Annexin A2 expression and partners during epithelial cell differentiation.

The members of the annexin family of calcium- and phospholipid-binding proteins participate in different cellular processes. Annexin A2 binds to S100A10 forming a functional heterotetrameric protein that has been involved in many cellular functions such as exocytosis, endocytosis, cell junction formation and actin cytoskeleton dynamics. Herein, we studied annexin A2 cellular movements and looked for its partners during epithelial cell differentiation. By using immunofluorescence, mass spectrometry and western blot analyses after S100A10 affinity column separation, we identified several annexin A2-S100A10 partner candidates. The association of putative annexin A2-S100A10 partner candidates obtained by MS after column affinity was validated by immunofluorescence and sucrose density gradient separation. The results show that three proteins were clearly associated to AnxA2: E-cadherin, actin and caveolin 1. Overall the data show that annexin A2 is able to associate to molecular complexes containing actin, caveolin 1 and flotillin 2 before epithelial differentiation and to complexes containing E-Cadherin, actin and caveolin 1, but not flotillin 2 after cell differentiation. The results indicate that actin, caveolin 1 and E-cadherin are the principal protein partners of annexin A2 in epithelial cells and that the serine phosphorylation of the N-terminal domain does not play an essential role during epithelial cell differentiation.