Department of Cell Biology, Erasmus Medical Center, 3000 CA Rotterdam, The Netherlands.
Curr Biol. 2011 Jun 7;21(11):967-74. doi: 10.1016/j.cub.2011.04.030. Epub 2011 May 19.
Rab6 is a conserved small GTPase that localizes to the Golgi apparatus and cytoplasmic vesicles and controls transport and fusion of secretory carriers [1]. Another Rab implicated in trafficking from the trans-Golgi to the plasma membrane is Rab8 [2-5]. Here we show that Rab8A stably associates with exocytotic vesicles in a Rab6-dependent manner. Rab8A function is not needed for budding or motility of exocytotic carriers but is required for their docking and fusion. These processes also depend on the Rab6-interacting cortical factor ELKS [1], suggesting that Rab8A and ELKS act in the same pathway. We show that Rab8A and ELKS can be linked by MICAL3, a member of the MICAL family of flavoprotein monooxygenases [6]. Expression of a MICAL3 mutant with an inactive monooxygenase domain resulted in a strong accumulation of secretory vesicles that were docked at the cell cortex but failed to fuse with the plasma membrane, an effect that correlated with the strongly reduced mobility of MICAL3. We propose that the monooxygenase activity of MICAL3 is required to regulate its own turnover and the concomitant remodeling of vesicle-docking protein complexes in which it is engaged. Taken together, the results of our study illustrate cooperation of two Rab proteins in constitutive exocytosis and implicates a redox enzyme in this process.
Rab6 是一种保守的小分子 GTPase，定位于高尔基体和细胞质小泡，控制着分泌载体的运输和融合 [1]。另一种参与从反式高尔基体到质膜运输的 Rab 是 Rab8 [2-5]。在这里，我们表明 Rab8A 以 Rab6 依赖的方式与胞吐小泡稳定地结合。Rab8A 功能对于胞吐载体的出芽或迁移不是必需的，但对于它们的停靠和融合是必需的。这些过程还依赖于 Rab6 相互作用的皮质因子 ELKS [1]，表明 Rab8A 和 ELKS 作用于相同的途径。我们表明，Rab8A 和 ELKS 可以通过 MICAL3 连接，MICAL3 是黄素蛋白单加氧酶 MICAL 家族的成员 [6]。表达具有失活单加氧酶结构域的 MICAL3 突变体导致分泌小泡强烈积累，这些小泡停靠在质膜，但未能与质膜融合，这一效应与 MICAL3 的迁移性大大降低相关。我们提出，MICAL3 的单加氧酶活性是调节其自身周转和与之相关的囊泡停靠蛋白复合物重构所必需的。总之，我们的研究结果说明了两种 Rab 蛋白在组成型胞吐作用中的合作，并暗示了一种氧化还原酶在这个过程中的作用。
