Fibrinogen and prothrombin binding is enhanced to the Pro33 isoform of purified integrin alphaIIbbeta3.
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Blood Platelets↗
Biomedical subjects
P F Bray
Publications and source records attributed to P F Bray.
Platelet hyperreactivity generalizes to multiple forms of stimulation.
BACKGROUND: Although platelet hyperreactivity constitutes an important cardiovascular risk factor, standardized methods for its measurement are lacking. We recently reported that aggregometry using a submaximal concentration of epinephrine identifies individuals with in vitro platelet hyperreactivity; this hyperreactivity was reproducible on multiple occasions over long periods of time. OBJECTIVE AND METHODS: To better understand this aberrant reactivity, we studied in a large group of subjects (n = 386) the relationship between healthy individuals' platelet reactivity to epinephrine and their platelet phenotype as measured by other functional assays. RESULTS: Subjects with hyperreactivity to epinephrine were more likely to exhibit hyperfunction in each major aspect of platelet activity, including adhesion (response to low-dose ristocetin; P < 0.001), activation (surface P-selectin expression and PAC-1 binding after stimulation; P <or= 0.003) and aggregation to other agonists [no agonist, adenosine diphosphate (ADP), arachidonic acid, collagen, collagen-related peptide and ristocetin; P <or= 0.025] and to applied shear stress (PFA-100 and cone-and-plate viscometer; P < 0.05). These differences persisted after adjusting for demographic and hematologic differences between groups. We studied candidate genes relevant to epinephrine-mediated platelet activation and found that hyperreactivity to epinephrine was associated with a polymorphism on the gene (GNB3) encoding the beta-3 subunit of G proteins (P = 0.03). CONCLUSIONS: Robust aggregation to a submaximal concentration of epinephrine establishes a true hyperreactive platelet phenotype that is 'global' as opposed to agonist specific; detection of this phenotype could be useful for studying patients at risk for arterial thrombosis. The mechanisms underlying hyperreactivity to different types of platelet stimulation may share common signaling pathways, some of which may involve specific G protein subunits.
Adult↗
Platelet FcgammaRIIA His131Arg polymorphism and platelet function: antibodies to platelet-bound fibrinogen induce platelet activation.
The His131Arg polymorphism of platelet FcgammaRIIA affects the binding affinity of certain IgG subclasses. The Arg131 allele has been associated with (auto)immune thrombocytopenia and heparin-induced thrombocytopenia in some studies. Because FcgammaRIIA can transmit platelet activation signals, we studied platelet responsiveness from 73 healthy donors to determine if this polymorphism modulated platelet function. Platelet function was studied by agonist and shear-induced activation, and standard aggregation. FcgammaRIIA was genotyped by allele-specific PCR. Compared with His131, the Arg131 allele was associated with significantly greater binding of activation-dependent antibodies. This effect was most prominent for the receptor-induced binding site (RIBS) antibodies F26 (P < 0.0001) and RIBS1 (P = 0.0057), and the ligand-induced binding site antibody LIBS1 (P = 0.0367). Unexpectedly, Arg131-positive platelets did not show greater fibrinogen binding, platelet aggregation or shear-induced platelet activation. We considered whether enhanced Fc binding and FcgammaRIIA cross-linking were responsible for those discrepancies. The increased binding of the two RIBS antibodies to the Arg131 isoform was abolished by blocking FcgammaRIIA, and the FcgammaRIIA genotype effect on F26 IgG binding was lost when F26 F(ab')2 fragments were used. Furthermore, intact F26 and RIBS1 IgG directly and specifically induced P-selectin expression, and this effect was greatest in Arg131-positive platelets. We concluded that (a) the His131Arg polymorphism of FcgammaRIIA does not affect intrinsic platelet reactivity; (b) RIBS antibodies are able to cross-link FcgammaRIIA and activate platelets, and this activation has a modest effect on Arg131 platelets; and (c) flow cytometric based platelet assays may need to compensate for this FcgammaRIIA His131Arg effect on platelet activation.
Adult↗
The platelet Pl(A2) and angiotensin-converting enzyme (ACE) D allele polymorphisms and the risk of recurrent events after acute myocardial infarction.
Chromosome 17q21-23 harbors genes for platelet glycoprotein IIIa and angiotensin-converting enzyme (ACE), which are polymorphic for alleles Pl(A2) and ACE "D." These alleles have been independently and often associated with ischemic coronary artery disease (CAD). We sought to determine if the Pl(A2) and ACE D polymorphisms were risk factors for recurrent coronary events. In the Cholesterol And Recurrent Events (CARE) trial, 4,159 men and women with documented myocardial infarction (MI) were randomized to receive either placebo or pravastatin, and were followed prospectively for 5 years. Pl(A) and ACE genotypes were determined in 767 patients: 385 cases who had experienced a recurrent primary event (death due to coronary disease or nonfatal MI), and 382 age- and gender-matched controls. In patients receiving placebo, the Pl(A1,A2) genotype conferred a relative risk (RR) of 1.38 (confidence intervals [CI] 1.04 to 1.83; p = 0.028; adjusted RR = 1.32, CI = 0.99 to 1.76; p = 0.058]) for the primary end point. Compared with the placebo group, pravastatin reduced the excess RR of coronary disease death and recurrent MI in the Pl(A1,A2) patient population by 31% (p = 0.06). The ACE D allele appeared to have modestly additive effects on the Pl(A1,A2) risk. Among the Pl(A1,A2) patients, pravastatin had little effect on the risk of recurrent events with the ACE II genotype, but reduced the adjusted RR from 1.42 (placebo) to 0.58 for ACE ID patients, and from 1.56 (placebo) to 0.83 for ACE DD. The Pl(A1,A2) genotype was associated with an excess of recurrent coronary events in patients after MI who did not receive pravastatin, and the ACE D allele added to this risk. These data suggest that it would be important to perform a larger study to address the potential role of these genotypes in therapeutic decision making.
Aged↗
Coagulation markers predicting cardiac transplant rejection.
BACKGROUND: Acute cellular rejection in cardiac allografts is a major cause of graft loss, and is associated with activation of the coagulation system. We investigated whether plasma markers of coagulation predict the presence of allograft rejection. METHODS: A total of 132 blood specimens and endomyocardial biopsies were collected from 35 patients, between February of 1997 and May of 1998. We measured plasma prothrombin fragment 1.2 (PF1.2) and p-selectin, fibrinogen, thrombomodulin, and d-dimer. Biopsies were graded according to the International Society of Heart and Lung Transplantation system, with a range of 0 to 4. Grades 0 and 1A were grouped as "no rejection," and the higher grades as "rejection." Linear and logistic regression, accounting for longitudinal data, were the principal analytic tools. RESULTS: p-Selectin level increased progressively with increasing rejection grade (P<0.001). With multivariate analysis, both p-selectin and prothrombin fragment levels significantly predicted rejection. p-Selectin levels were predictive of prothrombin fragment levels (P<0.0001) but not of d-dimer, fibrinogen, or thrombomodulin levels. This model allowed correct prediction of rejection, based on p-selectin and prothrombin fragment values, up to 85% of the time. Dichotomizing patients by a p-selectin level of 65 ng/ml resulted in an odds of rejection of 21.4 [95% C.I. 7.1-64.7] for the patients in the high- compared with the lower risk group. CONCLUSIONS: In heart transplant recipients, p-selectin levels and PF 1.2 levels are highly predictive of organ rejection. The elevation of PF 1.2 suggests that there is systemic generation of thrombin generation. These markers may be useful for noninvasively monitoring patients for organ rejection or for after response to treatment.
Biomarkers↗
Human platelets contain a glycosylated estrogen receptor beta.
Platelets play an important role in the coronary thrombus formation that leads to myocardial ischemia and infarction. Gender differences in the development of coronary heart disease and its outcomes are partly regulated by estrogen and its receptors, but the roles of the latter in thrombogenicity are less well-defined. We previously demonstrated the presence of estrogen receptor (ER) beta in cells of the megakaryocytic lineage. In this study, we characterize human platelet ERbeta and its expression using biochemical and molecular biological techniques. Western immunoblotting showed that platelet ERbeta migrated with an apparent molecular mass approximately 3.7 kDa larger than ERbeta in a variety of cell lines (including those of prostate and breast origin). A rigorous investigation of platelet ERbeta mRNA by reverse transcriptase-polymerase chain reaction revealed normal transcripts and a single alternately spliced mRNA. However, this variant form was smaller, lacking exon 2, and could not account for the larger protein size seen in platelets. Treatment of ERbeta with N-glycosidase F, which removes core carbohydrate residues, caused a more rapid migration through polyacrylamide gels but had no effect on ERbeta from human cell lines. We conclude that the larger form of ERbeta in human platelets is not attributable to alternate mRNA splicing but primarily to tissue-specific glycosylation.
Adult↗
Induction of beta3-integrin gene expression by sustained activation of the Ras-regulated Raf-MEK-extracellular signal-regulated kinase signaling pathway.
Alterations in the expression of integrin receptors for extracellular matrix (ECM) proteins are strongly associated with the acquisition of invasive and/or metastatic properties by human cancer cells. Despite this, comparatively little is known of the biochemical mechanisms that regulate the expression of integrin genes in cells. Here we demonstrate that the Ras-activated Raf-MEK-extracellular signal-regulated kinase (ERK) signaling pathway can specifically control the expression of individual integrin subunits in a variety of human and mouse cell lines. Pharmacological inhibition of MEK1 in a number of human melanoma and pancreatic carcinoma cell lines led to reduced cell surface expression of alpha6- and beta3-integrin. Consistent with this, conditional activation of the Raf-MEK-ERK pathway in NIH 3T3 cells led to a 5 to 20-fold induction of cell surface alpha6- and beta3-integrin expression. Induced beta3-integrin was expressed on the cell surface as a heterodimer with alphav-integrin; however, the overall level of alphav-integrin expression was not altered by Ras or Raf. Raf-induced beta3-integrin was observed in primary and established mouse fibroblast lines and in mouse and human endothelial cells. Consistent with previous reports of the ability of the Raf-MEK-ERK signaling pathway to induce beta3-integrin gene transcription in human K-562 erythroleukemia cells, Raf activation in NIH 3T3 cells led to elevated beta3-integrin mRNA. However, unlike immediate-early Raf targets such as heparin binding epidermal growth factor and Mdm2, beta3-integrin mRNA was induced by Raf in a manner that was cycloheximide sensitive. Surprisingly, activation of the Raf-MEK-ERK signaling pathway by growth factors and mitogens had little or no effect on beta3-integrin expression, suggesting that the expression of this gene requires sustained activation of this signaling pathway. In addition, despite the robust induction of cell surface alphavbeta3-integrin expression by Raf in NIH 3T3 cells, such cells display decreased spreading and adhesion, with a loss of focal adhesions and actin stress fibers. These data suggest that oncogene-induced alterations in integrin gene expression may participate in the changes in cell adhesion and migration that accompany the process of oncogenic transformation.
3T3 Cells↗
Genetics of arterial prothrombotic risk states.
Coronary artery disease is a leading cause of death worldwide and the largest killer of men and women in the United States. The pathophysiology of myocardial infarction is multifactorial, and numerous physiologic systems converge to dictate the formation of the two fundamental lesions, thrombosis and atherosclerosis. In this review we address genetic aspects of arterial thrombosis and the key thrombotic factors that have been associated with the increased risk for its development. Specifically, we consider components of coagulation, fibrinolysis, and platelet adhesive receptors, and we review the genetic epidemiology and in vitro laboratory data regarding their risk for the acute coronary syndromes. In combination with traditional risk factor assessment, in the near future these inherited markers can be used to manage patients with vascular disease through a better utilization of invasive or expensive diagnostic testing, as well as pharmacologic intervention.
Blood Coagulation Factors↗
The PlA polymorphism of glycoprotein IIIa functions as a modifier for the effect of estrogen on platelet aggregation.
BACKGROUND: Although estrogen has been shown to contribute to retardation of the development of coronary heart disease in premenopausal women, the efficacy of hormone replacement therapy for coronary heart disease prevention in women with established coronary heart disease remains controversial. Hence, additional research is needed to clarify the effects of hormone replacement therapy on the cardiovascular and clotting systems. We investigated the effect of estrogen on platelet aggregation induced by standard agonists (epinephrine and adenosine diphosphate), with and without the platelet antagonist aspirin. Furthermore, we analyzed our data according to the presence or absence of a prevalent polymorphism of the glycoprotein (GP) IIIa subunit of the platelet fibrinogen receptor GPIIb-IIIa, PlA2. METHODS AND RESULTS: The effect of estrogen on aggregation of platelets was studied in healthy men (n = 20, 10 PlA1/A1 and 10 PlA1/A2) and premenopausal healthy women (n = 10, 5 PlA1/A1 and 5 PlA1/A2). The PlA1/A1 and PlA1/A2 individuals were matched for age and race. Platelet response to agonists was investigated in the presence of (1) estrogen (10(-11) to 10(-8) mol/L), (2) aspirin (0.056 to 56 micromol/L), (3) estrogen plus aspirin, and (4) estrogen plus ICI 182 780 (ICI, 10(-9) mol/L, an inhibitor of the estrogen receptor). We found that physiologic concentrations of estrogen strongly and significantly inhibited the aggregation of PlA1/A2 platelets (P<.005 for epinephrine and P<.05 for adenosine diphosphate, induced aggregation, respectively) in both men and women. Concentrations of estrogen that were 1000-fold greater were required to observe the same level of inhibition with PlA1/A1 platelets. In the presence of aspirin, estrogen failed to provide additional inhibitory effect on aggregation of both PlA1/A1 and PlA1/A2 platelets. The estrogen-specific inhibitor ICI blocked the effect of estrogen on aggregation, suggesting that this effect is mediated by the estrogen receptor. CONCLUSIONS: Estrogen inhibits the aggregation of platelets, but such inhibition is highly dependent on the presence or absence of the PlA2 polymorphism of GPIIIa. However, in the presence of aspirin, the inhibitory effect of estrogen on aggregation was no longer detectable.
Adult↗
Immobilized platelets support human colon carcinoma cell tethering, rolling, and firm adhesion under dynamic flow conditions.
Accumulating evidence suggests that successful metastatic spread may depend on the ability of tumor cells to undergo extensive interactions with platelets. However, the mechanisms mediating tumor cell adhesion to platelets under conditions of flow remain largely unknown. Therefore, this study was designed to analyze the ability of 3 human colon carcinoma cell lines (LS174T, COLO205, and HCT-8) to bind to surface-anchored platelets under flow and to identify the receptors involved in these processes. Immobilized platelets support LS174T cell adhesion at wall shear stresses up to 1.4 dyn/cm(2). Our data suggest that platelets primarily recruit LS174T cells through a 2-step, sequential process of adhesive interactions that shares common features but is distinct from that elaborated for neutrophils. Platelet P-selectin mediates LS174T cell tethering and rolling in a PSGL-1- and CD24-independent manner. Moreover, platelet alpha(IIb)beta(3)-integrins appear to be capable of directly capturing LS174T cells from the fluid stream, and also convert instantaneously transient tethers initiated by P-selectin into stable adhesion. This step is at least partially mediated by von Willebrand factor, but not fibrinogen or fibronectin, that bridges platelet alpha(IIb)beta(3) with a yet unidentified receptor on the LS174T cell surface via an RGD-dependent mechanism. The sequential engagement of platelet P-selectin and alpha(IIb)beta(3) is also requisite for the optimal adhesion of COLO205. Furthermore, HCT-8 cells, which fail to interact with P-selectin, tether minimally to surface-anchored platelets under flow, despite their extensive adhesive interactions under static conditions. This cascade of events depicts an efficacious process for colon carcinoma arrest at sites of vascular injury. (Blood. 2000;96:1789-1797)
Biomechanical Phenomena↗
Megakaryocyte-targeted synthesis of the integrin beta(3)-subunit results in the phenotypic correction of Glanzmann thrombasthenia.
Glanzmann thrombasthenia is an inherited bleeding disorder characterized by qualitative or quantitative defects of the platelet-specific integrin, alphaIIbbeta(3). As a result, alphaIIbbeta(3) cannot be activated and cannot bind to fibrinogen, leading to a loss of platelet aggregation. Thrombasthenia is clinically characterized by mucocutaneous hemorrhage with episodes of intracranial and gastrointestinal bleeding. To develop methods for gene therapy of Glanzmann thrombasthenia, a murine leukemia virus (MuLV)-derived vector, -889Pl(A2)beta(3), was transduced into peripheral blood CD34(+) cells from 2 patients with thrombasthenia with defects in the beta(3) gene. The human alphaIIb promoter was used in this vector to drive megakaryocyte-targeted expression of the wild-type beta(3) subunit. Proviral DNA and alphaIIbbeta(3) biosynthesis were detected after in vitro differentiation of transduced thrombasthenic CD34(+) cells with megakaryocyte growth and development factor. Flow cytometric analysis of transduced patient samples indicated that 19% of megakaryocyte progeny expressed alphaIIbbeta(3) on the surface at 34% of normal receptor levels. Treatment of transduced megakaryocytes with a combination of agonists including epinephrine and the thrombin receptor-activating peptide induced the alphaIIbbeta(3) complex to form an activated conformation capable of binding fibrinogen as measured by PAC-1 antibody binding. Transduced cells retracted a fibrin clot in vitro similar to megakaryocytes derived from a normal nonthrombasthenic individual. These results demonstrate ex vivo phenotypic correction of Glanzmann thrombasthenia and support the potential use of hematopoietic CD34(+) cells as targets for alphaIIb promoter-driven MuLV vectors for gene therapy of platelet disorders. (Blood. 2000;95:3645-3651)
Antigens, CD↗
Human megakaryocytes and platelets contain the estrogen receptor beta and androgen receptor (AR): testosterone regulates AR expression.
Gender differences in vascular thromboses are well known, and there is evidence that platelets may be involved in these differences and that sex hormones affect platelet function. We characterized the expression of the estrogen receptor alpha (ER alpha), estrogen receptor beta (ER beta), progesterone receptor (PR), and androgen receptor (AR) in the megakaryocyte lineage. Megakaryocytes generated ex vivo from normal human CD34(+) stem cells contained RNA for ER beta and AR, which increased with cell differentiation. Platelets and human erythroleukemia (HEL) cells also contained ER beta and AR transcripts. No ER alpha or PR messenger RNA or protein was detected in the megakaryocyte lineage. Immunofluorescence microscopy showed that ER beta protein was present in glycoprotein (GP) IIb(+) megakaryocytes and the HEL megakaryocytic cell line in a predominantly cytoplasmic location. AR showed a cytoplasmic and nuclear distribution in GPIIb(+) and GPIIb(-) cells derived from CD34(+) cells and in HEL cells. Western immunoblotting confirmed the presence of ER beta and AR in platelets. Megakaryocyte and HEL AR expression was up-regulated by 1, 5, and 10 nmol/L testosterone, but down-regulated by 100 nmol/L testosterone. These findings indicate a regulated ability of megakaryocytes to respond to testosterone and suggest a potential mechanism through which sex hormones may mediate gender differences in platelet function and thrombotic diseases.
Antigens, CD34↗
Platelet GP IIIa Pl(A) polymorphisms display different sensitivities to agonists.
BACKGROUND: Both inherited predisposition and platelet hyperreactivity have been associated with ischemic coronary events, but mechanisms that support genetic differences among platelets from different subjects are generally lacking. Associations between the platelet Pl(A2) polymorphism of GP IIIa and coronary syndromes raise the question as to whether this inherited variation may contribute to platelet hyperreactivity. METHODS AND RESULTS: In this study, we characterized functional parameters in platelets from healthy donors with the Pl(A) (HPA-1) polymorphism, a Leu (Pl(A1)) to Pro (Pl(A2)) substitution at position 33 of the GP IIIa subunit of the platelet GP IIb/IIIa receptor (integrin alpha(IIb)beta(3)). We studied 56 normal donors (20 Pl(A1,A1), 20 Pl(A1,A2), and 16 Pl(A2,A2)). Compared with Pl(A1,A1) platelets, Pl(A2)-positive platelets showed a gene dosage effect for significantly greater surface-expressed P-selectin, GP IIb/IIIa-bound fibrinogen, and activated GP IIb/IIIa in response to low-dose ADP. Surface expression of GP IIb/IIIa was similar in resting platelets of all 3 genotypes but was significantly greater on Pl(A2,A2) platelets after ADP stimulation (P=0.003 versus Pl(A1,A1); P=0.03 versus Pl(A1,A2)). Pl(A1,A2) platelets were more sensitive to inhibition of aggregation by pharmacologically relevant concentrations of aspirin and abciximab. CONCLUSIONS: Pl(A2)-positive platelets displayed a lower threshold for activation, and platelets heterozygous for Pl(A) alleles showed increased sensitivity to 2 antiplatelet drugs. These in vitro platelet studies may have relevance for in vivo thrombotic conditions.
Abciximab↗
Platelet glycoprotein polymorphisms as risk factors for thrombosis.
Both blood platelets and genetics contribute to the development of acute ischemic arterial diseases. A careful analysis of the various clinical association studies supports a modest increased risk for coronary artery disease events in carriers of the PIA2 polymorphism of GPIIIa. Investigations with both platelets and stable cells lines have shown the PIA2 polymorphism is prothrombotic. Only a handful of studies have been performed for platelet GPla (integrin alpha2) and GPIb-IX-V, but there is support for the 807 T/C polymorphism of GPIa and the met145 and VNTR B/C genotype of GPIbalpha as risk factors in younger age groups. And isolated reports suggest other platelet polymorphisms (GPIIb, FcgammaRIIa, P-selectin, alpha2 adrenergic receptor, transforming growth factor [TGF]beta) are risk factors for arterial disease or produce a prothrombotic phenotype. Platelet glycoprotein polymorphisms should be added to the list of genetic risk factors for arterial thrombosis, particularly in younger patients and women.
Humans↗
The Pl(A2) polymorphism of integrin beta(3) enhances outside-in signaling and adhesive functions.
Genetic factors are believed to influence the development of arterial thromboses. Because integrin alpha(IIb)beta(3) plays a crucial role in thrombus formation, we analyzed receptor adhesive properties using Chinese hamster ovary and human kidney embryonal 293 cells overexpressing the Pl(A1) or Pl(A2) polymorphic forms of alpha(IIb)beta(3). Soluble fibrinogen binding was no different between Pl(A1) and Pl(A2) cells, either in a resting state or when alpha(IIb)beta(3) was activated with anti-LIBS6. Pl(A1) and Pl(A2) cells bound equivalently to immobilized fibronectin. In contrast, significantly more Pl(A2) cells bound to immobilized fibrinogen in an alpha(IIb)beta(3)-dependent manner than did Pl(A1) cells. Disruption of the actin cytoskeleton by cytochalasin D abolished the increased binding of Pl(A2) cells. Compared with Pl(A1) cells, Pl(A2) cells exhibited a greater extent of polymerized actin and cell spreading, enhanced tyrosine phosphorylation of pp125(FAK), and greater fibrin clot retraction. These adhesion differences appear to depend on a signaling mechanism sensitive to receptor occupancy. Thus, the Pl(A2) polymorphism altered integrin-mediated functions of adhesion, spreading, actin cytoskeleton rearrangement, and clot retraction.
Actins↗
Ex vivo cultured megakaryocytes express functional glycoprotein IIb-IIIa receptors and are capable of adenovirus-mediated transgene expression.
Investigation of the molecular basis of megakaryocyte (MK) and platelet biology has been limited by an inadequate source of genetically manipulable cells exhibiting physiologic MK and platelet functions. We hypothesized that ex vivo cultured MKs would exhibit agonist inducible glycoprotein (GP) IIb-IIIa activation characteristic of blood platelets and that these cultured MKs would be capable of transgene expression. Microscopic and flow cytometric analyses confirmed that human hematopoietic stem cells cultured in the presence of pegylated recombinant human MK growth and development factor (PEG-rHuMGDF) differentiated into morphologic and phenotypic MKs over 2 weeks. Cultured MKs expressed functional GPIIb-IIIa receptors as assessed by agonist inducible soluble fibrinogen and PAC1 binding. The specificity and kinetics of fibrinogen binding to MK GPIIb-IIIa receptors were similar to those described for blood platelets. The reversibility and internalization of ligands bound to MK GPIIb-IIIa also shared similarities with those observed in platelets. Cultured MKs were transduced with an adenoviral vector encoding green fluorescence protein (GFP) or beta-galactosidase (beta-gal). Efficiency of gene transfer increased with increasing multiplicities of infection and incubation time, with 45% of MKs expressing GFP 72 hours after viral infection. Transduced MKs remained capable of agonist induced GPIIb-IIIa activation. Thus, ex vivo cultured MKs (1) express agonist responsive GPIIb-IIIa receptors, (2) are capable of expressing transgenes, and (3) may prove useful for investigation of the molecular basis of MK differentiation and GPIIb-IIIa function.
Adenoviridae↗
Integrin-dependent control of translation: engagement of integrin alphaIIbbeta3 regulates synthesis of proteins in activated human platelets.
Integrins are widely expressed plasma membrane adhesion molecules that tether cells to matrix proteins and to one another in cell-cell interactions. Integrins also transmit outside-in signals that regulate functional responses of cells, and are known to influence gene expression by regulating transcription. In previous studies we found that platelets, which are naturally occurring anucleate cytoplasts, translate preformed mRNA transcripts when they are activated by outside-in signals. Using strategies that interrupt engagement of integrin alphaIIbbeta3 by fibrinogen and platelets deficient in this integrin, we found that alphaIIbbeta3 regulates the synthesis of B cell lymphoma 3 (Bcl-3) when platelet aggregation is induced by thrombin. We also found that synthesis of Bcl-3, which occurs via a specialized translation control pathway regulated by mammalian target of rapamycin (mTOR), is induced when platelets adhere to immobilized fibrinogen in the absence of thrombin and when integrin alphaIIbbeta3 is engaged by a conformation-altering antibody against integrin alphaIIbbeta3. Thus, outside-in signals delivered by integrin alphaIIbbeta3 are required for translation of Bcl-3 in thrombin-stimulated aggregated platelets and are sufficient to induce translation of this marker protein in the absence of thrombin. Engagement of integrin alpha2beta1 by collagen also triggered synthesis of Bcl-3. Thus, control of translation may be a general mechanism by which surface adhesion molecules regulate gene expression.
Antibodies, Monoclonal↗
Higher prevalence of GPIIIa PlA2 polymorphism in siblings of patients with premature coronary heart disease.
BACKGROUND: The Pl(A2) polymorphism of GPIIIa has been associated with unstable coronary syndromes in some studies, but the association has remained debated. None of the previous studies have focused on families at high risk. Risk factors tend to cluster within kindreds with high prevalence of premature coronary heart disease (CHD). Therefore, a heightened prevalence of the Pl(A2) polymorphism among siblings of patients with CHD would support the hypothesis that Pl(A2) is linked, directly or indirectly, to CHD. OBJECTIVES: To measure the prevalence of the Pl(A2) polymorphism among siblings of patients with CHD before the age of 60 years and to seek an association between the Pl(A2) polymorphism and established atherosclerotic and thrombogenic risk factors. METHODS: From January 1994 to April 1996, we genotyped 116 asymptomatic siblings (60 Caucasians, 56 Afro-Caribbeans) of patients with CHD manifestations before the age of 60 years for the Pl(A) polymorphism (also called HPA-1). A control cohort was used for comparison, consisting of individuals that were matched for race and geographic area but were free of CHD (n = 268, 168 Caucasians and 100 Afro-Caribbeans). In addition, we have characterized the sibling cohort for other atherogenic and thrombogenic risk factors. RESULTS: The prevalence of Pl(A2)-positive individuals (Pl(A2)[+], Pl(A1/A2) heterozygotes plus Pl(A2/A2) homozygotes) in the sibling cohort was high: 41.4%. When analyzed separately, the prevalence of Pl(A2)(+) siblings was 53.3% among Caucasians and 28.6% among Afro-Caribbeans. There was no association between Pl(A2) and other established atherogenic or thrombogenic risk factors. Interestingly, the clustering of other risk factors was lesser among Pl(A2)(+) siblings than their Pl(A1) counterparts. CONCLUSIONS: This study supports the hypothesis that the prevalence of Pl(A2)(+) individuals is high in kindreds with premature CHD. Hence, like the established risk factors that tend to cluster in families with premature CHD and contribute strongly to the accelerated atherosclerotic process affecting these individuals, the Pl(A2) polymorphism of GPIIIa may represent an inherited risk that promotes the thromboembolic complications of CHD. That these asymptomatic Pl(A2)(+) siblings had overall less established risk factors than their Pl(A1) counterparts might represent an explanation for why they remained asymptomatic despite their Pl(A2) positivity.
Adult↗