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Biomedical subjects

A Nantel

Publications and source records attributed to A Nantel.

15 recordsLinked to original sources
PubMed2006

Calnexin-dependent regulation of tunicamycin-induced apoptosis in breast carcinoma MCF-7 cells.

The endoplasmic reticulum (ER) has evolved specific mechanisms to ensure protein folding as well as the maintenance of its own homeostasis. When these functions are not achieved, specific ER stress signals are triggered to activate either adaptive or apoptotic responses. Here, we demonstrate that MCF-7 cells are resistant to tunicamycin-induced apoptosis. We show that the expression level of the ER chaperone calnexin can directly influence tunicamycin sensitivity in this cell line. Interestingly, the expression of a calnexin lacking the chaperone domain (DeltaE) partially restores their sensitivity to tunicamycin-induced apoptosis. Indeed, we show that DeltaE acts as a scaffold molecule to allow the cleavage of Bap31 and thus generate the proapoptotic p20 fragment. Utilizing the ability of MCF-7 cells to resist tunicamycin-induced apoptosis, we have characterized a molecular mechanism by which calnexin regulates ER-stress-mediated apoptosis in a manner independent of its chaperone functions but dependent of its binding to Bap31.

Amino Acid Sequence↗
PubMed2001

Specific inhibition by hGRB10zeta of insulin-induced glycogen synthase activation: evidence for a novel signaling pathway.

Grb10 is a member of a family of adapter proteins that binds to tyrosine-phosphorylated receptors including the insulin receptor kinase (IRK). In this study recombinant adenovirus was used to over-express hGrb10zeta, a new Grb10 isoform, in primary rat hepatocytes and the consequences for insulin signaling were evaluated. Over-expression of hGrb10zeta resulted in 50% inhibition of insulin-stimulated IRK autophosphorylation and activation. Analysis of downstream events showed that hGrb10zeta over-expression specifically inhibits insulin-stimulated glycogen synthase (GS) activity and glycogen synthesis without affecting insulin-induced IRS1/2 phosphorylation, PI3-kinase activation, insulin like growth factor binding protein-1 (IGFBP-1) mRNA expression, and ERK1/2 MAP kinase activity. The classical pathway from PI3-kinase through Akt-PKB/GSK-3 leading to GS activation by insulin was also not affected by hGrb10zeta over-expression. These results indicate that hGrb10zeta inhibits a novel and presently unidentified insulin signaling pathway leading to GS activation in liver.

Animals↗
PubMed1999

Localization of endogenous Grb10 to the mitochondria and its interaction with the mitochondrial-associated Raf-1 pool.

Grb10 belongs to a small family of adapter proteins that are known to interact with a number of receptor tyrosine kinases and signaling molecules. We have recently demonstrated that the Grb10 SH2 domain interacts with both the Raf-1 and MEK1 kinases. Overexpression of Grb10 genes with mutations in their SH2 domains promotes apoptosis in cultured cells, a phenotype that is reversed by concomitant overexpression of the wild type gene. Using immunofluorescence microscopy and subcellular fractionation we now show that most of the Grb10 molecules are peripherally associated with mitochondria. Following insulin-like growth factor I or serum treatment, small pools of Grb10 can also be found at the plasma membrane and in actin-rich membrane ruffles, whereas overexpression of Grb10 leads to its mislocalization to the cytosol. Two-hybrid analysis shows that the Grb10-binding site on Raf-1 co-localizes with its Ras-binding domain. Finally, we show that the endogenous Grb10 and Raf-1 proteins can be co-immunoprecipitated from a partially purified mitochondrial extract, an interaction that is enhanced following the activation of Raf-1 by ultraviolet radiation. Thus, we infer that Grb10 may regulate signaling between plasma membrane receptors and the apoptosis-inducing machinery on the mitochondrial outer membrane by modulating the anti-apoptotic activity of mitochondrial Raf-1.

Animals↗
PubMed1999

Argyremia in septal cauterization with silver nitrate.

OBJECTIVE: The purpose of this study was to demonstrate silver absorption in blood and hair specimens after septal cauterization with silver nitrate and to discuss the potential toxicity of silver. METHOD: A prospective study of 11 volunteers without any known occupational exposure to silver products or past history of septal cauterization with silver nitrate was undertaken. Subjects were recruited in an academic tertiary care centre from October 1996 to September 1997. The study population consisted of five patients with anterior epistaxis and six healthy volunteers without any bleeding problem. Cauterization was done with one or two silver nitrate applicators directly on the bleeding vessel or Kiesselbach's area. Blood was sampled before cauterization and at specified times after application, while hair strands were sampled only 3 months later. Measurements of silver concentration in whole blood and in hair segments were obtained by inductively coupled plasma mass spectrometry. RESULTS: Silver concentrations in whole blood increased significantly after cauterization (p = .02). The measured peak level seemed to correlate with the number of applicators used. No significant increase in silver concentration was observed in hair samples. CONCLUSIONS: Effective silver absorption occurs with only one or two silver nitrate applicators. Hair has not been as reliable as whole blood to document an acute and fragmentary exposure. The indiscriminate use of silver nitrate is a potential source of silver intoxication.

Absorption↗
PubMed1998

Interaction of the Grb10 adapter protein with the Raf1 and MEK1 kinases.

Grb10 and its close homologues Grb7 and Grb14, belong to a family of adapter proteins characterized by a proline-rich region, a central PH domain, and a carboxyl-terminal Src homology 2 (SH2) domain. Their interaction with a variety of activated tyrosine kinase receptors is well documented, but their actual function remains a mystery. The Grb10 SH2 domain was isolated from a two-hybrid screen using the MEK1 kinase as a bait. We show that this unusual SH2 domain interacts, in a phosphotyrosine-independent manner, with both the Raf1 and MEK1 kinases. Mutation of the MEK1 Thr-386 residue, which is phosphorylated by mitogen-activated protein kinase in vitro, reduces binding to Grb10 in a two-hybrid assay. Interaction of Grb10 with Raf1 is constitutive, while interaction between Grb10 and MEK1 needs insulin treatment of the cells and follows mitogen-activated protein kinase activation. Random mutagenesis of the SH2 domain demonstrated that the Arg-betaB5 and Asp-EF2 residues are necessary for binding to the epidermal growth factor and insulin receptors as well as to the two kinases. In addition, we show that a mutation in Ser-betaB7 affects binding only to the receptors, while a mutation in Thr-betaC5 abrogates binding only to MEK1. Finally, transfection of Grb10 genes with specific mutations in their SH2 domains induces apoptosis in HTC-IR and COS-7 cells. These effects can be competed by co-expression of the wild type protein, suggesting that these mutants act by sequestering necessary signaling components.

Amino Acid Sequence↗
PubMed1996

Characterization of three rice basic/leucine zipper factors, including two inhibitors of EmBP-1 DNA binding activity.

The promoter of the wheat Em gene contains elements with a CACGTG core sequence (G-boxes), which are recognized by EmBP-1, a wheat basic/leucine zipper (bZIP) protein. G-boxes are required for Em expression in response to the phytohormone abscisic acid and for transactivation by the Viviparous-1 protein (VP1) using transient expression systems. In order to identify other factors that are part of the transcriptional complex that associates with G-boxes, we have screened a rice (Oryza sativa) cDNA library with biotinylated EmBP-1. We have isolated osZIP-1a, a homolog of EmBP-1 and other plant G-box-binding factors. We show that EmBP-1 and osZIP-1a will preferentially heterodimerize in vitro. Overexpression of osZIP-1a in rice protoplasts can enhance expression from the Em promoter only in the presence of abscisic acid. Two other clones have been identified by screening with EmBP-1: osZIP-2a and osZIP-2b. These osZIP-2 factors represent a novel class of bZIP proteins with an unusual DNA-binding domain that does not recognize G-boxes. The osZIP-2 factors can heterodimerize with EmBP-1 and prevent it from binding to the Em promoter. Interestingly, osZIP-1a does not heterodimerize with the osZIP-2 factors and its DNA binding activity is unaffected by their presence. Thus, osZIP-2 factors may be involved in sequestering a particular group of G-box-binding factors into inactive heterodimers.

Amino Acid Sequence↗
PubMed1996

A conserved domain of the viviparous-1 gene product enhances the DNA binding activity of the bZIP protein EmBP-1 and other transcription factors.

The maize VP1 protein is a seed-specific regulator of gene expression that effects the expression of a subset of abscisic acid (ABA)-regulated genes that are expressed during the maturation program of the seed. In addition, VP1 has pleiotropic effects on seed development that are not related to ABA. In transient expression assays, VP1 has been shown to transactivate gene expression through at least two distinct promoter elements: the G boxes from the ABA-inducible wheat Em gene and the SphI box from the maize C1 gene. We have investigated how VP1 can transactivate gene expression through diverse promoter elements by analyzing its association in vitro with EmBP-1, a factor that binds the Em promoter. We demonstrate that VP1 can greatly enhance the DNA binding activity of EmBP-1 in a gel retardation assay. This enhancing activity has also been observed on transcription factors as diverse as Opaque-2, Max, Sp1, and NF-kappaB. Deletion of a small but highly conserved region (BR2) in VP1 eliminates the enhancement in vitro as well as the ability of VP1 to transactivate Em gene expression in a transient expression assay. A 40-amino acid fragment from VP1 sandwiched between the maltose-binding protein and LacZ can confer the enhancement function to this fusion protein in vitro. A weak and relatively nonspecific interaction between BR2 and DNA is demonstrated by UV cross-linking. The in vitro properties we observe for VP1 might explain the regulatory effects of VP1 on a diverse set of genes and why mutations in the vp1 locus have pleiotropic effects.

Base Sequence↗
PubMed1988

Visits to physicians before and after exposure to urea formaldehyde foam insulation.

The average number of visits to a physician made by a sample of 351 residents of homes insulated with urea formaldehyde foam insulation in Montreal in the one year period before exposure was 5.25, and in the year following 5.62, an increase of 7 per cent (odds ratio 1.07, 95% CI = 1.00, 1.15). The increase in visits in the post insulation year was limited to subjects who had the product installed in the winter (OR = 1.48, 95% CI = 1.18,1.85), and was not seen for study subjects who insulated their homes during other seasons of the year.

Construction Materials↗
PubMed1977

Acute lindane poisoning with development of muscle necrosis.

A 35-year-old man ingested food contaminated with lindane, an insecticide containing almost pure gamma hexachlorocyclohexane. Grand mal seizures and severe acidemia developed rapidly. The seizures recurred for nearly 2 hours, then ceased. In addition, the patient had muscle weakness and pain, headaches, episodic hypertension, myoglobinuria, acute renal failure and anemia. Pancreatitis developed 13 days after the ingestion of lindane. A muscle biopsy on the 15th day of illness demonstrated widespread necrosis and regeneration of muscle fibres. The patient's condition improved and he was discharged 24 days after the onset of his illness. During the year following the poisoning the patient noted difficulty with recent memory, loss of libido and easy fatigability. One year after lindane ingestion the results of physical examination, including those for muscle power and bulk, were normal.

Acute Disease↗