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Biomedical subjects

G Jones

Publications and source records attributed to G Jones.

At least 199 records · Page 11Linked to original sources
PubMed1997

Ultraspiracle: an invertebrate nuclear receptor for juvenile hormones.

Juvenile hormones (JH), a sesquiterpenoid group of ligands that regulate developmental transitions in insects, bind to the nuclear receptor ultraspiracle (USP). In fluorescence-based binding assays, USP protein binds JH III and JH III acid with specificity, adopting for each ligand a different final conformational state. JH III treatment of Saccharomyces cerevisiae expressing a LexA-USP fusion protein stabilizes an oligomeric association containing this protein, as detected by formation of a protein-DNA complex, and induces USP-dependent transcription in a reporter assay. We propose that regulation of morphogenetic transitions in invertebrates involves binding of JH or JH-like structures to USP.

Animals↗
PubMed1997

Can skull morphology be used to predict ecological relationships between bat species? A test using two cryptic species of pipistrelle.

Can ecological relationships between bat species be predicted largely on the basis of morphology? This question was addressed by investigating skull morphology of two cryptic species of the pipistrelle bat. Since 45 Pipistrellus pipistrellus apparently eats larger prey than 55 P. pipistrellus, we predicted that it would have a larger overall skull size, a larger dentary apparatus, and a larger gape. To test these predictions, variables were measured from skulls of the two cryptic species, and comparisons made between them. In accordance with our predictions, overall skull size was larger in 45 P. pipistrellus than in 55 P. pipistrellus, and 45 P. pipistrellus had a longer lower jaw and the distance between the jaws at maximum gape was larger. In addition, 45 P. pipistrellus had longer upper canines, which may allow it to pierce harder prey items than 55 P. pipistrellus. Only some aspects of dietary differences between the two cryptic species could be explained by differences in skull morphology, and we suggest that empirical data, at least on diet and habitat use, are also required to explain mechanisms of resource partitioning among species in bat communities.

Analysis of Variance↗
PubMed1997

Inactivation of the Fanconi anemia group C gene augments interferon-gamma-induced apoptotic responses in hematopoietic cells.

Hematopoietic progenitor cells (HPC) from mice nullizygous at the Fanconi anemia (FA) group C locus (FAC -/-) are hypersensitive to the mitotic inhibitory effects of interferon (IFN-gamma). We tested the hypothesis that HPC from the bone marrow of Fanconi group C children are similarly hypersensitive and that the fas pathway is involved in affecting programmed cell death in response to low doses of IFN-gamma. In normal human and murine HPC, IFN-gamma primed the fas pathway and induced both fas and interferon response factor-1 (IRF-1) gene expression. These IFN-gamma-induced apoptotic responses in HPC from the marrow of a child with FA of the C group (FA-C) and in FAC -/- mice occurred at significantly lower IFN doses (by an order of magnitude) than did the apoptotic responses of normal HPC. Treatment of FA-C CD34+ cells with low doses of recombinant IFN-gamma, inhibited growth of colony forming unit granulocyte-macrophage and burst-forming unit erythroid, while treatment with blocking antibodies to fas augmented clonal growth and abrogated the clonal inhibitory effect of IFN-gamma. Transfer of the normal FAC gene into FA-C B-cell lines prevented mitomycin C-induced apoptosis, but did not suppress fas expression or inhibit the primed fas pathway. However, the kinetics of Stat1-phosphate decay in IFN-gamma-treated cells was prolonged in mutant cells and was normalized by transduction of the normal FAC gene. Therefore, the normal FAC protein serves, in part, to modulate IFN-gamma signals. HPC bearing inactivating mutations of FAC fail to normally modulate IFN-gamma signals and, as a result, undergo apoptosis executed through the fas pathway.

Anemia, Aplastic↗
PubMed1997

X-ray diffraction and far-UV CD studies of filaments formed by a leucine-rich repeat peptide: structural similarity to the amyloid fibrils of prions and Alzheimer's disease beta-protein.

The development of neuro-degenerative diseases often involves amyloidosis, that is the formation of polymeric fibrillar structures from normal cellular proteins or peptides. For example, in Alzheimer's disease, a 42 amino acid peptide processed from the amyloid precursor protein forms filaments with a beta-sheet structure. Because of this, the structure and dynamics of polymeric peptide filaments is of considerable interest. We showed previously that a 23 amino acid peptide constituting a single leucine-rich repeat (LRRN) polymerises spontaneously in solution to form long filaments of a beta-sheet structure, a property similar to that of Alzheimer's beta-amyloid and prion peptides. Here we report that a variant of LRRN in which a highly conserved asparagine residue is replaced by aspartic acid does not form either filaments or beta structure. By contrast, a variant which replaces this asparagine residue with glutamine forms filaments ultrastructurally indistinguishable from those of LRRN. Electron micrographs of LRRN filaments show that many consist of two interleaved strands which appear to have a ribbon-like morphology. X-ray diffraction patterns from oriented LRRN fibres reveal that they are composed of long beta-sheet arrays, with the interstrand hydrogen bonding parallel to the filament axis. This 'cross-beta' structure is similar to that adopted by beta-amyloid and prion derived fibres. Taken together, these results indicate that the LRR filaments are stabilised by inter- or intra-strand hydrogen bonded interactions comparable to the asparagine ladders of beta-helix proteins or the 'glutamine zippers' of poly-glutamine peptides. We propose that similar stabilising interactions may underlie a number of characterised predispositions to neuro-degenerative diseases that are caused by mutations to amide residues. Our finding that amyloid-like filaments can form from a peptide motif not at present correlated with degenerative disease suggests that a propensity for beta-filament formation is a common feature of protein sub-domains.

Alzheimer Disease↗
PubMed1997

cDNA cloning of human retinoic acid-metabolizing enzyme (hP450RAI) identifies a novel family of cytochromes P450.

Retinoids, including all-trans-retinoic acid (RA) and its stereoisomer 9-cis-RA play important roles in regulating gene expression, through interactions with nuclear receptors, during embryonic development and in the maintenance of adult epithelial tissues (Chambon, P. (1995) Rec. Prog. Horm. Res. 50, 317-32; Mangelsdorf, D. J., and Evans, R. M. (1995) Cell 83, 841-850; Petkovich, M. (1992) Annu. Rev. Nutr. 12, 443-471). Evidence suggests that 4-hydroxylation of RA inside the target cell limits its biological activity and initiates a degradative process of RA leading to its eventual elimination. However, 18-hydroxylation and glucuronidation may also be important steps in this process. In this paper, we describe the cloning and characterization of the first mammalian retinoic acid-inducible retinoic acid-metabolizing cytochrome P450 (hP450RAI), which belongs to a novel class of cytochromes (CYP26). We demonstrate that hP450RAI is responsible for generation of several hydroxylated forms of RA, including 4-OH-RA, 4-oxo-RA, and 18-OH-RA. We also show that hP450RAI mRNA expression is highly induced by RA in certain human tumor cell lines and further show that RA-inducible RA metabolism may correlate with P450RAI expression. We conclude that this enzyme plays a key role in RA metabolism, functioning in a feedback loop where RA levels are controlled in an autoregulatory manner.

Amino Acid Sequence↗
PubMed1997

Metabolism of the vitamin D analog EB 1089: identification of in vivo and in vitro liver metabolites and their biological activities.

1(S),3(R)-dihydroxy-20(R)-(5'-ethyl-5'-hydroxy-hepta-1'(E),3'(E)-dien -1'-yl)-9,10-secopregna-5(Z),7(E),10(19)-triene (EB 1089) is a novel analog of the vitamin D hormone, calcitriol that has been modified in the side-chain resulting in an increased metabolic stability relative to other side-chain modified analogs (e.g. calcipotriol and 22-oxacalcitriol). To further investigate the metabolism of EB 1089, we set out to study this metabolism both in the rat in vivo as well as in the postmitochondrial liver fractions from rat, man, and minipig in vitro. The same pattern of metabolism was observed in all biological systems employed, both in vivo and in vitro, namely 26- and 26a-hydroxylation of EB 1089. The same metabolites were produced using cultured cell systems (Shankar et al., see this issue). All the possible isomers of 26- and 26a-hydroxy EB 1089 were synthesised and these were compared to biologically generated material using HPLC, NMR, and GC-MS techniques. The predominant natural isomer observed in vitro and in vivo in rats as well as in vitro in humans was identified to be (25S),26R-hydroxy EB 1089. The biological activities of the EB 1089 metabolites on cell growth regulation were 10- to 100-fold lower than that of EB 1089. The effects of the metabolites on calcium metabolism in vivo were comparable to the effect of EB 1089; however, these effects were reduced for the major metabolite in rat and man and for the isomers of 26a-hydroxy EB 1089. We conclude that EB 1089 is metabolised by a different route of side-chain metabolism than calcitriol and that this may explain its relative metabolic stability in pharmacokinetic experiments in vivo compared to that of other vitamin D analogs.

Animals↗
PubMed1997

Development and validation of a genetic algorithm for flexible docking.

Prediction of small molecule binding modes to macromolecules of known three-dimensional structure is a problem of paramount importance in rational drug design (the "docking" problem). We report the development and validation of the program GOLD (Genetic Optimisation for Ligand Docking). GOLD is an automated ligand docking program that uses a genetic algorithm to explore the full range of ligand conformational flexibility with partial flexibility of the protein, and satisfies the fundamental requirement that the ligand must displace loosely bound water on binding. Numerous enhancements and modifications have been applied to the original technique resulting in a substantial increase in the reliability and the applicability of the algorithm. The advanced algorithm has been tested on a dataset of 100 complexes extracted from the Brookhaven Protein DataBank. When used to dock the ligand back into the binding site, GOLD achieved a 71% success rate in identifying the experimental binding mode.

Algorithms↗
PubMed1997

Metabolism of the vitamin D analog EB1089 by cultured human cells: redirection of hydroxylation site to distal carbons of the side-chain.

1(S),3(R)-dihydroxy-20(R)-(5'-ethyl-5'-hydroxy-hepta-1'(E),3' (E)-dien-1'-yl)-9,10-secopregna-5(Z),7(E),10(19)-triene (EB1089) is a novel synthetic analog of 1 alpha,25-dihydroxyvitamin D [1,25-(OH)2D3] with potential for use in the treatment of hyperproliferative disorders. It has an altered side-chain structure compared to 1,25-(OH)2D3, featuring 26,27 dimethyl groups, insertion of an extra carbon atom (24a) at C-24, and two double bonds at C-22,23 and C-24,24a. In vitro metabolism of EB1089 was studied in a human keratinocyte cell model, HPK1A-ras, previously shown to metabolize 1,25-(OH)2D3. Four metabolites were formed, all of which possessed the same UV chromophore as EB1089, indicating the retention of the side-chain conjugated double bond system. Two metabolites were present in sufficient quantities to identify them as 26-hydroxy EB1089 (major product) and 26a-hydroxy EB1089 (minor product), based on mass spectral analysis and cochromatography with synthetic standards. Similar metabolites were generated in vivo and using a liver postmitochondrial fraction in vitro (Kissmeyer et al., companion paper). Studies with the human hepatoma Hep G2 gave rise to 2 isomers of 26-hydroxy EB1089. Studies using ketoconazole, a general cytochrome P450 inhibitor, implicated cytochrome P450s in the formation of the EB1089 metabolites. COS-1 transfection cell experiments using vectors containing CYP27 and CYP24 suggest that these cytochrome P450s are probably not involved in 26- or 26a-hydroxylation of EB1089. Other experiments that examined the HPK1A-ras metabolism of related analogs containing only a single side-chain double bond: 1(S),3(R)-dihydroxy-20(R)-(5'-ethyl-5'-hydroxy-hepta-1' (E)-en-1'-yl)-9,10-secopregna-5(Z),7(E),10(19)-triene (MC1473; double bond at C-22,23) and 1(S),3(R)-dihydroxy-20(R)-(5'-ethyl-5'-hydroxy-hepta-3'(E)-en-1'-yl)-9, 10-secopregna-5(Z),7(E),10(19)-triene (MC1611; double bond at C-24,24a) revealed that the former compound was subject to 24-hydroxylation and the latter compound was mainly 23-hydroxylated. Metabolism experiments involving EB1089, MC1473, and MC1611 in competition with [1 beta-3H]1,25-(OH)2D3 in HPK1A-ras confirmed that CYP24 is probably not involved in the metabolism of EB1089 whereas, in the case of MC1473 and MC1611, it does appear to carry out side-chain hydroxylation. Our interpretation is that the conjugated double bond system in the side-chain of EB1089 is responsible for directing the target cell hydroxylation to the distal positions, C-26 and C-26a. We conclude that EB1089 is slowly metabolized via unique in vitro metabolic pathways, and that these features may explain the relative stability of EB1089 compared to other analogs in vivo.

Antineoplastic Agents↗
PubMed1997

Induction by agrin of ectopic and functional postsynaptic-like membrane in innervated muscle.

Two factors secreted from the nerve terminal, agrin and neuregulin, have been postulated to induce localization of the acetylcholine receptors (AChRs) to the subsynaptic membrane in skeletal muscle fibers. The principal function ascribed to neuregulin is induction of AChR subunit gene expression and to agrin is the aggregation of AChRs. Here we report that when myoblasts engineered to secrete an agrin fragment were placed into the nerve-free region of denervated rodent muscle, the host muscle fibers expressed AChR epsilon-subunit gene transcripts, characteristic of the neuromuscular synapse in adult muscle. Transcripts were colocalized with agrin deposits and AChR clusters that were resistant to electrical muscle activity. More directly, single innervated muscle fibers injected intracellularly with agrin expression plasmids in their extrasynaptic region developed a functional ectopic postsynaptic membrane with clusters of adult-type AChR channels and acetylcholinesterase and accumulation of myonuclei. The results demonstrate that agrin is the principal neural signal that induces the formation of the subsynaptic apparatus in the muscle fiber and controls locally, either indirectly or directly, the transcription of AChR subunit genes and the aggregation of AChRs.

Agrin↗
PubMed1997

A population-based study of the relationship between salt intake, bone resorption and bone mass.

OBJECTIVE: To explore the relationship between urinary sodium (the best measure of salt intake), urinary calcium, urinary deoxypyridinoline (DPYR) and bone mass. DESIGN: Cross-sectional study. SETTING: Population based sample of healthy Hobart residents. SUBJECTS: One hundred and fifty-four (M = 34, F = 120) subjects invited to take part from a systematic sample of the electoral roll and a single newspaper advertisement. RESULTS: In both sexes, urinary sodium correlated moderately with urinary DPYR (r = 0.32, P < 0.0001) and urinary calcium (r = 0.37, P < 0.0001). In multivariate analysis, the combination of urinary sodium, total body bone area, age and sex explained 22% of the variation in log-transformed DPYR (P < 0.00001). In univariate analysis, both urinary sodium and urinary DPYR were strongly associated with bone mineral content and bone mineral density at all sites but this association disappeared after adjustment for confounders particularly body weight. CONCLUSIONS: This study has shown that salt intake is associated with markers of bone resorption in a population-based sample of males and females and appears likely to be a risk factor for osteoporosis despite the lack of a demonstrable association between bone mass and a single measure of urinary sodium excretion. Further studies are needed to define the effect of salt intake on bone mass and fractures more clearly. These studies will need to be either longitudinal or interventional in design with repeated measures of urinary sodium so that habitual sodium intake can be accurately assessed and regression dilution bias can be minimised.

Adult↗
PubMed1997

Goal difficulty, anxiety and performance.

This study reports a detailed investigation of the interaction between goal setting, anxiety and perceptuo-motor performance. Forty-four subjects completed familiarization, control and treatment conditions in which they were required to perform a series of perceptual speed trials. In the control condition, subjects were assigned a vague, general goal of 'do your best', whilst in the treatment condition, increasingly difficult, specific goals were assigned. During each condition, subjective goal difficulty, goal acceptance, performance, cognitive anxiety, somatic anxiety and self-confidence were examined. The results suggested that the manipulation of the control and treatment conditions were successful. In the treatment condition, an increase in cognitive anxiety and a reduction in self-confidence accompanied increasing goal difficulty but these remained stable in the control condition. Performance was greater when 'do your best' as opposed to 'very easy' goals were assigned, but this situation was reversed when 'very hard' goals were assigned. The results of these laboratory-based findings are discussed with particular reference to the implications for practitioners in applied settings.

Adolescent↗
PubMed1997

The role of vision and spatial orientation in the maintenance of posture.

This article reviews and analyzes the role of vision and spatial orientation in maintaining posture and balance. The key issues that relate to the development of postural control across the life span are discussed. Use of vision as a critical source of information that specifies spatial orientation in the environment is considered. We argue that the visual system functions as part of the perception-action cycle as promoted in ecological psychology by James Gibson. We compare and contrast theory and evidence of both standard and ecological accounts of how the visual system perceives the information and the findings relative to the role of the retinal vision in processing and acting on information related to motion. Changes in the ambient optical array (optical flow) as a non-force field are compared with gravity-based perturbations relative to the possible influence of the non-force field to changes in the motor system. Finally, a summary of some of our own work is presented, with comments about implications for further research and possible applications to clinical practice.

Humans↗