Nuclear Localization of PTEN by a Ran-dependent Mechanism Enhances Apoptosis: Involvement of an N-Terminal Nuclear Localization Domain and Multiple Nuclear Exclusion Motifs

Abstract

The targeting of the tumor suppressor PTEN protein to distinct subcellular compartments is a major regulatory mechanism of PTEN function, by controlling its access to substrates and effector proteins. Here, we investigated the molecular basis and functional consequences of PTEN nuclear/cytoplasmic distribution. PTEN accumulated in the nucleus of cells treated with apoptotic stimuli. Nuclear accumulation of PTEN was enhanced by mutations targeting motifs in distinct PTEN domains, and it was dependent on an N-terminal nuclear localization domain. Coexpression of a dominant negative Ran GTPase protein blocked PTEN accumulation in the nucleus, which was also affected by coexpression of importin ␣ proteins. The lipid-and protein-phosphatase activity of PTEN differentially modulated PTEN nuclear accumulation. Furthermore, catalytically active nuclear PTEN enhanced cell apoptotic responses. Our findings indicate that multiple nuclear exclusion motifs and a nuclear localization domain control PTEN nuclear localization by a Ran-dependent mechanism and suggest a proapoptotic role for PTEN in the cell nucleus. INTRODUCTIONPTEN is a tumor suppressor phosphatase involved in the control of cell growth and cell cycle traverse, apoptosis, cell size, and cell migration Waite and Eng, 2002;Leslie and Downes, 2004;Parsons, 2004;Sansal and Sellers, 2004). The PTEN gene is mutated or lost in a wide variety of human tumors, including malignant glioblastomas, an aggressive tumor of the CNS in humans (Bonneau and Longy, 2000;Eng, 2003). The major tumor suppressor function of PTEN is mediated by the dephosphorylation of phosphatidylinositol-3,4,5-triphosphate (PIP3; Maehama and Dixon, 1998). Through this lipid phosphatase activity, PTEN counteracts the action of the prosurvival proto-oncogenes, the phosphatidylinositol 3-kinases, and protein kinase B/Akt, which control the function of key downstream effectors of this pathway, including cell cycle regulators (such as p27Kip1, cyclin D1, and CHK1) and transcription factors (such as NF-B and FKHR;Li and Sun, 1998;Nakamura et al., 2000;Gustin et al., 2001;Weng et al., 2001;Radu et al., 2003;Puc et al., 2005). To control the PIP3 levels at the plasma membrane, PTEN possesses, in addition to its N-terminal phosphatase catalytic domain (residues 14 -185), a C-terminal phospholipidbinding C2 domain (residues 186 -350), which is critical for optimal binding to membranes and PIP3 dephosphorylation (Lee et al., 1999). In addition, the N-terminus of PTEN contains a phosphatidylinositol-4,5-diphosphate (PIP2) binding motif (residues 6 -15), which is also essential for PTEN membrane binding and activity Funamoto et al., 2002;Iijima and Devreotes, 2002;Campbell et al., 2003;McConnachie et al., 2003;Iijima et al., 2004;Walker et al., 2004;Vazquez et al., 2006). On the other hand, PTEN possesses a C-terminal tail (residues 350 -403) that plays a major role in the stabilization of the molecule and that is the target of posttranslational modifications, including phosphorylation by the protein kinase CK2 ...

Specific apoptosis induction by the dual PI3K/mTor inhibitor NVP-BEZ235 in HER2 amplified and PIK3CA mutant breast cancer cells

“…In this context, the absence of PTEN might have consequences in blocking p53-dependent apoptotic phenomena, in genomically unstable tumor cells. Moreover, other evidences exist that PTEN might positively and directly regulate apoptosis, when localized either in the cytosol or in the nucleus (27,28). Further studies would be needed to delineate the PI3K independent prosurvival molecules involved in the insensitive cell lines.…”

SIRT1 Deficiency Downregulates PTEN/JNK/FOXO1 Pathway to Block Reactive Oxygen Species-Induced Apoptosis in Mouse Embryonic Stem Cells

“…Nuclear PTEN is enhanced upon apoptotic stresses and C-terminal deleted PTEN favors nuclear localization. Given that the deleted Cterminal tail is required for PTEN binding to PDZ-domain scaffolding proteins [41] and Lys402 acetylation in the Cterminal tail has been reported to enhance interaction with PDZ domains [33], nuclear export of PTEN is promoted to protect cells from intracellular ROS by activating nuclear Akt and blocking the nuclear PTEN-mediated apoptotic pathway in SIRT1…”

Inhibition of active nuclear transport is an intrinsic trigger of programmed cell death in trypanosomatids

“…1,25 Indeed, its role in the nucleocytoplasmic transport of apoptotic factors is necessary to apoptosis triggering (reviewed in Ferrando-May et al 1 and Fahrenkrog 25 ), as shown, for example, by the expression of a dominant negative Ran GTPase protein. 26 Conversely, in response to external stimuli triggering apoptosis, a change in the RanGTP/RanGDP gradient is observed, leading to the inhibition of active nuclear transport. 7,9 In this study, using trypanosomatid protozoa, we have (i) identified Ran and several of its main partners in this divergent cell model, (ii) specified their subcellular localisation at the NPCs and (iii) characterized the apoptotic phenotypes induced by the depletion of their expression.…”