Biomedical subjects

J M Peters

Publications and source records attributed to J M Peters.

At least 37 records · Page 2Linked to original sources

PubMed2001

Splitting the chromosome: cutting the ties that bind sister chromatids.

In eukaryotic cells, replicated DNA molecules remain physically connected from their synthesis in S phase until they are separated during anaphase. This phenomenon, called sister chromatid cohesion, is essential for the temporal separation of DNA replication and mitosis and for the equal separation of the duplicated genome. Recent work has identified a number of chromosomal proteins required for cohesion. In this review we discuss how these proteins may connect sister chromatids and how they are removed from chromosomes to allow sister chromatid separation at the onset of anaphase.

Animals↗

PubMed2001

Three-dimensional structure of the anaphase-promoting complex.

The anaphase-promoting complex (APC) is a cell cycle-regulated ubiquitin-protein ligase, composed of at least 11 subunits, that controls progression through mitosis and G1. Using cryo-electron microscopy and angular reconstitution, we have obtained a three-dimensional model of the human APC at a resolution of 24 A. The APC has a complex asymmetric structure 140 A x 140 A x 135 A in size, in which an outer protein wall surrounds a large inner cavity. We discuss the possibility that this cavity represents a reaction chamber in which ubiquitination reactions take place, analogous to the inner cavities formed by other protein machines such as the 26S proteasome and chaperone complexes. This cage hypothesis could help to explain the great subunit complexity of the APC.

Anaphase-Promoting Complex-Cyclosome↗

PubMed2001

Scc1/Rad21/Mcd1 is required for sister chromatid cohesion and kinetochore function in vertebrate cells.

Proteolytic cleavage of the cohesin subunit Scc1 is a consistent feature of anaphase onset, although temporal differences exist between eukaryotes in cohesin loss from chromosome arms, as distinct from centromeres. We describe the effects of genetic deletion of Scc1 in chicken DT40 cells. Scc1 loss caused premature sister chromatid separation but did not disrupt chromosome condensation. Scc1 mutants showed defective repair of spontaneous and induced DNA damage. Scc1-deficient cells frequently failed to complete metaphase chromosome alignment and showed chromosome segregation defects, suggesting aberrant kinetochore function. Notably, the chromosome passenger INCENP did not localize normally to centromeres, while the constitutive kinetochore proteins CENP-C and CENP-H behaved normally. These results suggest a role for Scc1 in mitotic regulation, along with cohesion.

Animals↗

PubMed2001

Crystal structure of the APC10/DOC1 subunit of the human anaphase-promoting complex.

The anaphase-promoting complex (APC), or cyclosome, is a cell cycle-regulated ubiquitin ligase that controls progression through mitosis and the G1 phase of the cell cycle. The APC is composed of at least 11 subunits; no structure has been determined for any of these subunits. The subunit APC10/DOC1, a one-domain protein consisting of 185 amino acids, has a conserved core (residues 22-161) that is homologous to domains found in several other putative ubiquitin ligases and, therefore, may play a role in ubiquitination reactions. Here we report the crystal structure of human APC10 at 1.6 A resolution. The core of the protein is formed by a beta-sandwich that adopts a jellyroll fold. Unexpectedly, this structure is highly similar to ligand-binding domains of several bacterial and eukaryotic proteins, such as galactose oxidase and coagulation factor Va, raising the possibility that APC10 may function by binding a yet unidentified ligand. We further provide biochemical evidence that the C-terminus of APC10 binds to CDC27/APC3, an APC subunit that contains multiple tetratrico peptide repeats.

Amino Acid Sequence↗

PubMed2001

Clumsiness, dyspraxia and developmental co-ordination disorder: how do health and educational professionals in the UK define the terms?

At the turn of the century, the idea that there might be a discrete childhood syndrome, which had 'clumsiness' of movement as its defining symptom, began to emerge. Since then numerous labels have been applied to the syndrome. In spite of recent attempts to standardise the terminology used, variation continues to compromise inter-professional communication and interpretation of research. The aim of this study was to determine how the three terms 'Clumsy', 'Dyspraxia' and 'Developmental Co-ordination Disorder (DCD)' are viewed by health and educational professionals in the UK. Two hundred and thirty-four adults (57% from the health professions and 43% from education) provided a written definition of each term. Content analysis of the 702 definitions was used to determine: (1) the extent to which the terms were familiar/acceptable to the respondents; and (2) to capture differences in the meaning of the term being defined. The results indicated that the terms 'DCD' and 'Dyspraxia' were less familiar than the term 'clumsy' which was, however, least acceptable. Amongst those professionals who were familiar with all three terms, there was general agreement that all were used to describe some sort of overall movement difficulty. Beyond that point, divergence of understanding and inter-professional differences in emphasis emerged. The implications of these differences for clinical and educational practice, research and policy making are discussed.

Adult↗

PubMed2001

Evidence that reduction of hepatocyte growth factor (HGF) is not required for peroxisome proliferator-induced hepatocyte proliferation.

The mechanisms underlying peroxisome proliferator-induced hepatocarcinogenesis are not understood. Because of the uncertainty of human cancer risk associated with peroxisome proliferators, delineating the mechanisms of carcinogenesis by these agents is of great interest. Alterations in liver growth factors were postulated to contribute to the carcinogenic effect of peroxisome proliferators. Administration of these compounds to rodents results in down-regulation of hepatocyte growth factor (HGF) and supplementing culture medium with HGF is reported to suppress cell proliferation of preneoplastic and neoplastic cells from WY-14,643-treated livers. Combined, these observations suggest that reduced levels of hepatic HGF contribute to the mechanisms underlying peroxisome proliferator-induced hepatocarcinogenesis. To determine if HGF can prevent the effects of peroxisome proliferators in liver, the short-term influence of WY-14,643 in two different lines of HGF transgenic mice was examined. Mice were fed either a control diet or one containing 0.1% WY-14-643 for one week. Hepatomegaly was found in both HGF transgenic mouse lines fed WY-14,643 compared with controls. Additionally, hepatic expression of typical mRNA markers of peroxisome proliferation including those encoding peroxisomal fatty acid metabolizing enzymes and cell cycle control proteins were all significantly elevated in HGF transgenic mice fed WY-14,643 compared with controls. Down-regulation of HGF was found to be dependent on PPARalpha since lower levels of HGF mRNA and protein were observed in wild-type mice fed WY-14,643 for 1 week and not in similarly treated PPARalpha-null mice. These results demonstrate that the early increase in hepatic mRNAs associated with peroxisome and cell proliferation induced by WY-14,643 treatment can not be prevented by overexpression of HGF in vivo.

Animals↗

PubMed2001

The effects of ambient air pollution on school absenteeism due to respiratory illnesses.

We investigated the relations between ozone (O3), nitrogen dioxide (NO2), and respirable particles less than 10 microm in diameter (PM10) and school absenteeism in a cohort of 4th-grade school children who resided in 12 southern California communities. An active surveillance system ascertained the numbers and types of absences during the first 6 months of 1996. Pollutants were measured hourly at central-site monitors in each of the 12 communities. To examine acute effects of air pollution on absence rates, we fitted a two-stage time-series model to the absence count data that included distributed lag effects of exposure adjusted for long-term pollutant levels. Short-term change in O3, but not NO2 or PM10, was associated with a substantial increase in school absences from both upper and lower respiratory illness. An increase of 20 ppb of O3 was associated with an increase of 62.9% [95% confidence interval (95% CI) = 18.4-124.1%] for illness-related absence rates, 82.9% (95% CI = 3.9-222.0%) for respiratory illnesses, 45.1% (95% CI = 21.3-73.7%) for upper respiratory illnesses, and 173.9% (95% CI = 91.3-292.3%) for lower respiratory illnesses with wet cough. The short-term effects of a 20-ppb change of O3 on illness-related absenteeism were larger in communities with lower long-term average PM10 [223.5% (95% CI = 90.4-449.7)] compared with communities with high average levels [38.1% (95% CI = 8.5-75.8)]. Increased school absenteeism from O3 exposure in children is an important adverse effect of ambient air pollution worthy of public policy consideration.

Absenteeism↗

PubMed2001

Family history and the risk of early-onset persistent, early-onset transient, and late-onset asthma.

Family history of asthma and allergies strongly influences asthma risk in children, but the association may differ for early-onset persistent, early-onset transient, and late-onset asthma. We analyzed the relation between family history and these types of asthma using cross-sectional data from a school-based study of 5,046 Southern California children. Parental and/or sibling history of asthma and allergy were generally more strongly associated with early-onset persistent asthma compared with early-onset transient or late-onset asthma. For children with two asthmatic parents relative to those with none, the prevalence ratio for early-onset persistent asthma was 12.1 [95% confidence interval (CI) = 7.91-18.7] compared with 7.51 (95% CI = 2.62-21.5) for early-onset transient asthma and 5.38 (95% CI = 3.40-8.50) for late-onset asthma. Maternal smoking in pregnancy was predominantly related to the risk of early-onset persistent asthma in the presence of parental history of allergy and asthma, and the joint effects were more than additive (interaction contrast ratio = 3.10, 95% CI = 1.45-4.75). Our results confirm earlier data that parental history of asthma and allergy is most strongly associated with early-onset persistent asthma and suggest that among genetically predisposed children, an early-life environmental exposure, maternal smoking during pregnancy, favors the development of early-onset asthma that persists into later early childhood.

Adolescent↗

PubMed2001

Phthalates rapidly increase production of reactive oxygen species in vivo: role of Kupffer cells.

The role of oxidants in the mechanism of tumor promotion by peroxisome proliferators remains controversial. The idea that induction of acyl-coenzyme A oxidase leads to increased production of H(2)O(2), which damages DNA, seems unlikely; still, free radicals might be important in signaling in specialized cell types such as Kupffer cells, which produce mitogens. Because hard evidence for increased oxidant production in vivo after treatment with peroxisome proliferators is lacking, the spin-trapping technique and electron spin resonance spectroscopy were used. Rats were given di(2-ethylhexyl) phthalate (DEHP) acutely. The spin trapping agent alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone was also given and bile samples were collected for 4 h. Under these conditions, the intensity of the six-line radical adduct signal increased to a maximum value of 2.5-fold 2 h after administration of DEHP, before peroxisomal oxidases were induced. Furthermore, DEHP given with [(13)C(2)]dimethyl sulfoxide produced a 12-line electron spin resonance spectrum, providing evidence that DEHP stimulates (*)OH radical formation in vivo. Furthermore, when rats were pretreated with dietary glycine, which inactivates Kupffer cells, DEHP did not increase radical signals. Moreover, similar treatments were performed in knockout mice deficient in NADPH oxidase (p47(phox) subunit). Importantly, DEHP increased oxidant production in wild-type but not in NADPH oxidase-deficient mice. These data provide evidence for the hypothesis that the molecular source of free radicals induced by peroxisome proliferators is NADPH oxidase in Kupffer cells. On the contrary, radical adduct formation was not affected in peroxisome proliferator-activated receptor alpha knockout mice. These observations represent the first direct, in vivo evidence that phthalates increase free radicals in liver before peroxisomal oxidases are induced.

Animals↗

PubMed2001

A conserved cyclin-binding domain determines functional interplay between anaphase-promoting complex-Cdh1 and cyclin A-Cdk2 during cell cycle progression.

Periodic activity of the anaphase-promoting complex (APC) ubiquitin ligase determines progression through multiple cell cycle transitions by targeting cell cycle regulators for destruction. At the G(1)/S transition, phosphorylation-dependent dissociation of the Cdh1-activating subunit inhibits the APC, allowing stabilization of proteins required for subsequent cell cycle progression. Cyclin-dependent kinases (CDKs) that initiate and maintain Cdh1 phosphorylation have been identified. However, the issue of which cyclin-CDK complexes are involved has been a matter of debate, and the mechanism of how cyclin-CDKs interact with APC subunits remains unresolved. Here we substantiate the evidence that mammalian cyclin A-Cdk2 prevents unscheduled APC reactivation during S phase by demonstrating its periodic interaction with Cdh1 at the level of endogenous proteins. Moreover, we identified a conserved cyclin-binding motif within the Cdh1 WD-40 domain and show that its disruption abolished the Cdh1-cyclin A-Cdk2 interaction, eliminated Cdh1-associated histone H1 kinase activity, and impaired Cdh1 phosphorylation by cyclin A-Cdk2 in vitro and in vivo. Overexpression of cyclin binding-deficient Cdh1 stabilized the APC-Cdh1 interaction and induced prolonged cell cycle arrest at the G(1)/S transition. Conversely, cyclin binding-deficient Cdh1 lost its capability to support APC-dependent proteolysis of cyclin A but not that of other APC substrates such as cyclin B and securin Pds1. Collectively, these data provide a mechanistic explanation for the mutual functional interplay between cyclin A-Cdk2 and APC-Cdh1 and the first evidence that Cdh1 may activate the APC by binding specific substrates.

Amino Acid Sequence↗

PubMed2001

Effects of maternal smoking during pregnancy and environmental tobacco smoke on asthma and wheezing in children.

The effects of maternal smoking during pregnancy and childhood environmental tobacco smoke (ETS) exposure on asthma and wheezing were investigated in 5,762 school-aged children residing in 12 Southern California communities. Responses to a self- administered questionnaire completed by parents of 4th, 7th, and 10th grade students were used to ascertain children with wheezing or physician-diagnosed asthma. Lifetime household exposures to tobacco smoke were assessed using responses about past and current smoking histories of household members and any history of maternal smoking during pregnancy. Logistic regression models were fitted to cross-sectional data to estimate the effects of in utero exposure to maternal smoking and previous and current ETS exposure on the prevalence of wheezing and physician-diagnosed asthma. In utero exposure to maternal smoking without subsequent postnatal ETS exposure was associated with increased prevalence of physician-diagnosed asthma (OR, 1.8; 95% CI, 1.1 to 2.9), asthma with current symptoms (OR, 2.3; 95% CI, 1.3 to 4.0), asthma requiring medication use in the previous 12 mo (OR, 2.1; 95% CI, 1.2 to 3.6), lifetime history of wheezing (OR, 1.8; 95% CI, 1.2 to 2.6), current wheezing with colds (OR, 2.1; 95% CI, 1.3 to 3.4) and without colds (OR, 2.5; 95% CI, 1.4 to 4.4), persistent wheezing (OR, 3.1; 95% CI, 1.6 to 6.1), wheezing with exercise (OR, 2.4; 95% CI; 1.3 to 4.3), attacks of wheezing causing shortness of breath (OR, 2.4; 95% CI, 1.3 to 4.4) or awakening at night in the previous 12 mo (OR, 3.2; 95% CI, 1.7 to 5.8), and wheezing requiring medication (OR, 2.1; 95% CI, 1.2 to 3.7) or emergency room visits during the previous year (OR, 3.4; 95% CI, 1.4 to 7.8). In contrast, current and previous ETS exposure was not associated with asthma prevalence, but was consistently associated with subcategories of wheezing. Current ETS exposure was associated with lifetime wheezing (OR, 1.3; 95% CI, 1.1 to 1.5), current wheezing with colds (OR, 1.6; 95% CI, 1.3 to 2.0) and without colds (OR, 1.5; 95% CI, 1.1 to 1.9), wheezing with exercise (OR, 1.7; 95% CI, 1.3 to 2.2), attacks of wheezing causing shortness of breath (OR, 1.6; 95% CI, 1.2 to 2.1) or awakening at night (OR, 1.5; 95% CI, 1.1 to 2.0), and wheezing requiring medication (OR, 1.4; 95% CI, 1.1 to 1.8) or emergency room visits within the previous year (OR, 1.9; 95% CI, 1.2 to 3.0). The effects of current ETS exposure on subcategories of wheezing were most pronounced among children exposed to two or more smokers and remained significant after adjusting for maternal smoking during pregnancy. We conclude that maternal smoking during pregnancy increases the occurrence of physician-diagnosed asthma and wheezing during childhood. In contrast, current ETS exposure is associated with wheezing, but not physician-diagnosed asthma. Taken together, our findings support the hypothesis that ETS operates as a cofactor with other insults such as intercurrent infections as a trigger of wheezing attacks, rather than as a factor that induces asthma, whereas in utero exposure acts to increase physician-diagnosed asthma

Adolescent↗

PubMed2001

PPARalpha-dependent induction of liver microsomal esterification of estradiol and testosterone by a prototypical peroxisome proliferator.

Fatty acyl-coenzyme A:estradiol acyltransferase in liver microsomes catalyzes the formation of estradiol fatty acid esters. These estrogen esters are extremely lipophilic and have prolonged hormonal activity because they are slowly metabolized and slowly release estradiol. Our previous studies showed that treatment of female rats with clofibrate or gemfibrozil (peroxisome proliferators commonly used as hypolipidemic drugs) markedly stimulated the liver microsomal esterification of estradiol. Although clofibrate administration is a potent inducer of liver microsomal fatty acyl-coenzyme A:estradiol acyltransferase in rats, it is a poor inducer in mice. In contrast to these observations, Wy-14,643 (an exceptionally potent prototypical peroxisome proliferator) is a strong inducer of fatty acyl-coenzyme A:estradiol acyltransferase in mice. To explore the role of PPARalpha in the induction of fatty acyl-coenzyme A:estradiol acyltransferase and fatty acyl-coenzyme A:testosterone acyltransferase activities by peroxisome proliferators, we fed 0.1% Wy-14,643 to female wild-type and PPARalpha null mice for 11 d. The liver microsomal acyl-coenzyme A:estradiol acyltransferase and acyl-coenzyme A:testosterone acyltransferase activities were increased 4- to 5-fold in wild-type mice fed Wy-14,643, but no increase was observed in null mice. These results demonstrate that induction of acyl-coenzyme A:estradiol acyltransferase and acyl-coenzyme A:testosterone acyltransferase activities by a prototypical peroxisome proliferator is dependent on PPARalpha.

Acyltransferases↗

PubMed2001

PPAR-alpha-null mice are protected from high-fat diet-induced insulin resistance.

Peroxisome proliferator-activated receptor (PPAR)-alpha controls the expression of genes involved in lipid metabolism. PPAR-alpha furthermore participates to maintain blood glucose during acute metabolic stress, as shown in PPAR-alpha-null mice, which develop severe hypoglycemia when fasted. Here, we assessed a potential role for PPAR-alpha in glucose homeostasis in response to long-term high-fat feeding. When subjected to this nutritional challenge, PPAR-alpha-null mice remained normoglycemic and normoinsulinemic, whereas wild-type mice became hyperinsulinemic (190%; P < 0.05) and slightly hyperglycemic (120%; NS). Insulin tolerance tests (ITTs) and glucose tolerance tests (GTTs) were performed to evaluate insulin resistance (IR). Under standard diet, the response to both tests was similar in wild-type and PPAR-alpha-null mice. Under high-fat diet, however, the efficiency of insulin in ITT was reduced and the amount of hyperglycemia in GTT was increased only in wild-type and not in PPAR-alpha-null mice. The IR index, calculated as the product of the areas under glucose and insulin curves in GTT, increased fourfold in high-fat-fed wild-type mice, whereas it remained unchanged in PPAR-alpha-null mice. In contrast, PPAR-alpha deficiency allowed the twofold rise in adiposity and blood leptin levels elicited by the diet. Thus, the absence of PPAR-alpha dissociates IR from high-fat diet-induced increase in adiposity. The effects of PPAR-alpha deficiency on glucose homeostasis seem not to occur via the pancreas, because glucose-stimulated insulin secretion of islets was not influenced by the PPAR-alpha genotype. These data suggest that PPAR-alpha plays a role for the development of IR in response to a Western-type high-fat diet.

1-Methyl-3-isobutylxanthine↗

PubMed2001

Molecular cloning and regulation of expression of two novel mouse CYP4F genes: expression in peroxisome proliferator-activated receptor alpha-deficient mice upon lipopolysaccharide and clofibrate challenges.

Cytochrome P450 4F isoforms catalyze the hydroxylation of eicosanoids such as leukotriene B(4), prostaglandins, and lipoxins as well as hydroxyeicosatetraenoic acids. In the present study, we report the molecular cloning of two novel mouse CYP4F isoforms, CYP4F15 and CYP4F16. Sequence comparison showed that CYP4F15 has 93.5% homology to CYP4F4 and CYP4F16 has 90.8% homology to CYP4F5, therefore they are the orthologs for rat CYP4F4 and CYP4F5, respectively. Both isoforms are expressed in liver and also in extrahepatic tissues but the patterns of expression are slightly different. To elucidate further the regulation and regulatory mechanism of the two isoforms, renal and hepatic CYP4F15 and CYP4F16 expression were analyzed using wild-type (SV/129) mice and peroxisome proliferator-activated receptor (PPAR) alpha null mice with or without challenge by bacterial endotoxin (LPS) or clofibrate. Renal expression of CYP4F15 was induced by LPS and clofibrate in (+/+) mice, and these effects were absent in the (-/-) mice. Renal expression of CYP4F16 was not affected by LPS or clofibrate in (+/+) or (-/-) mice. In contrast, hepatic expression of CYP4F15 and CYP4F16 was significantly reduced by LPS-treatment in (+/+) mice. A lesser reduction was also seen in the (-/-) mice, suggesting that PPARalpha is partially responsible for this down-regulation. Clofibrate treatment caused the reduction of hepatic CYP4F16 expression and this effect was not dependent on PPARalpha. Clofibrate treatment had no effect on hepatic CYP4F15 expression. Together, our data indicate that CYP4Fs are regulated in an isoform-specific, tissue-specific, and species-specific manner.

Amino Acid Sequence↗

PubMed2001

Peroxisome proliferator-activated receptors (PPAR) and the mitochondrial aldehyde dehydrogenase (ALDH2) promoter in vitro and in vivo.

BACKGROUND: The aldehyde dehydrogenase 2 (ALDH2) promoter contains a nuclear receptor response element (NRRE) that represents an overlapping direct repeat-1 (DR-1) and -5 (DR-5) element. Because DR-1 elements are preferred binding sites for peroxisome proliferator-activated receptors (PPARs), we tested the hypothesis that PPARs regulate ALDH2 expression. METHODS: We examined the ability of PPAR isoforms to bind to the ALDH2 NRRE in electrophoretic mobility shift assays, their ability to activate the transcription of promoter-reporter constructs containing this NRRE, the effect of PPAR ligands on ALDH2 expression in liver, and the role of the PPARalpha on the expression of ALDH2 by using PPARalpha-null mice. RESULTS: In vitro translated PPARs bound the ALDH NRRE with high affinity. Mutation of the NRRE indicated that binding was mediated by the DR-1 element. Cotransfection of PPAR expression plasmids showed that PPARalpha had no effect on expression of heterologous promoter constructs containing the NRRE. PPARgamma slightly induced expression, whereas PPARdelta repressed basal activity of the promoter and blocked induction by hepatocyte nuclear factor 4. Treatment of rats with the PPAR ligand clofibrate repressed expression of ALDH2 in rats fed either stock rodent chow or a low-protein diet. Consistent with the transfection data, expression of ALDH2 protein was not different in PPARalpha-null mice. Treatment of the mice with the PPARalpha agonist WY14643 slightly decreased the level of ALDH2 protein in both wild-type and PPARalpha-null mice, suggesting that the effect of WY14643 was not mediated by the receptor. CONCLUSIONS: These data indicate that ALDH2 is not part of the battery of lipid metabolizing enzymes and proteins regulated by PPARalpha

Aldehyde Dehydrogenase↗

PubMed2000

Characterization of vertebrate cohesin complexes and their regulation in prophase.

In eukaryotes, sister chromatids remain connected from the time of their synthesis until they are separated in anaphase. This cohesion depends on a complex of proteins called cohesins. In budding yeast, the anaphase-promoting complex (APC) pathway initiates anaphase by removing cohesins from chromosomes. In vertebrates, cohesins dissociate from chromosomes already in prophase. To study their mitotic regulation we have purified two 14S cohesin complexes from human cells. Both complexes contain SMC1, SMC3, SCC1, and either one of the yeast Scc3p orthologs SA1 and SA2. SA1 is also a subunit of 14S cohesin in Xenopus. These complexes interact with PDS5, a protein whose fungal orthologs have been implicated in chromosome cohesion, condensation, and recombination. The bulk of SA1- and SA2-containing complexes and PDS5 are chromatin-associated until they become soluble from prophase to telophase. Reconstitution of this process in mitotic Xenopus extracts shows that cohesin dissociation does neither depend on cyclin B proteolysis nor on the presence of the APC. Cohesins can also dissociate from chromatin in the absence of cyclin-dependent kinase 1 activity. These results suggest that vertebrate cohesins are regulated by a novel prophase pathway which is distinct from the APC pathway that controls cohesins in yeast.

Amino Acid Sequence↗

PubMed2000

Two distinct pathways remove mammalian cohesin from chromosome arms in prophase and from centromeres in anaphase.

In yeast, anaphase depends on cohesin cleavage. How anaphase is controlled in vertebrates is unknown because their cohesins dissociate from chromosomes before anaphase. We show that residual amounts of the cohesin SCC1 remain associated with human centromeres until the onset of anaphase when a similarly small amount of SCC1 is cleaved. In Xenopus extracts, SCC1 cleavage depends on the anaphase-promoting complex and separin. Separin immunoprecipitates are sufficient to cleave SCC1, indicating that separin is associated with a protease activity. Separin activation coincides with securin destruction and partial separin cleavage, suggesting that several mechanisms regulate separin activity. We propose that in vertebrates, a cleavage-independent pathway removes cohesin from chromosome arms during prophase, whereas a separin-dependent pathway cleaves centromeric cohesin at the metaphase-anaphase transition.

Anaphase↗

PubMed2000

Peroxisome proliferator-activated receptor alpha is not rate-limiting for the lipoprotein-lowering action of fish oil.

Similar to fibrate hypolipidemic drugs, long chain polyunsaturated fatty acids contained in fish oil are activators of peroxisome proliferator-activated receptor alpha (PPARalpha). The goal of this study was to assess the contribution of PPARalpha in mediating the effect of fish oil on plasma lipid, lipoprotein, and apolipoprotein levels. To this end, PPARalpha-deficient mice and wild-type littermates were fed isocaloric fish oil or coconut oil diets, the content of which varied reciprocally between 0, 3, 7, and 10% for 1 week. In both wild-type and PPARalpha-deficient mice, fish oil feeding was associated with a dose-dependent decrease in triglycerides, cholesterol, and phospholipids associated with lower levels of very low density lipoprotein (VLDL) triglycerides and high density lipoprotein (HDL) cholesterol. The lowering of triglycerides and VLDL triglycerides was associated with a significant decrease of plasma apoC-III in both genotypes. Fish oil treatment did not influence hepatic apoC-III mRNA levels in either genotype indicating that apoC-III is not under transcriptional control by fish oil. The lowering of HDL cholesterol observed in both genotypes was associated with reduced plasma apoA-II without changes in liver apoA-II mRNA levels. In contrast, plasma apoA-I and liver apoA-I mRNA levels were decreased in wild-type but not in PPARalpha-deficient mice after fish oil feeding indicating that PPARalpha contributes to the effect of fish oil on apoA-I gene expression. In conclusion, PPARalpha is not rate-limiting for fish oil to exert its triglyceride- and HDL-lowering action. Furthermore, PPARalpha mediates, at least partly, the decrease of apoA-I after fish oil treatment, whereas apoC-III and apoA-II levels are affected in a PPARalpha-independent manner. Altogether, these results show major molecular differences in action between fibrates and fish oil providing a molecular rationale for combination treatment with these compounds.

Acyl-CoA Oxidase↗