1
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Activation of PAR2 by tissue factor induces the release of the PTEN from MAGI proteins and regulates PTEN and Akt activities. Sci Rep 2020; 10:20908. [PMID: 33262514 PMCID: PMC7708427 DOI: 10.1038/s41598-020-77963-6] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2020] [Accepted: 11/13/2020] [Indexed: 01/06/2023] Open
Abstract
Tissue factor (TF) signalling has been associated with alterations in Akt activity influencing cellular survival and proliferation. TF is also shown to induce signalling through activation of the protease activated receptor (PAR)2. Seven cell lines were exposed to recombinant-TF (rec-TF), or activated using a PAR2-agonist peptide and the phosphorylation state of PTEN, and the activities of PTEN and Akt measured. Furthermore, by measuring the association of PTEN with MAGI proteins a mechanism for the induction of signalling by TF was proposed. Short term treatment of cells resulted in de-phosphorylation of PTEN, increased lipid-phosphatase activity and reduced Akt kinase activity in most of the cell lines examined. In contrast, continuous exposure to rec-TF up to 14 days, resulted in lower PTEN antigen levels, enhanced Akt activity and increased rate of cell proliferation. To explore the mechanism of activation of PTEN by TF, the association of "membrane-associated guanylate kinase-with inverted configuration" (MAGI)1–3 proteins with PTEN was assessed using the proximity ligation assay and by co-immunoprecipitation. The interaction of PTEN with all three MAGI proteins was transiently reduced following PAR2 activation and explains the changes in PTEN activity. Our data is first to show that PAR2 activation directly, or through exposure of cells to TF releases PTEN from MAGI proteins and is concurrent with increases in PTEN phosphatase activity. However, prolonged exposure to TF results in the reduction in PTEN antigen with concurrent increase in Akt activity which may explain the aberrant cell survival, proliferation and invasion associated with TF during chronic diseases.
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2
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Stumpf M, den Hertog J. Differential Requirement for Pten Lipid and Protein Phosphatase Activity during Zebrafish Embryonic Development. PLoS One 2016; 11:e0148508. [PMID: 26848951 PMCID: PMC4743836 DOI: 10.1371/journal.pone.0148508] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2015] [Accepted: 01/19/2016] [Indexed: 12/14/2022] Open
Abstract
The lipid- and protein phosphatase PTEN is one of the most frequently mutated tumor suppressor genes in human cancers and many mutations found in tumor samples directly affect PTEN phosphatase activity. In order to understand the functional consequences of these mutations in vivo, the aim of our study was to dissect the role of Pten phosphatase activities during zebrafish embryonic development. As in other model organisms, zebrafish mutants lacking functional Pten are embryonically lethal. Zebrafish have two pten genes and pten double homozygous zebrafish embryos develop a severe pleiotropic phenotype around 4 days post fertilization, which can be largely rescued by re-introduction of pten mRNA at the one-cell stage. We used this assay to characterize the rescue-capacity of Pten and variants with mutations that disrupt lipid, protein or both phosphatase activities. The pleiotropic phenotype at 4dpf could only be rescued by wild type Pten, indicating that both phosphatase activities are required for normal zebrafish embryonic development. An earlier aspect of the phenotype, hyperbranching of intersegmental vessels, however, was rescued by Pten that retained lipid phosphatase activity, independent of protein phosphatase activity. Lipid phosphatase activity was also required for moderating pAkt levels at 4 dpf. We propose that the role of Pten during angiogenesis mainly consists of suppressing PI3K signaling via its lipid phosphatase activity, whereas the complex process of embryonic development requires lipid and protein phosphatase of Pten.
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Affiliation(s)
- Miriam Stumpf
- Hubrecht Institute, Koninklijke Nederlandse Akademie van Wetenschappen (KNAW) and University Medical Center Utrecht, Utrecht, the Netherlands
| | - Jeroen den Hertog
- Hubrecht Institute, Koninklijke Nederlandse Akademie van Wetenschappen (KNAW) and University Medical Center Utrecht, Utrecht, the Netherlands
- Institute of Biology Leiden, Leiden University, Leiden, the Netherlands
- * E-mail:
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3
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Lin X, Zhou X, Liu D, Yun L, Zhang L, Chen X, Chai Q, Li L. MicroRNA-29 regulates high-glucose-induced apoptosis in human retinal pigment epithelial cells through PTEN. In Vitro Cell Dev Biol Anim 2016; 52:419-26. [PMID: 26822433 DOI: 10.1007/s11626-015-9990-z] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2015] [Accepted: 12/09/2015] [Indexed: 11/29/2022]
Abstract
Hyperglycemia or high-glucose (HG)-induced apoptosis in human retinal pigment epithelial (RPE) cells is a characteristic process in diabetic retinopathy. In our study, we examined whether microRNA-29 (miR-29) may regulate HG-induced RPE cell apoptosis. Human RPE cell line, ARPE-19 cells, was treated with various high concentration of glucose in vitro. HG-induced RPE cell apoptosis was examined by terminal deoxynucleotide transferase-mediated dUTP nick end labeling (TUNEL) assay and miR-29 gene expression by quantitative RT-PCR (qRT-PCR). miR-29 was then downregulated in RPE cells, and its effect on HG-induced apoptosis was examined by TUNEL assay and western blot assay on caspase-7 protein. Association of miR-29 on its downstream target, PTEN, in HG-induced RPE cell apoptosis was evaluated by dual-luciferase assay and qRT-PCR. PTEN was silenced in RPE cells. The effects of PTEN downregulation on miR-29-mediated HG-induced RPE cell apoptosis were also examined by TUNEL and western blot assays. HG induced significant apoptosis in RPE cells in a dose-dependent manner. miR-29 was upregulated by HG in RPE cells. miR-29 downregulation protected HG-induced apoptosis and reduced the production of caspase-7 protein in RPE cells. PTEN was shown to be directly downregulated by HG and then upregulated by miR-29 downregulation in RPE cells. Small interfering RNA (siRNA)-mediated PTEN downregulation reversed the protective effect of miR-29 downregulation on HG-induced RPE cell apoptosis. This study demonstrates that miR-29, through inverse association of PTEN, plays an important role in the process of HG-induced apoptosis in RPE cells.
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Affiliation(s)
- Xiaohui Lin
- Department of Ophthalmology, The Second Affiliated Hospital of Chongqing Medical University, 76 Linjiang Road, Chongqing, 400010, China
| | - Xiyuan Zhou
- Department of Ophthalmology, The Second Affiliated Hospital of Chongqing Medical University, 76 Linjiang Road, Chongqing, 400010, China.
| | - Danning Liu
- Department of Ophthalmology, The Second Affiliated Hospital of Chongqing Medical University, 76 Linjiang Road, Chongqing, 400010, China
| | - Lixia Yun
- Department of Ophthalmology, The Inner Mongolia Autonomous Region People's Hospital, 20 Zhaowuda Road, Hohhot, 010010, China
| | - Lina Zhang
- Department of Ophthalmology, The Inner Mongolia Autonomous Region People's Hospital, 20 Zhaowuda Road, Hohhot, 010010, China
| | - Xiaohai Chen
- Department of Ophthalmology, The Inner Mongolia Autonomous Region People's Hospital, 20 Zhaowuda Road, Hohhot, 010010, China
| | - Qinghe Chai
- Department of Ophthalmology, The Inner Mongolia Autonomous Region People's Hospital, 20 Zhaowuda Road, Hohhot, 010010, China
| | - Langen Li
- Department of Ophthalmology, The Inner Mongolia Autonomous Region People's Hospital, 20 Zhaowuda Road, Hohhot, 010010, China
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4
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Cherian MA, Baydoun HH, Al-Saleem J, Shkriabai N, Kvaratskhelia M, Green P, Ratner L. Akt Pathway Activation by Human T-cell Leukemia Virus Type 1 Tax Oncoprotein. J Biol Chem 2015; 290:26270-81. [PMID: 26324707 DOI: 10.1074/jbc.m115.684746] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2015] [Indexed: 12/12/2022] Open
Abstract
Human T-cell leukemia virus (HTLV) type 1, the etiological agent of adult T-cell leukemia, expresses the viral oncoprotein Tax1. In contrast, HTLV-2, which expresses Tax2, is non-leukemogenic. One difference between these homologous proteins is the presence of a C-terminal PDZ domain-binding motif (PBM) in Tax1, previously reported to be important for non-canonical NFκB activation. In contrast, this study finds no defect in non-canonical NFκB activity by deletion of the Tax1 PBM. Instead, Tax1 PBM was found to be important for Akt activation. Tax1 attenuates the effects of negative regulators of the PI3K-Akt-mammalian target of rapamycin pathway, phosphatase and tensin homologue (PTEN), and PHLPP. Tax1 competes with PTEN for binding to DLG-1, unlike a PBM deletion mutant of Tax1. Forced membrane expression of PTEN or PHLPP overcame the effects of Tax1, as measured by levels of Akt phosphorylation, and rates of Akt dephosphorylation. The current findings suggest that Akt activation may explain the differences in transforming activity of HTLV-1 and -2.
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Affiliation(s)
- Mathew A Cherian
- From the Division of Oncology, Department of Medicine, Washington University School of Medicine, St. Louis, Missouri 63110 and
| | - Hicham H Baydoun
- From the Division of Oncology, Department of Medicine, Washington University School of Medicine, St. Louis, Missouri 63110 and
| | - Jacob Al-Saleem
- the Center for Retrovirus Research and Veterinary Biosciences, The Ohio State University, Columbus, Ohio 43210
| | - Nikoloz Shkriabai
- the Center for Retrovirus Research and Departments of Pharmaceutics and Pharmaceutical Chemistry and
| | - Mamuka Kvaratskhelia
- the Center for Retrovirus Research and Departments of Pharmaceutics and Pharmaceutical Chemistry and
| | - Patrick Green
- the Center for Retrovirus Research and Veterinary Biosciences, The Ohio State University, Columbus, Ohio 43210
| | - Lee Ratner
- From the Division of Oncology, Department of Medicine, Washington University School of Medicine, St. Louis, Missouri 63110 and
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5
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Bononi A, Pinton P. Study of PTEN subcellular localization. Methods 2014; 77-78:92-103. [PMID: 25312582 PMCID: PMC4396696 DOI: 10.1016/j.ymeth.2014.10.002] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2014] [Revised: 09/28/2014] [Accepted: 10/02/2014] [Indexed: 01/26/2023] Open
Abstract
The tumor suppressor PTEN is a key regulator of a plethora of cellular processes that are crucial in cancer development. Through its lipid phosphatase activity PTEN suppresses the PI3K/AKT pathway to govern cell proliferation, growth, migration, energy metabolism and death. The repertoire of roles fulfilled by PTEN has recently been expanded to include crucial functions in the nucleus, where it favors genomic stability and restrains cell cycle progression, as well as protein phosphatase dependent activity at the endoplasmic reticulum (ER) and mitochondria-associated membranes (MAMs), where PTEN interacts with the inositol 1,4,5-trisphosphate receptors (IP3Rs) and regulates Ca2+ release from the ER and sensitivity to apoptosis. Indeed, PTEN is present in definite subcellular locations where it performs distinct functions acting on specific effectors. In this review, we summarize recent advantages in methods to study PTEN subcellular localization and the distinct biological functions of PTEN in different cellular compartments. A deeper understanding of PTEN’s compartmentalized-functions will guide the rational design of novel therapies.
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Affiliation(s)
- Angela Bononi
- Section of Pathology, Oncology and Experimental Biology, Laboratory for Technologies of Advanced Therapies (LTTA), Department of Morphology, Surgery and Experimental Medicine, University of Ferrara, Ferrara, Italy
| | - Paolo Pinton
- Section of Pathology, Oncology and Experimental Biology, Laboratory for Technologies of Advanced Therapies (LTTA), Department of Morphology, Surgery and Experimental Medicine, University of Ferrara, Ferrara, Italy.
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6
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Berglund F, Weerasinghe NR, Davidson L, Lim JC, Eickholt BJ, Leslie NR. Disruption of epithelial architecture caused by loss of PTEN or by oncogenic mutant p110α/PIK3CA but not by HER2 or mutant AKT1. Oncogene 2013; 32:4417-26. [PMID: 23085752 PMCID: PMC3648380 DOI: 10.1038/onc.2012.459] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2012] [Revised: 08/17/2012] [Accepted: 08/19/2012] [Indexed: 12/15/2022]
Abstract
Genetic changes in HER2, PTEN, PIK3CA and AKT1 are all common in breast cancer and lead to the elevated phosphorylation of downstream targets of the PI3K/AKT signalling pathway. Changes in HER2, PTEN, PIK3CA and AKT have all been reported to lead to both enhanced proliferation and failures in hollow lumen formation in three dimensional epithelial culture models, but it is not clear whether these failures in lumen formation are caused by any failure in the spatial coordination of lumen formation (hollowing) or purely a failure in the apoptosis and clearance of luminal cells (cavitation). Here, we use normal murine mammary gland (NMuMG) epithelial cells, which form a hollow lumen without significant apoptosis, to compare the transformation by these four genetic changes. We find that either mutant PIK3CA expression or PTEN loss, but not mutant AKT1 E17K, cause disrupted epithelial architecture, whereas HER2 overexpression drives strong proliferation without affecting lumen formation in these cells. We also show that PTEN requires both lipid and protein phosphatase activity, its extreme C-terminal PDZ binding sequence and probably Myosin 5A to control lumen formation through a mechanism that does not correlate with its ability to control AKT, but which is selectively lost through mutation in some tumours. These findings correlate AKT-independent signalling activated by mutant PIK3CA or PTEN loss, but not strongly by HER2, with disrupted epithelial architecture and tumour formation.
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Affiliation(s)
- Fredrik Berglund
- Division of Cell Signalling and Immunology, College of Life Sciences, University of Dundee, Dundee, DD1 5EH, UK
| | - Nimmi R. Weerasinghe
- Division of Cell Signalling and Immunology, College of Life Sciences, University of Dundee, Dundee, DD1 5EH, UK
| | - Lindsay Davidson
- Division of Cell Signalling and Immunology, College of Life Sciences, University of Dundee, Dundee, DD1 5EH, UK
| | - Joseph C. Lim
- Division of Cell Signalling and Immunology, College of Life Sciences, University of Dundee, Dundee, DD1 5EH, UK
| | - Britta J. Eickholt
- Charité – Universitätsmedizin Berlin, Cluster of Excellence NeuroCure and Institute of Biochemistry, 10115 Berlin, Germany
| | - Nick R. Leslie
- Division of Cell Signalling and Immunology, College of Life Sciences, University of Dundee, Dundee, DD1 5EH, UK
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7
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Tibarewal P, Zilidis G, Spinelli L, Schurch N, Maccario H, Gray A, Perera NM, Davidson L, Barton GJ, Leslie NR. PTEN Protein Phosphatase Activity Correlates with Control of Gene Expression and Invasion, a Tumor-Suppressing Phenotype, But Not with AKT Activity. Sci Signal 2012; 5:ra18. [DOI: 10.1126/scisignal.2002138] [Citation(s) in RCA: 93] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
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8
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Abstract
A byproduct of the largely stochastic generation of a diverse B-cell specificity repertoire is production of cells that recognize autoantigens. Indeed, recent studies indicate that more than half of the primary repertoire consists of autoreactive B cells that must be silenced to prevent autoimmunity. While this silencing can occur by multiple mechanisms, it appears that most autoreactive B cells are silenced by anergy, wherein they populate peripheral lymphoid organs and continue to express unoccupied antigen receptors yet are unresponsive to antigen stimulation. Here we review molecular mechanisms that appear operative in maintaining the antigen unresponsiveness of anergic B cells. In addition, we present new data indicating that the failure of anergic B cells to mobilize calcium in response to antigen stimulation is not mediated by inactivation of stromal interacting molecule 1, a critical intermediary in intracellular store depletion-induced calcium influx.
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Affiliation(s)
- Yuval Yarkoni
- Integrated Department of Immunology, University of Colorado School of Medicine and National Jewish Health, Denver, CO, USA
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9
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Maccario H, Perera NM, Gray A, Downes CP, Leslie NR. Ubiquitination of PTEN (phosphatase and tensin homolog) inhibits phosphatase activity and is enhanced by membrane targeting and hyperosmotic stress. J Biol Chem 2010; 285:12620-8. [PMID: 20177066 DOI: 10.1074/jbc.m109.072280] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The PTEN (phosphatase and tensin homolog) tumor suppressor is a phosphatase that inhibits phosphoinositide 3-kinase-dependent signaling by metabolizing the phosphoinositide lipid phosphatidylinositol 3,4,5-trisphosphate (PtdInsP(3)) at the plasma membrane. PTEN can be mono- or polyubiquitinated, and this appears to control its nuclear localization and stability, respectively. Although PTEN phosphorylation at a cluster of C-terminal serine and threonine residues has been shown to stabilize the protein and inhibit polyubiquitination and plasma membrane localization, details of the regulation of ubiquitination are unclear. Here, we show that plasma membrane targeting of PTEN greatly enhances PTEN ubiquitination and that phosphorylation of PTEN in vitro does not affect subsequent ubiquitination. These data suggest that C-terminal phosphorylation indirectly regulates ubiquitination by controlling membrane localization. We also show that either mono- or polyubiquitination in vitro greatly reduces PTEN phosphatase activity. Finally, we show that hyperosmotic stress increases both PTEN ubiquitination and cellular PtdInsP(3) levels well before a reduction in PTEN protein levels is observed. Both PTEN ubiquitination and elevated PtdInsP(3) levels were reduced within 10 min after removal of the hyperosmotic stress. Our data indicate that ubiquitination may represent a regulated mechanism of direct reversible control over the PTEN enzyme.
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Affiliation(s)
- Helene Maccario
- Division of Molecular Physiology, College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, United Kingdom
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10
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Leslie NR, Spinelli L, Tibarewal P, Zilidis G, Weerasinghe N, Lim JC, Maccario H, Downes CP. Indirect mechanisms of carcinogenesis via downregulation of PTEN function. ACTA ACUST UNITED AC 2009; 50:112-8. [PMID: 19895830 DOI: 10.1016/j.advenzreg.2009.10.015] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Affiliation(s)
- Nick R Leslie
- Division of Molecular Physiology, College of Life Sciences, University of Dundee, Dundee, DD1 5EH, UK
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11
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Tiedemann RE, Gonzalez-Paz N, Kyle RA, Santana-Davila R, Price-Troska T, Van Wier SA, Chng WJ, Ketterling RP, Gertz MA, Henderson K, Greipp PR, Dispenzieri A, Lacy MQ, Rajkumar SV, Bergsagel PL, Stewart AK, Fonseca R. Genetic aberrations and survival in plasma cell leukemia. Leukemia 2008; 22:1044-52. [PMID: 18216867 DOI: 10.1038/leu.2008.4] [Citation(s) in RCA: 215] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Plasma cell leukemia (PCL) is an aggressive and rare hematological malignancy that originates either as primary disease (pPCL) or as a secondary leukemic transformation (sPCL) of multiple myeloma (MM). We report here the genetic aberrations and survival of 80 patients with pPCL or sPCL and make comparisons with 439 cases of MM. pPCL presents a decade earlier than sPCL (54.7 vs 65.3 years) and is associated with longer median overall survival (11.1 vs 1.3 months; P<0.001). 14q32 (IgH) translocations are highly prevalent in both sPCL and pPCL (82-87%); in pPCL IgH translocations almost exclusively involve 11q13 (CCND1), supporting a central etiological role, while in sPCL multiple partner oncogenes are involved, including 11q13, 4p16 (FGFR3/MMSET) and 16q23 (MAF), recapitulating MM. Both show ubiquitous inactivation of TP53 (pPCL 56%; sPCL 83%) by coding mutation or 17p13 deletion; complemented by p14ARF epigenetic silencing in sPCL (29%). Both show frequent N-RAS or K-RAS mutation. Poor survival in pPCL was predicted by MYC translocation (P=0.006). Survival in sPCL was consistently short. Overall pPCL and sPCL are different disorders with distinct natural histories, genetics and survival.
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Affiliation(s)
- R E Tiedemann
- Division of Hematology and Oncology, Mayo Clinic, Scottsdale, AZ, USA
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12
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Abstract
The tumor suppressor phosphatase and tensin homolog (PTEN) functions as a phosphoinositide 3-phosphatase, that antagonizes phosphatidylinositol 3-kinase action, and negatively regulates cell proliferation and survival signals. Inactivation of PTEN by loss-of-function mutations gives rise to deregulated hyperproliferation of cells, leading to oncogenic transformation. Recent studies have identified a number of upstream regulatory factors for PTEN and unveiled that the impairment in the PTEN regulatory system potentially becomes a causal factor for oncogenic transformation of cells. This article will review the PTEN inactivation mechanism which is linked to human tumorigenesis, particularly focusing on recent research progress in PTEN regulators.
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Affiliation(s)
- Tomohiko Maehama
- Department of Biochemistry and Cell Biology, National Institute of Infectious Diseases, Shinjuku-ku, Tokyo 162-8640, Japan.
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13
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Maccario H, Perera N, Davidson L, Downes C, Leslie N. PTEN is destabilized by phosphorylation on Thr366. Biochem J 2007; 405:439-44. [PMID: 17444818 PMCID: PMC2267318 DOI: 10.1042/bj20061837] [Citation(s) in RCA: 126] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Although PTEN (phosphatase and tensin homologue deleted on chromosome 10) is one of the most commonly mutated tumour suppressors in human cancers, loss of PTEN expression in the absence of mutation appears to occur in an even greater number of tumours. PTEN is phosphorylated in vitro on Thr366 and Ser370 by GSK3 (glycogen synthase kinase 3) and CK2 (casein kinase 2) respectively, and specific inhibitors of these kinases block these phosphorylation events in cultured cells. Although mutation of these phosphorylation sites did not alter the phosphatase activity of PTEN in vitro or in cells, blocking phosphorylation of Thr366 by either mutation or GSK3 inhibition in glioblastoma cell lines led to a stabilization of the PTEN protein. Our data support a model in which the phosphorylation of Thr366 plays a role in destabilizing the PTEN protein.
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Affiliation(s)
- Helene Maccario
- Division of Molecular Physiology, School of Life Sciences, University of Dundee, Dundee DD1 5EH, U.K
| | - Nevin M. Perera
- Division of Molecular Physiology, School of Life Sciences, University of Dundee, Dundee DD1 5EH, U.K
| | - Lindsay Davidson
- Division of Molecular Physiology, School of Life Sciences, University of Dundee, Dundee DD1 5EH, U.K
| | - C. Peter Downes
- Division of Molecular Physiology, School of Life Sciences, University of Dundee, Dundee DD1 5EH, U.K
| | - Nick R. Leslie
- Division of Molecular Physiology, School of Life Sciences, University of Dundee, Dundee DD1 5EH, U.K
- To whom correspondence should be addressed (email )
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14
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Leslie NR, Yang X, Downes CP, Weijer CJ. PtdIns(3,4,5)P(3)-dependent and -independent roles for PTEN in the control of cell migration. Curr Biol 2007; 17:115-25. [PMID: 17240336 PMCID: PMC1885949 DOI: 10.1016/j.cub.2006.12.026] [Citation(s) in RCA: 144] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2006] [Revised: 12/01/2006] [Accepted: 12/01/2006] [Indexed: 11/26/2022]
Abstract
BACKGROUND Phosphatase and tensin homolog (PTEN) mediates many of its effects on proliferation, growth, survival, and migration through its PtdIns(3,4,5)P(3) lipid phosphatase activity, suppressing phosphoinositide 3-kinase (PI3K)-dependent signaling pathways. PTEN also possesses a protein phosphatase activity, the role of which is less well characterized. RESULTS We have investigated the role of PTEN in the control of cell migration of mesoderm cells ingressing through the primitive streak in the chick embryo. Overexpression of PTEN strongly inhibits the epithelial-to-mesenchymal transition (EMT) of mesoderm cells ingressing through the anterior and middle primitive streak, but it does not affect EMT of cells located in the posterior streak. The inhibitory activity on EMT is completely dependent on targeting PTEN through its C-terminal PDZ binding site, but can be achieved by a PTEN mutant (PTEN G129E) with only protein phosphatase activity. Expression either of PTEN lacking the PDZ binding site or of the PTEN C2 domain, or inhibition of PI3K through specific inhibitors, does not inhibit EMT, but results in a loss of both cell polarity and directional migration of mesoderm cells. The PTEN-related protein TPTE, which normally lacks any detectable lipid and protein phosphatase activity, can be reactivated through mutation, and only this reactivated mutant leads to nondirectional migration of these cells in vivo. CONCLUSIONS PTEN modulates cell migration of mesoderm cells in the chick embryo through at least two distinct mechanisms: controlling EMT, which involves its protein phosphatase activity; and controlling the directional motility of mesoderm cells, through its lipid phosphatase activity.
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Affiliation(s)
- Nick R Leslie
- Division of Molecular Physiology, University of Dundee, Dundee, DD1 5EH, Scotland, United Kingdom.
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15
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Lackey J, Barnett J, Davidson L, Batty IH, Leslie NR, Downes CP. Loss of PTEN selectively desensitizes upstream IGF1 and insulin signaling. Oncogene 2007; 26:7132-42. [PMID: 17486056 PMCID: PMC2773499 DOI: 10.1038/sj.onc.1210520] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Many tumors have chronically elevated activity of PI 3-kinase-dependent signaling pathways, caused largely by oncogenic mutation of PI 3-kinase itself or loss of the opposing tumor suppressor lipid phosphatase, PTEN. Several PI 3-kinase-dependent feedback mechanisms have been identified that may affect the sensitivity of upstream receptor signaling, but the events required to initiate an inhibited state have not been addressed. We show that in a variety of cell types, loss of PTEN via experimental knockdown or in tumor cell lines correlates with a block in insulin-like growth factor 1 (IGF1)/insulin signaling, without affecting the sensitivity of platelet-derived growth factor or epidermal growth factor signaling. These effects on IGF/insulin signaling include a reduction of up to five- to tenfold in IGF-stimulated PI 3-kinase activation, a failure to activate the ERK kinases and, in some cells, reduced expression of insulin receptor substrate 1, and both IGF1 and insulin receptors. These data indicate that chronically elevated PI 3-kinase-dependent signaling to the degree seen in many tumors causes a selective loss of sensitivity in IGF1/insulin signaling that could significantly reduce the selective advantage of deregulated activation of IGF1/IGF1-R signaling in tumor development.
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Affiliation(s)
| | | | | | | | - Nick R. Leslie
- Author for correspondence, Nick Leslie, Tel: 44-1382-386263 Fax: 44-1382-385507
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16
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Choy MS, Bay BH, Cheng HC, Cheung NS. PTEN is recruited to specific microdomains of the plasma membrane during lactacystin-induced neuronal apoptosis. Neurosci Lett 2006; 405:120-5. [PMID: 16857313 DOI: 10.1016/j.neulet.2006.06.037] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2006] [Revised: 06/16/2006] [Accepted: 06/16/2006] [Indexed: 10/24/2022]
Abstract
The tumor suppressor PTEN (phosphatase and tensin homolog deleted from chromosome 10) is a novel phosphatase displaying both protein and lipid phosphatase activities. In the central nervous system, PTEN plays an important role in the regulation of cell growth, differentiation and death. The tumor suppressor function of PTEN is attributed to its phospholipid phosphatase activity that dephosphorylates the plasma membrane phosphatidylinositol-(3,4,5)-triphosphate (PtdIns(3,4,5)P(3)). Since PTEN is normally localized in the cytosol, it needs to be targeted to the plasma membrane to dephosphorylate PtdIns(3,4,5)P(3). We previously demonstrated that lactacystin-induced apoptosis of culture cortical neuron is associated with: (i) cleavage of PTEN (55 kDa) to a 50 kDa truncated form and (ii) accumulation of PTEN and all the truncated PTEN in a detergent-insoluble membrane fraction of the neuronal cells. Herein we demonstrate that a caspase-3 inhibitor suppresses cleavage of PTEN to the 50kDa truncated form in culture cortical neurons in response to lactacystin treatment. Using immunogold transmission electron microscopy, we examined the distribution of PTEN in plasma membrane sheets stripped from cultured cortical neurons with and without treatment of lactacystin. Our results demonstrate that lactacystin treatment induces accumulation of PTEN to the inner surface of the plasma membrane sheets of the neuronal cells. Taken together, our data suggest that caspase-3-like proteases are involved in the conversion of PTEN to a 50-kDa truncated form and that PTEN and its truncated form accumulate at specific microdomains of the plasma membrane in neuronal cells undergoing apoptosis.
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Affiliation(s)
- Meng Shyan Choy
- Departments of Biochemistry, Yong Loo Lin School of Medicine, National University of Singapore, Blk MD7, 8 Medical Drive, Singapore 117597, Singapore
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Ning K, Miller LC, Laidlaw HA, Burgess LA, Perera NM, Downes CP, Leslie NR, Ashford MLJ. A novel leptin signalling pathway via PTEN inhibition in hypothalamic cell lines and pancreatic beta-cells. EMBO J 2006; 25:2377-87. [PMID: 16675953 PMCID: PMC1478173 DOI: 10.1038/sj.emboj.7601118] [Citation(s) in RCA: 85] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2005] [Accepted: 04/05/2006] [Indexed: 11/08/2022] Open
Abstract
In obesity and diabetes, the ability of hypothalamic neurons to sense and transduce changes in leptin and insulin levels is compromised. The effects of both hormones require intracellular signalling via the PI3-kinase pathway, which is inhibited by the phosphatase PTEN. We show that leptin-stimulated F-actin depolymerization in mouse hypothalamic cells is inhibited by PTEN, a process involving independent effects of both its lipid and protein phosphatase activities. Potentially mediating this F-actin depolymerization, leptin, but not insulin, stimulated the phosphorylation of PTEN in a CK2 dependent manner, and inhibited its phosphatase activity. Similarly, hyperpolarization of mouse pancreatic beta-cells by leptin also requires coincident PtdIns(3,4,5)P3 generation and actin depolymerization, and could be inhibited by mechanisms requiring both the lipid and protein phosphatase activities of PTEN. These results demonstrate a critical role for PTEN in leptin signalling and indicate a mechanism by which leptin and insulin can produce PI3K dependent differential cellular outputs.
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Affiliation(s)
- Ke Ning
- Neurosciences Institute, Division of Pathology & Neuroscience, Ninewells Hospital & Medical School, University of Dundee, Dundee, UK
| | - Lisa C Miller
- Neurosciences Institute, Division of Pathology & Neuroscience, Ninewells Hospital & Medical School, University of Dundee, Dundee, UK
| | - Hilary A Laidlaw
- Neurosciences Institute, Division of Pathology & Neuroscience, Ninewells Hospital & Medical School, University of Dundee, Dundee, UK
| | - Laura A Burgess
- Neurosciences Institute, Division of Pathology & Neuroscience, Ninewells Hospital & Medical School, University of Dundee, Dundee, UK
| | - Nevin M Perera
- Division of Molecular Physiology, School of Life Sciences, University of Dundee, Dundee, UK
| | - C Peter Downes
- Division of Molecular Physiology, School of Life Sciences, University of Dundee, Dundee, UK
| | - Nick R Leslie
- Division of Molecular Physiology, School of Life Sciences, University of Dundee, Dundee, UK
| | - Michael LJ Ashford
- Neurosciences Institute, Division of Pathology & Neuroscience, Ninewells Hospital & Medical School, University of Dundee, Dundee, UK
- Neurosciences Institute, Division of Pathology & Neuroscience, Ninewells Hospital & Medical School, University of Dundee, Dundee DD1 9SY, UK. Tel.: +44 1382 632497; Fax: +44 1382 667120; E-mail:
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18
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Leslie N, Downes C. PTEN function: how normal cells control it and tumour cells lose it. Biochem J 2005; 382:1-11. [PMID: 15193142 PMCID: PMC1133909 DOI: 10.1042/bj20040825] [Citation(s) in RCA: 328] [Impact Index Per Article: 17.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2004] [Revised: 06/10/2004] [Accepted: 06/11/2004] [Indexed: 01/26/2023]
Abstract
The PTEN (phosphatase and tensin homologue deleted on chromosome 10) tumour suppressor is a PI (phosphoinositide) 3-phosphatase that can inhibit cellular proliferation, survival and growth by inactivating PI 3-kinase-dependent signalling. It also suppresses cellular motility through mechanisms that may be partially independent of phosphatase activity. PTEN is one of the most commonly lost tumour suppressors in human cancer, and its deregulation is also implicated in several other diseases. Here we discuss recent developments in our understanding of how the cellular activity of PTEN is regulated, and the closely related question of how this activity is lost in tumours. Cellular PTEN function appears to be regulated by controlling both the expression of the enzyme and also its activity through mechanisms including oxidation and phosphorylation-based control of non-substrate membrane binding. Therefore mutation of PTEN in tumours disrupts not only the catalytic function of PTEN, but also its regulatory aspects. However, although mutation of PTEN is uncommon in many human tumour types, loss of PTEN expression seems to be more frequent. It is currently unclear how these tumours lose PTEN expression in the absence of mutation, and while some data implicate other potential tumour suppressors and oncogenes in this process, this area seems likely to be a key focus of future research.
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Affiliation(s)
- Nick R. Leslie
- Division of Cell Signalling, School of Life Sciences, University of Dundee, Dundee DD1 5EH, U.K
- email
| | - C. Peter Downes
- Division of Cell Signalling, School of Life Sciences, University of Dundee, Dundee DD1 5EH, U.K
- email
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19
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Walker SM, Leslie NR, Perera NM, Batty IH, Downes CP. The tumour-suppressor function of PTEN requires an N-terminal lipid-binding motif. Biochem J 2004; 379:301-7. [PMID: 14711368 PMCID: PMC1224073 DOI: 10.1042/bj20031839] [Citation(s) in RCA: 127] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2003] [Revised: 01/06/2004] [Accepted: 01/07/2004] [Indexed: 01/04/2023]
Abstract
The PTEN (phosphatase and tensin homologue deleted on chromosome 10) tumour-suppressor protein is a phosphoinositide 3-phosphatase which antagonizes phosphoinositide 3-kinase-dependent signalling by dephosphorylating PtdIns(3,4,5)P3. Most tumour-derived point mutations of PTEN induce a loss of function, which correlates with profoundly reduced catalytic activity. However, here we characterize a point mutation at the N-terminus of PTEN, K13E from a human glioblastoma, which displayed wild-type activity when assayed in vitro. This mutation occurs within a conserved polybasic motif, a putative PtdIns(4,5)P2-binding site that may participate in membrane targeting of PTEN. We found that catalytic activity against lipid substrates and vesicle binding of wild-type PTEN, but not of PTEN K13E, were greatly stimulated by anionic lipids, especially PtdIns(4,5)P2. The K13E mutation also greatly reduces the efficiency with which anionic lipids inhibit PTEN activity against soluble substrates, supporting the hypothesis that non-catalytic membrane binding orientates the active site to favour lipid substrates. Significantly, in contrast to the wild-type enzyme, PTEN K13E failed either to prevent protein kinase B/Akt phosphorylation, or inhibit cell proliferation when expressed in PTEN-null U87MG cells. The cellular functioning of K13E PTEN was recovered by targeting to the plasma membrane through inclusion of a myristoylation site. Our results establish a requirement for the conserved N-terminal motif of PTEN for correct membrane orientation, cellular activity and tumour-suppressor function.
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Affiliation(s)
- Steven M Walker
- Division of Cell Signalling, School of Life Sciences, University of Dundee, MSI/WTB Complex, Dow Street, Dundee DD1 5EH, UK
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20
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Abstract
Lipid signaling by phosphoinositides (PIP(n)s) involves an array of proteins with lipid recognition, kinase, phosphatase, and phospholipase functions. Understanding PIP(n) pathway signaling requires identification and characterization of PIP(n)-interacting proteins. Moreover, spatiotemporal localization and physiological function of PIP(n)-protein complexes must be elucidated in cellular and organismal contexts. For protein discovery to functional elucidation, reporter-linked phosphoinositides or tethered PIP(n)s have been essential. The phosphoinositide 3-kinase (PI 3-K) signaling pathway has recently emerged as an important source of potential "druggable" therapeutic targets in human pathophysiology in both academic and pharmaceutical environments. This review summarizes the chemistry of PIP(n) affinity probes and their use in identifying macromolecular targets. The process of target validation will be described, i.e., the use of tethered PIP(n)s in determining PIP(n) selectivity in vitro and in establishing the function of PIP(n)-protein complexes in living cells.
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Affiliation(s)
- Glenn D Prestwich
- Department of Medicinal Chemistry, The University of Utah, 419 Wakara Way, Suite 205, Salt Lake City, UT 84108, USA.
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Watt SA, Kimber WA, Fleming IN, Leslie NR, Downes CP, Lucocq JM. Detection of novel intracellular agonist responsive pools of phosphatidylinositol 3,4-bisphosphate using the TAPP1 pleckstrin homology domain in immunoelectron microscopy. Biochem J 2004; 377:653-63. [PMID: 14604433 PMCID: PMC1223916 DOI: 10.1042/bj20031397] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2003] [Revised: 10/31/2003] [Accepted: 11/03/2003] [Indexed: 11/17/2022]
Abstract
PtdIns(3,4) P (2), a breakdown product of the lipid second messenger PtdIns(3,4,5) P (3), is a key signalling molecule in pathways controlling various cellular events. Cellular levels of PtdIns(3,4) P (2) are elevated upon agonist stimulation, mediating downstream signalling pathways by recruiting proteins containing specialized lipid-binding modules, such as the pleckstrin homology (PH) domain. A recently identified protein, TAPP1 (tandem-PH-domain-containing protein 1), has been shown to interact in vitro with high affinity and specificity with PtdIns(3,4) P (2) through its C-terminal PH domain. In the present study, we have utilized this PH domain tagged with glutathione S-transferase (GST-TAPP1-PH) as a probe in an on-section immunoelectron microscopy labelling procedure, mapping the subcellular distribution of PtdIns(3,4) P (2). As expected, we found accumulation of PtdIns(3,4) P (2) at the plasma membrane in response to the agonists platelet-derived growth factor and hydrogen peroxide. Importantly, however, we also found agonist stimulated PtdIns(3,4) P (2) labelling of intracellular organelles, including the endoplasmic reticulum and multivesicular endosomes. Expression of the 3-phosphatase PTEN (phosphatase and tensin homologue deleted on chromosome 10) in PTEN-null U87MG cells revealed differential sensitivity of these lipid pools to the enzyme. These data suggest a role for PtdIns(3,4) P (2) in endomembrane function.
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Affiliation(s)
- Stephen A Watt
- Division of Cell Biology and Immunology, School of Life Sciences, MSI/WTB Complex, University of Dundee, Dow Street, Dundee DD1 5EH, Scotland, U.K
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Leslie NR, Bennett D, Lindsay YE, Stewart H, Gray A, Downes CP. Redox regulation of PI 3-kinase signalling via inactivation of PTEN. EMBO J 2004; 22:5501-10. [PMID: 14532122 PMCID: PMC213768 DOI: 10.1093/emboj/cdg513] [Citation(s) in RCA: 470] [Impact Index Per Article: 23.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
The tumour suppressor PTEN is a PtdIns(3,4,5)P(3) phosphatase that regulates many cellular processes through direct antagonism of PI 3-kinase signalling. Here we show that oxidative stress activates PI 3-kinase-dependent signalling via the inactivation of PTEN. We use two assay systems to show that cellular PTEN phosphatase activity is inhibited by oxidative stress induced by 1 mM hydrogen peroxide. PTEN inactivation by oxidative stress also causes an increase in cellular PtdIns(3,4,5)P(3) levels and activation of the downstream PtdIns(3,4,5)P(3) target, PKB/Akt, that does not occur in cells lacking PTEN. We then show that endogenous oxidant production in RAW264.7 macrophages inactivates a fraction of the cellular PTEN, and that this is associated with an oxidant-dependent activation of downstream signalling. These results show that oxidants, including those produced by cells, can activate downstream signalling via the inactivation of PTEN. This demonstrates a novel mechanism of regulation of the activity of this important tumour suppressor and the signalling pathways it regulates. These results may have significant implications for the many cellular processes in which PtdIns(3,4,5)P(3) and oxidants are produced concurrently.
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Affiliation(s)
- Nick R Leslie
- Division of Cell Signalling, School of Life Sciences, University of Dundee, Dundee DD1 5EH, UK.
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Goberdhan DCI, Wilson C. PTEN: tumour suppressor, multifunctional growth regulator and more. Hum Mol Genet 2003; 12 Spec No 2:R239-48. [PMID: 12928488 DOI: 10.1093/hmg/ddg288] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
The tumour suppressor gene PTEN is mutated in a wide range of human cancers at a frequency roughly comparable with p53. In addition, germline PTEN mutations are associated with several dominant growth disorders. The molecular and cellular basis of these disorders has been elucidated by detailed in vivo genetic analysis in model organisms, in particular the fruit fly and mouse. Studies in the fly have shown that PTEN's growth regulatory functions are primarily mediated via its lipid phosphatase activity, which specifically reduces the cellular levels of phosphatidylinositol 3,4,5-trisphosphate. This activity antagonizes the effects of activated PI3-kinase in the nutritionally controlled insulin receptor pathway, thereby reducing protein synthesis and restraining cell and organismal growth, while also regulating other biological processes, such as fertility and ageing. Remarkably, this range of functions appears to be conserved in all higher organisms. PTEN also plays a role as a specialized cytoskeletal regulator, which, for example, is involved in directional movement of some migratory cells and may be important in metastasis. Furthermore, conditional knockouts in the mouse have recently revealed functions for PTEN in other processes, such as cell type specification and cardiac muscle contractility. Genetic approaches have therefore revealed a surprising diversity of global and cell type-specific PTEN-regulated functions that appear to be primarily controlled by modulation of a single phosphoinositide. Together with evidence from studies in cell culture that suggests links between PTEN and other growth regulatory genes such as p53, these studies provide new insights into PTEN-linked disorders and are beginning to suggest potential clinical strategies to combat these and other diseases.
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Das S, Dixon JE, Cho W. Membrane-binding and activation mechanism of PTEN. Proc Natl Acad Sci U S A 2003; 100:7491-6. [PMID: 12808147 PMCID: PMC164614 DOI: 10.1073/pnas.0932835100] [Citation(s) in RCA: 269] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2002] [Indexed: 11/18/2022] Open
Abstract
PTEN is a tumor suppressor that reverses the action of phosphoinositide 3-kinase by catalyzing the removal of the 3' phosphate of phosphoinositides. Despite the critical role of PTEN in cell signaling and regulation, the mechanisms of its membrane recruitment and activation is still poorly understood. PTEN is composed of an N-terminal phosphatase domain, a C2 domain, and a C-terminal tail region that contains the PSD-95/Dlg/ZO-1 homology (PDZ) domain-binding sequence and multiple phosphorylation sites. Our in vitro surface plasmon resonance measurements using immobilized vesicles showed that both the phosphatase domain and the C2 domain, but not the C-terminal tail, are involved in electrostatic membrane binding of PTEN. Furthermore, the phosphorylation-mimicking mutation on the C-terminal tail of PTEN caused an approximately 80-fold reduction in its membrane affinity, mainly by slowing the membrane-association step. Subcellular localization studies of PTEN transfected into HEK293T and HeLa cells indicated that targeting of PTEN to the plasma membrane is coupled with rapid degradation and that the phosphatase domain and the C2 domain are both necessary and sufficient for its membrane recruitment. Results also indicated that the phosphorylation regulates the targeting of PTEN to the plasma membrane not by blocking the PDZ domain-binding site but by interfering with electrostatic membrane binding of PTEN. On the basis of these results, we propose a membrane-binding and activation mechanism for PTEN, in which the phosphorylation/dephosphorylation of the C-terminal region serves as an electrostatic switch that controls the membrane translocation of the protein.
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Affiliation(s)
- Sudipto Das
- Department of Chemistry, University of Illinois, Chicago, IL 60607, USA
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25
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Abstract
PDZ domains are small globular building blocks that are amongst the most abundant protein interaction domains in organisms. Over the past several years an avalanche of data has implicated these modules in the clustering, targeting and routing of associating proteins. An overview is given of the types of interactions displayed by PDZ domains and how this relates to the current knowledge on their spatial structure. Furthermore, the different levels on which PDZ--ligand binding can be regulated and the consequences of PDZ domain-mediated clustering for activity, routing and targeting of interacting proteins will be addressed. Finally, some cell and animal models that illustrate the impact of PDZ domain-containing proteins on (multi-) cellular processes will be discussed.
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Affiliation(s)
- Marco van Ham
- Department of Cell Biology, Institute of Cellular Signalling, Nijmegen Center for Molecular Life Sciences, University of Nijmegen, Geert Grooteplein 28, 6525 GA Nijmegen, The Netherlands
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McConnachie G, Pass I, Walker SM, Downes CP. Interfacial kinetic analysis of the tumour suppressor phosphatase, PTEN: evidence for activation by anionic phospholipids. Biochem J 2003; 371:947-55. [PMID: 12534371 PMCID: PMC1223325 DOI: 10.1042/bj20021848] [Citation(s) in RCA: 92] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2002] [Revised: 01/09/2003] [Accepted: 01/20/2003] [Indexed: 02/04/2023]
Abstract
We investigated the kinetic behaviour and substrate specificity of PTEN (phosphatase and tensin homologue deleted on chromosome 10) using unilamellar vesicles containing substrate lipids in a background of phosphatidylcholine. PTEN displays the characteristics expected of an interfacial enzyme, since the rate of enzyme activity is dependent on the surface concentration of the substrate lipids used (mol fraction), as well as the bulk concentration. Surface-dilution analysis revealed the catalytic efficiency of PTEN for PtdIns(3,4,5) P (3) to be 200-fold greater than for either PtdIns(3,4) P (2) or PtdIns(3,5) P (2), and 1000-fold greater than for PtdIns3 P. The interfacial K (m) value of PTEN for PtdIns(3,4,5) P (3) was very low, reflecting the small proportions of this lipid that are present in cellular membranes. The catalytic-centre activity ( k (cat)) for PtdIns(3,4,5) P (3) was at least 200-fold greater than that for the water-soluble substrate Ins(1,3,4,5) P (4). The preference for lipid substrates may result from an interfacial activation of the enzyme, rather than processive catalysis of vesicular substrates. Moreover, both PtdIns(4,5) P (2) and univalent salts stimulated the activity of PTEN for PtdIns(3,4,5) P (3), but profoundly inhibited activity against Ins(1,3,4,5) P (4). The stimulatory effect of PtdIns(4,5) P (2) was greater in magnitude and more potent in comparison with other anionic phospholipid species. A mutation in the lipid-binding C2 domain (M-CBR3) that is biologically inactive did not alter overall catalytic efficiency in this model, but decreased the efficiency of the interfacial binding step, demonstrating its importance in the catalytic mechanism of PTEN.
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Affiliation(s)
- George McConnachie
- Division of Cell Signalling, School of Life Sciences, University of Dundee, Dundee, DD1 5EH, Scotland, UK
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Deichmann M, Thome M, Benner A, Egner U, Hartschuh W, Näher H. PTEN/MMAC1 expression in melanoma resection specimens. Br J Cancer 2002; 87:1431-6. [PMID: 12454773 PMCID: PMC2376294 DOI: 10.1038/sj.bjc.6600653] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Revised: 09/16/2002] [Accepted: 09/19/2002] [Indexed: 12/03/2022] Open
Abstract
PTEN/MMAC1, a tumour suppressor gene located on chromosome 10q23.3, has been found to be deleted in several types of human malignancies. As the chromosomal region 10q22-qter commonly is affected by losses in melanomas, we addressed this gene as tumour suppressor candidate in melanomas. Investigating PTEN/MMAC1 expression at mRNA level by semi-quantitative reverse transcription-polymerase chain reaction, we did not find a statistically significant down-regulation in melanoma resection specimens in comparison to acquired melanocytic nevi from which melanomas quite often are known to arise. Upon immunohistochemistry, PTEN/MMAC1 protein expression in melanomas was not lost. Sequencing the PTEN/MMAC1 cDNAs in 26 melanoma resection specimens (21 primary melanomas, five metastases), we detected three point mutations and two nucleotide deletions which did not represent genetic polymorphisms. With respect to the predicted protein sequences, all three point mutations were silent whereas the two frame shifts at the extreme C-terminus resulted in a loss of the putative PDZ-targeting consensus sequence. As loss of this motif possibly impairs localization and function of PTEN/MMAC1 in the two corresponding primary tumours, alterations of this tumour suppressor protein may participate in some melanomas.
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Affiliation(s)
- M Deichmann
- Department of Dermatology, University Clinics of Heidelberg, Vossstrasse 2, 69115 Heidelberg, Germany.
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28
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Abstract
The PTEN (phosphatase and tensin homologue deleted on chromosome 10) tumour suppressor is a phosphatidylinositol 3,4,5-trisphosphate [PtdIns(3,4,5)P(3)] 3-phosphatase that plays a critical role in regulating many cellular processes by antagonizing the phosphoinositide 3-kinase signalling pathway. We have identified and characterized two human homologues of PTEN, which differ with respect to their subcellular localization and lipid phosphatase activities. The previously cloned, but uncharacterized, TPTE (transmembrane phosphatase with tensin homology) is localized to the plasma membrane, but lacks detectable phosphoinositide 3-phosphatase activity. TPIP (TPTE and PTEN homologous inositol lipid phosphatase) is a novel phosphatase that occurs in several differentially spliced forms of which two, TPIP alpha and TPIP beta, appear to be functionally distinct. TPIP alpha displays similar phosphoinositide 3-phosphatase activity compared with PTEN against PtdIns(3,4,5)P(3), PtdIns(3,5)P(2), PtdIns(3,4)P(2) and PtdIns(3)P, has N-terminal transmembrane domains and appears to be localized on the endoplasmic reticulum. This is unusual as most signalling-lipid-metabolizing enzymes are not integral membrane proteins. TPIP beta, however, lacks detectable phosphatase activity and is cytosolic. TPIP has a wider tissue distribution than the testis-specific TPTE, with specific splice variants being expressed in testis, brain and stomach. TPTE and TPIP do not appear to be functional orthologues of the Golgi-localized and more distantly related murine PTEN2. We suggest that TPIP alpha plays a role in regulating phosphoinositide signalling on the endoplasmic reticulum, and might also represent a tumour suppressor and functional homologue of PTEN in some tissues.
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Affiliation(s)
- S M Walker
- Division of Cell Signalling, School of Life Sciences, University of Dundee, MSI/WTB Complex, Dow Street, Dundee DD1 5EH, Scotland, UK
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