A null mutation in the inflammation-associated S100 protein S100A8 causes early resorption of the mouse embryo.
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S100A8 (also known as CP10 or MRP8) was the first member of the S100 family of calcium-binding proteins shown to be chemotactic for myeloid cells. The gene is expressed together with its dimerization partner S100A9 during myelopoiesis in the fetal liver and in adult bone marrow as well as in mature granulocytes. In this paper we show that S100A8 mRNA is expressed without S100A9 mRNA between 6.5 and 8. 5 days postcoitum within fetal cells infiltrating the deciduum in the vicinity of the ectoplacental cone. Targeted disruption of the S100A8 gene caused rapid and synchronous embryo resorption by day 9. 5 of development in 100% of homozygous null embryos. Until this point there was no evidence of developmental delay in S100A8-/- embryos and decidualization was normal. The results of PCR genotyping around 7.5-8.5 days postcoitum suggest that the null embryos are infiltrated with maternal cells before overt signs of resorption. This work is the first evidence for nonredundant function of a member of the S100 gene family and implies a role in prevention of maternal rejection of the implanting embryo. The S100A8 null provides a new model for studying fetal-maternal interactions during implantation. (+info)
S100A12 is expressed exclusively by granulocytes and acts independently from MRP8 and MRP14.
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Changes in cytosolic calcium concentrations regulate a wide variety of cellular processes, and calcium-binding proteins are the key molecules in signal transduction, differentiation, and cell cycle control. S100A12, a recently described member of the S100 protein family, has been shown to be coexpressed in granulocytes and monocytes together with two other S100 proteins, MRP8 (S100A8) and MRP14 (S100A9), and a functional relationship between these three S100 proteins has been suggested. Using Western blotting, calcium overlays, intracellular flow cytometry, and cytospin preparations, we demonstrate that S100A12 expression in leukocytes is specifically restricted to granulocytes and that S100A12 represents one of the major calcium-binding proteins in these cells. S100A12, MRP8, and MRP14 translocate simultaneously from the cytosol to cytoskeletal and membrane structures in a calcium-dependent manner. However, no evidence for direct protein-protein interactions of S100A12 with either MRP8 or MRP14 or the heterodimer was found by chemical cross-linking, density gradient centrifugation, mass spectrometric measurements, or yeast two hybrid detection. Thus, S100A12 acts individually during calcium-dependent signaling, independent of MRP8, MRP14, and the heterodimer MRP8/MRP14. This granulocyte-specific signal transduction pathway may offer attractive targets for therapeutic intervention with exaggerated granulocyte activity in pathological states. (+info)
S100A8: emerging functions and regulation.
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The functional importance of members of the S100 Ca2+-binding protein family is becoming apparent. Murine (m)S100A8 (initially named CP-10) is a potent chemoattractant (10(-13) to 10(-11) M) for myeloid cells and the chemotactic activity of other S100s has since been reported, suggesting a new class of chemoattractants. Murine S100A8 has been associated with a number of acute and chronic inflammatory conditions including bacterial infection, atherogenesis, and cystic fibrosis. It is expressed constitutively with S100A9 in neutrophils and is regulated by inflammatory stimulants in macrophages and microvascular endothelial cells. The lack of co-expression of S100A9 with S100A8 in activated macrophages suggests distinct functions for the proteins expressed by different cell types. Glucocorticoids up-regulate induction of mS100A8 by inflammatory mediators, and its exquisite sensitivity to oxidation suggests that it may protect against oxidative tissue damage. Inactivation of the mS100A8 gene is embryonic lethal, providing the first evidence for non-redundant function of a member of the S100 gene family. S100A8 may have an immunoregulatory role by contributing to the regulation of fetal-maternal interactions. It may play a protective role and its absence may allow infiltration by maternal cells, a process eventually manifesting as resorption. This review focuses on the variety of emerging functions attributed to murine S100A8, a protein implicated in embryogenesis, growth, differentiation, and immune and inflammatory processes. (+info)
Calcium-induced noncovalently linked tetramers of MRP8 and MRP14 detected by ultraviolet matrix-assisted laser desorption/ionization mass spectrometry.
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MRP8 and MRP14 are members of the S100 family of calcium-binding proteins which play an important role during calcium-induced activation of phagocytes. Both proteins form noncovalently associated complexes as a prerequisite for biological functions. The exact stoichiometric composition of these complexes, however, has not been completely clarified yet. In the present study we show for the first time by ultraviolet matrix-assisted laser desorption/ionization mass spectrometry (UV-MALDI-MS) the calcium-induced formation of noncovalently associated (MRP8/MRP14)2 tetramers. Furthermore, we could determine posttranslational modifications of MRP8 and MRP14, the stoichiometric proportion of the two known MRP14 isoforms in the complexes as well as the number of calcium ions bound to the single MRP8 and MRP14 monomers and tetramers. MRP14 showed a higher affinity for calcium than MRP8. Upon complex formation the calcium binding increased to maximal saturation of the known EF hands in the complexed forms. Calcium-induced stabilization of the MRP8/MRP14 complexes was confirmed by DSC studies. Our results extend scope and application of UV-MALDI-MS by allowing identification of noncovalent protein complexes, the identification of minor alterations of subunits in such complexes as well as the determination of bound calcium ions. (+info)
The two calcium-binding proteins, S100A8 and S100A9, are involved in the metabolism of arachidonic acid in human neutrophils.
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Recently, we identified the two myeloid related protein-8 (MRP8) (S100A8) and MRP14 (S100A9) as fatty acid-binding proteins (Klempt, M., Melkonyan, H., Nacken, W., Wiesmann, D., Holtkemper, U., and Sorg, C. (1997) FEBS Lett. 408, 81-84). Here we present data that the S100A8/A9 protein complex represents the exclusive arachidonic acid-binding proteins in human neutrophils. Binding and competition studies revealed evidence that (i) fatty acid binding was dependent on the calcium concentration; (ii) fatty acid binding was specific for the protein complex formed by S100A8 and S100A9, whereas the individual components were unable to bind fatty acids; (iii) exclusively polyunsaturated fatty acids were bound by S100A8/A9, whereas saturated (palmitic acid, stearic acid) and monounsaturated fatty acids (oleic acid) as well as arachidonic acid-derived eicosanoids (15-hydroxyeicosatetraenoic acid, prostaglandin E(2), thromboxane B(2), leukotriene B(4)) were poor competitors. Stimulation of neutrophil-like HL-60 cells with phorbol 12-myristate 13-acetate led to the secretion of S100A8/A9 protein complex, which carried the released arachidonic acid. When elevation of intracellular calcium level was induced by A23187, release of arachidonic acid occurred without secretion of S100A8/A9. In view of the unusual abundance in neutrophilic cytosol (approximately 40% of cytosolic protein) our findings assign an important role for S100A8/A9 as mediator between calcium signaling and arachidonic acid effects. Further investigations have to explore the exact function of the S100A8/A9-arachidonic acid complex both inside and outside of neutrophils. (+info)
Zinc binding reverses the calcium-induced arachidonic acid-binding capacity of the S100A8/A9 protein complex.
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Analysis of the calcium-induced arachidonic acid (AA) binding to S100A8/A9 revealed that maximal AA binding was achieved at molar ratios of 1 mol S100A8 and 1 mol S100A9 and for values greater than 3 calciums per EF-hand. The AA binding capacity was not induced by the binding of other bivalent cations, such as Zn2+, Cu2+, and Mg2+, to the protein complex. In contrast, the binding of AA was prevented by the addition of either Zn2+ or Cu2+ in the presence of calcium, whereas Mg2+ failed to abrogate the AA binding capacity. The inhibitory effect was not due to blocking the formation of S100A8/A9 as demonstrated by a protein-protein interaction assay. Fluorescence measurements gave evidence that both Zn2+ and Cu2+ induce different conformational changes thereby affecting the calcium-induced formation of the AA binding pocket within the protein complex. Due to the fact that the inhibitory effect of Zn2+ was present at physiological serum concentrations, it is assumed that released S100A8/A9 may carry AA at inflammatory lesions, but not within the blood compartment. (+info)
Biochemical characterization of the murine S100A9 (MRP14) protein suggests that it is functionally equivalent to its human counterpart despite its low degree of sequence homology.
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Due to the low degree of sequence similarity it has been speculated that murine and human S100A9 (MRP14), an inflammatory marker protein belonging to the S100 protein family, may have different cellular functions in mouse and man. The present study was undertaken to investigate the murine S100A9 protein (mS100A9) biochemically. We demonstrate that in murine peripheral CD11b+ cells up to 20% of the protein of the cytosolic fraction consists of mS100A9 and that several minor mS100A9 isoforms are present. Cell fractionation experiments with CD11b+ murine leukocytes showed that mS100A9 is found in the cytosol as well as in the insoluble fraction. Transient expression of a green fluorescence protein-mS100A9 fusion in mammalian cells revealed that mS100A9 is localized in neither the nucleus nor the vesicles. Recombinantly expressed murine S100A9 interacts in vitro with murine and human S100A8 in an in vitro glutathione S-transferase pull-down assay. Homodimerization was not observed. For further biochemical analysis the myeloid 32D cell line is presented as a suitable model, to study murine myeloid expressed S100 proteins. Both murine S100A9 and its dimerization partner mS100A8 are expressed at the onset of granulocyte-colony stimulating factor induced myeloid differentiation. Substantial amounts of this complex are constitutively secreted by granulocytic 32D cells into the medium. In summary, these data suggest, that the human and murine S100A9 may share a higher degree of functional homology than of sequence similarity. (+info)
Myeloid-related proteins 8 and 14 are specifically secreted during interaction of phagocytes and activated endothelium and are useful markers for monitoring disease activity in pauciarticular-onset juvenile rheumatoid arthritis.
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OBJECTIVE: To analyze which physiologic stimuli induce secretion of myeloid-related protein 8 (MRP8) and MRP14, two S100 proteins expressed in neutrophils and monocytes, and to determine whether serum concentrations of these proteins are reliable parameters for monitoring inflammatory activity in pauciarticular juvenile rheumatoid arthritis (JRA). METHODS: Secretion of MRP8 and MRP14 was analyzed using a coculture system of endothelial cells and monocytes. Concentrations of MRP8/MRP14 in the serum and synovial fluid of JRA patients or culture medium were determined by enzyme-linked immunosorbent assay. The expression of MRP8 and MRP14 by leukocytes in synovial tissue or fluid was investigated using immunohistochemistry. RESULTS: MRP8 and MRP14 were specifically released during interaction of activated monocytes with tumor necrosis factor-stimulated endothelial cells. Secretion was mediated via an increase in intracellular calcium levels in monocytes. In contrast, contact with resting endothelium inhibited protein kinase C-induced secretion of the proteins by monocytes. In JRA patients, MRP8 and MRP14 were strongly expressed in infiltrating neutrophils and monocytes within the inflamed joints and could be found in significantly higher concentrations in synovial fluid (mean 42,800 ng/ml) compared with serum (2,060 ng/ml). Concentrations of MRP8/MRP14 in serum correlated well with those in synovial fluid (r = 0.78) and showed a strong correlation with disease activity (r = 0.62). After intraarticular triamcinolone therapy, the serum concentrations of MRP8/MRP14 decreased significantly in therapy responders, whereas no differences were found in patients who showed no clinical benefit. CONCLUSION: MRP8 and MRP14 are specifically released during the interaction of monocytes with inflammatory activated endothelium, probably at sites of local inflammation. Their serum concentrations represent a useful marker for monitoring local inflammation in JRA. (+info)