Barel Monique, Balbo Michelle, Le Romancer Muriel, Frade Raymond
Immunochimie des Régulations Cellulaires et des Interactions Virales, INSERM U.354, Evry, France.
Eur J Immunol. 2003 Sep;33(9):2557-66. doi: 10.1002/eji.200324059.
We previously demonstrated that CR2 activation on human B lymphocyte surface specifically triggered tyrosine phosphorylation of the 95-kDa nucleolin, this leading to its binding on SH2 domains of p85 sub-unit of PI 3-kinase and to activation of this enzyme. The specificity of CR2 pathway was clearly demonstrated as neither CD19 nor BCR could induce tyrosine phosphorylation of nucleolin in normal B lymphocytes. These data led us to investigate herein additional molecular events, which were triggered by CR2 activation, upstream and downstream to PI 3-kinase activation. Upstream, we demonstrated that pp60src, a tyrosine kinase of the src family, was involved in tyrosine phosphorylation of nucleolin, while syk tyrosine kinase was not. We also demonstrated a direct protein-protein interaction of pp60src with nucleolin in a CR2-dependent and CD19-independent pathway. Downstream, we demonstrated that CR2 activation also triggered Akt and GSK3 enzyme activation, this pathway being under the control of pp60src tyrosine kinase activation. These regulatory functions of activated CR2 were specific as independent of syk tyrosine kinase and of CD19 and BCR activation. Thus, CR2 activation recruits a specific mechanism to activate PI 3-kinase and its subsequent pathways, this mechanism being different to those recruited by CD19 and BCR.
我们先前证明，人B淋巴细胞表面的CR2激活特异性触发了95-kDa核仁素的酪氨酸磷酸化，这导致其与PI 3-激酶p85亚基的SH2结构域结合并激活该酶。CR2途径的特异性得到了明确证明，因为CD19和BCR均不能诱导正常B淋巴细胞中核仁素的酪氨酸磷酸化。这些数据促使我们在此研究由CR2激活引发的、在PI 3-激酶激活的上游和下游的其他分子事件。在上游，我们证明src家族的酪氨酸激酶pp60src参与了核仁素的酪氨酸磷酸化，而syk酪氨酸激酶则没有。我们还证明了pp60src与核仁素在依赖CR2且不依赖CD19的途径中存在直接的蛋白质-蛋白质相互作用。在下游，我们证明CR2激活还触发了Akt和GSK3酶的激活，该途径受pp60src酪氨酸激酶激活的控制。活化的CR2的这些调节功能是特异性的，独立于syk酪氨酸激酶以及CD19和BCR的激活。因此，CR2激活募集了一种特异性机制来激活PI 3-激酶及其后续途径，该机制不同于CD19和BCR募集的机制。
