Abstract of related literatures |
1. MRP8 and MRP14 are two S100-like calcium-binding proteins of unknown function, associated with numbers of human inflammatory disorders. Both molecules have been described as L1 complex, cystic fibrosis antigen, or p8 and p14. We report here the cloning of mouse MRP8 and MRP14 and their pattern of expression during hematopoiesis. Mouse MRP8 and MRP14 proteins share 59% identity with their human counterparts, but they are more divergent than the other members of the S100 protein family. Mouse MRP proteins are coexpressed in fetal myeloid progenitors, where they are detected as early as day 11 of gestation. In fetal liver and yolk sac, MRP+ cell populations increased in number, in association with the development of the myeloid lineage. In adult mouse, we identified MRP8 and MRP14 proteins in immature myeloid cells of the bone marrow, myeloid cells in the splenic red pulp and marginal zone, in addition to monocytes and blood neutrophils. However, MRP expression is lost as cells terminally differentiate into tissue macrophages. In addition, using thioglycollate-induced peritoneal inflammatory exudates, we showed that MRP8 and MRP14 proteins are highly expressed in recruited neutrophils and monocytes. PMID: [1373330]
2. The genomic locus of the mouse S100A9 (MRP14) gene, a myeloid expressed gene belonging to the S100 family, is split in three exons and two introns. Insertions of B1 like and LINE elements as well as several sequence repeat structures are scattered over the gene suggesting that this region of the S100 gene cluster has been the subject of a high mutational activity in mouse evolution. The insertions may represent molecular footprints of a recently postulated inversion event, which resulted in a rearrangement of the S100 gene cluster in mouse compared to man. Deletion analysis of the promoter reveals, that a 1200 bp fragment is able to direct a cell type-specific expression of a reporter gene in granulocytic 32D cells. Unexpectedly, the myeloid-specific transcription factor C/EBPepsilon is not needed for the transcriptional upregulation of the S100A9 and S100A8 genes in neutrophils. The data described here provide further insights into the evolution of the S100 gene cluster and into the myeloid-specific regulation of the murine S100A9 gene expression. PMID: [11169745]
3. The National Institutes of Health's Mammalian Gene Collection (MGC) project was designed to generate and sequence a publicly accessible cDNA resource containing a complete open reading frame (ORF) for every human and mouse gene. The project initially used a random strategy to select clones from a large number of cDNA libraries from diverse tissues. Candidate clones were chosen based on 5'-EST sequences, and then fully sequenced to high accuracy and analyzed by algorithms developed for this project. Currently, more than 11,000 human and 10,000 mouse genes are represented in MGC by at least one clone with a full ORF. The random selection approach is now reaching a saturation point, and a transition to protocols targeted at the missing transcripts is now required to complete the mouse and human collections. Comparison of the sequence of the MGC clones to reference genome sequences reveals that most cDNA clones are of very high sequence quality, although it is likely that some cDNAs may carry missense variants as a consequence of experimental artifact, such as PCR, cloning, or reverse transcriptase errors. Recently, a rat cDNA component was added to the project, and ongoing frog (Xenopus) and zebrafish (Danio) cDNA projects were expanded to take advantage of the high-throughput MGC pipeline. PMID: [15489334]
4. MRP14 (macrophage migration-inhibitory factor-related protein of molecular mass 14 kDa) is an S100 calcium binding protein constitutively expressed in human neutrophils which may be associated with cellular activation/inflammation. Murine MRP14 expression was up-regulated following concanavalin A activation of spleen cells, and the protein was isolated from conditioned medium in high yield (approx. 500 ng/ml). MRP14 had a mass of 12972 +/- 2 Da by electrospray ionization MS, whereas the theoretical mass derived from the cDNA sequence, after removal of the initiator Met, was 12918 Da, suggesting that the protein was post-translationally modified. We identified four post-translational modifications of MRP14: removal of the N-terminal Met, N-terminal acetylation, disulphide bond formation between Cys79 and Cys90, and 1-methylation of His106; the calculated mass was then 12971.8 Da. Methylation of His106 was further characterized after incubation of spleen cells with L-[methyl-3H]Met during concanavalin A stimulation. Sequential analysis of a peptide (obtained by digestion with Lys C) containing methylated His indicated that > 80% of the label in the cycle corresponded to His106, suggesting that the methyl residue was transferred from S-adenosyl-L-methionine. Comparison of the C18 reverse-phase HPLC retention times of phenylthiocarbamoyl derivatives of a hydrolysed digest peptide of MRP14 with those of standards confirmed methyl substitution on the 1-position of the imidazole ring. MRP14 bound more 85Zn2+ than the same amounts of the 10 kDa chemotactic protein (CP10) or S100 beta. Ca2+ decreased Zn2+ binding in S100 beta but it did not influence binding to MRP14, suggesting that the Zn2+ binding site was distinct from and independent of the two Ca2+ binding domains. PMID: [8645219]
5. The S100A9 (MRP14) protein is abundantly expressed in myeloid cells and has been associated with various inflammatory diseases. The S100A9-deficient mice described here were viable, fertile, and generally of healthy appearance. The myelopoietic potential of the S100A9-null bone marrow was normal. S100A8, the heterodimerization partner of S100A9 was not detectable in peripheral blood cells, suggesting that even a deficiency in both S100A8 and S100A9 proteins was compatible with viable and mature neutrophils. Surprisingly, the invasion of S100A9-deficient leukocytes into the peritoneum and into the skin in vivo was indistinguishable from that in wild-type mice. However, stimulation of S100A9-deficient neutrophils with interleukin-8 in vitro failed to provoke an up-regulation of CD11b. Migration upon a chemotactic stimulus through an endothelial monolayer was markedly diminished in S100A9-deficient neutrophils. Attenuated chemokinesis of the S100A9-deficient neutrophils was observed by using a three-dimensional collagen matrix migration assay. The altered migratory behavior was associated with a microfilament system that was highly polarized in unstimulated S100A9-deficient neutrophils. Our data suggest that loss of the calcium-binding S100A9 protein reduces the responsiveness of the neutrophils upon chemoattractant stimuli at least in vitro. Alternative pathways for neutrophil emigration may be responsible for the lack of any effect in the two in vivo models we have investigated so far. PMID: [12529407]
6. MRP14 (S100A9) is the major calcium-binding protein of neutrophils and monocytes. Targeted gene disruption reveals an essential role of this S100 protein for transendothelial migration of phagocytes. The underlying molecular mechanism comprises major alterations of cytoskeletal metabolism. MRP14, in complex with its binding partner MRP8 (S100A8), promotes polymerization of microtubules. MRP14 is specifically phosphorylated by p38 mitogen-activated protein kinase (MAPK). This phosphorylation inhibits MRP8/MRP14-induced tubulin polymerization. Phosphorylation of MRP14 is antagonistically regulated by binding of MRP8 and calcium. The biologic relevance of these findings is confirmed by the fact that MAPK p38 fails to stimulate migration of MRP14(-/-) granulocytes in vitro and MRP14(-/-) mice show a diminished recruitment of granulocytes into the granulation tissue during wound healing in vivo. MRP14(-/-) granulocytes contain significantly less polymerized tubulin, which subsequently results in minor activation of Rac1 and Cdc42 after stimulation of p38 MAPK. Thus, the complex of MRP8/MRP14 is the first characterized molecular target integrating MAPK- and calcium-dependent signals during migration of phagocytes. PMID: [15331440]
7. To identify new components that regulate the inflammatory cascade during sepsis, we characterized the functions of myeloid-related protein-8 (Mrp8, S100A8) and myeloid-related protein-14 (Mrp14, S100A9), two abundant cytoplasmic proteins of phagocytes. We now demonstrate that mice lacking Mrp8-Mrp14 complexes are protected from endotoxin-induced lethal shock and Escherichia coli-induced abdominal sepsis. Both proteins are released during activation of phagocytes, and Mrp8-Mrp14 complexes amplify the endotoxin-triggered inflammatory responses of phagocytes. Mrp8 is the active component that induces intracellular translocation of myeloid differentiation primary response protein 88 and activation of interleukin-1 receptor-associated kinase-1 and nuclear factor-kappaB, resulting in elevated expression of tumor necrosis factor-alpha (TNF-alpha). Using phagocytes expressing a nonfunctional Toll-like receptor 4 (TLR4), HEK293 cells transfected with TLR4, CD14 and MD2, and by surface plasmon resonance studies in vitro, we demonstrate that Mrp8 specifically interacts with the TLR4-MD2 complex, thus representing an endogenous ligand of TLR4. Therefore Mrp8-Mrp14 complexes are new inflammatory components that amplify phagocyte activation during sepsis upstream of TNFalpha-dependent effects. PMID: [17767165]
8. Despite more than 25 years of research, the molecular targets of quinoline-3-carboxamides have been elusive although these compounds are currently in Phase II and III development for treatment of autoimmune/inflammatory diseases in humans. Using photoaffinity cross-linking of a radioactively labelled quinoline-3-carboxamide compound, we could determine a direct association between human S100A9 and quinoline-3-carboxamides. This interaction was strictly dependent on both Zn++ and Ca++. We also show that S100A9 in the presence of Zn++ and Ca++ is an efficient ligand of receptor for advanced glycation end products (RAGE) and also an endogenous Toll ligand in that it shows a highly specific interaction with TLR4/MD2. Both these interactions are inhibited by quinoline-3-carboxamides. A clear structure-activity relationship (SAR) emerged with regard to the binding of quinoline-3-carboxamides to S100A9, as well as these compounds potency to inhibit interactions with RAGE or TLR4/MD2. The same SAR was observed when the compound's ability to inhibit acute experimental autoimmune encephalomyelitis in mice in vivo was analysed. Quinoline-3-carboxamides would also inhibit TNFalpha release in a S100A9-dependent model in vivo, as would antibodies raised against the quinoline-3-carboxamide-binding domain of S100A9. Thus, S100A9 appears to be a focal molecule in the control of autoimmune disease via its interactions with proinflammatory mediators. The specific binding of quinoline-3-carboxamides to S100A9 explains the immunomodulatory activity of this class of compounds and defines S100A9 as a novel target for treatment of human autoimmune diseases. PMID: [19402754]
Back to Top |