Signaling through the EBV/C3d receptor (CR2, CD21) in human B lymphocytes: activation of phosphatidylinositol 3-kinase via a CD19-independent pathway.
We herein analyzed the regulation of phosphatidylinositol 3-kinase (PI 3-kinase) activity by CR2 activated on B lymphocyte cell surface. We demonstrated that CR2 activation triggered in vivo PI 3-kinase activity and interaction of PI 3-kinase p85 subunit with a tyrosine-phosphorylated p95 component. The specificity of PI 3-kinase activity was controlled using wortmannin and LY294002. CR2 activation did not trigger tyrosine phosphorylation of PI 3-kinase p85 subunit, but induced direct interaction of tyrosine phosphorylated p95 with the Src homology 2 domain of p85 subunit, as shown using glutathione-S-transferase fusion proteins. Despite identical molecular masses, immunoblotting analysis demonstrated that tyrosine-phosphorylated p95 that interacted in vivo and in vitro with p85 was neither CD19, the 95-kDa proto-oncogene vav, nor Gab1 (a 95-kDa adaptor molecule). Furthermore, p95 tyrosine phosphoprotein also expressed in K562A cells (CR2+ CD19- cells) interacted with Src homology 2 domain of PI 3-kinase p85 subunit after CR2 activation. Activated CR2 did not interact directly with p85 subunit or tyrosine-phosphorylated p95. This suggests the presence of an intermediate molecule between activated CR2 and tyrosine-phosphorylated p95, which may be 3BP2. In addition, in contrast to CD19 activation, CR2 activation did not trigger interaction of CD19 or Vav with PI 3-kinase p85 subunit or coprecipitation of PI 3-kinase activity with CD19. Together, these data clearly demonstrated that CR2 activation triggered in vivo PI 3-kinase activation through a pathway distinct from that triggered through CD19 activation.
Bouillie
S
S
Immunochimie des Régulations Cellulaires et des Interactions Virales, Institut National de la Santé et de la Recherche Médicale, Unit 354, Centre INSERM, Hôpital Saint-Antoine, Paris, France.
Barel
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M
Frade
R
R
D048868:Adaptor Proteins, Signal Transducing; D018941:Antigens, CD19 / Q000502:physiology*; D001402:B-Lymphocytes / Q000201:enzymology* / Q000276:immunology / Q000378:metabolism*; D002051:Burkitt Lymphoma / Q000201:enzymology; D018797:Cell Cycle Proteins; D003167:Complement Activation / Q000276:immunology; D004789:Enzyme Activation / Q000276:immunology; D006801:Humans; D020014:K562 Cells / Q000201:enzymology; D008970:Molecular Weight; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010750:Phosphoproteins / Q000502:physiology; D010766:Phosphorylation; D000090063:Proto-Oncogene Mas; D011518:Proto-Oncogene Proteins / Q000502:physiology; D051567:Proto-Oncogene Proteins c-vav; D017464:Receptors, Complement 3d / Q000502:physiology*; D015398:Signal Transduction / Q000276:immunology*; D014407:Tumor Cells, Cultured; D014443:Tyrosine / Q000378:metabolism; D018909:src Homology Domains / Q000276:immunology
D048868:Adaptor Proteins, Signal Transducing; D018941:Antigens, CD19; D018797:Cell Cycle Proteins; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins; D000090063:Proto-Oncogene Mas; D011518:Proto-Oncogene Proteins; D051567:Proto-Oncogene Proteins c-vav; D017464:Receptors, Complement 3d; D014443:Tyrosine; C098587:GAB1 protein, human; C000715470:MAS1 protein, human; C496618:VAV1 protein, human