title: Activation of the Ras signaling pathway by the CD40 receptor.
abstract: The CD40 receptor is an important molecule regulating B lymphocyte proliferation, maturation, Ab class switching, and cell survival. In the present study, we identified signal transduction events triggered by cross-linking the CD40 receptor. Stimulation of Daudi B cells with anti-CD40 resulted in activation of p21ras, an important switch point in the regulation of cell growth and differentiation. Ras activation correlated with a stimulation of Rac1 and MEK-1 as well as tyrosine phosphorylation of phosphatidylinositol 3-kinase. Inhibition of endogenous Ras by transfection of transdominant inhibitory Ras prevented tyrosine phosphorylation or stimulation of phosphatidylinositol 3-kinase, Rac1, or MEK-1 upon CD40 receptor triggering, proving an activation of the Ras pathway by CD40. Ras activation was partially inhibited by either herbimycin A or calphostin pretreatment and completely inhibited by preincubation with a combination of both inhibitors, indicating a synergistic role for protein tyrosine kinases and diglycerides in Ras activation after CD40 stimulation. In support of a role for diglycerides, we detected a 30 +/- 5% decrease of cellular phosphatidylcholine content, correlating with a threefold increase of diacylglycerol synthesis induced by CD40. Supporting a role for protein tyrosine kinase, we measured a five- to eightfold stimulation of p56lyn and p58blk kinase activity. These results suggest the activation of the Ras pathway via an additive function of src kinases and phospholipases that may be important in the mediation of biologic effects after CD40 receptor engagement.
authors.affiliation: I. Institute of Physiology, University of Tuebingen, Germany.
authors.forename: E
authors.initials: E
authors.lastname: Gulbins
authors.forename: B
authors.initials: B
authors.lastname: Brenner
authors.forename: K
authors.initials: K
authors.lastname: Schlottmann
authors.forename: U
authors.initials: U
authors.lastname: Koppenhoefer
authors.forename: O
authors.initials: O
authors.lastname: Linderkamp
authors.forename: K M
authors.initials: KM
authors.lastname: Coggeshall
authors.forename: F
authors.initials: F
authors.lastname: Lang
mesh_terms: D000911:Antibodies, Monoclonal / Q000494:pharmacology; D001402:B-Lymphocytes / Q000187:drug effects / Q000276:immunology*; D016227:Benzoquinones; D002051:Burkitt Lymphoma / Q000473:pathology; D019013:CD40 Antigens / Q000187:drug effects / Q000502:physiology*; D004075:Diglycerides / Q000502:physiology; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000502:physiology; D006801:Humans; D047029:Lactams, Macrocyclic; D048369:MAP Kinase Kinase 1; D020929:Mitogen-Activated Protein Kinase Kinases; D009281:Naphthalenes / Q000494:pharmacology; D009363:Neoplasm Proteins / Q000502:physiology; D010713:Phosphatidylcholines / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D017346:Protein Serine-Threonine Kinases / Q000502:physiology; D011505:Protein-Tyrosine Kinases / Q000502:physiology; D016283:Proto-Oncogene Proteins p21(ras) / Q000037:antagonists & inhibitors / Q000502:physiology*; D011809:Quinones / Q000494:pharmacology; D017828:Rifabutin / Q000031:analogs & derivatives; D015398:Signal Transduction / Q000502:physiology*; D014407:Tumor Cells, Cultured; D020744:rac GTP-Binding Proteins; D019061:src-Family Kinases / Q000502:physiology
chemical_list: D000911:Antibodies, Monoclonal; D016227:Benzoquinones; D019013:CD40 Antigens; D004075:Diglycerides; D004791:Enzyme Inhibitors; D047029:Lactams, Macrocyclic; D009281:Naphthalenes; D009363:Neoplasm Proteins; D010713:Phosphatidylcholines; D011809:Quinones; C061465:calphostin complex; D017828:Rifabutin; C020754:herbimycin; C082599:protein-tyrosine kinase p55(blk); D011505:Protein-Tyrosine Kinases; C060902:lyn protein-tyrosine kinase; D019061:src-Family Kinases; D017346:Protein Serine-Threonine Kinases; D048369:MAP Kinase Kinase 1; C482125:MAP2K1 protein, human; D020929:Mitogen-Activated Protein Kinase Kinases; D019204:GTP-Binding Proteins; C501009:HRAS protein, human; D016283:Proto-Oncogene Proteins p21(ras); D020744:rac GTP-Binding Proteins