Membrane-binding and activation mechanism of PTEN
PTEN is a tumor suppressor that reverses the action of phosphoinositide 3-kinase by catalyzing the removal of the 3′ phosphate of phosphoinositides. Despite the critical role of PTEN in cell signaling and regulation, the mechanisms of its membrane recruitment and activation is still poorly understood. PTEN is composed of an N-terminal phosphatase domain, a C2 domain, and a C-terminal tail region that contains the PSD-95/Dlg/ZO-1 homology (PDZ) domain-binding sequence and multiple phosphorylation sites. Our in vitro surface plasmon resonance measurements using immobilized vesicles showed that both the phosphatase domain and the C2 domain, but not the C-terminal tail, are involved in electrostatic membrane binding of PTEN. Furthermore, the phosphorylation-mimicking mutation on the C-terminal tail of PTEN caused an ≈80-fold reduction in its membrane affinity, mainly by slowing the membrane-association step. Subcellular localization studies of PTEN transfected into HEK293T and HeLa cells indicated that targeting of PTEN to the plasma membrane is coupled with rapid degradation and that the phosphatase domain and the C2 domain are both necessary and sufficient for its membrane recruitment. Results also indicated that the phosphorylation regulates the targeting of PTEN to the plasma membrane not by blocking the PDZ domain-binding site but by interfering with electrostatic membrane binding of PTEN. On the basis of these results, we propose a membrane-binding and activation mechanism for PTEN, in which the phosphorylation/dephosphorylation of the C-terminal region serves as an electrostatic switch that controls the membrane translocation of the protein.