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Yamane D, Zahoor MA, Mohamed YM, Azab W, Kato K, Tohya Y, Akashi H. Inhibition of sphingosine kinase by bovine viral diarrhea virus NS3 is crucial for efficient viral replication and cytopathogenesis. J Biol Chem 2009; 284:13648-13659. [PMID: 19293152 DOI: 10.1074/jbc.m807498200] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Sphingosine 1-phosphate (S1P) is a bioactive sphingolipid implicated in diverse cellular functions including survival, proliferation, tumorigenesis, inflammation, and immunity. Sphingosine kinase (SphK) contributes to these functions by converting sphingosine to S1P. We report here that the nonstructural protein NS3 from bovine viral diarrhea virus (BVDV), a close relative of hepatitis C virus (HCV), binds to and inhibits the catalytic activity of SphK1 independently of its serine protease activity, whereas HCV NS3 does not affect SphK1 activity. Uncleaved NS2-3 from BVDV was also found to interact with and inhibit SphK1. We suspect that inhibition of SphK1 activity by BVDV NS3 and NS2-3 may benefit viral replication, because SphK1 inhibition by small interfering RNA, chemical inhibitor, or overexpression of catalytically inactive SphK1 results in enhanced viral replication, although the mechanisms by which SphK1 inhibition leads to enhanced viral replication remain unknown. A role of SphK1 inhibition in viral cytopathogenesis is also suggested as overexpression of SphK1 significantly attenuates the induction of apoptosis in cells infected with cytopathogenic BVDV. These findings suggest that SphK is targeted by this virus to regulate its catalytic activity.
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Affiliation(s)
- Daisuke Yamane
- Department of Veterinary Microbiology, Graduate School of Agricultural and Life Sciences, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan
| | - Muhammad A Zahoor
- Department of Veterinary Microbiology, Graduate School of Agricultural and Life Sciences, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan
| | - Yassir M Mohamed
- Department of Veterinary Microbiology, Graduate School of Agricultural and Life Sciences, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan
| | - Walid Azab
- Department of Veterinary Microbiology, Graduate School of Agricultural and Life Sciences, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan
| | - Kentaro Kato
- Department of Veterinary Microbiology, Graduate School of Agricultural and Life Sciences, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan
| | - Yukinobu Tohya
- Department of Veterinary Microbiology, Graduate School of Agricultural and Life Sciences, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan
| | - Hiroomi Akashi
- Department of Veterinary Microbiology, Graduate School of Agricultural and Life Sciences, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan.
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52
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Machesky NJ, Zhang G, Raghavan B, Zimmerman P, Kelly SL, Merrill AH, Waldman WJ, Van Brocklyn JR, Trgovcich J. Human cytomegalovirus regulates bioactive sphingolipids. J Biol Chem 2008; 283:26148-60. [PMID: 18644793 DOI: 10.1074/jbc.m710181200] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Sphingolipids are present in membranes of all eukaryotic cells. Bioactive sphingolipids also function as signaling molecules that regulate cellular processes such as proliferation, migration, and apoptosis. Human cytomegalovirus (HCMV) exploits a variety of cellular signaling pathways to promote its own replication. However, whether HCMV modulates lipid signaling pathways is an essentially unexplored area of research in virus-host cell interactions. In this study, we examined the accumulation of the bioactive sphingolipids and the enzymes responsible for the biosynthesis and degradation of these lipids. HCMV infection results in increased accumulation and activity of sphingosine kinase (SphK), the enzyme that generates sphingosine 1-phosphate (S1P) and dihydrosphingosine 1-phosphate (dhS1P). We also utilized a mass spectrometry approach to generate a sphingolipidomic profile of HCMV-infected cells. We show that HCMV infection results in increased levels of dhS1P and ceramide at 24 h, suggesting an enhancement of de novo sphingolipid synthesis. Subsequently dihydrosphingosine and dhS1P decrease at 48 h consistent with attenuation of de novo sphingolipid synthesis. Finally, we present evidence that de novo sphingolipid synthesis and sphingosine kinase activity directly impact virus gene expression and virus growth. Together, these findings demonstrate that host cell sphingolipids are dynamically regulated upon infection with a herpes virus in a manner that impacts virus replication.
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Affiliation(s)
- Nicholas J Machesky
- Department of Pathology, The Ohio State University, Columbus, Ohio 43210, USA
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53
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Sphingosine-1-phosphate receptors: biology and therapeutic potential in kidney disease. Kidney Int 2008; 73:1220-30. [PMID: 18322542 DOI: 10.1038/ki.2008.34] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
The major sphingolipid metabolite, sphingosine-1-phosphate (S1P), has important biological functions. S1P is the ligand for a family of five G-protein-coupled receptors with distinct signaling pathways that regulate angiogenesis, vascular maturation, immunity, chemotaxis, and other important biological pathways. Recently, clinical trials have targeted S1P receptors (S1PRs) for autoimmune diseases and transplantation and have generated considerable interest in developing additional, more selective compounds. This review summarizes current knowledge on the biology of S1P and S1PRs that forms the basis for future drug development and the treatment of kidney disease.
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Méndez-Samperio P, Pérez A, Trejo A. Sphingosine kinase, phosphatidylinositol 3-kinase, Akt, NF-κB, and p300 are required for CCL5 production in Mycobacterium bovis Bacillus Calmette–Guérin (BCG)-infected epithelial cells. Cell Immunol 2007; 249:94-100. [DOI: 10.1016/j.cellimm.2007.11.008] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2007] [Revised: 11/27/2007] [Accepted: 11/28/2007] [Indexed: 01/23/2023]
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55
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Monick MM, Powers LS, Hassan I, Groskreutz D, Yarovinsky TO, Barrett CW, Castilow EM, Tifrea D, Varga SM, Hunninghake GW. Respiratory syncytial virus synergizes with Th2 cytokines to induce optimal levels of TARC/CCL17. THE JOURNAL OF IMMUNOLOGY 2007; 179:1648-58. [PMID: 17641031 PMCID: PMC4060898 DOI: 10.4049/jimmunol.179.3.1648] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Respiratory syncytial virus (RSV) is a ubiquitous virus that preferentially infects airway epithelial cells, causing asthma exacerbations and severe disease in immunocompromised hosts. Acute RSV infection induces inflammation in the lung. Thymus- and activation-regulated chemokine (TARC) recruits Th2 cells to sites of inflammation. We found that acute RSV infection of BALB/c mice increased TARC production in the lung. Immunization of BALB/c mice with individual RSV proteins can lead to the development of Th1- or Th2-biased T cell responses in the lung after RSV infection. We primed animals with a recombinant vaccinia virus expressing either the RSV fusion (F) protein or the RSV attachment (G) protein, inducing Th1- and Th2-biased pulmonary memory T cell responses, respectively. After RSV infection, TARC production significantly increased in the vaccinia virus G-primed animals only. These data suggest a positive feedback loop for TARC production between RSV infection and Th2 cytokines. RSV-infected lung epithelial cells cultured with IL-4 or IL-13 demonstrated a marked increase in the production of TARC. The synergistic effect of RSV and IL-4/IL-13 on TARC production reflected differential induction of NF kappa B and STAT6 by the two stimuli (both are in the TARC promoter). These findings demonstrate that RSV induces a chemokine TARC that has the potential to recruit Th2 cells to the lung.
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Affiliation(s)
- Martha M Monick
- Department of Internal Medicine, University of Iowa Carver College of Medicine and Veterans Administration Medical Center, Iowa City, IA 52242, USA.
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56
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Kim HJ, Lee Y, Chang EJ, Kim HM, Hong SP, Lee ZH, Ryu J, Kim HH. Suppression of osteoclastogenesis by N,N-dimethyl-D-erythro-sphingosine: a sphingosine kinase inhibition-independent action. Mol Pharmacol 2007; 72:418-28. [PMID: 17504945 DOI: 10.1124/mol.107.034173] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
N,N-Dimethyl-D-erythro-sphingosine (DMS) competitively inhibits sphingosine kinase (SPHK) and has been widely used to assess the role of SPHK during cellular events, including motility, proliferation, and differentiation. In the present study, the effect of DMS on the differentiation of bone marrow macrophages (BMMs) to osteoclasts was investigated. When the osteoclast precursor cells were treated with DMS, the receptor activator of nuclear factor kappaB ligand (RANKL)-induced osteoclastogenesis was completely blocked. We were surprised to find, however, that knock-down of SPHK by small interfering RNA (siRNA) in BMMs did not reduce osteoclastogenesis. Furthermore, both overexpression of SPHK and exogenous addition of sphingosine-1-phosphate, the product of SPHK activity, failed to overcome the antiosteoclastogenic effect of DMS. These results suggest that DMS inhibited osteoclastogenesis independently of SPHK. Subsequent characterization of the DMS-mediated suppression of osteoclastogenesis revealed that DMS did not affect RANKL-induced activation of JNK, p38, NF-kappaB, and Ca2+ oscillation. On the other hand, DMS strongly inhibited two separate signaling pathways, the RANKL-induced activation of ERK and Akt, which eventually converged on the transcription factors c-Fos and NFATc1. There was significant increase in the osteoclast formation in the presence of DMS when BMMs were overexpressed with c-Fos, suggesting that c-Fos was a critical downstream target of DMS for the inhibition of osteoclastogenesis. Taken together, our data demonstrate that DMS has an antiosteoclastogenic function independently of its SPHK inhibitory activity. Considering previously reported anticancer properties of DMS, our study may also propose that DMS is an ideal drug candidate for bone metastases, for which osteoclastic bone-resorption is crucial.
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Affiliation(s)
- Hyung Joon Kim
- Department of Cell and Developmental Biology, Seoul National University, 28 Yeongon-Dong, Chongno-Gu, Seoul 110-749, Korea
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57
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Francy JM, Nag A, Conroy EJ, Hengst JA, Yun JK. Sphingosine kinase 1 expression is regulated by signaling through PI3K, AKT2, and mTOR in human coronary artery smooth muscle cells. ACTA ACUST UNITED AC 2007; 1769:253-65. [PMID: 17482291 DOI: 10.1016/j.bbaexp.2007.03.005] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2007] [Revised: 03/23/2007] [Accepted: 03/23/2007] [Indexed: 10/23/2022]
Abstract
Sphingosine kinase 1 (SphK1) is a lipid kinase implicated in mitogenic signaling pathways in vascular smooth muscle cells. We demonstrate that human coronary artery smooth muscle (HCASM) cells require SphK1 for growth and that SphK1 mRNA and protein levels are elevated in PDGF stimulated HCASM cells. To determine the mechanism of PDGF-induced SphK1 expression, we used pharmacological inhibitors of the PI3K/AKT/mTOR signaling pathway. Wortmannin, SH-5, and rapamycin significantly blocked PDGF-stimulated induction of SphK1 mRNA and protein expression, indicating a regulatory role of the PI3K/AKT/mTOR pathway in SphK1 expression. To determine which isoform of AKT regulates SphK1 mRNA and protein levels, siRNAs specific for AKT1, AKT2, and AKT3 were used. We show that AKT2 siRNA significantly blocked PDGF-stimulated increases in SphK1 mRNA and protein expression levels as well as SphK1 enzymatic activity levels. In contrast, AKT1 or AKT3 siRNA did not have an effect. Together, these results demonstrate that the PI3K/AKT/mTOR signaling pathway is involved in regulation of SphK1, with AKT2 playing a key role in PDGF-induced SphK1 expression in HCASM cells.
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Affiliation(s)
- Jacquelyn M Francy
- Department of Pharmacology, Jake Gittlen Cancer Research Foundation, H059, The Pennsylvania State University College of Medicine, Hershey, PA 17033-0850, USA
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58
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Bitko V, Shulyayeva O, Mazumder B, Musiyenko A, Ramaswamy M, Look DC, Barik S. Nonstructural proteins of respiratory syncytial virus suppress premature apoptosis by an NF-kappaB-dependent, interferon-independent mechanism and facilitate virus growth. J Virol 2006; 81:1786-95. [PMID: 17151097 PMCID: PMC1797585 DOI: 10.1128/jvi.01420-06] [Citation(s) in RCA: 128] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
The two nonstructural (NS) proteins NS1 and NS2 of respiratory syncytial virus (RSV) are abundantly expressed in the infected cell but are not packaged in mature progeny virions. We found that both proteins were expressed early in infection, whereas the infected cells underwent apoptosis much later. Coincident with NS protein expression, a number of cellular antiapoptotic factors were expressed or activated at early stages, which included NF-kappaB and phosphorylated forms of protein kinases AKT, phosphoinositide-dependent protein kinase, and glycogen synthase kinase. Using specific short interfering RNAs (siRNAs), we achieved significant knockdown of one or both NS proteins in the infected cell, which resulted in abrogation of the antiapoptotic functions and led to early apoptosis. NS-dependent suppression of apoptosis was observed in Vero cells that are naturally devoid of type I interferons (IFN). The siRNA-based results were confirmed by the use of NS-deleted RSV mutants. Early activation of epidermal growth factor receptor (EGFR) in the RSV-infected cell did not require NS proteins. Premature apoptosis triggered by the loss of NS or by apoptosis-promoting drugs caused a severe reduction of RSV growth. Finally, recombinantly expressed NS1 and NS2, individually and together, reduced apoptosis by tumor necrosis factor alpha, suggesting an intrinsic antiapoptotic property of both. We conclude that the early-expressed nonstructural proteins of RSV boost viral replication by delaying the apoptosis of the infected cell via a novel IFN- and EGFR-independent pathway.
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Affiliation(s)
- Vira Bitko
- Department of Biochemistry and Molecular Biology, University of South Alabama, College of Medicine, 307 University Blvd., Mobile, AL 36688-0002, USA
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59
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Yadav M, Clark L, Schorey JS. Macrophage’s Proinflammatory Response to a Mycobacterial Infection Is Dependent on Sphingosine Kinase-Mediated Activation of Phosphatidylinositol Phospholipase C, Protein Kinase C, ERK1/2, and Phosphatidylinositol 3-Kinase. THE JOURNAL OF IMMUNOLOGY 2006; 176:5494-503. [PMID: 16622018 DOI: 10.4049/jimmunol.176.9.5494] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Previous studies have shown that the ability of Mycobacterium tuberculosis to block a Ca(2+) flux is an important step in its capacity to halt phagosome maturation. This affect on Ca(2+) release results from M. tuberculosis inhibition of sphingosine kinase (SPK) activity. However, these studies did not address the potential role of SPK and Ca(2+) in other aspects of macrophage activation including production of proinflammatory mediators. We previously showed that nonpathogenic Mycobacterium smegmatis and to a lesser extent pathogenic Mycobacterium avium, activate Ca(2+)-dependent calmodulin/calmodulin kinase and MAPK pathways in murine macrophages leading to TNF-alpha production. However, whether SPK functions in promoting MAPK activation upon mycobacterial infection was not defined in these studies. In the present work we found that SPK is required for ERK1/2 activation in murine macrophages infected with either M. avium or M. smegmatis. Phosphoinositide-specific phospholipase C (PI-PLC) and conventional protein kinase C (cPKC) were also important for ERK1/2 activation. Moreover, there was increased activation of cPKC and PI3K in macrophages infected with M. smegmatis compared with M. avium. This cPKC and PI3K activation was dependent on SPK and PI-PLC. Finally, in macrophages infected with M. smegmatis compared with M. avium, we observed enhanced secretion of TNF-alpha, IL-6, RANTES, and G-CSF and found production of these inflammatory mediators to be dependent on SPK, PI-PLC, cPKC, and PI3K. These studies are the first to show that the macrophage proinflammatory response following a mycobacterial infection is regulated by SPK/PI-PLC/PKC activation of ERK1/2 and PI3K pathways.
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Affiliation(s)
- Mahesh Yadav
- Department of Biological Sciences, Center for Tropical Disease Research and Training, University of Notre Dame, Notre Dame, IN 46556, USA
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60
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Berdyshev EV, Gorshkova IA, Usatyuk P, Zhao Y, Saatian B, Hubbard W, Natarajan V. De novo biosynthesis of dihydrosphingosine-1-phosphate by sphingosine kinase 1 in mammalian cells. Cell Signal 2006; 18:1779-92. [PMID: 16529909 DOI: 10.1016/j.cellsig.2006.01.018] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2005] [Revised: 01/25/2006] [Accepted: 01/26/2006] [Indexed: 10/24/2022]
Abstract
Sphingosine kinase 1 (SK1) is one of the two known kinases, which generates sphingosine-1-phosphate (S1P), a potent endogenous lipid mediator involved in cell survival, proliferation, and cell-cell interactions. Activation of SK1 and intracellular generation of S1P were suggested to be part of the growth and survival factor-induced signaling, and overexpression of SK1 provoked cell tumorigenic transformation. Using a highly selective and sensitive LC-MS/MS approach, here we show that SK1 overexpression, but not SK2, in different primary cells and cultured cell lines results in predominant upregulation of the synthesis of dihydrosphingosine-1-phosphate (DHS1P) compared to S1P. Stable isotope pulse-labeling experiments in conjunction with LC-MS/MS quantitation of different sphingolipids demonstrated strong interference of overexpressed SK1 with the de novo sphingolipid biosynthesis by deviating metabolic flow of newly formed sphingoid bases from ceramide formation toward the synthesis of DHS1P. On the contrary, S1P biosynthesis was not directly linked to the de novo sphingoid bases transformations and was dependent on catabolic generation of sphingosine from complex sphingolipids. As a result of SK1 overexpression, migration and Ca2+-response of human pulmonary artery endothelial cells (HPAEC) to stimulation with external S1P, but not thrombin, was strongly impaired. In contrast, selective increase in intracellular content of DHS1P or S1P through the uptake and phosphorylation of corresponding sphingoid bases had no effect on S1P-induced signaling or facilitation of wound healing. Furthermore, infection of human bronchial epithelial cells (HBEpC) with RSV A-2 virus increased SK1-mediated synthesis of DHS1P and S1P, whereas TNF-alpha enhanced only S1P production in HPAEC. These findings uncover a new functional role for SK1, which can control survival/death (DHS1P-S1P/ceramides) balance by targeting sphingolipid de novo biosynthesis and selectively generating DHS1P at a metabolic step preceding ceramide formation.
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Affiliation(s)
- Evgeny V Berdyshev
- The University of Chicago, Biological Sciences Division, Department of Medicine, 929 E. 57th Street, Room W403M, Chicago, IL 60637, USA.
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The Role of Phosphoinositide 3-Kinase-Akt Signaling in Virus Infection. APOPTOSIS, CELL SIGNALING, AND HUMAN DISEASES 2006. [PMCID: PMC7120950 DOI: 10.1007/978-1-59745-199-4_3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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62
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Rixon HWM, Brown G, Murray JT, Sugrue RJ. The respiratory syncytial virus small hydrophobic protein is phosphorylated via a mitogen-activated protein kinase p38-dependent tyrosine kinase activity during virus infection. J Gen Virol 2005; 86:375-384. [PMID: 15659757 DOI: 10.1099/vir.0.80563-0] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The phosphorylation status of the small hydrophobic (SH) protein of respiratory syncytial virus (RSV) was examined in virus-infected Vero cells. The SH protein was isolated from [35S]methionine- and [33P]orthophosphate-labelled RSV-infected cells and analysed by SDS-PAGE. In each case, a protein product of the expected size for the SH protein was observed. Phosphoamino acid analysis and reactivity with the phosphotyrosine specific antibody PY20 showed that the SH protein was modified by tyrosine phosphorylation. The role of tyrosine kinase activity in SH protein phosphorylation was confirmed by the use of genistein, a broad-spectrum tyrosine kinase inhibitor, to inhibit SH protein phosphorylation. Further analysis showed that the different glycosylated forms of the SH protein were phosphorylated, as was the oligomeric form of the protein. Phosphorylation of the SH protein was specifically inhibited by the mitogen-activated protein kinase (MAPK) p38 inhibitor SB203580, suggesting that SH protein phosphorylation occurs via a MAPK p38-dependent pathway. Analysis of virus-infected cells using fluorescence microscopy showed that, although the SH protein was distributed throughout the cytoplasm, it appeared to accumulate, at low levels, in the endoplasmic reticulum/Golgi complex, confirming recent observations. However, in the presence of SB203580, an increased accumulation of the SH protein in the Golgi complex was observed, although other virus structures, such as virus filaments and inclusion bodies, remained largely unaffected. These results showed that during RSV infection, the SH protein is modified by an MAPK p38-dependent tyrosine kinase activity and that this modification influences its cellular distribution.
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Affiliation(s)
- H W McL Rixon
- MRC Virology Unit, Institute of Virology, Church Street, Glasgow G11 5JR, UK
| | - G Brown
- MRC Virology Unit, Institute of Virology, Church Street, Glasgow G11 5JR, UK
| | - J T Murray
- MRC Protein Phosphorylation Unit, MSI/WTB Complex, University of Dundee, Dundee DD1 5EH, UK
| | - R J Sugrue
- MRC Virology Unit, Institute of Virology, Church Street, Glasgow G11 5JR, UK
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Truong SV, Monick MM, Yarovinsky TO, Powers LS, Nyunoya T, Hunninghake GW. Extracellular Signal–Regulated Kinase Activation Delays Hyperoxia-Induced Epithelial Cell Death in Conditions of Akt Downregulation. Am J Respir Cell Mol Biol 2004; 31:611-8. [PMID: 15308507 DOI: 10.1165/rcmb.2004-0141oc] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Hyperoxia (fraction of inspired oxygen = 95%) induces death of lung epithelial cells. The duration of cell survival in the setting of hyperoxia depends on hyperoxia-induced activation of intracellular survival pathways. Two survival pathways with known effects on lung epithelial cells are the propidium iodide 3-kinase/Akt and extracellular signal-regulated kinase (ERK)/mitogen-activated protein (MAP) kinase pathways. We investigated the effect of hyperoxia on activity of both the Akt and ERK pathways in the A549 lung epithelial cell line. Hyperoxia-exposed cells show progressive loss of Akt activation and total Akt protein. Hyperoxia decreases Akt mRNA, consistent with the loss of total Akt. In addition, hyperoxia induces ERK activation. Inhibition of ERK with the MAP kinase kinase 1/2 inhibitor, U0126, shortens the survival time of cells in hyperoxia, suggesting that increased ERK activity partially compensates for the hyperoxia-induced Akt downregulation. Our findings show, for the first time, that hyperoxia has divergent effects on two survival pathways (Akt and ERK), and that ERK activity compensates for the loss of the Akt survival effects, delaying the death of hyperoxia-exposed lung epithelial cells.
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Affiliation(s)
- Son V Truong
- Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, IA 52242, USA
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