Structure and ligand-induced conformational change of the 39-kDa glycoprotein from human articular chondrocytes.
(25/819)
The 39-kDa human cartilage glycoprotein (HCGP39), a member of a novel family of chitinase-like lectins (Chilectins), is overexpressed in articular chondrocytes and certain cancers. Proposed functions of this protein include a role in connective tissue remodeling and defense against pathogens. Similar to other Chi-lectins, HCGP39 promotes the growth of connective tissue cells. The ability of HCGP39 to activate cytoplasmic signaling pathways suggests the presence of a ligand for this protein at the cell surface. There is currently no information regarding the identity of any physiological or pathological ligands of the Chi-lectins or the nature of the protein-ligand interaction. Here, we show that HCGP39 is able to bind chitooligosaccharides with micromolar affinity. Crystal structures of the native protein and a complex with GlcNAc8 show that the ligand is bound in identical fashion to family 18 chitinases. However, unlike the chitinases, binding of the oligosaccharide ligand to HCGP39 induces a large conformational change. Thus, HCGP39 could be a lectin that binds chitin-like oligosaccharide ligands and possibly plays a role in innate responses to chitinous pathogens, such as fungi and nematodes. (+info)
Genomic organization, chromosomal localization and adipocytic expression of the murine gene for CORS-26 (collagenous repeat-containing sequence of 26 kDa protein).
(26/819)
The murine gene for CORS-26 shows striking homologies to the adipocyte-specific secretory protein adiponectin (belonging to the newly discovered C1q/TNF molecular superfamily) and its expression has been reported to be restricted to fibroblasts, cartilage and kidney. However, the present data demonstrate specific induction of CORS-26 mRNA expression in hormonally differentiated 3T3-L1 adipocytes, but not in preadipocytes. Furthermore, CORS-26 mRNA expression could be demonstrated in human synovial adipocytes of the knee by in situ hybridization. Since the genes for CORS-26 and adiponectin are homologous for their COOH-terminal globular domain and of their N-terminal collagenous domain, they might have originated by divergence from an innate mesenchymal precursor molecule directing the development of myocytes, adipocytes and chondrocytes from a mesenchymal stem cell. Here, the complete genomic organization with exon/intron boundaries together with exon-specific primer combinations are presented. Additionally, approximately 1 kb of the TATA-box-containing promoter region was cloned and analyzed for putative transcription factor binding sites. The chromosomal localization of the murine CORS-26 gene was mapped to mouse chromosome 15 A2 by fluorescence in situ hybridization (FISH). Since the linkage loci for proteoglycan-induced arthritis and MRL/lpr arthritis in mice have been mapped to that chromosomal region, CORS-26 might represent the underlying mechanism of disease. The present data provide the basis for further investigation of the CORS-26 gene regulation in the context of mesenchymal tissue development, chondrocyte/adipocyte function and bone or skeletal disease. (+info)
Crystal structure and carbohydrate-binding properties of the human cartilage glycoprotein-39.
(27/819)
The human cartilage glycoprotein-39 (HCgp-39 or YKL40) is expressed by synovial cells and macrophages during inflammation. Its precise physiological role is unknown. However, it has been proposed that HCgp-39 acts as an autoantigen in rheumatoid arthritis, and high expression levels have been associated with cancer development. HCgp-39 shares high sequence homology with family 18 chitinases, and although it binds to chitin it lacks enzymatic activity. The crystal structure of HCgp-39 shows that the protein displays a (beta/alpha)8-barrel fold with an insertion of an alpha + beta domain. A 43-A long carbohydrate-binding cleft is present at the C-terminal side of the beta-strands in the (beta/alpha)8 barrel. Binding of chitin fragments of different lengths identified nine sugar-binding subsites in the groove. Protein-carbohydrate interactions are mainly mediated by stacking of side chains of aromatic amino acid residues. Surprisingly, the specificity of chitin binding to HCgp-39 depends on the length of the oligosaccharide. Although chitin disaccharides tend to occupy the distal subsites, longer chains bind preferably to the central subsites in the groove. Despite the absence of enzymatic activity, long chitin fragments are distorted upon binding, with the GlcNAc at subsite -1 in a boat conformation, similar to what has been observed in chitinases. The presence of chitin in the human body has never been documented so far. However, the binding features observed in the complex structures suggest that either chitin or a closely related oligosaccharide could act as the physiological ligand for HCgp-39. (+info)
Cytokines elicited by T cell epitopes from a synovial autoantigen: altered peptide ligands can reduce interferon-gamma and interleukin-10 production.
(28/819)
OBJECTIVE: To explore the cytokine responses associated with T cell epitopes from human cartilage glycoprotein 39 (HC gp-39) and the potential for modifying cytokine secretion using altered peptide ligands (APLs). METHODS: Draining lymph node cells were harvested from HLA-DR*0401 transgenic mice that had been immunized with HC gp-39. Cytokine responses to 5 previously identified HLA-DR*0401-restricted HC gp-39 T cell epitopes were studied in vitro. The anchor and T cell receptor (TCR) contact residues of peptide 322-337 were identified, and this information was used to design alanine-substituted APLs. T cells were primed in vivo with wild-type peptide 322-337, restimulated with wild-type peptide or APLs, and the cytokine profiles were compared. RESULTS: Restimulation with individual peptides elicited distinct cytokine profiles. HC gp-39 (peptide 322-337) elicited a dominant interferon-gamma (IFNgamma) response. Residues within the core (positions P1-P9) 322-337 peptide sequence were critical for T cell recognition. Surprisingly, the N-terminal flanking region was also important for recognition by 6 of 10 specific T cell hybridomas. Substitutions of charged TCR contact residues in the 322-337 core epitope (E332A and K335A) were associated with a significant reduction in the IFNgamma and interleukin-10 (IL-10) stimulation indices. Restimulation with peptides W325A and V326A was also associated with a trend toward reduced IFNgamma and IL-10 secretion. In contrast, restimulation with peptide D330N elicited cytokine profiles more comparable with those resulting from restimulation with wild-type peptide. CONCLUSION: This study indicates that APLs of a proinflammatory HC gp-39 T cell epitope may be used to alter the cytokine response from a memory T cell population. (+info)
Transcriptional regulation of CHI3L1, a marker gene for late stages of macrophage differentiation.
(29/819)
The protein product of the CHI3L1 gene, human cartilage 39-kDa glycoprotein (HC-gp39), is a tissue-restricted, chitin-binding lectin and member of glycosyl hydrolase family 18. In contrast to many other monocyte/macrophage markers, its expression is absent in monocytes and strongly induced during late stages of human macrophage differentiation. To gain insights into the molecular mechanisms underlying its cell type-restricted and maturation-associated expression in macrophages, we initiated a detailed study of the proximal HC-gp39 promoter. Deletion analysis of reporter constructs in macrophage-like THP-1 cells localized a region directing high levels of macrophage-specific reporter gene expression to approximately 300 bp adjacent to the major transcriptional start site. The promoter sequence contained consensus binding sites for several known factors, and specific binding of nuclear PU.1, Sp1, Sp3, USF, AML-1, and C/EBP proteins was detectable in gel shift assays. In vivo footprinting assays with dimethyl sulfate demonstrate that the protection of corresponding sequences was enhanced in macrophages compared with monocytes. Mutational analysis of transcription factor binding sites indicated a predominant role for a single Sp1 binding site in regulating HC-gp39 promoter activity. In addition, gel shift assays using nuclear extracts of monocytes and macrophages demonstrated that the binding of nuclear Sp1, but not Sp3, markedly increases during macrophage differentiation. Our results further highlight the important role of Sp1 in macrophage gene regulation. (+info)
YKL-39 (chitinase 3-like protein 2), but not YKL-40 (chitinase 3-like protein 1), is up regulated in osteoarthritic chondrocytes.
(30/819)
OBJECTIVE: To investigate quantitatively the mRNA expression levels of YKL-40, an established marker of rheumatoid and osteoarthritic cartilage degeneration in synovial fluid and serum, and a closely related molecule YKL-39, in articular chondrocytes. METHODS: cDNA array and online quantitative polymerase chain reaction (PCR) were used to measure mRNA expression levels of YKL-39 and YKL-40 in chondrocytes in normal, early degenerative, and late stage osteoarthritic cartilage samples. RESULTS: Expression analysis showed high levels of both proteins in normal articular chondrocytes, with lower levels of YKL-39 than YKL-40. Whereas YKL-40 was significantly down regulated in late stage osteoarthritic chondrocytes, YKL-39 was significantly up regulated. In vitro both YKLs were down regulated by interleukin 1beta. CONCLUSIONS: The up regulation of YKL-39 in osteoarthritic cartilage suggests that YKL-39 may be a more accurate marker of chondrocyte activation than YKL-40, although it has yet to be established as a suitable marker in synovial fluid and serum. The decreased expression of YKL-40 by osteoarthritic chondrocytes is surprising as increased levels have been reported in rheumatoid and osteoarthritic synovial fluid, where it may derive from activated synovial cells or osteophytic tissue or by increased matrix destruction in the osteoarthritic joint. YKL-39 and YKL-40 are potentially interesting marker molecules for arthritic joint disease because they are abundantly expressed by both normal and osteoarthritic chondrocytes. (+info)
High levels of serum HER-2/neu and YKL-40 independently reflect aggressiveness of metastatic breast cancer.
(31/819)
PURPOSE: To evaluate serum levels of HER2 (an epithelial growth factor) and YKL-40 (a growth factor participating in inflammation and remodeling of the extracellular matrix) in relation to outcome in patients with their first diagnosis of recurrent breast cancer. DESIGN: Serum HER2 and YKL-40 levels were measured in 100 patients referred with their first metastatic manifestation of breast cancer before first line anthracycline-based therapy and related to response to therapy, metastatic pattern, time to progression, and overall survival. During the observation period of 64-84 months, 89 patients died of breast cancer. RESULTS: The patients had higher serum HER2 and YKL-40 levels than healthy females (P < 0.0001). Serum HER2 was elevated in 32% of the patients and serum YKL-40 in 30%. These patients were more sick (P < 0.01) and more often had parenchymal involvement (P < 0.0005), especially liver metastases (P < 0.00005). In multivariate Cox analysis, high serum levels of HER2 or YKL-40 or lack of estrogen receptors independently doubled the relative risk of progression and dying (P < 0.001) even after accounting for other independent prognostic variables, such as axillary nodal involvement at primary diagnosis, liver metastases, and more than two metastatic sites. Fewer patients with high serum HER2 or YKL-40 or lack of estrogen receptors responded with a complete remission on chemotherapy (P = 0.005, 0.036, and 0.006). In these patients, high serum YKL-40 was a stronger predictor of survival than high serum HER2 or lack of estrogen receptors. CONCLUSIONS: High serum HER2 and YKL-40 independently identified subgroups of patients with metastatic breast cancer with a poor prognosis. (+info)
Serum human cartilage glycoprotein 39 as a marker of arthritis associated with inflammatory bowel disease.
(32/819)
BACKGROUND: Common blood markers of arthritis are difficult to interpret in arthritis associated with inflammatory bowel disease (IBD) owing to the coexistence of two inflammatory events. No specific serological disease marker is available for IBD. OBJECTIVE: To determine a value of serum human cartilage glycoprotein 39 (HC gp39) as a marker of arthritis associated with IBD. METHODS: Serum levels of HC gp39 and ultrasensitive C reactive protein (CRP) were determined in 121 patients with IBD: 58 without arthritis (IBD-nonA) and 63 with arthritis (IBD-A), and in 20 healthy controls. IBD was classified as active (aIBD) and non-active (naIBD), and patients with IBD-A were classified as type I, II, and III arthritis by clinical activity indices. RESULTS: HC gp39 was higher in IBD-A than in IBD-nonA (p<0.001) and controls (p<0.01), while no difference was found between IBD-nonA and controls. CRP was increased in both IBD-A and IBD-nonA compared with the controls (p<0.01 and <0.05, respectively) and in aIBD-nonA v naIBD-nonA (p<0.05), but no difference in CRP was found between aIBD-A and naIBD-A. Finally, a correlation was found between the number of affected joints (NAJ) and HC gp39 (r = 0.6, p<0.001). DISCUSSION: Increased serum levels of HC gp39, which were higher in IBD-A than in IBD-nonA, suggest that this substance might be a marker of arthropathy in IBD. HC gp39, because of its relationship with NAJ in IBD-A, may also be proposed as a disease activity marker in arthritis associated with IBD. (+info)