Search

PTEN, a tumor suppressor protein that dephosphorylates phosphoinositides at the 3-position of the inositol ring, is a cytosolic protein that needs to associate with the plasma membrane or other subcellular membranes to exert its lipid phosphatase function. Upon membrane association PTEN interacts with at least three different lipid entities: An anionic lipid that is present in sufficiently high concentration to create a negative potential that allows PTEN to interact electrostatically with the membrane, phosphatidylinositol-4,5-bisphosphate, which interacts with PTEN's N-terminal end and the substrate, usually phosphatidylinositol-3,4,5-trisphosphate. Many parameters influence PTEN's interaction with the lipid bilayer, for example, the lateral organization of the lipids or the presence of other chemical species like cholesterol or other lipids. To investigate systematically the different steps of PTEN's complex binding mechanism and to explore its dynamic behavior in the membrane bound state, in vitro methods need to be employed that allow for a systematic variation of the experimental conditions. In this review we survey a variety of methods that can be used to assess PTEN lipid binding affinity, the dynamics of its membrane association as well as its dynamic behavior in the membrane bound state., (Copyright © 2015 Elsevier Inc. All rights reserved.)

The tumor suppressor, phosphatase, and tensin homologue deleted on chromosome 10 (PTEN), is a phosphoinositide (PI) phosphatase specific for the 3-position of the inositol ring. PTEN has been implicated in autism for a subset of patients with macrocephaly. Various studies identified patients in this subclass with one normal and one mutated PTEN gene. We characterize the binding, structural properties, activity, and subcellular localization of one of these autism-related mutants, H93R PTEN. Even though this mutation is located at the phosphatase active site, we find that it affects the functions of neighboring domains. H93R PTEN binding to phosphatidylserine-bearing model membranes is 5.6-fold enhanced in comparison to wild-type PTEN. In contrast, we find that binding to phosphatidylinositol-4,5-bisphosphate (PI(4,5)P(2)) model membranes is 2.5-fold decreased for the mutant PTEN in comparison to wild-type PTEN. The structural change previously found for wild-type PTEN upon interaction with PI(4,5)P(2), is absent for H93R PTEN. Consistent with the increased binding to phosphatidylserine, we find enhanced plasma membrane association of PTEN-GFP in U87MG cells. However, this enhanced plasma membrane association does not translate into increased PI(3,4,5)P(3) turnover, since in vivo studies show a reduced activity of the H93R PTEN-GFP mutant. Because the interaction of PI(4,5)P(2) with PTEN's N-terminal domain is diminished by this mutation, we hypothesize that the interaction of PTEN's N-terminal domain with the phosphatase domain is impacted by the H93R mutation, preventing PI(4,5)P(2) from inducing the conformational change that activates phosphatase activity.

Phosphatase and tensin homologue deleted on chromosome 10 (PTEN) was originally cloned as a tumor suppressor for brain tumors. Now it is known as a tumor suppressor for many tumor types. In this review, we ask the simple question: why is PTEN such a common and important tumor suppressor? The most obvious answer is that there are no other family members that can replace PTEN. As a result, several pathways critical for cell transformation are misregulated. The most important of these is the phosphoinositide 3-kinase (P13K) PI3K-Akt pathway, which has downstream effects on transcription, proliferation, cell survival, invasiveness, and angiogenesis. In addition, PTEN is linked via several mechanisms to the p53 tumor suppressor. Through p53 and additional mechanisms, loss of PTEN leads to genomic instability. Hence, PTEN is important because its loss misregulates multiple Akt-dependent and -independent pathways critical for the development of cancer., (Copyright (c) 2007 Wiley-Liss, Inc.)

Phosphatase and tensin homologue deleted on chromosome 10 (PTEN) is a phosphatidylinositol phosphate phosphatase and is frequently inactivated in human cancers. The balance between phosphoinositide 3-kinase (PI3K) and PTEN determines PI(3,4,5)P3 levels. PI3K is regulated by a variety of intracellular and extracellular signals, but little is known about the regulation of PTEN. In this article, we review control of PTEN function by phosphorylation as well as by binding of lipid and protein partners.

PTEN is a lipid phosphatase, and PTEN mutations are associated with gliomas, macrocephaly, and mental deficiencies. We have used PTEN +/- and PTEN +/+ mice to prepare subventricular zone (SVZ) precursor cells. Using DNA microarrays, we compared the expression profiles of PTEN +/+ and PTEN +/- cells and identified 91 differentially expressed genes in PTEN +/- precursor cells. Many of the PTEN-regulated genes are involved with signaling, cytoskeleton, extracellular matrix, metabolism, and transcription factors. Some of these changes are likely mediated by the transcription factor, HIF-1. We confirmed a subset of these changes by real-time PCR. In addition, we examined protein levels for two of the PTEN-up-regulated genes, vascular endothelial growth factor (VEGF) and doublecortin (DCX). PTEN haploinsufficiency increases immunostaining for VEGF for both cultured precursor cells and sections of the SVZ. PTEN haploinsufficiency shifted most of the DCX-positive cells from the SVZ to the olfactory bulb. These observations indicate that even a small decrease in PTEN levels results in substantial changes in gene expression and precursor cell function.

Phosphatase and tensin homologue deleted on chromosome 10 (PTEN) is a tumor suppressor that is lost in many human tumors and encodes a phosphatidylinositol phosphate phosphatase specific for the 3-position of the inositol ring. Here we report a novel mechanism of PTEN regulation. Binding of di-C8-phosphatidylinositol 4,5-P2 (PI(4,5)P2) to PTEN enhances phosphatase activity for monodispersed substrates, PI(3,4,5)P3 and PI(3,4)P2. PI(5)P also is an activator, but PI(4)P, PI(3,4)P2, and PI(3,5)P2 do not activate PTEN. Activation by exogenous PI(4,5)P2 is more apparent with PI(3,4)P2 as a substrate than with PI(3,4,5)P3, probably because hydrolysis of PI(3,4)P2 yields PI(4)P, which is not an activator. In contrast, hydrolysis of PI(3,4,5)P3 yields a potent activator, PI(4,5)P2, creating a positive feedback loop. In addition, neither di-C4-PI(4,5)P2 nor inositol trisphosphate-activated PTEN. Hence, the interaction between PI(4,5)P2 and PTEN requires specific, ionic interactions with the phosphate groups on the inositol ring as well as hydrophobic interactions with the fatty acid chains, likely mimicking the physiological interactions that PTEN has with the polar surface head groups and the hydrophobic core of phospholipid membranes. Mutations of the apparent PI(4,5)P2-binding motif in the PTEN N terminus severely reduced PTEN activity. In contrast, mutation of the C2 phospholipid-binding domain had little effect on PTEN activation. These results suggest a model in which a PI(4,5)P2 monomer binds to PTEN, initiates an allosteric conformational change and, thereby, activates PTEN independent of membrane binding.

Even though phosphorylation of phosphatidylinositols by phosphoinositide 3-kinase (PI3K) has an important and pervasive role in the nervous system, there is little known about the phosphatases that reverse this reaction. Such a phosphatase, phosphatase and tensin homologue deleted on chromosome 10 (PTEN), was cloned as a tumor suppressor for gliomas. PTEN is expressed in most, if not all, neurons and is localized in the nucleus and cytoplasm. Recently, a series of papers using PTEN conditional knockouts has greatly extended our knowledge of PTEN's role during development. Loss of PTEN results in disorganization of the brain, probably due to a flaw in cell migration. In addition, there is a gradual increase in the size of neuronal soma, mimicking Lhermitte-Duclos disease. Recent experiments in our laboratory with adult PTEN +/- mice demonstrate that PTEN regulates migration of precursor cells in the subventricular zone to the olfactory bulb. We also found that PTEN haploinsufficiency can protect precursor cells from apoptosis in response to oxidative stress. Collectively, these studies demonstrate that PTEN does much more than suppressing tumors. It is a master regulator in developing and adult brain., (Copyright 2002 Wiley-Liss, Inc.)

PTEN is a lipid phosphatase, and PTEN mutations are associated with gliomas, macrocephaly, and mental deficiencies. We have used PTEN +/- mice to assess PTEN's role in subventricular zone (SVZ) precursor cells. For cultured SVZ neurosphere cells, haploinsufficiency for PTEN increases phosphorylation of Akt and forkhead transcription factor and slightly enhances proliferation. Based on a filter penetration assay, PTEN +/- cells are substantially more migratory and invasive than +/+ cells. The +/- cells also are more resistant to H(2)O(2)-induced apoptosis. Analysis of PTEN +/- and +/+ mice by BrdU labeling reveals no difference in the rate of cell proliferation in the SVZ. Exit of BrdU-labeled cells from the SVZ and radial migration to the outer layers of the olfactory bulb are more rapid for +/- cells. These observations indicate that PTEN regulates SVZ precursor cell function and is particularly important for migration and apoptosis in response to oxidative stress., ((c) 2002 Elsevier Science (USA).)

The structure and function of the PTEN phosphatase is investigated by studying its membrane affinity and localization on in-plane fluid, thermally disordered synthetic membrane models. The membrane association of the protein depends strongly on membrane composition, where phosphatidylserine (PS) and phosphatidylinositol diphosphate (PI(4,5)P2) act pronouncedly synergistic in pulling the enzyme to the membrane surface. The equilibrium dissociation constants for the binding of wild type (wt) PTEN to PS and PI(4,5)P2 were determined to be Kd∼12 μM and 0.4 μ, respectively, and Kd∼50 nM if both lipids are present. Membrane affinities depend critically on membrane fluidity, which suggests multiple binding sites on the protein for PI(4,5)P2. The PTEN mutations C124S and H93R show binding affinities that deviate strongly from those measured for the wt protein. Both mutants bind PS more strongly than wt PTEN. While C124S PTEN has at least the same affinity to PI(4,5)P2 and an increased apparent affinity to PI(3,4,5)P3, due to its lack of catalytic activity, H93R PTEN shows a decreased affinity to PI(4,5)P2 and no synergy in its binding with PS and PI(4,5)P2. Neutron reflection measurements show that the PTEN phosphatase "scoots" along the membrane surface (penetration <5 Å) but binds the membrane tightly with its two major domains, the C2 and phosphatase domains, as suggested by the crystal structure. The regulatory C-terminal tail is most likely displaced from the membrane and organized on the far side of the protein, ∼60 Å away from the bilayer surface, in a rather compact structure. The combination of binding studies and neutron reflection allows us to distinguish between PTEN mutant proteins and ultimately may identify the structural features required for membrane binding and activation of PTEN. [ABSTRACT FROM AUTHOR]