Selective expression of a protein-tyrosine kinase, p56lyn, in hematopoietic cells and association with production of human T-cell lymphotropic virus type I

Coordinated NADPH oxidase/hydrogen peroxide functions regulate cutaneous sensory axon de- and regeneration

Tissue wounding induces cutaneous sensory axon regeneration via hydrogen peroxide (H2O2) that is produced by the epithelial NADPH oxidase, Duox1. Sciatic nerve injury instead induces axon regeneration through neuronal uptake of the NADPH oxidase, Nox2, from macrophages. We therefore reasoned that the tissue environment in which axons are damaged stimulates distinct regenerative mechanisms. Here, we show that cutaneous axon regeneration induced by tissue wounding depends on both neuronal and keratinocyte-specific mechanisms involving H2O2 signaling. Genetic depletion of H2O2 in sensory neurons abolishes axon regeneration, whereas keratinocyte-specific H2O2 depletion promotes axonal repulsion, a phenotype mirrored in duox1 mutants. Intriguingly, cyba mutants, deficient in the essential Nox subunit, p22Phox, retain limited axon regenerative capacity but display delayed Wallerian degeneration and axonal fusion, observed so far only in invertebrates. We further show that keratinocyte-specific oxidation of the epidermal growth factor receptor (EGFR) at a conserved cysteine thiol (C797) serves as an attractive cue for regenerating axons, leading to EGFR-dependent localized epidermal matrix remodeling via the matrix-metalloproteinase, MMP-13. Therefore, wound-induced cutaneous axon de- and regeneration depend on the coordinated functions of NADPH oxidases mediating distinct processes following injury.

Optimization of Indazole-Based GSK-3 Inhibitors with Mitigated hERG Issue and In Vivo Activity in a Mood Disorder Model

Bipolar disorders still represent a global unmet medical need and pose a requirement for novel effective treatments. In this respect, glycogen synthase kinase 3β (GSK-3β) aberrant activity has been linked to the pathophysiology of several disease conditions, including mood disorders. Therefore, the development of GSK-3β inhibitors with good in vivo efficacy and safety profile associated with high brain exposure is required. Accordingly, we have previously reported the selective indazole-based GSK-3 inhibitor 1, which showed excellent efficacy in a mouse model of mania. Despite the favorable preclinical profile, analog 1 suffered from activity at the hERG ion channel, which prevented its further progression. Herein, we describe our strategy to improve this off-target liability through modulation of physicochemical properties, such as lipophilicity and basicity. These efforts led to the potent inhibitor 14, which possessed reduced hERG affinity, promising in vitro ADME properties, and was very effective in a mood stabilizer in vivo model.

Focal adhesion kinase and Src mediate microvascular hyperpermeability caused by fibrinogen- γC- terminal fragments

Objectives

We previously reported microvascular leakage resulting from fibrinogen-γ chain C-terminal products (γC) occurred via a RhoA-dependent mechanism. The objective of this study was to further elucidate the signaling mechanism by which γC induces endothelial hyperpermeability. Since it is known that γC binds and activates endothelial αvβ3, a transmembrane integrin receptor involved in intracellular signaling mediated by the tyrosine kinases FAK and Src, we hypothesized that γC alters endothelial barrier function by activating the FAK-Src pathway leading to junction dissociation and RhoA driven cytoskeletal stress-fiber formation.

Methods and results

Using intravital microscopy of rat mesenteric microvessels, we show increased extravasation of plasma protein (albumin) resulting from γC administration. In addition, capillary fluid filtration coefficient (K_fc) indicated γC-induced elevated lung vascular permeability. Furthermore, γC decreased transendothelial barrier resistance in a time-dependent and dose-related fashion in cultured rat lung microvascular endothelial cells (RLMVECs), accompanied by increased FAK/Src phosphorylation detection by western blot. Experiments with pharmacological inhibition or gene silencing of FAK showed significantly reduced γC-induced albumin and fluid leakage across microvessels, stress-fiber formation, VE-cadherin tyrosine phosphorylation, and improved γC-induced endothelial barrier dysfunction, indicating the involvement of FAK in γC mediated hyperpermeability. Comparable results were found when Src was targeted in a similar manner, however inhibition of FAK prevented Src activation, suggesting that FAK is upstream of Src in γC-mediated hyperpermeability. In addition, γC-induced cytoskeletal stress-fiber formation was attenuated during inhibition or silencing of these tyrosine kinases, concomitantly with RhoA inhibition.

Conclusion

The FAK-Src pathway contributes to γC-induced microvascular barrier dysfunction, junction protein phosphorylation and disorganization in a manner that involves RhoA and stress-fiber formation.

Systematic Immunotherapy Target Discovery Using Genome-Scale In Vivo CRISPR Screens in CD8 T Cells

CD8 T cells play essential roles in anti-tumor immune responses. Here, we performed genome-scale CRISPR screens in CD8 T cells directly under cancer immunotherapy settings and identified regulators of tumor infiltration and degranulation. The in vivo screen robustly re-identified canonical immunotherapy targets such as PD-1 and Tim-3, along with genes that have not been characterized in T cells. The infiltration and degranulation screens converged on an RNA helicase Dhx37. Dhx37 knockout enhanced the efficacy of antigen-specific CD8 T cells against triple-negative breast cancer in vivo. Immunological characterization in mouse and human CD8 T cells revealed that DHX37 suppresses effector functions, cytokine production, and T cell activation. Transcriptomic profiling and biochemical interrogation revealed a role for DHX37 in modulating NF-κB. These data demonstrate high-throughput in vivo genetic screens for immunotherapy target discovery and establishes DHX37 as a functional regulator of CD8 T cells.

Lyn is involved in host defense against S. agalactiae infection and BCR signaling in Nile tilapia (Oreochromis niloticus)

Lyn, a member of Src protein kinase family, plays a crucial role in immune reactions against pathogenic infection. In this study, Lyn from Nile tilapia (Oreochromis niloticus) (OnLyn) was identified and characterized at expression pattern against bacterial infection, and regulation function in BCR signaling. The open reading frame of OnLyn contained 1536 bp of nucleotide sequence encoded a protein of 511 amino acids. The OnLyn protein was highly conversed to other species Lyn, including SH3, SH2 and a catalytic Tyr kinase (TyrKc) domain. Transcriptional expression analysis revealed that OnLyn was detected in all examined tissues and was highly expressed in the head kidney. The up-regulation OnLyn expression was observed in the head kidney and spleen following challenge with Streptococcus agalactiae (S. agalactiae) in vivo, and was also displayed in head kidney leukocytes challenge with S. agalactiae and LPS in vitro. In addition, after induction with mouse anti-OnIgM mAb in vitro, the OnLyn expression and phosphorylation of OnLyn (Y⁵⁰⁷) were significantly up-regulated in the head kidney leukocytes. Moreover, after treatment with AZD0530 and mouse anti-OnIgM monoclonal antibody, the down-regulation of cytoplasmic free-Ca²⁺ concentration was detected in the head kidney leukocytes in vitro. Taken together, the findings of this study revealed that OnLyn might play potential roles in BCR signaling and get involved in host defense against bacterial infection in Nile tilapia.

The Role of Tyrosine Phosphorylation of Protein Kinase C Delta in Infection and Inflammation

Protein Kinase C (PKC) is a family composed of phospholipid-dependent serine/threonine kinases that are master regulators of inflammatory signaling. The activity of different PKCs is context-sensitive and these kinases can be positive or negative regulators of signaling pathways. The delta isoform (PKCδ) is a critical regulator of the inflammatory response in cancer, diabetes, ischemic heart disease, and neurodegenerative diseases. Recent studies implicate PKCδ as an important regulator of the inflammatory response in sepsis. PKCδ, unlike other members of the PKC family, is unique in its regulation by tyrosine phosphorylation, activation mechanisms, and multiple subcellular targets. Inhibition of PKCδ may offer a unique therapeutic approach in sepsis by targeting neutrophil-endothelial cell interactions. In this review, we will describe the overall structure and function of PKCs, with a focus on the specific phosphorylation sites of PKCδ that determine its critical role in cell signaling in inflammatory diseases such as sepsis. Current genetic and pharmacological tools, as well as in vivo models, that are used to examine the role of PKCδ in inflammation and sepsis are presented and the current state of emerging tools such as microfluidic assays in these studies is described.

Lyn, Lupus, and (B) Lymphocytes, a Lesson on the Critical Balance of Kinase Signaling in Immunity

Systemic lupus erythematosus (SLE) is a progressive autoimmune disease characterized by increased sensitivity to self-antigens, auto-antibody production, and systemic inflammation. B cells have been implicated in disease progression and as such represent an attractive therapeutic target. Lyn is a Src family tyrosine kinase that plays a major role in regulating signaling pathways within B cells as well as other hematopoietic cells. Its role in initiating negative signaling cascades is especially critical as exemplified by Lyn-/- mice developing an SLE-like disease with plasma cell hyperplasia, underscoring the importance of tightly regulating signaling within B cells. This review highlights recent advances in our understanding of the function of the Src family tyrosine kinase Lyn in B lymphocytes and its contribution to positive and negative signaling pathways that are dysregulated in autoimmunity.

DCZ3301, a novel cytotoxic agent, inhibits proliferation in diffuse large B-cell lymphoma via the STAT3 pathway

Diffuse large B-cell lymphoma (DLBCL) is the most common type of lymphoma in adults, characterized by a rapidly increasing painless mass. A novel compound, DCZ3301, was synthesized that exerted direct cytotoxicity against DLBCL cell lines. The effects of DCZ3301 on DLBCL cells in vitro and in vivo and the associated mechanisms were investigated. DCZ3301 inhibited the viability of DLBCL cell lines, even in the presence of protumorigenesis cytokines. Additionally, the compound induced apoptosis and cell cycle arrest at the G2/M phase by reducing mitochondrial membrane potential. DCZ3301 exerted an antitumor effect through modulation of Akt, extracellular signal-regulated kinases 1/2 (ERK1/2) and janus kinase 2 (JAK2)/signal transducer and activator of transcription 3 (STAT3) signaling pathways. Furthermore, DCZ3301 downregulates STAT3 phosphorylation by inhibiting Lck/Yes-related novel protein tyrosine kinase (Lyn) activation in DLBCL. A synergistic cytotoxic effect on DLBCL cells was observed upon combination of DCZ3301 with panobinostat. In vivo, intraperitoneal injection of xenograft mice with DCZ3301 resulted in reduced tumor volume. Our preliminary results collectively support the utility of the small-molecule inhibitor DCZ3301 as an effective novel therapeutic option for DLBCL that requires further clinical evaluation.

Selective Targeting of SH2 Domain-Phosphotyrosine Interactions of Src Family Tyrosine Kinases with Monobodies

The binding of Src-homology 2 (SH2) domains to phosphotyrosine (pY) sites is critical for the autoinhibition and substrate recognition of the eight Src family kinases (SFKs). The high sequence conservation of the 120 human SH2 domains poses a significant challenge to selectively perturb the interactions of even the SFK SH2 family against the rest of the SH2 domains. We have developed synthetic binding proteins, termed monobodies, for six of the SFK SH2 domains with nanomolar affinity. Most of these monobodies competed with pY ligand binding and showed strong selectivity for either the SrcA (Yes, Src, Fyn, Fgr) or SrcB subgroup (Lck, Lyn, Blk, Hck). Interactome analysis of intracellularly expressed monobodies revealed that they bind SFKs but no other SH2-containing proteins. Three crystal structures of monobody-SH2 complexes unveiled different and only partly overlapping binding modes, which rationalized the observed selectivity and enabled structure-based mutagenesis to modulate inhibition mode and selectivity. In line with the critical roles of SFK SH2 domains in kinase autoinhibition and T-cell receptor signaling, monobodies binding the Src and Hck SH2 domains selectively activated respective recombinant kinases, whereas an Lck SH2-binding monobody inhibited proximal signaling events downstream of the T-cell receptor complex. Our results show that SFK SH2 domains can be targeted with unprecedented potency and selectivity using monobodies. They are excellent tools for dissecting SFK functions in normal development and signaling and to interfere with aberrant SFK signaling networks in cancer cells.

Human T-cell Lymphotropic Viruses: Review and Prospects for Antiviral Therapy

The human T-cell lymphotropic viruses types I and II (HTLV-I, II) pose challenges to researchers and clinicians who seek to unveil mechanisms of viral transformation and pathogenesis. HTLV-I infection in humans is associated with a wide array of primary and secondary diseases ranging from mild immunosuppression to adult T-cell leukaemia/lymphoma and HTLV-associated myelopathy/tropical spastic paraparesis (HAM/TSP), a neurological degenerative syndrome. As retroviruses, HTLV-I and II share similar replicative cycles with human immunodeficiency virus (HIV), the causative agent of acquired immunodeficiency syndrome. However, in contrast to HIV-I which destroys CD4+ T cells, HTLV-I and II can preferentially transform a CD4+ T-cell subset to an unrestricted growth state.

HTLV-I and II, along with simian T-lymphotropic virus (STLV) and bovine leukaemia virus (BLV), form a phylogenetic group which is distinct from ungulate, non-human primate and human lentiviruses such as visna, simian immunodeficiency virus (SIV), and human immunodeficiency viruses types 1 and 2. The proviral genome of HTLV-I is flanked at the 5′ and 3′ ends by long terminal repeats (LTR) and is further subdivided into structural gag and env genes, a pro gene encoding an aspartyl protease, a pol gene which encodes reverse transcriptase and endonuclease, and the regulatory gene elements tax and rex. Regions within the LTR contain recognition sites for cellular proteins and the tax gene product that collectively promote viral expression. Tax-mediated activation of cellular genes involved in growth and differentiation is suspected to play a dominant role in the leukaemogenic process associated with HTLV-I infection. Differential rex-regulated splicing of viral message gives rise to transcripts encoding the polyprotein precursor gag-pro-pol (unspliced), envelope (single spliced), or tax/rex (doubly spliced). The 100nm HTLV virion contains an electron-dense core surrounding a divalent-single stranded DNA genome. This core is in turn enclosed by concentric shells of matrix protein and an outer lipid bilayer, the latter acquired as the virus buds from the surface of the infected cell. Envelope glycoproteins associated with the outside of this lipid bilayer can interact with viral receptors on cells and mediate virus entry. Antiviral strategies have been directed at inhibiting viral entry into cells (sulphated and non-sulphated polysaccharides, vaccines), blocking of viral replication (AZT, suramin), intracellular immunization (transdominant repression of rex), and elimination of virus infected cells (IL-2 receptor-directed toxins). Serological screening of the blood supply and curtailing breast feeding of children by HTLV-I + mothers have likely had a major impact in preventing HTLV-I infection.

Hit Optimization of 5-Substituted-N-(piperidin-4-ylmethyl)-1H-indazole-3-carboxamides: Potent Glycogen Synthase Kinase-3 (GSK-3) Inhibitors with in Vivo Activity in Model of Mood Disorders

Novel treatments for bipolar disorder with improved efficacy and broader spectrum of activity are urgently needed. Glycogen synthase kinase 3β (GSK-3β) has been suggested to be a key player in the pathophysiology of bipolar disorder. A series of novel GSK-3β inhibitors having the common N-[(1-alkylpiperidin-4-yl)methyl]-1H-indazole-3-carboxamide scaffold were prepared taking advantage of an X-ray cocrystal structure of compound 5 with GSK-3β. We probed different substitutions at the indazole 5-position and at the piperidine-nitrogen to obtain potent ATP-competitive GSK-3β inhibitors with good cell activity. Among the compounds assessed in the in vivo PK experiments, 14i showed, after i.p. dosing, encouraging plasma PK profile and brain exposure, as well as efficacy in a mouse model of mania. Compound 14i was selected for further in vitro/in vivo pharmacological evaluation, in order to elucidate the use of ATP-competitive GSK-3β inhibitors as new tools in the development of new treatments for mood disorders.

Characterization of Novel Src Family Kinase Inhibitors to Attenuate Microgliosis

Microgliosis is a major hallmark of Alzheimer's disease (AD) brain pathology. Aβ peptide is hypothesized to act as a stimulus for microglia leading to activation of non-receptor tyrosine kinases and subsequent secretion of pro-inflammatory cytokines. Therefore, the signaling pathways mediating microglial activation may be important therapeutic targets of anti-inflammatory therapy for AD. Four novel compounds were chosen after high throughput screening kinase activity assays determined them as potential Lyn kinase inhibitors. Their kinase inhibitory and anti-inflammatory effect on Aβ-stimulated activation was assessed using the murine microglial cell line, BV2. Cells were treated with the compounds to determine effects on active, phosphorylated levels of Src family kinases, Src and Lyn, as well as MAP kinases ERK, JNK and p38. Only one compound, LDDN-0003499, produced a dose dependent decrease in basal levels of active, phosphorylated Src and Lyn in the BV2 cells. LDDN-0003499 treatment also attenuated the Aβ-stimulated increase in active, phosphorylated levels of Lyn/Src and TNFα and IL-6 secretion. This study identifies a novel small molecule Src family tyrosine kinase inhibitor with anti-inflammatory effects in response to Aβ stimulation of microglia. Further in vitro/in vivo characterization of LDDN-0003499 as well as structural modification may provide a new tool for attenuating microglial-mediated brain inflammatory conditions such as that occurring in AD.

Macrophage migration inhibitory factor down-regulates the RANKL-RANK signaling pathway by activating Lyn tyrosine kinase in mouse models

OBJECTIVE

Macrophage migration inhibitory factor (MIF) is an important modulator of innate and adaptive immunity as well as local inflammatory responses. We previously reported that MIF down-regulated osteoclastogenesis through a mechanism that requires CD74. The aim of the current study was to examine whether MIF modulates osteoclastogenesis through Lyn phosphorylation, and whether down-regulation of RANKL-mediated signaling requires the association of CD74, CD44, and Lyn.

METHODS

CD74-knockout (CD74-KO), CD44-KO, and Lyn-KO mouse models were used to investigate whether Lyn requires these receptors and coreceptors. The effects of MIF on osteoclastogenesis were assessed using Western blot analysis, small interfering RNA (siRNA)-targeted down-regulation of Lyn, Lyn-KO mice, and real-time imaging of Lyn molecules to surface proteins.

RESULTS

MIF treatment induced Lyn expression, and MIF down-regulated RANKL-induced activator protein 1 (AP-1) and the Syk/phospholipase Cγ cascade during osteoclastogenesis through activated Lyn tyrosine kinase. The results of immunoprecipitation studies revealed that MIF receptors associated with Lyn in response to MIF treatment. Studies using Lyn-specific siRNA and Lyn-KO mice confirmed our findings.

CONCLUSION

Our findings indicate that the tyrosine kinase Lyn is activated when MIF binds to its receptor CD74 and its coreceptor CD44 and, in turn, down-regulates the RANKL-mediated signaling cascade by suppressing NF-ATc1 protein expression through down-regulation of AP-1 and calcium signaling components.

Engineered kinase activation reveals unique morphodynamic phenotypes and associated trafficking for Src family isoforms

The Src kinase family comprises nine homologous members whose distinct expression patterns and cellular distributions indicate that they have unique roles. These roles have not been determined because genetic manipulation has not produced clearly distinct phenotypes, and the kinases' homology complicates generation of specific inhibitors. Through insertion of a modified FK506 binding protein (insertable FKBP12, iFKBP) into the protein kinase isoforms Fyn, Src, Lyn, and Yes, we engineered kinase analogs that can be activated within minutes in living cells (RapR analogs). Combining our RapR analogs with computational tools for quantifying and characterizing cellular dynamics, we demonstrate that Src family isoforms produce very different phenotypes, encompassing cell spreading, polarized motility, and production of long, thin cell extensions. Activation of Src and Fyn led to patterns of kinase translocation that correlated with morphological changes in temporally distinct stages. Phenotypes were dependent on N-terminal acylation, not on Src homology 3 (SH3) and Src homology 2 (SH2) domains, and correlated with movement between a perinuclear compartment, adhesions, and the plasma membrane.

Src family kinases: at the forefront of platelet activation

Src family kinases (SFKs) play a central role in mediating the rapid response of platelets to vascular injury. They transmit activation signals from a diverse repertoire of platelet surface receptors, including the integrin αIIbβ3, the immunoreceptor tyrosine-based activation motif-containing collagen receptor complex GPVI-FcR γ-chain, and the von Willebrand factor receptor complex GPIb-IX-V, which are essential for thrombus growth and stability. Ligand-mediated clustering of these receptors triggers an increase in SFK activity and downstream tyrosine phosphorylation of enzymes, adaptors, and cytoskeletal proteins that collectively propagate the signal and coordinate platelet activation. A growing body of evidence has established that SFKs also contribute to Gq- and Gi-coupled receptor signaling that synergizes with primary activation signals to maximally activate platelets and render them prothrombotic. Interestingly, SFKs concomitantly activate inhibitory pathways that limit platelet activation and thrombus size. In this review, we discuss past discoveries that laid the foundation for this fundamental area of platelet signal transduction, recent progress in our understanding of the distinct and overlapping functions of SFKs in platelets, and new avenues of research into mechanisms of SFK regulation. We also highlight the thrombotic and hemostatic consequences of targeting platelet SFKs.

A balance between B cell receptor and inhibitory receptor signaling controls plasma cell differentiation by maintaining optimal Ets1 levels

Signaling through the BCR can drive B cell activation and contribute to B cell differentiation into Ab-secreting plasma cells. The positive BCR signal is counterbalanced by a number of membrane-localized inhibitory receptors that limit B cell activation and plasma cell differentiation. Deficiencies in these negative signaling pathways may cause autoantibody generation and autoimmune disease in both animal models and human patients. We have previously shown that the transcription factor Ets1 can restrain B cell differentiation into plasma cells. In this study, we tested the roles of the BCR and inhibitory receptors in controlling the expression of Ets1 in mouse B cells. We found that Ets1 is downregulated in B cells by BCR or TLR signaling through a pathway dependent on PI3K, Btk, IKK2, and JNK. Deficiencies in inhibitory pathways, such as a loss of the tyrosine kinase Lyn, the phosphatase Src homology region 2 domain-containing phosphatase 1 (SHP1) or membrane receptors CD22 and/or Siglec-G, result in enhanced BCR signaling and decreased Ets1 expression. Restoring Ets1 expression in Lyn- or SHP1-deficient B cells inhibits their enhanced plasma cell differentiation. Our findings indicate that downregulation of Ets1 occurs in response to B cell activation via either BCR or TLR signaling, thereby allowing B cell differentiation and that the maintenance of Ets1 expression is an important function of the inhibitory Lyn → CD22/SiglecG → SHP1 pathway in B cells.

A critical role for Lyn kinase in strengthening endothelial integrity and barrier function

The Src family kinases (SFKs) c-Src and Yes mediate vascular leakage in response to various stimuli including lipopolysaccharide (LPS) and vascular endothelial growth factor (VEGF). Here, we define an opposing function of another SFK, Lyn, which in contrast to other SFKs, strengthens endothelial junctions and thereby restrains the increase in vascular permeability. Mice lacking Lyn displayed increased mortality in LPS-induced endotoxemia and increased vascular permeability in response to LPS or VEGF challenge compared with wild-type littermates. Lyn knockout mice repopulated with wild-type bone marrow-derived cells have higher vascular permeability than wild-type mice, suggesting a role of endothelial Lyn in the maintenance of the vascular barrier. Small interfering RNA-mediated down-regulation of Lyn disrupted endothelial barrier integrity, whereas expression of a constitutively active mutant of Lyn enhanced the barrier. However, down-regulation of Lyn did not affect LPS-induced endothelial permeability. We demonstrate that Lyn association with focal adhesion kinase (FAK) and phosphorylation of FAK at tyrosine residues 576/577 and 925 were required for Lyn-dependent stabilization of endothelial adherens junctions. Thus, in contrast to c-Src and Yes, which increase vascular permeability in response to stimuli, Lyn stabilizes endothelial junctions through phosphorylation of FAK. Therefore, therapeutics activating Lyn kinase may strengthen the endothelial barrier junction and hence have anti-inflammatory potential.

Molecular identification and expression of Lyn tyrosine kinase isoforms in marsupials

Lyn is a tyrosine kinase molecule required for modulation of signalling cascades in cell populations including B lymphocytes of the mammalian immune system. We have characterised the coding domain of the marsupial lyn gene of two macropod marsupials; the Tammar Wallaby (Macropus eugenii) and the Bridled Nailtail Wallaby (Onychogalea fraenata) and show the co-expression of two Lyn isoforms in cells and tissues of these and three other marsupials (Brush-tail Possum, Trichosurus vulpecula; American Grey Short-tailed Opossum, Monodelphis domestica and Red-tailed Phascogale, Phascogale calura). The predicted Lyn proteins (LynA and LynB) were highly conserved across vertebrate species, with amino acid identities of 94% with their human orthologues and conservation of key tyrosine kinase motifs that suggests that marsupial Lyn most likely functions in cell signalling. Comparison of our cDNA data to annotations for Lyn transcripts (available through the Ensembl Genome Browser) for the Tammar Wallaby confirm splice sites for a number of exons in the wallaby transcript that are missing from the current annotation. This is the first report of the expression of kinase signalling molecules that influence immunity in metatherian mammals and provides key information to support ongoing studies of immune regulation in marsupials.

Interleukin 2-inducible T cell kinase (ITK) facilitates efficient egress of HIV-1 by coordinating Gag distribution and actin organization

Interleukin 2-inducible T cell kinase (ITK) influences T cell signaling by coordinating actin polymerization and polarization as well as recruitment of kinases and adapter proteins. ITK regulates multiple steps of HIV-1 replication, including virion assembly and release. Fluorescent microscopy was used to examine the functional interactions between ITK and HIV-1 Gag during viral particle release. ITK and Gag colocalized at the plasma membrane and were concentrated at sites of F-actin accumulation and membrane lipid rafts in HIV-1 infected T cells. There was polarized staining of ITK, Gag, and actin towards sites of T cell conjugates. Small molecule inhibitors of ITK disrupted F-actin capping, perturbed Gag-ITK colocalization, inhibited virus like particle release, and reduced HIV replication in primary human CD4+ T cells. These data provide insight as to how ITK influences HIV-1 replication and suggest that targeting host factors that regulate HIV-1 egress provides an innovative strategy for controlling HIV infection.

Basophils and autoreactive IgE in the pathogenesis of systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a heterogeneous disease that can affect multiple organs. A hallmark of this disease, as is the case for other autoimmune diseases, is the presence of large numbers of autoantibodies. As such, SLE is considered to be a B-cell disease perpetuated by the expansion of autoreactive T and B cells. The T cells involved have long been considered to be T-helper type 1 (Th1) and Th17 cells, as these potent proinflammatory cells can be found in the tissues of SLE patients. Recent advances point to a role for the Th2 environment in contributing to SLE through promotion of autoantibody production. Here we describe the recent work focusing on autoreactive IgE and the activation of basophils as promoting the production of autoantibodies in SLE. The findings, both in a murine model of SLE and in humans with SLE, support the concept that the activation of the basophil by autoreactive IgE-containing immune complexes serves to amplify the production of autoantibodies and contributes to the pathogenesis of disease. We propose that therapeutic targeting of this amplification loop by reducing the levels of circulating autoreactive IgE may have benefit in SLE.

Association of SRC-related kinase Lyn with the interleukin-2 receptor and its role in maintaining constitutive phosphorylation of JAK/STAT in human T-cell leukemia virus type 1-transformed T cells

Human T-cell leukemia virus type 1 (HTLV-1) infection and transformation are associated with an incremental switch in the expression of the Src-related protein tyrosine kinases Lck and Lyn. We examined the physical and functional interactions of Lyn with receptors and signal transduction proteins in HTLV-1-infected T cells. Lyn coimmunoprecipitates with the interleukin-2 beta receptor (IL-2Rβ) and JAK3 proteins; however, the association of Lyn with the IL-2Rβ and Lyn kinase activity was independent of IL-2 stimulation. Phosphorylation of Janus kinase 3 (JAK3) and signal transducers and activator of transcription 5 (STAT5) proteins was reduced by treatment of cells with the Src kinase inhibitor PP2 or by ectopic expression of a dominant negative Lyn kinase protein.

Involvement of Src family kinase activation in angiotensin II-induced hyperresponsiveness of rat bronchial smooth muscle

Angiotensin II (Ang II) might be an important mediator in pathogenesis of airway hyperresponsiveness (AHR) that is the asthmatic characteristic feature of asthma, although the mechanisms of AHR caused by Ang II are not yet clear. Presently, the RT-PCR analyses revealed that all the Src family kinases (SFKs), such as Fyn, Lck, Lyn, Hck, Src, Yes, Blk, Fgr and Frk, were expressed in the lungs and main bronchi of rats. The phosphorylation (activation) of SFK (Tyr416) was increased in bronchial smooth muscle (BSM) by Ang II. The Ang II-induced SFK phosphorylation was inhibited by pretreatment with SU6656, an SFK inhibitor. The concentration-contraction curves to carbachol (CCh) were shifted to the left in the presence of Ang II. The maximal contraction of CCh was also significantly increased by pretreatment with Ang II. These results indicate that Ang II causes BSM hyperresponsiveness. The Ang II-induced BSM hyperresponsiveness was significantly inhibited by SU6656, although the carbachol (CCh)-induced contraction itself was not changed by SU6656. In conclusion, Ang II induced a BSM hyperresponsiveness through activation of SFK, and might play an important role in pathophysiology of bronchial asthma.

Rhadinovirus vector-derived human telomerase reverse transcriptase expression in primary T cells

The rhadinovirus herpesvirus saimiri (HVS) as a gene delivery vector allows large DNA insertions and long-termed gene expression. In the case of T-cell transduction, such vectors use the viral transformation-associated genes of HVS C488 for T-cell amplification. In this report, we investigated whether the gene for the catalytic telomerase subunit human telomerase reverse transcriptase (hTERT) can substitute for the transformation-associated genes in rhadinoviral T-cell transduction and amplification. By using virus mutants generated by en passant mutagenesis from bacterial artificial chromosomes, we observed a very early and functional transgene expression even by virus mutants without transformation-associated genes. The markers of T-cell transformation by HVS, namely CD2 hyperreactivity, overexpression of interleukin-26, and of the tyrosine kinase Lyn could neither be induced nor enhanced by ectopic hTERT expression. When the viral transformation-associated genes were replaced by the hTERT gene, it was not sufficient for growth transformation, although hTERT was efficiently transduced and functionally expressed by the rhadinovirus vector. Thus, the transformation-associated proteins StpC and Tip are responsible for the T-cell phenotype after transduction by HVS and, additionally, modulate telomerase activity independently of hTERT expression.

Autoimmune disease in Lyn-deficient mice is dependent on an inflammatory environment established by IL-6

Lyn-deficient mice develop Ab-mediated autoimmune disease resembling systemic lupus erythematosus where hyperactive B cells are major contributors to pathology. In this study, we show that an inflammatory environment is established in Lyn(-/-) mice that perturbs several immune cell compartments and drives autoimmune disease. Lyn(-/-) leukocytes, notably B cells, are able to produce IL-6, which facilitates hyperactivation of B and T cells, enhanced myelopoiesis, splenomegaly, and, ultimately, generation of pathogenic autoreactive Abs. Lyn(-/-) dendritic cells show increased maturation, but this phenotype is independent of autoimmunity as it is reiterated in B cell-deficient Lyn(-/-) mice. Genetic deletion of IL-6 on a Lyn-deficient background does not alter B cell development, plasma cell accumulation, or dendritic cell hypermaturation, suggesting that these characteristics are intrinsic to the loss of Lyn. However, hyperactivation of B and T cell compartments, extramedullary hematopoiesis, expansion of the myeloid lineage and autoimmune disease are all ameliorated in Lyn(-/-)IL-6(-/-) mice. Importantly, our studies show that although Lyn(-/-) B cells may be autoreactive, it is the IL-6-dependent inflammatory environment they engender that dictates their disease-causing potential. These findings improve our understanding of the mode of action of anti-IL-6 and B cell-directed therapies in autoimmune and inflammatory disease treatment.

Perturbation of the CD4 T cell compartment and expansion of regulatory T cells in autoimmune-prone Lyn-deficient mice

Regulatory T cells (Tregs) are a subset of T lymphocytes that are responsible for suppressing the function of other immune cells, and preventing potentially harmful autoimmune responses. Studies in autoimmune-prone mice and human autoimmune diseases have shown reduced Treg number or function as a causative factor for the apparent loss of tolerance that contributes to disease. We have found that Lyn-deficient mice, which develop high titers of autoantibodies with age, have a perturbed Treg compartment. Contrary to what has been observed in some strains of autoimmune-prone mice, aged Lyn-deficient mice have increased numbers of Tregs. This expansion occurs in the presence of elevated serum IL-2 and diminished TGF-beta. Despite expansion of the Treg compartment, Lyn-deficient mice succumb at approximately 1 year of age due to immune complex-mediated glomerulonephritis. We have shown that Lyn is not expressed in Tregs or indeed in any T cell subset, suggesting that the expansion and apparent functional deficiency in Tregs in Lyn-deficient mice is due to extrinsic factors rather than an intrinsic Treg defect. Indeed, using an in vivo colitis model, we have shown that Lyn-deficient Tregs can suppress inflammation. These results suggest that Tregs are expanding in Lyn-deficient mice in an effort to control the autoimmune disease but are simply overwhelmed by the disease process. This study highlights the role of the inflammatory setting in autoimmune disease and its consideration when contemplating the use of Tregs as an autoimmune therapy.

Lyn kinase controls basophil GATA-3 transcription factor expression and induction of Th2 cell differentiation

T helper 1 (Th1)-Th2 cell balance is key to host defense and its dysregulation has pathophysiological consequences. Basophils are important in Th2 cell differentiation. However, the factors controlling the onset and extent of basophil-mediated Th2 cell differentiation are unknown. Here, we demonstrate that Lyn kinase dampened basophil expression of the transcription factor GATA-3 and the initiation and extent of Th2 cell differentiation. Lyn-deficient mice had a marked basophilia, a constitutive Th2 cell skewing that was exacerbated upon in vivo challenge of basophils, produced antibodies to a normally inert antigen, and failed to appropriately respond to a Th1 cell-inducing pathogen. The Th2 cell skewing was dependent on basophils, immunoglobulin E, and interleukin-4, but was independent of mast cells. Our findings demonstrate that basophil-expressed Lyn kinase exerts regulatory control on Th2 cell differentiation and function.

New targets and treatments in multiple myeloma: Src family kinases as central regulators of disease progression

Multiple myeloma is a malignant condition that most commonly occurs in the seventh decade of life. Recent improvements in treatment may result in a more favourable outlook for recently diagnosed patients. Multiple myeloma is an incurable clonal B-cell malignancy, which is initially responsive to conventional chemotherapy; one-third of the patients achieve complete remission but multidrug resistance eventually develops. Although autologous stem cell transplantation remains an important option, many older patients are less tolerant to the toxicity associated with conditioning treatment, as well as being intrinsically less likely to do well after transplantation. Most patients eventually relapse with or without transplantation, and salvage therapy is only moderately effective. Thalidomide and subsequently, lenalidomide and bortezomib, have demonstrated improved outcomes for these patients, as well as proving efficacious in front-line regimens. A deeper understanding of the molecular mechanisms underlying multiple myeloma has given rise to novel targeted approaches. This review will focus in particular on Src-dependent signalling pathways, reflecting the expanding realisation of the critical and ubiquitous role of Src family kinases (SFKs) in normal and abnormal hematopoiesis.

MyD88-dependent autoimmune disease in Lyn-deficient mice

Recent evidence suggests that systemic autoimmune disease depends on signals from TLR ligands, but little is known about how TLR-dependent pathways lead to the loss of self tolerance in vivo. To address this, we have examined the role of TLR signaling in Lyn-deficient mice, which develop an autoimmune disease similar to SLE. We found that absence of the TLR signaling adaptor molecule MyD88 suppresses plasma cell differentiation of switched and unswitched B cells, and prevents the generation of antinuclear IgG antibodies and glomerulonephritis. In mixed chimeras the increased IgM and IgG antibody secretion in Lyn-deficient mice is at least partially due to B cell-independent effects of Lyn. We now show that MyD88 deficiency blocks the expansion and activation of DC in which Lyn is also normally expressed, and prevents the hypersecretion of proinflammatory cytokines IL-6 and IL-12 by Lyn-deficient DC. These findings further highlight the important role of TLR-dependent signals in both lymphocyte activation and autoimmune pathogenesis.

Protein tyrosine kinases belonging to the src family

There are nine non-receptor-type protein tyrosine kinases that show a high level of similarity in their primary structures and in the structures of their functional domains. Together, they are called the src family. They seem to have common sites specific for oncogenic activation. Recent findings suggest that the kinases are closely associated with cell surface molecules and that they mediate extracellular signals through the activation of their tyrosine kinase activity. They appear to act more on the differentiated phenotype than in haemopoietic cell proliferation. Possible functions of the products of the lck, fyn, lyn and fgr genes in lymphocytes and monocytes are discussed.

Erlin-1 and erlin-2 are novel members of the prohibitin family of proteins that define lipid-raft-like domains of the ER

Our laboratory was interested in characterizing the molecular composition of non-caveolar lipid rafts. Thus, we generated monoclonal antibodies to lipid raft proteins of human myelomonocytic cells. Two of these proteins, KE04p and C8orf2, were found to be highly enriched in the detergent-insoluble, buoyant fraction of sucrose gradients in a cholesterol-dependent manner. They contain an evolutionarily conserved domain placing them in the prohibitin family of proteins. In contrast to other family members, these two proteins localized to the ER. Furthermore, the extreme N-termini of KE04p and C8orf2 were found to be sufficient for heterologous targeting of GFP to the ER in the absence of classical ER retrieval motifs. We also demonstrate that all prohibitin family members rely on sequences in their extreme N-termini for their distinctive subcellular distributions including the mitochondria, plasma membrane and Golgi vesicles. Owing to their subcellular localization and their presence in lipid rafts, we have named KE04p and C8orf2, ER lipid raft protein (erlin)-1 and erlin-2, respectively. Interestingly, the ER contains relatively low levels of cholesterol and sphingolipids compared with other organelles. Thus, our data support the existence of lipid-raft-like domains within the membranes of the ER.

Lyn kinase promotes erythroblast expansion and late-stage development

Lyn kinase is known to modulate the formation and function of B cells, monocytes, and mast cells. However, Lyn-/- mice also develop erythrosplenomegaly, and cases for both negative and positive erythropoietic actions of Lyn recently have been outlined. In phenylhydrazine-treated Lyn-/- mice, extramedullary splenic erythropoiesis was hyperactivated, but this did not lead to accelerated recovery from anemia. Furthermore, ex vivo analyses of the development of bone marrow-derived Lyn-/- erythroblasts in unique primary culture systems indicated positive roles for Lyn at 2 stages. Late-stage Lyn-/- erythroblasts exhibited deficit Ter119(pos) cell formation, and this was paralleled by increased apoptosis (and decreased Bcl-xL expression). During early development, Lyn-/- erythroblasts accumulated at a Kit(pos)CD71(high) stage, possessed decreased proliferative capacity, and were attenuated in entering an apparent G1/S cell-cycle phase. In proposed compensatory responses, Lyn-/- erythroblasts expressed increased levels of activated Akt and p60-Src and decreased levels of death-associated protein kinase-2. Stat5 activation and Bcl-xL expression, in contrast, were significantly decreased in keeping with decreased survival and developmental potentials. Lyn, therefore, is proposed to function via erythroid cell-intrinsic mechanisms to promote progenitor cell expansion beyond a Kit(pos)CD71(high) stage and to support subsequent late-stage development.

Inhibition of Src Kinases Combined with CD40 Ligand Blockade Prolongs Murine Cardiac Allograft Survival

BACKGROUND

Members of the Src family of tyrosine kinases (SFKs) are requisite signaling molecules activated by multiple receptors during immune responses. Their expression and catalytic activity has not been characterized in allograft rejection in vivo.

METHODS

We measured expression and catalytic activity of SFKs in MHC- mismatched murine cardiac allografts. We also examined the effects of a Src inhibitor (CGP77675) with or without anti-CD154 mAb on graft survival, histology, and expression and catalytic activity of SFKs within the grafts.

RESULTS

In acutely rejecting allografts from untreated controls, total activity of Hck and Lyn increased 10-fold, predominantly reflecting increases in the amount of protein. Total activity of Lck increased only fourfold, reflecting small changes in both the amount of protein and specific activity. One dose of anti-CD154 plus CGP77675 markedly diminished cellular infiltration, but survival was only moderately prolonged despite inhibition of all SFKs in the rejected grafts. Two doses of anti-CD154 plus CGP77675 allowed permanent graft acceptance in 60% of recipients even after discontinuation of the inhibitor. Both rejected and long surviving grafts showed increased activity of all SFKs. Recipients that rejected their grafts showed serum alloantibody production, and grafts rejected during treatment demonstrated deposition of complement indicating the contribution of antibody to rejection.

CONCLUSIONS

The myeloid and B cell Src family kinases, Hck and Lyn, rather than the T cell Src kinase Lck, show the greatest increase in expression and total activity in rejecting allografts. Both rejected and long-surviving grafts show significant increases in SFK expression and acitivity.

Lyn-deficient mice develop severe, persistent asthma: Lyn is a critical negative regulator of Th2 immunity

The etiology of asthma, a chronic inflammatory disorder of the airways, remains obscure, although T cells appear to be central disease mediators. Lyn tyrosine kinase has been implicated as both a facilitator and inhibitor of signaling pathways that play a role in allergic inflammation, although its role in asthma is unclear because Lyn is not expressed in T cells. We show in the present study that Lyn-/- mice develop a severe, persistent inflammatory asthma-like syndrome with lung eosinophilia, mast cell hyperdegranulation, intensified bronchospasm, hyper IgE, and Th2-polarizing dendritic cells. Dendritic cells from Lyn-/- mice have a more immature phenotype, exhibit defective inhibitory signaling pathways, produce less IL-12, and can transfer disease when adoptively transferred into wild-type recipients. Our results show that Lyn regulates the intensity and duration of multiple asthmatic traits and indicate that Lyn is an important negative regulator of Th2 immune responses.

Expression and muscarinic receptor coupling of Lyn kinase in cultured human airway smooth muscle cells

Src family tyrosine kinases are signaling intermediates in a diverse array of cellular events including cell differentiation, motility, proliferation, and survival. In nonairway smooth muscle cells, muscarinic receptors directly interact with Src family tyrosine kinases. As little is known about the expression and signaling of these Src family tyrosine kinases in human airway smooth muscle cells, we determined the expression of Src family members and characterized the muscarinic receptor-mediated activation of Lyn kinase in these cells. RT-PCR revealed mRNA transcripts for FYN, c-SRC, YES, FRK, and LYN. Fyn, c-Src, Yes, and Lyn were identified in cultured airway smooth muscle cells by immunoblot analysis. In both nontransformed human cultured airway smooth muscle cells and cells transduced with wild-type human Lyn kinase, carbachol increased Lyn kinase activity. Pertussis toxin pretreatment failed to block carbachol activation of Lyn kinase but did attenuate the carbachol-induced increase in ERK/MAPK phosphorylation. Moreover, carbachol inhibited adenylyl cyclase but failed to increase total inositol phosphate synthesis in these cells. The present study shows that Lyn kinase is expressed in human cultured airway smooth muscle cells at both the mRNA and protein levels and that carbachol, an M2 muscarinic receptor agonist in these cells, activates Lyn kinase by a pertussis toxin-insensitive signaling pathway.

T-cell transformation and oncogenesis by gamma2-herpesviruses

gamma2-Herpesviruses, also termed rhadinoviruses, have long been known as animal pathogens causing lymphoproliferative diseases such as malignant catarrhal fever in cattle or T-cell lymphoma in certain Neotropical primates. The rhadinovirus prototype is Herpesvirus saimiri (HVS), a T-lymphotropic agent of squirrel monkeys (Saimiri sciureus); Herpesvirus ateles (HVA) is closely related to HVS. The first human rhadinovirus, human herpesvirus type 8 (HHV-8), was discovered a decade ago in Kaposi's sarcoma (KS) biopsies. It was found to be strongly associated with all forms of KS, as well as with multicentric Castleman's disease and primary effusion lymphoma (PEL). Since DNA of this virus is regularly found in all KS forms, and specifically in the spindle cells of KS, it was also termed KS-associated herpesvirus (KSHV). Several simian rhadinoviruses related to KSHV have been discovered in various Old World primates, though they seem only loosely associated with pathogenicity or tumor induction. In contrast, HVS and HVA cause T-cell lymphoma in numerous non-natural primate hosts; HVS strains of the subgroup C are capable of transforming human and simian T-lymphocytes to continuous growth in cell culture and can provide useful tools for T-cell immunology or gene transfer. Here, we describe their natural history, genome structure, biology, and pathogenesis in T-cell transformation and oncogenesis.

Lyn tyrosine kinase: accentuating the positive and the negative

Lyn, one of several Src-family tyrosine kinases in immune cells, is noted for its ability to negatively regulate signaling pathways through phosphorylation of inhibitory receptors, enzymes, and adaptors. Somewhat paradoxically, it is also a key mediator in several pathways of B cell activation, such as CD19 and CD180. Whether Lyn functions to promote or inhibit immune cell activation depends on the stimulus and the developmental state, meaning that the consequences of Lyn activity are context dependent. The importance of regulating Lyn activity is exemplified by the pathological conditions that develop in both lyn-/- and lyn gain-of-function mice (lynup/up), including lethal antibody-mediated autoimmune diseases and myeloid neoplasia. Here, we review the outcomes of altered Lyn activity within the framework of B cell development and differentiation and the circumstances that appear to dictate the outcome.

Activation of Src kinase Lyn by the Kaposi sarcoma-associated herpesvirus K1 protein: implications for lymphomagenesis

The K1 gene of Kaposi sarcoma-associated herpesvirus (KSHV) encodes a transmembrane glycoprotein bearing a functional immunoreceptor tyrosine-based activation motif (ITAM). Previously, we reported that the K1 protein induced plasmablastic lymphomas in K1 transgenic mice, and that these lymphomas showed enhanced Lyn kinase activity. Here, we report that systemic administration of the nuclear factor kappa B (NF-kappaB) inhibitor Bay 11-7085 or an anti-vascular endothelial growth factor (VEGF) antibody significantly reduced K1 lymphoma growth in nude mice. Furthermore, in KVL-1 cells, a cell line derived from a K1 lymphoma, inhibition of Lyn kinase activity by the Src kinase inhibitor PP2 decreased VEGF induction, NF-kappaB activity, and the cell proliferation index by 50% to 75%. In contrast, human B-cell lymphoma BJAB cells expressing K1, but not the ITAM sequence-deleted mutant K1, showed a marked increase in Lyn kinase activity with concomitant VEGF induction and NF-kappaB activation, indicating that ITAM sequences were required for the Lyn kinase-mediated activation of these factors. Our results suggested that K1-mediated constitutive Lyn kinase activation in K1 lymphoma cells is crucial for the production of VEGF and NF-kappaB activation, both strongly implicated in the development of KSHV-induced lymphoproliferative disorders.

Autocrine stimulation of rhadinovirus-transformed T cells by the chemokine CCL1/I-309

The rhadinovirus herpesvirus saimiri transforms human T lymphocytes to stable growth in culture. Besides the viral oncogenes stpC and tip, little is understood about the transformation process at the cellular level. To identify cellular factors that might contribute to growth transformation, we compared cellular gene expression in pairs of herpesvirus saimiri-transformed and nontransformed human T-cell clones. Using cDNA arrays and suppressive subtractive hybridization, we were able to identify the chemokine CCL1/I-309 as one of the few cellular genes that are strongly overexpressed in T cells after growth transformation with herpesvirus saimiri. The transformed T cells expressed CCR8, the receptor for CCL1, which rapidly induced intracellular calcium ion levels. Neutralizing antibodies to CCL1 led to reduced secretion of interferon-gamma and tumor necrosis factor-alpha as well as to reduced proliferation rates in transformed T cells. Thus, we propose that growth transformation of human T cells with herpesvirus saimiri gives rise to an autocrine loop where the proliferation of transformed T cells is supported by the endogenous production of the chemokine CCL1.

Abrogation of autoimmune disease in Lyn-deficient mice by the deletion of IL-5 receptor alpha chain gene

Lyn, the src-family protein tyrosine kinase, plays a crucial role in the regulation of B cell antigen receptor (BCR)- and IL-5-receptor (IL-5R)-mediated signaling. Lyn-deficient mice have been reported to exhibit an increase in B-1 cell numbers, splenomegaly and accumulation of lymphoblast-like cells in the spleen with age, resulting in hyperimmunoglobulinemia and glomerulonephritis caused by the deposition of autoantibody complexes. To elucidate the role of IL-5 in B-1 cell activation, autoantibody production and autoimmune diseases, Lyn-deficient mice were crossed with IL-5Ralpha chain (IL-5Ralpha)-deficient mice and generated Lyn- and IL-5Ralpha-deficient (DKO) mice. In contrast to Lyn-deficient mice, DKO mice showed significantly reduced splenomegaly and lymphoadenopathy and reduced B-1 cell number in the peritoneal cavity. DKO mice also secreted low levels of IgM and IgG autoantibodies. Biochemical and histological analyses revealed that DKO mice showed milder pathogenesis of autoimmune-like disorders than Lyn-deficient mice. These results suggest involvement of IL-5 in enhanced B-1 cell activation, autoantibody production, and development of autoimmune disease in Lyn-deficient mice.

LynIs a Target Gene for Prostate Cancer

The Src-related protein kinase Lyn plays an important role in B-cell activation. However, several lines of evidence suggest that it is also involved in the control of cellular proliferation and the inhibition of apoptosis. We have discovered that Lyn is expressed in normal prostate epithelia, in 95% of primary human prostate cancer (PC) specimens examined, and in all of the PC cell lines that we assayed. Moreover, Lyn knockout mice display abnormal prostate gland morphogenesis, which suggests that Lyn plays an important role in prostate epithelium development and implies that Lyn is a candidate target for specific therapy for PC. Using a drug-design strategy to construct sequence-based peptide inhibitors, a Lyn-specific inhibitor, KRX-123, targeting a unique interaction site within Lyn, was synthesized. KRX-123 was found to inhibit cellular proliferation in three hormone-refractory PC cell lines, DU145, PC3, and TSU-Pr1 with IC(50) values of 2-4 micro M. In vivo, tumor volume of DU145 explants in nude mice was significantly reduced after once-a-week injections of KRX-123, at a dose of 10 mg/kg, for a period of 5 weeks. Histological analyses of the treated tumors indicated extensive apoptosis. Thus, we suggest that Lyn inhibition may serve as a prime target for the treatment of hormone-refractory PC.

Impairment of N-methyl-D-aspartate receptor-controlled motor activity in LYN-deficient mice

The N-methyl-D-aspartate (NMDA) receptor, an ionotropic glutamate receptor, is implicated in motor activity that is regulated in the striatum and nucleus accumbens of the brain. A Src family kinase Lyn is highly expressed in striatum, cortex, thalamus, and cerebellum in the brain. Here we show that spontaneous motor activity is suppressed in lyn-/- mice. S.c. injection of methylphenidate, which causes accumulation of dopamine in synapses, reveals that dopaminergic pathway is normal in lyn-/- mice. After blocking the NMDA receptor, motor activity of lyn-/- mice increased to the same level as that of wild type mice. Therefore, the NMDA receptor-mediated signaling is enhanced in lyn-/- mice, indicating that Lyn regulates the NMDA receptor pathway negatively. Intriguingly, the activity of protein kinase C (PKC), an enzyme regulated downstream of NMDA receptors, is increased in lyn-/- mice. The present data suggest that the NMDA receptor signal that is enhanced in the absence of Lyn suppresses the motor activity, probably through inhibition of dopaminergic pathway at striatum. We conclude that Lyn contributes to coordination of motor activity through regulation of the NMDA pathway. It appears that this negative regulation involves suppression of downstream signaling of NMDA receptor such as those mediated by PKC.

The FcR gamma subunit and Syk kinase replace the CD3 zeta-chain and ZAP-70 kinase in the TCR signaling complex of human effector CD4 T cells

The TCR-mediated signals required to activate resting T cells have been well characterized; however, it is not known how TCR-coupled signals are transduced in differentiated effector T cells that coordinate ongoing immune responses. Here we demonstrate that human effector CD4 T cells up-regulate the expression of the CD3zeta-related FcRgamma signaling subunit that becomes part of an altered TCR/CD3 signaling complex containing CD3epsilon, but not CD3zeta. The TCR/CD3/FcRgamma complex in effector cells recruits and activates the Syk, but not the ZAP-70, tyrosine kinase. This physiologic switch in TCR signaling occurs exclusively in effector, and not naive or memory T cells, suggesting a potential target for manipulation of effector responses in autoimmune, malignant, and infectious diseases.

Essential role of Src-family protein tyrosine kinases in NF-kappaB activation during B cell development

The nature of signals that govern the development of immunoglobulin heavy chain-dependent B cells is largely unknown. Using mice deficient for the B cell-expressed Src-family protein tyrosine kinases (SFKs) Blk, Fyn and Lyn, we show an essential role of these kinases in pre-B cell receptor (pre-BCR)- mediated NF-kappaB activation and B cell development. This signaling defect is SFK specific, as a deficiency in Syk, which controls pre-B cell development, does not affect NF-kappaB induction. Impaired NF-kappaB induction was overcome by the activation of protein kinase C (PKC)-lambda, thus suggesting the involvement of PKC-lambda in pre-BCR-mediated SFK-dependent activation of NF-kappaB. Our data show the existence of a functionally distinct SFK signaling module responsible for pre-BCR-mediated NF-kappaB activation and B cell development.

Crosstalk between BCR/ABL oncoprotein and CXCR4 signaling through a Src family kinase in human leukemia cells

Stromal-derived factor (SDF)-1 and its G protein-coupled receptor, CXCR4, regulate stem/progenitor cell migration and retention in the marrow and are required for hematopoiesis. We show here an interaction between CXCR4 and the Src-related kinase, Lyn, in normal progenitors. We demonstrate that CXCR4-dependent stimulation of Lyn is associated with the activation of phosphatidylinositol 3-kinase (PI3-kinase). This chemokine signaling, which involves a Src-related kinase and PI3-kinase, appears to be a target for BCR/ABL, a fusion oncoprotein expressed only in leukemia cells. We show that the binding of phosphorylated BCR/ABL to Lyn results in the constitutive activation of Lyn and PI3-kinase, along with a total loss of responsiveness of these kinases to SDF-1 stimulation. Inhibition of BCR/ABL tyrosine kinase with STI571 restores Lyn responsiveness to SDF-1 signaling. Thus, BCR/ABL perturbs Lyn function through a tyrosine kinase-dependent mechanism. Accordingly, the blockade of Lyn tyrosine kinase inhibits both BCR/ABL-dependent and CXCR4-dependent cell movements. Our results demonstrate, for the first time, that Lyn-mediated pathological crosstalk exists between BCR/ABL and the CXCR4 pathway in leukemia cells, which disrupts chemokine signaling and chemotaxis, and increases the ability of immature cells to escape from the marrow. These results define a Src tyrosine kinases-dependent mechanism whereby BCR/ABL (and potentially other oncoproteins) dysregulates G protein-coupled receptor signaling and function of mammalian precursors.

Requirements of src family kinase activity associated with CD45 for myeloma cell proliferation by interleukin-6

Specific intracellular signals mediated by interleukin-6 (IL-6) receptor complexes, such as signal transducer and activator of transcription 3 (STAT 3) and extracellular signal-regulated kinase (ERK) 1/2, are considered to be responsible for inducing a variety of cellular responses. In multiple myeloma, IL-6 only enhanced the proliferation of CD45+ tumor cells that harbored the IL-6-independent activation of src family kinases even though STAT3 and ERK1/2 could be activated in response to IL-6 in both CD45+ and CD45(minus sign) cells. Furthermore, the IL-6-induced proliferation of CD45+ U266 myeloma cells was significantly suppressed by Lyn-specific antisense oligodeoxynucleotides or a selective src kinase inhibitor. These results indicate that the activation of both STAT3 and ERK1/2 is not enough for IL-6-induced proliferation of myeloma cell lines that require src family kinase activation independent of IL-6 stimulation. Thus, the activation of the src family kinases associated with CD45 expression is a prerequisite for the proliferation of myeloma cell lines by IL-6. We propose a mechanism for IL-6-induced cell proliferation that is strictly dependent upon the cellular context in myelomas.

Increased severity of experimental allergic encephalomyelitis in lyn-/- mice in the absence of elevated proinflammatory cytokine response in the central nervous system

lyn, a member of the src kinase family, is an important signaling molecule in B cells. lyn(-/-) mice display hyperactive B-1 cells and IgM hyperglobulinemia. The role of lyn on T cell function and development of Th1-mediated inflammatory disease is not known. Therefore, we examined the effect of disruption of the lyn gene on the development of experimental allergic encephalomyelitis (EAE), a well-established Th1-mediated autoimmune disease. Following immunization with myelin oligodendrocyte protein (MOG) p35-55, lyn(-/-) mice had higher clinical and pathological severity scores of EAE when compared with wild type (WT). The increase in the severity of EAE in lyn(-/-) mice was not associated with a commensurate increase in the production of proinflammatory cytokines in the CNS. lyn(-/-) mice with EAE showed elevation in serum anti-IgM MOG Ab levels over that seen in WT mice, along with a modest increase in the mRNA levels of complement C5 and its receptor, C5aR, in the spinal cord. Transfer of serum from MOG-immunized lyn(-/-) mice worsened EAE in WT mice, suggesting a pathogenic role for anti-MOG IgM Abs in EAE. These observations underscore the potential role of lyn in regulation of Th1-mediated disease and the role of autoantibodies and complement in the development of EAE.

BANK regulates BCR-induced calcium mobilization by promoting tyrosine phosphorylation of IP(3) receptor

B-cell activation mediated through the antigen receptor is dependent on activation of protein tyrosine kinases (PTKs) such as Lyn and Syk and subsequent phosphorylation of various signaling proteins. Here we report on the identification and characterization of the B-cell scaffold protein with ankyrin repeats (BANK), a novel substrate of tyrosine kinases. BANK is expressed in B cells and is tyrosine phosphorylated upon B-cell antigen receptor (BCR) stimulation, which is mediated predominantly by Syk. Overexpres sion of BANK in B cells leads to enhancement of BCR-induced calcium mobilization. We found that both Lyn and inositol 1,4,5-trisphosphate receptor (IP(3)R) associate with the distinct regions of BANK and that BANK promotes Lyn-mediated tyrosine phosphorylation of IP(3)R. Given that IP(3)R channel activity is up-regulated by its tyrosine phosphorylation, BANK appears to be a novel scaffold protein regulating BCR-induced calcium mobilization by connecting PTKs to IP(3)R. Because BANK expression is confined to functional BCR-expressing B cells, BANK-mediated calcium mobilization may be specific to foreign antigen-induced immune responses rather than to signaling required for B-cell development.