PTEN Associates with the Vault Particles in HeLa Cells

Abstract

PTEN is a tumor suppressor that primarily dephosphorylates phosphatidylinositol 3,4,5-trisphosphate to down-regulate the phosphoinositide 3-kinase/Akt signaling pathway. Although the cellular functions of PTEN as a tumor suppressor have been well characterized, the mechanism by which PTEN activity is modulated by other signal molecules in vivo remains poorly understood. In searching for potential PTEN modulators through protein-protein interaction, we identified the major vault protein (MVP) as a dominant PTENbinding protein in a yeast two-hybrid screen. MVP is the major structural component of vault, the largest intracellular ribonucleoprotein particle. PTEN was originally identified as a tumor suppressor gene based on its high frequency of mutation in a variety of tumors (1-3). Germ-line mutations of PTEN are the cause of Cowden disease, an autosomal-dominant hamartoma syndrome that results in an increased risk for development of tumors in a variety of tissues (4 -7). The genetic evidence that PTEN is an important tumor suppressor is supported by the fact that heterozygous disruption of the PTEN gene in knockout mice results in the spontaneous development of tumors (8 -10). Although PTEN as a protein phosphatase is capable of dephosphorylating tyrosine and threonine/serine residues (11, 12), the primary substrates of PTEN are 3Ј-phosphoinositides, PtdIns-3,4-P 2 and PtdIns-3,4,5-P 3 (13). Genetic and biochemical studies have demonstrated that the tumor suppressor functions of PTEN are linked primarily with the lipid phosphatase activity and its association with the well defined phosphoinositide 3-kinase pathway (reviewed in Refs. 14 -20). Substantial progress has been made in the characterization of PTEN as a tumor suppressor as well as in the regulation of many cellular processes including growth, adhesion, migration, invasion, and apoptosis. Nevertheless, the mechanism by which PTEN activity is modulated in various cellular signaling complexes remains elusive. It is assumed that the activity and the cellular function of PTEN may be regulated through in vivo proteinprotein interactions. PTEN contains a number of putative regulatory modules, including the N-terminal phosphoinositide binding motif, a C2 domain, a PDZ-binding site, and two proline-, glutamic acid-, serine-, and threonine-rich segments (21). The C2 domain of PTEN has been implicated in mediating membrane association (22). The C-terminal tail of PTEN interacts with several PDZ domain-containing proteins such as hDLG, hMAST205, MAGI-2, and MAGI-3 (23-25). The interaction of PTEN with these proteins may be important for its biological function, as it has been reported that MAGI-2 and MAGI-3 can enhance the activity of PTEN (23, 24). In contrast, several groups found that the PDZ-binding site of PTEN is not required for tumor suppression or other biological activities (21,(25)(26)(27)(28). Therefore, the complete spectrum of PTEN-interacting proteins and the effects of the interactions on PTEN function are not yet defined.To date, the vault complex w...

The nuclear affairs of PTEN

“…PTEN binds to MVP, a protein hypothesized to be a general carrier molecule for nuclear-cytoplasmic transport (Mossink et al, 2003), in yeast two-hybrid screens (Yu et al, 2002). Further analysis confirmed that this interaction occurs in both 293T and HeLa cells and localized the binding sites to the C2 domain of PTEN and the EF-hand pair (a calcium-binding motif) of MVP.…”

Genome-wide functional screening of miR-23b as a pleiotropic modulator suppressing cancer metastasis

“…1e ; Supplementary Fig. S1d ) 17,18 . A high-density pattern of siRNA spots, such as 5,000 spots per chip, has been previously demonstrated without any obvious cross-contamination 19 .…”

Nuclear Localization of PTEN Is Regulated by Ca2+ through a Tyrosil Phosphorylation–Independent Conformational Modification in Major Vault Protein

“…It has been reported that the interaction between PTEN and MVP depends on the presence of Ca 2+ in glutathione S-transferase pull-down assay (10). Because phosphorylation of MVP is reportedly dependent on the presence of Mg 2+ (15), and because Ca 2+ and Mg 2+ are known to exert opposing effects in many cellular functions (18,19), we hypothesized that Ca 2+ and Mg 2+ might be involved in the interaction between PTEN and MVP.…”

“…MVP reportedly interacts with the C2 domain of PTEN through the EF hand-like motif in a Ca 2+ -dependent manner in HeLa cells (10). Phosphorylation of MVP depends on the presence of Mg 2+ in PC12 cells (15), and epidermal growth factor (EGF) stimulation increases tyrosil phosphorylation of MVP in WI38 cells (12).…”