Participation of annexins in protein phosphorylation.

Simultaneous discovery of members of the annexin family of calcium and phospholipid binding proteins by several groups is intimately linked to the possibility that these proteins may be controlled by phosphorylation. Indeed, annexin I and annexin II have been identified as major substrates for the tyrosine kinase activity associated with epidermal growth factor receptor (EGF-R) and for the retrovirus encoded protein tyrosine kinase pp60v-arc. Both annexins are also in vitro and/or in situ substrates for platelet derived growth factor (PDGF), insulin and hepatocyte growth factor/scatter factor (HGF/SF) receptor tyrosine kinases. In addition, to serve as substrates for tyrosine protein kinases some annexins are cellular targets for serine threonine protein kinases such as protein kinase C (PKC) and cAMP-dependent protein kinase A (PKA). Although the role of annexin phosphorylation has not been studied in detail, it is thought to influence their vesicle aggregation and phospholipid binding properties. Some annexins are also potent inhibitors of various serine/threonine and tyrosine kinases. The physiological functions of the annexins have still not been clearly defined. Therefore the identification of the ability of these proteins to undergo phosphorylation may be helpful in assigning them a precise biological role.