Search PubMed⌕ Search

Biomedical subjects

J M Taylor

Publications and source records attributed to J M Taylor.

At least 91 records · Page 5Linked to original sources
PubMed1998

Characterization of graf, the GTPase-activating protein for rho associated with focal adhesion kinase. Phosphorylation and possible regulation by mitogen-activated protein kinase.

Graf is a GTPase-activating protein for Rho that interacts with focal adhesion kinase and co-localizes with the actin cytoskeleton (Hildebrand, J. D., Taylor, J. M. and Parsons, J. T. (1996) Mol. Cell. Biol. 16, 3169-3178). We examined the expression and regulation of Graf as a prelude to understanding the role of Graf in mediating signal transduction in vivo. We demonstrated that Graf is a ubiquitously expressed 95-kDa protein with high levels observed in heart and brain and cells derived from these tissues. Stimulation of PC12 cells with epidermal growth factor or nerve growth factor induced a phosphatase-reversible mobility shift upon gel electrophoresis, indicative of phosphorylation. In vitro, purified mitogen-activated protein (MAP) kinase catalyzed the phosphorylation of Graf on serine 510, suggesting that Graf phosphorylation may be mediated through MAP kinase signaling. In addition, the mutation of serine 510 to alanine inhibited the epidermal growth factor-induced mobility shift of mutant Graf protein in vivo, consistent with serine 510 being the site of in vivo phosphorylation. Based on these data we suggest that phosphorylation of Graf by MAP kinase or related kinases may be a mechanism by which growth factor signaling modulates Rho-mediated cytoskeletal changes in PC12 and perhaps other cells.

Amino Acid Sequence↗
PubMed1998

Atypical splicing of the latency-associated transcripts of herpes simplex type 1.

We previously have shown that two latency-associated transcripts (LATs) of herpes simplex type 1 (HSV-1) are probably lariats, produced during splicing. By RNaseH digestion analysis, we now show that the major branchpoint of the 2.0-kb LAT was within 46 nt 5' of the splice acceptor site. A more detailed mapping by primer extension revealed the branchpoint as an adenosine 29 nt 5' of the splice acceptor site. Introduction of two branchpoint sequences with good matches to the consensus at position -25 had no effect on the splicing efficiency but reduced the accumulation of the 2.0-kb LATs at least 90-fold. The second focus of our studies was the 1.5-kb LAT. It was not detected by Northern analyses in either productively infected or transfected cultured cells or even in cells of neuronal origin. However, it was detected in the trigeminal ganglia of mice experimentally infected with HSV-1 after 10 days. Moreover, its abundance relative to that of the 2.0-kb species increased 4-fold from 10 to 30 days after infection, consistent with an interpretation that the 1.5-kb species, once formed, was more stable than the 2.0-kb species.

Animals↗
PubMed1998

Overexpression of hepatic lipase in transgenic mice decreases apolipoprotein B-containing and high density lipoproteins. Evidence that hepatic lipase acts as a ligand for lipoprotein uptake.

To determine the mechanisms by which human hepatic lipase (HL) contributes to the metabolism of apolipoprotein (apo) B-containing lipoproteins and high density lipoproteins (HDL) in vivo, we developed and characterized HL transgenic mice. HL was localized by immunohistochemistry to the liver and to the adrenal cortex. In hemizygous (hHLTg+/0) and homozygous (hHLTg+/+) mice, postheparin plasma HL activity increased by 25- and 50-fold and plasma cholesterol levels decreased by 80% and 85%, respectively. In mice fed a high fat, high cholesterol diet to increase endogenous apoB-containing lipoproteins, plasma cholesterol decreased 33% (hHLTg+/0) and 75% (hHLTg+/+). Both apoB-containing remnant lipoproteins and HDL were reduced. To extend this observation, the HL transgene was expressed in human apoB transgenic (huBTg) and apoE-deficient (apoE-/-) mice, both of which have high plasma levels of apoB-containing lipoproteins. (Note that the huBTg mice that were used in these studies were all hemizygous for the human apoB gene.) In both the huBTg,hHLTg+/0 mice and the apoE-/-,hHLTg+/0 mice, plasma cholesterol decreased by 50%. This decrease was reflected in both the apoB-containing and the HDL fractions. To determine if HL catalytic activity is required for these decreases, we expressed catalytically inactive HL (HL-CAT) in apoE-/- mice. The postheparin plasma HL activities were similar in the apoE-/- and the apoE-/-,HL-CAT+/0 mice, reflecting the activity of the endogenous mouse HL and confirming that the HL-CAT was catalytically inactive. However, the postheparin plasma HL activity was 20-fold higher in the apoE-/-,hHLTg+/0 mice, indicating expression of the active human HL. Immunoblotting demonstrated high levels of human HL in postheparin plasma of both apoE-/-,hHLTg+/0 and apoE-/-,HL-CAT+/0 mice. Plasma cholesterol and apoB-containing lipoprotein levels were approximately 60% lower in apoE-/-,HL-CAT+/0 mice than in apoE-/- mice. However, the HDL were only minimally reduced. Thus, the catalytic activity of HL is critical for its effects on HDL but not for its effects on apoB-containing lipoproteins. These results provide evidence that HL can act as a ligand to remove apoB-containing lipoproteins from plasma.

Animals↗
PubMed1998

An evaluation of a measure of the proportion of the treatment effect explained by a surrogate marker.

Time-dependent markers, such as CD4 and viral load, are potential surrogate markers in AIDS clinical trials. A critical issue with surrogate markers is whether changes in these markers explain the beneficial effect of treatment on the real end point of the clinical trial. A statistic to measure the proportion of the treatment effect explained by the surrogate is p(FGS) = 1 - gamma/alpha, where alpha is the treatment effect coefficient in a Cox model and gamma is the treatment effect coefficient from a time-dependent Cox model adjusted for the marker. In this article we evaluate the statistical properties of p(FGS). Using a Monte Carlo study we show that the statistic is not well calibrated, because it can fall outside the range zero to one, even in very large samples. In the simulation study we consider situations where the time-dependent marker is measured with error at a fixed number of times. We show that a method of fitting a time-dependent Cox model involving smoothing the marker reduces the bias in the estimate of p(FGS) compared with the standard method of using the current or last observed marker value. We also show that the estimate of p(FGS) has considerable variability and can have wide confidence intervals. We conclude that p(FGS) is only likely to be useful in large trials with a strong treatment effect. The methods are illustrated using CD4 counts from an AIDS clinical trial of zidovidine versus placebo.

Acquired Immunodeficiency Syndrome↗
PubMed1998

A non-parametric method of reconstructing single-dose survival curves from multi-fraction experiments.

PURPOSE: A method of estimating the single-dose curve from designed multifraction experiments is described and applied to three datasets. MATERIALS AND METHODS: The method, which is non-parametric and based on standard statistical regression techniques, can be used for functional endpoints which are either continuous or binary. The datasets are concerned with wound healing on mice, myelopathy in guinea pigs and spermatogenesis in mice. The results are compared with the results from fitting the linear quadratic model. The statistical methods of Bootstrapping and residual plots are illustrated. RESULTS: The method is based in part on an assumed statistical model, however, exact knowledge of the correct statistical model is not necessary to obtain an estimate of the shape of the single-dose survival curve. We find no good evidence from the reconstructed single-dose survival curve of an "induced repair" phenomena at low doses for the wound healing and spermatogenesis experiments. For the myelopathy experiment the data are consistent with the LQ model with a low alpha-beta ratio down to doses of at least 1.5 Gy per fraction. CONCLUSIONS: A robust statistical method of estimating the shape of the single-dose survival curve is demonstrated using standard statistical software on three datasets.

Animals↗
PubMed1998

Longitudinal models for AIDS marker data.

Over the past decade, researchers have put a great amount of effort into developing suitable models for the analysis of longitudinal CD4 data and other markers of AIDS progression. These models must be general enough to allow for different patterns of change in the marker data. In this paper, we review the existing literature including our preferred models which involve mixed effects, stochastic terms and independent measurement error. Adding stochastic terms to standard mixed effects models gives an interpretable and parsimonious method for generalizing the covariance structure of the measurement error and short-term variability. We focus on univariate and bivariate models with integrated Ornstein-Uhlenbeck (IOU) stochastic terms. The IOU process allows for a range of biologically plausible derivative tracking that encompasses both random trajectory and Brownian motion behaviour. We illustrate these modelling techniques on longitudinal CD4 and viral RNA data.

Acquired Immunodeficiency Syndrome↗
PubMed1997

Two hepatic enhancers, HCR.1 and HCR.2, coordinate the liver expression of the entire human apolipoprotein E/C-I/C-IV/C-II gene cluster.

We show that the liver-specific expression of all four genes in the human apolipoprotein (apo) E/C-I/C-IV/C-II gene cluster in transgenic mice is determined by the coordinate action of two distinct hepatic control regions (HCR). These enhancers are positioned 15 kilobases (kb) (HCR.1) and 26 kb (HCR.2) downstream of the apoE gene. To investigate the action of each HCR, transgenic mice were generated with a 70-kb human genomic fragment that contained the complete apoE gene cluster or with this fragment modified by the specific deletion of HCR.1, HCR.2, or both HCR domains. Hepatic expression of all four apolipoprotein genes was observed in transgenic mice in which either HCR.1 or HCR.2 was deleted, but no transgene expression was found in the liver in the absence of both HCR domains. The overall patterns of transgene expression suggested that HCR.2 was the dominant element for apoC-IV and apoC-II expression and that HCR.1 was dominant for the apoE/C-I expression. No liver-specific transcriptional activity was identified for the proximal promoter of any gene in the cluster; all liver-specific activity was associated with HCR.1 and HCR.2. Thus, the HCRs of the apoE gene cluster constitute unique regulatory domains for determining the requirements for apolipoprotein gene expression in the liver.

Animals↗
PubMed1997

Transgenic rabbit models for the study of atherosclerosis.

The rabbit rapidly develops severe hypercholesterolemia leading to premature atherosclerosis in response to dietary manipulation. Transgenic rabbit models with altered expression of specific genes will provide new approaches to understanding the underlying mechanisms that contribute to this disease. Recently established lines of transgenic rabbits that overexpress hepatic lipase and apolipoprotein E are yielding fresh insights into the functions of these proteins and their role in lesion development

APOBEC-1 Deaminase↗
PubMed1997

Pacific ciguatoxin-1 associated with a large common-source outbreak of ciguatera in east Arnhem Land, Australia.

We report a retrospective study of the clinical signs and symptoms associated with a point-source outbreak of fish poisoning that occurred with a fish captured from the Arafura Sea, northern Australia. Twenty cases (16 Aboriginal and 4 non-Aboriginal) characteristic of ciguatera, including 4 inpatients and 16 outpatients from the Gove Hospital, were identified based on the pattern of clinical symptoms and signs after ingestion of a large coral cod from a known ciguatera-prone coral reef. In the absence of a serologic test for the victim, laboratory analysis of a 230-g sample of the coral cod (Cephalopolis miniatus), using both mouse bioassay and HPLC/mass spectometry, showed that Pacific ciguatoxin-1 was the principal toxin involved. Intravenous mannitol was administered to one patient without clear benefit. Risk factors for ciguatera poisoning are ingestion of larger portions of reef fish from ciguatera-prone areas. Despite apparent local awareness of the distribution and etiology of the disease, large common-source outbreaks of ciguatera still occur.

Adult↗
PubMed1997

Non-linear effects in dose-time analyses: application of modern statistical techniques.

BACKGROUND AND PURPOSE: The non-linear effect of overall treatment time and total dose on the outcome of fractionated head and neck radiotherapy is of interest. This and other non-linear effects can be investigated using recently developed statistical techniques. This article provides an illustration of the ability of these statistical methods. MATERIALS AND METHODS: Recently developed statistical methods (Hastie, T.J. and Tibshirani, R.J. Generalised Additive Models. Chapman-Hall, London, 1990), called generalized additive models, are applied to data from the patterns of fractionation study (Withers, H.R., Peters, L.J., Taylor, J.M.G., Owen, J.B., Morrison, W.H., Schultheiss, T.E., Keane, T., O'Sullivan, B., van Dyk, J., Gupta, N., Wang, C.C., Jones, C.U., Doppke, K.P., Myint, S., Thompson, M., Parsons, J.T., Mendenhall, W.M., Dische, S., Aird, E.G.A., Henk, J.M., Bidmead, M.A.M., Svoboda, V., Chon, Y., Hanlon, A.L., Peters, T.L. and Hanks, G.E. Local control of carcinoma of the tonsil by radiation therapy: an analysis of patterns of fractionation in nine institutions. Int. J. Radiat. Oncol. Biol. Phys. 33: 549-562, 1995) of tonsil cancer. These techniques enable one to develop models which more accurately represent the relationship between multivariate predictor variables and the outcome variable in a regression analysis. These data driven methods allow the effect of each predictor variable on the outcome to be non-linear and estimated from the data. This is achieved by replacing the standard linear model combination of predictor variables, such as 'alpha0 + alpha1dose + alpha2time' by 'S1(dose) + S2(time)', where S1 and S2 are smooth non-linear functions of dose and time, respectively, which are estimated from the data. RESULTS: In the pattern of fractionation study these methods indicate that the effect of total dose on the probability of local recurrence is linear, but there is a suggestion that the effect of overall treatment time is non-linear. There is no effect of dose and time on the latency time to recurrence of those who do recur, but there is a weak suggestion of a non-linear effect of patients age, with younger patients recurring earlier. CONCLUSIONS: Generalized additive models provide a flexible and powerful means of exploring non-linear effects in experimental data.

Adult↗
PubMed1997

Annexin I concentration and prostacyclin production in rat lung and alveolar macrophages following irradiation.

The purpose of this study was to gather additional evidence in irradiated rat lung on the relationship between annexin I and prostaglandin synthesis. The right hemithorax of the animal was exposed to a single dose of 0 or 30 Gy of X-rays, and the animals were killed 3 months postirradiation. Levels of annexin I and synthesis of prostacyclin (PGI2) were determined in lungs, in cell-free bronchoalveolar lavage (BAL) fluid, and in macrophages lavaged from those lungs. In addition, protein concentration, lactate dehydrogenase (LDH) activity and macrophage count in BAL fluid obtained from irradiated lung were compared with that from sham-irradiated (0 Gy) lung. Levels of annexin I, the putative inhibitor of phospholipase A2, in lung and cell-free BAL fluid were decreased in samples from irradiated animals. By contrast, the level of annexin I in macrophages lavaged from irradiated lung was higher than that in macrophages from sham-irradiated lung. The irradiated lung produced nearly 3.5 times more prostacyclin than did the control lung. However, prostacyclin synthesis by macrophages lavaged from irradiated lung was no different than that of macrophages from sham-irradiated lung. Protein, LDH and macrophage number in BAL fluid from irradiated lungs were significantly higher than in corresponding specimens from sham-irradiated lungs. These data demonstrate that reduced levels of annexin I, as well as increased protein concentration, LDH activity and macrophage numbers in irradiated rat lung are reflected in BAL fluid. Therefore, information obtained from BAL fluid, but not from BAL macrophages, reflects lung status, and may serve as a minimally invasive index of radiation pneumonitis in this model. In irradiated lung, increased PGI2 synthesis coupled with a decreased annexin I level are consistent with the hypothesis of an inhibitory role of annexin I in prostaglandin metabolism. However, this hypothesis is not supported by findings in BAL macrophages, where increased annexin I concentration is not accompanied by a decrease in PGI2 production. In view of the latter findings, and a previous study from our laboratory demonstrating that phospholipase activity in irradiated rat lung is in fact decreased, despite the reduction in annexin I concentration and the hyperproduction of prostanoids, it would seem unlikely that annexin I negatively modulates prostaglandin synthesis via inhibition of phospholipase in this model.

6-Ketoprostaglandin F1 alpha↗
PubMed1997

Captopril modulates hormone receptor concentration and inhibits proliferation of human mammary ductal carcinoma cells in culture.

The present study evaluated the effect of the angiotensin converting enzyme (ACE) inhibitor captopril on estrogen (ER) and progesterone (PR) receptor concentration and on proliferation in two lines of human mammary ductal carcinoma cells in culture: T-47D (ER+/PR+) and Hs578T (ER-/PR-). The incorporation of [3H]thymidine, validated by cell count, served as an index of proliferation. Compared to control cells, T-47D cells incubated for 48 hrs in 1, 2, or 5 mM captopril (but not in 0.5 mM) exhibited a reduction in ER from 130 +/- 6 to 32 +/- 32 fmol/mg cytosolic protein, and an increase in PR from 1780 +/- 120 to 2740 +/- 400 fmol/ mg protein (p < 0.05). Western analysis confirmed these drug-induced changes in the concentration of immunoreactive receptor proteins. Captopril also induced the appearance of low but detectable PR in the Hs578T cells at concentrations as low as 50 microM. Captopril inhibited the incorporation of [3H]thymidine by both cell types during a 48 hr incubation, although Hs578T cells were 2-3 times more resistant than were T-47D cells. This cytostatic effect of captopril was not due to cytotoxicity as indicated by 51Cr release, and was not accompanied by significant changes in cell cycle distribution as determined by flow cytometry. The incorporation of [3H]uridine (RNA synthesis) and [14C]alanine (protein synthesis) also were inhibited by captopril, suggesting a general antimetabolic effect of the drug in the ductal carcinoma cells. These are novel actions of a common antihypertensive agent. In contrast, the nonthiol ACE inhibitor lisinopril, and penicillamine, a thiol compound with virtually no ACE inhibitory activity, had no effect on any of these endpoints.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1997

Early levels of CD4, neopterin, and beta 2-microglobulin indicate future disease progression.

Reduced CD4 T cell level and increased serum neopterin and beta 2-microglobulin levels, which reflect immunological activation and dysregulation, are three important markers of HIV disease. The aim in this study is to delineate more clearly the relation of activation to future CD4 values and disease progression. By analyzing a cohort of 198 seroconverters from the Multicenter AIDS Cohort Study with 9 years' follow-up, the dynamic changes and levels of these three markers and their interrelationships are explored. We observed that the levels of markers in the first year after seroconversion have a much stronger impact on the progression of the disease than the preseroconversion marker levels. The actual change during the year after seroconversion is not as important as the final level reached during that year. The early levels of markers after seroconversion appear to be good indicators of the subsequent course of disease as defined by CD4 level and slightly better than the quantitative changes following seroconversion or the changes in the period 1 to 2.5 years after seroconversion. To investigate the variation between subjects, the 198 seroconverters were stratified into three approximately equal-sized groups in 12 ways based on their pre- and postseroconversion levels and changes in the three markers. The group with the highest CD4 level within a year after seroconversion maintains the highest CD4 level 8 years after seroconversion. The group with the lowest level of neopterin or beta 2-microglobulin in this period has much higher future CD4 counts than the other two groups. The level of markers during the first year after seroconversion has a high predictive power for AIDS onset. Substantial differences in the hazards of AIDS are found between the groups with the highest and lowest CD4 count, neopterin, and beta 2-microglobulin following seroconversion. The three markers are generally correlated throughout the postseroconversion period but can provide distinct information. High current levels of neopterin or beta 2-microglobulin tend to be associated with low future CD4 count, while current levels of CD4 count have less association with future neopterin and beta 2-microglobulin levels.

Acquired Immunodeficiency Syndrome↗
PubMed1997

B-cell target DNA quantity is a critical factor in the interpretation of B-cell clonality by PCR.

Criteria for the assessment of clonality by Southern blotting are well established but this is not the case for polymerase chain reaction (PCR)-based assays. Our studies, and infrequent reports in the literature, indicate that B-cell clonality may be erroneously inferred if only small numbers of polyclonal B-cells are present in test samples. In order to establish criteria to minimise the false positive assignment of B-cell clonality, DNA was analysed in a semi-nested PCR to detect rearrangement of the immunoglobulin heavy chain gene using a range (1 microgram-0.1 ng) of target DNA amounts from four tonsils and five lymph nodes showing reactive follicular hyperplasia, and from six B-cell lymphomas. A discrete, narrow band of PCR product of constant size was detected throughout the range of target DNA amounts in most lymphomas indicating the presence of a monoclonal B-cell population. In contrast, from the non-malignant tonsils and lymph nodes, larger target amounts generated a broad band of PCR products indicating populations of polyclonal B-cells, but smaller target amounts generated discrete, narrow PCR product bands of inconstant size indicating oligo- or monoclonal B-cell populations. Results of this study demonstrate that a range of DNA target amounts should be tested when the proportion of B-cells in a sample is unknown, thus preventing the analysis of insufficient target DNA which may lead to the false assignment of clonality.

Clone Cells↗
PubMed1997

Effect of low-dose radiation on mouse dermal tissue using wound strength as an endpoint.

PURPOSE: To investigate the existence of enhanced sensitivity of dermal tissue to low radiation doses in the range of 0.1 Gy to 4 Gy/fraction. MATERIALS AND METHODS: Top-up technique of giving higher radiation doses to skin alone from 150 kVp X-rays followed by fractionated experimental doses to total body from 137Cs were given to C3H mice. Full-depth incisions were made and the tensile strength of skin from 14 day wounds were measured as a response of dermal tissue to radiation. RESULTS: There was no evidence of enhanced radiosensitivity to doses as low as 0.1 Gy. The data were better fitted by a nonparametric method that predicted the shape of survival curve better than an induced-repair model. CONCLUSIONS: Dermal tissue like spinal cord has a low sensitive fraction of cells, unlike jejunum, kidney or lung that showed sensitivity at these doses. Tissue kinetics play an important role in the use of low dose fractions to avoid injury to normal tissues.

Animals↗