title: Cbl-b is a negative regulator of inflammatory cytokines produced by IgE-activated mast cells.
abstract: c-Cbl and Cbl-b E3 ubiquitin ligases are abundantly expressed in hemopoietic cells where they negatively regulate the activity and levels of many cell surface receptors and associated signaling molecules. By comparing bone marrow-derived mast cells from c-Cbl and Cbl-b-deficient mice it has recently been shown that Cbl-b is the dominant family member for negatively regulating signaling responses from high-affinity IgE receptors. In this study, we suggest that a possible reason for the greater enhancement of IgE receptor signaling in Cbl-b-deficient mice is the relatively higher levels of Cbl-b protein over c-Cbl in mast cells compared with other hemopoietic cells. We also directly compare mast cells from c-Cbl and Cbl-b-deficient mice and find that loss of Cbl-b, but not c-Cbl, increases cell growth, retards receptor internalization, and causes the sustained tyrosine phosphorylation of Syk and its substrates. However, loss of Cbl-b does not enhance the activation of ERK or Akt, nor does it promote a greater calcium response. Furthermore, loss of Cbl-b or c-Cbl does not increase levels of the Syk or Lyn protein tyrosine kinases. Most notable, however, is the extremely large increase in the production of proinflammatory cytokines TNF-alpha, IL-6, and MCP-1 by Cbl-b(-/-) mast cells compared with levels produced by c-Cbl(-/-) or wild-type cells. This marked induction, which appears to be restricted to these three cytokines, is dependent on IgE receptor activation and correlates with enhanced IkappaB kinase phosphorylation. Thus, Cbl-b functions as a potent negative regulator of cytokines that promote allergic and inflammatory reactions.
authors.affiliation: School of Surgery and Pathology, University of Western Australia, Crawley, Western Australia 6009, Australia.
authors.forename: Sonja E
authors.initials: SE
authors.lastname: Gustin
authors.forename: Christine B F
authors.initials: CB
authors.lastname: Thien
authors.forename: Wallace Y
authors.initials: WY
authors.lastname: Langdon
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000502:physiology*; D000818:Animals; D001854:Bone Marrow Cells / Q000187:drug effects / Q000276:immunology*; D002118:Calcium / Q000378:metabolism; D016207:Cytokines / Q000096:biosynthesis*; D015536:Down-Regulation; D004789:Enzyme Activation; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D006412:Hematopoietic Stem Cells / Q000187:drug effects / Q000276:immunology; D020672:I-kappa B Proteins / Q000378:metabolism; D007073:Immunoglobulin E / Q000276:immunology; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D008407:Mast Cells / Q000276:immunology*; D051379:Mice; D008817:Mice, Mutant Strains; D010766:Phosphorylation; D019000:Phosphotyrosine / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D050721:Proto-Oncogene Proteins c-cbl / Q000235:genetics / Q000502:physiology*; D017455:Receptors, IgE / Q000819:agonists / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D000072377:Syk Kinase; D019061:src-Family Kinases / Q000378:metabolism
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C118387:Cblb protein, mouse; D016207:Cytokines; D020672:I-kappa B Proteins; D047908:Intracellular Signaling Peptides and Proteins; D017455:Receptors, IgE; D019000:Phosphotyrosine; D007073:Immunoglobulin E; D050721:Proto-Oncogene Proteins c-cbl; D011505:Protein-Tyrosine Kinases; D000072377:Syk Kinase; C000606897:Syk protein, mouse; C060902:lyn protein-tyrosine kinase; D019061:src-Family Kinases; D051057:Proto-Oncogene Proteins c-akt; D048049:Extracellular Signal-Regulated MAP Kinases; C493849:Cbl protein, mouse; D002118:Calcium