Structure of mammalian AMPK and its regulation by ADP

The heterotrimeric AMP-activated protein kinase (AMPK) has a key role in regulating cellular energy metabolism; in response to a fall in intracellular ATP levels it activates energy-producing pathways and inhibits energy-consuming processes. AMPK has been implicated in a number of diseases related to energy metabolism including type 2 diabetes, obesity and, most recently, cancer. AMPK is converted from an inactive form to a catalytically competent form by phosphorylation of the activation loop within the kinase domain: AMP binding to the γ-regulatory domain promotes phosphorylation by the upstream kinase, protects the enzyme against dephosphorylation, as well as causing allosteric activation. Here we show that ADP binding to just one of the two exchangeable AXP (AMP/ADP/ATP) binding sites on the regulatory domain protects the enzyme from dephosphorylation, although it does not lead to allosteric activation. Our studies show that active mammalian AMPK displays significantly tighter binding to ADP than to Mg-ATP, explaining how the enzyme is regulated under physiological conditions where the concentration of Mg-ATP is higher than that of ADP and much higher than that of AMP. We have determined the crystal structure of an active AMPK complex. The structure shows how the activation loop of the kinase domain is stabilized by the regulatory domain and how the kinase linker region interacts with the regulatory nucleotide-binding site that mediates protection against dephosphorylation. From our biochemical and structural data we develop a model for how the energy status of a cell regulates AMPK activity.     

A function for cyclin D1 in DNA repair uncovered by protein interactome analyses in human cancers

Cyclin D1 is a component of the core cell cycle machinery. Abnormally high levels of cyclin D1 are detected in many human cancer types. To elucidate the molecular functions of cyclin D1 in human cancers, we performed a proteomic screen for cyclin D1 protein partners in several types of human tumours. Analyses of cyclin D1 interactors revealed a network of DNA repair proteins, including RAD51, a recombinase that drives the homologous recombination process. We found that cyclin D1 directly binds RAD51, and that cyclin D1-RAD51 interaction is induced by radiation. Like RAD51, cyclin D1 is recruited to DNA damage sites in a BRCA2-dependent fashion. Reduction of cyclin D1 levels in human cancer cells impaired recruitment of RAD51 to damaged DNA, impeded the homologous recombination-mediated DNA repair, and increased sensitivity of cells to radiation in vitro and in vivo. This effect was seen in cancer cells lacking the retinoblastoma protein, which do not require D-cyclins for proliferation. These findings reveal an unexpected function of a core cell cycle protein in DNA repair and suggest that targeting cyclin D1 may be beneficial also in retinoblastoma-negative cancers which are currently thought to be unaffected by cyclin D1 inhibition.     

A genetically humanized mouse model for hepatitis C virus infection

Hepatitis C virus (HCV) remains a major medical problem. Antiviral treatment is only partially effective and a vaccine does not exist. Development of more effective therapies has been hampered by the lack of a suitable small animal model. Although xenotransplantation of immunodeficient mice with human hepatocytes has shown promise, these models are subject to important challenges. Building on the previous observation that CD81 and occludin comprise the minimal human factors required to render mouse cells permissive to HCV entry in vitro, we attempted murine humanization via a genetic approach. Here we show that expression of two human genes is sufficient to allow HCV infection of fully immunocompetent inbred mice. We establish a precedent for applying mouse genetics to dissect viral entry and validate the role of scavenger receptor type B class I for HCV uptake. We demonstrate that HCV can be blocked by passive immunization, as well as showing that a recombinant vaccinia virus vector induces humoral immunity and confers partial protection against heterologous challenge. This system recapitulates a portion of the HCV life cycle in an immunocompetent rodent for the first time, opening opportunities for studying viral pathogenesis and immunity and comprising an effective platform for testing HCV entry inhibitors in vivo.     

The genome of the green anole lizard and a comparative analysis with birds and mammals

The evolution of the amniotic egg was one of the great evolutionary innovations in the history of life, freeing vertebrates from an obligatory connection to water and thus permitting the conquest of terrestrial environments. Among amniotes, genome sequences are available for mammals and birds, but not for non-avian reptiles. Here we report the genome sequence of the North American green anole lizard, Anolis carolinensis. We find that A. carolinensis microchromosomes are highly syntenic with chicken microchromosomes, yet do not exhibit the high GC and low repeat content that are characteristic of avian microchromosomes. Also, A. carolinensis mobile elements are very young and diverse-more so than in any other sequenced amniote genome. The GC content of this lizard genome is also unusual in its homogeneity, unlike the regionally variable GC content found in mammals and birds. We describe and assign sequence to the previously unknown A. carolinensis X chromosome. Comparative gene analysis shows that amniote egg proteins have evolved significantly more rapidly than other proteins. An anole phylogeny resolves basal branches to illuminate the history of their repeated adaptive radiations.     

Stabilization of Discrete-Time Dynamical Systems Under Event-Triggered Impulsive Control with and Without Time-Delays

This paper investigates the issue of stabilization for discrete-time dynamical systems (DDS) by event-triggered impulsive control (ETIC). Based on some relatively simple threshold constants, three levels of event conditions are set and thus the ETIC scheme is designed. Three cases for ETIC with and without time-delays and data dropouts are studied respectively, and the criteria on exponential stability are derived for the controlled DDS. The stabilization in the form of exponential stability is achieved for DDS under the designed ETIC with or without time-delays. And in the case of the ETIC data dropouts, the conditions of exponential stabilization are derived for DDS and the maximal allowable dropout rates for ETIC are estimated. Finally, one example with numerical simulations is worked out for illustration.     

The Concerns-Based Adoption Model: Teachers’ Participation in Action Research

This article views a particular example of action research through the theoretical lens provided by the Concerns Based Adoption Model of professional development. A small group of teachers in Lesotho, used action research to investigate their understanding and practice in the midst of externally initiated change. Data was collected from teachers’ discussions during the 2 years of the project. Teachers interacted during planning sessions; lesson observations and reflection meetings. Results indicated that these teachers’ development and change through action research corresponded with the seven levels of the Concerns-Based Adoption Model (CBAM) which are awareness, information, personal concerns, management, consequences, collaboration and refocusing. The demonstrated resonance between CBAM and action research is significant, given the differing orientations of the two models. There is a need however to conduct further studies with larger samples and possibly from diverse areas to further explore the relationship between the Concerns-Based Adoption Model and action research.     

Science,truth and dictatorship: Wishful thinking or wishful speaking?

This paper argues for a novel way of addressing questions about the relationship between politics and science: in terms of norms of communication, rather than norms of cognition. The first half of the paper motivates this general shift through close study of the concept of "wishful speaking"; arguing that this vice - rather than the more familiar "wishful thinking" - better captures real-life cases, such as the Lysenko affair. The second half builds on the ethics of communication to develop an account of the proper role of non-epistemic values in justification in terms of "value-aptness".