Role of Molecular Chaperones in Ig Biosynthesis

分子伴侣在 Ig 生物合成中的作用

• 批准号: 7218000
• 负责人: Linda M Hendershot
• 金额: $ 32万
• 依托单位: ST. JUDE CHILDREN'S RESEARCH HOSPITAL
• 依托单位国家: 美国
• 财政年份: 1996
• 资助国家: 美国
• 起止时间: 1996-04-01 至 2009-03-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/7218000
• 关键词: ATP Hydrolysis; ATP phosphohydrolase; Affinity; Anabolism; Antibodies; Antibody Diversity; Architecture; B cell differentiation; B-Lymphocytes; Binding; Binding Sites; Biochemical; Bleomycin/Doxorubicin/Prednisone; Cell Line; Cell surface; Cells; Coupled; Cultured Cells; Endoplasmic Reticulum; Ensure; Environment; Enzymes; Funding; Genetic; Guanine Nucleotide Exchange Factors; Homologous Gene; Immune; Immune system; Immunoglobulins; Light; Localized; Mammalian Cell; Maps; Measures; Molecular Chaperones; Monitor; N-terminal; Nucleotides; Operative Surgical Procedures; Pathway interactions; Personal Satisfaction; Plasma Cells; Play; Process; Production; Proteins; Publishing; Quality Control; Rate; Reliance; Research Personnel; Role; Stress; Ubiquitin; Work; in vivo; molecular chaperone GRP78; novel; plasma cell differentiation; prevent; programs; protein degradation; protein folding; research study; response; secretory protein; success; transcription factor

DESCRIPTION (provided by applicant): The differentiation of a B cell to a plasma cell represents one of the most dramatic changes in cellular architecture known. The massive increase in the secretory pathway is necessary to allow the plasma cell to become a factory dedicated to the synthesis, assembly and transport of immunoglobulin (Ig) molecules. The production of mature antibodies is aided and monitored by a group of resident ER proteins known as molecular chaperones. The ER concentration of these proteins is regulated by the unfolded protein response (UPR) pathway to accommodate cellular demands for the production of secretory pathway proteins. Recent studies revealed that the UPR is activated during plasma cell differentiation, and that the XBP-1 transcription factor, which is a component of this pathway, is essential for the production of plasma cells. It has been well-documented that the ER chaperone BiP binds to unassembled Ig heavy chains and prevents their premature transport. The release of BiP from unfolded substrates is a tightly controlled process that is regulated by ATP. We have identified three novel proteins that regulate BiP's ATPase activity and are therefore likely to be involved in the release of BiP from Ig substrates. Two of these, ERdj3 and ERdj4, are DnaJ homologues and increase BiP's rate of ATP hydrolysis and should serve to stabilize BiP's binding to unfolded Ig heavy chain substrates. The third protein, BAP, is the only known nucleotide exchange factor for BiP and should enhance the release of BiP from substrates. All three proteins are up-regulated during B cell differentiation. Both ERdj3 and ERdj4 are targets of the XBP-1 transcription factor, and ERdj3 is bound directly to unassembled Ig heavy chains. Thus, we hypothesize these BiP regulators may be required for terminal differentiation of B cells. Lastly, we have found that the ER-localized Herp protein, which contains a ubiquitin-like domain and may be involved in targeting ER proteins for degradation, is up-regulated by the UPR and during plasma cell differentiation. We hypothesize that these different proteins work together in a carefully orchestrated fashion to aid Ig assembly, monitor the success of this operation, and finally to target improperly folded or assembled Ig subunits for degradation. We propose a combination of biochemical, cell culture, and genetic experiments to determine the roles and requirements of the various BiP regulators in controlling Ig synthesis and the differentiation of B cells to plasma cells.

描述(申请人提供)：B细胞向浆细胞的分化代表了已知细胞结构中最戏剧性的变化之一。分泌途径的大量增加是使浆细胞成为致力于合成、组装和运输免疫球蛋白(Ig)分子的工厂所必需的。成熟抗体的产生是由一组被称为分子伴侣的常驻ER蛋白协助和监测的。这些蛋白的内质网浓度受未折叠蛋白反应(UPR)途径的调节，以适应细胞对分泌途径蛋白的生产需求。最近的研究表明，UPR在浆细胞分化过程中被激活，XBP-1转录因子是这一途径的组成部分，对浆细胞的产生是必不可少的。已有充分的文献证明，内质网伴侣Bip与未组装的Ig重链结合，防止其过早运输。BiP从未折叠的底物中释放是一个严格控制的过程，受ATP的调节。我们已经确定了三种新的蛋白质，它们调节Bip的ATPase活性，因此很可能参与Bip从Ig底物中的释放。其中两个，ERdj3和ERdj4，是DNAJ同系物，增加了Bip的ATP水解率，应该有助于稳定Bip与未折叠的Ig重链底物的结合。第三种蛋白质，BAP，是唯一已知的Bip的核苷酸交换因子，应该能促进Bip从底物中释放。在B细胞分化过程中，这三种蛋白都表达上调。ERdj3和ERdj4都是XBP-1转录因子的靶标，ERdj3直接与未组装的Ig重链结合。因此，我们推测这些Bip调节子可能是B细胞终末分化所必需的。最后，我们发现ER定位的Herp蛋白包含一个泛素样结构域，可能参与靶向ER蛋白的降解，在UPR和浆细胞分化过程中上调。我们假设这些不同的蛋白质以一种精心编排的方式共同作用，以帮助Ig组装，监测这一操作的成功，并最终针对错误折叠或组装的Ig亚基进行降解。我们建议结合生化、细胞培养和遗传学实验来确定各种Bip调节因子在控制免疫球蛋白合成和B细胞向浆细胞分化方面的作用和要求。