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Biomedical subjects

M Guérin

Publications and source records attributed to M Guérin.

At least 55 records · Page 3Linked to original sources
PubMed1993

Effect of anisotropic inhibitors of ATP synthesis in mitochondria of Saccharomyces cerevisiae. Comparison between a wild-type and a mutant strain altered in the stoichiometry of the MT DNA encoded proteolipids of ATP synthase.

The effect of a group of non-usual inhibitors of ATP synthesis was investigated in yeast mitochondria. Tetraphenylphosphonium, tetraphenylarsonium and ethidium decreased the rate of ATP synthesis but did not decrease the ATP/O ratio. They did not inhibit the ATPase activity and the translocase, and did not decrease the proton-motive force. They inhibited phosphate transport under conditions in which it was strictly energy-dependent, but did not under conditions in which it was energy-independent. These inhibitors had a poor effect on ATP synthesis in mitochondria isolated from a nuclear mutant which contained a reduced amount of the subunits 8 and 6 of the Fo part of the ATP synthase as compared to wild-type and which were unable to support any energy-dependent phosphate-transport. Thus, it appeared that the phosphate-dependence of ATP synthesis was altered in the same way by both tetraphenylphosphonium and the mutation.

Adenosine Triphosphate↗
PubMed1992

K+/H+ exchange in yeast mitochondria: sensitivity to inhibitors, solubilization and reconstitution of the activity in proteoliposomes.

The K+/H+ exchange activity of the inner mitochondrial membrane was investigated in the yeast Saccharomyces cerevisiae. Swelling experiments in potassium acetate indicated that the K+/H+ exchange was active without any additional treatment after the mitochondria isolation, such as a Mg2+ depletion. As in mammalian mitochondria, the activity of yeast mitochondria was stimulated by increasing pH and was inhibited by the amphiphilic amines quinine and propranolol and by the carboxyl reagent dicyclohexylcarbodiimide. However, the activity was poorly inhibited by Mg2+ and consequently was only slightly stimulated by the Mg2+/H+ exchanger A23187. On the other hand, Zn2+ was very efficient for inhibiting the exchange and consequently the activity was strongly stimulated by the permeant metal-chelator o-phenanthroline. The [86Rb]Rb+ accumulation in mitochondria and mitoplasts was only partially inhibited by quinine and propranolol suggesting that part of the accumulation monitored under these conditions was due to cation leak through the inner membrane together with adsorption on the membrane. The DCCD-sensitive activity could be reconstituted from mitochondria and from mitoplasts solubilized with Triton X-100; this activity, measured by [86Rb]Rb+ accumulation, was quinine- and propranolol-sensitive. A spectrophotometric method, based on the capacity of negatively charged proteoliposomes to swell, was then developed in order to continuously follow the reconstituted activity.

Hydrogen↗
PubMed1991

Isolation of the ATP synthase subunit 6 and sequence of the mitochondrial ATP6 gene of the yeast Candida parapsilosis.

The mitochondrially translated product called subunit 6 was extracted from the yeast Candida parapsilosis mitochondria using an organic solvent mixture and purified by reverse-phase HPLC. The partial N-terminal sequence of subunit 6 reveals a post-translational cleavage site as in Saccharomyces cerevisiae. The structural mitochondrial gene ATP6 was isolated form a mitochondrial DNA library using the oligonucleotide probe procedure. The gene and the surrounding regions were cloned into M13tg130 and M13tg131 phage vectors. The insert contained an open reading frame 738-bp encoding a 246-amino-acid polypeptide. Mature subunit 6 contains 243 amino acid residues and the predicted molecular mass is 26,511 Da. The subunit shows 52% similarity with ATP synthase subunit 6 of the yeast S. cerevisiae. Comparison between protein and DNA sequences shows that the CUN codon family codes for a leucine in C. parapsilosis mitochondria.

Amino Acid Sequence↗
PubMed1991

Hybrid cell lines constitute a potential reservoir of polarized cells: isolation and study of highly differentiated hepatoma-derived hybrid cells able to form functional bile canaliculi in vitro.

A large number of hepatoma cell lines has been used to study expression and regulation of liver-specific function. However these cells, even the most differentiated, are morphologically far from hepatocytes. In no case is the typical hepatocyte cell polarity well maintained. Cell hybridization has been used as a potential means for turning on specific genes. From hybrids between well differentiated Fao rat hepatoma cells and WI 38 human fibroblasts, we have attempted to isolate segregated cells that are highly differentiated and polarized. Such cells, detected in aged cultures of only one hybrid (WIF12), were isolated by subcloning. One subclone, WIF12-1 was analyzed. Expression of liver-specific functions extinguished in the original hybrid is restored in all WIF12-1 cells at a very high level, similar to that of hepatocytes and 5-30 times higher that that of parental cells. Moreover human genes coding for liver-specific proteins (albumin, fibrinogen, and alcohol dehydrogenase) are actively expressed. WIF12-1 cells have acquired a polarized phenotype as attested by the presence of bile canaliculi between adjacent cells and by the asymmetrical localization of apical (Mg(2+)-ATPase, gamma-glutamyl transpeptidase) and basolateral membrane markers. The bile canaliculi formed are dynamic and functional structures, characterized by long periods of expansion followed by rapid contractions. The ability to polarize is a general and permanent property of WIF12-1 cells. These cells appear to constitute a valid model for the in vitro study of hepatocyte cell polarity, membrane domain formation and mechanisms of membrane protein sorting.

Animals↗
PubMed1990

Strong association between c-myb and oestrogen-receptor expression in human breast cancer.

Previous articles have reported that the c-myb proto-oncogene was activated in various types of tumours of the hematopoietic system suggesting that this gene plays a role in the development of these malignancies. However no studies of the c-myb gene have as yet been performed in solid primary tumours. In the present study we have analysed in breast cancer the c-myb gene with the aim to determine its involvement in tumour progression. Expression of the c-myb oncogene was analysed from 169 carcinoma specimens obtained from untreated patients with non-inflammatory breast cancer (NBC) (112 patients) and inflammatory breast cancer (IBC) (57 patients). A 3.5 kb c-myb transcript band was detected in 108 (64%) tumours. c-myb expression was found to be associated with good prognostic factors (lowest histopathologic grade (P = 0.01), oestrogen and progesterone receptor status (P less than 10(-4)) and pS2 gene expression (P less than 10(-4)) and negatively correlated with breast cancers of poorer prognosis, namely IBC (P = 0.03) and NBC with multiple involved nodes (P = 0.15). Other genes (c-myc, c-erbB2, c-fos and epidermal growth factor receptor) were also studied. The c-myb gene expression was found to be inversely correlated (P less than 0.03) with only c-erbB2 overexpression in NBC. When data were analysed with a logistic regression model using a stepwise procedure, c-myb expression was found to be associated only with the oestrogen receptor status (P less than 10(-4)). In conclusion, our data indicate that analysis of c-myb expression in breast cancer could allow the characterization of a new class of oestrogen-dependent tumours.

Breast Neoplasms↗
PubMed1989

Structure and expression of c-erbB-2 and EGF receptor genes in inflammatory and non-inflammatory breast cancer: prognostic significance.

C-erbB-2 and epidermal growth factor receptor (EGFR) genes were independently shown to be associated with breast cancer progression. In this report, we have analyzed the structure and expression of these 2 genes in the same tumor specimens of a large series of breast cancers. Two clinical types of tumor were studied: inflammatory (IBC) and non-inflammatory breast cancers (NBC) obtained from 221 untreated patients at different clinical stages. Amplification and over-expression of the c-erbB-2 proto-oncogene were observed in 27% and 47% of tumors, respectively, and were strongly associated with breast cancers of the most unfavorable prognosis, namely IBC and NBC with multiple positive axillary nodes. EGFR gene was neither amplified nor rearranged. A restriction fragment length polymorphism (RFLP) for HindIII endonuclease was observed. EGFR transcripts were detected in 46% of tumors and observed more frequently in IBC than in NBC (p less than 0.02). In NBC the presence of EGFR transcripts increased linearly with lymph-node involvement and was associated with estrogen-receptor-negative tumors (p = 0.01). Analysis of both genes from the same tumor samples indicated that genes are associated with cancer aggressiveness. Furthermore, in NBC these 2 genes were independently activated, in contrast to IBC in which activated genes were negatively correlated, suggesting that c-erbB-2 and EGFR genes play different roles in NBC and IBC.

Breast Neoplasms↗
PubMed1988

In vivo and in vitro evidence for a proton leakage through the inner mitochondrial membrane in a mutant of Saccharomyces cerevisiae.

Mutants of Saccharomyces cerevisiae were isolated which supported three mutations: two unlinked chromosomic mutations conferring thermosensitivity and cold sensitivity respectively, and a mitochondrial mutation conferring paromomycin sensitivity. When studied on isolated mitochondria, these mutants exhibited low phosphorylation efficiency and great proton permeability of their inner mitochondrial membrane. Experiments were carried out on whole cells: determination of growth rates, cellular yields and cellular respiration, either in the presence of triethyltin, an ATP synthase inhibitor, or in the presence of uncoupler, demonstrating that the proton leakage is actually a physiological phenomenon linked to the cold-sensitive phenotype. Experiments performed on isolated mitochondria confirmed the existence of such a proton leakage.

Biological Transport, Active↗
PubMed1988

Discrimination between different groups of Candida parapsilosis by mitochondrial DNA restriction analysis.

The analysis of mitochondrial DNA (mtDNA) from several strains of Candida parapsilosis and Candida rhagii by restriction endonucleases enabled us to discriminate between several groups within the C. parapsilosis species and to allocate laboratory strains to one of these. The mtDNAs isolated ranged in size from 20 to 31 kb. The mtDNA isolated from group 1 C. parapsilosis hybridises with both ATPase subunit 6 and 8 gene probes, the same restriction fragment hybridising with both probes.

Candida↗
PubMed1988

Overexpression of either c-myc or c-erbB-2/neu proto-oncogenes in human breast carcinomas: correlation with poor prognosis.

Tumor specimens from 116 untreated patients with primary breast carcinoma at different clinical stages were analyzed for the structure and/or the expression of c-myc and c-erbB-2/neu proto-oncogenes. An amplification of the c-myc proto-oncogene (3 to greater than 50 fold) was detected only in 6% of carcinomas, with no evidence of locus rearrangement. High c-myc RNA levels detected in 45% of tumors were found significantly (p less than 0.01) correlated with lymph node involvement. Amplification (3 to greater than 30 fold) of the c-erbB-2/neu gene was observed in 20% of cancers. A 5 kb c-erbB-2/neu gene transcript was detected in the 103 cancer specimens analyzed. High levels of transcripts were observed in 36% of tumors. Overexpression did not depend only on amplification since found in 14 tumor samples with a single gene copy. The gene amplification and overexpression were found significantly associated with cancers of poor prognosis. Moreover our data show that both proto-oncogenes are overexpressed only in 12.5% of tumor samples and suggest that each gene might play a different role in tumor progression.

Blotting, Northern↗
PubMed1987

The cytochrome c oxidase from the yeast Candida parapsilosis.

In the yeast Candida parapsilosis, the proteins encoded by mitochondrial DNA are different in number and size from those of Saccharomyces cerevisiae. Nevertheless, the purified cytochrome c oxidase from Candida parapsilosis shows kinetic properties similar to those of Saccharomyces cerevisiae.

Candida↗
PubMed1986

The alternative oxidase of Candida parapsilosis.

The yeast Candida parapsilosis is able to grow on a glycerol medium, supplemented with antimycin A, due to a secondary mitochondrial pathway, able to reoxidize specifically cytoplasmic NADH. It is antimycin-A-insensitive, but inhibited by salicylhydroxamic acid and high cyanide concentrations. This pathway involves the participation of a specific pool cytochrome c, reducible by NADH but not by ascorbate/N,N,N',N'-tetramethyl-p-phenylenediamine, and a cytochrome 590 named cytochrome a1 in bacteria. In C. parapsilosis, both oxidases aa3 and a1 are implicated in the electron transfer pathway.

Antimycin A↗
PubMed1985

[Analysis of the expression of the oncogene c-myc in human breast adenocarcinoma].

The c-myc oncogene was characterized and its expression analyzed in 32 mammary adenocarcinomas and in 2 benign breast tumors from 34 untreated patients. Southern blot hybridization experiments have demonstrated the amplification of the oncogene (3 to 30 fold) in 3 carcinomas. The analysis of total RNA by Northern blot revealed the presence of a 2.4 kb c-myc RNA band. In 7 out of 10 carcinomas from patients with 3 or more than 3 lymph node metastases the level of c-myc expression evaluated by dot blot analysis was 4 to 14 fold greater than that of normal human tissues. In only 5 out of 22 carcinomas from patients without lymph node metastases or less than 3 invaded nodes the level of c-myc expression was also higher (4 to 10 fold). The level of c-myc expression was not significantly enhanced in the 2 benign tumors. It is suggested that the c-myc gene activation could be associated to a higher degree of malignancy of mammary carcinomas.

Adenocarcinoma↗
PubMed1983

[Centronuclear myopathy. Apropos of a new case].

The observation of a thirteen-year-old boy who presented with motor developmental delay, muscular weakness and a waddling gait is reported. Moderately increased muscular enzyme activities and electromyographic findings suggested muscular disease. Histological and ultrastructural examinations of muscle biopsy specimens showed both hypotrophia of type 1 fibers and characteristic distribution of the nuclei within the sarcomere in a chainlike pattern in the center of the fiber surrounded by a space devoid of myofibrils. A few aspects of myophagia were found explaining why muscular enzyme activities were increased. The mother was clinically normal with slightly increased muscular enzyme activities and normal muscle biopsy specimens. The maternal grandmother had delayed gait abnormalities with normal muscular enzyme activities. Approximately one-hundred cases such as ours, isolated within a family, have been published. The course and the mode of inheritance suggest heterogeneity.

Adolescent↗
PubMed1982

Cardiolipin-protein interactions in the phosphate binding activity of a proteolipid from yeast mitochondria. Action of phospholipases A2 and C and of cations.

A proteolipid able to bind phosphate has been isolated from yeast mitochondria. During the purification the active protein was always associated with cardiolipin. The cardiolipin requirement for the phosphate binding activity of this proteolipid has been studied using controlled lipid depletion with two phospholipases A2 and with phospholipase C. Only phospholipase A2 from pig pancreas, that deacylated cardiolipin, promoted inhibition of the proteolipid activity (but never more than 70 per cent). Phospholipase A2 from snake venom did not inhibit the binding activity of the proteolipid. Using thin layer chromatography with two sequential solvents it was possible to separate two cardiolipin subspecies; one of them was preferentially hydrolysed by phospholipase C of Bacillus cereus, leading to inhibition of the proteolipid activity. Ca2+ complexed to cardiolipin stoichiometrically (1-1) inhibited the proteolipid activity. This effect could be due to a conformational change in the cardiolipin-protein association.

Animals↗