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Biomedical subjects

A Weiss

Publications and source records attributed to A Weiss.

At least 199 records · Page 11Linked to original sources
PubMed1994

GRB2 and phospholipase C-gamma 1 associate with a 36- to 38-kilodalton phosphotyrosine protein after T-cell receptor stimulation.

GRB2, a 25-kDa protein comprising a single SH2 domain flanked by two SH3 domains, has been implicated in linking receptor protein tyrosine kinases (PTKs) to the Ras pathway by interacting with the guanine nucleotide exchange protein SOS. Previous studies have demonstrated that GRB2 directly interacts with Shc, a proto-oncogene product that is tyrosine phosphorylated upon receptor and nonreceptor PTK activation. In this report, we detected low levels of tyrosine phosphorylation of Shc and induced association with GRB2 upon T-cell receptor (TCR) stimulation. Instead, a prominent 36- to 38-kDa tyrosine phosphoprotein (pp36-38) associated with the SH2 domain of GRB2 and formed a stable complex with GRB2/SOS upon TCR stimulation. Cellular fractionation studies showed that whereas both GRB2 and SOS partitioned to the soluble and particulate fractions, pp36-38 was present exclusively in the particulate fraction. This phosphoprotein had the same apparent mobility in sodium dodecyl sulfate-polyacrylamide gel electrophoresis as the phosphoprotein that associates with phospholipase C-gamma 1 (PLC-gamma 1). Furthermore, following partial immunodepletion of GRB2 and of the associated pp36-38, there was a significant reduction in the amount of the 36-kDa phosphoprotein associated with PLC-gamma 1, suggesting that a trimeric PLC-gamma 1/pp36-38/GRB2 complex could form. In support of this notion, we have also been able to detect low levels of PLC-gamma 1 in GRB2 immunoprecipitates. We suggest that pp36-38 may be a bridging protein, coupling different signalling molecules to cytoplasmic PTKs regulated by the TCR.

Adaptor Proteins, Signal Transducing↗
PubMed1994

The role of protein tyrosine kinases and protein tyrosine phosphatases in T cell antigen receptor signal transduction.

Engagement of the T cell antigen receptor (TCR) by peptide antigen bound to the major histocompatibility complex (MHC) molecules initiates a biochemical cascade involving protein tyrosine kinases (PTKs) and protein tyrosine phosphatases (PTPases). Recent biochemical and genetic evidence has implicated at least three cytoplasmic protein tyrosine kinases (PTKs), Lck, Fyn, and ZAP-70, that are involved in the initiation of TCR signal transduction. In addition, genetic evidence has demonstrated the requirement of the transmembrane PTPase, CD45, for TCR function. Activation of T cells through the TCR represents an alteration in the dynamic equilibrium between PTKs and PTPases. The TCR is a multi-subunit complex composed of at least six different gene products. Dissection of the TCR utilizing chimeric receptors and TCR mutants has demonstrated that the multi-subunit receptor is composed of at least two signal transducing modules, the CD3 and the zeta chain subunits. These two modules have in common peptide sequences within their cytoplasmic domains termed antigen recognition activation motifs (ARAMs) that are responsible for transducing signaling events. Moreover, the ARAM sequence is also found in subunits associated with a variety of other hematopoietic cell antigen receptors and is likely to form the basis for interactions with effector molecules within the signaling cascades of these receptors. Here we review the mechanism by which the ARAM sequences interact with PTKs and the cascades of PTKs and PTPases that are involved in mediating TCR function.

Amino Acid Sequence↗
PubMed1993

In vitro effect of hormones and growth factors on the incorporation of [3H]leucine, [35S]sulfate and [3H]proline by chondrocytes of aging mice.

The ability of parathyroid hormone (PTH 1-84), dexamethasone, prostaglandin E1 (PGE1), prostaglandin E2 (PGE2) and human transforming growth factor beta (hTGF-beta) to stimulate the synthesis of matrical components in articular cartilage of aging mice, was studied in an organ culture system. A marked age-dependent decrease was observed in the synthesis of sulfated glycosaminoglycans (GAGs), protein, collagen digestible protein (CDP) and non-collagen protein (NCP) between 1 and 18 months of age. The addition of hTGF-beta (1 ng/ml) into the culture medium resulted in a significant (P < 0.01) increase of both protein and sulfated GAGs in condylar cartilage from animals aged 1, 3, 6 and 12 months. PGE2 (10 micrograms/ml) induced [3H]leucine and [35S]SO4 incorporation into condylar cartilage from 1, 3 and 6 months old animals. A stimulatory effect of PGE1 (10 micrograms/ml) on [3H]leucine incorporation was noted at 1 and 3 months of age. The effect of PTH appeared to be stimulatory only for protein synthesis in young (1 and 3 months old) animals, whereas it had no effect at 6, 12 and 18 months of age. In contrast, dexamethasone exerted a stimulatory effect on young adults (6 months old) and in matured (12 months old) animals, respectively and a slight inhibitory effect on young (1 and 3 months old) animals. [3H]Proline incorporation was enhanced by all the factors tested in 1-month-old animals. In cultures from 6- and 18-month-old animals only PGE1 and PGE2 appeared to be stimulatory. It is concluded that synthesis of protein, sulfated GAGs and collagen by chondrocytes from maturing and osteoarthritic senescent animals can be stimulated by hormones and growth factors. The efficiency of this response, however, varied according to the animal's age and the factor studied.

Aging↗
PubMed1993

Characterization of platelet-activating factor receptors on canine T lymphocytes.

The ability of purified canine T lymphocytes to selectively bind platelet activating factor (PAF) was characterized. Authentic radiolabeled PAF rapidly and selectively bound to T lymphocytes and reached saturation within 1 min. This binding was reversible and highly selective for (R) PAF because (S) PAF, lyso-PAF, and diacyl PAF did not displace the bound (R) PAF probe. Only increasing quantities of chemically pure (R) PAF displaced the radiolabeled (R) PAF probe. The binding maximum of PAF was determined to be 35 pM per 2 x 10(6) lymphocytes. Competitive radioligand binding studies and Scatchard analysis indicated a single class of high affinity receptors with a dissociation constant of 0.077 nM and a receptor density of 6419 receptors per cell. The ability of purified canine T lymphocytes to hydrolyze PAF to the biologically inactive metabolite lyso-PAF was also studied. Over a 30-min incubation period, about 5% of PAF was metabolized to lyso PAF. This rate of PAF hydrolysis was the same as the rate observed with the media without cells, suggesting a small degree of nonenzymatic hydrolysis. The effects of varying concentrations of authentic PAF on intracellular free Ca2+ release in purified T lymphocytes was evaluated using the fluorescent probe Fura-2 and excitation-emission spectrofluorometry. PAF below the concentration of 1.0 nM did not significantly increase intracellular Ca2+ in T lymphocytes. More than 1 nM PAF, intracellular-free Ca2+ modestly, but significantly, increased in T lymphocytes. In other experiments, canine PBMC proliferated in response to Con A and in the one way MLR. These proliferative responses were abolished when the selective PAF receptor antagonist SC-47014A was added to the culture medium. In the MLR, this inhibitory effect was dependent on the length of time that the antagonist was in the culture. Specifically, inhibition of proliferation was incrementally reversed when the PAF antagonist was introduced progressively later into the 7-day MLR stimulation period, suggesting that PAF receptor blockade prevents an MLR response from occurring, but is unable to suppress an existing MLR response. Although the Con A-induced mononuclear cell proliferation was abolished with PAF receptor antagonists, the addition of authentic biologically active PAF or PAF analogs did not alter the proliferative response to Con A. In conclusion, canine T lymphocytes possess high affinity receptors for PAF. These binding sites are highly selective and reversible. PAF binding slightly increases intracellular free Ca2+ in T lymphocytes and appears to be involved in lymphocyte proliferation in response to soluble plant mitogen and alloantigen.

Animals↗
PubMed1993

The CD3 chains of the T cell antigen receptor associate with the ZAP-70 tyrosine kinase and are tyrosine phosphorylated after receptor stimulation.

Recent work indicates that signaling events resulting from stimulation of the T cell antigen receptor (TCR) can be initiated by the CD3 complex (gamma, delta, epsilon) as well as the zeta chains of the receptor. To help characterize the signaling function of CD3 we examined its associated tyrosine kinase activity since induction of tyrosine phosphorylation is one of the earliest signaling events. Our results indicate that at least two kinases, lck and ZAP-70, contribute to the CD3-associated kinase activity. A likely target of this activity is the CD3 complex itself since we observed that TCR stimulation resulted in rapid tyrosine phosphorylation of the CD3 epsilon and delta chains. To examine the function of the CD3 epsilon chain in particular, we constructed a chimera that fused the extracellular and transmembrane domains of CD8 to the cytoplasmic domain of CD3 epsilon. This chimera demonstrated that CD3 epsilon was independently capable of associating with proteins having tyrosine kinase activity, including ZAP-70. Our results show that the kinase activity that associates with the CD3 complex has characteristics that are quite similar to the previously characterized zeta-associated kinase activity. This finding suggests that both these components of the TCR initiate signaling events using a common mechanism. However, differences in their signaling function could result from recognition of distinct substrates.

Antibodies, Monoclonal↗
PubMed1993

Ligand-mediated negative regulation of a chimeric transmembrane receptor tyrosine phosphatase.

CD45, a transmembrane protein tyrosine phosphatase (PTPase), is required for TCR signaling. Multiple CD45 isoforms, differing in the extracellular domain, are expressed in a tissue- and activation-specific manner, suggesting an important function for this domain. We report that a chimeric protein in which the extracellular and transmembrane domains of CD45 are replaced with those of the EGF receptor (EGFR) is able to restore TCR signaling in a CD45-deficient cell. Thus, the cytoplasmic domain of CD45 is necessary and sufficient for TCR signal transduction. Moreover, EGFR ligands functionally inactivate the EGFR-CD45 chimera in a manner that is dependent on dimerization of the chimeric protein. Inactivation of EGFR-CD45 chimera function results in the loss of TCR signaling, indicating that CD45 function is continuously required for TCR-mediated proximal signaling events. These results suggest that ligand-mediated regulation of receptor-PTPases may have mechanistic similarities with receptor tyrosine kinases.

Blotting, Western↗
PubMed1993

Functional characterization of a signal transducing motif present in the T cell antigen receptor zeta chain.

A conserved sequence motif has been identified in a number of signaling subunits associated with hematopoietic cell antigen receptors. Here, we characterize signaling by a 17 amino acid motif that is triplicated in the T cell antigen receptor zeta chain. Analysis of zeta truncations and constructs containing the isolated motif demonstrates that this motif is sufficient for the induction of both proximal and distal events associated with T cell activation. Stimulation of truncations that contain either one, two, or three copies of the motif results in induction of an identical pattern of tyrosine phosphoproteins. Moreover, triplication of the NH2-terminal zeta motif results in enhanced signaling, suggesting a redundant role in signal amplification for the three motifs in zeta. Finally, we demonstrate the association of a recently identified protein tyrosine kinase ZAP-70 with this motif, and provide evidence for its involvement in zeta function.

Amino Acid Sequence↗
PubMed1993

CD45 specifically modulates binding of Lck to a phosphopeptide encompassing the negative regulatory tyrosine of Lck.

CD45 is a tyrosine phosphatase expressed in all hematopoietic cells which is important for signal transduction through the T cell antigen receptor (TCR). Studies using CD45-deficient cells have revealed that Lck, a tyrosine kinase thought to be essential for TCR signaling, is hyperphosphorylated on Y505 in the absence of CD45. This site of tyrosine phosphorylation negatively regulates the function of the Src family of kinases. Here we provide evidence that CD45 can modulate the binding of the Lck to an 11 amino acid tyrosine phosphorylated peptide containing the carboxy-terminus of Lck (lckP). Significantly, CD45 did not influence the binding of Fyn, PLC gamma 1, GAP and Vav to the same phosphopeptide. Lck protein which bound the peptide was dephosphorylated on Y505 and consisted of only 5-10% of the total cellular Lck. Interestingly, there was a marked increase in binding 15-30 min after CD4 or TCR cross-linking. Taken together, our data suggest that CD45 specifically modulates the conformation of Lck in a manner consistent with the intramolecular model of regulation of Src-like kinases.

Amino Acid Sequence↗
PubMed1993

Signal transduction events leading to T-cell lymphokine gene expression.

The expression of T-cell derived lymphokines is regulated by signal transduction events initiated by the T-cell antigen receptor and other T-cell surface molecules. Substantial progress has been made in characterizing the signal transduction events initiated at the plasma membrane of the T cell and their targets which control lymphokine gene expression in the nucleus. This review will summarize recent progress in this area of investigation.

Animals↗
PubMed1993

Acute conjunctivitis in childhood.

We obtained specimens for culture from the lids and conjunctivae of 95 patients with acute conjunctivitis and 91 control children of similar age and, in addition, stained the conjunctival scrapings with Giemsa and Gram stains. The conjunctivitis was attributed to bacterial infection in 76 patients, viral infection in 12 children, and allergy in 2 patients; no cause was identified in the remaining 5 patients. In most cases the etiologic diagnosis was based on the results of laboratory studies. By separately culturing microorganisms in specimens from the lids and conjunctivae of patients and control subjects, we could distinguish normal flora from pathogens, and blepharitis from conjunctivitis. Staphylococci, corynebacteria, and alpha-hemolytic streptococci were the predominant organisms recovered from the lids of control subjects. In contrast, Haemophilus influenzae, Streptococcus pneumoniae, and Moraxella catarrhalis were the major pathogens cultured from the conjunctival specimens from patients with bacterial conjunctivitis. Gram stains of conjunctival scrapings provided a rapid means of predicting the pathogen in 51 of 55 cases of bacterial conjunctivitis. Giemsa stains of conjunctival scrapings provided etiologic information in 81 of 84 cases, showing neutrophilia in bacterial infections, lymphocytosis in viral infections, and eosinophilia in allergic disease. These results indicate that most cases of acute conjunctivitis in children can be diagnosed on the basis of differential cultures of microorganisms from the lid and conjunctiva, together with Giemsa stains of conjunctival scrapings.

Acute Disease↗
PubMed1993

Single physician approach to radiofrequency catheter ablation in patients with supraventricular tachycardia.

The minimal requirements for safe and effective performance of catheter ablation using radiofrequency current are still unclear. To determine the feasibility and safety of single physician approach to catheter ablation of supraventricular tachycardia substrate using radiofrequency energy, the results of the ablation procedure in 52 consecutive patients were evaluated. The procedures were performed during 1 year by the same physician and nurse. Twenty-one patients had selective atrioventricular (AV) nodal pathway ablation and 31 patients had accessory AV pathway ablation. Forty-eight patients (89%) had the diagnostic and the ablative procedure during the same electrophysiological test. In the 21 patients with AV nodal reentrant tachycardia, all had successful selective ablation of the fast (13) or the slow (8) pathways. Eight patients had recurrence of the clinical tachycardia and had a successful reablation. No patient developed complete AV block or other significant complications. The mean fluoroscopy time during the procedure was 16.0 +/- 8.6 minutes. In the eight patients with Wolff-Parkinson-White syndrome, all concealed accessory pathways were successfully ablated with a mean fluoroscopy time of 30.0 +/- 27.9 minutes. Two patients had recurrence of the conduction through the accessory pathway and had a successful reablation. Eighteen of 19 patients with a single overt accessory pathway had successful ablation, with a fluoroscopy time of 22.7 +/- 20.6 minutes. Three patients had an early recurrence of the conduction through the accessory pathway, reablation was successful in two of them. Ten accessory pathways were ablated in four patients with multiple pathways during nine procedures. Only two patients developed minor peripheral vascular complications.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Obstetric correlates of neonatal retinal hemorrhage.

OBJECTIVE: To determine whether maternal or fetal factors, other than vacuum-assisted delivery, play a role in neonatal retinal hemorrhage, and whether correlates are similar in retinal hemorrhage after spontaneous vaginal delivery. METHODS: A cross-section of assisted deliveries at an urban hospital (n = 156) over 7 months were compared with contemporaneous spontaneous vaginal deliveries (n = 122). A subset of assisted deliveries (n = 87) was prospectively randomized to forceps or vacuum-assisted delivery by sealed envelope. Maternal and neonatal biometric data were collected, and Apgar scores, umbilical artery blood gas analysis, and neonatal ophthalmologic evaluations were performed. RESULTS: Moderate to severe retinal hemorrhage was found in 18% of spontaneous, 13% of forceps, 28% of vacuum-assisted, and 50% of sequential vacuum and forceps-assisted deliveries. Fetal distress (P < .008), vacuum-assisted delivery (P < .02), decreased birth weight for gestation (P < .004), umbilical artery pH less than 7.20 (P < .004), and second stage of labor less than 30 minutes (P < .05) were most closely associated with increased degrees of retinal hemorrhage. Maternal parity, preeclampsia, length of labor, and head circumference were not correlated with retinal hemorrhage. Vacuum-assisted delivery among low birth weight infants (P < .0001), short second stage of labor (P < .006), fetal acidosis (P < .045), and sequential use of vacuum and forceps for assisted delivery (P < .005) formed a logistic model that correctly predicted 81% of moderate to severe retinal hemorrhage cases. Logistic analysis of the randomized assisted deliveries gave similar results. CONCLUSIONS: Maternal and fetal factors other than vacuum-assisted delivery are significant correlates of moderate to severe retinal hemorrhage. Vacuum-assisted delivery among small for gestational age infants is closely correlated with moderate to severe retinal hemorrhage.

Adult↗
PubMed1992

ZAP-70: a 70 kd protein-tyrosine kinase that associates with the TCR zeta chain.

Protein-tyrosine kinases (PTKs) play an integral role in T cell activation. Stimulation of the T cell antigen receptor (TCR) results in tyrosine phosphorylation of a number of cellular substrates. One of these is the TCR zeta chain, which can mediate the transduction of extracellular stimuli into cellular effector functions. We have recently identified a 70 kd tyrosine phosphoprotein (ZAP-70) that associates with zeta and undergoes tyrosine phosphorylation following TCR stimulation. Here we report the isolation of a cDNA clone encoding ZAP-70. ZAP-70 represents a novel PTK and is expressed in T and natural killer cells. Moreover, tyrosine phosphorylation and association of ZAP-70 with zeta require the presence of src family PTKs and provide a potential mechanism by which the src family PTKs and ZAP-70 may interact to mediate TCR signal transduction.

Amino Acid Sequence↗
PubMed1992

Angiographic findings in the coronary arteries after thrombolysis in acute myocardial infarction.

The angiographic appearance of the coronary arteries was examined in 308 patients with acute myocardial infarction (AMI) who received high-dose intravenous thrombolytic therapy. Coronary angiography was performed on day 7 after admission to the hospital. Patients had an average of 2.4 discrete arterial narrowings or obstructions. The narrowings were proximal and related to bifurcations. Four fifths of the culprit arteries were patient; 104 (34%) had a ruptured plaque, 22 (7%) had an ulcerated plaque, and in 190 (62%) the lesions were eccentric. Patients differed from a comparable, previously studied, control series of 302 patients with chronic stable angina pectoris who had more extensive disease. They had 5.7 narrowings/patient, also located proximally and at bifurcations, but more widely distributed in the coronary tree. Patients with AMI who are suitable for thrombolysis have a unique coronary angiographic picture. The data confirm that AMI is caused by sudden rupture of a localized atheromatous plaque that initiates an obstructive thrombotic cascade.

Angina Pectoris↗