Chen L, Zhang W, Fregien N, Pierce M
Department of Biochemistry and Molecular Biology and Complex Carbohydrate Research Center, University of Georgia, Athens 30602, USA.
Oncogene. 1998 Oct 22;17(16):2087-93. doi: 10.1038/sj.onc.1202124.
Malignant transformation is associated with changes in the glycosylation of cell surface proteins. For example, the N-linked oligosaccharides containing the [GlcNAc beta(1,6)Man] branch are increased after transformation of many cell types by a number of tumor viruses and oncogenes which induce the expression of N-acetylglucosaminyl-transferase V (GlcNAc-T V), the enzyme that adds this branch. A large percentage of human breast carcinomas have increased N-linked beta(1,6) branches on glycoproteins, while up to 30% of breast carcinomas have amplified the oncogene her-2/neu (erb-B2). We tested the hypothesis that expression of her-2/neu stimulates GlcNAc-T V gene expression and increases the beta(1,6) branching of N-linked oligosaccharides. We found that neu-transformed NIH3T3 cells have a threefold increase in GlcNAc-T V enzyme activity and increased beta(1,6) branching on a specific set of glycoproteins. Promoter/reporter experiments showed that her-2/neu stimulates transcription from the human GlcNAc-T V promoter and that the her-2/neu response element was located about 400 bp 5' of the transcription initiation site and includes three Ets transcription factor binding sequences. Co-transfections with dominant-negative Raf and Ets expression plasmids demonstrated that the transcriptional activation of the GlcNAc-T V promoter by neu is mediated by the Ras-Raf-Ets signal transduction pathway.
恶性转化与细胞表面蛋白糖基化的变化有关。例如，许多细胞类型被多种肿瘤病毒和致癌基因转化后，含有[GlcNAc β(1,6)Man]分支的N-连接寡糖会增加，这些病毒和致癌基因可诱导N-乙酰葡糖胺基转移酶V（GlcNAc-T V）的表达，该酶可添加此分支。很大比例的人类乳腺癌糖蛋白上的N-连接β(1,6)分支增加，而高达30%的乳腺癌扩增了致癌基因her-2/neu（erb-B2）。我们检验了her-2/neu的表达刺激GlcNAc-T V基因表达并增加N-连接寡糖β(1,6)分支的假说。我们发现，neu转化的NIH3T3细胞中GlcNAc-T V酶活性增加了三倍，并且一组特定糖蛋白上的β(1,6)分支增加。启动子/报告基因实验表明，her-2/neu刺激人GlcNAc-T V启动子的转录，并且her-2/neu反应元件位于转录起始位点上游约400 bp处，包括三个Ets转录因子结合序列。用显性负性Raf和Ets表达质粒进行的共转染表明，neu对GlcNAc-T V启动子的转录激活是由Ras-Raf-Ets信号转导途径介导的。
