Arrestin-2 Differentially Regulates PAR4 and P2Y12 Receptor Signaling in Platelets

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 110-110 ◽  
Author(s):  
Dongjun Li ◽  
Donna Woulfe

Abstract Arrestins play important roles in the function of G Protein-Coupled Receptors (GPCRs) in many cells, but their roles in platelets remain uncharacterized. While the classical role of arrestins is considered to be the internalization and desensitization of GPCRs, more recent studies suggest that arrestins can serve as molecular scaffolds to recruit phosphatidyl inositol-3 kinases (PI3Ks) to GPCRs and promote PI3K-dependent signaling. Due to the multifunctional role of arrestins, we sought to determine whether arrestins regulate Akt activation in platelets and thrombosis in living animals. Co-immunoprecipitation experiments indicate that arrestin-2 associates with PAR4 in thrombin-treated platelets and P2Y12 in ADP-treated platelets, but neither receptor in resting cells. Interestingly, association of arrestin-2 with PAR4 was also stimulated by ADP and PAR4-induced association of arrestin with PAR4 was inhibited by P2Y12 antagonists or apyrase. To determine the functional role of arrestin-2 in platelets, ADP- and thrombin receptor-stimulated Akt phosphorylation was compared in platelets from arrestin-2 knock-out versus WT mice. Akt phosphorylation stimulated by 0.8 mM AYPGKF PAR4 agonist peptide was reduced by an average of 77% in arrestin-2 knock-out platelets compared to WT controls (significantly different, p=0.007, n=3 in each group), but ADP-stimulated Akt phosphorylation was unaffected (p=.38, n=3 each). PAR4-stimulated fibrinogen binding was also reduced in arrestin2−/− platelets (by 58.5% in 1 mM AYPGKF-stimulated platelets compared to WT controls), whereas ADP-stimulated fibrinogen binding was not. Finally, arrestin2 knock-out mice were less sensitive to ferric chloride-induced thrombosis than WT mice: 55% of WT mice (n-=9) formed occlusive thrombi after 2min15sec exposure of the carotid artery to 10% ferric chloride, whereas only 11% of WT mice (n=9) formed occlusive thrombi under the same conditions. In conclusion, arrestin-2 associates with both PAR4 and P2Y12 receptors, but differentially regulates their signaling to Akt and fibrinogen binding and appears to play a net positive role in regulating thrombosis in vivo.

Bone Reports ◽  
2021 ◽  
Vol 14 ◽  
pp. 101054
Author(s):  
Laura Leoni ◽  
Valentina Daponte ◽  
Francesca Tonelli ◽  
Roberta Gioia ◽  
Silvia Cotti ◽  
...  
Keyword(s):  

Cancers ◽  
2021 ◽  
Vol 13 (6) ◽  
pp. 1330
Author(s):  
Filipe Pinto ◽  
Liliana Santos-Ferreira ◽  
Marta T. Pinto ◽  
Catarina Gomes ◽  
Celso A. Reis

Biglycan (BGN gene), an extracellular proteoglycan, has been described to be associated with cancer aggressiveness. The purpose of this study was to clarify the clinical value of biglycan as a biomarker in multiple independent GC cohorts and determine the in vitro and in vivo role of biglycan in GC malignant features. We found that BGN is commonly over-expressed in all analyzed cohorts, being associated with disease relapse and poor prognosis in patients with advanced stages of disease. In vitro and in vivo experiments demonstrated that biglycan knock-out GC cells display major phenotypic changes with a lower cell survival, migration, and angiogenic potential when compared with biglycan expressing cells. Biglycan KO GC cells present increased levels of PARP1 and caspase-3 cleavage and a decreased expression of mesenchymal markers. Importantly, biglycan deficient GC cells that were supplemented with exogenous biglycan were able to restore biological features, such as survival, clonogenic and migratory capacities. Our in vitro and in vivo findings were validated in human GC samples, where BGN expression was associated with several oncogenic gene signatures that were associated with apoptosis, cell migration, invasion, and angiogenesis. This study provided new insights on biglycan role in GC that should be taken in consideration as a key cellular regulator with major impact in tumor progression and patients’ clinical outcome.


Blood ◽  
2010 ◽  
Vol 115 (23) ◽  
pp. 4862-4869 ◽  
Author(s):  
Mia Golder ◽  
Cynthia M. Pruss ◽  
Carol Hegadorn ◽  
Jeffrey Mewburn ◽  
Kimberly Laverty ◽  
...  

Abstract Type 2B von Willebrand disease (2B VWD) results from von Willebrand factor (VWF) A1 mutations that enhance VWF-GPIbα binding. These “gain of function” mutations lead to an increased affinity of the mutant VWF for platelets and the binding of mutant high-molecular-weight VWF multimers to platelets in vivo, resulting in an increase in clearance of both platelets and VWF. Three common 2B VWD mutations (R1306W, V1316M, and R1341Q) were independently introduced into the mouse Vwf cDNA sequence and the expression vectors delivered to 8- to 10-week-old C57Bl6 VWF−/− mice, using hydrodynamic injection. The resultant phenotype was examined, and a ferric chloride–induced injury model was used to examine the thrombogenic effect of the 2B VWD variants in mice. Reconstitution of only the plasma component of VWF resulted in the generation of the 2B VWD phenotype in mice. Variable thrombocytopenia was observed in mice expressing 2B VWF, mimicking the severity seen in 2B VWD patients: mice expressing the V1316M mutation showed the most severe thrombocytopenia. Ferric chloride–induced injury to cremaster arterioles showed a marked reduction in thrombus development and platelet adhesion in the presence of circulating 2B VWF. These defects were only partially rescued by normal platelet transfusions, thus emphasizing the key role of the abnormal plasma VWF environment in 2B VWD.


Biomolecules ◽  
2020 ◽  
Vol 10 (5) ◽  
pp. 729
Author(s):  
Bahar Khonsari ◽  
Roland Klassen

Pus1-dependent pseudouridylation occurs in many tRNAs and at multiple positions, yet the functional impact of this modification is incompletely understood. We analyzed the consequences of PUS1 deletion on the essential decoding of CAG (Gln) codons by tRNAGlnCUG in yeast. Synthetic lethality was observed upon combining the modification defect with destabilized variants of tRNAGlnCUG, pointing to a severe CAG-decoding defect of the hypomodified tRNA. In addition, we demonstrated that misreading of UAG stop codons by a tRNAGlnCUG variant is positively affected by Pus1. Genetic approaches further indicated that mildly elevated temperature decreases the decoding efficiency of CAG and UAG via destabilized tRNAGlnCAG variants. We also determined the misreading of CGC (Arg) codons by tRNAHisGUG, where the CGC decoder tRNAArgICG contains Pus1-dependent pseudouridine, but not the mistranslating tRNAHis. We found that the absence of Pus1 increased CGC misreading by tRNAHis, demonstrating a positive role of the modification in the competition against non-synonymous near-cognate tRNA. Part of the in vivo decoding defects and phenotypes in pus1 mutants and strains carrying destabilized tRNAGlnCAG were suppressible by additional deletion of the rapid tRNA decay (RTD)-relevant MET22, suggesting the involvement of RTD-mediated tRNA destabilization.


Blood ◽  
2006 ◽  
Vol 108 (11) ◽  
pp. 1525-1525
Author(s):  
Dongjun Li ◽  
Donna S. Woulfe

Abstract Arrestins have been shown to play important roles in G Protein-Coupled Receptor (GPCR) function in many cells, but their roles in platelets remain uncharacterized. While the classical role of arrestins is considered to be the internalization and desensitization of GPCRs, more recent studies suggest that arrestins can serve as scaffolds to recruit phosphatidyl inositol-3 kinases (PI3K)s to Gq-coupled receptors and promote PI3K-dependent signaling. Thrombin stimulates the PI3K-dependent activation of Akt in platelets in a Gq-dependent manner. Therefore, we sought to determine whether arrestins are involved in the PI3K-dependent activation of Akt in platelets. Comparative immunoblots show that of the two non-visual mammalian arrestins, only one, arrestin-2 (β-arrestin-1), is expressed in human and mouse platelets. Immunoprecipitation of arrestin-2 or p85-PI3K from platelet lysates demonstrated that arrestin-2 associates with the p85 subunit of PI3Ka/b in thrombin or ADP-stimulated platelets, but not resting cells. The association can be inhibited by inhibitors of the P2Y12 receptor for ADP, but not by P2Y1 inhibitors. p85-arrestin association is also blocked by inhibitors of src family kinases, as is Akt phosphorylation. To determine whether src family members were part of the p85-arrestin complexes, immunoblots were re-probed with antibodies to src, lyn and fyn. The results show that Lyn is incorporated into thrombin-stimulated arrestin complexes in a P2Y12-dependent manner. To determine whether arrestin-2 is important for Akt phosphorylation in platelets, megakaryocytes differentiated in culture from mouse embryonic stem cells were used as models of platelet signaling, since these cells are amenable to genetic manipulation. Arrestin-2 was inhibited in the cultured megakaryocytes using a siRNA approach, then cells were stimulated with thrombin and Akt phosphorylation was assessed by immunoblotting. Arrestin-2 expression in the cultured megakaryocytes treated with arrestin-2 specific siRNA was suppressed by an average of 53% compared to cells treated with scrambled siRNA, while thrombin-stimulated Akt phosphorylation was suppressed by 98% compared to scrambled siRNA-treated control cells (n=3 experiments, difference is significant, p=.01, unpaired student’s t-test). In conclusion, the results show that arrestin-2, lyn and PI3Kform a tri-molecular complex following stimulation of platelets with ADP or thrombin. Formation of arrestin complexes at activated receptor sites is important for the localized recruitment and src-dependent activation of p85-PI3K, thus promoting activation of Akt by G protein-coupled receptors.


2021 ◽  
Vol 12 ◽  
Author(s):  
Saul Lema A ◽  
Marina Klemenčič ◽  
Franziska Völlmy ◽  
Maarten Altelaar ◽  
Christiane Funk

Caspases are proteases, best known for their involvement in the execution of apoptosis—a subtype of programmed cell death, which occurs only in animals. These proteases are composed of two structural building blocks: a proteolytically active p20 domain and a regulatory p10 domain. Although structural homologs appear in representatives of all other organisms, their functional homology, i.e., cell death depending on their proteolytical activity, is still much disputed. Additionally, pseudo-caspases and pseudo-metacaspases, in which the catalytic histidine-cysteine dyad is substituted with non-proteolytic amino acid residues, were shown to be involved in cell death programs. Here, we present the involvement of a pseudo-orthocaspase (SyOC), a prokaryotic caspase-homolog lacking the p10 domain, in oxidative stress in the model cyanobacterium Synechocystis sp. PCC 6803. To study the in vivo impact of this pseudo-protease during oxidative stress its gene expression during exposure to H2O2 was monitored by RT-qPCR. Furthermore, a knock-out mutant lacking the pseudo-orthocaspase gene was designed, and its survival and growth rates were compared to wild type cells as well as its proteome. Deletion of SyOC led to cells with a higher tolerance toward oxidative stress, suggesting that this protein may be involved in a pro-death pathway.


2021 ◽  
Vol 12 ◽  
Author(s):  
Mohammad Abdullah ◽  
Tomohisa Nakamura ◽  
Taslima Ferdous ◽  
Yuan Gao ◽  
Yuxin Chen ◽  
...  

Exosomes are vesicles secreted by various kinds of cells, and they are rich in cholesterol, sphingomyelin (SM), phosphatidylcholine, and phosphatidylserine. Although cellular sphingolipid-mediated exosome release has been reported, the involvement of other lipid components of cell membranes in the regulation of exosome release is poorly understood. Here, we show that the level of exosome release into conditioned media is significantly reduced in cultured astrocytes prepared from apolipoprotein E (ApoE) knock-out mice when compared to those prepared from wild-type (WT) mice. The reduced level of exosome release was accompanied by elevated levels of cellular cholesterol. The addition of cholesterol to WT astrocytes significantly increased the cellular cholesterol levels and reduced exosome release. PI3K/Akt phosphorylation was enhanced in ApoE-deficient and cholesterol-treated WT astrocytes. In contrast, the depletion of cholesterol in ApoE-deficient astrocytes due to treatment with β-cyclodextrin recovered the exosome release level to a level similar to that in WT astrocytes. In addition, the reduced levels of exosome release due to the addition of cholesterol recovered to the control levels after treatment with a PI3K inhibitor (LY294002). The cholesterol-dependent regulation of exosome release was also confirmed by in vivo experiments; that is, exosome levels were significantly reduced in the CSF and blood serum of WT mice that were fed a high-fat diet and had increased cholesterol levels when compared to those in WT mice that were fed a normal diet. These results suggest that exosome release is regulated by cellular cholesterol via stimulation of the PI3K/Akt signal pathway.


2020 ◽  
Vol 4 (Supplement_1) ◽  
Author(s):  
Isabelle Beau ◽  
Charlotte Sonigo ◽  
Nadine Binart

Abstract Chemotherapy-induced ovarian failure and infertility is an important concern in female cancer patients. The follicular ovarian reserve is established early in life then keeps declining regularly along reproductive life. This reserve is constituted by dormant primordial follicles (PMF) which are necessary to maintain female reproductive function. There is a continuous repression of PMF activation in early growing follicle through the balance between factors activating the initiation of follicular growth, mainly actors of the phosphatidyl-inositol-3-kinase (PI3K) signaling pathway, and inhibiting factors such as Anti-Müllerian Hormone (AMH). Any alteration of this equilibrium may induce early follicle depletion and subsequent infertility. Cyclophosphamide (Cy) one of the alkylating agents commonly used for treating breast cancer is able to trigger PMF activation further leading to premature ovarian insufficiency. Preventing chemotherapy-induced ovarian dysfunction might represent an option for preserving optimal chances of natural or medically assisted conceptions after healing. We showed in a model of Cy-treated pubertal mice, that AMH administration was able to restrain PMF depletion by counting the total PMF number within mouse ovaries. Moreover, the PI3K signaling pathway was evaluated following Cy administration with and without AMH injection. We showed that AMH decreased the phosphorylation of FOXO3A, a transcription factor of PMF activation and induced its nuclear translocation. Altogether, the results support a protective role of AMH against Cy-induced follicular loss. To better understand AMH action in the ovary, we investigated the molecular mechanism to explain the protective effect of this hormone on the PMF pool. It has been reported that autophagy, a lysosomal degradative ubiquitous process implicated in cellular homeostasis, was involved in both ovarian follicular death and survival mostly by PI3K pathway (Gawriluk et al. Reproduction 2011 141, 759–765). We show in mice that Cy inhibits autophagy in the ovary while AMH induces autophagy. In vivo analysis of autophagic flux is currently in progress to dissect this process more finely. Interestingly, FOXO3A was shown to be related to autophagy activation. To investigate the role of FOXO3A in AMH-induced autophagy further, we analyzed mRNA and protein expression of autophagy-related genes controlled by FOXO3A, including BECLIN-1, ATG12, ULK1, BNIP3, GABARAP, and LC3B. These findings establish a close relationship between AMH and autophagy to protect PMF stockpile and to limit follicular depletion induced by Cy.


2007 ◽  
Vol 293 (2) ◽  
pp. H1154-H1163 ◽  
Author(s):  
Jorge F. Giani ◽  
Mariela M. Gironacci ◽  
Marina C. Muñoz ◽  
Clara Peña ◽  
Daniel Turyn ◽  
...  

Angiotensin (ANG) II exerts a negative modulation on insulin signal transduction that might be involved in the pathogenesis of hypertension and insulin resistance. ANG-(1–7), an endogenous heptapeptide hormone formed by cleavage of ANG I and ANG II, counteracts many actions of ANG II. In the current study, we have explored the role of ANG-(1–7) in the signaling crosstalk that exists between ANG II and insulin. We demonstrated that ANG-(1–7) stimulates the phosphorylation of Janus kinase 2 (JAK2) and insulin receptor substrate (IRS)-1 in rat heart in vivo. This stimulating effect was blocked by administration of the selective ANG type 1 (AT1) receptor blocker losartan. In contrast to ANG II, ANG-(1–7) stimulated cardiac Akt phosphorylation, and this stimulation was blunted in presence of the receptor Mas antagonist A-779 or the phosphatidylinositol 3-kinase (PI3K) inhibitor wortmannin. The specific JAK2 inhibitor AG-490 blocked ANG-(1–7)-induced JAK2 and IRS-1 phosphorylation but had no effect on ANG-(1–7)-induced phosphorylation of Akt, indicating that activation of cardiac Akt by ANG-(1–7) appears not to involve the recruitment of JAK2 but proceeds through the receptor Mas and involves PI3K. Acute in vivo insulin-induced cardiac Akt phosphorylation was inhibited by ANG II. Interestingly, coadministration of insulin with an equimolar mixture of ANG II and ANG-(1–7) reverted this inhibitory effect. On the basis of our present results, we postulate that ANG-(1–7) could be a positive physiological contributor to the actions of insulin in heart and that the balance between ANG II and ANG-(1–7) could be relevant for the association among insulin resistance, hypertension, and cardiovascular disease.


Blood ◽  
2013 ◽  
Vol 122 (21) ◽  
pp. 3512-3512
Author(s):  
Minh Hua ◽  
Leonardo Pasalic ◽  
Robert Lindeman ◽  
Philip Hogg ◽  
Vivien M Chen

Abstract Strong agonist stimulation generates a platelet subpopulation characterized by phosphatidylserine (PS) exposure, loss of mitochondrial membrane potential and high fibrinogen retention. This population is proposed to be procoagulant, dependent on formation of the mitochondrial permeability transition pore (mPTP) with a distinct role from activated aggregratory platelets. These platelets have features of necrosis. The functional relevance of necrotic platelets in vivo is unknown due to lack of a suitable marker for these platelets. We show that a novel small molecule cellular necrosis marker, GSAO1, labels a procoagulant platelet subpopulation with features of necrosis and use it to explore the functional role of these platelets. We demonstrated using flow cytometry analysis of washed human platelets that fluorescently tagged GSAO labels a subpopulation of P-selectin positive platelets after thrombin and collagen stimulation with features of necrosis: high annexin V binding, calcein loss and dependence on exogenous calcium. This population is not dependent on the intrinsic apoptosis pathway as there was no change with pancaspase inhibition using ZVADFMK prior to dual agonist stimulation (p=0.567, n=5). In contrast, inhibition of mPTP formation through cyclophilin-D inhibition with cyclosporine A significantly inhibited GSAO+ve platelet generation (p<0.001, n=5), confirming dependence on the mitochondrial necrosis pathway. Mass spectrometry analysis of biotin-GSAO labelled proteins from platelets after streptavidin pull down identified thromboxane A synthase (TBXAS-1) as the major binding ligand after dual stimulation. Binding to TBXAS-1 was abrogated by dithiol alkylation, showing the mechanism of retention of GSAO in necrotic platelets is via covalent cross linking of closely-spaced cysteine thiols in the ligand. This allows persistent signal from the probe within the necrotic platelet with no evidence of washout. GSAO+ve platelets correlated with procoagulant potential as measured by peak and endogenous thrombin potential in the calibrated automated thrombogram (CAT) assay. Linear regression analysis showed a significant relationship between % change in GSAO+ve platelets and % change in peak thrombin after treatment with cyclosporine A or in absence of exogenous calcium (R2=0.648, p<0.01), indicating that GSAO identifies a procoagulant subpopulation. In contrast, no relationship was seen between P-selectin and peak thrombin values (R2=0.002). Inhibition of platelet activation by aspirin had no effect on the generation of GSAO+ve platelets indicating a potential uncoupling between platelet activation and necrosis pathways. After establishing that the imaging compound does not affect platelet function and coagulation in vitro, or thrombus formation in vivo, we went on to investigate the presence of GSAO+ve necrotic platelets in thrombus formation in a collagen dependent (ferric chloride) and collagen independent (laser injury) murine model of thrombosis. Confocal intravital imaging of the cremaster arterioles with fluorescent GSAO and tagged-CD42b demonstrated GSAO+ve platelets in the occlusive platelet aggregate after initiation with 10% ferric chloride. The GSAO+ve aggregating platelets specifically colabeled with calcium sensing dye rhodamine 2 indicating high sustained intracellular calcium, consistent with a necrotic phenotype. There was no signal with active site replaced control GSCA. In contrast, the laser injury model showed minimal staining with GSAO three minutes post laser injury. Using a novel platelet necrosis marker, we are able to demonstrate that necrotic platelets are procoagulant and present in the occlusive ferric chloride model and not in the non-occlusive laser injury model of thrombosis. This suggests excess platelet necrosis may be a key driving factor underlying pathological occlusive thrombi. GSAO is a promising tool for understanding factors that potentiate platelet necrosis which may offer attractive anti-thrombotic targets. 1. Park D, Don AS, Massamiri T, et al. Noninvasive imaging of cell death using an hsp90 ligand. J Am Chem Soc. 2011;133(9):2832-2835. Disclosures: No relevant conflicts of interest to declare.


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