CXCR4, inhibitors and mechanisms of action

Effect of an low-energy Nd: YAG laser on periodontal ligament stem cell homing through the SDF-1/CXCR4 signaling pathway

BACKGROUND

The key to the success of endogenous regeneration is to improve the homing rate of stem cells, and low-energy laser is an effective auxiliary means to promote cell migration and proliferation. The purpose of this study was to observe whether low-energy neodymium (Nd: YAG) laser with appropriate parameters can affect the proliferation and migration of periodontal ligament stem cells (PDLSCs) through SDF-1/CXCR4 pathway.

METHODS

h PDLSCs were cultured and identified. CCK8 assay was used to detect the proliferation of h PDLSCs after different power (0, 0.25, 0.5, 1, and 1.5 W) Nd: YAG laser (MSP, 10 Hz, 30 s, 300 μ m) irradiation at 2th, 3rd,5th, and 7th days, and the optimal laser irradiation parameters were selected for subsequent experiments. Then, the cells were categorized into five groups: control group (C), SDF-1 group (S), AMD3100 group (A), Nd: YAG laser irradiation group (N), and Nd: YAG laser irradiation + AMD3100 group (N + A). the migration of h PDLSCs was observed using Transwell, and the SDF-1 expression was evaluated using ELISA andRT-PCR. The SPSS Statistics 21.0 software was used for statistical analysis.

RESULTS

The fibroblasts cultured were identified as h PDLSCs. Compared with the C, when the power was 1 W, the proliferation rate of h PDLSCs was accelerated (P < 0.05). When the power was 1.5 W, the proliferation rate decreased (P < 0.05). When the power was 0.25 and 0.5 W, no statistically significant difference in the proliferation rate was observed (P > 0.05). The number of cell perforations values as follows: C (956.5 ± 51.74), A (981.5 ± 21.15), S (1253 ± 87.21), N (1336 ± 48.54), and N + A (1044 ± 22.13), that increased significantly in group N (P < 0.05), but decreased in group N + A (P < 0.05). The level of SDF-1 and the expression level of SDF-1 mRNA in groups N and N + A was higher than that in group C (P < 0.05) but lower than that in group A (P < 0.05).

CONCLUSIONS

Nd: YAG laser irradiation with appropriate parameters provides a new method for endogenous regeneration of periodontal tissue. SDF-1/CXCR4 signaling pathway may be the mechanism of LLLT promoting periodontal regeneration.

Biparatopic Protein Nanoparticles for the Precision Therapy of CXCR4+ Cancers

The accumulated molecular knowledge about human cancer enables the identification of multiple cell surface markers as highly specific therapeutic targets. A proper tumor targeting could significantly avoid drug exposure of healthy cells, minimizing side effects, but it is also expected to increase the therapeutic index. Specifically, colorectal cancer has a particularly poor prognosis in late stages, being drug targeting an appropriate strategy to substantially improve the therapeutic efficacy. In this study, we have explored the potential of the human albumin-derived peptide, EPI-X4, as a suitable ligand to target colorectal cancer via the cell surface protein CXCR4, a chemokine receptor overexpressed in cancer stem cells. To explore the potential use of this ligand, self-assembling protein nanoparticles have been generated displaying an engineered EPI-X4 version, which conferred a modest CXCR4 targeting and fast and high level of cell apoptosis in tumor CXCR4+ cells, in vitro and in vivo. In addition, when EPI-X4-based building blocks are combined with biologically inert polypeptides containing the CXCR4 ligand T22, the resulting biparatopic nanoparticles show a dramatically improved biodistribution in mouse models of CXCR4+ human cancer, faster cell internalization and enhanced target cell death when compared to the version based on a single ligand. The generation of biparatopic materials opens exciting possibilities in oncotherapies based on high precision drug delivery based on the receptor CXCR4.

Fluorescent Dye Labeling Changes the Biodistribution of Tumor-Targeted Nanoparticles

Fluorescent dye labeling is a common strategy to analyze the fate of administered nanoparticles in living organisms. However, to which extent the labeling processes can alter the original nanoparticle biodistribution has been so far neglected. In this work, two widely used fluorescent dye molecules, namely, ATTO488 (ATTO) and Sulfo-Cy5 (S-Cy5), have been covalently attached to a well-characterized CXCR4-targeted self-assembling protein nanoparticle (known as T22-GFP-H6). The biodistribution of labeled T22-GFP-H6-ATTO and T22-GFP-H6-S-Cy5 nanoparticles has been then compared to that of the non-labeled nanoparticle in different CXCR4+ tumor mouse models. We observed that while parental T22-GFP-H6 nanoparticles accumulated mostly and specifically in CXCR4+ tumor cells, labeled T22-GFP-H6-ATTO and T22-GFP-H6-S-Cy5 nanoparticles showed a dramatic change in the biodistribution pattern, accumulating in non-target organs such as liver or kidney while reducing tumor targeting capacity. Therefore, the use of such labeling molecules should be avoided in target and non-target tissue uptake studies during the design and development of targeted nanoscale drug delivery systems, since their effect over the fate of the nanomaterial can lead to considerable miss-interpretations of the actual nanoparticle biodistribution.

Efficient bioactive oligonucleotide-protein conjugation for cell-targeted cancer therapy

Oligonucleotide-protein conjugates have important applications in biomedicine. Simple and efficient methods are described for the preparation of these conjugates. Specifically, we describe a new method in which a bifunctional linker is attached to thiol-oligonucleotide to generate a reactive intermediate that is used to link to the protein. Having similar conjugation efficacy compared with the classical method in which the bifunctional linker is attached first to the protein, this new approach produces significantly more active conjugates with higher batch to batch reproducibility. In a second approach, direct conjugation is proposed using oligonucleotides carrying carboxyl groups. These methodologies have been applied to prepare nanoconjugates of an engineered nanoparticle protein carrying a T22 peptide with affinity for the CXCR4 chemokine receptor and oligomers of the antiproliferative nucleotide 2'-deoxy-5-fluorouridine in a very efficient way. The protocols have potential uses for the functionalization of proteins, amino-containing polymers or amino-lipids in order to produce complex therapeutic nucleic acid delivery systems.

Engineering tumor cell targeting in nanoscale amyloidal materials

Bacterial inclusion bodies are non-toxic, mechanically stable and functional protein amyloids within the nanoscale size range that are able to naturally penetrate into mammalian cells, where they deliver the embedded protein in a functional form. The potential use of inclusion bodies in protein delivery or protein replacement therapies is strongly impaired by the absence of specificity in cell binding and penetration, thus preventing targeting. To address this issue, we have here explored whether the genetic fusion of two tumor-homing peptides, the CXCR4 ligands R9 and T22, to an inclusion body-forming green fluorescent protein (GFP), would keep the interaction potential and the functionality of the fused peptides and then confer CXCR4 specificity in cell binding and further uptake of the materials. The fusion proteins have been well produced in Escherichia coli in their full-length form, keeping the potential for fluorescence emission of the partner GFP. By using specific inhibitors of CXCR4 binding, we have demonstrated that the engineered protein particles are able to penetrate CXCR4⁺ cells, in a receptor-mediated way, without toxicity or visible cytopathic effects, proving the availability of the peptide ligands on the surface of inclusion bodies. Since no further modification is required upon their purification, the biological production of genetically targeted inclusion bodies opens a plethora of cost-effective possibilities in the tissue-specific intracellular transfer of functional proteins through the use of structurally and functionally tailored soft materials.

Association of eukaryotic translation initiation factor eIF2B with fully solubilized CXCR4

Chemokine receptors are key regulators of leukocyte trafficking but also have an important role in development, tumor growth, and metastasis. Among the chemokine receptors, CXCR4 is the only one that leads to perinatal death when genetically ablated in mice, indicating a more-widespread function in development. To identify pathways that are activated downstream of CXCR4, a solubilization protocol was elaborated, which allows for the isolation of the endogenous receptor from human cells in its near-native conformation. Solubilized CXCR4 is recognized by the conformation-sensitive monoclonal antibody 12G5 and retains the ability to bind CXCL12 in solution, which was abolished in the presence of receptor antagonists. Mass spectrometry of CXCR4 immunoprecipitates revealed a specific interaction with the pentameric eukaryotic translation initiation factor 2B. The observation that the addition of CXCL12 leads to the dissociation of eukaryotic translation initiation factor 2B from CXCR4 suggests that stimulation of the receptor may trigger the local protein synthesis required for efficient cell movement.

International Union of Basic and Clinical Pharmacology. [corrected]. LXXXIX. Update on the extended family of chemokine receptors and introducing a new nomenclature for atypical chemokine receptors

Sixteen years ago, the Nomenclature Committee of the International Union of Pharmacology approved a system for naming human seven-transmembrane (7TM) G protein-coupled chemokine receptors, the large family of leukocyte chemoattractant receptors that regulates immune system development and function, in large part by mediating leukocyte trafficking. This was announced in Pharmacological Reviews in a major overview of the first decade of research in this field [Murphy PM, Baggiolini M, Charo IF, Hébert CA, Horuk R, Matsushima K, Miller LH, Oppenheim JJ, and Power CA (2000) Pharmacol Rev 52:145-176]. Since then, several new receptors have been discovered, and major advances have been made for the others in many areas, including structural biology, signal transduction mechanisms, biology, and pharmacology. New and diverse roles have been identified in infection, immunity, inflammation, development, cancer, and other areas. The first two drugs acting at chemokine receptors have been approved by the U.S. Food and Drug Administration (FDA), maraviroc targeting CCR5 in human immunodeficiency virus (HIV)/AIDS, and plerixafor targeting CXCR4 for stem cell mobilization for transplantation in cancer, and other candidates are now undergoing pivotal clinical trials for diverse disease indications. In addition, a subfamily of atypical chemokine receptors has emerged that may signal through arrestins instead of G proteins to act as chemokine scavengers, and many microbial and invertebrate G protein-coupled chemokine receptors and soluble chemokine-binding proteins have been described. Here, we review this extended family of chemokine receptors and chemokine-binding proteins at the basic, translational, and clinical levels, including an update on drug development. We also introduce a new nomenclature for atypical chemokine receptors with the stem ACKR (atypical chemokine receptor) approved by the Nomenclature Committee of the International Union of Pharmacology and the Human Genome Nomenclature Committee.

Peptide and protein-based inhibitors of HIV-1 co-receptors

Human immunodeficiency virus (HIV) afflicts an estimated 30 million people globally, making it a continuing pandemic. Despite major research efforts, the rate of new infections has remained relatively static over time. This article reviews an emerging strategy for the treatment of HIV, the inhibition of the co-receptors necessary for HIV entry, CCR5 and CXCR4. The aim of this article is to highlight potential therapeutics derived from peptides and proteins that show particular promise in HIV treatment. Molecules that act on CCR5, CXCR4 or on both receptors will be discussed herein.

Scavenging strategy for specific activity improvement: application to a new CXCR4-specific cyclopentapeptide positron emission tomography tracer

Huisgen cycloaddition is attractive to label peptide because of its rapidity and bioorthogonality. However, for larger tracers, the physico-chemical differences between the precursor and the tracer are usually insufficient to allow their separation by HPLC, reducing the specific activity. This is of importance for peptidic tracers because the combination of their high-affinity receptor with low specific activity results in the precursor saturating the receptors, causing non-specific tracer binding. Here, we report a fast, one-pot, general strategy to circumvent this issue, yielding a tracer of improved specific activity. It consists in adding a lipophilic azide after the labeling step to scavenge unreacted precursor into a more lipophilic species that does not co-elute with the tracer. We applied this strategy to a new fluorinated cyclopentapeptidic CXCR4 antagonist for the PET imaging of cancer, CCIC15, for which we managed to reduce the apparent peptide concentration by a factor of 34 in 10 min. This tracer was radiolabeled by click chemistry with 2-[(18) F]fluoroethylazide, yielding the tracer in 18 ± 6% (n = 5) end-of-synthesis radiochemical yields (EOS-RCY) in 1.5 h from [(18) F]fluoride with a specific activity of 19.4 GBq µmol(-1) . Preliminary biological evaluation of the probe confirmed potency and specificity for CXCR4; further biological evaluation is underway.

Recruitment of exogenous mesenchymal stem cells in mandibular distraction osteogenesis by the stromal cell-derived factor-1/chemokine receptor-4 pathway in rats

Distraction osteogenesis is widely used in orthopaedic and craniofacial surgery. However, its exact mechanism is still poorly understood. The purpose of this study was to find out whether there is systemic recruitment of mesenchymal stem cells (MSC) to the neocallus in the distraction gap by the stromal cell-derived factor-1 (SDF-1)/CXC chemokine receptor 4 (CXCR4) axis during osteogenesis. We examined the migration of MSC towards a gradient of SDF-1 in vitro. We also transplanted MSC labelled with green fluorescent protein (GFP) intravenously, with or without treatment with CXCR4-blocking antibody, into rats that had had unilateral mandibular distraction osteogenesis, and investigated the distribution of cells labelled with GFP in the soft callus after 24 h. We found that SDF-1 facilitated the migration potency of MSC both in vitro and in vivo, and this migration could be inhibited by AMD3100, an antagonist of CXCR4, and promoted by local infusion of exogenous SDF-1 into the distraction gap. This study provides a new insight into the molecular basis of how new bone is regenerated during distraction osteogenesis.

Arrest Functions of the MIF Ligand/Receptor Axes in Atherogenesis

Macrophage migration inhibitory factor (MIF) has been defined as an important chemokine-like function (CLF) chemokine with an essential role in monocyte recruitment and arrest. Adhesion of monocytes to the vessel wall and their transendothelial migration are critical in atherogenesis and many other inflammatory diseases. Chemokines carefully control all steps of the monocyte recruitment process. Those chemokines specialized in controlling arrest are typically immobilized on the endothelial surface, mediating the arrest of rolling monocytes by chemokine receptor-triggered pathways. The chemokine receptor CXCR2 functions as an important arrest receptor on monocytes. An arrest function has been revealed for the bona fide CXCR2 ligands CXCL1 and CXCL8, but genetic studies also suggested that additional arrest chemokines are likely to be involved in atherogenic leukocyte recruitment. While CXCR2 is known to interact with numerous CXC chemokine ligands, the CLF chemokine MIF, which structurally does not belong to the CXC chemokine sub-family, was surprisingly identified as a non-cognate ligand of CXCR2, responsible for critical arrest functions during the atherogenic process. MIF was originally identified as macrophage migration inhibitory factor (this function being eponymous), but is now known as a potent inflammatory cytokine with CLFs including chemotaxis and leukocyte arrest. This review will cover the mechanisms underlying these functions, including MIF’s effects on LFA1 integrin activity and signal transduction, and will discuss the structural similarities between MIF and the bona fide CXCR2 ligand CXCL8 while emphasizing the structural differences. As MIF also interacts with CXCR4, a chemokine receptor implicated in CXCL12-elicited lymphocyte arrest, the arrest potential of the MIF/CXCR4 axis will also be scrutinized as well as the recently identified role of pericyte MIF in attracting leukocytes exiting through venules as part of the pericyte “motility instruction program.”

Biological activities of guanidine compounds, 2008 - 2012 update

INTRODUCTION

Compounds incorporating guanidine moiety have found many practical applications in diverse areas of chemistry, such as nucleophilic organocatalysis, anion recognition and coordination chemistry. Moreover, guanidine functional group is found in natural products, pharmaceuticals and cosmetic ingredients produced by synthetic methods. Thus, knowledge of their biological activities and therapeutic uses is of utmost importance for researchers involved in drug discovery processes.

AREAS COVERED

In this review the authors highlight the continued development and therapeutic applications of newly synthesized guanidine-containing compounds including small peptides and peptidomimetics incorporating arginine. The review presents patents and patent applications filed in the years 2008 - 2012 with emphasis placed on new mechanisms of pharmacological action of guanidine derivatives.

EXPERT OPINION

While guanidines are often thought of as strong organic bases and compounds hydrophilic in nature, over the last 4 years there has been an enormous increase in discovery of new promising lead structures with guanidine core, suitable for development of potential drugs acting at central nervous system, anti-inflammatory agents, anti-diabetic and chemotherapeutic agents as well as cosmetics.

Intracellular CXCR4⁺ cell targeting with T22-empowered protein-only nanoparticles

BACKGROUND

Cell-targeting peptides or proteins are appealing tools in nanomedicine and innovative medicines because they increase the local drug concentration and reduce potential side effects. CXC chemokine receptor 4 (CXCR4) is a cell surface marker associated with several severe human pathologies, including colorectal cancer, for which intracellular targeting agents are currently missing.

RESULTS

Four different peptides that bind CXCR4 were tested for their ability to internalize a green fluorescent protein-based reporter nanoparticle into CXCR4⁺ cells. Among them, only the 18 mer peptide T22, an engineered segment derivative of polyphemusin II from the horseshoe crab, efficiently penetrated target cells via a rapid, receptor-specific endosomal route. This resulted in accumulation of the reporter nanoparticle in a fully fluorescent and stable form in the perinuclear region of the target cells, without toxicity either in cell culture or in an in vivo model of metastatic colorectal cancer.

CONCLUSION

Given the urgent demand for targeting agents in the research, diagnosis, and treatment of CXCR4-linked diseases, including colorectal cancer and human immunodeficiency virus infection, T22 appears to be a promising tag for the intracellular delivery of protein drugs, nanoparticles, and imaging agents.

Imaging agents for the chemokine receptor 4 (CXCR4)

The interaction between the chemokine receptor 4 (CXCR4) and stromal cell-derived factor-1 (SDF-1, also known as CXCL12) is a natural regulatory process in the human body. However, CXCR4 over-expression is also found in diseases such as cancer, where it plays a role in, among others, the metastatic spread. For this reason it is an interesting biomarker for the field of diagnostic oncology, and therefore, it is gaining increasing interest for applications in molecular imaging. Especially "small-molecule" imaging agents based on T140, FC131 and AMD3100 have been extensively studied. SDF-1, antibodies, pepducins and bioluminescence have also been used to visualize CXCR4. In this critical review reported CXCR4 targeting imaging agents are described based on their affinity, specificity and biodistribution. The level wherein CXCR4 is up-regulated in cancer patients and its relation to the different cell lines and animal models used to evaluate the efficacy of the imaging agents is also discussed (221 references).

The role of cancer-associated myofibroblasts in intrahepatic cholangiocarcinoma

Intrahepatic cholangiocarcinoma is typically characterized by a dense desmoplastic stroma, of which cancer-associated myofibroblasts (which express α-smooth muscle actin), are a major cellular component. These stromal myofibroblasts have a crucial role in accelerating the progression of intrahepatic cholangiocarcinoma and in promoting resistance to therapy through interactive autocrine and paracrine signaling pathways that promote malignant cell proliferation, migration, invasiveness, apoptosis resistance and/or epithelial-mesenchymal transition. These changes correlate with aggressive tumor behavior. Hypoxic desmoplasia and aberrant Hedgehog signaling between stromal myofibroblastic cells and cholangiocarcinoma cells are also critical modulators of intrahepatic cholangiocarcinoma progression and therapy resistance. A novel strategy has been developed to achieve improved therapeutic outcomes in patients with advanced intrahepatic cholangiocarcinoma, based on targeting of multiple interactive pathways between cancer-associated myofibroblasts and intrahepatic cholangiocarcinoma cells that are associated with disease progression and poor survival. Unique organotypic cell culture and orthotopic rat models of cholangiocarcinoma progression are well suited to the rapid preclinical testing of this potentially paradigm-shifting strategy.

The role of cancer-associated myofibroblasts in intrahepatic cholangiocarcinoma

Intrahepatic cholangiocarcinoma is typically characterized by a dense desmoplastic stroma, of which cancer-associated myofibroblasts (which express α-smooth muscle actin), are a major cellular component. These stromal myofibroblasts have a crucial role in accelerating the progression of intrahepatic cholangiocarcinoma and in promoting resistance to therapy through interactive autocrine and paracrine signaling pathways that promote malignant cell proliferation, migration, invasiveness, apoptosis resistance and/or epithelial-mesenchymal transition. These changes correlate with aggressive tumor behavior. Hypoxic desmoplasia and aberrant Hedgehog signaling between stromal myofibroblastic cells and cholangiocarcinoma cells are also critical modulators of intrahepatic cholangiocarcinoma progression and therapy resistance. A novel strategy has been developed to achieve improved therapeutic outcomes in patients with advanced intrahepatic cholangiocarcinoma, based on targeting of multiple interactive pathways between cancer-associated myofibroblasts and intrahepatic cholangiocarcinoma cells that are associated with disease progression and poor survival. Unique organotypic cell culture and orthotopic rat models of cholangiocarcinoma progression are well suited to the rapid preclinical testing of this potentially paradigm-shifting strategy.

Design, synthesis, and functionalization of dimeric peptides targeting chemokine receptor CXCR4

The chemokine receptor CXCR4 is a critical regulator of inflammation and immune surveillance, and it is specifically implicated in cancer metastasis and HIV-1 infection. On the basis of the observation that several of the known antagonists remarkably share a C(2) symmetry element, we constructed symmetric dimers with excellent antagonistic activity using a derivative of a cyclic pentapeptide as monomer. To optimize the binding affinity, we investigated the influence of the distance between the monomers and the pharmacophoric sites in the synthesized constructs. The affinity studies in combination with docking computations support a two-site binding model. In a final step, 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) was introduced as chelator for (radio-)metals, thus allowing to exploit these compounds as a new group of CXCR4-binding peptidic probes for molecular imaging and endoradiotherapeutic purposes. Both the DOTA conjugates and some of their corresponding metal complexes retain good CXCR4 affinity, and one (68)Ga labeled compound was studied as PET tracer.

Engineered biological entities for drug delivery and gene therapy protein nanoparticles

The development of genetic engineering techniques has speeded up the growth of the biotechnological industry, resulting in a significant increase in the number of recombinant protein products on the market. The deep knowledge of protein function, structure, biological interactions, and the possibility to design new polypeptides with desired biological activities have been the main factors involved in the increase of intensive research and preclinical and clinical approaches. Consequently, new biological entities with added value for innovative medicines such as increased stability, improved targeting, and reduced toxicity, among others have been obtained. Proteins are complex nanoparticles with sizes ranging from a few nanometers to a few hundred nanometers when complex supramolecular interactions occur, as for example, in viral capsids. However, even though protein production is a delicate process that imposes the use of sophisticated analytical methods and negative secondary effects have been detected in some cases as immune and inflammatory reactions, the great potential of biodegradable and tunable protein nanoparticles indicates that protein-based biotechnological products are expected to increase in the years to come.

CXCR4 nanobodies (VHH-based single variable domains) potently inhibit chemotaxis and HIV-1 replication and mobilize stem cells

The important family of G protein-coupled receptors has so far not been targeted very successfully with conventional monoclonal antibodies. Here we report the isolation and characterization of functional VHH-based immunoglobulin single variable domains (or nanobodies) against the chemokine receptor CXCR4. Two highly selective monovalent nanobodies, 238D2 and 238D4, were obtained using a time-efficient whole cell immunization, phage display, and counterselection method. The highly selective VHH-based immunoglobulin single variable domains competitively inhibited the CXCR4-mediated signaling and antagonized the chemoattractant effect of the CXCR4 ligand CXCL12. Epitope mapping showed that the two nanobodies bind to distinct but partially overlapping sites in the extracellular loops. Short peptide linkage of 238D2 with 238D4 resulted in significantly increased affinity for CXCR4 and picomolar activity in antichemotactic assays. Interestingly, the monovalent nanobodies behaved as neutral antagonists, whereas the biparatopic nanobodies acted as inverse agonists at the constitutively active CXCR4-N3.35A. The CXCR4 nanobodies displayed strong antiretroviral activity against T cell-tropic and dual-tropic HIV-1 strains. Moreover, the biparatopic nanobody effectively mobilized CD34-positive stem cells in cynomolgus monkeys. Thus, the nanobody platform may be highly effective at generating extremely potent and selective G protein-coupled receptor modulators.

Thermal stability of the human immunodeficiency virus type 1 (HIV-1) receptors, CD4 and CXCR4, reconstituted in proteoliposomes

BACKGROUND

The entry of human immunodeficiency virus (HIV-1) into host cells involves the interaction of the viral exterior envelope glycoprotein, gp120, and receptors on the target cell. The HIV-1 receptors are CD4 and one of two chemokine receptors, CCR5 or CXCR4.

METHODOLOGY/PRINCIPAL FINDINGS

We created proteoliposomes that contain CD4, the primary HIV-1 receptor, and one of the coreceptors, CXCR4. Antibodies against CD4 and CXCR4 specifically bound the proteoliposomes. CXCL12, the natural ligand for CXCR4, and the small-molecule CXCR4 antagonist, AMD3100, bound the proteoliposomes with affinities close to those associated with the binding of these molecules to cells expressing CXCR4 and CD4. The HIV-1 gp120 exterior envelope glycoprotein bound tightly to proteoliposomes expressing only CD4 and, in the presence of soluble CD4, bound weakly to proteoliposomes expressing only CXCR4. The thermal stability of CD4 and CXCR4 inserted into liposomes was examined. Thermal denaturation of CXCR4 followed second-order kinetics, with an activation energy (E(a)) of 269 kJ/mol (64.3 kcal/mol) and an inactivation temperature (T(i)) of 56°C. Thermal inactivation of CD4 exhibited a reaction order of 1.3, an E(a) of 278 kJ/mol (66.5 kcal/mol), and a T(i) of 52.2°C. The second-order denaturation kinetics of CXCR4 is unusual among G protein-coupled receptors, and may result from dimeric interactions between CXCR4 molecules.

CONCLUSIONS/SIGNIFICANCE

Our studies with proteoliposomes containing the native HIV-1 receptors allowed an examination of the binding of biologically important ligands and revealed the higher-order denaturation kinetics of these receptors. CD4/CXCR4-proteoliposomes may be useful for the study of virus-target cell interactions and for the identification of inhibitors.

Macrophage migration inhibitory factor: a noncanonical chemokine important in atherosclerosis

In the recent years, atherogenesis has increasingly been linked to inflammatory processes in the injured vessel wall. Recruitment and arrest of monocytes, T cells, and neutrophils via the concerted actions of multiple chemokines and their chemokine receptors have been the subject of intense research and are being appreciated as key events underlying atherosclerotic lesion formation and progression. The evolutionary conserved cytokine macrophage migration inhibitory factor (MIF) exhibits prominent proinflammatory and proatherogenic functions, and the latest findings on its chemotactic and chemokine-like properties imply MIF as a crucial drug target for the treatment of inflammatory diseases. In this review, the role of MIF in atherosclerosis and injury-induced neointima formation is discussed. We place an emphasis on its proinflammatory and chemokine-like functions in the context of underlying extra- and intracellular signaling mechanisms. These findings clearly distinguish MIF from other cytokines in atherosclerosis and justify the intensive search for inhibitors targeting MIF in the treatment of inflammatory diseases, including advanced atherosclerosis.

Sequence analysis, characterization and mRNA distribution of channel catfish (Ictalurus punctatus Rafinesque, 1818) chemokine (C-X-C motif) receptor 4 (CXCR4) cDNA

Chemokine receptor CXCR4, a member of the G protein-coupled receptor superfamily, binds selectively CXCL12. This protein plays many important roles in immunological as well as pathophysiological functions. In this study, we identified and characterized the channel catfish CXCR4 transcript. The full-length nucleic acid sequence of channel catfish CXCR4 cDNA comprised of 1994 nucleotides, including an open reading frame, which appears to encode a putative peptide of 357 amino acid residues with a calculated molecular mass of 40.1kDa. By comparison with the human counterpart, the channel catfish CXCR4 peptide can be divided into domains, including seven transmembrane domains, four cytoplasmic domains, and four extracellular domains. The CXCR4 transcript was detected in spleen, anterior kidney, liver, intestine, skin and gill of all catfish examined in this study. Because four CXCL of channel catfish have been identified, the result provides valuable information for further exploring the channel catfish chemokine signalling pathways and their roles in immune responses to infection.

Structural comparison of different antibodies interacting with parvovirus capsids

The structures of canine parvovirus (CPV) and feline parvovirus (FPV) complexed with antibody fragments from eight different neutralizing monoclonal antibodies were determined by cryo-electron microscopy (cryoEM) reconstruction to resolutions varying from 8.5 to 18 A. The crystal structure of one of the Fab molecules and the sequence of the variable domain for each of the Fab molecules have been determined. The structures of Fab fragments not determined crystallographically were predicted by homology modeling according to the amino acid sequence. Fitting of the Fab and virus structures into the cryoEM densities identified the footprints of each antibody on the viral surface. As anticipated from earlier analyses, the Fab binding sites are directed to two epitopes, A and B. The A site is on an exposed part of the surface near an icosahedral threefold axis, whereas the B site is about equidistant from the surrounding five-, three-, and twofold axes. One antibody directed to the A site binds CPV but not FPV. Two of the antibodies directed to the B site neutralize the virus as Fab fragments. The differences in antibody properties have been linked to the amino acids within the antibody footprints, the position of the binding site relative to the icosahedral symmetry elements, and the orientation of the Fab structure relative to the surface of the virus. Most of the exposed surface area was antigenic, although each of the antibodies had a common area of overlap that coincided with the positions of the previously mapped escape mutations.