Formation of microdomains of the plasma membrane that are involved in intracellular signal transduction

越来越多的证据表明，质膜上微结构域的形成是细胞内信号转导的重要过程。特别是，筏的形成是通过gpi锚定蛋白进行细胞内信号转导的必要条件。先前已经发现syntaxin-3是SNARWE机制的一个组成部分，通过调节细胞内囊泡运输参与筏的形成。然而，syntaxin-3调控筏体形成的分子机制尚不清楚。然后，在本研究中，我们试图鉴定新的syntaxin-3相互作用分子。我们发现，α-fodrin是亚膜细胞骨架的主要成分，与syntaxin-3相互作用。α-Fodrin与syntaxin-1、syntaxin-4和syntaxin-3结合，而与syntaxin-7和-8不结合。α-Fodrin和nc18或SNAP-25与syntaxin-1相互作用。这些结果表明SNARE复合物的形成受α-fodrin的调控，并提示质膜下的肌动蛋白/fodrin网参与了raft的形成。此外，我们还发现了一种新的syntaxin结合蛋白，并将其命名为Taxilin。Taxilin是一种计算Mr为61890和546个氨基酸的蛋白质。Taxilin在它的c端有一个非常长的螺旋状区域。Taxilin与syntaxin-1和-4以及syntaxin-3结合，但不与syntaxin-7和-8结合。Taxilin被普遍表达。Taxilin在细胞内囊泡运输中的精确功能尚不清楚。然而，由于Taxilin影响PC12细胞Ca^<2+>依赖性胞外分泌，因此至少有可能Taxilin参与了神经内分泌细胞Ca^<2+>依赖性胞外分泌。未来，我们将试图揭示α-fodrin和Taxilin在木筏形成中的确切功能。

Accumulating evidence suggests that formation of microdomains on the plasma membrane is an important process for intracellular signal transduction. Especially, the formation of raft is essential for intracellular signal transduction through GPI-anchored proteins. It has been previously revealed that syntaxin-3, a component of the SNARWE machinery, is implicated in the formation of raft through the regulation of intracellular vesicle transport. However, the molecular mechanism by which the formation of raft is regulated by syntaxin-3 is obscure. Then, in this study, we attempted to identify new syntaxin-3-interacting molecules. We revealed that α-fodrin, a major component of the submembranes cytoskelton, interacted with syntaxin-3. α-Fodrin bound to syntaxin-1 and syntaxin-4 as well as syntaxin-3 but no to syntaxin-7 or -8. α-Fodrin and nc18 or SNAP-25 mutually interacted with syntaxin-1. These results indicate that the formation of the SNARE complex is regulated by α-fodrin and suggest that actin/fodrin meshworks beneath the plasma membrane are involved in the formation of raft. Moreover, we identified a novel syntaxin-binding protein and named it Taxilin. Taxilin was a protein with a calculated Mr of 61,890 and 546 amino acids. Taxilin had an extraordinarily long coiled-coil region in its C-terminal half. Taxilin bound to syntaxin-1 and -4 as well as syntaxin-3 but not to syntaxin-7 or -8. Taxilin was ubiquitously expressed. A precise function of Taxilin in intracellular vesicle transport is not known. However, since Taxilin affected Ca^<2+>-dependent exocytosis in PC12 cells, it is at least possible that Taxilin is involved in Ca^<2+>-dependent exocytosis in neuroendocrine cells. In future, we attempt to reveal precise functions of α-fodrin and Taxilin in the formation of raft.