Nucleotide sugar transporters: Structure and function, and physiological regulation

本研究克隆并鉴定了几种核苷酸糖转运蛋白，包括人UDP-GlcNAc转运蛋白、人CMP -唾液酸转运蛋白、人UDP-GlcA/UDP-GalNAc/UDP-GlcNAc多特异性转运蛋白（hUGTrel 7）、果蝇多特异性UDP-糖转运蛋白（UST 74 C）。这些转运蛋白的底物特异性令人信服地定义了它们在酿酒酵母高尔基体膜中的功能表达。HUGTrel 7定位于ER膜，并可能参与外源性物质的葡萄糖醛酸化和蛋白聚糖的生物合成。UST 74 C是果蝇frc基因的产物，其缺陷导致类似无翅和Notch的表型。对frc突变体的表型分析表明，核苷酸-糖水平的变化可以不同地影响这些信号通路，构建并分析了UDP-半乳糖转运体和CMP-唾液酸转运体之间的分子嵌合体，以确定负责决定这些信号通路的亚分子区域。 ...更多信息 底物特异性我们发现在UDP-Gal转运蛋白背景下含有来自CMP-唾液酸转运蛋白的跨膜螺旋2、3和7的嵌合体可以同时转运UDP-Gal和CMP-唾液酸。这表明，决定这两种转运蛋白底物特异性的关键区域位于两种转运蛋白的不同亚分子位点，并且这些不同的决定子可以存在于同一个蛋白质中，而不干扰彼此的功能。结肠癌组织中UDP-Gal转运蛋白mRNA的表达量显著高于正常粘膜组织。这种增加在杜克C期和D期的晚期结直肠癌患者中更为显著。将UDP-Gal转运蛋白cDNA转染培养的结肠癌细胞，导致转染细胞中的唾液酸刘易斯A和唾液酸刘易斯X决定簇的表达增加，这导致细胞与血管E-选择素的粘附显著增强。这些结果表明，核苷酸糖转运蛋白可以通过其对细胞表面糖复合物的结构的影响，作为细胞行为的调节元件之一。少

Several nucleotide sugar transporters including human UDP-GlcNAc transporter, human CMP -sialic acid transporter, human UDP-GlcA/UDP-GalNAc/UDP-GlcNAc multi-specific transporter (hUGTrel7), Drosophila multi-specific UDP-sugar transporter (UST74C) were cloned and characterized. Substrate specificity of these transporters were convincingly defined by their functional expression in Saccharomyces cerevisiae Golgi membranes. HUGTrel7 is localized to the ER membranes and may be involved in glucuronidation of xenobiotics and the biosynthesis of proteoglycans. UST74C is the product of Drosophila frc gene whose defect results in phenotypes resembling wingless and Notch. Analysis of the phenotypes of frc mutants suggested that change s in nucleotide-sugar levels could differently affect these signaling pathways.Molecular chimeras between UDP-Gal transporter and CMP-sialic acid transporter were constructed and analyzed in order to identify submolecular regions responsible for the determination of … More substrate specificity. We found that chimeras that contain transmembrane helices 2,3 and 7 derived from CMP-sialic acid transporter in the UDP-Gal transporter background could transport both UDP-Gal and CMP-sialic acid. This indicates that the regions which are critical for determining the substrate specificity of these two transporters resided in different submolecular sites in the two transporters, and that these different determinants could be present within one protein without interfering each other's function.The amount of mRNA for UDP-Gal transporter was significantly increased in colon cancer tissues compared with nonmalignant mucosa tissues. The increase was more prominent in patients with advanced colorectal cancer of Duke's stages C and D. Transfection of UDP-Gal transporter cDNA to cultured colon cancer cells led to increased expression of Thomsen-Freidenreich antigen and of sialyl Lewis A and sialyl Lewis X determinants in transfected cells, which resulted in markedly enhanced cell adhesion to vascular E-selectin. These findings suggest that nucleotide sugar transporters can act as one of the regulatory elements of cellular behavior through their effects on the structure of cell surface glycoconjugates. Less