Signaling through CD19 activates Vav/mitogen-activated protein kinase pathway and induces formation of a CD19/Vav/phosphatidylinositol 3-kinase complex in human B cell precursors.
The B cell-specific cell surface molecule CD19 plays a role in regulating immunoglobulin (Ig) receptor signaling, and cross-linking CD19 activates several signaling molecules in mature human B cells. In surface Ig-negative B cell precursors, a protein tyrosine kinase (PTK)-dependent homotypic aggregation response can be triggered by cross-linking CD19. In the current study, we examined the outcome of PTK-mediated signal transduction following CD19 cross-linking on surface Ig negative and surface Ig positive B cell lines, as well as freshly isolated surface Ig-negative B cell precursors. PTK activation resulted in the tyrosine phosphorylation of multiple protein substrates and peaked at 0.5-1 min following CD19 cross-linking in all B-lineage cells examined. One of the tyrosine-phosphorylated substrates was identified as the hematopoietic-specific protein Vav, a guanine nucleotide exchange factor that activates the Ras pathway. Evidence consistent with Ras pathway activation was also demonstrated by MEK activation and subsequent phosphorylation of a MAP kinase fusion protein. CD19 cross-linking, sequential immunoprecipitation, and Western blotting revealed that: (a) Vav becomes associated with CD19, (b) phosphatidylinositol 3-kinase (PI 3-kinase) becomes associated with CD19, and (c) PI 3-kinase becomes associated with Vav. No such physical interaction occurred following control IgG1 cross-linking or cross-linking of class I major histocompatability complex cell surface molecules. Coupled with a previous report (Tuveson, D.A., Carter, R.H., Soltoff, S.P., and Fearon, D.T. (1993) Science 260, 986-988), our data support a model in which CD19 cross-linking induces the formation of a signaling complex that leads to the activation of two pathways involving Ras and PI 3-kinase.
Weng
W K
WK
Department of Laboratory Medicine and Pathology, University of Minnesota Medical School, Minneapolis 55455.
Jarvis
L
L
LeBien
T W
TW
D015703:Antigens, CD / Q000378:metabolism*; D018941:Antigens, CD19; D000944:Antigens, Differentiation, B-Lymphocyte / Q000378:metabolism*; D001402:B-Lymphocytes / Q000166:cytology / Q000378:metabolism*; D004789:Enzyme Activation; D006412:Hematopoietic Stem Cells / Q000378:metabolism; D006801:Humans; D015513:Oncogene Proteins / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases; D010766:Phosphorylation; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism*; D011494:Protein Kinases / Q000378:metabolism*; D051567:Proto-Oncogene Proteins c-vav; D015398:Signal Transduction; D014443:Tyrosine / Q000378:metabolism
D015703:Antigens, CD; D018941:Antigens, CD19; D000944:Antigens, Differentiation, B-Lymphocyte; D015513:Oncogene Proteins; D051567:Proto-Oncogene Proteins c-vav; C496618:VAV1 protein, human; D014443:Tyrosine; D011494:Protein Kinases; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor)