Annexin A2-dependent actin bundling promotes secretory granule docking to the plasma membrane and exocytosis.
Bottom Line: Annexin A2, a calcium-, actin-, and lipid-binding protein involved in exocytosis, mediates the formation of lipid microdomains required for the structural and spatial organization of fusion sites at the plasma membrane.When an annexin A2 mutant with impaired actin filament-bundling activity was expressed, the formation of plasma membrane lipid microdomains and the number of exocytotic events were decreased and the fusion kinetics were slower, whereas the pharmacological activation of the intrinsic actin-bundling activity of endogenous annexin A2 had the opposite effects.Thus, annexin A2-induced actin bundling is apparently essential for generating active exocytotic sites.
Affiliation: Institut des Neurosciences Cellulaires et Intégratives, UPR3212 Centre National de la Recherche Scientifique, Université de Strasbourg, F-67084 Strasbourg, France.Show MeSH
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Mentions: Amperometric spikes are often preceded by the so-called prespike foot (PSF) currents, believed to reflect the slow release of catecholamines through an initial narrow fusion pore, before its subsequent rapid expansion that gives rise to the spike. Significant changes in PSF parameters were also observed (Fig. 8 and Table 1). Chromaffin cells expressing AnxA2-K286A exhibited significantly longer PSF (24.3 ± 2.1 ms versus 15.7 ± 2.1 ms in nontransfected cells) and an increase in foot charge (+30%), whereas WA-treated cells showed shorter and smaller PSF. Thus, these amperometric data are consistent with a role for AnxA2-dependent actin filament-bundling activity in the recruitment of secretory granules (number of exocytotic events), and possibly in the stabilization of the nascent fusion pore and its enlargement, thereby allowing full fusion in the late stage of exocytosis.
Affiliation: Institut des Neurosciences Cellulaires et Intégratives, UPR3212 Centre National de la Recherche Scientifique, Université de Strasbourg, F-67084 Strasbourg, France.