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Schaffer AM, Fiala GJ, Hils M, Natali E, Babrak L, Herr LA, Romero-Mulero MC, Cabezas-Wallscheid N, Rizzi M, Miho E, Schamel WWA, Minguet S. Kidins220 regulates the development of B cells bearing the λ light chain. eLife 2024; 13:e83943. [PMID: 38271217 PMCID: PMC10810608 DOI: 10.7554/elife.83943] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2022] [Accepted: 12/27/2023] [Indexed: 01/27/2024] Open
Abstract
The ratio between κ and λ light chain (LC)-expressing B cells varies considerably between species. We recently identified Kinase D-interacting substrate of 220 kDa (Kidins220) as an interaction partner of the BCR. In vivo ablation of Kidins220 in B cells resulted in a marked reduction of λLC-expressing B cells. Kidins220 knockout B cells fail to open and recombine the genes of the Igl locus, even in genetic scenarios where the Igk genes cannot be rearranged or where the κLC confers autoreactivity. Igk gene recombination and expression in Kidins220-deficient B cells is normal. Kidins220 regulates the development of λLC B cells by enhancing the survival of developing B cells and thereby extending the time-window in which the Igl locus opens and the genes are rearranged and transcribed. Further, our data suggest that Kidins220 guarantees optimal pre-BCR and BCR signaling to induce Igl locus opening and gene recombination during B cell development and receptor editing.
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Affiliation(s)
- Anna-Maria Schaffer
- Faculty of Biology, Albert-Ludwigs-University of FreiburgFreiburgGermany
- Signalling Research Centers BIOSS and CIBSS, University of FreiburgFreiburgGermany
- Center of Chronic Immunodeficiency CCI, University Clinics and Medical FacultyFreiburgGermany
| | - Gina Jasmin Fiala
- Faculty of Biology, Albert-Ludwigs-University of FreiburgFreiburgGermany
- Signalling Research Centers BIOSS and CIBSS, University of FreiburgFreiburgGermany
- Center of Chronic Immunodeficiency CCI, University Clinics and Medical FacultyFreiburgGermany
| | - Miriam Hils
- Faculty of Biology, Albert-Ludwigs-University of FreiburgFreiburgGermany
- Center of Chronic Immunodeficiency CCI, University Clinics and Medical FacultyFreiburgGermany
- Department of Dermatology and Allergy Biederstein, School of Medicine, Technical University of MunichMunichGermany
| | - Eriberto Natali
- Institute of Medical Engineering and Medical Informatics, School of Life Sciences, FHNW 15 University of Applied Sciences and Arts Northwestern SwitzerlandMuttenzSwitzerland
| | - Lmar Babrak
- Institute of Medical Engineering and Medical Informatics, School of Life Sciences, FHNW 15 University of Applied Sciences and Arts Northwestern SwitzerlandMuttenzSwitzerland
| | - Laurenz Alexander Herr
- Faculty of Biology, Albert-Ludwigs-University of FreiburgFreiburgGermany
- Signalling Research Centers BIOSS and CIBSS, University of FreiburgFreiburgGermany
- Center of Chronic Immunodeficiency CCI, University Clinics and Medical FacultyFreiburgGermany
| | - Mari Carmen Romero-Mulero
- Faculty of Biology, Albert-Ludwigs-University of FreiburgFreiburgGermany
- Max Planck Institute of Immunobiology and EpigeneticsFreiburgGermany
| | - Nina Cabezas-Wallscheid
- Max Planck Institute of Immunobiology and EpigeneticsFreiburgGermany
- CIBSS – Centre for Integrative Biological Signalling Studies, University of FreiburgFreiburgGermany
| | - Marta Rizzi
- Center of Chronic Immunodeficiency CCI, University Clinics and Medical FacultyFreiburgGermany
- CIBSS – Centre for Integrative Biological Signalling Studies, University of FreiburgFreiburgGermany
- Division of Clinical and Experimental Immunology, Institute of Immunology, Center for Pathophysiology, Infectiology and Immunology, Medical University of ViennaViennaAustria
- Department of Rheumatology and Clinical Immunology, University Medical Center Freiburg, Faculty of Medicine, University of FreiburgFreiburgGermany
| | - Enkelejda Miho
- Institute of Medical Engineering and Medical Informatics, School of Life Sciences, FHNW 15 University of Applied Sciences and Arts Northwestern SwitzerlandMuttenzSwitzerland
- aiNET GmbHBaselSwitzerland
- SIB Swiss Institute of BioinformaticsLausanneSwitzerland
| | - Wolfgang WA Schamel
- Faculty of Biology, Albert-Ludwigs-University of FreiburgFreiburgGermany
- Signalling Research Centers BIOSS and CIBSS, University of FreiburgFreiburgGermany
- Center of Chronic Immunodeficiency CCI, University Clinics and Medical FacultyFreiburgGermany
| | - Susana Minguet
- Faculty of Biology, Albert-Ludwigs-University of FreiburgFreiburgGermany
- Signalling Research Centers BIOSS and CIBSS, University of FreiburgFreiburgGermany
- Center of Chronic Immunodeficiency CCI, University Clinics and Medical FacultyFreiburgGermany
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2
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Wu TH, Bolt AM, Chou H, Plourde D, De Jay N, Guilbert C, Young YK, Kleinman CL, Mann KK. Tungsten Blocks Murine B Lymphocyte Differentiation and Proliferation Through Downregulation of IL-7 Receptor/Pax5 Signaling. Toxicol Sci 2019; 170:45-56. [DOI: 10.1093/toxsci/kfz080] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Affiliation(s)
- Ting Hua Wu
- Lady Davis Institute for Medical Research
- Department of Experimental Medicine
| | - Alicia M Bolt
- Lady Davis Institute for Medical Research
- Department of Oncology
| | - Hsiang Chou
- Lady Davis Institute for Medical Research
- Department of Experimental Medicine
| | | | - Nicolas De Jay
- Lady Davis Institute for Medical Research
- Department of Human Genetics, McGill University, Montréal, Québec, Canada
| | | | | | - Claudia L Kleinman
- Lady Davis Institute for Medical Research
- Department of Human Genetics, McGill University, Montréal, Québec, Canada
| | - Koren K Mann
- Lady Davis Institute for Medical Research
- Department of Experimental Medicine
- Department of Oncology
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3
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Benhamou D, Labi V, Getahun A, Benchetrit E, Dowery R, Rajewsky K, Cambier JC, Melamed D. The c-Myc/miR17-92/PTEN Axis Tunes PI3K Activity to Control Expression of Recombination Activating Genes in Early B Cell Development. Front Immunol 2018; 9:2715. [PMID: 30524445 PMCID: PMC6262168 DOI: 10.3389/fimmu.2018.02715] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2018] [Accepted: 11/05/2018] [Indexed: 11/13/2022] Open
Abstract
Appropriate PI3K signals generated by the antigen receptor are essential to promote B cell development. Regulation of recombination activating gene (RAG)-1 and RAG-2 expression is one key process that is mediated by PI3K to ensure developmental progression and selection. When PI3K signals are too high or too low, expression of RAGs does not turn off and B cell development is impaired or blocked. Yet, the mechanism which tunes PI3K activity to control RAG expression during B cell development in the bone marrow is unknown. Recently we showed that a c-Myc/miR17-92/PTEN axis regulates PI3K activity for positive and negative selection of immature B cells. Here, we show that the c-Myc/miR17-92/PTEN axis tunes PI3K activity to control the expression of RAGs in proB cells. Using different genetically engineered mouse models we show that impaired function of the c-Myc/miR17-92/PTEN axis alters the PI3K/Akt/Foxo1 pathway to result in dis-regulated expression of RAG and a block in B cell development. Studies using 38c-13 B lymphoma cells, where RAGs are constitutively expressed, suggest that this regulatory effect is mediated post-translationally through Foxo1.
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Affiliation(s)
- David Benhamou
- Department of Immunology, Faculty of Medicine, Technion-Israel Institute of Technology, Haifa, Israel
| | - Verena Labi
- Max Delbrück Center for Molecular Medicine, Berlin, Germany.,Division of Developmental Immunology, Biocenter, Medical University of Innsbruck, Innsbruck, Austria
| | - Andrew Getahun
- Department of Immunology and Microbiology, University of Colorado School of Medicine, Aurora, CO, United States
| | - Eli Benchetrit
- Department of Immunology, Faculty of Medicine, Technion-Israel Institute of Technology, Haifa, Israel
| | - Reem Dowery
- Department of Immunology, Faculty of Medicine, Technion-Israel Institute of Technology, Haifa, Israel
| | - Klaus Rajewsky
- Max Delbrück Center for Molecular Medicine, Berlin, Germany
| | - John C Cambier
- Department of Immunology and Microbiology, University of Colorado School of Medicine, Aurora, CO, United States
| | - Doron Melamed
- Department of Immunology, Faculty of Medicine, Technion-Israel Institute of Technology, Haifa, Israel
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4
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Greaves SA, Peterson JN, Torres RM, Pelanda R. Activation of the MEK-ERK Pathway Is Necessary but Not Sufficient for Breaking Central B Cell Tolerance. Front Immunol 2018; 9:707. [PMID: 29686680 PMCID: PMC5900439 DOI: 10.3389/fimmu.2018.00707] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2018] [Accepted: 03/22/2018] [Indexed: 01/12/2023] Open
Abstract
Newly generated bone marrow B cells are positively selected into the peripheral lymphoid tissue only when they express a B cell receptor (BCR) that is nonautoreactive or one that binds self-antigen with only minimal avidity. This positive selection process, moreover, is critically contingent on the ligand-independent tonic signals transduced by the BCR. We have previously shown that when autoreactive B cells express an active form of the rat sarcoma (RAS) oncogene, they upregulate the receptor for the B cell activating factor (BAFFR) and undergo differentiation in vitro and positive selection into the spleen in vivo, overcoming central tolerance. Based on the in vitro use of pharmacologic inhibitors, we further showed that this cell differentiation process is critically dependent on the activation of the mitogen-activated protein kinase kinase pathway MEK (MAPKK)-extracellular signal-regulated kinase (ERK), which is downstream of RAS. Here, we next investigated if activation of ERK is not only necessary but also sufficient to break central B cell tolerance and induce differentiation of autoreactive B cells in vitro and in vivo. Our results demonstrate that activation of ERK is critical for upregulating BAFFR and overcoming suboptimal levels of tonic BCR signals or low amounts of antigen-induced BCR signals during in vitro B cell differentiation. However, direct activation of ERK does not lead high avidity autoreactive B cells to increase BAFFR levels and undergo positive selection and differentiation in vivo. B cell-specific MEK-ERK activation in mice is also unable to lead to autoantibody secretion, and this in spite of a general increase of serum immunoglobulin levels. These findings indicate that additional pathways downstream of RAS are required for high avidity autoreactive B cells to break central and/or peripheral tolerance.
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Affiliation(s)
- Sarah A Greaves
- Department of Immunology and Microbiology, University of Colorado School of Medicine, Aurora, CO, United States
| | - Jacob N Peterson
- Department of Immunology and Microbiology, University of Colorado School of Medicine, Aurora, CO, United States
| | - Raul M Torres
- Department of Immunology and Microbiology, University of Colorado School of Medicine, Aurora, CO, United States.,Department of Biomedical Research, National Jewish Health, Denver, CO, United States
| | - Roberta Pelanda
- Department of Immunology and Microbiology, University of Colorado School of Medicine, Aurora, CO, United States.,Department of Biomedical Research, National Jewish Health, Denver, CO, United States
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5
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An aberrant NOTCH2-BCR signaling axis in B cells from patients with chronic GVHD. Blood 2017; 130:2131-2145. [PMID: 28851699 DOI: 10.1182/blood-2017-05-782466] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2017] [Accepted: 08/24/2017] [Indexed: 12/16/2022] Open
Abstract
B-cell receptor (BCR)-activated B cells contribute to pathogenesis in chronic graft-versus-host disease (cGVHD), a condition manifested by both B-cell autoreactivity and immune deficiency. We hypothesized that constitutive BCR activation precluded functional B-cell maturation in cGVHD. To address this, we examined BCR-NOTCH2 synergy because NOTCH has been shown to increase BCR responsiveness in normal mouse B cells. We conducted ex vivo activation and signaling assays of 30 primary samples from hematopoietic stem cell transplantation patients with and without cGVHD. Consistent with a molecular link between pathways, we found that BCR-NOTCH activation significantly increased the proximal BCR adapter protein BLNK. BCR-NOTCH activation also enabled persistent NOTCH2 surface expression, suggesting a positive feedback loop. Specific NOTCH2 blockade eliminated NOTCH-BCR activation and significantly altered NOTCH downstream targets and B-cell maturation/effector molecules. Examination of the molecular underpinnings of this "NOTCH2-BCR axis" in cGVHD revealed imbalanced expression of the transcription factors IRF4 and IRF8, each critical to B-cell differentiation and fate. All-trans retinoic acid (ATRA) increased IRF4 expression, restored the IRF4-to-IRF8 ratio, abrogated BCR-NOTCH hyperactivation, and reduced NOTCH2 expression in cGVHD B cells without compromising viability. ATRA-treated cGVHD B cells had elevated TLR9 and PAX5, but not BLIMP1 (a gene-expression pattern associated with mature follicular B cells) and also attained increased cytosine guanine dinucleotide responsiveness. Together, we reveal a mechanistic link between NOTCH2 activation and robust BCR responses to otherwise suboptimal amounts of surrogate antigen. Our findings suggest that peripheral B cells in cGVHD patients can be pharmacologically directed from hyperactivation toward maturity.
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6
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Abstract
Immune tolerance hinders the potentially destructive responses of lymphocytes to host tissues. Tolerance is regulated at the stage of immature B cell development (central tolerance) by clonal deletion, involving apoptosis, and by receptor editing, which reprogrammes the specificity of B cells through secondary recombination of antibody genes. Recent mechanistic studies have begun to elucidate how these divergent mechanisms are controlled. Single-cell antibody cloning has revealed defects of B cell central tolerance in human autoimmune diseases and in several human immunodeficiency diseases caused by single gene mutations, which indicates the relevance of B cell tolerance to disease and suggests possible genetic pathways that regulate tolerance.
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7
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Gao X, Balan V, Tai G, Raz A. Galectin-3 induces cell migration via a calcium-sensitive MAPK/ERK1/2 pathway. Oncotarget 2015; 5:2077-84. [PMID: 24809457 PMCID: PMC4039146 DOI: 10.18632/oncotarget.1786] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
The presence and level of circulating galectin-3 (Gal-3), a member of the galectin family, is associated with diverse diseases ranging from heart failure, immune disorders to cancer metastasis and serves as a biomarker of diagnosis and treatment response. However, the mechanisms by which exogenous Gal-3 affects pathobiology events remain elusive. In the current study, we found that exogenous Gal-3 slightly delays, while prolonging tyrosine phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2) in HeLa cells through a calcium-sensitive and PKC-dependent signaling pathway. The activation was dependent on the sugar-binding properties of Gal-3, since the antagonist lactose could inhibit it. The sugar-binding motif of Gal-3 was required for the activation of ERK1/2. The activation of ERK1/2 was necessary for the initiation and induction of cell migration associated with the phosphorylation of paxillin. All the results presented in this study suggest a novel calcium-sensitive and PKC-dependent pathway through which circulating Gal-3 promotes cell migration and activating the ERK1/2. Taken together, the data depicted here propose a biological function and a target for the diseases' associated circulating Gal-3.
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Affiliation(s)
- Xiaoge Gao
- ¹Department of Oncology, Karmanos Cancer Institute, Wayne State University, Detroit, MI, USA. ²School of Life Sciences, Northeast Normal University, Changchun, PR China
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8
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Activation of Ras overcomes B-cell tolerance to promote differentiation of autoreactive B cells and production of autoantibodies. Proc Natl Acad Sci U S A 2014; 111:E2797-806. [PMID: 24958853 DOI: 10.1073/pnas.1402159111] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Newly generated immature B cells are selected to enter the peripheral mature B-cell pool only if they do not bind (or bind limited amount of) self-antigen. We previously suggested that this selection relies on basal extracellular signal-regulated kinase (Erk) activation mediated by tonic B-cell antigen receptor (BCR) signaling and that this signal can be replaced by an active rat sarcoma (Ras), which are small GTPase proteins. In this study we compared the activity of Ras and Erk in nonautoreactive and autoreactive immature B cells and investigated whether activation of Ras can break tolerance. Our results demonstrate lower levels of active Erk and Ras in autoreactive immature B cells, although this is evident only when these cells display medium/high avidity for self-antigen. Basal activation of Erk in immature B cells is proportional to surface IgM and dependent on sarcoma family kinases, whereas it is independent of B-cell activating factor, IFN, and Toll-like receptor signaling. Ectopic expression of the constitutively active mutant Ras form N-RasD12 in autoreactive cells raises active Erk, halts receptor editing via PI3 kinase, and promotes differentiation via Erk, breaking central tolerance. Moreover, when B cells coexpress autoreactive and nonautoreactive BCRs, N-RasD12 leads also to a break in peripheral tolerance with the production of autoantibodies. Our findings indicate that in immature B cells, basal activation of Ras and Erk are controlled by tonic BCR signaling, and that positive changes in Ras activity can lead to a break in both central and peripheral B-cell tolerance.
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9
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Pierau M, Na SY, Simma N, Lowinus T, Marx A, Schraven B, Bommhardt UH. Constitutive Akt1 signals attenuate B-cell receptor signaling and proliferation, but enhance B-cell migration and effector function. Eur J Immunol 2013; 42:3381-93. [PMID: 22930469 DOI: 10.1002/eji.201242397] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2012] [Revised: 07/27/2012] [Accepted: 08/20/2012] [Indexed: 11/07/2022]
Abstract
Ligation of the BCR induces a complex signaling network that involves activation of Akt, a family of serine/threonine protein kinases associated with B-cell development, proliferation, and tumor formation. Here, we analyzed the effect of enhanced Akt1 signals on B-cell maturation and function. Unexpectedly, we found that peripheral B cells overexpressing Akt1 were less responsive to BCR stimuli. This correlated with a decrease in Ca(2+) -mobilization and proliferation, in an impaired activation of Erk1/2 and mammalian target of rapamycin (mTOR) kinases and poor mobilization of NFATc1 and NF-κB/p65 factors. In contrast, activation of STAT5 and migration of B cells toward the chemokine SDF1α was found to be enhanced. Akt1 Tg mice showed an altered maturation of peritoneal and splenic B1 B cells and an enhanced production of IgG1 and IgG3 upon immunization with the T-cell independent Ag TNP-Ficoll. Furthermore, mice homo-zygous for Tg Akt1 showed a severe block in the maturation of B-cell precursors in BM and a strong enrichment of plasma cells in spleen. Altogether, our data reveal that enhanced Akt1 signals modify BCR signaling strength and, thereby, B-cell development and effector function.
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Affiliation(s)
- Mandy Pierau
- Institute of Molecular and Clinical Immunology, Otto-von-Guericke University Magdeburg, Magdeburg, Germany
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10
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Bicocca VT, Chang BH, Masouleh BK, Muschen M, Loriaux MM, Druker BJ, Tyner JW. Crosstalk between ROR1 and the Pre-B cell receptor promotes survival of t(1;19) acute lymphoblastic leukemia. Cancer Cell 2012; 22:656-67. [PMID: 23153538 PMCID: PMC3500515 DOI: 10.1016/j.ccr.2012.08.027] [Citation(s) in RCA: 129] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/06/2011] [Revised: 03/22/2012] [Accepted: 08/28/2012] [Indexed: 12/21/2022]
Abstract
We report that t(1;19) ALL cells universally exhibit expression of and dependence on the cell surface receptor ROR1. We further identify t(1;19) ALL cell sensitivity to the kinase inhibitor dasatinib due to its inhibition of the pre-B cell receptor (pre-BCR) signaling complex. These phenotypes are a consequence of developmental arrest at an intermediate/late stage of B-lineage maturation. Additionally, inhibition of pre-BCR signaling induces further ROR1 upregulation, and we identify distinct ROR1 and pre-BCR downstream signaling pathways that are modulated in a counterbalancing manner-both leading to AKT phosphorylation. Consistent with this, AKT phosphorylation is transiently eliminated after dasatinib treatment, but is partially restored following dasatinib potentiation of ROR1 expression. Consequently, ROR1 silencing accentuates dasatinib killing of t(1;19) ALL cells.
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Affiliation(s)
- Vincent T Bicocca
- Division of Hematology and Medical Oncology, Oregon Health & Science University, Portland, OR 97239, USA.
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Corfe SA, Paige CJ. The many roles of IL-7 in B cell development; mediator of survival, proliferation and differentiation. Semin Immunol 2012; 24:198-208. [PMID: 22421572 DOI: 10.1016/j.smim.2012.02.001] [Citation(s) in RCA: 124] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/16/2011] [Revised: 01/07/2012] [Accepted: 02/15/2012] [Indexed: 01/21/2023]
Abstract
Interleukin-7 (IL-7) plays several important roles during B cell development including aiding in; the specification and commitment of cells to the B lineage, the proliferation and survival of B cell progenitors; and maturation during the pro-B to pre-B cell transition. Regulation and modulation of IL-7 receptor (IL-7R) signaling is critical during B lymphopoiesis, because excessive or deficient IL-7R signaling leads to abnormal or inhibited B cell development. IL-7 works together with E2A, EBF, Pax-5 and other transcription factors to regulate B cell commitment, while also functions to regulate Ig rearrangement by modulating FoxO protein activation and Rag enhancer activity. Suppressor of cytokine signaling (SOCS) proteins are inhibitors of cytokine activation and, in B cells, function to fine tune IL-7R signaling; ensuring that appropriate IL-7 signals are transmitted to allow for efficient B cell commitment and development.
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Affiliation(s)
- Steven A Corfe
- Ontario Cancer Institute, Princess Margaret Hospital, University Health Network, 610 University Ave., Toronto, Ontario, Canada.
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12
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Biochemical and phosphoproteomic analysis of the helix-loop-helix protein E47. Mol Cell Biol 2012; 32:1671-82. [PMID: 22354994 DOI: 10.1128/mcb.06452-11] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Numerous in vitro as well as genetic studies have demonstrated that the activities of the E2A proteins are regulated at multiple levels, including modulation of DNA binding by the Id proteins, association with the transcriptional modulators p300 and ETO, and posttranslational modifications. Here, we use affinity purification of tagged E47 combined with mass spectrometry in order to show that E47 interacts with the entire ensemble of Id proteins, namely, Id1, Id2, Id3, and Id4. Furthermore, we find that the lysine-specific histone demethylase 1 (LSD1), the protein arginine N-methyltransferase 5 (PRMT5), the corepressor CoREST, and the chaperones of the 14-3-3 family associate with affinity-purified E47. We also identify a spectrum of amino acid residues in E47 that are phosphorylated, including an AKT substrate site. We did, however, find that mutation of the identified AKT substrate site by itself did not perturb B cell development. In sum, these studies show that the entire ensemble of Id proteins has the ability to interact with E47, identify factors that associate with E47, and reveal a spectrum of phosphorylated residues in E47, including an AKT substrate site.
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