Search PubMed⌕ Search

Biomedical subjects

M Carrington

Publications and source records attributed to M Carrington.

At least 37 records · Page 2Linked to original sources
PubMed2001

The coatomer of Trypanosoma brucei.

Coatomer is a multisubunit complex involved in trafficking of vesicles between the endoplasmatic reticulum and the Golgi apparatus. From sequence homologies, all seven subunits, alpha-, beta-, beta'-, gamma-, delta-, epsilon-, and zeta-COP, are encoded in the genome of Trypanosoma brucei. The complete predicted amino-acid sequences of beta-, beta'-, and zeta-COP show only 20-30% identity with higher eucaryotic homologues. The trypanosome coatomer complex was partially purified using a procedure similar to that used for bovine coatomer.

Amino Acid Sequence↗
PubMed2001

HLA and AIDS: a cautionary tale.

The human major histocompatibility complex HLA has been implicated repeatedly as a regulator of the outcome of HIV exposure and infection. A new study of long-term survivors who naturally depress HIV-1 replication and avoid the signs of AIDS for years after infection suggests that homozygosity for a group of HLA-B locus alleles termed Bw4 confers resistance, ostensibly by regulating natural killer cell-ligand interactions. However, close inspection of the accumulated evidence raises some questions and urges validation of the potential Bw4 effects in additional studies.

Acquired Immunodeficiency Syndrome↗
PubMed2001

Autonomic activity during human sleep as a function of time and sleep stage.

While there is a developing understanding of the influence of sleep on cardiovascular autonomic activity in humans, there remain unresolved issues. In particular, the effect of time within the sleep period, independent of sleep stage, has not been investigated. Further, the influence of sleep on central sympathetic nervous system (SNS) activity is uncertain because results using the major method applicable to humans, the low frequency (LF) component of heart rate variability (HRV), have been contradictory, and because the method itself is open to criticism. Sleep and cardiac activity were measured in 14 young healthy subjects on three nights. Data was analysed in 2-min epochs. All epochs meeting specified criteria were identified, beginning 2 h before, until 7 h after, sleep onset. Epoch values were allocated to 30-min bins and during sleep were also classified into stage 2, slow wave sleep (SWS) and rapid eye movement (REM) sleep. The measures of cardiac activity were heart rate (HR), blood pressure (BP), high frequency (HF) and LF components of HRV and pre-ejection period (PEP). During non-rapid eye movement (NREM) sleep autonomic balance shifted from sympathetic to parasympathetic dominance, although this appeared to be more because of a shift in parasympathetic nervous system (PNS) activity. Autonomic balance during REM was in general similar to wakefulness. For BP and the HF and LF components the change occurred abruptly at sleep onset and was then constant over time within each stage of sleep, indicating that any change in autonomic balance over the sleep period is a consequence of the changing distribution of sleep stages. Two variables, HR and PEP, did show time effects reflecting a circadian influence over HR and perhaps time asleep affecting PEP. While both the LF component and PEP showed changes consistent with reduced sympathetic tone during sleep, their pattern of change over time differed.

Adolescent↗
PubMed2001

The long form of CDK2 arises via alternative splicing and forms an active protein kinase with cyclins A and E.

We have reinvestigated the long form of cyclin-dependent kinase (CDK)2 that is expressed in many rodent cells. We show that the mRNA encoding CDK2L arises by alternative splicing and that the encoded protein can bind to, and be activated by, cyclins A and E. The complex of CDK2L with cyclin A has about half the specific activity of the equivalent CDK2-cyclin A complex. Also, CDK2L--cyclin A is inhibited to the same extent and by the same concentrations of p21(CIP1) as CDK2--cyclin A. The nucleotide sequences of intron V in the human and murine CDK2 genes, where the sequences encoding the 48-residue insert in CDK2L are located, show very high conservation in the position of the alternatively spliced exon and its surroundings. Despite this, we were not able to detect significant expression of CDK2L in human cell lines, although a low level is expressed in COS-1 cells from monkeys.

Alternative Splicing↗
PubMed2001

Accumulation of the proteolytic marker peptide ubiquitin in the trophoblast of mammalian blastocysts.

Ubiquitination is a universal protein degradation pathway in which the molecules of 8.5-kDa proteolytic peptide ubiquitin are covalently attached to the epsilon-amino group of the substrate's lysine residues. Little is known about the importance of this highly conserved mechanism for protein recycling in mammalian gametogenesis and fertilization. The data obtained by the students and faculty of the international training course Window to the Zygote 2000 demonstrate the accumulation of ubiquitin-cross-reactive structures in the trophoblast, but not in the inner cell mass of the expanding bovine and mouse blastocysts. This observation suggests that a major burst of ubiquitin-dependent proteolysis occurs in the trophoblast of mammalian peri-implantation embryos. This event may be important for the success of blastocyst hatching, differentiation of embryonic stem cells into soma and germ line, and/or implantation in both naturally conceived and reconstructed mammalian embryos.

Animals↗
PubMed2001

Partial activation and induction of apoptosis in CD4(+) and CD8(+) T lymphocytes by conformationally authentic noninfectious human immunodeficiency virus type 1.

Increased levels of apoptosis are seen in human immunodeficiency virus (HIV) infection, and this has been proposed as an important mechanism contributing to HIV pathogenesis. However, interpretation of in vitro studies aimed at understanding HIV-related apoptosis has been complicated by the use of high concentrations of recombinant proteins or by direct cytopathic effects of replicating virus. We have developed an inactivation procedure that destroys retroviral infectivity while preserving the structural and functional integrity of the HIV surface proteins. These noninfectious virions interact authentically with target cells, providing a powerful tool to dissect mechanisms of HIV pathogenesis that do or do not require viral replication. Noninfectious CXCR4-tropic HIV-1 virions, but not microvesicles, partially activated freshly isolated CD4(+) and CD8(+) peripheral blood mononuclear cell T lymphocytes to express FasL and Fas, but not CD69 or CD25 (interleukin-2 receptor alpha) and eventually die via apoptosis starting 4 to 6 days postexposure. These effects required conformationally intact virions, as heat-denatured virions or equivalent amounts of recombinant gp120 did not induce apoptosis. The maximal apoptotic effect was dependent on major histocompatibility complex (MHC) class II proteins being present on the virion, but was not MHC restricted. The results suggest that the immunopathogenesis of HIV infection may not depend solely on direct cytopathic effects of HIV replication, but that effects due to noninfectious HIV-1 virions may also contribute importantly.

Apoptosis↗
PubMed2000

Influence of CCR5 promoter haplotypes on AIDS progression in African-Americans.

OBJECTIVES: To test the hypothesis that the CCR5 promoter variants in HIV-1-infected African-Americans affect the rate of progression to AIDS and to determine the extent of linkage disequilibrium between the CCR5P1 allele and the CCR5 59029A variant (referred to here as CCR5-2459A), both of which have been shown independently to accelerate AIDS progression in Caucasians. DESIGN: We used survival analysis to assess the effects of CCR5 promoter variants in HIV-1 seroincident Caucasians and African-Americans. SUBJECTS AND METHODS: Genotypes were determined for 806 Caucasians and 1067 African-Americans, which included 700 seroconverters, enrolled in four HIV/AIDS natural history cohort studies. These genotypes were used to determine linkage and haplotypes for CCR2 and CCR5 alleles. Survival analysis was used to assess the effect of CCR2, CCR5, and CCR5 promoter haplotypes on progression to AIDS in seroincident African-Americans. RESULTS: A survey of Caucasians and African-Americans demonstrated complete linkage disequilibrium between CCR5P1 and CCR5-2459A sites. The composite CCR5P1 haplotype (including the CCR5-2459A allele) is shown to be associated with rapid progression to AIDS endpoints in both African-American and Caucasian cohorts, but the effect is recessive in Caucasians and dominant in African-Americans. This is probably due to the presence of modulating genes or as yet unidentified polymorphisms that may differ between racial groups.

Acquired Immunodeficiency Syndrome↗
PubMed2000

Early development of mouse embryos null mutant for the cyclin A2 gene occurs in the absence of maternally derived cyclin A2 gene products.

Progression through the mammalian cell cycle is regulated by the sequential activation and inactivation of the cyclin-dependent kinases. In adult cells, cyclin A2-dependent kinases are required for entry into S and M phases, completion of S phase, and centrosome duplication. However, mouse embryos lacking the cyclin A2 gene nonetheless complete preimplantation development, but die soon after implantation. In this report, we investigated whether a contribution of maternal cyclin A2 mRNA and protein to early embryonic cell cycles might explain these conflicting observations. Our data show that a maternal stock of cyclin A2 mRNA is present in the oocyte and persists after fertilization until the second mitotic cell cycle, when it is degraded to undetectable levels coincident with transcriptional activation of the zygotic genome. A portion of maternally derived cyclin A2 protein is stable during the first mitosis and persists in the cytoplasm, but is completely degraded at the second mitosis. The ability of cyclin A2-null mutants to develop normally from the four-cell to the postimplantation stage in the absence of detectable cyclin A2 gene product indicates therefore that cyclin A2 is dispensable for cellular progression during the preimplantation nongrowth period of mouse embryo development.

Amanitins↗
PubMed2000

Effect of chemokine receptor gene polymorphisms on the response to potent antiretroviral therapy.

BACKGROUND: Both the natural history of HIV infection and the response to antiretroviral therapy are heterogeneous. Polymorphisms in chemokine receptor genes modulate the natural history of HIV-1 infection. In comparison with subjects with other genotypes, the prognosis for HIV-1-infected CCR5-delta32 heterozygotes is more favorable and that for CCR5 promoter allele 59029A homozygotes is less favorable. METHODS: HIV-1-infected adults with a CD4+ lymphocyte count > or = 200 cells x 10(6)/l and a plasma HIV RNA level > or = 1000 copies/ml were treated with indinavir, zidovudine and lamivudine for 6 months. HIV RNA levels were measured at 4-week intervals. Genotyping for chemokine receptor gene polymorphisms (CCR5-delta32, CCR5 59029A/G, CCR2-641) was performed. We examined whether the time to first HIV RNA < 200 copies/ml, frequency of viral suppression failure (HIV RNA > or = 200 copies/ml between weeks 16 and 28 of therapy), or reduction from the pre-treatment HIV RNA level differed by genotype. RESULTS: Time to first HIV RNA < 200 copies/ml was not predicted by genotype. Among 272 Caucasian patients, viral suppression failure was more common among patients with the CCR5 +/+ ¿ CCR2+/+ ¿ CCR5-59029 A/A genotype (28%) than among all other subjects combined (relative risk, 2.0; P = 0.06). After 24 weeks of therapy, genotype groups differed in the reduction of the HIV RNA level from baseline (P = 0.02); patients with the CCR5 +/+ ¿ CCR2+/+ ¿ CCR5-59029 A/A genotype had a mean reduction of 2.12 log10 copies/ml compared to 2.64 log10 copies/ml among all other groups combined. CONCLUSION: Polymorphisms in chemokine receptor genes may explain some of the heterogeneity in sustaining viral suppression observed among patients receiving potent antiretroviral therapy.

Adult↗
PubMed2000

A role for the dynamic acylation of a cluster of cysteine residues in regulating the activity of the glycosylphosphatidylinositol-specific phospholipase C of Trypanosoma brucei.

The glycosylphosphatidylinositol-specific phospholipase C or VSG lipase is the enzyme responsible for the cleavage of the glycosylphosphatidylinositol anchor of the variant surface glycoprotein (VSG) and concomitant release of the surface coat in Trypanosoma brucei during osmotic shock or extracellular acidic stress. In Xenopus laevis oocytes the VSG lipase was expressed as a nonacylated and a thioacylated form. This thioacylation occurred within a cluster of three cysteine residues but was not essential for catalytic activity per se. These two forms were also detected in trypanosomes and appeared to be present at roughly equivalent amounts. A reversible shift to the acylated form occurred when cells were triggered to release the VSG by either nonlytic acid stress or osmotic lysis. A wild type VSG lipase or a gene mutated in the three codons for the acylated cysteines were reinserted in the genome of a trypanosome null mutant for this gene. A comparative analysis of these revertant trypanosomes indicated that thioacylation might be involved in regulating enzyme access to the VSG substrate.

Acylation↗
PubMed2000

Fine mapping of IGAD1 in IgA deficiency and common variable immunodeficiency: identification and characterization of haplotypes shared by affected members of 101 multiple-case families.

To limit the region containing a mutation predisposing to selective IgA deficiency (IgAD) and common variable immunodeficiency (CVID), 554 informative members of 101 multiple-case families were haplotyped at the IGAD1 candidate locus in the MHC. Microsatellite markers were placed onto the physical map of IGAD1 to establish their order and permit rapid haplotype analyses. Linkage analysis of this extended family set provided additional support for a strong susceptibility locus at IGAD1 with a maximum multipoint nonparametric linkage score in excess of 3. Although the transmission of maternal IGAD1 haplotypes from unaffected heterozygous parents to the affected offspring was in excess, this was not apparent in multiple-case families with a predominance of affected mothers, suggesting that this parental bias is influenced by the affection status of transmitting parents and supporting a maternal effect in disease susceptibility. Of 110 haplotypes shared by 258 affected family members, a single haplotype (H1) was found in 44 pairs of affected relatives, accounting for the majority of the IGAD1 contribution to the development of IgAD/CVID in our families. The H1 allelic variability was higher in the telomeric part of the class III region than in the distal part of the class II region in both single- and multiple-case families. Incomplete H1 haplotypes had most variant alleles in the telomeric part of the analyzed region in homozygous IgAD/CVID patients, whereas this was not observed in unaffected homozygotes. These data suggest that a telomeric part of the class II region or centromeric part of the class III region is the most likely location of IGAD1.

Alleles↗
PubMed2000

Interleukin-1 polymorphisms associated with increased risk of gastric cancer.

Helicobacter pylori infection is associated with a variety of clinical outcomes including gastric cancer and duodenal ulcer disease. The reasons for this variation are not clear, but the gastric physiological response is influenced by the severity and anatomical distribution of gastritis induced by H. pylori. Thus, individuals with gastritis predominantly localized to the antrum retain normal (or even high) acid secretion, whereas individuals with extensive corpus gastritis develop hypochlorhydria and gastric atrophy, which are presumptive precursors of gastric cancer. Here we report that interleukin-1 gene cluster polymorphisms suspected of enhancing production of interleukin-1-beta are associated with an increased risk of both hypochlorhydria induced by H. pylori and gastric cancer. Two of these polymorphism are in near-complete linkage disequilibrium and one is a TATA-box polymorphism that markedly affects DNA-protein interactions in vitro. The association with disease may be explained by the biological properties of interleukin-1-beta, which is an important pro-inflammatory cytokine and a powerful inhibitor of gastric acid secretion. Host genetic factors that affect interleukin-1-beta may determine why some individuals infected with H. pylori develop gastric cancer while others do not.

Alleles↗
PubMed2000

Class I and class II MHC bind self peptide sets that are strikingly different in their evolutionary characteristics.

Comparison of peptides eluted from human class I and class II major histocompatibility complex (MHC) molecules and the proteins from which they are derived (source proteins) revealed that class I MHC bind peptides derived from proteins that are highly conserved, hydrophilic, and universally expressed, while the peptides themselves are hydrophobic and even more conserved than their source proteins. In contrast, source proteins for class II-bound peptides were not significantly more conserved than a random sample of proteins. Class II-bound peptides were generally more conserved than their source proteins but were significantly less conserved than class I-bound peptides. The characteristics of class I-bound peptides can probably be explained by the selectivity of processing and transport of peptides for binding by class I, while the relative lack of selectivity of peptide binding for class II may explain the high incidence of autoimmune diseases associated with alleles of these molecules.

Alleles↗
PubMed2000

Polymorphisms of the human IFNG gene noncoding regions.

Interferon gamma (IFN-gamma) is a multifunctional cytokine that is essential in the development of Th1 cells and in cellular responses to a variety of intracellular pathogens including human immunodeficiency virus (HIV-1). We screened genomic DNA samples from a predominately Caucasian male population of HIV-infected and healthy donors for polymorphisms in the human IFNG gene from -777 to +5608 by single-stranded conformational polymorphism. Surprisingly, the proximal promoter (-777 to transcription start) is invariant as no polymorphisms were found in over 100 samples tested. However, further screening revealed polymorphisms in other regions of the gene including a single base insertion in a poly-T tract in the first intron, three single base pair substitutions in the third intron, and another single base pair substitution in the 3' untranslated region (UTR). Electrophoretic mobility shift assay was used to investigate whether these variants have altered DNA-binding abilities, since intronic enhancer elements have been reported for the IFNG gene. Oligonucleotides constructed for two third intron variants showed no difference in DNA-binding abilities as compared with wild-type sequences. However, the 3'UTR variant showed the formation of unique DNA-binding complexes to radiolabeled oligonucleotide probes as compared with the wild-type sequence. The influence of a CA-repeat microsatellite on AIDS disease progression in HIV-1 seroconverters was tested by a Cox proportional hazards model. There is no evidence of an association between alleles and infection with HIV-1 or progression to AIDS. We report an invariant proximal human IFNG promoter and the existence of multiple intronic variants and a potentially functional 3'UTR polymorphism.

3' Untranslated Regions↗
PubMed2000

Attenuation of Trypanosoma brucei is associated with reduced immunosuppression and concomitant production of Th2 lymphokines.

Mechanisms regulating resistance to African trypanosomes were addressed by comparing the immune responses of mice infected with attenuated Trypanosoma brucei brucei lacking the phospholipase C gene (PLC-/-) and those of mice infected with wild-type (WT) parasites. Inhibition of concanavalin A (ConA)-induced T cell proliferation occurred in spleen and lymph nodes of PLC-/-- and WT-infected mice. Although suppressive cells were elicited in spleen and lymph nodes of WT-infected animals, such cells were not detected in lymph nodes of PLC-/--infected mice. PLC-/--infected mice had more interleukin-4 and -10 in their blood than did WT-infected mice. Correspondingly, PLC-/--infected mice had higher IgG1 antibody levels against variant surface glycoprotein than did WT-infected mice. These data indicate that attenuation of T. b. brucei correlates with the absence of cells suppressing ConA-induced T cell proliferation in the lymph nodes, with increased production of Th2 cytokines and a stronger IgG1 antibody response to trypanosome antigens.

Animals↗