Mechanism for the Organization of the Golgi apparatus

高尔基体由成堆的贮池组成，是转运分泌蛋白的站点。当秘书蛋白通过这个细胞器从内质网转运到质膜时，膜从高尔基体进出。此外，膜外排发生与从高尔基体到内质网的逆行运输一致。尽管有大量的膜流动，但在哺乳动物细胞的间期，高尔基体的结构是维持的。本项目的目的是阐明高尔基体的组织机制，并在早期分泌途径中发现参与囊泡运输的新蛋白。得到了以下结果：过表达Gαi2和Gαz对北二氢愈创木酸诱导的高尔基分解有抑制作用，但对其他Gα物种无抑制作用。Gαz特异性的RGS （g蛋白信号调节因子）蛋白的表达也引起高尔基体解体，这表明Gαz的活性形式在高尔基体的维持中起作用。短链神经酰胺阻断了高尔基分解试剂如brefeldin A引起的高尔基分解，而长链神经酰胺增强了它们的作用。这表明鞘脂代谢与高尔基体的稳定性有关。一个新的蛋白被称为p125，可以与COPII的一个亚基Sec23p相互作用，被分离出来。它具有一个富pro区和一个磷脂酶a结构域。P125与拴系蛋白p115共定位。数据库搜索显示存在一种与p125.4高度相似的蛋白质（KIAA0725p）。在内质网中发现了一种新的syntaxin （syntaxin 18）。Syntaxin 18可能参与了逆行转运。已鉴定出几个syntaxin 18结合蛋白，目前正在进行鉴定。

The Golgi apparatus consisting of stacks of cisternae is a station for the transit of secretory proteins. Membranes flow into and out from the Golgi apparatus as secretary proteins are transported from the endoplasmic reticulum to the plasma membrane through this organelle. In addition, membrane efflux occurs in accordance with retrograde transport from the Golgi to the endoplasmic reticulum. In spite of massive membrane flow, the structure of the Golgi apparatus is maintained during the interphase of mammalian cells. The purpose of the present project is to elucidate the mechanism of the organization of the Golgi apparatus, and to identify new proteins involved in vesicular transport in the early secretory pathway. The following results were obtained.1. Nordihydroguaiaretic acid-induced Golgi disassembly was prevented by overexpression of Gαi2 or Gαz, but not other Gα species. Expression of RGS (regulator of G-protein signaling) proteins specific for Gαz also caused Golgi disassembly, suggesting that the active form of Gαz plays a role in the maintenance of the Golgi apparatus.2. Short chain ceramide blocked Golgi disassembly caused by Golgi-disrupting reagents such as brefeldin A, whereas long chain ceramide enhanced their effects. This suggests that sphingolipid metabolism is implicated in the stability of the Golgi apparatus.3. A novel protein termed p125 that can interact with a subunit of COPII, Sec23p, was isolated. It possesses a Pro-rich region and a phospholipase A domain. p125 was colocalized with a tethering protein, p115. A data base search revealed the presence of a protein (KIAA0725p) which shows high similarity to p125.4. A novel syntaxin species (syntaxin 18) localized in the endoplasmic reticulum was identified. Syntaxin 18 is possibly involved in the retrograde transport. Several syntaxin 18-binding proteins were identified and their characterization is now in progress.