Zhang Miao, Veselits Margaret, O'Neill Shannon, Hou Ping, Reddi Alagarsamy L, Berlin Ilana, Ikeda Masato, Nash Piers D, Longnecker Richard, Band Hamid, Clark Marcus R
Section of Rheumatology, Department of Medicine, University of Chicago, IL 60637, USA.
J Immunol. 2007 Oct 1;179(7):4435-43. doi: 10.4049/jimmunol.179.7.4435.
In both infection and autoimmunity, the development of high-affinity Abs and memory requires B cells to efficiently capture and process Ags for presentation to cognate T cells. Although a great deal is known about how Ags are processed, the molecular mechanisms by which the BCR captures Ag for processing are still obscure. In this study, we demonstrate that the Ig beta component of the BCR is diubiquitinylated and that this is dependent on the E3 ligase Itch. Itch-/- B lymphocytes manifest both a defect in ligand-induced BCR internalization and endocytic trafficking to late endosomal Ag-processing compartments. In contrast, analysis of ubiquitinylation-defective receptors demonstrated that the attachment of ubiquitins to Ig beta is required for endosomal sorting and for the presentation of Ag to T cells, yet, ubiquitinylation is dispensable for receptor internalization. Membrane-bound Ig mu was not detectably ubiquitinylated nor were the conserved lysines in the mu cytosolic tail required for trafficking to late endosomes. These results demonstrate that ubiquitinylation of a singular substrate, Ig beta, is required for a specific receptor trafficking event. However, they also reveal that E3 ligases play a broader role in multiple processes that determine the fate of Ag-engaged BCR complexes.
在感染和自身免疫过程中，高亲和力抗体和记忆细胞的发育需要B细胞有效地捕获和处理抗原，以呈递给同源T细胞。尽管人们对抗原的处理方式了解很多，但BCR捕获抗原进行处理的分子机制仍不清楚。在本研究中，我们证明BCR的Igβ组分被双泛素化，且这依赖于E3连接酶Itch。Itch基因敲除的B淋巴细胞在配体诱导的BCR内化以及向晚期内体抗原处理区室的内吞运输方面均表现出缺陷。相反，对泛素化缺陷受体的分析表明，将泛素连接到Igβ是内体分选以及将抗原呈递给T细胞所必需的，然而，泛素化对于受体内化是可有可无的。膜结合的Igμ未检测到泛素化，且μ胞质尾部中对于运输到晚期内体所必需的保守赖氨酸也未检测到泛素化。这些结果表明，单个底物Igβ的泛素化是特定受体运输事件所必需的。然而，它们也揭示了E3连接酶在决定抗原结合BCR复合物命运的多个过程中发挥着更广泛作用。
