Functional Interactions between KCNE1 C-Terminus and the KCNQ1 Channel

The KCNE1 gene product (minK protein) associates with the cardiac KvLQT1 potassium channel (encoded by KCNQ1) to create the cardiac slowly activating delayed rectifier, IKs. Mutations throughout both genes are linked to the hereditary cardiac arrhythmias in the Long QT Syndrome (LQTS). KCNE1 exerts its specific regulation of KCNQ1 activation via interactions between membrane-spanning segments of the two proteins. Less detailed attention has been focused on the role of the KCNE1 C-terminus in regulating channel behavior. We analyzed the effects of an LQT5 point mutation (D76N) and the truncation of the entire C-terminus (Δ70) on channel regulation, assembly and interaction. Both mutations significantly shifted voltage dependence of activation in the depolarizing direction and decreased IKs current density. They also accelerated rates of channel deactivation but notably, did not affect activation kinetics. Truncation of the C-terminus reduced the apparent affinity of KCNE1 for KCNQ1, resulting in impaired channel formation and presentation of KCNQ1/KCNE1 complexes to the surface. Complete saturation of KCNQ1 channels with KCNE1-Δ70 could be achieved by relative over-expression of the KCNE subunit. Rate-dependent facilitation of K+ conductance, a key property of IKs that enables action potential shortening at higher heart rates, was defective for both KCNE1 C-terminal mutations, and may contribute to the clinical phenotype of arrhythmias triggered by heart rate elevations during exercise in LQTS mutations. These results support several roles for KCNE1 C-terminus interaction with KCNQ1: regulation of channel assembly, open-state destabilization, and kinetics of channel deactivation

Small Interfering RNA Targeted to IGF-IR Delays Tumor Growth and Induces Proinflammatory Cytokines in a Mouse Breast Cancer Model

Insulin-like growth factor I (IGF-I) and its type I receptor (IGF-IR) play significant roles in tumorigenesis and in immune response. Here, we wanted to know whether an RNA interference approach targeted to IGF-IR could be used for specific antitumor immunostimulation in a breast cancer model. For that, we evaluated short interfering RNA (siRNAs) for inhibition of in vivo tumor growth and immunological stimulation in immunocompetent mice. We designed 2′-O-methyl-modified siRNAs to inhibit expression of IGF-IR in two murine breast cancer cell lines (EMT6, C4HD). Cell transfection of IGF-IR siRNAs decreased proliferation, diminished phosphorylation of downstream signaling pathway proteins, AKT and ERK, and caused a G0/G1 cell cycle block. The IGF-IR silencing also induced secretion of two proinflammatory cytokines, TNF- α and IFN-γ. When we transfected C4HD cells with siRNAs targeting IGF-IR, mammary tumor growth was strongly delayed in syngenic mice. Histology of developing tumors in mice grafted with IGF-IR siRNA treated C4HD cells revealed a low mitotic index, and infiltration of lymphocytes and polymorphonuclear neutrophils, suggesting activation of an antitumor immune response. When we used C4HD cells treated with siRNA as an immunogen, we observed an increase in delayed-type hypersensitivity and the presence of cytotoxic splenocytes against wild-type C4HD cells, indicative of evolving immune response. Our findings show that silencing IGF-IR using synthetic siRNA bearing 2′-O-methyl nucleotides may offer a new clinical approach for treatment of mammary tumors expressing IGF-IR. Interestingly, our work also suggests that crosstalk between IGF-I axis and antitumor immune response can mobilize proinflammatory cytokines

The ELBA Force Field for Coarse-Grain Modeling of Lipid Membranes

A new coarse-grain model for molecular dynamics simulation of lipid membranes is presented. Following a simple and conventional approach, lipid molecules are modeled by spherical sites, each representing a group of several atoms. In contrast to common coarse-grain methods, two original (interdependent) features are here adopted. First, the main electrostatics are modeled explicitly by charges and dipoles, which interact realistically through a relative dielectric constant of unity (). Second, water molecules are represented individually through a new parametrization of the simple Stockmayer potential for polar fluids; each water molecule is therefore described by a single spherical site embedded with a point dipole. The force field is shown to accurately reproduce the main physical properties of single-species phospholipid bilayers comprising dioleoylphosphatidylcholine (DOPC) and dioleoylphosphatidylethanolamine (DOPE) in the liquid crystal phase, as well as distearoylphosphatidylcholine (DSPC) in the liquid crystal and gel phases. Insights are presented into fundamental properties and phenomena that can be difficult or impossible to study with alternative computational or experimental methods. For example, we investigate the internal pressure distribution, dipole potential, lipid diffusion, and spontaneous self-assembly. Simulations lasting up to 1.5 microseconds were conducted for systems of different sizes (128, 512 and 1058 lipids); this also allowed us to identify size-dependent artifacts that are expected to affect membrane simulations in general. Future extensions and applications are discussed, particularly in relation to the methodology's inherent multiscale capabilities

Biodiversity and the Functioning of Ecosystems in the Age of Global Change: Integrating Knowledge Across Scales

The dramatic decline of biodiversity worldwide has raised a general concern on the impacts this process could have for the well-being of humanity. Human societies strongly depend on the benefits provided by natural ecosystems, which are the result of biogeochemical processes governed by species activities and their interaction with abiotic compartments. After decades of experimental research on the biodiversity-functioning relationship, a relative agreement has been reached on the mechanisms underlying the impacts that biodiversity loss can have on ecosystem processes. However, a general consensus is still missing. We suggest that the reason preventing an integration of existing knowledge is the scale discrepancy between observations on global change impacts and biodiversity-functioning experiments. The present chapter provides an overview of global change impacts on biodiversity across various ecological scales and its consequences for ecosystem functioning, highlighting what is known and where knowledge gaps still persist. Furthermore, the reader will be introduced to a set of tools that allow a multi-scale analysis of how global change drivers impact ecosystem functioning

Factors controlling soil development in sand dunes: evidence from a coastal dune soil cronosequence

Aerial photographs, maps and optically stimulated luminescence dates were combined with existing soil data to construct high resolution chronosequences of soil development over 140 years at a temperate Atlantic UK dune system. Since soil formation had progressed for varying duration under different climate and nitrogen deposition regimes, it was possible to infer their relative influence on soil development compared with location-specific variables such as soil pH, slope and distance to the sea. Results suggest that soil development followed a sigmoid curve. Soil development was faster in wet than in dry dune habitats. In dry dunes, rates were greater than in the literature: they increased with increasing temperature and nitrogen deposition and decreased with increasing summer gales. The combination explained 62% of the variation. Co-correlation meant that effects of nitrogen deposition could not be differentiated from temperature. In wet dune habitats rates increased with temperature and decreased with gales. The combination explained only 23% of the variation; surprisingly, rainfall was not significant. Effects of location-specific variables were not significant in either habitat type. Nitrogen accumulation was faster in wet than dry dune habitats, averaging 43 kg N ha−1 per year overall. Nitrogen accumulation greatly exceeded inputs from atmospheric deposition, suggesting rates of input for biological N fixation are 10–60 kg N ha−1 per year. Recent climate and/or nitrogen deposition regimes may have accelerated soil development compared with past rates. These data suggest the importance of changing climate on soil development rates and highlight the contribution of biological N fixation in early successional systems

Insulin-Like Growth Factor I Promotes Maturation and Inhibits Apoptosis of Immature Cord Blood Monocyte-Derived Dendritic Cells through MEK and PI 3-Kinase Pathways

IGF-I has profound effects on the immune system. We previously reported that IGF-I promoted cord blood (CB)-naïve T-cell maturation and now show that IGF-I promoted maturation of CB monocyte-derived dendritic cells (DC) with up-regulation of CD83, CD86, CD40, and major histocompatibility complex (MHC) class II molecules, and down-regulation of mannose receptor. Furthermore, IGF-I inhibited apoptosis of CB DC and increased the production of tumor necrosis factor α (TNF-α). These effects were blocked by specific mitogen-activated protein kinase kinase (MEK) inhibitor (PD98059) and phosphoinositol 3-kinase inhibitor (LY294002). PD98059 partially inhibited the IGF-I-induced up-regulation of MHC class II. In contrast, LY294002 was additive in the IGF-I-induced up-regulation of MHC class II. Moreover, LY294002 significantly increased the percentage of late apoptotic cells in CB. These results imply the involvement of different pathways for the differential regulation of co-stimulatory molecule expression and apoptosis. The addition of anti-TNF-α did not neutralize the effects of IGF-I on CB DC maturation and apoptosis. On the contrary, neutralizing TNF-α significantly increased the IGF-I-induced up-regulation of CD83 and CD40. We conclude that IGF-I has maturation and survival effects on CB DC. These effects are mediated through both MEK and PI 3-kinase pathways but not through the IGF-I induction of TNF-α production by the DC.link_to_subscribed_fulltex

Classical Results and Modern Approaches to Nonconservative Stability

Stability of nonconservative systems is nontrivial already on the linear level, especially, if the system depends on multiple parameters. We present an overview of results and methods of stability theory that are specific for nonconservative applications. Special attention is given to the topics of flutter and divergence, reversible- and Hamiltonian-Hopf bifurcation, Krein signature, modes and waves of positive and negative energy, dissipation-induced instabilities, destabilization paradox, influence of structure of forces on stability and stability optimization