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Dense Granule Secretion (dense + granule_secretion)
Selected AbstractsElucidation of the molecular mechanism of platelet activation: Dense granule secretion is regulated by small guanosine triphosphate-binding protein Rab27 and its effector Munc13-4GERIATRICS & GERONTOLOGY INTERNATIONAL, Issue 4 2006Hisanori Horiuchi Cardiovascular diseases such as myocardial and cerebral infarction are common critical diseases occurring more frequently in the elderly. The trigger of the diseases is platelet activation following plaque rupture or erosion. Investigation of the molecular mechanism in platelet activation has been exclusively performed pharmacologically. We have succeeded in establishing the granule secretion and aggregation assays using permeabilized platelets. These systems enabled us to examine the molecular mechanism in platelet activation with molecular biological and biochemical methods. Using these assay systems, we have been investigating the molecular mechanism of platelet activation. With a support grant from the Novartis Foundation for Gerontological Research, we found several molecules involved in the regulation. In this report, I present the progress in the research of the granule secretion mechanism in activated platelets, which was reported in the Japanese Geriatric Society Meeting in 2005. [source] Differential phosphorylation of myosin light chain (Thr)18 and (Ser)19 and functional implications in plateletsJOURNAL OF THROMBOSIS AND HAEMOSTASIS, Issue 10 2010T. M. GETZ Summary. Background:, Myosin IIA is an essential platelet contractile protein that is regulated by phosphorylation of its regulatory light chain (MLC) on residues (Thr)18 and (Ser)19 via the myosin light chain kinase (MLCK). Objective:, The present study was carried out to elucidate the mechanisms regulating MLC (Ser)19 and (Thr)18 phosphorylation and the functional consequence of each phosphorylation event in platelets. Results:, Induction of 2MeSADP-induced shape change occurs within 5 s along with robust phosphorylation of MLC (Ser)19 with minimal phosphorylation of MLC (Thr)18. Selective activation of G12/13 produces both slow shape change and comparably slow MLC (Thr)18 and (Ser)19 phosphorylation. Stimulation with agonists that trigger ATP secretion caused rapid MLC (Ser)19 phosphorylation while MLC (Thr)18 phosphorylation was coincident with secretion. Platelets treated with p160ROCK inhibitor Y-27632 exhibited a partial inhibition in secretion and had a substantial inhibition in MLC (Thr)18 phosphorylation without effecting MLC (Ser)19 phosphorylation. These data suggest that phosphorylation of MLC (Ser)19 is downstream of Gq/Ca2+ -dependent mechanisms and sufficient for shape change, whereas MLC (Thr)18 phosphorylation is substantially downstream of G12/13 -regulated Rho kinase pathways and necessary, probably in concert with MLC (Ser)19 phosphorylation, for full contractile activity leading to dense granule secretion. Overall, we suggest that the amplitude of the platelet contractile response is differentially regulated by a least two different signaling pathways, which lead to different phosphorylation patterns of the myosin light chain, and this mechanism results in a graded response rather than a simple on/off switch. [source] Molecular basis of platelet activation by an ,IIb,3-CHAMPS peptideJOURNAL OF THROMBOSIS AND HAEMOSTASIS, Issue 2 2009B. GRYGIELSKA Summary.,Background:,A novel method, known as computed helical anti-membrane protein (CHAMP), for the design of peptides that bind with high affinity and selectivity to transmembrane helices was recently described and illustrated using peptides that bind ,IIb- and ,v-integrin subunits, which induce selective activation of integrins ,IIb,3 and ,v,3, respectively [1]. Objectives:,In the present study, we have investigated the ability of an ,IIb-CHAMPS peptide (termed integrin-activatory-peptide or IAP) to stimulate protein tyrosine phosphorylation and aggregation in human and mouse platelets. Methods:,The ability of IAP to stimulate platelet aggregation and dense granule secretion was measured in washed preparations of human and mouse platelets. Samples were taken for measurement of tyrosine phosphorylation. Results:,IAP stimulates robust tyrosine phosphorylation of the tyrosine kinase Syk and the FcR ,-chain, but only weak phosphorylation of PLC,2. Aggregation to low but not high concentrations of IAP is reduced in the presence of the Src kinase inhibitor, PP1, or by inhibitors of the two feedback agonists, ADP and thromboxane A2 (TxA2) suggesting that activation is reinforced by Src kinase-driven release of ADP and TxA2. Unexpectedly, aggregation by IAP is only partially inhibited in human and mouse platelets deficient in integrin ,IIb,3. Further, IAP induces partial aggregation of formaldehyde-fixed platelets. Conclusions:,The present study demonstrates that the ,IIb-CHAMPS peptide induces platelet activation through integrin ,IIb,3-dependent and independent pathways with the former mediating tyrosine phosphorylation of FcR ,-chain and Syk. The use of the ,IIb-CHAMPS peptide to study integrin ,IIb,3 function is compromised by non-integrin-mediated effects. [source] Nitric oxide specifically inhibits integrin-mediated platelet adhesion and spreading on collagenJOURNAL OF THROMBOSIS AND HAEMOSTASIS, Issue 12 2008W. ROBERTS Summary.,Background:,Nitric oxide (NO) inhibits platelet adhesion to collagen, although the precise molecular mechanisms underlying this process are unclear. Objectives:,Collagen-mediated adhesion is a multifaceted event requiring multiple receptors and platelet-derived soluble agonists. We investigated the influence of NO on these processes. Results:,S-nitrosoglutathione (GSNO) induced a concentration-dependent inhibition of platelet adhesion to immobilized collagen. Maximal adhesion to collagen required platelet-derived ADP and TxA2. GSNO-mediated inhibition was lost in the presence of apyrase and indomethacin, suggesting that NO reduced the availability of, or signaling by, ADP and TxA2. Exogenous ADP, but not the TxA2 analogue U46619, reversed the inhibitory actions of GSNO on adhesion. Under adhesive conditions NO inhibited dense granule secretion but did not influence TxA2 generation. These data indicated that NO may block signaling by TxA2 required for dense granule secretion, thereby reducing the availability of ADP. Indeed, we found TxA2 -mediated activation of PKC was required to drive dense granule secretion, a pathway that was inhibited by NO. Because our data demonstrated that NO only inhibited the activation-dependent component of adhesion, we investigated the effects of NO on individual collagen receptors. GSNO inhibited platelet adhesion and spreading on ,2,1 specific peptide ligand GFOGER. In contrast, GSNO did not inhibit GPVI-mediated adhesion to collagen, or adhesion to the GPVI specific ligand, collagen related peptide (CRP). Conclusions:,NO targets activation-dependent adhesion mediated by ,2,1, possibly by reducing bioavailability of platelet-derived ADP, but has no effect on activation-independent adhesion mediated by GPVI. Thus, NO regulates platelet spreading and stable adhesion to collagen. [source] | ||||||||||