SV2A and SV2C are not vesicular Ca2+ transporters but control glucose-evoked granule recruitment
SV2A and SV2C are not vesicular Ca2+ transporters but control glucose-evoked granule recruitment
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DOI：
10.1242/jcs.02658
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发表时间：
2005-12-01
影响因子：
4
通讯作者：
Wollheim, CB
中科院分区：
文献类型：
--
作者：
Lezzi, M;Theander, S;Wollheim, CB
突触囊泡蛋白2（SV 2）在神经内分泌细胞中表达为三种同源同种型，SV 2A、SV 2B和SV 2C。胞吐中的Ca 2+依赖性功能归因于SV 2A和SV 2B，但机制尚未阐明。SV 2C的作用尚未得到解决。在这里，我们的特点是三个SV 2亚型，并确定其参与调节胰岛素分泌。SV 2A和SV 2C与INS-1 E胰岛素瘤和原代β细胞中的含胰岛素颗粒和突触样微泡（SLM）相关，而SV 2B仅存在于SLM上。用VAMP-2水母发光蛋白嵌合体测量，通过RNA干扰的SV 2A或SV 2C的过表达或亚型特异性沉默都不会改变去极化触发的胞质[Ca 2（+）]升高或分泌颗粒[Ca 2（+）]。这强烈反对SV 2的任何Ca 2（+）转运功能。此外，这些亚型的上调或下调对K+诱导的胰岛素释放没有影响，这表明SV 2不影响胞吐的Ca 2+依赖性步骤。相比之下，葡萄糖引起的分泌在持续而不是早期阶段受到抑制，将SV 2的作用置于颗粒从储备池到质膜的募集上。葡萄糖刺激的SV 2C缺陷细胞中的电容测量结果加强了这一结论。与电容一样，与SV 2A相比，SV 2C沉默更能减弱诱发和基础激素释放。这表明只有部分冗余，并强调了SV 2C在分泌过程中的关键作用。
Synaptic vesicle protein 2 (SV2) is expressed in neuroendocrine cells as three homologous isoforms, SV2A, SV2B and SV2C. Ca2+-dependent function in exocytosis has been attributed to SV2A and SV2B, without elucidation of the mechanism. The role of SV2C has not yet been addressed. Here we characterize the three SV2 isoforms and define their involvement in regulated insulin secretion. SV2A and SV2C are associated with insulin-containing granules and synaptic-like-microvesicles (SLM) in INS-1E insulinoma and primary beta-cells, whereas SV2B is only present on SLM. Neither overexpression nor isoform-specific silencing of SV2A or SV2C by RNA interference modifies depolarization-triggered cytosolic [Ca2(+)] rises or secretory granule [Ca2(+)], measured with a VAMP-2 aequorin chimera. This strongly argues against any Ca2(+) transport function of SV2. Moreover, up- or downregulation of these isoforms has no influence on K+-induced insulin release suggesting that SV2 does not affect the Ca2+-dependent step(s) of exocytosis. By contrast, glucose-elicited secretion is inhibited during the sustained rather than the early phase, placing the action of SV2 on the recruitment of granules from the reserve pool to the plasma membrane. This conclusion is reinforced by capacitance measurements in glucose-stimulated SV2C-deficient cells. Like capacitance, evoked and basal hormone release are attenuated more by silencing of SV2C compared with SV2A. This indicates only partial redundancy and highlights a key role for SV2C in the secretory process.