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Toita R, Asai D, Otani K, Kawano T, Murata M, Kang J. Suppression of Lysophosphatidylcholine‐Induced Human Aortic Smooth Muscle Cell Calcification by Protein Kinase A Inhibition. Lipids 2019; 54:465-470. [DOI: 10.1002/lipd.12178] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2019] [Revised: 05/31/2019] [Accepted: 06/03/2019] [Indexed: 11/07/2022]
Affiliation(s)
- Riki Toita
- Biomedical Research InstituteNational Institute of Advanced Industrial Science and Technology (AIST) 1‐8‐31 Midorigaoka, Ikeda, Osaka, 563‐8577 Japan
- AIST‐Osaka University Advanced Photonics and Biosensing Open Innovation Laboratory 2‐1 Yamadaoka, Suita, Osaka, 565‐0871 Japan
| | - Daisuke Asai
- Department of MicrobiologySt. Marianna University School of Medicine 2‐16‐1 Sugao, Miyamae, Kawasaki, 216‐8511 Japan
| | - Kentaro Otani
- Department of Regenerative Medicine and Tissue EngineeringNational Cerebral and Cardiovascular Center Research Institute 5‐7‐1 Fujishiro‐dai, Suita, Osaka, 565‐8565 Japan
| | - Takahito Kawano
- Center for Advanced Medical InnovationKyushu University 3‐1‐1 Maidashi, Higashi‐ku, Fukuoka, 812‐8582 Japan
| | - Masaharu Murata
- Center for Advanced Medical InnovationKyushu University 3‐1‐1 Maidashi, Higashi‐ku, Fukuoka, 812‐8582 Japan
| | - Jeong‐Hun Kang
- Division of Biopharmaceutics and PharmacokineticsNational Cerebral and Cardiovascular Center Research Institute 5‐7‐1 Fujishiro‐dai, Suita, Osaka, 565‐8565, Japan
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Mice with Genetic Deletion of Group VIA Phospholipase A2β Exhibit Impaired Macrophage Function and Increased Parasite Load in Trypanosoma cruzi-Induced Myocarditis. Infect Immun 2016; 84:1137-1142. [PMID: 26857573 DOI: 10.1128/iai.01564-15] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2015] [Accepted: 01/27/2016] [Indexed: 11/20/2022] Open
Abstract
Trypanosoma cruzi infection, which is the etiological agent of Chagas disease, is associated with intense inflammation during the acute and chronic phases. The pathological progression of Chagas disease is influenced by the infiltration and transmigration of inflammatory cells across the endothelium to infected tissues, which are carefully regulated processes involving several molecular mediators, including adhesion molecules and platelet-activating factor (PAF). We have shown that PAF production is dependent upon calcium-independent group VIA phospholipase A2β (iPLA2β) following infection of human coronary artery endothelial cells (HCAECs) with T. cruzi, suggesting that the absence of iPLA2β may decrease the recruitment of inflammatory cells to the heart to manage parasite accumulation. Cardiac endothelial cells isolated from iPLA2β-knockout (iPLA2β-KO) mice infected withT. cruzi demonstrated decreased PAF production compared to that by cells isolated from wild-type (WT) mice but demonstrated increases in adhesion molecule expression similar to those seen in WT mice. Myocardial inflammation in iPLA2β-KO mice infected with T. cruzi was similar in severity to that in WT mice, but the iPLA2β-KO mouse myocardium contained more parasite pseudocysts. Upon activation, macrophages from iPLA2β-KO mice produced significantly less nitric oxide (NO) and caused lessT. cruzi inhibition than macrophages from wild-type mice. Thus, the absence of iPLA2β activity does not influence myocardial inflammation, but iPLA2β is essential forT. cruzi clearance.
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Nduhirabandi F, Lamont K, Albertyn Z, Opie LH, Lecour S. Role of toll-like receptor 4 in melatonin-induced cardioprotection. J Pineal Res 2016; 60:39-47. [PMID: 26465095 DOI: 10.1111/jpi.12286] [Citation(s) in RCA: 51] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/11/2015] [Accepted: 10/08/2015] [Indexed: 12/19/2022]
Abstract
Melatonin protects the heart against myocardial ischemia/reperfusion injury via the activation of the survivor activating factor enhancement (SAFE) pathway which involves tumor necrosis factor alpha (TNFα) and the signal transducer and activator of transcription 3 (STAT3). Toll-like receptor 4 (TLR4) plays a crucial role in myocardial ischemia/reperfusion injury and activates TNFα. In this study, we investigated whether melatonin may target TLR4 to activate the SAFE pathway. Isolated hearts from rats or mice were subjected to ischemia/reperfusion injury. Melatonin (75 ng/L) and/or TAK242 (a specific inhibitor of TLR4 signaling, 500 nm) were administered to the rat hearts before the induction of ischemia. Pre-ischemic myocardial STAT3 was evaluated by Western blotting. Lipopolysaccharide (LPS, a stimulator of TLR4) was administered to wild type, TNFα receptor 2 knockout or cardiomyocyte-specific STAT3-deficient mice (2.8 mg/kg, i.p) 45 min before the heart isolation. Myocardial infarct size was measured as an endpoint. Compared to the control, administration of melatonin reduced myocardial infarct size (34.7 ± 2.8% versus 62.6 ± 2.7%, P < 0.01). This protective effect was abolished in the presence of TAK242 (49.2 ± 6.5%). Melatonin administered alone increased the pre-ischemic activation of mitochondrial STAT3, and this effect was attenuated with TAK242. Furthermore, stimulation of TLR4 with LPS pretreatment to mice reduced myocardial infarct size of the hearts isolated from wild-type animals but failed to protect the hearts isolated from TNFα receptor 2-knockout mice or cardiomyocyte-specific STAT3-deficient mice (P < 0.001). Taken together, these data suggest that cardioprotection induced by melatonin is mediated by TLR4 to activate the SAFE pathway.
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Affiliation(s)
- Frederic Nduhirabandi
- Cardioprotection Group, Hatter Institute for Cardiovascular Research in Africa and South African Medical Research Council Inter-University Cape Heart Group, Department of Medicine, Faculty of Health Sciences, University of Cape Town, Cape Town, South Africa
| | - Kim Lamont
- Cardioprotection Group, Hatter Institute for Cardiovascular Research in Africa and South African Medical Research Council Inter-University Cape Heart Group, Department of Medicine, Faculty of Health Sciences, University of Cape Town, Cape Town, South Africa
| | - Zulfah Albertyn
- Cardioprotection Group, Hatter Institute for Cardiovascular Research in Africa and South African Medical Research Council Inter-University Cape Heart Group, Department of Medicine, Faculty of Health Sciences, University of Cape Town, Cape Town, South Africa
| | - Lionel H Opie
- Cardioprotection Group, Hatter Institute for Cardiovascular Research in Africa and South African Medical Research Council Inter-University Cape Heart Group, Department of Medicine, Faculty of Health Sciences, University of Cape Town, Cape Town, South Africa
| | - Sandrine Lecour
- Cardioprotection Group, Hatter Institute for Cardiovascular Research in Africa and South African Medical Research Council Inter-University Cape Heart Group, Department of Medicine, Faculty of Health Sciences, University of Cape Town, Cape Town, South Africa
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Shaheen ZR, Corbett JA. Macrophage Expression of Inflammatory Genes in Response to EMCV Infection. Biomolecules 2015; 5:1938-54. [PMID: 26295266 PMCID: PMC4598781 DOI: 10.3390/biom5031938] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2015] [Revised: 08/06/2015] [Accepted: 08/08/2015] [Indexed: 12/24/2022] Open
Abstract
The expression and production of type 1 interferon is the classic cellular response to virus infection. In addition to this antiviral response, virus infection also stimulates the production of proinflammatory mediators. In this review, the pathways controlling the induction of inflammatory genes and the roles that these inflammatory mediators contribute to host defense against viral pathogens will be discussed. Specific focus will be on the role of the chemokine receptor CCR5, as a signaling receptor controlling the activation of pathways leading to virus-induced inflammatory gene expression.
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Affiliation(s)
- Zachary R Shaheen
- Department of Biochemistry, Medical College of Wisconsin, 8701 W. Watertown Plank Rd, Milwaukee, WI 53226, USA.
| | - John A Corbett
- Department of Biochemistry, Medical College of Wisconsin, 8701 W. Watertown Plank Rd, Milwaukee, WI 53226, USA.
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Kelly-Laubscher RF, King JC, Hacking D, Somers S, Hastie S, Stewart T, Imamdin A, Maarman G, Pedretti S, Lecour S. Cardiac preconditioning with sphingosine-1-phosphate requires activation of signal transducer and activator of transcription-3. Cardiovasc J Afr 2015; 25:118-23. [PMID: 25000441 PMCID: PMC4120131 DOI: 10.5830/cvja-2014-016] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2013] [Accepted: 03/31/2014] [Indexed: 02/05/2023] Open
Abstract
Aims Sphingosine-1-phosphate (S1P) is a cardioprotective agent. Signal transducer and activator of transcription 3 (STAT-3) is a key mediator of many cardioprotective agents. We aimed to explore whether STAT-3 is a key mediator in S1P-induced preconditioning. Methods Langendorff-perfused hearts from Wistar rats and wild-type or cardiomyocyte-specific STAT-3 knockout mice were pre-treated with S1P (10 nmol/l), with or without the STAT-3 pathway inhibitor AG490, before an ischaemia–reperfusion insult. Triphenyltetrazolium chloride and Evans blue staining were used for the determination of infarct size. Western blot analysis was carried out on the S1P pre-treated hearts for detection of cytosolic, nuclear and mitochondrial phosphorylated and total STAT-3 proteins. Results Pre-treatment with S1P decreased the infarct size in isolated rat (5 ± 3% vs control 26 ± 8%, p < 0.01) and wild-type mouse hearts (13 ± 1% vs control 33 ± 3%, p < 0.05). This protective effect was abolished in the rat hearts pre-treated with AG490 (30 ± 10%, p = ns vs control) and in the hearts from STAT-3 knockout mice (35 ± 4% vs control 30 ± 3%, p = ns). Levels of phosphorylated STAT-3 were significantly increased in both the nuclear (p < 0.05 vs control) and mitochondrial (p < 0.05 vs control) fractions in the S1P pre-treated hearts, but remained unchanged in the cytosolic fraction (p = ns vs control). Conclusion These novel results demonstrate that pharmacological preconditioning with S1P in the isolated heart is mediated by activation of mitochondrial and nuclear STAT-3, therefore suggesting that S1P may be a novel therapeutic target to modulate mitochondrial and nuclear function in cardiovascular disease in order to protect the heart against ischaemia–reperfusion.
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Affiliation(s)
- Roisin F Kelly-Laubscher
- Hatter Institute for Cardiovascular Research in Africa, Chris Barnard Building, Medical School Campus, University of Cape Town, Cape Town, South Africa
| | - Jonathan C King
- Hatter Institute for Cardiovascular Research in Africa, Chris Barnard Building, Medical School Campus, University of Cape Town, Cape Town, South Africa
| | - Damian Hacking
- Hatter Institute for Cardiovascular Research in Africa, Chris Barnard Building, Medical School Campus, University of Cape Town, Cape Town, South Africa
| | - Sarin Somers
- Hatter Institute for Cardiovascular Research in Africa, Chris Barnard Building, Medical School Campus, University of Cape Town, Cape Town, South Africa
| | - Samantha Hastie
- Hatter Institute for Cardiovascular Research in Africa, Chris Barnard Building, Medical School Campus, University of Cape Town, Cape Town, South Africa
| | - Tessa Stewart
- Hatter Institute for Cardiovascular Research in Africa, Chris Barnard Building, Medical School Campus, University of Cape Town, Cape Town, South Africa
| | - Aqeela Imamdin
- Hatter Institute for Cardiovascular Research in Africa, Chris Barnard Building, Medical School Campus, University of Cape Town, Cape Town, South Africa
| | - Gerald Maarman
- Hatter Institute for Cardiovascular Research in Africa, Chris Barnard Building, Medical School Campus, University of Cape Town, Cape Town, South Africa
| | - Sarah Pedretti
- Hatter Institute for Cardiovascular Research in Africa, Chris Barnard Building, Medical School Campus, University of Cape Town, Cape Town, South Africa
| | - Sandrine Lecour
- Hatter Institute for Cardiovascular Research in Africa, Chris Barnard Building, Medical School Campus, University of Cape Town, Cape Town, South Africa
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Zhang T, Zhao LL, Cao X, Qi LC, Wei GQ, Liu JY, Yan SJ, Liu JG, Li XQ. Bioinformatics analysis of time series gene expression in left ventricle (LV) with acute myocardial infarction (AMI). Gene 2014; 543:259-67. [PMID: 24704022 DOI: 10.1016/j.gene.2014.04.002] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2013] [Revised: 03/25/2014] [Accepted: 04/01/2014] [Indexed: 12/18/2022]
Abstract
This study is to investigate the key genes and their possible function in acute myocardial infarction (AMI). The data of GSE4648 downloaded from the Gene Expression Omnibus (GEO) database include 6 time points (15 min, 60 min, 4h, 12h, 24h and 48 h) of 12 left ventricle (LV) samples, 12 surviving LV free wall (FW) samples, 12 inter-ventricular septum (IVS) samples after AMI operation and corresponding sham-operated samples. The data of each sample were analyzed with Affy and Bioconductor packages, and differentially expressed genes (DEGs) were screened out using BETR package with false discovery rate (FDR)<0.01. Then, functional enrichment analysis for DEGs was conducted with Database for Annotation, Visualization and Integrated Discovery (DAVID). Totally 194 DEGs were identified in LV, and only the gene tubulin beta 2a (Tubb2a) and natriuretic peptide B (Nppb) were respectively up-regulated in surviving FW tissue and IVS tissue. The biological process response to wounding and inflammatory response were significantly enriched, as well as leukocyte transendothelial migration pathway. Besides, the expression pattern analysis showed the DEGs mostly up-regulated at 4h after AMI, and these genes were mainly associated with immunity. Additionally, in transcriptional regulatory network, early growth response 1 (Egr1), activating transcription factor 3 (Atf3), Atf4, Myc and Fos were considered as the key transcription factors related to immune response. The key transcription factors and potential target genes might provide new information for the development of AMI, and leukocyte transendothelial migration pathway might play a vital role in AMI.
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Affiliation(s)
- Tong Zhang
- Department of Cardiology, The Fourth Affiliated Hospital of Harbin Medical University, Harbin 150001, Heilongjiang Province, China
| | - Li-Li Zhao
- Department of Gastroenterology, The Fourth Affiliated Hospital of Harbin Medical University, Harbin 150001, Heilongjiang Province, China
| | - Xue Cao
- Department of Cardiology, The Fourth Affiliated Hospital of Harbin Medical University, Harbin 150001, Heilongjiang Province, China
| | - Li-Chun Qi
- Department of Cardiology, The Fourth Affiliated Hospital of Harbin Medical University, Harbin 150001, Heilongjiang Province, China
| | - Guo-Qian Wei
- Department of Cardiology, The Fourth Affiliated Hospital of Harbin Medical University, Harbin 150001, Heilongjiang Province, China
| | - Jun-Yan Liu
- Department of Cardiology, The Fourth Affiliated Hospital of Harbin Medical University, Harbin 150001, Heilongjiang Province, China
| | - Shu-Jun Yan
- Department of Cardiology, The Fourth Affiliated Hospital of Harbin Medical University, Harbin 150001, Heilongjiang Province, China
| | - Jin-Gang Liu
- The Central Hospital of the Heilongjiang Prison Administrative Bureau, Harbin 150001, Heilongjiang Province, China
| | - Xue-Qi Li
- Department of Cardiology, The Fourth Affiliated Hospital of Harbin Medical University, Harbin 150001, Heilongjiang Province, China.
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Xie Z, Liu D, Liu S, Calderon L, Zhao G, Turk J, Guo Z. Identification of a cAMP-response element in the regulator of G-protein signaling-2 (RGS2) promoter as a key cis-regulatory element for RGS2 transcriptional regulation by angiotensin II in cultured vascular smooth muscles. J Biol Chem 2011; 286:44646-58. [PMID: 22057271 DOI: 10.1074/jbc.m111.265462] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Mice deficient in regulator of G-protein signaling-2 (RGS2) have severe hypertension, and RGS2 genetic variations occur in hypertensive humans. A potentially important negative feedback loop in blood pressure homeostasis is that angiotensin II (Ang II) increases vascular smooth muscle cell (VSMC) RGS2 expression. We reported that Group VIA phospholipase A(2) (iPLA(2)β) is required for this response (Xie, Z., Gong, M. C., Su, W., Turk, J., and Guo, Z. (2007) J. Biol. Chem. 282, 25278-25289), but the specific molecular causes and consequences of iPLA(2)β activation are not known. Here we demonstrate that both protein kinases C (PKC) and A (PKA) participate in Ang II-induced VSMC RGS2 mRNA up-regulation, and that actions of PKC and PKA precede and follow iPLA(2)β activation, respectively. Moreover, we identified a conserved cAMP-response element (CRE) in the murine RGS2 promoter that is critical for cAMP-response element-binding protein (CREB) binding and RGS2 promoter activation. Forskolin-stimulated RGS2 mRNA up-regulation is inhibited by CREB sequestration or specific disruption of the CREB-RGS2 promoter interaction, and Ang II-induced CREB phosphorylation and nuclear localization are blocked by iPLA(2)β pharmacologic inhibition or genetic ablation. Ang II-induced intracellular cyclic AMP accumulation precedes CREB phosphorylation and is diminished by inhibiting iPLA(2), cyclooxygenase, or lipoxygenase. Moreover, three single nucleotide polymorphisms identified in hypertensive patients are located in the human RGS2 promoter CREB binding site. Point mutations corresponding to these single nucleotide polymorphisms interfere with stimulation of human RGS2 promoter activity by forskolin. Our studies thus delineate a negative feedback loop to attenuate Ang II signaling in VSMC with potential importance in blood pressure homeostasis and the pathogenesis of human essential hypertension.
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Affiliation(s)
- Zhongwen Xie
- Department of Physiology, University of Kentucky School of Medicine, Lexington, Kentucky 40536, USA
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Naemi FMA, Ali S, Kirby JA. Antibody-mediated allograft rejection: the emerging role of endothelial cell signalling and transcription factors. Transpl Immunol 2011; 25:96-103. [PMID: 21782944 DOI: 10.1016/j.trim.2011.07.004] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2011] [Revised: 07/08/2011] [Accepted: 07/08/2011] [Indexed: 10/18/2022]
Abstract
The presence of antibodies against class I human leukocyte antigens (HLA) can cause the development of chronic allograft rejection. Although endothelial cell activation has been identified as a main effector, the mechanisms mediating this process are not fully understood. Exposure of endothelium to antibodies against HLA antigens induces cell activation which promotes rejection. This activation process can be divided into two phases: an early response in which intracellular signalling proteins and transcription factors are activated, and a later change in protein expression and cell function. In this review, antibody-mediated endothelial signalling and the role of transcription factors in organ transplantation will be described with a particular focus on their potential to mediate some of the graft-damaging effects of anti-HLA class I antibodies.
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Affiliation(s)
- Fatmah M A Naemi
- Applied Immunobiology and Transplantation Research Group, Institute of Cellular Medicine, Faculty of Medical Sciences, Newcastle University, Newcastle upon Tyne, NE2 4HH, UK
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Song H, Rohrs H, Tan M, Wohltmann M, Ladenson JH, Turk J. Effects of endoplasmic reticulum stress on group VIA phospholipase A2 in beta cells include tyrosine phosphorylation and increased association with calnexin. J Biol Chem 2010; 285:33843-57. [PMID: 20732873 DOI: 10.1074/jbc.m110.153197] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The Group VIA phospholipase A(2) (iPLA(2)β) hydrolyzes glycerophospholipids at the sn-2-position to yield a free fatty acid and a 2-lysophospholipid, and iPLA(2)β has been reported to participate in apoptosis, phospholipid remodeling, insulin secretion, transcriptional regulation, and other processes. Induction of endoplasmic reticulum (ER) stress in β-cells and vascular myocytes with SERCA inhibitors activates iPLA(2)β, resulting in hydrolysis of arachidonic acid from membrane phospholipids, by a mechanism that is not well understood. Regulatory proteins interact with iPLA(2)β, including the Ca(2+)/calmodulin-dependent protein kinase IIβ, and we have characterized the iPLA(2)β interactome further using affinity capture and LC/electrospray ionization/MS/MS. An iPLA(2)β-FLAG fusion protein was expressed in an INS-1 insulinoma cell line and then adsorbed to an anti-FLAG matrix after cell lysis. iPLA(2)β and any associated proteins were then displaced with FLAG peptide and analyzed by SDS-PAGE. Gel sections were digested with trypsin, and the resultant peptide mixtures were analyzed by LC/MS/MS with database searching. This identified 37 proteins that associate with iPLA(2)β, and nearly half of them reside in ER or mitochondria. They include the ER chaperone calnexin, whose association with iPLA(2)β increases upon induction of ER stress. Phosphorylation of iPLA(2)β at Tyr(616) also occurs upon induction of ER stress, and the phosphoprotein associates with calnexin. The activity of iPLA(2)β in vitro increases upon co-incubation with calnexin, and overexpression of calnexin in INS-1 cells results in augmentation of ER stress-induced, iPLA(2)β-catalyzed hydrolysis of arachidonic acid from membrane phospholipids, reflecting the functional significance of the interaction. Similar results were obtained with mouse pancreatic islets.
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Affiliation(s)
- Haowei Song
- Mass Spectrometry Resource, Division of Endocrinology, Metabolism, and Lipid Research, Washington University School of Medicine, St Louis, Missouri 63110, USA
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Song H, Bao S, Lei X, Jin C, Zhang S, Turk J, Ramanadham S. Evidence for proteolytic processing and stimulated organelle redistribution of iPLA(2)beta. BIOCHIMICA ET BIOPHYSICA ACTA 2010; 1801:547-58. [PMID: 20132906 PMCID: PMC2848069 DOI: 10.1016/j.bbalip.2010.01.006] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/07/2009] [Revised: 12/24/2009] [Accepted: 01/19/2010] [Indexed: 12/31/2022]
Abstract
Over the past decade, important roles for the 84-88kDa Group VIA Ca(2+)-independent phospholipase A(2) (iPLA(2)beta) in various organs have been described. We demonstrated that iPLA(2)beta participates in insulin secretion, insulinoma cells and native pancreatic islets express full-length and truncated isoforms of iPLA(2)beta, and certain stimuli promote perinuclear localization of iPLA(2)beta. To gain a better understanding of its mobilization, iPLA(2)beta was expressed in INS-1 cells as a fusion protein with EGFP, enabling detection of subcellular localization of iPLA(2)beta by monitoring EGFP fluorescence. Cells stably-transfected with fusion protein expressed nearly 5-fold higher catalytic iPLA(2)beta activity than control cells transfected with EGFP cDNA alone, indicating that co-expression of EGFP does not interfere with manifestation of iPLA(2)beta activity. Dual fluorescence monitoring of EGFP and organelle Trackers combined with immunoblotting analyses revealed expression of truncated iPLA(2)beta isoforms in separate subcellular organelles. Exposure to secretagogues and induction of ER stress are known to activate iPLA(2)beta in beta-cells and we find here that these stimuli promote differential localization of iPLA(2)beta in subcellular organelles. Further, mass spectrometric analyses identified iPLA(2)beta variants from which N-terminal residues were removed. Collectively, these findings provide evidence for endogenous proteolytic processing of iPLA(2)beta and redistribution of iPLA(2)beta variants in subcellular compartments. It might be proposed that in vivo processing of iPLA(2)beta facilitates its participation in multiple biological processes.
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Affiliation(s)
- Haowei Song
- Mass Spectrometry Resource, Division of Metabolism, Endocrinology, and Lipid Research, Department of Medicine, Washington University School of Medicine, St. Louis, MO, 63110, U.S.A
| | - Shunzhong Bao
- Mass Spectrometry Resource, Division of Metabolism, Endocrinology, and Lipid Research, Department of Medicine, Washington University School of Medicine, St. Louis, MO, 63110, U.S.A
| | - Xiaoyong Lei
- Mass Spectrometry Resource, Division of Metabolism, Endocrinology, and Lipid Research, Department of Medicine, Washington University School of Medicine, St. Louis, MO, 63110, U.S.A
| | - Chun Jin
- Mass Spectrometry Resource, Division of Metabolism, Endocrinology, and Lipid Research, Department of Medicine, Washington University School of Medicine, St. Louis, MO, 63110, U.S.A
| | - Sheng Zhang
- Mass Spectrometry Resource, Division of Metabolism, Endocrinology, and Lipid Research, Department of Medicine, Washington University School of Medicine, St. Louis, MO, 63110, U.S.A
| | - John Turk
- Mass Spectrometry Resource, Division of Metabolism, Endocrinology, and Lipid Research, Department of Medicine, Washington University School of Medicine, St. Louis, MO, 63110, U.S.A
| | - Sasanka Ramanadham
- Mass Spectrometry Resource, Division of Metabolism, Endocrinology, and Lipid Research, Department of Medicine, Washington University School of Medicine, St. Louis, MO, 63110, U.S.A
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Lei X, Zhang S, Barbour SE, Bohrer A, Ford EL, Koizumi A, Papa FR, Ramanadham S. Spontaneous development of endoplasmic reticulum stress that can lead to diabetes mellitus is associated with higher calcium-independent phospholipase A2 expression: a role for regulation by SREBP-1. J Biol Chem 2010; 285:6693-705. [PMID: 20032468 PMCID: PMC2825464 DOI: 10.1074/jbc.m109.084293] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2009] [Revised: 12/18/2009] [Indexed: 01/09/2023] Open
Abstract
Our recent studies indicate that endoplasmic reticulum (ER) stress causes INS-1 cell apoptosis by a Ca(2+)-independent phospholipase A(2) (iPLA(2)beta)-mediated mechanism that promotes ceramide generation via sphingomyelin hydrolysis and subsequent activation of the intrinsic pathway. To elucidate the association between iPLA(2)beta and ER stress, we compared beta-cell lines generated from wild type (WT) and Akita mice. The Akita mouse is a spontaneous model of ER stress that develops hyperglycemia/diabetes due to ER stress-induced beta-cell apoptosis. Consistent with a predisposition to developing ER stress, basal phosphorylated PERK and activated caspase-3 are higher in the Akita cells than WT cells. Interestingly, basal iPLA(2)beta, mature SREBP-1 (mSREBP-1), phosphorylated Akt, and neutral sphingomyelinase (NSMase) are higher, relative abundances of sphingomyelins are lower, and mitochondrial membrane potential (DeltaPsi) is compromised in Akita cells, in comparison with WT cells. Exposure to thapsigargin accelerates DeltaPsi loss and apoptosis of Akita cells and is associated with increases in iPLA(2)beta, mSREBP-1, and NSMase in both WT and Akita cells. Transfection of Akita cells with iPLA(2)beta small interfering RNA, however, suppresses NSMase message, DeltaPsi loss, and apoptosis. The iPLA(2)beta gene contains a sterol-regulatory element, and transfection with a dominant negative SREBP-1 reduces basal mSREBP-1 and iPLA(2)beta in the Akita cells and suppresses increases in mSREBP-1 and iPLA(2)beta due to thapsigargin. These findings suggest that ER stress leads to generation of mSREBP-1, which can bind to the sterol-regulatory element in the iPLA(2)beta gene to promote its transcription. Consistent with this, SREBP-1, iPLA(2)beta, and NSMase messages in Akita mouse islets are higher than in WT islets.
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Affiliation(s)
- Xiaoyong Lei
- From the Department of Medicine, Mass Spectrometry Resource, and Division of Endocrinology, Metabolism, and Lipid Research, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Sheng Zhang
- From the Department of Medicine, Mass Spectrometry Resource, and Division of Endocrinology, Metabolism, and Lipid Research, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Suzanne E. Barbour
- the Department of Biochemistry and Molecular Biology, Virginia Commonwealth University School of Medicine, Richmond, Virginia 23298
| | - Alan Bohrer
- From the Department of Medicine, Mass Spectrometry Resource, and Division of Endocrinology, Metabolism, and Lipid Research, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Eric L. Ford
- From the Department of Medicine, Mass Spectrometry Resource, and Division of Endocrinology, Metabolism, and Lipid Research, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Akio Koizumi
- the Department of Health and Environmental Sciences, Kyoto Graduate School of Medicine, Kyoto 606-8501, Japan, and
| | - Feroz R. Papa
- the California Institute for Quantitative Biosciences, University of California, San Francisco, California 94143
| | - Sasanka Ramanadham
- From the Department of Medicine, Mass Spectrometry Resource, and Division of Endocrinology, Metabolism, and Lipid Research, Washington University School of Medicine, St. Louis, Missouri 63110
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Lei X, Barbour SE, Ramanadham S. Group VIA Ca2+-independent phospholipase A2 (iPLA2beta) and its role in beta-cell programmed cell death. Biochimie 2010; 92:627-37. [PMID: 20083151 DOI: 10.1016/j.biochi.2010.01.005] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2009] [Accepted: 01/11/2010] [Indexed: 01/09/2023]
Abstract
Activation of phospholipases A(2) (PLA(2)s) leads to the generation of biologically active lipid mediators that can affect numerous cellular events. The Group VIA Ca(2+)-independent PLA(2), designated iPLA(2)beta, is active in the absence of Ca(2+), activated by ATP, and inhibited by the bromoenol lactone suicide inhibitor (BEL). Over the past 10-15 years, studies using BEL have demonstrated that iPLA(2)beta participates in various biological processes and the recent availability of mice in which iPLA(2)beta expression levels have been genetically-modified are extending these findings. Work in our laboratory suggests that iPLA(2)beta activates a unique signaling cascade that promotes beta-cell apoptosis. This pathway involves iPLA(2)beta dependent induction of neutral sphingomyelinase, production of ceramide, and activation of the intrinsic pathway of apoptosis. There is a growing body of literature supporting beta-cell apoptosis as a major contributor to the loss of beta-cell mass associated with the onset and progression of Type 1 and Type 2 diabetes mellitus. This underscores a need to gain a better understanding of the molecular mechanisms underlying beta-cell apoptosis so that improved treatments can be developed to prevent or delay the onset and progression of diabetes mellitus. Herein, we offer a general review of Group VIA Ca(2+)-independent PLA(2) (iPLA(2)beta) followed by a more focused discussion of its participation in beta-cell apoptosis. We suggest that iPLA(2)beta-derived products trigger pathways which can lead to beta-cell apoptosis during the development of diabetes.
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Affiliation(s)
- Xiaoyong Lei
- Department of Medicine, Mass Spectrometry Resource and Division of Endocrinology, Metabolism, and Lipid Research, Washington University School of Medicine, St. Louis, MO 63110, USA
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13
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Carper MJ, Zhang S, Turk J, Ramanadham S. Skeletal muscle group VIA phospholipase A2 (iPLA2beta): expression and role in fatty acid oxidation. Biochemistry 2008; 47:12241-9. [PMID: 18937505 DOI: 10.1021/bi800923s] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Among the phospholipases A 2 (PLA 2s) are the group VI Ca (2+)-independent PLA 2s (iPLA 2s), and expression of multiple transcripts of iPLA 2 in skeletal muscle has been reported. In the present study, phospholipase activity and sequential ATP and calmodulin affinity column chromatography analyses reveal that skeletal muscle iPLA 2 exhibits properties characteristic of the iPLA 2beta isoform. The phospholipase activity of iPLA 2beta has been demonstrated to participate in signal transduction, cell proliferation, and apoptosis. We report here that skeletal muscle from iPLA 2beta-null mice, relative to wild-type muscle, exhibits a reduced capacity to oxidize palmitate but not palmitoyl-CoA or acetyl-CoA in the absence of changes in fatty acid transporters CD36 and CPT1 or beta-hydroxyacyl-CoA dehydrogenase activity. Recently, purified iPLA 2beta was demonstrated to manifest a thioesterase activity which catalyzes hydrolysis of fatty acyl-CoAs. The liberated CoA-SH facilitates fatty acid transport into the mitochondria. In this regard, we find that fractions eluted from the ATP column and containing iPLA 2beta phospholipase activity also contained acyl-CoA thioesterase activity that was inhibited by the bromoenol lactone (BEL) suicide inhibitor of iPLA 2beta. We further find that acyl-CoA thioesterase activity in skeletal muscle preparations from iPLA 2beta-null mice is significantly reduced, relative to WT activity. These findings suggest that the absence of acyl-CoA thioesterase activity of iPLA 2beta can lead to reduced fatty acyl-CoA generation and impair fatty acid oxidation in iPLA 2beta-null mice. Our findings therefore reveal a novel function of iPLA 2beta, related not to its phospholipase activity but to its thioesterase activity, which contributes to optimal fatty acid oxidation in skeletal muscle.
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Affiliation(s)
- Michael J Carper
- Mass Spectrometry Resource, Division of Metabolism, Endocrinology, and Lipid Research, Department of Medicine, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
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14
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Xie Z, Gong MC, Su W, Turk J, Guo Z. Group VIA phospholipase A2 (iPLA2beta) participates in angiotensin II-induced transcriptional up-regulation of regulator of g-protein signaling-2 in vascular smooth muscle cells. J Biol Chem 2007; 282:25278-89. [PMID: 17613534 PMCID: PMC2096773 DOI: 10.1074/jbc.m611206200] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Rgs2 (regulator of G-protein signaling-2)-deficient mice exhibit severe hypertension, and genetic variations of RGS2 occur in hypertensive patients. RGS2 mRNA up-regulation by angiotensin II (Ang II) in vascular smooth muscle cells (VSMC) is a potentially important negative feedback mechanism in blood pressure homeostasis, but how it occurs is unknown. Here we demonstrate that group VIA phospholipase A2 (iPLA2beta) plays a pivotal role in Ang II-induced RGS2 mRNA up-regulation in VSMC by three independent approaches, including pharmacologic inhibition with a bromoenol lactone suicide substrate, suppression of iPLA2beta expression with antisense oligonucleotides, and genetic deletion in iPLA2beta-null mice. Selective inhibition of iPLA2beta by each of these approaches abolishes Ang II-induced RGS2 mRNA up-regulation. Furthermore, using adenovirus-mediated gene transfer, we demonstrate that restoration of iPLA2beta-expression in iPLA2beta-null VSMC reconstitutes the ability of Ang II to up-regulate RGS2 mRNA expression. In contrast, Ang II-induced vasodilator-stimulated phosphoprotein phosphorylation and Ang II receptor expression are unaffected. Moreover, in wild-type but not iPLA2beta-null VSMC, Ang II stimulates iPLA2 enzymatic activity significantly. Both arachidonic acid and lysophosphatidylcholine, products of iPLA2beta action, induce RGS2 mRNA up-regulation. Inhibition of lipoxygenases, particularly 15-lipoxygenase, and cyclooxygenases, but not cytochrome P450-dependent epoxygenases inhibits Ang II- or AA-induced RGS2 mRNA expression. Moreover, RGS2 protein expression is also up-regulated by Ang II, and this is attenuated by bromoenol lactone. Disruption of the Ang II/iPLA2beta/RGS2 feedback pathway in iPLA2beta-null cells potentiates Ang II-induced vasodilator-stimulated phosphoprotein and Akt phosphorylation in a time-dependent manner. Collectively, our results demonstrate that iPLA2beta participates in Ang II-induced transcriptional up-regulation of RGS2 in VSMC.
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MESH Headings
- Adenoviridae
- Angiotensin II/pharmacology
- Animals
- Arachidonic Acid/pharmacology
- Blood Pressure/drug effects
- Blood Pressure/physiology
- Cell Adhesion Molecules/metabolism
- Enzyme Activation/drug effects
- Enzyme Activation/physiology
- Gene Deletion
- Gene Expression Regulation, Enzymologic/drug effects
- Gene Expression Regulation, Enzymologic/physiology
- Group VI Phospholipases A2
- Homeostasis/drug effects
- Homeostasis/physiology
- Lysophosphatidylcholines/pharmacology
- Mice
- Mice, Knockout
- Microfilament Proteins/metabolism
- Muscle, Smooth, Vascular/enzymology
- Myocytes, Smooth Muscle/enzymology
- Naphthalenes/pharmacology
- Oligodeoxyribonucleotides, Antisense/pharmacology
- Oxidoreductases/antagonists & inhibitors
- Oxidoreductases/metabolism
- Phospholipases A/antagonists & inhibitors
- Phospholipases A/deficiency
- Phospholipases A/metabolism
- Phospholipases A2
- Phosphoproteins/metabolism
- Phosphorylation/drug effects
- Proto-Oncogene Proteins c-akt/metabolism
- Pyrones/pharmacology
- RGS Proteins/antagonists & inhibitors
- RGS Proteins/deficiency
- RGS Proteins/metabolism
- RNA, Messenger/biosynthesis
- RNA, Messenger/genetics
- Rats
- Rats, Sprague-Dawley
- Signal Transduction/drug effects
- Signal Transduction/physiology
- Time Factors
- Transcription, Genetic/drug effects
- Transcription, Genetic/physiology
- Transduction, Genetic
- Up-Regulation/drug effects
- Up-Regulation/physiology
- Vasoconstrictor Agents/pharmacology
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Affiliation(s)
- Zhongwen Xie
- Department of Physiology and the Graduate Center for Nutritional Sciences, University of Kentucky, Lexington, Kentucky 40536, USA
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15
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Lei XY, Zhang S, Bohrer A, Bao S, Song H, Ramanadham S. The group VIA calcium-independent phospholipase A2 participates in ER stress-induced INS-1 insulinoma cell apoptosis by promoting ceramide generation via hydrolysis of sphingomyelins by neutral sphingomyelinase. Biochemistry 2007; 46:10170-85. [PMID: 17685585 PMCID: PMC2530898 DOI: 10.1021/bi700017z] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Beta-cell mass is regulated by a balance between beta-cell growth and beta-cell death, due to apoptosis. We previously reported that apoptosis of INS-1 insulinoma cells due to thapsigargin-induced ER stress was suppressed by inhibition of the group VIA Ca2+-independent phospholipase A2 (iPLA2beta), associated with an increased level of ceramide generation, and that the effects of ER stress were amplified in INS-1 cells in which iPLA2beta was overexpressed (OE INS-1 cells). These findings suggested that iPLA2beta and ceramides participate in ER stress-induced INS-1 cell apoptosis. Here, we address this possibility and also the source of the ceramides by examining the effects of ER stress in empty vector (V)-transfected and iPLA2beta-OE INS-1 cells using apoptosis assays and immunoblotting, quantitative PCR, and mass spectrometry analyses. ER stress induced expression of ER stress factors GRP78 and CHOP, cleavage of apoptotic factor PARP, and apoptosis in V and OE INS-1 cells. Accumulation of ceramide during ER stress was not associated with changes in mRNA levels of serine palmitoyltransferase (SPT), the rate-limiting enzyme in de novo synthesis of ceramides, but both message and protein levels of neutral sphingomyelinase (NSMase), which hydrolyzes sphingomyelins to generate ceramides, were temporally increased in the INS-1 cells. The increases in the level of NSMase expression in the ER-stressed INS-1 cells were associated with corresponding temporal elevations in ER-associated iPLA2beta protein and catalytic activity. Pretreatment with BEL inactivated iPLA2beta and prevented induction of NSMase message and protein in ER-stressed INS-1 cells. Relative to that in V INS-1 cells, the effects of ER stress were accelerated and/or amplified in the OE INS-1 cells. However, inhibition of iPLA2beta or NSMase (chemically or with siRNA) suppressed induction of NSMase message, ceramide generation, sphingomyelin hydrolysis, and apoptosis in both V and OE INS-1 cells during ER stress. In contrast, inhibition of SPT did not suppress ceramide generation or apoptosis in either V or OE INS-1 cells. These findings indicate that iPLA2beta activation participates in ER stress-induced INS-1 cell apoptosis by promoting ceramide generation via NSMase-catalyzed hydrolysis of sphingomyelins, raising the possibility that this pathway contributes to beta-cell apoptosis due to ER stress.
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Affiliation(s)
| | | | | | | | | | - Sasanka Ramanadham
- *Address correspondence to: Sasanka Ramanadham, Dept. Medicine, Washington University School of Medicine, Campus Box 8127, 660 S. Euclid Ave., St. Louis, MO 63110; telephone 314-362-8194; FAX 314-362-7641; E-mail:
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16
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Song H, Bao S, Ramanadham S, Turk J. Effects of biological oxidants on the catalytic activity and structure of group VIA phospholipase A2. Biochemistry 2006; 45:6392-406. [PMID: 16700550 PMCID: PMC2044503 DOI: 10.1021/bi060502a] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Group VIA phospholipase A(2) (iPLA(2)beta) is expressed in phagocytes, vascular cells, pancreatic islet beta-cells, neurons, and other cells and plays roles in transcriptional regulation, cell proliferation, apoptosis, secretion, and other events. A bromoenol lactone (BEL) suicide substrate used to study iPLA(2)beta functions inactivates iPLA(2)beta by alkylating Cys thiols. Because thiol redox reactions are important in signaling and some cells that express iPLA(2)beta produce biological oxidants, iPLA(2)beta might be subject to redox regulation. We report that biological concentrations of H(2)O(2), NO, and HOCl inactivate iPLA(2)beta, and this can be partially reversed by dithiothreitol (DTT). Oxidant-treated iPLA(2)beta modifications were studied by LC-MS/MS analyses of tryptic digests and included DTT-reversible events, e.g., formation of disulfide bonds and sulfenic acids, and others not so reversed, e.g., formation of sulfonic acids, Trp oxides, and Met sulfoxides. W(460) oxidation could cause irreversible inactivation because it is near the lipase consensus sequence ((463)GTSTG(467)), and site-directed mutagenesis of W(460) yields active mutant enzymes that exhibit no DTT-irreversible oxidative inactivation. Cys651-sulfenic acid formation could be one DTT-reversible inactivation event because Cys651 modification correlates closely with activity loss and its mutagenesis reduces sensitivity to inhibition. Intermolecular disulfide bond formation might also cause reversible inactivation because oxidant-treated iPLA(2)beta contains DTT-reducible oligomers, and oligomerization occurs with time- and temperature-dependent iPLA(2)beta inactivation that is attenuated by DTT or ATP. Subjecting insulinoma cells to oxidative stress induces iPLA(2)beta oligomerization, loss of activity, and subcellular redistribution and reduces the rate of release of arachidonate from phospholipids. These findings raise the possibility that redox reactions affect iPLA(2)beta functions.
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Affiliation(s)
- Haowei Song
- Medicine Department Mass Spectrometry Facility, Division of Endocrinology, Metabolism, and Lipid Research, Washington University School of Medicine, St. Louis, Missouri 63110, USA
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17
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Lallemand C, Blanchard B, Palmieri M, Lebon P, May E, Tovey MG. Single-stranded RNA viruses inactivate the transcriptional activity of p53 but induce NOXA-dependent apoptosis via post-translational modifications of IRF-1, IRF-3 and CREB. Oncogene 2006; 26:328-38. [PMID: 16832344 DOI: 10.1038/sj.onc.1209795] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
To characterize the mechanisms underlying apoptosis induced by viral infection, transcriptional activation of genes encoding members of the 'BH3-only' family of proteins was analysed during the course of virus infection. Among these genes, only NOXA is transcriptionally activated by vesicular stomatitis virus (VSV), sendai virus (SV), measles virus, herpes simplex virus, or dsRNA and required for efficient apoptosis of cells. Transcriptional activation of NOXA by VSV or SV is independent of p53, but requires the presence of interferon regulatory factor 1 (IRF-1), IRF-3 and cAMP-responsive element binding protein (CREB). Binding to and transactivation of the NOXA promoter by each of these transcription factors is governed by post-translational modification involving different pathways for each factor. Thus, SV infection activates IRF-3 and CREB by phosphorylation triggered by Toll like receptor 3 signalling, and a pathway involving calcium-independent phopholipase A2, respectively. In addition transactivation induced by IRF-1 during viral infection correlates with a 10 kDa increase in its molecular weight, suggesting a covalent linkage with a previously unknown regulatory polypeptide.
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Affiliation(s)
- C Lallemand
- Laboratory of Viral Oncology, UPR CNRS 9045, Institut André Lwoff, Villejuif, France.
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18
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Beckett CS, Pennington K, McHowat J. Activation of MAPKs in thrombin-stimulated ventricular myocytes is dependent on Ca2+-independent PLA2. Am J Physiol Cell Physiol 2006; 290:C1350-4. [PMID: 16338969 DOI: 10.1152/ajpcell.00487.2005] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Thrombin stimulation of isolated rabbit ventricular myocytes activates a membrane-associated, Ca2+-independent PLA2(iPLA2) that selectively hydrolyzes plasmalogen phospholipids and results in increased production of arachidonic acid and lysoplasmenylcholine. To determine whether MAPK regulates myocardial iPLA2activity, we isolated ventricular myocytes from rabbit heart by collagenase digestion and pretreated them with MAPK inhibitors before stimulating them with thrombin. Pretreatment with PD-98059 to inhibit p42/44 MAPK or SB-203580 to inhibit p38 MAPK had no significant effect on thrombin-stimulated, membrane-associated iPLA2activity. Thrombin stimulation resulted in significant increases in both p42/44 and p38 MAPK activity after 2 min. Pretreatment with the iPLA2-selective inhibitor bromoenol lactone completely inhibited thrombin-stimulated MAPK activity, suggesting that activation of MAPKs was dependent on iPLA2activation. Ventricular myocyte MAPK activity was increased by incubation of the myocytes with lysoplasmenylcholine, a metabolite produced by iPLA2-catalyzed membrane plasmalogen phospholipid hydrolysis. Altogether, these data suggest that activation of MAPKs occurs downstream of and is dependent on iPLA2activation in thrombin-stimulated rabbit ventricular myocytes.
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Affiliation(s)
- Caroline S Beckett
- Department of Pathology, St. Louis University School of Medicine, 1402 S. Grand Blvd., St. Louis, MO 63104, USA
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19
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Song H, Ramanadham S, Bao S, Hsu FF, Turk J. A bromoenol lactone suicide substrate inactivates group VIA phospholipase A2 by generating a diffusible bromomethyl keto acid that alkylates cysteine thiols. Biochemistry 2006; 45:1061-73. [PMID: 16411783 PMCID: PMC2065752 DOI: 10.1021/bi052065q] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Phospholipases A2 (PLA2) comprise a superfamily of enzymes that hydrolyze phospholipids to a free fatty acid, e.g., arachidonate, and a 2-lysophospholipid. Dissecting their individual functions has relied in large part on pharmacological inhibitors that discriminate among PLA2. Group VIA PLA2 (iPLA2beta) has a GTSTG serine lipase consensus sequence, and studies with a bromoenol lactone (BEL) suicide substrate inhibitor have been taken to suggest that iPLA2beta participates in a wide variety of biological processes. Such conclusions presume inhibitor specificity. Inhibition by BEL requires its hydrolysis by and results in uncharacterized covalent modification(s) of iPLA2beta. We performed mass spectrometric analyses of proteolytic digests of BEL-treated iPLA2beta to identify modifications associated with loss of activity. The GTSTG active site and large flanking regions of sequence are not modified by BEL treatment, but most iPLA2beta Cys residues are alkylated at various BEL concentrations to form a thioether linkage to a BEL keto acid hydrolysis product. Synthetic Cys-containing peptides are alkylated when incubated with iPLA2beta and BEL, which reflects iPLA2beta-catalyzed BEL hydrolysis to a diffusible bromomethyl keto acid product that reacts with distant thiols. The BEL concentration dependence of Cys651 alkylation closely parallels that of loss of iPLA2beta activity. No amino acid residues other than Cys were found to be modified, suggesting that Cys alkylation is the covalent modification of iPLA2beta responsible for loss of activity, and the alkylating species appears to be a diffusible hydrolysis product of BEL rather than a tethered acyl-enzyme intermediate.
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Affiliation(s)
| | | | | | | | - John Turk
- To whom correspondence should be addressed: telephone, 314-362-8190; fax, 314-362-8188; e-mail,
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20
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Ichiki T. Role of cAMP response element binding protein in cardiovascular remodeling: good, bad, or both? Arterioscler Thromb Vasc Biol 2005; 26:449-55. [PMID: 16293792 DOI: 10.1161/01.atv.0000196747.79349.d1] [Citation(s) in RCA: 90] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
The cAMP response element binding protein (CREB) is a ubiquitously expressed nuclear transcription factor that is activated by various extracellular stimuli. CREB is known to regulate the expression of genes important to cell proliferation, differentiation, adaptation, and survival in many cell types. Loss of CREB function by transgenic overexpression of dominant negative CREB or targeted deletion of the CREB gene revealed that CREB is involved in the differentiation of T lymphocytes, production of growth hormone, and the long-term potentiation of neuronal memory. The role of CREB in cardiovascular system is incompletely characterized and several controversies remain. A growing body of recent evidence, however, has suggested that CREB plays an important role in the cardiovascular remodeling process, including inflammation, cell migration, and apoptosis. Thus, CREB may be a possible target for the treatment of cardiovascular diseases such as atherosclerosis, restenosis, and reperfusion injury.
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Affiliation(s)
- Toshihiro Ichiki
- Department of Cardiovascular Medicine, Kyushu University Graduate School of Medical Sciences, 3-1-1 Maidashi, 812-8582 Fukuoka, Japan.
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21
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Husse B, Isenberg G. CREB expression in cardiac fibroblasts and CREM expression in ventricular myocytes. Biochem Biophys Res Commun 2005; 334:1260-5. [PMID: 16043122 DOI: 10.1016/j.bbrc.2005.06.206] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2005] [Accepted: 06/29/2005] [Indexed: 10/25/2022]
Abstract
Activation of gene expression by the cAMP-dependent signaling pathway is regulated by members of the cAMP response element binding protein (CREB) family consisting of CREB, CREM, and ATF-1. It is decisively for the understanding of the heart function as to which type of heart cells expresses CREB and/or CREM. Ventricular myocytes and fibroblasts of young (3 months) and old (24 months) rat hearts were separately investigated to analyse CREB, CREM, and phospho-CREB. Western blot showed CREB expression exclusively in fibroblasts but CREM was predominantly detected in ventricular myocytes. CREB-positive nuclei in heart sections were only revealed in fibroblasts. CREB was activated by forskolin (10 microM), PMA (500 nM), and cyclical mechanical strain (1 Hz, 5% elongation) in fibroblasts. The number of CREB-positive myocytes in old rats was larger than in young rats. But CREB could not be activated by forskolin (10 microM) in all myocytes. Our results suggest that the expression of CREB depends on the cell type and the age of the animal. We discuss that modulation of gene expression as it occurs with a age could be affected by the change within the CREB family members.
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Affiliation(s)
- B Husse
- Department of Physiology, Martin-Luther-University Halle, D-06097 Halle, Germany.
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22
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Moran JM, Buller RML, McHowat J, Turk J, Wohltmann M, Gross RW, Corbett JA. Genetic and pharmacologic evidence that calcium-independent phospholipase A2beta regulates virus-induced inducible nitric-oxide synthase expression by macrophages. J Biol Chem 2005; 280:28162-8. [PMID: 15946940 DOI: 10.1074/jbc.m500013200] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Recent evidence supports a regulatory role for the calcium-independent phospholipase A2 (iPLA2) in the antiviral response of inducible nitric-oxide synthase (iNOS) expression by macrophages. Because two mammalian isoforms of iPLA2 (iPLA2beta and iPLA2gamma) have been cloned and characterized, the aim of this study was to identify the specific isoform(s) in macrophages that regulates the expression of iNOS in response to virus infection. Bromoenol lactone (BEL), a suicide substrate inhibitor of iPLA2, inhibits the activity of both isoforms at low micromolar concentrations. However, the R- and S-enantiomers of BEL display approximately 10-fold greater potency for inhibition of the enzymatic activity of iPLA2gamma and iPLA2beta, respectively. In this study, we show that the iPLA2beta-selective (S)-BEL inhibits encephalomyocarditis virus (EMCV)-induced iNOS expression, nitric oxide production, and iPLA2 enzymatic activity in macrophages in a concentration-related manner that closely resembles the inhibitory properties of racemic BEL. cAMP response element-binding protein (CREB) is one downstream target of iPLA2 that is required for the transcriptional activation of iNOS in response to virus infection, and consistent with the effects of BEL enantiomers on iNOS expression, (S)-BEL more effectively inhibits EMCV-induced CREB phosphorylation than (R)-BEL in macrophages. Using macrophages isolated from iPLA2beta-null mice, virus infection fails to stimulate iNOS mRNA accumulation and protein expression, thus providing genetic evidence that iPLA2beta is required for EMCV-induced iNOS expression. These findings provide evidence for a signaling role for iPLA2beta in virus-induced iNOS expression by macrophages.
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Affiliation(s)
- Jason M Moran
- The Edward A. Doisy Department of Biochemistry and Molecular Biology, St. Louis University School of Medicine, St. Louis, Missouri 63104, USA
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23
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Spruessel A, Steimann G, Jung M, Lee SA, Carr T, Fentz AK, Spangenberg J, Zornig C, Juhl HH, David KA. Tissue ischemia time affects gene and protein expression patterns within minutes following surgical tumor excision. Biotechniques 2005; 36:1030-7. [PMID: 15211754 DOI: 10.2144/04366rr04] [Citation(s) in RCA: 165] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
The aim of this study was to determine the impact of ischemia on gene and protein expression profiles of healthy and malignant colon tissue and, thus, on screening studies for identification of molecular targets and diagnostic molecular patterns. Healthy and malignant colon tissue were snap-frozen at various time points (3-30 min) after colon resection. Gene and protein expression were determined by microarray (HG-U133A chips) and surface-enhanced laser desorption/ionization time-of-flight mass spectrometry (SELDI-TOF MS) technology (CM10 chips, SAX2 chips, and IMAC3Ni chips), respectively. Real-time reverse transcription PCR (RT-PCR) was used for comparative measurement of expression of particular genes. Initial changes of gene and protein expression profiles were already observed 5-8 min after colon resection. Fifteen minutes after surgery, 10%-15% of molecules, and after 30 min, 20% of all detectable genes and proteins, respectively, differed significantly from the baseline values. Significant changes of expression were found in most functional groups. As confirmed by real-time RT-PCR, this included not only known hypoxia-related molecules (HIF-1 alpha, c-fos, HO-1) but also cytoskeletal genes (e.g., CK20) and tumor-associated antigens (e.g., CEA). In conclusion, preanalytical factors, such as tissue ischemia time, dramatically affect molecular data. Control of these variables is mandatory to obtain reliable data in screening programs for molecular targets and diagnostic molecular patterns.
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Affiliation(s)
- Annika Spruessel
- Center for Cancer Research, Israelitic Hospital, Hamburg, Germany
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24
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Bao S, Miller DJ, Ma Z, Wohltmann M, Eng G, Ramanadham S, Moley K, Turk J. Male mice that do not express group VIA phospholipase A2 produce spermatozoa with impaired motility and have greatly reduced fertility. J Biol Chem 2004; 279:38194-200. [PMID: 15252026 PMCID: PMC3733543 DOI: 10.1074/jbc.m406489200] [Citation(s) in RCA: 138] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The Group VIA Phospholipase A(2) (iPLA(2)beta) is the first recognized cytosolic Ca(2+)-independent PLA(2) and has been proposed to participate in arachidonic acid (20:4) incorporation into glycerophosphocholine lipids, cell proliferation, exocytosis, apoptosis, and other processes. To study iPLA(2)beta functions, we disrupted its gene by homologous recombination to generate mice that do not express iPLA(2)beta. Heterozygous iPLA(2)beta(+/-) breeding pairs yield a Mendelian 1:2:1 ratio of iPLA(2)beta(+/+), iPLA(2)beta(+/-), and iPLA(2)beta(-/-) pups and a 1:1 male:female gender distribution of iPLA(2)beta(-/-) pups. Several tissues of wild-type mice express iPLA(2)beta mRNA, immunoreactive protein, and activity, and testes express the highest levels. Testes or other tissues of iPLA(2)beta(-/-) mice express no iPLA(2)beta mRNA or protein, but iPLA(2)beta(-/-) testes are not deficient in 20:4-containing glycerophosphocholine lipids, indicating that iPLA(2)beta does not play an obligatory role in formation of such lipids in that tissue. Spermatozoa from iPLA(2)beta(-/-) mice have reduced motility and impaired ability to fertilize mouse oocytes in vitro and in vivo, and inhibiting iPLA(2)beta with a bromoenol lactone suicide substrate reduces motility of wild-type spermatozoa in a time- and concentration-dependent manner. Mating iPLA(2)beta(-/-) male mice with iPLA(2)beta(+/+), iPLA(2)beta(+/-), or iPLA(2)beta(-/-) female mice yields only about 7% of the number of pups produced by mating pairs with an iPLA(2)beta(+/+) or iPLA(2)beta(+/-) male, but iPLA(2)beta(-/-) female mice have nearly normal fertility. These findings indicate that iPLA(2)beta plays an important functional role in spermatozoa, suggest a target for developing male contraceptive drugs, and complement reports that disruption of the Group IVA PLA(2) (cPLA(2)alpha) gene impairs female reproductive ability.
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MESH Headings
- Alleles
- Animals
- Apoptosis
- Blotting, Northern
- Blotting, Southern
- Blotting, Western
- Calcium/metabolism
- Cytosol/enzymology
- Dose-Response Relationship, Drug
- Female
- Fertilization
- Fertilization in Vitro
- Genotype
- Group II Phospholipases A2
- Heterozygote
- Infertility, Male/genetics
- Male
- Mass Spectrometry
- Mice
- Models, Genetic
- Naphthalenes/pharmacology
- Oocytes/metabolism
- Phospholipases A/biosynthesis
- Phospholipases A/genetics
- Phospholipases A2
- Pyrones/pharmacology
- RNA, Messenger/metabolism
- Recombination, Genetic
- Spectrometry, Mass, Electrospray Ionization
- Sperm Motility/genetics
- Spermatozoa/metabolism
- Testis/metabolism
- Time Factors
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Affiliation(s)
- Shunzhong Bao
- Mass Spectrometry Resource, Division of Endocrinology, Department of Medicine, Washington University School of Medicine, St. Louis, Missouri 63110
| | - David J. Miller
- Department of Animal Sciences, University of Illinois, Urbana, Illinois 61801
| | - Zhongmin Ma
- Division of Experimental Diabetes, Mount Sinai School of Medicine, New York, New York 10029
| | - Mary Wohltmann
- Mass Spectrometry Resource, Division of Endocrinology, Department of Medicine, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Grace Eng
- Mass Spectrometry Resource, Division of Endocrinology, Department of Medicine, Washington University School of Medicine, St. Louis, Missouri 63110
- Mass Spectrometry Resource, Department of Obstetrics and Gynecology, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Sasanka Ramanadham
- Mass Spectrometry Resource, Division of Endocrinology, Department of Medicine, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Kelle Moley
- Mass Spectrometry Resource, Department of Obstetrics and Gynecology, Washington University School of Medicine, St. Louis, Missouri 63110
| | - John Turk
- Mass Spectrometry Resource, Division of Endocrinology, Department of Medicine, Washington University School of Medicine, St. Louis, Missouri 63110
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25
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Ramanadham S, Song H, Hsu FF, Zhang S, Crankshaw M, Grant GA, Newgard CB, Bao S, Ma Z, Turk J. Pancreatic islets and insulinoma cells express a novel isoform of group VIA phospholipase A2 (iPLA2 beta) that participates in glucose-stimulated insulin secretion and is not produced by alternate splicing of the iPLA2 beta transcript. Biochemistry 2004; 42:13929-40. [PMID: 14636061 PMCID: PMC3716001 DOI: 10.1021/bi034843p] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Many cells express a group VIA 84 kDa phospholipase A(2) (iPLA(2)beta) that is sensitive to inhibition by a bromoenol lactone (BEL) suicide substrate. Inhibition of iPLA(2)beta in pancreatic islets and insulinoma cells suppresses, and overexpression of iPLA(2)beta in INS-1 insulinoma cells amplifies, glucose-stimulated insulin secretion, suggesting that iPLA(2)beta participates in secretion. Western blotting analyses reveal that glucose-responsive 832/13 INS-1 cells express essentially no 84 kDa iPLA(2)beta-immunoreactive protein but predominantly express a previously unrecognized immunoreactive iPLA(2)beta protein in the 70 kDa region that is not generated by a mechanism of alternate splicing of the iPLA(2)beta transcript. To determine if the 70 kDa-immunoreactive protein is a short isoform of iPLA(2)beta, protein from the 70 kDa region was digested with trypsin and analyzed by mass spectrometry. Such analyses reveal several peptides with masses and amino acid sequences that exactly match iPLA(2)beta tryptic peptides. Peptide sequences identified in the 70 kDa tryptic digest include iPLA(2)beta residues 7-53, suggesting that the N-terminus is preserved. We also report here that the 832/13 INS-1 cells express iPLA(2)beta catalytic activity and that BEL inhibits secretagogue-stimulated insulin secretion from these cells but not the incorporation of arachidonic acid into membrane PC pools of these cells. These observations suggest that the catalytic iPLA(2)beta activity expressed in 832/13 INS-1 cells is attributable to a short isoform of iPLA(2)beta and that this isoform participates in insulin secretory but not in membrane phospholipid remodeling pathways. Further, the finding that pancreatic islets also express predominantly a 70 kDa iPLA(2)beta-immunoreactive protein suggests that a signal transduction role of iPLA(2)beta in the native beta-cell might be attributable to a 70 kDa isoform of iPLA(2)beta.
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Affiliation(s)
- Sasanka Ramanadham
- Mass Spectrometry Resource, Division of Endocrinology, Diabetes, and Metabolism, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
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26
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Ramanadham S, Song H, Bao S, Hsu FF, Zhang S, Ma Z, Jin C, Turk J. Islet complex lipids: involvement in the actions of group VIA calcium-independent phospholipase A(2) in beta-cells. Diabetes 2004; 53 Suppl 1:S179-85. [PMID: 14749285 PMCID: PMC3713612 DOI: 10.2337/diabetes.53.2007.s179] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
The beta-isoform of group VIA calcium-independent phospholipase A(2) (iPLA(2)beta) does not require calcium for activation, is stimulated by ATP, and is sensitive to inhibition by a bromoenol lactone suicide substrate. Several potential functions have been proposed for iPLA(2)beta. Our studies indicate that iPLA(2)beta is expressed in beta-cells and participates in glucose-stimulated insulin secretion but is not involved in membrane phospholipid remodeling. If iPLA(2)beta plays a signaling role in glucose-stimulated insulin secretion, then conditions that impair iPLA(2)beta functions might contribute to the diminished capacity of beta-cells to secrete insulin in response to glucose, which is a prominent characteristic of type 2 diabetes. Our recent studies suggest that iPLA(2)beta might also participate in beta-cell proliferation and apoptosis and that various phospholipid-derived mediators are involved in these processes. Detailed characterization of the iPLA(2)beta protein level reveals that beta-cells express multiple isoforms of the enzyme, and our studies involve the hypothesis that different isoforms have different functions.
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Affiliation(s)
- Sasanka Ramanadham
- Department of Medicine, Washington University School of Medicine, St Louis, Missouri 63110,
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27
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Cummings BS, McHowat J, Schnellmann RG. Role of an endoplasmic reticulum Ca2+-independent phospholipase A2 in cisplatin-induced renal cell apoptosis. J Pharmacol Exp Ther 2003; 308:921-8. [PMID: 14634037 DOI: 10.1124/jpet.103.060541] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
It has been demonstrated recently that rabbit renal proximal tubule cells (RPTC) express a novel Ca(2+)-independent phospholipase A(2) (iPLA(2)) whose activity localizes to the endoplasmic reticulum (ER-iPLA(2)) and is similar to group VIB PLA(2). In this study, the expression of group VIB PLA(2) was examined and the role of ER-iPLA(2) in cisplatin-induced apoptosis was determined. Cisplatin induced both time- and concentration-dependent RPTC apoptosis as determined by p53 nuclear localization, annexin V staining, caspase 3 activity, and chromatin condensation. Inhibition of ER-iPLA(2) with bromoenol lactone (5 microM) reduced cisplatin-induced annexin V binding 40%, chromatin condensation 55%, and caspase 3 activity 42%, but had no effect on p53 nuclear localization. Treatment of RPTC with the protein kinase C stimulator phorbol 12-myristate 13-acetate increased the activity of ER-iPLA(2) 2-fold and increased cisplatin-induced RPTC apoptosis. These studies demonstrate that group VIB PLA(2) is expressed in RPTC and suggest that RPTC ER-iPLA(2) is the rabbit homolog of group VIB PLA(2). These data also demonstrate that ER-iPLA(2) acts downstream of p53 and upstream of caspase 3 to mediate cisplatin-induced RPTC apoptosis. Finally, ER-iPLA(2) seems to be regulated by protein kinase C.
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Affiliation(s)
- Brian S Cummings
- Department of Pharmaceutical Sciences, Medical University of South Carolina, Charleston, SC 29425, USA
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28
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Sanchez T, Moreno JJ. Calcium-independent phospholipase A2 through arachidonic acid mobilization is involved in Caco-2 cell growth. J Cell Physiol 2002; 193:293-8. [PMID: 12384982 DOI: 10.1002/jcp.10162] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Several studies indicate that phospholipase A(2) (PLA(2)) expression and/or activation account for the high levels of arachidonic acid (AA) detected in cancer and, together with the elevated expression of cyclooxygenase-2, lead to cell proliferation and tumor formation. Using Caco-2 cells, a human colorectal carcinoma cell, we studied the role of high-molecular-weight PLA(2)s, cytosolic PLA(2) (cPLA(2)), and calcium-independent PLA(2) (iPLA(2)) in the AA cascade and in cell growth. Treatment with an antisense oligonucleotide against cPLA(2)alpha decreased [(3)H]AA release induced by ionophore A23187 or by a phorbol ester but did not affect the release of [(3)H]AA, [(3)H]thymidine incorporation, or Caco-2 growth induced by fetal calf serum (FCS). However, these parameters were significantly modified by iPLA(2) inhibitors and by an antisense oligonucleotide against iPLA(2)beta. Our results show that iPLA(2) was involved in AA release and the subsequent prostaglandin production induced by serum. Moreover, these data indicate that iPLA(2) may be involved in the signaling pathways involved in the control of Caco-2 proliferation.
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Affiliation(s)
- Teresa Sanchez
- Department of Physiology, Faculty of Pharmacy, Barcelona University, Barcelona, Spain
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29
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Cummings BS, McHowat J, Schnellmann RG. Role of an endoplasmic reticulum Ca(2+)-independent phospholipase A(2) in oxidant-induced renal cell death. Am J Physiol Renal Physiol 2002; 283:F492-8. [PMID: 12167600 DOI: 10.1152/ajprenal.00022.2002] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Phospholipase A(2) (PLA(2)) hydrolyzes the sn-2 ester bond in phospholipids, releasing a fatty acid and a lysophospholipid. Recently, a novel 85-kDa membrane-bound-Ca(2+)-independent PLA(2) (iPLA(2)) was identified in insect and bacterial cells transfected with candidate PLA(2) sequences. However, few data exist demonstrating a membrane-bound-iPLA(2) in mammalian cells, its subcellular localization, or its physiological role. Herein, we demonstrate the expression of an 85-kDa endoplasmic reticulum (ER)-Ca(2+)-iPLA(2) (ER-iPLA(2)) in rabbit renal proximal tubule cells (RPTC) that is plasmalogen selective and is inhibited by the specific Ca(2+)-iPLA(2) inhibitor bromoenol lactone (BEL). RPTC exposed to tert-butylhydroperoxide for 24 h exhibited 20% oncosis compared with 2% in controls. Inhibition of ER-iPLA(2) with BEL before tert-butylhydroperoxide exposure resulted in 50% oncosis. To determine whether this effect was common to oxidants, we tested the ability of BEL to potentiate oncosis induced by cumene hydroperoxide, menadione, duraquinone, cisplatin, and the nonoxidant antimycin A. All oxidants tested produced oncosis after 24 h, and prior inhibition of ER-iPLA(2) potentiated oncosis at least twofold. In contrast, inhibition of ER-iPLA(2) did not alter antimycin A-induced oncosis. Lipid peroxidation increased from 1.4- to 5.2-fold in RPTC treated with BEL before oxidant exposure, whereas no change was seen in antimycin A-treated RPTC. These results are the first to demonstrate the expression and subcellular localization of an ER-iPLA(2). These results also suggest that ER-iPLA(2) functions to protect against oxidant-induced lipid peroxidation and oncosis.
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Affiliation(s)
- Brian S Cummings
- Department of Pharmaceutical Sciences, Medical University of South Carolina, Charleston, South Carolina 29425, USA
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