Regulation of phagocyte migration and recruitment by Src-family kinases

Src-family kinases (SFKs) regulate different granulocyte and monocyte/macrophage responses. Accumulating evidence suggests that members of this family are implicated in signal transduction pathways regulating phagocytic cell migration and recruitment into inflammatory sites. Macrophages with a genetic deficiency of SFKs display marked alterations in cytoskeleton dynamics, polarization and migration. This same phenotype is found in cells with either a lack of SFK substrates and/or interacting proteins such as Pyk2/FAK, c-Cbl and p190RhoGAP. Notably, SFKs and their downstream targets also regulate monocyte recruitment into inflammatory sites. Depending on the type of assay used, neutrophil migration in vitro may be either dependent on or independent of SFKs. Also neutrophil recruitment in in vivo models of inflammation may be regulated differently by SFKs depending on the tissue involved. In this review we will discuss possible mechanisms by which SFKs may regulate phagocytic cell migratory abilities.     

ERK activation by Ca2+ ionophores depends on Ca2+ entry in lymphocytes but not in platelets, and does not conduct membrane scrambling

Rapid Ca²⁺-dependent phospholipid (PL) reorganization (scrambling) at the plasma membrane is a mechanism common to hematopoietic cells exposing procoagulant phosphatidylserine (PS). The aim of this research was to determine whether activation of the extracellular signal-regulated kinase (ERK) pathway was required for PL scrambling, based on a single report analyzing both responses induced by Ca²⁺ ionophores in megakaryoblastic HEL cells. Ca²⁺ ionophore-stimulated ERK phosphorylation was induced in platelets without external Ca²⁺, whereas exogenous Ca²⁺ entry was crucial for ERK activation in Jurkat T cells. In both cells, membrane scrambling only occurred following Ca²⁺ entry and was not blocked by inhibiting ERK phosphorylation. Furthermore, ERK proteins are strongly phosphorylated in transformed B lymphoblastic cell lines, which do not expose PS in their resting state. Overall, the data demonstrated that ERK activation and membrane scrambling are independent mechanisms. A. Arachiche, I. Badirou: These authors contributed equally to this work. Received 18 June 2008; received after revision 24 September 2008; accepted 1 October 2008     

Olfactory receptor trafficking to the plasma membrane

Olfactory receptors typically exhibit poor plasma membrane localization and functionality when heterologously expressed in most cell types. It has therefore proven difficult to effectively study olfactory receptor pharmacology and signaling mechanisms using traditional cell culture systems. Over the past few years, a variety of distinct proteins have been reported to interact with olfactory receptors and facilitate olfactory receptor trafficking to the plasma membrane in heterologous cells. Advances in this area have shed significant light on the fundamental factors governing the cell-specific control of olfactory receptor trafficking.     

Announcement

Announcement

Announcement     

Biological and Potential Therapeutic Roles of Sirtuin Deacetylases

Sirtuins comprise a unique class of nicotinamide adenine dinucleotide (NAD⁺)-dependent deacetylases that target multiple protein substrates to execute diverse biological functions. These enzymes are key regulators of clinically important cellular and organismal processes, including metabolism, cell division and aging. The desire to understand the important determinants of human health and lifespan has resulted in a firestorm of work on the seven mammalian sirtuins in less than a decade. The implication of sirtuins in medically important areas such as diabetes, cancer, cardiovascular dysfunction and neurodegenerative disease has further catapulted them to a prominent status as potential targets for nutritional and therapeutic development. Here, we present a review of published results on sirtuin biology and its relevance to human disease. Received 25 June 2008; received after revision 20 August 2008; accepted 29 August 2008     

Na+ binding to meizothrombin desF1

Meizothrombin is the physiologically active intermediate generated by a single cleavage of prothrombin at R320 to separate the A and B chains. Recent evidence has suggested that meizothrombin, like thrombin, is a Na(+)-activated enzyme. In this study we present the first X-ray crystal structure of human meizothrombin desF1 solved in the presence of the active site inhibitor PPACK at 2.1 A resolution. The structure reveals a Na(+) binding site whose architecture is practically identical to that of human thrombin. Stopped-flow measurements of Na(+) binding to meizothrombin desF1 document a slow phase of fluorescence change with a k(obs) decreasing hyperbolically with increasing [Na(+)], consistent with the existence of three conformations in equilibrium, E*, E and E:Na(+), as for human thrombin. Evidence that meizothrombin exists in multiple conformations provides valuable new information for studies of the mechanism of prothrombin activation.     

Molecular mechanisms of phagocytic uptake in mammalian cells

Phagocytosis is a highly conserved, complex process that has evolved to counter the constant threat posed by pathogens, effete cells and debris. Classically defined as a mechanism for internalising and destroying particles greater than 0.5 mum in size, it is a receptor-mediated, actin-driven process. The best-studied phagocytic receptors are the opsono-receptors, FcgammaR and CR3. Phagocytic uptake involves actin dynamics including polymerisation, bundling, contraction, severing and depolymerisation of actin filaments. Recent evidence points to the importance of membrane remodelling during phagocytosis, both in terms of changes in lipid composition and delivery of new membrane to the sites of particle binding. Here we review the molecular mechanisms of phagocytic uptake and some of the strategies developed by microbial pathogens to manipulate this process.     

Cardiolipin, the heart of mitochondrial metabolism

Cardiolipin is a unique phospholipid, which is almost exclusively localized in the mitochondrial inner membrane where it is synthesized from phosphatidylglycerol and cytidinediphosphate-diacylglycerol. After primary synthesis, the mature acyl chain composition of cardiolipin is achieved by at least two remodeling mechanisms. In the mitochondrial membrane cardiolipin plays an important role in energy metabolism, mainly by providing stability for the individual enzymes and enzyme complexes involved in energy production. Moreover, cardiolipin is involved in different stages of the mitochondrial apoptotic process and in mitochondrial membrane dynamics. Cardiolipin alterations have been described in various pathological conditions. Patients suffering from Barth syndrome have an altered cardiolipin homeostasis caused by a primary deficiency in cardiolipin remodeling. Alterations in cardiolipin content or composition have also been reported in more frequent diseases such as diabetes and heart failure. In this review we provide an overview of cardiolipin metabolism, function and its role in different pathological states. Received 16 January 2008; received after revision 26 February 2008; accepted 26 March 2008     

The three-fingered protein domain of the human genome

Extracellular domains of some cellular receptors expressed in the organisms at different levels of development belong to three-fingered protein (TFP) fold. The Homo sapiens genome encodes at least 45 genes containing from one to three TFP domains (TFPDs), namely diverse paralogues of the Ly6 gene, CD59 and the receptors of activins, bone morphogenetic proteins, Mullerian inhibiting substance and transforming growth factor-β. C4.4a and urokinase/plasminogen activatory receptor contain two and three TFPD repeats, respectively. These diverse proteins have a low overall sequence similarity with each other and their hydrophobicity levels vary to a considerable degree. It is suggested that sequence differentiation within the TFPD led to distinct groups of proteins whose attributes were optimized to fit both the physicochemical properties specific to their functional microenvironment and selective targeting of their highly diversified extracellular cofactors. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Received 7 August 2008; accepted 29 August 2008     

Common variants near MC4R are associated with fat mass, weight and risk of obesity

To identify common variants influencing body mass index (BMI), we analyzed genome-wide association data from 16,876 individuals of European descent. After previously reported variants in FTO, the strongest association signal (rs17782313, P = 2.9 x 10(-6)) mapped 188 kb downstream of MC4R (melanocortin-4 receptor), mutations of which are the leading cause of monogenic severe childhood-onset obesity. We confirmed the BMI association in 60,352 adults (per-allele effect = 0.05 Z-score units; P = 2.8 x 10(-15)) and 5,988 children aged 7-11 (0.13 Z-score units; P = 1.5 x 10(-8)). In case-control analyses (n = 10,583), the odds for severe childhood obesity reached 1.30 (P = 8.0 x 10(-11)). Furthermore, we observed overtransmission of the risk allele to obese offspring in 660 families (P (pedigree disequilibrium test average; PDT-avg) = 2.4 x 10(-4)). The SNP location and patterns of phenotypic associations are consistent with effects mediated through altered MC4R function. Our findings establish that common variants near MC4R influence fat mass, weight and obesity risk at the population level and reinforce the need for large-scale data integration to identify variants influencing continuous biomedical traits.