Bortezomib induces nuclear translocation of IκBα resulting in gene-specific suppression of NF-κB--dependent transcription and induction of apoptosis in CTCL

Cutaneous T-cell lymphoma (CTCL) is characterized by constitutive activation of nuclear factor κB (NF-κB), which plays a crucial role in the survival of CTCL cells and their resistance to apoptosis. NF-κB activity in CTCL is inhibited by the proteasome inhibitor bortezomib; however, the mechanisms remained unknown. In this study, we investigated mechanisms by which bortezomib suppresses NF-κB activity in CTCL Hut-78 cells. We demonstrate that bortezomib and MG132 suppress NF-κB activity in Hut-78 cells by a novel mechanism that consists of inducing nuclear translocation and accumulation of IκBα (nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor, alpha), which then associates with NF-κB p65 and p50 in the nucleus and inhibits NF-κB DNA binding activity. Surprisingly, however, while expression of NF-κB-dependent antiapoptotic genes cIAP1 and cIAP2 is inhibited by bortezomib, expression of Bcl-2 is not suppressed. Chromatin immunoprecipitation indicated that cIAP1 and cIAP2 promoters are occupied by NF-κB p65/50 heterodimers, whereas Bcl-2 promoter is occupied predominantly by p50/50 homodimers. Collectively, our data reveal a novel mechanism of bortezomib function in CTCL and suggest that the inhibition of NF-κB-dependent gene expression by bortezomib is gene specific and depends on the subunit composition of NF-κB dimers recruited to NF-κB-responsive promoters.     

Nucleoside diphosphate kinase, a source of GTP, is required for dynamin-dependent synaptic vesicle recycling

Nucleoside diphosphate kinase (NDK), an enzyme encoded by the Drosophila abnormal wing discs (awd) or human nm23 tumor suppressor genes, generates nucleoside triphosphates from respective diphosphates. We demonstrate that NDK regulates synaptic vesicle internalization at the stage where function of the dynamin GTPase is required. awd mutations lower the temperature at which behavioral paralysis, synaptic failure, and blocked membrane internalization occur at dynamin-deficient, shi(ts), mutant nerve terminals. Hypomorphic awd alleles display shi(ts)-like defects. NDK is present at synapses and its enzymatic activity is essential for normal presynaptic function. We suggest a model in which dynamin activity in nerve terminals is highly dependent on NDK-mediated supply of GTP. This connection between NDK and membrane internalization further strengthens an emerging hypothesis that endocytosis, probably of activated growth factor receptors, is an important tumor suppressor activity in vivo.     

Is NMDA receptor-coincidence detection required for learning and memory?

The Mg2+ block of NMDA-type glutamate receptors (NMDARs) is crucial to their function as synaptic coincidence detectors. An analysis of Drosophila expressing a Mg2+-independent NMDAR by in this issue of Neuron concludes that the Mg2+ block is required primarily for long-term memory.     

Enumeration of Viral Capsid Assembly Pathways: Tree Orbits Under Permutation Group Action

This paper uses combinatorics and group theory to answer questions about the assembly of icosahedral viral shells. Although the geometric structure of the capsid (shell) is fairly well understood in terms of its constituent subunits, the assembly process is not. For the purpose of this paper, the capsid is modeled by a polyhedron whose facets represent the monomers. The assembly process is modeled by a rooted tree, the leaves representing the facets of the polyhedron, the root representing the assembled polyhedron, and the internal vertices representing intermediate stages of assembly (subsets of facets). Besides its virological motivation, the enumeration of orbits of trees under the action of a finite group is of independent mathematical interest. If G is a finite group acting on a finite set X, then there is a natural induced action of G on the set \(\mathcal{T}_{X}\) of trees whose leaves are bijectively labeled by the elements of X. If G acts simply on X, then |X|:=|X _n |=n?|G|, where n is the number of G-orbits in X. The basic combinatorial results in this paper are (1) a formula for the number of orbits of each size in the action of G on \(\mathcal{T}_{X_{n}}\), for every n, and (2) a simple algorithm to find the stabilizer of a tree \(\tau\in\mathcal{T} _{X}\) in G that runs in linear time and does not need memory in addition to its input tree. These results help to clarify the effect of symmetry on the probability and number of assembly pathways for icosahedral viral capsids, and more generally for any finite, symmetric macromolecular assembly.     

The Water Withdrawal Footprint of Energy Supply to Cities

Water footprints traditionally estimate water lost as a result of evapotranspiration (or otherwise unavailable for downstream uses) associated with producing a certain good, and the same embodied in trade across regions is used to estimate regional and national water footprints. These footprints, however, do not address risk posed to city energy supplies characterized by insufficient streamflow to support energy production, such as cooling water intake (e.g., withdrawals) at thermoelectric power plants. Water withdrawal intensity factors for producing goods and services are being developed at the national scale, but lack sufficient spatial resolution to address these types of water‐energy challenges facing cities. To address this need, this article presents a water withdrawal footprint for energy supply (WWFES) to cities and places it in the context of other water footprints defined in the literature. Analysis of electricity use versus electricity generation in 43 U.S. cities highlights the need for developing WWFES to estimate risks to transboundary city energy supplies resulting from water constraints. The magnitude of the WWFES is computed for Denver, Colorado, and compared to the city's direct use of water to offer perspective. The baseline WWFES for Denver is found to be 66% as large as all direct water uses in the city combined (mean estimate). Minimum, mean, and maximum estimates are computed to demonstrate sensitivity of the WWFES to selection of water withdrawal intensity factors. Finally, scenario analysis explores the effect of energy technology and energy policy choices in shaping the future water footprint of cities.     

Syndapin Promotes Formation of a Postsynaptic Membrane System in Drosophila

Syndapins belong to the F-BAR domain protein family whose predicted functions in membrane tubulation remain poorly studied in vivo. At Drosophila neuromuscular junctions, syndapin is associated predominantly with a tubulolamellar postsynaptic membrane system known as the subsynaptic reticulum (SSR). We show that syndapin overexpression greatly expands this postsynaptic membrane system. Syndapin can expand the SSR in the absence of dPAK and Dlg, two known regulators of SSR development. Syndapin's N-terminal F-BAR domain, required for membrane tubulation in cultured cells, is required for SSR expansion. Consistent with a model in which syndapin acts directly on postsynaptic membrane, SSR expansion requires conserved residues essential for membrane binding in vitro. However, syndapin's Src homology (SH) 3 domain, which negatively regulates membrane tubulation in cultured cells, is required for synaptic targeting and strong SSR induction. Our observations advance knowledge of syndapin protein function by 1) demonstrating the in vivo relevance of membrane remodeling mechanisms suggested by previous in vitro and structural analyses, 2) showing that SH3 domains are necessary for membrane expansion observed in vivo, and 3) confirming that F-BAR proteins control complex membrane structures.     

Stoned

The stoned proteins, stoned A (STNA) and stoned B (STNB), are essential for normal vesicle trafficking in Drosophila melanogaster neurons, and deletion of the stoned locus is lethal. Although there is a growing body of research aimed at defining the roles of these proteins, particularly for STNB where homologues have now been identified in all multicellular species, their functions and mechanisms of action are not yet established. The two proteins are structurally unrelated, consistent with two distinct cellular functions. The evidence suggests a critical requirement for stoned proteins in recycling/regulation or specification of a competent synaptic vesicle pool. As stoned proteins may be specific to a particular pathway of endocytosis, studies of their function are likely to be valuable in distinguishing between the different mechanisms of membrane retrieval and their respective contributions to synaptic vesicle recycling, a subject of considerable scientific debate. In this review, we examine the published literature on stoned and comment on the available data, conclusions from these analyses and how they may relate to alternative models of vesicle cycling.     

A Novel Paradigm for Nonassociative Long-Term Memory in Drosophila: Predator-Induced Changes in Oviposition Behavior

Learning processes in Drosophila have been studied through the use of Pavlovian associative memory tests, and these paradigms have been extremely useful in identifying both genetic factors and neuroanatomical structures that are essential to memory formation. Whether these same genes and brain compartments also contribute to memory formed from nonassociative experiences is not well understood. Exposures to environmental stressors such as predators are known to induce innate behavioral responses and can lead to new memory formation that allows a predator response to persist for days after the predator threat has been removed. Here, we utilize a unique form of nonassociative behavior in Drosophila where female flies detect the presence of endoparasitoid predatory wasps and alter their oviposition behavior to lay eggs in food containing high levels of alcohol. The predator-induced change in fly oviposition preference is maintained for days after wasps are removed, and this persistence in behavior requires a minimum continuous exposure time of 14 hr. Maintenance of this behavior is dependent on multiple long-term memory genes, including orb2, dunce, rutabaga, amnesiac, and Fmr1. Maintenance of the behavior also requires intact synaptic transmission of the mushroom body. Surprisingly, synaptic output from the mushroom body (MB) or the functions of any of these learning and memory genes are not required for the change in behavior when female flies are in constant contact with wasps. This suggests that perception of this predator that leads to an acute change in oviposition behavior is not dependent on the MB or dependent on learning and memory gene functions. Because wasp-induced oviposition behavior can last for days and its maintenance requires a functional MB and the wild-type products of several known learning and memory genes, we suggest that this constitutes a paradigm for a bona fide form of nonassociative long-term memory that is not dependent on associated experiences.