Lee G, Rook S L
Program in Neuroscience, Harvard Medical School, Boston, MA.
J Cell Sci. 1992 Jun;102 ( Pt 2):227-37. doi: 10.1242/jcs.102.2.227.
The microtubule-associated protein tau is a developmentally regulated family of neuronal phosphoproteins that promotes the assembly and stabilization of microtubules. The carboxy-terminal half of the protein contains three copies of an imperfectly repeated sequence; this region has been found to bind microtubules in vitro. In addition, a fourth copy of the repeat has been found in adult-specific forms of tau protein. To examine the structure and function of tau protein in vivo, we have transiently expressed fetal and adult forms of tau protein and tau protein fragments in tissue culture cells. Biochemical analysis reveals full-length products with heterogeneity in post-translational modification synthesized in the cells. Immunofluorescent staining of transfected cells shows that, under our conditions, sequences on both sides of the repeat region are required for in vivo microtubule co-localization. These additional regions may be required either for enhancing microtubule contacts or for proper protein folding in the cell. In our expression system, the bundling of cellular microtubules occurs only in transfections using four-repeat tau constructs; any four-repeat construct capable of binding is also able to induce bundling. Our data suggest that the presence of bundles is correlated with enhanced microtubule stability; factors that increase stability such as higher levels of tau protein expression or the presence of the fourth repeat, increase the fraction of transfected cells showing bundles. Finally, the presence of tau protein in the cell allows all interphase microtubules to become acetylated, a post-translational modification usually reserved for a subset of stable cellular microtubules.
微管相关蛋白tau是一类受发育调控的神经元磷酸化蛋白家族，可促进微管的组装和稳定。该蛋白的羧基末端部分包含三个不完全重复序列的拷贝；已发现该区域在体外可与微管结合。此外，在成人特异性形式的tau蛋白中还发现了该重复序列的第四个拷贝。为了在体内研究tau蛋白的结构和功能，我们在组织培养细胞中瞬时表达了胎儿和成人形式的tau蛋白以及tau蛋白片段。生化分析显示，细胞中合成的全长产物在翻译后修饰上存在异质性。对转染细胞的免疫荧光染色表明，在我们的条件下，体内微管共定位需要重复区域两侧的序列。这些额外的区域可能是增强微管接触或细胞内蛋白质正确折叠所必需的。在我们的表达系统中，细胞微管的成束仅发生在使用四重复tau构建体的转染中；任何能够结合的四重复构建体也能够诱导成束。我们的数据表明，微管束的存在与微管稳定性增强相关；增加稳定性的因素，如更高水平的tau蛋白表达或第四个重复序列的存在，会增加显示微管束的转染细胞比例。最后，细胞中tau蛋白的存在使所有间期微管都发生乙酰化，这是一种通常仅存在于一部分稳定细胞微管中的翻译后修饰。
