Lantéri Marion, Giordanengo Valérie, Vidal Frédérique, Gaudray Patrick, Lefebvre Jean-Claude
INSERM U526, IFR50, Faculté de Médecine, 06107 Nice Cedex 2, France.
Glycobiology. 2002 Dec;12(12):785-92. doi: 10.1093/glycob/cwf087.
The synthesis of Galalpha1-3Gal-terminated oligosaccharides (alpha-Gal) epitopes has been interrupted during the course of evolution, starting with Old World primates. Partial sequences similar to the alpha1,3-galactosyltransferase (alpha1,3GalT) gene, which governs the synthesis of alpha-Gal epitopes, have been detected in the human genome and were found to correspond to pseudogenes. We completed the sequence of the human alpha1,3GalT pseudogene present on chromosome 9 and found it to be organized like the murine alpha1,3GalT gene. In human cell lines and several normal and tumor tissues we detected truncated transcripts corresponding to this pseudogene. Considering these mRNAs, translation of an open reading frame containing the first four translated exons but missing the two catalytic exons could predict a truncated alpha1,3GalT polypeptide that should be enzymatically inactive. We show that transcription of human alpha1,3GalT is prematurely terminated at the level of a strong transcriptional stop signal in the middle of intron VII. We were able to reproduce this effect in vitro by subcloning the implicated DNA region upstream from a reporter cDNA. The premature transcriptional arrest of human alpha1,3-GalT gene leads to an ectopic splicing event and to the connection of a short intronic sequence downstream from translated exons. Finally, we show that these truncated transcripts are overexpressed in cell lines with modifications of O-glycans.
从旧世界灵长类动物开始，在进化过程中，α-半乳糖（Galα1-3Gal）末端寡糖（α-Gal）表位的合成被中断。在人类基因组中已检测到与控制α-Gal表位合成的α1,3-半乳糖基转移酶（α1,3GalT）基因相似的部分序列，并且发现这些序列对应于假基因。我们完成了位于9号染色体上的人类α1,3GalT假基因的序列测定，发现其结构与鼠类α1,3GalT基因相似。在人类细胞系以及几种正常和肿瘤组织中，我们检测到了与该假基因对应的截短转录本。考虑到这些mRNA，一个包含前四个编码外显子但缺少两个催化外显子的开放阅读框的翻译可能会预测出一种截短的α1,3GalT多肽，该多肽应该没有酶活性。我们发现人类α1,3GalT的转录在第VII内含子中部的一个强转录终止信号水平处提前终止。我们通过将相关DNA区域亚克隆到报告基因cDNA上游，在体外重现了这种效应。人类α1,3-半乳糖基转移酶基因的转录提前终止导致了异位剪接事件，并使一个短的内含子序列与编码外显子下游相连。最后，我们发现这些截短的转录本在O-聚糖发生修饰的细胞系中过表达。
