MOLECULAR MECHANISMS MEDIATING CD22 ACCESSORY FUNCTION

B细胞的激活依赖于配体的结合和交叉喜欢 导致多种蛋白酪氨酸活化的抗原受体 激活剂。抗原受体相关蛋白的酪氨酸磷酸化 是进入细胞周期和细胞增殖增殖的关键 激活的B细胞。CD22是一种B系限制性跨膜蛋白 一种在酪氨酸上快速磷酸化的糖蛋白 抗原受体交联化。最近的研究表明，CD22 起黏附分子和辅助蛋白的作用，调节 通过B细胞抗原受体的信号转导。同时交叉- CD22和膜免疫球蛋白的连接显著降低了 进入B细胞周期所需的激活阈值。此外， CD22表达的缺失被证明改变了信号转导 通过与抗原受体的配体结合而启动的过程。因此，它是 显然，膜免疫球蛋白和CD22对B细胞都很重要 通过它们协同作用来调节细胞的激活 信号的产生导致体内基因转录的增加 牢房。 我们建议研究调节附件的分子机制。 CD22在B细胞中的功能。将进行研究，以确定 CD22与抗原相互作用的重要区域 受体和蛋白酪氨酸磷酸酶CD45，两者都有 已被证明可以调节CD22的酪氨酸磷酸化。具体的 抗原受体相关蛋白酪氨酸激酶(S)即负责 CD22的磷酸化作用将被确定。CD22的调控 相关蛋白酪氨酸激酶的酪氨酸磷酸化和 蛋白酪氨酸磷酸酶，CD45将被检测以确定 CD22上作为这些酶的底物的特定靶标残基。 此外，CD22磷酸化的生理重要性将是 关于含有SH2的蛋白质的结合的检查。 将进行实验以测量磷酸酪氨酸依赖 CD22和含SH2的信号转导蛋白的相互作用 以及定义这些蛋白质与之结合的特定酪氨酸残基 捆绑。最后，将进行研究以确定生理上的 辅助蛋白与CD22结合的重要性。CD22阴性细胞系 将与不再关联的突变形式的CD22重组 与含有SH2的特定蛋白质结合。突变型CD22的功能 通过抗原受体重建信号转导的分子将 被评估。 这些结构/功能研究将对我们的 对CD22调节B细胞分子基础的认识 激活。鉴于CD22似乎扮演着重要的角色 在调节和/或增强B细胞进入细胞周期时， 这些研究可能有助于阐明与自身免疫性疾病相关的过程。 和/或导致B细胞异常激活和增殖的癌症 细胞。

B cell activation is dependent on ligand binding and cross-liking of the antigen receptor resulting in activation of multiple protein tyrosine kinases. Tyrosine phosphorylation of antigen receptor-associated proteins is critical for entry into the cell cycle and proliferative expansion of the activated B cell. CD22 is a B lineage-restricted transmembrane glycoprotein that is rapidly phosphorylated on tyrosine in response to antigen receptor cross-linking. Recent studies have demonstrated that CD22 functions as an adhesion molecule and an accessory protein that regulates signal transduction via the B cell antigen receptor. Simultaneous cross- linking of CD22 and membrane immunoglobulin significantly decreases the threshold of activation required for entry of the B cell cycle. Moreover, the lack of CD22 expression has been shown to alter signal transduction processes initiated by ligand binding to the antigen receptor. Thus, it is apparent that membrane immunoglobulin and CD22 are both important for B cell activation by virtue of the fact that they act in concert to regulate the generation of signals that lead to increased gene transcription within the cell. We propose to examine the molecular mechanisms that regulate the accessory function of CD22 in the B cell. Studies will be performed to identify the regions of CD22 that are important for its interaction with the antigen receptor and the protein tyrosine phosphatase, CD45, both of which have been shown to regulate tyrosine phosphorylation of CD22. The specific antigen receptor-associated protein tyrosine kinase(s) that is responsible for phosphorylation of CD22 will be identified. Regulation of CD22 tyrosine phosphorylation by the relevant protein tyrosine kinase and the protein tyrosine phosphatase, CD45, will be examined in order to identify the specific target residues on CD22 that are substrates for these enzymes. Additionally, the physiological importance of CD22 phosphorylation will be examined with regard to the binding of SH2-containing proteins. Experiments will be performed to measure phosphotyrosine-dependent interactions between CD22 and SH2-containing signal transduction proteins as well as to define the specific tyrosine residues to which these proteins bind. Finally, studies will be performed to determine the physiological importance of accessory protein binding to CD22. CD22-negative cell lines will be reconstituted with mutated forms of CD22 that no longer associate with specific SH2-containing proteins. The ability of mutated CD22 molecules to reconstitute signal transduction via the antigen receptor will be assessed. These structure/function studies will contribute significantly to our understanding of the molecular basis by which CD22 regulates B cell activation. In view of the fact the CD22 appears to play an important role in regulating and/or potentiating entry of the B cell into the cell cycle, these studies may shed light on processes related to autoimmune disease and/or cancer that result in aberrant activation and proliferation of B cells.