Annexin A2, an essential partner of the exocytotic process in chromaffin cells.

Annexin A2 is a calcium-, actin-, and lipid-binding protein implicated in exocytosis in different cell types, such as neuroendocrine cells. In chromaffin cells, cytosolic annexin A2 is recruited to the plasma membrane upon cell stimulation. Here, we review the latest evidence detailing the functional importance of annexin A2 in different stages of exocytosis. These include the recruitment of annexin A2 to the plasma membrane near soluble N-ethylmaleimide-sensitive factor attachment protein receptor complexes, the role of annexin A2 in the formation of lipid domains at exocytotic sites, and finally the annexin A2 bundling of actin microfilaments associated with chromaffin granules. These structures induce first the coalescence of lipid domains required for the formation of the exocytotic site, and in the second time, exert mechanical force on the granule to favor fusion pore expansion and squeeze the granule to facilitate catecholamine release. Annexin A2 is a calcium-, actin-, and lipid-binding protein implicated in exocytosis in different cell types, including neuroendocrine cells. Upon cell stimulation, annexin A2 translocates from the cytosol to the plasma membrane of chromaffin cells and bundles actin filaments associated with chromaffin granules. This promotes the formation of lipid domains required for granule docking, and facilitates catecholamine release by compressing the granule. This article is part of a mini review series on Chromaffin cells (ISCCB Meeting, 2015).