Docking is not a prerequisite but a temporal constraint for fusion of secretory granules
Docking is not a prerequisite but a temporal constraint for fusion of secretory granules
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DOI：
10.1111/j.1600-0854.2008.00744.x
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发表时间：
2008-07-01
期刊：
影响因子：
4.5
通讯作者：
Izumi, Tetsuro
中科院分区：
文献类型：
--
作者：
Kasai, Kazuo;Fujita, Takuji;Izumi, Tetsuro
我们使用全内反射荧光显微镜检查正常胰腺β细胞及其缺乏Rab 27 a和/或其效应物颗粒亲蛋白的突变体中的分泌颗粒动力学，所述颗粒亲蛋白在胰岛素颗粒到质膜的对接和募集中起关键作用。在野生型细胞中葡萄糖刺激的早期阶段，我们观察到从相对较远的区域招募的颗粒的显著融合，与位于质膜下的颗粒的融合平行。此外，尽管缺乏直接附着在质膜上的颗粒，自发和诱发的融合在颗粒素空细胞中增加。除了这些颗粒蛋白空表型，Rab 27 a/颗粒蛋白双缺陷细胞显示，在葡萄糖刺激分泌的早期阶段，位于停靠区域旁边的颗粒和质膜附近的颗粒融合减少，类似于Rab 27 a突变的细胞。因此，这两种蛋白质在胰岛素胞吐作用中发挥不重叠的作用：颗粒蛋白作用于质膜下的颗粒，而Rab 27 a作用于更远端区域的颗粒。这些研究结果表明，与我们传统的理解相反，分泌颗粒与质膜的稳定附着不是先决条件，而是对自发和诱发融合的暂时抑制。
We examined secretory granule dynamics using total internal reflection fluorescence microscopy in normal pancreatic beta cells and their mutants devoid of Rab27a and/or its effector, granuphilin, which play critical roles in the docking and recruitment of insulin granules to the plasma membrane. In the early phase of glucose stimulation in wild-type cells, we observed marked fusion of granules recruited from a relatively distant area, in parallel with that from granules located underneath the plasma membrane. Furthermore, despite a lack of granules directly attached to the plasma membrane, both spontaneous and evoked fusion was increased in granuphilin-null cells. In addition to these granuphilin-null phenotypes, Rab27a/granuphilin doubly deficient cells showed the decreases in granules located next to the docked area and in fusion from granules near the plasma membrane in the early phase of glucose-stimulated secretion, similar to Rab27a-mutated cells. Thus, the two proteins play nonoverlapping roles in insulin exocytosis: granuphilin acts on the granules underneath the plasma membrane, whereas Rab27a acts on those in a more distal area. These findings demonstrate that, in contrast to our conventional understanding, stable attachment of secretory granules to the plasma membrane is not prerequisite but temporally inhibitory for both spontaneous and evoked fusion.