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Ebner JK, König GM, Kostenis E, Siegert P, Aktories K, Orth JHC. Activation of G q signaling by Pasteurella multocida toxin inhibits the osteoblastogenic-like actions of Activin A in C2C12 myoblasts, a cell model of fibrodysplasia ossificans progressiva. Bone 2019; 127:592-601. [PMID: 31376533 DOI: 10.1016/j.bone.2019.07.031] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/11/2018] [Revised: 07/29/2019] [Accepted: 07/30/2019] [Indexed: 01/15/2023]
Abstract
The human disease fibrodysplasia ossificans progressiva (FOP) is a rare and highly disabling disorder of extensive heterotopic bone growth that is caused by a point mutation (R206H) in the activation domain of Alk2, a BMP (bone morphogenic protein) type 1 receptor. The mutation leads to extensive BMP-signaling induced by Activin A, which is normally an antagonist for wildtype receptors, resulting in excessive and uncontrolled bone formation. Here, we studied the effects of Pasteurella multocida toxin (PMT), which activates osteoclasts and inhibits osteoblast activity, in C2C12 myoblasts expressing the mutant Alk2(R206H) receptor as model of FOP. In our study, we mainly used alkaline phosphatase (ALP) activity as marker to determine osteoblast differentiation. BMP-4 stimulated an increase in ALP activity in C2C12-Alk2wt and C2C12-Alk2(R206H) cells. By contrast, Activin A only induced ALP activity in C2C12-Alk2(R206H) cells. In both cases, PMT acted as a potent inhibitor of ALP activity. PMT-induced inhibition of ALP activity was paralleled by a constitutive activation of the heterotrimeric Gq protein. Expression of a permanently active Gαq blocked Activin A/Alk2(R206H)-dependent increase in ALP activity. Inactivation of Gq by specific inhibitor FR900359 blocked the PMT effect. Similarly, canonical second messengers and effectors of Gαq (e.g. ionophore A23187-induced increase in intracellular Ca2+ and activation of PKC by PMA (phorbol 12-myristate 13-acetate)) inhibited Alk2(R206H)-mediated induction of ALP activity. Notably, Activin A-induced increase in ALP activity in C2C12-Alk2(R206H) cells was also inhibited by stimulation of the α1A-adrenoceptor, which couples to Gαq, by phenylephrine. PMT did not alter tail phosphorylation of the major downstream effectors of the Alk2 receptor, Smad1/5/9; neither did the toxin affect nuclear translocation of the Smad-complex. However, PMT diminished BMP responsive element-induced gene expression. The data indicate that PMT potently inhibits the induction of osteoblast markers in a FOP model via activation of G proteins. Moreover, our findings indicate that activation of G protein-coupled receptors and of G protein signaling might be a rationale for pharmacological therapy of FOP.
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Affiliation(s)
- Julia K Ebner
- Institute for Experimental and Clinical Pharmacology and Toxicology, Faculty of Medicine, University of Freiburg, Albertstr. 25, 79104 Freiburg, Germany; Faculty of Biology, University of Freiburg, Schänzlestr. 1, 79104 Freiburg, Germany; Spemann Graduate School for Biology and Medicine, University of Freiburg, Albertstr. 19A, 79104 Freiburg, Germany
| | - Gabriele M König
- Molecular, Cellular and Pharmacobiology Section, Institute of Pharmaceutical Biology, University of Bonn, Nussallee 6, 53115 Bonn, Germany
| | - Evi Kostenis
- Molecular, Cellular and Pharmacobiology Section, Institute of Pharmaceutical Biology, University of Bonn, Nussallee 6, 53115 Bonn, Germany
| | - Peter Siegert
- Institute for Experimental and Clinical Pharmacology and Toxicology, Faculty of Medicine, University of Freiburg, Albertstr. 25, 79104 Freiburg, Germany
| | - Klaus Aktories
- Institute for Experimental and Clinical Pharmacology and Toxicology, Faculty of Medicine, University of Freiburg, Albertstr. 25, 79104 Freiburg, Germany; Spemann Graduate School for Biology and Medicine, University of Freiburg, Albertstr. 19A, 79104 Freiburg, Germany; BIOSS Centre for Biological Signalling Studies, University of Freiburg, Schänzlestr. 18, 79104 Freiburg, Germany.
| | - Joachim H C Orth
- Institute for Experimental and Clinical Pharmacology and Toxicology, Faculty of Medicine, University of Freiburg, Albertstr. 25, 79104 Freiburg, Germany
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Brink T, Leiss V, Siegert P, Jehle D, Ebner JK, Schwan C, Shymanets A, Wiese S, Nürnberg B, Hensel M, Aktories K, Orth JHC. Salmonella Typhimurium effector SseI inhibits chemotaxis and increases host cell survival by deamidation of heterotrimeric Gi proteins. PLoS Pathog 2018; 14:e1007248. [PMID: 30102745 PMCID: PMC6107295 DOI: 10.1371/journal.ppat.1007248] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2018] [Revised: 08/23/2018] [Accepted: 07/27/2018] [Indexed: 12/20/2022] Open
Abstract
Salmonella enterica serotype Typhimurium (S. Typhimurium) is one of the most frequent causes of food-borne illness in humans and usually associated with acute self-limiting gastroenteritis. However, in immunocompromised patients, the pathogen can disseminate and lead to severe systemic diseases. S. Typhimurium are facultative intracellular bacteria. For uptake and intracellular life, Salmonella translocate numerous effector proteins into host cells using two type-III secretion systems (T3SS), which are encoded within Salmonella pathogenicity islands 1 (SPI-1) and 2 (SPI-2). While SPI-1 effectors mainly promote initial invasion, SPI-2 effectors control intracellular survival and proliferation. Here, we elucidate the mode of action of Salmonella SPI-2 effector SseI, which is involved in control of systemic dissemination of S. Typhimurium. SseI deamidates a specific glutamine residue of heterotrimeric G proteins of the Gαi family, resulting in persistent activation of the G protein. Gi activation inhibits cAMP production and stimulates PI3-kinase γ by Gαi-released Gβγ subunits, resulting in activation of survival pathways by phosphorylation of Akt and mTOR. Moreover, SseI-induced deamidation leads to non-polarized activation of Gαi and, thereby, to loss of directed migration of dendritic cells. Salmonella Typhimurium is one of the most common causes of gastroenteritis in humans. In immunocompromised patients, the pathogen can cause systemic infections. Crucial virulence factors are encoded on two Salmonella pathogenicity islands SPI-1 and SPI-2. While SPI-1 encodes virulence factors essential for host cell invasion, intracellular proliferation of the pathogen depends mainly on SPI-2 effectors. Here, we elucidate the mode of action of Salmonella SPI-2 effector SseI. SseI activates heterotrimeric G proteins of the Gαi family by deamidation of a specific glutamine residue. Deamidation blocks GTP hydrolysis by Gαi, resulting in a persistently active G protein. Gi activation inhibits cAMP production and stimulates PI3Kγ by Gαi-released Gβγ subunits, resulting in activation of survival pathways by phosphorylation of Akt and mTOR. Moreover, deamidation of Gαi leads to a loss of directed migration in dendritic cells. The data offers a new perspective in the understanding of the actions of SseI.
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Affiliation(s)
- Thorsten Brink
- Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Medizinische Fakultät, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
| | - Veronika Leiss
- Abteilung für Pharmakologie und Experimentelle Therapie, Medizinische Fakultät und ICePhA, Eberhard-Karls-Universität Tübingen, Germany
| | - Peter Siegert
- Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Medizinische Fakultät, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
| | - Doris Jehle
- Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Medizinische Fakultät, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
| | - Julia K. Ebner
- Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Medizinische Fakultät, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
- Spemann Graduate School of Biology and Medicine (SGBM), Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
- Fakultät für Biologie, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
| | - Carsten Schwan
- Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Medizinische Fakultät, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
| | - Aliaksei Shymanets
- Abteilung für Pharmakologie und Experimentelle Therapie, Medizinische Fakultät und ICePhA, Eberhard-Karls-Universität Tübingen, Germany
| | - Sebastian Wiese
- Zentrum für Biosystemanalyse, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
| | - Bernd Nürnberg
- Abteilung für Pharmakologie und Experimentelle Therapie, Medizinische Fakultät und ICePhA, Eberhard-Karls-Universität Tübingen, Germany
| | - Michael Hensel
- Abteilung Mikrobiologie, Fachbereich Biologie/Chemie, Universität Osnabrück, Osnabrück, Germany
| | - Klaus Aktories
- Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Medizinische Fakultät, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
- BIOSS Centre for Biological Signalling Studies, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
- * E-mail:
| | - Joachim H. C. Orth
- Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Medizinische Fakultät, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
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Heni H, Ebner JK, Schmidt G, Aktories K, Orth JHC. Involvement of Osteocytes in the Action of Pasteurella multocida Toxin. Toxins (Basel) 2018; 10:toxins10080328. [PMID: 30104531 PMCID: PMC6115833 DOI: 10.3390/toxins10080328] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2018] [Revised: 08/06/2018] [Accepted: 08/08/2018] [Indexed: 01/24/2023] Open
Abstract
Pasteurella multocida toxin (PMT) causes progressive atrophic rhinitis with severe turbinate bone degradation in pigs. It has been reported that the toxin deamidates and activates heterotrimeric G proteins, resulting in increased differentiation of osteoclasts and blockade of osteoblast differentiation. So far, the action of PMT on osteocytes, which is the most abundant cell type in bone tissue, is not known. In MLO-Y4 osteocytes, PMT deamidated heterotrimeric G proteins, resulting in loss of osteocyte dendritic processes, stress fiber formation, cell spreading and activation of RhoC but not of RhoA. Moreover, the toxin caused processing of membrane-bound receptor activator of NF-κB ligand (RANKL) to release soluble RANKL and enhanced the secretion of osteoclastogenic TNF-α. In a co-culture model of osteocytes and bone marrow cells, PMT-induced osteoclastogenesis was largely increased as compared to the mono-culture model. The enhancement of osteoclastogenesis observed in the co-culture was blocked by sequestering RANKL with osteoprotegerin and by an antibody against TNF-α indicating involvement of release of the osteoclastogenic factors from osteocytes. Data support the crucial role of osteocytes in bone metabolism and osteoclastogenesis and identify osteocytes as important target cells of PMT in progressive atrophic rhinitis.
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Affiliation(s)
- Hannah Heni
- Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Medizinische Fakultät, Albert-Ludwigs-Universität Freiburg, Albertstr. 25, 79104 Freiburg, Germany.
- Hermann-Staudinger-Graduiertenschule, Universität Freiburg, 79104 Freiburg, Germany.
| | - Julia K Ebner
- Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Medizinische Fakultät, Albert-Ludwigs-Universität Freiburg, Albertstr. 25, 79104 Freiburg, Germany.
- Spemann Graduate School of Biology and Medicine (SGBM), Universität Freiburg, 79104 Freiburg, Germany.
- Faculty of Biology, Universität Freiburg, 79104 Freiburg, Germany.
| | - Gudula Schmidt
- Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Medizinische Fakultät, Albert-Ludwigs-Universität Freiburg, Albertstr. 25, 79104 Freiburg, Germany.
| | - Klaus Aktories
- Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Medizinische Fakultät, Albert-Ludwigs-Universität Freiburg, Albertstr. 25, 79104 Freiburg, Germany.
- BIOSS Centre for Biological Signalling Studies, Universität Freiburg, 79104 Freiburg, Germany.
| | - Joachim H C Orth
- Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Medizinische Fakultät, Albert-Ludwigs-Universität Freiburg, Albertstr. 25, 79104 Freiburg, Germany.
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Castonguay J, Orth JHC, Müller T, Sleman F, Grimm C, Wahl-Schott C, Biel M, Mallmann RT, Bildl W, Schulte U, Klugbauer N. The two-pore channel TPC1 is required for efficient protein processing through early and recycling endosomes. Sci Rep 2017; 7:10038. [PMID: 28855648 PMCID: PMC5577145 DOI: 10.1038/s41598-017-10607-4] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2017] [Accepted: 08/11/2017] [Indexed: 02/06/2023] Open
Abstract
Two-pore channels (TPCs) are localized in endo-lysosomal compartments and assumed to play an important role for vesicular fusion and endosomal trafficking. Recently, it has been shown that both TPC1 and 2 were required for host cell entry and pathogenicity of Ebola viruses. Here, we investigate the cellular function of TPC1 using protein toxins as model substrates for distinct endosomal processing routes. Toxin uptake and activation through early endosomes but not processing through other compartments were reduced in TPC1 knockout cells. Detailed co-localization studies with subcellular markers confirmed predominant localization of TPC1 to early and recycling endosomes. Proteomic analysis of native TPC1 channels finally identified direct interaction with a distinct set of syntaxins involved in fusion of intracellular vesicles. Together, our results demonstrate a general role of TPC1 for uptake and processing of proteins in early and recycling endosomes, likely by providing high local Ca2+ concentrations required for SNARE-mediated vesicle fusion.
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Affiliation(s)
- Jan Castonguay
- Institute of Experimental and Clinical Pharmacology and Toxicology, Faculty of Medicine, Albert-Ludwigs-University, Albertstrasse 25, 79104, Freiburg, Germany
| | - Joachim H C Orth
- Institute of Experimental and Clinical Pharmacology and Toxicology, Faculty of Medicine, Albert-Ludwigs-University, Albertstrasse 25, 79104, Freiburg, Germany
| | - Thomas Müller
- Institute of Experimental and Clinical Pharmacology and Toxicology, Faculty of Medicine, Albert-Ludwigs-University, Albertstrasse 25, 79104, Freiburg, Germany
| | - Faten Sleman
- Institute of Experimental and Clinical Pharmacology and Toxicology, Faculty of Medicine, Albert-Ludwigs-University, Albertstrasse 25, 79104, Freiburg, Germany
| | - Christian Grimm
- Department of Pharmacy, Center for Drug Research and Center for Integrated Protein Science Munich (CIPSM), Ludwig-Maximilians-University, Munich, Germany
| | - Christian Wahl-Schott
- Department of Pharmacy, Center for Drug Research and Center for Integrated Protein Science Munich (CIPSM), Ludwig-Maximilians-University, Munich, Germany
| | - Martin Biel
- Department of Pharmacy, Center for Drug Research and Center for Integrated Protein Science Munich (CIPSM), Ludwig-Maximilians-University, Munich, Germany
| | - Robert Theodor Mallmann
- Institute of Experimental and Clinical Pharmacology and Toxicology, Faculty of Medicine, Albert-Ludwigs-University, Albertstrasse 25, 79104, Freiburg, Germany
| | - Wolfgang Bildl
- Institute of Physiology II, Faculty of Medicine, Albert-Ludwigs-University, Hermann-Herder-Strasse 7, 79104, Freiburg, Germany
| | - Uwe Schulte
- Institute of Physiology II, Faculty of Medicine, Albert-Ludwigs-University, Hermann-Herder-Strasse 7, 79104, Freiburg, Germany.,Logopharm GmbH, Schlossstrasse 14, 79232, March-Buchheim, Germany.,Center for Biological Signaling Studies (BIOSS), Schänzlestrasse 18, 79104, Freiburg, Germany
| | - Norbert Klugbauer
- Institute of Experimental and Clinical Pharmacology and Toxicology, Faculty of Medicine, Albert-Ludwigs-University, Albertstrasse 25, 79104, Freiburg, Germany.
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Carle S, Brink T, Orth JHC, Aktories K, Barth H. Auranofin Inhibits the Enzyme Activity of Pasteurella multocida Toxin PMT in Human Cells and Protects Cells from Intoxication. Toxins (Basel) 2017; 9:toxins9010032. [PMID: 28098782 PMCID: PMC5308264 DOI: 10.3390/toxins9010032] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2016] [Revised: 12/23/2016] [Accepted: 01/10/2017] [Indexed: 11/16/2022] Open
Abstract
The AB-type protein toxin from Pasteurella multocida (PMT) contains a functionally important disulfide bond within its catalytic domain, which must be cleaved in the host cell cytosol to render the catalytic domain of PMT into its active conformation. Here, we found that the reductive potential of the cytosol of target cells, and more specifically, the activity of the thioredoxin reductase (TrxR) is crucial for this process. This was demonstrated by the strong inhibitory effect of the pharmacological TrxR inhibitor auranofin, which inhibited the intoxication of target cells with PMT, as determined by analyzing the PMT-catalyzed deamidation of GTP-binding proteins (G-proteins) in the cytosol of cells. The amount of endogenous substrate levels modified by PMT in cells pretreated with auranofin was reduced compared to cells treated with PMT alone. Auranofin had no inhibitory effect on the activity of the catalytic domain of constitutively active PMT in vitro, demonstrating that auranofin did not directly inhibit PMT activity, but interferes with the mode of action of PMT in cells. In conclusion, the results show that TrxR is crucial for the mode of action of PMT in mammalian cells, and that the drug auranofin can serve as an efficient inhibitor, which might be a starting point for novel therapeutic options against toxin-associated diseases.
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Affiliation(s)
- Stefan Carle
- Institute of Pharmacology and Toxicology, University of Ulm Medical Center, Albert-Einstein-Allee 11, Ulm 89081, Germany.
| | - Thorsten Brink
- Institute of Experimental and Clinical Pharmacology and Toxicology, University of Freiburg, Freiburg 79104, Germany.
| | - Joachim H C Orth
- Institute of Experimental and Clinical Pharmacology and Toxicology, University of Freiburg, Freiburg 79104, Germany.
| | - Klaus Aktories
- Institute of Experimental and Clinical Pharmacology and Toxicology, University of Freiburg, Freiburg 79104, Germany.
- Centre for Biological Signalling Studies (BIOSS), University of Freiburg, Freiburg 79104, Germany.
| | - Holger Barth
- Institute of Pharmacology and Toxicology, University of Ulm Medical Center, Albert-Einstein-Allee 11, Ulm 89081, Germany.
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Weise M, Vettel C, Spiger K, Gilsbach R, Hein L, Lorenz K, Wieland T, Aktories K, Orth JHC. A systemic Pasteurella multocida toxin aggravates cardiac hypertrophy and fibrosis in mice. Cell Microbiol 2015; 17:1320-31. [PMID: 25759205 DOI: 10.1111/cmi.12436] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2014] [Revised: 02/20/2015] [Accepted: 03/06/2015] [Indexed: 11/30/2022]
Abstract
Pasteurella multocida toxin (PMT) persistently activates heterotrimeric G proteins of the Gαq/11 , Gα12/13 and Gαi family without interaction with G protein-coupled receptors (GPCRs). We show that PMT acts on heart tissue in vivo and on cardiomyocytes and cardiac fibroblasts in vitro by deamidation of heterotrimeric G proteins. Increased normalized ventricle weights and fibrosis were detected after intraperitoneal administration of PMT in combination with the GPCR agonist phenylephrine. In neonatal rat cardiomyocytes, PMT stimulated the mitogen-activated protein kinase pathway, which is crucial for the development of cellular hypertrophy. The toxin induced phosphorylation of the canonical phosphorylation sites of the extracellular-regulated kinase 1/2 and, additionally, caused phosphorylation of the recently recognized autophosphorylation site, which appears to be important for the development of cellular hypertrophy. Moreover, PMT stimulated the small GTPases Rac1 and RhoA. Both switch proteins are involved in cardiomyocyte hypertrophy. In addition, PMT stimulated RhoA and Rac1 in neonatal rat cardiac fibroblasts. RhoA and Rac1 have been implicated in the regulation of connective tissue growth factor (CTGF) secretion and expression. Accordingly, we show that PMT treatment increased secretion and expression of CTGF in cardiac fibroblasts. Altogether, the data indicate that PMT is an inducer of pathological remodelling of cardiac cells and identifies the toxin as a promising tool for studying heterotrimeric G protein-dependent signalling in cardiac cells.
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Affiliation(s)
- Markus Weise
- Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Dept. I, Albert-Ludwigs-Universität Freiburg, Albertstr. 25, Freiburg, 79104, Germany
| | - Christiane Vettel
- Institute of Experimental and Clinical Pharmacology and Toxicology, Medical Faculty Mannheim, University of Heidelberg, Mannheim, Germany
| | - Katharina Spiger
- Institute of Experimental and Clinical Pharmacology and Toxicology, Medical Faculty Mannheim, University of Heidelberg, Mannheim, Germany
| | - Ralf Gilsbach
- Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Dept. II, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
| | - Lutz Hein
- Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Dept. II, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
| | - Kristina Lorenz
- Institute of Pharmacology and Toxicology, University of Würzburg, Würzburg, Germany.,Comprehensive Heart Failure Center, University of Würzburg, Würzburg, Germany
| | - Thomas Wieland
- Institute of Experimental and Clinical Pharmacology and Toxicology, Medical Faculty Mannheim, University of Heidelberg, Mannheim, Germany
| | - Klaus Aktories
- Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Dept. I, Albert-Ludwigs-Universität Freiburg, Albertstr. 25, Freiburg, 79104, Germany.,BIOSS Centre for Biological Signalling Studies, Universität Freiburg, Freiburg, Germany
| | - Joachim H C Orth
- Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Dept. I, Albert-Ludwigs-Universität Freiburg, Albertstr. 25, Freiburg, 79104, Germany
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Hildebrand D, Bode KA, Rieß D, Cerny D, Waldhuber A, Römmler F, Strack J, Korten S, Orth JHC, Miethke T, Heeg K, Kubatzky KF. Granzyme A produces bioactive IL-1β through a nonapoptotic inflammasome-independent pathway. Cell Rep 2014; 9:910-7. [PMID: 25437548 DOI: 10.1016/j.celrep.2014.10.003] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2014] [Revised: 09/22/2014] [Accepted: 09/29/2014] [Indexed: 01/21/2023] Open
Abstract
Bacterial components are recognized by the immune system through activation of the inflammasome, eventually causing processing of the proinflammatory cytokine interleukin-1? (IL-1?), a pleiotropic cytokine and one of the most important mediators of inflammation, through the protease caspase-1. Synthesis of the precursor protein and processing into its bioactive form are tightly regulated, given that disturbed control of IL-1? release can cause severe autoinflammatory diseases or contribute to cancer development. We show that the bacterial Pasteurella multocida toxin (PMT) triggers Il1b gene transcription in macrophages independently of Toll-like receptor signaling through RhoA/Rho-kinase-mediated NF-?? activation. Furthermore, PMT mediates signal transducer and activator of transcription (STAT) protein-controlled granzyme A (a serine protease) expression in macrophages. The exocytosed granzyme A enters target cells and mediates IL-1? maturation independently of caspase-1 and without inducing cytotoxicity. These findings show that macrophages can induce an IL-1?-initiated immune response independently of inflammasome activity.
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Affiliation(s)
- Dagmar Hildebrand
- Department für Infektiologie, Medizinische Mikrobiologie und Hygiene, Universitätsklinikum Heidelberg, Im Neuenheimer Feld 324, 69120 Heidelberg, Germany
| | - Konrad A Bode
- Department für Infektiologie, Medizinische Mikrobiologie und Hygiene, Universitätsklinikum Heidelberg, Im Neuenheimer Feld 324, 69120 Heidelberg, Germany
| | - David Rieß
- Department für Infektiologie, Medizinische Mikrobiologie und Hygiene, Universitätsklinikum Heidelberg, Im Neuenheimer Feld 324, 69120 Heidelberg, Germany
| | - Daniela Cerny
- Department für Infektiologie, Medizinische Mikrobiologie und Hygiene, Universitätsklinikum Heidelberg, Im Neuenheimer Feld 324, 69120 Heidelberg, Germany
| | - Anna Waldhuber
- Institut für Medizinische Mikrobiologie, Immunologie und Hygiene, Technische Universität München, Trogerstraße 30, 81675 München, Germany
| | - Franziska Römmler
- Institut für Medizinische Mikrobiologie, Immunologie und Hygiene, Technische Universität München, Trogerstraße 30, 81675 München, Germany
| | - Julia Strack
- Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Albert-Ludwigs-Universität Freiburg, Albertstraße 25, 79104 Freiburg, Germany
| | - Simone Korten
- Labor Lademannbogen MVZ GmbH, Lademannbogen 61-63, 22339 Hamburg, Germany
| | - Joachim H C Orth
- Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Albert-Ludwigs-Universität Freiburg, Albertstraße 25, 79104 Freiburg, Germany
| | - Thomas Miethke
- Institut für Medizinische Mikrobiologie und Hygiene, Medizinische Fakultät Mannheim der Universität Heidelberg, Theodor-Kutzer-Ufer 1-3, 68167 Mannheim, Germany
| | - Klaus Heeg
- Department für Infektiologie, Medizinische Mikrobiologie und Hygiene, Universitätsklinikum Heidelberg, Im Neuenheimer Feld 324, 69120 Heidelberg, Germany
| | - Katharina F Kubatzky
- Department für Infektiologie, Medizinische Mikrobiologie und Hygiene, Universitätsklinikum Heidelberg, Im Neuenheimer Feld 324, 69120 Heidelberg, Germany.
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Siegert P, Schmidt G, Papatheodorou P, Wieland T, Aktories K, Orth JHC. Pasteurella multocida toxin prevents osteoblast differentiation by transactivation of the MAP-kinase cascade via the Gα(q/11)--p63RhoGEF--RhoA axis. PLoS Pathog 2013; 9:e1003385. [PMID: 23696743 PMCID: PMC3656108 DOI: 10.1371/journal.ppat.1003385] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2013] [Accepted: 04/11/2013] [Indexed: 11/19/2022] Open
Abstract
The 146-kDa Pasteurella multocida toxin (PMT) is the main virulence factor to induce P. multocida-associated progressive atrophic rhinitis in various animals. PMT leads to a destruction of nasal turbinate bones implicating an effect of the toxin on osteoblasts and/or osteoclasts. The toxin induces constitutive activation of Gα proteins of the Gq/11-, G12/13- and Gi-family by deamidating an essential glutamine residue. To study the PMT effect on bone cells, we used primary osteoblasts derived from rat calvariae and stromal ST-2 cells as differentiation model. As marker of functional osteoblasts the expression and activity of alkaline phosphatase, formation of mineralization nodules or expression of specific transcription factors as osterix was determined. Here, we show that the toxin inhibits differentiation and/or function of osteoblasts by activation of Gαq/11. Subsequently, Gαq/11 activates RhoA via p63RhoGEF, which specifically interacts with Gαq/11 but not with other G proteins like Gα12/13 and Gαi. Activated RhoA transactivates the mitogen-activated protein (MAP) kinase cascade via Rho kinase, involving Ras, MEK and ERK, resulting in inhibition of osteoblast differentiation. PMT-induced inhibition of differentiation was selective for the osteoblast lineage as adipocyte-like differentiation of ST-2 cells was not hampered. The present work provides novel insights, how the bacterial toxin PMT can control osteoblastic development by activating heterotrimeric G proteins of the Gαq/11-family and is a molecular pathogenetic basis for understanding the role of the toxin in bone loss during progressive atrophic rhinitis induced by Pasteurella multocida. Pasteurella multocida causes as a facultative pathogen various diseases in men and animals. One induced syndrome is atrophic rhinitis, which is a form of osteopenia, mainly characterized by facial distortion due to degradation of nasal turbinate bones. Strains, which especially affect bone tissue, produce the protein toxin P. multocida toxin (PMT). Importantly, PMT alone is capable to induce all symptoms of atrophic rhinitis. To cause osteopenia PMT influences the development and/or activity of specialized bone cells like osteoblasts and osteoclasts. Recently, we could identify the molecular mechanism of PMT. The toxin constitutively activates certain heterotrimeric G proteins by deamidation. Here, we studied the effect of PMT on the differentiation of osteoblasts. We demonstrate the direct action of PMT on osteoblasts and osteoblast-like cells and as a consequence inhibition of osteoblastic differentiation. Moreover, we revealed the underlying signal transduction pathway to impair proper osteoblast development. We show that PMT activates small GTPases in a Gαq/11 dependent manner via a non-ubiquitously expressed RhoGEF. In turn the mitogen-activated protein kinase pathway is transactivated leading to inhibition of osteoblastogenesis. Our findings present a mechanism how PMT hijacks host cell signaling pathways to hinder osteoblast development, which contributes to the syndrome of atrophic rhinitis.
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Affiliation(s)
- Peter Siegert
- Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
- Hermann–Staudinger–Graduiertenschule Universität Freiburg, Freiburg, Germany
| | - Gudula Schmidt
- Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
| | - Panagiotis Papatheodorou
- Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
| | - Thomas Wieland
- Institute of Experimental and Clinical Pharmacology and Toxicology, Medical Faculty Mannheim, University of Heidelberg, Mannheim, Germany
| | - Klaus Aktories
- Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
- BIOSS Centre for Biological Signalling Studies, Universität Freiburg, Freiburg, Germany
- * E-mail: (KA); (JO)
| | - Joachim H. C. Orth
- Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
- * E-mail: (KA); (JO)
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Orth JHC, Fester I, Siegert P, Weise M, Lanner U, Kamitani S, Tachibana T, Wilson BA, Schlosser A, Horiguchi Y, Aktories K. Substrate specificity of Pasteurella multocida toxin for α subunits of heterotrimeric G proteins. FASEB J 2012; 27:832-42. [PMID: 23150526 DOI: 10.1096/fj.12-213900] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Pasteurella multocida is the causative agent of a number of epizootic and zoonotic diseases. Its major virulence factor associated with atrophic rhinitis in animals and dermonecrosis in bite wounds is P. multocida toxin (PMT). PMT stimulates signal transduction pathways downstream of heterotrimeric G proteins, leading to effects such as mitogenicity, blockade of apoptosis, or inhibition of osteoblast differentiation. On the basis of Gα(i2), it was demonstrated that the toxin deamidates an essential glutamine residue of the Gα(i2) subunit, leading to constitutive activation of the G protein. Here, we studied the specificity of PMT for its G-protein targets by mass spectrometric analyses and by utilizing a monoclonal antibody, which recognizes specifically G proteins deamidated by PMT. The studies revealed deamidation of 3 of 4 families of heterotrimeric G proteins (Gα(q/11), Gα(i1,2,3), and Gα(12/13) of mouse or human origin) by PMT but not by a catalytic inactive toxin mutant. With the use of G-protein fragments and chimeras of responsive or unresponsive G proteins, the structural basis for the discrimination of heterotrimeric G proteins was studied. Our results elucidate substrate specificity of PMT on the molecular level and provide evidence for the underlying structural reasons of substrate discrimination.
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Affiliation(s)
- Joachim H C Orth
- Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany.
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Aktories K, Orth JHC, Adler B. Pasteurella multocida.(Preface). Curr Top Microbiol Immunol 2012; 361:v. [PMID: 23230602] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Affiliation(s)
- Klaus Aktories
- Medizinische Fakultät, Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Abt.I Albert-Ludwigs-Universität Freiburg, Albertstr. 25, 79104, Freiburg, Germany
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Abstract
Pasteurella multocida toxin (PMT) is the causative agent of progressive atrophic rhinitis in swine. The 146 kDa single-chain toxin harbours discrete domains important for receptor binding, internalisation and biological activity. The molecular basis of the toxin's activity is the deamidation of a specific glutamine residue in the α-subunit of heterotrimeric G proteins. This results in an inhibition of the inherent GTPase activity leading to a constitutively active phenotype of the G protein. Due to the ability of the toxin to act on various families of heterotrimeric G proteins, a large subset of signal transduction pathways is stimulated.
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Affiliation(s)
- Joachim H C Orth
- Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Albert-Ludwigs-Universität Freiburg, Albertstr. 25, 79104, Freiburg, Germany.
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Preuß I, Hildebrand D, Orth JHC, Aktories K, Kubatzky KF. Pasteurella multocida toxin is a potent activator of anti-apoptotic signalling pathways. Cell Microbiol 2010; 12:1174-85. [DOI: 10.1111/j.1462-5822.2010.01462.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
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Stratmann H, Schwan C, Orth JHC, Schmidt G, Aktories K. Pleiotropic role of Rac in mast cell activation revealed by a cell permeable Bordetella dermonecrotic fusion toxin. Cell Signal 2010; 22:1124-31. [PMID: 20211724 DOI: 10.1016/j.cellsig.2010.03.007] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2010] [Accepted: 03/01/2010] [Indexed: 12/01/2022]
Abstract
To activate the GTPase Rac in rat basophilic leukemia (RBL) cells and mouse bone marrow-derived mast cells (BMMC) a TAT fusion toxin of Bordetella dermonecrotic toxin (DNT-TAT) was constructed. The fusion toxin activated Rac1 and RhoA in vitro but only Rac in RBL cells and BMMC. DNT-TAT caused an increase in inositol phosphate formation, calcium mobilization, ERK activation and degranulation of mast cells. All these effects were inhibited by the Rho GTPase-inactivating Clostridium difficile toxin B and Clostridium sordellii lethal toxin. Also the calcium ionophore A23187 caused mast cell activation, including ERK phosphorylation, by processes involving an activation of Rac. The data indicate pleiotropic functions of Rac in mast cell activation.
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Affiliation(s)
- Heidi Stratmann
- Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Albert-Ludwigs-Universität Freiburg, Germany
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Orth JHC, Fester I, Preuss I, Agnoletto L, Wilson BA, Aktories K. Activation of Galpha (i) and subsequent uncoupling of receptor-Galpha(i) signaling by Pasteurella multocida toxin. J Biol Chem 2008; 283:23288-94. [PMID: 18583341 DOI: 10.1074/jbc.m803435200] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Bacterial protein toxins are powerful tools for elucidating signaling mechanisms in eukaryotic cells. A number of bacterial protein toxins, e.g. cholera toxin, pertussis toxin (PTx), or Pasteurella multocida toxin (PMT), target heterotrimeric G proteins and have been used to stimulate or block specific signaling pathways or to demonstrate the contribution of their target proteins in cellular effects. PMT is a major virulence factor of P. multocida causing pasteurellosis in man and animals and is responsible for atrophic rhinitis in pigs. PMT modulates various signaling pathways, including phospholipase Cbeta and RhoA, by acting on the heterotrimeric G proteins Galpha(q) and Galpha(12/13), respectively. Here we report that PMT is a powerful activator of G(i) protein. We show that PMT decreases basal isoproterenol and forskolin-stimulated cAMP accumulation in intact Swiss 3T3 cells, inhibits adenylyl cyclase activity in cell membrane preparations, and enhances the inhibition of cAMP accumulation caused by lysophosphatidic acid via endothelial differentiation gene receptors. PMT-mediated inhibition of cAMP production is independent of toxin activation of Galpha(q) and/or Galpha(12/13). Although the effects of PMT are not inhibited by PTx, PMT blocks PTx-catalyzed ADP-ribosylation of G(i). PMT also inhibits steady-state GTPase activity and GTP binding of G(i) in Swiss 3T3 cell membranes stimulated by lysophosphatidic acid. The data indicate that PMT is a novel activator of G(i), modulating its GTPase activity and converting it into a PTx-insensitive state.
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Affiliation(s)
- Joachim H C Orth
- Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Albert-Ludwigs-Universität Freiburg, D-79104 Freiburg, Germany
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Orth JHC, Lang S, Preuss I, Milligan G, Aktories K. Action of Pasteurella multocida toxin on Galpha(q) is persistent and independent of interaction with G-protein-coupled receptors. Cell Signal 2007; 19:2174-82. [PMID: 17669624 DOI: 10.1016/j.cellsig.2007.06.016] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2007] [Accepted: 06/19/2007] [Indexed: 11/30/2022]
Abstract
Pasteurella multocida toxin (PMT) activates Galpha(q) and facilitates stimulation of inositol phosphate accumulation induced by agonists via G(q)-coupled membrane receptors. Here, we studied the effects of PMT on agonist-induced GTPgammaS binding to G(q) in cell membranes and a role of G-protein-coupled receptors in the action of PMT. Pre-treatment of Swiss 3T3 cells with PMT increased bombesin or vasopressin-induced GTPgammaS-binding in cell membranes by about 50 to 150%. Increase in agonist-stimulated GTPgammaS-binding caused by PMT pretreatment was specific for Galpha(q) and not observed with Galpha(11). PMT-induced effects on GTPgammaS-binding were persistent after removing the toxin or in the presence of anti-PMT antibody. Stimulation of agonist-induced GTPgammaS-binding by PMT was independent of phosphorylation of the C-terminal tyrosine356 of Galpha(q). Activation of phospholipase C by PMT occurred via Galpha(q) which was fused to the alpha(1b)-adrenoceptor and also with a C-terminally deleted Galpha(q), which is not able to interact with G protein-coupled membrane receptors. The data indicate that activation of Galpha(q) by PMT is persistent and independent of a functional interaction of G(q) with G-protein-coupled receptors.
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Affiliation(s)
- Joachim H C Orth
- Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Albert-Ludwigs-Universität Freiburg, Albertstrasse 25, D-79104 Freiburg, Germany
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Orth JHC, Aktories K, Kubatzky KF. Modulation of host cell gene expression through activation of STAT transcription factors by Pasteurella multocida toxin. J Biol Chem 2006; 282:3050-7. [PMID: 17150962 DOI: 10.1074/jbc.m609018200] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
The Pasteurella multocida toxin (PMT) is highly mitogenic and has potential carcinogenic properties. PMT causes porcine atrophic rhinitis that is characterized by bone resorption and loss of nasal turbinates, but experimental nasal infection also leads to excess proliferation of bladder epithelial cells. PMT acts intracellularly and activates phospholipase C-linked signals and MAPK pathways via the heterotrimeric Galpha(q) and Galpha(12/13) proteins. We found that PMT induces activation of STAT proteins, and we identified STAT1, STAT3, and STAT5 as new targets of PMT-induced Galpha(q) signaling. Inhibition of Janus kinases completely abolished STAT activation. PMT-dependent STAT phosphorylation remained constitutive for at least 18 h. PMT caused down-regulation of the expression of the suppressor of cytokine signaling-3, indicating a novel mechanism to maintain activation of STATs. Moreover, stimulation of Swiss 3T3 cells with PMT increased transcription of the cancer-associated STAT-dependent gene cyclooxygenase-2. Because constitutive activation of STATs has been found in a number of cancers, our findings offer a new mechanism for a carcinogenic role of PMT.
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Affiliation(s)
- Joachim H C Orth
- Institut für Experimentelle and Klinische Pharmakologie and Toxikologie, Albert-Ludwigs-Universität, Albertstrasse 25, D-79104 Freiburg, Germany
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Orth JHC, Lang S, Taniguchi M, Aktories K. Pasteurella multocida Toxin-induced Activation of RhoA Is Mediated via Two Families of Gα Proteins, Gαq and Gα12/13. J Biol Chem 2005; 280:36701-7. [PMID: 16141214 DOI: 10.1074/jbc.m507203200] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Pasteurella multocida toxin (PMT) is a potent mitogen, which is known to activate phospholipase Cbeta by stimulating the alpha-subunit of the heterotrimeric G protein G(q). PMT also activates RhoA and RhoA-dependent pathways. Using YM-254890, a specific inhibitor of G(q/11), we studied whether activation of RhoA involves G proteins other than G(q/11). YM-254890 inhibited PMT or muscarinic M3-receptor-mediated stimulation of phospholipase Cbeta at similar concentrations in HEK293m3 cells. In these cells, PMT-induced RhoA activation and enhancement of RhoA-dependent luciferase activity were partially inhibited by YM-254890. In Galpha(q/11)-deficient fibroblasts, PMT induced activation of RhoA, increase in RhoA-dependent luciferase activity, and increase in ERK phosphorylation. None of these effects were influenced by YM-254890. However, RhoA activation by PMT was inhibited by RGS2, RGS16, lscRGS, and dominant negative G(13)(GA), indicating involvement of Galpha(12/13) in the PMT effect on RhoA. In Galpha(12/13) gene-deficient cells, PMT-induced stimulation of RhoA, luciferase activity, and ERK phosphorylation were blocked by YM-254890, indicating the involvement of G(q). Infection with a virus harboring the gene of Galpha(13) reconstituted the increase in RhoA-dependent luciferase activity by PMT even in the presence of YM-254890. The data show that YM-254890 is able to block PMT activation of Galpha(q) and indicate that, in addition to Galpha(q), the Galpha(12/13) G proteins are targets of PMT.
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Affiliation(s)
- Joachim H C Orth
- Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Albert-Ludwigs Universität Freiburg, D-79104 Freiburg, Germany
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Abstract
Pasteurella multocida produces a 146-kDa protein toxin (PMT), which activates multiple cellular signal transduction pathways, resulting in the activation of phospholipase Cbeta, RhoA, Jun kinase, and extracellular signal-regulated kinase. Using Galpha(q)/Galpha(11) -deficient cells, it was shown that the PMT-induced pleiotropic effects are mediated by Galpha(q) but not by the highly related Galpha(11) protein (Zywietz, A., Gohla, A., Schmelz, M., Schultz, G., and Offermanns, S. (2001) J. Biol. Chem. 276, 3840-3845). Here we studied the molecular basis of the unique specificity of PMT to distinguish between Galpha(q) and/or Galpha(11). Infection of Galpha(q) -deficient cells with retrovirus-encoding Galpha(q) caused reconstitution of PMT-induced activation of phospholipase Cbeta, whereas Galpha(11) -encoding virus did not reconstitute PMT activity. Chimeras between Galpha(q) and/or Galpha(11) revealed that a peptide region of Galpha(q), covering amino acid residues 105-113, is essential for the action of PMT to activate phospholipase Cbeta. Exchange of glutamine 105 or asparagine 109 of Galpha(11), which are located in the all-helical domain of the Galpha subunit, with the equally positioned histidines of Galpha(q), renders Galpha(11) capable of transmission PMT-induced phospholipase Cbeta activation. The data indicate that the all-helical domain of Galpha(q) is essential for the action of PMT and suggest an essential functional role of this domain in signal transduction via G(q) proteins.
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Affiliation(s)
- Joachim H C Orth
- Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Albert-Ludwigs Universität Freiburg, Albertstrasse 25, D-79104 Freiburg, Germany
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Abstract
Pasteurella multocida produces a 146-kDa protein toxin (PMT), which activates multiple cellular signal-transduction pathways, resulting in the activation of PLCbeta, Rho, JNK, and ERK. In addition to an essential cysteine residue at position 1165, PMT contains several histidine residues in the catalytically important C-terminal part of the protein. To elucidate the role of the histidine residues, we treated PMT with the histidine-modifying substance diethyl pyrocarbonate (DEPC). DEPC inhibited PMT in a time- and concentration-dependent manner, suggesting that one or several histidine residues are essential for the biological activity of PMT. In experiments in which PMT was directly delivered into the cytosol of EBL cells by electroporation, we show that DEPC treatment inhibits the catalytically important histidine residues. Leucine substitutions of eight individual histidine residues in the C-terminal catalytic domain of PMT were constructed, and the effect on the biological activity of PMT was analyzed by determining PLCbeta, Rho, and ERK activation. Substitution of two histidine residues, H1205 and H1223, led to inactivation of the resulting PMT proteins, indicating that H1205 and H1223 play an important role in biological activity of the toxin. In addition, we show that the mutant toxins appear to be correctly folded, as judged by protease digestion. The precise function of H1205 and H1223 is not yet known. However, treatment of PMT with the cation chelating substance 1,10-phenantroline led to inactivation of the toxin, indicating that the essential histidine residues and cysteine 1165 might be involved in metal ion binding.
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Affiliation(s)
- Joachim H C Orth
- Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Albert-Ludwigs-Universität Freiburg, Albertstrasse 25, D-79104 Freiburg, Germany
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