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M Charbonneau

Publications and source records attributed to M Charbonneau.

At least 19 recordsLinked to original sources
PubMed2003

Effects of postnatal exposure to mixtures of non-ortho-PCBs, PCDDs, and PCDFs in prepubertal female rats.

There are concerns that postnatal exposure to organochlorines present in breast milk could lead to adverse health effects. We reconstituted four mixtures of aryl-hydrocarbon receptor (AhR) agonists (3 non-ortho polychlorinated biphenyls [PCBs], 6 polychlorinated dibenzodioxins [PCDDs], 7 polychlorinated dibenzofurans [PCDFs], or all 16 chemicals together [referred to as AhRM]) based on their concentrations in breast milk, and examined their effects following exposure by gavage from day 1 until day 20 of age. Female neonates received dosages of AhRM equivalent to 1, 10, 100, or 1000 times the amount consumed by an infant over the first 24 days of life. Other groups received the PCBs, the PCDDs, or the PCDFs at the 1000x level. All rats were sacrificed at 21 days of age. Changes in ethoxyresorufin-o-deethylase hepatic activity, thymus and body weights, and serum thyroxin were linked to the 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) toxic equivalents (TEQ) of the four mixtures (1000x-AhRM > PCDDs > PCBs > PCDFs). To test for AhRM antiestrogenicity, two additional groups received 1.5 microg/kg of 17alpha-ethynyl estradiol (EE) with or without the 1000x-AhRM. The AhRM had no effect on uterine weight or EE-stimulated uterine growth. The actions of the combined EE and AhRM treatments suggest additive effects in decreasing pentoxyresorufin-o-deethylase activity and spleen weight, but nonadditive/antagonistic effects on adrenal weight and serum thyroxin. In conclusion, (1) 10x-AhRM had no detectable effects, (2) TEQ values relate to observed toxicities, even when testing complex mixtures of AhR agonists, and (3) indications of tissue-specific additive and nonadditive/antagonistic effects, but no synergism, were observed when doses of AhRM were increased, or combined with EE.

Animals↗
PubMed2001

Cdc13 prevents telomere uncapping and Rad50-dependent homologous recombination.

Cdc13 performs an essential function in telomere end protection in budding yeast. Here, we analyze the consequences on telomere dynamics of cdc13-induced telomeric DNA damage in proliferating cells. Checkpoint-deficient cdc13-1 cells accumulated DNA damage and eventually senesced. However, these telomerase-proficient cells could survive by using homologous recombination but, contrary to telomerase-deficient cells, did so without prior telomere shortening. Strikingly, homologous recombination in cdc13-1 mec3, as well as in telomerase-deficient cdc13-1 cells, which were Rad52- and Rad50-dependent but Rad51-independent, exclusively amplified the TG(1-3) repeats. This argues that not only short telomeres are substrates for type II recombination. The Cdc13-1 mutant protein harbored a defect in its association with Stn1 and Ten1 but also an additional, unknown, defect that could not be cured by expressing a Cdc13-1- Ten1-Stn1 fusion. We propose that Cdc13 prevents telomere uncapping and inhibits recombination between telomeric sequences through a pathway distinct from and complementary to that used by telomerase.

Cell Cycle Proteins↗
PubMed2001

Ten1 functions in telomere end protection and length regulation in association with Stn1 and Cdc13.

In Saccharomyces cerevisiae, Cdc13 has been proposed to mediate telomerase recruitment at telomere ends. Stn1, which associates with Cdc13 by the two-hybrid interaction, has been implicated in telomere maintenance. Ten1, a previously uncharacterized protein, was found to associate physically with both Stn1 and Cdc13. A binding defect between Stn1-13 and Ten1 was responsible for the long telomere phenotype of stn1-13 mutant cells. Moreover, rescue of the cdc13-1 mutation by STN1 was much improved when TEN1 was simultaneously overexpressed. Several ten1 mutations were found to confer telomerase-dependent telomere lengthening. Other, temperature-sensitive, mutants of TEN1 arrested at G(2)/M via activation of the Rad9-dependent DNA damage checkpoint. These ten1 mutant cells were found to accumulate single-stranded DNA in telomeric regions of the chromosomes. We propose that Ten1 is required to regulate telomere length, as well as to prevent lethal damage to telomeric DNA.

Alleles↗
PubMed2001

Hsp90 levels affect telomere length in yeast.

Cdc13 is a Saccharomyces cerevisiae protein that binds to telomeric single-stranded DNA and regulates telomerase activity. Stnl has been shown by two-hybrid analysis to form a physical complex with Cdc13. Temperature-sensitive mutations in CDC13 and STN1, which are both essential genes, activate a DNA damage-dependent checkpoint which is the cause of the arrest seen in the mutant strains. The stn1-13 mutation induces dramatic telomere elongation which is telomerase dependent, as shown here. Additional mutants for STN1, which show a tighter arrest phenotype than stn1-13, were generated in order to perform genetic screens aiming at uncovering new regulators of telomerase. HSC82, which encodes a conserved molecular chaperone of the Hsp90 family, was thus isolated as a high-dosage suppressor of a temperature-sensitive mutation in STN1. Overexpression of HSC82 also partially suppressed the growth defect of cdc13-1 cells. Overexpression of HSC82 was found to correct the telomeric defect associated with stn1 mutations. Shortening of telomeres was also observed in wild-type cells upon overexpression of HSC82, or of its temperature-inducible homologue, HSP82. These results identify Hsc82/Hsp82 as potential regulators of telomerase in yeast cells.

Blotting, Northern↗
PubMed2000

Cdc13 cooperates with the yeast Ku proteins and Stn1 to regulate telomerase recruitment.

The Saccharomyces cerevisiae CDC13 protein binds single-strand telomeric DNA. Here we report the isolation of new mutant alleles of CDC13 that confer either abnormal telomere lengthening or telomere shortening. This deregulation not only depended on telomerase (Est2/TLC1) and Est1, a direct regulator of telomerase, but also on the yeast Ku proteins, yKu70/Hdf1 and yKu80/Hdf2, that have been previously implicated in DNA repair and telomere maintenance. Expression of a Cdc13-yKu70 fusion protein resulted in telomere elongation, similar to that produced by a Cdc13-Est1 fusion, thus suggesting that yKu70 might promote Cdc13-mediated telomerase recruitment. We also demonstrate that Stn1 is an inhibitor of telomerase recruitment by Cdc13, based both on STN1 overexpression and Cdc13-Stn1 fusion experiments. We propose that accurate regulation of telomerase recruitment by Cdc13 results from a coordinated balance between positive control by yKu70 and negative control by Stn1. Our results represent the first evidence of a direct control of the telomerase-loading function of Cdc13 by a double-strand telomeric DNA-binding complex.

Antigens, Nuclear↗
PubMed1999

Unsuspected intrathyroidal parathyroid adenoma: mimic of lymphocytic thyroiditis in fine-needle aspiration specimens-a case report.

Fine-needle aspirations (FNAs) of parathyroid adenomas (PA) are infrequently encountered, but the scant literature on this topic emphasizes the difficulties in distinguishing them from thyroid neoplasms. We report on a case of an unsuspected intrathyroidal PA whose two FNA specimens mimicked almost perfectly the features of lymphocytic thyroiditis (LT). The smears from two FNAs of a "thyroid nodule" in a 22-yr-old woman were received with a clinical diagnosis of "LT." The cytological features of both specimens were similar and consisted of groups of epithelial cells in a background of numerous "naked" nuclei, interpreted as Hurthle cells and lymphocytes respectively, and leading to a cytological diagnosis of LT. Subsequent surgical excision of the "nodule" revealed a large intrathyroidal PA. The oxyphil cells and chief cells (the latter devoid of cytoplasm) present in the PA resembled Hurthle cells and lymphocytes respectively, in the FNA specimens. In conclusion, PA can give a cytological picture almost identical to that of LT in FNA material. Important clues to the diagnosis of PA in FNA specimens include the presence of prominent capillaries and the knowledge of a clinical history of hyperparathyroidism. Diagn. Cytopathol. 1999;21:276-279.

Adenoma↗
PubMed1999

Dbf2 is implicated in a Cbt1-dependent pathway following a shift from glucose to galactose or non-fermentable carbon sources in Saccharomyces cerevisiae.

Dbf2, a cell cycle-regulated protein kinase, has been shown recently to be part of the CCR4 transcriptional regulatory complex in the yeast Saccharomyces cerevisiae. We report here that temperature-sensitive (ts) dhf2-2 mutant cells can be rescued by overexpression of CDC14, which encodes a dual-specificity protein phosphatase, when grown on glucose-containing medium, as reported previously, but not on galactose. Screening of two S. cerevisiae cDNA libraries led to the identification of CBT1 as a gene which, if overexpressed simultaneously with CDC14, results in the rescue of the dbJ2-2 mutation at restrictive temperature on galactose-based medium, as well as on media containing non-fermentable carbon sources such as glycerol, lactate and acetate. Cbt1 has been shown previously to be essential for formation of cytochrome b in the mitochondria. On the other hand, the ts defects of ccr4delta and caf1delta mutants on glycerol medium at 37 degrees C (Ccr4 and Caf1/Pop2 are two other members of the CCR4 complex) could not be complemented by simultaneous overexpression of CBT1 and CDC14. CCR4 and CAF1 have been shown to play an essential role in activating the expression of genes for non-fermentative growth. Our results strongly suggest that, within the CCR4 complex, Dbf2 is directly involved in some mitochondrial function that depends on cytochrome b or on one of its main regulators, Cbt1. Therefore, Dbf2 may be required not only during mitosis but also during growth on non-fermentable carbon sources.

Carbon↗
PubMed1999

Maximal exercise capacity and peripheral skeletal muscle function following lung transplantation.

BACKGROUND: There have been many suggestions that diminished exercise capacity in patients that have undergone lung transplantation is due, in part, to peripheral muscle dysfunction, brought on by either detraining or immunosuppressive therapy. There is limited data quantifying skeletal muscle function in this population, especially in those more than 18 months post-procedure. The present study sought to quantitate skeletal muscle function and cardiopulmonary responses to graded exercise in 19 lung transplant recipients, 15 of which were mostly more than 18 months post-procedure. METHODS: Ten single- (SLT) and 9 double-lung transplantation (DLT) underwent anthropometric measures and performed expiratory spirometry, whole body plethysmography to assess lung volumes, static maximal mouth pressures to assess respiratory muscle strength, progressive exercise testing on a cycle ergometer (with cardiac output measurements being performed every second workload) and isokinetic cycling to assess peripheral muscle power and work capacity. RESULTS: The DLT group was younger than the SLT group (23.0 [21.0-32.0] vs 47.5 [43.0-55.0] median [interquartile range], p < .05) with no differences in height, weight, or BMI. Despite the DLT group having significantly better spirometric values (FEV1: 86% vs 56.5% median) and less airtrapping (RV/TLC: 30% vs 53.5%), both groups were equally limited in exercise capacity (Wmax)(38.0 percent predicted [30.0-65.0] vs 37.5 percent predicted [30.0-44.0], SLT vs DLT), leg power (76.1 percent predicted [53.8-81.4] vs 69.0 percent predicted [58.3-76.0]) and leg work capacity (63.3 percent predicted [34.7-66.8] vs 38.4 percent predicted [27.5-57.3]). This lack of difference in performance persisted when the analysis was limited to those more than 18 months post-procedure. Respiratory muscle strength was also not different for the two groups, and was within normal limits. Wmax was best correlated with leg work capacity (r = .84), but also with leg power, RV/TLC, FEV1 (r = .49, -.52, .58). When normalized for age, height, and sex, percent predicted Wmax only correlated with percent predicted leg work capacity (r = .58). Cardiac output was appropriate for the work performed. CONCLUSIONS: We conclude that peripheral skeletal muscle work capacity is reduced following lung transplantation and mostly responsible for the limitation of exercise performance. While the causes of muscular dysfunction have yet to be clarified, the preservation of respiratory muscle strength with the concomitant reduction in leg power and work capacity suggests that most of the muscular dysfunction post-transplantation is attributable to detraining.

Adult↗
PubMed1999

The Saccharomyces cerevisiae Cdc14 phosphatase is implicated in the structural organization of the nucleolus.

Cdc14, a dual-specificity protein phosphatase, has been previously implicated in triggering exit from mitosis in the yeast Saccharomyces cerevisiae. Using immunofluorescence microscopy and immunogold labeling, we demonstrate that a functional HA-tagged version of the phosphatase Cdc14 localizes to the nucleolus. Moreover, Cdc14-HA co-localized with the nucleolar NOP2 and GAR1 proteins. By immunofluorescence, Cdc14-HA was found in the nucleolus during most of the mitotic cell cycle, except during anaphase-telophase when it redistributed along the mitotic spindle. While this work was in progress, the same pattern of Cdc14 localization was described by others (Visintin et al, Nature 398 (1999) 818). Constitutive overexpression of CDC14 was toxic and led to cell cycle arrest of cells, mainly in G1. This correlated with the appearance of abnormal nuclear structures. A genetic search for suppressors of the lethality associated with CDC14 overexpression identified YJL076W. Because overproduction of Yj1076w buffered the toxic effect of Cdc14 overproduction, this suggested that it might be a substrate of Cdc14. This has indeed been found to be the case by others who recently described Yj1076w/Netl as a nucleolar protein that physically associates with Cdc14 (Shou et al, Cell 97 (1999) 233). The present data confirm several recently uncovered aspects of the regulation of Cdc14 localization and activity and suggest that the level of expression of CDC14 influences the structural organization of the nucleolus.

Cell Cycle↗
PubMed1998

The Cdc14 phosphatase is functionally associated with the Dbf2 protein kinase in Saccharomyces cerevisiae.

The Saccharomyces cerevisiae Cdc14 protein phosphatase and Dbf2 protein kinase have been implicated to act during late M phase, but their functions are not known. We report here that CDC14 is a low-copy suppressor of the dbf2-2 mutation at 37 degrees C. The kinase activity of Dbf2 accumulated at a high level, in vivo, during a cdc14 arrest and was also much higher in cdc14 mutant cells at the permissive temperature of growth, therefore in cycling mutant cells than in cycling wild-type cells. This correlated with the accumulation of the more slowly migrating form of Dbf2, previously shown to correspond to the hyperphosphorylated form of the protein. The finding that the dbf2-2 mutation could be rescued following overproduction of catalytically inactive forms of Cdc14 suggested that the control of Dbf2 activity by Cdc14 might be only indirect and independent of Cdc14 phosphatase activity. However, it was found that Cdc14 could form oligomers within the cell, thus leaving open the possibility that catalytically inactive Cdc14 might associate with wild-type Cdc14 and rescue dbf2-2 in a phosphatase-dependent manner. We confirmed that overexpression of CDC14 could rescue mutations in CDC15, which encodes another kinase also implicated to act in late M phase. Cells of a cdc15-2 dbf2-2 double mutant died at temperatures much lower than did either single mutant, whereas there was only a slight additive phenotype in the cdc14-1 dbf2-2 and cdc14-1 cdc15-2 double mutant cells. Finally, functional association between Cdc14 and Dbf2 (and also Cdc15) was confirmed by the finding that the cdc14, dbf2 and cdc15 mutations could be partially rescued by the addition of 1.2 M sorbitol to the culture medium. Our data are the first to demonstrate a functional link between Cdc14 and Dbf2 based on both biochemical and genetic information.

Cell Cycle↗
PubMed1998

Inhaled nitric oxide in acute respiratory distress syndrome: a pilot randomized controlled study.

This pilot randomized controlled clinical trial of patients with ARDS was implemented to study the impact of inhaled nitric oxide (inhNO) on lung function, morbidity, and mortality. Thirty patients with ARDS were randomly allocated to usual care or usual care plus inhNO. The optimal dose of inhNO was determined to be between 0.5 and 40 parts-per-million daily. All therapeutic interventions were standardized. ARDS resulted mainly from sepsis (25 of the 30). During the first 24 h, the hypoxia score increased greatly in patients treated with inhNO +70.4 mm Hg (+59%) versus +14.2 mm Hg (+9.3%) for the control group (p = 0.02), venous admixture decreased from 25.7 to 15.2% in the inhNO group, and from only 19.4 to 14.9% in the control group (p = 0.05). After the first day of therapy no further beneficial effect of inhNO was detected. Forty percent of the patients treated with inhNO were alive and weaned from mechanical ventilation within 30 d after randomization compared with 33.3% in the control group (p = 0.83). The 30-d mortality rate was similar in the two groups; most deaths (11 of 17) were due to multiple organ dysfunction syndrome. This study shows that inhNO, in this population, may improve gas exchange but does not affect mortality.

Administration, Inhalation↗
PubMed1997

Effect of estradiol on the induction of porphyria by hexachlorobenzene in the rat.

Hexachlorobenzene (HCB) is porphyrinogenic in adult female but not in male rats. This study aimed to assess the role of 17beta-estradiol in the induction of porphyria by HCB in both sexes by adding or removing the hormone. Groups of intact females, ovariectomized females (Ova), castrated males (Cas), and Cas receiving 17beta-estradiol (4 mg/kg, i.m., once a week beginning 2 weeks prior to HCB) were given five consecutive daily doses of HCB (100 mg/kg in corn oil, p.o.). Porphyria was assessed by urinary uroporphyrin excretion measured at days 16, 31, 38, 45, 52, 59, and 87. The percentage of porphyric rats in intact females increased from day 31 (58%) to day 87 (75%), whereas none of the Ova or Cas rats responded. However, administration of estradiol (days 120-169) and another sequence of HCB doses (days 134-138) to the same Ova rats caused porphyria (50% at day 186). Cas rats given estradiol also developed porphyria (43 and 86% on days 31 and 87, respectively). HCB-treated Ova rats given two doses of estradiol at either days 1 and 8 or days 22 and 29 developed a porphyria of similar magnitude (day 52). The role of estradiol cannot be explained by a reduction of pentachlorothiophenol formation, a putative detoxication pathway. Overall, results show that both sexes have the ability to respond to HCB when 17beta-estradiol is present and suggest that the sexual dimorphism in HCB-induced porphyria in the rat is related to the hormonal status.

Animals↗
PubMed1997

Stn1, a new Saccharomyces cerevisiae protein, is implicated in telomere size regulation in association with Cdc13.

We have isolated STN1, an essential Saccharomyces cerevisiae gene, as a suppressor of the cdc13-1 mutation. A synthetic lethal interaction between a temperature-sensitive mutant allele of STN1, stn1-13, and cdc13-1 was observed. Stn1 and Cdc13 proteins displayed a physical interaction by two-hybrid analysis. As shown previously for cdc13-1, stn1-13 cells at the restrictive temperature accumulate single-stranded DNA in subtelomeric regions of the chromosomes, but to a lesser extent than cdc13-1 cells. In addition, both Cdc13 and Stn1 were found to be involved in the regulation of telomere length, mutations in STN1 or CDC13 conferring an increase in telomere size. Loss of Stn1 function activated the RAD9 and MEC3 G2/M checkpoints, therefore confirming that DNA damage is generated. We propose that Stn1 functions in telomere metabolism during late S phase in cooperation with Cdc13.

Cell Cycle↗
PubMed1997

Studies on the mechanism of uroporphyrinogen decarboxylase inhibition in hexachlorobenzene-induced porphyria in the female rat.

Hexachlorobenzene (HCB)-induced porphyria occurs in female, but not male, rats after a delay of 35 days following HCB treatment. Uroporphyrinogen decarboxylase (UROD) inhibition has been proposed as a primary causative event. To determine whether there also exists a delay phase and a sexual dimorphism for UROD inhibition, groups of male and female rats were given HCB (100 mg/kg/day) from Days 1 to 5. Hepatic uroporphyrin III was markedly increased only after Day 33. Liver cytosol UROD activity in HCB-treated female rats with porphyria at Days 33, 40, 47, 54, and 100 was decreased by over 70% compared to concurrent control, whereas treated male rats as well as nonporphyric female rats had UROD activity comparable to control levels at Days 6, 12, 19, 26, 33, 40, 47, and 54. Level of immunoreactive UROD in cytosol of porphyric rats was not modified by HCB. No gender-related differences in liver cytosol radiolabel level ([14C]HCB given as the fifth dose) were found at Days 6 and 30. Chromatography of liver cytosol showed nonspecific binding of radiolabel to proteins for males, porphyric and nonporphyric females, and loss of UROD activity did not correlate with the amount of radiolabel in the UROD-containing fractions. Thus, the gender-specific decrease in UROD activity observed when porphyria develops in female rats (delay of about 4 weeks), as well as the persistence of low activity and porphyria for months, suggests that UROD inhibition was causally related to porphyria.

Analysis of Variance↗
PubMed1997

Extra-pulmonary effects of inhaled nitric oxide in swine with and without phenylephrine.

We have compared the effects of inhaled nitric oxide (iNO) and i.v. nitroglycerin (ivGTN) on the haemodynamic response to phenylephrine-induced hypertension (PEHT) in anaesthetized pigs. PEHT did not change either pulmonary vascular resistance or gas exchange throughout all experiments. Both treatments lowered pulmonary arterial pressure to the same extent (-12.4% iNO; -13.7% ivGTN) and passively via an effect on left atrial pressure (-26.3% iNO; -31.4% ivGTN). Both treatments failed to reverse the decrease in renal blood flow (RBFc) induced by PEHT, but both increased urinary flow (UF) (+128% iNO; +148% ivGTN). IvGTN significantly increased plasma concentrations of nitrite and nitrate during (+22.7% arterial blood; +26.2% venous blood) and beyond the period of infusion (iNO: +6.4% and +4.9%, respectively). In four control pigs (no PEHT), iNO markedly increased RBFc (+109%), glomerular filtration rate (+72.5%) and UF (+68.7%). We conclude that iNO may have direct cardiac and renal effects, probably via intervention of NO carrier forms such as S-nitroso compounds.

Administration, Inhalation↗
PubMed1996

Assessment of the role of glutathione conjugation in the protection afforded by anethol dithiolthione against hexachloro-1,3-butadiene-induced nephrotoxicity.

Administration of anethol dithiolthione (ADT) to rodents can afford protection against some chemically induced toxicities. The aim of the present study was to assess the effects of ADT on hexachloro-1,3-butadiene (HCBD)-induced nephrotoxicity in the rat and to determine the mechanism of its action. Renal integrity was evaluated by measuring urinary excretion of glucose, protein, and gamma-glutamyl transpeptidase and by histological evaluation. A 3-day pretreatment with ADT (300 mg/kg/day) protected against the toxicity of various doses of HCBD (ranging from 15.6 to 62.5 mg/kg). The pretreatment increased (1.4-fold) the nonprotein sulfhydryl content (NPSH) of the liver. However, it did not modify the biliary excretion of radiolabeled materials in [14C]HCBD- treated (20 mg/kg) rats, nor that of the bioactivated HCBD metabolite, S-(1,2,3,4,4-pentachloro-1,3-butadienyl)-glutathione (PCBG). Moreover, ADT pretreatment protected rats against the nephrotoxicity induced by PCBG (20 mg/kg) itself. The extent of covalent binding to kidney proteins of [14C]HCBD-derived metabolites was not modified by pretreatment with ADT. Incubation of rat kidney cortical slices in a medium containing 0.1 mM of the nephrotoxic glutathione (PCBG) or cysteine (PCBC, S-(1,2,3,4,4-pentachloro-1,3-butadienyl)-L-cysteine) conjugates of HCBD for 30 min resulted in a 75% reduction in the slice/medium ratio of p-aminohipurate (PAH) compared to that seen in controls. When the cortical slices were incubated with ADT (30 min, 0.2 mM) prior to incubation with the nephrotoxic conjugates, the reduction was only 33%. Neither the in vitro nor the in vivo treatments did modify the activity of renal cytosolic beta-lyase; however, the latter treatment caused an increase in NPSH content. A 15-min incubation of kidney cortical slices with glutathione (10 mM) resulted in a 5-fold increase of NPSH, but failed to prevent the reduction in PAH uptake caused by PCBG and PCBC. Altogether, the in vivo and renal slice data suggest that ADT protects rats against HCBD-induced nephrotoxicity by a mechanism that does not involve the modulation of HCBD conjugation with liver GSH, nor the modulation of the kidney NPSH level and beta-lyase activity. The mechanism of protection conferred to rats by an ADT pretreatment against HCBD-induced nephrotoxicity appears to take place in the kidney at a step beyond the generation of ultimate toxic metabolites derived from PCBC.

Anethole Trithione↗