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Santos-López J, de la Paz K, Fernández FJ, Vega MC. Structural biology of complement receptors. Front Immunol 2023; 14:1239146. [PMID: 37753090 PMCID: PMC10518620 DOI: 10.3389/fimmu.2023.1239146] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2023] [Accepted: 08/16/2023] [Indexed: 09/28/2023] Open
Abstract
The complement system plays crucial roles in a wide breadth of immune and inflammatory processes and is frequently cited as an etiological or aggravating factor in many human diseases, from asthma to cancer. Complement receptors encompass at least eight proteins from four structural classes, orchestrating complement-mediated humoral and cellular effector responses and coordinating the complex cross-talk between innate and adaptive immunity. The progressive increase in understanding of the structural features of the main complement factors, activated proteolytic fragments, and their assemblies have spurred a renewed interest in deciphering their receptor complexes. In this review, we describe what is currently known about the structural biology of the complement receptors and their complexes with natural agonists and pharmacological antagonists. We highlight the fundamental concepts and the gray areas where issues and problems have been identified, including current research gaps. We seek to offer guidance into the structural biology of the complement system as structural information underlies fundamental and therapeutic research endeavors. Finally, we also indicate what we believe are potential developments in the field.
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Affiliation(s)
- Jorge Santos-López
- Centro de Investigaciones Biológicas Margarita Salas, Consejo Superior de Investigaciones Científicas (CSIC), Madrid, Spain
| | - Karla de la Paz
- Centro de Investigaciones Biológicas Margarita Salas, Consejo Superior de Investigaciones Científicas (CSIC), Madrid, Spain
- Research & Development, Abvance Biotech SL, Madrid, Spain
| | | | - M. Cristina Vega
- Centro de Investigaciones Biológicas Margarita Salas, Consejo Superior de Investigaciones Científicas (CSIC), Madrid, Spain
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2
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Cheng H, Guo P, Su T, Jiang C, Zhu Z, Wei W, Zhang L, Wang Q. G protein-coupled receptor kinase type 2 and β-arrestin2: Key players in immune cell functions and inflammation. Cell Signal 2022; 95:110337. [DOI: 10.1016/j.cellsig.2022.110337] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2022] [Revised: 04/15/2022] [Accepted: 04/15/2022] [Indexed: 02/07/2023]
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3
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Gschwandtner M, Derler R, Midwood KS. More Than Just Attractive: How CCL2 Influences Myeloid Cell Behavior Beyond Chemotaxis. Front Immunol 2019; 10:2759. [PMID: 31921102 PMCID: PMC6923224 DOI: 10.3389/fimmu.2019.02759] [Citation(s) in RCA: 341] [Impact Index Per Article: 68.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2019] [Accepted: 11/11/2019] [Indexed: 12/15/2022] Open
Abstract
Monocyte chemoattractant protein-1 (MCP-1/CCL2) is renowned for its ability to drive the chemotaxis of myeloid and lymphoid cells. It orchestrates the migration of these cell types both during physiological immune defense and in pathological circumstances, such as autoimmune diseases including rheumatoid arthritis and multiple sclerosis, inflammatory diseases including atherosclerosis, as well as infectious diseases, obesity, diabetes, and various types of cancer. However, new data suggest that the scope of CCL2's functions may extend beyond its original characterization as a chemoattractant. Emerging evidence shows that it can impact leukocyte behavior, influencing adhesion, polarization, effector molecule secretion, autophagy, killing, and survival. The direction of these CCL2-induced responses is context dependent and, in some cases, synergistic with other inflammatory stimuli. The involvement of CCL2 signaling in multiple diseases renders it an interesting therapeutic target, although current targeting strategies have not met early expectations in the clinic. A better understanding of how CCL2 affects immune cells will be pivotal to the improvement of existing therapeutic approaches and the development of new drugs. Here, we provide an overview of the pleiotropic effects of CCL2 signaling on cells of the myeloid lineage, beyond chemotaxis, and highlight how these actions might help to shape immune cell behavior and tumor immunity.
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Affiliation(s)
- Martha Gschwandtner
- Kennedy Institute of Rheumatology, Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Oxford, United Kingdom
| | - Rupert Derler
- Department of Pharmaceutical Chemistry, Institute of Pharmaceutical Sciences, University of Graz, Graz, Austria
| | - Kim S. Midwood
- Kennedy Institute of Rheumatology, Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Oxford, United Kingdom
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Gupta K, Kotian A, Subramanian H, Daniell H, Ali H. Activation of human mast cells by retrocyclin and protegrin highlight their immunomodulatory and antimicrobial properties. Oncotarget 2016; 6:28573-87. [PMID: 26378047 PMCID: PMC4745678 DOI: 10.18632/oncotarget.5611] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2015] [Accepted: 08/30/2015] [Indexed: 01/21/2023] Open
Abstract
Preclinical evaluation of Retrocyclins (RC-100, RC-101) and Protegrin-1 (PG-1) antimicrobial peptides (AMPs) is important because of their therapeutic potential against bacterial, fungal and viral infections. Human mast cells (HMCs) play important roles in host defense and wound healing but the abilities of retrocyclins and protegrin-1 to harness these functions have not been investigated. Here, we report that chemically synthesized RC-100 and PG-1 caused calcium mobilization and degranulation in HMCs but these responses were not blocked by an inhibitor of formyl peptide receptor-like 1 (FPRL1), a known receptor for AMPs. However, RC-100 and PG-1 induced degranulation in rat basophilic leukemia (RBL-2H3) cells stably expressing Mas related G protein coupled receptor X2 (MrgX2). Chemical synthesis of these AMPs is prohibitively expensive and post-synthesis modifications (cyclization, disulfide bonds, folding) are inadequate for optimal antimicrobial activity. Indeed, we found that synthetic RC-100, which caused mast cell degranulation via MrgX2, did not display any antimicrobial activity. Green-fluorescent protein (GFP)-tagged RC-101 (analog of RC-100) and GFP-tagged PG-1 purified from transgenic plant chloroplasts killed bacteria and induced mast cell degranulation. Furthermore, GFP-PG1 bound specifically to RBL-2H3 cells expressing MrgX2. These findings suggest that retrocyclins and protegrins activate HMCs independently of FPRL1 but via MrgX2. Harnessing this novel feature of AMPs to activate mast cell's host defense/wound healing properties in addition to their antimicrobial activities expands their clinical potential. Low cost production of AMPs in plants should facilitate their advancement to the clinic overcoming major hurdles in current production systems.
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Affiliation(s)
- Kshitij Gupta
- Department of Pathology, School of Dental Medicine, University of Pennsylvania, Philadelphia, PA, USA
| | - Akhil Kotian
- Department of Biochemistry, School of Dental Medicine, University of Pennsylvania, Philadelphia, PA, USA
| | - Hariharan Subramanian
- Department of Pathology, School of Dental Medicine, University of Pennsylvania, Philadelphia, PA, USA
| | - Henry Daniell
- Department of Biochemistry, School of Dental Medicine, University of Pennsylvania, Philadelphia, PA, USA
| | - Hydar Ali
- Department of Pathology, School of Dental Medicine, University of Pennsylvania, Philadelphia, PA, USA
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5
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Sharma D, Parameswaran N. Multifaceted role of β-arrestins in inflammation and disease. Genes Immun 2015; 16:499-513. [PMID: 26378652 PMCID: PMC4670277 DOI: 10.1038/gene.2015.37] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2015] [Revised: 07/05/2015] [Accepted: 07/31/2015] [Indexed: 12/19/2022]
Abstract
Arrestins are intracellular scaffolding proteins known to regulate a range of biochemical processes including G protein-coupled receptor (GPCR) desensitization, signal attenuation, receptor turnover and downstream signaling cascades. Their roles in regulation of signaling network have lately been extended to receptors outside of the GPCR family, demonstrating their roles as important scaffolding proteins in various physiological processes including proliferation, differentiation and apoptosis. Recent studies have demonstrated a critical role for arrestins in immunological processes including key functions in inflammatory signaling pathways. In this review, we provide a comprehensive analysis of the different functions of the arrestin family of proteins especially related to immunity and inflammatory diseases.
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Affiliation(s)
- Deepika Sharma
- Department of Physiology and Division of Pathology Michigan State University East Lansing, MI 48824
| | - Narayanan Parameswaran
- Department of Physiology and Division of Pathology Michigan State University East Lansing, MI 48824
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Subramanian H, Gupta K, Parameswaran N, Ali H. Regulation of Fc∈RI signaling in mast cells by G protein-coupled receptor kinase 2 and its RH domain. J Biol Chem 2015; 289:20917-27. [PMID: 24904059 DOI: 10.1074/jbc.m113.523969] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Agonist-induced phosphorylation of G protein-coupled receptors (GPCRs) by GPCRkinases (GRKs) promotes their desensitization and internalization. Here, we sought to determine the role of GRK2 on Fc∈RI signaling and mediator release in mast cells. The strategies utilized included lentiviral shRNA-mediated GRK2 knockdown, GRK2 gene deletion (GRK2(flox/flox)/cre recombinase) and overexpression of GRK2 and its regulator of G protein signaling homology (RH) domain (GRK2-RH). We found that silencing GRK2 expression caused ~50% decrease in antigen-induced Ca(2+) mobilization and degranulation but resulted in ablation of cytokine (IL-6 and IL-13) generation. The effect of GRK2 on cytokine generation does not require its catalytic activity but is mediated via the phosphorylation of p38 and Akt. Overexpression of GRK2 or its RH domain (GRK2-RH) enhanced antigen-induced mast cell degranulation and cytokine generation without affecting the expression levels of any of the Fc∈RI subunits (α, β, and γ). GRK2 or GRK2-RH had no effect on antigen-induced phosphorylation of Fc∈RIγ or Src but enhanced tyrosine phosphorylation of Syk. These data demonstrate that GRK2 modulates Fc∈RI signaling in mast cells via at least two mechanisms.One involves GRK2-RH and modulates tyrosine phosphorylation of Syk, and the other is mediated via the phosphorylation of p38 and Akt.
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Rizzo M, Bayo J, Piccioni F, Malvicini M, Fiore E, Peixoto E, García MG, Aquino JB, Gonzalez Campaña A, Podestá G, Terres M, Andriani O, Alaniz L, Mazzolini G. Low molecular weight hyaluronan-pulsed human dendritic cells showed increased migration capacity and induced resistance to tumor chemoattraction. PLoS One 2014; 9:e107944. [PMID: 25238610 PMCID: PMC4169605 DOI: 10.1371/journal.pone.0107944] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2014] [Accepted: 08/18/2014] [Indexed: 12/12/2022] Open
Abstract
We have shown that ex vivo pre-conditioning of bone marrow-derived dendritic cells (DC) with low molecular weight hyaluronan (LMW HA) induces antitumor immunity against colorectal carcinoma (CRC) in mice. In the present study we investigated the effects of LMW HA priming on human-tumor-pulsed monocytes-derived dendritic cells (DC/TL) obtained from healthy donors and patients with CRC. LMW HA treatment resulted in an improved maturation state of DC/TL and an enhanced mixed leucocyte reaction activity in vivo. Importantly, pre-conditioning of DC/TL with LMW HA increased their ability to migrate and reduced their attraction to human tumor derived supernatants. These effects were associated with increased CCR7 expression levels in DC. Indeed, a significant increase in migratory response toward CCL21 was observed in LMW HA primed tumor-pulsed monocyte-derived dendritic cells (DC/TL/LMW HA) when compared to LWM HA untreated cells (DC/TL). Moreover, LMW HA priming modulated other mechanisms implicated in DC migration toward lymph nodes such as the metalloproteinase activity. Furthermore, it also resulted in a significant reduction in DC migratory capacity toward tumor supernatant and IL8 in vitro. Consistently, LMW HA dramatically enhanced in vivo DC recruitment to tumor-regional lymph nodes and reduced DC migration toward tumor tissue. This study shows that LMW HA--a poorly immunogenic molecule--represents a promising candidate to improve human DC maturation protocols in the context of DC-based vaccines development, due to its ability to enhance their immunogenic properties as well as their migratory capacity toward lymph nodes instead of tumors.
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Affiliation(s)
- Manglio Rizzo
- Gene Therapy Laboratory, Facultad de Ciencias Biomédicas, Universidad Austral, Derqui-Pilar, Buenos Aires, Argentina
| | - Juan Bayo
- Gene Therapy Laboratory, Facultad de Ciencias Biomédicas, Universidad Austral, Derqui-Pilar, Buenos Aires, Argentina
| | - Flavia Piccioni
- Gene Therapy Laboratory, Facultad de Ciencias Biomédicas, Universidad Austral, Derqui-Pilar, Buenos Aires, Argentina
| | - Mariana Malvicini
- Gene Therapy Laboratory, Facultad de Ciencias Biomédicas, Universidad Austral, Derqui-Pilar, Buenos Aires, Argentina
- CONICET (Consejo Nacional de Investigaciones Científicas y Técnicas), CABA, Buenos Aires, Argentina
| | - Esteban Fiore
- Gene Therapy Laboratory, Facultad de Ciencias Biomédicas, Universidad Austral, Derqui-Pilar, Buenos Aires, Argentina
| | - Estanislao Peixoto
- Gene Therapy Laboratory, Facultad de Ciencias Biomédicas, Universidad Austral, Derqui-Pilar, Buenos Aires, Argentina
| | - Mariana G. García
- Gene Therapy Laboratory, Facultad de Ciencias Biomédicas, Universidad Austral, Derqui-Pilar, Buenos Aires, Argentina
- CONICET (Consejo Nacional de Investigaciones Científicas y Técnicas), CABA, Buenos Aires, Argentina
| | - Jorge B. Aquino
- Gene Therapy Laboratory, Facultad de Ciencias Biomédicas, Universidad Austral, Derqui-Pilar, Buenos Aires, Argentina
- CONICET (Consejo Nacional de Investigaciones Científicas y Técnicas), CABA, Buenos Aires, Argentina
| | - Ariel Gonzalez Campaña
- Department of Surgery, Hospital Austral, Universidad Austral, Derqui-Pilar, Buenos Aires, Argentina
| | - Gustavo Podestá
- Department of Surgery, Hospital Austral, Universidad Austral, Derqui-Pilar, Buenos Aires, Argentina
| | - Marcelo Terres
- Department of Surgery, Hospital Austral, Universidad Austral, Derqui-Pilar, Buenos Aires, Argentina
| | - Oscar Andriani
- Department of Surgery, Hospital Austral, Universidad Austral, Derqui-Pilar, Buenos Aires, Argentina
| | - Laura Alaniz
- CONICET (Consejo Nacional de Investigaciones Científicas y Técnicas), CABA, Buenos Aires, Argentina
- CIT NOBA, Universidad Nacional del Noroeste de la Pcia de Bs. As (UNNOBA), Junín, Buenos Aires, Argentina
- * E-mail: (GM); (LA)
| | - Guillermo Mazzolini
- Gene Therapy Laboratory, Facultad de Ciencias Biomédicas, Universidad Austral, Derqui-Pilar, Buenos Aires, Argentina
- CONICET (Consejo Nacional de Investigaciones Científicas y Técnicas), CABA, Buenos Aires, Argentina
- * E-mail: (GM); (LA)
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Klos A, Wende E, Wareham KJ, Monk PN. International Union of Basic and Clinical Pharmacology. [corrected]. LXXXVII. Complement peptide C5a, C4a, and C3a receptors. Pharmacol Rev 2013; 65:500-43. [PMID: 23383423 DOI: 10.1124/pr.111.005223] [Citation(s) in RCA: 178] [Impact Index Per Article: 16.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
The activation of the complement cascade, a cornerstone of the innate immune response, produces a number of small (74-77 amino acid) fragments, originally termed anaphylatoxins, that are potent chemoattractants and secretagogues that act on a wide variety of cell types. These fragments, C5a, C4a, and C3a, participate at all levels of the immune response and are also involved in other processes such as neural development and organ regeneration. Their primary function, however, is in inflammation, so they are important targets for the development of antiinflammatory therapies. Only three receptors for complement peptides have been found, but there are no satisfactory antagonists as yet, despite intensive investigation. In humans, there is a single receptor for C3a (C3a receptor), no known receptor for C4a, and two receptors for C5a (C5a₁ receptor and C5a₂ receptor). The most recently characterized receptor, the C5a₂ receptor (previously known as C5L2 or GPR77), has been regarded as a passive binding protein, but signaling activities are now ascribed to it, so we propose that it be formally identified as a receptor and be given a name to reflect this. Here, we describe the complex biology of the complement peptides, introduce a new suggested nomenclature, and review our current knowledge of receptor pharmacology.
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Affiliation(s)
- Andreas Klos
- Department for Medical Microbiology, Medical School Hannover, Hannover, Germany
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Abstract
β-Arrestins regulate G protein-coupled receptors through receptor desensitization while also acting as signaling scaffolds to facilitate numerous effector pathways. Recent studies have provided evidence that β-arrestins play a key role in inflammatory responses. Here, we summarize these advances on the roles of β-arrestins in immune regulation and inflammatory responses under physiological and pathological conditions, with an emphasis on translational implications of β-arrestins on human diseases.
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Subramanian H, Gupta K, Ali H. Roles for NHERF1 and NHERF2 on the regulation of C3a receptor signaling in human mast cells. PLoS One 2012; 7:e51355. [PMID: 23284683 PMCID: PMC3527443 DOI: 10.1371/journal.pone.0051355] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2012] [Accepted: 11/01/2012] [Indexed: 12/04/2022] Open
Abstract
Background The anaphylatoxin C3a binds to the G protein coupled receptor (GPCR, C3aR) and activates divergent signaling pathways to induce degranulation and cytokine production in human mast cells. Adapter proteins such as the Na+/H+ exchange regulatory factor (NHERF1 and NHERF2) have been implicated in regulating functions of certain GPCRs by binding to the class I PDZ (PSD-95/Dlg/Zo1) motifs present on their cytoplasmic tails. Although C3aR possesses a class I PDZ motif, the possibility that it interacts with NHERF proteins to modulate signaling in human mast cells has not been determined. Methodology/Principal Findings Using reverse transcription PCR and Western blotting, we found that NHERF1 and NHERF2 are expressed in human mast cell lines (HMC-1, LAD2) and CD34+-derived primary human mast cells. Surprisingly, however, C3aR did not associate with these adapter proteins. To assess the roles of NHERFs on signaling downstream of C3aR, we used lentiviral shRNA to stably knockdown the expression of these proteins in human mast cells. Silencing the expression of NHERF1 and NHERF2 had no effect on C3aR desensitization, agonist-induced receptor internalization, ERK/Akt phosphorylation or chemotaxis. However, loss of NHERF1 and NHERF2 resulted in significant inhibition of C3a-induced mast cell degranulation, NF-κB activation and chemokine production. Conclusion/Significance This study demonstrates that although C3aR possesses a class I PDZ motif, it does not associate with NHERF1 and NHERF2. Surprisingly, these proteins provide stimulatory signals for C3a-induced degranulation, NF-κB activation and chemokine generation in human mast cells. These findings reveal a new level of complexity for the functional regulation of C3aR by NHERFs in human mast cells.
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Affiliation(s)
- Hariharan Subramanian
- Department of Pathology, School of Dental Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
| | - Kshitij Gupta
- Department of Pathology, School of Dental Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
| | - Hydar Ali
- Department of Pathology, School of Dental Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
- * E-mail:
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Gupta K, Subramanian H, Klos A, Ali H. Phosphorylation of C3a receptor at multiple sites mediates desensitization, β-arrestin-2 recruitment and inhibition of NF-κB activity in mast cells. PLoS One 2012; 7:e46369. [PMID: 23077507 PMCID: PMC3471852 DOI: 10.1371/journal.pone.0046369] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2012] [Accepted: 08/29/2012] [Indexed: 01/21/2023] Open
Abstract
Background Phosphorylation of G protein coupled receptors (GPCRs) by G protein coupled receptor kinases (GRKs) and the subsequent recruitment of β-arrestins are important for their desensitization. Using shRNA-mediated gene silencing strategy, we have recently shown that GRK2, GRK3 and β-arrestin-2 promote C3a receptor (C3aR) desensitization in human mast cells. We also demonstrated that β-arrestin-2 provides an inhibitory signal for NF-κB activation. C3aR possesses ten potential phosphorylation sites within its carboxyl terminus but their role on desensitization, β-arrestin recruitment and NF-κB activation has not been determined. Methodology/Principal Findings We utilized a site directed mutagenesis approach in transfected HEK293 cells to determine the role of receptor phosphorylation on β-arrestin-2 recruitment and RBL-2H3 cells for functional studies. We found that although Ala substitution of Ser475/479, Thr480/481 residues resulted in 58±3.8% decrease in agonist-induced C3aR phosphorylation there was no change in β-arrestin-2 binding or receptor desensitization. By contrast, Ala substitution of Thr463, Ser465, Thr466 and Ser470 led to 40±1.3% decrease in agonist-induced receptor phosphorylation but this was associated with 74±2.4% decreases in β-arrestin-2 binding, significantly reduced desensitization and enhanced NF-κB activation. Combined mutation of these Ser/Thr residues along with Ser459 (mutant MT7), resulted in complete loss of receptor phosphorylation and β-arrestin-2 binding. RBL-2H3 cells expressing MT7 responded to C3a for greater Ca2+ mobilization, degranulation and NF-κB activation when compared to the wild-type receptor. Interestingly, co-expression of MT7 with a constitutively active mutant of β-arrestin (R169E) inhibited C3a-induced degranulation by 28±2.4% and blocked NF-κB activation by 80±2.4%. Conclusion/Significance This study demonstrates that although C3a causes phosphorylation of its receptor at multiple sites, Ser459, Thr463, Ser465, Thr466 and Ser470 participate in C3aR desensitization, β-arrestin-2 recruitment and inhibition of NF-κB activity. Furthermore, β-arrestin-2 inhibits C3a-induced NF-κB activation via receptor desensitization-dependent and independent pathways.
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Affiliation(s)
- Kshitij Gupta
- Department of Pathology, School of Dental Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
| | - Hariharan Subramanian
- Department of Pathology, School of Dental Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
| | - Andreas Klos
- Institute of Medical Microbiology and Hospital Epidemiology, Medical School Hannover, Hannover, Germany
| | - Hydar Ali
- Department of Pathology, School of Dental Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
- * E-mail:
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Abstract
G protein-coupled receptors (GPCRs) play important roles in inflammation. Inflammatory cells such as polymorphonuclear leukocytes (PMN), monocytes and macrophages express a large number of GPCRs for classic chemoattractants and chemokines. These receptors are critical to the migration of phagocytes and their accumulation at sites of inflammation, where these cells can exacerbate inflammation but also contribute to its resolution. Besides chemoattractant GPCRs, protease activated receptors (PARs) such as PAR1 are involved in the regulation of vascular endothelial permeability. Prostaglandin receptors play different roles in inflammatory cell activation, and can mediate both proinflammatory and anti-inflammatory functions. Many GPCRs present in inflammatory cells also mediate transcription factor activation, resulting in the synthesis and secretion of inflammatory factors and, in some cases, molecules that suppress inflammation. An understanding of the signaling paradigms of GPCRs in inflammatory cells is likely to facilitate translational research and development of improved anti-inflammatory therapies.
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Subramanian H, Gupta K, Guo Q, Price R, Ali H. Mas-related gene X2 (MrgX2) is a novel G protein-coupled receptor for the antimicrobial peptide LL-37 in human mast cells: resistance to receptor phosphorylation, desensitization, and internalization. J Biol Chem 2011; 286:44739-49. [PMID: 22069323 PMCID: PMC3247983 DOI: 10.1074/jbc.m111.277152] [Citation(s) in RCA: 171] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2011] [Revised: 10/29/2011] [Indexed: 01/14/2023] Open
Abstract
Human LL-37 is a multifunctional antimicrobial peptide that promotes inflammation, angiogenesis, wound healing, and tumor metastasis. Most effects of LL-37 are mediated via the activation of the cell surface G protein-coupled receptor FPR2 on leukocytes and endothelial cells. Although LL-37 induces chemotaxis, degranulation, and chemokine production in mast cells, the receptor involved and the mechanism of its regulation remain unknown. MrgX2 is a member of Mas-related genes that is primarily expressed in human dorsal root ganglia and mast cells. We found that a human mast cell line LAD2 and CD34(+) cell-derived primary mast cells, which natively express MrgX2, responded to LL-37 for sustained Ca(2+) mobilization and substantial degranulation. However, an immature human mast cell line, HMC-1, that lacks functional MrgX2 did not respond to LL-37. shRNA-mediated knockdown of MrgX2 in LAD2 mast cell line and primary CD34(+) cell-derived mast cells caused a substantial reduction in LL-37-induced degranulation. Furthermore, mast cell lines stably expressing MrgX2 responded to LL-37 for chemotaxis, degranulation, and CCL4 production. Surprisingly, MrgX2 was resistant to LL-37-induced phosphorylation, desensitization, and internalization. In addition, shRNA-mediated knockdown of the G protein-coupled receptor kinases (GRK2 and GRK3) had no effect on LL-37-induced mast cell degranulation. This study identified MrgX2 as a novel G protein-coupled receptor for the antibacterial peptide LL-37 and demonstrated that unlike most G protein-coupled receptors it is resistant to agonist-induced receptor phosphorylation, desensitization, and internalization.
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Affiliation(s)
- Hariharan Subramanian
- From the Department of Pathology, School of Dental Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104
| | - Kshitij Gupta
- From the Department of Pathology, School of Dental Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104
| | - Qiang Guo
- From the Department of Pathology, School of Dental Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104
| | - Ryan Price
- From the Department of Pathology, School of Dental Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104
| | - Hydar Ali
- From the Department of Pathology, School of Dental Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104
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Guo Q, Subramanian H, Gupta K, Ali H. Regulation of C3a receptor signaling in human mast cells by G protein coupled receptor kinases. PLoS One 2011; 6:e22559. [PMID: 21799898 PMCID: PMC3143157 DOI: 10.1371/journal.pone.0022559] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2011] [Accepted: 06/27/2011] [Indexed: 12/03/2022] Open
Abstract
Background The complement component C3a activates human mast cells via its cell surface G protein coupled receptor (GPCR) C3aR. For most GPCRs, agonist-induced receptor phosphorylation leads to receptor desensitization, internalization as well as activation of downstream signaling pathways such as ERK1/2 phosphorylation. Previous studies in transfected COS cells overexpressing G protein coupled receptor kinases (GRKs) demonstrated that GRK2, GRK3, GRK5 and GRK6 participate in agonist-induced C3aR phosphorylation. However, the roles of these GRKs on the regulation of C3aR signaling and mediator release in human mast cells remain unknown. Methodology/Principal Findings We utilized lentivirus short hairpin (sh)RNA to stably knockdown the expression of GRK2, GRK3, GRK5 and GRK6 in human mast cell lines, HMC-1 and LAD2, that endogenously express C3aR. Silencing GRK2 or GRK3 expression caused a more sustained Ca2+ mobilization, attenuated C3aR desensitization, and enhanced degranulation as well as ERK1/2 phosphorylation when compared to shRNA control cells. By contrast, GRK5 or GRK6 knockdown had no effect on C3aR desensitization, but caused a significant decrease in C3a-induced mast cell degranulation. Interestingly, GRK5 or GRK6 knockdown rendered mast cells more responsive to C3a for ERK1/2 phosphorylation. Conclusion/Significance This study demonstrates that GRK2 and GRK3 are involved in C3aR desensitization. Furthermore, it reveals the novel finding that GRK5 and GRK6 promote C3a-induced mast cell degranulation but inhibit ERK1/2 phosphorylation via C3aR desensitization-independent mechanisms. These findings thus reveal a new level of complexity for C3aR regulation by GRKs in human mast cells.
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Affiliation(s)
- Qiang Guo
- Department of Pathology, School of Dental Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
| | - Hariharan Subramanian
- Department of Pathology, School of Dental Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
| | - Kshitij Gupta
- Department of Pathology, School of Dental Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
| | - Hydar Ali
- Department of Pathology, School of Dental Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
- * E-mail:
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15
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Kashem SW, Subramanian H, Collington SJ, Magotti P, Lambris JD, Ali H. G protein coupled receptor specificity for C3a and compound 48/80-induced degranulation in human mast cells: roles of Mas-related genes MrgX1 and MrgX2. Eur J Pharmacol 2011; 668:299-304. [PMID: 21741965 DOI: 10.1016/j.ejphar.2011.06.027] [Citation(s) in RCA: 86] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2011] [Revised: 06/08/2011] [Accepted: 06/15/2011] [Indexed: 01/28/2023]
Abstract
Although human mast cells express G protein coupled receptors for the anaphylatoxin C3a, previous studies indicated that C3a causes mast cell degranulation, at least in part, via a C3a receptor-independent mechanism similar to that proposed for polycationic molecules such as compound 48/80. The purpose of the present study was to delineate the receptor specificity of C3a-induced degranulation in human mast cells. We found that C3a, a C3a receptor "superagonist" (E7) and compound 48/80 induced Ca(2+) mobilization and degranulation in a differentiated human mast cell line, LAD2. However, C3a and E7 caused Ca(2+) mobilization in an immature mast cell line, HMC-1 but compound 48/80 did not. We have previously shown that LAD2 cells express MrgX1 and MrgX2 but HMC-1 cells do not. To delineate the receptor specificity for C3a and compound 48/80 further, we generated stable transfectants expressing MrgX1 and MrgX2 in a rodent mast cell line, RBL-2H3 cells. We found that compound 48/80 caused degranulation in RBL-2H3 cells expressing MrgX1 and MrgX2 but C3a did not. By contrast, E7 activated RBL-2H3 cells expressing MrgX2 but not MrgX1. These findings demonstrate that in contrast to previous reports, C3a and compound 48/80 do not use a shared mechanism for mast cell degranulation. It shows that while compound 48/80 utilizes MrgX1 and MrgX2 for mast cell degranulation C3a does not. It further reveals the novel finding that the previously characterized synthetic peptide, C3a receptor "superagonist" E7 activates human mast cells via two mechanisms; one involving the C3a receptor and the other MrgX2.
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Affiliation(s)
- Sakeen W Kashem
- Department of Pathology, School of Dental Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
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16
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Distinct and shared roles of β-arrestin-1 and β-arrestin-2 on the regulation of C3a receptor signaling in human mast cells. PLoS One 2011; 6:e19585. [PMID: 21589858 PMCID: PMC3093384 DOI: 10.1371/journal.pone.0019585] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2011] [Accepted: 04/06/2011] [Indexed: 11/19/2022] Open
Abstract
Background The complement component C3a induces degranulation in human mast cells via the activation of cell surface G protein coupled receptors (GPCR; C3aR). For most GPCRs, agonist-induced receptor phosphorylation leads to the recruitment of β-arrestin-1/β-arrestin-2; resulting in receptor desensitization and internalization. Activation of GPCRs also leads to ERK1/2 phosphorylation via two temporally distinct pathways; an early response that reflects G protein activation and a delayed response that is G protein independent but requires β-arrestins. The role of β-arrestins on C3aR activation/regulation in human mast cells, however, remains unknown. Methodology/Principal Findings We utilized lentivirus short hairpin (sh)RNA to stably knockdown the expression of β-arrestin-1 and β-arrrestin-2 in human mast cell lines, HMC-1 and LAD2 that endogenously expresses C3aR. Silencing β-arrestin-2 attenuated C3aR desensitization, blocked agonist-induced receptor internalization and rendered the cells responsive to C3a for enhanced NF-κB activity as well as chemokine generation. By contrast, silencing β-arrestin-1 had no effect on these responses but resulted in a significant decrease in C3a-induced mast cell degranulation. In shRNA control cells, C3a caused a transient ERK1/2 phosphorylation, which peaked at 5 min but disappeared by 10 min. Knockdown of β-arrestin-1, β-arrestin-2 or both enhanced the early response to C3a and rendered the cells responsive for ERK1/2 phosphorylation at later time points (10–30 min). Treatment of cells with pertussis toxin almost completely blocked both early and delayed C3a-induced ERK1/2 phosphorylation in β-arrestin1/2 knockdown cells. Conclusion/Significance This study demonstrates distinct roles for β-arrestins-1 and β-arrestins-2 on C3aR desensitization, internalization, degranulation, NF-κB activation and chemokine generation in human mast cells. It also shows that both β-arrestin-1 and β-arrestin-2 play a novel and shared role in inhibiting G protein-dependent ERK1/2 phosphorylation. These findings reveal a new level of complexity for C3aR regulation by β-arrestins in human mast cells.
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Hollingsworth JW, Theriot BS, Li Z, Lawson BL, Sunday M, Schwartz DA, Walker JKL. Both hematopoietic-derived and non-hematopoietic-derived {beta}-arrestin-2 regulates murine allergic airway disease. Am J Respir Cell Mol Biol 2010; 43:269-75. [PMID: 19805483 PMCID: PMC2933545 DOI: 10.1165/rcmb.2009-0198oc] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2009] [Accepted: 08/27/2010] [Indexed: 11/24/2022] Open
Abstract
Allergic asthma, a major cause of morbidity and leading cause of hospitalizations, is an inflammatory disease orchestrated by T helper cells and characterized by the lung migration of eosinophils, which are important asthma effector cells. Lung migration of inflammatory cells requires, among other events, the chemokine receptor transduction of lung-produced inflammatory chemokines. Despite the widespread prevalence of this disease, the molecular mechanisms regulating chemokine production and receptor regulation in asthma are poorly understood. Previous work from our laboratory demonstrated that beta-arrestin-2 positively regulates the development of allergic airway disease in a mouse model, partly through positive regulation of T-lymphocyte chemotaxis to the lung. However, beta-arrestin-2 is expressed in many cell types, including other hematopoietic cells and lung structural cells, which are involved in the development and manifestation of allergic airway disease. To determine the cell types required for beta-arrestin-2-dependent allergic inflammation, we generated bone marrow chimera mice. Using the ovalbumin murine model of allergic airway disease, we show that eosinophilic and lymphocytic inflammation is restored in chimeric mice, with expression of beta-arrestin-2 exclusively on hematopoietic-derived cell types. In contrast, airway hyperresponsiveness is dependent on the expression of beta-arrestin-2 in structural cells. Our data demonstrate that the expression of beta-arrestin-2 in at least two divergent cell types contributes to the pathogenesis of allergic airway disease.
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Affiliation(s)
- John W. Hollingsworth
- Division of Pulmonary, Allergy, and Critical Care Medicine, and Department of Pathology, Duke University Medical Center, Durham, North Carolina; and National Jewish Medical Center, Denver, Colorado
| | - Barbara S. Theriot
- Division of Pulmonary, Allergy, and Critical Care Medicine, and Department of Pathology, Duke University Medical Center, Durham, North Carolina; and National Jewish Medical Center, Denver, Colorado
| | - Zhouwei Li
- Division of Pulmonary, Allergy, and Critical Care Medicine, and Department of Pathology, Duke University Medical Center, Durham, North Carolina; and National Jewish Medical Center, Denver, Colorado
| | - Barbara L. Lawson
- Division of Pulmonary, Allergy, and Critical Care Medicine, and Department of Pathology, Duke University Medical Center, Durham, North Carolina; and National Jewish Medical Center, Denver, Colorado
| | - Mary Sunday
- Division of Pulmonary, Allergy, and Critical Care Medicine, and Department of Pathology, Duke University Medical Center, Durham, North Carolina; and National Jewish Medical Center, Denver, Colorado
| | - David A. Schwartz
- Division of Pulmonary, Allergy, and Critical Care Medicine, and Department of Pathology, Duke University Medical Center, Durham, North Carolina; and National Jewish Medical Center, Denver, Colorado
| | - Julia K. L. Walker
- Division of Pulmonary, Allergy, and Critical Care Medicine, and Department of Pathology, Duke University Medical Center, Durham, North Carolina; and National Jewish Medical Center, Denver, Colorado
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18
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Ali H. Regulation of human mast cell and basophil function by anaphylatoxins C3a and C5a. Immunol Lett 2009; 128:36-45. [PMID: 19895849 DOI: 10.1016/j.imlet.2009.10.007] [Citation(s) in RCA: 86] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2009] [Revised: 10/21/2009] [Accepted: 10/23/2009] [Indexed: 12/18/2022]
Abstract
Allergic diseases such as asthma result from inappropriate immunologic responses to common environmental allergens in genetically susceptible individuals. Following allergen exposure, interaction of dendritic cells (DC) with CD4(+) T cells leads to the production of Th2 cytokines, which induce B cells to synthesize IgE molecules (sensitization phase). These IgE molecules bind to their high affinity receptors (FcvarepsilonRI) on the surface of mast cells and basophils and their subsequent cross-linking by allergen results in the release of preformed and newly synthesized mediators, which cause bronchoconstriction, lung inflammation and airway hyperresponsiveness (AHR) in asthma (effector phase). The complement components C3a and C5a levels are increased in the lungs of patients with asthma and are likely generated via the actions of both allergen and mast cell proteases. In vivo studies with rodents have shown that while C3a facilitates allergen sensitization in some models C5a inhibits this response. Despite this difference, both anaphylatoxins promote lung inflammation and AHR in vivo indicating that cells other than DC and T cells likely mediate the functional effects of C3a and C5a in asthma. This review focuses on the contribution of C3a and C5a in the pathogenesis of asthma with a particular emphasis on mast cells and basophils. It discusses the mechanisms by which anaphylatoxins activate mast cells and basophils and the associated signaling pathways via which their receptors are regulated by priming and desensitization.
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Affiliation(s)
- Hydar Ali
- Department of Pathology, University of Pennsylvania School of Dental Medicine, 240 South 40th Street, Philadelphia, PA 19104-6030, USA.
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19
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Zaidi AK, Ali H. C3a receptors signaling in mast cells. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2007; 598:126-40. [PMID: 17892209 DOI: 10.1007/978-0-387-71767-8_10] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Grants] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Affiliation(s)
- Asifa K Zaidi
- University of Pennsylvania School of Dental Medicine, Department of Pathology, Philadelphia, PA 19104, USA.
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20
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Thangam EB, Venkatesha RT, Zaidi AK, Jordan-Sciutto KL, Goncharov DA, Krymskaya VP, Amrani Y, Panettieri RA, Ali H. Airway smooth muscle cells enhance C3a-induced mast cell degranulation following cell-cell contact. FASEB J 2005; 19:798-800. [PMID: 15758041 DOI: 10.1096/fj.04-2797fje] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Growing evidence suggests that anaphylatoxins, C3a and C5a, play important roles in innate immunity and may also participate in the pathogenesis of asthma. Previous studies with animal models and immunohistochemistry analysis of lung tissue indicated that anaphylatoxins may regulate airway hyperresponsiveness (AHR) in asthma via the activation of their cell surface G protein-coupled receptors (C3aR and C5aR) in airway smooth muscle (ASM) cells. Using RT-PCR, flow cytometry, and confocal microscopy, we made the surprising observation that while C3aR and C5aR were expressed in human mast cells, they were not present in cultured primary human or murine ASM cells. Furthermore, we could not detect C3aR in smooth muscle-positive cells of human trachea or bronchus. Interestingly, incubation of human mast cells with ASM cells, but not its culture supernatant, caused a significant enhancement of C3a-induced mast cell degranulation. Although stem cell factor (SCF) and its receptor c-kit are constitutively expressed on ASM cells and mast cells, respectively, neutralizing antibodies to SCF and c-kit failed to inhibit ASM cell-mediated enhancement of mast cell degranulation. However, dexamethasone-treated ASM cells were normal for cell surface SCF expression but were significantly less effective in enhancing C3a-induced mast cell degranulation when compared with untreated cells. These findings suggest that cell-cell interaction between ASM cells and mast cells, via a SCF-c-kit-independent but dexamethasone-sensitive mechanism, enhances C3a-induced mast cell degranulation, which likely regulates ASM function, thus contributing to the pathogenesis of asthma.
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Affiliation(s)
- E Berla Thangam
- Department of Pathology, School of Dental Medicine, University of Pennsylvania, Philadelphia, PA 19104-6002, USA
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21
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Arun KHS, Kaul CL, Ramarao P. Green fluorescent proteins in receptor research: An emerging tool for drug discovery. J Pharmacol Toxicol Methods 2005; 51:1-23. [PMID: 15596111 DOI: 10.1016/j.vascn.2004.07.006] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2003] [Accepted: 07/27/2004] [Indexed: 01/20/2023]
Abstract
In the last five years, green fluorescent protein (GFP) has emerged from being a mere curiosity to become a reliable tool for molecular pharmacological research. GFP produces an intense and stable green fluorescence noncatalytically by absorbing blue light maximally at 395 nm and emitting green light with a peak at 509 nm. It consists of 238 amino acids and its molecular mass is 27-30 kDa. GFP fluorescence occurs without cofactors and this property allows GFP fluorescence to be utilised in nonnative organisms, wherein it can be used as a reporter. This use of GFP permits real-time analysis of receptor dynamics. The emitted fluorescence can be used as a nontoxic marker and detected using fluorescence-activated cell sorting (FACS), thus avoiding any staining procedure, expensive mRNA analysis or hazardous radiolabeled binding assays. The potential value of GFP has also been recognized in orphan receptor research, where various GFP-tagged therapeutic proteins have been constructed in an attempt to identify the endogenous ligand(s). These chimeric proteins have been used to determine the site and time course of receptor expression and to relate receptor dynamics with therapeutic outcome. The preparation of new GFP constructs for identifying germ layer cells (endodermal, ectodermal, and mesodermal), as well as neuronal, haematopoietic, endothelial, and cartilage cells, has provided a useful battery of tissue/receptor-specific screening assays for new chemical entities. Genetically engineered cells with GFP expression have provided a valuable tool for automated analysis, and can be adapted for high-throughput systems. GFP is being increasingly utilised for the study of receptor dynamics, where, having already proved beneficial, it will likely continue to contribute towards the search for new classes of drugs, as well as to "de-orphaning" orphan receptors.
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Affiliation(s)
- K H S Arun
- Cardiovascular and Receptorology Laboratory, Department of Pharmacology and Toxicology, National Institute of Pharmaceutical Education and Research, Phase-X, Sector 67, S.A.S. Nagar (Mohali)-160 062, Punjab, India
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22
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Venkatesha RT, Ahamed J, Nuesch C, Zaidi AK, Ali H. Platelet-activating factor-induced chemokine gene expression requires NF-kappaB activation and Ca2+/calcineurin signaling pathways. Inhibition by receptor phosphorylation and beta-arrestin recruitment. J Biol Chem 2004; 279:44606-12. [PMID: 15308653 DOI: 10.1074/jbc.m408035200] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Previously, we reported that platelet-activating factor (PAF) stimulates higher G protein activation and a more robust Ca2+ mobilization in RBL-2H3 cells expressing carboxyl terminus deletion, phosphorylation-deficient mutant of PAF receptor (mPAFR) when compared with the wild-type receptor (PAFR). However, PAF did not provide sufficient signal for CC chemokine receptor ligand 2 (CCL2) production in cells expressing mPAFR. Based on these findings, we hypothesized that receptor phosphorylation provides a G protein-independent signal that synergizes with Ca2+ mobilization to induce CCL2 production. Here, we show that a mutant of PAFR (D289A), which does not couple to G proteins, was resistant to agonist-induced receptor phosphorylation. Unexpectedly, we found that when this mutant was coexpressed with mPAFR, it restored NF-kappaB activation and CCL2 production. PAF caused translocation of beta-arrestin from the cytoplasm to the membrane in cells expressing PAFR but not a phosphorylation-deficient mutant in which all Ser/Thr residues were replaced with Ala (DeltaST-PAFR). Interestingly, PAF induced significantly higher NF-kappaB and nuclear factor of activated T cells (NFAT)-luciferase activity as well as CCL2 production in cells expressing DeltaST-PAFR than those expressing PAFR. Furthermore, a Ca2+/calcineurin inhibitor completely inhibited PAF-induced NFAT activation and CCL2 production but not NF-kappaB activation. These findings suggest that the carboxyl terminus of PAFR provides a G protein-independent signal for NF-kappaB activation, which synergizes with G protein-mediated Ca2+/calcineurin activation to induce CCL2 production. However, receptor phosphorylation and beta-arrestin recruitment inhibit CCL2 production by blocking both NF-kappaB activation and Ca2+/calcineurin-dependent signaling pathways.
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Affiliation(s)
- Rampura T Venkatesha
- Department of Pathology, University of Pennsylvania, School of Dental Medicine, Philadelphia, Pennsylvania 19104, USA
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Vines CM, Xue M, Maestas DC, Cimino DF, Prossnitz ER. Regulation of N-formyl peptide-mediated degranulation by receptor phosphorylation. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 2002; 169:6760-6. [PMID: 12471107 DOI: 10.4049/jimmunol.169.12.6760] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
One of the major functions of the N-formyl peptide receptor (FPR) is to mediate leukocyte degranulation. Phosphorylation of the C-terminal domain of the FPR is required for receptor internalization and desensitization. Although arrestins mediate phosphorylation-dependent desensitization, internalization, and initiation of novel signaling cascades for a number of G protein-coupled receptors, their roles in FPR regulation and signaling remain unclear. CXCR1-mediated degranulation of RBL-2H3 cells is promoted by arrestin binding. To determine whether receptor phosphorylation or arrestin binding is required to promote FPR-mediated degranulation, we used RBL-2H3 cells stably transfected with either the wild-type FPR or a mutant form, DeltaST, which is incapable of undergoing ligand-stimulated phosphorylation. We observed that stimulation of wild-type FPR resulted in very low levels of degranulation compared with that mediated by cross-linking of the Fc(epsilon)RI receptor. Stimulation of the DeltaST mutant, however, resulted in levels of degranulation comparable to those of the Fc(epsilon)RI receptor, demonstrating that neither receptor phosphorylation nor arrestin binding was necessary to initiate FPR-mediated degranulation. Degranulation initiated by the DeltaST mutant was proportional to the level of active cell surface receptor, suggesting that either receptor internalization or desensitization may be responsible for terminating degranulation of the wild-type FPR. To distinguish between these possibilities, we used a partially phosphorylation-deficient mutant of the FPR that can undergo internalization, but not desensitization. Degranulation by this mutant FPR was indistinguishable from that of the DeltaST mutant, indicating that FPR phosphorylation or binding of arrestin but not internalization terminates the degranulation response.
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Affiliation(s)
- Charlotte M Vines
- Department of Cell Biology and Physiology, University of New Mexico Health Science Center, Albuquerque, NM 87131, USA
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Ahamed J, Ali H. Distinct roles of receptor phosphorylation, G protein usage, and mitogen-activated protein kinase activation on platelet activating factor-induced leukotriene C(4) generation and chemokine production. J Biol Chem 2002; 277:22685-91. [PMID: 11934880 DOI: 10.1074/jbc.m110210200] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Platelet activating factor (PAF) interacts with cell surface G protein-coupled receptors on leukocytes to induce degranulation, leukotriene C(4) (LTC(4)) generation, and chemokine CCL2 production. Using a basophilic leukemia RBL-2H3 cell line expressing wild-type PAF receptor (PAFR) and a phosphorylation-deficient mutant (mPAFR), we have previously demonstrated that receptor phosphorylation mediates desensitization of PAF-induced degranulation. Here, we sought to determine the role of receptor phosphorylation on PAF-induced LTC(4) generation and CCL2 production. We found that PAF caused a significantly enhanced LTC(4) generation in cells expressing mPAFR when compared with PAFR cells. In contrast, PAF-induced CCL2 production was greatly reduced in mPAFR cells. Pertussis toxin and U0126, which inhibit G(i) and p44/42 mitogen-activated protein kinase (ERK) activation, respectively, caused very little inhibition of PAF-induced CCL2 production (approximately 20% inhibition). In contrast, these inhibitors almost completely blocked both PAF-induced ERK phosphorylation and LTC(4) generation in PAFR cells. However, in mPAFR cells pertussis toxin only partially inhibited PAF-induced ERK phosphorylation. A Ca(2+)/calmodulin inhibitor had no effect on PAF-induced ERK phosphorylation in PAFR cells but completely blocked the response in mPAFR cells. These data demonstrate that receptor phosphorylation, which serves to desensitize PAF-induced LTC(4) generation, is required for chemokine CCL2 production. They also indicate a previously unrecognized selectivity in G protein usage and ERK activation for PAF-induced responses. Whereas PAF-induced CCL2 production is, in large part, mediated independently of G(i) activation or ERK phosphorylation, LTC(4) generation requires ERK phosphorylation, which is mediated by different G proteins depending on the phosphorylation status of the receptor.
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Affiliation(s)
- Jasimuddin Ahamed
- Department of Pathology, University of Pennsylvania School of Dental Medicine, Philadelphia, Pennsylvania 19104, USA
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Cain SA, Monk PN. The orphan receptor C5L2 has high affinity binding sites for complement fragments C5a and C5a des-Arg(74). J Biol Chem 2002; 277:7165-9. [PMID: 11773063 DOI: 10.1074/jbc.c100714200] [Citation(s) in RCA: 196] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The substantial variations in the responses of cells to the anaphylatoxin C5a and its desarginated form, C5adR(74), suggest that more than one type of cell surface receptor for these ligands might exist. However, only a single receptor for C5a and C5adR(74), CD88, has been characterized to date. Here we report that the orphan receptor C5L2/gpr77, which shares 35% amino acid identity with CD88, binds C5a with high affinity but has a 10-fold higher affinity for C5adR(74) than CD88. C5L2 also has a moderate affinity for anaphylatoxin C3a, but cross-competition studies suggest that C3a binds to a distinct site from C5a. C4a was able to displace C3a, suggesting that C5L2, like the C3a receptor, may have a low binding affinity for this anaphylatoxin. Unlike CD88 and C3a receptor, C5L2 transfected into RBL-2H3 cells does not support degranulation or increases in intracellular [Ca(2+)] and is not rapidly internalized in response to ligand binding. However, ligation of C5L2 by anaphylatoxin did potentiate the degranulation response to cross-linkage of the high affinity IgE receptor by a pertussis toxin-sensitive mechanism. These results suggest that C5L2 is an anaphylatoxin-binding protein with unique ligand binding and signaling properties.
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MESH Headings
- Amino Acid Sequence
- Anaphylatoxins
- Animals
- Antigens, CD/chemistry
- Binding Sites
- Binding, Competitive
- Cloning, Molecular
- Complement C5a/chemistry
- Complement C5a, des-Arginine/chemistry
- Humans
- Inhibitory Concentration 50
- Ligands
- Membrane Proteins
- Molecular Sequence Data
- Protein Binding
- Rats
- Receptor, Anaphylatoxin C5a
- Receptors, Chemokine/chemistry
- Receptors, Chemokine/metabolism
- Receptors, Complement/chemistry
- Recombinant Proteins/metabolism
- Sequence Homology, Amino Acid
- Signal Transduction
- Time Factors
- Transfection
- Tumor Cells, Cultured
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Affiliation(s)
- Stuart A Cain
- Department of Neurology, University of Sheffield Medical School, Beech Hill Road, Sheffield, S10 2RX, United Kingdom
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