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Biomedical subjects

E J Brown

Publications and source records attributed to E J Brown.

At least 19 recordsLinked to original sources
PubMed1998

The protein tyrosine phosphatase SHP-1 regulates integrin-mediated adhesion of macrophages.

The Src homology 2 domain phosphatase-1 (SHP-1) is a tyrosine phosphatase containing two amino-terminal SH2 domains and is expressed primarily by hematopoietic-derived cells [1]. The viable motheaten (Hcphme-v) mutant mice (mev) suffer from progressive inflammation due to a deficiency of SHP-1 enzyme activity [2,3] and die at 3-4 months of age from macrophage and neutrophil accumulation in the lung [4]. The mechanism by which SHP-1 deficiency leads to inflammation is unknown. We found that macrophages from mev mice adhered and spread to a greater extent than normal macrophages through alpha m beta 2 integrin-mediated contacts. Whereas macrophages deficient in the transmembrane tyrosine phosphatase CD45 (CD45-/-) spontaneously detached from alpha m beta 2 integrin contacts [5], cells deficient in both CD45 and SHP-1 did not. In SHP-1 deficient macrophages there was a 10-15-fold increase in D-3 phospholipid products of phosphatidylinositol (PI) 3-kinase. Concomitantly, there was a 2-5-fold increase in membrane-associated PI 3-kinase activity in mev macrophages relative to normal macrophages. Treatment of macrophages with the PI 3-kinase inhibitors wortmannin or LY294002 resulted in a dramatic detachment of cells, indicating that PI 3-kinase activity is required for adhesion. These data demonstrate that SHP-1 is necessary for detachment from alpha m beta 2 integrin-mediated contacts in primary macrophages and suggest that a defect in this pathway may contribute to inflammatory disease.

Animals↗
PubMed1998

A role for the actin-bundling protein L-plastin in the regulation of leukocyte integrin function.

Regulation of leukocyte integrin avidity is a crucial aspect of inflammation and immunity. The actin cytoskeleton has an important role in the regulation of integrin function, but the cytoskeletal proteins involved are largely unknown. Because inflammatory stimuli that activate integrin-mediated adhesion in human polymorphonuclear neutrophils (PMN) and monocytes cause phosphorylation of the actin-bundling protein L-plastin, we tested whether L-plastin phosphorylation was involved in integrin activation. L-plastin-derived peptides that included the phosphorylation site (Ser-5) rapidly induced leukocyte integrin-mediated adhesion when introduced into the cytosol of freshly isolated primary human PMN and monocytes. Substitution of Ala for Ser-5 abolished the ability of the peptide to induce adhesion. Peptide-induced adhesion was sensitive to pharmacologic inhibition of phosphoinositol 3-kinase and protein kinase C, but adhesion induced by a peptide containing a phosphoserine at position 5 was insensitive to inhibition. These data establish a novel role for L-plastin in the regulation of leukocyte adhesion and suggest that many signaling events implicated in integrin regulation act via induction of L-plastin phosphorylation.

Amino Acid Sequence↗
PubMed1998

A role for the alphavbeta3 integrin in the transmigration of monocytes.

The beta2 integrins and intercellular adhesion molecule-1 (ICAM-1) are important for monocyte migration through inflammatory endothelium. Here we demonstrate that the integrin alphavbeta3 is also a key player in this process. In an in vitro transendothelial migration assay, monocytes lacking beta3 integrins revealed weak migratory ability, whereas monocytes expressing beta3 integrins engaged in stronger migration. This migration could be partially blocked by antibodies against the integrin chains alphaL, beta2, alphav, or IAP, a protein functionally associated with alphavbeta3 integrin. Transfection of beta3 integrin chain cDNA into monocytes lacking beta3 integrins resulted in expression of the alphavbeta3 integrin and conferred on these cells an enhanced ability to transmigrate through cell monolayers expressing ICAM-1. These monocytes also engaged in alphaLbeta2-dependent locomotion on recombinant ICAM-1 which was enhanced by alphavbeta3 integrin occupancy. Antibodies against IAP were able to revert this alphavbeta3 integrin-dependent cell locomotion to control levels. Finally, adhesion assays revealed that occupancy of alphavbeta3 integrin could decrease monocyte binding to ICAM-1. In conclusion, we show that alphavbeta3 integrin modulates alphaLbeta2 integrin-dependent monocyte adhesion to and migration on ICAM-1. This could represent a novel mechanism to promote monocyte motility on vascular ICAM-1 and initiate subsequent transendothelial migration.

Animals↗
PubMed1998

Two signaling mechanisms for activation of alphaM beta2 avidity in polymorphonuclear neutrophils.

Circulating polymorphonuclear neutrophils (PMN) are quiescent, nonadherent cells that rapidly activate at sites of inflammation, where they develop the capacity to perform a repertoire of functions that are essential for host defense. Induction of integrin-mediated adhesion, which requires an increase in integrin avidity, is critical for the development of these effector functions. Although a variety of stimuli can activate integrins in PMN, the signaling cascades involved are unclear. Phosphatidylinositol (PI) 3-kinase has been implicated in integrin activation in a variety of cells, including PMN. In this work, we have examined activation of the PMN integrin alphaM beta2, assessing both adhesion and generation of the epitope recognized by the activation-specific antibody CBRM1/5. We have found that PI 3-kinase has a role in activation of alphaM beta2 by immune complexes, but we have found no role for it in alphaM beta2 activation by ligands for trimeric G protein-coupled receptors, including formylmethionylleucylphenylalanine (fMLP), interleukin-8, and C5a. Cytochalasin D inhibition suggests a role for the actin cytoskeleton in immune complex activation of alphaM beta2, but cytochalasin has no effect on fMLP-induced activation. Similarly, immune complex activation of the Rac/Cdc42-dependent serine/threonine kinase Pak1 is blocked by PI 3-kinase inhibitors, but fMLP-induced activation is not. These results demonstrate that two signaling pathways exist in PMN for activation of alphaM beta2. One, induced by FcgammaR ligation, is PI 3-kinase-dependent and requires the actin cytoskeleton. The second, initiated by G protein-linked receptors, is PI 3-kinase-independent and cytochalasin-insensitive. Pak1 may be in a final common pathway leading to activation of alphaM beta2.

Cell Adhesion↗
PubMed1998

Early exercise after experimental myocardial infarction: effect on left ventricular remodeling.

BACKGROUND: The effect of exercise on left ventricular remodeling after myocardial infarction is unclear. The purpose of this investigation was to test whether exercise undertaken during the healing phase of an acute myocardial infarction has an adverse effect on left ventricular remodeling. METHODS: Before surgery, rats (n = 94) were allocated randomly to one of four groups: 1) infarct, swimming exercise; 2) infarct, no exercise; 3) sham operation, swimming exercise; 4) sham operation, no exercise. Beginning 1 week after infarction or sham operation, the rats in the exercise groups swam twice daily for 2 weeks. After a deconditioning period of 5 days, the rats were re-anesthetized, hemodynamic measurements were made, and the hearts were fixed for morphometric analysis. RESULTS: Swimming exercise had no effect on remodeling of infarcted myocardium. Rats with infarcts in the swimming and no exercise groups had similar infarct thicknesses (1.1 +/- 0.2 mm and 0.8 +/- 0.2 mm respectively; NS), and similar degrees of infarct expansion (expansion index 1.2 +/- 0.3 and 1.4 +/- 0.3 respectively; NS). Swimming exercise also had no effect on remodeling of non-infarcted myocardium. Left ventricular volumes and pressure-volume relationships were similar in exercised and non-exercised infarcted rats. CONCLUSION: In rats, 2 weeks of swimming exercise, started 1 week after acute experimental myocardial infarction and followed by 5 days of deconditioning, does not have an adverse effect on left ventricular remodeling.

Analysis of Variance↗
PubMed1998

Early angiotensin converting enzyme inhibitor therapy after experimental myocardial infarction prevents left ventricular dilation by reducing infarct expansion: a possible mechanism of clinical benefits.

OBJECTIVE: To examine the effects of early angiotensin-converting enzyme (ACE) inhibitor therapy after myocardial infarction on infarct expansion in an experimental rat model. BACKGROUND: ACE inhibitor therapy within 24 h of acute myocardial infarction (AMI) reduces mortality by unknown mechanism(s). METHODS: Rats underwent permanent coronary artery occlusion. A treated group received enalapril (1.9+/-0.2 mg/kg) daily in drinking water beginning 2 h after coronary artery occlusion, a time too late to reduce infarct size. Rats were sacrificed 2 days or 2 weeks after myocardial infarction. Hearts were arrested and fixed at a constant pressure, then sectioned and photographed for morphometric analysis. RESULTS: Infarcts in the control group expanded between 2 days and 2 weeks after myocardial infarction (expansion index 0.7+/-0.1 versus 2.5+/-0.4, P< 0.05). However, infarct expansion remained unchanged in the enalapril group between 2 days and 2 weeks after myocardial infarction (expansion index 0.8+/-0.1 versus 1.3+/-0.1, NS). Two weeks after myocardial infarction, the enalapril group had fewer expanded infarcts than the control group (expansion index 1.3+/-0.1 versus 2.5+/-0.4, P< 0.05). While left ventricular volume increased in the control group between 2 days and 2 weeks after myocardial infarction (0.17+/-0.01 ml versus 0.36+/-0.03 ml, P< 0.05), it remained constant in the enalapril group (0.22+/-0.02 ml versus 0.25+/-0.03 ml, NS). Two weeks after myocardial infarction, the left ventricles were larger in the control group than in the enalapril group (0.36+/-0.03 ml versus 0.25+/-0.03 ml, P< 0.05). CONCLUSIONS: Treatment with enalapril initiated 2 h after AMI prevented left ventricular dilation by limiting infarct expansion. This may explain the mechanism by which ACE inhibitor therapy started within 24 h of an AMI improves survival 5-6 weeks after infarction.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1998

Foot-and-mouth disease virus virulent for cattle utilizes the integrin alpha(v)beta3 as its receptor.

Adsorption and plaque formation of foot-and-mouth disease virus (FMDV) serotype A12 are inhibited by antibodies to the integrin alpha(v)beta3 (A. Berinstein et al., J. Virol. 69:2664-2666, 1995). A human cell line, K562, which does not normally express alpha(v)beta3 cannot replicate this serotype unless cells are transfected with cDNAs encoding this integrin (K562-alpha(v)beta3 cells). In contrast, we found that a tissue culture-propagated FMDV, type O1BFS, was able to replicate in nontransfected K562 cells, and replication was not inhibited by antibodies to the endogenously expressed integrin alpha5beta1. A recent report indicating that cell surface heparan sulfate (HS) was required for efficient infection of type O1 (T. Jackson et al., J. Virol. 70:5282-5287, 1996) led us to examine the role of HS and alpha(v)beta3 in FMDV infection. We transfected normal CHO cells, which express HS but not alpha(v)beta3, and two HS-deficient CHO cell lines with cDNAs encoding human alpha(v)beta3, producing a panel of cells that expressed one or both receptors. In these cells, type A12 replication was dependent on expression of alpha(v)beta3, whereas type O1BFS replicated to high titer in normal CHO cells but could not replicate in HS-deficient cells even when they expressed alpha(v)beta3. We have also analyzed two genetically engineered variants of type O1Campos, vCRM4, which has greatly reduced virulence in cattle and can bind to heparin-Sepharose columns, and vCRM8, which is highly virulent in cattle and cannot bind to heparin-Sepharose. vCRM4 replicated in wild-type K562 cells and normal, nontransfected CHO (HS+ alpha(v)beta3-) cells, whereas vCRM8 replicated only in K562 and CHO cells transfected with alpha(v)beta3 cDNAs. A similar result was also obtained in assays using a vCRM4 virus with an engineered RGD-->KGE mutation. These results indicate that virulent FMDV utilizes the alpha(v)beta3 integrin as a primary receptor for infection and that adaptation of type O1 virus to cell culture results in the ability of the virus to utilize HS as a receptor and a concomitant loss of virulence.

Animals↗
PubMed1998

Bilateral otoacoustic emissions pass in a baby with Mondini deformity and subsequently confirmed profound bilateral hearing loss.

Evoked otoacoustic emissions are well established as a hearing screening technique and are used extensively in paediatric audiology. They are believed to originate from the outer hair cells and can be detected in almost 100% of normally hearing ears; even a mild hearing loss has been shown to abolish otoacoustic emissions. Results are presented of a baby boy born at 29 weeks' gestation requiring 77 days of neonatal care, but experiencing no complications following discharge from the neonatal unit. This child had clear bilateral evoked otoacoustic emissions at almost four months of age, but was subsequently found to have a profound bilateral hearing impairment and absent otoacoustic emissions. Radiological investigations revealed bilateral Mondini dysplasia, and this child has now been implanted with a multi-channel MXM Digisonic cochlear implant. He is progressing well and shows awareness of sound. Approximately 10 previous cases of otoacoustic emissions occurring in profoundly deaf ears have been reported in the literature. Although it is likely that this child's hearing loss was progressive in nature, the authors believe that this is the first reported case of otoacoustic emissions being recorded in the presence of Mondini dysplasia. This raises concerns about the use of neonatal screening in isolation without adequate mechanisms for later identification of hearing impairment, although it is acknowledged that it represents a rare situation.

Child, Preschool↗
PubMed1998

College students' AIDS risk perception.

1. Students in this study appraised their AIDS risk using their sexual and drug-use behavior as criteria, which accurately reflects their knowledge of HIV transmission. 2. AIDS risk perceptions were not always congruent with the students' self-reported sexual and drug use behavior. Some students reporting high-risk behavior perceived their AIDS risk as "nil" or "small." 3. Perceived riskiness of behavior increased as distance from the students increased. The students viewed their friends' AIDS risk as moderately greater than their own risk and their peers' risk even greater.

Acquired Immunodeficiency Syndrome↗
PubMed1997

Role for a glycan phosphoinositol anchor in Fc gamma receptor synergy.

While many cell types express receptors for the Fc domain of IgG (Fc gamma R), only primate polymorphonuclear neutrophils (PMN) express an Fc gamma R linked to the membrane via a glycan phosphoinositol (GPI) anchor. Previous studies have demonstrated that this GPI-linked Fc gamma R (Fc gamma RIIIB) cooperates with the transmembrane Fc gamma R (Fc gamma RIIA) to mediate many of the functional effects of immune complex binding. To determine the role of the GPI anchor in Fc gamma receptor synergy, we have developed a model system in Jurkat T cells, which lack endogenously expressed Fc gamma receptors. Jurkat T cells were stably transfected with cDNA encoding Fc gamma RIIA and/or Fc gamma RIIIB. Cocrosslinking the two receptors produced a synergistic rise in intracytoplasmic calcium ([Ca2+]i) to levels not reached by stimulation of either Fc gamma RIIA or Fc gamma RIIIB alone. Synergy was achieved by prolonged entry of extracellular Ca2+. Cocrosslinking Fc gamma RIIA with CD59 or CD48, two other GPI-linked proteins on Jurkat T cells also led to a synergistic [Ca2+]i rise, as did crosslinking CD59 with Fc gamma RIIA on PMN, suggesting that interactions between the extracellular domains of the two Fc gamma receptors are not required for synergy. Replacement of the GPI anchor of Fc gamma RIIIB with a transmembrane anchor abolished synergy. In addition, tyrosine to phenylalanine substitutions in the immunoreceptor tyrosine-based activation motif (ITAM) of the Fc gamma RIIA cytoplasmic tail abolished synergy. While the ITAM of Fc gamma RIIA was required for the increase in [Ca2+]i, tyrosine phosphorylation of crosslinked Fc gamma RIIA was diminished when cocrosslinked with Fc gamma RIIIB. These data demonstrate that Fc gamma RIIA association with GPI-linked proteins facilitates Fc gamma R signal transduction and suggest that this may be a physiologically significant role for the unusual GPI-anchored Fc gamma R of human PMN.

Antigens, CD↗
PubMed1997

Requirement of integrin beta3 tyrosine 747 for beta3 tyrosine phosphorylation and regulation of alphavbeta3 avidity.

Leukocytes and platelets require stimulation for optimal beta3 integrin receptor function, whereas beta3 function is constitutive in many other cells. The molecular mechanisms that enhance integrin function in stimulated hematopoietic cells are poorly understood. Phosphorylation of the beta3 cytoplasmic tail is a recently described but prevalent phenomenon, with unknown effects on alphavbeta3 function. Here, we show that mutation of the beta3 cytoplasmic tail tyrosine 747 to phenylalanine (Y747F) prevents beta3 tyrosine phosphorylation in two cell lines. Whereas this mutation has no effect on alphavbeta3-mediated adhesion in a cell with constitutive beta3 function, it completely abolishes adhesion and clot retraction by a cell that requires stimulation for beta3 function. Ligand-induced conformational change as detected by LIBS-1 antibody occurs normally in Y747F mutant alphavbeta3. Thus, tyrosine 747 of beta3 is required for stimulation of alphavbeta3-mediated adhesion, probably due to its phosphorylation. Because the motif in beta3 required for tyrosine phosphorylation is shared by several integrin beta-chains, this may be a conserved mechanism for regulation of integrin-dependent adhesion.

Amino Acid Sequence↗
PubMed1997

A macrophage invasion mechanism of pathogenic mycobacteria.

Tuberculosis is the leading cause of death due to an infectious organism, killing an estimated 3 million people annually. Mycobacterium tuberculosis, the causative agent of tuberculosis, and other pathogenic mycobacteria require entry into host macrophages to initiate infection. An invasion mechanism was defined that was shared among pathogenic mycobacteria including M. tuberculosis, M. leprae, and M. avium but not by nonpathogenic mycobacteria or nonmycobacterial intramacrophage pathogens. This pathway required the association of the complement cleavage product C2a with mycobacteria resulting in the formation of a C3 convertase. The mycobacteria-associated C2a cleaved C3, resulting in C3b opsonization of the mycobacteria and recognition by macrophages.

Amino Acid Sequence↗
PubMed1997

Integrin-associated protein (CD47) is a comitogenic molecule on CD3-activated human T cells.

IAP is a glycoprotein functionally and physically associated with some integrins, i.e., the leukocyte response integrin and the beta3 integrin chain on placenta, platelets, and polymorphonuclear cells. IAP may act as a transducer element in activation mediated via these integrins. Since IAP is present at high density on peripheral T lymphocytes we have investigated its involvement in T cell activation. We tested three mAbs against IAP, namely B6H12, BRIC126, and 2D3, which recognize two distinct epitopes. IAP cross-linking with B6H12 or BRIC126, but not 2D3, transduces costimulatory signals within highly purified CD3-activated T lymphocytes, i.e., enhancement of proliferation, CD25 expression, and IL-2 secretion, while no effect was observed upon CD2 stimulation. However, we could not observe any functional association between IAP and integrins on peripheral T cells. In an attempt to explore further the activation signal delivered by IAP, we show here that IAP cross-linking with the comitogenic B6H12 mAb induces the phosphorylation on tyrosine of several proteins, one of which is identified as p56(lck) protein tyrosine kinase. Moreover, we observed that IAP is associated with p56(lck) on PMA-activated, but not on resting, T cells. These data suggest that on T cells, IAP may be involved directly via a specific ligand in cell-matrix or cell-cell interactions. Such interactions could trigger protein tyrosine phosphorylation pathways, which play an important role in both maturation and activation of T cells.

Antibodies, Monoclonal↗
PubMed1997

Costimulation of T cell activation by integrin-associated protein (CD47) is an adhesion-dependent, CD28-independent signaling pathway.

The integrin-associated protein (IAP, CD47) is a 50-kD plasma membrane protein with a single extracellular immunoglobulin variable (IgV)-like domain, a multiply membrane-spanning segment, and alternatively spliced short cytoplasmic tails. On neutrophils, IAP has been shown to function in a signaling complex with beta 3 integrins. However, the function of IAP on T cells, which express little or no beta 3 integrin, is not yet defined. Here, we show that mAbs recognizing IAP can enhance proliferation of primary human T cells in the presence of low levels of anti-CD3, but have no effect on T cell proliferation on their own. Together with suboptimal concentrations of anti-CD3, engagement of IAP also enhances IL-2 production in Jurkat cells, an apparently integrin-independent function of IAP. Nonetheless, costimulation by IAP ligation requires cell adhesion. IAP costimulation does not require CD28. Furthermore, anti-IAP, but not anti-CD28, synergizes with suboptimal anti-CD3 to enhance tyrosine phosphorylation of the CD3 zeta chain and the T cell-specific tyrosine kinase Zap70. Ligation of human IAP transfected into the hemoglobin-specific 3.L2 murine T cell hybridoma costimulates activation for IL-2 secretion both with anti-CD3 and with antigenic peptides on antigen-presenting cells (APCs). Moreover, ligation of IAP but not CD28 can convert antagonist peptides into agonists in 3.L2 cells. Using costimulation by IAP ligation as an assay to analyze the structure-function relationships in IAP signaling, we find that both the extracellular and multiply membrane-spanning domains of IAP are necessary for synergy with the antigen receptor, but the alternatively spliced cytoplasmic tails are not. These data demonstrate that IAP ligation initiates an adhesion-dependent costimulatory pathway distinct from CD28. We hypothesize that anti-IAP generates the costimulatory signal because it modulates interactions of the IgV domain with other plasma membrane molecules; this in turn activates effector functions of the multiply membrane-spanning domain of IAP. This model may have general significance for how IAP functions in cell activation.

Antibodies, Monoclonal↗
PubMed1997

Cytologic diagnosis of Ki-1 lymphoma in pleural and peritoneal effusions: a case report.

This is a report of a case of Ki-1-positive large-cell anaplastic lymphoma in an 87-year-old man diagnosed on pleural and peritoneal fluids by cytomorphologic and immunohistochemical examination. Papanicolaou-stained smears revealed many single, large neoplastic cells containing one or two nuclei with occasional multinucleated cells having a wreath-like nuclear arrangement. The tumor cells expressed Ki-1 antigen and epithelial membrane antigen. This is the first known report of Ki-1 lymphoma diagnosed initially on cytologic examination of pleural and peritoneal fluids.

Aged↗
PubMed1997

Cross talk between alpha(v)beta3 and alpha4beta1 integrins regulates lymphocyte migration on vascular cell adhesion molecule 1.

Local inflammation leads to increased expression of the vascular cell adhesion molecule (VCAM)-1 on vascular endothelium which contributes to the encapture of leukocytes from the circulating blood through the leukocyte ligand alpha4beta1 integrin. Inflammatory vascular endothelium expresses VCAM-1 at high density. We found that the speed of locomotion of activated lymphocytes migrating along surfaces coated with recombinant VCAM-1 at a comparable density to that found on inflammatory endothelium was slow. However, lymphocytes do migrate and extravasate rapidly under inflammatory conditions, indicating that there must be mechanisms that regulate the interaction between alpha4beta1 and VCAM-1 in vivo. Here we show that the lymphocyte alpha(v)beta3 integrin and integrin-associated protein (IAP) is able to regulate this interaction. The occupancy of lymphocyte alpha(v)beta3 integrin by platelet cell adhesion molecule-1 or vitronectin regulated the speed of alpha4beta1 integrin-dependent locomotion of lymphocytes on recombinant VCAM-1. This allowed rapid lymphocyte migration at VCAM-1 densities which are typical of inflammatory vessels. This alpha(v)beta3-mediated enhanced migration of lymphocytes via alpha4beta1 is likely to depend on the interaction of alpha(v)beta3 integrin with the IAP. Furthermore, this motile process correlates with polarization of the actin cytoskeleton in lymphocytes. Our results suggest that cross talk between alpha(v)beta3 integrin and alpha4beta1 integrin is a mechanism in the regulation of lymphocyte locomotion along inflammatory endothelium and subsequent transendothelial migration. This can explain how lymphocytes overcome tight adhesion to the vascular endothelium and start rapid migration along and through the endothelial lining of blood vessels into inflammatory tissue.

Animals↗