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Biomedical subjects

A Weiss

Publications and source records attributed to A Weiss.

At least 73 records · Page 4Linked to original sources
PubMed2000

The T-cell receptor regulates Akt (protein kinase B) via a pathway involving Rac1 and phosphatidylinositide 3-kinase.

The serine/threonine kinase Akt (also known as protein kinase B) (Akt/PKB) is activated upon T-cell antigen receptor (TCR) engagement or upon expression of an active form of phosphatidylinositide (PI) 3-kinase in T lymphocytes. Here we report that the small GTPase Rac1 is implicated in this pathway, connecting the receptor with the lipid kinase. We show that in Jurkat cells, activated forms of Rac1 or Cdc42, but not Rho, stimulate an increase in Akt/PKB activity. TCR-induced Akt/PKB activation is inhibited either by PI 3-kinase inhibitors (LY294002 and wortmannin) or by overexpression of a dominant negative mutant of Rac1 but not Cdc42. Accordingly, triggering of the TCR rapidly stimulates a transient increase in GTP-Rac content in these cells. Similar to TCR stimulation, L61Rac-induced Akt/PKB kinase activity is also LY294002 and wortmannin sensitive. However, induction of Akt/PKB activity by constitutive active PI 3-kinase is unaffected when dominant negative Rac1 is coexpressed, placing Rac1 upstream of PI 3-kinase in the signaling pathway. When analyzing the signaling hierarchy in the pathway leading to cytoskeleton rearrangements, we found that Rac1 acts downstream of PI 3-kinase, a finding that is in accordance with numerous studies in fibroblasts. Our results reveal a previously unrecognized role of the GTPase Rac1, acting upstream of PI 3-kinase in linking the TCR to Akt/PKB. This is the first report of a membrane receptor employing Rac1 as a downstream transducer for Akt/PKB activation.

Chromones↗
PubMed2000

Macrocyclic Imidazolylboranes.

Cycles, not chains: 1-imidazolylboranes exist in polymeric form as a consequence of donor/acceptor interactions. Through the use of suitable substituents and under high dilution tetrameric and pentameric macrocyclic imidazolylboranes were synthesized. The picture shows the structure of the tetrameric 4,5-dimethylimidazolylborane (black: C, gray: B, white: N).

Journal Article↗
PubMed2000

Osseointegration of Ti6Al4V alloy implants coated with titanium nitride by a new method.

Coating titanium alloy implants with titanium nitride (TiN) by the method of Powder Immersion Reaction Assisted Coating (PIRAC) produces a stable layer on their surface. We have examined the ability of the new TiN coating to undergo osseointegration. We implanted TiN-coated and uncoated Ti6Al4V alloy pins into the femora of six-month-old female Wistar rats. SEM after two months showed a bone collar around both TiN-coated and uncoated implants. Morphometrical analysis revealed no significant differences between the percentage of the implant-bone contact and the area and volume of the bone around TiN-coated compared with uncoated implants. Electron-probe microanalysis indicated the presence of calcium and phosphorus at the implant-bone interface. Mineralisation around the implants was also confirmed by labelling with oxytetracycline. Strong activity of alkaline phosphatase and weak activity of tartrate-resistant acid phosphatase were shown histochemically. Very few macrophages were detected by the non-specific esterase reaction at the site of implantation. Our findings indicate good biocompatibility and bone-bonding properties of the new PIRAC TiN coatings which are comparable to those of uncoated Ti6Al4V alloy implants.

Alloys↗
PubMed1999

Galvanic stimulation in bilateral vestibular failure: 3-D ocular motor effects.

Bilateral galvanic vestibular stimulation (GVS) with current intensity of 3 mA was applied at mastoid level in 11 patients with chronic bilateral vestibular failure, in order to determine ocular motor responses by 3-D video-oculography. The following abnormal features were found: (1) a predominantly torsional or mixed torsional-horizontal nystagmus at the onset of stimulation with lower current intensities (1.0-3.0 mA) in nine patients; (2) a reduced amplitude of tonic ocular torsion by about 50% in nine patients (1.3 +/- 0.6 degrees at 3 mA); (3) a nystagmus in the opposite direction at stimulation offset in five patients (rebound); (4) no eye movements at all in a patient with bilateral nerve failure. GVS stimulates the vestibular nerve, thus allowing differentiation of nerve failure from labyrinthine failure. The low thresholds for initiating nystagmus and the rebound, which appear to be the most typical features of bilateral labyrinthine failure, can be explained by central compensation mechanisms.

Acceleration↗
PubMed1999

Localization of LAT in glycolipid-enriched microdomains is required for T cell activation.

LAT, a transmembrane adapter protein found in glycolipid-enriched microdomains (GEMs), is essential for T cell activation. In this study, we have utilized a LAT-deficient mutant of the Jurkat T cell line, J.CaM2, to explore various requirements for LAT function. First, we demonstrate that LAT must be present in GEMs for coupling T cell receptor (TCR) engagement to activation of the Ras signaling pathway, increases in intracellular Ca(2+), and induction of the transcription factor nuclear factor of activated T cells (NF-AT). Second, we show that the extracellular and transmembrane domains of LAT are dispensable for these TCR-mediated events once LAT has localized to GEMs. These results provide important insights into both the structural domains of LAT and its subcellular localization that are required for effective TCR signaling.

Adaptor Proteins, Signal Transducing↗
PubMed1999

A disulfide conjugate between anti-tetanus antibodies and HIV (37-72)Tat neutralizes tetanus toxin inside chromaffin cells.

Conjugates between anti-tetanus F(ab')2 fragments and the (37-72) fragment of the HIV Tat protein were taken up by chromaffin cells, NG108-15 neurohybridoma cells and Rev-2-T-6 lymphoma cells. The uptake could not be inhibited by competition with (37-72)Tat, but was reduced in the presence of metabolic inhibitors or at low temperature. The disulfide as well as the thioether conjugate were translocated to the cytoplasmic space, but only the disulfide conjugate moderately restored the stimulated transmitter release inhibited by tetanus toxin. Therefore, disulfide conjugates are more promising than thioethers for the neutralization of intracellular antigens. These conjugates provide new tools to study neuroprotection against bacterial neurotoxins.

Animals↗
PubMed1999

Pre-T cell receptor signals are responsible for the down-regulation of Syk protein tyrosine kinase expression.

Thymocyte development proceeds through two critical checkpoints that involve signaling events through two different receptors, the TCR and the pre-TCR. These receptors employ two families of protein tyrosine kinases to propagate their signals, the Src and Syk families. Genetic and biochemical evidence has shown that the Src family kinases are critical for normal T cell maturation. ZAP-70, a Syk family kinase, has similarly been implicated as a critical component in thymocyte development. Although genetic evidence has suggested that Syk is involved during thymocyte development, a definitive study of Syk expression has not been performed. In this paper we report our reanalysis of Syk expression in subpopulations of murine and human thymocytes by intracellular staining and flow cytometry using anti-Syk mAbs. Syk is expressed at increased levels during the stages in which pre-TCR signaling occurs. Furthermore, Syk is down-regulated after the pre-TCR checkpoint has been passed. Syk may play an important role in thymic development during pre-TCR signal transduction. Finally, incomplete down-regulation of Syk expression was noted in human thymocytes, offering a possible explanation for the distinct phenotypes of mice and humans deficient in ZAP-70.

Animals↗
PubMed1999

High-Frequency Viscosity and Shear Modulus of Sterically Stabilized Colloid Particles as Probed by Torsional Resonance Oscillation.

A study of the high-frequency viscosity etainfinity' and of the high-frequency shear modulus Ginfinity' of a sterically stabilized latex is presented. The experimental measurements have been done using a torsional resonator described recently (J. Bergenholtz et al., J. Colloid Interface Sci. 202, 430 (1998)). The data of etainfinity' compare favorably with recent theoretical predictions and point to a partial draining of the steric layer by the solvent as expected. The high-shear modulus, however, is much lower than predicted by theory. The pair potential calculated from Ginfinity' by neglect of hydrodynamic interaction has a considerably longer range than expected from the structure of the steric layer. This points to the fact that hydrodynamic interactions are not negligible for these systems and must be included in a quantitative analysis of the high-frequency shear modulus Ginfinity'. Copyright 1999 Academic Press.

Journal Article↗
PubMed1999

Comparative sequence analysis of the complete human sarcomeric myosin heavy chain family: implications for functional diversity.

The conventional myosin motor proteins that drive mammalian skeletal and cardiac muscle contraction include eight sarcomeric myosin heavy chain (MyHC) isoforms. Six skeletal MyHCs are encoded by genes found in tightly linked clusters on human and mouse chromosomes 17 and 11, respectively. The full coding regions of only two out of six mammalian skeletal MyHCs had been sequenced prior to this work. In an effort to assess the extent of sequence diversity within the human MyHC family we present new full-length coding sequences corresponding to four additional human genes: MyHC-IIb, MyHC-extraocular, MyHC-IIa and MyHC-IIx/d. This represents the first opportunity to compare the full coding sequences of all eight sarcomeric MyHC isoforms within a vertebrate organism. Sequence variability has been analyzed in the context of available structure/function data with an emphasis on potential functional diversity within the family. Results indicate that functional diversity among MyHCs is likely to be accomplished by having small pockets of sequence diversity in an otherwise highly conserved molecule.

Amino Acid Sequence↗
PubMed1999

Induction of NF-kappaB by the Akt/PKB kinase.

The serine/threonine kinase Akt (also known as protein kinase B, PKB) is activated by numerous growth-factor and immune receptors through lipid products of phosphatidylinositol (PI) 3-kinase. Akt can couple to pathways that regulate glucose metabolism or cell survival [1]. Akt can also regulate several transcription factors, including E2F, CREB, and the Forkhead family member Daf-16 [2] [3] [4]. Here, we show that Akt can regulate signaling pathways that lead to induction of the NF-kappaB family of transcription factors in the Jurkat T-cell line. This induction occurs, at least in part, at the level of degradation of the NF-kappaB inhibitor IkappaB, and is specific for NF-kappaB, as other inducible transcription factors are not affected by Akt overexpression. Furthermore, the effect requires the kinase activity and pleckstrin homology (PH) domain of Akt. Also, Akt does not act alone to induce cytokine promoters and NF-kappaB reporters, because signals from other pathways are required to observe the effect. These studies uncover a previously unappreciated connection between Akt and NF-kappaB induction that could have implications for the control of T-cell growth and survival.

DNA-Binding Proteins↗
PubMed1999

Analysis of Attractive Interactions between Latex Particles in the Presence of Nonadsorbing Polymers by Turbidimetry.

The analysis of attractive forces between latex particles by scattering measurements is reconsidered. The change effected on the structure factor S(q) (q = (4pin0/lambda0)sin(θ/2), where θ is the scattering angle, n0 is the refractive index of the medium, and lambda0 is the wavelength in vacuo) of a suspension of latex particles by weak attractions is considered in terms of the HMSA-integral equation theory as presented recently by Bergenholtz et al. (1996, Mol. Phys. 87, 331). Model calculations using this approach show that turbidimetry is highly suitable to obtain quantitative information on attractive forces between the latex particles. The method of analysis developed here is applied to previous turbidimetric data obtained from mixtures of a polystyrene latex and a nonadsorbing polymer, hydroxyethylcellulose (HEC) (1997, Langmuir 13, 551). Here the addition of HEC leads to attractive depletion forces between the PS particles by the nonbalanced osmotic pressure of the polymeric HEC molecules. The turbidimetric data which are not afflicted by multiple scattering can be analyzed quantitatively in terms of an Asakura-Oosawa interaction potential between the latex particles. The osmotic pressure derived from this analysis is much smaller than the actual osmotic pressure exerted by the dissolved HEC. Possible reasons for this discrepancy are discussed. Copyright 1999 Academic Press.

Journal Article↗
PubMed1999

Deregulated signal transduction by the K1 gene product of Kaposi's sarcoma-associated herpesvirus.

The Kaposi's sarcoma (KS)-associated herpesvirus is a lymphotropic virus strongly implicated in the pathogenesis of KS and several lymphoproliferative disorders. The KS-associated herpesvirus K1 gene encodes a transmembrane protein bearing a functional immunoreceptor tyrosine-based activation motif (ITAM)-like sequence; it previously has been proposed to be important in viral tumorigenesis because its expression can trigger cell proliferation in vitro and in vivo. Here we show that expression of the full-length K1 protein can initiate calcium-dependent signal transduction in B cells; however, unlike other ITAM-based signal transduction events, K1 signaling occurs constitutively, in the absence of exogenous crosslinking ligands. This property is caused by its cysteine-rich ectodomain, which when transferred to other consensus ITAMs induces constitutive signaling. Although ITAM-based signaling by K1 involves classical syk and phospholipase C gamma2 activation, both ITAM- and syk-independent signaling pathways are activated by K1 expression. These studies indicate that K1 is a deregulated signaling molecule with pleitropic effects that may explain its known growth deregulatory properties.

Animals↗
PubMed1999

Organization of human and mouse skeletal myosin heavy chain gene clusters is highly conserved.

Myosin heavy chains (MyHCs) are highly conserved ubiquitous actin-based motor proteins that drive a wide range of motile processes in eukaryotic cells. MyHC isoforms expressed in skeletal muscles are encoded by a multigene family that is clustered on syntenic regions of human and mouse chromosomes 17 and 11, respectively. In an effort to gain a better understanding of the genomic organization of the skeletal MyHC genes and its effects on the regulation, function, and molecular genetics of this multigene family, we have constructed high-resolution physical maps of both human and mouse loci using PCR-based marker content mapping of P1-artificial chromosome clones. Genes encoding six MyHC isoforms have been mapped with respect to their linear order and transcriptional orientations within a 350-kb region in both human and mouse. These maps reveal that the order, transcriptional orientation, and relative intergenic distances of these genes are remarkably conserved between these species. Unlike many clustered gene families, this order does not reflect the known temporal expression patterns of these genes. However, the conservation of gene organization since the estimated divergence of these species (approximately 75-110 million years ago) suggests that the physical organization of these genes may be significant for their regulation and function.

Animals↗
PubMed1999

Interactions of the AP-1 Golgi adaptor with the polymeric immunoglobulin receptor and their possible role in mediating brefeldin A-sensitive basolateral targeting from the trans-Golgi network.

We provide morphological, biochemical, and functional evidence suggesting that the AP-1 clathrin adaptor complex of the trans-Golgi network interacts with the polymeric immunoglobulin receptor in transfected Madin-Darby canine kidney cells. Our results indicate that immunofluorescently labeled gamma-adaptin subunit of the adaptor complex and the polymeric immunoglobulin receptor partially co-localize in polarized and semi-polarized cells. gamma-Adaptin is co-immunoisolated with membranes expressing the wild-type receptor. The entire AP-1 adaptor complex could be chemically cross-linked to the receptor in filter-grown cells. gamma-Adaptin could be co-immunoprecipitated with the wild-type receptor, with reduced efficiency with receptor mutant whose basolateral sorting motif has been deleted, and not with receptor lacking its cytoplasmic tail. Co-immunoprecipitation of gamma-adaptin was inhibited by brefeldin A. Mutation of cytoplasmic serine 726 inhibited receptor interactions with AP-1 but did not abrogate the fidelity of its basolateral targeting from the trans-Golgi network. However, the kinetics of receptor delivery to the basolateral cell surface were slowed by the mutation. Although surface delivery of the wild-type receptor was inhibited by brefeldin A, the delivery of the mutant receptor was insensitive to the drug. Our results are consistent with a working model in which phosphorylated cytoplasmic serine modulates the recruitment of the polymeric immunoglobulin receptor into AP-1/clathrin-coated areas in the trans-Golgi network. This process may regulate the efficiency of receptor targeting from the trans-Golgi network.

Adaptor Protein Complex alpha Subunits↗