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Biomedical subjects

A J Clark

Publications and source records attributed to A J Clark.

At least 73 records · Page 4Linked to original sources
PubMed1999

Nitroreductase-mediated cell ablation is very rapid and mediated by a p53-independent apoptotic pathway.

Nitroreductase (NTR)-mediated selective cell ablation using the prodrug CB1954 has been achieved in vivo by targeting the nitroreductase gene to the luminal cells of the mammary gland in transgenic mice. We report that the cell ablation occurs very rapidly, starting as early as 7 h after administration of the prodrug. By cross-breeding the BLG-NTR transgenic mice to a p53-deficient mouse strain, we have generated BLG-NTR transgenic mice on a p53 null background and tested NTR-mediated cell ablation in these mice. The transgenic mice lacking a functional p53 gene showed cell ablation at a similar level compared with p53 wild-type transgenic mice, showing that functional p53 is not required for CB1954-NTR mediated cell death. These results provide further support for using this system in anti-cancer therapy.

Animals↗
PubMed1999

The insulin-like growth factor-I (IGF-I) gene in individuals born small for gestational age (SGA).

OBJECTIVE: To investigate the association of genetic variation of the insulin-like growth factor-I (IGF-I) gene with birth size small for gestational age (SGA). SUBJECTS: We have studied a cohort of 120 SGA patients and 147 appropriate for gestational age (AGA) controls from Haguenau, France. METHODS: PCR-SSCP analysis was performed to detect sequence variation in the coding region of the IGF-I gene. Microsatellite markers near the IGF-I gene (intronic and D12S78) were selected and amplified to perform further analysis by association studies. RESULTS: A novel polymorphism in intron 2 was discovered, but allele-specific PCR analysis in the 120 SGA patients and 147 AGA controls found no association between this polymorphism and birth size SGA. Chi squared (chi2) analysis found no statistically significant association between the allele distribution of the microsatellite markers in the SGA subjects and the AGA controls. Power calculations estimate that the D12S78 marker has an 80% chance of detecting a 10-15% difference. CONCLUSIONS: These studies suggest that genetic variation of IGF-I alone does not result in birth size small for gestational age in this population. Thus, if this gene influences fetal size, it plays only a minor role in a multifactorial disorder which involves other genetic and environmental factors.

Case-Control Studies↗
PubMed1999

dnaC mutations suppress defects in DNA replication- and recombination-associated functions in priB and priC double mutants in Escherichia coli K-12.

PriA, PriB and PriC were originally discovered as proteins essential for the PhiX174 in vitro DNA replication system. Recent studies have shown that PriA mutants are poorly viable, have high basal levels of SOS expression (SOSH), are recombination deficient (Rec-), sensitive to UV irradiation (UVS) and sensitive to rich media. These data suggest that priA's role may be more complex than previously thought and may involve both DNA replication and homologous recombination. Based on the PhiX174 system, mutations in priB and priC should cause phenotypes like those seen in priA2:kan mutants. To test this, mutations in priB and priC were constructed. We found that, contrary to the PhiX174 model, del(priB)302 and priC303:kan mutants have almost wild-type phenotypes. Most unexpectedly, we then found that the priBC double mutant had very poor viability and/or a slow growth rate (even less than a priA2:kan mutant). This suggests that priB and priC have a redundant and important role in Escherichia coli. The priA2:kan suppressor, dnaC809, partially suppressed the poor viability/slow growth phenotype of the priBC double mutant. The resulting triple mutant (priBC dnaC809 ) had small colony size, recombination deficiency and levels of SOS expression similar to a priA2:kan mutant. The priBC dnaC809 mutant, however, was moderately UVR and had good viability, unlike a priA2:kan mutant. Additional mutations in the triple mutant were selected to suppress the slow growth phenotype. One suppressor restored all phenotypes tested to nearly wild-type levels. This mutation was identified as dnaC820 (K178N) [mapping just downstream of dnaC809 (E176G)]. Experiments suggest that dnaC820 makes dnaC809 suppression of priA and or priBC mutants priB and or priC independent. A model is proposed for the roles of these proteins in terms of restarting collapsed replication forks from recombinational intermediates.

Bacterial Proteins↗
PubMed1999

Insertion of a casein kinase recognition sequence induces phosphorylation of ovine beta-lactoglobulin in transgenic mice.

We have shown that the cellular mechanisms of the mammary gland can be used to produce a phosphorylated form of a normally unphosphorylated milk protein. This was achieved by the insertion of a beta-casein DNA sequence coding for a group of mammary gland casein kinase recognition sites into ovine beta-lactoglobulin. Transgenic mice carrying this modified gene were generated and lactating females were shown to produce a novel beta-lactoglobulin in their milk. The infrared spectrum, reactivity to antiphosphoserine antibody and reduction of electrophoretic mobility on treatment with alkaline phosphatase showed that the novel protein recovered from the milk whey (serum) was phosphorylated and molecular mass determination by mass spectrometry was consistent with the phosphorylation of one or two residues. A similar level of phosphorylation was measured by quantitative infrared spectroscopy. Centrifugation of the milk to pellet the casein micelles showed that most of the phosphorylated beta-lactoglobulin was in the whey and hence not incorporated into casein micelles.

Amino Acid Sequence↗
PubMed1999

Requirement for the heart-type fatty acid binding protein in cardiac fatty acid utilization.

Nonenzymatic cytosolic fatty acid binding proteins (FABPs) are abundantly expressed in many animal tissues with high rates of fatty acid metabolism. No physiological role has been demonstrated for any FABP, although these proteins have been implicated in transport of free long-chain fatty acids (LCFAs) and protection against LCFA toxicity. We report here that mice lacking heart-type FABP (H-FABP) exhibit a severe defect of peripheral (nonhepatic, non-fat) LCFA utilization. In these mice, the heart is unable to efficiently take up plasma LCFAs, which are normally its main fuel, and switches to glucose usage. Altered plasma levels of LCFAs, glucose, lactate and beta-hydroxybutyrate are consistent with depressed peripheral LCFA utilization, intensified carbohydrate usage, and increased hepatic LCFA oxidation; these changes are most pronounced under conditions favoring LCFA oxidation. H-FABP deficiency is only incompletely compensated, however, causing acute exercise intolerance and, at old age, a localized cardiac hypertrophy. These data establish a requirement for H-FABP in cardiac intracellular lipid transport and fuel selection and a major role in metabolic homeostasis. This new animal model should be particularly useful for investigating the significance of peripheral LCFA utilization for heart function, insulin sensitivity, and blood pressure.

3-Hydroxybutyric Acid↗
PubMed1999

Relationship between phenotype and genotype in growth hormone insensitivity syndrome.

Growth hormone insensitivity syndrome (GHIS) of genetic origin is associated with many different mutations of the growth hormone receptor (GHR) gene and a recently described genetic defect of the insulin-like growth factor I (IGF-I) gene. Phenotypic and biochemical features were examined in a cohort of 82 patients with GHIS from 23 countries. The mean age of these patients was 8.3 years, their mean height SDS was -6.09 and their median IGF-binding protein-3 (IGFBP-3) SDS was -8.5. In total, 19 of the 82 patients (23%) were growth hormone-binding protein (GHBP)-positive (> 10%). The mean heights in GHBP-negative and GHBP-positive patients were -6.45 SDS and -4.89 SDS, respectively (p < 0.001). Sixteen different GHR gene mutations were identified in 27 patients with GHIS. All of these patients had homozygous mutations, except one who had a compound heterozygous mutation. There was no relationship between the type or site within the GHR gene of the mutation and the height SDS or IGFBP-3 SDS of the patients. GHIS is associated with a wide variation in the severity of clinical and biochemical phenotypes. This variation cannot clearly be accounted for by defects in the GHR gene alone. Other genes or environmental factors must contribute to the control of growth in patients with GHIS.

Adolescent↗
PubMed1999

Diversity of radA genes from cultured and uncultured archaea: comparative analysis of putative RadA proteins and their use as a phylogenetic marker.

Archaea-specific radA primers were used with PCR to amplify fragments of radA genes from 11 cultivated archaeal species and one marine sponge tissue sample that contained essentially an archaeal monoculture. The amino acid sequences encoded by the PCR fragments, three RadA protein sequences previously published (21), and two new complete RadA sequences were aligned with representative bacterial RecA proteins and eucaryal Rad51 and Dmc1 proteins. The alignment supported the existence of four insertions and one deletion in the archaeal and eucaryal sequences relative to the bacterial sequences. The sizes of three of the insertions were found to have taxonomic and phylogenetic significance. Comparative analysis of the RadA sequences, omitting amino acids in the insertions and deletions, shows a cladal distribution of species which mimics to a large extent that obtained by a similar analysis of archaeal 16S rRNA sequences. The PCR technique also was used to amplify fragments of 15 radA genes from uncultured natural sources. Phylogenetic analysis of the amino acid sequences encoded by these fragments reveals several clades with affinity, sometimes only distant, to the putative RadA proteins of several species of Crenarcheota. The two most deeply branching archaeal radA genes found had some amino acid deletion and insertion patterns characteristic of bacterial recA genes. Possible explanations are discussed. Finally, signature codons are presented to distinguish among RecA protein family members.

Amino Acid Sequence↗
PubMed1999

Desensitization of CGRP and adrenomedullin receptors in SK-N-MC cells: implications for the RAMP hypothesis.

Recent evidence (1) suggests that the related peptides calcitonin gene-related peptide (CGRP) and adrenomedullin (AM) bind to the same heptahelical transmembrane receptor, with receptor specificity being determined by a receptor associated modifying protein (RAMP). If correct, this hypothesis would predict that each peptide should desensitize the cellular response to subsequent stimulation by itself or the other peptide. We have therefore studied the patterns of desensitization of these receptors in SK-N-MC cells. SK-N-MC cells were stimulated for 20 minutes in either serum free medium alone (control) or SFM containing AM 10(-8) M or CGRP 10(-7) M. Cells were then incubated for a further 20 minutes in SFM containing a second agonist and 1 mM isobutyryl methylxanthine (IBMX), before harvesting and assay for cAMP. Pre-exposure of cells to CGRP or AM decreased cAMP generation in response to subsequent stimulation with CGRP by 58% (+/-14) and 42% (+/-14) (SD) respectively. Pre-incubation of cells with 100 nM H-89 abolished this effect, indicating that desensitization was mediated through PKA. In contrast, there was no attenuation of the cAMP response to stimulation with AM by pre-exposure to AM or CGRP. These results suggest that CGRP and AM receptors exhibit different patterns of desensitization in SK-N-MC cells: a finding with significant implications for the RAMP hypothesis.

1-Methyl-3-isobutylxanthine↗
PubMed1999

Effects of recombinant human insulin-like growth factor I (IGF-I) therapy on the growth hormone-IGF system of a patient with a partial IGF-I gene deletion.

We have previously reported a 17.2-yr-old boy with severe growth retardation and undetectable serum levels of insulin-like growth factor I (IGF-I) due to a partial deletion of the IGF-I gene. The aim of this study was to investigate the effects of recombinant human IGF-I (rhIGF-I) therapy on the GH-IGF system of this patient to gain further insights into its growth-promoting and metabolic actions. To assess the changes in GH, IGFs, IGF-binding proteins (IGFBPs), acid-labile subunit (ALS), and insulin levels, blood samples were obtained before therapy and during the first year of treatment. Hormones were analyzed by specific RIAs. Overnight GH profiles were performed before and at 1, 6, and 12 months of therapy. Fasting ALS, IGF-II, IGFBP-3, IGFBP-2, IGFBP-1, and insulin levels before rhIGF-I treatment were 46.3 mg/L, 1044 microg/L, 5.8 mg/L, 73 ng/mL, 4.7 ng/mL, and 27.3 mU/L, respectively. IGF-II, ALS, and insulin levels were elevated, whereas IGFBP-1 and IGFBP-2 levels were decreased compared to reference values. Twenty-four hours after a single s.c. injection of rhIGF-I (40 microg/kg), the concentrations were 46 mg/L, 888 microg/L, 6.9 mg/L, 112 ng/mL, 5.0 ng/mL, and 21.0 mU/L, respectively. After a single s.c. injection of rhIGF-I of 40 or 80 microg/kg x day and modelling the data using a two-compartment model, the half-lives of elimination were 15.7 and 14.3 h, with a maximum increase in IGF-I levels to 341 and 794 microg/L around 7 h, respectively. An increase in IGFBP-3 levels was observed with both doses of rhIGF-I, with a peak values of 9 mg/L. GH profiles showed a decrease in peak amplitude from 342 to 84 mU/L at 1 month, to 67 mU/L at 6 months, and to 40 mU/L at 1 yr of therapy, with no significant changes in peak number. A significant increase in IGFBP-1 levels was observed during treatment with 80 microg/kg x day IGF-I, reflecting the inhibitory effect of rhIGF-I on insulin secretion. The clinical response to rhIGF-I therapy was an increased height velocity from 3.8 cm/yr before treatment to 6.6 cm/yr. Increased lean body mass correlated with changes in the doses of rhIGF-I and, in turn, with the biochemical changes in the GH-IGF axis. Similar to healthy individuals, this patient had normal IGFBP-3 and ALS levels, which are the major regulators of the pharmacokinetics of rhIGF-I. In summary, rhIGF-I treatment has improved linear growth and insulin sensitivity in this patient by restoring IGF-I levels and by normalizing circulating GH, IGFBP, and insulin levels.

Adolescent↗
PubMed1999

Functional characterization of naturally occurring mutations of the human adrenocorticotropin receptor: poor correlation of phenotype and genotype.

Several missense mutations of the ACTH receptor (MC2-R) gene have been associated with the autosomal recessive syndrome of familial glucocorticoid deficiency. Attempts to demonstrate the functional role of these mutations have been confounded by difficulties in expression of the cloned receptor in cells lacking endogenous melanocortin receptors. The Y6 cell line, a mutant derived from the Y1 cell line, lacks any endogenous MC2-R and can be used for this purpose. We demonstrate that several MC2-R mutations associated with familial glucocorticoid deficiency result in an impaired maximal cAMP response (S74I, I44M, R146H) or loss of sensitivity for cAMP generation (D103N, R128C, T159K) compared to the wild-type receptor. Considerable variation in clinical phenotype exists even for patients with identical mutations of the MC2-R, and correlation between the estimated severity of the receptor defect in vitro and the age at clinical presentation and degree of clinical severity, as judged by basal and stimulated plasma cortisol concentration, is poor.

Cell Line↗
PubMed1999

The influence of plasma on basal and ACTH-stimulated in vitro adrenocortical steroidogenesis.

Early descriptions of in vitro ACTH bioassays all emphasised the need to use extracted plasma samples due to interference by an unidentified component. The aim of these studies was to elucidate the effects of whole plasma on ACTH steroidogenic activity in vitro and to identify the responsible factor. A sensitive in vitro dispersed bovine adrenocortical cell bioassay was established. The addition of 10% ACTH-depleted human pooled plasma to the incubation media resulted in basal steroidogenesis equivalent to that achieved with 10(-9) M ACTH1-24 and potentiated the steroidogenic activity of 10(-9) M ACTH1-24 by 7.8-fold. This potentiation was dependent on the concentration of both ACTH and plasma in the media, but did not result from the mitogenic effect of plasma. A pituitary source was excluded and the potentiating activity was not extractable by Vycor glass. Column chromatography demonstrated two peaks of activity corresponding to molecular weights of 650 and 220x10(3) Da. These peaks did not correspond to the plasma binding of 125I-ACTH which resulted from non-specific binding to albumin. Lipoprotein-deficient serum had no effect on either basal or ACTH-stimulated steroidogenesis, but both were restored by the addition of purified lipoproteins. However, novel findings demonstrated a differential effect of low (LDL) and high (HDL) density lipoproteins on basal and ACTH-stimulated steroid production; thus, LDL exerted a greater effect on the former, whilst HDL potentiated the steroidogenic activity of added ACTH more than LDL. The addition of the lipoproteins to lipoprotein-deficient serum restored its basal and ACTH potentiating effects, the cholesterol concentrations of the chromatographic fractions exactly paralleling their ACTH potentiating effect. These findings suggest that not only are lipoproteins the plasma factor(s) which potentiates ACTH steroidogenic activity in in vitro bioassays, but also that they exert differential effects on basal and ACTH-stimulated steroid production.

Adrenocorticotropic Hormone↗
PubMed1999

ACTH resistance syndromes.

Inherited adrenocorticotropin (ACTH) insensitivity syndromes comprise a group of rare diseases in which resistance to ACTH is either the sole feature or associated with other symptoms. This review focuses on two autosomal recessive disorders, familial glucocorticoid deficiency (FGD) (MIM*202200) and the triple A syndrome (MIM*231550), which have at least three different molecular aetiologies. In FGD, several missense mutations within the coding region of the ACTH receptor (MC2-R) have been identified in some, but not all patients, and segregation analyses and functional studies in a Y6 cell expression system confirmed that these mutations cause the disease. Some cases of FGD are not linked to the MC2-R locus on chromosome 18p11.2 suggesting genetic heterogeneity. The triple A syndrome is clinically characterized by the triad of adrenal insufficiency, achalasia and alacrima and a variety of neurological symptoms. After excluding several candidate genes we mapped this syndrome to a 6 cM interval on chromosome 12q13 with no indication for genetic heterogeneity. The identification of the gene(s) causing FGD without mutations in the MC2-R and causing the triple A syndrome may reveal novel aspects in cell signalling and neuroendocrinology.

Adrenocorticotropic Hormone↗
PubMed1998

RadA protein is an archaeal RecA protein homolog that catalyzes DNA strand exchange.

With the discovery that the Saccharomyces cerevisiae Rad51 protein is both structurally and functionally similar to the Escherichia coli RecA protein, the RecA paradigm for homologous recombination was extended to the Eucarya. The ubiquitous presence of RecA and Rad51 protein homologs raises the question of whether this archetypal protein exists within the third domain of life, the Archaea. Here we present the isolation of a Rad51/RecA protein homolog from the archaeon Sulfolobus solfataricus, and show that this protein, RadA, possesses the characteristics of a DNA strand exchange protein: The RadA protein is a DNA-dependent ATPase, forms a nucleoprotein filament on DNA, and catalyzes DNA pairing and strand exchange.

Adenosine Triphosphatases↗
PubMed1998

General transducing phages like Salmonella phage P22 isolated using a smooth strain of Escherichia coli as host.

A smooth colony strain, resistant to phages lambda and P22, was isolated from sewage and identified as Escherichia coli (strain H). Four temperate phages plaquing on strain H were isolated from sewage. The archetype, HK620, does not plaque on strains C and K12 of E. coli nor on the LT2 strain of Salmonella enterica. Bacterial mutants resistant to a clear plaque mutant of HK620 produce rough colonies. Some are also galactose-negative, a few are histidine auxotrophs, and most show sensitivity to lambda. HK620 can transduce a wide variety of auxotrophic mutants of E. coli H to prototrophy. It can recombine with lambda but its virions resemble those of P22.

Escherichia coli↗
PubMed1998

Cloning of bovine preproadrenomedullin and inhibition of its basal expression in vascular endothelial cells by staurosporine.

The cDNA encoding preproadrenomedullin (preproAM) was cloned using reverse transcriptase polymerase chain reaction (RT-PCR) and 5' rapid amplification of cDNA ends from total RNA from bovine aortic endothelial cells (BAEC). Bovine preproAM cDNA shows high sequence homology with human, porcine and rat preproAM. Bovine-specific primers derived from this sequence were used in RT-PCR to study regulation of this gene. Treatment of BAEC or a human endothelial cell line (Ea.hy 926) with the non-selective protein kinase inhibitor staurosporine resulted in significantly reduced preproAM mRNA levels. The reduction in preproAM mRNA appeared to be absolute when Ea.hy 926 cells were exposed to 100 nM staurosporine for 2 h. However, this dramatic reduction could not be reproduced by treatment with the protein kinase A (PKA) inhibitor H-89, or the protein kinase C (PKC) inhibitors chelerythrine chloride and bisindolylmaleimide I. These observations suggest that activation of a novel staurosporine-sensitive protein kinase is necessary for basal expression of the preproAM gene in these cells.

Adrenomedullin↗
PubMed1998

"Mirror pain" as an unusual presentation of renal colic.

Although most patients suffering from pain related to upper urinary tract stones feel the discomfort on the same side as the stone, rarely it is perceived on the opposite side. We sought to identify the prevalence of this clinical scenario and to review possible explanations. The charts and x-rays of all patients with unilateral, symptomatic, radiologically identifiable upper urinary tract stones, seen at an outpatient clinic between June 1993 and August 1996, were reviewed retrospectively in terms of the side of the discomfort in comparison to the side of the stone. Three of 631 patients presented with contralateral or "mirror pain" secondary to a renal or ureteric calculus. In each case the symptoms resolved completely following successful extracorporeal shock wave lithotripsy or spontaneous passage of the stone.

Adult↗