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T Elliott

Publications and source records attributed to T Elliott.

At least 73 records · Page 4Linked to original sources
PubMed1998

HLA-A*0201 presents TAP-dependent peptide epitopes to cytotoxic T lymphocytes in the absence of tapasin.

Tapasin is a 48-kDa endoplasmic reticulum (ER)-resident glycoprotein that binds to the transporter associated with antigen processing (TAP) and mediates an interaction between TAP and newly synthesized MHC class I molecules. It is also essential for the proper antigen presenting function of HLA-A*0101 (HLA-A1), HLA-A*0801 (HLA-B8) and HLA-B*4402 (HLA-B4402). We show here that while tapasin is required for HLA-A*0201 (HLA-A2) molecules to bind to TAP, its absence does not block the presentation of HLA-A2-restricted TAP-dependent epitopes to cytotoxic T lymphocytes indicating that, unlike HLA-A1, HLA-B8 and HLA-B4402, HLA-A2 has access to the TAP-dependent peptide pool even in the absence of tapasin. Nevertheless, the overall efficiency with which HLA-A2 was loaded with optimal, stabilizing peptides was impaired in the cell line .220, resulting in a significant increase in the fraction of HLA-A2 molecules being released from the ER in a "peptide-receptive" state.

Antigen Presentation↗
PubMed1998

A model of activity-dependent anatomical inhibitory plasticity applied to the mammalian auditory system.

We construct a model of activity-dependent, anatomical inhibitory plasticity. We apply the model to the mammalian auditory system. Specifically, we model the activity-dependent topographic refinement of inhibitory projections in the auditory brain stem, and we construct an anatomically abstract model of binaural band formation in the primary auditory cortex involving the segregation of different populations of inhibitory and excitatory afferents. Issues raised and predictions made include the nature of interactions between excitatory and inhibitory afferents innervating the same population of target cells, and the possibility that pharmacological manipulations of the developing primary auditory cortex might induce a shift in the periodicity of binaural bands. Any model of inhibitory plasticity must confront the issue of postulating mechanisms underlying such plasticity. In order to attempt to understand, at least theoretically, what the mechanisms underlying inhibitory plasticity might be, we propose the existence of a new class of neurotrophic factors that promote neurite outgrowth from and mediate competitive interactions between inhibitory afferents. We suppose that such factors are up-regulated by hyperpolarisation and down-regulated by depolarisation. Furthermore, we suppose that their activity-dependent release from target cells depends on Cl- influx. Such factors are therefore assumed to be the physiological inverse of such factors as nerve growth factor and brain-derived neurotrophic factor, which are up-regulated by depolarisation and down-regulated by hyperpolarisation, with their activity-dependent release depending on Na+, and not Ca2+, influx.

Animals↗
PubMed1998

Assessment of insulin sensitivity in older adults using the hyperglycemic clamp technique.

OBJECTIVE: The euglycemic glucose clamp technique is the gold standard for the measurement of insulin sensitivity in older adults, whereas the hyperglycemic glucose clamp technique is used to assess insulin release. The objective of this study was to evaluate the ability of the hyperglycemic glucose clamp technique to assess insulin sensitivity and insulin release in older people. RESEARCH DESIGN AND METHODS: Healthy older controls (n = 26, age 72 +/- 1) and older non-insulin-dependent diabetes mellitus (NIDDM) patients (n = 35, age 75 +/- 1) underwent a 2-hour hyperglycemic glucose clamp study (glucose 5.4 mM above basal) and a 3-hour euglycemic clamp study (insulin infusion rate 40 mU/m2/min). The average glucose infusion rate (last 30 minutes) of each clamp was divided by the average insulin value (last 30 minutes). This value was then divided by the average plasma glucose value to give glucose clearance per plasma insulin concentration. RESULTS: In control subjects (Eug: 0.80 +/- .05 mL/kg/min/pM; Hyper: 0.88 +/- .07 mL/kg/min/pM, P = .357) and NIDDM patients (Eug: 0.48 +/- .03 mL/kg/min/pM; Hyper: 0.42 +/- .03 mL/kg/min/pM, P = .162), glucose clearance values were similar whether calculated from the euglycemic or the hyperglycemic clamp. The correlation between glucose clearance values derived from the euglycemic and hyperglycemic clamp was excellent in normal controls (r = .76, P < .001) and patients with NIDDM (r = .71, P < .001). CONCLUSIONS: We conclude that the hyperglycemic glucose clamp technique can reliably assess both insulin release and insulin sensitivity in older people.

Aged↗
PubMed1998

Promoter substitution and deletion analysis of upstream region required for rpoS translational regulation.

The RpoS sigma factor of enteric bacteria is required for the increased expression of a number of genes that are induced during nutrient limitation and growth into stationary phase and in response to high osmolarity. RpoS is also a virulence factor for several pathogenic species, including Salmonella typhimurium. The activity of RpoS is regulated at both the level of synthesis and protein turnover. Here we investigate the posttranscriptional control of RpoS synthesis by using rpoS-lac protein and operon fusions. Substitution of the native rpoS promoters with the tac or lac UV5 promoters allowed essentially normal regulation after growth into stationary phase in rich medium or after osmotic challenge. Regulation of these fusions required the function of hfq, encoding the RNA-binding protein host factor I (HF-I). Short deletions from the 5' end of the rpoS transcript did not affect regulation very much; however, a larger deletion mutation that still retains 220 bp upstream of the rpoS ATG codon, including a proposed antisense element inhibitory for rpoS translation, was no longer regulated by HF-I. Several models for regulation of rpoS expression by HF-I are discussed.

Bacterial Proteins↗
PubMed1998

The major component of IkappaBalpha proteolysis occurs independently of the proteasome pathway in respiratory syncytial virus-infected pulmonary epithelial cells.

Previously we showed that infection of human type II airway epithelial (A549) cells with purified respiratory syncytial virus (pRSV) induced interleukin-8 transcription by a mechanism involving cytokine-inducible cytoplasmic-nuclear translocation of the RelA transcription factor. In unstimulated cells, RelA is tethered in the cytoplasm by association with the IkappaB inhibitor and can be released only following IkappaB degradation. In this study, we examined the spectrum of IkappaB isoform expression and kinetics of proteolysis of the isoforms in A549 cells following pRSV infection. In contrast to the rapid and robust activation of RelA DNA binding that peaked within 15 min of treatment produced by the prototypic activator tumor necrosis factor alpha (TNF-alpha), pRSV produced a weaker increase in RelA binding that began at 3 h and did not peak until 24 h after infection. A549 cells expressed the IkappaB inhibitory subunits IkappaBalpha, IkappaBbeta, and p105; however, following either stimulus, only the IkappaBalpha and IkappaBbeta steady-state levels declined in parallel with the increase in RelA DNA-binding activity. The >120-min half-life of IkappaBalpha in control cells was shortened to 5 min in TNF-alpha-stimulated cells and to 90 min in pRSV-infected cells. Although IkappaBalpha was resynthesized within 30 min following recombinant human TNFalpha treatment due to a robust 25-fold increase of IkappaBalpha mRNA expression (the RelA:IkappaBalpha positive feedback loop), following pRSV infection, there was no reaccumulation of IkappaBalpha protein, as infected cells produced only a 3-fold increase in IkappaBalpha mRNA at 24 h, indicating the RelA:IkappaBalpha positive feedback loop was insufficient to restore control IkappaBalpha levels. IkappaBalpha proteolysis induced by TNF-alpha occurred through the 26S proteasome, as both 26S proteasome activity and IkappaBalpha proteolysis were blocked by specific inhibitors lactacystin, MG-132, and ZLLF-CHO. Although total proteasome activity in 24-h pRSV-infected lysates increased twofold, its activity was >90% inhibited by the proteasome inhibitors; surprisingly, however, IkappaBalpha proteolysis was not. We conclude that RSV infection produces IkappaBalpha proteolysis through a mechanism primarily independent of the proteasome pathway.

Cell Line↗
PubMed1998

Alterations in non-insulin-mediated glucose uptake in the elderly patient with diabetes.

It is increasingly recognized that alterations in non-insulin-mediated glucose uptake (NIMGU) play an important pathogenic role in disorders of carbohydrate metabolism. This study was conducted to determine whether NIMGU is impaired in elderly patients with type 2 diabetes. Healthy elderly control subjects (n = 19, age 76 +/- 1 years, BMI 26.8 +/- 1.1 kg/m2) and elderly patients with type 2 diabetes (n = 19, age 76 +/- 2 years, BMI 27.5 +/- 0.9 kg/m2) underwent a 240-min glucose clamp study. Octreotide was infused to suppress endogenous insulin release, and tritiated glucose methodology was used to measure glucose uptake and disposal rates. For the first 180 min, glucose was kept at fasting levels. From 180 to 240 min, glucose was increased to 11 mmol/l. At fasting glucose levels, glucose uptake was similar in both groups. However, glucose clearance was reduced in patients with diabetes (control 1.68 +/- 0.05 ml x kg(-1) x min(-1); diabetes 1.34 +/- 0.07 ml x kg(-1) x min(-1), P < 0.0001). During hyperglycemia, glucose uptake was reduced in patients with diabetes (control 3.16 +/- 0.09 mg x kg(-1) x min(-1); diabetes 2.57 +/- 0.11 mg x kg(-1) x min(-1), P < 0.0001). Peripheral glucose effectiveness (SG) was less in patients with diabetes (control 1.28 +/- 0.04 ml x kg(-1) x min(-1); diabetes 0.94 +/- 0.08 ml x kg(-1) x min(-1), P < 0.0001). Hepatic glucose output and hepatic SG were not different between groups. We conclude that the effect of glucose on glucose uptake is impaired in elderly patients with type 2 diabetes, a finding that may have therapeutic implications for this patient population.

Adipose Tissue↗
PubMed1997

Axonal processes and neural plasticity. III. Competition for dendrites.

In previous work we have developed a computational framework for topographic map formation and plasticity based on axonal process sprouting and retraction, in which sprouting and retraction are governed by competition for neurotrophic support. Here we show that such an approach can account for certain aspects of the dendritic morphology of cortical maps. In particular, we model the development of ocular dominance columns in the primary visual cortex and show that cortical cells near to column boundaries prefer to elaborate dendritic fields which avoid crossing the boundaries. This emerges as different functional inputs are spatially separated. We predict that afferent segregation occurs before or simultaneously with, but not after, the emergence of dendritic bias. We predict that animals reared with complete but asynchronous stimulation of the optic nerves do not develop a dendritic bias. We suggest that the emergence of a dendritic bias might provide a partial account for the critical period for a response to monocular deprivation. In particular, we predict that animals reared with asynchronous optic nerve stimulation might exhibit an extended critical period. Our results also indicate that the number of synapses supported by cortical cells depends on the intra-ocular image correlations used in our simulations. This suggests that inter-ocular image correlations, and thus strabismic rearing of kittens, may also affect the innervation density.

Afferent Pathways↗
PubMed1997

An improved assembly assay for peptide binding to HLA-B*2705 and H-2K(k) class I MHC molecules.

The assembly assay for peptide binding to class I major histocompatibility complex (MHC) is based on the ability to stabilise MHC class I molecules from mutant cell lines by the addition of suitable peptides. Such cell lines lack a functional transporter associated with antigen presentation (TAP) and as a result accumulate empty, unstable class I molecules in the ER. These dissociate rapidly in cell lysates unless they are stabilised by the addition of an appropriate binding peptide during lysis. The extent of stabilisation of class I molecules is directly related to the binding affinity of the added peptide. However, some MHC class I molecules, including HLA-B * 2705 and H-2Kk are unusually stable in their peptide-receptive state making them inappropriate for analysis using this assay or assays which depend on the ability of peptides to stabilise MHC class I molecules at the cell surface. Here we present an improved method that permits reliable measurements of peptide binding to such class I MHC molecules that are unusually stable in the absence of peptide. Cells are lysed in the presence of peptide and incubated at 4 degrees C. After 2 h, during which peptide binding to empty MHC molecules occurs, the lysate is heated to a temperature which preferentially destabilises those MHC molecules that remain empty. We have used this technique to assay peptide binding to HLA-B * 2705, as well as to the murine allele H-2Kk which also displays a stable phenotype when transfected into TAP-deficient T2 cells and show that this method represents a marked improvement over previous methods in terms of lower background signal and higher recovery of peptide bound molecules.

Amino Acid Sequence↗
PubMed1997

A review of 24 cases of Mohs surgery and ophthalmic plastic reconstruction.

PURPOSE: Mohs surgery (micrographically controlled excision) has been advocated as an effective method of dealing with infiltrative periorbital skin tumours. It has been shown to have high rates of tumour clearance with minimal loss of normal tissue, thus making oculoplastic reconstruction easier and functional preservation better. The aim of the present study was to confirm this. Guidelines for the selection of patients for Mohs surgery are discussed. METHODS: We retrospectively reviewed 24 cases of primary (n = 18) and recurrent (n = 6) periorbital basal and squamous cell carcinomas managed by Mohs micrographic excision and plastic reconstruction who presented to the Royal Perth Hospital between 1992 and 1996. RESULTS: Our high rate of tumour clearance (100%) was similar to that of previous studies, although our follow-up period was only 14.6 months. The fact that 50% of our patients with lid involvement had an intact posterior lamella after Mohs excision correlates with the high level of normal tissue preservation. The low rate of postoperative symptomatic problems suggests good maintenance of function. The infiltrative nature of these tumours was highlighted by the substantial proportion of cases (37.5%) that had a much larger excision defect than what was expected prior to excision. CONCLUSIONS: Our analysis confirms that Mohs excision and subsequent oculoplastic reconstruction is an effective method to use when managing periorbital infiltrative skin tumours.

Adult↗
PubMed1997

Developmental outcomes in children receiving resection surgery for medically intractable infantile spasms.

Two-year postsurgical developmental outcomes were assessed in 24 children with infantile spasms who underwent resective surgery. The mean age of onset of infantile spasms was 12.0 weeks and the mean age at surgery was 20.8 months. Developmental outcomes were assessed using the Vineland Adaptive Behavior Scales (VABS). There was a significant increase in developmental level at 2 years postsurgery compared with presurgical levels. At 2 years postsurgery only one of the children in this series was severely retarded. The developmental outcomes of patients in the series were better than those in prior studies of symptomatic patients receiving medical treatment for infantile spasms. It is surprising that the children in the UCLA series frequently had developmental outcomes equal to and sometimes superior to other groups of children with infantile spasms, since all the UCLA patients were symptomatic, had neurologic deficits and had failed to respond to adrenocorticotrophic hormone (ACTH) and antiepileptic drugs. The 2-year postsurgery developmental outcomes were best for the children who received surgery when they were relatively young and who had the highest level of developmental attainments presurgically.

Activities of Daily Living↗
PubMed1997

Mutations that increase expression of the rpoS gene and decrease its dependence on hfq function in Salmonella typhimurium.

The RpoS transcription factor (also called sigmaS or sigma38) is required for the expression of a number of stationary-phase and osmotically inducible genes in enteric bacteria. RpoS is also a virulence factor for several pathogenic species, including Salmonella typhimurium. The activity of RpoS is regulated in response to many different signals, at the levels of both synthesis and proteolysis. Previous work with rpoS-lac protein fusions has suggested that translation of rpoS requires hfq function. The product of the hfq gene, host factor I (HF-I), is a ribosome-associated, site-specific RNA-binding protein originally characterized for its role in replication of the RNA bacteriophage Qbeta of Escherichia coli. In this study, the role of HF-I was explored by isolating suppressor mutations that map to the region directly upstream of rpoS. These mutations increase rpoS-lac expression in the absence of HF-I and also confer substantial independence from HF-I. DNA sequence analysis of the mutants suggests a model in which the RNA secondary structure near the ribosome binding site of the rpoS mRNA plays an important role in limiting expression in the wild type. Genetic tests of the model confirm its predictions, at least in part. It seems likely that the mutations analyzed here activate a suppression pathway that bypasses the normal HF-I-dependent route of rpoS expression; however, it is also possible that some of them identify a sequence element with an inhibitory function that is directly counteracted by HF-I.

Amino Acid Sequence↗
PubMed1997

Regulation of heme biosynthesis in Salmonella typhimurium: activity of glutamyl-tRNA reductase (HemA) is greatly elevated during heme limitation by a mechanism which increases abundance of the protein.

In Salmonella typhimurium and Escherichia coli, the hemA gene encodes the enzyme glutamyl-tRNA reductase, which catalyzes the first committed step in heme biosynthesis. We report that when heme limitation is imposed on cultures of S. typhimurium, glutamyl-tRNA reductase (HemA) enzyme activity is increased 10- to 25-fold. Heme limitation was achieved by a complete starvation for heme in hemB, hemE, and hemH mutants or during exponential growth of a hemL mutant in the absence of heme supplementation. Equivalent results were obtained by both methods. To determine the basis for this induction, we developed a panel of monoclonal antibodies reactive with HemA, which can detect the small amount of protein present in a wild-type strain. Western blot (immunoblot) analysis with these antibodies reveals that the increase in HemA enzyme activity during heme limitation is mediated by an increase in the abundance of the HemA protein. Increased HemA protein levels were also observed in heme-limited cells of a hemL mutant in two different E. coli backgrounds, suggesting that the observed regulation is conserved between E. coli and S. typhimurium. In S. typhimurium, the increase in HemA enzyme and protein levels was accompanied by a minimal (less than twofold) increase in the expression of hemA-lac operon fusions; thus HemA regulation is mediated either at a posttranscriptional step or through modulation of protein stability.

Acclimatization↗
PubMed1996

Point mutations in the alpha 2 domain of HLA-A2.1 define a functionally relevant interaction with TAP.

BACKGROUND: Glycoproteins encoded by the major histocompatibility complex class I region (MHC class I) present peptide antigens to cytotoxic T cells (CTLs). Peptides are delivered to the site of MHC class I assembly by the transporter associated with antigen processing (TAP), and cell lines that lack this transporter are unable to present endogenous antigens to CTLs. Although it has been shown that a fraction of newly synthesized class I molecules are in physical association with TAP, it is not known whether this interaction is functionally relevant, or where on the class I molecule the TAP binding site might be. RESULTS: C1R cells transfected with a mutant HLA-A2.1 heavy chain (HC), where threonine at position 134 in the alpha 2 domain is changed to lysine (T134K), are unable to present endogenous antigens to CTLs. We have studied the biochemistry of this mutant in C1R cells, and found that a large pool of unstable empty class I HC-beta 2m (beta-2 microglobulin) heterodimers exist that are rapidly transported to the cell surface. The T134K mutant seemed to bind peptide antigens and assemble with beta 2m as efficiently as wild-type HLA-A2.1. However, we show here that the inefficiency with which T134K presents intracellular antigen is associated with its inability to interact with the TAP heterodimer. CONCLUSIONS: These experiments establish that the class I-TAP interaction is obligatory for the presentation of peptide epitopes delivered to the endoplasmic reticulum (ER) by TAP. Wild-type HLA-A2.1 molecules in TAP-deficient cells are retained in the ER, whereas T134K is rapidly released to the cell surface, but is unstable, suggesting a role for the TAP complex as an intracellular checkpoint that only affects the release of class I molecules with stably bound peptide ligands.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1996

Neural competition and statistical mechanics.

Computational models of activity-dependent competitive neural plasticity typically impose competition in networks in which plasticity is accommodated by permitting changes in the efficacies of synapses in an anatomically fixed network. This is despite the fact that much evidence suggests that neurons compete for neurotrophins, during both target innervation and activity-dependent synaptic re-arrangement, which influence the sprouting and retraction of axonal processes. We therefore present a new approach to the computational modelling of competitive neural plasticity which permits neurons to compete explicitly for neurotrophins. This competition is associated with the sprouting and retraction of axonal processes. Because there is much uncertainty regarding the basic mechanisms, we adopt the powerful machinery of statistical mechanics to avoid the need to address these issues. We show that such an approach can readily account for a wide range of plasticity phenomena in a range of systems, including the results of various pharmacological manipulations.

Animals↗
PubMed1996

Recognition of out-of-frame major histocompatibility complex class I-restricted epitopes in vivo.

In the course of constructing a recombinant vaccinia virus encoding the influenza A nucleoprotein (NP) gene preceded by the hemagglutinin leader sequence, we isolated a single base-pair deletion mutant which gave rise to L+NP(1-159) in which only the first 159 amino acids were in frame. Despite this, when we infected target cells, we found that the point mutant was able to sensitize them for lysis not only by cytotoxic T cells recognizing residues 50-58 (the in-frame portion), but also by CTL to epitopes which are downstream of the mutation (366-374 and 378-386). Furthermore, normal C57BL/6 mice can be primed with the frameshift NP to recognize the immunodominant Db-restricted epitope 366-374 (which is out of frame). Experiments in which the mutant gene product was processed in the endoplasmic reticulum of target cells suggested that the apparent suppression occurred during polypeptide extension.

Animals↗