Heather F. Bigg

Specific, High Affinity Binding of Tissue Inhibitor of Metalloproteinases-4 (TIMP-4) to the COOH-terminal Hemopexin-like Domain of Human Gelatinase A TIMP-4 BINDS PROGELATINASE A AND THE COOH-TERMINAL DOMAIN IN A SIMILAR MANNER TO TIMP-2

The binding properties of the newly described tissue inhibitor of metalloproteinases-4 (TIMP-4) to progelatinase A and to the COOH-terminal hemopexin-like domain (C domain) of the enzyme were examined. We present evidence for the first time of a specific, high affinity interaction between TIMP-4 and the C domain of human gelatinase A and show that TIMP-4 binds both progelatinase A and the C domain in a similar manner to that of TIMP-2. Saturable binding of recombinant C domain to TIMP-4 and to TIMP-2 but not to TIMP-1 was demonstrated using a microwell protein binding assay. The recombinant collagen binding domain of gelatinase A, comprised of the three fibronectin type II-like repeats, did not bind to TIMP-4, indicating that binding is mediated selectively by the C domain. Binding to TIMP-4 was of high affinity with an apparent K d of 1.7 × 10−7 m but slightly weaker than that to TIMP-2 (apparent K d of 0.66 × 10−7 m). Affinity chromatography confirmed the TIMP-4-C domain interaction and also showed that the complex could not be disrupted by 1 m NaCl or 10% dimethyl sulfoxide, thereby further demonstrating the tight binding. To verify the biological significance of this interaction, binding of full-length progelatinase A to TIMP-4 was investigated. TIMP-4 and TIMP-2 but not TIMP-1 bound specifically to purified TIMP-2-free human recombinant full-length progelatinase A and to full-length rat proenzyme from the conditioned culture medium of ROS 17/2.8 cells. Preincubation of the C domain with TIMP-2 was found to reduce subsequent binding to TIMP-4 in a concentration-dependent manner. Competition between TIMP-2 and TIMP-4 for a common or overlapping binding sites on the gelatinase A C domain may occur; alternatively TIMP-2 may prevent the binding of TIMP-4 by steric hindrance or induction of a conformational change in the C domain. We propose that the binding of progelatinase A to TIMP-4 represents a third TIMP-progelatinase interaction in addition to that of progelatinase A with TIMP-2 and progelatinase B with TIMP-1 described previously. This new phenomenon may be of important physiological significance in modulating the cell surface activation of progelatinase A.

Tissue inhibitor of metalloproteinase (TIMP)-2 acts synergistically with synthetic matrix metalloproteinase (MMP) inhibitors but not with TIMP-4 to enhance the (Membrane type 1)-MMP-dependent activation of pro-MMP-2.

The membrane-type 1 matrix metalloproteinase (MT1-MMP) has been shown to be a key enzyme in tumor angiogenesis and metastasis. MT1-MMP hydrolyzes a variety of extracellular matrix components and is a physiological activator of pro-MMP-2, another MMP involved in malignancy. Pro-MMP-2 activation by MT1-MMP involves the formation of an MT1-MMP·tissue inhibitors of metalloproteinases 2 (TIMP-2)·pro-MMP-2 complex on the cell surface that promotes the hydrolysis of pro-MMP-2 by a neighboring TIMP-2-free MT1-MMP. The MT1-MMP·TIMP-2 complex also serves to reduce the intermolecular autocatalytic turnover of MT1-MMP, resulting in accumulation of active MT1-MMP (57 kDa) on the cell surface. Evidence shown here inTimp2-null cells demonstrates that pro-MMP-2 activation by MT1-MMP requires TIMP-2. In contrast, a C-terminally deleted TIMP-2 (Δ-TIMP-2), unable to form ternary complex, had no effect. However, Δ-TIMP-2 and certain synthetic MMP inhibitors, which inhibit MT1-MMP autocatalysis, can act synergistically with TIMP-2 in the promotion of pro-MMP-2 activation by MT1-MMP. In contrast, TIMP-4, an efficient MT1-MMP inhibitor, had no synergistic effect. These studies suggest that under certain conditions the pericellular activity of MT1-MMP in the presence of TIMP-2 can be modulated by synthetic and natural (TIMP-4) MMP inhibitors.

The Mammalian Chitinase-like Lectin, YKL-40, Binds Specifically to Type I Collagen and Modulates the Rate of Type I Collagen Fibril Formation

YKL-40 is expressed in arthritic cartilage and produced in large amounts by cultured chondrocytes, but its exact role is unclear, and the identities of its physiological ligands remain unknown. Purification of YKL-40 from resorbing bovine nasal cartilage and chondrocyte monolayers demonstrated the existence of three isoforms, a major and minor form from resorbing cartilage and a third species from chondrocytes. Affinity chromatography experiments with purified YKL-40 demonstrated specific binding of all three forms to collagen types I, II, and III, thus identifying collagens as potential YKL-40 ligands. Binding to immobilized type I collagen was inhibited by soluble native ligand, but not heat-denatured ligand, confirming a specific interaction. Binding of the chondrocyte-derived species to type I collagen was also demonstrated by surface plasmon resonance analysis, and the dissociation rate constant was calculated (3.42 × 10-3 to 4.50 × 10-3 s-1). The chondrocyte-derived species was found to prevent collagenolytic cleavage of type I collagen and to stimulate the rate of type I collagen fibril formation in a concentration-dependent manner. By contrast, the cartilage major form had an inhibitory effect on type I collagen fibrillogenesis. Digestion with N-glycosidase F, endoglycosidase H and lectin blotting did not reveal any difference in the carbohydrate component of these two YKL-40 species, indicating that this does not account for the opposing effects on fibril formation rate.

Domain Interactions in the Gelatinase A·TIMP-2·MT1-MMP Activation Complex THE ECTODOMAIN OF THE 44-kDa FORM OF MEMBRANE TYPE-1 MATRIX METALLOPROTEINASE DOES NOT MODULATE GELATINASE A ACTIVATION

On the cell surface, the 59-kDa membrane type 1-matrix metalloproteinase (MT1-MMP) activates the 72-kDa progelatinase A (MMP-2) after binding the tissue inhibitor of metalloproteinases (TIMP)-2. A 44-kDa remnant of MT1-MMP, with an N terminus at Gly285, is also present on the cell after autolytic shedding of the catalytic domain from the hemopexin carboxyl (C) domain, but its role in gelatinase A activation is unknown. We investigated intermolecular interactions in the gelatinase A activation complex using recombinant proteins, domains, and peptides, yeast two-hybrid analysis, solid- and solution-phase assays, cell culture, and immunocytochemistry. A strong interaction between the TIMP-2 C domain (Glu153-Pro221) and the gelatinase A hemopexin C domain (Gly446-Cys660) was demonstrated by the yeast two-hybrid system. Epitope masking studies showed that the anionic TIMP-2 C tail lost immunoreactivity after binding, indicating that the tail was buried in the complex. Using recombinant MT1-MMP hemopexin C domain (Gly285-Cys508), no direct role for the 44-kDa form of MT1-MMP in cell surface activation of progelatinase A was found. Exogenous hemopexin C domain of gelatinase A, but not that of MT1-MMP, blocked the cleavage of the 68-kDa gelatinase A activation intermediate to the fully active 66-kDa enzyme by concanavalin A-stimulated cells. The MT1-MMP hemopexin C domain did not form homodimers nor did it bind the gelatinase A hemopexin C domain, the C tail of TIMP-2, or full-length TIMP-2. Hence, the ectodomain of the remnant 44-kDa form of MT1-MMP appears to play little if any role in the activation of gelatinase A favoring the hypothesis that it accumulates on the cell surface as an inactive, stable degradation product.

The Involvement of the Fibronectin Type II-like Modules of Human Gelatinase A in Cell Surface Localization and Activation*

Recombinant collagen-binding domain (rCBD) comprising the three fibronectin type II-like modules of human gelatinase A was found to compete the zymogen form of this matrix metalloproteinase from the cell surface of normal human fibroblasts in culture. Upon concanavalin A treatment of cells, the induced cellular activation of gelatinase A was markedly elevated in the presence of the rCBD. Therefore, the mechanistic aspects of gelatinase A binding to cells by this domain were further studied using cell attachment assays. Fibroblasts attached to rCBD-coated microplate wells in a manner that was inhibited by soluble rCBD, blocking antibodies to the β1-integrin subunit but not the α2-integrin subunit, and bacterial collagenase treatment. Addition of soluble collagen rescued the attachment of collagenase-treated cells to the rCBD. As a probe on ligand blots of octyl-β-d-thioglucopyranoside-solubilized cell membrane extracts, the rCBD bound 140- and 160-kDa protein bands. Their identities were likely procollagen chains being both bacterial collagenase-sensitive and also converted upon pepsin digestion to 112- and 126-kDa bands that co-migrated with collagen α1(I) and α2(I) chains. A rCBD mutant protein (Lys263 → Ala) with reduced collagen affinity showed less cell attachment, whereas a heparin-binding deficient mutant (Lys357 → Ala), heparinase treatment, or heparin addition did not alter attachment. Thus, a cell-binding mechanism for gelatinase A is revealed that does not involve the hemopexin COOH domain. Instead, an attachment complex comprising gelatinase A-native type I collagen-β1-integrin forms as a result of interactions involving the collagen-binding domain of the enzyme. Moreover, this distinct pool of cell collagen-bound proenzyme appears recalcitrant to cellular activation.

Activity of matrix metalloproteinase-9 against native collagen types I and III

Interstitial collagen types I, II and III are highly resistant to proteolytic attack, due to their triple helical structure, but can be cleaved by matrix metalloproteinase (MMP) collagenases at a specific site, approximately three‐quarters of the length from the N‐terminus of each chain. MMP‐2 and ‐9 are closely related at the structural level, but MMP‐2, and not MMP‐9, has been previously described as a collagenase. This report investigates the ability of purified recombinant human MMP‐9 produced in insect cells to degrade native collagen types I and III. Purified MMP‐9 was able to cleave the soluble, monomeric forms of native collagen types I and III at 37 °C and 25 °C, respectively. Activity against collagens I and III was abolished by metalloproteinase inhibitors and was not present in the concentrated crude medium of mock‐transfected cells, demonstrating that it was MMP‐9‐derived. Mutated, collagenase‐resistant type I collagen was not digested by MMP‐9, indicating that the three‐quarters/one‐quarter locus was the site of initial attack. Digestion of type III collagen generated a three‐quarter fragment, as shown by comparison with MMP‐1‐mediated cleavage. These data demonstrate that MMP‐9, like MMP‐2, is able to cleave collagens I and III in their native form and in a manner that is characteristic of the unique collagenolytic activity of MMP collagenases.

Identification, regulation and role of tissue inhibitor of metalloproteinases-4 (TIMP-4) in human platelets

Matrix metalloproteinase‐2 (MMP‐2) released during activation of human platelets by aggregating agents and cancer cells is known to stimulate platelet aggregation. The expression, activity and role of tissue inhibitors of metalloproteinases (TIMPs), natural inhibitors of MMPs, in isolated human platelets were investigated. Western blot, reverse zymography, immunogold electron microscopy, aggregometry (collagen‐, thrombin and HT‐1080 human fibrosarcoma cells‐induced aggregation), flow cytometry and the release of 14C‐serotonin from labelled platelets recruited to the aggregate were used to characterize the presence and function of platelet TIMPs. TIMP‐4 (23 kDa) has been identified as the major MMP inhibitor (12–16 ng per 108 platelets) in human platelets. Platelets expressed lower (<1 ng per 108 platelets) amounts of TIMP‐1. No other TIMPs were detected using Western blot analysis. TIMP‐4 co‐localized with MMP‐2 in resting platelets and was released upon platelet aggregation induced by collagen and thrombin. Collagen resulted also in the release of higher molecular weight (60 kDa) complexes of TIMP‐4. The release of TIMP‐4 was reduced by prostacyclin and S‐nitroso‐glutathione (GSNO), an NO donor. Human recombinant TIMP‐4 (rTIMP‐4), but not human rTIMP‐1, inhibited partially both platelet aggregation and recruitment. The recombinant TIMP‐4 potentiated the recruitment inhibitor effects of GSNO. TIMP‐4 was not released during platelet aggregation induced by HT‐1080 cells. Human rTIMP‐4 exerted a biphasic effect on HT‐1080 cells‐induced aggregation. Thus, TIMP‐4 is the major intraplatelet MMP inhibitor and it is involved in regulation of platelet aggregation and recruitment.

The inhibition of metalloproteinases as a therapeutic target in rheumatoid arthritis and osteoarthritis

The collagenases of the matrix metalloproteinase family are key enzymes in mediating irreversible cartilage collagen loss in arthritis. Inhibition of these enzymes is, therefore, an important therapeutic target. New approaches to collagenase inhibition include active site inhibitors designed for specific enzymes, inhibition of cell signalling molecules and transcription factors involved in collagenase gene expression, prevention of zymogen activation and induction of natural inhibitor production.

Interleukin-4 blocks the release of collagen fragments from bovine nasal cartilage treated with cytokines

Interleukin-1 (IL-1) in combination with other cytokines can induce a reproducible release of collagen fragments from bovine nasal cartilage in culture. Over 70% of the total collagen is released by day 14 and this release is accompanied by the appearance of collagenolytic activity in the medium that cleaves collagen specifically at the one quarter/three quarter position. Interleukin-4 is able to prevent the release of collagen fragments from the tissue and this is accompanied by a reduced secretion and activation of collagenase (MMP-1) with an increase in tissue inhibitor of metalloproteinases-1 (TIMP-1). IL-4, especially in the presence of IL-1, increased TIMP secretion by bovine nasal cartilage in culture. These results suggest that IL-4 is able to specifically block cartilage collagen resorption by down-regulating the production of collagenase (MMP-1) and up-regulating TIMP-1 by chondrocytes within the cartilage.

Fragments of human fibroblast collagenase : interaction with metalloproteinase inhibitors and substrates

On purification, active human fibroblast collagenase breaks down by an autolytic mechanism into two major forms (M(r) 22,000 and M(r) 27,000) and one minor form (M(r) 25,000). The ability of human collagenase to bind to the tissue inhibitor of metalloproteinases (TIMP) and to TIMP-2 resides mainly in the active site area of the 22,000 M(r) N-terminal domain of the molecule, but the 27,000 M(r) C-terminal domain also has a role in stabilizing these interactions. The 22,000 M(r) fragment is able to form a complex with TIMP and TIMP-2 which is stable to gel filtration in a similar manner to the whole molecule, but no such complexes are formed by the 27,000 M(r) fragment. Complex formation with the whole molecule is prevented by EDTA and by 1,10-phenanthroline demonstrating the importance of the active site; additionally TIMP and TIMP-2 will compete with a reversibly bound peptide hydroxamic acid inhibitor for the active site. The inhibition of enzyme activity by TIMP and TIMP-2 is less pronounced in the 22,000 M(r) fragment when compared to the whole molecule and a similar effect is seen with the peptide hydroxamic acid inhibitor and also with alpha 2-macroglobulin, suggesting a role for the C-terminal domain in interacting with these inhibitors. Whole molecule collagenase and the 27,000 M(r) fragment bind to type 1 collagen-Sepharose while the 22,000 M(r) fragment exhibits no such binding, suggesting that the C-terminal domain has an important role in the binding of enzyme to substrate.