MOLECULAR MECHANISMS MEDIATING CD22 ACCESSORY FUNCTION

B细胞的活化依赖于配体结合和配体的交联。 导致多种蛋白酪氨酸活化的抗原受体 激酶。 抗原受体相关蛋白的酪氨酸磷酸化 是进入细胞周期和增殖扩张的关键 激活的B细胞。 CD 22是一种B谱系限制性跨膜 一种糖蛋白，在酪氨酸上迅速磷酸化，以响应 抗原受体交联。 最近的研究表明，CD 22 作为粘附分子和辅助蛋白发挥作用， 通过B细胞抗原受体进行信号转导。 同时交叉- CD 22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，委员会认为， 已经显示缺乏CD 22表达改变了信号转导 由配体与抗原受体结合引发的过程。 照经上所 很明显，膜免疫球蛋白和CD 22对B 细胞激活，因为它们协同作用调节 产生的信号，导致增加基因转录内 牢房 我们建议检查调节附件的分子机制， CD 22在B细胞中的功能。 将进行研究，以确定 CD 22与抗原相互作用的重要区域 受体和蛋白酪氨酸磷酸酶，CD 45，两者都有 已显示调节CD 22的酪氨酸磷酸化。 具体 抗原受体相关蛋白酪氨酸激酶 将鉴定CD 22的磷酸化。 CD 22的调节 通过相关蛋白酪氨酸激酶的酪氨酸磷酸化， 将检查蛋白酪氨酸磷酸酶CD 45，以确定 作为这些酶底物的CD 22上的特定靶残基。 此外，CD 22磷酸化的生理重要性将是 检查关于含SH 2蛋白的结合。 将进行实验以测量磷酸酪氨酸依赖性 CD 22和含SH 2的信号转导蛋白之间的相互作用 以及确定这些蛋白质与之结合的特定酪氨酸残基 这家公司进退两难. 最后，将进行研究，以确定生理 辅助蛋白与CD 22结合的重要性。 CD 22阴性细胞系 将用突变形式的CD 22重建， 与特定的含SH 2的蛋白质结合 突变的CD 22 通过抗原受体重建信号转导的分子将 进行评估。 这些结构/功能研究将大大有助于我们 了解CD 22调节B细胞的分子基础 activation. 鉴于CD 22似乎发挥重要作用， 在调节和/或增强B细胞进入细胞周期中， 这些研究可能会揭示与自身免疫性疾病相关的过程， 导致B异常活化和增殖的癌症 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.