The annexin II-p11 complex is involved in regulated exocytosis in bovine pulmonary artery endothelial cells

Annexin II is a member of a multigene family of Ca2+-regulated, membrane-binding proteins implicated through biochemical and perforated cell experiments in Ca2+-triggered secretion. Within most cells annexin II resides in a tight heterotetrameric complex with a cellular protein ligand, pll, and complex formation is mediated via the N-terminal 14 residues of annexin II including the N-terminal acetyl group. To analyze at the single cell level whether the annexin II-pll complex is involved in regulated secretion, we used membrane capacitance measurements to follow exocytotic fusion events in bovine aortic endothelial cells manipulated with respect to their annexin II-pll complex formation. Upon guanosine 5'-O-(thiotriphosphate) (GTP gamma S) stimulation, the endothelial cells show a significant increase in membrane capacitance which is generally preceded by a transient rise in intracellular Ca2+ and thus indicative of the occurrence of Ca2+-regulated secretion. The GTP gamma S-induced capacitance increase is markedly reduced in cells loaded with a synthetic peptide, Acl-14, which corresponds in sequence to the N-terminal 14 residues of annexin II in their correctly acetylated form and which is capable of disrupting preformed annexin II-pll complexes. The effect of the peptide is highly specific as the nonacetylated variant, N1-14, which is incapable of disrupting annexin II-pll, does not interfere with the GTP gamma S-induced increase in membrane capacitance, These data show that intact annexin II-p11 complexes are indispensable for regulated exocytosis to occur in an efficient manner in endothelial cells.