The C2A Domain of JFC1 Binds to 3′-Phosphorylated Phosphoinositides and Directs Plasma Membrane Association in Living Cells

Phosphatidylinositol 3-kinase products play a central role in the regulation of several intracellular pathways via adaptor proteins that share the ability to bind to 3′-phosphoinositides with high affinity and specificity. JFC1 is a C2 domain-containing protein involved in cellular trafficking that has been shown to bind 3′-phosphoinositides in vitro. In this work, we demonstrate that the C2A domain of JFC1 is the module responsible for its binding to the plasma membrane via 3′-phosphoinositides in vivo. We show that the C2A domain of JFC1 is the only domain present in this protein that localizes to the plasma membrane in living cells. Moreover, the C2A domain of JFC1 binds 3′-phosphoinositides in vitro with similar specificity as that described for full-length JFC1, suggesting that the domain mediates the specific membrane localization of the full-length protein. Furthermore, the C2A domain of JFC1 colocalized with the pleckstrin homology domain of Akt in vivo, and both the JFC1 C2A domain and the full-length JFC1 dissociated from the membrane in the presence of PI 3-kinase specific inhibitors. We also show that the association of the C2A domain to the membrane is modulated by calcium. From these results we analyze possible mechanisms for the role of JFC1 in cellular trafficking.