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Biomedical subjects

L Christen

Publications and source records attributed to L Christen.

12 recordsLinked to original sources
PubMed2001

Intracellular chelation of iron by bipyridyl inhibits DNA virus replication: ribonucleotide reductase maturation as a probe of intracellular iron pools.

The efficient replication of large DNA viruses requires dNTPs supplied by a viral ribonucleotide reductase. Viral ribonucleotide reductase is an early gene product of both vaccinia and herpes simplex virus. For productive infection, the apoprotein must scavenge iron from the endogenous, labile iron pool(s). The membrane-permeant, intracellular Fe(2+) chelator, 2,2'-bipyridine (bipyridyl, BIP), is known to sequester iron from this pool. We show here that BIP strongly inhibits the replication of both vaccinia and herpes simplex virus, type 1. In a standard plaque assay, 50 microm BIP caused a 50% reduction in plaque-forming units with either virus. Strong inhibition was observed only when BIP was added within 3 h post-infection. This time dependence was observed also in regards to inhibition of viral late protein and DNA synthesis by BIP. BIP did not inhibit the activity of vaccinia ribonucleotide reductase (RR), its synthesis, nor its stability indicating that BIP blocked the activation of the apoprotein. In parallel with its inhibition of vaccinia RR activation, BIP treatment increased the RNA binding activity of the endogenous iron-response protein, IRP1, by 1.9-fold. The data indicate that the diiron prosthetic group in vaccinia RR is assembled from iron taken from the BIP-accessible, labile iron pool that is sampled also by ferritin and the iron-regulated protein found in the cytosol of mammalian cells.

2,2'-Dipyridyl↗
PubMed1999

Randomized, placebo-controlled trial of Chinese herb therapy for HIV-1-infected individuals.

CONTEXT: Alternative medicine or complementary remedies that have not been scientifically tested are nonetheless widely used to treat chronic illnesses, particularly if curative options are limited. OBJECTIVES: To assess the effectiveness of Chinese medicinal herbs in reducing symptoms and improving the quality of life of HIV-infected persons. DESIGN: Prospective, placebo-controlled double-blind study. SETTING: University-based HIV outpatient clinic. PATIENTS: 68 HIV-infected adults with CD4 cell counts <0.5 x 10(9)/L. INTERVENTION: Participants were randomized to receive four daily doses of seven pills containing a standardized preparation of 35 Chinese herbs or placebo for 6 months. MAIN OUTCOME MEASURES: Symptoms, HIV disease progression, HIV-1 RNA plasma viral loads, CD4 and CD8 cell counts, and scores on standard questionnaires for quality of life, depression, anxiety, and coping. RESULTS: Intervention and placebo groups were equivalent at baseline regarding, respectively, previous antiretroviral therapy (74% versus 79%), median CD4 cell counts (0.20 x 10(9)/L versus 0.25 x 10(9)/L), and median HIV-1 plasma viral loads (35,612 copies/ml versus 52,027 copies/ml). At enrollment, none of the study subjects was seriously ill or depressed, and average coping and quality of life scores were in the normal range. In all, 53 (78%) participants completed the study. Patients taking Chinese herbs reported significantly more gastrointestinal disturbances (79% versus 38%; p = .003) than those receiving placebo. No therapy-related toxicities were observed. At completion of the study, no significant differences between the intervention and placebo groups were found regarding plasma viral loads, CD4 cell counts, symptoms, and psychometric parameters. HIV-1 RNA level was unchanged at study end. Among participants who were not on concomitant antiretroviral therapy, median CD4 cell counts declined by 0.05 x 10(9)/L in both the intervention and placebo groups. CONCLUSIONS: This standardized formulation of Chinese herbs for HIV-infected individuals did not improve quality of life, clinical manifestations, plasma virus loads, or CD4 cell counts. The data suggest that this formulation of Chinese herbs is not effective when administered in a Western medicine setting.

Adult↗
PubMed1999

Identification of a cDNA encoding a retinoid X receptor homologue from Schistosoma mansoni. Evidence for a role in female-specific gene expression.

Schistosoma mansoni, a multicelluar eukaryotic blood fluke, is a major cause of morbidity worldwide in humans. The study of female parasite growth, development, and gene regulation is important because the eggs produced are responsible for the pathogenesis observed in schistosomiasis. p14, an eggshell precursor gene expressed only in sexually mature females in response to a male stimulus, is a model for female-specific gene regulation. The upstream region of the p14 gene shares sequences present in insect genes known to be regulated in a sex-, temporal-, and tissue-specific manner by members of the steroid receptor superfamily. Herein, we report the identification and characterization of a cDNA that encodes the S. mansoni (Sm) RXR homologue. Sequence analysis predicts and Western blot analysis confirms the synthesis of a 74-kDa protein, the largest member of the RXR family reported to date. We show by electrophoretic mobility shift assay analysis that SmRXR binds to cis-elements of the p14 gene including a direct repeat that follows the "3-4-5" rule of binding elements recognized by members of the steroid receptor superfamily. Furthermore, we demonstrate that SmRXR can act as a transcription activator in the yeast one-hybrid system. Through quantitative reverse transcriptase-polymerase chain reaction, we show that the SmRXR gene is constitutively expressed and thus must play multiple roles throughout the schistosome life cycle.

Amino Acid Sequence↗
PubMed1998

[Successful coping with declining objective life style by institutionalized long-term patients. Results of a follow-up analysis of quality of life in long-term care institutions with the Zurich Quality of Life Inventory].

Measurement of quality of life in institutionalized frail patients is difficult considering the high prevalence of dementia. The Zurich quality of life inventory was developed specifically for this purpose and applied to describe longitudinally 103 institutionalized long-term care patients 3-12 months after entry: 11 slow-stream-rehabilitation patients (SSR), 16 severely dependent patients (ASL), 61 moderately dependent patients (ALL), and 15 young severely dependent patients, all of whom were assessed at least twice. The objective conditions of life deteriorated in all 4 groups, significantly in the SSR and ASL, and with high significance in the whole population from 121 +/- 54 to 139 +/- 58 (P < 0.001). Well-being did not change significantly in any of the groups or overall (from 122 +/- 59 to 117 +/- 54, p = 0.90). Deteriorating life conditions were due to a decline in clinical dementia rating, (p < 0.01) and living space diameter (p < 0.001), whereas the remaining subscores of life condition, i.e., number of falls, days of sickness, life style rating, and all subscores of well-being, i.e., number of medicines, valuation of handicap and of suffering, visual self-rating of well-being and caregivers' stress did not change significantly.

Activities of Daily Living↗
PubMed1994

Direct photolinkage of GTP to the vaccinia virus mRNA (guanine-7-) methyltransferase GTP methyl acceptor site.

Direct UV photolinkage of [alpha-32P]GTP to the methyl acceptor site of the vaccinia virus (guanine-7-) methyltransferase was attempted in order to identify the GTP binding region of this enzyme. Low-efficiency photolinkage of GTP to the carboxyl terminal domain of the large subunit, D1R498-844, was achieved and shown to be specific by several criteria. The half-saturation value for GTP was determined to be 35 microM which is equivalent to the catalytic Km for the substrate. GTP photolinkage was shown to be inhibited by GpppA, a substrate for the methyltransferase reaction, better than GMepppA, the reaction product. The addition of MgCl2, known to prevent GTP from serving as a methyl group acceptor in this reaction, was found to eliminate GTP photolinkage. Finally, AdoHcy, a potent product inhibitor of AdoMet binding, failed to inhibit GTP photolinkage, demonstrating that GTP was not linked to the AdoMet binding site. Chemical cleavage of the GTP-labeled enzyme permitted the identification of multiple radioactive peptides, demonstrating the existence of multiple interaction sites in the carboxyl terminal domain of the D1R subunit. The addition of the small D12L subunit has been shown to activate the (guanine-7-) methyltransferase activity in D1R498-844 30-50-fold. The efficiency of GTP photolinkage to the isolated D1R498-844 domain, however, was found to be only marginally effected by the addition of the D12L subunit, demonstrating that this enhancement of mRNA (guanine-7-) methyltransferase activity mediated by D12L was not achieved by altering the strength of GTP binding.

Binding Sites↗
PubMed1993

Identification of the vaccinia virus mRNA guanyltransferase active site lysine.

The vaccinia virus mRNA capping enzyme is a heterodimeric protein containing subunits of 97 and 33 kDa, the products of genes D1R and D12L, respectively. The enzyme catalyzes the first three reactions in the mRNA cap formation pathway: mRNA triphosphatase, guanyltransferase and (guanine-7-)methyltransferase. The guanyltransferase reaction proceeds by way of a covalent enzyme GMP (E-GMP) intermediate (Shuman, S. and Hurwitz, J. (1981) Proc. Natl. Acad. Sci. U.S.A. 78, 187-191) in which the GMP is linked to the large subunit through a lysine residue (Toyama, R., Mizumoto, K., Nakahara, Y., Tatsuno, T., and Kaziro, Y. (1983) Eur. J. Biochem. 2, 2195-2201; Roth, M. J., and Hurwitz, J. (1984) J. Biol Chem. 259, 13488-13494). In order to identify the map position of the guanyltransferase active site lysine residue, high specific activity [32P]E-GMP was prepared. Digestion of the E-GMP with hydroxylamine at pH 9.5 yielded a 31-kDa radioactive fragment derived from amino acids 1-273. Cleavage of E-GMP with cyanogen bromide produced a radioactive peptide of 14 kDa corresponding to amino acids 242-365. Lysine residues are found at positions 244 and 260. Staphylococcus aureus V8 protease digestion of cyanogen bromide-cleaved E-GMP yields a radioactive product of about 5 kDa in molecular mass corresponding to the peptide generated by cleavage at glutamic acid residues 253 and 297, demonstrating that lysine 260 is the site of linkage of GMP.

Amino Acid Sequence↗
PubMed1992

Phenotypic characterization of three temperature-sensitive mutations in the vaccinia virus early gene transcription initiation factor.

Vaccinia virus gene D6R encodes the small subunit of the virion early gene transcription initiation factor. Three temperature-sensitive mutations have been mapped to this gene. The biochemical phenotype exhibited by each mutation was examined. All mutants displayed altered viral protein synthesis in pulse-labelling analyses at both the permissive and non-permissive temperatures. The onset of early protein synthesis was delayed, and the rate of early protein synthesis was reduced in each case. Furthermore the shut-off of both host and early protein synthesis was delayed. In pulse-chase experiments, the stability of the D6R protein in E93- or C46-infected cells was shown to be reduced at 40 degrees C relative to that at 31 degrees C. Early mRNA was quantified in cells at 2 h post-infection and shown to be reduced substantially. The ability of each mutant virus to support transcription in vitro was examined at both temperatures and, of the three mutants, only S4 transcription was shown to exhibit reversible temperature sensitivity.

Gene Expression Regulation, Viral↗
PubMed1992

Dissociated hemispheric and stimulus effects upon affective choice and recognition.

Following lateralized tachistoscopic presentations of faces and pronounceable nonsense words, subjects made two kinds of choices, affective (AFF) and recognition (REC). Subliminal presentations influenced later affective choices for faces (but not for nonsense words), while recognition was not influenced. Liminal presentations produced no effects. Supraliminal presentations influenced later affective choices for nonsense words (but not for faces), while recognition choices showed the expected LVF advantage for faces and a RVF advantage for nonsense words. Affective and recognition judgments appeared to be competing processes since only one or the other but not both differed significantly from chance in a visual field for a given stimulus type and exposure duration.

Adult↗
PubMed1990

Superinfection exclusion of vaccinia virus in virus-infected cell cultures.

Vaccinia virus-infected BSC 40 cells do not permit the replication of superinfecting vaccinia virus. The extent of superinfecting virus propagation depends on the time of superinfection; there is 90% exclusion by 4 hr after the initial infection, and more than 99% by 6 hr. When superinfection is attempted at 6 hr after infection, the superinfecting virus is incapable of carrying out DNA replication or early gene transcription, demonstrating that an early event in the virus life cycle is inhibited. The rate of adsorption of the superinfecting virus is unaltered which shows that exclusion is affected at a point between adsorption and early gene transcription. In order to exclude superinfection, the primary infecting virus does not require replication of its DNA or expression of its late genes but it must express one or more early genes.

Adsorption↗
PubMed1986

Are unilateral right posterior cerebral lesions sufficient to cause prosopagnosia? Clinical and radiological findings in six additional patients.

Controversy has arisen regarding the neuropathological basis of prosopagnosia. Some investigators suggest that bilateral lesions are needed to cause the deficit, whereas others felt that a unilateral right posterior lesion is sufficient. Six patients with prosopagnosia with clinical and radiological evidence of unilateral right posterior lesions are presented. Our observations together with evidence from similar cases described in the literature suggest that an appropriately placed right hemispheric lesion may be sufficient to produce prosopagnosia.

Agnosia↗
PubMed1985

Left hemispheric functional compensation in prosopagnosia? A tachistoscopic study with unilaterally lesioned patients.

Clinical observations suggest left hemispheric compensation for prosopagnosia in patients with isolated right posterior lesions. To test this hypothesis we investigated six patients with right posterior lesions, three with and three without prosopagnosia, with a series of tachistoscopic matching experiments. Faces with and without paraphernalia, shapes, objects and words were presented at different exposure durations (unlimited, 1000, 200, 50 and 20 ms). Prosopagnosia patients performed better than non-prosopagnosia patients if pure faces (eyes, nose and mouth only) were presented for an unlimited time, but performed worse than non-prosopagnosia patients if exposure duration was reduced. Patients with prosopagnosia were especially handicapped when required to match emotional expressions. Both patient groups had no difficulty in matching objects and words, even at short exposure durations. The results are discussed with respect to a possible left hemispheric compensation in prosopagnosia patients.

Adult↗