RESUMO
Mutations in SNCA, the gene encoding α-synuclein (αSyn), cause familial Parkinson's disease (PD) and aberrant αSyn is a key pathological hallmark of idiopathic PD. This α-synucleinopathy leads to mitochondrial dysfunction, which may drive dopaminergic neurodegeneration. PARKIN and PINK1, mutated in autosomal recessive PD, regulate the preferential autophagic clearance of dysfunctional mitochondria ("mitophagy") by inducing ubiquitylation of mitochondrial proteins, a process counteracted by deubiquitylation via USP30. Here we show that loss of USP30 in Usp30 knockout mice protects against behavioral deficits and leads to increased mitophagy, decreased phospho-S129 αSyn, and attenuation of SN dopaminergic neuronal loss induced by αSyn. These observations were recapitulated with a potent, selective, brain-penetrant USP30 inhibitor, MTX115325, with good drug-like properties. These data strongly support further study of USP30 inhibition as a potential disease-modifying therapy for PD.
Assuntos
Doença de Parkinson , Tioléster Hidrolases , Animais , Camundongos , alfa-Sinucleína/genética , alfa-Sinucleína/metabolismo , Neurônios Dopaminérgicos/metabolismo , Camundongos Knockout , Mitocôndrias/metabolismo , Doença de Parkinson/metabolismo , Ubiquitina-Proteína Ligases/genética , Ubiquitina-Proteína Ligases/metabolismo , Ubiquitinação , Tioléster Hidrolases/genéticaRESUMO
B-cell lymphoma 6 (BCL6) is a zinc finger transcriptional repressor possessing a BTB-POZ (BR-C, ttk, and bab for BTB; pox virus and zinc finger for POZ) domain, which is required for homodimerization and association with corepressors. BCL6 has multiple roles in normal immunity, autoimmunity, and some types of lymphoma. Mice bearing disrupted BCL6 loci demonstrate suppressed high-affinity antibody responses to T-dependent antigens. The corepressor binding groove in the BTB-POZ domain is a potential target for small compound-mediated therapy. Several inhibitors targeting this binding groove have been described, but these compounds have limited or absent in vivo activity. Biophysical studies of a novel compound, GSK137, showed an in vitro pIC50 of 8 and a cellular pIC50 of 7.3 for blocking binding of a peptide derived from the corepressor silencing mediator for retinoid or thyroid hormone receptors to the BCL6 BTB-POZ domain. The compound has good solubility (128 µg/ml) and permeability (86 nM/s). GSK137 caused little change in cell viability or proliferation in four BCL6-expressing B-cell lymphoma lines, although there was modest dose-dependent accumulation of G1 phase cells. Pharmacokinetic studies in mice showed a profile compatible with achieving good levels of target engagement. GSK137, administered orally, suppressed immunoglobulin G responses and reduced numbers of germinal centers and germinal center B cells following immunization of mice with the hapten trinitrophenol. Overall, we report a novel small-molecule BCL6 inhibitor with in vivo activity that inhibits the T-dependent antigen immune response.
Assuntos
Proteínas Proto-Oncogênicas c-bcl-6 , Animais , Linfócitos B/metabolismo , Humanos , Camundongos , Transcrição Gênica , Dedos de ZincoRESUMO
α1-antitrypsin deficiency is characterised by the misfolding and intracellular polymerisation of mutant α1-antitrypsin protein within the endoplasmic reticulum (ER) of hepatocytes. Small molecules that bind and stabilise Z α1-antitrypsin were identified via a DNA-encoded library screen. A subsequent structure based optimisation led to a series of highly potent, selective and cellular active α1-antitrypsin correctors.
Assuntos
Desenho de Fármacos , Dobramento de Proteína , alfa 1-Antitripsina/metabolismo , Cristalização , Desenvolvimento de Medicamentos/métodos , Avaliação Pré-Clínica de Medicamentos , Retículo Endoplasmático/metabolismo , Biblioteca Gênica , Hepatócitos/metabolismo , Humanos , Modelos Moleculares , Conformação Proteica , alfa 1-Antitripsina/genéticaRESUMO
Regulation of proteolytic activity in the skin plays a pivotal role in epidermal homeostasis. This is best exemplified in Netherton syndrome, a severe genetic skin condition caused by loss-of-function mutations in the gene serine protease inhibitor Kazal-type 5 encoding lympho-epithelial Kazal-type-related inhibitor, a serine protease inhibitor that regulates kallikrein (KLK)-related peptidase 5, 7, and 14 activities. KLK5 plays a central role in stratum corneum shedding and inflammatory cell signaling, activates KLK7 and KLK14, and is therefore an optimal therapeutic target. We aimed to identify a potent and selective small-molecule inhibitor of KLK5 amenable to epidermal delivery. GSK951 was identified using a structure-based design strategy and showed a half maximal inhibitory concentration of 250 pM for KLK5 and greater than 100-fold selectivity over KLK7 and KLK14. Cocrystal structure analysis identified the critical catalytic site interactions to a surrogate for KLK5. Topical application of GSK951-containing cream inhibited KLK5 activity in TgKLK5 mouse skin, reduced transepidermal water loss, and decreased proinflammatory cytokine expression. GSK951 achieved high concentrations in healthy human epidermis following topical application in a cream formulation. Finally, KLK5 protease activity was increased in stratum corneum of patients with Netherton syndrome and significantly inhibited by GSK951. These findings unveil a KLK5-specific small-molecule inhibitor with a high therapeutic potential for patients with Netherton syndrome.
Assuntos
Anti-Inflamatórios/uso terapêutico , Compostos de Boro/uso terapêutico , Inflamação/tratamento farmacológico , Calicreínas/antagonistas & inibidores , Síndrome de Netherton/tratamento farmacológico , Pele/patologia , Administração Tópica , Animais , Modelos Animais de Doenças , Humanos , Calicreínas/genética , Camundongos , Camundongos Transgênicos , Transdução de Sinais , Pele/efeitos dos fármacos , Creme para a PeleRESUMO
Severe α1 -antitrypsin deficiency results from the Z allele (Glu342Lys) that causes the accumulation of homopolymers of mutant α1 -antitrypsin within the endoplasmic reticulum of hepatocytes in association with liver disease. We have used a DNA-encoded chemical library to undertake a high-throughput screen to identify small molecules that bind to, and stabilise Z α1 -antitrypsin. The lead compound blocks Z α1 -antitrypsin polymerisation in vitro, reduces intracellular polymerisation and increases the secretion of Z α1 -antitrypsin threefold in an iPSC model of disease. Crystallographic and biophysical analyses demonstrate that GSK716 and related molecules bind to a cryptic binding pocket, negate the local effects of the Z mutation and stabilise the bound state against progression along the polymerisation pathway. Oral dosing of transgenic mice at 100 mg/kg three times a day for 20 days increased the secretion of Z α1 -antitrypsin into the plasma by sevenfold. There was no observable clearance of hepatic inclusions with respect to controls over the same time period. This study provides proof of principle that "mutation ameliorating" small molecules can block the aberrant polymerisation that underlies Z α1 -antitrypsin deficiency.
Assuntos
Deficiência de alfa 1-Antitripsina , alfa 1-Antitripsina , Animais , Retículo Endoplasmático , Hepatócitos , Camundongos , alfa 1-Antitripsina/genéticaRESUMO
The formation of ordered Z (Glu342Lys) α1 -antitrypsin polymers in hepatocytes is central to liver disease in α1 -antitrypsin deficiency. In vitro experiments have identified an intermediate conformational state (M*) that precedes polymer formation, but this has yet to be identified in vivo. Moreover, the mechanism of polymer formation and their fate in cells have been incompletely characterised. We have used cell models of disease in conjunction with conformation-selective monoclonal antibodies and a small molecule inhibitor of polymerisation to define the dynamics of polymer formation, accumulation and secretion. Pulse-chase experiments demonstrate that Z α1 -antitrypsin accumulates as short-chain polymers that partition with soluble cellular components and are partially secreted by cells. These precede the formation of larger, insoluble polymers with a longer half-life (10.9 ± 1.7 h and 20.9 ± 7.4 h for soluble and insoluble polymers, respectively). The M* intermediate (or a by-product thereof) was identified in the cells by a conformation-specific monoclonal antibody. This was completely abrogated by treatment with the small molecule, which also blocked the formation of intracellular polymers. These data allow us to conclude that the M* conformation is central to polymerisation of Z α1 -antitrypsin in vivo; preventing its accumulation represents a tractable approach for pharmacological treatment of this condition; polymers are partially secreted; and polymers exist as two distinct populations in cells whose different dynamics have likely consequences for the aetiology of the disease.
Assuntos
Chaperonas Moleculares/genética , Conformação Proteica/efeitos dos fármacos , Deficiência de alfa 1-Antitripsina/tratamento farmacológico , alfa 1-Antitripsina/genética , Anticorpos Monoclonais/farmacologia , Hepatócitos/efeitos dos fármacos , Humanos , Chaperonas Moleculares/antagonistas & inibidores , Chaperonas Moleculares/química , Chaperonas Moleculares/ultraestrutura , Polímeros/química , Bibliotecas de Moléculas Pequenas/química , Bibliotecas de Moléculas Pequenas/farmacologia , alfa 1-Antitripsina/química , alfa 1-Antitripsina/efeitos dos fármacos , alfa 1-Antitripsina/ultraestrutura , Deficiência de alfa 1-Antitripsina/genéticaRESUMO
The connection between Netherton syndrome and overactivation of epidermal/dermal proteases, particularly Kallikrein 5 (KLK5) has been well established and it is expected that a KLK5 inhibitor would improve the dermal barrier and also reduce the pain and itch that afflict Netherton syndrome patients. One of the challenges of covalent protease inhibitors has been achieving selectivity over closely related targets. In this paper we describe the use of structural insight to design and develop a selective and highly potent reversibly covalent KLK5 inhibitor from an initial weakly binding fragment.
Assuntos
Benzamidinas/química , Calicreínas/antagonistas & inibidores , Síndrome de Netherton/tratamento farmacológico , Inibidores de Serina Proteinase/química , Sequência de Aminoácidos , Benzamidinas/farmacologia , Sítios de Ligação , Avaliação Pré-Clínica de Medicamentos , Humanos , Isomerismo , Modelos Moleculares , Estrutura Molecular , Mutação , Ligação Proteica , Inibidor de Serinopeptidase do Tipo Kazal 5/genética , Inibidores de Serina Proteinase/farmacologia , Relação Estrutura-AtividadeRESUMO
The inhibition of kallikrein 5 (KLK5) has been identified as a potential strategy for treatment of the genetic skin disorder Netherton syndrome, in which loss-of-function mutations in the SPINK5 gene lead to down-regulation of the endogenous inhibitor LEKTI-1 and profound skin-barrier defects with severe allergic manifestations. To aid in the development of a medicine for this target, an X-ray crystallographic system was developed to facilitate fragment-guided chemistry and knowledge-based drug-discovery approaches. Here, the development of a surrogate crystallographic system in place of KLK5, which proved to be challenging to crystallize, is described. The biochemical robustness of the crystallographic surrogate and the suitability of the system for the study of small nonpeptidic fragments and lead-like molecules are demonstrated.
Assuntos
Benzamidinas/química , Calicreínas/química , Inibidores de Proteases/química , Sequência de Aminoácidos , Animais , Baculoviridae/genética , Baculoviridae/metabolismo , Benzamidinas/farmacologia , Sítios de Ligação , Clonagem Molecular , Cristalografia por Raios X , Descoberta de Drogas , Expressão Gênica , Vetores Genéticos/química , Vetores Genéticos/metabolismo , Humanos , Calicreínas/antagonistas & inibidores , Calicreínas/genética , Calicreínas/metabolismo , Cinética , Modelos Moleculares , Mutação , Síndrome de Netherton/tratamento farmacológico , Síndrome de Netherton/enzimologia , Inibidores de Proteases/farmacologia , Ligação Proteica , Estrutura Secundária de Proteína , Proteínas Recombinantes/química , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismo , Células Sf9 , Spodoptera , Eletricidade Estática , Especificidade por SubstratoRESUMO
A series of potent PDGFR inhibitors has been identified. The series was optimized for duration of action in the lung. A novel kinase occupancy assay was used to directly measure target occupancy after i.t. dosing. Compound 25 shows 24 h occupancy of the PDGFR kinase domain, after a single i.t. dose and has efficacy at 0.03 mg/kg, in the rat moncrotaline model of pulmonary arterial hypertension. Examination of PK/PD data from the optimization effort has revealed in vitro:in vivo correlations which link duration of action in vivo with low permeability and high basicity and demonstrate that nonspecific binding to lung tissue increases with lipophilicity.
Assuntos
Remodelação das Vias Aéreas/efeitos dos fármacos , Hipertensão Pulmonar/tratamento farmacológico , Niacinamida/análogos & derivados , Pirazóis/química , Receptores do Fator de Crescimento Derivado de Plaquetas/antagonistas & inibidores , Remodelação Vascular/efeitos dos fármacos , Administração por Inalação , Animais , Linhagem Celular , Proliferação de Células , Hipertensão Pulmonar/patologia , Pulmão/irrigação sanguínea , Membranas Artificiais , Simulação de Acoplamento Molecular , Músculo Liso Vascular/efeitos dos fármacos , Músculo Liso Vascular/patologia , Niacinamida/síntese química , Niacinamida/química , Niacinamida/farmacologia , Permeabilidade , Proteínas Proto-Oncogênicas c-kit/antagonistas & inibidores , Proteínas Proto-Oncogênicas c-kit/química , Pirazóis/síntese química , Pirazóis/farmacologia , Ratos , Receptor alfa de Fator de Crescimento Derivado de Plaquetas/antagonistas & inibidores , Receptor alfa de Fator de Crescimento Derivado de Plaquetas/química , Receptor beta de Fator de Crescimento Derivado de Plaquetas/antagonistas & inibidores , Receptor beta de Fator de Crescimento Derivado de Plaquetas/química , Receptores do Fator de Crescimento Derivado de Plaquetas/química , Relação Estrutura-AtividadeRESUMO
Previous studies from our group have demonstrated that bone morphogenetic protein receptor-II (BMPR-II), expressed on pulmonary artery endothelial cells, imparts profound anti-inflammatory effects by regulating the release of proinflammatory cytokines and promoting barrier function by suppressing the transmigration of leukocytes into the pulmonary vessel wall. Here we demonstrate that, in mice with endothelial-specific loss of BMPR-II expression (L1Cre(+);Bmpr2(f/f)), reduction in barrier function and the resultant pulmonary hypertension observed in vivo are the result of increased leukocyte recruitment through increased CXCR1/2 signaling. Loss of endothelial expressed BMPR-II leads to elevated plasma levels of a wide range of soluble mediators important in regulating leukocyte migration and extravasation, including the CXCR1/2 ligand, KC. Treatment of L1Cre(+);Bmpr2(f/f) mice with the CXCR1/2 antagonist SCH527123 inhibits leukocyte transmigration into lung and subsequently reverses the pulmonary hypertension. Our data have uncovered a previously unrecognized regulatory function of BMPR-II, which acts to regulate the expression of CXCR2 on endothelial cells, suggesting that increased CXCR2 signaling may also be a feature of the human pathology and that CXCR1/2 pathway antagonists may represent a novel therapeutic approach for treating pulmonary hypertension because of defects in BMPR-II expression.
Assuntos
Benzamidas/uso terapêutico , Receptores de Proteínas Morfogenéticas Ósseas Tipo II/genética , Quimiotaxia de Leucócito/efeitos dos fármacos , Quimiotaxia de Leucócito/genética , Ciclobutanos/uso terapêutico , Hipertensão Pulmonar/tratamento farmacológico , Receptores de Interleucina-8A/antagonistas & inibidores , Receptores de Interleucina-8B/antagonistas & inibidores , Animais , Anti-Hipertensivos/farmacologia , Anti-Hipertensivos/uso terapêutico , Benzamidas/farmacologia , Receptores de Proteínas Morfogenéticas Ósseas Tipo II/fisiologia , Células Cultivadas , Ciclobutanos/farmacologia , Modelos Animais de Doenças , Progressão da Doença , Regulação para Baixo/genética , Células Endoteliais/efeitos dos fármacos , Células Endoteliais/metabolismo , Células Endoteliais/patologia , Deleção de Genes , Humanos , Hipertensão Pulmonar/genética , Hipertensão Pulmonar/patologia , Camundongos , Camundongos Transgênicos , Especificidade de Órgãos/efeitos dos fármacos , Especificidade de Órgãos/genética , Artéria Pulmonar/imunologia , Artéria Pulmonar/metabolismo , Artéria Pulmonar/patologiaRESUMO
Megakaryopoiesis is a complex process that involves major cellular and nuclear changes and relies on controlled coordination of cellular proliferation and differentiation. These mechanisms are orchestrated in part by transcriptional regulators. The key hematopoietic transcription factor stem cell leukemia (SCL)/TAL1 is required in early hematopoietic progenitors for specification of the megakaryocytic lineage. These early functions have, so far, prevented full investigation of its role in megakaryocyte development in loss-of-function studies. Here, we report that SCL critically controls terminal megakaryocyte maturation. In vivo deletion of Scl specifically in the megakaryocytic lineage affects all key attributes of megakaryocyte progenitors (MkPs), namely, proliferation, ploidization, cytoplasmic maturation, and platelet release. Genome-wide expression analysis reveals increased expression of the cell-cycle regulator p21 in Scl-deleted MkPs. Importantly, p21 knockdown-mediated rescue of Scl-mutant MkPs shows full restoration of cell-cycle progression and partial rescue of the nuclear and cytoplasmic maturation defects. Therefore, SCL-mediated transcriptional control of p21 is essential for terminal maturation of MkPs. Our study provides a mechanistic link between a major hematopoietic transcriptional regulator, cell-cycle progression, and megakaryocytic differentiation.
Assuntos
Fatores de Transcrição Hélice-Alça-Hélice Básicos/metabolismo , Inibidor de Quinase Dependente de Ciclina p21/metabolismo , Células-Tronco Hematopoéticas/fisiologia , Megacariócitos/fisiologia , Proteínas Proto-Oncogênicas/metabolismo , Trombocitopenia/fisiopatologia , Trombopoese/fisiologia , Animais , Fatores de Transcrição Hélice-Alça-Hélice Básicos/genética , Células da Medula Óssea/fisiologia , Células da Medula Óssea/ultraestrutura , Divisão Celular/fisiologia , Linhagem da Célula/fisiologia , Células Cultivadas , Inibidor de Quinase Dependente de Ciclina p21/genética , Citoplasma/fisiologia , Técnicas de Silenciamento de Genes , Células-Tronco Hematopoéticas/ultraestrutura , Megacariócitos/ultraestrutura , Camundongos , Microscopia Eletrônica , Poliploidia , Proteínas Proto-Oncogênicas/genética , Proteína 1 de Leucemia Linfocítica Aguda de Células T , Trombocitopenia/patologiaRESUMO
BACKGROUND: Increasing evidence suggests that individual isoforms of protein kinase C (PKC) play distinct roles in regulating platelet activation. METHODOLOGY/PRINCIPAL FINDINGS: In this study, we focus on the role of two novel PKC isoforms, PKCdelta and PKCepsilon, in both mouse and human platelets. PKCdelta is robustly expressed in human platelets and undergoes transient tyrosine phosphorylation upon stimulation by thrombin or the collagen receptor, GPVI, which becomes sustained in the presence of the pan-PKC inhibitor, Ro 31-8220. In mouse platelets, however, PKCdelta undergoes sustained tyrosine phosphorylation upon activation. In contrast the related isoform, PKCepsilon, is expressed at high levels in mouse but not human platelets. There is a marked inhibition in aggregation and dense granule secretion to low concentrations of GPVI agonists in mouse platelets lacking PKCepsilon in contrast to a minor inhibition in response to G protein-coupled receptor agonists. This reduction is mediated by inhibition of tyrosine phosphorylation of the FcRgamma-chain and downstream proteins, an effect also observed in wild-type mouse platelets in the presence of a PKC inhibitor. CONCLUSIONS: These results demonstrate a reciprocal relationship in levels of the novel PKC isoforms delta and epsilon in human and mouse platelets and a selective role for PKCepsilon in signalling through GPVI.
Assuntos
Plaquetas/enzimologia , Ativação Plaquetária , Proteína Quinase C-delta/fisiologia , Proteína Quinase C-épsilon/fisiologia , Animais , Humanos , Camundongos , Fosforilação , Glicoproteínas da Membrana de Plaquetas , Isoformas de Proteínas/fisiologia , Proteína Quinase C , Receptores de Colágeno , Transdução de Sinais , TrombinaRESUMO
Platelets play an essential role in wound healing by forming thrombi that plug holes in the walls of damaged blood vessels. To achieve this, platelets express a diverse array of cell surface receptors and signaling proteins that induce rapid platelet activation. In this study we show that two platelet glycoprotein receptors that signal via an immunoreceptor tyrosine-based activation motif (ITAM) or an ITAM-like domain, namely the collagen receptor complex glycoprotein VI (GPVI)-FcR gamma-chain and the C-type lectin-like receptor 2 (CLEC-2), respectively, support constitutive (i.e. agonist-independent) signaling in a cell line model using a nuclear factor of activated T-cells (NFAT) transcriptional reporter assay that can detect low level activation of phospholipase Cgamma (PLCgamma). Constitutive and agonist signaling by both receptors is dependent on Src and Syk family kinases, and is inhibited by G6b-B, a platelet immunoglobulin receptor that has two immunoreceptor tyrosine-based inhibitory motifs in its cytosolic tail. Mutation of the conserved tyrosines in the two immunoreceptor tyrosine-based inhibitory motifs prevents the inhibitory action of G6b-B. Interestingly, the inhibitory activity of G6b-B is independent of the Src homology 2 (SH2)-domain containing tyrosine phosphatases, SHP1 and SHP2, and the inositol 5'-phosphatase, SHIP. Constitutive signaling via Src and Syk tyrosine kinases is observed in platelets and is associated with tyrosine phosphorylation of GPVI-FcR gamma-chain and CLEC-2. We speculate that inhibition of constitutive signaling through Src and Syk tyrosine kinases by G6b-B may help to prevent unwanted platelet activation.
Assuntos
Plaquetas/metabolismo , Lectinas Tipo C/metabolismo , Glicoproteínas de Membrana/metabolismo , Ativação Plaquetária/fisiologia , Glicoproteínas da Membrana de Plaquetas/metabolismo , Receptores Imunológicos/metabolismo , Transdução de Sinais/fisiologia , Motivos de Aminoácidos/fisiologia , Animais , Linhagem Celular , Galinhas , Humanos , Peptídeos e Proteínas de Sinalização Intracelular/genética , Peptídeos e Proteínas de Sinalização Intracelular/metabolismo , Lectinas Tipo C/genética , Glicoproteínas de Membrana/genética , Fatores de Transcrição NFATC/genética , Fatores de Transcrição NFATC/metabolismo , Fosfolipase C gama/genética , Fosfolipase C gama/metabolismo , Glicoproteínas da Membrana de Plaquetas/genética , Isoformas de Proteínas/genética , Isoformas de Proteínas/metabolismo , Estrutura Terciária de Proteína/fisiologia , Proteínas Tirosina Quinases/genética , Proteínas Tirosina Quinases/metabolismo , Receptores de IgG/genética , Receptores de IgG/metabolismo , Receptores Imunológicos/genética , Quinase Syk , Quinases da Família src/genética , Quinases da Família src/metabolismoRESUMO
We have recently shown that the C-type lectin-like receptor, CLEC-2, is expressed on platelets and that it mediates powerful platelet aggregation by the snake venom toxin rhodocytin. In addition, we have provided indirect evidence for an endogenous ligand for CLEC-2 in renal cells expressing HIV-1. This putative ligand facilitates transmission of HIV through its incorporation into the viral envelope and binding to CLEC-2 on platelets. The aim of the present study was to identify the ligand on these cells which binds to CLEC-2 on platelets. Recombinant CLEC-2 exhibits specific binding to HEK-293T (human embryonic kidney) cells in which the HIV can be grown. Furthermore, HEK-293T cells activate both platelets and CLEC-2-transfected DT-40 B-cells. The transmembrane protein podoplanin was identified on HEK-293T cells and was demonstrated to mediate both binding of HEK-293T cells to CLEC-2 and HEK-293T cell activation of CLEC-2-transfected DT-40 B-cells. Podoplanin is expressed on renal cells (podocytes). Furthermore, a direct interaction between CLEC-2 and podoplanin was confirmed using surface plasmon resonance and was shown to be independent of glycosylation of CLEC-2. The interaction has an affinity of 24.5+/-3.7 microM. The present study identifies podoplanin as a ligand for CLEC-2 on renal cells.
Assuntos
Rim/citologia , Lectinas Tipo C/metabolismo , Glicoproteínas de Membrana/metabolismo , Linhagem Celular , Clonagem Molecular , Glicosilação , Humanos , Rim/química , Ligantes , Glicoproteínas de Membrana/análise , Podócitos/química , Ligação Proteica , Ressonância de Plasmônio de Superfície , TransfecçãoRESUMO
The two lectin receptors, CLEC-2 and Dectin-1, have been shown to signal through a Syk-dependent pathway, despite the presence of only a single YXXL in their cytosolic tails. In this study, we show that stimulation of CLEC-2 in platelets and in two mutant cell lines is dependent on the YXXL motif and on proteins that participate in signaling by immunoreceptor tyrosine-based activation motif receptors, including Src, Syk, and Tec family kinases, and on phospholipase Cgamma. Strikingly, mutation of either Src homology (SH) 2 domain of Syk blocks signaling by CLEC-2 despite the fact that it has only a single YXXL motif. Furthermore, signaling by CLEC-2 is only partially dependent on the BLNK/SLP-76 family of adapter proteins in contrast to that of immunoreceptor tyrosine-based activation motif receptors. The C-type lectin receptor, Dectin-1, which contains a YXXL motif preceded by the same four amino acids as for CLEC-2 (DEDG), signals like CLEC-2 and also requires the two SH2 domains of Syk and is only partially dependent on the BLNK/SLP-76 family of adapters. In marked contrast, the C-type lectin receptor, DC-SIGN, which has a distinct series of amino acids preceding a single YXXL, signals independent of this motif. A mutational analysis of the DEDG sequence of CLEC-2 revealed that the glycine residue directly upstream of the YXXL tyrosine is important for CLEC-2 signaling. These results demonstrate that CLEC-2 and Dectin-1 signal through a single YXXL motif that requires the tandem SH2 domains of Syk but is only partially dependent on the SLP-76/BLNK family of adapters.
Assuntos
Plaquetas/metabolismo , Moléculas de Adesão Celular/metabolismo , Lectinas Tipo C/metabolismo , Glicoproteínas de Membrana/metabolismo , Proteínas de Membrana/metabolismo , Proteínas do Tecido Nervoso/metabolismo , Receptores de Superfície Celular/metabolismo , Transdução de Sinais/fisiologia , Proteínas Adaptadoras de Transdução de Sinal/metabolismo , Motivos de Aminoácidos/genética , Animais , Moléculas de Adesão Celular/genética , Linhagem Celular , Galinhas , Humanos , Peptídeos e Proteínas de Sinalização Intracelular , Lectinas Tipo C/genética , Glicoproteínas de Membrana/genética , Proteínas de Membrana/genética , Mutação , Proteínas do Tecido Nervoso/genética , Proteínas Tirosina Quinases/metabolismo , Receptores de Superfície Celular/genética , Quinase Syk , Domínios de Homologia de src/genética , Quinases da Família src/metabolismoRESUMO
Vav proteins belong to the family of guanine-nucleotide-exchange factors for the Rho/Rac family of small G-proteins. In addition, they serve as important adapter proteins for the activation of PLCgamma (phospholipase Cgamma) isoforms by ITAM (immunoreceptor tyrosine-based activation motif) receptors, including the platelet collagen receptor GPVI (glycoprotein VI). Vav proteins are also regulated downstream of integrins, including the major platelet integrin alphaIIbbeta3, which has recently been shown to regulate PLCgamma2. In the present study, we have investigated the role of Vav family proteins in filopodia and lamellipodia formation on fibrinogen using platelets deficient in Vav1 and Vav3. Wild-type mouse platelets undergo a limited degree of spreading on fibrinogen, characterized by the formation of numerous filopodia and limited lamellipodia structures. Platelets deficient in Vav1 and Vav3 exhibit reduced filopodia and lamellipodia formation during spreading on fibrinogen. This is accompanied by reduced alphaIIbbeta3-mediated PLCgamma2 tyrosine phosphorylation and reduced Ca(2+) mobilization. In contrast, the G-protein agonist thrombin stimulates full spreading of control and Vav1/3-deficient platelets. Consistent with this, stimulation of F-actin (filamentous actin) formation and Rac activation by thrombin is not altered in Vav-deficient cells. These results demonstrate that Vav1 and Vav3 are required for optimal spreading and regulation of PLCgamma2 by integrin alphaIIbbeta3, but that their requirement is by-passed upon G-protein receptor activation.
Assuntos
Fatores de Troca do Nucleotídeo Guanina/metabolismo , Fosfolipase C gama/metabolismo , Complexo Glicoproteico GPIIb-IIIa de Plaquetas/metabolismo , Proteínas Proto-Oncogênicas c-vav/metabolismo , Animais , Plaquetas/metabolismo , Fibrinogênio/metabolismo , Deleção de Genes , Regulação da Expressão Gênica , Fatores de Troca do Nucleotídeo Guanina/genética , Camundongos , Proteínas Proto-Oncogênicas c-vav/genéticaRESUMO
Platelets can engulf human immunodeficiency virus type 1 (HIV-1), and a significant amount of HIV-1 in the blood of infected individuals is associated with these cells. However, it is unclear how platelets capture HIV-1 and whether platelet-associated virus remains infectious. DC-SIGN and other lectins contribute to capture of HIV-1 by dendritic cells (DCs) and facilitate HIV-1 spread in DC/T-cell cocultures. Here, we show that platelets express both the C-type lectin-like receptor 2 (CLEC-2) and low levels of DC-SIGN. CLEC-2 bound to HIV-1, irrespective of the presence of the viral envelope protein, and facilitated HIV-1 capture by platelets. However, a substantial fraction of the HIV-1 binding activity of platelets was dependent on DC-SIGN. A combination of DC-SIGN and CLEC-2 inhibitors strongly reduced HIV-1 association with platelets, indicating that these lectins are required for efficient HIV-1 binding to platelets. Captured HIV-1 was maintained in an infectious state over several days, suggesting that HIV-1 can escape degradation by platelets and might use these cells to promote its spread. Our results identify CLEC-2 as a novel HIV-1 attachment factor and provide evidence that platelets capture and transfer infectious HIV-1 via DC-SIGN and CLEC-2, thereby possibly facilitating HIV-1 dissemination in infected patients.
Assuntos
Plaquetas/virologia , Moléculas de Adesão Celular/fisiologia , HIV-1/metabolismo , Lectinas Tipo C/fisiologia , Glicoproteínas de Membrana/fisiologia , Receptores de Superfície Celular/fisiologia , Animais , Linhagem Celular , Linhagem Celular Tumoral , Chlorocebus aethiops , Células Dendríticas/virologia , Infecções por HIV/sangue , Humanos , Células Jurkat , Leucócitos Mononucleares/virologia , Megacariócitos/virologiaRESUMO
The snake venom rhodocytin has been reported to bind to integrin alpha2beta1 and glycoprotein (GP) Ibalpha on platelets, but it is also able to induce activation independent of the 2 receptors and of GPVI. Using rhodocytin affinity chromatography, we have identified a novel C-type lectin receptor, CLEC-2, in platelets that confers signaling responses to rhodocytin when expressed in a cell line. CLEC-2 has a single tyrosine residue in a YXXL motif in its cytosolic tail, which undergoes tyrosine phosphorylation upon platelet activation by rhodocytin or an antibody to CLEC-2, but not to collagen, thrombin receptor agonist peptide (TRAP), or convulxin. Tyrosine phosphorylation of CLEC-2 and other signaling proteins by rhodocytin is inhibited by the Src family kinase inhibitor PP2. Further, activation of murine platelets by rhodocytin is abolished in the absence of Syk and PLCgamma2, and partially reduced in the absence of LAT, SLP-76, and Vav1/Vav3. These findings define a novel signaling pathway in platelets whereby activation of CLEC-2 by rhodocytin leads to tyrosine phosphorylation of its cytosolic tail, binding of Syk and initiation of downstream tyrosine phosphorylation events, and activation of PLCgamma2. CLEC-2 is the first C-type lectin receptor to be found on platelets which signals through this novel pathway.
Assuntos
Precursores Enzimáticos/metabolismo , Lectinas Tipo C/metabolismo , Ativação Plaquetária , Proteínas Tirosina Quinases/metabolismo , Receptores Imunológicos/metabolismo , Transdução de Sinais , Venenos de Víboras/metabolismo , Proteínas Adaptadoras de Transdução de Sinal/genética , Proteínas Adaptadoras de Transdução de Sinal/fisiologia , Animais , Anticorpos Monoclonais/imunologia , Western Blotting , Colágeno/metabolismo , Venenos de Crotalídeos/farmacologia , Citosol/metabolismo , Precursores Enzimáticos/genética , Citometria de Fluxo , Fatores de Troca do Nucleotídeo Guanina/genética , Fatores de Troca do Nucleotídeo Guanina/fisiologia , Humanos , Imunoprecipitação , Peptídeos e Proteínas de Sinalização Intracelular , Lectinas Tipo C/imunologia , Proteínas de Membrana/genética , Proteínas de Membrana/fisiologia , Camundongos , Camundongos Knockout , Fragmentos de Peptídeos , Fosfolipase C gama/genética , Fosfolipase C gama/fisiologia , Fosfoproteínas/genética , Fosfoproteínas/fisiologia , Fosforilação , Agregação Plaquetária , Proteínas Tirosina Quinases/genética , Proteínas Proto-Oncogênicas c-vav/genética , Proteínas Proto-Oncogênicas c-vav/fisiologia , Pirimidinas/farmacologia , Receptores dos Hormônios Gastrointestinais , Receptores Imunológicos/imunologia , Receptores de Neuropeptídeo Y , Receptores de Trombina , Quinase Syk , Tirosina/metabolismoRESUMO
The role of Rac family proteins in platelet spreading on matrix proteins under static and flow conditions has been investigated by using Rac-deficient platelets. Murine platelets form filopodia and undergo limited spreading on fibrinogen independent of Rac1 and Rac2. In the presence of thrombin, marked lamellipodia formation is observed on fibrinogen, which is abrogated in the absence of Rac1. However, Rac1 is not required for thrombin-induced aggregation or elevation of F-actin levels. Formation of lamellipodia on collagen and laminin is also Rac1-dependent. Analysis of platelet adhesion dynamics on collagen under flow conditions in vitro revealed that Rac1 is required for platelet aggregate stability at arterial rates of shear, as evidenced by a dramatic increase in platelet embolization. Furthermore, studies employing intravital microscopy demonstrated that Rac1 plays a critical role in the development of stable thrombi at sites of vascular injury in vivo. Thus, our data demonstrated that Rac1 is essential for lamellipodia formation in platelets and indicated that Rac1 is required for aggregate integrity leading to thrombus formation under physiologically relevant levels of shear both in vitro and in vivo.