Interaction of tetranectin with sulphated polysaccharides and trypan blue

Insight into the function of tetranectin in human diseases: A review and prospects for tetranectin-targeted disease treatment

Tetranectin (TN), a serum protein, is closely associated with different types of cancers. TN binds plasminogen and promotes the proteolytic activation of plasminogen into plasmin, which suggests that TN is involved in remodeling the extracellular matrix and cancer tissues during cancer development. TN is also associated with other diseases, such as developmental disorders, cardiovascular diseases, neurological diseases, inflammation, and diabetes. Although the functional mechanism of TN in diseases is not fully elucidated, TN binds different proteins, such as structural protein, a growth factor, and a transcription regulator. Moreover, TN changes and regulates protein functions, indicating that TN-binding proteins mediate the association between TN and diseases. This review summarizes the current knowledge of TN-associated diseases and TN functions with TN-binding proteins in different diseases. In addition, potential TN-targeted disease treatment by inhibiting the interaction between TN and its binding proteins is discussed.

Tetranectin targeting by epigallocatechin gallate suppresses colon cancer cell proliferation

Tetranectin is a serum protein that binds to plasminogen and enhances its proteolytic activation, which underlies the involvement of tetranectin in the development of several carcinomas including colon cancer. In the present study, structure-based in silico screening of natural products showed that epigallocatechin gallate with anticancer effects binds to tetranectin. Binding to epigallocatechin gallate to tetranectin was confirmed by intrinsic fluorescence quenching assays and isothermal titration calorimetry. Furthermore, epigallocatechin gallate efficiently inhibited the activity of tetranectin to enhance the activation of plasminogen. We also found that tetranectin enhanced the proliferation of CT-26 colon cancer cells. Epigallocatechin gallate showed its cytotoxic effect on CT-26 cells due to its binding to tetranectin and the consequent suppression of the cell proliferation. These results demonstrate that the anticancer effect of epigallocatechin gallate is mediated, at least in part, by inhibiting tetranectin as a binding target.

An overview on human serum lectins

An extensive literature survey done on the various naturally occurring lectins in human serum upon its salient features such as methods of detection, level and sites of synthesis, binding specificity, cation dependency, modes of isolation, molecular and functional characterization way back from 1930s to till date was presented in a tabulated section. In addition, the generation of lectin and other immune molecules in vertebrates upon treatment with exogenous elicitors has also been framed in a tabular form. Furthermore, ANEW lectin induced in human serum for the very first time by an exogenous elicitor was detected, isolated and characterized by us whose features are also tabulated explicitly.

Temporal changes guided by mesenchymal stem cells on a 3D microgel platform enhance angiogenesis in vivo at a low-cell dose

Therapeutic factors secreted by mesenchymal stem cells (MSCs) promote angiogenesis in vivo. However, delivery of MSCs in the absence of a cytoprotective environment offers limited efficacy due to low cell retention, poor graft survival, and the nonmaintenance of a physiologically relevant dose of growth factors at the injury site. The delivery of stem cells on an extracellular matrix (ECM)-based platform alters cell behavior, including migration, proliferation, and paracrine activity, which are essential for angiogenesis. We demonstrate the biophysical and biochemical effects of preconditioning human MSCs (hMSCs) for 96 h on a three-dimensional (3D) ECM-based microgel platform. By altering the macromolecular concentration surrounding cells in the microgels, the proangiogenic phenotype of hMSCs can be tuned in a controlled manner through cell-driven changes in extracellular stiffness and "outside-in" integrin signaling. The softest microgels were tested at a low cell dose (5 × 10⁴ cells) in a preclinical hindlimb ischemia model showing accelerated formation of new blood vessels with a reduced inflammatory response impeding progression of tissue damage. Molecular analysis revealed that several key mediators of angiogenesis were up-regulated in the low-cell-dose microgel group, providing a mechanistic insight of pathways modulated in vivo. Our research adds to current knowledge in cell-encapsulation strategies by highlighting the importance of preconditioning or priming the capacity of biomaterials through cell-material interactions. Obtaining therapeutic efficacy at a low cell dose in the microgel platform is a promising clinical route that would aid faster tissue repair and reperfusion in "no-option" patients suffering from peripheral arterial diseases, such as critical limb ischemia (CLI).

Identification of tetranectin as adipogenic serum protein

Fetal bovine serum (FBS) is an essential culture supplement for adipocyte differentiation of various adipogenic precursor cells. Adipocyte differentiation greatly varies depending on the type of serum in the differentiation medium. In this study, we found that FBS supported adipocyte differentiation of 3T3-L1 cells to a significantly higher extent than other types of bovine serum such as adult bovine serum (ABS). This differential adipogenic effect of bovine serum was shown to be due to the protein contents of bovine sera, indicating the presence of an adipogenic protein(s) in FBS. Serum proteome analysis identified tetranectin as an adipogenic protein. The adipogenic effect of tetranectin was confirmed by supplementation of FBS-containing differentiation medium with anti-tetranectin antibody, which suppressed adipocyte differentiation of 3T3-L1 cells. These results demonstrate that tetranectin is an adipogenic serum protein mediating the adipogenic effect of FBS.

The roles of direct recognition by animal lectins in antiviral immunity and viral pathogenesis

Lectins are a group of proteins with carbohydrate recognition activity. Lectins are categorized into many families based on their different cellular locations as well as their specificities for a variety of carbohydrate structures due to the features of their carbohydrate recognition domain (CRD) modules. Many studies have indicated that the direct recognition of particular oligosaccharides on viral components by lectins is important for interactions between hosts and viruses. Herein, we aim to globally review the roles of this recognition by animal lectins in antiviral immune responses and viral pathogenesis. The different classes of mammalian lectins can either recognize carbohydrates to activate host immunity for viral elimination or can exploit those carbohydrates as susceptibility factors to facilitate viral entry, replication or assembly. Additionally, some arthropod C-type lectins were recently identified as key susceptibility factors that directly interact with multiple viruses and then facilitate infection. Summarization of the pleiotropic roles of direct viral recognition by animal lectins will benefit our understanding of host-virus interactions and could provide insight into the role of lectins in antiviral drug and vaccine development.

Serum tetranectin as a preoperative indicator for postoperative complications in Danish ovarian cancer patients

OBJECTIVE

The association between tetranectin (TN) and selected lifestyle factors (smoking and alcohol) and the postoperative complication rate for ovarian cancer (OC) patients undergoing primary cytoreductive surgery has not yet been characterized. The aim of the study was to examine the value of TN, smoking and alcohol as indicators of postoperative complications in OC patients.

METHODS

Serum TN was measured for 374 OC patients undergoing primary cytoreductive surgery. In addition, they reported their smoking and alcohol status. The prognostic value of variables was found with univariate and multivariate analyses using logistic regression analysis.

RESULTS

In univariate analysis TN was the only one out of 8 variables that significantly predicted postoperative complications (OR=0.55 (95% CI: 0.34-0.87), P=0.01). High preoperative serum TN was associated with a low risk of postoperative complications. Stepwise reduction of the multivariate model demonstrated that TN and histology were the only significant co-variables (TN, OR=0.51 (95% CI: 0.32-0.83), P=0.006; histology, OR=1.70 (95% CI: 1.02-2.82), P=0.041). TN was the only indicator, which was statistical significant in both univariate and multivariate analyses.

CONCLUSION

Preoperative serum TN is a significant indicator of postoperative complications in Danish OC patients and deserves to be validated in larger future studies.

Glycogenome expression dynamics during mouse C2C12 myoblast differentiation suggests a sequential reorganization of membrane glycoconjugates

Background

Several global transcriptomic and proteomic approaches have been applied in order to obtain new molecular insights on skeletal myogenesis, but none has generated any specific data on glycogenome expression, and thus on the role of glycan structures in this process, despite the involvement of glycoconjugates in various biological events including differentiation and development. In the present study, a quantitative real-time RT-PCR technology was used to profile the dynamic expression of 375 glycogenes during the differentiation of C2C12 myoblasts into myotubes.

Results

Of the 276 genes expressed, 95 exhibited altered mRNA expression when C2C12 cells differentiated and 37 displayed more than 4-fold up- or down-regulations. Principal Component Analysis and Hierarchical Component Analysis of the expression dynamics identified three groups of coordinately and sequentially regulated genes. The first group included 12 down-regulated genes, the second group four genes with an expression peak at 24 h of differentiation, and the last 21 up-regulated genes. These genes mainly encode cell adhesion molecules and key enzymes involved in the biosynthesis of glycosaminoglycans and glycolipids (neolactoseries, lactoseries and ganglioseries), providing a clearer indication of how the plasma membrane and extracellular matrix may be modified prior to cell fusion. In particular, an increase in the quantity of ganglioside G_M3 at the cell surface of myoblasts is suggestive of its potential role during the initial steps of myogenic differentiation.

Conclusion

For the first time, these results provide a broad description of the expression dynamics of glycogenes during C2C12 differentiation. Among the 37 highly deregulated glycogenes, 29 had never been associated with myogenesis. Their biological functions suggest new roles for glycans in skeletal myogenesis.

Tetranectin in cerebrospinal fluid of patients with multiple sclerosis

OBJECTIVE

Tetranectin (TN) is a glycoprotein and C-type lectin thought to play a prominent role in tissue remodelling. The aim of this study was to determine the TN serum and cerebrospinal fluid (CSF) concentration in patients with multiple sclerosis (MS) and controls.

MATERIAL AND METHODS

Two-hundred-and-four patients, divided into four diagnostic groups, i.e. definite MS (n = 76), possible onset symptoms of MS (n = 48), other non-inflammatory neurological diseases (n = 61) and other inflammatory neurological diseases (n = 19) and 47 controls with no history of neurological disease were analysed for TN in serum and CSF using a polyclonal sandwich ELISA.

RESULTS

All tested groups, e.g. definite MS, possible onset symptoms of MS, other neurological disease, both inflammatory and non-inflammatory, had decreased concentrations of TN in the CSF compared to the concentrations in controls. The quotient of TN in CSF divided by the concentration in serum (QTN) correlated significantly with the same quotient of albumin (QALB), was significantly correlated with the same quotient of albumin QALB. To account for differences in blood brain barrier permeability, we calculated a TN-index defined as: TN-index = QTN/QALB. QTN was significantly decreased in all groups compared to that in controls. However, in definite MS and patients with first attack of MS, the TN-index was not significantly different from that of controls. In contrast, other neurological diseases, both inflammatory and non-inflammatory, were associated with a decreased TN-index.

CONCLUSION

These results indicate that TN may play a role in neurological diseases and may serve as a diagnostic aid in MS.

Impaired cutaneous wound healing in mice lacking tetranectin

Tetranectin was originally purified from human serum on the basis of plasminogen kringle 4-binding properties. Tetranectin enhances plasminogen activation by a tissue-type plasminogen activator so that it has been suggested to play a role in tissue remodeling. We have generated mice with a targeted disruption of the tetranectin gene to elucidate the biological function of tetranectin. In this study, we showed that wound healing was markedly delayed in tetranectin-null mice compared with wild-type mice. A single full-thickness incision was made in the dorsal skin. By 14 days after the incision, the wounds fully healed in all wild-type mice based on the macroscopic closure; in contrast, the progress of wound healing in the tetranectin null mice appeared to be impaired. In histological analysis, wounds of wild-type mice showed complete reepithelialization and healed by 14 days after the incision. However, those of tetranectin-null mice never showed complete reepithelialization at 14 days. At 21 days after the injury, the wound healed and was covered with an epidermis. These results supported the fact that tetranectin may play a role in the wound healing process.

The C-type lectin-like domain superfamily

The superfamily of proteins containing C-type lectin-like domains (CTLDs) is a large group of extracellular Metazoan proteins with diverse functions. The CTLD structure has a characteristic double-loop ('loop-in-a-loop') stabilized by two highly conserved disulfide bridges located at the bases of the loops, as well as a set of conserved hydrophobic and polar interactions. The second loop, called the long loop region, is structurally and evolutionarily flexible, and is involved in Ca2+-dependent carbohydrate binding and interaction with other ligands. This loop is completely absent in a subset of CTLDs, which we refer to as compact CTLDs; these include the Link/PTR domain and bacterial CTLDs. CTLD-containing proteins (CTLDcps) were originally classified into seven groups based on their overall domain structure. Analyses of the superfamily representation in several completely sequenced genomes have added 10 new groups to the classification, and shown that it is applicable only to vertebrate CTLDcps; despite the abundance of CTLDcps in the invertebrate genomes studied, the domain architectures of these proteins do not match those of the vertebrate groups. Ca2+-dependent carbohydrate binding is the most common CTLD function in vertebrates, and apparently the ancestral one, as suggested by the many humoral defense CTLDcps characterized in insects and other invertebrates. However, many CTLDs have evolved to specifically recognize protein, lipid and inorganic ligands, including the vertebrate clade-specific snake venoms, and fish antifreeze and bird egg-shell proteins. Recent studies highlight the functional versatility of this protein superfamily and the CTLD scaffold, and suggest further interesting discoveries have yet to be made.

Tetranectin in cerebrospinal fluid: Biochemical characterisation and evidence of intrathecal synthesis or selective uptake into CSF

BACKGROUND

Tetranectin (TN) is a 67 kDa glycoprotein thought to play a prominent role in the regulation of proteolytic processes via its binding to plasminogen and indirect activation of plasminogen. The TN concentration in serum is approximately 10 mg/l and is reduced in patients with several cancers. The TN concentration in the normal CSF has not been examined.

METHODS

The TN concentration in the serum and CSF of 47 normal subjects without neurological disorders was established using a polyclonal sandwich ELISA.

RESULTS

The median TN concentration (quartile range) was 10.8 mg/l (9.0-12.1) in serum and 0.43 mg/l (0.3-0.53) in CSF. The TN index median (quartile range), defined as (TN CSF concentration/TN serum concentration)/(Albumin CSF concentration/Albumin serum concentration), was found to be 5.5 (4.7-7.6), suggesting intrathecal synthesis or selective uptake of TN in CNS. Immunohistochemistry showed TN immunoreactivity in neurons and dendrites, but no staining in glial cells in the cerebrum and cerebellum. In plexus choroideus, the ependymal cells exhibited strong immunoreactivity. TN in serum and CSF were immunochemically identical and of similar size.

CONCLUSION

TN is present in normal brain and CSF, and the TN index is very high, but further studies are necessary to decide whether TN is synthesised in the CNS or selectively transported over the blood-brain barrier.

Aberrant tetranectin expression in human breast carcinomas as a predictor of survival

AIMS

Tetranectin (TN), a plasminogen kringle 4 binding protein, is thought to play a prominent role in the regulation of proteolytic processes via binding to plasminogen. The aim of this study was to evaluate the expression of TN in human breast cancer and adjacent normal breast tissue and to determine the impact of this expression on survival.

METHODS

A retrospective analysis was performed on 189 patients with breast cancer, with a median follow up time of 10.6 years. The expression of TN was assessed in tumour tissue and adjacent normal breast tissue by immunohistochemistry, and the prognostic relevance of its expression in tumour cells was evaluated.

RESULTS

TN was highly expressed in connective tissue fibres surrounding normal breast epithelium, but not in normal epithelial cells. High expression of TN in tumour cells was found in 131 (69%) of the tumour samples. By western blot analysis, no significant difference in the amount and molecular weight of TN was seen between tumour tissue and normal tissue. Strong TN immunoreactivity in tumour tissue was predictive of poor disease free and tumour specific overall survival. By multivariate analysis, high TN expression in cancer cells was an independent prognostic factor for disease free and tumour specific overall survival.

CONCLUSIONS

Our results demonstrate differential TN expression in normal and malignant breast tissue and a prognostic impact of TN protein expression in breast carcinoma tissue. These data suggest a possible role of TN in invasiveness and the metastatic spread of human breast cancer.

Tetranectin binds hepatocyte growth factor and tissue-type plasminogen activator

In the search for new ligands for the plasminogen kringle 4 binding-protein tetranectin, it has been found by ligand blot analysis and ELISA that tetranectin specifically bound to the plasminogen-like hepatocyte growth factor and tissue-type plasminogen activator. The dissociation constants of these complexes were found to be within the same order of magnitude as the one for the plasminogen-tetranectin complex. The study also revealed that tetranectin did not interact with the kindred proteins: macrophage-stimulating protein, urokinase-type plasminogen activator and prothrombin. In order to examine the function of tetranectin, a kinetic analysis of the tPA-catalysed plasminogen activation was performed. The kinetic parameters of the tetranectin-stimulated enhancement of tPA were comparable to fibrinogen fragments, which are so far the best inducer of tPA-catalysed plasminogen activation. The enhanced activation was suggested to be caused by tetranectin's ability to bind and accumulate tPA in an active conformation.

Specificity determinants in the interaction of apolipoprotein(a) kringles with tetranectin and LDL

Lipoprotein(a) is composed of low density lipoprotein and apolipoprotein(a). Apolipoprotein(a) has evolved from plasminogen and contains 10 different plasminogen kringle 4 homologous domains [KIV(1-110)]. Previous studies indicated that lipoprotein(a) non-covalently binds the N-terminal region of lipoprotein B100 and the plasminogen kringle 4 binding plasma protein tetranectin. In this study recombinant KIV(2), KIV(7) and KIV(10) derived from apolipoprotein(a) were produced in E. coli and the binding to tetranectin and low density lipoprotein was examined. Only KIV(10) bound to tetranectin and binding was similar to that of plasminogen kringle 4 to tetranectin. Only KIV(7) bound to LDL. In order to identify the residues responsible for the difference in specificity between KIV(7) and KIV(10), a number of surface-exposed residues located around the lysine binding clefts were exchanged. Ligand binding analysis of these derivatives showed that Y62, and to a minor extent W32 and E56, of KIV(7) are important for LDL binding to KIV(7), whereas R32 and D56 of KIV(10) are required for tetranectin binding of KIV(10).

Serum tetranectin is an independent prognostic marker in colorectal cancer and weakly correlated with plasma suPAR, plasma PAI-1 and serum CEA

Soluble tetranectin (TN) was measured preoperatively in serum from 567 patients with primary colorectal cancer and levels were tested for association with prognosis. The prognostic significance of TN was also compared to that of plasminogen-activator inhibitor-1 (PAI-1), urokinase plasminogen activator (uPAR) and carcinoembryonic antigen (CEA). Significantly shorter survival was found for patients with TN levels below a cut-off point of 7.5 mg/l compared to patients with levels above, as illustrated by Kaplan-Meier curves. By Cox analyses, log TN, log soluble uPAR as well as log CEA were found to have an independent prognostic value for survival (log TN: HR = 0.47, 95% CI: 0.29-0.76); log soluble uPAR: HR = 1.65, 95% CI: 1.18-2.31; log CEA: HR = 1.I1, 95% CI: 1.03-1.20). Based on the multivariate model, a patient with a combination of low levels of TN and PAI-1 and elevated levels of soluble uPAR and CEA had a 2.43 increased risk as compared to a patient with median levels of these biochemical markers. Significant correlations were found with Dukes' stages for all the biochemical markers and between the respective biochemical markers. The findings confirm that TN is a strong prognostic factor in patients with colorectal cancer. TN may be valuable as a prognostic variable in future studies evaluating new treatment strategies for colorectal cancer.

Tetranectin in slow intra- and extrafusal chicken muscle fibers

Tetranectin is a C-type lectin that occurs in the mammalian musculoskeletal system. In the present report we describe the first studies on an avian tetranectin. A full-length chicken tetranectin cDNA was isolated. Comparison of the deduced amino acid sequence of chicken tetranectin with mouse and human tetranectin showed an identity of 67 and 68%, respectively. Northern blot analysis demonstrated broad expression of chicken tetranectin mRNA, which was first detected on embryonic day 4. Tetranectin protein was detected in chicken serum and egg yolk. Since muscle is one of few tissues in which tetranectin protein is retained, we examined the distribution of tetranectin in various muscle types in chicken. Myofibers strongly positive for tetranectin were observed in several muscles including m. tibialis ant. and m. sartorius (from embryonic day 10 to adult). Using antibodies to fast and slow myosin heavy chains (MHC) and double immunostaining techniques, we found that tetranectin was restricted to slow (type I) muscle fibers. Similarly only slow intrafusal fibers accumulated tetranectin. The pattern of immunostaining in chickens differs markedly from that seen in mouse muscles, indicating that tetranectin performs a role in muscle that is not associated with a hitherto recognized muscle type or function.

Tetranectin-like protein in vertebrate serum: a comparative immunochemical analysis

The glycoprotein tetranectin (TN) found in human serum is a 90-kDa homotrimeric C-type lectin binding Ca2+, heparin and plasminogen kringle 4. TN is suggested as being implicated in tissue remodelling. The antigenic reactivity of putative TN was examined in serum from 14 different animal species using three sandwich enzyme immunoassays for human TN. Crab-eating macaque serum showed the strongest reaction, followed by horse and cat. Serum from cow, goat, pig, mouse and chicken reacted weakly, while dog, trout, and the amphibian and the reptile species did not react. The TN-like protein from macaque, horse and cat serum bound heparin and showed the same dependence on Ca2+ for interaction with the monoclonal antibodies as human TN. Gel filtration of sera from the three animal species showed that the TN-like protein eluted as single peaks with a M(r) of 70-90 kDa. Western blotting of horse and cat TN-like protein electrophoresed under reducing conditions showed that the antibodies against human TN reacted with a single band with an approximate M(r) of 30 kDa, indicating that the TN-like protein is also a homotrimer. Horse and cat TN-like protein interacted with human kringle 4-sepharose. Most likely, the reacting protein represents crab-eating macaque, horse and cat homologues of human TN.

The prognostic value of pretherapeutic tetranectin and CA-125 in patients with relapse of ovarian cancer

OBJECTIVE

The aim of the study was to examine the prognostic values of, respectively, tetranectin (TN) and CA-125 measured in serum from patients presenting with relapse of ovarian cancer (OC).

METHODS

TN and CA-125 were measured in serum samples from 75 patients with relapse of OC before the start of second-line chemotherapy. The endpoint used was death of OC. The variables were analyzed by univariate life table analysis and multivariate Cox analysis.

RESULTS

A significantly shortened survival was found for patients with low serum TN values compared to patients with serum TN levels above one of the cutoff levels. The survivals are illustrated by life tables. No prognostic function was found for CA-125. TN and relapse </=12 months after primary treatment were the only significant independent prognostic variables among the following variables tested in the Cox analyses: primary and second-line treatment, CA-125, age, histology, performance score, tumor localization, and size.

CONCLUSION

Serum TN determination may be valuable in the selection of patients with relapse of OC for new treatment strategies in future studies.

Mutational analysis of affinity and selectivity of kringle-tetranectin interaction. Grafting novel kringle affinity ontp the trtranectin lectin scaffold

C-type lectin-like domains are found in many proteins, where they mediate binding to a wide diversity of compounds, including carbohydrates, lipids, and proteins. The binding of a C-type lectin-like domain to a ligand is often influenced by calcium. Recently, we have identified a site in the C-type lectin-like domain of tetranectin, involving Lys-148, Glu-150, and Asp-165, which mediates calcium-sensitive binding to plasminogen kringle 4. Here, we investigate the effect of conservative substitutions of these and a neighboring amino acid residue. Substitution of Thr-149 in tetranectin with a tyrosine residue considerably increases the affinity for plasminogen kringle 4, and, in addition, confers affinity for plasminogen kringle 2. As shown by isothermal titration calorimetry analysis, this new interaction is stronger than the binding of wild-type tetranectin to plasminogen kringle 4. This study provides further insight into molecular determinants of importance for binding selectivity and affinity of C-type lectin kringle interactions.

Tetranectin-binding site on plasminogen kringle 4 involves the lysine-binding pocket and at least one additional amino acid residue

Kringle domains are found in a number of proteins where they govern protein-protein interactions. These interactions are often sensitive to lysine and lysine analogues, and the kringle-lysine interaction has been used as a model system for investigating kringle-protein interactions. In this study, we analyze the interaction of wild-type and six single-residue mutants of recombinant plasminogen kringle 4 expressed in Escherichia coli with the recombinant C-type lectin domain of tetranectin and trans-aminomethyl-cyclohexanoic acid (t-AMCHA) using isothermal titration calorimetry. We find that all amino acid residues of plasminogen kringle 4 found to be involved in t-AMCHA binding are also involved in binding tetranectin. Notably, one amino acid residue of plasminogen kringle 4, Arg 32, not involved in binding t-AMCHA, is critical for binding tetranectin. We also find that Asp 57 and Asp 55 of plasminogen kringle 4, which both were found to interact with the low molecular weight ligand with an almost identical geometry in the crystal of the complex, are not of equal functional importance in t-AMCHA binding. Mutating Asp 57 to an Asn totally eliminates binding, whereas the Asp 55 to Asn, like the Arg 71 to Gln mutation, was found only to decrease affinity.

The cartilage-derived, C-type lectin (CLECSF1): structure of the gene and chromosomal location

Cartilage is a tissue that is primarily extracellular matrix, the bulk of which consists of proteoglycan aggregates constrained within a collagen framework. Candidate components that organize the extracellular assembly of the matrix consist of collagens, proteoglycans and multimeric glycoproteins. We describe the human gene structure of a potential organizing factor, a cartilage-derived member of the C-type lectin superfamily (CLECSF1; C-type lectin superfamily) related to the serum protein, tetranectin. We show by Northern analysis that this protein is restricted to cartilage and locate the gene on chromosome 16q23. We have characterized 10.9 kb of sequence upstream of the first exon. Similarly to human tetranectin, there are three exons. The residues that are conserved between CLECSF1 and tetranectin suggest that the cartilage-derived protein forms a trimeric structure similar to that of tetranectin, with three N-terminal alpha-helical domains aggregating through hydrophobic faces. The globular, C-terminal domain that has been shown to bind carbohydrate in some members of the family and plasminogen in tetranectin, is likely to have a similar overall structure to that of tetranectin.

The plasminogen binding site of the C-type lectin tetranectin is located in the carbohydrate recognition domain, and binding is sensitive to both calcium and lysine

Tetranectin, a homotrimeric protein belonging to the family of C-type lectins and structurally highly related to corresponding regions of the mannose-binding proteins, is known specifically to bind the plasminogen kringle 4 protein domain, an interaction sensitive to lysine. Surface plasmon resonance and isothermal calorimetry binding analyses using single-residue and deletion mutant tetranectin derivatives produced in Escherichia coli showed that the kringle 4 binding site resides in the carbohydrate recognition domain and includes residues of the putative carbohydrate binding site. Furthermore, the binding analysis revealed that the interaction is sensitive to calcium in addition to lysine.

Comparative study of tetranectin levels in serum and synovial fluid of patients with rheumatoid arthritis, seronegative spondylarthritis and osteoarthritis

Tetranectin (TN) was assessed in paired synovial fluid (SF) and serum (S) samples from 27 patients with rheumatoid arthritis (RA), 23 with seronegative spondylarthritis (SSA) and 22 with osteoarthritis (OA). RA patients had a stronger correlation between serum and SF TN and a higher SF/S TN ratio than did SSA and OA patients. Moreover, the SF/S TN ratio exceeded 1 in most RA patients but not in SSA and OA patients, indicating the possibility of intra-articular TN synthesis in RA. A strong correlation of serum and SF TN with known inflammatory markers was observed in RA. The TN/proteinase inhibitors (PIs: alpha1-antitrypsin, alpha2-macroglobulin) molar ratio in SF was lower in RA and SSA patients to a statistically significant degree than in OA patients. In RA, in contrast to SSA and OA, this ratio correlated positively with the SF interleukin-8 (IL-8), responsible for neutrophil recruitment and degranulation, and negatively with erythrocyte sedimentation rate, serum C-reactive protein and fibrinogen, known markers of disease activity. In conclusion, patients with RA showed lower serum TN levels, a higher SF/S TN ratio and a lower SF TN/PI molar ratio than did SSA and OA patients, suggesting the implication of TN in the impaired regulation of fibrinolysis associated with the inflammatory process.

Determination of serum tetranectin: technical and clinical evaluation of three sandwich immunoassays

The performance of two sandwich-type immunoassays for the determination of the tumour marker tetranectin using monoclonal antibodies Hyb 130-13 and 130-14 as catching layer was compared with the performance of a polyclonal assay. Sensitivities were 0.4-0.6 microg/l, and intra- and inter-assay coefficients of variation were < 10% in all assays. One-hundred-and-ten blood donors were examined, and women had higher concentrations of tetranectin in serum than men when measured with monoclonal assays (P < 0.05). In preoperative serum samples from 43 patients with ovarian cancer, tetranectin concentrations were reduced (P < 0.001), and the mean tetranectin concentration decreased with increasing FIGO stage of the patients (P < 0.05). In sera from patients with ovarian cancer, tetranectin concentrations were lower in the polyclonal assay than in the monoclonal assays. This could, hypothetically, be explained by ligand-binding or other conformational changes in tetranectin, influencing the antigenicity of the molecule.

Crystal structure of tetranectin, a trimeric plasminogen-binding protein with an alpha-helical coiled coil

Tetranectin is a plasminogen kringle 4-binding protein. The crystal structure has been determined at 2.8 A resolution using molecular replacement. Human tetranectin is a homotrimer forming a triple alpha-helical coiled coil. Each monomer consists of a carbohydrate recognition domain (CRD) connected to a long alpha-helix. Tetranectin has been classified in a distinct group of the C-type lectin superfamily but has structural similarity to the proteins in the group of collectins. Tetranectin has three intramolecular disulfide bridges. Two of these are conserved in the C-type lectin superfamily, whereas the third is present only in long-form CRDs. Tetranectin represents the first structure of a long-form CRD with intact calcium-binding sites. In tetranectin, the third disulfide bridge tethers the CRD to the long helix in the coiled coil. The trimerization of tetranectin as well as the fixation of the CRDs relative to the helices in the coiled coil indicate a demand for high specificity in the recognition and binding of ligands.

Tetranectin, a trimeric plasminogen-binding C-type lectin

Tetranectin, a plasminogen-binding protein belonging to the family of C-type lectins, was expressed in E. coli and converted to its native form by in vitro refolding and proteolytic processing. Recombinant tetranectin-as well as natural tetranectin from human plasma-was shown by chemical cross-linking analysis and SDS-PAGE to be a homo-trimer in solution as are other known members of the collectin family of C-type lectins. Biochemical evidence is presented showing that an N-terminal domain encoded within exons 1 and 2 of the tetranectin gene is necessary and sufficient to govern subunit trimerization.

Use of tetranectin, CA-125 and CASA to predict residual tumor and survival at second- and third-look operations for ovarian cancer

Tetranectin (TN), CA-125 and CASA were measured in serum prior to 63 second-look and 5 third-look operations for ovarian cancer. Patients with residual tumor had significantly lower levels of TN and higher levels of CASA and CA-125 compared with tumor-free patients. The predictive values PVPos = 100% and PVNeg = 50.9% were found for TN at 9.3 mg/l. For CASA, a predictive value PVPos = 100% was found at 10 U/ml with a corresponding PVNeg = 52.7%. At the cut-off 35 U/ml for CA-125, the PVPos was 100% and the PVNeg = 53.6%. By combining the markers, PVNeg increased to 61.7% with a PVPos on 100%. Significantly differences in survival were found by lifetable analysis between patients tested as positive and negative respectively for any of the markers. Using multivariate Cox analyses, it was found that every marker had an independent prognostic function for survival.

Mouse tetranectin: cDNA sequence, tissue-specific expression, and chromosomal mapping

Tetranectin is a plasminogen-binding tetrameric protein originally isolated from plasma. Expression of tetranectin appears ubiquitous, although particularly high expression is noted in the stroma of malignant tumors and during mineralization. To dissect the molecular basis of tetranectin gene regulation, mouse tetranectin cDNA was cloned from a 16-day-old mouse embryo library. Sequence analysis revealed a 992-bp cDNA with an open reading frame of 606 bp, which is identical in length to the human tetranectin cDNA. The deduced amino acid sequence showed high homology to the human cDNA with 76% identity and 87% similarity at the amino acid level. Sequence comparisons between mouse and human tetranectin and some C-type lectins confirmed a complete conservation in the position of six cysteines as well as numerous other amino acid residues, indicating an essential structure for potential function(s) of tetranectin. The sequence analysis revealed a difference in both sequence and size of the noncoding regions between mouse and human cDNAs. Northern analysis of the various tissues from mouse, rat, and cow showed the major transcript(s) to be approximately 1 kb, which is similar in size to that observed in human. Although additional minor bands of 1.5 and 3.3 kb were found in Northern blots, RT-PCR (reverse transcription polymerase chain reaction) analysis failed to provide evidence that these minor bands are products of the tetranectin gene. Finally, the genetic map location for this gene, Tna, was determined to be on distal mouse Chromosome (Chr) 9 by analysis of two sets of multilocus crosses.

Plasma tetranectin and colorectal cancer

The prognostic significance of plasma tetranectin (PL-TN) in colorectal cancer was retrospectively examined in 504 patients (80 Dukes' A, 174 Dukes' B, 98 Dukes' C and 152 Dukes' D). Follow-up time was 7-12 years. No significant prognostic variable was found for Dukes' A patients by Cox multivariate analysis. In stage B, PL-TN was the second strongest prognostic variable [relative hazard (RH) = 3.3 for patients with PL-TN < or = 7.5 mg/l]. The other prognostic variables were perineural invasion (RH = 3.7), tumour distance < or = 10 cm from the anal verge (RH = 3.0), postoperative radiotherapy (RH = 2.9) and a high carcinoembryonic antigen (CEA) score (RH = 1.8). In Dukes' C, only CEA score and gender were of prognostic significance. For Dukes' D, PL-TN was the only prognostic variable (RH = 1.7). Testing all patients in one multivariate analysis, Dukes' staging was the strongest and PL-TN the second strongest prognostic variable. The shortened survival for patients with low PL-TN levels is illustrated with lifetables.

A potential role for tetranectin in mineralization during osteogenesis

Tetranectin is a protein shared by the blood and the extracellular matrix. Tetranectin is composed of four identical, noncovalently bound polypeptides each with a molecular mass of approximately 21 kD. There is some evidence that tetranectin may be involved in fibrinolysis and proteolysis during tissue remodeling, but its precise biological function is not known. Tetranectin is enriched in the cartilage of the shark, but the gene expression pattern in the mammalian skeletal system has not been determined. In the present study we have examined the expression pattern and putative function of tetranectin during osteogenesis. In the newborn mouse, strong tetranectin immunoreactivity was found in the newly formed woven bone around the cartilage anlage in the future bone marrow and along the periosteum forming the cortex. No tetranectin immunoreactivity was found in the proliferating and hypertrophic cartilage or in the surrounding skeletal muscle. Using an in vitro mineralizing system, we examined osteoblastic cells at different times during their growth and differentiation. Tetranectin mRNA appeared in the cultured osteoblastic cells in parallel with mineralization, in a pattern similar to that of bone sialoprotein, which is regarded as one of the late bone differentiation markers. To explore the putative biological role of tetranectin in osteogenesis we established stably transfected cell lines (PC12-tet) overexpressing recombinant tetranectin as evidenced by Northern and Western blot analysis and immunoprecipitation. Both control PC12 cells and PC12-tet cells injected into nude mice produced tumors containing bone material, as evidenced by von Kossa staining for calcium and immunostaining with bone sialoprotein and alkaline phosphatase antiserum. Nude mice tumors established from PC12-tet cells contained approximately fivefold more bone material than those produced by the untransfected PC12 cell line or by the PC12 cells transfected with the expression vector with no insert (Mann Whitney rank sum test, p < 0.01), supporting the notion that tetranectin may play an important direct and/or indirect role during osteogenesis. In conclusion, we have established a potential role for tetranectin as a bone matrix protein expressed in time and space coincident with mineralization in vivo and in vitro.

Animal lectins as self/non-self recognition molecules. Biochemical and genetic approaches to understanding their biological roles and evolution

In recent years, the significant contributions from molecular research studies on animal lectins have elucidated structural aspects and provided clues not only to their evolution but also to their multiple biological functions. The experimental evidence has suggested that distinct, and probably unrelated, groups of molecules are included under the term "lectin." Within the invertebrate taxa, major groups of lectins can be identified: One group would include lectins that show significant homology to membrane-integrated or soluble vertebrate C-type lectins. The second would include those beta-galactosyl-specific lectins homologous to the S-type vertebrate lectins. The third group would be constituted by lectins that show homology to vertebrate pentraxins that exhibit lectin-like properties, such as C-reactive protein and serum amyloid P. Finally, there are examples that do not exhibit similarities to any of the aforementioned categories. Moreover, the vast majority of invertebrate lectins described so far cannot yet be placed in one or another group because of the lack of information regarding their primary structure. (See Table 1.) Animal lectins do not express a recombinatorial diversity like that of antibodies, but a limited diversity in recognition capabilities would be accomplished by the occurrence of multiple lectins with distinct specificities, the presence of more than one binding site, specific for different carbohydrates in a single molecule, and by certain "flexibility" of the binding sites that would allow the recognition of a range of structurally related carbohydrates. In order to identify the lectins' "natural" ligands, we have investigated the interactions between those proteins and the putative endogenous or exogenous glycosylated substances or cells that may be relevant to their biological function. Results from these studies, together with information on the biochemical properties of invertebrate and vertebrate lectins, including their structural relationships with other vertebrate recognition molecules, are discussed.

The prognostic value of tetranectin immunoreactivity and plasma tetranectin in patients with ovarian cancer

BACKGROUND

Tetranectin (TN), a tetrameric, plasminogen-binding protein, was reduced in the plasma of patients with cancer and appears extracellularly in "stimulated" connective tissues, such as the proliferative, connective tissue response to carcinomas known as desmoplasia.

METHODS

Tissue samples from 37 patients with ovarian cancer were examined immunohistochemically for stromal and cellular TN. Plasma samples obtained before the primary surgery were quantitated for TN. The univariate log-rank test and the multivariate Cox proportional hazards regression model were used to analyze the prognostic function of the variables.

RESULTS

A significantly higher survival rate was found for patients with a low-stromal TN score and a high-plasma TN concentration, whereas the cellular TN score did not have any significance. A significant negative correlation was found between plasma TN and stromal TN (RS = -0.36; P = 0.03). Independent significant correlations were found between stromal immunoreactivity for TN and tumor grade (R = 0.67; P = 0.03) and between plasma TN and tumor stage (R = -0.29; P = 0.01).

CONCLUSIONS

This study gives great expectations to TN as a useful parameter for prognostic evaluation of patients with ovarian cancer. According to the correlations, stromal TN may partly originate from plasma and enhance proteolytic degradation in the interstitial tissue, a process necessary for the spread and growth of cancer. Because plasma TN measurements are only valid when taken preoperatively, it is of great value that stromal TN immunoreactivity of stored tumor tissue can be used as a prognostic factor for ovarian cancer.

Tetranectin: a novel secretory protein from human monocytes

Tetranectin is a recently described human plasma protein, which is found in most secretory cells throughout the body, including neutrophils. We present evidence for the presence of tetranectin in human monocytes and macrophages as well, and that these cells upon adherence or weak stimulation release a 20 kDa protein identified as tetranectin by immunoblotting. The amount of tetranectin released is 3-18 ng/h/10(6) monocytes. The possible influence of tetranectin on cellular functions was tested in migration and oxidative metabolism assays. Monocyte spontaneous migration was significantly stimulated by preincubation with purified tetranectin, whereas chemotactic and chemiluminescence responses to fMLP and C5a were unchanged. Neutrophil functions were not affected. It is concluded that tetranectin is secreted from human mononuclear phagocytes upon weak stimulation, and that the secreted tetranectin facilities spontaneous migration of these cells.

Prognostic value of serum tetranectin in patients with metastatic breast cancer

To evaluate serum tetranectin as a prognostic marker before first-line chemotherapy, serum levels were studied in 67 patients with metastatic breast cancer. In the Cox analyses, the relative risk (RR) for death of cancer varied with the cut-off level of serum tetranectin. A maximal RR of 5.0 was found for patients with serum tetranectin < or = 5.4 mg/l. The maximal RR of death for the other prognostic variables were multiple metastases 2.8, and for a poor performance status 2.0. Testing for the outcome, progressive disease, a maximal RR of 3.8 was found for patients with serum tetranectin < or = 5.3 mg/l, a maximal RR of 3.7 for multiple metastases and a maximal RR of 1.8 for a poor performance status. Significantly lower serum tetranectin values were found in patients with a poor treatment response compared to well responding patients. Serum tetranectrin seems to be useful as an additional prognostic factor in metastatic breast cancer.

The gene structure of tetranectin, a plasminogen binding protein

The gene for human tetranectin was isolated from a genomic library with a mixture of degenerate oligonucleotide probes. The gene is about 12 kbp and contains two intervening sequences. The gene encodes a protein of 202 amino acid residues, with a signal peptide of 21 amino acid residues, followed by the tetranectin sequence of 181 amino acid residues. Northern blot analysis revealed that tetranectin mRNA was present in all eight tissues tested with the highest concentration in lung. Southern blot analysis showed hybridization to two genes. Further investigations are needed to determine whether the genes are allelic or non-allelic.

Changes in plasma tetranectin following hip surgery with or without thrombotic complications

The fibrinolytic system seems to play a role in the development of postoperative thromboembolic complications (DVT). The newly described tetrameric protein tetranectin (TN), which has been found to enhance the activation of plasminogen to plasmin, therefore was studied in 55 patients who had total hip replacement and solely elastic stockings as physical thromboprophylaxis. No significant difference in plasma TN was found between the 5 patients with DVT and those without DVT, neither preoperatively or postoperatively at day 0, 1, 3, 7 or 10. A significant decrease in plasma TN was found from preoperative to postoperative values, indicating that TN may be a possible marker for other postoperative events. Because of the observed postoperative decrease it is important to consider the sampling time in the future research with TN.

Primary structure of a protein isolated from reef shark (Carcharhinus springeri) cartilage that is similar to the mammalian C-type lectin homolog, tetranectin

During the course of characterization of low molecular weight proteins in cartilage, we have isolated a protein from reef shark (Carcharhinus springeri) cartilage that bears a striking resemblance to the tetranectin monomer originally described by Clemmensen et al. (1986, Eur. J. Biochem. 156, 327-333). The protein was isolated by extraction of neural arch cartilage with 4 M guanidine hydrochloride, dialysis of the extract to bring the guanidine to 0.4 M (reassociating proteoglycan aggregates), followed by cesium chloride density gradient removal of the proteoglycans. The amino acid sequence had 166 amino acids and a calculated molecular weight of 18,430. The shark protein was 45% identical to human tetranectin, indicating that it was in the family of mammalian C-type lectins and that it was likely to be a shark analog of human tetranectin. The function of tetranectin is unknown; it was originally isolated by virtue of its affinity for the kringle-4 domain of plasminogen. Sequence comparison of human tetranectin and the shark-derived protein gives clues to potentially important regions of the molecule.

Tetranectin in amniotic fluid, maternal serum and fetal fluids

The concentration of the newly discovered protein tetranectin has been measured in different fetal and maternal compartments. In amniotic fluid a significant, positive correlation between the tetranectin concentration and gestational age was found (a mean of 0.2 mg l-1 at week 14 to a mean of 0.5 mg l-1 at week 21). In maternal serum a slight negative correlation was found between tetranectin concentration and gestational week (a mean of 6.17 mg l-1 at week 14 to a mean of 5.79 mg l-1 at week 21). In-term cord blood collected at delivery a mean level of 6.0 mg l-1 was found, and no difference was found between arterial- and venous-blood tetranectin concentration. In fetal serum the overall mean level was 2.6 mg l-1 and a significant positive correlation between tetranectin concentration and gestational age was found. The mean level was 1.1 mg l-1 in fetal cerebrospinal fluid and no correlation to gestational age was found. Fetal tetranectin may, therefore, be correlated to fetal maturation.

Differences in tetranectin immunoreactivity between benign and malignant breast tissue

Tetranectin (TN) is a human, plasminogen kringle 4 binding plasma protein with ubiquitous cellular distribution and lectin-like characteristics. By means of the peroxidase-antiperoxidase staining technique a polyclonal and a monoclonal antibody were used to demonstrate TN within the intracellular as well as the extracellular compartment of invasive breast carcinoma. Whereas cell associated TN was universal showing only quantitative differences depending of the growth pattern of the tumor, 78 of 133 tumors displayed TN extracellularly as well. The occurrence of this stromal TN immunoreactivity was closely associated with desmoplasia, recognized morphologically by an increase in fibroblastic cells and immunohistochemically by an intense staining for the connective tissue glycoprotein fibronectin (FN). Benign breast tissue displayed a universal, intense cytoplasmic but no extracellular reaction for TN, with the exception of rare foci of granulation tissue and around dilated cysts. Functional studies have shown that human embryonal lung fibroblasts increase their release of TN to the growth medium upon stimulation. The presence of TN extracellularly within fibroblast-rich foci of desmoplasia (and granulation tissue) suggests that a similar increased release of the protein takes place in vivo during active states. Desmoplasia has been found to have a protective effect on tumor cell propagation and metastasis in a murine model. The molecular interactions, which are responsible for this effect, are undoubtedly complex. However, TN may, by its specific binding to kringle 4 of plasminogen and its high affinity for sulphated polysaccharides, add to the understanding of how plasminogen activation is modulated at the local extracellular level.

A tetranectin-related protein is produced and deposited in extracellular matrix by human embryonal fibroblasts

Tetranectin is a tetrameric human plasma protein that binds to plasminogen kringle 4. Its amino acid sequence is homologous with the C-terminal parts of asialoglycoprotein receptors and proteoglycan core proteins. In the present study, we have demonstrated that the human embryonal fibroblast cell line WI-38 produce a tetranectin-related molecule, which might, by several criteria, be similar to tetranectin from plasma. These criteria include immunoblotting analysis of conditioned cell medium revealing a protein band with Mr 17,000, indistinguishable from the Mr of plasma tetranectin. A preparation obtained by purification of conditioned medium by affinity chromatography on an anti-(plasma tetranectin) IgG column also contained the Mr 17,000 protein. This protein (partly purified from the conditioned medium) was shown by crossed immunoelectrophoresis to bind to heparin, CaCl2 and plasminogen kringle 4, as previously described for tetranectin in plasma. Importantly, this tetranectin-related protein is not only present in conditioned culture medium, but the Mr 17,000 protein reacting with anti-(plasma tetranectin) IgG was also present in the extracellular material, remaining after removal of WI-38 cells from the culture dishes, as demonstrated by immunoblotting analysis and immunocytochemical staining. We conclude that WI-38 cells produce a tetranectin-related protein and secrete it into the extracellular matrix.

Tetranectin immunoreactivity in normal human tissues. An immunohistochemical study of exocrine epithelia and mesenchyme

A recently discovered human plasma protein, tetranectin (TN), which has previously been demonstrated immunohistochemically within various endocrine tissues, was in this study identified in an additional number of epithelial and mesenchymal cells by two polyclonal antibodies and one monoclonal using the conventional immunoperoxidase staining technique and a modification of the CLONO-GLAD procedure. TN was found in endothelial and epithelial tissues, particularly in cells with a high turn-over or storage function such as gastric parietal and zymogenic cells, absorptive surface epithelium of the small intestine, ducts of exocrine glands and pseudostratified respiratory epithelium. Also mesenchymal cells produced a TN positive staining reaction, which was most conspicuous in mast cells, but also present in some lymphocytes, plasma cells, macrophages, granulocytes, striated and smooth muscle cells and fibroblasts. SDS-PAGE and Western blotting analysis of cultured human embryonal fibroblasts (WI-38) showed that the cells besides TN contain another protein with a molecular weight of 82,000. As this protein, however, reacted with our affinity purified antibodies it probably represents a precursor of TN or a protein with a molecular weight of approximately 60,000, which is covalently linked to TN. This and the fact that TN shows amino acid sequence homologies to the carboxyterminal part of the asialo-glycoprotein receptor and a cartilage proteoglycan core protein as well a binding affinity to plasminogen points to TN as being part of a larger molecule, which possibly has been cleaved by proteolysis at the cellular site and then passed into the blood, where it polymerizes into a tetramer.