Search PubMed⌕ Search

Biomedical subjects

I Martin

Publications and source records attributed to I Martin.

At least 145 records · Page 8Linked to original sources
PubMed1995

Lysophosphatidylcholine inhibits vesicles fusion induced by the NH2-terminal extremity of SIV/HIV fusogenic proteins.

Intermediate lipid structures such as inverted micelles and interlamellar attachments are thought to play a crucial role in different biological processes like exocytosis, intracellular trafficking and viral infection. In the present study, we provide evidence that lipid mixing of large unilamellar lipid vesicles (LUV) mediated by the NH2-terminal sequence of the SIV gp32 and of HIV gp41 is inhibited by external addition of lysophosphatidylcholine (lysoPC) to LUV containing phosphatidylethanolamine in their lipid bilayer. Leakage experiments confirm that lysoPC enhances the stability of the lipids organization. The temperature dependence of the two processes as well as the complementary shape of PE and lysoPC suggest that the PE-lysoPC interaction is involved in the fusion inhibition and stabilization of the bilayer.

Amino Acid Sequence↗
PubMed1995

Structure and topology of the influenza virus fusion peptide in lipid bilayers.

The secondary structure of a 20-amino acid length synthetic peptide corresponding to the N terminus of the second subunit of hemagglutinin (HA2) of influenza virus A/PR8/34 and its interaction with phospholipid bilayers are investigated using ESR, Fourier transform infrared (FTIR), and CD spectroscopy. N-terminal spin labeling of the peptide did not affect the secondary structure of the peptide either in solution or when bound to liposomes as revealed by FTIR and CD spectroscopy. ESR spectra show that the mobility of the labeled peptide is dramatically restricted in the presence of phosphatidylcholine liposomes, suggesting a strong binding to the lipid membranes. The N terminus of the peptide penetrates into the membrane and is located within the hydrophobic core. We find an oblique insertion of the peptide into the lipid bilayer with an angle of about 45 degrees between helix axis and membrane plane using FTIR spectroscopy. No gross changes of the peptide's orientation, motion, and secondary structure were observed between pH 7.4 and pH 5.0. A model of the insertion of the fusion sequence of HA2 into a lipid bilayer is presented taking into account recent investigations on the low pH conformation of HA2 (Bullough, P. A., Hughson, F. M., Skehel, J. J., and Wiley, D. C. (1994) Nature 371, 37-43).

Amino Acid Sequence↗
PubMed1995

Interaction between cardiolipin and the mitochondrial presequence of cytochrome c oxidase subunit IV favours lipid mixing without destabilizing the bilayer structure.

We demonstrate the ability of a peptide corresponding to the presequence of the cytochrome c oxidase subunit IV to induce lipid mixing between large unilamellar liposomes. This lipid mixing requires the presence of CL or PE, lipids able to form non-bilayer structures, and is not observed with other negatively charged lipids. However, the fact that this mixing occurs without mixing of the liposome aqueous phases and without destabilizing the lipid organisation is unusual and has not been observed for other amphiphilic peptides. This observation supports the idea that the presequence could play a role in the formation of translocation contact sites between the two mitochondrial membranes and facilitate the structural rearrangements of the outer and inner membrane proteins involved in the two import machineries in a way to permit the formation of a continuous import channel through the two mitochondrial membranes without mixing the cytoplasmic and mitochondrial aqueous contents.

Amino Acid Sequence↗
PubMed1995

Co-ordinate decrease in the expression of the mitochondrial genome and nuclear genes for mitochondrial proteins in the lactation-induced mitochondrial hypotrophy of rat brown fat.

The relative abundance of the mitochondrial-encoded mRNAs for cytochrome c oxidase subunit II and NADH dehydrogenase subunit I was lower in brown adipose tissue (BAT) from lactating rats than in virgin controls. This decrease was in parallel with a significant decrease in mitochondrial 16 S rRNA levels and in the relative content of mitochondrial DNA in the tissue. BAT from lactating rats showed lowered mRNA expression of the nuclear-encoded genes for the mitochondrial uncoupling protein, subunit IV of cytochrome c oxidase and the adenine nucleotide translocase isoforms ANT1 and ANT2, whereas mRNA levels for the ATP synthase beta-subunit were unchanged. However, the relative content of this last protein was lower in BAT mitochondria from lactating rats than in virgin controls. It is concluded that lactation-induced mitochondrial hypotrophy in BAT is associated with a co-ordinate decrease in the expression of the mitochondrial genome and nuclear genes for mitochondrial proteins. This decrease is caused by regulatory events acting at different levels, including pre- and post-transcriptional regulation. BAT appears to be a useful model with which to investigate the molecular mechanisms involved in the co-ordination of the expression of the mitochondrial and nuclear genomes during mitochondrial biogenesis.

Adipose Tissue, Brown↗
PubMed1995

Microsatellite instability in colorectal cancer: improved assessment using fluorescent polymerase chain reaction.

BACKGROUND & AIMS: Microsatellite instability was first described in hereditary nonpolyposis colorectal cancers and sporadic colorectal cancers, in which it was associated with a good prognosis. The aim of this study was to assess the advantages of a novel fluorescent assay for detecting microsatellite instability. METHODS: Eleven fluorescently tagged microsatellites and an automated DNA sequencer were used to investigate 54 sporadic colorectal adenocarcinomas. RESULTS: This fluorescent assay combined accurate allele sizing with cross-sectional data display and allowed improved assessment of microsatellite instability. Twenty-two percent of cancers (12 of 54) showed microsatellite instability with at least one marker. For tumors showing microsatellite instability, results were obtained for a minimum of eight markers. Six tumors showed microsatellite instability at high frequency (at least 63% of markers affected), and 42% of the patients who had a tumor showing microsatellite instability had a synchronous and/or metachronous colorectal tumor (vs. 7% of patients whose tumor did not show microsatellite instability). Patients with a microsatellite instability-positive tumor had an improved prognosis (P = 0.03). CONCLUSIONS: The use of this fluorescent assay improved the assessment of microsatellite instability with the automated analysis and cross-sectional data display. The assay identified a subgroup of patients who showed microsatellite instability and who also showed clinical features that differed from the microsatellite instability-negative cases.

Adenocarcinoma↗
PubMed1995

Preservation of the spleen improves survival after radical surgery for gastric cancer.

One hundred and ninety five consecutive, potentially curative resections for adenocarcinoma of the stomach were performed in one surgical department between 1970 and 1989: 76 patients underwent gastrectomy with splenectomy and 119 gastrectomy without splenectomy. Operative mortality was 12% after gastrectomy with splenectomy, but only 2.5% after gastrectomy without splenectomy (p < 0.05). Postoperative complications were also significantly more common when splenectomy was combined with gastrectomy (41% v 14%, p < 0.01). Cumulative five year survival was 45% after gastrectomy with splenectomy, compared with 71% after gastrectomy alone (p < 0.01). When the results of the two groups of patients were compared, stage for pathological stage, no evidence was found that splenectomy improved survival. Application of Cox's proportional hazards model, which makes allowance for other variables such as the T and N stages, showed that splenectomy had an adverse influence on patients' survival. Splenectomy does not benefit the patient and its routine use in the course of radical resections for carcinoma of the stomach should be abandoned.

Adenocarcinoma↗
PubMed1995

An alternative synthesis of the NMDA antagonist CGS 19755 via free radical carbamoylation of ethyl isonicotinate.

The NMDA antagonist CGS 19755 (cis-4-phosphonomethyl-2-piperidinecarboxylic acid) has been prepared by applying Minisci reaction conditions [formamide, hydrogen peroxide, iron(II) sulfate] to ethyl isonicotinate, reduction of the ester with sodium borohydride, alcoholysis of the 2-carboxamide, formation of 4-(diethylphosphonomethyl)-2-pyridinecarboxylate, hydrogenation of the pyridine nucleus, and acid hydrolysis. The overall, unoptimized yield was around 11%. The procedure employs cheap starting materials, is practical and avoids the use of toxic and hazardous cyanotrimethylsilane which is used in the published procedure.

Free Radicals↗
PubMed1995

Disseminating quality care for upper gastrointestinal cancer.

This presentation discusses the problem involved in providing quality care for patients with Upper GI Cancer throughout a healthcare delivery system. It is argued that appropriate telecommunications technology exists for widespread dissemination of "best clinical practice", but that it cannot be used effectively at present because of some limiting factors. These include lack of precisely defined aims concerning use of technology, lack of interactive quality control, and insufficient involvement of end-users. Upper gastrointestinal cancer is selected as a model for discussion-since there is wide discrepancy between outcome of therapy in early and late cases, there is evidence that early diagnosis is possible-and there is substantial evidence that it does not take place widely in practice. Prospects for the future (with special reference to the 4th Framework) are discussed. It is argued that considerable opportunities exist. Future work should build on existing experience in informatics (eg. the "Telegastro" program) and in clinical practice (e.g. the Leeds "outreach" programmes) for (a) widespread dissemination of effective "best" clinical practice; and (b) continuing medical education.

Computer Communication Networks↗
PubMed1994

Membrane orientation of the SIV fusion peptide determines its effect on bilayer stability and ability to promote membrane fusion.

The amino terminal segment of the gp32 glycoprotein of SIV has been identified as an important region for membrane fusion. A synthetic dodecapeptide corresponding to this amino terminal segment, SIVwt, can promote the fusion of liposomes. This peptide inserts at an oblique angle into the membrane. If the amino acid sequence of this peptide is changed, while maintaining the same amino acid composition, the resulting peptide, SIVmutV, no longer promotes fusion and it is oriented perpendicular to the plane of the bilayer. In the present work we demonstrate that SIVwt, but not SIVmutV, can lower the bilayer to hexagonal phase transition temperature of model membranes composed of dipalmitoleoyl phosphatidylethanolamine. In addition the SIVwt promotes the formation of structures which give rise to isotropic 31P NMR signals in mixtures with monomethyldioleoyl phosphatidylethanolamine. These structures are not formed with SIVmutV and their formation with SIVwt is suppressed with lysophosphatidylcholine. Taken together these results suggest that the observed correlation between oblique insertion of viral fusion peptides into membranes and their fusogenicity may be a consequence on these peptides increasing negative monolayer curvature.

Amino Acid Sequence↗
PubMed1994

ETS transcription factors regulate the expression of the gene for the human mitochondrial ATP synthase beta-subunit.

Elements responsible for the transcriptional activity of the human ATP synthase beta-subunit (ATPsyn beta) gene promoter have been studied through transient expression in HepG2 hepatoma cells of a CAT gene connected with various 5'-deletion mutants of the 5'-flanking region. Promoter activity was mostly dependent upon a single CCAAT motif as well as a nearby Ets domain binding region. This last region contains two sites that bind Ets-related proteins present in liver nuclear extracts as well as recombinant purified Ets-1 protein. The ATPsyn beta promoter was trans-activated by Ets-1 and Ets-2 expression vectors, and this effect was lost when the Ets binding region was deleted. The Ets binding region of the ATPsyn beta promoter increased basal expression and conferred Ets-1- and Ets-2-dependent trans-activation to the herpes symplex thymidine kinase minimal promoter. A double-point mutation of the main Ets-binding site, which suppresses Ets binding, blocks Ets-dependent trans-activation. It is concluded that the gene for the mitochondrial ATPsyn beta is a target of transcriptional activation by members of the Ets family of transcription factors. It is suggested that Ets transcription factors may be involved in the enhanced expression of the ATPsyn beta gene in highly proliferating cells and in the coordinate transcription of nuclear genes for mitochondrial proteins.

Base Sequence↗
PubMed1994

The effects of pH on the interaction of anthrax toxin lethal and edema factors with phospholipid vesicles.

Bacillus anthracis secretes three distinct proteins which interact in binary combinations to produce two toxins. The two effector moieties, edema factor (EF) and lethal factor (LF), interact competitively with the cell receptor-binding moiety, protective antigen (PA), to produce biologically distinct effects. The passage of the toxins through an acidified endosomal compartment is an essential step in the intoxication process, and it has been shown that low pH triggers the insertion of the activated form of PA, PA63, into model lipid bilayers. In this study, we have examined the effects of pH on the interaction of LF and EF with a model membrane system. Protein labeling by radioactive phospholipid probes indicated that both LF and EF are able to insert into asolectin lipid bilayers in a pH-dependent manner. For LF, the extent of insertion into the bilayer was accompanied in parallel by the release of calcein from preloaded LUV (large unilamellar vesicles). The transition pH for protein insertion, however, was somewhat higher than that for membrane destabilization. The extent of protein radiolabeling and the release of calcein from LUV incubated with EF was similar to that seen with LF; however, the pH dependency was significantly less. Low pH-induced membrane insertion by both proteins was accompanied by only a minimal change in conformation. These results suggest that LF and EF may be actively involved in the process of toxin translocation.

Antigens, Bacterial↗
PubMed1994

The evaluative response: primitive but necessary.

We do not believe the claim that "evaluative conditioning is a qualitatively distinct form of classical conditioning" [Davey (1994). Behaviour Research and Therapy, 32, 291-299]. We view all classical conditioning as a learning process which leads organisms to assign a positive or negative value to previously neutral stimuli and to respond to them accordingly. The evaluative response is a necessary component of this process and hence it is central to all classical conditioning, not a separate type. Davey concentrates on a signal-based information processing view of learning, i.e. the formation of linear associations between CS and UCS of which human subjects are aware and which they can verbalize. We propose a more primitive and more general model in which stimulus evaluation (like/dislike) occurs with a minimal degree of processing, and enters into a representation of stimulus (CS and UCS) and response (CR and UCR) characteristics which is reintegrative rather than associative.

Animals↗
PubMed1994

Correlation between fusogenicity of synthetic modified peptides corresponding to the NH2-terminal extremity of simian immunodeficiency virus gp32 and their mode of insertion into the lipid bilayer: an infrared spectroscopy study.

The amino-terminal extremity of the simian immunodeficiency virus (SIV) transmembrane protein (gp32) has been shown to play a pivotal role in cell-virus fusion and syncytium formation. We provide here evidence of a correlation between the structure and orientation of the modified SIV fusion peptide after insertion into the lipid membrane and its fusogenic activity. The sequence of the wild-type SIV peptide has been modified in such a way that the calculated angles of insertion correspond to an oblique, parallel, or normal orientation with respect to the lipid-water interface. Fourier transform infrared spectroscopy was used to gain experimental informations about the structures and orientations, of the membrane-inserted peptides with respect to the lipid acyl chains. The peptides adopt mainly a beta-sheet conformation in the absence of lipids. After interaction with large unilamellar liposomes, this beta sheet is partly converted into alpha helix. The ability of the modified peptides to promote lipid mixing was assessed by a fluorescence energy transfer assay. The data provide evidence that alpha-helix formation is not sufficient to induce lipid mixing and that the fusogenic activity of the peptide depends on its orientation in the lipid bilayer.

Amino Acid Sequence↗
PubMed1993

Effects of cold environment on mitochondrial genome expression in the rat: evidence for a tissue-specific increase in the liver, independent of changes in mitochondrial gene abundance.

The abundance of the mitochondrially encoded mRNA for subunit II of cytochrome c oxidase (COII mRNA) increases in the liver of rats exposed to environmental cold stress (4 degrees C ambient temperature). Only transient increases or no changes in COII mRNA levels were observed in brown fat and soleus muscle respectively. The time course of the liver COII mRNA increase was compared with the effects of cold stress on mitochondrial 16S ribosomal RNA expression and indicated that cold induces a rapid (few hours) increase in the liver mitochondrial mRNA levels and high levels of both messenger and ribosomal RNA mitochondrial transcripts are present after a few days of cold exposure. No changes in mitochondrial DNA abundance relative to total cellular DNA were observed in the liver of rats at any time during cold stress. It is concluded that mitochondrial genome expression is specifically increased in the liver of cold-exposed rats through different mechanisms, independent of changes in mitochondrial genome abundance.

Acclimatization↗
PubMed1993

Lysophosphatidylcholine mediates the mode of insertion of the NH2-terminal SIV fusion peptide into the lipid bilayer.

We report here on the interaction of a synthetic 12 residue peptide corresponding to the N-terminal sequence of gp32 from SIV with phospholipid bilayers. This peptide has been shown to induce lipid mixing of PC/PE/SM/Chol LUV (large unilamellar vesicles) at pH 7.4 and 37 degrees C [(1992) in: Advances in Membrane Fluidity, vol. 6, pp. 365-376, Wiley-Liss]. In the present study, this fusion process was inhibited by the addition of lysophosphatidylcholine (lysoPC) to the lipid bilayer of PC/PE/SM/Chol LUV. Fourier transform infrared spectroscopy (FTIR) reveals that the orientation of the SIV fusion peptide with respect to the lipid acyl chains depends on the presence of lysoPC in the lipid bilayer but that the peptide secondary structure and the amount of lipid-associated peptides do not depend on the lipid composition. The peptide is obliquely inserted into the lipid bilayer of vesicles without lysoPC, whereas it is oriented parallel to the lipid-water interface in the vesicles containing lysoPC. The data provide evidence that the orientation of the SIV fusion peptide depends on the lipid composition, and that this mediates its fusogenic activity.

Kinetics↗