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Bruton's Tyrosine Kinase Is Not Essential for B Cell Survival beyond Early Developmental Stages.
Nyhoff LE, Clark ES, Barron BL, Bonami RH, Khan WN, Kendall PL
(2018) J Immunol 200: 2352-2361
MeSH Terms: Agammaglobulinaemia Tyrosine Kinase, Animals, Autoimmune Diseases, B-Lymphocyte Subsets, Cell Survival, Cells, Cultured, Immunoglobulin M, Mice, Mice, Inbred C57BL, Mice, Knockout, Receptors, Antigen, B-Cell, Signal Transduction
Show Abstract · Added March 3, 2020
Bruton's tyrosine kinase (Btk) is a crucial regulator of B cell signaling and is a therapeutic target for lymphoma and autoimmune disease. BTK-deficient patients suffer from humoral immunodeficiency, as their B cells fail to progress beyond the bone marrow. However, the role of Btk in fully developed, mature peripheral B cells is not well understood. Analysis using BTK inhibitors is complicated by suboptimal inhibition, off-target effects, or failure to eliminate BTK's adaptor function. Therefore a mouse model was developed and used to excise after B cell populations were established. Mice lacking from birth are known to have reduced follicular (FO) compartments, with expanded transitional populations, suggesting a block in development. In adult mice, excision did not reduce FO B cells, which persisted for weeks. Autoimmune-prone B1 cells also survived conditional excision, contrasting their near absence in global -deficient mice. Therefore, Btk supports BCR signaling during selection into the FO and B1 compartments, but is not needed to maintain these cell populations. B1-related natural IgM levels remained normal, contrasting global deficiency, but B cell proliferation and T-independent type II immunization responses were blunted. Thus, B cells have nuanced signaling responses that are differentially regulated by Btk for development, survival, and function. These findings raise the possibility that Btk may also be expendable for survival of mature human B cells, therefore requiring prolonged dosing to be effective, and that success of BTK inhibitors may depend in part on off-target effects.
Copyright © 2018 by The American Association of Immunologists, Inc.
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MeSH Terms
Myc enhances B-cell receptor signaling in precancerous B cells and confers resistance to Btk inhibition.
Moyo TK, Wilson CS, Moore DJ, Eischen CM
(2017) Oncogene 36: 4653-4661
MeSH Terms: Agammaglobulinaemia Tyrosine Kinase, Animals, B-Lymphocytes, CD79 Antigens, Cell Proliferation, Flow Cytometry, Humans, Lymphoma, Non-Hodgkin, Male, Mice, Mice, Inbred C57BL, Mitogen-Activated Protein Kinase 3, Phosphatidylinositol 3-Kinases, Phospholipase C gamma, Phosphorylation, Precancerous Conditions, Protein-Tyrosine Kinases, Proto-Oncogene Proteins c-myc, Pyrazoles, Pyrimidines, Receptors, Antigen, B-Cell, Splenic Neoplasms, Syk Kinase
Show Abstract · Added April 6, 2017
Dysregulation of the oncogenic transcription factor MYC induces B-cell transformation and is a driver for B-cell non-Hodgkin lymphoma (B-NHL). MYC overexpression in B-NHL is associated with more aggressive phenotypes and poor prognosis. Although genomic studies suggest a link between MYC overexpression and B-cell receptor (BCR) signaling molecules in B-NHL, signaling pathways essential to Myc-mediated B-cell transformation have not been fully elucidated. We utilized intracellular phospho-flow cytometry to investigate the relationship between Myc and BCR signaling in pre-malignant B cells. Utilizing the Eμ-myc mouse model, where Myc is overexpressed specifically in B cells, both basal and stimulated BCR signaling were increased in precancerous B lymphocytes from Eμ-myc mice compared with wild-type littermates. B cells overexpressing Myc displayed constitutively higher levels of activated CD79α, Btk, Plcγ2 and Erk1/2. Notably, Myc-overexpressing B cells maintained elevated BCR signaling despite treatment with ibrutinib, a Bruton's tyrosine kinase inhibitor. Furthermore, PI3K/Akt pathway signaling was also increased in Eμ-myc B cells, and this increase was partially suppressed with ibrutinib. In addition, experiments with Btk-null B cells revealed off-target effects of ibrutinib on BCR signaling. Our data show that in pre-malignant B cells, Myc overexpression is sufficient to activate BCR and PI3K/Akt signaling pathways and further enhances signaling following BCR ligation. Therefore, our results indicate that precancerous B cells have already acquired enhanced survival and growth capabilities before transformation, and that elevated MYC levels confer resistance to pharmacologic inhibitors of BCR signaling, which has significant implications for B-NHL treatment.
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23 MeSH Terms
Distinct patterns of B-cell receptor signaling in non-Hodgkin lymphomas identified by single-cell profiling.
Myklebust JH, Brody J, Kohrt HE, Kolstad A, Czerwinski DK, Wälchli S, Green MR, Trøen G, Liestøl K, Beiske K, Houot R, Delabie J, Alizadeh AA, Irish JM, Levy R
(2017) Blood 129: 759-770
MeSH Terms: Agammaglobulinaemia Tyrosine Kinase, CD79 Antigens, Diagnosis, Differential, Flow Cytometry, Gene Expression Regulation, Neoplastic, Humans, Immunoglobulin M, Leukemia, Lymphocytic, Chronic, B-Cell, Lymphoma, Follicular, Lymphoma, Large B-Cell, Diffuse, Lymphoma, Mantle-Cell, Mitogen-Activated Protein Kinase 1, Mitogen-Activated Protein Kinase 3, Phospholipase C gamma, Phosphoproteins, Phosphorylation, Protein-Tyrosine Kinases, Proto-Oncogene Proteins c-akt, Receptors, Antigen, B-Cell, STAT1 Transcription Factor, STAT5 Transcription Factor, Signal Transduction, Single-Cell Analysis, Syk Kinase, p38 Mitogen-Activated Protein Kinases, src-Family Kinases
Show Abstract · Added December 31, 2016
Kinases downstream of B-cell antigen receptor (BCR) represent attractive targets for therapy in non-Hodgkin lymphoma (NHL). As clinical responses vary, improved knowledge regarding activation and regulation of BCR signaling in individual patients is needed. Here, using phosphospecific flow cytometry to obtain malignant B-cell signaling profiles from 95 patients representing 4 types of NHL revealed a striking contrast between chronic lymphocytic leukemia (CLL) and mantle cell lymphoma (MCL) tumors. Lymphoma cells from diffuse large B-cell lymphoma patients had high basal phosphorylation levels of most measured signaling nodes, whereas follicular lymphoma cells represented the opposite pattern with no or very low basal levels. MCL showed large interpatient variability in basal levels, and elevated levels for the phosphorylated forms of AKT, extracellular signal-regulated kinase, p38, STAT1, and STAT5 were associated with poor outcome. CLL tumors had elevated basal levels for the phosphorylated forms of BCR-signaling nodes (Src family tyrosine kinase, spleen tyrosine kinase [SYK], phospholipase Cγ), but had low α-BCR-induced signaling. This contrasted MCL tumors, where α-BCR-induced signaling was variable, but significantly potentiated as compared with the other types. Overexpression of CD79B, combined with a gating strategy whereby signaling output was directly quantified per cell as a function of CD79B levels, confirmed a direct relationship between surface CD79B, immunoglobulin M (IgM), and IgM-induced signaling levels. Furthermore, α-BCR-induced signaling strength was variable across patient samples and correlated with BCR subunit CD79B expression, but was inversely correlated with susceptibility to Bruton tyrosine kinase (BTK) and SYK inhibitors in MCL. These individual differences in BCR levels and signaling might relate to differences in therapy responses to BCR-pathway inhibitors.
© 2017 by The American Society of Hematology.
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26 MeSH Terms
Reply.
Nyhoff LE, Crofford LJ, Kendall PL
(2017) Arthritis Rheumatol 69: 475-477
MeSH Terms: Agammaglobulinaemia Tyrosine Kinase, Arthritis, Rheumatoid, Humans
Added July 18, 2017
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3 MeSH Terms
Bruton's Tyrosine Kinase Deficiency Inhibits Autoimmune Arthritis in Mice but Fails to Block Immune Complex-Mediated Inflammatory Arthritis.
Nyhoff LE, Barron BL, Johnson EM, Bonami RH, Maseda D, Fensterheim BA, Han W, Blackwell TS, Crofford LJ, Kendall PL
(2016) Arthritis Rheumatol 68: 1856-68
MeSH Terms: Agammaglobulinaemia Tyrosine Kinase, Animals, Antigen-Antibody Complex, Arthritis, Autoimmune Diseases, Male, Mice, Protein-Tyrosine Kinases
Show Abstract · Added October 12, 2016
OBJECTIVE - Bruton's tyrosine kinase (BTK) is a B cell signaling protein that also contributes to innate immunity. BTK inhibitors prevent autoimmune arthritis but have off-target effects, and the mechanisms of protection remain unknown. We undertook these studies using genetic deletion to investigate the role of BTK in adaptive and innate immune responses that drive inflammatory arthritis.
METHODS - BTK-deficient K/BxN mice were generated to study the role of BTK in a spontaneous model that requires both adaptive and innate immunity. The K/BxN serum-transfer model was used to bypass the adaptive system and elucidate the role of BTK in innate immune contributions to arthritis.
RESULTS - BTK deficiency conferred disease protection to K/BxN mice, confirming outcomes of BTK inhibitors. B lymphocytes were profoundly reduced, more than in other models of BTK deficiency. Subset analysis revealed loss of B cells at all developmental stages. Germinal center B cells were also decreased, with downstream effects on numbers of follicular helper T cells and greatly reduced autoantibodies. In contrast, total IgG was only mildly decreased. Strikingly, and in contrast to small molecule inhibitors, BTK deficiency had no effect in the serum-transfer model of arthritis.
CONCLUSION - BTK contributes to autoimmune arthritis primarily through its role in B cell signaling and not through innate immune components.
© 2016, American College of Rheumatology.
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8 MeSH Terms
The role of Bruton's tyrosine kinase in autoimmunity and implications for therapy.
Crofford LJ, Nyhoff LE, Sheehan JH, Kendall PL
(2016) Expert Rev Clin Immunol 12: 763-73
MeSH Terms: Agammaglobulinaemia Tyrosine Kinase, Animals, Anti-Inflammatory Agents, Autoantibodies, Autoimmune Diseases, Autoimmunity, B-Lymphocytes, Humans, Immune Tolerance, Lymphocyte Activation, Protein-Tyrosine Kinases, Receptors, Antigen, B-Cell, Signal Transduction
Show Abstract · Added July 18, 2017
Bruton's tyrosine kinase (BTK) mediates B cell signaling and is also present in innate immune cells but not T cells. BTK propagates B cell receptor (BCR) responses to antigen-engagement as well as to stimulation via CD40, toll-like receptors (TLRs), Fc receptors (FCRs) and chemokine receptors. Importantly, BTK can modulate signaling, acting as a "rheostat" rather than an "on-off" switch; thus, overexpression leads to autoimmunity while decreased levels improve autoimmune disease outcomes. Autoreactive B cells depend upon BTK for survival to a greater degree than normal B cells, reflected as loss of autoantibodies with maintenance of total antibody levels when BTK is absent. This review describes contributions of BTK to immune tolerance, including studies testing BTK-inhibitors for treatment of autoimmune diseases.
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13 MeSH Terms
Bruton's Tyrosine Kinase Synergizes with Notch2 To Govern Marginal Zone B Cells in Nonobese Diabetic Mice.
Case JB, Bonami RH, Nyhoff LE, Steinberg HE, Sullivan AM, Kendall PL
(2015) J Immunol 195: 61-70
MeSH Terms: Agammaglobulinaemia Tyrosine Kinase, Animals, Autoantibodies, Autoimmunity, B-Lymphocyte Subsets, Cell Differentiation, Cell Survival, Diabetes Mellitus, Experimental, Female, Gene Expression Regulation, Immunoglobulin Heavy Chains, Insulin, Male, Mice, Mice, Inbred C57BL, Mice, Inbred NOD, Protein-Tyrosine Kinases, Receptor, Notch2, Receptors, Antigen, B-Cell, Signal Transduction
Show Abstract · Added December 4, 2015
Expansion of autoimmune-prone marginal zone (MZ) B cells has been implicated in type 1 diabetes. To test disease contributions of MZ B cells in NOD mice, Notch2 haploinsufficiency (Notch2(+/-)) was introduced but failed to eliminate the MZ, as it does in C57BL/6 mice. Notch2(+/-)/NOD have MZ B cell numbers similar to those of wild-type C57BL/6, yet still develop diabetes. To test whether BCR signaling supports Notch2(+/-)/NOD MZ B cells, Bruton's tyrosine kinase (Btk) deficiency was introduced. Surprisingly, MZ B cells failed to develop in Btk-deficient Notch2(+/-)/NOD mice. Expression of Notch2 and its transcriptional target, Hes5, was increased in NOD MZ B cells compared with C57BL/6 MZ B cells. Btk deficiency reduced Notch2(+/-) signaling exclusively in NOD B cells, suggesting that BCR signaling enhances Notch2 signaling in this autoimmune model. The role of BCR signaling was further investigated using an anti-insulin transgenic (Tg) BCR (125Tg). Anti-insulin B cells in 125Tg/Notch2(+/-)/NOD mice populate an enlarged MZ, suggesting that low-level BCR signaling overcomes reliance on Notch2. Tracking clonotypes of anti-insulin B cells in H chain-only VH125Tg/NOD mice showed that BTK-dependent selection into the MZ depends on strength of antigenic binding, whereas Notch2-mediated selection does not. Importantly, anti-insulin B cell numbers were reduced by Btk deficiency, but not Notch2 haploinsufficiency. These studies show that 1) Notch2 haploinsufficiency limits NOD MZ B cell expansion without preventing type 1 diabetes, 2) BTK supports the Notch2 pathway in NOD MZ B cells, and 3) autoreactive NOD B cell survival relies on BTK more than Notch2, regardless of MZ location, which may have important implications for disease-intervention strategies.
Copyright © 2015 by The American Association of Immunologists, Inc.
2 Communities
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20 MeSH Terms
Bruton's tyrosine kinase promotes persistence of mature anti-insulin B cells.
Bonami RH, Sullivan AM, Case JB, Steinberg HE, Hoek KL, Khan WN, Kendall PL
(2014) J Immunol 192: 1459-70
MeSH Terms: Agammaglobulinaemia Tyrosine Kinase, Animals, B-Lymphocytes, Cells, Cultured, Diabetes Mellitus, Type 1, Immunoglobulins, Insulin, Insulin Antibodies, Mice, Mice, Inbred C57BL, Mice, Inbred NOD, Mice, Transgenic, Protein-Tyrosine Kinases, Receptors, Antigen, B-Cell
Show Abstract · Added May 19, 2014
Autoreactive B lymphocytes are essential for the development of T cell-mediated type 1 diabetes (T1D). Cytoplasmic Bruton's tyrosine kinase (BTK) is a key component of B cell signaling, and its deletion in T1D-prone NOD mice significantly reduces diabetes. However, the role of BTK in the survival and function of autoreactive B cells is not clear. To evaluate the contributions of BTK, we used mice in which B cells express an anti-insulin BCR (125Tg) and promote T1D, despite being anergic. Crossing Btk deficiency onto 125Tg mice reveals that, in contrast to immature B cells, mature anti-insulin B cells are exquisitely dependent upon BTK, because their numbers are reduced by 95%. BTK kinase domain inhibition reproduces this effect in mature anti-insulin B cells, with less impact at transitional stages. The increased dependence of anti-insulin B cells on BTK became particularly evident in an Igκ locus site-directed model, in which 50% of B cells edit their BCRs to noninsulin specificities; Btk deficiency preferentially depletes insulin binders from the follicular and marginal zone B cell subsets. The persistent few Btk-deficient anti-insulin B cells remain competent to internalize Ag and invade pancreatic islets. As such, loss of BTK does not significantly reduce diabetes incidence in 125Tg/NOD mice as it does in NOD mice with a normal B cell repertoire. Thus, BTK targeting may not impair autoreactive anti-insulin B cell function, yet it may provide protection in an endogenous repertoire by decreasing the relative availability of mature autoreactive B cells.
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14 MeSH Terms
Reduced diabetes in btk-deficient nonobese diabetic mice and restoration of diabetes with provision of an anti-insulin IgH chain transgene.
Kendall PL, Moore DJ, Hulbert C, Hoek KL, Khan WN, Thomas JW
(2009) J Immunol 183: 6403-12
MeSH Terms: Agammaglobulinaemia Tyrosine Kinase, Animals, Autoantibodies, B-Lymphocyte Subsets, Diabetes Mellitus, Type 1, Immune Tolerance, Immunoglobulin Heavy Chains, Insulin, Insulin Antibodies, Mice, Mice, Inbred C57BL, Mice, Inbred NOD, Mice, Knockout, Mutation, Protein-Tyrosine Kinases, Receptors, Antigen, B-Cell, Signal Transduction, T-Lymphocyte Subsets, Transgenes
Show Abstract · Added December 10, 2013
Type 1 diabetes results from T cell-mediated destruction of insulin-producing beta cells. Although elimination of B lymphocytes has proven successful at preventing disease, modulation of B cell function as a means to prevent type 1 diabetes has not been investigated. The development, fate, and function of B lymphocytes depend upon BCR signaling, which is mediated in part by Bruton's tyrosine kinase (BTK). When introduced into NOD mice, btk deficiency only modestly reduces B cell numbers, but dramatically protects against diabetes. In NOD, btk deficiency mirrors changes in B cell subsets seen in other strains, but also improves B cell-related tolerance, as indicated by failure to generate insulin autoantibodies. Introduction of an anti-insulin BCR H chain transgene restores diabetes in btk-deficient NOD mice, indicating that btk-deficient B cells are functionally capable of promoting autoimmune diabetes if they have a critical autoimmune specificity. This suggests that the disease-protective effect of btk deficiency may reflect a lack of autoreactive specificities in the B cell repertoire. Thus, signaling via BTK can be modulated to improve B cell tolerance, and prevent T cell-mediated autoimmune diabetes.
3 Communities
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19 MeSH Terms
Kinetics of B cell receptor signaling in human B cell subsets mapped by phosphospecific flow cytometry.
Irish JM, Czerwinski DK, Nolan GP, Levy R
(2006) J Immunol 177: 1581-9
MeSH Terms: Agammaglobulinaemia Tyrosine Kinase, B-Lymphocyte Subsets, Flow Cytometry, Humans, Hydrogen Peroxide, Immunoglobulin G, Immunoglobulin M, Intracellular Signaling Peptides and Proteins, Kinetics, MAP Kinase Signaling System, Mitogen-Activated Protein Kinase 1, Mitogen-Activated Protein Kinase 3, Peptide Mapping, Phosphorylation, Protein-Tyrosine Kinases, Receptors, Antigen, B-Cell, Syk Kinase
Show Abstract · Added February 15, 2013
Differences in BCR signaling may govern outcomes as diverse as proliferation and cell death. We profiled BCR signaling kinetics in subsets of primary human B cells using flow cytometry. In the predominant population expressing IgM, BCR cross-linking led to a quick burst of Syk, ERK1/2, and p38 signaling. In contrast, IgG B cells sustained higher per-cell ERK1/2 phosphorylation over time. This dichotomy suggested a mechanism for dampening signals transmitted by IgM. Regulatory phosphatase activity in IgM B cells was BCR-mediated and initiated more slowly than kinase activity. This BCR-mediated phosphatase activity was sensitive to inhibition by H(2)O(2) and required to attenuate IgM BCR signaling. These results provide the first kinetic maps of BCR signaling in primary human B cell subsets and enable new studies of signaling in B cell disorders, such as autoimmunity and cancer.
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17 MeSH Terms