Leukocyte recruitment in atherosclerosis: Potential targets for therapeutic approaches?

Atherosclerosis is a complex inflammatory disease involving cellular migration and interaction. Vascular injury in response to different cardiovascular risk factors enhances endothelial dysfunction, which in turn promotes the expression of inflammatory markers and transendothelial leukocyte migration. Recruitment of leukocytes from the blood stream into the vessel intima is a crucial step for the development of the disease. Recent findings have highlighted the role of chemokines, chemokine receptors, adhesion molecules, and gap junctions in this process by acting as chemoattractant, adhesive, or intercellular communication molecules. In this short review, we summarize new data concerning the different steps from leukocyte arrest to transendothelial migration and discuss potential new therapeutic approaches concerning these processes. Received 15 March 2006; received after revision 19 May 2006; accepted 13 June 2006     

Structural view of cadherin-mediated cell-cell adhesion

Following the multiplication of biochemical, biophysical and structural studies describing cadherin molecules and their interactions, several ideas have emerged to explain the mechanisms of cadherin-mediated cell adhesion. Although different models were proposed for cadherin interactions, a consensus has come forth considering lateral dimerization of cadherins as being a central component of the cell-cell adhesion process. This review summarizes the recent development in structural studies of cadherins. Received 14 September 1998; received after revision 14 November 1998; accepted 16 November 1998     

Cationic host defence peptides: Innate immune regulatory peptides as a novel approach for treating infections

An increase in antibiotic resistance and the emergence of new pathogens has led to an urgent need for alternative approaches to infection management. Immunomodulatory molecules that do not target the pathogen directly, but rather selectively enhance and/or alter host defence mechanisms, are attractive candidates for therapeutic development. Natural cationic host defence peptides represent lead molecules that boost innate immune responses and selectively modulate pathogen-induced inflammatory responses. This review discusses recent evidence exploring the mechanisms of cationic host defence peptides as innate immune regulators, their role in the interface of innate and adaptive immunity, and their potential application as beneficial therapeutics in overcoming infectious diseases. Received 3 November 2006; received after revision 14 December 2006; accepted 22 January 2007     

Leukocyte integrins and inflammation

Leukocyte adhesion is of pivotal functional importance. Without adequate adhesion, T lymphocytes and natural killer cells are not cytotoxic, B cells cannot develop into antibody secreting plasma cells, leukocytes do not home into inflamed tissues and myeloid cells are not able to phagocytize or exhibit chemotactic responses. During evolution several leukocyte adhesion molecules have developed belonging to a few molecular families. Among these, the leukocyte-specific integrins (β ₂ integrins, CD11/CD18 molecules) are among the most important. Much progress has taken place during the past few years, and at present we have a considerable knowledge of their structure and function. Inflammation is critically dependent on integrin activity, and its regulation forms the topic of this short review.     

Tetraspanin-enriched microdomains regulate digitation junctions

Tetraspanins co-emerged with multi-cellular organisms during evolution are typically localized at the cell–cell interface, and form tetraspanin-enriched microdomains (TEMs) by associating with each other and other membrane molecules. Tetraspanins affect various biological functions, but how tetraspanins engage in multi-faceted functions at the cellular level is largely unknown. When cells interact, the membrane microextrusions at the cell–cell interfaces form dynamic, digit-like structures between cells, which we term digitation junctions (DJs). We found that (1) tetraspanins CD9, CD81, and CD82 and (2) TEM-associated molecules integrin α3β1, CD44, EWI2/PGRL, and PI-4P are present in DJs of epithelial, endothelial, and cancer cells. Tetraspanins and their associated molecules also regulate the formation and development of DJs. Moreover, (1) actin cytoskeleton, RhoA, and actomyosin activities and (2) growth factor receptor-Src-MAP kinase signaling, but not PI-3 kinase, regulate DJs. Finally, we showed that DJs consist of various forms in different cells. Thus, DJs are common, interactive structures between cells, and likely affect cell adhesion, migration, and communication. TEMs probably modulate various cell functions through DJs. Our findings highlight that DJ morphogenesis reflects the transition between cell–matrix adhesion and cell–cell adhesion and involves both cell–cell and cell–matrix adhesion molecules.     

ALCAM/CD166 adhesive function is regulated by the tetraspanin CD9

ALCAM/CD166 is a member of the immunoglobulin superfamily of cell adhesion molecules (Ig-CAMs) which mediates intercellular adhesion through either homophilic (ALCAM–ALCAM) or heterophilic (ALCAM–CD6) interactions. ALCAM-mediated adhesion is crucial in different physiological and pathological phenomena, with particular relevance in leukocyte extravasation, stabilization of the immunological synapse, T cell activation and proliferation and tumor growth and metastasis. Although the functional implications of ALCAM in these processes is well established, the mechanisms regulating its adhesive capacity remain obscure. Using confocal microscopy colocalization, and biochemical and functional analyses, we found that ALCAM directly associates with the tetraspanin CD9 on the leukocyte surface in protein complexes that also include the metalloproteinase ADAM17/TACE. The functional relevance of these interactions is evidenced by the CD9-induced upregulation of both homophilic and heterophilic ALCAM interactions, as reflected by increased ALCAM-mediated cell adhesion and T cell migration, activation and proliferation. The enhancement of ALCAM function induced by CD9 is mediated by a dual mechanism involving (1) augmented clustering of ALCAM molecules, and (2) upregulation of ALCAM surface expression due to inhibition of ADAM17 sheddase activity.     

Differential roles of multiple adhesion molecules in cell migration: granule cell migration in cerebellum

The migration of cerebellar granule cells from the external granular layer to the internal granular layer is mediated by the radical Bergmann glial fiber. Recent works have shown that cell adhesion molecules, extra-cellular matrix proteins and proteolytic enzymes or their activators are involved in this process. Immuno-localization studies showed differential temporal and spatial expression patterns of different adhesion molecules, their isoforms, and post-translational modification during different stages of granule cell migration. Functional perturbation experiments using cerebellar explant cultures demonstrated that several adhesion molecules as well as plasminogen activator are involved in granule cell migration and are required in different stages. Other systems used to study granule cell migration including dissociated microwell cultures and granule cell deficient mouse mutants are discussed in the context of adhesion molecules. The results accumulated so far suggest that the migration of granule cells is a complex process in which the cooperation of a group of molecules with different functions, some for adhesion some for de-adhesion, are required to fulfill the different needs during the migratory course.     

Differential roles of multiple adhesion molecules in cell migration: Granule cell migration in cerebellum

Summary The migration of cerebellar granule cells from the external granular layer to the internal granular layer is mediated by the radial Bergmann glial fiber. Recent works have shown that cell adhesion molecules, extra-cellular matrix proteins and proteolytic enzymes or their activators are involved in this process. Immuno-localization studies showed differential temporal and spatial expression patterns of different adhesion molecules, their isoforms, and post-translational modification during different stages of granule cell migration. Functional perturbation experiments using cerebellar explant cultures demonstrated that several adhesion molecules as well as plasminogen activator are involved in granule cell migration and are required in different stages. Other systems used to study granule cell migration including dissociated microwell cultures and granule cell deficient mouse mutants are discussed in the context of adhesion molecules. The results accumulated so far suggest that the migration of granule cells is a complex process in which the cooperation of a group of molecules with different functions, some for adhesion some for de-adhesion, are required to fulfill the different needs during the migratory course.     

Adhesion molecules and animal development

In recent years considerable progress has been made in the identification and characterization of molecules that mediate cell adhesion during animal development. This review attempts to pick out from the vast amount of information in this rapidly expanding field some of the key features of adhesion molecules, to present ideas about their role in development, and to indicate the directions in which the field is now moving.     

Adhesion molecules and animal development

Summary In recent years considerable progress has been made in the identification and characterization of molecules that mediate cell adhesion during animal development. This review attempts to pick out from the vast amount of information in this rapidly expanding field some of the key features of adhesion molecules, to present ideas about their role in development, and to indicate the directions in which the field is now moving.     

Influence of temperature on taste perception

Daily experience tells us that temperature has a strong influence on how we taste. Despite the longstanding interest of many specialists in this aspect of taste, we are only starting to understand the molecular mechanisms underlying the temperature dependence of different taste modalities. Recent research has led to the identification of some strong thermosensitive molecules in the taste transduction pathway. The cold activation of the epithelial Na⁺ channel and the heat activation of the taste variant of the vanilloid receptor (TRPV1t) may underlie the temperature dependence of salt responses. Heat activation of the transient receptor potential channel TRPM5 explains the enhancement of sweet taste perception by warm temperatures. Current development of methods to study taste cell physiology will help to determine the contribution of other temperature-sensitive events in the taste transduction pathways. Vice versa, the analysis of the thermodynamic properties of these events may assist to unveil the nature of several taste processes. Received 29 August 2006; received after revision 5 October 2006; accepted 20 November 2006     

Scavenger, transducer, RNA chaperone? What ligands of the prion protein teach us about its function

Prion protein, a misfolded isoform of which is the essential component of the agent of prion diseases, still remains an enigmatic protein whose physiological functions are at best hypothetical. To gain a better insight into its putative role, many studies were undertaken to look for molecules that bind prion protein, and have notably identified divalent metal ions, several proteins, and nucleic acids. At first sight, the diversity of prion protein’s ligands seems of little help to infer a plausible function. However, the intrinsically disordered property of its N-terminal tail and the potential of the protein to adopt a transmembrane topology, can both be taken into account to predict its different states during its cellular cycle and its possible functions, of which the most promising correspond to a general scavenger, a sensor or adaptor in a signaling cascade, and an RNA chaperone. Received 16 August 2006; received after revision 7 November 2006; accepted 13 December 2006     

Integrin antagonists

Integrins are a family of cell surface glycoproteins that mediate numerous cell-cell and cell-matrix interactions and are involved in biological processes such as tissue morphogenesis, leukocyte recirculation and migration, wound healing, blood clotting and immune response. Aberrant cell adhesion has been implicated in the pathogenesis of several diseases, including a number of inflammatory disorders such as rheumatoid arthritis, inflammatory bowel disease and asthma, as well as cancer and coronary heart disease. As such integrins are seen as excellent targets for the development of therapeutic agents. This report begins with an examination of the structure of integrin molecules and their ligands and then goes on to review the current state of development of antiintegrin antagonists. Received 13 April 1999; received after revision 28 May 1999; accepted 28 May 1999     

Effects of ulapualide A and synthetic macrolide analogues on actin dynamics and gene regulation

Several marine macrolide toxins act as potent and specific actin-severing molecules. Recent elucidation of their stereochemistries and modes of interaction with actin has allowed the syntheses of bioactive analogues. Here we used synthetic analogues in a structure-function analysis of ulapualide A, a trisoxazole-based macrolide. Ulapualide A harboured potent actin-depolymerising activity both in cells and in vitro. Its synthetic diastereoisomer was three orders of magnitude less active than the natural toxin and synthetic macrolide fragments lacked actin-capping/ severing activity altogether. Modulation of serum response factor (SRF)-dependent gene expression, as described for other actin-binding toxins, was also examined. Specific changes in response to ulapualide A were not observed, primarily due to its profound effects on cytoskeletal integrity and cell adhesion. Several synthetic fragments of ulapualide A also had no effect on SRF-dependent gene expression. However, inhibition was observed with a molecule corresponding to the extended aliphatic side chain of halichondramide, a structurally related macrolide. These findings indicate that side-chain derivatives of trisoxazole-based macrolides may serve to uncouple gene-regulatory events from actin dynamics. E. Vincent and J. Saxton: These two authors contributed equally Received 27 September 2006; received after revision 30 November 2006; accepted 8 January 2007     

The utility F-box for protein destruction

A signature feature of all living organisms is their utilization of proteins to construct molecular machineries that undertake the complex network of cellular activities. The abundance of a protein element is temporally and spatially regulated in two opposing aspects: de novo synthesis to manufacture the required amount of the protein, and destruction of the protein when it is in excess or no longer needed. One major route of protein destruction is coordinated by a set of conserved molecules, the F-box proteins, which promote ubiquitination in the ubiquitin-proteasome pathway. Here we discuss the functions of F-box proteins in several cellular scenarios including cell cycle progression, synapse formation, plant hormone responses, and the circadian clock. We particularly emphasize the mechanisms whereby F-box proteins recruit specific substrates and regulate their abundance in the context of SCF E3 ligases. For some exceptions, we also review how F-box proteins function through non-SCF mechanisms.     

Using a recombinant bispecific antibody to block Na<Superscript>+</Superscript>-channel toxins protects against experimental scorpion envenoming

In recent years, several molecular engineering methods of designing bispecific antibodies in various formats have been developed. Tandem-scFvs comprising two scFvs fused together via a peptide are 55-kDa molecules, and are one of the most promising and most straightforward approaches to bispecific antibody production. We report an attempt to design more effective antivenoms to the Androctonus australis scorpion using murine scFvs as building blocks to create a unique bispecific molecule that neutralizes the potent neurotoxins AahI and AahII. The tandem-scFv was produced in recombinant bacteria, purified by immobilized metal ion affinity chromatography, and analyzed by polyacrylamide gel electrophoresis, Western blot, gel filtration, mass spectrometry, and direct and competitive radioimmunoassay. In vivo, it neutralized the binding of the AahI and AahII toxins to their receptor, and protected mice against experimental envenomation. The findings reported here highlight the potential of recombinant antibody fragments for protecting against scorpion venom toxicity. Received 8 September 2006; received after revision 10 November 2006; accepted 27 November 2006     

Nanobody-induced perturbation of LFA-1/L-plastin phosphorylation impairs MTOC docking, immune synapse formation and T cell activation

The T cell integrin receptor LFA-1 orchestrates adhesion between T cells and antigen-presenting cells (APCs), resulting in formation of a contact zone known as the immune synapse (IS) which is supported by the cytoskeleton. L-plastin is a leukocyte-specific actin bundling protein that rapidly redistributes to the immune synapse following T cell–APC engagement. We used single domain antibodies (nanobodies, derived from camelid heavy-chain only antibodies) directed against functional and structural modules of L-plastin to investigate its contribution to formation of an immune synapse between Raji cells and human peripheral blood mononuclear cells or Jurkat T cells. Nanobodies that interact either with the EF hands or the actin binding domains of L-plastin both trapped L-plastin in an inactive conformation, causing perturbation of IS formation, MTOC docking towards the plasma membrane, T cell proliferation and IL-2 secretion. Both nanobodies delayed Ser⁵ phosphorylation of L-plastin which is required for enhanced bundling activity. Moreover, one nanobody delayed LFA-1 phosphorylation, reduced the association between LFA-1 and L-plastin and prevented LFA-1 enrichment at the IS. Our findings reveal subtle mechanistic details that are difficult to attain by conventional means and show that L-plastin contributes to immune synapse formation at distinct echelons.     

New developments in the biological functions of lysophospholipids

Lysophospholipids have long been recognized as membrane phospholipid metabolites, but only recently has their role as intercellular signaling molecules been appreciated. Two of the best-studied lysophospholipids, LPA and S1P, signal through cognate G-protein-coupled receptors to activate many well-known intracellular signaling pathways, leading to a variety of biologically important cell responses. Lysophospholipids and their receptors have been found in a wide range of tissues and cell types, indicating their importance in many physiological processes, including reproduction, vascular development, cancer and nervous system function. This article will focus on the most recent findings regarding the biological functions of lysophospholipids in mammalian systems, specifically as they relate to health and disease. Received 5 April 2006; received after revision 22 June 2006; accepted 9 August 2006     

Myelin basic protein: a multifunctional protein

Myelin basic protein (MBP), the second most abundant protein in central nervous system myelin, is responsible for adhesion of the cytosolic surfaces of multilayered compact myelin. A member of the ‘intrinsically disordered’ or conformationally adaptable protein family, it also appears to have several other functions. It can interact with a number of polyanionic proteins including actin, tubulin, Ca²⁺-calmodulin, and clathrin, and negatively charged lipids, and acquires structure on binding to them. It may act as a membrane actin-binding protein, which might allow it to participate in transmission of extracellular signals to the cytoskeleton in oligodendrocytes and tight junctions in myelin. Some size isoforms of MBP are transported into the nucleus and thus they may also bind polynucleotides. Extracellular signals received by myelin or cultured oligodendrocytes cause changes in phosphorylation of MBP, suggesting that MBP is also involved in signaling. Further study of this very abundant protein will reveal how it is utilized by the oligodendrocyte and myelin for different purposes. Received 2 March 2006; received after revision 12 April 2006; accepted 16 May 2006