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Biomedical subjects

A Weiss

Publications and source records attributed to A Weiss.

At least 145 records · Page 8Linked to original sources
PubMed1996

DNA demethylation in vitro: involvement of RNA.

An in vitro system for studying DNA demethylation has been established using extracts from tissue culture cells. This reaction, which is unusually resistant to proteinase K, takes place through the removal of a 5-methylcytosine nucleotide unit from the DNA substrate and its conversion to an RNase-sensitive form. It is likely that this represents the in vivo mechanism, as well, since extracts from L8 myoblasts specifically demethylate an alpha-actin gene, while extracts from F9 teratocarcinoma cells specifically demodify the Aprt CpG island. After pretreatment with proteinase K, these extracts demethylate both genes equally, suggesting that gene specificity may be controlled by protein factors.

Actins↗
PubMed1996

Phosphotyrosines in the killer cell inhibitory receptor motif of NKB1 are required for negative signaling and for association with protein tyrosine phosphatase 1C.

NKB1 is one member of a growing family of killer cell inhibitory receptors (KIR). It is expressed on natural killer (NK) cells and T cells, and has been shown to inhibit cytolytic functions of these cells upon interacting with its ligand, HLA-B (Bw4). We demonstrate here that the cytoplasmic region of NKB1 is capable of inhibiting T cell activation in Jurkat cells. The tyrosine phosphorylation of the NKB1 KIR consensus motif, YxxL(x)26 YxxL, induces an association with the protein tyrosine phosphatase 1C (PTP1C). Importantly, mutation of both tyrosines in the motif abolished the inhibitory functions of NKB1 and abrogated PTP1C association. Mutational analysis of the individual tyrosines suggest that the membrane proximal tyrosine may play a crucial role in mediating the inhibitory signal. These results demonstrate that KIR can not only inhibit cytolytic activity, but can also negatively regulate T cell receptor activation events that lead to downstream gene activation, and further supports a model that implicates PTP1C as a mediator in the KIR inhibitory signal.

Amino Acid Sequence↗
PubMed1996

SH2 domain function is essential for the role of the Lck tyrosine kinase in T cell receptor signal transduction.

Tyrosine kinase activity is required for signal transduction through the T cell antigen receptor (TCR). The Src family tyrosine kinase Lck appears to play a key role in the initiation of TCR signaling events. We have investigated the role of the phosphotyrosine-binding Src homology-2 (SH2), domain of Lck in TCR signaling. Lck containing a mutation in the phosphotyrosine binding pocket of the SH2 domain was expressed in an Lck-deficient cell line. We found that, in contrast to wild-type Lck, the SH2 domain mutant was unable to restore even the earliest TCR-mediated signaling events. To investigate the role of the Lck SH2 domain, we examined the association of tyrosine phosphoproteins with Lck. The predominant associated phosphoprotein was the ZAP-70 tyrosine kinase, which has also been implicated in the initiation of TCR signaling. In addition, the zeta subunit of the T cell receptor was found to weakly associate with Lck. Further analysis indicated that the SH2 domain of Lck can directly recognize both ZAP-70 and zeta in immunoprecipitates from TCR-stimulated cells. Our findings demonstrate that the SH2 domain of Lck is essential for the initiation of signaling events following TCR stimulation probably as a result of its ability to mediate an interaction between Lck and the ZAP-70 tyrosine kinase and/or the zeta subunit of the T cell receptor.

Calcium↗
PubMed1996

Lck regulates the tyrosine phosphorylation of the T cell receptor subunits and ZAP-70 in murine thymocytes.

The Src-family and Syk/ZAP-70 family of protein tyrosine kinases (PTK) are required for T cell receptor (TCR) functions. We provide evidence that the Src-family PTK Lck is responsible for regulating the constitutive tyrosine phosphorylation of the TCR zeta subunit in murine thymocytes. Moreover, ligation of the TCR expressed on thymocytes from Lck-deficient mice largely failed to induce the phosphorylation of TCR-zeta, CD3 epsilon, or ZAP-70. In contrast, we find that the TCR-zeta subunit is weakly constitutively tyrosine phosphorylated in peripheral T cells isolated from Lck-null mice. These data suggest that Lck has a functional role in regulation of TCR signal transduction in thymocytes. In peripheral T cells, other Src-family PTKs such as Fyn may partially compensate for the absence of Lck.

Animals↗
PubMed1996

Dominant-negative zeta-associated protein 70 inhibits T cell antigen receptor signaling.

Zeta-associated protein (ZAP)-70 is a cytoplasmic protein tyrosine required for T cell antigen receptor (TCR) signaling and development. Mutations in ZAP-70 result in severe combined immunodeficiency in humans. ZAP-70 interacts with the TCR by binding to tyrosine-phosphorylated immunoreceptor tyrosine-based activation motifs (ITAMs) present in the invariant subunits of the TCR complex. Here we report that two ZAP-70 mutants devoid of kinase activity, generated either by a point mutation in the kinase domain to create an inactive kinase, or by truncation of the entire kinase domain (SH2[N+C]), functioned as dominant-negative mutants to specifically suppress TCR-mediated activation of NFAT, a nuclear factor essential for inducible interleukin 2 gene expression. Biochemical studies with the SH2(N+C) mutant showed that it also blocked early TCR signaling events, such as p95vav tyrosine phosphorylation, extracellular signal-regulated kinase 2 activation, and the association of a number of tyrosine-phosphorylated proteins with growth factor receptor-binding protein 2 (GRB2). The inhibitory effects of the SH2(N+C) mutant revealed that it requires an intact phosphotyrosine-binding site in its COOH-terminal SH2 domain. Using a CD8-zeta chimeric receptor to analyze the interaction of the SH2(N+C) mutant with ITAMs of TCR-zeta, we found that this mutant was constitutively bound to the hyperphosphorylated CD8-zeta chimera. These results indicate that tyrosine-phosphorylated ITAM is the target for the action of this dominant-negative mutant, suggesting that the assembly of a functional receptor signaling complex on ITAMs is a critical proximal TCR signaling event leading to downstream activation.

Adaptor Proteins, Signal Transducing↗
PubMed1996

Improved outcome in adult B-cell acute lymphoblastic leukemia.

A total of 68 adult patients with B-cell acute lymphoblastic leukemia (B-ALL) were treated in three consecutive adult multicenter ALL studies. The diagnosis of B-ALL was confirmed by L3 morphology and/or by surface immunoglobulin (Slg) expression with > 25% blast cell infiltration in the bone marrow (BM). They were characterized by male predominance (78%) and a median age of 34 years (15 to 65 y) with only 9% adolescents (15 to 20 y), but 28% elderly patients (50 to 65 y). The patients received either a conventional (N = 9) ALL treatment regimen (ALL study 01/81) or protocols adapted from childhood B-ALL with six short, intensive 5-day cycles, alternately A and B. In study B-NHL83 (N = 24) cycle A consisted of fractionated doses of cyclophosphamide 200 mg/m2 for 5 days, intermediate-dose methotrexate (IdM) 500 mg/m2 (24 hours), in addition to cytarabine (AraC), teniposide (VM26) and prednisone. Cycle B was similar except that AraC and VM26 were replaced by doxorubicin. Major changes in study B-NHL86 (N = 35) were replacement of cyclophosphamide by ifosphamide 800 mg/m2 for 5 days, an increase of IdM to high-dose, 1,500 mg/m2 (HdM) and the addition of vincristine. A cytoreductive pretreatment with cyclophosphamide 200 mg/m2, and prednisone 60 mg/m2, each for 5 days was recommended in study B-NHL83 for patients with high white blood cell (WBC) count (> 2,500/m2) or large tumor burden and was obligatory for all patients in study B-NHL86. Central nervous system (CNS) prophylaxis/treatment consisted of intrathecal methotrexate (MTX) therapy, later extended to the triple combination of MTX, AraC, and dexamethasone, and a CNS irradiation (24 Gy) after the second cycle. Compared with the ALL 01/81 study where all the patients died, results obtained with the pediatric protocols B-NHL83 and B-NHL86 were greatly improved. The complete remission (CR) rates increased from 44% to 63% and 74%, the probability of leukemia free survival (LFS) from 0% to 50% and 71% (P = .04), and the overall survival rates from 0% to 49% and 51% (P = .001). Toxicity, mostly hematotoxicity and mucositis, was severe but manageable. In both studies B-NHL83 and B-NHL86, almost all relapses occurred within 1 year. The time to relapse was different for BM, 92 days, and for isolated CNS and combined BM and CNS relapses, 190 days (P = .08). The overall CNS relapses changed from 50% to 57% and 17%, most probably attributable to the high-dose MTX and the triple intrathecal therapy. LFS in studies B-NHL83 and B-NHL86 was significantly influenced by the initial WBC count < or > 50,000/microL, LFS 71% versus 29% (P = .003) and hemoglobin value > or < 8 g/dL, LFS 67% versus 27% (P = .02). Initial CNS involvement had no adverse impact on the outcome. Elderly B-ALL patients (> 50 years) also benefited from this treatment with a CR rate of 56% and a LFS of 56%. It is concluded that this short intensive therapy with six cycles is effective in adult B-ALL. HdM and fractionated higher doses of cyclophosphamide or ifosphamide seem the two major components of treatment.

Adolescent↗
PubMed1996

"Congenital" coronary arteriovenous malformations: are they truly congenital?

We report a patient with ischemic chest pain due to obstructive coronary artery disease. The patient underwent a second cardiac catheterization 2 years later that revealed progression of the coronary disease and the appearance of a new arteriovenous malformation. Unless a prior angiogram was available, this malformation would have been classified as congenital. This case report raises the question of whether all congenital arteriovenous malformations are truly congenital.

Aged↗
PubMed1996

Acceleration of experimental diabetic retinopathy in the rat by omega-3 fatty acids.

Omega-3 fatty acids exert several important biological effects on factors that may predispose to diabetic retinopathy. Potential pathogenetic mechanisms include platelet dysfunction, altered eicosanoid production, increased blood viscosity in association with impaired cell deformability and pathologic leucocyte/endothelium interaction. Therefore, we tested whether a 6-month administration of fish oil (750 mg Maxepa, 5 times per week), containing 14% eicosapentaenoic acid (EPA) and 10% docosahexaenic acid, could inhibit the development of experimental retinopathy of the streptozotocin-diabetic rat. The efficiency of fish oil supplementation was evaluated by measuring EPA concentrations in total, plasma and membrane fatty acids and by measuring the generation of lipid mediators (leukotrienes and thromboxanes). Retinal digest preparations were quantitatively analysed for pericyte loss, and the formation of acellular capillaries. Omega-3 fatty acid administration to diabetic rats resulted in a twofold increase of EPA 20:5 in total fatty acids, and a reduction of the thromboxane ratio from 600 (untreated diabetic rats) to 50 (treated diabetic rats). Despite these biochemical changes, diabetes-associated pericyte loss remained unaffected and the formation of acellular, occluded capillaries was increased by 75% in the fish oil treated diabetic group (115.1 +/- 26.8; untreated diabetic 65.2 +/- 15.0 acellular capillary segments/mm2 of retinal area). We conclude from this study that dietary fish oil supplementation may be harmful for the diabetic microvasculature in the retina.

Animals↗
PubMed1996

Use of surrogate respondents in studies of stroke and dementia.

A study was performed to determine the misclassification of information on exposure when surrogate informants are interviewed. Information from nondementia patients admitted to a geriatric ward was compared with that obtained from the patients' family members or friends (informants). Thirty-seven patients were recruited (17 with current or previous stroke, and 20 no history of stroke). Information on past medical and family history, cigarette smoking and alcohol consumption was collected using a questionnaire that was administered independently to patients and informants. For nonstroke patients, agreement on smoking and alcohol consumption at different ages was generally good. Informants reported slightly lower smoking and alcohol intake than patients: 1.3 fewer total pack-years (95% CI, -3.8, +6.5) and 2.7 fewer units/week (95% CI, -1.5, +6.9), respectively. For stroke patients, informants tended to report a greater smoking consumption at all ages, and a slightly higher alcohol consumption. Informants reported an excess of 7.4 total pack-years (95% CI, -1.2, + 16.0) and 2.19 units/week (95% CI, -1.0, +5.3). Agreement for medical history was good, except for hypertension. There was poor agreement for family medical history. The impact of misclassification is discussed.

Aged↗
PubMed1996

Vav and SLP-76 interact and functionally cooperate in IL-2 gene activation.

T cell antigen receptor (TCR) stimulation induces tyrosine phosphorylation of many intracellular proteins, including the proto-oncogene Vav, which is expressed exclusively in hematopoietic and trophoblast cells. Vav is critical for lymphocyte development and activation. Overexpression of Vav in Jurkat T cells leads to potentiation of TCR-mediated IL-2 gene activation. However, the biochemical function of Vav is unknown. Here, we demonstrate that the major induced tyrosine phosphoprotein associated with Vav is the hematopoietic cell-specific SLP-76. The Vav SH2 domain is required for this interaction and for TCR-mediated Vav tyrosine phosphorylation. Similar to Vav, overexpression of SLP-76 markedly potentiates TCR-mediated NF-AT and IL-2 gene activation. Furthermore, overexpression of both Vav and SLP-76 synergistically induces basal and TCR-stimulated NF-AT activation. These results suggest that a signaling complex containing Vav and SLP-76 plays an important role in lymphocyte activation.

Adaptor Proteins, Signal Transducing↗
PubMed1996

alpha beta T cell development is abolished in mice lacking both Lck and Fyn protein tyrosine kinases.

Two families of protein tyrosine kinases (PTKs), the Src and Syk/ZAP-70 families, are required for T cell development. Lck is the major Src family member required for thymopoiesis, since there is a severe deficit of CD4+CD8+ thymocytes and mature T cells in its absence. However, some peripheral T cells are evident in these mice, suggesting that additional PTKs may contribute to T cell development. Here we show that the combined disruption of Lck and Fyn (lck(-/-)fyn(-/-)) completely arrests alpha beta T cell development at the CD4-CD8- stage. The development of V gamma 3+ dendritic epidermal T cells is also severely impaired, but natural killer cell development and cytolytic activity is unaffected in lck(-/-)fyn(-/-) mice. These findings reveal the potential for redundant functions mediated by Src family PTKs while emphasizing crucial roles for Lck and Fyn in T cell development.

Animals↗
PubMed1996

Community-based resilient peer treatment of withdrawn maltreated preschool children.

The purpose of the present study was to evaluate differences in the social play of maltreated and nonmaltreated preschool children and the effectiveness of a resilient peer treatment (RPT) for socially withdrawn victims of physical abuse and neglect. RPT is a peer-mediated classroom intervention based on a developmental-ecological model. It involves pairing withdrawn children with resilient peers in the natural classroom under the supervision of a parent assistant. Forty-six Head Start children, of whom 22 were maltreated, were randomly assigned to RPT and control conditions. Outcome variables were observational categories of social play and standardized teacher ratings. Before treatment, maltreated children were significantly more isolated and less interactive in peer play than nonmaltreated children. RPT resulted in a significant increase in positive interactive peer play and a decrease in solitary play for maltreated and nonmaltreated, socially withdrawn children. Moreover, treatment gains in social interactions were validated 2 months following treatment. Findings are discussed in terms of a developmental-ecological model.

Child Abuse↗
PubMed1996

TCR- and IL-1-mediated co-stimulation reveals an IL-4-independent way of Th2 cell proliferation.

Previously, it has been shown that Th1 cells, when triggered solely via their TCR, are blocked from proliferation in response to IL-2. Herein, we describe a similar characteristic for Th2 cells in that immobilized mAb directed to the TCR blocked proliferation of Th2 cells in response to IL-4. This "proliferative block' was observed in all four Th2 cell clones tested, but not in a subline of one of the clones which has been cultured in vitro for several years. Addition of IL-1 neutralized the proliferative block in all four Th2 cell clones. Surprisingly, blocking experiments with sIL-4R and anti-IL-4 mAb revealed that in three out of four Th2 cell clones this effect of IL-1 was IL-4-independent and could also not be blocked by cyclosporin A (CsA). In contrast, the proliferation of one Th2 cell clone in response to the TCR- and IL-1-mediated signals was indeed inhibited by sIL-4R, anti-IL-4 mAb and CsA. Thus, our data illustrate that in addition to the well-known IL-4-dependent proliferation, there also exists an IL-4-independent, IL-1-mediated way of Th2 cell proliferation.

Animals↗
PubMed1996

Recommendations for the use of routine bone marrow aspiration and lumbar punctures in the follow-up of patients with retinoblastoma.

PURPOSE: Patients with metastatic retinoblastoma have a poor outcome. Hope that early detection of extraocular spread will improve survival has led to routine monitoring with bone marrow and cerebrospinal fluid (CSF) examinations. In light of cost and patient morbidity, the clinical utility of this practice is questioned. PATIENTS AND METHODS: We have performed 254 serial bone marrow aspirations and 164 lumbar punctures in 60 children with retinoblastoma. RESULTS: Two patients with extensive intraocular disease at diagnosis developed positive bone marrow aspirations, although no patient died of distant metastasis. Three patients developed positive CSF examinations. All had neurologic symptoms at the time of CSF positivity. CONCLUSIONS: We recommend performing staging bone marrow and CSF evaluations only in patients with clinical, histologic, or radiologic evidence of local or systemic extension (Pratt stage III-IV), or in patients presenting with one Reese-Ellsworth group V eye and retrolaminar or extrascleral extension of their tumor. We recommend limiting follow-up bone marrow and CSF evaluations to patients who develop objective signs and symptoms of metastatic or regionally recurrent disease.

Biopsy, Needle↗
PubMed1996

High-dose catecholamine treatment decreases polymorphonuclear leukocyte phagocytic capacity and reactive oxygen production.

Flow cytometry was used to study phagocytic function (uptake of fluorescein isothiocyanate-labeled bacteria) and release of reactive oxygen products (dihydrorhodamine 123 converted to rhodamine 123) following phagocytosis by neutrophil granulocytes of heparinized whole blood treated with adrenaline, noradrenaline, dopamine, dobutamine, or orciprenaline. Reduced neutrophil phagocytosis and reactive oxygen production were seen at 12 micrograms of adrenaline per liter (72% each compared with control values); at 120 micrograms of noradrenaline (72% each), dobutamine (83 and 80%, respectively), and orciprenaline (81 and 80%, respectively) per liter; and at 100 micrograms of dopamine per liter (66 and 70%) (P < 0.05 for all). At these dosages, neutrophil chemotaxis was reduced to < 50% of control values for all catecholamines. Treatment with catecholamines at lower dosages had no significant effect on phagocytosis or generation of reactive oxygen products or chemotaxis. The phagocytic capacity of granulocytes was related to the generation of reactive oxygen products (r = 0.789; P < 0.05). The results demonstrate that catecholamines have a suppressive effect on the response of phagocytic cells to bacterial pathogens at high therapeutic levels in blood.

Adult↗
PubMed1996

Enhancement of lymphocyte responsiveness by a gain-of-function mutation of ZAP-70.

The protein tyrosine kinase ZAP-70 plays an essential role in T-cell activation and development. After T-cell receptor stimulation, ZAP-70 is associated with the receptor and is phosphorylated on many tyrosine residues, including tyrosine 292 (Y-292), in the region between the C-terminal SH2 domain and the kinase domain (interdomain B). Here we show that a mutation of Y-292 (292F) or deletion of interdomain B enhanced the ability of ZAP-70 to reconstitute B-cell receptor stimulation-dependent NF-AT induction in a B-cell line deficient in Syk. In contrast, in a T-cell line, expression of 292F led to basal NF-AT induction independent of T-cell receptor stimulation. These results demonstrate that the role of Y-292 is to negatively regulate the function of ZAP-70 in lymphocytes. This appears to be a dominant function of interdomain B because deletion of most of interdomain B also resulted in a mutant of ZAP-70 with enhanced ability to reconstitute Syk-deficient DT-40 B cells. Since our biochemical studies did not reveal an effect of the 292F mutation on either the kinase activity of ZAP-70 or on the ability of ZAP-70 to bind to the receptor, we propose a model in which Y-292 interacts with an inhibitory protein to negatively regulate ZAP-70 function.

Gene Expression Regulation↗