SIGNAL TRANSDUCTION IN B CELL ACTIVATION

B 淋巴细胞抗原受体、膜免疫球蛋白 (mIg) 的功能 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 抗原用于后续处理和呈递给 T 细胞。 最近 研究结果表明，在某些情况下，膜的结扎 免疫球蛋白也会导致细胞能力失活 未连接的受体来转导信号。 这种“脱敏”可能是 B 细胞库中克隆无能介导的耐受性基础。 的 所有这些功能的执行需要 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，涉及桥接的次级膜蛋白 受体 mIg 与胞质蛋白，或者可以是间接的，通过 mIg 的细胞质尾部与胞质蛋白的相互作用，或者可以 是间接的，涉及桥接受体的次级膜蛋白 mIg 至胞浆蛋白。 缺乏重要的细胞质结构 mIg 分子实际上排除了前一种可能性，直到 最近，只有零碎的数据支持后者 可能性。 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物相关 异二聚体和这些复合物的成分之间略有不同 mIgM 相关和 mIgD 相关形式。 mIgM 与 IgMalpha (32kDa) 和 Igbeta (37kDa) 以及 IgMalpha 和 Igamma 的异二聚体 (34kDa) 蛋白质。 mIgD 与 IgDalpha 异二聚体相关 (33kDa)、Igbeta、IgDalpha 和 Igamma 蛋白。 最近的研究 表明 IgMalpha 和 IgDalpha 是 mb-1 基因的产物，并且 Igbeta 和 Igalpha 是 B29 基因的产物。 独特的阿尔法 亚基的使用可能决定了先前提到的生物学差异 mIgM 与 mIgD 连接后的反应。 与角色一致 信号转导和受体脱敏，多个亚基 上述复合物在酪氨酸残基上被诱导磷酸化。 在此应用中，我们建议确定这些蛋白质的功能 以及它们在介导受体中表现出的特定结构基序 功能。 这些研究将涉及 IgMalpha、IgDalpha、 Igbeta 和 Igamma 编码基因的蛋白质。 根据推导 序列，我们将生产针对复合物亚基的特异性抗体 并使用这些抗体来研究亚基分布和功能。 我们 将利用生化方法来识别特定位点 在信号转导、脱敏和 细胞骨架相互作用。 我们将确定具体的角色 通过产生和分析受体功能中的磷酸化事件 转染的 B 细胞表达突变受体亚基，其中特异性 磷酸化位点发生改变或缺失。 拟议的研究应该 为我们了解 B 的分子基础做出了重大贡献 淋巴细胞活化、抗原加工和耐受。

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.