Molecular basis of the complex formation between the two calcium-binding proteins S100A8 (MRP8) and S100A9 (MRP14)

Heterogeneous effects of S100 proteins during cell interactions between immune cells and stromal cells from synovium or skin

Cell interactions represent an important mechanism involved in the pathogenesis of chronic inflammation. The key S100 proteins A8 and A9 have been studied in several models of chronic inflammatory diseases with highly heterogeneous conclusions. In this context, the aim of this study was to determine the role of cell interactions on S100 protein production and their effect on cytokine production during cell interactions, between immune and stromal cells from synovium or skin. Peripheral blood mononuclear cells (PBMC) were cultured alone or with synoviocytes or skin fibroblasts, with or without phytohemagglutinin, exogenous A8, A9, A8/A9 proteins or anti-A8/A9 antibody. Production of IL-6, IL-1β, IL-17, TNF, A8, A9, and A8/A9 was measured by ELISA. Cell interactions with synoviocytes had no effect on A8, A9, or A8/A9 secretion, while cell interactions with skin fibroblasts decreased A8 production. This highlights the importance of stromal cell origin. The addition of S100 proteins in co-cultures with synoviocytes did not increase the production of IL-6, IL-17, or IL-1β, except for an increase of IL-6 secretion with A8. The presence of anti-S100A8/A9 antibody did not show obvious effects. Low concentration or absence of serum in the culture medium decreased the production of IL-17, IL-6, and IL-1β but despite these conditions, the addition of S100 proteins did not increase cytokine secretion. In conclusion, the role of A8/A9 in cell interactions during chronic inflammation appears complex and heterogeneous, depending on multiple factors, notably the origin of stromal cells that can affect their secretion.

RAGE Inhibitors for Targeted Therapy of Cancer: A Comprehensive Review

The receptor for advanced glycation end products (RAGE) is a member of the immunoglobulin family that is overexpressed in several cancers. RAGE is highly expressed in the lung, and its expression increases proportionally at the site of inflammation. This receptor can bind a variety of ligands, including advanced glycation end products, high mobility group box 1, S100 proteins, adhesion molecules, complement components, advanced lipoxidation end products, lipopolysaccharides, and other molecules that mediate cellular responses related to acute and chronic inflammation. RAGE serves as an important node for the initiation and stimulation of cell stress and growth signaling mechanisms that promote carcinogenesis, tumor propagation, and metastatic potential. In this review, we discuss different aspects of RAGE and its prominent ligands implicated in cancer pathogenesis and describe current findings that provide insights into the significant role played by RAGE in cancer. Cancer development can be hindered by inhibiting the interaction of RAGE with its ligands, and this could provide an effective strategy for cancer treatment.

S100A8 as a Promising Biomarker and Oncogenic Immune Protein in the Tumor Microenvironment: An Integrative Pancancer Analysis

Background

S100 Calcium Binding Protein A8 (S100A8) is beneficial for cancer immunotherapy. However, the processes underlying its therapeutic potential have not been completely studied.

Methods

The Cancer Genome Atlas provides raw data on 33 different cancer types. GEO made available GSE67501, GSE78220, and IMvigor210. We investigated S100A8's genetic changes, expression patterns, and survival studies. The linkages between S100A8 and TME, as well as its association with immunological processes/elements and the major histocompatibility complex, were explored to effectively understand the role of S100A8 in cancer immunotherapy. Three distinct immunotherapeutic cohorts were employed to examine the relationship between S100A8 and immunotherapeutic response.

Results

S100A8 expression was high in tumor tissue. The overexpression of S100A8 is associated with poor clinical outcome in patients with overall survival. S100A8 is associated with immune cell infiltration, immunological modulators, and immunotherapeutic indicators. S100A8 overexpression is connected to immune-related pathways. However, no statistically significant connection between S100A8 and immunotherapeutic response was identified.

Conclusions

S100A8 may be a reliable biomarker for tumor prognosis and a viable prospective therapeutic target for human cancer immunotherapy (e.g., GBM, KIRC, LGG, and LIHC).

S100A8/A9 in Myocardial Infarction: A Promising Biomarker and Therapeutic Target

Myocardial infarction (MI), the main cause of cardiovascular-related deaths worldwide, has long been a hot topic because of its threat to public health. S100A8/A9 has recently attracted an increasing amount of interest as a crucial alarmin that regulates the pathogenesis of cardiovascular disease after its release from myeloid cells. However, the role of S100A8/A9 in the etiology of MI is not well understood. Here, we elaborate on the critical roles and potential mechanisms of S100A8/A9 driving the pathogenesis of MI. First, cellular source of S100A8/A9 in infarcted heart is discussed. Then we highlight the effect of S100A8/A9 heterodimer in the early inflammatory period and the late reparative period of MI as well as myocardial ischemia/reperfusion (I/R) injury. Moreover, the predictive value of S100A8/A9 for the risk of recurrence of cardiovascular events is elucidated. Therefore, this review focuses on the molecular mechanisms of S100A8/A9 in MI pathogenesis to provide a promising biomarker and therapeutic target for MI.

Characterization of changes in global gene expression in the hearts and kidneys of transgenic mice overexpressing human angiotensin-converting enzyme 2

Human angiotensin-converting enzyme 2 (hACE2) has recently received a great attention due to it play a critical role as SARS-CoV receptor in the infection of human body. However, no further analysis for gene regulation has been performed in target tissues of model mice during hACE2 overproduction. To characterize changes in global gene expression in the hearts and kidneys of rtTA/hACE2 double transgenic (dTg) mice in response to hACE2 overexpression, total RNA extracted from these tissues from dTg mice after doxycycline (Dox) treatment was hybridized to oligonucleotide microarrays. Briefly, dTg mice were generated by cross-mating pα-MHC/rtTA Tg mice with pTRE/hACE2 Tg mice. The expression level of hACE2 protein was determined to be high in hearts, kidneys, and brains of dTg mice, whereas lung, liver, and testis tissues expressed low levels. The level of hACE2 was significantly enhanced in hearts and kidneys of the Dox+dTg group compared to that in Vehicle+dTg mice although consistent levels of mouse ACE2 (mACE2) remained in the same tissues. Based on the microarray analysis of heart tissue, 385 genes were differentially expressed, including 168 upregulated and 217 downregulated, when comparing non-Tg and Vehicle+dTg mice, whereas 216 genes were differentially expressed, including 136 upregulated and 80 downregulated, between Vehicle+dTg and Dox+dTg mice. In the kidneys, 402 genes were differentially expressed, including 159 upregulated and 243 downregulated, between non-Tg and Vehicle+dTg mice. Dox-treated dTg mice exhibited the differential expression of 4735 genes including 1636 upregulated and 3109 downregulated. Taken together, these findings suggested that several functional groups and individual genes can be considered biomarkers that respond to hACE2 overexpression in dTg mice. Moreover, our results provided a lot of useful information to predict physiological responses when these dTg mice are applied as a susceptible model for novel coronavirus (SARS-CoV, COVID-19) in both vaccine and drug development.

In silico assessment of human Calprotectin subunits (S100A8/A9) in presence of sodium and calcium ions using Molecular Dynamics simulation approach

Calprotectin is a heterodimeric protein complex which consists of two subunits including S100A8 and S100A9. This protein has a major role in different inflammatory disease and various types of cancers. In current study we aimed to evaluate the structural and thermodynamic changes of the subunits and the complex in presence of sodium and calcium ions using molecular dynamics (MD) simulation. Therefore, the residue interaction network (RIN) was visualized in Cytoscape program. In next step, to measure the binding free energy, the potential of mean force (PMF) method was performed. Finally, the molecular mechanics Poisson-Boltzmann surface area (MMPBSA) method was applied as an effective tool to calculate the molecular model affinities. The MD simulation results of the subunits represented their structural changes in presence of Ca2+. Moreover, the RIN and Hydrogen bond analysis demonstrated that cluster interactions between Calprotectin subunits in presence of Ca2+ were greater in comparison with Na+. Our findings indicated that the binding free energy of the subunits in presence of Ca2+ was significantly greater than Na+. The results revealed that Ca2+ has the ability to induce structural changes in subunits in comparison with Na+ which lead to create stronger interactions between. Hence, studying the physical characteristics of the human proteins could be considered as a powerful tool in theranostics and drug design purposes.

Intracellular calprotectin (S100A8/A9) controls epithelial differentiation and caspase-mediated cleavage of EGFR in head and neck squamous cell carcinoma

OBJECTIVES

Calprotectin (S100A8/A9) appears to function as a tumor suppressor in head and neck squamous cell carcinoma (HNSCC) and expression in the carcinoma cells and patient survival rates are directly related. We seek to characterize the suppressive role of calprotectin in HNSCC.

AIMS

(1) Investigate changes in S100A8/A9 expression as oral carcinogenesis progresses and (2) determine whether intracellular calprotectin can regulate epidermal growth factor receptor (EGFR), a negative prognostic factor, in HNSCC.

MATERIALS AND METHODS

Using immunohistochemistry (IHC), S100A8/A9 was analyzed in HNSCC specimens (N = 46), including well-differentiated (WD, N = 19), moderately-differentiated (MD, N = 14), poorly-differentiated (PD, N = 5) and non-keratinizing/basaloid (NK/BAS, N = 8), and premalignant epithelial dysplasias (PED, N = 16). Similarly, EGFR was analyzed in HNSCCs (N = 21). To determine whether calprotectin and EGFR expression are mechanistically linked, TR146 HNSCC cells that are S100A8/A9-expressing or silenced (shRNA) were compared for EGFR levels and caspase-3/7 activity using western blotting and immunofluorescence microscopy.

RESULTS

In normal oral mucosal epithelium, S100A8/A9 stained strongly in the cytoplasm and nucleus of suprabasal cells; basal cells were consistently S100A8/A9 negative. In PED and HNSCC, S100A8/A9 expression was lower than in adjacent normal epithelial tissues (NAT) and declined progressively in WD, MD, PD and NK/BAS HNSCCs. S100A8/A9 and EGFR levels appeared inversely related, which was simulated in vitro when S100A8/A9 was silenced in TR146 cells. Silencing S100A8/A9 significantly reduced caspase-3/7 activity, whereas EGFR levels increased.

CONCLUSIONS

In HNSCC, S100A8/A9 is directly associated with cellular differentiation and appears to promote caspase-3/7-mediated cleavage of EGFR, which could explain why patients with S100A8/A9-high tumors survive longer.

Alarmins of the S100-Family in Juvenile Autoimmune and Auto-Inflammatory Diseases

Autoimmune and auto-inflammatory diseases in children are causing chronic inflammation, organ damage, and pain. Although several options for treatment are nowadays available a significant number of patients does not respond sufficiently to current therapies. In these diseases inflammatory processes are triggered by numerous exogenous and endogenous factors. There is now increasing evidence that especially a novel family of pro-inflammatory molecules, named alarmins, play a significant role in inflammatory processes underlying these diseases. Alarmins are endogenous proteins released during stress reactions that confer inflammatory signaling via Pattern Recognition Receptors (PRRs), like the Toll-like receptor 4 (TLR4). The most abundant alarmins in juvenile rheumatic diseases belong to the family of pro-inflammatory calcium-binding S100-proteins. In this review we will give a general introduction in S100-biology. We will demonstrate the functional relevance of these proteins in animal models of autoimmune and auto-inflammatory diseases. We will show the expression patterns of S100-alarmins and correlation to disease activity in different forms of juvenile idiopathic arthritis, auto-inflammatory diseases, and systemic autoimmune disorders. Finally, we will discuss the clinical use of S100-alarmins as biomarkers for diagnosis and monitoring of rheumatic diseases in children and will point out potential future therapeutic approaches targeting inflammatory effects mediated by S100-alarmins.

Calprotectin (S100A8/S100A9): a key protein between inflammation and cancer

BACKGROUND

Calprotectin (S100A8/S100A9), a heterodimeric EF-hand Ca²⁺ binding protein, are abundant in cytosol of neutrophils and are involved in inflammatory processes and several cancerous pathogens.

OBJECTIVE

The purpose of the present systematic review is to evaluate the pro- and anti-tumorigenic functions of calprotectin and its relation to inflammation.

MATERIALS AND METHODS

We conducted a review of studies published in the Medline (1966-2018), Scopus (2004-2018), ClinicalTrials.gov (2008-2018) and Google Scholar (2004-2018) databases, combined with studies found in the reference lists of the included studies.

RESULTS

Elevated levels of S100A8/S100A9 were detected in inflammation, neoplastic tumor cells and various human cancers. Recent data have explained that many cancers arise from sites of infection, chronic irritation, and inflammation. The inflammatory microenvironment which largely includes calprotectin, has an essential role on high producing of inflammatory factors and then on neoplastic process and metastasis.

CONCLUSION

Scientists have shown different outcomes in inflammation, malignancy and apoptosis whether the source of the aforementioned protein is extracellular or intracellular. These findings are offering new insights that anti-inflammatory therapeutic agents and anti-tumorigenic functions of calprotectin can lead to control cancer development.

Transition Metal Sequestration by the Host-Defense Protein Calprotectin

In response to microbial infection, the human host deploys metal-sequestering host-defense proteins, which reduce nutrient availability and thereby inhibit microbial growth and virulence. Calprotectin (CP) is an abundant antimicrobial protein released from neutrophils and epithelial cells at sites of infection. CP sequesters divalent first-row transition metal ions to limit the availability of essential metal nutrients in the extracellular space. While functional and clinical studies of CP have been pursued for decades, advances in our understanding of its biological coordination chemistry, which is central to its role in the host-microbe interaction, have been made in more recent years. In this review, we focus on the coordination chemistry of CP and highlight studies of its metal-binding properties and contributions to the metal-withholding innate immune response. Taken together, these recent studies inform our current model of how CP participates in metal homeostasis and immunity, and they provide a foundation for further investigations of a remarkable metal-chelating protein at the host-microbe interface and beyond.

Autoinhibitory regulation of S100A8/S100A9 alarmin activity locally restricts sterile inflammation

Autoimmune diseases, such as psoriasis and arthritis, show a patchy distribution of inflammation despite systemic dysregulation of adaptive immunity. Thus, additional tissue-derived signals, such as danger-associated molecular patterns (DAMPs), are indispensable for manifestation of local inflammation. S100A8/S100A9 complexes are the most abundant DAMPs in many autoimmune diseases. However, regulatory mechanisms locally restricting DAMP activities are barely understood. We now unravel for the first time, to our knowledge, a mechanism of autoinhibition in mice and humans restricting S100-DAMP activity to local sites of inflammation. Combining protease degradation, pull-down assays, mass spectrometry, and targeted mutations, we identified specific peptide sequences within the second calcium-binding EF-hands triggering TLR4/MD2-dependent inflammation. These binding sites are free when S100A8/S100A9 heterodimers are released at sites of inflammation. Subsequently, S100A8/S100A9 activities are locally restricted by calcium-induced (S100A8/S100A9)2 tetramer formation hiding the TLR4/MD2-binding site within the tetramer interphase, thus preventing undesirable systemic effects. Loss of this autoinhibitory mechanism in vivo results in TNF-α-driven fatal inflammation, as shown by lack of tetramer formation in crossing S100A9-/- mice with 2 independent TNF-α-transgene mouse strains. Since S100A8/S100A9 is the most abundant DAMP in many inflammatory diseases, specifically blocking the TLR4-binding site of active S100 dimers may represent a promising approach for local suppression of inflammatory diseases, avoiding systemic side effects.

Calprotectin and the Initiation and Progression of Head and Neck Cancer

Calprotectin (S100A8/A9), a heterodimeric complex of calcium-binding proteins S100A8 and S100A9, is encoded by genes mapping to the chromosomal locus 1q21.3 of the epidermal differentiation complex. Whereas extracellular calprotectin shows proinflammatory and antimicrobial properties by signaling through RAGE and TLR4, intracytoplasmic S100A8/A9 appears to be important for cellular development, maintenance, and survival. S100A8/A9 is constitutively expressed in myeloid cells and the stratified mucosal epithelia lining the oropharyngeal and genitourinary mucosae. While upregulated in adenocarcinomas and other cancers, calprotectin mRNA and protein levels decline in head and neck squamous cell carcinoma (HNSCC). S100A8/A9 is also lost during head and neck preneoplasia (dysplasia). Calprotectin decrease does not correlate with the clinical stage (TNM) of HNSCC. When expressed in carcinoma cells, S100A8/A9 downregulates matrix metalloproteinase 2 expression and inhibits invasion and migration in vitro. S100A8/A9 regulates cell cycle progression and decelerates cancer cell proliferation by arresting at the G2/M checkpoint in a protein phosphatase 2α-dependent manner. In HNSCC, S100A8 and S100A9 coregulate with gene networks controlling cellular development and differentiation, cell-to-cell signaling, and cell morphology, while S100A8/A9 appears to downregulate expression of invasion- and tumorigenesis-associated genes. Indeed, tumor formation capacity is attenuated in S100A8/A9-expressing carcinoma cells in vivo. Hence, intracellular calprotectin appears to function as a tumor suppressor in head and neck carcinogenesis. When compared with S100A8/A9-low HNSCC based on analysis of TCGA, S100A8/A9-high HNSCC shows significant upregulation of apoptosis-related genes, including multiple caspases. Accordingly, S100A8/A9 facilitates DNA damage responses in HNSCC, promotes apoptotic cell death, and confers sensitivity to cisplatin and X-radiation in vitro. In the tumor milieu, loss of S100A8/A9 strongly associates with poor squamous differentiation and higher tumor grading, EGFR upregulation, increased DNA methylation, and, finally, poorer overall survival for patients with HNSCC. Hence, intracellular calprotectin shows a multifaceted protective role against the development of HNSCC.

Monitoring storage induced changes in the platelet proteome employing label free quantitative mass spectrometry

Shelf life of platelet concentrates is limited to 5-7 days due to loss of platelet function during storage, commonly referred to as the platelet storage lesion (PSL). To get more insight into the development of the PSL, we used label free quantitative mass spectrometry to identify changes in the platelet proteome during storage. In total 2501 proteins were accurately quantified in 3 biological replicates on at least 1 of the 7 different time-points analyzed. Significant changes in levels of 21 proteins were observed over time. Gene ontology enrichment analysis of these proteins revealed that the majority of this set was involved in platelet degranulation, secretion and regulated exocytosis. Twelve of these proteins have been shown to reside in α-granules. Upon prolonged storage (13-16 days) elevated levels of α-2-macroglobulin, glycogenin and Ig μ chain C region were identified. Taken together this study identifies novel markers for monitoring of the PSL that may potentially also be used for the detection of "young" and "old" platelets in the circulation.

S100-alarmins: potential therapeutic targets for arthritis

INTRODUCTION

In arthritis, inflammatory processes are triggered by numerous factors that are released from joint tissues, promoting joint destruction and pathological progression. During inflammation, a novel family of pro-inflammatory molecules called alarmins is released, amplifying inflammation and joint damage. Areas covered: With regard to the role of the alarmins S100A8 and S100A9 in the pathogenesis of arthritis, recent advances and the future prospects in terms of therapeutic implications are considered. Expert opinion: There is still an urgent need for novel treatment strategies addressing the local mechanisms of joint inflammation and tissue destruction, offering promising therapeutic alternatives. S100A8 and S100A9, which are the most up-regulated alarmins during arthritis, are endogenous triggers of inflammation, defining these proteins as promising targets for local suppression of arthritis. In murine models, the blockade of S100A8/S100A9 ameliorates inflammatory processes, including arthritis, and there are several lines of evidence that S100-alarmins may already be targeted in therapeutic approaches in man.

S100A8/A9: From basic science to clinical application

Neutrophils and monocytes belong to the first line of immune defence cells and are recruited to sites of inflammation during infection or sterile injury. Both cells contain huge amounts of the heterodimeric protein S100A8/A9 in their cytoplasm. S100A8/A9 belongs to the Ca²⁺ binding S100 protein family and has recently gained a lot of interest as a critical alarmin modulating the inflammatory response after its release (extracellular S100A8/A9) from neutrophils and monocytes. Extracellular S100A8/A9 interacts with the pattern recognition receptors Toll-like receptor 4 (TLR4) and Receptor for Advanced Glycation Endproducts (RAGE) promoting cell activation and recruitment. Besides its biological function, S100A8/A9 (also known as myeloid related protein 8/14, MRP8/14) was identified as interesting biomarker to monitor disease activity in chronic inflammatory disorders including inflammatory bowel disease and rheumatoid arthritis. Furthermore, S100A8/A9 has been tested successfully in pre-clinical imaging studies to localize sites of infection or sterile injury. Finally, recent evidence using small molecule inhibitors for S100A8/A9 also suggests that blocking S100A8/A9 activity exerts beneficial effects on disease activity in animal models of autoimmune diseases including multiple sclerosis, systemic lupus erythematosus, rheumatoid arthritis and inflammatory bowel disease. This review will provide a comprehensive and detailed overview into the structure and biological function of S100A8/A9 and also will give an outlook in terms of diagnostic and therapeutic applications targeting S100A8/A9.

Contributions of the S100A9 C-terminal tail to high-affinity Mn(II) chelation by the host-defense protein human calprotectin

Human calprotectin (CP) is an antimicrobial protein that coordinates Mn(II) with high affinity in a Ca(II)-dependent manner at an unusual histidine-rich site (site 2) formed at the S100A8/S100A9 dimer interface. We present a 16-member CP mutant family where mutations in the S100A9 C-terminal tail (residues 96-114) are employed to evaluate the contributions of this region, which houses three histidines and four acidic residues, to Mn(II) coordination at site 2. The results from analytical size-exclusion chromatography, Mn(II) competition titrations, and electron paramagnetic resonance spectroscopy establish that the C-terminal tail is essential for high-affinity Mn(II) coordination by CP in solution. The studies indicate that His103 and His105 (HXH motif) of the tail complete the Mn(II) coordination sphere in solution, affording an unprecedented biological His6 site. These solution studies are in agreement with a Mn(II)-CP crystal structure reported recently (Damo, S. M.; et al. Proc. Natl. Acad. Sci. U.S.A. 2013, 110, 3841). Remarkably high-affinity Mn(II) binding is retained when either H103 or H105 are mutated to Ala, when the HXH motif is shifted from positions 103-105 to 104-106, and when the human tail is substituted by the C-terminal tail of murine S100A9. Nevertheless, antibacterial activity assays employing human CP mutants reveal that the native disposition of His residues is important for conferring growth inhibition against Escherichia coli and Staphylococcus aureus. Within the S100 family, the S100A8/S100A9 heterooligomer is essential for providing high-affinity Mn(II) binding; the S100A7, S100A9(C3S), S100A12, and S100B homodimers do not exhibit such Mn(II)-binding capacity.

High-affinity manganese coordination by human calprotectin is calcium-dependent and requires the histidine-rich site formed at the dimer interface

Calprotectin (CP) is a transition metal-chelating antimicrobial protein of the calcium-binding S100 family that is produced and released by neutrophils. It inhibits the growth of various pathogenic microorganisms by sequestering the transition metal ions manganese and zinc. In this work, we investigate the manganese-binding properties of CP. We demonstrate that the unusual His(4) motif (site 2) formed at the S100A8/S100A9 dimer interface is the site of high-affinity Mn(II) coordination. We identify a low-temperature Mn(II) spectroscopic signal for this site consistent with an octahedral Mn(II) coordination sphere with simulated zero-field splitting parameters D = 270 MHz and E/D = 0.30 (E = 81 MHz). This analysis, combined with studies of mutant proteins, suggests that four histidine residues (H17 and H27 of S100A8; H91 and H95 of S100A9) coordinate Mn(II) in addition to two as-yet unidentified ligands. The His(3)Asp motif (site 1), which is also formed at the S100A8/S100A9 dimer interface, does not provide a high-affinity Mn(II) binding site. Calcium binding to the EF-hand domains of CP increases the Mn(II) affinity of the His(4) site from the low-micromolar to the mid-nanomolar range. Metal-ion selectivity studies demonstrate that CP prefers to coordinate Zn(II) over Mn(II). Nevertheless, the specificity of Mn(II) for the His(4) site provides CP with the propensity to form mixed Zn:Mn:CP complexes where one Zn(II) ion occupies site 1 and one Mn(II) ion occupies site 2. These studies support the notion that CP responds to physiological calcium ion gradients to become a high-affinity transition metal ion chelator in the extracellular space where it inhibits microbial growth.

Review of S100A9 biology and its role in cancer

S100A9 is a calcium binding protein with multiple ligands and post-translation modifications that is involved in inflammatory events and the initial development of the cancer cell through to the development of metastatic disease. This review has a threefold purpose: 1) describe the S100A9 structural elements important for its biological activity, 2) describe the S100A9 biology in the context of the immune system, and 3) illustrate the role of S100A9 in the development of malignancy via interactions with the immune system and other cellular processes.

Calcium ion gradients modulate the zinc affinity and antibacterial activity of human calprotectin

Calprotectin (CP) is an antimicrobial protein produced and released by neutrophils that inhibits the growth of pathogenic microorganisms by sequestering essential metal nutrients in the extracellular space. In this work, spectroscopic and thermodynamic metal-binding studies are presented to delineate the zinc-binding properties of CP. Unique optical absorption and EPR spectroscopic signatures for the interfacial His(3)Asp and His(4) sites of human calprotectin are identified by using Co(II) as a spectroscopic probe. Zinc competition titrations employing chromophoric Zn(II) indicators provide a 2:1 Zn(II):CP stoichiometry, confirm that the His(3)Asp and His(4) sites of CP coordinate Zn(II), and reveal that the Zn(II) affinity of both sites is calcium-dependent. The calcium-insensitive Zn(II) competitor ZP4 affords dissociation constants of K(d1) = 133 ± 58 pM and K(d2) = 185 ± 219 nM for CP in the absence of Ca(II). These values decrease to K(d1) ≤ 10 pM and K(d2) ≤ 240 pM in the presence of excess Ca(II). The K(d1) and K(d2) values are assigned to the His(3)Asp and His(4) sites, respectively. In vitro antibacterial activity assays indicate that the metal-binding sites and Ca(II)-replete conditions are required for CP to inhibit the growth of both Gram-negative and -positive bacteria. Taken together, these data provide a working model whereby calprotectin responds to physiological Ca(II) gradients to become a potent Zn(II) chelator in the extracellular space.

Presence of S100A9-positive inflammatory cells in cancer tissues correlates with an early stage cancer and a better prognosis in patients with gastric cancer

Background

S100A9 was originally discovered as a factor secreted by inflammatory cells. Recently, S100A9 was found to be associated with several human malignancies. The purpose of this study is to investigate S100A9 expression in gastric cancer and explore its role in cancer progression.

Methods

S100A9 expression in gastric tissue samples from 177 gastric cancer patients was assessed by immunohistochemistry. The expression of its dimerization partner S100A8 and the S100A8/A9 heterodimer were also assessed by the same method. The effect of exogenous S100A9 on motility of gastric cancer cells AGS and BGC-823 was then investigated.

Results

S100A9 was specifically expressed by inflammatory cells such as macrophages and neutrophils in human gastric cancer and gastritis tissues. Statistical analysis showed that a high S100A9 cell count (> = 200) per 200x magnification microscopic field in cancer tissues was predictive of early stage gastric cancer. High S100A9-positive cell count was negatively correlated with lymph node metastasis (P = 0.009) and tumor invasion (P = 0.011). S100A9 was identified as an independent prognostic predictor of overall survival of patients with gastric cancer (P = 0.04). Patients with high S100A9 cell count were with favorable prognosis (P = 0.021). Further investigation found that S100A8 distribution in human gastric cancer tissues was similar to S100A9. However, the number of S100A8-positive cells did not positively correlate with patient survival. The inflammatory cells infiltrating cancer were S100A8/A9 negative, while those in gastritis were positive. Furthermore, exogenous S100A9 protein inhibited migration and invasion of gastric cancer cells.

Conclusions

Our results suggested S100A9-positive inflammatory cells in gastric cancer tissues are associated with early stage of gastric cancer and good prognosis.

iPLA2, a novel determinant in Ca2+- and phosphorylation-dependent S100A8/A9 regulated NOX2 activity

The neutrophil NADPH oxidase (NOX2) is a key enzyme responsible for host defense against invading pathogens, via the production of reactive oxygen species. Dysfunction of NOX2 can contribute to inflammatory processes, which could lead to the development of diseases such as atherosclerosis. In this paper, we characterize a pathway leading to NOX2 activation in which iPLA(2)-regulated p38 MAPK activity is a key regulator of S100A8/A9 translocation via S100A9 phosphorylation. Studies in cell-free or recombinant systems involved two Ca2+-binding proteins of the S100 family, namely S100A8 and S100A9, in NOX2 activation dependent on intracellular Ca2+ concentration ([Ca2+](i)) elevation. Using differentiated HL-60 cells as a model of neutrophils, we provide evidence that [Ca2+](i)-regulated S100A8/A9 translocation is mediated by an increase in [Ca2+](i) through intracellular Ca2+ store depletion. Moreover, we confirm that p38 MAPK induces S100A9 phosphorylation, a mandatory precondition for S100 translocation. Based on a pharmacological approach and an siRNA strategy, we identify iPLA(2) as a new molecular player aiding S100 translocation and NOX2 activity. Inhibition of p38 MAPK activity and S100A9 phosphorylation by bromoenol lactone, a selective inhibitor of iPLA(2), indicated that p38 MAPK-mediated S100A9 phosphorylation is dependent on iPLA(2). In conclusion, we have characterized a pathway leading to NOX2 activation in which iPLA(2)-regulated p38 MAPK activity is a key regulator of S100A8/A9 translocation via S100A9 phosphorylation.

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.

Amyloid formation by the pro-inflammatory S100A8/A9 proteins in the ageing prostate

Background

The conversion of soluble peptides and proteins into polymeric amyloid structures is a hallmark of many age-related degenerative disorders, including Alzheimer's disease, type II diabetes and a variety of systemic amyloidoses. We report here that amyloid formation is linked to another major age-related phenomenon − prostate tissue remodelling in middle-aged and elderly men.

Methodology/Principal Findings

By using multidisciplinary analysis of corpora amylacea inclusions in prostate glands of patients diagnosed with prostate cancer we have revealed that their major components are the amyloid forms of S100A8 and S100A9 proteins associated with numerous inflammatory conditions and types of cancer. In prostate protease rich environment the amyloids are stabilized by dystrophic calcification and lateral thickening. We have demonstrated that material closely resembling CA can be produced from S100A8/A9 in vitro under native and acidic conditions and shows the characters of amyloids. This process is facilitated by calcium or zinc, both of which are abundant in ex vivo inclusions. These observations were supported by computational analysis of the S100A8/A9 calcium-dependent aggregation propensity profiles. We found DNA and proteins from Escherichia coli in CA bodies, suggesting that their formation is likely to be associated with bacterial infection. CA inclusions were also accompanied by the activation of macrophages and by an increase in the concentration of S100A8/A9 in the surrounding tissues, indicating inflammatory reactions.

Conclusions/Significance

These findings, taken together, suggest a link between bacterial infection, inflammation and amyloid deposition of pro-inflammatory proteins S100A8/A9 in the prostate gland, such that a self-perpetuating cycle can be triggered and may increase the risk of malignancy in the ageing prostate. The results provide strong support for the prediction that the generic ability of polypeptide chains to convert into amyloids could lead to their involvement in an increasing number of otherwise apparently unrelated diseases, particularly those associated with ageing.

Calprotectin S100A9 calcium-binding loops I and II are essential for keratinocyte resistance to bacterial invasion

Epithelial cells expressing calprotectin, a heterodimer of S100A8 and S100A9 proteins, are more resistant to bacterial invasion. To determine structural motifs that affect resistance to bacterial invasion, mutations were constructed in S100A9 targeting the calcium-binding loops I and II (E36Q, E78Q, E36Q,E78Q) and the C terminus (S100A9(1-99) and S100A9(1-112)), which contains putative antimicrobial zinc-binding and phosphorylation sites. The S100A8 and mutated S100A9 encoding plasmids were transfected into calprotectin-negative KB carcinoma cells. All transfected cells (except KB-sham) expressed 27E10-reactive heterodimers. In bacterial invasion assays with Listeria monocytogenes and Salmonella enterica serovar Typhimurium (Salmonella typhimurium), cell lines expressing S100A8 in complex with S100A9E36Q, S100A9E78Q, S100A9(1-99), or S100A9(1-112) mutants or the S100A9(1-114) (full-length) calprotectin resisted bacterial invasion better than KB-sham. When compared with KB-S100A8/A9(1-114), cells expressing truncated S100A9(1-99) or S100A9(1-112) with S100A8 also showed increased resistance to bacterial invasion. In contrast, glutamic acid residues 36 and 78 in calcium-binding loops I and II promote resistance in epithelial cells, because cells expressing S100A9E36Q,E78Q with S100A8 were unable to resist bacterial invasion. Mutations in S100A9 E36Q, E78Q were predicted to cause loss of the calcium-induced positive face in calprotectin, reducing interactions with microtubules and appearing to be crucial for keratinocyte resistance to bacterial invasion.

S100A8, S100A9, and the S100A8/A9 complex in circulating blood are not associated with prostate cancer risk-A re-evaluation study

BACKGROUND

To evaluate the diagnostic performance of plasma S100A8, S100A9, and the S100A8/A9 complex as novel markers to discriminate between benign and malignant prostatic diseases as recently suggested for S100A9.

METHODS

The study included 90 prostate cancer (PCa) patients (pN0M0, n = 50; pN1M0, n = 27; M1, n = 13), 50 controls without PCa, and six patients within 72 hr after radical prostatectomy for repeated measurements. The S100 proteins were analyzed with specific ELISAs. Comparisons were made to the prostate-specific antigen (tPSA) and the ratio of free to tPSA (%fPSA).

RESULTS

The plasma concentrations of the S100 proteins in controls had either significantly higher values (S100A8; P = 0.020) or the tendency to higher values compared with the results in PCa patients. Differences between the three PCa groups were almost negligible. No correlation could be found between S100 protein levels and PSA concentration (r(s) = -0.110 to 0.433, P = 0.317-0.433) or prostate volume (r(s) = -0.038 to 0.018, P = 0.676-0.844). Tumor stage and tumor grade had no observed effect on S100 protein concentrations. After prostatectomy, there were discordant elimination kinetics for PSA and the S100 proteins, as the S100 proteins partially increased while PSA continuously decreased. Analyses of receiver-operating curves showed that, compared with PSA, S100A8, S100A9, and S100A8/A9 did not improve the differentiation between patients with and without PCa, while the discrimination ability was significantly lower than that of %fPSA.

CONCLUSIONS

Our re-evaluation study showed that S100A8, S100A9, and the complex S100A8/A9 were less indicative than %fPSA and that they are not suitable to replace PSA.

The Crystal Structure of the Human (S100A8/S100A9)2 Heterotetramer, Calprotectin, Illustrates how Conformational Changes of Interacting α-Helices Can Determine Specific Association of Two EF-hand Proteins

The EF-hand proteins S100A8 and S100A9 are important calcium signalling proteins that are involved in wound healing and provide clinically relevant markers of inflammatory processes, such as rheumatoid arthritis and inflammatory bowel disease. Both can form homodimers via distinct modes of association, probably of lesser stability in the case of S100A9, whereas in the presence of calcium S100A8 and S100A9 associate to calprotectin, the physiologically active heterooligomer. Here we describe the crystal structure of the (S100A8/S100A9)(2) heterotetramer at 1.8 A resolution. Its quaternary structure illustrates how specific heteroassociation is energetically driven by a more extensive burial of solvent accessible surface areas in both proteins, most pronounced for S100A9, thus leading to a dimer of heterodimers. A major contribution to tetramer association is made by the canonical calcium binding loops in the C-terminal halves of the two proteins. The mode of heterodimerisation in calprotectin more closely resembles the subunit association previously observed in the S100A8 homodimer and provides trans stabilisation for S100A9, which manifests itself in a significantly elongated C-terminal alpha-helix in the latter. As a consequence, two different putative zinc binding sites emerge at the S100A8/S100A9 subunit interface. One of these corresponds to a high affinity arrangement of three His residues and one Asp side-chain, which is unique to the heterotetramer. This structural feature explains the well known Zn(2+) binding activity of calprotectin, whose overexpression can cause strong dysregulation of zinc homeostasis with severe clinical symptoms.

S100A8 and S100A9 in inflammation and cancer

Calprotectin (S100A8/A9), a heterodimer of the two calcium-binding proteins S100A8 and S100A9, was originally discovered as immunogenic protein expressed and secreted by neutrophils. Subsequently, it has emerged as important pro-inflammatory mediator in acute and chronic inflammation. More recently, increased S100A8 and S100A9 levels were also detected in various human cancers, presenting abundant expression in neoplastic tumor cells as well as infiltrating immune cells. Although, many possible functions have been proposed for S100A8/A9, its biological role still remains to be defined. Altogether, its expression and potential cytokine-like function in inflammation and in cancer suggests that S100A8/A9 may play a key role in inflammation-associated cancer.

Calcium-dependent and -independent interactions of the S100 protein family

The S100 proteins comprise at least 25 members, forming the largest group of EF-hand signalling proteins in humans. Although the proteins are expressed in many tissues, each S100 protein has generally been shown to have a preference for expression in one particular tissue or cell type. Three-dimensional structures of several S100 family members have shown that the proteins assume a dimeric structure consisting of two EF-hand motifs per monomer. Calcium binding to these S100 proteins, with the exception of S100A10, results in an approx. 40 degrees alteration in the position of helix III, exposing a broad hydrophobic surface that enables the S100 proteins to interact with a variety of target proteins. More than 90 potential target proteins have been documented for the S100 proteins, including the cytoskeletal proteins tubulin, glial fibrillary acidic protein and F-actin, which have been identified mostly from in vitro experiments. In the last 5 years, efforts have concentrated on quantifying the protein interactions of the S100 proteins, identifying in vivo protein partners and understanding the molecular specificity for target protein interactions. Furthermore, the S100 proteins are the only EF-hand proteins that are known to form both homo- and hetero-dimers, and efforts are underway to determine the stabilities of these complexes and structural rationales for their formation and potential differences in their biological roles. This review highlights both the calcium-dependent and -independent interactions of the S100 proteins, with a focus on the structures of the complexes, differences and similarities in the strengths of the interactions, and preferences for homo- compared with hetero-dimeric S100 protein assembly.

Expression of macrophage migration inhibitory factor in rat skin during embryonic development

We have previously shown that human epidermal keratinocytes express macrophage migration inhibitory factor (MIF) mRNA, and immunohistochemical studies showed that MIF is expressed in human epidermis. To explore the possible pathophysiological roles of MIF in skin during rat fetal development, we examined the expression patterns of MIF during rat epidermal development using Northern blot analysis and in situ hybridization. Expression of MIF mRNA was first detected by in situ hybridization in the developing epidermis and hair germ cells from embryonic day (ED) 16. From ED 19, moderate levels of MIF expression were detected in the epidermis and epithelial sheath cells of growing hair follicles. In postnatal rat skin, higher MIF expression was detected in the epidermis and hair follicles on postnatal day 3. These observations were also confirmed by Northern blot analysis. Immunohistochemical analysis with an anti-MIF antibody showed a similar distribution to that of the mRNA. Our results suggest that MIF is associated with epidermal and hair follicle development.