每日一文(0311)

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 October September August July June May April March February January 2002 2001

November 30,2003 Maintenance of chromatin states: an open-and-shut case Opinion
  The traditional view of chromatin envisions two states: one is ‘active’ and accessible to nucleases, whereas the other is ‘silent’ and relatively inaccessible. Recent evidence that combinations of diverse histone tail modifications represent a spectrum of chromatin states challenges this simple view. Here, we examine inter-relationships between chromatin remodeling, histone modification, DNA methylation, RNA interference, and nucleosome assembly activities. We find that the two-state view can accommodate these new findings, and that nucleosome assembly pathways may ultimately maintain euchromatic and heterochromatic states.
November 29,2003 Tissue Engineering Therapy for Cardiovascular Disease
  The present treatments for the loss or failure of cardiovascular function include organ transplantation, surgical reconstruction, mechanical or synthetic devices, or the administration of metabolic products. Although routinely used, these treatments are not without constraints and complications. The emerging and interdisciplinary field of tissue engineering has evolved to provide solutions to tissue creation and repair. Tissue engineering applies the principles of engineering, material science, and biology toward the development of biological substitutes that restore, maintain, or improve tissue function. Progress has been made in engineering the various components of the cardiovascular system, including blood vessels, heart valves, and cardiac muscle. Many pivotal studies have been performed in recent years that may support the move toward the widespread application of tissue-engineered therapy for cardiovascular diseases. The studies discussed include endothelial cell seeding of vascular grafts, tissue-engineered vascular conduits, generation of heart valve leaflets, cardiomyoplasty, genetic manipulation, and in vitro conditions for optimizing tissue-engineered cardiovascular constructs.
November 28,2003 T-Tubule Function in Mammalian Cardiac Myocytes
  The transverse tubules (t-tubules) of mammalian cardiac ventricular myocytes are invaginations of the surface membrane. Recent studies have suggested that the structure and function of the t-tubules are more complex than previously believed; in particular, many of the proteins involved in cellular Ca2+ cycling appear to be concentrated at the t-tubule. Thus, the t-tubules are an important determinant of cardiac cell function, especially as the main site of excitation-contraction coupling, ensuring spatially and temporally synchronous Ca2+ release throughout the cell. Changes in t-tubule structure and protein expression occur during development and in heart failure, so that changes in the t-tubules may contribute to the functional changes observed in these conditions. The purpose of this review is to provide an overview of recent studies of t-tubule structure and function in cardiac myocytes.
November 27,2003 A structural basis for immunodominant human T cell receptor recognition
  The anti-influenza CD8+ T cell response in HLA-A2–positive adults is almost exclusively directed at residues 58–66 of the virus matrix protein (MP(58–66)). Vβ17Vα10.2 T cell receptors (TCRs) containing a conserved arginine-serine-serine sequence in complementarity determining region 3 (CDR3) of the Vβ segment dominate this response. To investigate the molecular basis of immunodominant selection in an outbred population, we have determined the crystal structure of Vβ17Vα10.2 in complex with MP(58–66)–HLA-A2 at a resolution of 1.4 ?. We show that, whereas the TCR typically fits over an exposed side chain of the peptide, in this structure MP(58–66) exposes only main chain atoms. This distinctive orientation of Vβ17Vα10.2, which is almost orthogonal to the peptide-binding groove of HLA-A2, facilitates insertion of the conserved arginine in Vβ CDR3 into a notch in the surface of MP(58–66)–HLA-A2. This previously unknown binding mode underlies the immunodominant T cell response.
November 26,2003 Principles and practice of functional MRI of the human brain
  Conventional MRI is used extensively for radiological diagnosis and produces spatial maps of the properties of mobile hydrogen nuclei (single protons) that are contained mainly in water molecules. Conventional magnetic resonance images portray anatomic details with exquisite resolution (on the order of 1 mm or better), in three dimensions, and differentiate soft tissues very well. The contrast within images results from variations mainly in the density of water within tissues and in the manner in which water interacts with macromolecules. Functional MRI (fMRI) is now also well established in many centers and uses similar imaging techniques and the same equipment as conventional MRI.
November 25,2003 ExCITED about HIF
  How a cell responds to low oxygen conditions has been the subject of many recent studies, and the molecular details of this process are beginning to take shape. On page 504 of this issue of Nature Structural Biology, Freedman et al.1 have taken another step forward and report the structure of the transactivation domain of CITED2 in complex with the CH1 (the first cysteine-histidine– rich) domain of p300. p300 and its paralog CBP are transcriptional co-activators and histone acetyltransferases; these proteins link diverse DNA-binding transcription factors, such as CREB, AP-1, Stat2, p53, NFκB, to the transcriptional apparatus (for a review, see ref. 2). The new data follow recent structures of the CH1 domain of p300 in complex with the key transcriptional mediator of responses to hypoxia, hypoxia inducible factor (HIF)- 1α3,4. A comparison of these structures provides important insights into the complex processes that regulate transcriptional activation and biological responses to oxygen availability.
November 24,2003 Novel antibody switching defects in human patients
  Hyper-IgM syndrome (HIGM) is a primary immunodeficiency characterized by normal to elevated serum levels of IgM and low levels or the absence of IgG, IgA, and IgE. A new study (see related article on pages 136–142) characterizes HIGM type 4, a previously undocumented defect in antibody gene diversification caused by a selective block in classswitch recombination, providing significant insight towards understanding HIGM immunodeficiencies.
November 23,2003 Pharmacogenomics — Drug Disposition, Drug Targets, and Side Effects
  It is well recognized that different patients respond in differ- ent ways to the same medication. These differences are often greater among members of a population than they are within the same person at different times (or between monozygotic twins).The existence of large population differences with small intrapatient variability is consistent with inheritance as a determinant of drug response; it is estimated that genetics can account for 20 to 95 percent of variability in drug disposition and effects.Although many nongenetic factors influence the effects of medications, including age, organ function, concomitant therapy, drug interactions, and the nature of the disease, there are now numerous examples of cases in which interindividual differences in drug response are due to sequence variants in genes encoding drug-metabolizing enzymes, drug transporters, or drug targets.Unlike other factors influencing drug response, inherited determinants generally remain stable throughout a person’s lifetime.
November 22,2003 Molecular Diagnosis of the Hematologic Cancers
  The diagnosis of the hematologic cancers presents a daunting challenge. The many stages of normal hematopoietic differentiation give rise to a number of biologically and clinically distinct cancers. Inherited DNA-sequence variants do not appear to have a prominent causative role; rather, these diverse cancers are typically initiated by acquired alterations to the genome of the cancer cell, such as chromosomal translocations, mutations, and deletions. The diagnosis of the hematologic cancers is commonly based on morphologic evaluation supplemented by analysis of a few molecular markers. However, in some diagnostic categories defined in this fashion, the response of patients to treatment is markedly heterogeneous, arousing the suspicion that there can be several molecularly distinct diseases within the same morphologic category.
November 21,2003 Heart Failure
  The clinical syndrome of heart failure is the final pathway for myriad diseases that affect the heart. Since the mid-1990s, when the last review of heart failure appeared in the Journal,discoveries from basic research and findings from key clinical trials have resulted in considerable change in the scope of therapies available and the continuing advancement of our understanding of the pathophysiological mechanisms of heart failure. In this article, we highlight these new developments.
November 20,2003 Novel Therapies Based on Mechanisms of HIV-1 Cell Entry
  Infection with human immunodeficiency virus type 1 (hiv-1), the retrovirus that causes the acquired immunodeficiency syndrome (AIDS), is one of the leading causes of death worldwide. All currently available antiretroviral agents inhibit essential HIV-1 enzymes — either the reverse transcriptase or the protease (Fig. 1). Recent advances have markedly improved the outcome for many patients who receive these classes of antiretroviral drugs. However, the success of current therapy is limited by the emergence of drug-resistant viruses, the necessity of sustained adherence to complex regimens, and the potential for toxic effects. Novel classes of safe and effective agents with a low risk of cross-resistance with other antiretroviral drugs are needed.
November 19,2003 Breast and Ovarian Cancer
  Despite years of intensive study and substantial progress in understanding susceptibility to breast and ovarian cancer, these diseases remain important causes of death in women. However, several recent critical advances — sequencing of the human genome and the development of high-throughput techniques for identifying DNA-sequence variants, changes in copy numbers, and global expression profiles — have dramatically accelerated the pace of research aimed at preventing and curing these diseases. We review some of the important discoveries in the genetics of breast and ovarian cancer, ongoing studies to isolate additional susceptibility genes, and early work on molecular profiling involving microarrays.
November 18,2003 Mitochondrial Respiratory-Chain Diseases
  More than a billion years ago, aerobic bacteria colonized primordial eukaryotic cells that lacked the ability to use oxygen metabolically. A symbiotic relationship developed and became permanent. The bacteria evolved into mitochondria, thus endowing the host cells with aerobic metabolism, a much more efficient way to produce energy than anaerobic glycolysis. Structurally, mitochondria have four compartments: the outer membrane, the inner membrane, the intermembrane space, and the matrix (the region inside the inner membrane). They perform numerous tasks, such as pyruvate oxidation, the Krebs cycle, and metabolism of amino acids, fatty acids, and steroids, but the most crucial is probably the generation of energy as adenosine triphosphate (ATP), by means of the electron-transport chain and the oxidative- phosphorylation system (the “respiratory chain”) (Fig. 1).
November 17,2003 Angiotensin Receptor Blockers
  Angiotensin receptor blockers (also known as ARBs) are a class of medications that are widely used by patients with high blood pressure, kidney disease, and heart failure. This article provides information for patients who receive this type of medication. The Table lists the brand and chemical names for the angiotensin receptor blockers that are available in the United States.
November 16,2003 Biglycan, a Nitric Oxide-regulated Gene, Affects Adhesion, Growth, and Survival of Mesangial Cells
  During glomerular inflammation mesangial cells are the major source and target of nitric oxide that profoundly influences proliferation, adhesion, and death of mesangial cells. The effect of nitric oxide on the mRNA expression pattern of cultured rat mesangial cells was therefore investigated by RNA-arbitrarily-primed polymerase chain reaction. Employing this approach, biglycan expression turned out to be down-regulated timeand dose-dependently either by interleukin-1-stimulated endogenous nitric oxide production or by direct application of the exogenous nitric oxide donor, diethylenetriamine nitric oxide. There was a corresponding decline in the rate of biglycan biosynthesis and in the steady state level of this proteoglycan.
November 15,2003 Cardiovascular Disease
  Cardiovascular disease, including stroke, is the leading cause of illness and death in the United States. There are an estimated 62 million people with cardiovascular disease and 50 million people with hypertension in this country.1.In 2000, approximately 946,000 deaths were attributable to cardiovascular disease, accounting for 39 percent of all deaths in the United States. 2.Epidemiologicstudies and randomized clinical trials have provided compelling evidence that coronary heart disease is largely preventable.3.However, there is also reason to believe that there is a heritable component to the disease. In this review, I highlight what we know now about genetic factors in cardiovascular disease. As future genomic discoveries are translated to the care of patients with cardiovascular disease, it is likely that what we can do will change.
November 14,2003 Targeting DNA methylation in cancer
  There is overwhelming evidence that DNA methylation patterns are altered in cancer. Methylation of CG-rich islands in regulatory regions of genes marks them for transcriptional silencing. Multiple genes, which confer selective advantage upon cancer cells such as tumor suppressors, adhesion molecules, inhibitors of angiogenesis and repair enzymes are silenced. In parallel, tumor cell genomes are globally less methylated than their normal counterparts. In contrast to regional hypermethylation, this loss of methylation in cancer cells occurs in sparsely distributed CG sequences. We now understand that DNA methylation machineries might include a number of DNA methyltransferases, proteins that direct DNA methyltransferases to specific promoters, chromatin modifying enzymes as well as demethylases.
November 13,2003 The first half-century of nuclear transplantation
  Fifty years after Briggs and King first succeeded in obtaining normal tadpoles from transplanted embryo nuclei in vertebrates, two general principles have emerged from work in amphibia and mammals. One is the conservation of the genome during cell differentiation. A small percentage of adult or differentiated cells have totipotent nuclei, and a much higher percentage of cells committed to one pathway of cell differentiation have multipotent nuclei. The other is the remarkable reprogramming capacity of cell, and especially egg, cytoplasm. The eventual identification of reprogramming molecules and mechanisms could facilitate a route toward cell replacement therapy in humans.
November 12,2003 Role of Smad4 (DPC4) inactivation in human cancer
  The tumor suppressor gene Smad4 (DPC4) at chromosome 18q21.1 belongs to the Smad family, which mediates the TGFb signaling pathway suppressing epithelial cell growth. This review summarizes the mutational events of the Smad4 gene in human cancer. The Smad4 gene is genetically responsible for familial juvenile polyposis, an autosomal dominant disease characterized by predisposition to gastrointestinal polyps and cancer. In this syndrome, polyps are formed by inactivation of the Smad4 gene through germline mutation and loss of the una.ected wild-type allele. In pancreatic and colorectal cancer, inactivation of the Smad4 gene through homozygous deletion or intragenic mutation occurs frequently in association with malignant progression. However, mutation of this gene is seen only occasionally in the rest of human cancers.
November 11,2003 Analyzing tumor gene expression profiles
  A brief introduction to high throughput technologies for measuring and analyzing gene expression is given. Various supervised and unsupervised data mining methods for analyzing the produced highdimensional data are discussed. The main emphasis is on supervised machine learning methods for classification and prediction of tumor gene expression profiles. Furthermore, methods to rank the genes according to their importance for the classification are explored. The approaches are illustrated by exploratory studies using two examples of retrospective clinical data from routine tests; diagnostic prediction of small round blue cell tumors (SRBCT) of childhood and determining the estrogen receptor (ER) status of sporadic breast cancer. The classification performance is gauged using blind tests. These studies demonstrate the feasibility of machine learning-based molecular cancer classification.
November 10,2003 The Spindle Checkpoint: From Normal Cell Division to Tumorigenesis
  Faithful chromosome segregation during each cell division is regulated by the spindle checkpoint. This surveillance mechanism monitors kinetochore-microtubule attachment and the integrity of the mitotic apparatus, delaying mitotic exit until all chromosomes are properly aligned at the metaphase plate. Failure of this mechanism can generate gross aneuploidy. Since its discovery, mutations in genes involved in the spindle checkpoint response were predicted to be serious candidates for the chromosomal instability phenotype observed in many tumors. During the last few years, significant advances have been made in understanding the molecular basis of the spindle checkpoint. However, many studies of tumor cell lines and primary cancer isolates have failed to show a direct correlation with mutations in spindle checkpoint components. Nevertheless, it was shown that many tumor cells have an abnormal spindle checkpoint.
November 9,2003 The DNA sequence of human chromosome 7
  Human chromosome 7 has historically received prominent attention in the human genetics community, primarily related to the search for the cystic fibrosis gene and the frequent cytogenetic changes associated with various forms of cancer. Here we present more than 153 million base pairs representing 99.4% of the euchromatic sequence of chromosome 7, the first metacentric chromosome completed so far. The sequence has excellent concordance with previously established physical and genetic maps, and it exhibits an unusual amount of segmentally duplicated sequence (8.2%), with marked differences between the two arms. Our initial analyses have identified 1,150 protein-coding genes, 605 of which have been confirmed by complementary DNA sequences, and an additional 941 pseudogenes. Of genes confirmed by transcript sequences, some are polymorphic for mutations that disrupt the reading frame.
November 8,2003 Regulatory issues in human gene therapy
  Protection of human subjects is the ethical and legal responsibility of investigators conducting clinical trials. Public concerns regarding recombinant DNA technology led to additional levels of oversight which are unique to human gene therapy trials. The deaths of a normal volunteer and a gene therapy subject in the late 1990s led to an intensification of oversight with new initiatives that impact gene therapy as well as other clinical investigators. This paper will review the current oversight agencies and identify areas of evolving regulations that pose particular challenges to gene therapy investigators.
November 7,2003 JNK phosphorylates paxillin and regulates cell migration
  The c-Jun amino-terminal kinase (JNK) is generally thought to be involved in inflammation, proliferation and apoptosis. Accordingly, its substrates are transcription factors and antiapoptotic proteins. However, JNK has also been shown to be required for Drosophila dorsal closure, and MAP kinase/ERK kinase kinase 1, an upstream kinase in the JNK pathway, has been shown to be essential for cell migration. Both results imply that JNK is important in cell migration. Here we show that JNK1 is required for the rapid movement of both fish keratocytes and rat bladder tumour epithelial cells (NBT-II). Moreover, JNK1 phosphorylates serine 178 on paxillin, a focal adhesion adaptor, both in vitro and in intact cells. NBT-II cells expressing the Ser 178-Ala mutant of paxillin (PaxS178A) formed focal adhesions and exhibited the limited movement associated with such contacts in both single-cell-migration and wound-healing assays. In contrast, cells expressing wild-type paxillin moved rapidly and retained close contacts as the predominant adhesion. Expression of PaxS178A also inhibited the migration of two other cell lines. Thus, phosphorylation of paxillin by JNK seems essential for maintaining the labile adhesions required for rapid cell migration.
November 6,2003 T-type calcium channel regulation by specific G-proteinbg βγ subunits
  Low-voltage-activated (LVA) T-type calcium channels have awide tissue distribution and have well-documented roles in the control of action potential burst generation and hormone secretion. In neurons of the central nervous system and secretory cells of the adrenal and pituitary, LVA channels are inhibited by activation of G-protein-coupled receptors that generate membrane-delimited signals, yet these signals have not been identified. Here we show that the inhibition of α1H (Cav3.2), but not α1G (Cav3.1) LVA Ca2+ channels is mediated selectively by β2γ2 subunits that bind to the intracellular loop connecting channel transmembrane domains II and III. This region of the α1H channel is crucial for inhibition, because its replacement abrogates inhibition and its transfer to non-modulated α1G channels confers β2γ2-dependent inhibition.βγ reduces channel activity independent of voltage, a mechanism distinct from the established βγ-dependent inhibition of non-L-type high-voltage-activated channels of the Cav2 family. These studies identify the α1H channel as a new effector for G-protein βγ subunits, and highlight the selective signalling roles available for particular βγ combinations.
November 5,2003 Timing will tell
  A sophisticated model of the effects of mutating the retinoblastoma gene reveals a window of opportunity in which cells can be released from the normal control of proliferation, before back-up mechanisms take effect. How much flexibility is there in the molecular circuits that regulate the functions of cells? If some genes are inactivated, do back-up systems restore the status quo? On page 223 of this issue, Jacks and co-workers address this question with regard to the retinoblastoma gene, Rb, which works in a key cellular signalling pathway that protects organisms against cancer.
November 4,2003 The molecules that make muscle
  Every conscious action we perform requires skeletal muscle. Without it, we wouldn’t be able to run for the bus, lift a pipette or turn the pages of this journal. So called because it attaches to the skeleton, this type of muscle has been studied for centuries; incredibly, the idea that it works by contracting can be traced back more than two millennia. As a consequence, a great deal is known about the structure of skeletal muscle and about how it functions. The step-by-step process by which it forms has also been well studied, at least at the cellular level.Nowadays, however, the goal of much research effort is to identify the molecules that are involved in specific biological processes — and the molecular mechanisms underlying muscle formation have long eluded researchers.
November 3,2003 Cancer-Associated Thrombosis
  Thrombosis was identified as a complication of cancer by Trousseau in 1865, and the combination of the two conditions is still often called Trousseau’s syndrome. Arterial and, more commonly, venous thrombosis is a frequent complication of cancer and sometimes a harbinger of occult cancer. Moreover, the use of new and aggressive therapy for cancer increases the risk of thrombosis.
November 2,2003 Human Embryonic Stem Cells Develop Into Multiple Types of Cardiac Myocytes
  Human embryonic stem (hES) cells can differentiate in vitro, forming embryoid bodies (EBs) composed of derivatives of all three embryonic germ layers. Spontaneously contracting outgrowths from these EBs contain cardiomyocytes (CMs); however, the types of human CMs and their functional properties are unknown. This study characterizes the contractions and action potentials (APs) from beating EB outgrowths cultured for 40 to 95 days. Spontaneous and electrical field–stimulated contractions were measured with video edge-detection microscopy. -Adrenergic stimulation with 1.0 mol/L isoproterenol resulted in a significant increase in contraction magnitude. Intracellular electrical recordings using sharp KCl microelectrodes in beating EB outgrowths revealed three distinct classes of APs: nodal-like, embryonic atrial-like, and embryonic ventricular-like.
November 1,2003 T cell receptor-independent CD4 signalling: CD4–MHC class II interactions regulate intracellular calcium and cyclic AMP
  CD4 is a coreceptor on T helper (Th) cells that interacts with MHC class II molecules (MHCII). The mechanisms mediating the effects of CD4 on responses by T helper cells to stimulation of the antigen-specific T cell receptor (TCR) are still poorly understood. Here, we demonstrate T cell costimulation via CD4 signalling independent of T cell receptor-mediated signals. Incubation of T helper cells with peptide mimetics of the CD4-binding region on the MHC class II h2 domain caused intracellular calcium mobilization in the absence of antigen or other T cell receptor stimuli. Engagement of CD4 by peptide mimetics or wild-type MHC class II, but not by mutant MHC class II molecules incapable of engaging CD4, inhibited the T cell receptor-mediated increase in cyclic AMP (cAMP) concentrations in T helper cells.

November September August July June May April March February January 2002 2001