51
|
Maekawa M, Yang Y, Fairn GD. Perfringolysin O Theta Toxin as a Tool to Monitor the Distribution and Inhomogeneity of Cholesterol in Cellular Membranes. Toxins (Basel) 2016; 8:toxins8030067. [PMID: 27005662 PMCID: PMC4810212 DOI: 10.3390/toxins8030067] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2016] [Revised: 02/26/2016] [Accepted: 02/26/2016] [Indexed: 11/23/2022] Open
Abstract
Cholesterol is an essential structural component of cellular membranes in eukaryotes. Cholesterol in the exofacial leaflet of the plasma membrane is thought to form membrane nanodomains with sphingolipids and specific proteins. Additionally, cholesterol is found in the intracellular membranes of endosomes and has crucial functions in membrane trafficking. Furthermore, cellular cholesterol homeostasis and regulation of de novo synthesis rely on transport via both vesicular and non-vesicular pathways. Thus, the ability to visualize and detect intracellular cholesterol, especially in the plasma membrane, is critical to understanding the complex biology associated with cholesterol and the nanodomains. Perfringolysin O (PFO) theta toxin is one of the toxins secreted by the anaerobic bacteria Clostridium perfringens and this toxin forms pores in the plasma membrane that causes cell lysis. It is well understood that PFO recognizes and binds to cholesterol in the exofacial leaflets of the plasma membrane, and domain 4 of PFO (D4) is sufficient for the binding of cholesterol. Recent studies have taken advantage of this high-affinity cholesterol-binding domain to create a variety of cholesterol biosensors by using a non-toxic PFO or the D4 in isolation. This review highlights the characteristics and usefulness of, and the principal findings related to, these PFO-derived cholesterol biosensors.
Collapse
Affiliation(s)
- Masashi Maekawa
- Keenan Research Centre for Biomedical Science, St. Michael's Hospital, 209 Victoria Street, 6th Floor, Toronto, ON M5S 1T8, Canada.
| | - Yanbo Yang
- Keenan Research Centre for Biomedical Science, St. Michael's Hospital, 209 Victoria Street, 6th Floor, Toronto, ON M5S 1T8, Canada.
- Department of Biochemistry, University of Toronto, Toronto, ON M5S 1A8, Canada.
| | - Gregory D Fairn
- Keenan Research Centre for Biomedical Science, St. Michael's Hospital, 209 Victoria Street, 6th Floor, Toronto, ON M5S 1T8, Canada.
- Department of Biochemistry, University of Toronto, Toronto, ON M5S 1A8, Canada.
- Department of Surgery, University of Toronto, Toronto, ON M5T 1P5, Canada.
- Institute of Medical Science, Faculty of Medicine, University of Toronto, Toronto, ON M5S 1A8, Canada.
- Institute for Biomedical Engineering and Science Technology (IBEST), Ryerson University and St. Michael's Hospital, Toronto, ON M5B 2K3, Canada.
| |
Collapse
|
52
|
Banerjee A, Jang H, Nussinov R, Gaponenko V. The disordered hypervariable region and the folded catalytic domain of oncogenic K-Ras4B partner in phospholipid binding. Curr Opin Struct Biol 2016; 36:10-7. [PMID: 26709496 PMCID: PMC4785042 DOI: 10.1016/j.sbi.2015.11.010] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2015] [Accepted: 11/20/2015] [Indexed: 01/08/2023]
Abstract
The C-terminal hypervariable region (HVR) of the splice variant KRAS4B is disordered. Classically, the role of the post-translationally-modified HVR is to navigate Ras in the cell and to anchor it in localized plasma membrane regions. Here, we propose additional regulatory roles, including auto-inhibition by shielding the effector binding site in the GDP-bound state and release upon GTP binding and in the presence of certain oncogenic mutations. The released HVR can interact with calmodulin. We show that oncogenic mutations (G12V/G12D) modulate the HVR-phospholipid binding specificity, resulting in preferential interactions with phosphatidic acid. The shifts in the conformational preferences and binding specificity in the disordered state exemplify the critical role of the unstructured tail of K-Ras4B in cancer.
Collapse
Affiliation(s)
- Avik Banerjee
- Department of Chemistry, University of Illinois at Chicago, Chicago, IL 60607, USA
| | - Hyunbum Jang
- Cancer and Inflammation Program, National Cancer Institute at Frederick, Basic Science Program, Leidos Biomedical Research, Inc., Frederick National Laboratory for Cancer Research, Frederick, MD 21702, USA
| | - Ruth Nussinov
- Cancer and Inflammation Program, National Cancer Institute at Frederick, Basic Science Program, Leidos Biomedical Research, Inc., Frederick National Laboratory for Cancer Research, Frederick, MD 21702, USA; Department of Human Molecular Genetics and Biochemistry, Sackler School of Medicine, Tel Aviv University, Tel Aviv 69978, Israel
| | - Vadim Gaponenko
- Department of Biochemistry and Molecular Genetics, University of Illinois at Chicago, Chicago, IL 60607, USA.
| |
Collapse
|
53
|
Cox AD, Der CJ, Philips MR. Targeting RAS Membrane Association: Back to the Future for Anti-RAS Drug Discovery? Clin Cancer Res 2016; 21:1819-27. [PMID: 25878363 DOI: 10.1158/1078-0432.ccr-14-3214] [Citation(s) in RCA: 278] [Impact Index Per Article: 34.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
RAS proteins require membrane association for their biologic activity, making this association a logical target for anti-RAS therapeutics. Lipid modification of RAS proteins by a farnesyl isoprenoid is an obligate step in that association, and is an enzymatic process. Accordingly, farnesyltransferase inhibitors (FTI) were developed as potential anti-RAS drugs. The lack of efficacy of FTIs as anticancer drugs was widely seen as indicating that blocking RAS membrane association was a flawed approach to cancer treatment. However, a deeper understanding of RAS modification and trafficking has revealed that this was an erroneous conclusion. In the presence of FTIs, KRAS and NRAS, which are the RAS isoforms most frequently mutated in cancer, become substrates for alternative modification, can still associate with membranes, and can still function. Thus, FTIs failed not because blocking RAS membrane association is an ineffective approach, but because FTIs failed to accomplish that task. Recent findings regarding RAS isoform trafficking and the regulation of RAS subcellular localization have rekindled interest in efforts to target these processes. In particular, improved understanding of the palmitoylation/depalmitoylation cycle that regulates RAS interaction with the plasma membrane, endomembranes, and cytosol, and of the potential importance of RAS chaperones, have led to new approaches. Efforts to validate and target other enzymatically regulated posttranslational modifications are also ongoing. In this review, we revisit lessons learned, describe the current state of the art, and highlight challenging but promising directions to achieve the goal of disrupting RAS membrane association and subcellular localization for anti-RAS drug development. Clin Cancer Res; 21(8); 1819-27. ©2015 AACR. See all articles in this CCR Focus section, "Targeting RAS-Driven Cancers."
Collapse
Affiliation(s)
- Adrienne D Cox
- University of North Carolina at Chapel Hill, Lineberger Comprehensive Cancer Center, Chapel Hill, North Carolina.
| | - Channing J Der
- University of North Carolina at Chapel Hill, Lineberger Comprehensive Cancer Center, Chapel Hill, North Carolina.
| | - Mark R Philips
- Perlmutter Cancer Institute, New York University School of Medicine, New York, New York.
| |
Collapse
|
54
|
Cho KJ, van der Hoeven D, Zhou Y, Maekawa M, Ma X, Chen W, Fairn GD, Hancock JF. Inhibition of Acid Sphingomyelinase Depletes Cellular Phosphatidylserine and Mislocalizes K-Ras from the Plasma Membrane. Mol Cell Biol 2016; 36:363-74. [PMID: 26572827 PMCID: PMC4719297 DOI: 10.1128/mcb.00719-15] [Citation(s) in RCA: 78] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2015] [Revised: 08/07/2015] [Accepted: 10/28/2015] [Indexed: 11/20/2022] Open
Abstract
K-Ras must localize to the plasma membrane for biological activity; thus, preventing plasma membrane interaction blocks K-Ras signal output. Here we show that inhibition of acid sphingomyelinase (ASM) mislocalizes both the K-Ras isoforms K-Ras4A and K-Ras4B from the plasma membrane to the endomembrane and inhibits their nanoclustering. We found that fendiline, a potent ASM inhibitor, reduces the phosphatidylserine (PtdSer) and cholesterol content of the inner plasma membrane. These lipid changes are causative because supplementation of fendiline-treated cells with exogenous PtdSer rapidly restores K-Ras4A and K-Ras4B plasma membrane binding, nanoclustering, and signal output. Conversely, supplementation with exogenous cholesterol restores K-Ras4A but not K-Ras4B nanoclustering. These experiments reveal different operational pools of PtdSer on the plasma membrane. Inhibition of ASM elevates cellular sphingomyelin and reduces cellular ceramide levels. Concordantly, delivery of recombinant ASM or exogenous ceramide to fendiline-treated cells rapidly relocalizes K-Ras4B and PtdSer to the plasma membrane. K-Ras4B mislocalization is also recapitulated in ASM-deficient Neimann-Pick type A and B fibroblasts. This study identifies sphingomyelin metabolism as an indirect regulator of K-Ras4A and K-Ras4B signaling through the control of PtdSer plasma membrane content. It also demonstrates the critical and selective importance of PtdSer to K-Ras4A and K-Ras4B plasma membrane binding and nanoscale spatial organization.
Collapse
Affiliation(s)
- Kwang-Jin Cho
- Department of Integrative Biology and Pharmacology, University of Texas Health Science Center at Houston, Medical School, Houston, Texas, USA
| | - Dharini van der Hoeven
- Department of Diagnostic and Biomedical Sciences, University of Texas Health Science Center at Houston, School of Dentistry, Houston, Texas, USA
| | - Yong Zhou
- Department of Integrative Biology and Pharmacology, University of Texas Health Science Center at Houston, Medical School, Houston, Texas, USA
| | - Masashi Maekawa
- Keenan Research Centre for Biomedical Science, St. Michael's Hospital, Toronto, Ontario, Canada Departments of Surgery and Biochemistry, University of Toronto, Toronto, Ontario, Canada Department of Biochemistry and Molecular Genetics, Ehime University Graduate School of Medicine, Toon, Ehime, Japan
| | - Xiaoping Ma
- Department of Integrative Biology and Pharmacology, University of Texas Health Science Center at Houston, Medical School, Houston, Texas, USA
| | - Wei Chen
- Department of Integrative Biology and Pharmacology, University of Texas Health Science Center at Houston, Medical School, Houston, Texas, USA
| | - Gregory D Fairn
- Keenan Research Centre for Biomedical Science, St. Michael's Hospital, Toronto, Ontario, Canada Departments of Surgery and Biochemistry, University of Toronto, Toronto, Ontario, Canada
| | - John F Hancock
- Department of Integrative Biology and Pharmacology, University of Texas Health Science Center at Houston, Medical School, Houston, Texas, USA
| |
Collapse
|
55
|
Sohn M, Balla T. Lenz-Majewski syndrome: How a single mutation leads to complex changes in lipid metabolism. ACTA ACUST UNITED AC 2016; 2:47-51. [PMID: 30854527 DOI: 10.29245/2572-9411/2017/1.1080] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Lenz-Majewski syndrome (LMS) is a rare disease presenting with complex physical and mental abnormalities. Whole exome sequencing performed on five LMS-affected individuals has identified gain-of-function mutations in the PTDSS1 gene encoding phosphatidylserine synthase 1 (PSS1) enzyme. These mutations all rendered PSS1 insensitive to PS-mediated product inhibition. In a recent study we showed that uncontrolled PS production by these mutant PSS1 enzymes lead to the accumulation of PS in the ER where it is not detected in normal cells. This increased PS in the ER in turn, activated the Sac1 phosphatase, which is responsible for the dephosphorylation of the minor lipid, phosphatidylinositol 4-phosphate (PI4P) in the ER. Increased Sac1 activity decreased PI4P levels both in the Golgi and the plasma membrane thereby dissipating the PI4P gradients set up by PI 4-kinase enzymes (PI4Ks) between these membranes and the ER. Such PI4P gradients at membrane contact sites have been shown to support the transports of structural lipids such as cholesterol and PS out of the ER by non-vesicular lipid transfer. Therefore, uncontrolled production of PS not only affects the PS status of cells but also initiates an avalanche of changes in the metabolism of other membrane lipids via affecting PI4P gradients throughout the cell. Recognition of the close metabolic interaction between PS synthesis and PI4P metabolism provided a new clue to better understand the molecular underpinning of this rare and severe disease.
Collapse
Affiliation(s)
- Mira Sohn
- Section on Molecular Signal Transduction, Program for Developmental Neuroscience, Eunice Kennedy Shriver NICHD, National Institutes of Health, Bethesda, Maryland 20892, USA
| | - Tamas Balla
- Section on Molecular Signal Transduction, Program for Developmental Neuroscience, Eunice Kennedy Shriver NICHD, National Institutes of Health, Bethesda, Maryland 20892, USA
| |
Collapse
|
56
|
McCarthy M, Prakash P, Gorfe AA. Computational allosteric ligand binding site identification on Ras proteins. Acta Biochim Biophys Sin (Shanghai) 2016; 48:3-10. [PMID: 26487442 DOI: 10.1093/abbs/gmv100] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2015] [Accepted: 08/16/2015] [Indexed: 12/19/2022] Open
Abstract
A number of computational techniques have been proposed to expedite the process of allosteric ligand binding site identification in inherently flexible and hence challenging drug targets. Some of these techniques have been instrumental in the discovery of allosteric ligand binding sites on Ras proteins, a group of elusive anticancer drug targets. This review provides an overview of these techniques and their application to Ras proteins. A summary of molecular docking and binding site identification is provided first, followed by a more detailed discussion of two specific techniques for binding site identification in ensembles of Ras conformations generated by molecular simulations.
Collapse
Affiliation(s)
- Michael McCarthy
- Department of Integrative Biology and Pharmacology, University of Texas Health Science Center at Houston, Houston, TX 77030, USA
| | - Priyanka Prakash
- Department of Integrative Biology and Pharmacology, University of Texas Health Science Center at Houston, Houston, TX 77030, USA
| | - Alemayehu A Gorfe
- Department of Integrative Biology and Pharmacology, University of Texas Health Science Center at Houston, Houston, TX 77030, USA
| |
Collapse
|
57
|
Investigation of the Lipid Binding Properties of the Marburg Virus Matrix Protein VP40. J Virol 2015; 90:3074-85. [PMID: 26719280 DOI: 10.1128/jvi.02607-15] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2015] [Accepted: 12/27/2015] [Indexed: 11/20/2022] Open
Abstract
UNLABELLED Marburg virus (MARV), which belongs to the virus family Filoviridae, causes hemorrhagic fever in humans and nonhuman primates that is often fatal. MARV is a lipid-enveloped virus that during the replication process extracts its lipid coat from the plasma membrane of the host cell it infects. MARV carries seven genes, one of which encodes its matrix protein VP40 (mVP40), which regulates the assembly and budding of the virions. Currently, little information is available on mVP40 lipid binding properties. Here, we have investigated the in vitro and cellular mechanisms by which mVP40 associates with lipid membranes. mVP40 associates with anionic membranes in a nonspecific manner that is dependent upon the anionic charge density of the membrane. These results are consistent with recent structural determination of mVP40, which elucidated an mVP40 dimer with a flat and extensive cationic lipid binding interface. IMPORTANCE Marburg virus (MARV) is a lipid-enveloped filamentous virus from the family Filoviridae. MARV was discovered in 1967, and yet little is known about how its seven genes are used to assemble and form a new viral particle in the host cell it infects. The MARV matrix protein VP40 (mVP40) underlies the inner leaflet of the virus and regulates budding from the host cell plasma membrane. In vitro and cellular assays in this study investigated the mechanism by which mVP40 associates with lipids. The results demonstrate that mVP40 interactions with lipid vesicles or the inner leaflet of the plasma membrane are electrostatic but nonspecific in nature and are dependent on the anionic charge density of the membrane surface. Small molecules that can disrupt lipid trafficking or reduce the anionic charge of the plasma membrane interface may be useful in inhibiting assembly and budding of MARV.
Collapse
|
58
|
Zhou Y, Wong CO, Cho KJ, van der Hoeven D, Liang H, Thakur DP, Luo J, Babic M, Zinsmaier KE, Zhu MX, Hu H, Venkatachalam K, Hancock JF. SIGNAL TRANSDUCTION. Membrane potential modulates plasma membrane phospholipid dynamics and K-Ras signaling. Science 2015; 349:873-6. [PMID: 26293964 DOI: 10.1126/science.aaa5619] [Citation(s) in RCA: 213] [Impact Index Per Article: 23.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Plasma membrane depolarization can trigger cell proliferation, but how membrane potential influences mitogenic signaling is uncertain. Here, we show that plasma membrane depolarization induces nanoscale reorganization of phosphatidylserine and phosphatidylinositol 4,5-bisphosphate but not other anionic phospholipids. K-Ras, which is targeted to the plasma membrane by electrostatic interactions with phosphatidylserine, in turn undergoes enhanced nanoclustering. Depolarization-induced changes in phosphatidylserine and K-Ras plasma membrane organization occur in fibroblasts, excitable neuroblastoma cells, and Drosophila neurons in vivo and robustly amplify K-Ras-dependent mitogen-activated protein kinase (MAPK) signaling. Conversely, plasma membrane repolarization disrupts K-Ras nanoclustering and inhibits MAPK signaling. By responding to voltage-induced changes in phosphatidylserine spatiotemporal dynamics, K-Ras nanoclusters set up the plasma membrane as a biological field-effect transistor, allowing membrane potential to control the gain in mitogenic signaling circuits.
Collapse
Affiliation(s)
- Yong Zhou
- Department of Integrative Biology and Pharmacology, Medical School, University of Texas Health Science Center at Houston, Houston, TX 77030, USA
| | - Ching-On Wong
- Department of Integrative Biology and Pharmacology, Medical School, University of Texas Health Science Center at Houston, Houston, TX 77030, USA
| | - Kwang-jin Cho
- Department of Integrative Biology and Pharmacology, Medical School, University of Texas Health Science Center at Houston, Houston, TX 77030, USA
| | - Dharini van der Hoeven
- Department of Diagnostic and Biomedical Sciences, Dental School, University of Texas Health Science Center at Houston, Houston, TX 77054, USA
| | - Hong Liang
- Department of Integrative Biology and Pharmacology, Medical School, University of Texas Health Science Center at Houston, Houston, TX 77030, USA
| | - Dhananiay P Thakur
- Department of Integrative Biology and Pharmacology, Medical School, University of Texas Health Science Center at Houston, Houston, TX 77030, USA
| | - Jialie Luo
- Department of Integrative Biology and Pharmacology, Medical School, University of Texas Health Science Center at Houston, Houston, TX 77030, USA
| | - Milos Babic
- Department of Neuroscience, University of Arizona, Tucson, AZ 85721, USA
| | - Konrad E Zinsmaier
- Department of Neuroscience, University of Arizona, Tucson, AZ 85721, USA
| | - Michael X Zhu
- Department of Integrative Biology and Pharmacology, Medical School, University of Texas Health Science Center at Houston, Houston, TX 77030, USA. Program in Cell and Regulatory Biology, University of Texas Graduate School of Biomedical Sciences, Houston, TX 77030, USA
| | - Hongzhen Hu
- Department of Integrative Biology and Pharmacology, Medical School, University of Texas Health Science Center at Houston, Houston, TX 77030, USA. Program in Cell and Regulatory Biology, University of Texas Graduate School of Biomedical Sciences, Houston, TX 77030, USA
| | - Kartik Venkatachalam
- Department of Integrative Biology and Pharmacology, Medical School, University of Texas Health Science Center at Houston, Houston, TX 77030, USA. Program in Cell and Regulatory Biology, University of Texas Graduate School of Biomedical Sciences, Houston, TX 77030, USA
| | - John F Hancock
- Department of Integrative Biology and Pharmacology, Medical School, University of Texas Health Science Center at Houston, Houston, TX 77030, USA. Program in Cell and Regulatory Biology, University of Texas Graduate School of Biomedical Sciences, Houston, TX 77030, USA.
| |
Collapse
|
59
|
Salim AA, Xiao X, Cho KJ, Piggott AM, Lacey E, Hancock JF, Capon RJ. Rare Streptomyces sp. polyketides as modulators of K-Ras localisation. Org Biomol Chem 2015; 12:4872-8. [PMID: 24875924 DOI: 10.1039/c4ob00745j] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Chemical investigations of a soil-derived Streptomyces sp. led to the isolation of five new polyketides, (+)-oxanthromicin, (±)-hemi-oxanthromicins A/B, (±)-spiro-oxanthromicin A and oxanthroquinone, and the known alkaloid staurosporine, and the detection of four new metastable analogues, (±)-spiro-oxanthromicins B1/B2/C1/C2. Among the compounds tested, SAR investigations established that the synthetic oxanthroquinone ethyl ester and 3-O-methyl-oxanthroquinone ethyl ester were optimal at mislocalising oncogenic mutant K-Ras from the plasma membrane of intact Madin-Darby canine kidney (MDCK) cells (IC50 4.6 and 1.2 μM), while a sub-EC50 dose of (±)-spiro-oxanthromicin A was optimal at potentiating (750%) the K-Ras inhibitory activity of staurosporine (IC50 60 pM). These studies demonstrate that a rare class of Streptomyces polyketide modulates K-Ras plasma membrane localisation, with implications for the future treatment of K-Ras dependent cancers.
Collapse
Affiliation(s)
- Angela A Salim
- Institute for Molecular Bioscience, The University of Queensland, St. Lucia, QLD 4072, Australia.
| | | | | | | | | | | | | |
Collapse
|
60
|
Varela Chavez C, Hoos S, Haustant GM, Chenal A, England P, Blondel A, Pauillac S, Lacy DB, Popoff MR. The catalytic domains of Clostridium sordellii lethal toxin and related large clostridial glucosylating toxins specifically recognize the negatively charged phospholipids phosphatidylserine and phosphatidic acid. Cell Microbiol 2015; 17:1477-93. [PMID: 25882477 DOI: 10.1111/cmi.12449] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2015] [Accepted: 04/15/2015] [Indexed: 12/23/2022]
Abstract
Clostridium sordellii lethal toxin (TcsL) is a potent virulence factor belonging to the large clostridial glucosylating toxin family. TcsL enters target cells via receptor-mediated endocytosis and delivers the N-terminal catalytic domain (TcsL-cat) into the cytosol upon an autoproteolytic process. TcsL-cat inactivates small GTPases including Rac and Ras by glucosylation with uridine-diphosphate (UDP)-glucose as cofactor leading to drastic changes in cytoskeleton and cell viability. TcsL-cat was found to preferentially bind to phosphatidylserine (PS)-containing membranes and to increase the glucosylation of Rac anchored to lipid membrane. We here report binding affinity measurements of TcsL-cat for brain PS-containing membranes by surface plasmon resonance and enzyme-linked immunosorbent assay (ELISA). In addition, TcsL-cat bound to phosphatidic acid (PA) and, to a lesser extent, to other anionic lipids, but not to neutral lipids, sphingolipids or sterol. We further show that the lipid unsaturation status influenced TcsL-cat binding to phospholipids, PS with unsaturated acyl chains and PA with saturated acyl chains being the preferred bindingsubstrates. Phospholipid binding site is localized at the N-terminal four helical bundle structure (1-93 domain). However, TcsL-1-93 bound to a broad range of substrates, whereas TcsL-cat, which is the active domain physiologically delivered into the cytosol, selectively bound to PS and PA. Similar findings were observed with the other large clostridial glucosylating toxins from C. difficile, C. novyi and C. perfringens.
Collapse
Affiliation(s)
| | - Sylviane Hoos
- Plateforme de Biophysique Moléculaire, Institut Pasteur, Paris, France
| | | | - Alexandre Chenal
- Unité de Biochimie des Interactions Macromoléculaires, Institut Pasteur, Paris, France
| | - Patrick England
- Plateforme de Biophysique Moléculaire, Institut Pasteur, Paris, France
| | - Arnaud Blondel
- Unité de Bioinformatique Structurale, Institut Pasteur, Paris, France
| | - Serge Pauillac
- Unité des Bactéries anaérobies et Toxines, Institut Pasteur, Paris, France
| | - D Borden Lacy
- Unité de Bioinformatique Structurale, Institut Pasteur, Paris, France.,Department of Pathology, Microbiology, and Immunology, Vanderbilt University School of Medicine, Nashville, TN, USA
| | | |
Collapse
|
61
|
Schmick M, Kraemer A, Bastiaens PIH. Ras moves to stay in place. Trends Cell Biol 2015; 25:190-7. [PMID: 25759176 DOI: 10.1016/j.tcb.2015.02.004] [Citation(s) in RCA: 78] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2014] [Revised: 02/06/2015] [Accepted: 02/09/2015] [Indexed: 10/23/2022]
Abstract
Ras is a major intracellular signaling hub. This elevated position comes at a precarious cost: a single point mutation can cause aberrant signaling. The capacity of Ras for signaling is inextricably linked to its enrichment at the plasma membrane (PM). This PM localization is dynamically maintained by three essential elements: alteration of membrane affinities via lipidation and membrane-interaction motifs; trapping on specific membranes coupled with unidirectional vesicular transport to the PM; and regulation of diffusion via interaction with a solubilization factor. This system constitutes a cycle that primarily corrects for the entropic equilibration of Ras to all membranes that dilutes its signaling capacity. We illuminate how this reaction-diffusion system maintains an out-of-equilibrium localization of Ras GTPases and thereby confers signaling functionality to the PM.
Collapse
Affiliation(s)
- Malte Schmick
- Department of Systemic Cell Biology, Max Planck Institute of Molecular Physiology, Otto-Hahn-Strasse 11, 44227 Dortmund, Germany
| | - Astrid Kraemer
- Department of Systemic Cell Biology, Max Planck Institute of Molecular Physiology, Otto-Hahn-Strasse 11, 44227 Dortmund, Germany
| | - Philippe I H Bastiaens
- Department of Systemic Cell Biology, Max Planck Institute of Molecular Physiology, Otto-Hahn-Strasse 11, 44227 Dortmund, Germany; Faculty of Chemistry and Chemical Biology, TU Dortmund, Otto-Hahn-Strasse 6, 44227 Dortmund, Germany.
| |
Collapse
|
62
|
Maekawa M, Fairn GD. Complementary probes reveal that phosphatidylserine is required for the proper transbilayer distribution of cholesterol. J Cell Sci 2015; 128:1422-33. [PMID: 25663704 DOI: 10.1242/jcs.164715] [Citation(s) in RCA: 169] [Impact Index Per Article: 18.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Cholesterol is an essential component of metazoan cellular membranes and it helps to maintain the structural integrity and fluidity of the plasma membrane. Here, we developed a cholesterol biosensor, termed D4H, based on the fourth domain of Clostridium perfringens theta-toxin, which recognizes cholesterol in the cytosolic leaflet of the plasma membrane and organelles. The D4H probe disassociates from the plasma membrane upon cholesterol extraction and after perturbations in cellular cholesterol trafficking. When used in combination with a recombinant version of the biosensor, we show that plasmalemmal phosphatidylserine is essential for retaining cholesterol in the cytosolic leaflet of the plasma membrane. In vitro experiments reveal that 1-stearoy-2-oleoyl phosphatidylserine can induce phase separation in cholesterol-containing lipid bilayers and shield cholesterol from cholesterol oxidase. Finally, the altered transbilayer distribution of cholesterol causes flotillin-1 to relocalize to endocytic organelles. This probe should be useful in the future to study pools of cholesterol in the cytosolic leaflet of the plasma membrane and organelles.
Collapse
Affiliation(s)
- Masashi Maekawa
- Keenan Research Centre for Biomedical Science, St. Michael's Hospital, 209 Victoria Street, Toronto, ON, M5S 1T8, Canada
| | - Gregory D Fairn
- Keenan Research Centre for Biomedical Science, St. Michael's Hospital, 209 Victoria Street, Toronto, ON, M5S 1T8, Canada Department of Biochemistry, University of Toronto, Toronto, ON M5S 1A8, Canada Department of Surgery, University of Toronto, Toronto, ON M5T 1P5, Canada Institute of Medical Science, Faculty of Medicine, University of Toronto, Toronto, ON M5S 1A8, Canada Institute for Biomedical Engineering and Science Technology (iBEST) at Ryerson University and St. Michael's Hospital, Toronto, ON M5B 2K3, Canada
| |
Collapse
|
63
|
Najumudeen AK, Guzmán C, Posada IMD, Abankwa D. Rab-NANOPS: FRET biosensors for Rab membrane nanoclustering and prenylation detection in mammalian cells. Methods Mol Biol 2015; 1298:29-45. [PMID: 25800830 DOI: 10.1007/978-1-4939-2569-8_3] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Rab proteins constitute the largest subfamily of Ras-like small GTPases. They are central to vesicular transport and organelle definition in eukaryotic cells. Unlike their Ras counterparts, they are not a hallmark of cancer. However, a number of diseases, including cancer, show a misregulation of Rab protein activity. As for all membrane-anchored signaling proteins, correct membrane organization is critical for Rabs to operate. In this chapter, we provide a detailed protocol for the use of a flow cytometry-based Fluorescence Resonance Energy Transfer (FRET)-biosensors assay, which allows to detect changes in membrane anchorage, subcellular distribution, and of the nanoscale organization of Rab-GTPases in mammalian cell lines. This assay is high-throughput amenable and can therefore be utilized in chemical-genomic and drug discovery efforts.
Collapse
Affiliation(s)
- Arafath Kaja Najumudeen
- Turku Centre for Biotechnology, Åbo Akademi University, Tykistökatu 6B, 20520, Turku, Finland
| | | | | | | |
Collapse
|
64
|
TMEM16 proteins: unknown structure and confusing functions. J Mol Biol 2014; 427:94-105. [PMID: 25451786 DOI: 10.1016/j.jmb.2014.09.028] [Citation(s) in RCA: 106] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2014] [Revised: 09/24/2014] [Accepted: 09/29/2014] [Indexed: 11/23/2022]
Abstract
The TMEM16 family of membrane proteins, also known as anoctamins, plays key roles in a variety of physiological functions that range from ion transport to phospholipid scrambling and to regulating other ion channels. The first two family members to be functionally characterized, TMEM16A (ANO1) and TMEM16B (ANO2), form Ca(2+)-activated Cl(-) channels and are important for transepithelial ion transport, olfaction, phototransduction, smooth muscle contraction, nociception, cell proliferation and control of neuronal excitability. The roles of other family members, such as TMEM16C (ANO3), TMEM16D (ANO4), TMEM16F (ANO6), TMEM16G (ANO7) and TMEM16J (ANO9), remain poorly understood and controversial. These homologues were reported to be phospholipid scramblases, ion channels, to have both functions or to be regulatory subunits of other channels. Mutations in TMEM16F cause Scott syndrome, a bleeding disorder caused by impaired Ca(2+)-dependent externalization of phosphatidylserine in activated platelets, suggesting that this homologue might be a scramblase. However, overexpression of TMEM16F has also been associated with a remarkable number of different ion channel types, raising the possibility that this protein might be involved in both ion and lipid transports. The recent identification of an ancestral TMEM16 homologue with intrinsic channel and scramblase activities supports this hypothesis. Thus, the TMEM16 family might have diverged in two or three different subclasses, channels, scramblases and dual-function channel/scramblases. The structural bases and functional implication of such a functional diversity within a single protein family remain to be elucidated and the links between TMEM16 functions and human physiology and pathologies need to be investigated.
Collapse
|
65
|
Salim AA, Cho KJ, Tan L, Quezada M, Lacey E, Hancock JF, Capon RJ. Rare Streptomyces N-formyl amino-salicylamides inhibit oncogenic K-Ras. Org Lett 2014; 16:5036-9. [PMID: 25238489 DOI: 10.1021/ol502376e] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
During a search for inhibitors of oncogenic K-Ras, we detected two known and two new examples of the rare neoantimycin structure class from a liquid cultivation of Streptomyces orinoci, and reassigned/assigned structures to all based on detailed spectroscopic analysis and microscale C3 Marfey's and C3 Mosher chemical degradation/derivatization/analysis. SAR investigations inclusive of the biosynthetically related antimycins and respirantin, and synthetic benzoxazolone, documented a unique N-formyl amino-salicylamide pharmacophore as a potent inhibitor of oncogenic K-Ras.
Collapse
Affiliation(s)
- Angela A Salim
- Institute for Molecular Bioscience, The University of Queensland , St. Lucia, QLD 4072, Australia
| | | | | | | | | | | | | |
Collapse
|
66
|
Zhou Y, Hancock JF. Ras nanoclusters: Versatile lipid-based signaling platforms. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2014; 1853:841-9. [PMID: 25234412 DOI: 10.1016/j.bbamcr.2014.09.008] [Citation(s) in RCA: 174] [Impact Index Per Article: 17.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/17/2014] [Revised: 09/05/2014] [Accepted: 09/08/2014] [Indexed: 12/31/2022]
Abstract
Ras proteins assemble into transient nanoclusters on the plasma membrane. Nanoclusters are the sites of Ras effector recruitment and activation and are therefore essential for signal transmission. The dynamics of nanocluster formation and disassembly result in interesting emergent properties including high-fidelity signal transmission. More recently the lipid structure of Ras nanoclusters has been reported and shown to contribute to isoform-specific Ras signaling. In addition specific lipids play critical roles in mediating the formation, stability and dynamics of Ras nanoclusters. In consequence the spatiotemporal organization of these lipids has emerged as important and novel regulators of Ras function. This article is part of a Special Issue entitled: Nanoscale membrane organisation and signalling.
Collapse
Affiliation(s)
- Yong Zhou
- Department of Integrative Biology and Pharmacology, University of Texas Medical School, Houston, TX 77030, USA.
| | - John F Hancock
- Department of Integrative Biology and Pharmacology, University of Texas Medical School, Houston, TX 77030, USA.
| |
Collapse
|
67
|
Mioka T, Fujimura-Kamada K, Tanaka K. Asymmetric distribution of phosphatidylserine is generated in the absence of phospholipid flippases in Saccharomyces cerevisiae. Microbiologyopen 2014; 3:803-21. [PMID: 25220349 PMCID: PMC4234269 DOI: 10.1002/mbo3.211] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2014] [Revised: 07/23/2014] [Accepted: 08/01/2014] [Indexed: 11/20/2022] Open
Abstract
In eukaryotic cells, phosphatidylserine (PS) is predominantly located in the cytosolic leaflet of the plasma membrane; this asymmetry is generated by an unknown mechanism. In this study, we used the PS-specific probe mRFP-Lact-C2 to investigate the possible involvement of type 4 P-type ATPases, also called phospholipid flippases, in the generation of this asymmetry in Saccharomyces cerevisiae. PS was not found in the trans-Golgi Network in wild-type cells, but it became exposed when vesicle formation was compromised in the sec7 mutant, and it was also exposed on secretory vesicles (SVs), as reported previously. However, flippase mutations did not reduce the exposure of PS in either case, even at low levels that would only be detectable by quantitative analysis of mRFP-Lact-C2 fluorescence in isolated SVs. Furthermore, no reduction in the PS level was observed in a mutant with multiple flippase mutations. Because PS was not exposed in a mutant that accumulates ER or cis/medial-Golgi membranes, Golgi maturation seems to be a prerequisite for PS translocation. Our results suggest that an unknown mechanism, possibly a protein with flippase-like activity, acts in conjunction with known flippases to regulate PS translocation.
Collapse
Affiliation(s)
- Tetsuo Mioka
- Division of Molecular Interaction, Institute for Genetic Medicine, Hokkaido University Graduate School of Life Science, N15 W7, Kita-ku, Sapporo, 060-0815, Japan
| | | | | |
Collapse
|
68
|
A high-throughput assay for small molecule destabilizers of the KRAS oncoprotein. PLoS One 2014; 9:e103836. [PMID: 25093678 PMCID: PMC4122376 DOI: 10.1371/journal.pone.0103836] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2014] [Accepted: 07/02/2014] [Indexed: 12/30/2022] Open
Abstract
Mutations in the Ras family of small GTPases, particularly KRAS, occur at high frequencies in cancer and represent a major unmet therapeutic need due to the lack of effective targeted therapies. Past efforts directed at inhibiting the activity of the Ras oncoprotein have proved difficult. We propose an alternative approach to target Ras by eliminating Ras protein from cells with pharmacological means. In this study, we developed a cell-based, high-content screening platform to identify small molecules that could promote the degradation of the KRAS oncoprotein. We generated an EGFP-KRASG12V fluorescence reporter system and implemented it for automated screening in 1536-well plates using high-throughput cellular imaging. We screened a library of clinically relevant compounds at wide dose range and identified Ponatinib and AMG-47a as two candidate compounds that selectively reduced the levels of EGFP-KRASG12V protein but did not affect EGFP protein in cells. This proof-of-principle study demonstrates that it is feasible to use a high-throughput screen to identify compounds that promote the degradation of the Ras oncoprotein as a new approach to target Ras.
Collapse
|
69
|
KRas localizes to the plasma membrane by spatial cycles of solubilization, trapping and vesicular transport. Cell 2014; 157:459-471. [PMID: 24725411 DOI: 10.1016/j.cell.2014.02.051] [Citation(s) in RCA: 181] [Impact Index Per Article: 18.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2013] [Revised: 11/29/2013] [Accepted: 02/20/2014] [Indexed: 11/22/2022]
Abstract
KRas is a major proto-oncogene product whose signaling activity depends on its level of enrichment on the plasma membrane (PM). This PM localization relies on posttranslational prenylation for membrane affinity, while PM specificity has been attributed to electrostatic interactions between negatively charged phospholipids in the PM and basic amino-acids in the C terminus of KRas. By measuring kinetic parameters of KRas dynamics in living cells with a cellular-automata-based data-fitting approach in realistic cell-geometries, we show that charge-based specificity is not sufficient to generate PM enrichment in light of the total surface area of endomembranes. Instead, mislocalized KRas is continuously sequestered from endomembranes by cytosolic PDEδ to be unloaded in an Arl2-dependent manner to perinuclear membranes. Electrostatic interactions then trap KRas at the recycling endosome (RE), from where vesicular transport restores enrichment on the PM. This energy driven reaction-diffusion cycle explains how small molecule targeting of PDEδ affects the spatial organization of KRas.
Collapse
|
70
|
Kim HY, Huang BX, Spector AA. Phosphatidylserine in the brain: metabolism and function. Prog Lipid Res 2014; 56:1-18. [PMID: 24992464 DOI: 10.1016/j.plipres.2014.06.002] [Citation(s) in RCA: 212] [Impact Index Per Article: 21.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2014] [Revised: 06/18/2014] [Accepted: 06/21/2014] [Indexed: 01/08/2023]
Abstract
Phosphatidylserine (PS) is the major anionic phospholipid class particularly enriched in the inner leaflet of the plasma membrane in neural tissues. PS is synthesized from phosphatidylcholine or phosphatidylethanolamine by exchanging the base head group with serine, and this reaction is catalyzed by phosphatidylserine synthase 1 and phosphatidylserine synthase 2 located in the endoplasmic reticulum. Activation of Akt, Raf-1 and protein kinase C signaling, which supports neuronal survival and differentiation, requires interaction of these proteins with PS localized in the cytoplasmic leaflet of the plasma membrane. Furthermore, neurotransmitter release by exocytosis and a number of synaptic receptors and proteins are modulated by PS present in the neuronal membranes. Brain is highly enriched with docosahexaenoic acid (DHA), and brain PS has a high DHA content. By promoting PS synthesis, DHA can uniquely expand the PS pool in neuronal membranes and thereby influence PS-dependent signaling and protein function. Ethanol decreases DHA-promoted PS synthesis and accumulation in neurons, which may contribute to the deleterious effects of ethanol intake. Improvement of some memory functions has been observed in cognitively impaired subjects as a result of PS supplementation, but the mechanism is unclear.
Collapse
Affiliation(s)
- Hee-Yong Kim
- Laboratory of Molecular Signaling, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, MD 20892-9410, United States.
| | - Bill X Huang
- Laboratory of Molecular Signaling, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, MD 20892-9410, United States
| | - Arthur A Spector
- Laboratory of Molecular Signaling, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, MD 20892-9410, United States
| |
Collapse
|
71
|
Zimmermann G, Schultz-Fademrecht C, Küchler P, Murarka S, Ismail S, Triola G, Nussbaumer P, Wittinghofer A, Waldmann H. Structure guided design and kinetic analysis of highly potent benzimidazole inhibitors targeting the PDEδ prenyl binding site. J Med Chem 2014; 57:5435-48. [PMID: 24884780 DOI: 10.1021/jm500632s] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
K-Ras is one of the most frequently mutated signal transducing human oncogenes. Ras signaling activity requires correct cellular localization of the GTPase. The spatial organization of K-Ras is controlled by the prenyl binding protein PDEδ, which enhances Ras diffusion in the cytosol. Inhibition of the Ras-PDEδ interaction by small molecules impairs Ras localization and signaling. Here we describe in detail the identification and structure guided development of Ras-PDEδ inhibitors targeting the farnesyl binding pocket of PDEδ with nanomolar affinity. We report kinetic data that characterize the binding of the most potent small molecule ligands to PDEδ and prove their binding to endogenous PDEδ in cell lysates. The PDEδ inhibitors provide promising starting points for the establishment of new drug discovery programs aimed at cancers harboring oncogenic K-Ras.
Collapse
Affiliation(s)
- Gunther Zimmermann
- Max Planck Institute of Molecular Physiology , Otto-Hahn-Strasse 11, 44227 Dortmund, Germany
| | | | | | | | | | | | | | | | | |
Collapse
|
72
|
Gelabert-Baldrich M, Soriano-Castell D, Calvo M, Lu A, Viña-Vilaseca A, Rentero C, Pol A, Grinstein S, Enrich C, Tebar F. Dynamics of KRas on endosomes: involvement of acidic phospholipids in its association. FASEB J 2014; 28:3023-37. [PMID: 24719356 DOI: 10.1096/fj.13-241158] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The endocytic compartment is emerging as a functional platform for controlling important cellular processes. We have found that ∼10 to 15% of total KRas, a protein that is frequently mutated in cancer, is present on endosomes, independent of its activation state. The dynamics of GFP-KRas wild-type (WT) and constitutively active or inactive mutants on endosomes were analyzed by fluorescence recovery after photobleaching (FRAP) microscopy. The measurements revealed an extraordinarily fast recovery of KRas WT [half-time (HT), ∼1.3 s] compared to HRas, Rab5, and EGFR, with the active KRasG12V mutant being significantly faster and more mobile (HT, ∼1 s, and ∼82% of exchangeable fraction) than the inactive KRasS17N (HT, ∼1.6 s, and ∼60% of exchangeable fraction). KRas rapidly switches from the cytoplasm to the endosomal membranes by an electrostatic interaction between its polybasic region and the endosomal acidic phospholipids, mainly phosphatidylserine.-Gelabert-Baldrich, M., Soriano-Castell, D., Calvo, M., Lu, A., Viña-Vilaseca, A., Rentero, C., Pol, A., Grinstein, S. Enrich, C., Tebar, F. Dynamics of KRas on endosomes: involvement of acidic phospholipids in its association.
Collapse
Affiliation(s)
- Mariona Gelabert-Baldrich
- Departament de Biologia Cel·lular, Immunologia i Neurociències, Facultat de Medicina, Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), and
| | - David Soriano-Castell
- Departament de Biologia Cel·lular, Immunologia i Neurociències, Facultat de Medicina, Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), and
| | - Maria Calvo
- Unitat de Microscopia Òptica Avançada, Facultat de Medicina, Centres Científics i Tecnològics, Universitat de Barcelona, Barcelona, Spain
| | - Albert Lu
- Department of Biochemistry, Stanford University School of Medicine, Stanford, California, USA
| | - Arnau Viña-Vilaseca
- Departament de Biologia Cel·lular, Immunologia i Neurociències, Facultat de Medicina, Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), and
| | - Carles Rentero
- Departament de Biologia Cel·lular, Immunologia i Neurociències, Facultat de Medicina, Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), and
| | - Albert Pol
- Departament de Biologia Cel·lular, Immunologia i Neurociències, Facultat de Medicina, Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), and Institució Catalana de Recerca i Estudis Avançats (ICREA), Barcelona, Spain; and
| | - Sergio Grinstein
- Division of Cell Biology, Hospital for Sick Children, Toronto, Ontario, Canada
| | - Carlos Enrich
- Departament de Biologia Cel·lular, Immunologia i Neurociències, Facultat de Medicina, Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), and
| | - Francesc Tebar
- Departament de Biologia Cel·lular, Immunologia i Neurociències, Facultat de Medicina, Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), and
| |
Collapse
|
73
|
Ariotti N, Fernández-Rojo MA, Zhou Y, Hill MM, Rodkey TL, Inder KL, Tanner LB, Wenk MR, Hancock JF, Parton RG. Caveolae regulate the nanoscale organization of the plasma membrane to remotely control Ras signaling. ACTA ACUST UNITED AC 2014; 204:777-92. [PMID: 24567358 PMCID: PMC3941050 DOI: 10.1083/jcb.201307055] [Citation(s) in RCA: 103] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Caveolae transduce mechanical stress into plasma membrane lipid alterations that disrupt Ras organization in an isoform-specific manner and modulate downstream signal transduction. The molecular mechanisms whereby caveolae exert control over cellular signaling have to date remained elusive. We have therefore explored the role caveolae play in modulating Ras signaling. Lipidomic and gene array analyses revealed that caveolin-1 (CAV1) deficiency results in altered cellular lipid composition, and plasma membrane (PM) phosphatidylserine distribution. These changes correlated with increased K-Ras expression and extensive isoform-specific perturbation of Ras spatial organization: in CAV1-deficient cells K-RasG12V nanoclustering and MAPK activation were enhanced, whereas GTP-dependent lateral segregation of H-Ras was abolished resulting in compromised signal output from H-RasG12V nanoclusters. These changes in Ras nanoclustering were phenocopied by the down-regulation of Cavin1, another crucial caveolar structural component, and by acute loss of caveolae in response to increased osmotic pressure. Thus, we postulate that caveolae remotely regulate Ras nanoclustering and signal transduction by controlling PM organization. Similarly, caveolae transduce mechanical stress into PM lipid alterations that, in turn, modulate Ras PM organization.
Collapse
Affiliation(s)
- Nicholas Ariotti
- The University of Queensland, Institute for Molecular Bioscience, Queensland 4072, Australia
| | | | | | | | | | | | | | | | | | | |
Collapse
|
74
|
Signal integration by lipid-mediated spatial cross talk between Ras nanoclusters. Mol Cell Biol 2013; 34:862-76. [PMID: 24366544 DOI: 10.1128/mcb.01227-13] [Citation(s) in RCA: 106] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Lipid-anchored Ras GTPases form transient, spatially segregated nanoclusters on the plasma membrane that are essential for high-fidelity signal transmission. The lipid composition of Ras nanoclusters, however, has not previously been investigated. High-resolution spatial mapping shows that different Ras nanoclusters have distinct lipid compositions, indicating that Ras proteins engage in isoform-selective lipid sorting and accounting for different signal outputs from different Ras isoforms. Phosphatidylserine is a common constituent of all Ras nanoclusters but is only an obligate structural component of K-Ras nanoclusters. Segregation of K-Ras and H-Ras into spatially and compositionally distinct lipid assemblies is exquisitely sensitive to plasma membrane phosphatidylserine levels. Phosphatidylserine spatial organization is also modified by Ras nanocluster formation. In consequence, Ras nanoclusters engage in remote lipid-mediated communication, whereby activated H-Ras disrupts the assembly and operation of spatially segregated K-Ras nanoclusters. Computational modeling and experimentation reveal that complex effects of caveolin and cortical actin on Ras nanoclustering are similarly mediated through regulation of phosphatidylserine spatiotemporal dynamics. We conclude that phosphatidylserine maintains the lateral segregation of diverse lipid-based assemblies on the plasma membrane and that lateral connectivity between spatially remote lipid assemblies offers important previously unexplored opportunities for signal integration and signal processing.
Collapse
|
75
|
Iglesias DA, Yates MS, van der Hoeven D, Rodkey TL, Zhang Q, Co NN, Burzawa J, Chigurupati S, Celestino J, Bowser J, Broaddus R, Hancock JF, Schmandt R, Lu KH. Another surprise from Metformin: novel mechanism of action via K-Ras influences endometrial cancer response to therapy. Mol Cancer Ther 2013; 12:2847-56. [PMID: 24077915 DOI: 10.1158/1535-7163.mct-13-0439] [Citation(s) in RCA: 60] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Metformin is an oral biguanide commonly used for the treatment of type II diabetes and has recently been demonstrated to possess antiproliferative properties that can be exploited for the prevention and treatment of a variety of cancers. The mechanisms underlying this effect have not been fully elucidated. Using both in vitro and in vivo models, we examined the effects of metformin on endometrial tumors with defined aberrations in the PI3K/PTEN/mTOR and MAPK signaling pathways to understand metformin mechanism of action and identify clinically useful predictors of response to this agent. In vitro assays of proliferation, cytotoxicity, and apoptosis were used to quantify the effects of metformin on endometrial cancer cell lines with mutations in the PI3K/PTEN/mTOR and MAPK signaling pathways. The in vivo effects of oral metformin on tumor progression were further examined using xenograft mouse models of endometrial cancer. K-Ras localization was analyzed by confocal microscopy using GFP-labeled oncogenic K-Ras and by immunoblot following subcellular fractionation. Metformin inhibited cell proliferation, induced apoptosis, and decreased tumor growth in preclinical endometrial cancer models, with the greatest response observed in cells harboring activating mutations in K-Ras. Furthermore, metformin displaces constitutively active K-Ras from the cell membrane, causing uncoupling of the MAPK signaling pathway. These studies provide a rationale for clinical trials using metformin in combination with PI3K-targeted agents for tumors harboring activating K-Ras mutations, and reveal a novel mechanism of action for metformin.
Collapse
Affiliation(s)
- David A Iglesias
- Corresponding Author: Karen H. Lu, Department of Gynecologic Oncology and Reproductive Medicine, 1155 Hermann Pressler Dr., Unit 1362, Houston, TX 77030.
| | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
76
|
Abstract
Oncogenic mutant K-Ras is highly prevalent in multiple human tumors. Despite significant efforts to directly target Ras activity, no K-Ras-specific inhibitors have been developed and taken into the clinic. Since Ras proteins must be anchored to the inner leaflet of the plasma membrane (PM) for full biological activity, we devised a high-content screen to identify molecules with ability to displace K-Ras from the PM. Here we summarize the biochemistry and biology of three classes of compound identified by this screening method that inhibit K-Ras PM targeting: staurosporine and analogs, fendiline, and metformin. All three classes of compound significantly abrogate cell proliferation and Ras signaling in K-Ras-transformed cancer cells. Taken together, these studies provide an important proof of concept that blocking PM localization of K-Ras is a tractable therapeutic target.
Collapse
Affiliation(s)
- Kwang-Jin Cho
- Department of Integrative Biology and Pharmacology, The University of Texas Medical School at Houston, Houston, Texas, USA
| | - Dharini van der Hoeven
- Department of Diagnostic and Biomedical Sciences, The University of Texas School of Dentistry at Houston, Houston, Texas, USA
| | - John F Hancock
- Department of Integrative Biology and Pharmacology, The University of Texas Medical School at Houston, Houston, Texas, USA.
| |
Collapse
|
77
|
Prakash P, Gorfe AA. Lessons from computer simulations of Ras proteins in solution and in membrane. Biochim Biophys Acta Gen Subj 2013; 1830:5211-8. [PMID: 23906604 DOI: 10.1016/j.bbagen.2013.07.024] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2013] [Revised: 07/23/2013] [Accepted: 07/24/2013] [Indexed: 12/22/2022]
Abstract
BACKGROUND A great deal has been learned over the last several decades about the function of Ras proteins in solution and membrane environments. While much of this knowledge has been derived from a plethora of experimental techniques, computer simulations have also played a substantial role. SCOPE OF REVIEW Our goal here is to summarize the contribution of molecular simulations to our current understanding of normal and aberrant Ras function. We focus on lessons from molecular dynamics simulations in aqueous and membrane environments. MAJOR CONCLUSIONS The central message is that a close interaction between theory and simulation on the one hand and cell-biological, spectroscopic and other experimental approaches on the other has played, and will likely continue to play, a vital role in Ras research. GENERAL SIGNIFICANCE Atomistic insights emerging from detailed simulations of Ras in solution and in bilayers may be the key to unlock the secret that to date prevented development of selective anti-Ras inhibitors for cancer therapy.
Collapse
Affiliation(s)
- Priyanka Prakash
- University of Texas Health Science Center at Houston, Department of Integrative Biology and Pharmacology, 6431 Fannin St., Houston, TX 77030, USA
| | | |
Collapse
|
78
|
Andrographolide derivatives inhibit guanine nucleotide exchange and abrogate oncogenic Ras function. Proc Natl Acad Sci U S A 2013; 110:10201-6. [PMID: 23737504 DOI: 10.1073/pnas.1300016110] [Citation(s) in RCA: 117] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Aberrant signaling by oncogenic mutant rat sarcoma (Ras) proteins occurs in ∼15% of all human tumors, yet direct inhibition of Ras by small molecules has remained elusive. Recently, several small-molecule ligands have been discovered that directly bind Ras and inhibit its function by interfering with exchange factor binding. However, it is unclear whether, or how, these ligands could lead to drugs that act against constitutively active oncogenic mutant Ras. Using a dynamics-based pocket identification scheme, ensemble docking, and innovative cell-based assays, here we show that andrographolide (AGP)--a bicyclic diterpenoid lactone isolated from Andrographis paniculata--and its benzylidene derivatives bind to transient pockets on Kirsten-Ras (K-Ras) and inhibit GDP-GTP exchange. As expected for inhibitors of exchange factor binding, AGP derivatives reduced GTP loading of wild-type K-Ras in response to acute EGF stimulation with a concomitant reduction in MAPK activation. Remarkably, however, prolonged treatment with AGP derivatives also reduced GTP loading of, and signal transmission by, oncogenic mutant K-RasG12V. In sum, the combined analysis of our computational and cell biology results show that AGP derivatives directly bind Ras, block GDP-GTP exchange, and inhibit both wild-type and oncogenic K-Ras signaling. Importantly, our findings not only show that nucleotide exchange factors are required for oncogenic Ras signaling but also demonstrate that inhibiting nucleotide exchange is a valid approach to abrogating the function of oncogenic mutant Ras.
Collapse
|
79
|
Cho KJ, Park JH, Hancock JF. Staurosporine: A new tool for studying phosphatidylserine trafficking. Commun Integr Biol 2013; 6:e24746. [PMID: 23986809 PMCID: PMC3737755 DOI: 10.4161/cib.24746] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2013] [Revised: 04/18/2013] [Accepted: 04/19/2013] [Indexed: 12/12/2022] Open
Abstract
The Ras GTPases comprising three main isoforms H-, N- and K-Ras operate at the plasma membrane as molecular switches in essential signaling pathways. Active concentration of the minor phospholipid phosphatidylserine in the inner leaflet of the plasma membrane contributes to the electrostatic potential that is required for K-Ras anchoring to the plasma membrane. We recently observed that staurosporine and related analogs: 7-oxostaurosporine, UCN-01 and UCN-02, long known as relatively non-specific protein kinase inhibitors, block endosomal sorting and recycling of phosphatidylserine, resulting in redistribution of phosphatidylserine to endosomes and endomembranes with concomitant mislocalization of K-Ras. Staurosporines are therefore a new tool to study phosphatidylserine trafficking. We discuss whether the mechanism of action of UCN-01, an FDA-approved staurosporine analog used as an anti-cancer therapeutic, is related to effects on phosphatidylserine subcellular distribution. Given the high prevalence of expression of constitutively active K-Ras in human cancers, we ask whether inhibitors of phosphatidylserine trafficking may have important therapeutic applications.
Collapse
Affiliation(s)
- Kwang-Jin Cho
- Department of Integrative Biology and Pharmacology; The University of Texas Medical School at Houston; Houston, TX USA
| | | | | |
Collapse
|
80
|
Abstract
Ras proteins on the plasma membrane are laterally segregated into transient nanoclusters that are essential for high-fidelity signal transmission by the Ras/MAPK cascade. The dynamics of Ras nanocluster assembly and disassembly control MAPK signal output. BRaf inhibitors paradoxically activate CRaf and MAPK signaling in Ras-transformed cells. In our recent study, we showed that BRaf inhibition significantly enhances nanoclustering of oncogenic K- and N-Ras, but not H-Ras by increasing the frequency of Ras nanocluster formation. This disrupted spatiotemporal dynamics of Ras nanocluster fully accounts for the observed effects of Raf inhibitors on Ras signal transmission. Here together with other studies, we propose that the dynamics of Ras nanoclusters may represent a novel target for future therapeutic intervention.
Collapse
Affiliation(s)
- Kwang-Jin Cho
- Department of Integrative Biology and Pharmacology, The University of Texas Medical School, Houston, Houston, TX, USA
| | | |
Collapse
|