Abstract

Annexins, protein kinases C and cytosolic phospholipase A₂ belong to three families of ubiquitous cytoplasmic proteins involved in signal transduction. All annexins share the property of binding to phospholipids in the presence of calcium. Most annexins are substrates for protein kinases C except annexin V, the most ubiquitous and abundant annexin. Protein kinases C (PKC) belong to three distinct groups of kinases, conventional PKCs (cPKCs) that depend on calcium, diacylglycerol and negatively charged phospholipids for their activity, novel PKCs (nPKCs) and atypical PKCs (aPKCs), that do not require calcium for their activity, although they both require negatively charged phospholipids. Cytosolic phospholipase A₂ (cPLA2) depends on calcium for its catalytic activity as well as on serine phosphorylation by MAP kinases. We report that annexin V modulates the activity of cPKCs as well as of cPLA2 by interfering with their ability to bind to negatively charged phospholipids and calcium. We propose that annexin V could interfere with the calcium and phospholipid signalling pathway.