Search PubMed⌕ Search

Biomedical subjects

A Weiss

Publications and source records attributed to A Weiss.

At least 163 records · Page 9Linked to original sources
PubMed1996

The mammalian myosin heavy chain gene family.

Myosin is a highly conserved, ubiquitous protein found in all eukaryotic cells, where it provides the motor function for diverse movements such as cytokinesis, phagocytosis, and muscle contraction. All myosins contain an amino-terminal motor/head domain and a carboxy-terminal tail domain. Due to the extensive number of different molecules identified to date, myosins have been divided into seven distinct classes based on the properties of the head domain. One such class, class II myosins, consists of the conventional two-headed myosins that form filaments and are composed of two myosin heavy chain (MYH) subunits and four myosin light chain subunits. The MYH subunit contains the ATPase activity providing energy that is the driving force for contractile processes mentioned above, and numerous MYH isoforms exist in vertebrates to carry out this function. The MYHs involved in striated muscle contraction in mammals are the focus of the current review. The genetics, molecular biology, and biochemical properties of mammalian MYHs are discussed below. MYH gene expression patterns in developing and adult striated muscles are described in detail, as are studies of regulation of MYH genes in the heart. The discovery that mutant MYH isoforms have a causal role in the human disease familial hypertrophic cardiomyopathy (FHC) has implemented structure/function investigations of MYHs. The regulation of MYH genes expressed in skeletal muscle and the potential functional implications that distinct MYH isoforms may have on muscle physiology are addressed.

Animals↗
PubMed1996

Autopsy findings in patients with human immunodeficiency virus infection with emphasis on the risk factor of hemophilia.

The autopsy findings of 80 human immunodeficiency virus (HIV)-infected adults, who died between 1982-1995, are presented with special emphasis on the risk factor of hemophilia. The study included 23 blood product recipients (hemophiliacs n = 21; non-hemophiliacs n = 2), 34 homosexuals, four intravenous drug abusers, and 19 patients with no known risk factor. Nearly all individuals (93%) showed the late stage of acquired immunodeficiency syndrome (AIDS). Blood product recipients had a significantly lower overall frequency of opportunistic infections (p < 0.05). Homosexuality was associated with the highest overall frequency of opportunistic infections and HIV-associated malignancies, such as Kaposi's sarcoma and malignant non-Hodgkin's lymphoma. Exclusive visceral involvement of Kaposi's sarcoma was frequent, and no decrease of Kaposi's sarcoma was observed during the study period. Pneumocystis infections, atypical mycobacteriosis, and non-Hodgkin's lymphoma showed a significant increase during the last five years (1991-1995) of the observation interval. Opportunistic infections and malignancies were the cause of death in approximately one-half of the patients. In blood product recipients, hepatic failure due to posthepatitic cirrhosis and hemorrhage due to hepatic failure with subsequent coagulopathy and in non-blood product recipients, bacterial bronchopneumonia, and diffuse alveolar damage were additional major causes of death. The data suggest a lower risk for HIV-infected blood product recipients, particularly hemophiliacs, to acquire opportunistic infections and malignant neoplasms.

Adult↗
PubMed1996

Modification of vitronectin by advanced glycation alters functional properties in vitro and in the diabetic retina.

Early diabetic retinopathy is characterized by areas of acellular capillaries and the accumulation of advanced glycation end products (AGE). Endothelial cell maintenance, growth, and migration is regulated by a complex system involving the partitioning of growth factors between extracellular matrix-bound proteoglycans and cells, as well as by the activation and control of pericellular proteolysis. Using specific antibodies, we compared the immunolocalization of the vascular heparan sulfate proteoglycan (HSPG)-binding protein vitronectin (VN), HSPG, basic fibroblast growth factor, and collagen type 1 in retinae prepared from 11-month-old diabetic and nondiabetic Wistar rats. In normal rats, VN immunostaining was prominent in vascularized parts of the inner retina and colocalized with HSPG, which itself showed costaining with basic fibroblast growth factor in the extracellular matrix, vascular walls, and the inner limiting membrane. In contrast, the recognition of VN, HSPG, and basic fibroblast growth factor in diabetic retinae was greatly reduced in the inner limiting membrane and the extracellular matrix, where increased immunoreactive AGE colocalizing with VN were detectable. Capillary labeling of retinal vessel walls for plasminogen activator inhibitor-1 was moderate in both normal and diabetic retinae. AGE-VN was demonstrated in tissue extracts from retina by immunoprecipitation and Western blotting and presented a similar increase of AGE-related immunoreactivity compared with AGE-VN generated in vitro. AGE-VN in vitro had lost its native conformation, yielded high Mr SDS-resistant products, and was resistant to proteolysis because of modification of about 30% of lysines. Because binding of glycosaminoglycans, as well as interaction of type I collagen and the morphoregulatory proteins osteonectin and tenascin with AGE-VN, were reduced to at least 50% of control, alteration of basic residues in the heparin-binding domain of VN is plausible. In comparison to nonmodified VN, AGE-VN exhibited reduced cell attachment-promoting activity. Together, these in vitro results suggest that AGE-VN found in vivo is related to morphologic and functional changes in the diabetic retina and may contribute to the genesis of acellular capillaries in early diabetic retinopathy.

Animals↗
PubMed1995

Syk mutation in Jurkat E6-derived clones results in lack of p72syk expression.

The human leukemic Jurkat cell line is commonly used as a model cellular system to study T lymphocyte signal transduction. Various clonal derivatives of Jurkat T cells exist which display different characteristics with regard to responses to external stimuli. Among these, the E6-1 clone of Jurkat T cells has been used as a parental line from which numerous important somatic mutant clones have been generated. During the course of experiments examining signals initiated by the T cell antigen receptor in an E6-1-derived Jurkat cell clone J.CaM1, we observed that the 72-kilodalton Syk protein tyrosine kinase previously found in other Jurkat cells was not detected. Upon further analysis it was determined that Syk transcripts from the J.CaM1 cells as well as the parental E6-1 cells contain a single guanine nucleotide insertion at position 92. This nucleotide insertion results in a shift in the Syk open reading frame leading to alternate codon usage as well as the generation of a termination codon at position 109. Thus, Syk transcripts in E6-1 cells and E6-1-derived clones are predicted to be capable of encoding only the first 33 amino acids of the 630-amino acid wild type Syk. These findings are incompatible with a recently proposed model of T cell antigen receptor signal transduction based, in part, on experiments conducted using E6-1-derived cells, suggesting that Syk might play a role upstream of Lck and Zap70.

Amino Acid Sequence↗
PubMed1995

The pre-T cell receptor (TCR) complex is functionally coupled to the TCR-zeta subunit.

The pre-T cell receptor (TCR) complex regulates early T cell development and consists of a heterodimer of the TCR-beta subunit in association with the pre-TCR-alpha chain. Notably, in contrast to alpha/beta-expressing T cells, several studies suggested that the TCR-zeta chain is not stably associated with this pre-TCR complex. To examine the proximal signaling processes mediated by the pre-TCR complex and the role of the TCR-zeta chain in these processes, we stimulated pre-TCR-expressing cells and analyzed the interactions of the TCR/CD3 invariant chains with the Syk/ZAP-70 family of protein tyrosine kinases. Stimulation of the pre-TCR complex led to the tyrosine phosphorylation of the CD3 epsilon and TCR-zeta chains, as well as the phosphorylation and association of ZAP-70 and Syk with phosphorylated CD3 epsilon and TCR-zeta. These results demonstrate that the pre-TCR complex is functionally coupled to the TCR-zeta subunit and to the ZAP-70 and Syk protein tyrosine kinases.

Amino Acid Sequence↗
PubMed1995

Absence of ZAP-70 prevents signaling through the antigen receptor on peripheral blood T cells but not on thymocytes.

Recently, a severe combined immunodeficiency syndrome with a deficiency of CD8+ peripheral T cells and a TCR signal transduction defect in peripheral CD4+ T cells was associated with mutations in ZAP-70. Since TCR signaling is required in developmental decisions resulting in mature CD4 (and CD8) T cells, the presence of peripheral CD4+ T cells expressing TCRs incapable of signaling in these patients is paradoxical. Here, we show that the TCRs on thymocytes, but not peripheral T cells, from a ZAP-70-deficient patient are capable of signaling. Moreover, the TCR on a thymocyte line derived from this patient can signal, and the homologous kinase Syk is present at high levels and is tyrosine phosphorylated after TCR stimulation. Thus, Syk may compensate for the loss of ZAP-70 and account for the thymic selection of at least a subset of T cells (CD4+) in ZAP-70-deficient patients.

Cell Line↗
PubMed1995

The Syk/ZAP-70 protein tyrosine kinase connection to antigen receptor signalling processes.

The T- and B-cell receptor (TCR and BCR) signal transduction processes involve a coordinated interplay between two classes of non-receptor protein tyrosine kinases (PTKs), the Src-family and the Syk/ZAP-70 family of PTKs. Following antigen-receptor stimulation, the Src-family of PTKs mediate the phosphorylation of tyrosine residues contained in a signalling motif localized in the TCR and BCR subunits. The phosphorylation of this signalling motif recruits the Syk/ZAP-70 family of PTKs into the antigen receptor complex. This mechanism requires the tandem SH2 domains in ZAP-70 complexing to two critically spaced phosphotyrosine residues within the signalling motif. The clustering of Syk/ZAP-70 and cross-talk between this family and the Src-PTKs regulates subsequent signalling events that lead to a variety of cellular responses, such as antibody secretion, lymphokine production, cytolytic activity, proliferation, differentiation and cell survival.

Amino Acid Sequence↗
PubMed1995

Aminoguanidine does not inhibit the initial phase of experimental diabetic retinopathy in rats.

We have previously shown that long-term administration of aminoguanidine, an inhibitor of advanced glycosylation product formation, reduces the extent of experimental diabetic retinopathy in the rat by 85%. In order to determine whether the residual retinopathy that developed despite aminoguanidine was attributable to advanced glycation endproduct formation, a time-course study was performed in three different groups of male Wistar rats: non-diabetic controls (NC), streptozotocin-diabetic controls (DC) and streptozotocin-diabetic rats treated with aminoguanidine HCL, 50 mg/100 ml drinking water (D-AG). Eyes were obtained at 24, 32, 44 and 56 weeks of diabetes/treatment duration and morphologic evaluation was done on retinal digest preparations. At 56 weeks, retinal basement membrane thickness was additionally measured. After 24 weeks of diabetes, the number of acellular capillaries was significantly elevated in DC (44.6 +/- 5.7/mm2 of retinal area, NC 19.6 +/- 4.9; p < 0.001) and increased continuously over time (DC 56 weeks 87.4 +/- 15.1; p < 0.001 vs DC24 weeks). In contrast, acellular capillaries in D-AG increased over the first 24 weeks and then remained constant for the rest of the study (D-AG 24 weeks 35.7 +/- 5.18; p < 0.01 vs NC 24 weeks and NS vs DC 24 weeks; D-AG 56 weeks 42.0 +/- 6.20; p NS vs D-AG 24 weeks).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Secondary intervention with aminoguanidine retards the progression of diabetic retinopathy in the rat model.

Primary prevention with aminoguanidine-an inhibitor of advanced glycation end product (AGE) formation--has been successfully employed to prevent diabetic retinopathy in the rat. However, it is unknown whether inhibition of AGE formation is still effective in a secondary intervention strategy. The present study addresses this question by comparing secondary intervention with aminoguanidine with syngeneic islet transplantation in the rat model. After 6 months of diabetes, one group was treated with aminoguanidine (50 mg/100 ml drinking water; D-AG) while another group received syngeneic transplantation of collagenase-ficoll isolated islets by intraportal injection (Tx). After an additional 4 months, both groups were compared to a normal (NC 10) and diabetic (DC 10) control group. Retinal autofluorescence was increased 2.5-fold after 6 months and increased 3.7-fold after 10 months of diabetes (p < 0.001). Aminoguanidine and islet Tx retarded the further accumulation of autofluorescence equally (p < 0.001 vs DC 10), although the values were higher than those observed in DC at 6 months (p < 0.001). Diabetes was associated with a 2.7-fold increase in acellular capillaries after 6 months and a 4.1-fold increase after 10 months. Treatment with aminoguanidine or islet Tx reduced but did not completely attenuate the progression of vascular occlusion (p < 0.001 vs DC 10; D-AG vs DC 6, p < 0.05; Tx vs DC 6, p < 0.01). Both treatments reduced endothelial proliferation (22.4% after 10 months; p < 0.001) and completely arrested pericyte dropout (40% after 10 months; p < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Oral↗
PubMed1995

Multiple kinases mediate T-cell-receptor signaling.

T-cell-receptor stimulation results in an array of early responses similar to those evoked by activation of receptor tyrosine kinases, including rapid induction of tyrosine phosphorylation, although no tyrosine kinase activity resides within any of the chains of the T-cell receptor. However, a 70 kDa tyrosine kinase, ZAP-70, has been found to associate with the zeta and CD3 chains of the T-cell receptor following stimulation. Recently, several immunodeficient individuals have been identified with loss-of-function mutations of ZAP-70. T cells from these patients have impaired responses to T-cell-receptor ligands, implying a central role for ZAP-70 in T-cell signaling. Here we examine the likely interactions of ZAP-70 and Src family kinases in generating a T-cell response.

Amino Acid Sequence↗
PubMed1995

CD28-mediated costimulation in the absence of phosphatidylinositol 3-kinase association and activation.

T-cell activation involves two distinct signal transduction pathways. Antigen-specific signaling events are initiated by T-cell receptor recognition of cognate peptide presented by major histocompatibility complex molecules. Costimulatory signals, which are required for optimal T-cell activation and for overcoming the induction of anergy, can be provided by the homodimeric T-cell glycoprotein CD28 through its interaction with the counterreceptors B7-1 and B7-2 on antigen-presenting cells. Ligation of CD28 results in its phosphorylation on tyrosines and the subsequent recruitment and activation of phosphatidylinositol 3-kinase (PI 3-kinase). It has been suggested that the induced association of CD28 and PI 3-kinase is required for costimulation. We report here that ligation of CD19, a heterologous B-cell receptor that also associates with and activates PI 3-kinase upon ligation, failed to costimulate interleukin-2 production. Moreover, pharmacological inhibition of PI 3-kinase activity failed to block costimulation mediated by CD28. By mutational analysis, we demonstrate that disruption of PI 3-kinase association with CD28 also did not abrogate costimulation. These results argue that PI 3-kinase association with CD28 is neither necessary nor sufficient for costimulation of interleukin-2 production. Finally, we identify specific amino acid residues required for CD28-mediated costimulatory activity.

Amino Acid Sequence↗
PubMed1995

A functional T-cell receptor signaling pathway is required for p95vav activity.

Stimulation of the T-cell antigen receptor (TCR) induces activation of multiple tyrosine kinases, resulting in phosphorylation of numerous intracellular substrates. One substrate is p95vav, which is expressed exclusively in hematopoietic and trophoblast cells. It contains a number of structural motifs, including Src homology 2, Src homology 3, and pleckstrin homology domains and a putative guanine nucleotide exchange domain. The role of p95vav in TCR-mediated signaling processes is unclear. Here, we show that overexpression of p95vav alone in Jurkat T cells leads to activation of the nuclear factors, including NFAT, involved in interleukin-2 expression. Furthermore, p95vav synergizes with TCR stimulation in inducing NFAT- and interleukin-2-dependent transcription. In contrast, NFAT activation by a G-protein-coupled receptor is not modulated by p95vav overexpression, suggesting that the effect is specific to the TCR signaling pathways. Although removal of the first 67 amino acids of p95vav activates its transforming potential in NIH 3T3 cells, this region appears to be required for its function in T cells. We further demonstrate that the p95vav-induced NFAT activation is not mimicked by Ras activation, though its function is dependent upon Ras and Raf. Furthermore, the activating function of p95vav is blocked by FK506, suggesting that its activity also depends on calcineurin. To further dissect p95vav involvement in TCR signaling, we analyzed various Jurkat mutants deficient in TCR signaling function or TCR expression and showed that an intact TCR signaling pathway is required for p95vav to function. However, overexpression of p95vav does not appear to influence TCR-induced protein tyrosine phosphorylation or increases in cytoplasmic free calcium. Taken together, our data suggest that p95vav plays an important role at an yet unidentified proximal position in the TCR signaling cascade.

Calcineurin↗
PubMed1994

The protein tyrosine kinase ZAP-70 can associate with the SH2 domain of proto-Vav.

Stimulation of the T cell antigen receptor (TCR) leads to tyrosine phosphorylation of a number of cellular proteins, including the vav proto-oncogene product. We now report the detection of several phosphotyrosine proteins (80, 74, and 70 kDa) from TCR-stimulated T cells that bind to the Src homology 2 (SH2) domain of proto-Vav (Vav-SH2) and co-immunoprecipitate with the proto-Vav product. Their binding to Vav-SH2 differs from that observed with SH2 domains from other proteins. None of the Vav-SH2-associated phosphoproteins bind to either of the Src homology 3 (SH3) domains of proto-Vav or to mutant Vav-SH2 proteins. The association of the phosphoproteins with Vav-SH2 requires induction of tyrosine phosphorylation of cellular proteins since proteins from lysates of herbimycin A-treated TCR-activated T cells fail to associate with Vav-SH2. Among the proteins from T cells that co-immunoprecipitate with the proto-Vav product and bind to its SH2 domain, specific antibodies identified the 70-kDa tyrosine phosphoprotein as ZAP-70, a protein tyrosine kinase (PTK) involved in TCR signal transduction. Binding of this PTK to Vav-SH2 is inhibited by a ZAP-70-specific synthetic tyrosine phosphopeptide. We suggest that ZAP-70 may function as a PTK for proto-Vav.

3T3 Cells↗