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Annexin A2 (AnxA2) is a calcium and lipid binding protein involved in neuroendocrine secretion. We have previously demonstrated that AnxA2 participates in the formation and/or stabilization of lipid microdomains required for structural and spatial organization of the exocytotic machinery in chromaffin cells. However, the regulation of AnxA2 is not fully understood. Numerous phosphorylation sites have been identified in the amino-terminal domain of AnxA2. Phosphorylation of Ser25 and Tyr23 are well established and confirmed to be functionally significant. In particular, phosphorylation of Tyr23 by the tyrosine kinase pp60Src reduces the binding of AnxA2 to both actin filaments and the plasma membrane, two major actors of exocytosis, thus, we examined whether AnxA2 was phosphorylated on Tyr23 during exocytosis. Using immunolabelling and a biochemical approach, we found that nicotine stimulation triggered the phosphorylation of Anx A2 on Tyr23. The expression of two AnxA2 mutants carrying phosphorylation deficient (Y23A) or phosphomimetic (Y23E) mutations reduced the number exocytotic sites. Furthermore, expression of AnxA2-Y23A inhibited the formation of lipid microdomains, whereas the expression of AnxA2-Y23E altered actin filaments associated with docked granules. These results suggest that phosphorylation/dephosphorylation switch at Tyr23 in AnxA2 is critical for calcium-regulated exocytosis in neuroendocrine cells. This article is part of a Special Issue entitled: ECS Meeting edited by Claus Heizmann, Joachim Krebs and Jacques Haiech.
This article was published in the following journal.
Name: Biochimica et biophysica acta. Molecular cell research
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An annexin family member that plays a role in MEMBRANE FUSION and signaling via VOLTAGE-DEPENDENT CALCIUM CHANNELS.
A member of the annexin family that is a substrate for a tyrosine kinase, ONCOGENE PROTEIN PP60(V-SRC). Annexin A2 occurs as a 36-KDa monomer and in a 90-KDa complex containing two subunits of annexin A2 and two subunits of S100 FAMILY PROTEIN P11. The monomeric form of annexin A2 was formerly referred to as calpactin I heavy chain.
A set of opposing, nonequilibrium reactions catalyzed by different enzymes which act simultaneously, with at least one of the reactions driven by ATP hydrolysis. The results of the cycle are that ATP energy is depleted, heat is produced and no net substrate-to-product conversion is achieved. Examples of substrate cycling are cycling of gluconeogenesis and glycolysis pathways and cycling of the triglycerides and fatty acid pathways. Rates of substrate cycling may be increased many-fold in association with hypermetabolic states resulting from severe burns, cold exposure, hyperthyroidism, or acute exercise.
A monomeric calcium-calmodulin-dependent protein kinase subtype that is primarily expressed in neuronal tissues; T-LYMPHOCYTES and TESTIS. The activity of this enzyme is regulated by its phosphorylation by CALCIUM-CALMODULIN-DEPENDENT PROTEIN KINASE KINASE.
A monomeric calcium-calmodulin-dependent protein kinase subtype that specifically phosphorylates PEPTIDE ELONGATION FACTOR 2. The enzyme lacks a phosphorylatable activation domain that can respond to CALCIUM-CALMODULIN-DEPENDENT PROTEIN KINASE KINASE, however it is regulated by phosphorylation by PROTEIN KINASE A and through intramolecular autophosphorylation.
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