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Balmer EA, Wirdnam CD, Faso C. A core UPS molecular complement implicates unique endocytic compartments at the parasite-host interface in Giardia lamblia. Virulence 2023; 14:2174288. [PMID: 36730629 PMCID: PMC9928461 DOI: 10.1080/21505594.2023.2174288] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Unconventional protein secretion (UPS) plays important roles in cell physiology. In contrast to canonical secretory routes, UPS does not generally require secretory signal sequences and often bypasses secretory compartments such as the ER and the Golgi apparatus. Giardia lamblia is a protist parasite with reduced subcellular complexity which releases several proteins, some of them virulence factors, without canonical secretory signals. This implicates UPS at the parasite-host interface. No dedicated machinery nor mechanism(s) for UPS in Giardia are currently known, although speculations on the involvement of endocytic organelles called PV/PECs, have been put forth. To begin to address the question of whether PV/PECs are implicated in virulence-associated UPS and to define the composition of molecular machinery involved in protein release, we employed affinity purification and mass spectrometry, coupled to microscopy-based subcellular localization and signal correlation quantification to investigate the interactomes of 11 reported unconventionally secreted proteins, all predicted to be cytosolic. A subset of these are associated with PV/PECs. Extended and validated interactomes point to a core PV/PECs-associated UPS machinery, which includes uncharacterized and Giardia-specific coiled-coil proteins and NEK kinases. Finally, a subset of the alpha-giardin protein family was enriched in all PV/PECs-associated protein interactomes, highlighting a previously unappreciated role for these proteins at PV/PECs and in UPS. Taken together, our results provide the first characterization of a virulence-associated UPS protein complex in Giardia lamblia at PV/PECs, suggesting a novel link between these primarily endocytic and feeding organelles and UPS at the parasite-host interface.
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Affiliation(s)
- Erina A. Balmer
- Institute of Cell Biology, University of Bern, Bern, Switzerland,Graduate School for Cellular and Biomedical Sciences, University of Bern, Bern, Switzerland
| | | | - Carmen Faso
- Institute of Cell Biology, University of Bern, Bern, Switzerland,Multidisciplinary Center for Infectious Diseases, University of Bern, Bern, Switzerland,CONTACT Carmen Faso
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2
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Esteves S, Costa I, Luelmo S, Santarém N, Cordeiro-da-Silva A. Leishmania Vesicle-Depleted Exoproteome: What, Why, and How? Microorganisms 2022; 10:microorganisms10122435. [PMID: 36557688 PMCID: PMC9781507 DOI: 10.3390/microorganisms10122435] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2022] [Revised: 11/30/2022] [Accepted: 12/03/2022] [Indexed: 12/14/2022] Open
Abstract
Leishmaniasis, a vector-borne parasitic protozoan disease, is among the most important neglected tropical diseases. In the absence of vaccines, disease management is challenging. The available chemotherapy is suboptimal, and there are growing concerns about the emergence of drug resistance. Thus, a better understanding of parasite biology is essential to generate new strategies for disease control. In this context, in vitro parasite exoproteome characterization enabled the identification of proteins involved in parasite survival, pathogenesis, and other biologically relevant processes. After 2005, with the availability of genomic information, these studies became increasingly feasible and revealed the true complexity of the parasite exoproteome. After the discovery of Leishmania extracellular vesicles (EVs), most exoproteome studies shifted to the characterization of EVs. The non-EV portion of the exoproteome, named the vesicle-depleted exoproteome (VDE), has been mostly ignored even if it accounts for a significant portion of the total exoproteome proteins. Herein, we summarize the importance of total exoproteome studies followed by a special emphasis on the available information and the biological relevance of the VDE. Finally, we report on how VDE can be studied and disclose how it might contribute to providing biologically relevant targets for diagnosis, drug, and vaccine development.
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Affiliation(s)
- Sofia Esteves
- Laboratory of Microbiology, Department of Biological Sciences, Faculty of Pharmacy, University of Porto, 4050-313 Porto, Portugal
- Institute for Research and Innovation in Health (i3S), University of Porto, 4200-135 Porto, Portugal
| | - Inês Costa
- Laboratory of Microbiology, Department of Biological Sciences, Faculty of Pharmacy, University of Porto, 4050-313 Porto, Portugal
- Institute for Research and Innovation in Health (i3S), University of Porto, 4200-135 Porto, Portugal
| | - Sara Luelmo
- Institute for Research and Innovation in Health (i3S), University of Porto, 4200-135 Porto, Portugal
| | - Nuno Santarém
- Laboratory of Microbiology, Department of Biological Sciences, Faculty of Pharmacy, University of Porto, 4050-313 Porto, Portugal
- Institute for Research and Innovation in Health (i3S), University of Porto, 4200-135 Porto, Portugal
- Correspondence: (N.S.); (A.C.-d.-S.)
| | - Anabela Cordeiro-da-Silva
- Laboratory of Microbiology, Department of Biological Sciences, Faculty of Pharmacy, University of Porto, 4050-313 Porto, Portugal
- Institute for Research and Innovation in Health (i3S), University of Porto, 4200-135 Porto, Portugal
- Correspondence: (N.S.); (A.C.-d.-S.)
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3
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A Novel Role of Secretory Cytosolic Tryparedoxin Peroxidase in Delaying Apoptosis of Leishmania-Infected Macrophages. Mol Cell Biol 2022; 42:e0008122. [PMID: 36073913 PMCID: PMC9583715 DOI: 10.1128/mcb.00081-22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
The cytosolic tryparedoxin peroxidase (cTXNPx) of Leishmania donovani is a defensive enzyme. Apart from the nonsecretory form, the cTXNPx is released in the spent media of Leishmania cultures and also in the host cell cytosol. The secretory form of the enzyme from the parasite interacts with multiple proteins in the host cell cytosol, the apoptosis-inducing factor (AIF) being one of them. Immunoprecipitation with anti-cTXNPx and anti-AIF antibodies suggests a strong interaction between AIF and cTXNPx. Consequent to parasite invasion, the migration of AIF to the nucleus to precipitate apoptosis is inhibited in the presence of recombinant cTXNPx expressed in the host cell. This inhibition of AIF movement results in lesser host cell death, giving an advantage to the parasite for continued survival. Staurosporine-induced AIF migration to the nucleus was also inhibited in the presence of recombinant cTXNPx in the host cell. Therefore, this study demonstrates the ability of a Leishmania parasite enzyme, cTXNPx, to interfere with the migration of the host AIF protein, providing a survival advantage to the Leishmania parasite.
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Sparn C, Dimou E, Meyer A, Saleppico R, Wegehingel S, Gerstner M, Klaus S, Ewers H, Nickel W. Glypican-1 drives unconventional secretion of Fibroblast Growth Factor 2. eLife 2022; 11:75545. [PMID: 35348113 PMCID: PMC8986318 DOI: 10.7554/elife.75545] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2021] [Accepted: 03/24/2022] [Indexed: 11/13/2022] Open
Abstract
Fibroblast Growth Factor 2 (FGF2) is a tumor cell survival factor that is transported into the extracellular space by an unconventional secretory mechanism. Cell surface heparan sulfate proteoglycans are known to play an essential role in this process. Unexpectedly, we found that among the diverse sub-classes consisting of syndecans, perlecans, glypicans and others, Glypican-1 (GPC1) is the principle and rate-limiting factor that drives unconventional secretion of FGF2. By contrast, we demonstrate GPC1 to be dispensable for FGF2 signaling into cells. We provide first insights into the structural basis for GPC1-dependent FGF2 secretion, identifying disaccharides with N-linked sulfate groups to be enriched in the heparan sulfate chains of GPC1 to which FGF2 binds with high affinity. Our findings have broad implications for the role of GPC1 as a key molecule in tumor progression.
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Affiliation(s)
| | | | | | | | | | | | | | - Helge Ewers
- Institut für Chemie und Biochemie, Freie Universität Berlin
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Balmer EA, Faso C. The Road Less Traveled? Unconventional Protein Secretion at Parasite-Host Interfaces. Front Cell Dev Biol 2021; 9:662711. [PMID: 34109175 PMCID: PMC8182054 DOI: 10.3389/fcell.2021.662711] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2021] [Accepted: 04/07/2021] [Indexed: 01/01/2023] Open
Abstract
Protein secretion in eukaryotic cells is a well-studied process, which has been known for decades and is dealt with by any standard cell biology textbook. However, over the past 20 years, several studies led to the realization that protein secretion as a process might not be as uniform among different cargos as once thought. While in classic canonical secretion proteins carry a signal sequence, the secretory or surface proteome of several organisms demonstrated a lack of such signals in several secreted proteins. Other proteins were found to indeed carry a leader sequence, but simply circumvent the Golgi apparatus, which in canonical secretion is generally responsible for the modification and sorting of secretory proteins after their passage through the endoplasmic reticulum (ER). These alternative mechanisms of protein translocation to, or across, the plasma membrane were collectively termed “unconventional protein secretion” (UPS). To date, many research groups have studied UPS in their respective model organism of choice, with surprising reports on the proportion of unconventionally secreted proteins and their crucial roles for the cell and survival of the organism. Involved in processes such as immune responses and cell proliferation, and including far more different cargo proteins in different organisms than anyone had expected, unconventional secretion does not seem so unconventional after all. Alongside mammalian cells, much work on this topic has been done on protist parasites, including genera Leishmania, Trypanosoma, Plasmodium, Trichomonas, Giardia, and Entamoeba. Studies on protein secretion have mainly focused on parasite-derived virulence factors as a main source of pathogenicity for hosts. Given their need to secrete a variety of substrates, which may not be compatible with canonical secretion pathways, the study of mechanisms for alternative secretion pathways is particularly interesting in protist parasites. In this review, we provide an overview on the current status of knowledge on UPS in parasitic protists preceded by a brief overview of UPS in the mammalian cell model with a focus on IL-1β and FGF-2 as paradigmatic UPS substrates.
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Affiliation(s)
- Erina A Balmer
- Institute of Cell Biology, University of Bern, Bern, Switzerland
| | - Carmen Faso
- Institute of Cell Biology, University of Bern, Bern, Switzerland
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Abstract
In yeast, many proteins are found in both the cytoplasmic and extracellular compartments, and consequently it can be difficult to distinguish nonconventional secretion from cellular leakage. Therefore, we monitored the extracellular glyceraldehyde-3-phosphate dehydrogenase (GAPDH) activity of intact cells as a specific marker for nonconventional secretion. Extracellular GAPDH activity was proportional to the number of cells assayed, increased with incubation time, and was dependent on added substrates. Preincubation of intact cells with 100 μM dithiothreitol increased the reaction rate, consistent with increased access of the enzyme after reduction of cell wall disulfide cross-links. Such treatment did not increase cell permeability to propidium iodide, in contrast to effects of higher concentrations of reducing agents. An amine-specific membrane-impermeant biotinylation reagent specifically inactivated extracellular GAPDH. The enzyme was secreted again after a 30- to 60-min lag following the inactivation, and there was no concomitant increase in propidium iodide staining. There were about 4 × 104 active GAPDH molecules per cell at steady state, and secretion studies showed replenishment to that level 1 h after inactivation. These results establish conditions for specific quantitative assays of cell wall proteins in the absence of cytoplasmic leakage and for subsequent quantification of secretion rates in intact cells.IMPORTANCE Eukaryotic cells secrete many proteins, including many proteins that do not follow the classical secretion pathway. Among these, the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is unexpectedly found in the walls of yeasts and other fungi and in extracellular space in mammalian cell cultures. It is difficult to quantify extracellular GAPDH, because leakage of just a little of the very large amount of cytoplasmic enzyme can invalidate the determinations. We used enzymatic assays of intact cells while also maintaining membrane integrity. The results lead to estimates of the amount of extracellular enzyme and its rate of secretion to the wall in intact cells. Therefore, enzyme assays under controlled conditions can be used to investigate nonconventional secretion more generally.
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Cohen MJ, Chirico WJ, Lipke PN. Through the back door: Unconventional protein secretion. Cell Surf 2020; 6:100045. [PMID: 33225116 PMCID: PMC7666356 DOI: 10.1016/j.tcsw.2020.100045] [Citation(s) in RCA: 46] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2020] [Revised: 09/08/2020] [Accepted: 09/08/2020] [Indexed: 12/19/2022] Open
Abstract
Proteins are secreted from eukaryotic cells by several mechanisms besides the well-characterized classical secretory system. Proteins destined to enter the classical secretory system contain a signal peptide for translocation into the endoplasmic reticulum. However, many proteins lacking a signal peptide are secreted nonetheless. Contrary to conventional belief, these proteins are not just released as a result of membrane damage leading to cell leakage, but are actively packaged for secretion in alternative pathways. They are called unconventionally secreted proteins, and the best-characterized are from fungi and mammals. These proteins have extracellular functions including cell signaling, immune modulation, as well as moonlighting activities different from their well-described intracellular functions. Among the pathways for unconventional secretion are direct transfer across the plasma membrane, release within plasma membrane-derived microvesicles, use of elements of autophagy, or secretion from endosomal/multivesicular body-related components. We review the fungal and metazoan unconventional secretory pathways and their regulation, and propose experimental criteria to identify their mode of secretion.
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Affiliation(s)
- Michael J. Cohen
- The Graduate Center of the City University of New York, United States
- Biology Department, Brooklyn College of the City University of New York, United States
| | - William J. Chirico
- Department of Cell Biology, Molecular and Cellular Biology Program, SUNY Downstate Medical Center, United States
| | - Peter N. Lipke
- The Graduate Center of the City University of New York, United States
- Biology Department, Brooklyn College of the City University of New York, United States
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Kumar M, Ranjan K, Singh V, Pathak C, Pappachan A, Singh DD. Hydrophilic Acylated Surface Protein A (HASPA) of Leishmania donovani: Expression, Purification and Biophysico-Chemical Characterization. Protein J 2017. [PMID: 28634775 DOI: 10.1007/s10930-017-9726-x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Hydrophilic acylated surface proteins (HASPs) are acidic surface proteins which get localized on the surface of Leishmania parasite during infective stages through a "non-classical" pathway. In this study, we report the heterologous expression and purification of Leishmania donovani HASPA (r-LdHASPA) in E. coli system and its partial characterization. The structural aspects of the purified protein were analyzed using CD spectroscopy and modeling studies which indicate that r-LdHASPA consists of random coils. Studies in mouse macrophage RAW264.7 cell lines indicate that r-LdHASPA enhances reactive oxygen species (ROS) production. Co-immunoprecipitation (IP) studies indicate that r-LdHASPA interacts with certain macrophage proteins which however could not be identified unambiguously. The present study provides key insights into the structural and functional aspects of an important Leishmania protein, HASPA, which we believe could be useful for further research on vaccine/drug development.
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Affiliation(s)
- Manoj Kumar
- Department of Bioinformatics and Structural Biology, Indian Institute of Advanced Research, Gandhinagar, Gujarat, 382007, India
| | - Kishu Ranjan
- Department of Cell Biology, Indian Institute of Advanced Research, Gandhinagar, Gujarat, 382007, India
| | - Vijay Singh
- Department of Bioinformatics and Structural Biology, Indian Institute of Advanced Research, Gandhinagar, Gujarat, 382007, India
| | - Chandramani Pathak
- Department of Cell Biology, Indian Institute of Advanced Research, Gandhinagar, Gujarat, 382007, India
| | - Anju Pappachan
- Department of Bioinformatics and Structural Biology, Indian Institute of Advanced Research, Gandhinagar, Gujarat, 382007, India
| | - Desh Deepak Singh
- Department of Bioinformatics and Structural Biology, Indian Institute of Advanced Research, Gandhinagar, Gujarat, 382007, India.
- Department of Biotechnology, Panjab University, Chandigarh, 160014, India.
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9
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Shibata T, Hadano J, Kawasaki D, Dong X, Kawabata SI. Drosophila TG-A transglutaminase is secreted via an unconventional Golgi-independent mechanism involving exosomes and two types of fatty acylations. J Biol Chem 2017; 292:10723-10734. [PMID: 28476891 DOI: 10.1074/jbc.m117.779710] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2017] [Revised: 04/26/2017] [Indexed: 01/07/2023] Open
Abstract
Transglutaminases (TGs) play essential intracellular and extracellular roles by covalently cross-linking many proteins. Drosophila TG is encoded by one gene and has two alternative splicing-derived isoforms, TG-A and TG-B, which contain distinct N-terminal 46- and 38-amino acid sequences, respectively. The TGs identified to date do not have a typical endoplasmic reticulum (ER)-signal peptide, and the molecular mechanisms of their secretion under physiologic conditions are unclear. Immunocytochemistry revealed that TG-A localizes to multivesicular-like structures, whereas TG-B localizes to the cytosol. We also found that TG-A, but not TG-B, was modified concomitantly by N-myristoylation and S-palmitoylation, and N-myristoylation was a pre-requisite for S-palmitoylation. Moreover, TG-A, but not TG-B, was secreted in response to calcium signaling induced by Ca2+ ionophores and uracil, a pathogenic bacteria-derived substance. Brefeldin A and monensin, inhibitors of the ER/Golgi-mediated conventional pathway, did not suppress TG-A secretion, whereas inhibition of S-palmitoylation by 2-bromopalmitate blocked TG-A secretion. Ultracentrifugation, electron microscopy analyses, and treatments with inhibitors of multivesicular body formation revealed that TG-A was secreted via exosomes together with co-transfected mammalian CD63, an exosomal marker, and the secreted TG-A was taken up by other cells. The 8-residue N-terminal fragment of TG-A containing the fatty acylation sites was both necessary and sufficient for the exosome-dependent secretion of TG-A. In conclusion, TG-A is secreted through an unconventional ER/Golgi-independent pathway involving two types of fatty acylations and exosomes.
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Affiliation(s)
- Toshio Shibata
- From the Department of Biology, Faculty of Science.,Institute for Advanced Study, and
| | - Jinki Hadano
- the Graduate School of Systems Life Sciences, Kyushu University, Fukuoka 819-0395, Japan
| | - Daichi Kawasaki
- the Graduate School of Systems Life Sciences, Kyushu University, Fukuoka 819-0395, Japan
| | - Xiaoqing Dong
- the Graduate School of Systems Life Sciences, Kyushu University, Fukuoka 819-0395, Japan
| | - Shun-Ichiro Kawabata
- From the Department of Biology, Faculty of Science, .,the Graduate School of Systems Life Sciences, Kyushu University, Fukuoka 819-0395, Japan
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10
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MacLean L, Price H, O'Toole P. Exploring the Leishmania Hydrophilic Acylated Surface Protein B (HASPB) Export Pathway by Live Cell Imaging Methods. Methods Mol Biol 2016; 1459:191-203. [PMID: 27665560 DOI: 10.1007/978-1-4939-3804-9_13] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Leishmania major is a human-infective protozoan parasite transmitted by the bite of the female phlebotomine sand fly. The L. major hydrophilic acylated surface protein B (HASPB) is only expressed in infective parasite stages suggesting a role in parasite virulence. HASPB is a "nonclassically" secreted protein that lacks a conventional signal peptide, reaching the cell surface by an alternative route to the classical ER-Golgi pathway. Instead HASPB trafficking to and exposure on the parasite plasma membrane requires dual N-terminal acylation. Here, we use live cell imaging methods to further explore this pathway allowing visualization of key events in real time at the individual cell level. These methods include live cell imaging using fluorescent reporters to determine the subcellular localization of wild type and acylation site mutation HASPB18-GFP fusion proteins, fluorescence recovery after photobleaching (FRAP) to analyze the dynamics of HASPB in live cells, and live antibody staining to detect surface exposure of HASPB by confocal microscopy.
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Affiliation(s)
- Lorna MacLean
- Drug Discovery Unit, Division of Biological Chemistry and Drug Discovery, College of Life Sciences, University of Dundee, Dundee, DD1 5EH, UK.
| | - Helen Price
- Centre for Applied Entomology and Parasitology, School of Life Sciences, Keele University, Keele, Staffordshire, ST5 5BG, UK
| | - Peter O'Toole
- Technology Facility, Department of Biology, University of York, York, YO10 5DD, UK
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11
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Adamczyk M, Griffiths R, Dewitt S, Knäuper V, Aeschlimann D. P2X7 receptor activation regulates rapid unconventional export of transglutaminase-2. J Cell Sci 2015; 128:4615-28. [PMID: 26542019 PMCID: PMC4696497 DOI: 10.1242/jcs.175968] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2015] [Accepted: 10/29/2015] [Indexed: 12/24/2022] Open
Abstract
Transglutaminases (denoted TG or TGM) are externalized from cells via an unknown unconventional secretory pathway. Here, we show for the first time that purinergic signaling regulates active secretion of TG2 (also known as TGM2), an enzyme with a pivotal role in stabilizing extracellular matrices and modulating cell–matrix interactions in tissue repair. Extracellular ATP promotes TG2 secretion by macrophages, and this can be blocked by a selective antagonist against the purinergic receptor P2X7 (P2X7R, also known as P2RX7). Introduction of functional P2X7R into HEK293 cells is sufficient to confer rapid, regulated TG2 export. By employing pharmacological agents, TG2 release could be separated from P2X7R-mediated microvesicle shedding. Neither Ca2+ signaling alone nor membrane depolarization triggered TG2 secretion, which occurred only upon receptor membrane pore formation and without pannexin channel involvement. A gain-of-function mutation in P2X7R associated with autoimmune disease caused enhanced TG2 externalization from cells, and this correlated with increased pore activity. These results provide a mechanistic explanation for a link between active TG2 secretion and inflammatory responses, and aberrant enhanced TG2 activity in certain autoimmune conditions. Summary: Purinergic signaling regulates unconventional secretion of transglutaminase-2 (TG2) and explains the link between aberrant protein modifications and inflammatory responses in TG2-dependent autoimmunity.
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Affiliation(s)
- Magdalena Adamczyk
- Matrix Biology & Tissue Repair Research Unit and Arthritis Research UK Biomechanics and Bioengineering Center of Excellence, College of Biomedical and Life Sciences, Cardiff University, Cardiff CF14 4XY, UK
| | - Rhiannon Griffiths
- Matrix Biology & Tissue Repair Research Unit and Arthritis Research UK Biomechanics and Bioengineering Center of Excellence, College of Biomedical and Life Sciences, Cardiff University, Cardiff CF14 4XY, UK
| | - Sharon Dewitt
- Matrix Biology & Tissue Repair Research Unit and Arthritis Research UK Biomechanics and Bioengineering Center of Excellence, College of Biomedical and Life Sciences, Cardiff University, Cardiff CF14 4XY, UK
| | - Vera Knäuper
- Matrix Biology & Tissue Repair Research Unit and Arthritis Research UK Biomechanics and Bioengineering Center of Excellence, College of Biomedical and Life Sciences, Cardiff University, Cardiff CF14 4XY, UK
| | - Daniel Aeschlimann
- Matrix Biology & Tissue Repair Research Unit and Arthritis Research UK Biomechanics and Bioengineering Center of Excellence, College of Biomedical and Life Sciences, Cardiff University, Cardiff CF14 4XY, UK
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12
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Zacherl S, La Venuta G, Müller HM, Wegehingel S, Dimou E, Sehr P, Lewis JD, Erfle H, Pepperkok R, Nickel W. A direct role for ATP1A1 in unconventional secretion of fibroblast growth factor 2. J Biol Chem 2014; 290:3654-65. [PMID: 25533462 DOI: 10.1074/jbc.m114.590067] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Previous studies proposed a role for the Na/K-ATPase in unconventional secretion of fibroblast growth factor 2 (FGF2). This conclusion was based upon pharmacological inhibition of FGF2 secretion in the presence of ouabain. However, neither independent experimental evidence nor a potential mechanism was provided. Based upon an unbiased RNAi screen, we now report the identification of ATP1A1, the α1-chain of the Na/K-ATPase, as a factor required for efficient secretion of FGF2. As opposed to ATP1A1, down-regulation of the β1- and β3-chains (ATP1B1 and ATP1B3) of the Na/K-ATPase did not affect FGF2 secretion, suggesting that they are dispensable for this process. These findings indicate that it is not the membrane potential-generating function of the Na/K-ATPase complex but rather a so far unidentified role of potentially unassembled α1-chains that is critical for unconventional secretion of FGF2. Consistently, in the absence of β-chains, we found a direct interaction between the cytoplasmic domain of ATP1A1 and FGF2 with submicromolar affinity. Based upon these observations, we propose that ATP1A1 is a recruitment factor for FGF2 at the inner leaflet of plasma membranes that may control phosphatidylinositol 4,5-bisphosphate-dependent membrane translocation as part of the unconventional secretory pathway of FGF2.
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Affiliation(s)
- Sonja Zacherl
- From the Heidelberg University Biochemistry Center (BZH), Im Neuenheimer Feld 328, 69120 Heidelberg, Germany
| | - Giuseppe La Venuta
- From the Heidelberg University Biochemistry Center (BZH), Im Neuenheimer Feld 328, 69120 Heidelberg, Germany
| | - Hans-Michael Müller
- From the Heidelberg University Biochemistry Center (BZH), Im Neuenheimer Feld 328, 69120 Heidelberg, Germany
| | - Sabine Wegehingel
- From the Heidelberg University Biochemistry Center (BZH), Im Neuenheimer Feld 328, 69120 Heidelberg, Germany
| | - Eleni Dimou
- From the Heidelberg University Biochemistry Center (BZH), Im Neuenheimer Feld 328, 69120 Heidelberg, Germany
| | - Peter Sehr
- the European Molecular Biology Laboratory (EMBL), Meyerhofstrasse 1, 69117 Heidelberg, Germany, and
| | - Joe D Lewis
- the European Molecular Biology Laboratory (EMBL), Meyerhofstrasse 1, 69117 Heidelberg, Germany, and
| | - Holger Erfle
- BioQuant, Heidelberg University, Im Neuenheimer Feld 267, 69120 Heidelberg, Germany
| | - Rainer Pepperkok
- the European Molecular Biology Laboratory (EMBL), Meyerhofstrasse 1, 69117 Heidelberg, Germany, and
| | - Walter Nickel
- From the Heidelberg University Biochemistry Center (BZH), Im Neuenheimer Feld 328, 69120 Heidelberg, Germany,
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13
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Goldston AM, Sharma AI, Paul KS, Engman DM. Acylation in trypanosomatids: an essential process and potential drug target. Trends Parasitol 2014; 30:350-60. [PMID: 24954795 DOI: 10.1016/j.pt.2014.05.003] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2014] [Revised: 05/06/2014] [Accepted: 05/06/2014] [Indexed: 12/11/2022]
Abstract
Fatty acylation--the addition of fatty acid moieties such as myristate and palmitate to proteins--is essential for the survival, growth, and infectivity of the trypanosomatids: Trypanosoma brucei, Trypanosoma cruzi, and Leishmania. Myristoylation and palmitoylation are critical for parasite growth, targeting and localization, and the intrinsic function of some proteins. The trypanosomatids possess a single N-myristoyltransferase (NMT) and multiple palmitoyl acyltransferases, and these enzymes and their protein targets are only now being characterized. Global inhibition of either process leads to cell death in trypanosomatids, and genetic ablation of NMT compromises virulence. Moreover, NMT inhibitors effectively cure T. brucei infection in rodents. Thus, protein acylation represents an attractive target for the development of new trypanocidal drugs.
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Affiliation(s)
- Amanda M Goldston
- Departments of Pathology and Microbiology-Immunology, Northwestern University, Chicago, Illinois, USA
| | - Aabha I Sharma
- Departments of Pathology and Microbiology-Immunology, Northwestern University, Chicago, Illinois, USA
| | - Kimberly S Paul
- Department of Genetics and Biochemistry, Clemson University, Clemson, South Carolina, USA
| | - David M Engman
- Departments of Pathology and Microbiology-Immunology, Northwestern University, Chicago, Illinois, USA.
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14
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Santarém N, Racine G, Silvestre R, Cordeiro-da-Silva A, Ouellette M. Exoproteome dynamics in Leishmania infantum. J Proteomics 2013; 84:106-18. [DOI: 10.1016/j.jprot.2013.03.012] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2012] [Revised: 03/14/2013] [Accepted: 03/20/2013] [Indexed: 12/14/2022]
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15
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Pan X, Geist MM, Rudolph JM, Nickel W, Fackler OT. HIV-1 Nef disrupts membrane-microdomain-associated anterograde transport for plasma membrane delivery of selected Src family kinases. Cell Microbiol 2013; 15:1605-21. [DOI: 10.1111/cmi.12148] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2013] [Revised: 03/29/2013] [Accepted: 04/08/2013] [Indexed: 11/28/2022]
Affiliation(s)
- Xiaoyu Pan
- Department of Infectious Diseases, Virology; University Hospital Heidelberg; INF 324; 69120; Heidelberg; Germany
| | - Miriam M. Geist
- Department of Infectious Diseases, Virology; University Hospital Heidelberg; INF 324; 69120; Heidelberg; Germany
| | - Jochen M. Rudolph
- Department of Infectious Diseases, Virology; University Hospital Heidelberg; INF 324; 69120; Heidelberg; Germany
| | - Walter Nickel
- Biochemistry Center; Heidelberg University; INF 328; 69120; Heidelberg; Germany
| | - Oliver T. Fackler
- Department of Infectious Diseases, Virology; University Hospital Heidelberg; INF 324; 69120; Heidelberg; Germany
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16
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Rabouille C, Malhotra V, Nickel W. Diversity in unconventional protein secretion. J Cell Sci 2012; 125:5251-5. [DOI: 10.1242/jcs.103630] [Citation(s) in RCA: 208] [Impact Index Per Article: 17.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Affiliation(s)
- Catherine Rabouille
- Hubrecht Institute for, Developmental Biology and Stem Cell Research, Uppsalalaan 8, 3584 CT Utrecht, The Netherlands
| | - Vivek Malhotra
- Centre for Genomic Regulation, C/ Dr. Aiguader 88, 08003 Barcelona, Spain
- Institució Catalana de Recerca i Estudis Avançats (ICREA), Passeig Lluís Companys 23, 08010 Barcelona, Spain
| | - Walter Nickel
- Heidelberg University Biochemistry Center, Im Neuenheimer Feld 328, 69120 Heidelberg, Germany
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17
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Morrison LS, Goundry A, Faria MS, Tetley L, Eschenlauer SC, Westrop GD, Dostalova A, Volf P, Coombs GH, Lima APCA, Mottram JC. Ecotin-like serine peptidase inhibitor ISP1 of Leishmania major plays a role in flagellar pocket dynamics and promastigote differentiation. Cell Microbiol 2012; 14:1271-86. [PMID: 22486816 PMCID: PMC3440592 DOI: 10.1111/j.1462-5822.2012.01798.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Leishmania ISPs are ecotin-like natural peptide inhibitors of trypsin-family serine peptidases, enzymes that are absent from the Leishmania genome. This led to the proposal that ISPs inhibit host serine peptidases and we have recently shown that ISP2 inhibits neutrophil elastase, thereby enhancing parasite survival in murine macrophages. In this study we show that ISP1 has less serine peptidase inhibitory activity than ISP2, and in promastigotes both are generally located in the cytosol and along the flagellum. However, in haptomonad promastigotes there is a prominent accumulation of ISP1 and ISP2 in the hemidesmosome and for ISP2 on the cell surface. An L. major mutant deficient in all three ISP genes (Δisp1/2/3) was generated and compared with Δisp2/3 mutants to elucidate the physiological role of ISP1. In in vitro cultures, the Δisp1/2/3 mutant contained more haptomonad, nectomonad and leptomonad promastigotes with elongated flagella and reduced motility compared with Δisp2/3 populations, moreover it was characterized by very high levels of release of exosome-like vesicles from the flagellar pocket. These data suggest that ISP1 has a primary role in flagellar homeostasis, disruption of which affects differentiation and flagellar pocket dynamics.
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Affiliation(s)
- Lesley S Morrison
- Wellcome Trust Centre for Molecular Parasitology, Institute of Infection, Immunity and Inflammation, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow G12 8TA, UK
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18
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Maclean LM, O'Toole PJ, Stark M, Marrison J, Seelenmeyer C, Nickel W, Smith DF. Trafficking and release of Leishmania metacyclic HASPB on macrophage invasion. Cell Microbiol 2012; 14:740-61. [PMID: 22256896 PMCID: PMC3491706 DOI: 10.1111/j.1462-5822.2012.01756.x] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Proteins of the Leishmania hydrophilic acylated surface protein B (HASPB) family are only expressed in infective parasites (both extra- and intracellular stages) and, together with the peripheral membrane protein SHERP (small hydrophilic endoplasmic reticulum-associated protein), are essential for parasite differentiation (metacyclogenesis) in the sand fly vector. HASPB is a ‘non-classically’ secreted protein, requiring N-terminal acylation for trafficking to and exposure on the plasma membrane. Here, we use live cell imaging methods to further explore this pathway to the membrane and flagellum. Unlike HASPB trafficking in transfected mammalian cells, we find no evidence for a phosphorylation-regulated recycling pathway in metacyclic parasites. Once at the plasma membrane, HASPB18–GFP (green fluorescent protein) can undergo bidirectional movement within the inner leaflet of the membrane and on the flagellum. Transfer of fluorescent protein between the flagellum and the plasma membrane is compromised, however, suggesting the presence of a diffusion barrier at the base of the Leishmania flagellum. Full-length HASPB is released from the metacyclic parasite surface on to macrophages during phagocytosis but while expression is maintained in intracellular amastigotes, HASPB cannot be detected on the external surface in these cells. Thus HASPB may be a dual function protein that is shed by the infective metacyclic but retained internally once Leishmania are taken up by macrophages.
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Affiliation(s)
- Lorna M Maclean
- Centre for Immunology and Infection, Department of Biology/Hull York Medical School, University of York, York YO10 5DD, UK
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19
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Gierczak RF, Sutherland JS, Bhakta V, Toltl LJ, Liaw PC, Sheffield WP. Retention of thrombin inhibitory activity by recombinant serpins expressed as integral membrane proteins tethered to the surface of mammalian cells. J Thromb Haemost 2011; 9:2424-35. [PMID: 21972922 DOI: 10.1111/j.1538-7836.2011.04524.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
BACKGROUND Serpins form a widely distributed protein superfamily, but no integral membrane serpins have been described. OBJECTIVES To anchor three serpins -α(1) -proteinase inhibitor (α(1) PI) (M358R), antithrombin (AT), and heparin cofactor II (HCII) - in the plasma membranes of transfected mammalian cells and assess their ability to inhibit thrombin. METHODS Serpin cDNAs were altered to include N-terminal, non-cleavable plasma membrane-targeting sequences from the human transferrin receptor (TR) (TR-serpin) or the human asialoglycoprotein receptor (AR) (AR-serpin), and used to transfect COS-1 or HEK 293 cells. Cells were analyzed for serpin expression by immunoblotting of subcellular fractions, by immunofluorescence microscopy, or by flow cytometry, with or without exposure to exogenous thrombin; AR-serpins and TR-serpins were also compared with their soluble recombinant counterparts. RESULTS Both TR-α(1) PI (M358R) and AR-α(1) PI (M358R) were enriched in the integral membrane fraction of transfected COS-1 or HEK 293 cells, and formed inhibitory complexes with thrombin, although less rapidly than soluble α(1) PI (M358R). Thrombin inhibition was abrogated by an additional T345R mutation in AR-α(1) PI (M358R). Surface-displayed AR-AT also formed serpin-enzyme complexes with thrombin, but to a lesser extent than AR-α(1) PI (M358R); AR-HCII inhibitory function was not detected. Immunofluorescence detection and flow cytometric quantification of bound thrombin also supported the status of AR-α(1) PI (M358R) and AR-AT as thrombin inhibitors. CONCLUSIONS Two of three thrombin-inhibitory serpins retained functionality when expressed as integral membrane proteins. Our findings could be applied to create and screen hypervariable serpin libraries expressed in mammalian cells, or to confer protease resistance on engineered cells in vivo.
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Affiliation(s)
- R F Gierczak
- Department of Pathology and Molecular Medicine, McMaster University, Hamilton, Ontario, Canada
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20
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Ritzerfeld J, Remmele S, Wang T, Temmerman K, Brügger B, Wegehingel S, Tournaviti S, Strating JRPM, Wieland FT, Neumann B, Ellenberg J, Lawerenz C, Hesser J, Erfle H, Pepperkok R, Nickel W. Phenotypic profiling of the human genome reveals gene products involved in plasma membrane targeting of SRC kinases. Genome Res 2011; 21:1955-68. [PMID: 21795383 DOI: 10.1101/gr.116087.110] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
SRC proteins are non-receptor tyrosine kinases that play key roles in regulating signal transduction by a diverse set of cell surface receptors. They contain N-terminal SH4 domains that are modified by fatty acylation and are functioning as membrane anchors. Acylated SH4 domains are both necessary and sufficient to mediate specific targeting of SRC kinases to the inner leaflet of plasma membranes. Intracellular transport of SRC kinases to the plasma membrane depends on microdomains into which SRC kinases partition upon palmitoylation. In the present study, we established a live-cell imaging screening system to identify gene products involved in plasma membrane targeting of SRC kinases. Based on siRNA arrays and a human model cell line expressing two kinds of SH4 reporter molecules, we conducted a genome-wide analysis of SH4-dependent protein targeting using an automated microscopy platform. We identified and validated 54 gene products whose down-regulation causes intracellular retention of SH4 reporter molecules. To detect and quantify this phenotype, we developed a software-based image analysis tool. Among the identified gene products, we found factors involved in lipid metabolism, intracellular transport, and cellular signaling processes. Furthermore, we identified proteins that are either associated with SRC kinases or are related to various known functions of SRC kinases such as other kinases and phosphatases potentially involved in SRC-mediated signal transduction. Finally, we identified gene products whose function is less defined or entirely unknown. Our findings provide a major resource for future studies unraveling the molecular mechanisms that underlie proper targeting of SRC kinases to the inner leaflet of plasma membranes.
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Affiliation(s)
- Julia Ritzerfeld
- Heidelberg University Biochemistry Center, 69120 Heidelberg, Germany
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21
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Maric D, McGwire BS, Buchanan KT, Olson CL, Emmer BT, Epting CL, Engman DM. Molecular determinants of ciliary membrane localization of Trypanosoma cruzi flagellar calcium-binding protein. J Biol Chem 2011; 286:33109-17. [PMID: 21784841 DOI: 10.1074/jbc.m111.240895] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The flagellar calcium-binding protein (FCaBP) of Trypanosoma cruzi is localized to the flagellar membrane in all life cycle stages of the parasite. Myristoylation and palmitoylation of the N terminus of FCaBP are necessary for flagellar membrane targeting. Not all dually acylated proteins in T. cruzi are flagellar, however. Other determinants of FCaBP therefore likely contribute to flagellar specificity. We generated T. cruzi transfectants expressing the N-terminal 24 or 12 amino acids of FCaBP fused to GFP. Analysis of these mutants revealed that although amino acids 1-12 are sufficient for dual acylation and membrane binding, amino acids 13-24 are required for flagellar specificity and lipid raft association. Mutagenesis of several conserved lysine residues in the latter peptide demonstrated that these residues are essential for flagellar targeting and lipid raft association. Finally, FCaBP was expressed in the protozoan Leishmania amazonensis, which lacks FCaBP. The flagellar localization and membrane association of FCaBP in L. amazonensis suggest that the mechanisms for flagellar targeting, including a specific palmitoyl acyltransferase, are conserved in this organism.
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Affiliation(s)
- Danijela Maric
- Department of Pathology, Northwestern University, Chicago, Illinois 60611, USA
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22
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Zhu H, Wang L, Ruan Y, Zhou L, Zhang D, Min Z, Xie J, Yu M, Gu J. An efficient delivery of DAMPs on the cell surface by the unconventional secretion pathway. Biochem Biophys Res Commun 2011; 404:790-5. [DOI: 10.1016/j.bbrc.2010.12.061] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2010] [Accepted: 12/13/2010] [Indexed: 11/16/2022]
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23
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de Paulo Martins V, Okura M, Maric D, Engman DM, Vieira M, Docampo R, Moreno SNJ. Acylation-dependent export of Trypanosoma cruzi phosphoinositide-specific phospholipase C to the outer surface of amastigotes. J Biol Chem 2010; 285:30906-17. [PMID: 20647312 DOI: 10.1074/jbc.m110.142190] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Phosphoinositide phospholipase C (PI-PLC) plays an essential role in cell signaling. A unique Trypanosoma cruzi PI-PLC (TcPI-PLC) is lipid-modified in its N terminus and localizes to the plasma membrane of amastigotes. Here, we show that TcPI-PLC is located onto the extracellular phase of the plasma membrane of amastigotes and that its N-terminal 20 amino acids are necessary and sufficient to target the fused GFP to the outer surface of the parasite. Mutagenesis of the predicted acylated residues confirmed that myristoylation of a glycine residue in the 2nd position and acyl modification of a cysteine in the 4th but not in the 8th or 15th position of the coding sequence are required for correct plasma membrane localization in T. cruzi epimastigotes or amastigotes. Interestingly, mutagenesis of the cysteine at the 8th position increased its flagellar localization. When expressed as fusion constructs with GFP, the N-terminal 6 and 10 amino acids fused to GFP are predominantly located in the cytosol and concentrated in a compartment that co-localizes with a Golgi complex marker. The N-terminal 20 amino acids of TcPI-PLC associate with lipid rafts when dually acylated. Taken together, these results indicate that N-terminal acyl modifications serve as a molecular addressing system for sending TcPI-PLC to the outer surface of the cell.
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Affiliation(s)
- Vicente de Paulo Martins
- Department of Cellular Biology, University of Georgia, Center for Tropical and Emerging Global Diseases, Athens, Georgia 30602, USA
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24
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Unconventional secretion of AcbA in Dictyostelium discoideum through a vesicular intermediate. EUKARYOTIC CELL 2010; 9:1009-17. [PMID: 20472692 DOI: 10.1128/ec.00337-09] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The acyl coenzyme A (CoA) binding protein AcbA is secreted unconventionally and processed into spore differentiation factor 2 (SDF-2), a peptide that coordinates sporulation in Dictyostelium discoideum. We report that AcbA is localized in vesicles that accumulate in the cortex of prespore cells just prior to sporulation. These vesicles are not observed after cells are stimulated to release AcbA but remain visible after stimulation in cells lacking the Golgi reassembly stacking protein (GRASP). Acyl-CoA binding is required for the inclusion of AcbA in these vesicles, and the secretion of AcbA requires N-ethylmaleimide-sensitive factor (NSF). About 1% of the total cellular AcbA can be purified within membrane-bound vesicles. The yield of vesicles decreases dramatically when purified from wild-type cells that were stimulated to release AcbA, whereas the yield from GRASP mutant cells was only modestly altered by stimulation. We suggest that these AcbA-containing vesicles are secretion intermediates and that GRASP functions at a late step leading to the docking/fusion of these vesicles at the cell surface.
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25
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Gel free analysis of the proteome of intracellular Leishmania mexicana. Mol Biochem Parasitol 2010; 169:108-14. [DOI: 10.1016/j.molbiopara.2009.10.009] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2009] [Revised: 10/21/2009] [Accepted: 10/29/2009] [Indexed: 01/06/2023]
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26
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Corrales RM, Sereno D, Mathieu-Daudé F. Deciphering theLeishmaniaexoproteome: what we know and what we can learn. ACTA ACUST UNITED AC 2010; 58:27-38. [DOI: 10.1111/j.1574-695x.2009.00608.x] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
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27
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Proteomic characterization of the released/secreted proteins of Leishmania (Viannia) braziliensis promastigotes. J Proteomics 2009; 73:79-92. [DOI: 10.1016/j.jprot.2009.08.006] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2009] [Revised: 08/06/2009] [Accepted: 08/14/2009] [Indexed: 12/20/2022]
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28
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Liu W, Apagyi K, McLeavy L, Ersfeld K. Expression and cellular localisation of calpain-like proteins in Trypanosoma brucei. Mol Biochem Parasitol 2009; 169:20-6. [PMID: 19766148 DOI: 10.1016/j.molbiopara.2009.09.004] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2009] [Revised: 09/07/2009] [Accepted: 09/08/2009] [Indexed: 01/01/2023]
Abstract
Calpains are a ubiquitous family of calcium-dependent cysteine proteases involved in a wide range of cell regulatory and differentiation processes. In many protozoan organisms, atypical calpains have been discovered that lack the characteristic calcium-binding penta-EF-hand motif of typical vertebrate calpains and most of these novel calpain-like proteins are non-enzymatic homologues of typical calpains. The gene family is particularly expanded in ciliates and kinetoplastids, comprising 25 members in the parasite Trypanosoma brucei. Unique to kinetoplastids, some calpain-like proteins contain N-terminal dual myristoylation/palmitoylation signals, a protein modification involved in protein-membrane associations. We analyzed the expression of calpain-like proteins in the insect (procyclic) and bloodstream-stage of T. brucei using quantitative real time PCR and identified the differential expression of some of the calpain genes. We also present a comprehensive analysis of the subcellular localisation of selected members of this protein family in trypanosomes. Here, of particular interest is the role of protein acylation for targeting to the flagellum. We show that, although acylation is important for flagellar targeting, additional signals are required to specify the precise subcellular localisation.
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Affiliation(s)
- Wen Liu
- Department of Biological Sciences, University of Hull, UK
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29
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Hanrahan O, Webb H, O'Byrne R, Brabazon E, Treumann A, Sunter JD, Carrington M, Voorheis HP. The glycosylphosphatidylinositol-PLC in Trypanosoma brucei forms a linear array on the exterior of the flagellar membrane before and after activation. PLoS Pathog 2009; 5:e1000468. [PMID: 19503825 PMCID: PMC2685982 DOI: 10.1371/journal.ppat.1000468] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2008] [Accepted: 05/11/2009] [Indexed: 11/30/2022] Open
Abstract
Bloodstream forms of Trypanosoma brucei contain a glycosylphosphatidylinositol-specific phospholipase C (GPI-PLC) that cleaves the GPI-anchor of the variable surface glycoprotein (VSG). Its location in trypanosomes has been controversial. Here, using confocal microscopy and surface labelling techniques, we show that the GPI-PLC is located exclusively in a linear array on the outside of the flagellar membrane, close to the flagellar attachment zone, but does not co-localize with the flagellar attachment zone protein, FAZ1. Consequently, the GPI-PLC and the VSG occupy the same plasma membrane leaflet, which resolves the topological problem associated with the cleavage reaction if the VSG and the GPI-PLC were on opposite sides of the membrane. The exterior location requires the enzyme to be tightly regulated to prevent VSG release under basal conditions. During stimulated VSG release in intact cells, the GPI-PLC did not change location, suggesting that the release mechanism involves lateral diffusion of the VSG in the plane of the membrane to the fixed position of the GPI-PLC. African trypanosomes cause sleeping sickness, for which current therapy is inadequate. The parasite protects its surface from the host immune system by regularly switching its surface coat. The glycosylphosphatidylinositol-PLC only occurs in the bloodstream form, where it removes the surface coat after it enters the tsetse fly vector. Activation of the enzyme in the bloodstream would be fatal for the parasite and it is, therefore, a potential drug target. However, therapeutic strategies have been hampered by confusion over the location of the GPI-PLC despite great effort by many labs. We have used a wide variety of techniques, including one completely novel method, that exploits the dependence of detection for partially buried surface proteins on the temperature of fixation, to identify the location of the GPI-PLC in relation to other markers unequivocally. All approaches consistently show that the GPI-PLC is located exclusively in the outer leaflet of the plasma membrane covering the flagellum, where it is confined to a narrow linear array adjacent to the flagellar attachment zone. Our data have resolved the question of how enzyme and substrate meet and also suggest that chemotherapeutic agents would be able to target the GPI-PLC in its exterior location.
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Affiliation(s)
- Orla Hanrahan
- School of Biochemistry and Immunology, Trinity College Dublin, Dublin, Ireland
| | - Helena Webb
- Department of Biochemistry, University of Cambridge, Cambridge, United Kingdom
| | - Robert O'Byrne
- School of Biochemistry and Immunology, Trinity College Dublin, Dublin, Ireland
| | - Elaine Brabazon
- School of Biochemistry and Immunology, Trinity College Dublin, Dublin, Ireland
| | | | - Jack D. Sunter
- Department of Biochemistry, University of Cambridge, Cambridge, United Kingdom
| | - Mark Carrington
- Department of Biochemistry, University of Cambridge, Cambridge, United Kingdom
| | - H. Paul Voorheis
- School of Biochemistry and Immunology, Trinity College Dublin, Dublin, Ireland
- * E-mail:
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30
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Tournaviti S, Pietro ES, Terjung S, Schafmeier T, Wegehingel S, Ritzerfeld J, Schulz J, Smith DF, Pepperkok R, Nickel W. Reversible phosphorylation as a molecular switch to regulate plasma membrane targeting of acylated SH4 domain proteins. Traffic 2009; 10:1047-60. [PMID: 19453972 DOI: 10.1111/j.1600-0854.2009.00921.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Acylated SH4 domains represent N-terminal targeting signals that anchor peripheral membrane proteins such as Src kinases in the inner leaflet of plasma membranes. Here we provide evidence for a novel regulatory mechanism that may control the levels of SH4 proteins being associated with plasma membranes. Using a fusion protein of the SH4 domain of Leishmania HASPB and GFP as a model system, we demonstrate that threonine 6 is a substrate for phosphorylation. Substitution of threonine 6 by glutamate (to mimic a phosphothreonine residue) resulted in a dramatic redistribution from plasma membranes to intracellular sites with a particular accumulation in a perinuclear region. As shown by both pharmacological inhibition and RNAi-mediated down-regulation of the threonine/ serine-specific phosphatases PP1 and PP2A, recycling back to the plasma membrane required dephosphorylation of threonine 6. We provide evidence that a cycle of phosphorylation and dephosphorylation may also be involved in intracellular targeting of other SH4 proteins such as the Src kinase Yes.
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31
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Zhang NN, Liu X, Sun J, Wu Y, Li QW. [Nonclassical mechanisms of secretory protein in eukaryotic cells]. YI CHUAN = HEREDITAS 2009; 31:29-35. [PMID: 19138898 DOI: 10.3724/sp.j.1005.2009.00029] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Intercellular communication is fundamental in many biological processes involved in cell growth, differentiation, development, and reproduction of living organisms and secretory proteins are among the most important messengers in this network of information. The vast majority of extracellular proteins are exported from cells by the endoplasmic reticulum/Golgi-dependent secretory pathway. However, increasing evidence shows that there are a group of secretory proteins without signal peptides, defined as nonclassical secretory proteins, which are exported via an ER/Golgi-independent pathway to perform extracellular functions. This pathway has been termed nonclassical or unconventional secretion, which is an essential and beneficial supplement of the ER-Golgi secretion pathway. The nonclassical secretion pathway has close relation with cell multiplication, immune response, tumor formation, infection pathology and so on. Here, the characters, the possible secretory mechanism, and the biological significance of nonclassical secretory proteins were reviewed.
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Affiliation(s)
- Nan-Nan Zhang
- College of Life Sciences, Liaoning Normal University, Dalian 116029, China.
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32
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Tyler KM, Fridberg A, Toriello KM, Olson CL, Cieslak JA, Hazlett TL, Engman DM. Flagellar membrane localization via association with lipid rafts. J Cell Sci 2009; 122:859-66. [PMID: 19240119 DOI: 10.1242/jcs.037721] [Citation(s) in RCA: 113] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
The eukaryotic flagellar membrane has a distinct composition from other domains of the plasmalemma. Our work shows that the specialized composition of the trypanosome flagellar membrane reflects increased concentrations of sterols and saturated fatty acids, correlating with direct observation of high liquid order by laurdan fluorescence microscopy. These findings indicate that the trypanosome flagellar membrane possesses high concentrations of lipid rafts: discrete regions of lateral heterogeneity in plasma membranes that serve to sequester and organize specialized protein complexes. Consistent with this, a dually acylated Ca(2+) sensor that is concentrated in the flagellum is found in detergent-resistant membranes and mislocalizes if the lipid rafts are disrupted. Detergent-extracted cells have discrete membrane patches localized on the surface of the flagellar axoneme, suggestive of intraflagellar transport particles. Together, these results provide biophysical and biochemical evidence to indicate that lipid rafts are enriched in the trypanosome flagellar membrane, providing a unique mechanism for flagellar protein localization and illustrating a novel means by which specialized cellular functions may be partitioned to discrete membrane domains.
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Affiliation(s)
- Kevin M Tyler
- BioMedical Research Centre, School of Medicine, Health Policy and Practice, University of East Anglia, Norwich, Norfolk NR4 7TJ, UK
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33
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Prudovsky I, Tarantini F, Landriscina M, Neivandt D, Soldi R, Kirov A, Small D, Kathir KM, Rajalingam D, Kumar TKS. Secretion without Golgi. J Cell Biochem 2008; 103:1327-43. [PMID: 17786931 PMCID: PMC2613191 DOI: 10.1002/jcb.21513] [Citation(s) in RCA: 100] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
A growing number of proteins devoid of signal peptides have been demonstrated to be released through the non-classical pathways independent of endoplasmic reticulum and Golgi. Among them are two potent proangiogenic cytokines FGF1 and IL1alpha. Stress-induced transmembrane translocation of these proteins requires the assembly of copper-dependent multiprotein release complexes. It involves the interaction of exported proteins with the acidic phospholipids of the inner leaflet of the cell membrane and membrane destabilization. Not only stress, but also thrombin treatment and inhibition of Notch signaling stimulate the export of FGF1. Non-classical release of FGF1 and IL1alpha presents a promising target for treatment of cardiovascular, oncologic, and inflammatory disorders.
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Affiliation(s)
- Igor Prudovsky
- Maine Medical Center Research Institute, Maine Medical Center, Scarborough, Maine 04074, USA.
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Tournaviti S, Hannemann S, Terjung S, Kitzing TM, Stegmayer C, Ritzerfeld J, Walther P, Grosse R, Nickel W, Fackler OT. SH4-domain-induced plasma membrane dynamization promotes bleb-associated cell motility. J Cell Sci 2008; 120:3820-9. [PMID: 17959630 DOI: 10.1242/jcs.011130] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
SH4 domains provide bipartite membrane-targeting signals for oncogenic Src family kinases. Here we report the induction of non-apoptotic plasma membrane (PM) blebbing as a novel and conserved activity of SH4 domains derived from the prototypic Src kinases Src, Fyn, Yes and Lck as well as the HASPB protein of Leishmania parasites. SH4-domain-induced blebbing is highly dynamic, with bleb formation and collapse displaying distinct kinetics. These reorganizations of the PM are controlled by Rho but not Rac or Cdc42 GTPase signalling pathways. SH4-induced membrane blebbing requires the membrane association of the SH4 domain, is regulated by the activities of Rock kinase and myosin II ATPase, and depends on the integrity of F-actin as well as microtubules. Endogenous Src kinase activity is crucial for PM blebbing in SH4-domain-expressing cells, active Src and Rock kinases are enriched in SH4-domain-induced PM blebs, and PM blebbing correlates with enhanced cell invasion in 3D matrices. These results establish a novel link between SH4 domains, Src activity and Rho signalling, and implicate SH4-domain-mediated PM dynamization as a mechanism that influences invasiveness of cells transformed by SH4-domain-containing oncoproteins.
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Affiliation(s)
- Stella Tournaviti
- Heidelberg University Biochemistry Center, Im Neuenheimer Feld 328, 69120 Heidelberg, Germany
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Seelenmeyer C, Stegmayer C, Nickel W. Unconventional secretion of fibroblast growth factor 2 and galectin-1 does not require shedding of plasma membrane-derived vesicles. FEBS Lett 2008; 582:1362-8. [PMID: 18371311 DOI: 10.1016/j.febslet.2008.03.024] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2008] [Revised: 03/05/2008] [Accepted: 03/14/2008] [Indexed: 12/19/2022]
Abstract
Various molecular mechanisms of unconventional secretion of fibroblast growth factor 2 and galectin-1 have been proposed. A non-vesicular pathway that is based on direct translocation across the plasma membrane has been described. In other studies, however, release into the extracellular space of cell-derived vesicles was implicated in both FGF-2 and Gal-1 secretion. Such vesicles were proposed to originate either from plasma membrane shedding or by the release of exosomes. Employing an inhibitor of plasma membrane blebbing and based on a quantitative biochemical analysis of cell culture supernatants for vesicles potentially carrying FGF-2 or Gal-1, we demonstrate that both FGF-2 and Gal-1 are not exported by shedding of plasma membrane-derived vesicles.
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Affiliation(s)
- Claudia Seelenmeyer
- Heidelberg University Biochemistry Center (BZH), Im Neuenheimer Feld 328, 69120 Heidelberg, Germany
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Kinseth MA, Anjard C, Fuller D, Guizzunti G, Loomis WF, Malhotra V. The Golgi-Associated Protein GRASP Is Required for Unconventional Protein Secretion during Development. Cell 2007; 130:524-34. [PMID: 17655921 DOI: 10.1016/j.cell.2007.06.029] [Citation(s) in RCA: 187] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2007] [Revised: 05/17/2007] [Accepted: 06/15/2007] [Indexed: 10/23/2022]
Abstract
During Dictyostelium development, prespore cells secrete acyl-CoA binding protein (AcbA). Upon release, AcbA is processed to generate a peptide called spore differentiation factor-2 (SDF-2), which triggers terminal differentiation of spore cells. We have found that cells lacking Golgi reassembly stacking protein (GRASP), a protein attached peripherally to the cytoplasmic surface of Golgi membranes, fail to secrete AcbA and, thus, produce inviable spores. Surprisingly, AcbA lacks a signal sequence and is not secreted via the conventional secretory pathway (endoplasmic reticulum-Golgi-cell surface). GRASP is not required for conventional protein secretion, growth, and the viability of vegetative cells. Our findings reveal a physiological role of GRASP and provide a means to understand unconventional secretion and its role in development.
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Affiliation(s)
- Matthew A Kinseth
- Cell and Developmental Biology, Division of Biological Sciences, University of California, San Diego, La Jolla, CA 92093, USA
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Tjalsma H, Pluk W, van den Heuvel LP, Peters WHM, Roelofs R, Swinkels DW. Proteomic inventory of "anchorless" proteins on the colon adenocarcinoma cell surface. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2006; 1764:1607-17. [PMID: 17030026 DOI: 10.1016/j.bbapap.2006.09.002] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/22/2006] [Revised: 09/01/2006] [Accepted: 09/01/2006] [Indexed: 11/23/2022]
Abstract
Surface proteins play important pathophysiological roles in health and disease, and accumulating proteomics-based studies suggest that several "non-membrane" proteins are sorted to the cell surface by unconventional mechanisms. Importantly, these proteins may comprise attractive therapeutic targets and novel disease markers for colon cancer. To perform a proteomics-based inventory of these so-called "anchorless" surface proteins, intact colon adenocarcinoma SW480 cells were labeled with membrane-impermeable biotin after which only soluble biotinylated proteins were isolated and identified by nanoLC-MS/MS. Computer-assisted analysis predicted that only 9 of the 97 identified surface-exposed proteins have predicted secretory signal peptides, whereas 2 other proteins have a putative transmembrane segment. Of the 9 proteins with putative signal peptides, 1 was predicted to be retained at the cell surface by a GPI-anchor, whereas 5 other proteins contained an ER-retention motif (KDEL) that should prevent them from being sorted to the cell surface. The remaining 86 soluble "surface" proteins lack known export signals and the possibility that these proteins are candidate substrates of non-classical transporters or exported by unconventional mechanisms is discussed. Alternatively, the large number of "intracellular" and ER-resident proteins may imply that biotinylation approaches are not only specific for surface proteins, but also biased against a certain subset of non-surface proteins. This underscores the importance of post-proteomic verification of proteomics-based inventories on surface-exposed proteins, which eventually should reveal to which extent non-classical export and retention mechanisms contribute to the sorting of "anchorless" proteins to the surface of colon tumor cells.
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Affiliation(s)
- Harold Tjalsma
- Department of Clinical Chemistry, 441, Radboud University Nijmegen-Medical Centre, P.O. Box 9101, 6500 HB Nijmegen, The Netherlands.
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Prickett S, Gray PM, Colpitts SL, Scott P, Kaye PM, Smith DF. In vivo recognition of ovalbumin expressed by transgenic Leishmania is determined by its subcellular localization. THE JOURNAL OF IMMUNOLOGY 2006; 176:4826-33. [PMID: 16585577 PMCID: PMC2695601 DOI: 10.4049/jimmunol.176.8.4826] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The importance of the site of Ag localization within microbial pathogens for the effective generation of CD8+ T cells has been studied extensively, generally supporting the view that Ag secretion within infected target cells is required for optimal MHC class I-restricted Ag presentation. In contrast, relatively little is known about the importance of pathogen Ag localization for the activation of MHC class II-restricted CD4+ T cells, despite their clear importance for host protection. We have used the N-terminal targeting sequence of Leishmania major hydrophilic acylated surface protein B to generate stable transgenic lines expressing physiologically relevant levels of full-length OVA on the surface of metacyclic promastigotes and amastigotes. In addition, we have mutated the hydrophilic acylated surface protein B N-terminal acylation sequence to generate control transgenic lines in which OVA expression is restricted to the parasite cytosol. In vitro, splenic dendritic cells are able to present membrane-localized, but not cytosolic, OVA to OVA-specific DO.11 T cells. Strikingly and unexpectedly, surface localization of OVA is also a strict requirement for recognition by OVA-specific T cells (DO.11 and OT-II) and for the development of OVA-specific Ab responses in vivo. However, recognition of cytosolic OVA could be observed with increasing doses of infection. These data suggest that, even under in vivo conditions, where varied pathways of Ag processing are likely to operate, the site of Leishmania Ag localization is an important determinant of immunogenicity and hence an important factor when considering the likely candidacy of vaccine Ags for inducing CD4+ T cell-dependent immunity.
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Affiliation(s)
- Sara Prickett
- Wellcome Trust Laboratories for Molecular Parasitology, Centre for Molecular Microbiology and Infection, Imperial College, London, United Kingdom
- Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, United Kingdom
| | - Peter M. Gray
- Department of Pathobiology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA 19104
| | - Sara L. Colpitts
- Department of Pathobiology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA 19104
| | - Phillip Scott
- Department of Pathobiology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA 19104
| | - Paul M. Kaye
- Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, United Kingdom
| | - Deborah F. Smith
- Wellcome Trust Laboratories for Molecular Parasitology, Centre for Molecular Microbiology and Infection, Imperial College, London, United Kingdom
- Address correspondence and reprint requests to Dr. Deborah F. Smith, Immunology and Infection Unit, Department of Biology/Hull York Medical School, University of York, Heslington, York YO10 5YW, U.K. E-mail address:
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Seelenmeyer C, Wegehingel S, Tews I, Künzler M, Aebi M, Nickel W. Cell surface counter receptors are essential components of the unconventional export machinery of galectin-1. ACTA ACUST UNITED AC 2006; 171:373-81. [PMID: 16247033 PMCID: PMC2171196 DOI: 10.1083/jcb.200506026] [Citation(s) in RCA: 84] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Galectin-1 is a component of the extracellular matrix as well as a ligand of cell surface counter receptors such as β-galactoside–containing glycolipids, however, the molecular mechanism of galectin-1 secretion has remained elusive. Based on a nonbiased screen for galectin-1 export mutants we have identified 26 single amino acid changes that cause a defect of both export and binding to counter receptors. When wild-type galectin-1 was analyzed in CHO clone 13 cells, a mutant cell line incapable of expressing functional galectin-1 counter receptors, secretion was blocked. Intriguingly, we also find that a distant relative of galectin-1, the fungal lectin CGL-2, is a substrate for nonclassical export from Chinese hamster ovary (CHO) cells. Alike mammalian galectin-1, a CGL-2 mutant defective in β-galactoside binding, does not get exported from CHO cells. We conclude that the β-galactoside binding site represents the primary targeting motif of galectins defining a galectin export machinery that makes use of β-galactoside–containing surface molecules as export receptors for intracellular galectin-1.
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Kjaerulff S, Müller S, Jensen MR. Alternative protein secretion: The Mam1 ABC transporter supports secretion of M-factor linked GFP in fission yeast. Biochem Biophys Res Commun 2005; 338:1853-9. [PMID: 16288715 DOI: 10.1016/j.bbrc.2005.10.156] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2005] [Accepted: 10/21/2005] [Indexed: 11/18/2022]
Abstract
To examine whether the fission yeast Mam1 ABC transporter can be used for secretion of heterologous proteins, thereby bypassing the classical secretion pathway, we have analyzed chimeric forms of the M-factor precursor. It was demonstrated that GFP can be exported when fused to both the amino-terminal prosequence from mfm1 and a CaaX motif. This secretion was dependent on the Mam1 transporter and not the classical secretion pathway. The secretion efficiency of GFP, however, was relatively low and most of the reporter protein was trapped in the vacuolar membranes. Our findings suggest that the Mam1 ABC protein is a promiscuous peptide transporter that can accommodate globular proteins of a relatively large size. Furthermore, our results help in defining the sequences required for processing and secretion of natural M-factor.
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Abstract
The vast majority of extracellular proteins are exported from mammalian cells by the endoplasmic reticulum/Golgi-dependent secretory pathway. For poorly understood reasons, however, a heterogenous group of extracellular proteins has been discovered that does not make use of signal peptide-dependent secretory transport. Both the release mechanisms and the molecular identity of the secretory machines involved have remained elusive. Recent studies now have established a subgroup of unconventional secretory proteins capable of translocating from the cytoplasm directly across the plasma membrane to get access to the exterior of eukaryotic cells. This review aims to focus on a detailed comparison of the subcellular site of membrane translocation of various unconventional secretory proteins such as the proangiogenic molecule fibroblast growth factor-2 (FGF-2) and Leishmania hydrophilic acylated surface protein B (HASP B). A potential link between membrane translocation and quality control as an integral part of unconventional secretory processes is discussed.
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Affiliation(s)
- Walter Nickel
- Heidelberg University Biochemistry Center (BZH), Im Neuenheimer Feld 328, 69120 Heidelberg, Germany.
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