蛋白质O-GlcNAc糖基化修饰对tau蛋白磷酸化修饰的影响

蛋白质的O位N-乙酰葡萄糖胺(O-GlcNAc)糖基化修饰是一种新近发现的广泛存在于细胞核蛋白与细胞浆蛋白的蛋白质翻译后修饰.其性质与经典的膜蛋白和分泌蛋白的糖基化修饰不同，而与蛋白质磷酸化修饰更相似.O-GlcNAc糖基化和磷酸化均修饰tau蛋白的丝氨酸和苏氨酸残基，通过改变O-GlcNAc糖基化供体底物浓度以及其关键酶活性等方法,改变分化后成神经细胞样的PC12细胞中的蛋白质O-GlcNAc糖基化修饰水平，然后用特异性识别不同位点磷酸化的tau蛋白抗体,进行蛋白质印迹分析来检测tau蛋白磷酸化水平的变化.结果发现细胞内蛋白质O-GlcNAc糖基化对tau蛋白磷酸化的影响，在不同的磷酸化位点其影响不同.增加蛋白质O-GlcNAc糖基化修饰导致tau蛋白大多数磷酸位点的磷酸化水平降低，反之亦然.这些结果说明，tau磷酸化在大多数位点受到O-GlcNAc糖基化修饰的负性调节.这一研究为阐明调节tau蛋白磷酸化水平的机理和阿尔茨海默病脑中tau异常过度磷酸化的分子机制提供了新的线索.

The Effect of O-GlcNAcylation on Phosphorylation of tau

O-GlcNAcylation of proteins is a recently discovered post-translational modification of nuclear and cytoplasmic proteins. This modification is similar to protein phosphorylation rather than to classical protein glycosylation of membrane and secreted proteins. Both O-GlcNAcylation and phosphorylation modify the hydroxyl group of serine or threonine residues of tau, the effect of O-GlcNAcylation on phosphorylation of tau was studied. The level of O-GlcNAcylation in differenciated PC12 cells was modulated by changing the concentration of the donor of O-GlcNAcylation and activities of the key enzymes, then, the consequent changes of tau phosphorylation at various phosphorylation sites were examined by using Western blot developed with phosphorylation-dependent and site-specific tau antibodies. It was found that O-GlcNAcylation modulated phosphorylation of tau at many phosphorylation sites and in a site-specific manner. Increased protein O-GlcNAcylation induced a decrease in tau phosphorylation at most of phosphorylation sites, and vise versa. These results suggest that O-GlcNAcylation negatively modulates tau phosphorylation at most phosphorylation sites. Therefore, these studies provide novel insight into the regulation of tau phosphorylation and the molecular mechenism of abnormal hyperphosphorylation of tau in Alzheimer disease brain.