Geminin bans replication licence.
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Animals↗
Biomedical subjects
R Laskey
Publications and source records attributed to R Laskey.
Aggressive versus moderate lipid-lowering therapy in postmenopausal women with hypercholesterolemia: Rationale and design of the Beyond Endorsed Lipid Lowering with EBT Scanning (BELLES) trial.
BACKGROUND: Electron beam tomography (EBT) is a noninvasive technique that allows the study of the entire coronary artery tree during a brief imaging session without the injection of any contrast media. Atherosclerosis is identified vicariously through the visualization of coronary calcific deposits. Quantitative assessments of calcium burden, such as calcium volume scores, have been shown to be a useful means to assess treatment-related changes in the extent of atherosclerotic plaques. Historically, the elderly female population has received less medical recognition regarding the risk and severity of coronary heart disease (CHD). METHODS: In the BELLES (Beyond Endorsed Lipid Lowering with EBT Scanning) trial, the presence of asymptomatic CHD in 600 postmenopausal women will be assessed by EBT. In this 1-year, multicenter, randomized, double-blind, parallel-group study, aggressive lipid-lowering treatment will be compared with moderate lipid-lowering treatment in postmenopausal women with hypercholesterolemia. The hypothesis we will test is that aggressive lipid-lowering therapy with 80 mg/d atorvastatin can produce greater reductions in atherosclerotic plaque burden as assessed by volumetric calcium scores than a moderate treatment with 40 mg/d pravastatin. The primary outcome measure will be the percent change from baseline in total CVS determined by EBT at 12 months. CONCLUSIONS: The results of the BELLES trial will help assess the actual incidence of CHD in postmenopausal women and the relative ability of two different lipid-lowering therapies to halt its progression.
Aged↗
MCM3AP, a novel acetyltransferase that acetylates replication protein MCM3.
The MCM proteins are essential for the initiation of DNA replication. We have isolated an MCM3-associated protein (MCM3AP) in a two-hybrid screen using MCM3. Here we demonstrate that MCM3AP is an acetyltransferase which acetylates MCM3 and that chromatin-bound MCM3 is acetylated in vivo. The MCM3 acetylase, MCM3AP, is also chromatin-bound. This study also indicates that MCM3AP contains putative acetyl CoA binding motifs conserved within the GCN5-related N-acetyltransferase superfamily. Mutation of those motifs significantly inhibits the MCM3 acetylase activity. Over-expression of MCM3AP inhibits DNA replication, whereas mutation of the acetylase motifs abolishes this effect, suggesting that acetylation plays a role in DNA replication. Taken together, we suggest that MCM3 acetylation is a novel pathway which might regulate DNA replication.
Acetyl Coenzyme A↗
Viral cyclin-cyclin-dependent kinase 6 complexes initiate nuclear DNA replication.
The cyclins encoded by Kaposi sarcoma-associated herpesvirus and herpesvirus saimiri are homologs of human D-type cyclins. However, when complexed to cdk6, they have several activities that distinguish them from D-type cyclin-cdk6 complexes, including resistance to cyclin-dependent kinase inhibitors and an enhanced substrate range. We find that viral cyclins interact with and phosphorylate proteins involved in replication initiation. Using mammalian in vitro replication systems, we show that viral cyclin-cdk6 complexes can directly trigger the initiation of DNA synthesis in isolated late-G(1)-phase nuclei. Viral cyclin-cdk6 complexes share this capacity with cyclin A-cdk2, demonstrating that in addition to functioning as G(1)-phase cyclin-cdk complexes, they function as S-phase cyclin-cdk complexes.
3T3 Cells↗
MCM proteins are associated with RNA polymerase II holoenzyme.
MCMs are a family of proteins related to ATP-dependent helicases that bind to origin recognition complexes and are required for initiation of DNA replication. We report that antibodies against MCM2(BM28) specifically inhibited transcription by RNA polymerase II (Pol II) in microinjected Xenopus oocytes. Consistent with this observation, MCM2 and other MCMs copurified with Pol II and general transcription factors (GTFs) in high-molecular-weight holoenzyme complexes isolated from Xenopus oocytes and HeLa cells. Pol II and GTFs also copurified with MCMs isolated by anti-MCM3 immunoaffinity chromatography. MCMs were specifically displaced from the holoenzyme complex by antibody against the C-terminal domain (CTD) of Pol II. In addition, MCMs bound to a CTD affinity column, suggesting that their association with holoenzyme depends in part on this domain of Pol II. These results suggest a new function for MCM proteins as components of the Pol II transcriptional apparatus.
Animals↗
Influence of group B streptococci on piglet pulmonary artery response to bradykinin.
To study whether a sepsis-induced increase in des-Arg9-bradykinin (des-Arg9-BK) and bradykinin (BK) B1-receptor activity participates in the observed increase in pulmonary vascular resistance in neonatal group B streptococcal sepsis (GBS), isometric force bioassays of pulmonary artery (PA) rings were studied, after 4-h exposure to either Krebs or GBS, by using the following protocols: 1) BK dose-response curve, 2) vascular response to BK with NG-nitro-L-arginine methyl ester (L-NAME), and 3) response to des-Arg9-BK (BK metabolite and B1 agonist). PA rings exposed to BK resulted in contraction in the GBS group and a decrease in resting tension in the Control group (P = 0.034) at a concentration of 10(-5) M. GBS-treated PA rings contracted more to des-Arg9-BK than did Controls (P < 0.001). BK (10(-6) M) relaxed preconstricted PA rings incubated in GBS less than BK relaxed Controls (P < 0.001), and preincubation with L-NAME decreased relaxation in both. These results suggest that GBS decreased endothelium-dependent BK relaxation and increased contractile response to des-Arg9-BK. We speculate that this occurs secondary to upregulation of B1 receptors reflected by B1-agonist-mediated PA contraction.
Animals↗
The nuclear membrane.
The nuclear membrane forms a major barrier within the cell, permitting levels of regulation not found in prokaryotes. The dynamics and diverse functions of the nuclear membrane and its associated structures are considered in this review. The role of the nuclear pore complex in selective transport across the nuclear membrane has been studied to a considerable degree; however, many crucial questions remain. Components of a signal transduction mechanism are associated with the nucleus, suggesting that nuclear functions may be influenced directly by this system. The involvement of the heat shock cognate protein Hsc70 in nuclear protein import is discussed, and a specific signal-presentation role for this protein is proposed.
Animals↗
ATP-evoked calcium signal stimulates protein phosphorylation/dephosphorylation in astrocytes.
Extracellular adenosine 5'-triphosphate (ATP)-evoked increases in intracellular calcium and the consequent stimulation of calcium-mediated protein phosphorylation systems were investigated in primary cultures of rat cerebral cortical astrocytes. Measurement of calcium responses in fura-2-loaded astrocytes indicated that extracellular ATP stimulated a transient calcium peak followed by a sustained increase in intracellular calcium which declined to baseline when external calcium was removed, thereby indicating that ATP evokes mobilization of internal calcium as well as influx of external calcium. Protein phosphorylation studies revealed that application of extracellular ATP resulted in increased phosphorylation of 55 and 52 kDa proteins (4-fold and 2-fold, respectively) and decreased phosphorylation of 24 and 21 kDa proteins (approximately 50% for each protein). These effects were time- and dose-dependent. The changes in phosphate incorporation were (a) inhibited by lanthanum, (b) reduced when calcium was omitted from the bath and (c) mimicked by ionomycin, thus suggesting that the ATP-induced changes in protein phosphorylation were dependent on increased levels of intracellular calcium. Adenosine diphosphate (ADP) gave similar, but reduced, effects while adenosine and guanosine triphosphate (GTP) were ineffective, findings consistent with activation of P2 purinergic receptors. The 52 kDa protein co-migrated with glial fibrillary acidic protein. These results support the premise that calcium-dependent protein kinases and phosphatases are transducing elements for the calcium signal brought about by activation of P2 purinergic receptors in astrocytes. Since ATP is released from neurons and endothelial cells, this signal transduction mechanism may be an important component of neuronal- and endothelial-astrocytic communication.
Adenosine Triphosphate↗
Ion channels and regulation of intracellular calcium in vascular endothelial cells.
Endothelial cells in vivo form an interface between flowing blood and vascular tissue, responding to humoral and physical stimuli to secrete relaxing and contracting factors that contribute to vascular homeostasis and tone. The activation of endothelial cell-surface receptors by vasoactive agents is coupled to an elevation in cytosolic Ca2+, which is caused by Ca2+ entry via ion channels in the plasma membrane and by Ca2+ release from intracellular stores. Ca2+ entry may occur via four different mechanisms: 1) a receptor-mediated channel coupled to second messengers; 2) a Ca2+ leak channel dependent on the electrochemical gradient for Ca2+; 3) a stretch-activated nonselective cation channel; and 4) internal Na+-dependent Ca2+ entry (Na+-Ca2+ exchange). The rate of Ca2+ entry through these ion pathways can be modulated by the resting membrane potential. Membrane potential may be regulated by at least two types of K channels: inwardly rectifying K channels activated upon hyperpolarization or shear stress; and a Ca2+-activated K channel activated upon depolarization, which may function to repolarize the agonist-stimulated endothelial cell. After agonist stimulation, cytosolic Ca2+ increases in a biphasic manner, with an initial peak due to inositol 1,4,5-trisphosphate-mediated Ca2+ release from intracellular stores, followed by a sustained plateau that is dependent on the presence of [Ca2+]o and on membrane potential. The delay in agonist-activated Ca2+ influx is consistent with the coupling of receptor activation to Ca2+ entry via a second messenger. Oscillations in [Ca2+]i, which may involve both Ca2+ entry and release, have been observed in isolated and confluent endothelial cell monolayers stimulated by histamine and bradykinin. Receptor-mediated Ca2+ entry, release, and refilling of intracellular stores follows a cycle that involves the plasma membrane.
Animals↗
Naloxone inhibits the centrally-mediated hypotensive actions of BHT-933 (azepexole).
Central administration of BHT 933, a highly selective alpha 2 agonist, to pentobarbital-anesthetized, normotensive dogs resulted in a rapid, significant decrease in blood pressure. The maximal response occurred at 30 min and remained significantly decreased for 60 min. Concomitant with the hypotensive response was a decrease in heart rate. Pretreatment with naloxone 15 min prior to the administration of BHT 933 completely abolished the hypotensive response and significantly inhibited the bradycardia. These results suggest a role for central opioidergic systems in the control of blood pressure which may serve as important sites of antihypertensive drug action. The central regulation of sympathetic tone by catecholaminergic systems plays an important role in the control of cardiovascular function in both normal and pathological states. A high density of catecholaminergic nerve terminals is found in regions of the brainstem involved in cardiovascular control. Stimulation of the alpha receptors in these areas decreases peripheral sympathetic tone and subsequently lowers blood pressure. Recent histochemical evidence has demonstrated the presence of opioid peptides in the nucleus tractus solitarii, nucleus ambiguous and hypothalamus as well as other discrete brain areas associated with cardiovascular control. Activation of the opiate receptors in these brain areas decreases sympathetic tone and blood pressure. Additionally, both catecholaminergic and opioidergic systems have been implicated in the reaction to certain stimuli (i.e., pain, stress) which entail important hemodynamic adaptations. The similarity between the central opiate and catecholaminergic systems suggests a relationship between the two systems in blood pressure control and a potential site of antihypertensive drug action. The purpose of the present study was to determine if an opioidergic component is involved in the hypotensive action of BHT 933 (azepexole). BHT 933 is a relatively new hypotensive agent which is a much more specific alpha 2 agonist than clonidine.
Animals↗
A major transition for embryos and for embryologists.
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Animals↗