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Moradbeigi P, Hosseini S, Salehi M, Mogheiseh A. Methyl β-Cyclodextrin-sperm-mediated gene editing (MBCD-SMGE): a simple and efficient method for targeted mutant mouse production. Biol Proced Online 2024; 26:3. [PMID: 38279106 PMCID: PMC10811837 DOI: 10.1186/s12575-024-00230-9] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2023] [Accepted: 01/16/2024] [Indexed: 01/28/2024] Open
Abstract
BACKGROUND Generating targeted mutant mice is a crucial technology in biomedical research. This study focuses on optimizing the CRISPR/Cas9 system uptake into sperm cells using the methyl β-cyclodextrin-sperm-mediated gene transfer (MBCD-SMGT) technique to generate targeted mutant blastocysts and mice efficiently. Additionally, the present study elucidates the roles of cholesterol and reactive oxygen species (ROS) in the exogenous DNA uptake by sperm. RESULTS In this study, B6D2F1 mouse sperm were incubated in the c-TYH medium with different concentrations of MBCD (0, 0.75, 1, and 2 mM) in the presence of 20 ng/µl pCAG-eCas9-GFP-U6-gRNA (pgRNA-Cas9) for 30 min. Functional parameters, extracellular ROS, and the copy numbers of internalized plasmid per sperm cell were evaluated. Subsequently, in vitro fertilization (IVF) was performed and fertilization rate, early embryonic development, and transfection rate were assessed. Finally, our study investigated the potential of the MBCD-SMGT technique in combination with the CRISPR-Cas9 system, referred to as MBCD-SMGE (MBCD-sperm-mediated gene editing), for generating targeted mutant blastocysts and mice. Results indicated that cholesterol removal from the sperm membrane using MBCD resulted in a premature acrosomal reaction, an increase in extracellular ROS levels, and a dose-dependent influence on the copy numbers of the internalized plasmids per sperm cell. Moreover, the MBCD-SMGT technique led to a larger population of transfected motile sperm and a higher production rate of GFP-positive blastocysts. Additionally, the current study validated the targeted indel in blastocyst and mouse derived from MBCD-SMGE technique. CONCLUSION Overall, this study highlights the significant potential of the MBCD-SMGE technique for generating targeted mutant mice. It holds enormous promise for modeling human diseases and improving desirable traits in animals.
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Affiliation(s)
- Parisa Moradbeigi
- Department of Clinical Sciences, School of Veterinary Medicine, Shiraz University, P. O. Box: 7144169155, Shiraz, Iran
| | - Sara Hosseini
- Cellular and Molecular Biology Research Center, Shahid Beheshti University of Medical Sciences, P.O. Box: 193954717, Tehran, Iran
- Hasti Noavaran Gene Royan Co, Tehran, Iran
| | - Mohammad Salehi
- Cellular and Molecular Biology Research Center, Shahid Beheshti University of Medical Sciences, P.O. Box: 193954717, Tehran, Iran.
- Department of Biotechnology, School of Advanced Technologies in Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
| | - Asghar Mogheiseh
- Department of Clinical Sciences, School of Veterinary Medicine, Shiraz University, P. O. Box: 7144169155, Shiraz, Iran
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Maharjan S, Kirk RS, Lawton SP, Walker AJ. Human growth factor-mediated signalling through lipid rafts regulates stem cell proliferation, development and survival of Schistosoma mansoni. Open Biol 2024; 14:230262. [PMID: 38195062 PMCID: PMC10776228 DOI: 10.1098/rsob.230262] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2023] [Accepted: 11/16/2023] [Indexed: 01/11/2024] Open
Abstract
Although the mechanisms by which schistosomes grow and develop in humans are poorly defined, their unique outer tegument layer, which interfaces with host blood, is considered vital to homeostasis of the parasite. Here, we investigated the importance of tegument lipid rafts to the biology of Schistosoma mansoni in the context of host-parasite interactions. We demonstrate the temporal clustering of lipid rafts in response to human epidermal growth factor (EGF) during early somule development, concomitant with the localization of anteriorly orientated EGF receptors (EGFRs) and insulin receptors, mapped using fluorescent EGF/insulin ligand. Methyl-β-cyclodextrin (MβCD)-mediated depletion of cholesterol from lipid rafts abrogated the EGFR/IR binding at the parasite surface and led to modulation of protein kinase C, extracellular signal-regulated kinase, p38 mitogen-activated protein kinase and Akt signalling pathways within the parasite. Furthermore, MβCD-mediated lipid raft disruption, and blockade of EGFRs using canertinib, profoundly reduced somule motility and survival, and attenuated stem cell proliferation and somule growth and development particularly to the fast-growing liver stage. These findings provide a novel paradigm for schistosome development and vitality in the host, driven through host-parasite interactions at the tegument, that might be exploitable for developing innovative therapeutic approaches to combat human schistosomiasis.
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Affiliation(s)
- Shradha Maharjan
- Molecular Parasitology Laboratory, School of Life Sciences, Pharmacy and Chemistry, Kingston University, Penrhyn Road, Kingston upon Thames KT1 2EE, UK
| | - Ruth S. Kirk
- Molecular Parasitology Laboratory, School of Life Sciences, Pharmacy and Chemistry, Kingston University, Penrhyn Road, Kingston upon Thames KT1 2EE, UK
| | - Scott P. Lawton
- Centre for Epidemiology and Planetary Health, SRUC School of Veterinary Medicine, Scotland's Rural College, West Mains Road, Edinburgh EH9 3JG, UK
| | - Anthony J. Walker
- Molecular Parasitology Laboratory, School of Life Sciences, Pharmacy and Chemistry, Kingston University, Penrhyn Road, Kingston upon Thames KT1 2EE, UK
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Chen X, Wu Q, Depeille P, Chen P, Thornton S, Kalirai H, Coupland SE, Roose JP, Bastian BC. RasGRP3 Mediates MAPK Pathway Activation in GNAQ Mutant Uveal Melanoma. Cancer Cell 2017; 31:685-696.e6. [PMID: 28486107 PMCID: PMC5499527 DOI: 10.1016/j.ccell.2017.04.002] [Citation(s) in RCA: 100] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/21/2015] [Revised: 12/07/2016] [Accepted: 04/05/2017] [Indexed: 01/14/2023]
Abstract
Constitutive activation of Gαq signaling by mutations in GNAQ or GNA11 occurs in over 80% of uveal melanomas (UMs) and activates MAPK. Protein kinase C (PKC) has been implicated as a link, but the mechanistic details remained unclear. We identified PKC δ and ɛ as required and sufficient to activate MAPK in GNAQ mutant melanomas. MAPK activation depends on Ras and is caused by RasGRP3, which is significantly and selectively overexpressed in response to GNAQ/11 mutation in UM. RasGRP3 activation occurs via PKC δ- and ɛ-dependent phosphorylation and PKC-independent, DAG-mediated membrane recruitment, possibly explaining the limited effect of PKC inhibitors to durably suppress MAPK in UM. The findings nominate RasGRP3 as a therapeutic target for cancers driven by oncogenic GNAQ/11.
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Affiliation(s)
- Xu Chen
- Departments of Dermatology and Pathology, Helen Diller Family Comprehensive Cancer Center, University of California, San Francisco, San Francisco, CA 94143, USA.
| | - Qiuxia Wu
- Departments of Dermatology and Pathology, Helen Diller Family Comprehensive Cancer Center, University of California, San Francisco, San Francisco, CA 94143, USA
| | - Philippe Depeille
- Department of Anatomy, University of California, San Francisco, San Francisco, CA 94143, USA
| | - Peirong Chen
- Departments of Dermatology and Pathology, Helen Diller Family Comprehensive Cancer Center, University of California, San Francisco, San Francisco, CA 94143, USA
| | - Sophie Thornton
- Department of Molecular and Clinical Cancer Medicine, Institute of Translational Mewdicine, University of Liverpool, Liverpool L7 8TX, UK
| | - Helen Kalirai
- Department of Molecular and Clinical Cancer Medicine, Institute of Translational Mewdicine, University of Liverpool, Liverpool L7 8TX, UK
| | - Sarah E Coupland
- Department of Molecular and Clinical Cancer Medicine, Institute of Translational Mewdicine, University of Liverpool, Liverpool L7 8TX, UK
| | - Jeroen P Roose
- Department of Anatomy, University of California, San Francisco, San Francisco, CA 94143, USA
| | - Boris C Bastian
- Departments of Dermatology and Pathology, Helen Diller Family Comprehensive Cancer Center, University of California, San Francisco, San Francisco, CA 94143, USA.
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4
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Che DL, Duan L, Zhang K, Cui B. The Dual Characteristics of Light-Induced Cryptochrome 2, Homo-oligomerization and Heterodimerization, for Optogenetic Manipulation in Mammalian Cells. ACS Synth Biol 2015; 4:1124-35. [PMID: 25985220 DOI: 10.1021/acssynbio.5b00048] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The photoreceptor cryptochrome 2 (CRY2) has become a powerful optogenetic tool that allows light-inducible manipulation of various signaling pathways and cellular processes in mammalian cells with high spatiotemporal precision and ease of application. However, it has also been shown that the behavior of CRY2 under blue light is complex, as the photoexcited CRY2 can both undergo homo-oligomerization and heterodimerization by binding to its dimerization partner CIB1. To better understand the light-induced CRY2 activities in mammalian cells, this article systematically characterizes CRY2 homo-oligomerization in different cellular compartments, as well as how CRY2 homo-oligomerization and heterodimerization activities affect each other. Quantitative analysis reveals that membrane-bound CRY2 has drastically enhanced oligomerization activity compared to that of its cytoplasmic form. While CRY2 homo-oligomerization and CRY2-CIB1 heterodimerization could happen concomitantly, the presence of certain CIB1 fusion proteins can suppress CRY2 homo-oligomerization. However, the homo-oligomerization of cytoplasmic CRY2 can be significantly intensified by its recruitment to the membrane via interaction with the membrane-bound CIB1. These results contribute to the understanding of the light-inducible CRY2-CRY2 and CRY2-CIB1 interaction systems and can be used as a guide to establish new strategies utilizing the dual optogenetic characteristics of CRY2 to probe cellular processes.
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Affiliation(s)
- Daphne L. Che
- Department of Chemistry, Stanford University, Stanford, California 94305, United States
| | - Liting Duan
- Department of Chemistry, Stanford University, Stanford, California 94305, United States
| | - Kai Zhang
- Department of Chemistry, Stanford University, Stanford, California 94305, United States
| | - Bianxiao Cui
- Department of Chemistry, Stanford University, Stanford, California 94305, United States
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5
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Heo W, Kim SM, Eo SK, Rhim BY, Kim K. FSL-1, a Toll-like Receptor 2/6 Agonist, Induces Expression of Interleukin-1α in the Presence of 27-hydroxycholesterol. THE KOREAN JOURNAL OF PHYSIOLOGY & PHARMACOLOGY : OFFICIAL JOURNAL OF THE KOREAN PHYSIOLOGICAL SOCIETY AND THE KOREAN SOCIETY OF PHARMACOLOGY 2014; 18:475-80. [PMID: 25598661 PMCID: PMC4296036 DOI: 10.4196/kjpp.2014.18.6.475] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/13/2014] [Revised: 08/04/2014] [Accepted: 08/25/2014] [Indexed: 11/29/2022]
Abstract
We investigated the question of whether cholesterol catabolite can influence expression of inflammatory cytokines via Toll-like receptors (TLR) in monocytic cells. Treatment of THP-1 monocytic cells with 27-hydroxycholesterol (27OHChol) resulted in induction of gene transcription of TLR6 and elevated level of cell surface TLR6. Addition of FSL-1, a TLR6 agonist, to 27OHChol-treated cells resulted in transcription of the IL-1α gene and enhanced secretion of the corresponding gene product. However, cholesterol did not affect TLR6 expression, and addition of FSL-1 to cholesterol-treated cells did not induce expression of IL-1α. Using pharmacological inhibitors, we investigated molecular mechanisms underlying the expression of TLR6 and IL-1α. Treatment with Akt inhibitor IV or U0126 resulted in significantly attenuated expression of TLR6 and IL-1α induced by 27OHChol and 27OHChol plus FSL-1, respectively. In addition, treatment with LY294002, SB202190, or SP600125 resulted in significantly attenuated secretion of IL-1α. These results indicate that 27OHChol can induce inflammation by augmentation of TLR6-mediated production of IL-1α in monocytic cells via multiple signaling pathways.
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Affiliation(s)
- Weon Heo
- Department of Pharmacology, Pusan National University School of Medicine, Yangsan, 626-870, Korea
| | - Sun-Mi Kim
- Department of Pharmacology, Pusan National University School of Medicine, Yangsan, 626-870, Korea
| | - Seong-Kug Eo
- College of Veterinary Medicine and Bio-Safety Research Institute, Chonbuk National University, Iksan, 570-752, Korea
| | - Byung-Yong Rhim
- Department of Pharmacology, Pusan National University School of Medicine, Yangsan, 626-870, Korea
| | - Koanhoi Kim
- Department of Pharmacology, Pusan National University School of Medicine, Yangsan, 626-870, Korea
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6
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Guéguinou M, Gambade A, Félix R, Chantôme A, Fourbon Y, Bougnoux P, Weber G, Potier-Cartereau M, Vandier C. Lipid rafts, KCa/ClCa/Ca2+ channel complexes and EGFR signaling: Novel targets to reduce tumor development by lipids? BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2014; 1848:2603-20. [PMID: 25450343 DOI: 10.1016/j.bbamem.2014.10.036] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/30/2014] [Revised: 10/15/2014] [Accepted: 10/22/2014] [Indexed: 12/29/2022]
Abstract
Membrane lipid rafts are distinct plasma membrane nanodomains that are enriched with cholesterol, sphingolipids and gangliosides, with occasional presence of saturated fatty acids and phospholipids containing saturated acyl chains. It is well known that they organize receptors (such as Epithelial Growth Factor Receptor), ion channels and their downstream acting molecules to regulate intracellular signaling pathways. Among them are Ca2+ signaling pathways, which are modified in tumor cells and inhibited upon membrane raft disruption. In addition to protein components, lipids from rafts also contribute to the organization and function of Ca2+ signaling microdomains. This article aims to focus on the lipid raft KCa/ClCa/Ca2+ channel complexes that regulate Ca2+ and EGFR signaling in cancer cells, and discusses the potential modification of these complexes by lipids as a novel therapeutic approach in tumor development. This article is part of a Special Issue entitled: Membrane channels and transporters in cancers.
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Affiliation(s)
- Maxime Guéguinou
- Inserm, UMR1069, Nutrition, Croissance et Cancer, Tours F-37032, France; Université François Rabelais, Tours F-37032, France
| | - Audrey Gambade
- Inserm, UMR1069, Nutrition, Croissance et Cancer, Tours F-37032, France; Université François Rabelais, Tours F-37032, France
| | - Romain Félix
- Inserm, UMR1069, Nutrition, Croissance et Cancer, Tours F-37032, France; Université François Rabelais, Tours F-37032, France
| | - Aurélie Chantôme
- Inserm, UMR1069, Nutrition, Croissance et Cancer, Tours F-37032, France; Université François Rabelais, Tours F-37032, France
| | - Yann Fourbon
- Inserm, UMR1069, Nutrition, Croissance et Cancer, Tours F-37032, France; Université François Rabelais, Tours F-37032, France
| | - Philippe Bougnoux
- Inserm, UMR1069, Nutrition, Croissance et Cancer, Tours F-37032, France; Université François Rabelais, Tours F-37032, France; Centre HS Kaplan, CHRU Tours, Tours F-37032, France
| | - Günther Weber
- Inserm, UMR1069, Nutrition, Croissance et Cancer, Tours F-37032, France; Université François Rabelais, Tours F-37032, France
| | - Marie Potier-Cartereau
- Inserm, UMR1069, Nutrition, Croissance et Cancer, Tours F-37032, France; Université François Rabelais, Tours F-37032, France
| | - Christophe Vandier
- Inserm, UMR1069, Nutrition, Croissance et Cancer, Tours F-37032, France; Université François Rabelais, Tours F-37032, France.
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7
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Zhang K, Duan L, Ong Q, Lin Z, Varman PM, Sung K, Cui B. Light-mediated kinetic control reveals the temporal effect of the Raf/MEK/ERK pathway in PC12 cell neurite outgrowth. PLoS One 2014; 9:e92917. [PMID: 24667437 PMCID: PMC3965503 DOI: 10.1371/journal.pone.0092917] [Citation(s) in RCA: 79] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/25/2013] [Accepted: 02/26/2014] [Indexed: 11/29/2022] Open
Abstract
It has been proposed that differential activation kinetics allows cells to use a common set of signaling pathways to specify distinct cellular outcomes. For example, nerve growth factor (NGF) and epidermal growth factor (EGF) induce different activation kinetics of the Raf/MEK/ERK signaling pathway and result in differentiation and proliferation, respectively. However, a direct and quantitative linkage between the temporal profile of Raf/MEK/ERK activation and the cellular outputs has not been established due to a lack of means to precisely perturb its signaling kinetics. Here, we construct a light-gated protein-protein interaction system to regulate the activation pattern of the Raf/MEK/ERK signaling pathway. Light-induced activation of the Raf/MEK/ERK cascade leads to significant neurite outgrowth in rat PC12 pheochromocytoma cell lines in the absence of growth factors. Compared with NGF stimulation, light stimulation induces longer but fewer neurites. Intermittent on/off illumination reveals that cells achieve maximum neurite outgrowth if the off-time duration per cycle is shorter than 45 min. Overall, light-mediated kinetic control enables precise dissection of the temporal dimension within the intracellular signal transduction network.
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Affiliation(s)
- Kai Zhang
- Department of Chemistry, Stanford University, Stanford, California, United States of America
| | - Liting Duan
- Department of Chemistry, Stanford University, Stanford, California, United States of America
| | - Qunxiang Ong
- Department of Chemistry, Stanford University, Stanford, California, United States of America
| | - Ziliang Lin
- Department of Applied Physics, Stanford University, Stanford, California, United States of America
| | - Pooja Mahendra Varman
- Department of Chemistry, Stanford University, Stanford, California, United States of America
| | - Kijung Sung
- Biophysics Program, Stanford University, Stanford, California, United States of America
| | - Bianxiao Cui
- Department of Chemistry, Stanford University, Stanford, California, United States of America
- * E-mail:
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8
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Baek S, Kim SM, Lee SA, Rhim BY, Eo SK, Kim K. The cholesterol-binding antibiotic nystatin induces expression of macrophage inflammatory protein-1 in macrophages. Biomol Ther (Seoul) 2013; 21:42-8. [PMID: 24009857 PMCID: PMC3762298 DOI: 10.4062/biomolther.2012.082] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2012] [Revised: 12/11/2012] [Accepted: 12/14/2012] [Indexed: 01/03/2023] Open
Abstract
Nystatin, a polyene antifungal antibiotic, is a cholesterol sequestering agent. The antifungal agent alters composition of the plasma membrane of eukaryotic cells, whereas its effects on cells are poorly investigated. In the current study, we investigated the question of whether nystatin was able to induce expression of macrophage inflammatory protein-1 (MIP-1). THP-1 cells rarely express MIP-1α and MIP-1β, however, upon exposure to nystatin, significantly elevated expression of MIP-1α and MIP-1β was observed in a dose-dependent fashion at the messenger and protein levels. Cellular factors activated by nystatin as well as involved in nystatin-induced expression of MIP-1 proteins were identified in order to understand the molecular mechanisms of action of the anti-fungal agent. Treatment with nystatin resulted in enhanced phosphorylation of Akt, ERK, p38 MAPK, and JNK. Abrogation or significant attenuation of nystatin-induced expression of MIP-1α and MIP-1β was observed by treatment with Akt inhibitor IV, LY294002, and SP6001250. Inhibition of ERK or p38MAPK using U0126 and SB202190 did not lead to attenuation of MIP-1 expression. In addition, inhibitors of protein kinase C, such as GF109203X and Ro-318220, also attenuated expression of MIP-1. These results indicate that nystatin is able to activate multiple cellular kinases and, among them, Akt and JNK play primary roles in nystatin-induced expression of MIP-1 proteins.
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Affiliation(s)
- Seungil Baek
- Department of Pharmacology, School of Medicine, Pusan National University, Yangsan 626-870, Republic of Korea
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9
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Kim DH, Rhim BY, Eo SK, Kim K. Differential regulation of CC chemokine ligand 2 and CXCL8 by antifungal agent nystatin in macrophages. Biochem Biophys Res Commun 2013; 437:392-6. [PMID: 23831464 DOI: 10.1016/j.bbrc.2013.06.087] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2013] [Accepted: 06/24/2013] [Indexed: 10/26/2022]
Abstract
The polyene antifungal antibiotic nystatin can interact with cholesterol, thereby altering the composition of the plasma membrane in eukaryotic cells. We investigated whether nystatin influences responses to the infection by inducing expression of chemokines. THP-1 macrophages rarely expressed CC chemokine ligand 2 (CCL2) and CXCL8. However, nystatin dose-dependently increased CCL2 and CXCL8 expression at the mRNA and protein levels. To understand the molecular mechanisms of the antifungal agent, we identified cellular factors activated by nystatin and those involved in nystatin-induced upregulation of CCL2 and CXCL8. Treatment with nystatin resulted in enhanced phosphorylation of Akt, ERK1/2, p38 MAPK, and JNK. Treatment with cholesterol, LY294002, Akt inhibitor IV, U0126, and SP6001250 resulted in abrogation or significant attenuation of nystatin-induced CCL2 expression. Nystatin-mediated CXCL8 expression was attenuated in the presence of Akt inhibitor IV and SP6001250. These results indicate that exposure of human macrophages to nystatin can lead to differential regulation of CCL2 and CXCL8 via the activation of multiple cellular kinases. We propose that upregulation of CCL2 and CXCL8 contributes to pharmacological effects of nystatin.
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Affiliation(s)
- Do-Hyung Kim
- Department of Pharmacology, School of Medicine, Pusan National University, Yangsan 626-870, Republic of Korea
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10
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Tekpli X, Holme JA, Sergent O, Lagadic-Gossmann D. Role for membrane remodeling in cell death: Implication for health and disease. Toxicology 2013; 304:141-57. [DOI: 10.1016/j.tox.2012.12.014] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2012] [Revised: 11/29/2012] [Accepted: 12/20/2012] [Indexed: 12/31/2022]
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Fiegl M, Samudio I, Mnjoyan Z, Korchin B, Fritsche H, Andreeff M. Physiological hypoxia promotes lipid raft and PI3K-dependent activation of MAPK 42/44 in leukemia cells. Leukemia 2010; 24:1364-7. [PMID: 20508615 DOI: 10.1038/leu.2010.94] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
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12
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Zuo W, Chen YG. Specific activation of mitogen-activated protein kinase by transforming growth factor-beta receptors in lipid rafts is required for epithelial cell plasticity. Mol Biol Cell 2008; 20:1020-9. [PMID: 19056678 DOI: 10.1091/mbc.e08-09-0898] [Citation(s) in RCA: 105] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Transforming growth factor (TGF)-beta regulates a spectrum of cellular events, including cell proliferation, differentiation, and migration. In addition to the canonical Smad pathway, TGF-beta can also activate mitogen-activated protein kinase (MAPK), phosphatidylinositol 3-kinase (PI3K)/Akt, and small GTPases in a cell-specific manner. Here, we report that cholesterol depletion interfered with TGF-beta-induced epithelial-mesenchymal transition (EMT) and cell migration. This interference is due to impaired activation of MAPK mediated by cholesterol-rich lipid rafts. Cholesterol-depleting agents specifically inhibited TGF-beta-induced activation of extracellular signal-regulated kinase (ERK) and p38, but not Smad2/3 or Akt. Activation of ERK or p38 is required for both TGF-beta-induced EMT and cell migration, whereas PI3K/Akt is necessary only for TGF-beta-promoted cell migration but not for EMT. Although receptor heterocomplexes could be formed in both lipid raft and nonraft membrane compartments in response to TGF-beta, receptor localization in lipid rafts, but not in clathrin-coated pits, is important for TGF-beta-induced MAPK activation. Requirement of lipid rafts for MAPK activation was further confirmed by specific targeting of the intracellular domain of TGF-beta type I receptor to different membrane locations. Together, our findings establish a novel link between cholesterol and EMT and cell migration, that is, cholesterol-rich lipid rafts are required for TGF-beta-mediated MAPK activation, an event necessary for TGF-beta-directed epithelial plasticity.
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Affiliation(s)
- Wei Zuo
- State Key Laboratory of Biomembrane and Membrane Biotechnology, Department of Biological Sciences and Biotechnology, Tsinghua University, Beijing 100084, China
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13
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Vacaresse N, Møller B, Danielsen EM, Okada M, Sap J. Activation of c-Src and Fyn kinases by protein-tyrosine phosphatase RPTPalpha is substrate-specific and compatible with lipid raft localization. J Biol Chem 2008; 283:35815-24. [PMID: 18948260 DOI: 10.1074/jbc.m807964200] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Src family tyrosine kinases (SFKs) function in multiple signaling pathways, raising the question of how appropriate regulation and substrate choice are achieved. SFK activity is modulated by several protein-tyrosine phosphatases, among which RPTPalpha and SHP2 are the best established. We studied how RPTPalpha affects substrate specificity and regulation of c-Src and Fyn in response to epidermal growth factor and platelet-derived growth factor. We find that RPTPalpha, in a growth factor-specific manner, directs the specificity of these kinases toward a specific subset of SFK substrates, particularly the focal adhesion protein Paxillin and the lipid raft scaffolding protein Cbp/PAG. A significant fraction of RPTPalpha is present in lipid rafts, where its targets Fyn and Cbp/PAG reside, and growth factor-mediated SFK activation within this compartment is strictly dependent on RPTPalpha. Forced concentration of RPTPalpha into lipid rafts is compatible with activation of Fyn. Finally, RPTPalpha-induced phosphorylation of Paxillin and Cbp/PAG induces recruitment of the SFK inhibitory kinase Csk, indicative of negative feedback loops limiting SFK activation by RPTPalpha. Our findings indicate that individual SFK-controlling PTPs play important and specific roles in dictating SFK substrate specificity and regulatory mechanism.
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Affiliation(s)
- Nathalie Vacaresse
- Biotech Research and Innovation Center, Copenhagen Biocenter, Ole Maaløes Vej 5, 2200 Copenhagen N, Denmark
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14
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Abstract
Mutated ras has been identified in approximately 30% of human tumors, and dysregulation of ras function and signal transduction pathways is a critical step in tumorigenesis. Herein, we review the early data that supports the concept that the intrinsic radiosensitivity of tumor cells can be altered by oncogenic ras expression and that this impacts the PI3K-dependent signaling cascade. This ras-induced radioresistance can be reversed using prenyl transferase inhibitors (PTIs.). We discuss the effects of PTIs as a radiosensitizer in both in vivo and in vitro studies and show that PTIs can lead to increased radiosensitization in vivo through a variety of potential mechanisms that enhance radiation-induced cell kill. We critically evaluate the use of ras biomarkers in predicting the clinical response to PTIs that may explain the mixed results seen thus far in clinical trials using PTIs as a clinical radiosensitizer. We conclude that Ras-mediated radioresistance is the result of multiple intercommunicating pathways functioning against a complex genetic background and a solitary biomarker may not be adequate to predict for PTI-mediated radiosensitization. Nonetheless, our knowledge of the ras-signaling pathway has led to development and testing of specific therapies directed against PI3K-AKT signaling pathways as a future approach towards clinical radiosensitization.
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Affiliation(s)
- Ramesh Rengan
- Department of Radiation Oncology, University of Pennsylvania, 2-Donner, HUP, 3400 Spruce Street, Philadelphia, PA 19104, USA
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15
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Vitellogenin functions as a multivalent pattern recognition receptor with an opsonic activity. PLoS One 2008; 3:e1940. [PMID: 18398466 PMCID: PMC2277463 DOI: 10.1371/journal.pone.0001940] [Citation(s) in RCA: 105] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2007] [Accepted: 02/29/2008] [Indexed: 12/26/2022] Open
Abstract
Background Vitellogenin (Vg), a major reproductive protein, has been associated with infection-resistant response in fish. However, the underlying mechanisms by which Vg is involved in anti-infectious response are not understood. Methodology/Results By both protein-microbe interaction analysis and enzyme-linked immunosorbent assay as well as phagocytosis test, we demonstrate for the first time that fish Vg acts as a pattern recognition molecule with multiple specificities that can recognize bacteria as well as fungus rather than self components from fish, and functions as an opsonin that can enhance macrophage phagocytosis. Conclusions This study shows that fish Vg plays an integrative function in regulating immunity via its pleiotropic effects on both recognizing pathogen-associated molecular patterns and promoting macrophage phagocytosis. It also supports the notion that factors normally involved in control of female reproduction are associated with immunity in organisms that rely on Vg for oocyte development.
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16
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Differential regulation of cell death in head and neck cell carcinoma through alteration of cholesterol levels in lipid rafts microdomains. Biochem Pharmacol 2008; 75:761-72. [DOI: 10.1016/j.bcp.2007.10.004] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2007] [Revised: 09/25/2007] [Accepted: 10/01/2007] [Indexed: 11/18/2022]
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17
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de Laurentiis A, Donovan L, Arcaro A. Lipid rafts and caveolae in signaling by growth factor receptors. Open Biochem J 2007; 1:12-32. [PMID: 18949068 PMCID: PMC2570545 DOI: 10.2174/1874091x00701010012] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2007] [Revised: 08/15/2007] [Accepted: 08/16/2007] [Indexed: 12/29/2022] Open
Abstract
Lipid rafts and caveolae are microdomains of the plasma membrane enriched in sphingolipids and cholesterol, and hence are less fluid than the remainder of the membrane. Caveolae have an invaginated structure, while lipid rafts are flat regions of the membrane. The two types of microdomains have different protein compositions (growth factor receptors and their downstream molecules) suggesting that lipid rafts and caveolae have a role in the regulation of signaling by these receptors. The purpose of this review is to discuss this model, and the implications that it might have regarding a potential role for lipid rafts and caveolae in human cancer. Particular attention will be paid to the epidermal growth factor receptor, for which the largest amount of information is available. It has been proposed that caveolins act as tumor suppressors. The role of lipid rafts is less clear, but they seem to be capable of acting as 'signaling platforms', in which signal initiation and propagation can occur efficiently.
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Affiliation(s)
- Angela de Laurentiis
- Division of Clinical Chemistry and Biochemistry, University Children’s Hospital Zurich, Steinwiesstrasse 75, CH-8032 Zurich, Switzerland
| | - Lorna Donovan
- Division of Medicine, Imperial College Faculty of Medicine, Hammersmith Hospital, Du Cane Road, London W12 ONN, UK
| | - Alexandre Arcaro
- Division of Clinical Chemistry and Biochemistry, University Children’s Hospital Zurich, Steinwiesstrasse 75, CH-8032 Zurich, Switzerland
- Division of Medicine, Imperial College Faculty of Medicine, Hammersmith Hospital, Du Cane Road, London W12 ONN, UK
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18
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Liu YT, Song L, Templeton DM. Heparin suppresses lipid raft-mediated signaling and ligand-independent EGF receptor activation. J Cell Physiol 2007; 211:205-12. [PMID: 17226785 DOI: 10.1002/jcp.20924] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Heparin is well known to suppress vascular smooth muscle cell (VSMC) proliferation, and attempts to exploit this therapeutically have led to recognition of multiple pathways for heparin's anti-mitogenic actions. At low concentrations (ca. 1 microg.ml(-1)), these suppressive effects may reflect physiological activities of endogenous heparan sulfates, and appear to be rapid responses to extracellular or cell surface-associated heparin. Because heparin has been shown to influence expression of caveolin proteins, and caveolae/lipid rafts are critical structures modulating cell signaling, we examined the effect of heparin on signaling involving cholesterol-rich membrane microdomains. The VSMC line PAC-1 activates the MAP kinase Erk in response to the cholesterol-sequestering agents methyl-beta-cyclodextrin and nystatin. This follows a temporal sequence that involves Ras-GTP activation of MEK, and is independent of PKC, Src, and PI3 kinase. However, ligand-independent phosphorylation of the EGF receptor (EGFR) by removal of cholesterol precedes Ras activation, and the EGFR kinase inhibitor AG1478 blocks Erk phosphorylation, supporting occurrence of the signaling sequence EGFR-Ras-MEK-Erk. Phosphorylation of EGFR occurs predominantly in caveolin-rich microdomains as identified by Western blotting of fractions from density gradient centrifugation of membranes prepared under detergent-free conditions. In these situations, heparin inhibits phosphorylation of EGFR on the Src-dependent site Tyr(845), but not the autophosphorylation of Tyr(1173), and decreases Ras activation and Erk phosphorylation. We conclude that heparin can suppress Erk signaling in VSMC with effects on site-specific phosphorylation of EGFR localized in caveolin-enriched lipid rafts.
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Affiliation(s)
- Yuan-Tao Liu
- Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Canada
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19
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Hipler UC, Schönfelder U, Hipler C, Elsner P. Influence of cyclodextrins on the proliferation of HaCaT keratinocytesin vitro. J Biomed Mater Res A 2007; 83:70-9. [PMID: 17380497 DOI: 10.1002/jbm.a.31195] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Safety and efficacy of pharmaceutical agents can be greatly improved by encapsulation within, or covalent attachment to, a biomaterial carrier. Drug delivery systems must deliver the necessary amount of drug to the targeted site for a necessary period of time, both efficiently and precisely. Various kinds of high-performance biomaterials are being constantly developed for this purpose. Cyclodextrins are potential candidates for such a role, because of their ability to alter physical, chemical, and biological properties of guest molecules through the formation of inclusion complexes. The alpha-, beta-, and gamma-cyclodextrins are widely used natural cyclodextrins, consisting of six, seven, and eight D-glucopyranose residues, respectively, linked by -1,4 glycosidic bonds into a macro cycle. Each cyclodextrin has its own ability to form inclusion complexes with specific guests, an ability, which depends on a proper fit of the guest molecule into the hydrophobic cyclodextrin cavity. The most common pharmaceutical application of cyclodextrins is to enhance the solubility, stability, and bioavailability of drug molecules. Such kinds of ligand-receptor complexes can be used for different applications, e.g., for a transdermal therapeutic system (TTS) or in biofunctional textiles. The aim of this study was the investigation of the influence of the different cyclodextrins on the cell proliferation using HaCaT keratinocytes as an in vitro test system. Moreover, the study was performed to find harmless and nontoxic cyclodextrin concentrations for dermal applications. By means of different independent in vitro tests could be confirmed that alpha-, beta-, and gamma-cyclodextrins in concentrations up to 0.1% (w/v) do not show any antiproliferative influence on HaCaT keratinocytes. Sometimes even proliferative effects could be found. However, all used cyclodextrins (besides gamma-cyclodextrin and its derivatives) in concentrations of 0.5 and 1% (w/v), respectively, exert a cytotoxic influence on the proliferation of HaCaT keratinocytes. On the basis of these findings, the following rank order of cyclodextrins regarding their cytotoxicity was proposed: M-beta-CD > beta-CD > HP-beta-CD > alpha-CD > (gamma-CD). It could be confirmed that beta-CD and M-beta-CD trigger the activity of the effectors caspases -3 and -7. A significant increase of LDH release could be found for beta-CD and methyl-beta-CD in concentrations of 0.5 and 1% (w/v). The calculated cytotoxicity amounted 45 and 79%, respectively. The measurements of the interleukins IL-6 and IL-8 confirmed the findings of the proliferation assays as well as the LDH measurements. These findings may provide further rationale to the use of CDs in topical formulations for dermal and transdermal drug delivery or as raw material to functionalize textiles for medical applications.
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Affiliation(s)
- U C Hipler
- Department of Dermatology, Friedrich Schiller University, 07743 Jena, Germany.
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20
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Cengel KA, McKenna WG. Molecular targets for altering radiosensitivity: lessons from Ras as a pre-clinical and clinical model. Crit Rev Oncol Hematol 2005; 55:103-16. [PMID: 16006139 DOI: 10.1016/j.critrevonc.2005.02.001] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2004] [Revised: 01/01/2005] [Accepted: 02/03/2005] [Indexed: 11/19/2022] Open
Abstract
Ras activation has been correlated with malignant and metastatic cancer phenotypes and poor prognosis for cancer patients. In the preclinical setting, Ras activation by mutation or EGFR amplification results in increased clonogenic cell survival and decreased tumor growth delay following irradiation. Activation of the Ras pathway has also been associated with increased risk of local failure and decreased overall survival in patients receiving radiotherapy. Prenyltransferase inhibitors target the post-translational processing of Ras and have been shown to increase the radiosensitivity of human cancer cell lines. In the clinical setting, these inhibitors have been used with concurrent radiotherapy in a small number of phase I clinical trials with acceptable toxicity. Therefore, inhibiting Ras activation represents a promising molecular approach for radiosensitization in cancer therapy.
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Affiliation(s)
- Keith A Cengel
- Department of Radiation Oncology, University of Pennsylvania, 3400 Spruce Street, 2 Donner, Philadelphia, PA 19104, USA
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21
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Lei J, Mariash CN, Ingbar DH. 3,3′,5-Triiodo-l-thyronine Up-regulation of Na,K-ATPase Activity and Cell Surface Expression in Alveolar Epithelial Cells Is Src Kinase- and Phosphoinositide 3-Kinase-dependent. J Biol Chem 2004; 279:47589-600. [PMID: 15342623 DOI: 10.1074/jbc.m405497200] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
We previously reported that thyroid hormone, 3,3',5-triiodo-l-thyronine (T3), increased Na,K-ATPase activity of adult rat alveolar epithelial cells in a transcription-independent manner via increased cell surface expression of the alpha(1) and beta(1) subunits of Na,K-ATPase. Now we sought to identify signaling molecules necessary for T3 stimulation of Na,K-ATPase activity in alveolar epithelial cells. Whereas protein kinase A inhibitor H-8 and protein kinase C inhibitor bisindolymaleimide did not block the T3-induced increase in Na,K-ATPase activity, two inhibitors of phosphoinositide 3-kinase (PI3K), wortmannin and Ly294002, and two Src kinase inhibitors, PP1 and PP2, blocked the T3-induced Na,K-ATPase activity. T3 stimulated the activity of PI3K as measured by phosphatidylinositol 3-phosphate. T3 also stimulated the serine 473 phosphorylation of the PI3K downstream molecule PKB/Akt in a dose-dependent manner. Transient expression of a constitutively active mutant of the PI3K catalytic subunit p110 augmented Na,K-ATPase activity and increased the amount of cell surface Na,K-ATPase alpha(1) subunit protein. T3 also stimulated Src family kinase activity. Transient expression of a constitutively active Src kinase increased Na,K-ATPase activity, PI3K activity, and phosphorylation of PKB/Akt at serine 473. PP1 or PP2 blocked T3-stimulated PKB/Akt phosphorylation at serine 473 and PI3K activity that was activated by an active mutant of Src; however, wortmannin did not inhibit the T3-stimulated Src kinase activity. Although PP1 and wortmannin abolished the increase in Na,K-ATPase activity induced by the active mutant of Src, PP1 did not inhibit the active mutant of PI3K-up-regulated Na,K-ATPase activity. In summary, T3 stimulates the PI3K/PKB pathway via the Src family of tyrosine kinases, and activation of both the Src family kinases and PI3K is required for the T3-induced stimulation of Na,K-ATPase activity and its cell surface expression in adult rat alveolar epithelial cells.
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Affiliation(s)
- Jianxun Lei
- Department of Medicine, University of Minnesota, Minneapolis, Minnesota 55455, USA
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22
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Reinehr R, Becker S, Wettstein M, Häussinger D. Involvement of the Src family kinase yes in bile salt-induced apoptosis. Gastroenterology 2004; 127:1540-57. [PMID: 15521021 DOI: 10.1053/j.gastro.2004.08.056] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
BACKGROUND AND AIMS Hydrophobic bile acids induce CD95 (Fas, APO-1)-dependent hepatocyte apoptosis, which involves epidermal growth factor receptor (EGFR)-catalyzed CD95 tyrosine phosphorylation. The mechanisms underlying bile salt-induced EGFR activation remain unclear. METHODS Bile acid-induced EGFR activation was studied in 24-hour cultured rat hepatocytes and perfused rat liver. RESULTS The proapoptotic bile salts taurolithocholate-3-sulfate (TLCS), glycochenodesoxycholate (GCDC) and taurochenodeoxycholate (TCDC), but not taurocholate (TC), activate within 1 minute the Src kinase family member Yes, followed by an association of Yes with EGFR and subsequent EGFR activation. EGFR phosphorylation by TLCS involves tyrosines 845 and 1173 but not 1045. Yes/EGFR association and EGFR activation were sensitive to inhibition by SU6656 but not by PP-2. cAMP had no effect on TLCS and GCDC-induced Yes activation but induced Ser/Thr phosphorylation of Yes and prevented Yes/EGFR association and subsequent EGFR activation. Both SU6656 and cAMP had no effect on bile salt-induced c-Jun N-terminal kinase activation, but blocked bile salt-induced CD95 tyrosine phosphorylation, membrane trafficking of CD95, formation of the death-inducing signaling complex, and apoptosis. In 4-day cultured hepatocytes, knockdown of either Yes or EGFR strongly attenuated bile salt-induced CD95 activation and apoptosis. CONCLUSIONS The data identify the Src kinase Yes as an upstream target of proapoptotic bile acids, which triggers EGFR activation, subsequent CD95 tyrosine phosphorylation, and apoptosis. The antiapoptotic effect of cAMP involves a protein kinase A-dependent inhibition of Yes/EGFR association, thereby preventing EGFR activation, which is required for CD95 activation.
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Affiliation(s)
- Roland Reinehr
- Heinrich-Heine-University Düsseldorf, Düsseldorf, Germany
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23
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Jans R, Atanasova G, Jadot M, Poumay Y. Cholesterol Depletion Upregulates Involucrin Expression in Epidermal Keratinocytes Through Activation of p38. J Invest Dermatol 2004; 123:564-73. [PMID: 15304097 DOI: 10.1111/j.0022-202x.2004.23221.x] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Cholesterol has been recently suggested to regulate the early steps of keratinocyte differentiation through lipid rafts. In many cell types, depletion of cholesterol activates signaling proteins like epidermal growth factor receptor (EGFR), human epidermal growth factor receptor 2 (HER2), or extracellular signal-regulated kinase (ERK) known to affect cell differentiation. In this study, we explored the effects of cholesterol depletion on the phenotype of cultured keratinocytes, using a treatment with methyl-beta-cyclodextrin (MbetaCD) to extract cholesterol and a treatment with lovastatin to inhibit cholesterol neosynthesis. Analysis of the expression of differentiation marker genes in early differentiating confluent cultures reveals that cholesterol depletion induces downregulation of keratin 14 (K14) and keratin 10 (K10) and upregulation of involucrin. MbetaCD treatment induces phosphorylation of EGFR, HER2, and ERK, but not HER3. Inhibition of EGFR with PD153035 impairs the MbetaCD-induced phosphorylation of EGFR, HER2, and ERK, but does not impair the alteration of K14, K10, or involucrin gene expression, indicating that other signaling proteins regulate this phenomenon. p38 has been suggested to regulate the expression of involucrin during keratinocyte differentiation. We found that MbetaCD treatment induces a prolonged phosphorylation of p38 in general and p38alpha in particular. An inhibition of p38 with PD169316 impairs the upregulation of involucrin mRNAs by a treatment with MbetaCD, but not by a p38delta-activating TPA treatment, which might suggest that cholesterol depletion alters involucrin gene expression through activation of p38alpha/beta.
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Affiliation(s)
- Ralph Jans
- Département Histologie-Embryologie, Facultés Universitaires Notre-Dame de la Paix, B-5000 Namur, Belgium
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24
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Fessler MB, Arndt PG, Frasch SC, Lieber JG, Johnson CA, Murphy RC, Nick JA, Bratton DL, Malcolm KC, Worthen GS. Lipid Rafts Regulate Lipopolysaccharide-induced Activation of Cdc42 and Inflammatory Functions of the Human Neutrophil. J Biol Chem 2004; 279:39989-98. [PMID: 15262974 DOI: 10.1074/jbc.m401080200] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Lipid rafts are cholesterol-rich membrane microdomains that are thought to act as coordinated signaling platforms by regulating dynamic, agonist-induced translocation of signaling proteins. They have been described to play a role in multiple prototypical cascades, among them the lipopolysaccharide pathway, and to host multiple signaling proteins, including kinases and low molecular weight G-proteins. Here we report lipopolysaccharide-induced activation of the Rho family GTPase Cdc42, and we show its activation in the human neutrophil to be mediated by a p38 mitogen-activated protein kinase-dependent mechanism. Subcellular fractionation reveals that lipopolysaccharide induces translocation of Cdc42 to lipid rafts, where it and p38 are both found to be activated. By contrast, lipopolysaccharide causes translocation of Rac from the polymorphonuclear leukocyte (PMN) rafts and does not induce its activation. With the use of methyl-beta-cyclodextrin, a cholesterol-depleting agent that reversibly disrupts rafts, we confirm an important regulatory role for rafts in the activation state of p38 and Cdc42 and in the Rho GTPase-dependent functions superoxide anion production and actin polymerization. Methyl-beta-cyclodextrin induces activation of p38 and Cdc42, but not Rac, in the nonstimulated PMN, yet inhibits subsequent lipopolysaccharide-induced activation of p38 and Cdc42. In parallel, methyl-beta-cyclodextrin primes the human PMN for subsequent superoxide release triggered by the formylated bacterial tripeptide formyl-Met-Leu-Phe, and induces actin polymerization in a subcellular distribution distinct from that induced by lipopolysaccharide. In sum, these findings provide evidence for an important regulatory role of cholesterol in both transmission of the lipopolysaccharide signal and the inflammatory phenotype of the human neutrophil.
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Affiliation(s)
- Michael B Fessler
- Department of Medicine, National Jewish Medical and Research Center, Denver, Colorado 80206, USA.
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25
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Atkinson SJ, English JL, Holway N, Murphy G. Cellular cholesterol regulates MT1 MMP dependent activation of MMP 2 via MEK-1 in HT1080 fibrosarcoma cells. FEBS Lett 2004; 566:65-70. [PMID: 15147870 DOI: 10.1016/j.febslet.2004.04.040] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2004] [Revised: 03/31/2004] [Accepted: 04/01/2004] [Indexed: 11/17/2022]
Abstract
Unstimulated human fibrosarcoma cells (HT1080) constitutively secrete matrix metalloproteinase 2 (MMP 2) as a proenzyme requiring proteolytic cleavage by membrane type-1 MMP (MT1 MMP) for activation. Physiological and pharmacological stimuli induce clustering of MT1 MMP/tissue inhibitor of MMP 2 "receptors", promoting binding and activation of MMP 2. We now report that cholesterol depleted HT1080 cells accumulated MT1 MMP on the cell surface and activated MMP 2. A specific inhibitor of mitogen activated protein kinase kinase 1/2 inhibited both MMP 2 activation and extracellular signal-related kinase phosphorylation induced by cholesterol depletion. Our data indicate that the cholesterol content of unstimulated cells is critical for secretion of MMP 2 as an inactive zymogen and control of pericellular proteolysis.
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Affiliation(s)
- Susan J Atkinson
- Department of Oncology, Cambridge Institute for Medical Research, University of Cambridge, Cambridge CB2 2XY, UK
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26
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Reinehr R, Becker S, Höngen A, Haüssinger D. The Src family kinase Yes triggers hyperosmotic activation of the epidermal growth factor receptor and CD95. J Biol Chem 2004; 279:23977-87. [PMID: 15039424 DOI: 10.1074/jbc.m401519200] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Hyperosmotic exposure of rat hepatocytes triggers epidermal growth factor receptor (EGFR) activation, which results in an activation of the CD95 system and sensitizes the cells toward apoptosis (Reinehr, R., Schliess, F., and Haüssinger, D. (2003) FASEB J. 17, 731-733). The mechanisms underlying the hyperosmotic EGFR activation were studied. Hyperosmotic exposure (405 mosm) resulted in a rapid activation of the Src kinase family members Yes, Fyn, and Lck. Hyperosmotic Yes, but not Fyn activation, was antioxidant-sensitive and was followed by a rapid Yes/EGFR association. PP-2 abolished the hyperosmotic activation of Fyn and Lck but not activation of Yes and EGFR and their association. However, these latter processes were prevented in the presence of SU6656. SU6656 and antioxidants, but not PP-2 and AG1478, also inhibited the hyperosmotic JNK activation. Cyclic AMP had no effect on hyperosmotic Yes and JNK activation but prevented EGFR/Yes association and EGFR activation in an H89-sensitive way. When the hyperosmolarity-induced Yes-EGFR protein complex started to disappear after 30 min, an association between EGFR and CD95 became apparent, which was followed by CD95 tyrosine phosphorylation and activation. SU6656 but not PP-2 also inhibited EGFR/CD95 association, CD95 tyrosine phosphorylation, CD95 membrane trafficking, and death-inducing signaling complex (DISC) formation. EGFR knockdown had no effect on hyperosmotic Yes activation but prevented CD95 tyrosine phosphorylation, membrane targeting, and DISC formation. Hyperosmotic EGFR and CD95 activation was also largely blunted following Yes knockdown. The data suggest that hyperosmotic signaling triggers an oxidative stress-dependent Yes activation, which is followed by JNK and EGFR activation and subsequent activation of the CD95 system. However, the functional relevance of hyperosmolarity-induced Fyn and Lck activation remains to be elucidated.
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Affiliation(s)
- Roland Reinehr
- Clinic for Gastroenterology, Hepatology and Infectiology, Heinrich-Heine-University, Moorenstrasse 5, Düsseldorf D-40225, Germany
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Abstract
Upon binding to the poliovirus receptor (PVR), the poliovirus 160S particles undergo a conformational transition to generate 135S particles, which are believed to be intermediates in the virus entry process. The 135S particles interact with host cell membranes through exposure of the N termini of VP1 and the myristylated VP4 protein, and successful cytoplasmic delivery of the genomic RNA requires the interaction of these domains with cellular membranes whose identity is unknown. Because detergent-insoluble microdomains (DIMs) in the plasma membrane have been shown to be important in the entry of other picornaviruses, it was of interest to determine if poliovirus similarly required DIMs during virus entry. We show here that methyl-beta-cyclodextrin (MbetaCD), which disrupts DIMs by depleting cells of cholesterol, inhibits virus infection and that this inhibition was partially reversed by partially restoring cholesterol levels in cells, suggesting that MbetaCD inhibition of virus infection was mediated by removal of cellular cholesterol. However, fractionation of cellular membranes into DIMs and detergent-soluble membrane fractions showed that both PVR and poliovirus capsid proteins localize not to DIMs but to detergent-soluble membrane fractions during entry into the cells, and their localization was unaffected by treatment with MbetaCD. We further demonstrate that treatment with MbetaCD inhibits RNA delivery after formation of the 135S particles. These data indicate that the cholesterol status of the cell is important during the process of genome delivery and that these entry pathways are distinct from those requiring DIM integrity.
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Affiliation(s)
- Pranav Danthi
- Department of Microbiology and Immunology, University of Arkansas for Medical Sciences, Little Rock, Arkansas 72205
| | - Marie Chow
- Department of Microbiology and Immunology, University of Arkansas for Medical Sciences, Little Rock, Arkansas 72205
- Corresponding author. Mailing address: Department of Microbiology and Immunology, University of Arkansas for Medical Sciences, 4301 W. Markham, Slot 511, Little Rock, AR 72205. Phone: (501) 686-5155. Fax: (501) 686-5362. E-mail:
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28
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Assossou O, Besson F, Rouault JP, Persat F, Brisson C, Duret L, Ferrandiz J, Mayençon M, Peyron F, Picot S. Subcellular localization of 14-3-3 proteins in Toxoplasma gondii tachyzoites and evidence for a lipid raft-associated form. FEMS Microbiol Lett 2003; 224:161-8. [PMID: 12892878 DOI: 10.1016/s0378-1097(03)00479-8] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
A polyclonal antibody was raised against a Toxoplasma gondii 14-3-3-gluthatione S-transferase fusion protein obtained by cloning a 14-3-3 cDNA sequence determined from the T. gondii database. This antibody specifically recognized T. gondii 14-3-3 without any cross-reaction with mammalian proteins. Immunofluorescence microscopy studies of the tachyzoites or the T. gondii-infected cells suggested cytosolic and membranous localizations of 14-3-3 protein. Different subcellular fractions were prepared for electrophoresis analysis and immunodetection. 14-3-3 proteins were found in the cytosol, the membrane fraction and Triton X-100-resistant membranes. Two 14-3-3 isoforms were detected. The major one was mainly cytoplasmic and to a lesser extent membrane-associated, whereas the minor isoform was associated with the detergent-resistant lipid rafts.
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Affiliation(s)
- Olga Assossou
- Laboratoire de Parasitologie, Mycologie Médicale et Pathologie Exotique, Equipe d'accueil (EA) 3087 Faculté de Médecine, Université Claude Bernard, 8 avenue Rockefeller, 69373, Lyon, Cedex 08, France
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29
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Baker TL, Zheng H, Walker J, Coloff JL, Buss JE. Distinct rates of palmitate turnover on membrane-bound cellular and oncogenic H-ras. J Biol Chem 2003; 278:19292-300. [PMID: 12642594 DOI: 10.1074/jbc.m206956200] [Citation(s) in RCA: 77] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
H-Ras displays dynamic cycles of GTP binding and palmitate turnover. GTP binding is clearly coupled to activation, but whether the palmitoylated COOH terminus participates in signaling, especially when constrained by membrane tethering, is unknown. As a way to compare COOH termini of membrane-bound, lipid-modified H-Ras, palmitate removal rates were measured for various forms of H-Ras in NIH 3T3 cells. Depalmitoylation occurred slowly (t(1/2) approximately 2.4 h) in cellular (H-RasWT) or dominant negative (H-Ras17N) forms and more rapidly (t(1/2) approximately 1 h) in oncogenic H-Ras61L or H-RasR12,T59. Combining this data with GTP binding measurements, the palmitate half-life of H-Ras in the fully GTP-bound state was estimated to be less than 10 min. Slow palmitate removal from cellular H-Ras was not explained by sequestration in caveolae, as neither cellular nor oncogenic H-Ras showed alignment with caveolin by immunofluorescence. Conversely, although it had faster palmitate removal, oncogenic H-Ras was located in the same fractions as H-RasWT on four types of density gradients, and remained fully membrane-bound. Thus the different rates of deacylation occurred even though oncogenic and cellular H-Ras appeared to be in similar locations. Instead, these results suggest that acylprotein thioesterases access oncogenic H-Ras more easily because the conformation of its COOH terminus against the membrane is altered. This previously undetected difference could help produce distinctive effector interactions and signaling of oncogenic H-Ras.
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Affiliation(s)
- Tara L Baker
- Department of Zoology/Genetics, Iowa State University, Ames, Iowa 50011, USA
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30
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Abstract
Ras signalling has classically been thought to occur exclusively at the inner surface of a relatively uniform plasma membrane. Recent studies have shown that Ras proteins interact dynamically with specific microdomains of the plasma membrane as well as with other internal cell membranes. These different membrane microenvironments modulate Ras signal output and highlight the complex interplay between Ras location and function.
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Affiliation(s)
- John F Hancock
- Institute for Molecular Bioscience and Department of Molecular and Cellular Pathology, University of Queensland, Brisbane, Australia 4072.
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31
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Abstract
Lipid rafts are subdomains of the plasma membrane that contain high concentrations of cholesterol and glycosphingolipids. They exist as distinct liquid-ordered regions of the membrane that are resistant to extraction with nonionic detergents. Rafts appear to be small in size, but may constitute a relatively large fraction of the plasma membrane. While rafts have a distinctive protein and lipid composition, all rafts do not appear to be identical in terms of either the proteins or the lipids that they contain. A variety of proteins, especially those involved in cell signaling, have been shown to partition into lipid rafts. As a result, lipid rafts are thought to be involved in the regulation of signal transduction. Experimental evidence suggests that there are probably several different mechanisms through which rafts control cell signaling. For example, rafts may contain incomplete signaling pathways that are activated when a receptor or other required molecule is recruited into the raft. Rafts may also be important in limiting signaling, either by physical sequestration of signaling components to block nonspecific interactions, or by suppressing the intrinsic activity of signaling proteins present within rafts. This review provides an overview of the physical characteristics of lipid rafts and summarizes studies that have helped to elucidate the role of lipid rafts in signaling via receptor tyrosine kinases and G protein-coupled receptors.
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Affiliation(s)
- Linda J Pike
- Washington University School of Medicine, Department of Biochemistry and Molecular Biophysics, 660 So. Euclid, Box 8231, St. Louis, MO 63110, USA.
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Carey KD, Watson RT, Pessin JE, Stork PJS. The requirement of specific membrane domains for Raf-1 phosphorylation and activation. J Biol Chem 2003; 278:3185-96. [PMID: 12446733 DOI: 10.1074/jbc.m207014200] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Activation of Raf-1 by Ras requires recruitment to the membrane as well as additional phosphorylations, including phosphorylation at serine 338 (Ser-338) and tyrosine 341 (Tyr-341). In this study we show that Tyr-341 participates in the recruitment of Raf-1 to specialized membrane domains called "rafts," which are required for Raf-1 to be phosphorylated on Ser-338. Raf-1 is also thought to be recruited to the small G protein Rap1 upon GTP loading of Rap1. However, this does not result in Raf-1 activation. We propose that this is because Raf-1 is not phosphorylated on Tyr-341 upon recruitment to Rap1. Redirecting Rap1 to Ras-containing membranes or mimicking Tyr-341 phosphorylation of Raf-1 by mutation converts Rap1 into an activator of Raf-1. In contrast to Raf-1, B-Raf is activated by Rap1. We suggest that this is because B-Raf activation is independent of tyrosine phosphorylation. Moreover, mutants that render B-Raf dependent on tyrosine phosphorylation are no longer activated by Rap1.
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Affiliation(s)
- Kendall D Carey
- Vollum Institute, Department of Cell and Developmental Biology, L474 Oregon Health Sciences University, Portland, Oregon 97201, USA
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Chen X, Resh MD. Cholesterol depletion from the plasma membrane triggers ligand-independent activation of the epidermal growth factor receptor. J Biol Chem 2002; 277:49631-7. [PMID: 12397069 DOI: 10.1074/jbc.m208327200] [Citation(s) in RCA: 144] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We recently demonstrated that depletion of plasma membrane cholesterol with methyl-beta-cyclodextrin (MbetaCD) caused activation of MAPK (Chen, X., and Resh, M. D. (2001) J. Biol. Chem. 276, 34617-34623). MAPK activation was phosphatidylinositol 3-kinase (PI3K)-dependent and involved increased tyrosine phosphorylation of the p85 subunit of PI3K. We next determined whether MbetaCD treatment induced tyrosine phosphorylation of other cellular proteins. Here we report that cholesterol depletion of serum-starved COS-1 cells with MbetaCD or filipin caused an increase in Tyr(P) levels of a 180-kDa protein that was identified as the epidermal growth factor receptor (EGFR). Cross-linking experiments showed that MbetaCD induced dimerization of EGFR, indicative of receptor activation. Reagents that block release of membrane-bound EGFR ligands did not affect MbetaCD-induced tyrosine phosphorylation of EGFR, indicating that MbetaCD activation of EGFR is ligand-independent. Moreover, MbetaCD treatment resulted in increased tyrosine phosphorylation of EGFR downstream targets and Ras activation. Incubation of cells with the specific EGFR inhibitor AG4178 blocked MbetaCD-induced phosphorylation of EGFR, SHC, phospholipase C-gamma, and Gab-1 as well as MAPK activation. We conclude that cholesterol depletion from the plasma membrane by MbetaCD causes ligand-independent activation of EGFR, resulting in MAPK activation by PI3K and Ras-dependent mechanisms. Moreover, these studies reveal a novel mode of action of MbetaCD, in addition to its ability to disrupt membrane rafts.
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Affiliation(s)
- Xu Chen
- Cell Biology Program, Memorial Sloan-Kettering Cancer Center, 1275 York Avenue, New York, NY 10021, USA
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Bullis BL, Li X, Singh DN, Berthiaume LG, Fliegel L. Properties of the Na+/H+ exchanger protein. Detergent-resistant aggregation and membrane microdistribution. EUROPEAN JOURNAL OF BIOCHEMISTRY 2002; 269:4887-95. [PMID: 12354120 DOI: 10.1046/j.1432-1033.2002.03202.x] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The Na+/H+ exchanger is a ubiquitous membrane protein of bacteria, plants and mammals. The first isoform discovered (NHE1) is present on the mammalian plasma membrane and transports one H+ out of cells in exchange for one extracellular Na+. With solubilization in standard SDS/PAGE buffer, this protein had a high tendency to aggregate when subjected to elevated temperature. The aggregates were stable and did not dissociate in high concentrations of SDS or 2-mercaptoethanol. We examined the distribution of the Na+/H+ exchanger within membrane subfractions. The Na+/H+ exchanger was found both in caveolin-containing fractions and, in lesser amounts, in higher density membrane fractions where the bulk of proteins were contained. Treatment with cytochalasin D caused only a minor reduction of the amount of Na+/H+ exchanger present in caveolin-enriched fractions suggesting an intact cytoskeleton was not important for NHE1 localization to these microdomains. Treatment of cells with methyl beta-cyclodextrin had a small stimulatory effect on Na+/H+ exchanger activity and reduced the amount of Na+/H+ exchanger in low density membrane fractions. Our study demonstrates that SDS cannot maintain the protein in a monomeric state suggesting that strong hydrophobic interactions are responsible for this temperature dependent aggregation behavior. In addition a large proportion of the Na+/H+ exchanger protein is found to be enriched in low density caveolin-containing fractions.
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Affiliation(s)
- Bonnie L Bullis
- Department of Biochemistry, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta, Canada
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Lindwasser OW, Resh MD. Myristoylation as a target for inhibiting HIV assembly: unsaturated fatty acids block viral budding. Proc Natl Acad Sci U S A 2002; 99:13037-42. [PMID: 12244217 PMCID: PMC130582 DOI: 10.1073/pnas.212409999] [Citation(s) in RCA: 92] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Modification of HIV-1 Gag with myristic acid, a saturated 14-carbon fatty acid (14:0), is essential for HIV-1 assembly. We recently showed that exogenous treatment of cells with unsaturated 14-carbon fatty acids, 5-cis-tetradecenoic acid (14:1n-9) and 5-cis,8-cis-tetradecadienoic acid (14:2n-6), reduces the affinity of some myristoylated proteins for plasma membrane rafts, membrane subdomains that have been shown to be required for efficient assembly of HIV. Here we demonstrate that treatment of cells with 14:1n-9 and 14:2n-6 fatty acids reduced the affinity of Gag for rafts but not membranes in general. Furthermore, treatment of cells with 14-carbon unsaturated fatty acids inhibited Gag-driven particle assembly. These effects most likely reflect covalent modification of Gag with unsaturated fatty acids. Treatment with 14:1n-9 and 14:2n-6 fatty acids did not alter intracellular protein trafficking, nor did it reduce cell viability. These studies suggest a strategy to attack HIV assembly by selectively altering the patterns of fatty acid modification.
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Affiliation(s)
- O Wolf Lindwasser
- Cell Biology Program, Memorial Sloan-Kettering Cancer Center, 1275 York Avenue, Box 143, New York, NY 10021, USA
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Massotte D, Brillet K, Kieffer B, Milligan G. Agonists activate Gi1 alpha or Gi2 alpha fused to the human mu opioid receptor differently. J Neurochem 2002; 81:1372-82. [PMID: 12068084 DOI: 10.1046/j.1471-4159.2002.00946.x] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
As preferential coupling of opioid receptor to various inhibitory Galpha subunits is still under debate, we have investigated the selectivity of the human mu opioid receptor fused to a pertussis toxin insensitive C351I Gi1 alpha or C352I Gi2 alpha in stably transfected HEK 293 cells. Overall agonist binding affinities were increased for both fusion constructs when compared to the wild type receptor. [35 S]GTPgammaS binding was performed on pertussis toxin treated cells to monitor coupling efficiency of the fusion constructs. Upon agonist addition hMOR-C351I Gi1 a exhibited an activation profile similar to the non-fused receptor while hMOR-C352I Gi2 alpha was poorly activated. Interestingly no correlation could be drawn between agonist binding affinity and efficacy. Upon agonist addition, forskolin-stimulated cAMP production, as measured using a reporter gene assay, was inhibited by signals transduced via the fused Gi1 alpha and Gi2 alpha mainly. In contrast both fusion constructs were able to initiate ERK-MAPK phosphorylation via coupling to endogenous G proteins only. In conclusion our data indicate that hMOR couples more efficiently to Gi1 alpha than Gi2 alpha and that the coupling efficacy is clearly agonist-dependent.
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Affiliation(s)
- Dominique Massotte
- Département des Récepteurs et Protéines Membranaires, CNRS UPR 9050, Ecole Supérieure de Biotechnologie de Strasbourg, Illkirch-Graffenstaden, France.
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Jaumot M, Yan J, Clyde-Smith J, Sluimer J, Hancock JF. The linker domain of the Ha-Ras hypervariable region regulates interactions with exchange factors, Raf-1 and phosphoinositide 3-kinase. J Biol Chem 2002; 277:272-8. [PMID: 11689566 DOI: 10.1074/jbc.m108423200] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Ha-Ras and Ki-Ras have different distributions across plasma membrane microdomains. The Ras C-terminal anchors are primarily responsible for membrane micro-localization, but recent work has shown that the interaction of Ha-Ras with lipid rafts is modulated by GTP loading via a mechanism that requires the hypervariable region (HVR). We have now identified two regions in the HVR linker domain that regulate Ha-Ras raft association. Release of activated Ha-Ras from lipid rafts is blocked by deleting amino acids 173-179 or 166-172. Alanine replacement of amino acids 173-179 but not 166-172 restores wild type micro-localization, indicating that specific N-terminal sequences of the linker domain operate in concert with a more C-terminal spacer domain to regulate Ha-Ras raft association. Mutations in the linker domain that confine activated Ha-RasG12V to lipid rafts abrogate Raf-1, phosphoinositide 3-kinase, and Akt activation and inhibit PC12 cell differentiation. N-Myristoylation also prevents the release of activated Ha-Ras from lipid rafts and inhibits Raf-1 activation. These results demonstrate that the correct modulation of Ha-Ras lateral segregation is critical for downstream signaling. Mutations in the linker domain also suppress the dominant negative phenotype of Ha-RasS17N, indicating that HVR sequences are essential for efficient interaction of Ha-Ras with exchange factors in intact cells.
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Affiliation(s)
- Montserrat Jaumot
- Laboratory of Experimental Oncology, Department of Pathology, University of Queensland Medical School, Herston Road, Queensland 4006, Australia
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