Faure Ariane-Valérie, Migné Carole, Devilliers Ginnette, Ayala-Sanmartin Jesus
INSERM U332, Signalisation, Inflammation et Transformation Cellulaire, 22 rue Méchain, 75014 Paris, France.
Exp Cell Res. 2002 May 15;276(1):79-89. doi: 10.1006/excr.2002.5512.
Annexin 2 is a Ca(2+)-dependent phospholipid-binding protein that is involved in secretion. Despite the fact that this protein does not have signals for its secretion, many reports have shown its presence in the extracellular milieu. Here we demonstrate that, upon stimulation of exocytosis in chromaffin cells, a fraction of annexin 2 is secreted into the culture medium. This release of annexin 2 is specific, correlated with catecholamine secretion, and independent of cell death. To explain the liberation of cytosolic annexin 2 into the medium, we propose and bring evidence for a mechanism of multiporic membrane disruption during membrane fusion. Prior, in cross-linking experiments, annexin 2 forms aggregates of high molecular weight, revealing its capacity to form networks. Second, immunoelectron microscopy studies of fused chromaffin granules revealed the presence of annexin 2 and membrane proteins inside the fused vesicles, as would be predicted by the multiporic hypotheses. These data suggest that annexin 2 "secretion" in chromaffin cells is the consequence of membrane disruption during exocytosis. The role of annexin 2 in exocytosis is also discussed.
膜联蛋白2是一种依赖钙离子的磷脂结合蛋白，参与分泌过程。尽管该蛋白没有分泌信号，但许多报告显示其存在于细胞外环境中。在此我们证明，在嗜铬细胞中刺激胞吐作用时，一部分膜联蛋白2会分泌到培养基中。膜联蛋白2的这种释放是特异性的，与儿茶酚胺分泌相关，且与细胞死亡无关。为了解释胞质中的膜联蛋白2释放到培养基中的现象，我们提出并提供证据支持膜融合过程中多孔隙膜破坏的机制。首先，在交联实验中，膜联蛋白2形成高分子量聚集体，揭示了其形成网络的能力。其次，对融合的嗜铬颗粒进行免疫电子显微镜研究发现，融合囊泡内存在膜联蛋白2和膜蛋白，这与多孔隙假说的预测一致。这些数据表明，嗜铬细胞中膜联蛋白2的“分泌”是胞吐作用期间膜破坏的结果。同时也讨论了膜联蛋白2在胞吐作用中的作用。
