Phosphorylation of the PTEN Tail Regulates Protein Stability and Function

Abstract

The PTEN gene is a tumor suppressor localized in the frequently altered chromosomal region 10q23. The tumor suppressor function of the PTEN protein (PTEN) has been linked to its ability to dephosphorylate the lipid second-messenger phosphatidylinositol 3,4,5-trisphosphate and phosphatidylinositol 3,4-bisphosphate and, by doing so, to antagonize the phosphoinositide 3-kinase pathway. The PTEN protein consists of an amino-terminal phosphatase domain, a lipid binding C2 domain, and a 50-amino-acid C-terminal domain (the "tail") of unknown function. A number of studies have shown that the tail is dispensable for both phosphatase activity and blocking cell growth. Here, we show that the PTEN tail is necessary for maintaining protein stability and that it also acts to inhibit PTEN function. Thus, removing the tail results in a loss of stability but does not result in a loss of function because the resultant protein is more active. Furthermore, tail-dependent regulation of stability and activity is linked to the phosphorylation of three residues (S380, T382, and T383) within the tail. Therefore, the tail is likely to mediate the regulation of PTEN function through phosphorylation.The PTEN gene was cloned as a candidate tumor suppressor gene from the chromosome 10q23 region, a locus frequently targeted for genetic loss in tumors (24,26,42). Somatic inactivation of both PTEN alleles and loss of heterozygosity have been demonstrated in a number of tumors including glioblastoma, melanoma, and prostate, breast, and endometrial carcinomas (reviewed in reference 46). Germ line PTEN mutations are associated with the development of the related dominantly inherited disorders known as Cowden disease and BannayanZonana syndrome (28)(29)(30)34). These disorders are characterized by the presence of benign hamartomas of the skin, intestinal tract, and central nervous system and by an increased incidence of cancers of the thyroid and breast (28,29,34). Similarly, heterozygous PTEN mice develop a variety of tumors and proliferative lesions of multiple tissues (10,11,37,43).Reconstitution of PTEN expression to certain PTEN null cells results in an increase in the population of cells in the G 1 phase of the cell cycle (13,23,39); in other PTEN null cells it results in the induction of apoptosis or anoikis (9,25,32). Accumulating evidence suggests that these functions are linked to the lipid phosphatase activity of PTEN, which allows PTEN to antagonize the phosphatidylinositol 3-kinase (PI3K) pathway (reviewed in references 4 and 46). A number of downstream targets of phosphatidylinositol 3,4,5-triphosphate and phosphatidylinositol 3,4-bisphosphate including the serinethreonine kinase Akt, BTK, SGK, and p70 S6K

Activation of tumor suppressor protein PTEN and induction of apoptosis are involved in cAMP-mediated inhibition of cell number in B92 glial cells

“…PTEN phosphorylation of various sites, including Ser380, restricted PTEN activity [24]. The dephosphorylation of PTEN also resulted in an increase of PTEN activity [24]. The treatment of B92 cells with IBMX alone or with IBMX in combination with ISO induced the dephosphorylation of PTEN, which indicated an activation of PTEN phosphatase activity (Fig.…”

“…In order to further investigate the role of PTEN in cAMP-regulated cell growth, we performed western blotting analyses using the phospho-specific antibodies, phospho-PTEN (Ser380) antibody and phospho-Akt (Ser473) antibody. PTEN phosphorylation of various sites, including Ser380, restricted PTEN activity [24]. The dephosphorylation of PTEN also resulted in an increase of PTEN activity [24].…”

SUMO1 modification of PTEN regulates tumorigenesis by controlling its association with the plasma membrane

“…We have provided evidence that a consensus electropositive interface in SUMO1 -PTEN facilitates cooperative binding of PTEN with the electronegative phospholipid membrane or its substrates by electrostatic interaction. Phosphorylation leads to a closed conformation that prevents PTEN association with the plasma membrane 9,10 ; however, if taken into account the electrostatic status, phosphorylation actually supplies negative charges. Th erefore, SUMOylation appears to be a positive regulator in controlling PTEN membrane association, whereas phosphorylation is a negative regulator that may neutralize SUMOylation through intramolecular electrostatic interactions.…”

The Major Target of the Endogenously Generated Reactive Oxygen Species in Response to Insulin Stimulation Is Phosphatase and Tensin Homolog and Not Phosphoinositide-3 Kinase (PI-3 Kinase) in the PI-3 Kinase/Akt Pathway

“…Because PTEN has a critical role in antagonizing PI-3 kinase signaling pathways, it might be expected that PTEN would be the target of complex control mechanisms. Only limited studies have addressed this issue, but evidence is now emerging for functional regulation of PTEN at the level of protein stability and localization, as well as transcription of the PTEN gene (Adey et al, 2000;Vazquez et al, 2000Vazquez et al, , 2001Kurose et al, 2001;Bastola et al, 2002).…”

“…Because PTEN has a critical role in antagonizing PI-3 kinase signaling pathways, it might be expected that PTEN would be the target of complex control mechanisms. Only limited studies have addressed this issue, but evidence is now emerging for functional regulation of PTEN at the level of protein stability and localization, as well as transcription of the PTEN gene (Adey et al, 2000;Vazquez et al, 2000Vazquez et al, , 2001Kurose et al, 2001;Bastola et al, 2002).It has been demonstrated that the activity of PI-3 kinase, the level of 3-phosphorylated PIs, and the activity of Akt are increased in cells exposed to H 2 O 2 (Konishi et al, 1997;Shaw et al, 1998;Sonoda et al, 1999;Tanaka et al, 1999;Qin et al, 2000). This H 2 O 2 -mediated activation of PI-3 kinase/Akt pathway is considered to be the result of reversible oxidation and inactivation of protein tyrosine phosphatase (PTP) family protein such as PTEN that have a critical cysteine residue in the active site (Denu and Tanner, 1998;Lee et al, 1998;Meng et al, 2002).…”