SIGNAL TRANSDUCTION IN B CELL ACTIVATION

B淋巴细胞抗原受体，膜免疫球蛋白（mIg），在 跨质膜的信息转导导致改变 基因表达和细胞活化，以及聚焦和内化 用于随后的处理和呈递给T细胞。 最近 研究结果表明，在某些情况下， 免疫球蛋白也导致细胞免疫功能的失活。 未连接的受体与信号传导。 这种“脱敏”可能是 B细胞库中克隆性无能介导的耐受性的基础。 的 所有这些功能的发挥都需要免疫球蛋白分子 与细胞质中的分子进行物理交流。 这种蛋白质，或 可能是间接的，涉及二级膜蛋白， 受体mIg与胞质蛋白，或可以是间接的，发生通过 mIg的胞质尾区与胞质蛋白的相互作用，或者可以 是间接的，涉及连接受体的次级膜蛋白 对胞浆蛋白的免疫球蛋白。 缺乏明显的细胞质结构 在毫克分子中几乎排除了前一种可能性，直到 最近，只有零星的数据支持后者 可能性 我们已经发现，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组分在 mIgM相关和mIgD相关形式。 mIgM与 IgMalpha（32 kDa）和Igbeta（37 kDa）以及IgMalpha和Iggamma的异二聚体 （34 kDa）蛋白质。 mIgD与IgD α的异二聚体相关 （33 kDa），和Igbeta，和IgDalpha和Iggamma蛋白。 最近的研究 表明IgMalalpha和IgDalpha是mb-1基因的产物，和 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注意到的生物学差异， mIgM与mIgD连接后的应答。 与一个角色相一致， 信号转导和受体脱敏，多个亚单位的 上述复合物在酪氨酸残基上可诱导磷酸化。 在本申请中，我们建议确定这些蛋白质的功能 以及它们所展示的特定结构基序， 功能 这些研究将涉及IgMalpha，IgDalpha， Igbeta和Iggamma基因编码蛋白。 根据推断 序列，我们将产生针对复合物亚基的抗体。 用这些抗体来研究亚基的分布和功能。 我们 将利用生物化学的方法来确定特定的地点， 在信号转导、脱敏和 细胞骨架相互作用 我们将确定具体的作用 受体功能中的磷酸化事件， 转染的B细胞，其表达突变受体亚单位，其中特异性 磷酸化位点改变或缺失。 拟议的研究应 有助于我们理解B的分子基础 淋巴细胞活化、抗原加工和耐受性。

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.