Regulation of Insulin Exocytosis by Munc13-1*
Regulation of Insulin Exocytosis by Munc13-1*
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DOI：
10.1074/jbc.m303203200
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发表时间：
2003-07
影响因子：
4.8
通讯作者：
L. Sheu;E. Pasyk;J. Ji;Xiaohang Huang;Xiaodong Gao;F. Varoqueaux;N. Brose;H. Gaisano
中科院分区：
文献类型：
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作者：
L. Sheu;E. Pasyk;J. Ji;Xiaohang Huang;Xiaodong Gao;F. Varoqueaux;N. Brose;H. Gaisano
与其他受调节的分泌过程（如嗜铬颗粒分泌）相比，胰岛β细胞释放胰岛素的动力学较慢，部分原因是停靠在质膜上并易于释放的胰岛素颗粒数量较少。在2型糖尿病中，胰岛素分泌的动力学变得严重扭曲，并且为了在治疗上纠正这一点，必须阐明调节胰岛素分泌颗粒的引发和分泌的机制。Munc 13 -1是一种调节SNARE复合物组装的突触蛋白，是决定突触囊泡启动的主要蛋白。在这里，我们证明了Munc 13 -1在人类，大鼠和小鼠胰岛β细胞中的存在。在2型糖尿病非肥胖Goto-Kakizaki和肥胖Zucker fa/fa大鼠的胰岛中，Munc 13 -1沿着其同源配偶体突触融合蛋白1a和Munc 18 a的表达减少。在胰岛素瘤细胞中，过表达的Munc 13 -1增强的绿色荧光蛋白以温度依赖性方式易位至质膜。这反过来又极大地放大了胰岛素胞吐作用，如通过膜片钳电容测量和释放的胰岛素的放射免疫测定所确定的。Munc 13 -1的胞吐作用的增强依赖于内源性产生的二酰基甘油作用于过表达的Munc 13 -1，因为它被磷脂酶C抑制剂（U 73122）阻断，并且当表达二酰基甘油结合缺陷型Munc 13 - 1H 567 K突变体而不是野生型蛋白质时被废除。我们的数据表明，Munc 13介导的囊泡启动并不局限于神经递质释放，而且在胰岛素分泌中也发挥作用，其中它受到二酰基甘油第二信使途径的调节。鉴于我们的发现，Munc 13 -1是糖尿病胰岛素分泌治疗优化的潜在药物靶标。
The slower kinetics of insulin release from pancreatic islet beta cells, as compared with other regulated secretory processes such as chromaffin granule secretion, can in part be explained by the small number of the insulin granules that are docked to the plasma membrane and readily releasable. In type-2 diabetes, the kinetics of insulin secretion become grossly distorted, and, to therapeutically correct this, it is imperative to elucidate the mechanisms that regulate priming and secretion of insulin secretory granules. Munc13-1, a synaptic protein that regulates SNARE complex assembly, is the major protein determining the priming of synaptic vesicles. Here, we demonstrate the presence of Munc13-1 in human, rat, and mouse pancreatic islet beta cells. Expression of Munc13-1, along with its cognate partners, syntaxin 1a and Munc18a, is reduced in the pancreatic islets of type-2 diabetes non-obese Goto-Kakizaki and obese Zucker fa/fa rats. In insulinoma cells, overexpressed Munc13-1-enhanced green fluorescent protein is translocated to the plasma membrane in a temperature-dependent manner. This, in turn, greatly amplifies insulin exocytosis as determined by patch clamp capacitance measurements and radioimmunoassay of the insulin released. The potentiation of exocytosis by Munc13-1 is dependent on endogenously produced diacylglycerol acting on the overexpressed Munc13-1 because it is blocked by a phospholipase C inhibitor (U73122) and abrogated when the diacylglycerol binding-deficient Munc13-1H567K mutant is expressed instead of the wild type protein. Our data demonstrate that Munc13-mediated vesicle priming is not restricted to neurotransmitter release but is also functional in insulin secretion, where it is subject to regulation by the diacylglycerol second messenger pathway. In view of our findings, Munc13-1 is a potential drug target for therapeutic optimization of insulin secretion in diabetes.