Globotriaosyl Ceramide (Gb3/CD77) in Burkitt's Lymphoma

由大肠杆菌血清型0157:H7和其他血清型产生的毒毒素（VT’s，也称为志贺毒素）已被认为是溶血性尿毒症综合征、出血性结肠炎和血小板减少性紫癜的病原体。VT的受体是globotriaosyl神经酰胺（Gb3或CD77）和可能含有Gal α 1-4 Gal残基的其他鞘糖脂。Gb3在B淋巴细胞发育的生发中心阶段表达。由于其表型相似，Daudi细胞和其他Burkitt淋巴瘤衍生细胞系可作为GC B淋巴细胞的体外模型。gb3结合的VT B亚基在氨基酸序列上类似于干扰素α受体的IFNAR-1亚基、B细胞蛋白CD19和MHC II类蛋白。迄今为止的实验证据表明，Gb3和Gb3结合蛋白是伯基特淋巴瘤中许多信号转导途径的重要组成部分

Verotoxins (VT's, also called Shiga toxins) produced by E. coli serotype 0157:H7 and other serotypes have been implicated as causative agents of hemolytic uremic syndrome, hemorrhagic colitis, and thrombocytopenic purpura. The receptors for VT's are globotriaosyl ceramide (Gb3 or CD77) and possibly other glycosphingolipids which contain Gal alpha1-4 Gal residues. Gb3 is expressed at the germinal center stage of B lymphocyte development. Because of their phenotypic resemblance, Daudi cells and other Burkitt's lymphoma-derived cell lines serve as in vitro models of GC B lymphocytes. The Gb3-binding VT B subunits mimic the IFNAR-1 subunit of the interferon-alpha receptor, the B cell protein CD19, and MHC class II proteins in their amino acid sequences. Experimental evidence to date indicates that Gb3 and Gb3-binding proteins are essential components of a number of signal transduction pathways in Burkitt's lymphoma and GC B lymphocytes. These include a role for Gb3/IFNAR-1 in IFN-alpha induced growth inhibition and adhesion, Gb3/CD19 interaction in adhesion and Gb3/VT B-subunit interaction in the induction of apoptosis. However, there is relatively little data available concerning which signal transduction pathways require Gb3, or the precise role of Gb3 in the pathways leading to the observed responses. Our preliminary investigations indicate that Gb3 may play a major role in a number of apoptotic pathways in Gb3-positive B cells. We propose to further investigate the role of Gb3 in signal transduction relating to apoptosis using the Daudi cell line, which expresses high levels of Gb3, and the Daudi-derived Gb3-deficient VT500 cell line. The long term objectives of the proposed research are to determine the cellular functions of Gb3 and other Gal alpha 1-4 Galcontaining glycolipids and their endogenous protein ligands, and to determine how the targeting of Gb3-positive cells by VT affects immune responses and the pathogenesis of VT producing E. coli infection. Specific aims are to: 1) Identify and define apoptosis pathways which require Gb3 by comparing such pathways in Gb3+ and Gb3- Burkitt's lymphoma cell lines. 2) Determine differential gene expression in Gb3+ and Gb3- Burkitt's lymphoma cells prior to and following treatment with inducers of apoptosis by performing microarray analysis, RT-PCR and northern analysis. 3) Identify and model potential VT-like Gb3-binding sites on proteins involved in apoptosis pathways which require Gb3.