Potential interaction between annexin VI and a 56-kDa protein kinase in T cells

Annexins belong to a large family of calcium-dependent phospholipid binding proteins known to undergo post-translational modifications such as phosphorylation. Physiological function of each annexin is still unclear since they may participate in signal transduction. We have tested the presence of annexins in a T cell line (Jurkat) and studied their phosphorylation by protein tyrosine kinases of the src family. Among annexins I, II, V and VI found in Jurkat cells, annexin VI was shown to be phosphorylated in vitro by p56lck and annexins I and II by p60src. We could not detect the phosphorylation of A-VI in vivo, even after cell stimulation. However, a 56-kDa phosphoprotein was found to be associated with A-VI after T cell activation. This 56-kDa protein shares some characteristics with p56lck.