1
|
Li C, Zhang P, Hong PP, Niu GJ, Wang XP, Zhao XF, Wang JX. White spot syndrome virus hijacks host PP2A-FOXO axes to promote its propagation. Int J Biol Macromol 2024; 256:128333. [PMID: 38007022 DOI: 10.1016/j.ijbiomac.2023.128333] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2023] [Revised: 11/06/2023] [Accepted: 11/14/2023] [Indexed: 11/27/2023]
Abstract
Viruses have developed superior strategies to escape host defenses or exploit host components and enable their infection. The forkhead box transcription factor O family proteins (FOXOs) are reportedly utilized by human cytomegalovirus during their reactivation in mammals, but if FOXOs are exploited by viruses during their infection remains unclear. In the present study, we found that the FOXO of kuruma shrimp (Marsupenaeus japonicus) was hijacked by white spot syndrome virus (WSSV) during infection. Mechanistically, the expression of leucine carboxyl methyl transferase 1 (LCMT1) was up-regulated during the early stages of WSSV infection, which activated the protein phosphatase 2A (PP2A) by methylation, leading to dephosphorylation of FOXO and translocation into the nucleus. The FOXO directly promoted transcription of the immediate early gene, wsv079 of WSSV, which functioned as a transcriptional activator to initiate the expression of viral early and late genes. Thus, WSSV utilized the host LCMT1-PP2A-FOXO axis to promote its replication during the early infection stage. We also found that, during the late stages of WSSV infection, the envelope protein of WSSV (VP26) promoted PP2A activity by directly binding to FOXO and the regulatory subunit of PP2A (B55), which further facilitated FOXO dephosphorylation and WSSV replication via the VP26-PP2A-FOXO axis in shrimp. Overall, this study reveals novel viral strategies by which WSSV hijacks host LCMT1-PP2A-FOXO or VP26-PP2A-FOXO axes to promote its propagation, and provides clinical targets for WSSV control in shrimp aquaculture.
Collapse
Affiliation(s)
- Cang Li
- Shandong Provincial Key Laboratory of Animal Cells and Developmental Biology, School of Life Sciences, Shandong University, Qingdao, Shandong 266237, China
| | - Peng Zhang
- Shandong Provincial Key Laboratory of Animal Cells and Developmental Biology, School of Life Sciences, Shandong University, Qingdao, Shandong 266237, China
| | - Pan-Pan Hong
- Shandong Provincial Key Laboratory of Animal Cells and Developmental Biology, School of Life Sciences, Shandong University, Qingdao, Shandong 266237, China
| | - Guo-Juan Niu
- Shandong Provincial Key Laboratory of Animal Cells and Developmental Biology, School of Life Sciences, Shandong University, Qingdao, Shandong 266237, China
| | - Xiao-Pei Wang
- Shandong Provincial Key Laboratory of Animal Cells and Developmental Biology, School of Life Sciences, Shandong University, Qingdao, Shandong 266237, China
| | - Xiao-Fan Zhao
- Shandong Provincial Key Laboratory of Animal Cells and Developmental Biology, School of Life Sciences, Shandong University, Qingdao, Shandong 266237, China
| | - Jin-Xing Wang
- Shandong Provincial Key Laboratory of Animal Cells and Developmental Biology, School of Life Sciences, Shandong University, Qingdao, Shandong 266237, China; State Key Laboratory of Microbial Technology, Shandong University, Qingdao, Shandong 266237, China.
| |
Collapse
|
2
|
Alghanem L, Zhang X, Jaiswal R, Seyoum B, Mallisho A, Msallaty Z, Yi Z. Effect of Insulin and Pioglitazone on Protein Phosphatase 2A Interaction Partners in Primary Human Skeletal Muscle Cells Derived from Obese Insulin-Resistant Participants. ACS OMEGA 2022; 7:42763-42773. [PMID: 36467954 PMCID: PMC9713796 DOI: 10.1021/acsomega.2c04473] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/15/2022] [Accepted: 11/01/2022] [Indexed: 05/16/2023]
Abstract
Skeletal muscle insulin resistance is a major contributor to type-2 diabetes (T2D). Pioglitazone is a potent insulin sensitizer of peripheral tissues by targeting peroxisome proliferator-activated receptor gamma. Pioglitazone has been reported to protect skeletal muscle cells from lipotoxicity by promoting fatty acid mobilization and insulin signaling. However, it is unclear whether pioglitazone increases insulin sensitivity through changes in protein-protein interactions involving protein phosphatase 2A (PP2A). PP2A regulates various cell signaling pathways such as insulin signaling. Interaction of the catalytic subunit of PP2A (PP2Ac) with protein partners is required for PP2A specificity and activity. Little is known about PP2Ac partners in primary human skeletal muscle cells derived from lean insulin-sensitive (Lean) and obese insulin-resistant (OIR) participants. We utilized a proteomics method to identify PP2Ac interaction partners in skeletal muscle cells derived from Lean and OIR participants, with or without insulin and pioglitazone treatments. In this study, 216 PP2Ac interaction partners were identified. Furthermore, 26 PP2Ac partners exhibited significant differences in their interaction with PP2Ac upon insulin treatments between the two groups. Multiple pathways and molecular functions are significantly enriched for these 26 interaction partners, such as nonsense-mediated decay, metabolism of RNA, RNA binding, and protein binding. Interestingly, pioglitazone restored some of these abnormalities. These results provide differential PP2Ac complexes in Lean and OIR in response to insulin/pioglitazone, which may help understand molecular mechanisms underpinning insulin resistance and the insulin-sensitizing effects of pioglitazone treatments, providing multiple targets in various pathways to reverse insulin resistance and prevent and/or manage T2D with less drug side effects.
Collapse
Affiliation(s)
- Lana Alghanem
- Department
of Pharmaceutical Sciences, College of Pharmacy and Health Sciences, Wayne State University, Detroit, Michigan48201, United States
| | - Xiangmin Zhang
- Department
of Pharmaceutical Sciences, College of Pharmacy and Health Sciences, Wayne State University, Detroit, Michigan48201, United States
| | - Ruchi Jaiswal
- Department
of Pharmaceutical Sciences, College of Pharmacy and Health Sciences, Wayne State University, Detroit, Michigan48201, United States
| | - Berhane Seyoum
- Division
of Endocrinology, Wayne State University School of Medicine, Wayne State University, Detroit, Michigan48201, United States
| | - Abdullah Mallisho
- Division
of Endocrinology, Wayne State University School of Medicine, Wayne State University, Detroit, Michigan48201, United States
| | - Zaher Msallaty
- Division
of Endocrinology, Wayne State University School of Medicine, Wayne State University, Detroit, Michigan48201, United States
| | - Zhengping Yi
- Department
of Pharmaceutical Sciences, College of Pharmacy and Health Sciences, Wayne State University, Detroit, Michigan48201, United States
| |
Collapse
|
3
|
Laskovs M, Partridge L, Slack C. Molecular inhibition of RAS signalling to target ageing and age-related health. Dis Model Mech 2022; 15:276620. [PMID: 36111627 PMCID: PMC9510030 DOI: 10.1242/dmm.049627] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The RAS/MAPK pathway is a highly conserved signalling pathway with a well-established role in cancer. Mutations that hyperactivate this pathway are associated with unregulated cell proliferation. Evidence from a range of model organisms also links RAS/MAPK signalling to ageing. Genetic approaches that reduce RAS/MAPK signalling activity extend lifespan and also improve healthspan, delaying the onset and/or progression of age-related functional decline. Given its role in cancer, therapeutic interventions that target and inhibit this pathway's key components are under intense investigation. The consequent availability of small molecule inhibitors raises the possibility of repurposing these compounds to ameliorate the deleterious effects of ageing. Here, we review evidence that RAS/MAPK signalling inhibitors already in clinical use, such as trametinib, acarbose, statins, metformin and dihydromyricetin, lead to lifespan extension and to improved healthspan in a range of model systems. These findings suggest that the repurposing of small molecule inhibitors of RAS/MAPK signalling might offer opportunities to improve health during ageing, and to delay or prevent the development of age-related disease. However, challenges to this approach, including poor tolerance to treatment in older adults or development of drug resistance, first need to be resolved before successful clinical implementation. Summary: This Review critically discusses the links between RAS signalling and ageing, and how RAS inhibitors could extend lifespan and enhance healthspan.
Collapse
Affiliation(s)
- Mihails Laskovs
- School of Biosciences, College of Health and Life Sciences, Aston University 1 , Birmingham B4 7ET , UK
| | - Linda Partridge
- Institute of Healthy Ageing 2 , Department of Genetics, Evolution and Environment , , Darwin Building, Gower Street, London WC1E 6BT , UK
- University College London 2 , Department of Genetics, Evolution and Environment , , Darwin Building, Gower Street, London WC1E 6BT , UK
- Max Planck Institute for Biology of Ageing 3 , Joseph-Stelzmann-Strasse 9b, 50931 Cologne , Germany
| | - Cathy Slack
- School of Biosciences, College of Health and Life Sciences, Aston University 1 , Birmingham B4 7ET , UK
| |
Collapse
|
4
|
Li M, Cai Y, Chen X, Zhang L, Jiang Z, Yu Q. Tamoxifen induced hepatic steatosis in high-fat feeding rats through SIRT1-Foxo1 suppression and LXR-SREBP1c activation. Toxicol Res (Camb) 2022; 11:673-682. [PMID: 36051666 PMCID: PMC9424708 DOI: 10.1093/toxres/tfac043] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2021] [Revised: 04/05/2022] [Accepted: 06/27/2022] [Indexed: 07/24/2023] Open
Abstract
Background Clinically, long-term use of tamoxifen (TAM) would lead to fatty liver disease in breast cancer patients, especially obese women. However, the exact mechanism of TAM-induced hepatic steatosis is still unclear. Meanwhile, there is no drug to prevent and treat it. Aims and Methods In view of silent information regulator 1 (SIRT1) playing a key role in hepatic lipid metabolism regulation, this study was conducted to investigate whether SIRT1 is a potential therapeutic target for TAM-induced hepatic steatosis. In this study, obese female Wistar rats fed with high-fat diet (HFD) for 15 weeks were given TAM (4, 8 mg/kg, intragastric) for 14 days. In vitro, human hepatocarcinoma cell line HepG2 was used to establish a high-fat model with 50 μM oleic acid and TAM (10 μM) was treated simultaneously for 72 h. Results The results showed that TAM was more likely to upregulate the expression of lipid synthetase that caused the increase of lipid content in HepG2 cells and rat liver. The expression of SIRT1 was downregulated both in vitro and in vivo. SIRT1 agonist SRT1720 (15 mg/kg, 30 mg/kg, i.p.) could resist TAM-induced hepatic lipid synthetase overexpression to relieve TAM-induced hepatic steatosis. Meanwhile, the upregulation of p-forkhead box O1 and LXRα induced by TAM was reversed by SRT1720. Conclusions These results indicated that TAM-induced hepatic steatosis was based on SIRT1-p-FoxO/LXRα-sterol regulatory element binding protein 1c pathway under HFD condition. SIRT1 agonist might be a potential therapeutic drug to relieve this side effect. Highlights Tamoxifen increased lipid synthesis and regulated lipid transport in HFD rat liver.p-FoxO1/LXRα-SREBP1c signaling was upregulated through the inhibition of SIRT1 in tamoxifen-induced hepatic steatosis under HFD condition.SIRT1 agonist SRT1720 could relieve tamoxifen-induced hepatic steatosis.
Collapse
Affiliation(s)
- Miao Li
- New Drug Screening Center, Jiangsu Center for Pharmacodynamics Research and Evaluation, China Pharmaceutical University, Nanjing 210009, China
| | - Yu Cai
- New Drug Screening Center, Jiangsu Center for Pharmacodynamics Research and Evaluation, China Pharmaceutical University, Nanjing 210009, China
| | - Xi Chen
- New Drug Screening Center, Jiangsu Center for Pharmacodynamics Research and Evaluation, China Pharmaceutical University, Nanjing 210009, China
| | - Luyong Zhang
- Corresponding author: New Drug Screening Center, Jiangsu Center for Pharmacodynamics Research and Evaluation, China Pharmaceutical University, Nanjing 210009, China. ; ;
| | - Zhenzhou Jiang
- Corresponding author: New Drug Screening Center, Jiangsu Center for Pharmacodynamics Research and Evaluation, China Pharmaceutical University, Nanjing 210009, China. ; ;
| | - Qinwei Yu
- Corresponding author: New Drug Screening Center, Jiangsu Center for Pharmacodynamics Research and Evaluation, China Pharmaceutical University, Nanjing 210009, China. ; ;
| |
Collapse
|
5
|
PPP2R2A affects embryonic implantation by regulating the proliferation and apoptosis of Hu sheep endometrial stromal cells. Theriogenology 2021; 176:149-162. [PMID: 34619436 DOI: 10.1016/j.theriogenology.2021.09.026] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2021] [Revised: 09/24/2021] [Accepted: 09/24/2021] [Indexed: 12/13/2022]
Abstract
Embryonic implantation is a complex reproductive physiological process in mammals. Although several endometrial proteins affecting embryonic implantation have been reported in the past, there are still potential endometrial proteins that have been neglected, and their specific regulatory mechanisms are unclear. This study demonstrated that protein phosphatase 2A regulatory subunit B55α (PPP2R2A) served as a novel regulator in medication of sheep embryonic implantation in vitro. Our results showed that sheep PPP2R2A encoded 447 amino acids and shared 91.74%-92.36% amino acid sequences with its orthologs compared with other species. Meanwhile, PPP2R2A was widely expressed in sheep uterine tissues, and it could regulate the expression levels of key regulators of embryonic implantation in endometrial stromal cells (ESCs). Knockdown of PPP2R2A significantly inhibited cell proliferation by blocking cell cycle transfer G0/G1 into S phase accompanied by downregulation of CDK2, CDK4, CCND1, CCNE1 and upregulation of P21. In contrast to PPP2R2A overexpression, PPP2R2A interference greatly promoted cell apoptosis and the expression of BAX, CASP3, CASP9 and BAX/BCL-2. Taken together, these results suggest that PPP2R2A, as a novel regulatory factor, affects embryonic implantation via regulating the proliferation and apoptosis of Hu sheep ESCs in vitro.
Collapse
|
6
|
Zhang Y, Zhu P, Wu X, Yuan T, Su Z, Chen S, Zhou Y, Tao WA. Microcystin-LR Induces NLRP3 Inflammasome Activation via FOXO1 Phosphorylation, Resulting in Interleukin-1β Secretion and Pyroptosis in Hepatocytes. Toxicol Sci 2021; 179:53-69. [PMID: 33078829 DOI: 10.1093/toxsci/kfaa159] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Microcystin-LR (MC-LR), the most common and toxic microcystin (MC) present in freshwater, poses a substantial threat to human health, especially hepatotoxicity. Recent evidence reveals that the NLRP3 inflammasome plays an important role in liver injury by activating caspase-1 to promote interleukin-1β (IL-1β) secretion. In this study, we investigated the possible role of NLRP3 inflammasome activation in MC-LR-induced mouse liver inflammatory injury. We found that MC-LR administered to mice by oral gavage mainly accumulated in liver and induced the activation of the NLRP3 inflammasome and production of mature IL-1β. Additionally, we observed an increase in the levels of NLRP3 inflammasome-related proteins and the proportion of pyroptosis in MC-LR-treated AML-12 cells. We also found that inhibition of NLRP3 in mice attenuated MC-LR-induced IL-1β production, indicating an essential role for NLRP3 in MC-LR-induced liver inflammatory injury. In addition, we found that inhibition of FOXO1 by AKT-mediated hyperphosphorylation, due to protein phosphatase 2A (PP2A) inhibition, is required for MC-LR-induced expression of NLRP3. Taken together, our in vivo and in vitro findings suggest a model in which the NLRP3 inflammasome activation, a result of AKT-mediated hyperphosphorylation of FOXO1 through inhibition of PP2A, plays a key role in MC-LR-induced liver inflammatory injury via IL-1β secretion and pyroptotic cell death.
Collapse
Affiliation(s)
- Yali Zhang
- Department of Biochemistry and Molecular Biology, School of Medicine, Nantong University, Nantong, Jiangsu 226001, China
| | - Peipei Zhu
- Department of Biochemistry, Purdue University, West Lafayette, Indiana 47907
| | - Xiaofeng Wu
- Department of Biochemistry, Purdue University, West Lafayette, Indiana 47907
| | - Tianli Yuan
- Department of Biochemistry and Molecular Biology, School of Medicine, Nantong University, Nantong, Jiangsu 226001, China
| | - Zhangyao Su
- Department of Biochemistry and Molecular Biology, School of Medicine, Nantong University, Nantong, Jiangsu 226001, China
| | - Shiyin Chen
- Department of Biochemistry and Molecular Biology, School of Medicine, Nantong University, Nantong, Jiangsu 226001, China
| | - Yajun Zhou
- Department of Biochemistry and Molecular Biology, School of Medicine, Nantong University, Nantong, Jiangsu 226001, China
| | - Weiguo Andy Tao
- Department of Biochemistry, Purdue University, West Lafayette, Indiana 47907
| |
Collapse
|
7
|
Christodoulou E, Rashid M, Pacini C, Droop A, Robertson H, van Groningen T, Teunisse AFAS, Iorio F, Jochemsen AG, Adams DJ, van Doorn R. Analysis of CRISPR-Cas9 screens identifies genetic dependencies in melanoma. Pigment Cell Melanoma Res 2021; 34:122-131. [PMID: 32767816 PMCID: PMC7818247 DOI: 10.1111/pcmr.12919] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2020] [Revised: 07/03/2020] [Accepted: 07/29/2020] [Indexed: 12/13/2022]
Abstract
Targeting the MAPK signaling pathway has transformed the treatment of metastatic melanoma. CRISPR-Cas9 genetic screens provide a genome-wide approach to uncover novel genetic dependencies that might serve as therapeutic targets. Here, we analyzed recently reported CRISPR-Cas9 screens comparing data from 28 melanoma cell lines and 313 cell lines of other tumor types in order to identify fitness genes related to melanoma. We found an average of 1,494 fitness genes in each melanoma cell line. We identified 33 genes, inactivation of which specifically reduced the fitness of melanoma. This set of tumor type-specific genes includes established melanoma fitness genes as well as many genes that have not previously been associated with melanoma growth. Several genes encode proteins that can be targeted using available inhibitors. We verified that genetic inactivation of DUSP4 and PPP2R2A reduces the proliferation of melanoma cells. DUSP4 encodes an inhibitor of ERK, suggesting that further activation of MAPK signaling activity through its loss is selectively deleterious to melanoma cells. Collectively, these data present a resource of genetic dependencies in melanoma that may be explored as potential therapeutic targets.
Collapse
Affiliation(s)
| | - Mamunur Rashid
- Experimental Cancer Genetics GroupWellcome Trust Sanger InstituteCambridgeUK
| | - Clare Pacini
- Cancer Dependency Map AnalyticsWellcome Trust Sanger InstituteCambridgeUK
| | - Alastair Droop
- Experimental Cancer Genetics GroupWellcome Trust Sanger InstituteCambridgeUK
| | - Holly Robertson
- Experimental Cancer Genetics GroupWellcome Trust Sanger InstituteCambridgeUK
| | - Tim van Groningen
- Department of DermatologyLeiden University Medical CenterLeidenThe Netherlands
| | - Amina F. A. S. Teunisse
- Department of Cell and Chemical BiologyLeiden University Medical CenterLeidenThe Netherlands
| | - Francesco Iorio
- Cancer Dependency Map AnalyticsWellcome Trust Sanger InstituteCambridgeUK
- Centre for Computational BiologyHuman TechnopoleMilanoItaly
| | - Aart G. Jochemsen
- Department of Cell and Chemical BiologyLeiden University Medical CenterLeidenThe Netherlands
| | - David J. Adams
- Experimental Cancer Genetics GroupWellcome Trust Sanger InstituteCambridgeUK
| | - Remco van Doorn
- Department of DermatologyLeiden University Medical CenterLeidenThe Netherlands
| |
Collapse
|
8
|
Kowluru A. Potential roles of PP2A-Rac1 signaling axis in pancreatic β-cell dysfunction under metabolic stress: Progress and promise. Biochem Pharmacol 2020; 180:114138. [PMID: 32634437 DOI: 10.1016/j.bcp.2020.114138] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2020] [Revised: 07/01/2020] [Accepted: 07/02/2020] [Indexed: 12/16/2022]
Abstract
Recent estimates by the International Diabetes Federation suggest that the incidence of diabetes soared to an all-time high of 463 million in 2019, and the federation predicts that by 2045 the number of individuals afflicted with this disease will increase to 700 million. Therefore, efforts to understand the pathophysiology of diabetes are critical for moving toward the development of novel therapeutic strategies for this disease. Several contributors (oxidative stress, endoplasmic reticulum stress and others) have been proposed for the onset of metabolic dysfunction and demise of the islet β-cell leading to the pathogenesis of diabetes. Existing experimental evidence revealed sustained activation of PP2A and Rac1 in pancreatic β-cells exposed to metabolic stress (diabetogenic) conditions. Evidence in a variety of cell types implicates modulatory roles for specific signaling proteins (α4, SET, nm23-H1, Pak1) in the functional regulation of PP2A and Rac1. In this Commentary, I overviewed potential cross-talk between PP2A and Rac1 signaling modules in the onset of metabolic dysregulation of the islet β-cell leading to impaired glucose-stimulated insulin secretion (GSIS), loss of β-cell mass and the onset of diabetes. Potential knowledge gaps and future directions in this fertile area of islet biology are also highlighted. It is hoped that this Commentary will provide a basis for future studies toward a better understanding of roles of PP2A-Rac1 signaling module in pancreatic β-cell dysfunction, and identification of therapeutic targets for the treatment of islet β-cell dysfunction in diabetes.
Collapse
Affiliation(s)
- Anjaneyulu Kowluru
- Biomedical Laboratory Research Service, John D. Dingell VA Medical Center and Departments of Pharmaceutical Sciences and Internal Medicine, Wayne State University, Detroit, MI 48201, USA.
| |
Collapse
|
9
|
Huang P, Chen K, Ma T, Cao N, Weng D, Xu C, Xu L. The effects of short-term treatment of microcystin-LR on the insulin pathway in both the HL7702 cell line and livers of mice. ENVIRONMENTAL TOXICOLOGY 2020; 35:727-737. [PMID: 32073747 DOI: 10.1002/tox.22907] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/17/2019] [Revised: 12/07/2019] [Accepted: 01/17/2020] [Indexed: 06/10/2023]
Abstract
Our previous work indicated exposure of Human liver cell 7702 (HL7702) cells to Microcystin-leucine-arginine (MC-LR) for 24 hours can disrupt insulin (INS) signaling by the hyperphosphorylation of specific proteins. For further exploring the time-dependent effect posed by MC-LR on this pathway, in the current study, HL7702 cells together with mice were exposed to the MC-LR with different concentrations under short-term treatment, and then, protein phosphatase 2A (PP2A) activity and expression of proteins related to INS signaling, as well as the characteristics of their action in the liver, were investigated. The results indicated, in HL7702 cells with 0.5, 1, and 6 hours of treatment by MC-LR, PP2A activity showed an obvious decrease in a time and concentration-dependent manner. While the total protein level of Akt, glycogen synthase kinase 3 (GSK-3), and glycogen synthase remained unchanged, GSK-3 and Akt phosphorylation increased significantly. In livers of mice with 1 hour of intraperitoneal injection with MC-LR, a similar change in these proteins was observed. In addition, the levels of total IRS1 and p-IRS1 at serine sites showed decreasing and increasing trends,respectively, and the hematoxylin and eosin staining showed that liver tissues of mice in the maximum-dose group exhibited obvious hepatocyte degeneration and hemorrhage. Our results further proved that short-term treatment with MC-LR can inhibit PP2A activity and disrupt INS signaling proteins' phosphorylation level, thereby interfering with the INS pathway. Our findings provide a helpful understanding of the toxic effects posed by MC-LR on the glucose metabolism of liver via interference with the INS signaling pathway.
Collapse
Affiliation(s)
- Pu Huang
- Department of Biochemistry, School of Medicine, Zhejiang University, Hangzhou, China
| | - Kele Chen
- Department of Biochemistry, School of Medicine, Zhejiang University, Hangzhou, China
| | - Tianfeng Ma
- Department I of Clinical Medicine, First Affiliated Hospital, School of Medicine, Zhejiang University, Hangzhou, China
| | - Naifang Cao
- Department I of Clinical Medicine, First Affiliated Hospital, School of Medicine, Zhejiang University, Hangzhou, China
| | - Dengpo Weng
- Department of Biochemistry, School of Medicine, Zhejiang University, Hangzhou, China
| | - Chun Xu
- Department of Endocrinology, The Third Medical Center of Chinese PLA General Hospital, Beijing, China
| | - Lihong Xu
- Department of Biochemistry, School of Medicine, Zhejiang University, Hangzhou, China
| |
Collapse
|
10
|
Zhang Y, Yuan T, Su Z, Wang X, Wang Y, Ni Y, Zuo Y, Gu H. Reduced methylation of PP2Ac promotes ethanol-induced lipid accumulation through FOXO1 phosphorylation in vitro and in vivo. Toxicol Lett 2020; 331:65-74. [PMID: 32492475 DOI: 10.1016/j.toxlet.2020.05.035] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2020] [Revised: 04/21/2020] [Accepted: 05/28/2020] [Indexed: 12/12/2022]
Abstract
Although disturbance of the methionine cycle and sequent decrease in hepatic methylation capacity are known to be important factors in the development of alcoholic liver injury, the underlying mechanisms are not fully understood. Here, we investigated the importance of the methylation of protein phosphatase 2A (PP2A) in alcoholic liver disease (ALD). We found that the severity of ethanol-induced liver injury and the extent of demethylation of PP2A catalytic C subunit (PP2Ac) were reduced after treatment with betaine, a methyl donor involved in the methionine-homocysteine cycle. These results suggest that PP2Ac methylation is decreased due to a broad decrease in hepatic methylation capacity after exposure to ethanol. Moreover, we found that the reduction in PP2Ac methylation led to increased degradation of the regulatory Bα subunit, thus promoting the phosphorylation and nuclear exclusion of Forkhead box O1 (FOXO1) and reducing FOXO1 transcriptional activity. Ultimately, the reduced activity of FOXO1 led to increased expression of TXNIP, which caused hepatic lipid accumulation. Our findings suggest that the reduction of PP2A methylation, a result of decrease hepatic methylation capacity, played an important role in ethanol-induced lipid accumulation via down-regulation of PP2A/Bα and FOXO1 phosphorylation.
Collapse
Affiliation(s)
- Yali Zhang
- Department of Biochemistry and Molecular Biology, School of Medicine, Nantong University, Nantong, Jiangsu 226001, China.
| | - Tianli Yuan
- Department of Biochemistry and Molecular Biology, School of Medicine, Nantong University, Nantong, Jiangsu 226001, China
| | - Zhangyao Su
- Department of Biochemistry and Molecular Biology, School of Medicine, Nantong University, Nantong, Jiangsu 226001, China
| | - Xi Wang
- Department of Biochemistry and Molecular Biology, School of Medicine, Nantong University, Nantong, Jiangsu 226001, China
| | - Yilun Wang
- Department of Biochemistry and Molecular Biology, School of Medicine, Nantong University, Nantong, Jiangsu 226001, China
| | - Yao Ni
- Department of Biochemistry and Molecular Biology, School of Medicine, Nantong University, Nantong, Jiangsu 226001, China
| | - Yue Zuo
- Department of Biochemistry and Molecular Biology, School of Medicine, Nantong University, Nantong, Jiangsu 226001, China
| | - Haohao Gu
- Department of Biochemistry and Molecular Biology, School of Medicine, Nantong University, Nantong, Jiangsu 226001, China
| |
Collapse
|
11
|
Liang S, Guo J, Choi JW, Shin KT, Wang HY, Jo YJ, Kim NH, Cui XS. Protein phosphatase 2A regulatory subunit B55α functions in mouse oocyte maturation and early embryonic development. Oncotarget 2018; 8:26979-26991. [PMID: 28439046 PMCID: PMC5432312 DOI: 10.18632/oncotarget.15927] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2016] [Accepted: 02/17/2017] [Indexed: 12/20/2022] Open
Abstract
Protein phosphatase 2A regulatory subunit B55α (PP2A-B55α) has been studied in mitosis. However, its functions in mammalian meiosis and early embryonic development remain unknown. Here, we report that PP2A-B55α is critical for mouse oocyte meiosis and preimplantation embryo development. Knockdown of PP2A-B55α in oocytes led to abnormal asymmetric division, disordered spindle dynamics, defects in chromosome congression, an increase in aneuploidy, and induction of the DNA damage response. Moreover, knockdown of PP2A-B55α in fertilized mouse zygotes impaired development to the blastocyst stage. The impairment of embryonic development might have been due to induction of sustained DNA damage in embryos, which caused apoptosis and inhibited cell proliferation and outgrowth potential at the blastocyst stage. Overall, these results provide a novel insight into the role of PP2A-B55α as a novel meiotic and embryonic competence factor at the onset of life.
Collapse
Affiliation(s)
- Shuang Liang
- Department of Animal Science, Chungbuk National University, Cheongju, Chungbuk, 361-763, Republic of Korea
| | - Jing Guo
- Department of Animal Science, Chungbuk National University, Cheongju, Chungbuk, 361-763, Republic of Korea
| | - Jeong-Woo Choi
- Department of Animal Science, Chungbuk National University, Cheongju, Chungbuk, 361-763, Republic of Korea
| | - Kyung-Tae Shin
- Department of Animal Science, Chungbuk National University, Cheongju, Chungbuk, 361-763, Republic of Korea
| | - Hai-Yang Wang
- Department of Animal Science, Chungbuk National University, Cheongju, Chungbuk, 361-763, Republic of Korea
| | - Yu-Jin Jo
- Department of Animal Science, Chungbuk National University, Cheongju, Chungbuk, 361-763, Republic of Korea
| | - Nam-Hyung Kim
- Department of Animal Science, Chungbuk National University, Cheongju, Chungbuk, 361-763, Republic of Korea
| | - Xiang-Shun Cui
- Department of Animal Science, Chungbuk National University, Cheongju, Chungbuk, 361-763, Republic of Korea
| |
Collapse
|
12
|
Affiliation(s)
- X Charlie Dong
- Department of Biochemistry and Molecular Biology, Center for Diabetes and Metabolic Diseases, Indiana University School of Medicine, Indianapolis, IN
| |
Collapse
|
13
|
Beg M, Srivastava A, Shankar K, Varshney S, Rajan S, Gupta A, Kumar D, Gaikwad AN. PPP2R5B, a regulatory subunit of PP2A, contributes to adipocyte insulin resistance. Mol Cell Endocrinol 2016; 437:97-107. [PMID: 27521959 DOI: 10.1016/j.mce.2016.08.016] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/11/2016] [Revised: 07/04/2016] [Accepted: 08/09/2016] [Indexed: 12/29/2022]
Abstract
Insulin resistance is associated with deregulation of insulin signaling owing to the chronic exposure of insulin (hyperinsulinemia) to the tissues. Phosphorylation and dephosphorylation events in insulin signaling pathway play an essential role in signal transduction and glucose uptake. Amongst all, Akt protein is considered to be central to the overall insulin signaling proteins. In glucose responsive tissues like adipose and muscles, activation of Akt is responsible for triggering GLUT4 translocation and glucose transport. Several phosphatases such as PTEN, PP2A have been reported to be involved in dephosphorylation and inactivation of Akt protein. We have identified increased PP2A activity during state of chronic hyperinsulinemia exposure along-with development of adipocyte insulin resistance. This increased phosphatase activity leads activation of cAMP/PKA axis, which in turn increased cAMP levels in insulin resistant (IR) adipocytes. Okadaic acid, an inhibitor of PP2A restored and increased insulin stimulated glucose uptake in insulin resistant (IR) and insulin sensitive (IS) adipocytes respectively. In IS adipocyte, chemical activation of PP2A through MG132 and FTY720 showed decreased insulin sensitivity corroborated with decreased Akt phosphorylation and glucose uptake. We also observed an increased expression of PP2A-B (regulatory) subunit in IR adipocytes. We found PPP2R5B, a regulatory subunit of PP2A is responsible for the dephosphorylation and inactivation of Akt protein. Increased expression of PPP2R5B was also confirmed in white adipose tissue of high fat diet induced IR mice model. Overexpression and suppression strategies confirmed the role of PPP2R5B in regulating insulin signaling. Thus, we conclude that PPP2R5B, a B subunit of PP2A is a negative regulator of Akt phosphorylation contributing partly to the chronic hyperinsulinemia induced insulin resistance in adipocytes.
Collapse
Affiliation(s)
- Muheeb Beg
- Division of Pharmacology, CSIR-Central Drug Research Institute, Lucknow, 226031, India
| | - Ankita Srivastava
- Division of Pharmacology, CSIR-Central Drug Research Institute, Lucknow, 226031, India; Academy of Scientific and Innovative Research, CSIR-CDRI, India
| | - Kripa Shankar
- Division of Pharmacology, CSIR-Central Drug Research Institute, Lucknow, 226031, India
| | - Salil Varshney
- Division of Pharmacology, CSIR-Central Drug Research Institute, Lucknow, 226031, India
| | - Sujith Rajan
- Division of Pharmacology, CSIR-Central Drug Research Institute, Lucknow, 226031, India; Academy of Scientific and Innovative Research, CSIR-CDRI, India
| | - Abhishek Gupta
- Division of Pharmacology, CSIR-Central Drug Research Institute, Lucknow, 226031, India
| | - Durgesh Kumar
- Division of Pharmacology, CSIR-Central Drug Research Institute, Lucknow, 226031, India; Academy of Scientific and Innovative Research, CSIR-CDRI, India
| | - Anil N Gaikwad
- Division of Pharmacology, CSIR-Central Drug Research Institute, Lucknow, 226031, India; Academy of Scientific and Innovative Research, CSIR-CDRI, India.
| |
Collapse
|
14
|
Guillonneau M, Paris F, Dutoit S, Estephan H, Bénéteau E, Huot J, Corre I. Oxidative stress disassembles the p38/NPM/PP2A complex, which leads to modulation of nucleophosmin-mediated signaling to DNA damage response. FASEB J 2016; 30:2899-914. [PMID: 27142525 DOI: 10.1096/fj.201500194r] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2015] [Accepted: 04/26/2016] [Indexed: 11/11/2022]
Abstract
Oxidative stress is a leading cause of endothelial dysfunction. The p38 MAPK pathway plays a determinant role in allowing cells to cope with oxidative stress and is tightly regulated by a balanced interaction between p38 protein and its interacting partners. By using a proteomic approach, we identified nucleophosmin (NPM) as a new partner of p38 in HUVECs. Coimmunoprecipitation and microscopic analyses confirmed the existence of a cytosolic nucleophosmin (NPM)/p38 interaction in basal condition. Oxidative stress, which was generated by exposure to 500 µM H2O2, induces a rapid dephosphorylation of NPM at T199 that depends on phosphatase PP2A, another partner of the NPM/p38 complex. Blocking PP2A activity leads to accumulation of NPM-pT199 and to an increased association of NPM with p38. Concomitantly to its dephosphorylation, oxidative stress promotes translocation of NPM to the nucleus to affect the DNA damage response. Dephosphorylated NPM impairs the signaling of oxidative stress-induced DNA damage via inhibition of the phosphorylation of ataxia-telangiectasia mutated and DNA-dependent protein kinase catalytic subunit. Overall, these results suggest that the p38/NPM/PP2A complex acts as a dynamic sensor, allowing endothelial cells to react rapidly to acute oxidative stress.-Guillonneau, M., Paris, F., Dutoit, S., Estephan, H., Bénéteau, E., Huot, J., Corre, I. Oxidative stress disassembles the p38/NPM/PP2A complex, which leads to modulation of nucleophosmin-mediated signaling to DNA damage response.
Collapse
Affiliation(s)
- Maëva Guillonneau
- Centre National de la Recherche Scientifique (CNRS), Unité Mixte de Recherche 6299, Nantes, France; INSERM, Unité Mixte de Recherche 892, Nantes, France; Université de Nantes, Nantes, France; and Le Centre de Recherche du Centre Hospitalier Universitaire de Québec-Université Laval et le Centre de Recherche sur le Cancer de l'Université Laval, Québec City, Québec, Canada
| | - François Paris
- Centre National de la Recherche Scientifique (CNRS), Unité Mixte de Recherche 6299, Nantes, France; INSERM, Unité Mixte de Recherche 892, Nantes, France; Université de Nantes, Nantes, France; and
| | - Soizic Dutoit
- Centre National de la Recherche Scientifique (CNRS), Unité Mixte de Recherche 6299, Nantes, France; INSERM, Unité Mixte de Recherche 892, Nantes, France; Université de Nantes, Nantes, France; and
| | - Hala Estephan
- Centre National de la Recherche Scientifique (CNRS), Unité Mixte de Recherche 6299, Nantes, France; INSERM, Unité Mixte de Recherche 892, Nantes, France; Université de Nantes, Nantes, France; and
| | - Elise Bénéteau
- Centre National de la Recherche Scientifique (CNRS), Unité Mixte de Recherche 6299, Nantes, France; INSERM, Unité Mixte de Recherche 892, Nantes, France; Université de Nantes, Nantes, France; and
| | - Jacques Huot
- Le Centre de Recherche du Centre Hospitalier Universitaire de Québec-Université Laval et le Centre de Recherche sur le Cancer de l'Université Laval, Québec City, Québec, Canada
| | - Isabelle Corre
- Centre National de la Recherche Scientifique (CNRS), Unité Mixte de Recherche 6299, Nantes, France; INSERM, Unité Mixte de Recherche 892, Nantes, France; Université de Nantes, Nantes, France; and Le Centre de Recherche du Centre Hospitalier Universitaire de Québec-Université Laval et le Centre de Recherche sur le Cancer de l'Université Laval, Québec City, Québec, Canada
| |
Collapse
|
15
|
Goldsworthy M, Bai Y, Li CM, Ge H, Lamas E, Hilton H, Esapa CT, Baker D, Baron W, Juan T, Véniant MM, Lloyd DJ, Cox RD. Haploinsufficiency of the Insulin Receptor in the Presence of a Splice-Site Mutation in Ppp2r2a Results in a Novel Digenic Mouse Model of Type 2 Diabetes. Diabetes 2016; 65:1434-46. [PMID: 26868295 PMCID: PMC5947768 DOI: 10.2337/db15-1276] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/10/2015] [Accepted: 02/07/2016] [Indexed: 12/16/2022]
Abstract
Insulin resistance in mice typically does not manifest as diabetes due to multiple compensatory mechanisms. Here, we present a novel digenic model of type 2 diabetes in mice heterozygous for a null allele of the insulin receptor and an N-ethyl-N-nitrosourea-induced alternative splice mutation in the regulatory protein phosphatase 2A (PP2A) subunit PPP2R2A. Inheritance of either allele independently results in insulin resistance but not overt diabetes. Doubly heterozygous mice exhibit progressive hyperglycemia, hyperinsulinemia, and impaired glucose tolerance from 12 weeks of age without significant increase in body weight. Alternative splicing of Ppp2r2a decreased PPP2R2A protein levels. This reduction in PPP2R2A containing PP2A phosphatase holoenzyme was associated with decreased serine/threonine protein kinase AKT protein levels. Ultimately, reduced insulin-stimulated phosphorylated AKT levels were observed, a result that was confirmed in Hepa1-6, C2C12, and differentiated 3T3-L1 cells knocked down using Ppp2r2a small interfering RNAs. Altered AKT signaling and expression of gluconeogenic genes in the fed state contributed to an insulin resistance and hyperglycemia phenotype. This model demonstrates how genetic changes with individually small phenotypic effects interact to cause diabetes and how differences in expression of hypomorphic alleles of PPP2R2A and potentially other regulatory proteins have deleterious effects and may therefore be relevant in determining diabetes risk.
Collapse
Affiliation(s)
| | - Ying Bai
- Diabetes Group, Medical Research Council Harwell, Oxfordshire, U.K
| | - Chi-Ming Li
- Genome Analysis Unit, Amgen Inc., Thousand Oaks, CA
| | - Huanying Ge
- Genome Analysis Unit, Amgen Inc., Thousand Oaks, CA
| | - Edwin Lamas
- Genome Analysis Unit, Amgen Inc., Thousand Oaks, CA
| | - Helen Hilton
- Protein Core Facility, Medical Research Council Harwell, Oxfordshire, U.K
| | | | - Dan Baker
- Genome Analysis Unit, Amgen Inc., Thousand Oaks, CA
| | - Will Baron
- Genome Analysis Unit, Amgen Inc., Thousand Oaks, CA
| | - Todd Juan
- Genome Analysis Unit, Amgen Inc., Thousand Oaks, CA
| | | | - David J Lloyd
- Department of Metabolic Disorders, Amgen Inc., Thousand Oaks, CA
| | - Roger D Cox
- Diabetes Group, Medical Research Council Harwell, Oxfordshire, U.K.
| |
Collapse
|
16
|
Zhang X, Damacharla D, Ma D, Qi Y, Tagett R, Draghici S, Kowluru A, Yi Z. Quantitative proteomics reveals novel protein interaction partners of PP2A catalytic subunit in pancreatic β-cells. Mol Cell Endocrinol 2016; 424:1-11. [PMID: 26780722 PMCID: PMC4779412 DOI: 10.1016/j.mce.2016.01.008] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/25/2015] [Revised: 12/15/2015] [Accepted: 01/07/2016] [Indexed: 12/19/2022]
Abstract
Protein phosphatase 2A (PP2A) is one of the major serine/threonine phosphatases. We hypothesize that PP2A regulates signaling cascades in pancreatic β-cells in the context of glucose-stimulated insulin secretion (GSIS). Using co-immunoprecipitation (co-IP) and tandem mass spectrometry, we globally identified the protein interaction partners of the PP2A catalytic subunit (PP2Ac) in insulin-secreting pancreatic β-cells. Among the 514 identified PP2Ac interaction partners, 476 were novel. This represents the first global view of PP2Ac protein-protein interactions caused by hyperglycemic conditions. Additionally, numerous PP2Ac partners were found involved in a variety of signaling pathways in the β-cell function, such as insulin secretion. Our data suggest that PP2A interacts with various signaling proteins necessary for physiological insulin secretion as well as signaling proteins known to regulate cell dysfunction and apoptosis in the pancreatic β-cells.
Collapse
Affiliation(s)
- Xiangmin Zhang
- Department of Pharmaceutical Sciences, Eugene Applebaum College of Pharmacy and Health Sciences, Wayne State University, Detroit, MI, 48201, USA
| | - Divyasri Damacharla
- Department of Pharmaceutical Sciences, Eugene Applebaum College of Pharmacy and Health Sciences, Wayne State University, Detroit, MI, 48201, USA
| | - Danjun Ma
- Department of Pharmaceutical Sciences, Eugene Applebaum College of Pharmacy and Health Sciences, Wayne State University, Detroit, MI, 48201, USA
| | - Yue Qi
- Department of Pharmaceutical Sciences, Eugene Applebaum College of Pharmacy and Health Sciences, Wayne State University, Detroit, MI, 48201, USA
| | - Rebecca Tagett
- Department of Computer Science, College of Engineering, Wayne State University, Detroit, MI, USA
| | - Sorin Draghici
- Department of Computer Science, College of Engineering, Wayne State University, Detroit, MI, USA
| | - Anjaneyulu Kowluru
- Department of Pharmaceutical Sciences, Eugene Applebaum College of Pharmacy and Health Sciences, Wayne State University, Detroit, MI, 48201, USA; β-Cell Biochemistry Laboratory, John D. Dingell VA Medical Center, Detroit, MI, 48201, USA
| | - Zhengping Yi
- Department of Pharmaceutical Sciences, Eugene Applebaum College of Pharmacy and Health Sciences, Wayne State University, Detroit, MI, 48201, USA.
| |
Collapse
|
17
|
Garlapow ME, Huang W, Yarboro MT, Peterson KR, Mackay TFC. Quantitative Genetics of Food Intake in Drosophila melanogaster. PLoS One 2015; 10:e0138129. [PMID: 26375667 PMCID: PMC4574202 DOI: 10.1371/journal.pone.0138129] [Citation(s) in RCA: 62] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2015] [Accepted: 08/25/2015] [Indexed: 12/16/2022] Open
Abstract
Food intake is an essential animal activity, regulated by neural circuits that motivate food localization, evaluate nutritional content and acceptance or rejection responses through the gustatory system, and regulate neuroendocrine feedback loops that maintain energy homeostasis. Excess food consumption in people is associated with obesity and metabolic and cardiovascular disorders. However, little is known about the genetic basis of natural variation in food consumption. To gain insights in evolutionarily conserved genetic principles that regulate food intake, we took advantage of a model system, Drosophila melanogaster, in which food intake, environmental conditions and genetic background can be controlled precisely. We quantified variation in food intake among 182 inbred, sequenced lines of the Drosophila melanogaster Genetic Reference Panel (DGRP). We found significant genetic variation in the mean and within-line environmental variance of food consumption and observed sexual dimorphism and genetic variation in sexual dimorphism for both food intake traits (mean and variance). We performed genome wide association (GWA) analyses for mean food intake and environmental variance of food intake (using the coefficient of environmental variation, CVE, as the metric for environmental variance) and identified molecular polymorphisms associated with both traits. Validation experiments using RNAi-knockdown confirmed 24 of 31 (77%) candidate genes affecting food intake and/or variance of food intake, and a test cross between selected DGRP lines confirmed a SNP affecting mean food intake identified in the GWA analysis. The majority of the validated candidate genes were novel with respect to feeding behavior, and many had mammalian orthologs implicated in metabolic diseases.
Collapse
Affiliation(s)
- Megan E. Garlapow
- Program in Genetics, North Carolina State University, Raleigh, NC, 27695–7614, United States of America
- Department of Biological Sciences, North Carolina State University, Raleigh, NC, 27695, United States of America
- W. M. Keck Center for Behavioral Biology, North Carolina State University, Raleigh, NC, 27695, United States of America
| | - Wen Huang
- Program in Genetics, North Carolina State University, Raleigh, NC, 27695–7614, United States of America
- Department of Biological Sciences, North Carolina State University, Raleigh, NC, 27695, United States of America
- W. M. Keck Center for Behavioral Biology, North Carolina State University, Raleigh, NC, 27695, United States of America
| | - Michael T. Yarboro
- Department of Biological Sciences, North Carolina State University, Raleigh, NC, 27695, United States of America
| | - Kara R. Peterson
- Department of Biological Sciences, North Carolina State University, Raleigh, NC, 27695, United States of America
| | - Trudy F. C. Mackay
- Program in Genetics, North Carolina State University, Raleigh, NC, 27695–7614, United States of America
- Department of Biological Sciences, North Carolina State University, Raleigh, NC, 27695, United States of America
- W. M. Keck Center for Behavioral Biology, North Carolina State University, Raleigh, NC, 27695, United States of America
- * E-mail:
| |
Collapse
|
18
|
Abstract
The prevalence of diabetes is increasing rapidly worldwide. A cardinal feature of most forms of diabetes is the lack of insulin-producing capability, due to the loss of insulin-producing β-cells, impaired glucose-sensitive insulin secretion from the β-cell, or a combination thereof, the reasons for which largely remain elusive. Reversible phosphorylation is an important and versatile mechanism for regulating the biological activity of many intracellular proteins, which, in turn, controls a variety of cellular functions. For instance, significant changes in protein kinase activities and in protein phosphorylation patterns occur subsequent to the stimulation of insulin release by glucose. Therefore, the molecular mechanisms regulating the phosphorylation of proteins involved in the insulin secretory process by the β-cell have been extensively investigated. However, far less is known about the role and regulation of protein dephosphorylation by various protein phosphatases. Herein, we review extant data implicating serine/threonine and tyrosine phosphatases in various aspects of healthy and diabetic islet biology, ranging from control of hormonal stimulus-secretion coupling to mitogenesis and apoptosis.
Collapse
Affiliation(s)
- Henrik Ortsäter
- Biovation Park TelgeSödertälje, SwedenResearch UnitSödertälje Hospital, SE-152 86 Södertälje, SwedenDegenerative Disease ProgramSanford-Burnham Medical Research Institute, Del E. Webb Neuroscience, Aging and Stem Cell Research Center, 10901 North Torrey Pines Road, La Jolla, California 92037, USADepartment of Biochemistry and Molecular BiologyCollege of Medicine, University of South Alabama, Mobile, Alabama 36688, USADepartment of Internal MedicineSödertälje Hospital, Södertälje, SwedenBiovation Park TelgeSödertälje, SwedenResearch UnitSödertälje Hospital, SE-152 86 Södertälje, SwedenDegenerative Disease ProgramSanford-Burnham Medical Research Institute, Del E. Webb Neuroscience, Aging and Stem Cell Research Center, 10901 North Torrey Pines Road, La Jolla, California 92037, USADepartment of Biochemistry and Molecular BiologyCollege of Medicine, University of South Alabama, Mobile, Alabama 36688, USADepartment of Internal MedicineSödertälje Hospital, Södertälje, Sweden
| | - Nina Grankvist
- Biovation Park TelgeSödertälje, SwedenResearch UnitSödertälje Hospital, SE-152 86 Södertälje, SwedenDegenerative Disease ProgramSanford-Burnham Medical Research Institute, Del E. Webb Neuroscience, Aging and Stem Cell Research Center, 10901 North Torrey Pines Road, La Jolla, California 92037, USADepartment of Biochemistry and Molecular BiologyCollege of Medicine, University of South Alabama, Mobile, Alabama 36688, USADepartment of Internal MedicineSödertälje Hospital, Södertälje, Sweden
| | - Richard E Honkanen
- Biovation Park TelgeSödertälje, SwedenResearch UnitSödertälje Hospital, SE-152 86 Södertälje, SwedenDegenerative Disease ProgramSanford-Burnham Medical Research Institute, Del E. Webb Neuroscience, Aging and Stem Cell Research Center, 10901 North Torrey Pines Road, La Jolla, California 92037, USADepartment of Biochemistry and Molecular BiologyCollege of Medicine, University of South Alabama, Mobile, Alabama 36688, USADepartment of Internal MedicineSödertälje Hospital, Södertälje, Sweden
| | - Åke Sjöholm
- Biovation Park TelgeSödertälje, SwedenResearch UnitSödertälje Hospital, SE-152 86 Södertälje, SwedenDegenerative Disease ProgramSanford-Burnham Medical Research Institute, Del E. Webb Neuroscience, Aging and Stem Cell Research Center, 10901 North Torrey Pines Road, La Jolla, California 92037, USADepartment of Biochemistry and Molecular BiologyCollege of Medicine, University of South Alabama, Mobile, Alabama 36688, USADepartment of Internal MedicineSödertälje Hospital, Södertälje, SwedenBiovation Park TelgeSödertälje, SwedenResearch UnitSödertälje Hospital, SE-152 86 Södertälje, SwedenDegenerative Disease ProgramSanford-Burnham Medical Research Institute, Del E. Webb Neuroscience, Aging and Stem Cell Research Center, 10901 North Torrey Pines Road, La Jolla, California 92037, USADepartment of Biochemistry and Molecular BiologyCollege of Medicine, University of South Alabama, Mobile, Alabama 36688, USADepartment of Internal MedicineSödertälje Hospital, Södertälje, SwedenBiovation Park TelgeSödertälje, SwedenResearch UnitSödertälje Hospital, SE-152 86 Södertälje, SwedenDegenerative Disease ProgramSanford-Burnham Medical Research Institute, Del E. Webb Neuroscience, Aging and Stem Cell Research Center, 10901 North Torrey Pines Road, La Jolla, California 92037, USADepartment of Biochemistry and Molecular BiologyCollege of Medicine, University of South Alabama, Mobile, Alabama 36688, USADepartment of Internal MedicineSödertälje Hospital, Södertälje, Sweden
| |
Collapse
|
19
|
Xu E, Schwab M, Marette A. Role of protein tyrosine phosphatases in the modulation of insulin signaling and their implication in the pathogenesis of obesity-linked insulin resistance. Rev Endocr Metab Disord 2014; 15:79-97. [PMID: 24264858 DOI: 10.1007/s11154-013-9282-4] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Insulin resistance is a major disorder that links obesity to type 2 diabetes mellitus (T2D). It involves defects in the insulin actions owing to a reduced ability of insulin to trigger key signaling pathways in major metabolic tissues. The pathogenesis of insulin resistance involves several inhibitory molecules that interfere with the tyrosine phosphorylation of the insulin receptor and its downstream effectors. Among those, growing interest has been developed toward the protein tyrosine phosphatases (PTPs), a large family of enzymes that can inactivate crucial signaling effectors in the insulin signaling cascade by dephosphorylating their tyrosine residues. Herein we briefly review the role of several PTPs that have been shown to be implicated in the regulation of insulin action, and then focus on the Src homology 2 (SH2) domain-containing SHP1 and SHP2 enzymes, since recent reports have indicated major roles for these PTPs in the control of insulin action and glucose metabolism. Finally, the therapeutic potential of targeting PTPs for combating insulin resistance and alleviating T2D will be discussed.
Collapse
Affiliation(s)
- Elaine Xu
- Department of Medicine, Cardiology Axis of the Institut Universitaire de Cardiologie et de Pneumologie de Québec (Hôpital Laval), Ste-Foy, Québec, Canada, G1V 4G2
| | | | | |
Collapse
|
20
|
Arora DK, Machhadieh B, Matti A, Wadzinski BE, Ramanadham S, Kowluru A. High glucose exposure promotes activation of protein phosphatase 2A in rodent islets and INS-1 832/13 β-cells by increasing the posttranslational carboxylmethylation of its catalytic subunit. Endocrinology 2014; 155:380-91. [PMID: 24265448 PMCID: PMC3891936 DOI: 10.1210/en.2013-1773] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Existing evidence implicates regulatory roles for protein phosphatase 2A (PP2A) in a variety of cellular functions, including cytoskeletal remodeling, hormone secretion, and apoptosis. We report here activation of PP2A in normal rat islets and insulin-secreting INS-1 832/13 cells under the duress of hyperglycemic (HG) conditions. Small interfering RNA-mediated knockdown of the catalytic subunit of PP2A (PP2Ac) markedly attenuated glucose-induced activation of PP2A. HG, but not nonmetabolizable 3-O-methyl glucose or mannitol (osmotic control), significantly stimulated the methylation of PP2Ac at its C-terminal Leu-309, suggesting a novel role for this posttranslational modification in glucose-induced activation of PP2A. Moreover, knockdown of the cytosolic leucine carboxymethyl transferase 1 (LCMT1), which carboxymethylates PP2Ac, significantly attenuated PP2A activation under HG conditions. In addition, HG conditions, but not 3-O-methyl glucose or mannitol, markedly increased the expression of LCMT1. Furthermore, HG conditions significantly increased the expression of B55α, a regulatory subunit of PP2A, which has been implicated in islet dysfunction under conditions of oxidative stress and diabetes. Thapsigargin, a known inducer of endoplasmic reticulum stress, failed to exert any discernible effects on the carboxymethylation of PP2Ac, expression of LCMT1 and B55α, or PP2A activity, suggesting no clear role for endoplasmic reticulum stress in HG-induced activation of PP2A. Based on these findings, we conclude that exposure of the islet β-cell to HG leads to accelerated PP2A signaling pathway, leading to loss in glucose-induced insulin secretion.
Collapse
Affiliation(s)
- Daleep K Arora
- Beta-Cell Biochemistry Laboratory (D.K.A., A.K.), John D. Dingell Veterans Affairs Medical Center, and Department of Pharmaceutical Sciences (D.K.A., A.K.), Eugene Applebaum College of Pharmacy and Health Sciences, Wayne State University, Detroit, Michigan 48201; Section of Endocrinology, Diabetes and Metabolism (B.M.), University of Illinois at Chicago, Chicago, Illinois 60612; Department of Engineering and Science (A.M.), University of Detroit Mercy, Detroit, Michigan 48221; Department of Pharmacology (B.E.W.), Vanderbilt University Medical Center, Nashville, Tennessee 37232; and Department of Cell, Developmental, and Integrative Biology (S.R.), University of Alabama at Birmingham, Birmingham, Alabama 35294
| | | | | | | | | | | |
Collapse
|
21
|
Upregulation of miR-136 in human non-small cell lung cancer cells promotes Erk1/2 activation by targeting PPP2R2A. Tumour Biol 2013; 35:631-40. [DOI: 10.1007/s13277-013-1087-2] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2013] [Accepted: 08/05/2013] [Indexed: 12/17/2022] Open
|
22
|
Martin M, Geudens I, Bruyr J, Potente M, Bleuart A, Lebrun M, Simonis N, Deroanne C, Twizere JC, Soubeyran P, Peixoto P, Mottet D, Janssens V, Hofmann WK, Claes F, Carmeliet P, Kettmann R, Gerhardt H, Dequiedt F. PP2A regulatory subunit Bα controls endothelial contractility and vessel lumen integrity via regulation of HDAC7. EMBO J 2013; 32:2491-503. [PMID: 23955003 DOI: 10.1038/emboj.2013.187] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2013] [Accepted: 07/19/2013] [Indexed: 01/04/2023] Open
Abstract
To supply tissues with nutrients and oxygen, the cardiovascular system forms a seamless, hierarchically branched, network of lumenized tubes. Here, we show that maintenance of patent vessel lumens requires the Bα regulatory subunit of protein phosphatase 2A (PP2A). Deficiency of Bα in zebrafish precludes vascular lumen stabilization resulting in perfusion defects. Similarly, inactivation of PP2A-Bα in cultured ECs induces tubulogenesis failure due to alteration of cytoskeleton dynamics, actomyosin contractility and maturation of cell-extracellular matrix (ECM) contacts. Mechanistically, we show that PP2A-Bα controls the activity of HDAC7, an essential transcriptional regulator of vascular stability. In the absence of PP2A-Bα, transcriptional repression by HDAC7 is abrogated leading to enhanced expression of the cytoskeleton adaptor protein ArgBP2. ArgBP2 hyperactivates RhoA causing inadequate rearrangements of the EC actomyosin cytoskeleton. This study unravels the first specific role for a PP2A holoenzyme in development: the PP2A-Bα/HDAC7/ArgBP2 axis maintains vascular lumens by balancing endothelial cytoskeletal dynamics and cell-matrix adhesion.
Collapse
Affiliation(s)
- Maud Martin
- Laboratory of Protein Signaling and Interactions, Interdisciplinary Cluster for Applied Genoproteomics (GIGA-R), University of Liège, Sart-Tilman, Belgium
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
23
|
Guo S, Dai C, Guo M, Taylor B, Harmon JS, Sander M, Robertson RP, Powers AC, Stein R. Inactivation of specific β cell transcription factors in type 2 diabetes. J Clin Invest 2013; 123:3305-16. [PMID: 23863625 DOI: 10.1172/jci65390] [Citation(s) in RCA: 380] [Impact Index Per Article: 34.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2013] [Accepted: 05/01/2013] [Indexed: 01/03/2023] Open
Abstract
Type 2 diabetes (T2DM) commonly arises from islet β cell failure and insulin resistance. Here, we examined the sensitivity of key islet-enriched transcription factors to oxidative stress, a condition associated with β cell dysfunction in both type 1 diabetes (T1DM) and T2DM. Hydrogen peroxide treatment of β cell lines induced cytoplasmic translocation of MAFA and NKX6.1. In parallel, the ability of nuclear PDX1 to bind endogenous target gene promoters was also dramatically reduced, whereas the activity of other key β cell transcriptional regulators was unaffected. MAFA levels were reduced, followed by a reduction in NKX6.1 upon development of hyperglycemia in db/db mice, a T2DM model. Transgenic expression of the glutathione peroxidase-1 antioxidant enzyme (GPX1) in db/db islet β cells restored nuclear MAFA, nuclear NKX6.1, and β cell function in vivo. Notably, the selective decrease in MAFA, NKX6.1, and PDX1 expression was found in human T2DM islets. MAFB, a MAFA-related transcription factor expressed in human β cells, was also severely compromised. We propose that MAFA, MAFB, NKX6.1, and PDX1 activity provides a gauge of islet β cell function, with loss of MAFA (and/or MAFB) representing an early indicator of β cell inactivity and the subsequent deficit of more impactful NKX6.1 (and/or PDX1) resulting in overt dysfunction associated with T2DM.
Collapse
|
24
|
Gupta D, Leahy AA, Monga N, Peshavaria M, Jetton TL, Leahy JL. Peroxisome proliferator-activated receptor γ (PPARγ) and its target genes are downstream effectors of FoxO1 protein in islet β-cells: mechanism of β-cell compensation and failure. J Biol Chem 2013; 288:25440-25449. [PMID: 23788637 DOI: 10.1074/jbc.m113.486852] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
The molecular mechanisms and signaling pathways that drive islet β-cell compensation and failure are not fully resolved. We have used in vitro and in vivo systems to show that FoxO1, an integrator of metabolic stimuli, inhibits PPARγ expression in β-cells, thus transcription of its target genes (Pdx1, glucose-dependent insulinotropic polypeptide (GIP) receptor, and pyruvate carboxylase) that are important regulators of β-cell function, survival, and compensation. FoxO1 inhibition of target gene transcription is normally relieved when upstream activation induces its translocation from the nucleus to the cytoplasm. Attesting to the central importance of this pathway, islet expression of PPARγ and its target genes was enhanced in nondiabetic insulin-resistant rats and markedly reduced with diabetes induction. Insight into the impaired PPARγ signaling with hyperglycemia was obtained with confocal microscopy of pancreas sections that showed an intense nuclear FoxO1 immunostaining pattern in the β-cells of diabetic rats in contrast to the nuclear and cytoplasmic FoxO1 in nondiabetic rats. These findings suggest a FoxO1/PPARγ-mediated network acting as a core component of β-cell adaptation to metabolic stress, with failure of this response from impaired FoxO1 activation causing or exacerbating diabetes.
Collapse
Affiliation(s)
- Dhananjay Gupta
- From the Division of Endocrinology, Diabetes, and Metabolism and the Department of Medicine, University of Vermont, Burlington, Vermont 05405
| | - Averi A Leahy
- From the Division of Endocrinology, Diabetes, and Metabolism and the Department of Medicine, University of Vermont, Burlington, Vermont 05405
| | - Navjot Monga
- From the Division of Endocrinology, Diabetes, and Metabolism and the Department of Medicine, University of Vermont, Burlington, Vermont 05405
| | - Mina Peshavaria
- From the Division of Endocrinology, Diabetes, and Metabolism and the Department of Medicine, University of Vermont, Burlington, Vermont 05405
| | - Thomas L Jetton
- From the Division of Endocrinology, Diabetes, and Metabolism and the Department of Medicine, University of Vermont, Burlington, Vermont 05405
| | - Jack L Leahy
- From the Division of Endocrinology, Diabetes, and Metabolism and the Department of Medicine, University of Vermont, Burlington, Vermont 05405.
| |
Collapse
|
25
|
The B55α regulatory subunit of protein phosphatase 2A mediates fibroblast growth factor-induced p107 dephosphorylation and growth arrest in chondrocytes. Mol Cell Biol 2013; 33:2865-78. [PMID: 23716589 DOI: 10.1128/mcb.01730-12] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Fibroblast growth factor (FGF)-induced growth arrest of chondrocytes is a unique cell type-specific response which contrasts with the proliferative response of most cell types and underlies several genetic skeletal disorders caused by activating FGF receptor (FGFR) mutations. We have shown that one of the earliest key events in FGF-induced growth arrest is dephosphorylation of the retinoblastoma protein (Rb) family member p107 by protein phosphatase 2A (PP2A), a ubiquitously expressed multisubunit phosphatase. In this report, we show that the PP2A-B55α holoenzyme (PP2A containing the B55α subunit) is responsible for this phenomenon. Only the B55α (55-kDa regulatory subunit, alpha isoform) regulatory subunit of PP2A was able to bind p107, and this interaction was induced by FGF in chondrocytes but not in other cell types. Small interfering RNA (siRNA)-mediated knockdown of B55α prevented p107 dephosphorylation and FGF-induced growth arrest of RCS (rat chondrosarcoma) chondrocytes. Importantly, the B55α subunit bound with higher affinity to dephosphorylated p107. Since the p107 region interacting with B55α is also the site of cyclin-dependent kinase (CDK) binding, B55α association may also prevent p107 phosphorylation by CDKs. FGF treatment induces dephosphorylation of the B55α subunit itself on several serine residues that drastically increases the affinity of B55α for the PP2A A/C dimer and p107. Together these observations suggest a novel mechanism of p107 dephosphorylation mediated by activation of PP2A through B55α dephosphorylation. This mechanism might be a general signal transduction pathway used by PP2A to initiate cell cycle arrest when required by external signals.
Collapse
|
26
|
Jiao P, Feng B, Xu H. Mapping MKP-3/FOXO1 interaction and evaluating the effect on gluconeogenesis. PLoS One 2012; 7:e41168. [PMID: 22848439 PMCID: PMC3405053 DOI: 10.1371/journal.pone.0041168] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2012] [Accepted: 06/18/2012] [Indexed: 11/18/2022] Open
Abstract
Background MAP kinase phosphatase 3 (MKP-3) is known to attenuate the ERK signaling pathway. It has been recently demonstrated that MKP-3 is also a player in promoting hepatic glucose output in obese state by interacting and activating FOXO1. Reduction of hepatic MKP-3 expression is sufficient to reduce blood glucose levels in both diet-induced and genetically obese mice. Methodology/Principal Findings In current study, the mechanism of MKP-3/FOXO1 interaction and the effects on transcription of gluconeogenic gene and glucose output was investigated in Fao hepatoma cells by using mutated MKP-3 and FOXO1 adenoviral constructs. The results indicate that MKP-3 phosphatase activity is not required for MKP-3/FOXO1 interaction but is essential for FOXO1 nuclear translocation and MKP-3 promoted gluconeogenesis. Compared to GFP control (1±0.38), MKP-3 increased G6Pase gene expression by 242% (3.42±0.62) while inactive MKP-3 does not change G6Pase expression (0.98±0.17). The residues 200–260 of MKP-3 and the residues 360–456 of FOXO1 are essential for mediating MKP-3/FOXO1 interaction. Interestingly, ERK phosphorylation deficient but not Akt phosphorylation deficient FOXO1 mutant lost interaction with MKP-3. Furthermore, in vivo experiments showed that Akt phosphorylation resistant FOXO1 3A mutant is sufficient to rescue the hypoglycemia caused by MKP-3 knock down in the liver of lean mice (from 141±6.78 to 209±14.64 mg/dL). Conclusions/Significance 1) Critical residues mediating MKP-3/FOXO1 interaction have been identified; 2) ERK phosphorylation deficient FOXO1 mutant is as potent as Akt phosphorylation deficient FOXO1 mutant in activating transcription of gluconeogenic genes; 3) Constitutively active FOXO1 can rescue the hypoglycemic effect caused by reduced hepatic MKP-3 expression in vivo.
Collapse
Affiliation(s)
- Ping Jiao
- Hallett Center for Diabetes and Endocrinology, Rhode Island Hospital, Alpert Medical School of Brown University, Providence, Rhode Island, United States of America
- School of Pharmaceutical Sciences, Jilin University, Changchun, Jilin Province, China
| | - Bin Feng
- Hallett Center for Diabetes and Endocrinology, Rhode Island Hospital, Alpert Medical School of Brown University, Providence, Rhode Island, United States of America
| | - Haiyan Xu
- Hallett Center for Diabetes and Endocrinology, Rhode Island Hospital, Alpert Medical School of Brown University, Providence, Rhode Island, United States of America
- * E-mail:
| |
Collapse
|
27
|
Hyperactivation of protein phosphatase 2A in models of glucolipotoxicity and diabetes: potential mechanisms and functional consequences. Biochem Pharmacol 2012; 84:591-7. [PMID: 22583922 DOI: 10.1016/j.bcp.2012.05.003] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2012] [Revised: 05/03/2012] [Accepted: 05/03/2012] [Indexed: 01/22/2023]
Abstract
The protein phosphatase 2A [PP2A] family of enzymes has been implicated in the regulation of a variety of cellular functions including hormone secretion, growth, survival and apoptosis. PP2A accounts for ~1% of total cellular protein and ∼ 80% of total serine/threonine phosphatases, thus representing a major class of protein phosphatases in mammalian cells. Despite significant advances in our current understanding of regulation of cellular function by PP2A under physiological conditions, little is understood with regard to its regulation under various pathological conditions, such as diabetes. Emerging evidence suggests hyperactivation of PP2A in liver, muscle, retina and the pancreatic islet under the duress of glucolipotoxicity and diabetes. Interestingly, pharmacological inhibition of PP2A or siRNA-mediated depletion of the catalytic subunit of PP2A [PP2Ac] levels largely restored PP2A activity to near normal levels under these conditions. Herein, we provide an overview of PP2A subunit expression and activity in in vitro and in vivo models of glucolipotoxicity and diabetes, and revisit the existing data, which are suggestive of alterations in post-translational methylation, phosphorylation and nitration of PP2Ac under these conditions. Potential significance of hyperactive PP2A in the context of cell function, survival and apoptosis is also highlighted. It is hoped that this commentary will provide a basis for future studies to explore the potential for PP2Ac as a therapeutic target for the treatment of diabetes and other metabolic disorders.
Collapse
|