[Show abstract][Hide abstract]ABSTRACT: TNF-stimulated gene-6 (TSG-6) is a multifunctional protein secreted in response to pro-inflammatory stimuli by a wide range of cells including neutrophils, monocytes and endothelial cells. It has been shown to mediate anti-inflammatory and protective effects when administered in disease models, in part, by reducing neutrophil infiltration. Human TSG-6 inhibits neutrophil migration by binding CXCL8 through its Link module (Link_TSG6) and interfering with the presentation of CXCL8 on cell-surface glycosaminoglycans (GAGs), an interaction that is vital for the function of many chemokines. TSG-6 was also found to interact with chemokines CXCL11 and CCL5, suggesting the possibility that it may function as a broad specificity chemokine-binding protein, functionally similar to those encoded by viruses. The present study was therefore undertaken to explore the ability of TSG-6 to regulate the function of other chemokines. Herein, we demonstrate that Link_TSG6 binds chemokines from both the CXC and CC families, in
Full-text available · Article · Apr 2016 · Journal of Biological Chemistry
[Show abstract][Hide abstract]ABSTRACT: The matrix polysaccharide hyaluronan (HA) has a critical role in the expansion of the cumulus cell-oocyte complex (COC), a process that is necessary for ovulation and fertilization in most mammals. Hyaluronan is organized into a crosslinked network by the cooperative action of three proteins, inter-alpha-inhibitor (IalphaI), pentraxin-3 and TNF-induced protein-6 (TSG-6), driving the expansion of the COC and providing the cumulus matrix with its required viscoelastic properties. While it is known that matrix stabilization involves the TSG-6-mediated transfer of IalphaI heavy chains (HC) onto hyaluronan (to form covalent HC-HA complexes that are crosslinked by pentraxin-3), and that this occurs via the formation of covalent HC-TSG-6 intermediates, the underlying molecular mechanisms are not well understood. Here, we have determined the tertiary structure of the CUB module from human TSG-6, identifying a calcium ion-binding site and chelating glutamic acid residue that mediate the formation of HC-TSG-6. This occurs via an initial metal ion-dependent, non-covalent, interaction between TSG-6 and HCs that also requires the presence of a HC-associated magnesium ion. In addition, we have found that the well-characterised hyaluronan-binding site in the TSG-6 Link module is not used for recognition during transfer of HCs onto HA. Analysis of TSG-6 mutants (with either impaired transferase and/or hyaluronan-binding functions), revealed that while the TSG-6-mediated formation of HC-HA complexes is essential for the expansion of mouse COCs in vitro, the hyaluronan-binding function of TSG-6 does not play a major role in the stabilization of the murine cumulus matrix.
Full-text available · Article · Oct 2015 · Journal of Biological Chemistry
[Show abstract][Hide abstract]ABSTRACT: Mammalian oocytes are surrounded by a highly hydrated hyaluronan (HA)-rich extracellular matrix with embedded cumulus cells, forming the cumulus cell-oocyte complex (COC) matrix. The correct assembly, stability and mechanical properties of this matrix, which are crucial for successful ovulation, transport of the COC to the oviduct and its fertilization, depend on the interaction between HA and specific HA-organizing proteins. Although the proteins inter-αinhibitor (IαI), pentraxin 3 (PTX3) and TNF-stimulated gene-6 (TSG-6) have been identified as being critical for COC matrix formation, its supramolecular organization and the molecular mechanism of COC matrix stabilization remain unknown. Here we used films of end-grafted HA as a model system to investigate the molecular interactions involved in the formation and stabilization of HA matrices containing TSG-6, IαI and PTX3. We found that PTX3 binds neither to HA alone nor to HA films containing TSG-6. This long pentraxin also failed to bind to products of the interaction between IαI, TSG-6 and HA, among which are the covalent HC·HA and HC·TSG-6 complexes, despite the fact that both IαI and TSG-6 are ligands of PTX3. Interestingly, prior encounter with IαI was required for effective incorporation of PTX3 into TSG-6-loaded HA films. Moreover, we demonstrated that this ternary protein mixture made of IαI, PTX3 and TSG-6 is sufficient to promote formation of a stable (i.e. cross-linked) yet highly hydrated HA matrix. We propose that this mechanism is essential for correct assembly of the COC matrix, and may also have general implications in other inflammatory processes that are associated with HA-crosslinking.
Full-text available · Article · Sep 2014 · Journal of Biological Chemistry
[Show abstract][Hide abstract]ABSTRACT: TNF-stimulated gene/protein-6 (TSG-6) is expressed by many different cell types in response to proinflammatory cytokines and plays an important role in the protection of tissues from the damaging consequences of acute inflammation. Recently, TSG-6 was identified as being largely responsible for the beneficial effects of multipotent mesenchymal stem cells, for example in the treatment of animal models of myocardial infarction and corneal injury/allogenic transplant. The protective effect of TSG-6 is due in part to its inhibition of neutrophil migration, but the mechanisms underlying this activity remain unknown. In this study, we have shown that TSG-6 inhibits chemokine-stimulated transendothelial migration of neutrophils via a direct interaction (KD, ∼25 nM) between TSG-6 and the glycosaminoglycan binding site of CXCL8, which antagonizes the association of CXCL8 with heparin. Furthermore, we found that TSG-6 impairs the binding of CXCL8 to cell surface glycosaminoglycans and the transport of CXCL8 across an endothelial cell monolayer. In vivo this could limit the formation of haptotactic gradients on endothelial heparan sulfate proteoglycans and, hence, integrin-mediated tight adhesion and migration. We further observed that TSG-6 suppresses CXCL8-mediated chemotaxis of neutrophils; this lower potency effect might be important at sites where there is high local expression of TSG-6. Thus, we have identified TSG-6 as a CXCL8-binding protein, making it, to our knowledge, the first soluble mammalian chemokine-binding protein to be described to date. We have also revealed a potential mechanism whereby TSG-6 mediates its anti-inflammatory and protective effects. This could inform the development of new treatments for inflammation in the context of disease or following transplantation.
Full-text available · Article · Feb 2014 · The Journal of Immunology
[Show abstract][Hide abstract]ABSTRACT: Tumor necrosis factor-stimulated gene-6 (TSG-6) is an inflammation-associated hyaluronan (HA)-binding protein that contributes
to remodeling of HA-rich extracellular matrices during inflammatory processes and ovulation. The HA-binding domain of TSG-6
consists solely of a Link module, making it a prototypical member of the superfamily of proteins that interacts with this
high molecular weight polysaccharide composed of repeating disaccharides of d-glucuronic acid and N-acetyl-d-glucosamine (GlcNAc). Previously we modeled a complex of the TSG-6 Link module in association with an HA octasaccharide based
on the structure of the domain in its HA-bound conformation. Here we have generated a refined model for a HA/Link module complex
using novel restraints identified from NMR spectroscopy of the protein in the presence of 10 distinct HA oligosaccharides
(from 4- to 8-mers); the model was then tested using unique sugar reagents, i.e. chondroitin/HA hybrid oligomers and an octasaccharide in which a single sugar ring was 13C-labeled. The HA chain was found to make more extensive contacts with the TSG-6 surface than thought previously, such that
a d-glucuronic acid ring makes stacking and ionic interactions with a histidine and lysine, respectively. Importantly, this causes
the HA to bend around two faces of the Link module (resembling the way that HA binds to CD44), potentially providing a mechanism
for how TSG-6 can reorganize HA during inflammation. However, the HA-binding site defined here may not play a role in TSG-6-mediated
transfer of heavy chains from inter-α-inhibitor onto HA, a process known to be essential for ovulation.
Full-text available · Article · Jan 2014 · Journal of Biological Chemistry
[Show abstract][Hide abstract]ABSTRACT: The human endometrium undergoes repetitive, cyclical changes under the influence of endocrine signals (estrogen and progesterone). In particular, the extensive tissue remodeling, angiogenesis and leukocyte infiltration that occur during decidualization of the endometrium give rise to an environment that is permissive to blastocyst attachment. However, it is now well established that crosstalk (via paracrine signals) between the trophoblast and the endometrium is also a key for successful implantation. Microarray studies have identified TSG-6 as a gene with elevated expression in endometrial stromal cells following the exposure to trophoblast and immune cell products. TSG-6 is an inflammation-associated protein which acts as a potent inhibitor of neutrophil extravasation and also plays important roles in matrix remodeling, e.g., by promoting hyaluronan (HA) cross-linking and down-regulating the protease network. Female TSG-6 (-/-) mice are infertile and this has been attributed to their inability to ovulate; however, the importance of TSG-6 in implantation has not been directly investigated.
Real-time PCR, as well as immunofluorescence staining was performed on endometrial biopsies of proliferative and secretory phase samples. In addition stromal cell cultures of human endometrium were used to assess the influence of different stimulating factors on the TSG-6 gene and protein expression via real-time PCR and ELISA.
Herein demonstrate that TSG-6 mRNA is expressed by the endometrium during the proliferative and secretory phases of the menstrual cycle. We also show that conditioned media from placental tissues induce rapid upregulation of TSG-6 mRNA expression and sustained protein secretion, with evidence that TNF is an important factor in this effect. Furthermore, we demonstrate changes in protein expression in the mid-secretory phase in women affected by recurrent abortions.
These data suggest that TSG-6 expression might be essential in endometrial matrix organization and feto-maternal communication during the implantation process.
[Show abstract][Hide abstract]ABSTRACT: Under inflammatory conditions and in the matrix of the cumulus-oocyte complex (COC), the polysaccharide hyaluronan (HA) becomes decorated covalently with heavy chains (HCs) of the serum glycoprotein inter-α-inhibitor (IαI). This alters the functional properties of the HA as well as its structural role within extracellular matrices. The covalent transfer of HCs from IαI to HA is catalyzed by tumor necrosis factor-stimulated gene-6 (TSG-6) but TSG-6 is also known as a HA cross-linker that induces condensation of the HA matrix. Here, we investigate the interplay of these two distinct functions of TSG-6 by studying the ternary interactions of IαI and TSG-6 with well defined films of end-grafted HA chains. We demonstrate that TSG-6 mediated cross-linking of HA films is impaired in the presence of IαI, and that this effect suppresses the TSG-6-mediated enhancement of HA binding to CD44 positive cells. Furthermore, we find that the interaction of TSG-6 and IαI in the presence of HA gives rise to two types of complexes that independently promote the covalent transfer of heavy chains to HA. One type of complex interacts very weakly with HA and is likely to correspond to the previously reported covalent HC·TSG-6 complexes. The other type of complex is novel and binds stably but non-covalently to HA. Prolonged incubation with TSG-6 and IαI leads to HA films that contain, in addition to covalently HA-bound HCs, several tightly but non-covalently bound molecular species. These findings have important implications for understanding how the biological activities of TSG-6 are regulated, such that the presence or absence of IαI will dictate its function.
Full-text available · Article · Sep 2013 · Journal of Biological Chemistry
[Show abstract][Hide abstract]ABSTRACT: TSG-6 (the product of tumor necrosis factor [TNF]-stimulated gene 6) has a potent inhibitory effect on RANKL-mediated bone erosion. The aim of this study was to compare the activity of TSG-6 with that of osteoprotegerin (OPG) and to investigate its role as an autocrine modulator of cytokine-mediated osteoclast formation/activation. We also determined TSG-6 expression in inflammatory joint disease.
The effects of TSG-6, OPG, and the inflammation mediators TNFα, interleukin-1 (IL-1), and IL-6 on the formation of osteoclasts from peripheral blood mononuclear cells and synovial fluid (SF) macrophages were determined by tartrate-resistant acid phosphatase staining. Lacunar resorption and filamentous actin ring formation were measured as indicators of osteoclast activity. The amount of TSG-6 in culture media or SF was quantified by enzyme-linked immunosorbent assay, and expression of TSG-6 in synovial tissue was assessed by immunohistochemistry.
TSG-6 acted in synergy with OPG to inhibit RANKL-mediated bone resorption and was produced by osteoclast precursors and mature osteoclasts in response to TNFα, IL-1, and IL-6. Expression of TSG-6 correlated with inhibition of lacunar resorption; this effect was ameliorated by an anti-TSG-6 antibody. The level of TSG-6 protein was determined in SF from patients with various arthritides; it was highest in patients with inflammatory conditions such as rheumatoid arthritis, in which it correlated with the amount of TSG-6 immunostaining in the synovium. TSG-6 inhibited the activation but not the formation of osteoclasts from SF macrophages.
In the presence of inflammatory cytokines, osteoclasts produced TSG-6 at concentrations that are sufficient to inhibit lacunar resorption. This may represent an autocrine mechanism to limit the degree of bone erosion during joint inflammation.
[Show abstract][Hide abstract]ABSTRACT: Hyaluronan (HA) is a major component of the extracellular matrix (ECM) with increased synthesis during tissue repair. Tumour necrosis factor-stimulated gene-6 (TSG-6) is known to catalyze the covalent transfer of heavy chains (HC1 and HC2) from inter-α-inhibitor (IαI) onto HA, and resultant HC•HA complexes have been implicated in physiological and pathological processes related to remodelling and inflammation.
The aims of this study were to determine the expression of HA, TSG-6 and the IαI polypeptides in unscarred skin, normal scars and keloid scars.
Formalin-fixed paraffin-embedded sections of unscarred skin, normal scars and keloid scars were prepared from patient samples collected during scar revision surgery. Haematoxylin and eosin, as well as immunofluorescent staining for HA, TSG-6 and the three polypeptide chains of IαI (i.e. HC1, HC2 and bikunin) were performed.
All skin types stained positive for TSG-6, HC1, HC2 and bikunin, associated with keratinocytes, fibroblasts and skin appendages all in close proximity to HA. Keloid lesions showed altered HA organization patterns compared with unscarred skin and normal scars. TSG-6 staining was significantly more intense in the epidermis compared with the dermis of all sample types. There was a significant reduction in TSG-6 levels within keloid lesions compared with the dermis of unscarred skin (P=0.017).
TSG-6 is expressed in unscarred skin, where its close association with HA and IαI could give rise to TSG-6-mediated HC•HA formation within this tissue. A reduction in the beneficial effects of TSG-6, caused by diminished protein levels in keloid lesions, could contribute to this abnormal scarring process.
Full-text available · Article · Mar 2011 · Journal of the European Academy of Dermatology and Venereology
[Show abstract][Hide abstract]ABSTRACT: The exact mechanism of capsular contracture (CC) is still unknown. The covalent modification of hyaluronan (HA) with the heavy chains (HC) of inter-α-inhibitor (IαI) has been identified as an important pathway in inflammation and tissue remodeling, where HC·HA formation is catalyzed by TSG-6 (the protein product of tumor necrosis factor stimulated gene-6).
The authors quantitatively assess the correlation between severity of CC (measured by Baker grade) and expression of HA, TSG-6, and IαI (ie, the polypeptides HC1, HC2, and bikunin) in periprosthetic breast capsules.
Immunofluorescent staining for HA, TSG-6, HC1, HC2, and bikunin was carried out on periprosthetic breast capsules (n = 7) of each Baker grade from four anatomical locations. Quantitative analysis was performed to identify differences in staining intensity. Real-time quantitative polymerase chain reaction (RT-qPCR) was performed to determine differences in TSG-6 gene expression levels.
Severity of contracture was associated with reduced staining for both free HA (Pearson correlation coefficient, r = -0.645, P < .001) and TSG-6 (r = -0.642, P = .002). RT-qPCR showed a significant negative correlation between severity of contracture and TSG-6 gene expression levels (r = -0.750, P = .001).
The negative correlation between TSG-6 expression levels and severity of CC suggests a possible protective role for TSG-6 in the context of CC formation, and this may have a clinically relevant role in prevention of breast CC.
Full-text available · Article · Jan 2011 · Aesthetic surgery journal / the American Society for Aesthetic Plastic surgery
[Show abstract][Hide abstract]ABSTRACT: Migration Stimulating Factor (MSF) is a genetically truncated isoform of fibronectin (Fn). MSF is a potent stimulator of fibroblast migration, whereas full length Fn is devoid of motogenic activity. MSF and Fn contain four IGD motifs, located in the 3rd, 5th, 7th and 9th type I modules; these modules are referred to as (3)FnI, (5)FnI, (7)FnI and (9)FnI, respectively. We have previously reported that mutation of IGD motifs in modules (7)FnI and (9)FnI of MSF is sufficient to completely abolish the motogenic response of target adult skin fibroblasts. We now report that the IGD sequences in (3)FnI and (5)FnI are also capable of exhibiting motogenic activity when present within fragments of MSF. When present within (1-5)FnI, these sequences require the presence of serum or vitronectin for their motogenic activity to be manifest, whereas the IGD sequences in (7)FnI and (9)FnI are bioactive in the absence of serum factors. All MSF and IGD-containing peptides stimulated the phosphorylation of the integrin binding protein focal adhesion kinase (FAK) but did not necessarily affect migration. These results suggest that steric hindrance determines the motogenic activity of MSF and Fn, and that both molecules contain cryptic bioactive fragments.