phosphorylated on tyrosine residues in cells that carry KITD816V mutation, and this phosphorylation is KIT dependent. Reduction of FES expression using RNA interference results in decreased cell proliferation in human or murine cells harboring KITD816V or the homologous mouse mutation KITD814Y. The reduced cell growth can be rescued using another cytokine (granulocyte-macrophage colony-stimulating factor [GM-CSF]) and is not observed when the closely related fer gene is targeted. Finally, signaling downstream of KITD816V is altered in cells lacking FES expression. This study shows a major function of FES downstream of activated KIT receptor and thereby points to FES as a novel target in KIT-related pathologies.

The Fps/Fes kinase regulates leucocyte recruitment and extravasation during inflammation

Fps/Fes and Fer comprise a distinct subfamily of cytoplasmic protein-tyrosine kinases, and have both been implicated in the regulation of innate immunity. Previous studies showed that Fps/Fes-knockout mice were hypersensitive to systemic lipopolysaccharide (LPS) challenge, and Fer-deficient mice displayed enhanced recruitment of leucocytes in response to localized LPS challenge. We show here for the first time, a role for Fps in the regulation of leucocyte recruitment to areas of inflammation. Using the cremaster muscle intravital microscopy model, we observed increased leucocyte adherence to venules, and increased rates and degrees of transendothelial migration in Fps/Fes-knockout mice relative to wild-type animals subsequent to localized LPS challenge. There was also a decreased vessel wall shear rate in the post-capillary venules of LPS-challenged Fps/Fes-knockout mice, and an increase in neutrophil migration into the peritoneal cavity subsequent to thioglycollate challenge. Using flow cytometry to quantify the expression of surface molecules, we observed prolonged expression of the selectin ligand PSGL-1 on peripheral blood neutrophils from Fps/Fes-knockout mice stimulated ex vivo with LPS. These observations provide important insights into the observed in vivo behaviour of leucocytes in LPS-challenged Fps/Fes-knockout mice and provide evidence that the Fps/Fes kinase plays an important role in the innate immune response.

Novel chromosomal translocations in multiple myeloma: t(13;16)(q14;q24) and t(1;15)(q10;q26)

Multiple myeloma (MM) is a malignant plasma cell disorder that involves multiple genetic abnormalities. Chimeric transcription factors, created by gene fusion as a result of chromosomal translocations, have been implicated in the pathogenesis of the disease. Here, we report the conventional cytogenetic analysis of a MM patient that showed a complex set of novel chromosomal rearrangements, including t(13;16)(q14;q24) and t(1;15)(q10;q26). This is probably the result of fusion of previously known genes, and would contribute to prognostic significance of the disease.

The Fps/Fes kinase regulates the inflammatory response to endotoxin through down-regulation of TLR4, NF-kappaB activation, and TNF-alpha secretion in macrophages

Fps/Fes and Fer are members of a distinct subfamily of cytoplasmic protein tyrosine kinases that have recently been implicated in the regulation of innate immunity. Previous studies showed that mice lacking Fps/Fes are hypersensitive to systemic LPS challenge, and Fer-deficient mice displayed enhanced recruitment of leukocytes in response to local LPS challenge. This study identifies physiological, cellular, and molecular defects that contribute to the hyperinflammatory phenotype in Fps/Fes null mice. Plasma TNF-alpha levels were elevated in LPS challenged Fps/Fes null mice as compared with wild-type mice and cultured Fps/Fes null peritoneal macrophages treated with LPS showed increased TNF-alpha production. Cultured Fps/Fes null macrophages also displayed prolonged LPS-induced degradation of IkappaB-alpha, increased phosphorylation of the p65 subunit of NF-kappaB, and defective TLR4 internalization, compared with wild-type macrophages. Together, these observations provide a likely mechanistic basis for elevated proinflammatory cytokine secretion by Fps/Fes null macrophages and the increased sensitivity of Fps/Fes null mice to endotoxin. We posit that Fps/Fes modulates the innate immune response of macrophages to LPS, in part, by regulating internalization and down-regulation of the TLR4 receptor complex.

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

Mast cells express the high affinity IgE receptor FcepsilonRI, which upon aggregation by multivalent antigens elicits signals that cause rapid changes within the mast cell and in the surrounding tissue. We previously showed that FcepsilonRI aggregation caused a rapid increase in phosphorylation of both Fer and Fps/Fes kinases in bone marrow-derived mast cells. In this study, we report that FcepsilonRI aggregation leads to increased Fer/Fps kinase activities and that Fer phosphorylation downstream of FcepsilonRI is independent of Syk, Fyn, and Gab2 but requires Lyn. Activated Fer/Fps readily phosphorylate the C terminus of platelet-endothelial cell adhesion molecule 1 (Pecam-1) on immunoreceptor tyrosine-based inhibitory motifs (ITIMs) and a non-ITIM residue (Tyr(700)) in vitro and in transfected cells. Mast cells devoid of Fer/Fps kinase activities display a reduction in FcepsilonRI aggregation-induced tyrosine phosphorylation of Pecam-1, with no defects in recruitment of Shp1/Shp2 phosphatases observed. Lyn-deficient mast cells display a dramatic reduction in Pecam-1 phosphorylation at Tyr(685) and a complete loss of Shp2 recruitment, suggesting a role as an initiator kinase for Pecam-1. Consistent with previous studies of Pecam-1-deficient mast cells, we observe an exaggerated degranulation response in mast cells lacking Fer/Fps kinases at low antigen dosages. Thus, Lyn and Fer/Fps kinases cooperate to phosphorylate Pecam-1 and activate Shp1/Shp2 phosphatases that function in part to limit mast cell activation.

Absence of caprin-1 results in defects in cellular proliferation

Cytoplasmic activation/proliferation-associated protein-1 (Caprin-1) is a cytoplasmic phosphoprotein that is the prototype of a novel family of highly conserved proteins. Its levels, except in the brain, are tightly correlated with cellular proliferation. We disrupted caprin-1 alleles in the chicken B lymphocyte line DT40 using homologous recombination. We readily obtained clones with one disrupted allele (31% of transfectants), but upon transfection of heterozygous cells we obtained a 10-fold lower frequency of clones with disruption of the remaining allele. Clones of caprin-1-null DT40 cells exhibited marked reductions in their proliferation rate. To obviate the problem that we had selected for caprin-1-null clones with characteristics that partially compensated for the lack of Caprin-1, we generated clones of DT40 cells heterozygous for the caprin-1 gene in which, during disruption of the remaining wild-type allele of the chicken caprin-1 gene, the absence of endogenous Caprin-1 would be complemented by conditional expression of human Caprin-1. Suppression of expression of human Caprin-1 resulted in slowing of the proliferation rate, due to prolongation of the G1 phase of the cell cycle, formally demonstrating that Caprin-1 was essential for normal cellular proliferation.

Terminal deletion of chromosome 15q26.1: case report and brief literature review

Terminal deletions of chromosome 15q are rare events, with only six cases previously described. Here we describe a seventh case of a terminal deletion of the long arm of chromosome 15, with the present case exhibiting clinical features not previously described.

An Identity Crisis for fps/fes: Oncogene or Tumor Suppressor?

Fps/Fes proteins were among the first members of the protein tyrosine kinase family to be characterized as dominant-acting oncoproteins. Addition of retroviral GAG sequences or other experimentally induced mutations activated the latent transforming potential of Fps/Fes. However, activating mutations in fps/fes had not been found in human tumors until recently, when mutational analysis of a panel of colorectal cancers identified four somatic mutations in sequences encoding the Fps/Fes kinase domain. Here, we report biochemical and theoretical structural analysis demonstrating that three of these mutations result in inactivation, not activation, of Fps/Fes, whereas the fourth mutation compromised in vivo activity. These results did not concur with a classic dominant-acting oncogenic role for fps/fes involving activating somatic mutations but instead raised the possibility that inactivating fps/fes mutations might promote tumor progression in vivo. Consistent with this, we observed that tumor onset in a mouse model of breast epithelial cancer occurred earlier in mice targeted with either null or kinase-inactivating fps/fes mutations. Furthermore, a fps/fes transgene restored normal tumor onset kinetics in targeted fps/fes null mice. These data suggest a novel and unexpected tumor suppressor role for Fps/Fes in epithelial cells.

Modulation of TLR signalling by the C-terminal Src kinase (Csk) in macrophages

In macrophages and monocytes, lipopolysaccharide (LPS) triggers the production of pro-inflammatory cytokine through Toll-like receptor (TLR) 4. Although major TLR signalling pathways are mediated by serine or threonine kinases including IKK, TAK1, p38 and JNKs, a number of reports suggested that tyrosine phosphorylation of intracellular proteins is involved in LPS signalling. Here, we identified several tyrosine-phosphorylated proteins using mass spectrometric analysis in response to LPS stimulation. Among these proteins, we characterized C-terminal Src kinase (Csk), which negatively regulates Src-like kinases in RAW 264.7 cells using RNAi knockdown technology. Unexpectedly, LPS-induced CD40 activation and the secretion of pro-inflammatory cytokine such as IL-6 and TNF-alpha, was down-regulated in Csk knockdown cells. Furthermore, overall cellular tyrosine phosphorylation and TLR4-mediated activation of IkappaB-alpha, Erk and p38 but not of JNK, were also down-regulated in Csk knockdown cells. The protein expression levels of a tyrosine kinase, Fgr, were reduced in Csk knockdown cells, suggesting that Csk is a critical regulator of TLR4-mediated signalling by modifying the levels of Src-like kinases.

Activated Fps/Fes tyrosine kinase regulates erythroid differentiation and survival

OBJECTIVE

A substantial body of evidence implicates the cytoplasmic protein tyrosine kinase Fps/Fes in regulation of myeloid differentiation and survival. In this study we wished to determine if Fps/Fes also plays a role in the regulation of erythropoiesis.

METHODS

Mice tissue-specifically expressing a "gain-of-function" mutant fps/fes transgene (fps(MF)) encoding an activated variant of Fps/Fes (MFps), were used to explore the in vivo biological role of Fps/Fes. Erythropoiesis in these mice was assessed by hematological analysis, lineage marker analysis, bone-marrow colony assays, and biochemical approaches.

RESULTS

fps(MF) mice displayed reductions in peripheral red cell counts. However, there was an accumulation of immature erythroid precursors, which displayed increased survival. Fps/Fes and the related Fer kinase were both detected in early erythroid progenitors/blasts and in mature red cells. Fps/Fes was also activated in response to erythropoietin (EPO) and stem cell factor (SCF), two critical factors in erythroid development. In addition, increased Stat5A/B activation and reduced Erk1/2 phosphorylation was observed in fps(MF) primary erythroid cells in response to EPO or SCF, respectively.

CONCLUSIONS

These data support a role for Fps/Fes in regulating the survival and differentiation of erythroid cells through modulation of Stat5A/B and Erk kinase pathways induced by EPO and SCF. The increased numbers and survival of erythroid progenitors from fps(MF) mice, and their differential responsiveness to SCF and EPO, implicates Fps/Fes in the commitment of multilineage progenitors to the erythroid lineage. The anemic phenotype in fps(MF) mice suggests that downregulation of Fps/Fes activity might be required for terminal erythroid differentiation.

Hemostatic and hematological abnormalities in gain-of-function fps/fes transgenic mice are associated with the angiogenic phenotype

The Fps/Fes tyrosine kinase has been implicated in the regulation of hematopoiesis and inflammation. Mice expressing an activated variant of Fps/Fes (MFps) encoded by a gain-of-function mutant transgenic fps/fes allele (fps(MF)) exhibited hematological phenotypes, which suggested that Fps/Fes can direct hematopoietic lineage output. These mice also displayed marked hypervascularity and multifocal-hemangiomas which implicated this kinase in the regulation of angiogenesis. Here we explored the potential involvement of Fps/Fes in the regulation of hemostasis through effects on blood cells and the vascular endothelium. Hematological parameters of fps(MF) mice were characterized by peripheral blood analysis, histology, and transmission electron microscopy. Hemostasis parameters and platelet functions were assessed by flow cytometry and measurements of activated partial thromboplastin time, prothrombin time, thrombin clot time, platelet aggregation, bleeding times and in vitro fibrinolytic assays. Hematological and morphological analyses showed that fps(MF) mice displayed mild thrombocytopenia, anemia, red cell abnormalities and numerous hemostatic defects, including hypofibrinogenemia, hyper-fibrinolysis, impaired whole blood aggregation and a mild bleeding diathesis. fps(MF) mice displayed a complex array of hemostatic perturbations which are reminiscent of hemostatic disorders such as disseminated intravascular coagulation (DIC) and of hemangioma-associated pathologies such as Kasabach-Merritt phenomenon (KMS). These studies suggest that Fps/Fes influences both angiogenic and hemostatic function through regulatory effects on the endothelium.

Vascular defects in gain-of-function fps/fes transgenic mice correlate with PDGF- and VEGF-induced activation of mutant Fps/Fes kinase in endothelial cells

BACKGROUND

Fps/Fes is a cytoplasmic tyrosine kinase that is abundantly expressed in the myeloid, endothelial, epithelial, neuronal and platelet lineages. Genetic manipulation in mice has uncovered potential roles for this kinase in hematopoiesis, innate immunity, inflammation and angiogenesis.

OBJECTIVE

We have utilized a genetic approach to explore the role of Fps/Fes in angiogenesis.

METHODS

A hypervascular line of mice generated by expression of a 'gain-of-function' human fps/fes transgene (fps(MF)) encoding a myristoylated variant of Fps (MFps) was used in these studies. The hypervascular phenotype of this line was extensively characterized by intravital microscopy and biochemical approaches.

RESULTS

fps(MF) mice exhibited 1.6-1.7-fold increases in vascularity which was attributable to increases in the number of secondary vessels. Vessels were larger, exhibited varicosities and disorganized patterning, and were found to have defects in histamine-induced permeability. Biochemical characterization of endothelial cell (EC) lines derived from fps(MF) mice revealed that MFps was hypersensitive to activation by vascular endothelial growth factor (VEGF) and platelet-derived growth factor (PDGF).

CONCLUSIONS

MFps mediates enhanced sensitization to VEGF and PDGF signaling in ECs. We propose that this hypersensitization contributes to excessive angiogenic signaling and that this underlies the observed hypervascular phenotype of fps(MF) mice. These phenotypes recapitulate important aspects of the vascular defects observed in both VEGF and angiopoietin-1 transgenic mice. The fps/fes proto-oncogene product therefore represents a novel player in the regulation of angiogenesis, and the fps(MF) line of mice constitutes a unique new murine model for the study of this process.

The fps/fes proto-oncogene regulates hematopoietic lineage output

OBJECTIVE

The fps/fes proto-oncogene is abundantly expressed in myeloid cells, and the Fps/Fes cytoplasmic protein-tyrosine kinase is implicated in signaling downstream from hematopoietic cytokines, including interleukin-3 (IL-3), granulocyte-macrophage colony-stimulating factor (GM-CSF), and erythropoietin (EPO). Studies using leukemic cell lines have previously suggested that Fps/Fes contributes to granulomonocytic differentiation, and that it might play a more selective role in promoting survival and differentiation along the monocytic pathway. In this study we have used a genetic approach to explore the role of Fps/Fes in hematopoiesis.

METHODS

We used transgenic mice that tissue-specifically express a mutant human fps/fes transgene (fps(MF)) that was engineered to encode Fps/Fes kinase that is activated through N-terminal myristoylation (MFps). Hematopoietic function was assessed using lineage analysis, hematopoietic progenitor cell colony-forming assays, and biochemical approaches.

RESULTS

fps(MF) transgenic mice displayed a skewed hematopoietic output reflected by increased numbers of circulating granulocytic and monocytic cells and a corresponding decrease in lymphoid cells. Bone marrow colony assays of progenitor cells revealed a significant increase in the number of both granulomonocytic and multi-lineage progenitors. A molecular analysis of signaling in mature monocytic cells showed that MFps promoted GM-CSF-induced STAT3, STAT5, and ERK1/2 activation.

CONCLUSIONS

These observations support a role for Fps/Fes in signaling pathways that contribute to lineage determination at the level of multi-lineage hematopoietic progenitors as well as the more committed granulomonocytic progenitors.

Fps/Fes and Fer protein-tyrosinekinases play redundant roles in regulating hematopoiesis

OBJECTIVE

The highly related protein-tyrosine kinases Fps (also called Fes) and Fer are sole members of a subfamily of kinases. In this study, knock-in mice harboring kinase-inactivating mutations in both fps and fer alleles were used to assess functional redundancy between Fps and Fer kinases in regulating hematopoiesis.

METHODS

Mice harboring kinase-inactivating mutations in fps and fer alleles were generated previously. Compound homozygous mice were bred that lack both Fps and Fer kinase activities and progeny were analyzed for potential defects in viability and fertility. Potential differences in hematopoiesis were analyzed by lineage analysis of bone marrow cells, peripheral blood counts, and hematopoietic progenitor cell colony-forming assays.

RESULTS

Mice devoid of both Fps and Fer kinase activities were viable and displayed reduced fertility. Circulating levels of neutrophils, erythrocytes, and platelets were elevated in compound mutant mice compared to wild-type controls, suggesting that hematopoiesis is deregulated in the absence of Fps and Fer kinases. Compound mutant mice also showed reduced overall bone marrow cellularity, and lineage analysis revealed elevated CD11b(hi)Ly-6G(lo) myeloid cells, which may reflect increased granulocyte progenitors. Although no differences in the overall number of granulocyte/monocyte colony-forming progenitors were observed, qualitative differences in myeloid colonies from compound mutant mice suggested a role for Fps and Fer kinases in regulating cell-cell adhesion or a skewing in cellularity of colonies.

CONCLUSIONS

Mice lacking both Fps and Fer kinase activities develop normally, show reduced fertility, and display defects in hematopoiesis, thus providing evidence for functional redundancy between Fps and Fer kinases in regulating hematopoiesis.

Fps/Fes and Fer non-receptor protein-tyrosine kinases regulate collagen- and ADP-induced platelet aggregation

Fps/Fes and Fer proto-oncoproteins are structurally related non-receptor protein-tyrosine kinases implicated in signaling downstream from cytokines, growth factors and immune receptors. We show that Fps/Fes and Fer are expressed in human and mouse platelets, and are activated following stimulation with collagen and collagen-related peptide (CRP), suggesting a role in GPVI receptor signaling. Fer was also activated following stimulation with thrombin and a protease-activated receptor4 (PAR4)-activating peptide, suggesting a role in signaling downstream from the G protein-coupled PAR4. There were no detectable perturbations in CRP-induced activation of Syk, PLCgamma2, cortactin, Erk, Jnk, Akt or p38 in platelets from mice lacking Fps/Fes, Fer, or both kinases. Platelets lacking Fps/Fes, from a targeted fps/fes null strain of mice, showed increased rates and amplitudes of collagen-induced aggregation, relative to wild-type platelets. P-Selectin expression was also elevated on the surface of Fps/Fes-null platelets in response to CRP. Fer-deficient platelets, from mice targeted with a kinase-inactivating mutation, disaggregated more rapidly than wild-type platelets in response to ADP. This report provides the first evidence that Fps/Fes and Fer are expressed in platelets and become activated downstream from the GPVI collagen receptor, and that Fer is activated downstream from a G-protein coupled receptor. Furthermore, using targeted mouse models we show that deficiency in Fps/Fes or Fer resulted in disregulated platelet aggregation and disaggregation, demonstrating a role for these kinases in regulating platelet functions.

Fes tyrosine kinase promotes survival and terminal granulocyte differentiation of factor-dependent myeloid progenitors (32D) and activates lineage-specific transcription factors

The c-fps/fes proto-oncogene encodes a 92-kDa protein-tyrosine kinase that is involved in myeloid cell development and function. We have recently shown that expression of an activated allele of Fes (Fes(act)) in monocyte precursors resulted in their differentiation into functional macrophages through the activation of lineage-specific transcription factors. We now report that this kinase also plays a role in the survival and terminal differentiation of granulocyte progenitors. The expression of Fes(act) in factor-dependent 32D cells prevented their apoptotic death after interleukin-3 removal, but Fes(act)-expressing cells remained factor-dependent for proliferation. Removal of interleukin-3 from the Fes(act)-expressing cells was followed by granulocytic differentiation in the absence of granulocyte colony-stimulating factor within 4-8 days. The differentiated cells had distinctive granulocyte morphology and there was up-regulation of CD11b, Gr-1, and late differentiation markers such as lactoferrin, suggesting that this kinase induced terminal granulocytic differentiation. Concomitantly, Fes(act) down-regulated the macrophage marker F4/80, suggesting that the biological activity of Fes was coordinated in a lineage-specific manner. Further analysis showed that Fes(act) caused activation of CCAAT/enhancer-binding protein-alpha and STAT3, two transcription factors that are involved in granulocyte differentiation. Our results provide evidence that Fes may be a key component of the granulocyte differentiation machinery, and suggest a potential mechanism by which this kinase may regulate granulocyte-specific gene expression.

Decrease of the inflammatory response and induction of the Akt/protein kinase B pathway by poly-(ADP-ribose) polymerase 1 inhibitor in endotoxin-induced septic shock

The lack of efficacy of anti-inflammatory drugs, anti-coagulants, anti-oxidants, etc. in critically ill patients has shifted interest towards developing alternative treatments. Since inhibitors of the nuclear enzyme poly-(ADP-ribose) polymerase (PARP) were found to be beneficial in many pathophysiological conditions associated with oxidative stress and PARP-1 knock-out mice proved to be resistant to bacterial lipopolysaccharide (LPS)-induced septic shock, PARP inhibitors are candidates for such a role. In this study, the mechanism of the protective effect of a potent PARP-1 inhibitor, PJ34 was studied in LPS-induced (20mg/kg, i.p.) septic shock in mice. We demonstrated a significant inflammatory response by magnetic resonance imaging in the dorsal subcutaneous region, in the abdominal regions around the kidneys and in the inter-intestinal cavities. We have found necrotic and apoptotic histological changes as well as obstructed blood vessels in the liver and small intestine. Additionally, we have detected elevated tumor necrosis factor-alpha levels in the serum and nuclear factor kappa B activation in liver of LPS-treated mice. Pre-treating the animals with PJ34 (10mg/kg, i.p.), before the LPS challenge, besides rescuing the animals from LPS-induced death, attenuated all these changes presumably by activating the phosphatidylinositol 3-kinase-Akt/protein kinase B cytoprotective pathway.

Requirement of the coiled-coil domains of p92(c-Fes) for nuclear localization in myeloid cells upon induction of differentiation

The nonreceptor tyrosine kinase Fes is implicated in myeloid cells differentiation. It has been observed that its localization can be cytoplasmic, perinuclear, or nuclear. To further characterize this point, we studied Fes subcellular localization in myeloid cell lines (HL60 and K562) and in COS1 cells. Fes was observed in both the nucleus and the cytoplasm of HL60, K562 cells overexpressing Fes and only in the cytoplasm of COS1 cells, suggesting that nuclear localization is cell context dependent. Moreover, in myeloid cells, the treatment with differentiation-inducing agents such as retinoic acid, phorbol esters and vitamin D, is followed by an increase of the oligomeric form of Fes in the nucleus. In fact, oligomerization seems to be necessary for translocation to occur, since Fes mutants missing the coiled-coil domains are not able to form oligomers and fail to localize in the nucleus. The active form of Fes is tyrosine phosphorylated; however, phosphorylation is not required for Fes to localize in the nucleus, since tyrosine kinase inhibitors do not block the translocation process.

Absence of Fer protein-tyrosine kinase exacerbates leukocyte recruitment in response to endotoxin

The group IV cytoplasmic protein-tyrosine kinase Fer has been linked to cellular signaling responses to many different stimuli, including growth factors and cytokines. However, the biological relevance of Fer activation in vivo has not been demonstrated to date. Recently, we generated a transgenic mouse line in which Fer protein is expressed but lacks catalytic activity. Homozygous mutant mice were viable and fertile, and showed no overt defects. In this study, we used intravital microscopy to examine the role of Fer kinase in leukocyte recruitment (rolling adhesion and emigration) in response to LPS challenge in skeletal muscle microcirculation. In addition, we measured vascular permeability changes (FITC-albumin leakage, venular-to-interstitial space) in response to Ag to examine general endothelial cell function. Local administration of LPS induced decreased leukocyte rolling velocity and increased leukocyte adhesion and emigration in wild-type mice. LPS-induced changes in leukocyte rolling velocity and rolling flux were not significantly different in Fer mutants. However, LPS-induced leukocyte adhesion (23 +/- 3 vs 11 +/- 3 cells/100 microm) and emigration (100 +/- 5 vs 28 +/- 7 cells/field) were significantly elevated in Fer-mutant mice relative to wild-type mice, respectively, suggesting an essential role for the Fer kinase in regulating inflammation-induced leukocyte emigration. Vascular permeability increases in response to Ag were similar between the two groups, indicating that the ability of endothelial cells to retract is intact in the absence of Fer kinase. These data provide the first evidence for a biological role for Fer in regulation of leukocyte recruitment during the innate immune response.

Closing in on the biological functions of Fps/Fes and Fer

Fps/Fes and Fer are the only known members of a distinct subfamily of the non-receptor protein-tyrosine kinase family. Recent studies indicate that these kinases have roles in regulating cytoskeletal rearrangements and inside out signalling that accompany receptor ligand, cell matrix and cell cell interactions. Genetic analysis using transgenic mouse models also implicates these kinases in the regulation of inflammation and innate immunity.