Dynamic Studies of the Tumour Suppressor Protien PTEN Binding to Membranes Composed PI(4,5)P2 and Various Anionic Lipids

Abstract

The tumor suppressor gene, Phosphatase and tensin homolog deleted on chromosome 10 (PTEN) encodes a protein that is involved in many human cancers. It binds to the plasma membrane to dephosphorylate the 3-position of phosphatidylinositol-3,4,5-trisphosphate producing phosphatidylinositol-4,5-bisphosphate (PI[4,5]P2). PTEN is an agonist to PI 3-kinase, thereby inhibiting the PI3K/Akt signaling pathway and controlling cell proliferation and survival. PTEN membrane association depends strongly on the composition and lateral distribution of the lipids in the membrane. Using stopped flow kinetic and steady state fluorescence experiments, we characterize the different steps associated with PTEN membrane association and dissociation.We find that PTEN membrane association is governed by the nature of the anionic lipids in the model membrane and their lateral distribution. It has been found previously that PTEN interacts synergistically with phosphatidylserine (PS) and phosphatidylinositol-4,5-bisphosphate (PI(4,5)P2). When comparing the kinetics of PTEN binding to PC/PS (30%) and PC/PI(4,5)P2 (5%) vesicles, we find a faster kon value and slower koff rate constant for the PI(4,5)P2 containing vesicles. When both PS and PI(4,5)P2 are present in the vesicles, we find the fastest association rate constants. In model membrane systems, PS and PI(4,5)P2 show only limited co-localization. Therefore, the question arises whether PS in biological membranes is the second binding partner, in addition to PI(4,5)P2, of PTEN. We hypothesize that phosphatidylinositol (PI), which forms domains with PI(4,5)P2, may replace PS in at least some physiological scenarios as the second binding partner. We find that PTEN binding to PI vesicles is as strong as PTEN binding to PS vesicles, confirming the hypothesis that PTEN binding to PS or PI is non-specific electrostatic. This finding is a major paradigm shift in the PTEN field.