Cbl-b negatively regulates B cell antigen receptor signaling in mature B cells through ubiquitination of the tyrosine kinase Syk.
Members of the Cbl family of molecular adaptors play key roles in regulating tyrosine kinase-dependent signaling in a variety of cellular systems. Here we provide evidence that in B cells Cbl-b functions as a negative regulator of B cell antigen receptor (BCR) signaling during the normal course of a response. In B cells from Cbl-b-deficient mice cross-linking the BCRs resulted in sustained phosphorylation of Igalpha, Syk, and phospholipase C (PLC)-gamma2, leading to prolonged Ca2+ mobilization, and increases in extracellular signal-regulated kinase (ERK) and c-Jun NH2-terminal protein kinase (JNK) phosphorylation and surface expression of the activation marker, CD69. Image analysis following BCR cross-linking showed sustained polarization of the BCRs into large signaling-active caps associated with phosphorylated Syk in Cbl-b-deficient B cells in contrast to the BCRs in Cbl-b-expressing B cells that rapidly proceeded to form small, condensed, signaling inactive caps. Significantly, prolonged phosphorylation of Syk correlated with reduced ubiquitination of Syk indicating that Cbl-b negatively regulates BCR signaling by targeting Syk for ubiquitination.
Sohn
Hae Won
HW
The Laboratory of Immunogenetics, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Rockville, MD 20852, USA.
Gu
Hua
H
Pierce
Susan K
SK
D048868:Adaptor Proteins, Signal Transducing; D000077329:Agammaglobulinaemia Tyrosine Kinase; D000818:Animals; D001402:B-Lymphocytes / Q000166:cytology / Q000276:immunology* / Q000378:metabolism*; D020013:Calcium Signaling; D002352:Carrier Proteins / Q000235:genetics / Q000276:immunology* / Q000378:metabolism*; D018797:Cell Cycle Proteins; D002454:Cell Differentiation; D003432:Cross-Linking Reagents; D004792:Enzyme Precursors / Q000378:metabolism*; D007137:Immunoglobulin alpha-Chains / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins; D048031:JNK Mitogen-Activated Protein Kinases; D008213:Lymphocyte Activation; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D051966:Phospholipase C gamma; D010750:Phosphoproteins / Q000172:deficiency / Q000235:genetics / Q000276:immunology* / Q000378:metabolism*; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D050721:Proto-Oncogene Proteins c-cbl; D051567:Proto-Oncogene Proteins c-vav; D011940:Receptor Aggregation; D011947:Receptors, Antigen, B-Cell / Q000378:metabolism*; D015398:Signal Transduction; D000072377:Syk Kinase; D010738:Type C Phospholipases / Q000378:metabolism; D025801:Ubiquitin / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases
D048868:Adaptor Proteins, Signal Transducing; C113939:B cell linker protein; D002352:Carrier Proteins; C118387:Cblb protein, mouse; D018797:Cell Cycle Proteins; D003432:Cross-Linking Reagents; D004792:Enzyme Precursors; D007137:Immunoglobulin alpha-Chains; D047908:Intracellular Signaling Peptides and Proteins; D010750:Phosphoproteins; D011518:Proto-Oncogene Proteins; D051567:Proto-Oncogene Proteins c-vav; D011947:Receptors, Antigen, B-Cell; D025801:Ubiquitin; C496619:Vav1 protein, mouse; C492211:CBLB protein, human; D050721:Proto-Oncogene Proteins c-cbl; D044767:Ubiquitin-Protein Ligases; D011505:Protein-Tyrosine Kinases; D000077329:Agammaglobulinaemia Tyrosine Kinase; C000606896:SYK protein, human; D000072377:Syk Kinase; C000606897:Syk protein, mouse; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D010738:Type C Phospholipases; D051966:Phospholipase C gamma