SIGNAL TRANSDUCTION IN B CELL ACTIVATION

B淋巴细胞抗原受体，膜免疫球蛋白(MiG)，在 跨质膜的信息传递导致改变 基因表达和细胞激活，以及聚焦和内化 用于后续处理和呈递给T细胞的抗原。近期 结果表明，在某些情况下，结扎膜 免疫球蛋白还导致细胞的能力失活 未连接的受体来传递信号。这种“脱敏”可能是 B细胞池中克隆无能介导的耐受基础。这个 所有这些功能的实现都需要MiG分子 与细胞质中的分子进行物理交流。这种蛋白质，或者 可能是间接的，涉及桥接的次生膜蛋白 与胞浆蛋白结合的受体Mig，或可能是间接的，通过 MIG胞质尾部与胞浆蛋白的相互作用 间接的，涉及连接受体的次生膜蛋白 MIG转化为胞质蛋白。缺乏显著的细胞质结构 实际上排除了前一种可能性，直到 最近，只有零星的数据支持后者 有可能。我们发现膜免疫球蛋白是非共价的 与由两个二硫键组成的蛋白质复合体有关 杂二聚体和这些络合物组成略有不同 与mIgM关联的表单和与mIgD关联的表单。MIgM与 Ig Malpha(32 KDa)和Igβ(37 KDa)以及Ig Malpha和Iggamma的杂二聚体 (34 KDa)蛋白质。MIgD与IgDalpha的异源二聚体相关 (33 KDa)、Igβ、Ig-Dalpha和Iggamma蛋白。最新研究 表明IgMalpha和IgDalpha是mb-1基因(S)的产物，以及 免疫球蛋白β和免疫球蛋白α是B29基因的产物(S)。不同的Alpha 亚基的使用可以决定前面提到的生物学上的差异 MIgM与mIgD结扎后的反应。与中的角色一致 信号转导和受体脱敏，多个亚单位 上述复合体在酪氨酸残基上被诱导磷酸化。 在这一应用中，我们建议确定这些蛋白质的功能 以及它们在介导受体时表现出的特定结构基序 功能。这些研究将涉及到IgMalpha、IgDalpha、 Igβ和Iggamma编码基因的蛋白质。基于推导出的 序列，我们将产生针对复合体亚单位的抗体 并利用这些抗体研究亚基的分布和功能。我们 将利用生化方法来确定特定的位置 在信号转导、脱敏和 细胞骨架相互作用。我们将确定特定的角色 产生和分析受体功能中的磷酸化事件 表达突变型受体亚基的转基因B细胞 磷酸化位点改变或缺失。建议的研究应 对我们理解B的分子基础有很大帮助 淋巴细胞活化、抗原处理和耐受。

B lymphocyte antigen receptors, membrane immunoglobulins (mIg), function in transduction of information across the plasma membrane leading to altered gene expression and cell activation, and in focussing and internalization of antigen for subsequent processing and presentation to T cells. Recent findings indicate that under certain circumstances ligation of membrane immunoglobulin also leads to inactivation of the ability of the cell's unligated receptors to transduce signals. This "desensitization" may be the basis of tolerance mediated by clonal anergy in the B cell pool. The performance of all of these functions requires that mIg molecules communicate physically with molecules in the cytoplasm. This protein, or could be indirect, involving secondary membrane proteins which bridge receptor mIg with cytosolic protein, or could be indirect, occurring via interaction of the cytoplasmic tail of mIg with cytosolic protein, or could be indirect, involving secondary membrane proteins which bridge receptor mIg to cytosolic proteins. The lack of significant cytoplasmic structure in mIg molecules virtually excludes the former possibility and, until recently, only fragmentary data existed in support of the latter possibility. We have found that membrane immunoglobulins are noncovalently associated with a complex of proteins composed of two disulfide bonded heterodimers and that components of these complexes differ slightly between mIgM-associated and mIgD-associated forms. mIgM is associated with heterodimers of IgMalpha(32kDa) and Igbeta(37kDa), and IgMalpha and Iggamma (34kDa) proteins. mIgD is associated with heterodimers of IgDalpha (33kDa), and Igbeta, and IgDalpha and Iggamma proteins. Recent studies indicate that IgMalpha and IgDalpha are products of the mb-1 gene(s), and that Igbeta and Igalpha are products of the B29 gene(s). Distinct alpha subunit usage may determine the previously noted differences in biological responses which follow mIgM vs. mIgD ligation. Consistent with a role in signal transduction and receptor desensitization, multiple subunits of the above complex are inducibly phosphorylated on tyrosine residues. In this application, we propose to determine the function of these proteins and specific structural motifs which they exhibit, in mediating receptor function. These studies will involve the cloning of IgMalpha, IgDalpha, Igbeta and Iggamma encoding proteins of the genes. Based on deduced sequence, we will produce antibodies specific for subunits of the complex and use these antibodies to study subunit distribution and function. We will utilize biochemical approaches to identify specific sites phosphorylated during signal transduction, desensitization, and cytoskeletal interaction. We will determine the role of specific phosphorylation events in receptor function by production and analysis of transfected B cell which express mutant receptor subunits in which specific phosphorylation sites are altered or absent. The proposed studies should contribute significantly to our understanding of the molecular basis of B lymphocyte activation, antigen processing and tolerance.