Tyrosine Kinase Btk Research Articles

Tyrosine kinase Btk regulates E-selectin–mediated integrin activation and neutrophil recruitment by controlling phospholipase C (PLC) γ2 and PI3Kγ pathways

AbstractSelectins mediate leukocyte rolling, trigger β2-integrin activation, and promote leukocyte recruitment into inflamed tissue. E-selectin binding to P-selectin glycoprotein ligand 1 (PSGL-1) leads to activation of an immunoreceptor tyrosine-based activation motif (ITAM)–dependent pathway, which in turn activates the spleen tyrosine kinase (Syk). However, the signaling pathway linking Syk to integrin activation after E-selectin engagement is unknown. To identify the pathway, we used different gene-deficient mice in autoperfused flow chamber, intravital microscopy, peritonitis, and biochemical studies. We report here that the signaling pathway downstream of Syk divides into a phospholipase C (PLC) γ2– and phosphoinositide 3-kinase (PI3K) γ–dependent pathway. The Tec family kinase Bruton tyrosine kinase (Btk) is required for activating both pathways, generating inositol-3,4,5-trisphosphate (IP3), and inducing E-selectin–mediated slow rolling. Inhibition of this signal-transduction pathway diminished Gαi-independent leukocyte adhesion to and transmigration through endothelial cells in inflamed postcapillary venules of the cremaster. Gαi-independent neutrophil recruitment into the inflamed peritoneal cavity was reduced in Btk−/− and Plcg2−/− mice. Our data demonstrate the functional importance of this newly identified signaling pathway mediated by E-selectin engagement.

A genetically determined, serine-based and phosphorylation-dependent molecular switch regulates the anti-inflammatory potential of human IgA (87.34)

Abstract Monteiro and colleagues have suggested dual roles for FcαRI in immune regulation through tyrosine-based “inhibitory/activating” mechanisms mediated by the immunoreceptor tyrosine-based activation motif (ITAM) in the Fc receptor γ-chain (FcRγ) [Pasquier et al., Immunity 2005, 22(1)]. We report a second mechanism in which the natural S248G variants of the FcαRI α-chain alter the inflammatory capacity of FcαRI and constitute a serine-based, genetically determined switch for regulation of the anti-inflammatory potential of human IgA. To elucidate the basis for this α-chain mechanism, we sought allele-specific FcαRI-associated molecules. Sab (SH3-domain binding protein that preferentially associates with Btk), a trans-inhibitor of Bruton's tyrosine kinase (Btk), is recruited by the common Ser248 allele in a phosphorylation-dependent fashion, whereas the protein tyrosine kinase Lyn is reciprocally recruited by the Gly248 variant. Compared to FcαRI Gly248, recruitment of Sab by FcαRI Ser248 results in inhibition of Btk activation and suppression of IgA effector functions independent of FcRγ-pairing. Expression of dominant negative Sab releases FcαRI-mediated inhibition in a Ser248-allele specific manner. These findings suggest an immunoreceptor serine-based inhibition motif (ISIM) which functions as a molecular switch for receptor induced activation/inhibition and advances our understanding of the divergent properties of human IgA in inflammation.

Absence of Tec family kinases Itk and Btk significantly impairs FcϵRI dependent mast cell responses (86.26)

Abstract While the etiology of asthma can be multi factorial, signaling through the IgE receptor (Fcϵ receptor I) on mast cells is critical to its onset. The Tec family tyrosine kinases ITK and BTK serve important roles as signal amplifiers downstream of the FcϵRI, however, their individual contribution to FcϵRI signaling has not been fully established. We have generated Itk and Btk double deficient (DKO) mice in an effort to determine the relative role of Itk and Btk to FcϵRI signaling in mast cells. Analyses of skin mast cells from these mice revealed reduced mast cell granule content and density. However, in vitro cultured bone marrow derived mast cells (BMMCs) had normal gross morphology and granule density. Mast cell histamine release was also compromised in DKO mice, likely associated with elevated endogenous IgE expression in these mice. In vitro growth analysis indicated that Btk negatively regulates BMMC growth as previously published, while the absence of both Itk/Btk did not further contribute to this phenotype. However, there was a significant reduction in FcϵRI mediated calcium responses, accompanied by reduced phosphorylation of PLCγ2 and the mitogen activated protein kinase p38. Lastly, a reduction in the production of several cytokines was also observed in DKO BMMCs. Our results suggest that Itk and Btk have redundant, complementary, and unique functions in mast cell FcϵRI signaling that could be pharmacologically manipulated to treat asthma.

BCR mediated c-Rel induction facilitates NF-κB2 and RelB expression (84.22)

Abstract B cell receptor (BCR) and B cell activating factor receptor (BAFF-R) signaling are critical for the generation of mature splenic B cells. BCR expressing Transitional type 1 (T1) cells migrate from the bone marrow to the spleen where they must successfully pass BCR mediated checkpoints to become Transitional type 2 (T2) cells and subsequently mature follicular B (FoB) cells. T1 and T2 cells are fundamentally different in their response to BCR or BAFF-R stimulation; T1 cells do not survive whereas T2 cells do when triggered through BCR or BAFF-R. Our results demonstrate that Bruton’s tyrosine kinase (Btk) plays a critical role in both BCR and BAFF-R mediated T2 and mature B cell survival. These results suggest that a potential mechanism that provides T2 cells with a survival advantage is their ability to sustain c-Rel expression in response to BCR engagement via mechanisms involving Btk. The increased c-Rel expression coincides precisely with the up-regulation of anti-apoptotic members of the Bcl-2 family as well as BAFF-R and its substrate p100 (NF-κB2). Thus, BCR indirectly enhances the survival function of BAFF-R in part through c-Rel. Consistent with a supporting role for BCR/c-Rel signaling in the activation of alternative NF-κB pathway, c-Rel-deficient B cells are impaired for BCR-induced expression of p100 as well as RelB.

B cell–specific lentiviral gene therapy leads to sustained B-cell functional recovery in a murine model of X-linked agammaglobulinemia

AbstractThe immunodeficiency disorder, X-linked agammaglobulinemia (XLA), results from mutations in the gene encoding Bruton tyrosine kinase (Btk). Btk is required for pre-B cell clonal expansion and B-cell antigen receptor signaling. XLA patients lack mature B cells and immunoglobulin and experience recurrent bacterial infections only partially mitigated by life-long antibody replacement therapy. In pursuit of definitive therapy for XLA, we tested ex vivo gene therapy using a lentiviral vector (LV) containing the immunoglobulin enhancer (Eμ) and Igβ (B29) minimal promoter to drive B lineage–specific human Btk expression in Btk/Tec−/− mice, a strain that reproduces the features of human XLA. After transplantation of EμB29-Btk-LV–transduced stem cells, treated mice showed significant, albeit incomplete, rescue of mature B cells in the bone marrow, peripheral blood, spleen, and peritoneal cavity, and improved responses to T-independent and T-dependent antigens. LV-treated B cells exhibited enhanced B-cell antigen receptor signaling and an in vivo selective advantage in the peripheral versus central B-cell compartment. Secondary transplantation showed sustained Btk expression, viral integration, and partial functional responses, consistent with long-term stem cell marking; and serial transplantation revealed no evidence for cellular or systemic toxicity. These findings strongly support pursuit of B lineage–targeted LV gene therapy in human XLA.

X-linked agammaglobulinemia in a 10-year-old boy with a novel non-invariant splice-site mutation in Btk gene

X-linked agammaglobulinemia (XLA) is a primary immunodeficiency disease caused by mutations in the gene coding for Bruton's tyrosine kinase (Btk). Most XLA patients have severely reduced or absent peripheral blood B cells and serum immunoglobulins, since the expression or function of Btk, critical for the maturation of B cell lineages at pro-B and pre-B cell stages, is deficient. Early and accurate diagnosis of XLA is important, since the affected patients suffer from severe and recurrent infections unless they receive intravenous immunoglobulin (IVIG) replacement therapy. However, the diagnosis of XLA is not always easy because some patients have detectable (∼ 2%) B cells in the peripheral blood and have significant levels of serum immunoglobulins. In this study, we report on a patient who was diagnosed with XLA at the age of 10 years. The diagnosis was delayed due to near-normal levels of serum immunoglobulins, although he presented with severe and recurrent bacterial infections since the age of 1 year. He was demonstrated to have a novel non-invariant splice-site mutation in intron 10 (IVS10 − 11C → A) of the Btk gene, which was not detected by the standard PCR-based mutation analysis. This mutation resulted in no detectable Btk expression. This case suggests that patients suffering from severe or recurrent bacterial infection should be suspected to have XLA even though they may have significant levels of serum immunoglobulins. Furthermore, significant levels of serum immunoglobulins in XLA patients do not necessarily mean less severe phenotype.

Augmented B Lymphocyte Response to Antigen in the Absence of Antigen-Induced B Lymphocyte Signaling in an IgG-Transgenic Mouse Line

IgG-containing B cell antigen receptor (IgG-BCR), the BCR mostly expressed on memory B cells, contains a distinct signaling function from IgM-BCR or IgD-BCR expressed on naïve B cells. Because naïve B cells transgenic for IgG exhibit augmented response to antigens similar to memory B cells, the distinct signaling function of IgG-BCR appears to play a role in augmented antibody responses of memory B cells. However, how IgG-BCR signaling augments B cell responses is not yet well understood. Here we demonstrate that B cells from IgG-transgenic mice are anergic with defect in generation of BCR signaling upon BCR ligation. However, these IgG-transgenic B cells generate markedly augmented antibody response to a T cell-dependent antigen, probably due to hyper-responsiveness to a T cell-derived signal through CD40. Both BCR signaling defect and augmented response to CD40 ligation are partially restored in xid IgG-transgenic mice in which BCR signaling is down-modulated due to a loss-of-function mutation in the tyrosine kinase Btk crucial for BCR signaling. Thus, IgG-BCR induces augmented B cell responses in the absence of antigen-induced BCR signaling probably through high ligand-independent BCR signaling that may “idle” B cells to make them ready to respond to T cell help. This finding strongly suggests a crucial role of ligand-independent signaling in receptor function.

Constitutive Activity of the Human TRPML2 Channel Induces Cell Degeneration

The mucolipin (TRPML) ion channel proteins represent a distinct subfamily of channel proteins within the transient receptor potential (TRP) superfamily of cation channels. Mucolipin 1, 2, and 3 (TRPML1, -2, and -3, respectively) are channel proteins that share high sequence homology with each other and homology in the transmembrane domain with other TRPs. Mutations in the TRPML1 protein are implicated in mucolipidosis type IV, whereas mutations in TRPML3 are found in the varitint-waddler mouse. The properties of the wild type TRPML2 channel are not well known. Here we show functional expression of the wild type human TRPML2 channel (h-TRPML2). The channel is functional at the plasma membrane and characterized by a significant inward rectification similar to other constitutively active TRPML mutant isoforms. The h-TRPML2 channel displays nonselective cation permeability, which is Ca(2+)-permeable and inhibited by low extracytosolic pH but not Ca(2+) regulated. In addition, constitutively active h-TRPML2 leads to cell death by causing Ca(2+) overload. Furthermore, we demonstrate by functional mutation analysis that h-TRPML2 shares similar characteristics and structural similarities with other TRPML channels that regulate the channel in a similar manner. Hence, in addition to overall structure, all three TRPML channels also share common modes of regulation.

Lysine Acetylation Regulates Bruton’s Tyrosine Kinase in B Cell Activation

Bruton's tyrosine kinase (Btk) is essential for BCR signal transduction and has diverse functions in B cells. Although Btk has been extensively studied, the role of lysine acetylation in Btk regulation has not been reported. In this study, we show that BCR cross-linking induces histone lysine acetylation at the Btk promoter, correlating with marked recruitment of histone acetyltransferase E1A-associated 300-kDa protein (p300) to the locus. These effects enhance Btk promoter activity and increase the expression of Btk mRNA and protein. Consistent with these results, activated B cells display increased p300 expression and total histone acetyltransferase activity in vitro and in vivo, resulting in global histone acetylation. Interestingly, we found that BCR signaling induces Btk lysine acetylation mediated by p300. Moreover, lysine acetylation of Btk promotes its phosphorylation. Together, our results indicate a novel regulatory mechanism for Btk transcription and reveal a previously unrecognized posttranslational modification of the Btk protein and its association with phosphorylation in B cell activation.

A Phase I Dose Escalation Study of the Btk Inhibitor PCI-32765 in Relapsed and Refractory B Cell Non-Hodgkin Lymphoma and Use of a Novel Fluorescent Probe Pharmacodynamic Assay.

Abstract 3713Poster Board III-649 IntroductionB-cell receptor (BCR) signaling contributes to the growth of several types of B-cell non-Hodgkin lymphoma (NHL), and recent reports suggest there is clinical utility to targeting this pathway. Bruton's tyrosine kinase (Btk) is an important downstream mediator of BCR signaling as evidenced by genetic mutations in Btk that cause X-linked agammaglobulinemia, a B-cell specific immunodeficiency disease. PCI-32765 is an oral, potent and selective covalent inhibitor of Btk which blocks BCR signaling and inhibits tumor growth in both mouse and spontaneous canine NHL models. Here we report preliminary results of the first-in-human study with this novel agent. Patients and MethodsIn this Phase I dose escalation trial, patients with relapsed or refractory B-cell NHL are being enrolled in cohorts of 6 patients each, with predefined criteria for dose escalation from 1.25 mg/kg/day in cohort 1 to 17.5 mg/kg/day in cohort 6. Dose escalation proceeds if ≤1 patient experiences dose limiting toxicity (DLT). Each cycle includes 28 days of therapy followed by a 7 day observation period. Response assessments occur every 2 cycles, and patients without disease progression or DLT may receive a maximum of 6 cycles. The primary objectives are to determine the safety, pharmacokinetics (PK), and pharmacodynamic (PD) responses. The secondary objective is to evaluate tumor responses. The PD assays include a test for drug occupancy of Btk using a novel fluorescent probe derived from PCI-32765. The probe is added to peripheral blood mononuclear cell (PBMC) lysates ex vivo and probe-labeled Btk is visualized by fluorescent gel scanning. Because the probe binds to Btk at the same site as the drug, occupancy of Btk by PCI-32765 can be detected by the inhibition of probe labeling. The probe assay and other cell signaling assays are used to monitor target inhibition in patient blood samples collected pre-dose on days 1, 2, 8, 15, and 29 and at 4 hours after dosing on days 1 and 8. In the absence of DLTs, dose escalation will proceed to three cohorts above the dose level that achieves >90% occupancy of Btk by PCI-32765. ResultsThe study is currently open and enrolling. Seven patients (1 DLBCL, 2 MCL, 4 FL) with a median of 3 prior therapies have been enrolled in the first cohort (one more patient than originally planned). Therapy has been extremely well tolerated with no DLT or greater than grade 2 hematological or non- hematologic toxicity. Six patients have completed at least 1 cycle. PD studies showed the average drug occupancy of Btk in patient PBMCs in this cohort was 89% at 4 hours post-dose and 77% at 24 hours post-dose. Ex vivo stimulation assays showed near complete functional inhibition of the FcεRI signaling pathway in basophils and significant inhibition of the BCR pathway. T-cell responses were not affected, and no significant depletion of peripheral blood B, T or NK cell counts was observed. Two of 7 patients have stable disease (65 days and 135 days), 3 patients are not yet evaluable for response, and 2 have progressed. ConclusionPCI-32765 is a novel agent which targets Btk and appears to be well tolerated. The unique PD endpoint suggests high levels of Btk inhibition even at the lowest dosing cohort. Dose escalation to subsequent cohorts is ongoing. Disclosures:Smith:Pharmacyclics: Research Funding. Fowler:Pharmacyclics: Research Funding. Boyd:Pharmacyclics: Research Funding. Smith:Pharmacyclics: Employment, Equity Ownership. Sirisawad:Pharmacyclics: Employment, Equity Ownership. Honigberg:Pharmacyclics: Employment, Equity Ownership. Hamdy:Pharmacyclics: Employment, Equity Ownership. Advani:Pharmacyclics: Research Funding.

Clinical Characteristics and Genotype-phenotype Correlation in 62 Patients with X-linked Agammaglobulinemia

X-linked agammagobulinemia (XLA) is a primary immunodeficiency disorder caused by Bruton's tyrosine kinase (Btk) gene mutation. Recent studies suggested genotype-phenotype correlation in XLA, but a definitive association remains controversial. We examined the relationship between specific Btk gene mutations and severity of clinical presentation in 62 patients with XLA. Disease severity was assessed by the age of disease onset and the presence of severe infections, while mutations were classified into severe and mild based on structural and functional consequence by bioinformatics analysis. Fifty-six Btk mutations were identified in 62 patients from 57 kindreds. Variation in phenotypes was observed, and there was a tendency of association between genotype and age of disease onset as well as occurrence of severe infections. A critical analysis of the circumstances upon presentation also revealed that under-recognition of recurrent infections and relevant family history are important hurdles to timely diagnosis of XLA.

IL-5- and eosinophil-mediated inflammation: from discovery to therapy

IL-5 was originally defined as a T-cell-derived cytokine that triggers activated B cells for terminal differentiation into antibody-secreting plasma cells, at least in mice. Concurrently, IL-5 was recognized as the major maturation and differentiation factor for eosinophils in mice and humans. Over-expression of IL-5 significantly increases eosinophil numbers and antibody levels in vivo. Conversely, mice lacking a functional gene for IL-5 or the IL-5 receptor alpha chain (IL-5Ralpha) display a number of developmental and functional impairments in B-cell and eosinophil lineages. In addition to the Janus kinase-signal transducer and activator of transcription pathway, the tyrosine kinases Lyn and Btk (Bruton agammaglobulinemia tyrosine kinase) are involved, and Ras GTPase-extracellular signal-regulated kinase (Ras-ERK) signals are important for IL-5-dependent cell proliferation and survival. IL-5 critically regulates expression of genes involved in proliferation, cell survival and maturation and effector functions of B cells and eosinophils. Thus, IL-5 plays a pivotal role in innate and acquired immune responses and eosinophilia. In humans, the biologic effects of IL-5 are best characterized for eosinophils. The recent expansion in our understanding of the mechanisms of eosinophil development and activation in the context of IL-5 has led to advances in therapeutic options. A new therapy currently in clinical trials uses humanized mAbs against IL-5 or the IL-5R.

Augmented TLR9-induced Btk activation in PIR-B–deficient B-1 cells provokes excessive autoantibody production and autoimmunity

Pathogens are sensed by Toll-like receptors (TLRs) expressed in leukocytes in the innate immune system. However, excess stimulation of TLR pathways is supposed to be connected with provocation of autoimmunity. We show that paired immunoglobulin (Ig)-like receptor B (PIR-B), an immunoreceptor tyrosine-based inhibitory motif–harboring receptor for major histocompatibility class I molecules, on relatively primitive B cells, B-1 cells, suppresses TLR9 signaling via Bruton's tyrosine kinase (Btk) dephosphorylation, which leads to attenuated activation of nuclear factor κB p65RelA but not p38 or Erk, and blocks the production of natural IgM antibodies, including anti-IgG Fc autoantibodies, particularly rheumatoid factor. The autoantibody production in PIR-B–deficient (Pirb−/−) mice was further augmented in combination with the Faslpr mutation, which might be linked to the development of autoimmune glomerulonephritis. These results show the critical link between TLR9-mediated sensing and a simultaneously evoked, PIR-B–mediated inhibitory circuit with a Btk intersection in B-1 cells, and suggest a novel way toward preventing pathogenic natural autoantibody production.

Functionality of the Bruton’s tyrosine kinase from Mexican patients with XLA. (138.18)

Abstract X-linked agammaglobulinemia (XLA) is a primary immunodeficiency originated from mutations in the gene encoding Bruton's tyrosine Kinase (Btk). Btk is a vital protein in the B cell signaling machinery. L111P and E605G are two recently characterized mutations in Mexican patients suffering XLA; they gave us the basis for a more detailed study of the effects of these mutations in the conformation and functionality of Btk. In silico assays showed that L111 and E605 residues are fundamental for the activations and functionality of the Btk. Btk from the two patients and a healthy control were expressed in the Btk-deficient DT40 cell line, in order to confirm the predictions obtained in silico. The absence of the Btk catalytic activity of the patients was reflected in the lack of the Y551 phosphorylation. This may resulted in a reduced activation of PLC-ã2 that was reflected by reduction of intracellular calcium flux. This work show that L111 and E605 residues are fundamental in the structural conformation of the Btk and that in silico analysis can be a useful tool for the analysis of Btk mutations found in primary immunodeficiency patients. Supported by CONACyT, project No. 70062

A new mode of TNF-[alpha] inhibition by microRNA (99.26)

Abstract TNF-α, is a major cytokine implicated in rheumatoid arthritis (RA). TNF-α expression is regulated both at the transcriptional and the postranscriptional levels and recent data demonstrated that miRNAs are implicated in TNF-α response in macrophages. LPS-activated synoviocytes fibroblast-like (FLS) isolated from RA patients express TNF-α mRNA but they do not release TNF-α. This inhibition is due to a rapid degradation of TNF-α mRNA. We demonstrated previously that miR-346, which is overexpressed in LPS-activated FLS inhibits Bruton's tyrosine kinase (Btk) expression, which controls TNF-α stability. In fact, transfection of antisense oligonucleotides targeting miR-346 reestablished Btk and TNF-α expression in activated FLS. We also showed that transfection of miR-346 in THP-1 cells, inhibited TNF-α secretion in response to LPS. Tristetraprolin (TTP) is a protein which inhibited TNF-α synthesis by binding to AU rich elements of TNF-α mRNA. We demonstrated in LPS-activated RA FLS, that inhibition of miR-346 decreases TTP expression. In parallel we also showed that inhibition of Btk by LFMA13 or miR-346, increases the expression of TTP in LPS-activated THP-1 cells which results in inhibition of TNF-α synthesis. These results indicate that Btk controls TNF-α synthesis by regulating TTP expression. In conclusion, our findings provide evidence that miR-346 can act as a negative regulator of inflammation.

Expression of IL-5Rα on B-1 cell progenitors in mouse fetal liver and involvement of Bruton's tyrosine kinase in their development

B-1 cells are a subset of B cells responsible for the production of natural antibodies. Although the amount of natural antibody is tightly regulated, how this regulation occurs remains unknown. We examined the expression of IL-5 receptor, a cytokine receptor critical for homeostatic proliferation of B-1 cells, on B-1 cell progenitors in the fetal liver. We identified B-1 progenitors expressing low levels of IL-5 receptor α chain (IL-5Rα) and eosinophil progenitors expressing higher levels of IL-5Rα in the fetal liver. Moreover, the number of these B-1 progenitors were significantly reduced in the fetuses of mice deficient in Bruton's tyrosine kinase (Btk), even though IL-5 and thymic stroma lymphopoietin signaling are intact in early B lineage cells in Btk-deficient mice. These data suggest that IL-5 is possibly involved in B-1 cell development and an uncharacterized, Btk-dependent regulatory signaling pathway is involved in unexpectedly early stages of B-1 cell differentiation.

Bruton’s tyrosine kinase (Btk): function, regulation, and transformation with special emphasis on the PH domain

Bruton's agammaglobulinemia tyrosine kinase (Btk) is a cytoplasmic tyrosine kinase important in B-lymphocyte development, differentiation, and signaling. Btk is a member of the Tec family of kinases. Mutations in the Btk gene lead to X-linked agammaglobulinemia (XLA) in humans and X-linked immunodeficiency (Xid) in mice. Activation of Btk triggers a cascade of signaling events that culminates in the generation of calcium mobilization and fluxes, cytoskeletal rearrangements, and transcriptional regulation involving nuclear factor-kappaB (NF-kappaB) and nuclear factor of activated T cells (NFAT). In B cells, NF-kappaB was shown to bind to the Btk promoter and induce transcription, whereas the B-cell receptor-dependent NF-kappaB signaling pathway requires functional Btk. Moreover, Btk activation is tightly regulated by a plethora of other signaling proteins including protein kinase C (PKC), Sab/SH3BP5, and caveolin-1. For example, the prolyl isomerase Pin1 negatively regulates Btk by decreasing tyrosine phosphorylation and steady state levels of Btk. It is intriguing that PKC and Pin1, both of which are negative regulators, bind to the pleckstrin homology domain of Btk. To this end, we describe here novel mutations in the pleckstrin homology domain investigated for their transforming capacity. In particular, we show that the mutant D43R behaves similar to E41K, already known to possess such activity.

Ostéoimmunologie : une vision globale et intégrée du tissu squelettique et du système immunitaire

Study of dysregulations of the immune system resulting in abnormal bone homeostasis has led to the emergence of the field of osteoimmunology. Among the interactions between the immune system and bone, several signaling molecules and pathways previously identified in immune cells have been shown to be key players in the osteoclast, the bone resorbing cell. Osteoclast differentiation requires two signaling pathways: the RANK/RANKL pathway and the signal initiated by the ITAM-harboring adaptor proteins DAP12 and FcRgamma. Until recently, it was unclear how RANK and ITAM signals merge to cooperatively stimulate activation of NFATc1, the master transcription factor in osteoclastogenesis. A recent study from H. Takayanagi's group has shown that the tyrosine kinases Btk and Tec form a multiprotein complex with adaptor molecules such as BLNK, that is able to integrate these two signaling pathways and thus stimulate osteoclastogenesis. Taken together, these new data open novel clinical perspectives especially for osteoarticular inflammatory diseases.

Tec kinases regulate T‐lymphocyte development and function: new insights into the roles of Itk and Rlk/Txk

The Tec (tyrosine kinase expressed in hepatocellular carcinoma) family of non-receptor tyrosine kinases consists of five members: Tec, Bruton's tyrosine kinase (Btk), inducible T-cell kinase (Itk), resting lymphocyte kinase (Rlk/Txk), and bone marrow-expressed kinase (Bmx/Etk). Although their functions are probably best understood in antigen receptor signaling, where they participate in the phosphorylation and regulation of phospholipase C-gamma (PLC-gamma), it is now appreciated that these kinases contribute to signaling from many receptors and that they participate in multiple downstream pathways, including regulation of the actin cytoskeleton. In T cells, three Tec kinases are expressed, Itk, Rlk/Txk, and Tec. Itk is expressed at highest amounts and plays the major role in regulating signaling from the T-cell receptor. Recent studies provide evidence that these kinases contribute to multiple aspects of T-cell biology and have unique roles in T-cell development that have revealed new insight into the regulation of conventional and innate T-cell development. We review new findings on the Tec kinases with a focus on their roles in T-cell development and mature T-cell differentiation.

Advances in mechanisms of asthma, allergy, and immunology in 2008

This review summarizes selected articles appearing in 2008 in the Journal. Articles chosen include those improving our understanding of mechanisms of allergic diseases by focusing on human basophil, mast cell, and eosinophil biology; IgE and its high-affinity receptor on various cells; novel properties of omalizumab; airways remodeling; and genetics. Articles from other journals have been included to supplement the topics presented.