REGULATION OF BCR MEDIATED SIGNAL TRANSDUCTION BY CD45

B细胞的激活和分化依赖于配体结合 到抗原受体，膜免疫球蛋白(MIG)，它传递 一种穿过质膜的信号，激活了两个 肌醇磷脂途径和MIG调节的蛋白酪氨酸激酶(PTK)。 后续基因需要激活这些生化途径。 转录和进入细胞周期。另外，我们最近 证明了磷酸酪氨酸磷酸酶(PTPase)的表达， CD45是MiG结扎后信号转导所必需的。因此，基于 以上观察表明，MiG介导的信号转导是 受PTK和PTPase(CD45)之间的动态相互作用调节。 我们建议研究CD45在调节细胞周期中的生理作用。 抗原受体连接后的B细胞活化。研究将会是 以更好地了解物理相互作用 发生在CD45和抗原受体复合体之间。共同封顶和共同- 调制实验以及化学交联研究将被 以记录这些蛋白质之间的功能关联 质膜。此外，我们将确定CD45的表达是否 是激活PTK所必需的。特定PTK的识别 通过免疫共沉淀与抗原受体复合体结合 Mig或其相关蛋白(MB-1和B29)将使我们能够确定 酪氨酸磷酸化是如何调节其活性的，它的作用是什么？ CD45在这一过程中发挥作用。将进行更多的实验，以 确定CD45是否调节特定蛋白酪氨酸的磷酸化 从CD45变异细胞中分离的MB-1和B29上的残基 台词。酪氨酸磷酸化的差异将与 通过检测这些蛋白质与MiG偶联的能力来改变功能 CD45变异细胞系中的PTK。最后，我们将利用 对CD45催化结构域进行定点突变以获得 更好地理解结构与功能之间的关系 控制这个PTPase的活性。CD45的诱变形式将是 检查它们重建信号转导的能力 CD45阴性细胞。 这些研究将大大有助于我们对 并将为B细胞活化的分子基础提供基础 关于酪氨酸对细胞功能调节的进一步研究 磷酸化/去磷酸化。具体地说，有人建议， PTPase的表达对预防细胞癌至关重要 抵消PTK对细胞影响的转化 流程。因此，上述建议的研究可以提供以下信息 增强我们对导致异常的事件的理解 激活B细胞。

B cell activation and differentiation are dependent on ligand binding to the antigen receptor, membrane immunoglobulin (mIg), which transduces a signal across the plasma membrane that activates both the phosphoinositide pathway and a mIg-regulated protein tyrosine kinase (PTK). Activation of these biochemical pathways is required for subsequent gene transcription and entry into the cell cycle. In addition, we recently demonstrated that expression of a phosphotyrosine phosphatase (PTPase), CD45, is required for signaling following mIg ligation. Thus, based on the above observations it is apparent that mIg-mediated signal transduction is regulated by the dynamic interplay between a PTK and a PTPase (CD45). We propose to examine the physiologic role of CD45 in regulation of B cell activation following antigen receptor ligation. Studies will be carried out to gain a better understanding of the physical interaction that occurs between CD45 and the antigen receptor complex. Co-capping and co- modulation experiments as well as chemical crosslinking studies will be performed to document functional associations between these proteins in the plasma membrane. Further, we will determine whether CD45 expression is necessary for PTK activation. Identification of the specific PTK associated with the antigen receptor complex by coimmunoprecipitation with mIg or its associated proteins (MB-1 and B29) will enable us to determine how its activity is regulated by tyrosine phosphorylation, and what role CD45 plays in this process. Additional experiments will be carried out to determine whether CD45 regulates the tyrosine phosphorylation of specific residues on MB-1 and B29 following their isolation from CD45-variant cell lines. Differences in tyrosine phosphorylation will be correlated with altered function by examining the ability of these proteins to couple mIg to the PTK in CD45-variant cell lines. Finally, we will utilize site-directed mutagenesis of the catalytic domain of CD45 in order to gain a better understanding of the structure-function relationships which control the activity of this PTPase. Mutagenized forms of CD45 will be examined for their ability to reconstitute signal transduction in CD45-negative cells. These studies will contribute significantly to our understanding of the molecular basis of B cell activation and will provide the foundation for further studies concerning the regulation of cell function by tyrosine phosphorylation/dephosphorylation. Specifically, it has been suggested that PTPase expression is critical for the prevention of cellular transformation by counterbalancing the effects of PTK's on cellular processes. Thus, the studies proposed above may provide information that enhances our understanding of the events which result in aberrant activation of the B cell.