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Biomedical subjects

M Caron

Publications and source records attributed to M Caron.

At least 91 records · Page 5Linked to original sources
PubMed1990

Insulin receptor tyrosine residues 1162 and 1163 control insulin stimulation of myristoyl-diacylglycerol generation and subsequent activation of glucose transport.

Chinese hamster ovary (CHO) transfectants expressing human insulin receptors that were mutated at tyrosines 1162 and 1163 (CHO-Y2 cells) exhibit decreased insulin stimulation of both receptor tyrosine kinase and 2-deoxyglucose uptake compared with transfectants expressing wild-type human insulin receptors (CHO-R cells). We now provide evidence that insulin stimulation of myristoyl-diacylglycerol (DAG) production is also markedly impaired in CHO-Y2 cells; this is manifested as a decreased responsiveness and sensitivity to insulin as compared with CHO-R and parental CHO cells. Further, we report that (i) the concentration-response curves of insulin-stimulated myristoyl-DAG production and 2-deoxyglucose uptake were superimposable within each of the three cell lines. (ii) The insulin-induced increase in myristoyl-DAG production preceded that in 2-deoxyglucose uptake, and the time course was altered for both responses in CHO-Y2 cells. (iii) Insulin also increased the phosphorylation of a 40-kDa protein known to be a substrate for protein kinase C, but to a much lesser extent in CHO-Y2 cells than in CHO-R cells. (iv) Exogenously added 1,2-dimyristoyl-glycerol and 4 beta-phorbol 12 beta-myristate 13 alpha-acetate (PMA) again stimulated both the phosphorylation of the 40-kDa protein and 2-deoxyglucose uptake, but in contrast to insulin, they elicited the same level of response in both CHO-R and CHO-Y2 cells. (v) Finally, in protein kinase C-depleted CHO-R cells, insulin and PMA stimulation of 40-kDa protein phosphorylation as well as PMA stimulation of 2-deoxyglucose uptake were completely abolished whereas insulin-stimulated 2-deoxyglucose uptake was only partially decreased. Taken together, these results suggest that insulin stimulation of 2-deoxyglucose uptake involves myristoyl-DAG production and, at least in part, protein kinase C activation, all three of these processes being controlled by receptor tyrosines 1162 and 1163.

Adenosine Triphosphate↗
PubMed1990

Evidence for the involvement of vicinal sulfhydryl groups in the insulin stimulation of intracellular glucose metabolism in Zajdela hepatoma cells.

Phenylarsine oxide (PhAsO), a dithiol reagent that blocks insulin stimulation of glucose transport in 3T3 L1 cells, also altered insulin stimulation of intracellular glucose metabolism in Zajdela Hepatoma cultured cells. PhAsO (2 microM) similarly inhibited the insulin-induced glycogen and lipid syntheses without modifying the basal level of these processes, cell viability or the ATP content. Prior incubation of the cells with PhAsO did not prevent insulin binding to the cells, or activation of the receptor tyrosine kinase, while it minimally (16%) altered receptor internalization. These results indicate that cellular dithiols located at a post-receptor step are involved in the transduction of the insulin signal to intracellular glucose metabolism.

Adenosine Triphosphate↗
PubMed1990

Biotinylated derivative of a human brain lectin: synthesis and use in affinoblotting for endogenous ligand studies.

Coupling of biotin to an endogenous lectin yields a probe which can be used for selective nonradioactive detection of complementary endogenous ligands. To exemplify practical applications of this type of compounds, we have synthesized and characterized a biotinylated derivative of a beta-galactoside-specific human brain lectin. Proteins which bind this lectin can be located on nitrocellulose sheets after electrophoretic transfer from gradient polyacrylamide gels, by sequential incubation with biotinylated probes and streptavidin-peroxidase, with visualization by an insoluble reaction product (affinoblotting). Biotinylated galactoside-binding plant lectins were used in the same way to visualize human brain glycoproteins, and their binding specificity was compared with that of human brain lectin. The results obtained by means of these different probes showed the usefulness of the endogenous lectin derivative to actually identify its endogenous partners. Thus this approach may find extended applications in the study of biological activities of vertebrate lectins in homologous systems, i.e., with lectins and ligands coming from the same tissue origin.

Amides↗
PubMed1990

Soluble galactoside-binding vertebrate lectins: a protein family with common properties.

1. Soluble galactoside-binding lectins could play a key role in vertebrates by specifical binding to complementary glycoconjugates. 2. Their expression and localization are developmentally regulated. 3. They constitute a large family of structurally related proteins which contain a series of conserved aminoacids. 4. Their functional role could vary from an organ to another, and the same lectin may probably mediate several biological activities.

Amino Acid Sequence↗
PubMed1990

Soluble heparin-binding lectins from human brain: purification, specificity and relationship to an heparin-binding growth factor.

1. An heparin-binding lectin activity was detected in soluble extracts of human brain. Three polypeptide chains were purified by affinity chromatography on heparin-Sepharose. Their Mrs estimated by polyacrylamide gel electrophoresis were 13,000, 14,500 and 16,000. 2. Several glycosaminoglycans were potent inhibitors of their hemagglutination activity. 3. From the pool of purified lectins three peaks were separated by reversed-phase high-performance liquid chromatography. They were indistinguishable by activity criteria (hemagglutination, stimulation of endothelial cell growth), and immunological relationship was found between one of them and acidic fibroblast growth factor (aFGF).

Animals↗
PubMed1990

Dual effect of metformin in cultured rat hepatocytes: potentiation of insulin action and prevention of insulin-induced resistance.

The ability of the biguanide hypoglycemic agent metformin to improve the acute effects of insulin on glucose and/or lipid metabolism was investigated in both insulin-responsive and insulin-resistant cultured rat hepatocytes: (1) metformin (20 micrograms/mL, 16 hours) increased the insulin-dependent stimulation of glycogen and lipid synthesis through an exclusive enhancement of the responsiveness without modification of the cell sensitivity to the hormone; (2) metformin neither altered basal glycogenesis from [U-14C]glucose and basal lipogenesis from [1-14C]acetate nor insulin binding. These results indicate the ability of this drug to selectively potentiate the acute action of insulin at a postreceptor step in normal liver cells. A prolonged incubation with insulin (16 hours, 5 x 10(-7) mol/L) led the hepatocytes to a state of resistance evidenced by a 50% decrease in their maximal responsiveness and sensitivity to a subsequent acute stimulation by the hormone, as assessed on lipogenesis. Addition of metformin (20 micrograms/mL) during the overnight incubation of hepatocytes with insulin prevented the decrease in cell responsiveness and sensitivity to the hormone for the stimulation of lipogenesis, thus showing that metformin was able to hamper the development of the resistant state to the hormone in this pathway. These results strongly suggest that metformin improves type 2 diabetes through an effect at the hepatic level on both insulin action and insulin-induced resistance.

Animals↗
PubMed1990

Mutation of tyrosine residues 1162 and 1163 of the insulin receptor affects hormone and receptor internalization.

Insulin internalization and degradation, insulin receptor internalization and recycling, as well as long term receptor down-regulation were comparatively studied in Chinese hamster ovary (CHO) cell lines, either parental or expressing the wild-type human insulin receptor (CHO.R) or a mutated receptor in which the tyrosine residues in positions 1162 and 1163 were replaced by phenylalanines (CHO.Y2). The two transfected cell lines presented very similar binding characteristics, and their pulse labeling with [35S]methionine revealed that the receptors were processed normally. As expected, the mutation of these twin tyrosines resulted in a defective insulin stimulation of both receptor kinase activity and glycogen synthesis. We now present evidence that compared to CHO.R cells, which efficiently internalized and degraded insulin, CHO.Y2 cells exhibited a marked defect in hormone internalization, leading to impaired insulin degradation. Moreover, the mutated receptors were found to be less effective than the wild-type receptors in transducing the hormone signal for receptor internalization, whereas the process of receptor recycling after internalization seemed not to be altered. In parental CHO cells, insulin induced long term receptor down-regulation, but was totally ineffective in both transfected cell lines. These results reveal that the tyrosines 1162 and 1163 in the kinase regulatory domain of the receptor beta-subunit play a pivotal role in insulin and receptor internalization.

Animals↗
PubMed1990

Marketing alternatives for hospitals to the nursing crisis.

The current nursing shortage problem as defined in this article, is the result of a supply and demand imbalance. The demand for nurses is growing at a faster rate than the supply. If strategies are not implemented to correct this imbalance the demand for nurses will continue to surpass the supply, negatively affecting access to and delivery of quality patient care. Factors contributing to the increased demand for nurses and the dwindling supply must be examined if solutions to the problem are to be found and implemented. Factors contributing to the growing demand for nurses include the decreasing use of ancillary personnel by hospitals in an effort to tighten their budgets; the impact of Medicare's prospective payment system on hospital lengths of stay; the increase in patient acuity with advances in medical technology; and alternative health care opportunities pulling nurses away from the hospital setting. The supply of RNs is shrinking in relation to demand because of low retention rates; declining nursing school enrollment; non-competitive wages; poor working conditions; alternative career opportunities for women; and the lack of power and support within the nursing profession. An active marketing approach that relies on this assessment of contributing factors has been formulated in an attempt to resolve the problem and meet the increasing demand. Recommendations have been made and ranked in the order of their priority and pros and cons established for each. The strategies developed have been divided into four basic marketing categories of product, price, place, and promotion. If the problem is to be resolved these strategies must be marketed to hospitals, their administrators, nurses, other allied health professionals, third party payors, educators, and the general public. The nursing profession itself must find the unity and strength within its own group of professionals to build political and economic powers to enhance their product. Nursing is at a crossroad. Much depends on how we cope with the current shortage and its related issues. Nurses have the opportunity to shape their future. Hopefully, with proactive strategies, the profession will transform from a passive role to an active, vital force of the health care environment. The authors believe that through our marketing approaches this can be accomplished.

Employee Incentive Plans↗
PubMed1989

Purification and characterization of a galactoside-binding lectin from human brain.

A beta-galactoside-binding hemagglutinin was detected in soluble extracts of human brain. This soluble lectin was purified to homogeneity by affinity column chromatography on lactose coupled to divinylsulfone-activated agarose. The purified lectin had an isoelectric point of 3.9 and its subunit molecular mass estimated by polyacrylamide gel electrophoresis in sodium dodecyl sulfate was 14,500. Human brain lectin was not a glycoprotein and its amino acid composition was characterized by a high content of serine, glutamic acid, and glycine, and a low content of methionine and cysteine. The most potent saccharide inhibitors tested were thiodigalactoside, lactose, and p-nitrophenyl-beta-D-galactoside. An antibody was raised to the pure lectin. Immunological relationships were found between the brain lectin and several other soluble lectins of various vertebrate origins.

Adult↗
PubMed1989

A further comparison of insulin- and phorbol ester-stimulated glucose transport in adipocytes.

Insulin and 4 beta-phorbol 12 beta-myristate 13 alpha-acetate (PMA) stimulatory effects on adipocyte glucose transport were compared for their sensitivity to: (1) sphingosine and staurosporine, two potent protein kinase C (PKC) inhibitors; and (2) phenylarsine oxide (PhAsO), a dithiol reagent blocking insulin-stimulated glucose transport. None affected basal 2-deoxyglucose transport, cell viability, cellular ATP content, or insulin binding. Insulin- and PMA-stimulated 2-deoxyglucose transport were both markedly inhibited by sphingosine (5-50 microM) and staurosporine (0.1-2 microM), although with differences in the extents of maximal inhibitions (65 and 48% vs. 88 and 98%) and the concentrations of the drugs causing the half-maximal inhibitions observed in the experiments (2- to 3-fold higher for insulin). Insulin and PMA both altered PKC along with glucose transport, either by increasing its activity in the cytosol or by promoting its translocation to membrane. Insulin- and PMA-stimulated 2-deoxyglucose transport were both inhibited selectively by PhAsO (0.1-1 microM), at almost identical maximal inhibitions (84 and 90%) and IC50 values (0.18 and 0.16 microM). Furthermore, insulin- and PMA-induced increases in transport Vmax (6.5- and 3.4-fold) were both reduced by 89% by PhAsO, which, however, failed to affect the decrease in transport Km (1.7-fold) exclusively induced by insulin. Likewise, PhAsO did not affect insulin or PMA activation of PKC. The results suggest that insulin activates adipocyte glucose transport through: (1) a PKC-dependent mechanism requiring cellular dithiols, responsible for a part of the hormone-induced increase in transport Vmax; and (2) a PKC-independent mechanism responsible for both a further increase in transport Vmax and a decrease in transport Km.

Adenosine Triphosphate↗
PubMed1989

Glycosylation characteristics of the mouse liver lactogenic receptor.

The structural characteristics and glycosylation properties of the lactogenic receptor were examined in 3-[(3-cholamidopropyl)dimethylammonio]-1-propane sulfonate (CHAPS)-solubilized plasma membranes from female mouse liver. The specific binding of the radioiodinated human growth hormone [( 125I]hGH) was displaced with an equivalent potency by both hGH and prolactin. After a mild neuraminidase treatment, this binding was increased by 40%, as a result of an increase in receptor affinity. Affinity chromatography on immobilized lectins revealed that the [125I]hGH-receptor complexes were specifically retained and eluted from ricin lectin-agarose, concanavalin A and lentil lectin, indicating the presence of N-linked glycans. Covalent cross-linking of solubilized [125I]hGH-receptor complexes with disuccinimidyl suberate, followed by analysis by sodium dodecyl sulfate-gel electrophoresis (SDS-PAGE) under reducing conditions, and autoradiography resulted in the appearance of two bands with apparent Mr approximately 62,000 and approximately 100,000. The labelling of these bands was prevented by unlabelled hGH or ovine prolactin (oPrl) but not by bovine growth hormone (bGH). Neuraminidase treatment of the two receptor forms resulted in increased electrophoretic mobility which was inhibited by simultaneous addition of sialyl-lactose, a neuraminidase substrate. The both cross-linked forms were unaffected by endoglycosidase H, while endoglycosidase F decreased the molecular weight of each of the forms by about 8000 Da, yielding bands at Mr approximately 54,000 and approximately 92,000. In conclusion, taking into account that hGH is a Mr 22,000 polypeptide, the two forms of the receptor correspond to glycoproteins of Mr approximately 40,000 and approximately 78,000, respectively. They contain polypeptide backbones of Mr approximately 32,000 and approximately 70,000, and complex N-linked oligosaccharide chains with terminal sialic acid residues which could be involved in receptor binding affinity.

Acetylglucosaminidase↗
PubMed1989

Insulin action is mimicked by polyclonal antireceptor antibodies that activate the insulin receptor tyrosine kinase.

The insulin-like properties of anti-insulin receptor antibodies (P95 Ab) that have been characterized as being directed against the receptor beta-subunit, were studied as probes to assess the interrelationship between insulin action and receptor phosphorylation. When tested on intact cells, P95 Ab mimicked insulin effects. On isolated fat cells, they stimulated 2-deoxyglucose (2-DG) transport and lipogenesis and the P95 antibody maximal effects (173 and 232% of the control values, respectively) represented about 50% of the maximal effects elicited by insulin (317 and 475% of the control values). On cultured Zajdela hepatoma cells (ZHC cells), P95 Ab also mimicked insulin action on the incorporation of [U-14C]glucose into glycogen (158 and 207% of the control value for antibody- and insulin-treated cells, respectively). In all cases the antibody effects were dose-dependent, specific and, when maximal, were not additive with those elicited by insulin. When tested in a cell-free system, P95 Ab faithfully reproduced insulin action on the phosphorylation of the receptor beta-subunit. The maximal antibody and insulin effects (317 and 328% of the control value, respectively) were not additive. P95 Ab were also equally potent as insulin to stimulate the receptor-mediated phosphorylation of an exogenous substrate (365 and 379% of the control value in P95 antibody- and insulin-treated receptors, respectively). As well, P95 Ab proved as able as insulin in stimulating the tyrosine kinase activity of the receptor (89% of the hormone effect) when the activation was carried out in vivo. Taken together, these results are consistent with a role for the kinase activity of the insulin receptor in mediating the action of insulin.

Animals↗
PubMed1989

Immunohistochemical localization of a beta-galactoside-binding lectin in rat central nervous system. I. Light- and electron-microscopical studies on developing cerebral cortex and corpus callosum.

From a lectin isolated from human brain (HBL-14), that specifically binds beta-galactosides, a polyclonal antiserum was raised that also recognizes a similar rat brain lectin (RBL-16). These antibodies allowed the immunocytochemical localization of the lectin during rat brain development by optical and electron microscopy. The presence of RBL-16, first detected at embryonic day 15, was specially increased from postnatal day 1 to 10. Its level decreased thereafter but it could still be detected in adult rat brain. The lectin, predominantly neuronal until postnatal day 13, was also present in astrocytes and perivascular cells where no developmental regulation was observed in contrast to neurons. Electron microscopy showed that the lectin was transiently expressed in the axoplasm of almost all neurons in layer I around the birth date, after which it remained inside neurons, including cell bodies and dendrites, in all examined regions. The lectin was clearly localized in postsynaptic structures. This beta-galactoside-specific lectin may be involved in synaptogenesis and neurite fasciculation as well as in intracellular traffic as discussed.

Aging↗
PubMed1989

Immunohistochemical localization of a beta-galactoside-binding lectin in rat central nervous system. II. Light- and electron-microscopical studies in developing cerebellum.

An endogenous brain lectin exhibiting beta-galactoside specificity (RBL-16) was localized during postnatal cerebellum development both at the light- and electron-microscopical level. The lectin was widely distributed in neurons, astroglial and perivascular cells. Its levels were nearly constant during development in the two latter cell types. The lectin was developmentally regulated with a transient accumulation in Purkinje dendritic spines between the 10th- and 13th day, then it decreased until adult age. From electron-microscopical observations, it could be concluded that, in Purkinje cells, the lectin remained in the intracellular compartment, in dendrites and cell bodies. It was never externalized in the region where synaptogenesis takes place. A role in the intracellular transport of molecules should be expected from such a localization. The lectin was also transiently found on the surface of postmitotic neuroblasts in the external germinative layer and on the parallel fibers of the upper part of the molecular layer. However, it was not expressed inside neuroblasts. This suggests that part of the lectin found on the surface of neuroblasts originates from heavily stained astrocytes which could secrete it. RBL-16 could be making bridges between neuroblasts in the premigratory zone and between growing axons. A role in transient neuroblast adhesion in the external germinative layer and in parallel fiber fasciculation is expected from such a localization.

Aging↗
PubMed1989

Genetic convergence during serial in vitro passage of a polyclonal squamous cell carcinoma.

A cell line was established from an in situ squamous cell carcinoma of the skin (Bowen's disease), and its in vitro karyotypic evolution was cytogenetically analyzed. Initially, considerable genetic heterogeneity was evident. Nine cytogenetically abnormal clones, eight of which were apparently unrelated, were found among the 83 metaphases analyzed from the primary culture and the first passage. With increasing time in culture this complexity was reduced, so that a single clone dominated passages 7-11. The clone that emerged from this genetic convergence had a t(12;17)(p13;q21) as the sole abnormality. Our findings indicate that the cytogenetic multiclonality that has been repeatedly detected in short-term cultures of squamous cell carcinomas is not caused by the in vitro conditions. Instead, the principles of Darwinian selection apply: the altered, but stable, selection pressure facing a newly established and initially multiclonal cell line will lead to a reduction of genetic heterogeneity until the one clone that now has the proliferative advantage outgrows the other subpopulations.

Biological Evolution↗
PubMed1989

Tyrosine-kinase defect of the insulin receptor in cultured fibroblasts from patients with lipoatropic diabetes.

Postbinding defects in insulin action were described previously in cultured fibroblasts from six patients with lipoatropic diabetes. To define the contribution of the insulin receptor tyrosine kinase in these defects, we studied autophosphorylation and kinase activity of lectin purified receptors from these six patients and six normal cell lines. The patients' insulin receptors, prepared by precipitation with polyethylene glycol, had normal insulin binding characteristics and autophosphorylation properties, but a 56% decrease in the tyrosine kinase activity toward an exogenous substrate. To identify more subtle qualitative defects in autophosphorylation, insulin receptors were sequentially immunoprecipitated and analyzed for their phosphoaminoacid content. The phosphorylated receptors precipitated with an antiphosphotyrosine antibody contained labeled phosphotyrosine, whereas those in the supernatant, when further precipitated with an antireceptor antibody, contained only phosphoserine. Under these conditions, the insulin-stimulated autophosphorylation of tyrosine was significantly decreased by 54% in the patient receptors compared to normal subjects' receptors. In addition, insulin-like growth factor-I stimulation of autophosphorylation of its receptor was reduced by 59% in the patients' cells compared to those from normal subjects. We conclude that fibroblasts from patients with lipoatropic diabetes have defects in the tyrosine kinase activity of their insulin and their insulin-like growth factor-I receptors that might give rise to the in vitro hormone resistance and be related to the in vivo hormone resistance that occurs in these patients.

Adolescent↗
PubMed1988

Effect of protein kinase C activation and depletion on insulin stimulation of glycogen synthesis in cultured hepatoma cells.

Insulin stimulation of glycogen synthesis was nearly abolished in hepatoma cells shortly treated with 4 beta-phorbol 12 beta-myristate, 13 alpha-acetate (protein kinase C activation) but remained unmodified in cells chronically treated with the phorbol ester (protein kinase C depletion). Thus, although exogenous activation of protein kinase C results in an inhibition of insulin action, protein kinase C depletion has no influence on this process. The results suggest that, in hepatoma cells, no endogenous activation of protein kinase C may occur in response to the signal triggered by insulin.

Animals↗