Chemokine-like Activities Research Articles

Cryptic Antimicrobial Peptides: Identification Methods and Current Knowledge of their Immunomodulatory Properties.

Cationic antimicrobial peptides (CAMPs), also known as host defence peptides (HDPs), are essential evolutionarily conserved components of innate immunity, constitutively or inducibly expressed in response to invasion by pathogens. In addition to a direct antimicrobial action, they are able to synergistically operate with other defence molecules to combat infection by neutralization of endotoxins, chemokine-like activities, induction of angiogenesis and wound repair. The importance of CAMPs has been highlighted in animal models and supported by observations in patient studies. CAMPs are attractive alternative candidates to antibiotic treatment, because they offer several advantages over the currently used drugs, moreover, knowledge on these peptides, especially regarding the intertwinement between their structure, function and mechanism of action, could be applied in the rational design of antimicrobial/anti-inflammatory/wound healing enhancing drugs. CAMPs combat pathogens by targeting bacterial membranes and essential membrane-related functions, and, in some cases, also target intracellular components. Despite differences in their size and sequence, many of them share a net positive charge and fold into amphipathic structures after contact with bacterial surfaces or endotoxins like lipopolysaccharides and lipoteichoic acid. Due to their peculiar mechanism, acquisition of resistance towards these peptides would be difficult for the bacteria. Very interestingly it has been demonstrated that several proteins, including proteins apparently not involved in immunity, can behave as sources of CAMPs hidden in their primary structures and released by the action of host and/or bacterial proteases. The existence of these "cryptic CAMPs" suggests that the panel of antimicrobial peptides present in higher eukaryotes and the variety of functions they perform could be much wider and more complex than previously suspected. This review focuses on source, structure and mechanism of action of cryptic CAMPs, with special attention to their immunomodulatory functions.

Novel chemokine-like activities of histones in tumor metastasis.

Histones are intracellular nucleosomal components and extracellular damage-associated molecular pattern molecules that modulate chromatin remodeling, as well as the immune response. However, their extracellular roles in cell migration and invasion remain undefined. Here, we demonstrate that histones are novel regulators of tumor metastasis with chemokine-like activities. Indeed, exogenous histones promote both hepatocellular carcinoma (HCC) cell migration and invasion through toll-like receptor (TLR)4, but not TLR2 or the receptor for advanced glycosylation end product. TLR4-mediated activation of nuclear factor-κB (NF-κB) by extracellular signal-regulated kinase (ERK) is required for histone-induced chemokine (e.g., C-C motif ligand 9/10) production. Pharmacological and genetic inhibition of TLR4-ERK-NF-κB signaling impairs histone-induced chemokine production and HCC cell migration. Additionally, TLR4 depletion (by using TLR4−/− mice and TLR4-shRNA) or inhibition of histone release/activity (by administration of heparin and H3 neutralizing antibody) attenuates lung metastasis of HCC cells injected via the tail vein of mice. Thus, histones promote tumor metastasis of HCC cells through the TLR4-NF-κB pathway and represent novel targets for treating patients with HCC.

Macrophage Migration Inhibitory Factor-CXCR4 Receptor Interactions

An emerging number of non-chemokine mediators are found to bind to classical chemokine receptors and to elicit critical biological responses. Macrophage migration inhibitory factor (MIF) is an inflammatory cytokine that exhibits chemokine-like activities through non-cognate interactions with the chemokine receptors CXCR2 and CXCR4, in addition to activating the type II receptor CD74. Activation of the MIF-CXCR2 and -CXCR4 axes promotes leukocyte recruitment, mediating the exacerbating role of MIF in atherosclerosis and contributing to the wealth of other MIF biological activities. Although the structural basis of the MIF-CXCR2 interaction has been well studied and was found to engage a pseudo-ELR and an N-like loop motif, nothing is known about the regions of CXCR4 and MIF that are involved in binding to each other. Using a genetic strain of Saccharomyces cerevisiae that expresses a functional CXCR4 receptor, site-specific mutagenesis, hybrid CXCR3/CXCR4 receptors, pharmacological reagents, peptide array analysis, chemotaxis, fluorescence spectroscopy, and circular dichroism, we provide novel molecular information about the structural elements that govern the interaction between MIF and CXCR4. The data identify similarities with classical chemokine-receptor interactions but also provide evidence for a partial allosteric agonist compared with CXCL12 that is possible due to the two binding sites of CXCR4.

Interleukin-8-like activity in a filarial asparaginyl-tRNA synthetase

A wide range of secondary biological functions have been documented for eukaryotic aminoacyl-tRNA synthetases including roles in transcriptional regulation, mitochondrial RNA splicing, cell growth, and chemokine-like activities. The asparaginyl-tRNA synthetase (AsnRS) of the filarial nematode, Brugia malayi, is a highly expressed excretory–secretory molecule which activates interleukin 8 (IL-8) receptors via extracellular domains that are different from those used by IL-8. Recent success in determining the complete atomic structure of the B. malayi AsnRS provided the opportunity to map its chemokine-like activity. Chemotaxis assays demonstrated that IL-8-like activity is localized in a novel 80 amino acid amino terminal substructure. Structural homology searches revealed similarities between that domain in B. malayi AsnRS and substructures involved in receptor binding by human IL-8. These observations provide important new insights into how parasite-derived molecules may play a role in the modulation of immune cell function.

ANTI-INFECTIVE PROTECTIVE PROPERTIES OF S100 CALGRANULINS.

The calgranulins are a subgroup of proteins in the S100 family (calgranulin A, S100A8; calgranulin B, S100A9 and calgranulin C, S100A12) that provide protective anti-infective and anti-inflammatory functions for the mammalian host. In this review, we discuss the structure-function relationships whereby S100A8 and S100A9, and for comparison, S100A12, provide intra- and extracellular protection during the complex interplay between infection and inflammation and how the calgranulins are regulated to optimally protect the host. Ideally located to support epithelial barrier function, calprotectin, a complex of S100A8/S100A9, is expressed in squamous mucosal keratinocytes and innate immune cells present at mucosal surfaces. The calgranulins are also abundantly produced in neutrophils and monocytes, whereas expression is induced in epidermal keratinocytes, gastrointestinal epithelial cells and fibroblasts during inflammation. The calgranulins show species-specific expression and function. For example, S100A8 is chemotactic in rodents but not in humans. In humans, S100A12 appears to serve as a functional chemotactic homolog to murine S100A8. Transition metal-binding and oxidation sites within calgranulins are able to create structural changes that may orchestrate new protective functions or binding targets. The calgranulins thus appear to adopt a variety of roles to protect the host. In addition to serving as a leukocyte chemoattractant, protective functions include oxidant scavenging, antimicrobial activity, and chemokine-like activities. Each function may reflect the concentration of the calgranulin, post-transcriptional modifications, oligomeric forms, and the proximal intracellular or extracellular environments. Calprotectin and the calgranulins are remarkable as multifunctional proteins dedicated to protecting the intra- and extracellular environments during infection and inflammation.

The nuclear protein HMGB1, a new kind of chemokine?

The chromosomal protein HMGB1 is now regarded as a proinflammatory cytokine. Importantly, HMGB1 has chemotactic activity suggesting its involvement in the early and late events of the inflammatory reaction. Therefore, HMGB1 has all the hallmarks of a chemokine (chemotactic cytokine). We propose to classify HMGB1 into a new group of proteins unrelated structurally to chemokines but having chemokine-like functions, and to name this class CLF (chemokine-like functions). The CLF class should include other unrelated molecules such as urokinase and its receptor, cytokines macrophage migration inhibitory factor (MIF) and interleukin (IL)-6, anaphylatoxin C5a, ribosomal protein S19, and thioredoxin that have similar chemokine-like activities. This innovative concept may lead to the identification of new therapeutic targets.

Thioredoxin Superfamily and Thioredoxin‐Inducing Agents

Mammalian thioredoxin (TRX) with redox-active dithiol in the active site plays multiple roles in intracellular signaling and resistance against oxidative stress. TRX is induced by a variety of stresses including infectious agents as well as hormones and chemicals. TRX is secreted from activated cells such as HTLV-I-transformed T-cells as a redox-sensitive molecule with cytokine-like and chemokine-like activities. The promoter of the TRX gene contains a series of stress-responsive elements. In turn, TRX promotes activation of transcription factors such as NF-kappa B, AP-1, and p53. We have reported that natural substances including estrogen, prostaglandins, and cAMP induce mRNA, protein, and secretion of TRX. These agents seemed to exert their physiological functions including cytoprotective actions partly through the induction of TRX without massive oxidative stress, which induces TRX strongly as well as other stress proteins. We report here a new TRX inducer substance, geranylgeranylacetone (GGA), which is originally derived from a natural plant constituent and has been used in the clinical field as an anti-ulcer drug. We have demonstrated that GGA induces the messenger RNA and protein of TRX and affects the activation of transcription factors, AP-1 and NF-kappa B, and that GGA blunted ethanol-induced cytotoxicity of cultured hepatocytes and gastrointestine mucosal cells. We will discuss a possible novel molecular mechanism of GGA, which is to protect cells via the induction of TRX and activation of transcription factors such as NF-kappa B and AP-1. Identification of the particular TRX-inducing components may contribute to the elucidation of the molecular basis of the "French Paradox," in which good red wines are beneficial for the cardiovascular system.

Chronic elevation of plasma thioredoxin: inhibition of chemotaxis and curtailment of life expectancy in AIDS.

Thioredoxin (Trx) is an intracellular redox protein with extracellular cytokine-like and chemokine-like activities. We show here that, although plasma Trx levels are unrelated to survival of HIV-infected individuals with CD4 cell counts above 200/microl blood, survival is significantly impaired (P = 0.003) when plasma Trx is chronically elevated in HIV-infected subjects with CD4 T cell counts below this level (i.e., with Centers for Disease Control (CDC)-defined AIDS). Relevant to the mechanism potentially underlying this finding, we also present data from experimental studies in mice showing that elevated plasma Trx efficiently blocks lipopolysaccharide (LPS)-induced chemotaxis, an innate immune mechanism that is particularly crucial when adaptive immunity is compromised. Thus, we propose that elevated plasma Trx in HIV-infected individuals with low CD4 T cell counts directly impairs survival by blocking pathogen-induced chemotaxis, effectively eliminating the last (innate) barrier against establishment of opportunistic and other infections in these immunodeficient individuals.

Secretion of thioredoxin enhances cellular resistance to cis-diamminedichloroplatinum (II).

Thioredoxin (TRX) is a redox-active protein induced by a variety of stress and secreted from cells. Collecting evidence revealed that extracellular TRX shows cytokine- and chemokine-like activities. In the present study, we studied the role of secreted TRX on cellular resistance to cis-diamminedichloroplatinum (II) (CDDP). The CDDP-resistant variants of HeLa cells not only have enhanced expression of intracellular TRX, but also show increased secretion of TRX into the culture medium, compared to the parental cells. The CDDP-resistant cells also exhibit an enhanced L-cystine uptake capability, which results in a significant increase in the intracellular sulfhydryl content, including glutathione (GSH). Exogenous administration of recombinant TRX (rTRX) increases cellular resistance to CDDP and augments the L-cystine uptake in the parental HeLa cells. Moreover, depletion of L-cystine from the culture medium or combined treatment with L-cystine uptake inhibitors increases cellular sensitivity to CDDP in the CDDP-resistant cells. These findings suggest that secreted TRX may play an important role in the acquisition of cellular CDDP resistance through enhancement of the L-cystine uptake activity, and that the L-cystine transport system, as well as the TRX system, may be a novel therapeutic target in CDDP-resistant cancer cells.

Redox regulation by thioredoxin superfamily; protection against oxidative stress and aging

Thioredoxin (TRX) is a 12 kD protein with redox-active dithiol in the active site; -Cys-Gly-Pro-Cys-. We originally cloned human TRX as adult T cell leukemia derived factor (ADF) produced by HTLV-I transformed cells. TRX and related molecules maintain a cellular reducing environment, working in concert with the glutathione system. Physiologically, TRX has cytoprotective effects against oxidative stress. TRX promotes DNA binding of transcription factors such as NF-kB, AP-1, p53, and PEBP-2. The TRX superfamily, including thioredoxin-2 (mitochondrial thioredoxin) and glutaredoxin, are involved in biologically important phenomena via the redox-regulating system. Thioredoxin-binding protein-2, which we recently identified by a yeast two-hybrid system, is a type of endogenous modulator of TRX activity. TRX is secreted from the cells and exhibits cytokine-like and chemokine-like activities. Redox regulation by TRX plays a crucial role in biological responses against oxidative stress.