Abstract
CD72 is a 45-kDa B cell transmembrane glycoprotein that has been shown to be important for B cell activation. However, whether CD72 ligation induces B cell activation by delivering positive signals or sequestering negative signals away from B cell receptor (BCR) signals remains unclear. Here, by comparing the late signaling events associated with the mitogen-activated protein kinase pathway, we identified many similarities and some differences between CD72 and BCR signaling. Thus, CD72 and BCR activated the extracellular signal-regulated kinase (ERK) and the c-Jun N-terminal kinase (JNK) but not p38 mitogen-activated protein kinase. Both CD72- and BCR-mediated ERK and JNK activation required protein kinase C activity, which was equally important for CD72- and BCR-induced B cell proliferation. However, CD72 induced stronger JNK activation compared with BCR. Surprisingly, the JNK activation induced by both BCR and CD72 is Btk independent. Although both CD72 and BCR induced Btk-dependent ERK activation, CD72-mediated proliferation is more resistant to blocking of ERK activity than that of BCR, as shown by the proliferation response of B cells treated with PD98059 and dibutyryl cAMP, agents that inhibit ERK activity. Most importantly, CD72 signaling compensated for defective BCR signaling in X-linked immunodeficiency B cells and partially restored the proliferation response of X-linked immunodeficiency B cells to anti-IgM ligation. These results suggest that CD72 signals B cells by inducing BCR-independent positive signaling pathways.
Publication types
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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Agammaglobulinaemia Tyrosine Kinase
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Animals
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Antibodies, Monoclonal / pharmacology
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Antigens, CD / immunology
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Antigens, CD / metabolism
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Antigens, CD / physiology*
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Antigens, Differentiation, B-Lymphocyte / immunology
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Antigens, Differentiation, B-Lymphocyte / metabolism
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Antigens, Differentiation, B-Lymphocyte / physiology*
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B-Lymphocytes / immunology*
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Cells, Cultured
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Cyclic AMP / biosynthesis
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Cyclic AMP / physiology
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Drug Synergism
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Enzyme Activation / genetics
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Enzyme Activation / immunology
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Enzyme Induction / genetics
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Enzyme Induction / immunology
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Female
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JNK Mitogen-Activated Protein Kinases
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Lymphocyte Activation / genetics*
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MAP Kinase Kinase 1
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MAP Kinase Kinase 2
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Male
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Mice
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Mice, Inbred BALB C
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Mice, Inbred CBA
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Mice, Inbred DBA
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Mice, Knockout
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Mitogen-Activated Protein Kinase 1 / antagonists & inhibitors
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Mitogen-Activated Protein Kinase 1 / metabolism
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Mitogen-Activated Protein Kinase 3
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Mitogen-Activated Protein Kinase Kinases / physiology
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Mitogen-Activated Protein Kinases / antagonists & inhibitors
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Mitogen-Activated Protein Kinases / deficiency
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Mitogen-Activated Protein Kinases / genetics
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Mitogen-Activated Protein Kinases / metabolism*
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Protein Kinase C / physiology
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Protein Serine-Threonine Kinases / physiology
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Protein-Tyrosine Kinases / deficiency
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Protein-Tyrosine Kinases / genetics
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Protein-Tyrosine Kinases / physiology
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Receptors, Antigen, B-Cell / genetics
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Receptors, Antigen, B-Cell / physiology*
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Severe Combined Immunodeficiency / genetics*
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Severe Combined Immunodeficiency / immunology*
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Severe Combined Immunodeficiency / pathology
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Signal Transduction / genetics
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Signal Transduction / immunology*
Substances
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Antibodies, Monoclonal
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Antigens, CD
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Antigens, Differentiation, B-Lymphocyte
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CD72 protein, human
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Receptors, Antigen, B-Cell
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Cyclic AMP
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MAP2K2 protein, human
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Protein-Tyrosine Kinases
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Agammaglobulinaemia Tyrosine Kinase
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BTK protein, human
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Protein Serine-Threonine Kinases
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Protein Kinase C
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JNK Mitogen-Activated Protein Kinases
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Mitogen-Activated Protein Kinase 1
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Mitogen-Activated Protein Kinase 3
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Mitogen-Activated Protein Kinases
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MAP Kinase Kinase 1
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MAP Kinase Kinase 2
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MAP2K1 protein, human
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Map2k1 protein, mouse
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Mitogen-Activated Protein Kinase Kinases