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Lei X, Ma N, Du L, Liang Y, Zhang P, Han Y, Qu B. PP2A and tumor radiotherapy. Hereditas 2020; 157:36. [PMID: 32847617 PMCID: PMC7450598 DOI: 10.1186/s41065-020-00149-7] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2020] [Accepted: 08/13/2020] [Indexed: 02/07/2023] Open
Abstract
Protein phosphatase 2A (PP2A) is a serine/threonine phosphatase that serves as a key regulator of cellular physiology in the context of apoptosis, mitosis, and DNA damage responses. Canonically, PP2A functions as a tumor suppressor gene. However, recent evidence suggests that inhibiting PP2A activity in tumor cells may represent a viable approach to enhancing tumor sensitivity to chemoradiotherapy as such inhibition can cause cells to enter a disordered mitotic state that renders them more susceptible to cell death. Indeed, there is evidence that inhibiting PP2A can slow tumor growth following radiotherapy in a range of cancer types including ovarian cancer, liver cancer, malignant glioma, pancreatic cancer, and nasopharyngeal carcinoma. In the present review, we discuss current understanding of the role of PP2A in tumor radiotherapy and the potential mechanisms whereby it may influence this process.
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Affiliation(s)
- Xiao Lei
- The First Medical Center of Chinese PLA General Hospital, Department of Radiation Oncology, Beijing, P. R. China
| | - Na Ma
- The First Medical Center of Chinese PLA General Hospital, Department of Radiation Oncology, Beijing, P. R. China
| | - Lehui Du
- The First Medical Center of Chinese PLA General Hospital, Department of Radiation Oncology, Beijing, P. R. China
| | - Yanjie Liang
- The First Medical Center of Chinese PLA General Hospital, Department of Radiation Oncology, Beijing, P. R. China
| | - Pei Zhang
- The First Medical Center of Chinese PLA General Hospital, Department of Radiation Oncology, Beijing, P. R. China
| | - Yanan Han
- The First Medical Center of Chinese PLA General Hospital, Department of Radiation Oncology, Beijing, P. R. China
| | - Baolin Qu
- The First Medical Center of Chinese PLA General Hospital, Department of Radiation Oncology, Beijing, P. R. China.
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Wu CG, Chen H, Guo F, Yadav VK, Mcilwain SJ, Rowse M, Choudhary A, Lin Z, Li Y, Gu T, Zheng A, Xu Q, Lee W, Resch E, Johnson B, Day J, Ge Y, Ong IM, Burkard ME, Ivarsson Y, Xing Y. PP2A-B' holoenzyme substrate recognition, regulation and role in cytokinesis. Cell Discov 2017; 3:17027. [PMID: 28884018 PMCID: PMC5586252 DOI: 10.1038/celldisc.2017.27] [Citation(s) in RCA: 53] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2017] [Accepted: 07/12/2017] [Indexed: 12/11/2022] Open
Abstract
Protein phosphatase 2A (PP2A) is a major Ser/Thr phosphatase; it forms diverse heterotrimeric holoenzymes that counteract kinase actions. Using a peptidome that tiles the disordered regions of the human proteome, we identified proteins containing [LMFI]xx[ILV]xEx motifs that serve as interaction sites for B′-family PP2A regulatory subunits and holoenzymes. The B′-binding motifs have important roles in substrate recognition and in competitive inhibition of substrate binding. With more than 100 novel ligands identified, we confirmed that the recently identified LxxIxEx B′α-binding motifs serve as common binding sites for B′ subunits with minor variations, and that S/T phosphorylation or D/E residues at positions 2, 7, 8 and 9 of the motifs reinforce interactions. Hundreds of proteins in the human proteome harbor intrinsic or phosphorylation-responsive B′-interaction motifs, and localize at distinct cellular organelles, such as midbody, predicting kinase-facilitated recruitment of PP2A-B′ holoenzymes for tight spatiotemporal control of phosphorylation at mitosis and cytokinesis. Moroever, Polo-like kinase 1-mediated phosphorylation of Cyk4/RACGAP1, a centralspindlin component at the midbody, facilitates binding of both RhoA guanine nucleotide exchange factor (epithelial cell transforming sequence 2 (Ect2)) and PP2A-B′ that in turn dephosphorylates Cyk4 and disrupts Ect2 binding. This feedback signaling loop precisely controls RhoA activation and specifies a restricted region for cleavage furrow ingression. Our results provide a framework for further investigation of diverse signaling circuits formed by PP2A-B′ holoenzymes in various cellular processes.
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Affiliation(s)
- Cheng-Guo Wu
- McArdle Laboratory for Cancer Research, Department of Oncology, University of Wisconsin at Madison, School of Medicine and Public Health, Madison, WI, USA.,Biophysics Program, University of Wisconsin at Madison, Madison, WI, USA
| | - Hui Chen
- McArdle Laboratory for Cancer Research, Department of Oncology, University of Wisconsin at Madison, School of Medicine and Public Health, Madison, WI, USA
| | - Feng Guo
- McArdle Laboratory for Cancer Research, Department of Oncology, University of Wisconsin at Madison, School of Medicine and Public Health, Madison, WI, USA
| | - Vikash K Yadav
- Department of Chemistry-BMC, Uppsala University, Uppsala, Sweden
| | - Sean J Mcilwain
- Biostatistics and Medical Informatics, Wisconsin Institutes of Medical Research, University of Wisconsin at Madison, School of Medicine and Public Health, Madison, WI, USA
| | - Michael Rowse
- McArdle Laboratory for Cancer Research, Department of Oncology, University of Wisconsin at Madison, School of Medicine and Public Health, Madison, WI, USA
| | - Alka Choudhary
- Department of Medicine, Hematology/Oncology, UW Carbone Cancer Center, University of Wisconsin at Madison, School of Medicine and Public Health, Madison, WI, USA
| | - Ziqing Lin
- Department of Cell and Regenerative Biology, Human Proteomic Program, School of Medicine and Public Health, Madison, WI, USA
| | - Yitong Li
- McArdle Laboratory for Cancer Research, Department of Oncology, University of Wisconsin at Madison, School of Medicine and Public Health, Madison, WI, USA
| | - Tingjia Gu
- McArdle Laboratory for Cancer Research, Department of Oncology, University of Wisconsin at Madison, School of Medicine and Public Health, Madison, WI, USA
| | - Aiping Zheng
- McArdle Laboratory for Cancer Research, Department of Oncology, University of Wisconsin at Madison, School of Medicine and Public Health, Madison, WI, USA
| | - Qingge Xu
- Department of Cell and Regenerative Biology, Human Proteomic Program, School of Medicine and Public Health, Madison, WI, USA
| | - Woojong Lee
- McArdle Laboratory for Cancer Research, Department of Oncology, University of Wisconsin at Madison, School of Medicine and Public Health, Madison, WI, USA
| | - Eduard Resch
- Fraunhofer Institute for Molecular Biology and Applied Ecology IME, Project Group Translational Medicine and Pharmacology TMP, Frankfurt am Main, Germany
| | - Benjamin Johnson
- McArdle Laboratory for Cancer Research, Department of Oncology, University of Wisconsin at Madison, School of Medicine and Public Health, Madison, WI, USA
| | - Jenny Day
- McArdle Laboratory for Cancer Research, Department of Oncology, University of Wisconsin at Madison, School of Medicine and Public Health, Madison, WI, USA
| | - Ying Ge
- Department of Cell and Regenerative Biology, Human Proteomic Program, School of Medicine and Public Health, Madison, WI, USA
| | - Irene M Ong
- Biostatistics and Medical Informatics, Wisconsin Institutes of Medical Research, University of Wisconsin at Madison, School of Medicine and Public Health, Madison, WI, USA
| | - Mark E Burkard
- Department of Medicine, Hematology/Oncology, UW Carbone Cancer Center, University of Wisconsin at Madison, School of Medicine and Public Health, Madison, WI, USA
| | - Ylva Ivarsson
- Department of Chemistry-BMC, Uppsala University, Uppsala, Sweden
| | - Yongna Xing
- McArdle Laboratory for Cancer Research, Department of Oncology, University of Wisconsin at Madison, School of Medicine and Public Health, Madison, WI, USA.,Biophysics Program, University of Wisconsin at Madison, Madison, WI, USA
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Kawahara E, Maenaka S, Shimada E, Nishimura Y, Sakurai H. Dynamic regulation of extracellular signal-regulated kinase (ERK) by protein phosphatase 2A regulatory subunit B56γ1 in nuclei induces cell migration. PLoS One 2013; 8:e63729. [PMID: 23704935 PMCID: PMC3660565 DOI: 10.1371/journal.pone.0063729] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2012] [Accepted: 04/05/2013] [Indexed: 01/25/2023] Open
Abstract
Extracellular signal-regulated kinase (ERK) signalling plays a central role in various biological processes, including cell migration, but it remains unknown what factors directly regulate the strength and duration of ERK activation. We found that, among the B56 family of protein phosphatase 2A (PP2A) regulatory subunits, B56γ1 suppressed EGF-induced cell migration on collagen, bound to phosphorylated-ERK, and dephosphorylated ERK, whereas B56α1 and B56β1 did not. B56γ1 was immunolocalized in nuclei. The IER3 protein was immediately highly expressed in response to costimulation of cells with EGF and collagen. Knockdown of IER3 inhibited cell migration and enhanced dephosphorylation of ERK. Analysis of the time course of PP2A-B56γ1 activity following the costimulation showed an immediate loss of phosphatase activity, followed by a rapid increase in activity, and this activity then remained at a stable level that was lower than the original level. Our results indicate that the strength and duration of the nuclear ERK activation signal that is initially induced by ERK kinase (MEK) are determined at least in part by modulation of the phosphatase activity of PP2A-B56γ1 through two independent pathways.
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Affiliation(s)
- Ei Kawahara
- Department of Clinical Laboratory Science, Kanazawa University, Kanazawa, Japan
- * E-mail:
| | - Shiori Maenaka
- Department of Clinical Laboratory Science, Kanazawa University, Kanazawa, Japan
| | - Eri Shimada
- Department of Clinical Laboratory Science, Kanazawa University, Kanazawa, Japan
| | - Yoshihiro Nishimura
- Department of Clinical Laboratory Science, Kanazawa University, Kanazawa, Japan
| | - Hiroshi Sakurai
- Department of Clinical Laboratory Science, Kanazawa University, Kanazawa, Japan
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Slupe AM, Merrill RA, Strack S. Determinants for Substrate Specificity of Protein Phosphatase 2A. Enzyme Res 2011; 2011:398751. [PMID: 21755039 PMCID: PMC3132988 DOI: 10.4061/2011/398751] [Citation(s) in RCA: 69] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2011] [Accepted: 04/28/2011] [Indexed: 12/22/2022] Open
Abstract
Protein phosphatase 2A- (PP2A-) catalyzed dephosphorylation of target substrate proteins is widespread and critical for cellular function. PP2A is predominantly found as a heterotrimeric complex of a catalytic subunit (C), a scaffolding subunit (A), and one member of 4 families of regulatory subunits (B). Substrate specificity of the holoenzyme complex is determined by the subcellular locale the complex is confined to, selective incorporation of the B subunit, interactions with endogenous inhibitory proteins, and specific intermolecular interactions between PP2A and target substrates. Here, we discuss recent studies that have advanced our understanding of the molecular determinants for PP2A substrate specificity.
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Affiliation(s)
- Andrew M Slupe
- Department of Pharmacology, University of Iowa, 2-432 BSB, Iowa City, IA 52242, USA
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Hagiyama M, Ichiyanagi N, Kimura KB, Murakami Y, Ito A. Expression of a soluble isoform of cell adhesion molecule 1 in the brain and its involvement in directional neurite outgrowth. THE AMERICAN JOURNAL OF PATHOLOGY 2009; 174:2278-89. [PMID: 19435791 PMCID: PMC2684192 DOI: 10.2353/ajpath.2009.080743] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 02/19/2009] [Indexed: 11/20/2022]
Abstract
Cell adhesion molecule 1 (CADM1), an immunoglobulin superfamily member, is expressed on superior cervical ganglion neurites and mediates cell-cell adhesion by trans-homophilic binding. In addition to the membrane-bound form, we have previously shown that a soluble form (sCADM1) generated by alternative splicing possesses a stop codon immediately downstream of the immunoglobulin-like domain. Here, we demonstrate the presence of sCADM1 in vivo and its possible role in neurite extension. sCADM1 appears to be a stromal protein because extracellular-restricted, but not intracellular-restricted, anti-CADM1 antibody stained stromal protein-rich extract from mouse brains. Murine plasmacytoma cells, P3U1, were modified to secrete sCADM1 fused with either immunoglobulin (Ig)G Fc portion (sCADM1-Fc) or its deletion form that lacks the immunoglobulin-like domain (DeltasCADM1-Fc). When P3U1 derivatives expressing sCADM1-Fc or DeltasCADM1-Fc were implanted into collagen gels, Fc-fused proteins were present more abundantly around the cells. Superior cervical ganglion neurons, parental P3U1, and either derivative were implanted into collagen gels separately, and co-cultured for 4 days. Bodian staining of the gel sections revealed that most superior cervical ganglion neurites turned toward the source of sCADM1-Fc, but not DeltasCADM1-Fc. Furthermore, immunofluorescence signals for sCADM1-Fc and membrane-bound CADM1 were co-localized on the neurite surface. These results show that sCADM1 appears to be involved in directional neurite extension by serving as an anchor to which membrane-bound CADM1 on the neurites can bind.
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Affiliation(s)
- Man Hagiyama
- Division of Molecular Pathology, Department of Cancer Biology, Institute of Medical Science, The University of Tokyo, 4-6-1, Shirokanedai, Minato-ku, Tokyo 108-8639, Japan
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Arnold HK, Sears RC. A tumor suppressor role for PP2A-B56alpha through negative regulation of c-Myc and other key oncoproteins. Cancer Metastasis Rev 2008; 27:147-58. [PMID: 18246411 DOI: 10.1007/s10555-008-9128-9] [Citation(s) in RCA: 85] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Loss or inhibition of the serine/threonine protein phosphatase 2A (PP2A) has revealed a critical tumor suppressor function for PP2A. However, PP2A has also been shown to have important roles in cell cycle progression and survival. Therefore, PP2A is not a typical tumor suppressor. This is most likely due to the fact that PP2A represents a large number of different holoenzymes. Further understanding of PP2A function(s), and especially its tumor suppressor activity, will depend largely on our ability to determine specific targets for these different PP2A holoenzymes and to gain an understanding of how these targets confer tumor suppressor activity or contribute to cell cycle progression and cell survival. Recent work has identified c-Myc as a target of the PP2A holoenzyme, PP2A-B56alpha. This holoenzyme also negatively regulates beta-catenin expression and modulates the anti-apoptotic activity of Bcl2, thus characterizing PP2A-B56alpha as a tumor suppressor PP2A holoenzyme. This review will focus on the role of PP2A-B56alpha in regulating c-Myc and will place this tumor suppressor activity of PP2A within the context of its other tumor suppressor functions. Finally, the mechanism(s) through which PP2A-B56alpha tumor suppressor activity may be lost in cancer will be discussed.
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Affiliation(s)
- Hugh K Arnold
- Department of Molecular and Medical Genetics, Oregon Health & Sciences University, Portland, OR 97239, USA
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