Signaling Through the EBV/C3d Receptor (CR2, CD21) in Human B Lymphocytes: Activation of Phosphatidylinositol 3-Kinase via a CD19-Independent Pathway

• Published in: The Journal of immunology (1950) Vol. 162; no. 1; pp. 136 - 143
• Main Authors: Bouillie, Sylvie, Barel, Monique, Frade, Raymond
• Format: Journal Article
• Language: English
• Published: United States Am Assoc Immnol 01.01.1999
• Subjects: Adaptor Proteins, Signal Transducing; Antigens, CD19 - physiology; B-Lymphocytes - enzymology; B-Lymphocytes - immunology; B-Lymphocytes - metabolism; Burkitt Lymphoma - enzymology; Cell Cycle Proteins; Complement Activation - immunology; Enzyme Activation - immunology; Humans; K562 Cells - enzymology; Molecular Weight; Phosphatidylinositol 3-Kinases - metabolism; Phosphoproteins - physiology; Phosphorylation; Proto-Oncogene Proteins - physiology; Proto-Oncogene Proteins c-vav; Receptors, Complement 3d - physiology; Signal Transduction - immunology; src Homology Domains - immunology; Tumor Cells, Cultured; Tyrosine - metabolism
• ISSN: 0022-1767; 1550-6606
• DOI: 10.4049/jimmunol.162.1.136

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.