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O'Donoghue L, Smolenski A. Roles of G proteins and their GTPase-activating proteins in platelets. Biosci Rep 2024; 44:BSR20231420. [PMID: 38808367 PMCID: PMC11139668 DOI: 10.1042/bsr20231420] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2023] [Revised: 04/30/2024] [Accepted: 05/02/2024] [Indexed: 05/30/2024] Open
Abstract
Platelets are small anucleate blood cells supporting vascular function. They circulate in a quiescent state monitoring the vasculature for injuries. Platelets adhere to injury sites and can be rapidly activated to secrete granules and to form platelet/platelet aggregates. These responses are controlled by signalling networks that include G proteins and their regulatory guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs). Recent proteomics studies have revealed the complete spectrum of G proteins, GEFs, and GAPs present in platelets. Some of these proteins are specific for platelets and very few have been characterised in detail. GEFs and GAPs play a major role in setting local levels of active GTP-bound G proteins in response to activating and inhibitory signals encountered by platelets. Thus, GEFs and GAPs are highly regulated themselves and appear to integrate G protein regulation with other cellular processes. This review focuses on GAPs of small G proteins of the Arf, Rab, Ras, and Rho families, as well as of heterotrimeric G proteins found in platelets.
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Affiliation(s)
- Lorna O'Donoghue
- UCD School of Medicine, University College Dublin, UCD Conway Institute, Belfield, Dublin 4, Ireland
- Irish Centre for Vascular Biology, Royal College of Surgeons in Ireland, 123 St. Stephen’s Green 123, Dublin 2, Ireland
| | - Albert Smolenski
- UCD School of Medicine, University College Dublin, UCD Conway Institute, Belfield, Dublin 4, Ireland
- Irish Centre for Vascular Biology, Royal College of Surgeons in Ireland, 123 St. Stephen’s Green 123, Dublin 2, Ireland
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2
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Kaak JL, Lobo de Sá FD, Turner JR, Schulzke JD, Bücker R. Unraveling the intestinal epithelial barrier in cyanotoxin microcystin-treated Caco-2 cell monolayers. Ann N Y Acad Sci 2022; 1516:188-196. [PMID: 35883254 PMCID: PMC9588585 DOI: 10.1111/nyas.14870] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Microcystin is a widespread cyanobacterial toxin that affects the intestine to produce diarrheal symptoms after ingestion of freshwater blue-green algae. Our study aimed to characterize the mechanism by which the toxin leads to diarrhea via epithelial barrier dysfunction in a small intestine Caco-2 cell model. Microcystin-treated human Caco-2 epithelial monolayers were functionally and molecularly analyzed for barrier dysfunction. Tight junctions (TJs) and cell damage were analyzed in relation to transepithelial electrical resistance (TER) changes. TER of microcystin-treated Caco-2 cells was reduced by 65% of the initial value after 24 h; concomitantly, permeability for fluorescein increased 2.6-fold. Western blot analysis showed reduced claudin-1 expression, while expression of claudin-3 and -4 remained unchanged. Super-resolution stimulated emission depletion microscopy revealed that TJ integrity was compromised by fraying and splitting of the TJ domain of the epithelial cells. Epithelial apoptosis did not significantly contribute to epithelial barrier dysfunction, while cytoskeletal actomyosin constriction was associated with TJ disintegration and the barrier defect. Our results indicate that microcystin causes intestinal barrier leakiness, which helps to explain the leak flux type of diarrhea as the main pathomechanism after ingestion of cyanobacterial toxin.
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Affiliation(s)
- Jan-Leo Kaak
- Department of Gastroenterology, Infectious Diseases and Rheumatology, Clinical Physiology/Nutritional Medicine, Charité – Universitätsmedizin Berlin, Berlin, Germany
| | - Fábia D. Lobo de Sá
- Department of Gastroenterology, Infectious Diseases and Rheumatology, Clinical Physiology/Nutritional Medicine, Charité – Universitätsmedizin Berlin, Berlin, Germany
| | - Jerrold R. Turner
- Laboratory of Mucosal Barrier Pathobiology, Department of Pathology, Brigham and Women’s Hospital and Harvard Medical School, Boston, Massachusetts, USA
| | - Jörg-Dieter Schulzke
- Department of Gastroenterology, Infectious Diseases and Rheumatology, Clinical Physiology/Nutritional Medicine, Charité – Universitätsmedizin Berlin, Berlin, Germany
| | - Roland Bücker
- Department of Gastroenterology, Infectious Diseases and Rheumatology, Clinical Physiology/Nutritional Medicine, Charité – Universitätsmedizin Berlin, Berlin, Germany
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3
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Almutairi F, Sarr D, Tucker SL, Fantone K, Lee JK, Rada B. RGS10 Reduces Lethal Influenza Infection and Associated Lung Inflammation in Mice. Front Immunol 2021; 12:772288. [PMID: 34912341 PMCID: PMC8667315 DOI: 10.3389/fimmu.2021.772288] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2021] [Accepted: 11/10/2021] [Indexed: 01/05/2023] Open
Abstract
Seasonal influenza epidemics represent a significant global health threat. The exacerbated immune response triggered by respiratory influenza virus infection causes severe pulmonary damage and contributes to substantial morbidity and mortality. Regulator of G-protein signaling 10 (RGS10) belongs to the RGS protein family that act as GTPase activating proteins for heterotrimeric G proteins to terminate signaling pathways downstream of G protein-coupled receptors. While RGS10 is highly expressed in immune cells, in particular monocytes and macrophages, where it has strong anti-inflammatory effects, its physiological role in the respiratory immune system has not been explored yet. Here, we show that Rgs10 negatively modulates lung immune and inflammatory responses associated with severe influenza H1N1 virus respiratory infection in a mouse model. In response to influenza A virus challenge, mice lacking RGS10 experience enhanced weight loss and lung viral titers, higher mortality and significantly faster disease onset. Deficiency of Rgs10 upregulates the levels of several proinflammatory cytokines and chemokines and increases myeloid leukocyte accumulation in the infected lung, markedly neutrophils, monocytes, and inflammatory monocytes, which is associated with more pronounced lung damage. Consistent with this, influenza-infected Rgs10-deficent lungs contain more neutrophil extracellular traps and exhibit higher neutrophil elastase activities than wild-type lungs. Overall, these findings propose a novel, in vivo role for RGS10 in the respiratory immune system controlling myeloid leukocyte infiltration, viral clearance and associated clinical symptoms following lethal influenza challenge. RGS10 also holds promise as a new, potential therapeutic target for respiratory infections.
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Affiliation(s)
- Faris Almutairi
- Department of Infectious Diseases, College of Veterinary Medicine, University of Georgia, Athens, GA, United States
- Department of Pharmaceutical and Biomedical Sciences, College of Pharmacy, University of Georgia, Athens, GA, United States
| | - Demba Sarr
- Department of Infectious Diseases, College of Veterinary Medicine, University of Georgia, Athens, GA, United States
| | - Samantha L. Tucker
- Department of Infectious Diseases, College of Veterinary Medicine, University of Georgia, Athens, GA, United States
| | - Kayla Fantone
- Department of Infectious Diseases, College of Veterinary Medicine, University of Georgia, Athens, GA, United States
| | - Jae-Kyung Lee
- Department of Physiology and Pharmacology, College of Veterinary Medicine, University of Georgia, Athens, GA, United States
| | - Balázs Rada
- Department of Infectious Diseases, College of Veterinary Medicine, University of Georgia, Athens, GA, United States
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4
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Xu D, Xie L, Zhang Z, Wang D, Qiu J, Yu W, Xu C, He C, Xu X, Yin J. Preliminary Investigation about the Expression of G Protein-Coupled Receptors in Platelets from Patients with Chronic Immune Thrombocytopenic Purpura. Acta Haematol 2021; 144:551-559. [PMID: 33849009 DOI: 10.1159/000514907] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2020] [Accepted: 02/02/2021] [Indexed: 02/05/2023]
Abstract
OBJECTIVE The objective of this study was to determine the expression of G protein-coupled receptors (GPCRs) in platelets from adult patients with chronic immune thrombocytopenic purpura (ITP). METHODS Peripheral blood samples were collected from 40 patients with chronic ITP in the Second Affiliated Hospital of Shantou University Medical College, and 40 peripheral blood samples from healthy volunteers were collected; expressions of the adenosine diphosphate receptors (P2Y1 and P2Y12), alpha-2A adrenergic receptor (α2A-AR), and thromboxane A2 receptor (TP) in platelets were detected by flow cytometry. Gα protein, protease-activated receptor 1 (PAR1), and protease-activated receptor 4 (PAR4) were analyzed by Western blot and analyzed statistically. RESULTS Flow cytometry measurements of mean fluorescence intensities showed platelets from patients with chronic ITP, compared to healthy individuals, had significantly higher levels of P2Y1 (31.4 ± 2.2 vs. 7.8 ± 0.8), P2Y12 (29.6 ± 2.1 vs. 7.2 ± 1.3), α2A-AR (25.8 ± 2.9 vs. 9.8 ± 0.9), and TP (39.8 ± 3.1 vs. 4.7 ± 0.6) (all p < 0.01). Similarly, integrated optical density analysis of Western blots showed that platelets from patients with chronic ITP had significantly higher levels of Gα (1046.3 ± 159.96 vs. 254.49 ± 39.51), PAR1 (832.98 ± 98.81 vs. 203.92 ± 27.47), and PAR4 (1518.80 ± 272.45 vs. 431.27 ± 41.86) (all p < 0.01). CONCLUSION Expression of GPCRs is increased in platelets from patients with chronic ITP, suggesting that platelets of chronic ITP may participate in the complicated biological process by means of GPCR-mediated signaling pathways.
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Affiliation(s)
- Daming Xu
- Division of Urological Surgery, The Second Affiliated Hospital of Shantou University Medical College, Shantou, China
| | - Long Xie
- Department of Clinical Laboratory Medicine, The Second Affiliated Hospital of Shantou University Medical College, Shantou, China
| | - Zewen Zhang
- Division of Hematology, The Second Affiliated Hospital of Shantou University Medical College, Shantou, China
| | - Duanxu Wang
- Office of Medical Affairs Administration, The Second Affiliated Hospital of Shantou University Medical College, Shantou, China
| | - Jinfeng Qiu
- Division of Respirology, The Second Affiliated Hospital of Shantou University Medical College, Shantou, China
| | - Wenjun Yu
- Division of Hematology, The Second Affiliated Hospital of Shantou University Medical College, Shantou, China
| | - Chengwei Xu
- Department of Hemodialysis, The Second Affiliated Hospital of Shantou University Medical College, Shantou, China
| | - Chunling He
- Department of Pathology, The Second Affiliated Hospital of Shantou University Medical College, Shantou, China
| | - Xianru Xu
- Division of Inventional Ultrasonic Therapeutics, The Second Affiliated Hospital of Shantou University Medical College, Shantou, China
| | - Jun Yin
- Department of Clinical Laboratory Medicine, The Second Affiliated Hospital of Shantou University Medical College, Shantou, China
- Division of Hematology, The Second Affiliated Hospital of Shantou University Medical College, Shantou, China
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5
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Faria AVS, Andrade SS, Peppelenbosch MP, Ferreira-Halder CV, Fuhler GM. The role of phospho-tyrosine signaling in platelet biology and hemostasis. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2020; 1868:118927. [PMID: 33310067 DOI: 10.1016/j.bbamcr.2020.118927] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 08/05/2020] [Revised: 12/01/2020] [Accepted: 12/05/2020] [Indexed: 10/22/2022]
Abstract
Platelets are small enucleated cell fragments specialized in the control of hemostasis, but also playing a role in angiogenesis, inflammation and immunity. This plasticity demands a broad range of physiological processes. Platelet functions are mediated through a variety of receptors, the concerted action of which must be tightly regulated, in order to allow specific and timely responses to different stimuli. Protein phosphorylation is one of the main key regulatory mechanisms by which extracellular signals are conveyed. Despite the importance of platelets in health and disease, the molecular pathways underlying the activation of these cells are still under investigation. Here, we review current literature on signaling platelet biology and in particular emphasize the newly emerging role of phosphatases in these processes.
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Affiliation(s)
- Alessandra V S Faria
- Department of Gastroenterology and Hepatology, Erasmus University Medical Center Rotterdam, NL-3000 CA Rotterdam, the Netherlands; Department of Biochemistry and Tissue Biology, University of Campinas, UNICAMP, Campinas, SP 13083-862, Brazil
| | | | - Maikel P Peppelenbosch
- Department of Gastroenterology and Hepatology, Erasmus University Medical Center Rotterdam, NL-3000 CA Rotterdam, the Netherlands
| | - Carmen V Ferreira-Halder
- Department of Biochemistry and Tissue Biology, University of Campinas, UNICAMP, Campinas, SP 13083-862, Brazil
| | - Gwenny M Fuhler
- Department of Gastroenterology and Hepatology, Erasmus University Medical Center Rotterdam, NL-3000 CA Rotterdam, the Netherlands.
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6
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Almutairi F, Lee JK, Rada B. Regulator of G protein signaling 10: Structure, expression and functions in cellular physiology and diseases. Cell Signal 2020; 75:109765. [PMID: 32882407 PMCID: PMC7579743 DOI: 10.1016/j.cellsig.2020.109765] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2020] [Revised: 08/26/2020] [Accepted: 08/27/2020] [Indexed: 01/22/2023]
Abstract
Regulator of G protein signaling 10 (RGS10) belongs to the superfamily of RGS proteins, defined by the presence of a conserved RGS domain that canonically binds and deactivates heterotrimeric G-proteins. RGS proteins act as GTPase activating proteins (GAPs), which accelerate GTP hydrolysis on the G-protein α subunits and result in termination of signaling pathways downstream of G protein-coupled receptors. RGS10 is the smallest protein of the D/R12 subfamily and selectively interacts with Gαi proteins. It is widely expressed in many cells and tissues, with the highest expression found in the brain and immune cells. RGS10 expression is transcriptionally regulated via epigenetic mechanisms. Although RGS10 lacks multiple of the defined regulatory domains found in other RGS proteins, RGS10 contains post-translational modification sites regulating its expression, localization, and function. Additionally, RGS10 is a critical protein in the regulation of physiological processes in multiple cells, where dysregulation of its expression has been implicated in various diseases including Parkinson's disease, multiple sclerosis, osteopetrosis, chemoresistant ovarian cancer and cardiac hypertrophy. This review summarizes RGS10 features and its regulatory mechanisms, and discusses the known functions of RGS10 in cellular physiology and pathogenesis of several diseases.
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Affiliation(s)
- Faris Almutairi
- Department of Pharmaceutical and Biomedical Sciences, College of Pharmacy, University of Georgia, Athens, GA, USA; Department of Infectious Diseases, College of Veterinary Medicine, University of Georgia, Athens, GA, USA
| | - Jae-Kyung Lee
- Department of Physiology and Pharmacology, College of Veterinary Medicine, University of Georgia, Athens, GA, USA
| | - Balázs Rada
- Department of Infectious Diseases, College of Veterinary Medicine, University of Georgia, Athens, GA, USA.
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7
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Chen X, Zhao X, Cooper M, Ma P. The Roles of GRKs in Hemostasis and Thrombosis. Int J Mol Sci 2020; 21:ijms21155345. [PMID: 32731360 PMCID: PMC7432802 DOI: 10.3390/ijms21155345] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2020] [Revised: 07/20/2020] [Accepted: 07/27/2020] [Indexed: 12/20/2022] Open
Abstract
Along with cancer, cardiovascular and cerebrovascular diseases remain by far the most common causes of death. Heart attacks and strokes are diseases in which platelets play a role, through activation on ruptured plaques and subsequent thrombus formation. Most platelet agonists activate platelets via G protein-coupled receptors (GPCRs), which make these receptors ideal targets for many antiplatelet drugs. However, little is known about the mechanisms that provide feedback regulation on GPCRs to limit platelet activation. Emerging evidence from our group and others strongly suggests that GPCR kinases (GRKs) are critical negative regulators during platelet activation and thrombus formation. In this review, we will summarize recent findings on the role of GRKs in platelet biology and how one specific GRK, GRK6, regulates the hemostatic response to vascular injury. Furthermore, we will discuss the potential role of GRKs in thrombotic disorders, such as thrombotic events in COVID-19 patients. Studies on the function of GRKs during platelet activation and thrombus formation have just recently begun, and a better understanding of the role of GRKs in hemostasis and thrombosis will provide a fruitful avenue for understanding the hemostatic response to injury. It may also lead to new therapeutic options for the treatment of thrombotic and cardiovascular disorders.
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Affiliation(s)
- Xi Chen
- Cardeza Foundation for Hematologic Research, Department of Medicine, Sidney Kimmel Medical College, Thomas Jefferson University, Philadelphia, PA 19107, USA; (X.C.); (X.Z.); (M.C.)
| | - Xuefei Zhao
- Cardeza Foundation for Hematologic Research, Department of Medicine, Sidney Kimmel Medical College, Thomas Jefferson University, Philadelphia, PA 19107, USA; (X.C.); (X.Z.); (M.C.)
- Cyrus Tang Hematology Center, Soochow University, Suzhou 215123, China
| | - Matthew Cooper
- Cardeza Foundation for Hematologic Research, Department of Medicine, Sidney Kimmel Medical College, Thomas Jefferson University, Philadelphia, PA 19107, USA; (X.C.); (X.Z.); (M.C.)
| | - Peisong Ma
- Cardeza Foundation for Hematologic Research, Department of Medicine, Sidney Kimmel Medical College, Thomas Jefferson University, Philadelphia, PA 19107, USA; (X.C.); (X.Z.); (M.C.)
- Correspondence: ; Tel.: +1-215-955-3966
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8
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Wang C, Chen A, Ruan B, Niu Z, Su Y, Qin H, Zheng Y, Zhang B, Gao L, Chen Z, Huang H, Wang X, Sun Q. PCDH7 Inhibits the Formation of Homotypic Cell-in-Cell Structure. Front Cell Dev Biol 2020; 8:329. [PMID: 32457908 PMCID: PMC7225324 DOI: 10.3389/fcell.2020.00329] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2020] [Accepted: 04/16/2020] [Indexed: 12/13/2022] Open
Abstract
Though homotypic cell-in-cell (hoCIC) structures are implicated in the development and progression of multiple human tumors, the molecular mechanisms underlying their formation remain poorly understood. We found that the expression of Protocadherin-7 (PCDH7), an integral membrane protein, was negatively associated with the formation of hoCIC structures. Overexpression of PCDH7 efficiently inhibits, while its depletion significantly enhances, hoCIC formation, which was attributed to its regulation on intercellular adhesion and contractile actomyosin as well. Via directly interacting with and inactivating PP1α, a protein phosphatase that dephosphorylates pMLC2, PCDH7 increases the level of pMLC2 leading to enhanced actomyosin at the intercellular region and compromised hoCIC formation. Remarkably, PCDH7 enhanced anchorage-independent cell growth in a hoCIC-dependent manner. Together, we identified PCDH7 as the first trans-membrane protein that inhibits hoCIC formation to promote tumor growth.
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Affiliation(s)
- Chenxi Wang
- School of Biology and Biological Engineering, South China University of Technology, Guangzhou, China.,Laboratory of Cell Engineering, Institute of Biotechnology, Beijing, China
| | - Ang Chen
- Laboratory of Cell Engineering, Institute of Biotechnology, Beijing, China
| | - Banzhan Ruan
- Laboratory of Cell Engineering, Institute of Biotechnology, Beijing, China.,Department of Biology, Hainan Medical University, Haikou, China
| | - Zubiao Niu
- Laboratory of Cell Engineering, Institute of Biotechnology, Beijing, China
| | - Yan Su
- Laboratory of Cell Engineering, Institute of Biotechnology, Beijing, China
| | - Hongquan Qin
- Laboratory of Cell Engineering, Institute of Biotechnology, Beijing, China
| | - You Zheng
- Laboratory of Cell Engineering, Institute of Biotechnology, Beijing, China
| | - Bo Zhang
- Department of Oncology, Capital Medical University, Beijing, China
| | - Lihua Gao
- Laboratory of Cell Engineering, Institute of Biotechnology, Beijing, China
| | - Zhaolie Chen
- Laboratory of Cell Engineering, Institute of Biotechnology, Beijing, China
| | - Hongyan Huang
- Department of Oncology, Capital Medical University, Beijing, China
| | - Xiaoning Wang
- School of Biology and Biological Engineering, South China University of Technology, Guangzhou, China.,Beijing Key Laboratory of Aging and Geriatrics, Chinese PLA General Hospital, Beijing, China
| | - Qiang Sun
- Laboratory of Cell Engineering, Institute of Biotechnology, Beijing, China
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9
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Uncovering the pharmacological mechanism of Carthamus tinctorius L. on cardiovascular disease by a systems pharmacology approach. Biomed Pharmacother 2019; 117:109094. [PMID: 31203131 DOI: 10.1016/j.biopha.2019.109094] [Citation(s) in RCA: 47] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2019] [Revised: 06/02/2019] [Accepted: 06/04/2019] [Indexed: 02/07/2023] Open
Abstract
Carthamus tinctorius L. is widely used in traditional Chinese medicines for the treatment of cardiovascular disease. However, our current understanding of the molecular mechanisms supporting its clinical application still lags behind. In this study, a systems pharmacology approach integrating drug-likeness evaluation, oral bioavailability prediction, target exploration, GO enrichment analysis, KEGG pathway performance and network construction was adopted to explore its therapeutic mechanism. A total of 21 active ingredients contained in Carthamus tinctorius L. and 113 major proteins were screened out as effective players in the treatment of cardiovascular disease through some related pathways. And the association among the active ingredients, major hubs and main pathways was investigated, implying the potential biological progression of Carthamus tinctorius L. acting on cardiovascular disease. Importantly, the majority of hubs and pathways were found to be highly related with platelet activation process. Core genes that can be regulated by Carthamus tinctorius L. in platelet activation pathway were PRKACA, PIK3R1, MAPK1, PPP1CC, PIK3CA and SYK, and they may play a central role in suppressing platelet aggregation. The systems pharmacology approach used in this study may provide a feasible tool to clarify the mechanism of traditional Chinese medicines and further develop their therapeutic potentials.
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10
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RGS10 shapes the hemostatic response to injury through its differential effects on intracellular signaling by platelet agonists. Blood Adv 2019; 2:2145-2155. [PMID: 30150297 DOI: 10.1182/bloodadvances.2017008508] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2017] [Accepted: 07/27/2018] [Indexed: 11/20/2022] Open
Abstract
Platelets express ≥2 members of the regulators of G protein signaling (RGS) family. Here, we have focused on the most abundant, RGS10, examining its impact on the hemostatic response in vivo and the mechanisms involved. We have previously shown that the hemostatic thrombi formed in response to penetrating injuries consist of a core of fully activated densely packed platelets overlaid by a shell of less-activated platelets responding to adenosine 5'-diphosphate (ADP) and thromboxane A2 (TxA2). Hemostatic thrombi formed in RGS10-/- mice were larger than in controls, with the increase due to expansion of the shell but not the core. Clot retraction was slower, and average packing density was reduced. Deleting RGS10 had agonist-specific effects on signaling. There was a leftward shift in the dose/response curve for the thrombin receptor (PAR4) agonist peptide AYPGKF but no increase in the maximum response. This contrasted with ADP and TxA2, both of which evoked considerably greater maximum responses in RGS10-/- platelets with enhanced Gq- and Gi-mediated signaling. Shape change, which is G13-mediated, was unaffected. Finally, we found that free RGS10 levels in platelets are actively regulated. In resting platelets, RGS10 was bound to 2 scaffold proteins: spinophilin and 14-3-3γ. Platelet activation caused an increase in free RGS10, as did the endothelium-derived platelet antagonist prostacyclin. Collectively, these observations show that RGS10 serves as an actively regulated node on the platelet signaling network, helping to produce smaller and more densely packed hemostatic thrombi with a greater proportion of fully activated platelets.
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11
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The reduced activity of PP-1α under redox stress condition is a consequence of GSH-mediated transient disulfide formation. Sci Rep 2018; 8:17711. [PMID: 30531830 PMCID: PMC6286341 DOI: 10.1038/s41598-018-36267-6] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2018] [Accepted: 11/09/2018] [Indexed: 12/19/2022] Open
Abstract
Heart failure is the most common cause of morbidity and hospitalization in the western civilization. Protein phosphatases play a key role in the basal cardiac contractility and in the responses to β-adrenergic stimulation with type-1 phosphatase (PP-1) being major contributor. We propose here that formation of transient disulfide bridges in PP-1α might play a leading role in oxidative stress response. First, we established an optimized workflow, the so-called "cross-over-read" search method, for the identification of disulfide-linked species using permutated databases. By applying this method, we demonstrate the formation of unexpected transient disulfides in PP-1α to shelter against over-oxidation. This protection mechanism strongly depends on the fast response in the presence of reduced glutathione. Our work points out that the dimerization of PP-1α involving Cys39 and Cys127 is presumably important for the protection of PP-1α active surface in the absence of a substrate. We finally give insight into the electron transport from the PP-1α catalytic core to the surface. Our data suggest that the formation of transient disulfides might be a general mechanism of proteins to escape from irreversible cysteine oxidation and to prevent their complete inactivation.
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12
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Nagy Z, Smolenski A. Cyclic nucleotide-dependent inhibitory signaling interweaves with activating pathways to determine platelet responses. Res Pract Thromb Haemost 2018; 2:558-571. [PMID: 30046761 PMCID: PMC6046581 DOI: 10.1002/rth2.12122] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2018] [Accepted: 04/20/2018] [Indexed: 12/22/2022] Open
Abstract
Platelets are regulated by extracellular cues that impact on intracellular signaling. The endothelium releases prostacyclin and nitric oxide which stimulate the synthesis of cyclic nucleotides cAMP and cGMP leading to platelet inhibition. Other inhibitory mechanisms involve immunoreceptor tyrosine-based inhibition motif-containing receptors, intracellular receptors and receptor desensitization. Inhibitory cyclic nucleotide pathways are traditionally thought to represent a passive background system keeping platelets in a quiescent state. In contrast, cyclic nucleotides are increasingly seen to be dynamically involved in most aspects of platelet regulation. This review focuses on crosstalk between activating and cyclic nucleotide-mediated inhibitory pathways highlighting emerging new hub structures and signaling mechanisms. In particular, interactions of plasma membrane receptors like P2Y12 and GPIb/IX/V with the cyclic nucleotide system are described. Furthermore, differential regulation of the RGS18 complex, second messengers, protein kinases, and phosphatases are presented, and control over small G-proteins by guanine-nucleotide exchange factors and GTPase-activating proteins are outlined. Possible clinical implications of signaling crosstalk are discussed.
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Affiliation(s)
- Zoltan Nagy
- Institute of Cardiovascular SciencesCollege of Medical and Dental SciencesUniversity of BirminghamBirminghamUK
| | - Albert Smolenski
- UCD School of MedicineUniversity College DublinDublinIreland
- UCD Conway InstituteUniversity College DublinDublinIreland
- Irish Centre for Vascular BiologyRoyal College of Surgeons in IrelandDublinIreland
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13
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Pradhan S, Khatlani T, Nairn AC, Vijayan KV. The heterotrimeric G protein Gβ 1 interacts with the catalytic subunit of protein phosphatase 1 and modulates G protein-coupled receptor signaling in platelets. J Biol Chem 2017; 292:13133-13142. [PMID: 28615442 DOI: 10.1074/jbc.m117.796656] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2017] [Revised: 06/13/2017] [Indexed: 11/06/2022] Open
Abstract
Thrombosis is caused by the activation of platelets at the site of ruptured atherosclerotic plaques. This activation involves engagement of G protein-coupled receptors (GPCR) on platelets that promote their aggregation. Although it is known that protein kinases and phosphatases modulate GPCR signaling, how serine/threonine phosphatases integrate with G protein signaling pathways is less understood. Because the subcellular localization and substrate specificity of the catalytic subunit of protein phosphatase 1 (PP1c) is dictated by PP1c-interacting proteins, here we sought to identify new PP1c interactors. GPCRs signal via the canonical heterotrimeric Gα and Gβγ subunits. Using a yeast two-hybrid screen, we discovered an interaction between PP1cα and the heterotrimeric G protein Gβ1 subunit. Co-immunoprecipitation studies with epitope-tagged PP1c and Gβ1 revealed that Gβ1 interacts with the PP1c α, β, and γ1 isoforms. Purified PP1c bound to recombinant Gβ1-GST protein, and PP1c co-immunoprecipitated with Gβ1 in unstimulated platelets. Thrombin stimulation of platelets induced the dissociation of the PP1c-Gβ1 complex, which correlated with an association of PP1c with phospholipase C β3 (PLCβ3), along with a concomitant dephosphorylation of the inhibitory Ser1105 residue in PLCβ3. siRNA-mediated depletion of GNB1 (encoding Gβ1) in murine megakaryocytes reduced protease-activated receptor 4, activating peptide-induced soluble fibrinogen binding. Thrombin-induced aggregation was decreased in PP1cα-/- murine platelets and in human platelets treated with a small-molecule inhibitor of Gβγ. Finally, disruption of PP1c-Gβ1 complexes with myristoylated Gβ1 peptides containing the PP1c binding site moderately decreased thrombin-induced human platelet aggregation. These findings suggest that Gβ1 protein enlists PP1c to modulate GPCR signaling in platelets.
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Affiliation(s)
- Subhashree Pradhan
- From the Departments of Medicine.,Center for Translational Research on Inflammatory Diseases (CTRID), Michael E. DeBakey Veterans Affairs Medical Center (MEDVAMC), Houston, Texas 77030 and
| | - Tanvir Khatlani
- From the Departments of Medicine.,Center for Translational Research on Inflammatory Diseases (CTRID), Michael E. DeBakey Veterans Affairs Medical Center (MEDVAMC), Houston, Texas 77030 and
| | - Angus C Nairn
- Department of Psychiatry, Yale University School of Medicine, New Haven, Connecticut 06508
| | - K Vinod Vijayan
- From the Departments of Medicine, .,Center for Translational Research on Inflammatory Diseases (CTRID), Michael E. DeBakey Veterans Affairs Medical Center (MEDVAMC), Houston, Texas 77030 and.,Pediatrics.,Molecular Physiology and Biophysics, Baylor College of Medicine and
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14
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Biogenesis and activity regulation of protein phosphatase 1. Biochem Soc Trans 2017; 45:89-99. [DOI: 10.1042/bst20160154] [Citation(s) in RCA: 66] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2016] [Revised: 11/06/2016] [Accepted: 11/16/2016] [Indexed: 01/01/2023]
Abstract
Protein phosphatase 1 (PP1) is expressed in all eukaryotic cells and catalyzes a substantial fraction of phosphoserine/threonine dephosphorylation reactions. It forms stable complexes with PP1-interacting proteins (PIPs) that guide the phosphatase throughout its life cycle and control its fate and function. The diversity of PIPs is huge (≈200 in vertebrates), and most of them combine short linear motifs to form large and unique interaction interfaces with PP1. Many PIPs have separate domains for PP1 anchoring, PP1 regulation, substrate recruitment and subcellular targeting, which enable them to direct associated PP1 to a specific subset of substrates and mediate acute activity control. Hence, PP1 functions as the catalytic subunit of a large number of multimeric holoenzymes, each with its own subset of substrates and mechanism(s) of regulation.
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15
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Modulating platelet reactivity through control of RGS18 availability. Blood 2015; 126:2611-20. [PMID: 26407691 DOI: 10.1182/blood-2015-04-640037] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2015] [Accepted: 09/22/2015] [Indexed: 01/13/2023] Open
Abstract
Most platelet agonists activate platelets by binding to G-protein-coupled receptors. We have shown previously that a critical node in the G-protein signaling network in platelets is formed by a scaffold protein, spinophilin (SPL), the tyrosine phosphatase, Src homology region 2 domain-containing phosphatase-1 (SHP-1), and the regulator of G-protein signaling family member, RGS18. Here, we asked whether SPL and other RGS18 binding proteins such as 14-3-3γ regulate platelet reactivity by sequestering RGS18 and, if so, how this is accomplished. The results show that, in resting platelets, free RGS18 levels are relatively low, increasing when platelets are activated by thrombin. Free RGS18 levels also rise when platelets are rendered resistant to activation by exposure to prostaglandin I2 (PGI2) or forskolin, both of which increase platelet cyclic adenosine monophosphate (cAMP) levels. However, the mechanism for raising free RGS18 is different in these 2 settings. Whereas thrombin activates SHP-1 and causes dephosphorylation of SPL tyrosine residues, PGI2 and forskolin cause phosphorylation of SPL Ser94 without reducing tyrosine phosphorylation. Substituting alanine for Ser94 blocks cAMP-induced dissociation of the SPL/RGS/SHP-1 complex. Replacing Ser94 with aspartate prevents formation of the complex and produces a loss-of-function phenotype when expressed in mouse platelets. Together with the defect in platelet function we previously observed in SPL(-/-) mice, these data show that (1) regulated sequestration and release of RGS18 by intracellular binding proteins provides a mechanism for coordinating activating and inhibitory signaling networks in platelets, and (2) differential phosphorylation of SPL tyrosine and serine residues provides a key to understanding both.
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16
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The regulator of G-protein signaling 18 regulates platelet aggregation, hemostasis and thrombosis. Biochem Biophys Res Commun 2015; 462:378-82. [PMID: 25969426 DOI: 10.1016/j.bbrc.2015.04.143] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2015] [Accepted: 04/30/2015] [Indexed: 11/23/2022]
Abstract
Regulators of G protein signaling (RGS) proteins are known to interact with and negatively regulate/turn-off G protein activation. RGS18 is identified as an R4 subfamily member of this family with specific expression in hematopoietic progenitors, myeloerythroid cells, megakaryocytes and platelets. Studies focused on understanding its function in platelet biology have been limited, in part, due to lack of pharmacological inhibitors. Thus, the present study investigated the function of RGS18 in platelets, using the RGS18 knockout mouse model (RGS18(-/-)). We identified phenotypic differences between RGS18(-/-) and wild-type (WT) mice, and show that RGS18 plays a significant role in hemostasis and thrombosis. Hence, RGS18 deficiency markedly shortened bleeding as well as occlusion times (in vivo). Furthermore, RGS18(-/-) platelets displayed hyper-responsiveness with regards to agonist induced aggregation (in vitro). This gain of function phenotype may serve as the mechanism or explain, at least in part, the enhanced hemostasis and thrombosis phenotype observed in the RGS18 deletion mice. Collectively, our findings provide valuable insight and highlight a critical and direct role for RGS18 in modulating platelet function.
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