Biomedical subjects

A Borgne

Publications and source records attributed to A Borgne.

8 recordsLinked to original sources

PubMed2003

[How can we help pregnant women stop smoking?].

Smoking is a behavior maintained and enhanced by nicotine-induced dependence. Despite awareness and knowledge of the associated health risks many smokers find it considerably difficult to quit. Nicotine withdrawal symptoms and undesirable effects such as depression and weight gain serve as justification for the numerous unsuccessful attempts in smoking cessation. Yet, we have now come to the end of empiricism. Treatments that have been shown to work exist and international evidence-based recommendations for cessation interventions have been established: brief advice, nicotine replacement therapy and behavioral and cognitive therapies. Measuring nicotine dependence using the Fagerström test helps to define the therapeutic strategy. Blood cotinine level can be measured during pregnancy. It is obvious that therapies can only work for smokers who are motivated to stop smoking. Before reaching the decision to quit, the smoker goes through a process during the course of which the role of information and advice from health professionals are paramount. When they became pregnant, young women are not necessary ready to quit. For many of them, pregnancy is sufficient motivation enabling them to stop smoking, but for thirty percent of them, probably the most dependent, it would be very difficult to stop without a specific program of help.

Behavior Therapy↗

PubMed2002

[Smoking cessation: practice guidelines].

Smoking is a habit sustained and amplified by dependency on nicotine. Despite knowing the risks to their health, smokers have great difficulty in stopping. The syndrome of nicotine withdrawal and the related complications when stopping smoking: depression, weight gain, are adequate justifications of the many failures to stop smoking. However, we have now come out of the empiricism, effective treatment is available and scientifically validated international recommendations have been established. They involve: the practice of minimal advice which consists of questioning every patient about smoking habits and encouraging them to stop; the treatments of nicotine substitution, patch, chewing gum, tablets or inhaler, used at effective dosage and sometimes in association with each other; more recently, Bupropion (Zyban, LP), a psychotropic inhibitor of Dobutamine and Noradrenalin recapture; behavioural and cognitive therapies, alone or in association with pharmacological therapy. The measurement of the score of tobacco dependency with the Fagerström test enables definition of a therapeutic strategy. Of course, these treatments are only effective in smokers motivated to stop smoking. The decision to stop smoking should only be taken after a period of reflection during which the role of information and advice given by all health professionals is primordial. Also, the long-term follow-up and counsel are essential to prevent relapse, especially during the first year.

Counseling↗

PubMed2001

Recruitment of cdc2 kinase by DNA topoisomerase II is coupled to chromatin remodeling.

Although initiation of chromosome condensation during early prophase is linked temporally to the appearance of the mitotic cdc2 kinase in the nucleus, it is not known what targets the kinase to the nucleus and how this is coupled to chromatin remodeling. We now report that cdc2 kinase forms stable molecular complexes with the nuclear enzyme DNA topoisomerase II, which is associated with marked stimulation of both DNA binding and catalytic activity of topoisomerase II, albeit in a phosphorylation-independent manner. The molecular interaction is required for recruitment of cdc2 kinase, as shown by incubation of purified enzymes with chicken erythrocyte nuclei, which have neither endogenous topoisomerase II nor cdc2 kinase. The physical association between the two enzymes alters the DNA/topoisomerase II interaction as shown by pulse-field electrophoresis after incubation of intact nuclei with the specific topoisomerase II inhibitor VM-26. Furthermore, the presence of both enzymes, but not either enzyme alone, is accompanied by extensive chromatin remodeling converting the interphase nuclei into precondensation chromosomes with striking resemblance to early prophase structures. Our results reveal a novel property of cyclin-dependent kinases and demonstrate that the recruitment of cdc2 kinase by topoisomerase II is coupled to chromatin remodeling.

Active Transport, Cell Nucleus↗

PubMed2000

Purification of GSK-3 by affinity chromatography on immobilized axin.

Glycogen synthase kinase 3 (GSK-3), an element of the Wnt signalling pathway, plays a key role in numerous cellular processes including cell proliferation, embryonic development, and neuronal functions. It is directly involved in diseases such as cancer (by controlling apoptosis and the levels of beta-catenin and cyclin D1), Alzheimer's disease (tau hyperphosphorylation), and diabetes (as a downstream element of insulin action, GSK-3 regulates glycogen and lipid synthesis). We describe here a rapid and efficient method for the purification of GSK-3 by affinity chromatography on an immobilized fragment of axin. Axin is a docking protein which interacts with GSK-3ss, beta-catenin, phosphatase 2A, and APC. A polyhistidine-tagged axin peptide (residues 419-672) was produced in Escherichia coli and either immobilized on Ni-NTA agarose beads or purified and immobilized on CNBr-activated Sepharose 4B. These "Axin-His6" matrices were found to selectively bind recombinant rat GSK-3 beta and native GSK-3 from yeast, sea urchin embryos, and porcine brain. The affinity-purified enzymes displayed high kinase activity. This single step purification method provides a convenient tool to follow the status of GSK-3 (protein level, phosphorylation state, kinase activity) under various physiological settings. It also provides a simple and efficient way to purify large amounts of active recombinant or native GSK-3 for screening purposes.

Amino Acid Sequence↗

PubMed2000

The Spd1p S phase inhibitor can activate the DNA replication checkpoint pathway in fission yeast.

Spd1p (for S phase delayed) is a cell cycle inhibitor in Schizosaccharomyces pombe. Spd1p overexpression blocks the onset of both S phase and mitosis. In this study, we have investigated the mechanisms by which Spd1p overexpression blocks cell cycle progression, focussing on the block over mitotic onset. High levels of Spd1p lead to an increase in Y15 phosphorylation of Cdc2p and we show that the block over G(2) requires the Wee1p kinase and is dependent on the rad and chk1/cds1 checkpoint genes. We propose that high levels of Spd1p in G(2) cells activate the DNA replication checkpoint control, which leads to a Wee1p-dependent increase of Cdc2p Y15 phosphorylation blocking onset of mitosis. The Spd1p block at S phase onset may act by interfering directly with DNA replication, and also activates the G(2 )rad/hus checkpoint pathway to block mitosis.

CDC2 Protein Kinase↗

PubMed1999

Intra-M phase-promoting factor phosphorylation of cyclin B at the prophase/metaphase transition.

Activation of Cdc2-cyclin B (or M phase-promoting factor (MPF)) at the prophase/metaphase transition proceeds in two steps: dephosphorylation of Cdc2 and phosphorylation of cyclin B. We here investigated the regulation of cyclin B phosphorylation using the starfish oocyte model. Cyclin B phosphorylation is not required for Cdc2 kinase activity; both the prophase complex dephosphorylated on Cdc2 with Cdc25 and the metaphase complex dephosphorylated on cyclin B with protein phosphatase 2A display high kinase activities. An in vitro assay of cyclin B kinase activity closely mimics in vivo phosphorylation as shown by phosphopeptide maps of in vivo and in vitro phosphorylated cyclin B. We demonstrate that Cdc2 itself is the cyclin B kinase; cyclin B phosphorylation requires Cdc2 activity both in vivo (sensitivity to vitamin K3, a Cdc25 inhibitor) and in vitro (copurification with Cdc2-cyclin B, requirement of Cdc2 dephosphorylation, and sensitivity to chemical inhibitors of cyclin-dependent kinases). Furthermore, cyclin B phosphorylation occurs as an intra-M phase-promoting factor reaction as shown by the following: 1) active Cdc2 is unable to phosphorylate cyclin B associated to phosphorylated Cdc2, and 2) cyclin B phosphorylation is insensitive to enzyme/substrate dilution. We conclude that, at the prophase/metaphase transition, cyclin B is mostly phosphorylated by its own associated Cdc2 subunit.

Amino Acid Sequence↗

PubMed1997

Biochemical and cellular effects of roscovitine, a potent and selective inhibitor of the cyclin-dependent kinases cdc2, cdk2 and cdk5.

Cyclin-dependent kinases (cdk) play an essential role in the intracellular control of the cell division cycle (cdc). These kinases and their regulators are frequently deregulated in human tumours. Enzymatic screening has recently led to the discovery of specific inhibitors of cyclin-dependent kinases, such as butyrolactone I, flavopiridol and the purine olomoucine. Among a series of C2, N6, N9-substituted adenines tested on purified cdc2/cyclin B, 2-(1-ethyl-2-hydroxyethylamino)-6-benzylamino-9-isopropylpurine (roscovitine) displays high efficiency and high selectivity towards some cyclin-dependent kinases. The kinase specificity of roscovitine was investigated with 25 highly purified kinases (including protein kinase A, G and C isoforms, myosin light-chain kinase, casein kinase 2, insulin receptor tyrosine kinase, c-src, v-abl). Most kinases are not significantly inhibited by roscovitine. cdc2/cyclin B, cdk2/cyclin A, cdk2/cyclin E and cdk5/p35 only are substantially inhibited (IC50 values of 0.65, 0.7, 0.7 and 0.2 microM, respectively). cdk4/cyclin D1 and cdk6/cyclin D2 are very poorly inhibited by roscovitine (IC50 > 100 microM). Extracellular regulated kinases erk1 and erk2 are inhibited with an IC50 of 34 microM and 14 microM, respectively. Roscovitine reversibly arrests starfish oocytes and sea urchin embryos in late prophase. Roscovitine inhibits in vitro M-phase-promoting factor activity and in vitro DNA synthesis in Xenopus egg extracts. It blocks progesterone-induced oocyte maturation of Xenopus oocytes and in vivo phosphorylation of the elongation factor eEF-1. Roscovitine inhibits the proliferation of mammalian cell lines with an average IC50 of 16 microM. In the presence of roscovitine L1210 cells arrest in G1 and accumulate in G2. In vivo phosphorylation of vimentin on Ser55 by cdc2/cyclin B is inhibited by roscovitine. Through its unique selectivity for some cyclin-dependent kinases, roscovitine provides a useful antimitotic reagent for cell cycle studies and may prove interesting to control cells with deregulated cdc2, cdk2 or cdk5 kinase activities.

Adenosine Triphosphate↗

PubMed1996

Sequential dephosphorylation of p34(cdc2) on Thr-14 and Tyr-15 at the prophase/metaphase transition.

The G2-M transition of the cell cycle is triggered by the p34(cdc2)/cyclin B kinase. During the prophase/metaphase transition, the inactive, Thr-14/Tyr-15 phosphorylated form of p34(cdc2) (TP-YP) is modified to an active, Thr-14/Tyr-15 dephosphorylated form (T-Y) by the cdc25 dual-specificity phosphatase. Using highly synchronized starfish oocytes as a cellular model, we show that dephosphorylation in vivo and in vitro occurs in two steps: Thr-14 dephosphorylation precedes Tyr-15 dephosphorylation. The transient intermediate form (T-YP), which can be obtained in vitro by treatment of TP-YP by protein phosphatase 2A, displays low but significant kinase activity. These results raise the possibility that the intermediate form T-YP may be involved in the autocatalytic amplification of the p34(cdc2)/cyclin B complex through phosphorylation/activation of the cdc25 phosphatase and phosphorylation/inactivation of the wee1 kinase.

Amino Acid Sequence↗