IN-VIVO AND IN-VITRO PHOSPHORYLATION OF ANNEXIN-II IN T-CELLS - POTENTIAL REGULATION BY ANNEXIN-V

In order to understand how signal transduction occurs during T cell ac tivation, it is necessary to identify the key regulatory molecules who se function is influenced by phosphorylation. Annexins II (A-II) and V (A-V) belong to a large family of Ca2+ dependent phospholipid-binding proteins. Among many putative functions, annexins may be involved in signal transduction during cellular proliferation and differentiation. In the present study we show that A-II is phosphorylated in vivo in t he Jurkat human T cell line. Indeed, A-II is phosphorylated after stim ulation by phorbol myristate acetate and on serine residues after T ce ll antigen receptor (TcR) stimulation. In cytosol from Jurkat cells, A -II is phosphorylated only by Ca2+/phospholipid-stimulated kinases suc h as Ca2+-dependent protein kinases C (cPKCs). A-V inhibits the phosph orylation of A-II and other substrates of cPKCs and has no effect on k inases activated only by phospholipids. In conclusion, A-II is phospho rylated both in vitro and in vivo in Jurkat cells, and may play a role as a substrate during signal transduction in lymphocytes via the TcR through the PKC pathway. On the other hand, A-V could act as a potent modulator of cPKCs in Jurkat cells.