Mechanism of inhibition of the human matrix metalloproteinase stromelysin-1 by TIMP-1

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 Gly(285), 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 (Glu(153)-Pro(221)) and the gelatinase A hemopexin C domain (Gly(446)-Cys(660)) 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 (Gly(285)-Cys(508)), 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.

TIMP-1/MMP-9 imbalance in an EBV-immortalized B lymphocyte cellular model: evidence for TIMP-1 multifunctional properties

Tissue inhibitors of metalloproteinases (TIMPs) were initially described as agents controlling metalloproteinase activity. The purpose of this study was to investigate the expression and the roles of TIMP-1 secreted by Epstein-Barr-virus (EBV)-immortalized B lymphocytes. TIMP-1 was isolated from conditioned medium of interleukin (IL)-1beta stimulated EBV-B lymphocytes; purified TIMP-1 was identified by mass spectrometry and immunochemistry. TIMP-1-free MMP-9 was quantified after purification by zymography and enzyme-linked immunosorbent assay. EBV-B lymphocyte-secreted TIMP-1 inhibited MMP-9 gelatinolytic activity resulting in decreased B-cell transmigration as measured in vitro. The release of huge amounts of TIMP-1 in proportion to MMP-9 from B lymphocytes after EBV transformation was shown to be correlated with secretion of IL-10 and dependent on culture time. In contrast, there was little TIMP-1 and almost no IL-10 released from native B cells, suggesting a possible IL-10 mediated autocrine regulation mechanism of TIMP-1 synthesis. The MMP-9/TIMP-1 imbalance observed in the culture medium of EBV-B lymphocytes (TIMP-1>MMP-9) and of native B cells (MMP-9>TIMP-1) is suggestive of a new function for TIMP-1. We propose that TIMP-1 acts as a survival factor controlling B-cell growth and apoptosis through an autocrine regulation process involving IL-10 secreted by EBV-B lymphocytes.

Matrix metalloproteinases and the thyroid

Matrix metalloproteinases (MMPs) are proteolytic enzymes that degrade components of the extracellular matrix (ECM) and basement membrane. They play a critical role in many physiological and pathological processes, such as tumor metastasis. The original concept-that MMP activity during metastasis is restricted solely to invasion of the basement membrane and destruction of ECM components-has been modified to encompass multiple aspects of tumor progression: tumor establishment, growth, angiogenesis, intravasation, extravasation, and almost all metastatic steps. Moreover, the role of tissue inhibitors of matrix metalloproteinases (TIMPs), originally believed to exhibit anti-invasion properties solely by virtue of their inhibition of MMPs, has been extended to include their multiple biological effects, such as growth promotion. In thyroid neoplasia as well, MMPs, in particular MMP-2, seem to be associated with metastatic potential. It would seem that similar and divergent patterns regulate MMP and TIMP gene expression in benign and malignant human thyrocytes, in many instances in agreement with the concept of MMPs playing the role of stimulating, and TIMPs inhibiting cell invasion.

Stromelysin-1 and interleukin-6 gene promoter polymorphisms are determinants of asymptomatic carotid artery atherosclerosis

The functional 5A/6A polymorphism of the stromelysin-1 promoter has been implicated as a potential genetic marker for the progression of angiographically determined atherosclerosis in patients with coronary artery disease. Recently, a novel interleukin-6 (IL-6) gene functional G/C polymorphism at -174 in the promoter has also been reported. In this study, we analyzed the relation of these two polymorphisms with carotid artery atherosclerosis in 109 randomly selected, middle-aged men without exercise-induced ischemia. Atherosclerosis was quantified as intima-media thickness (IMT) by high-resolution ultrasonography. Univariately, stromelysin genotype was significantly (P:=0.015) associated with IMT, and this relation remained (P:=0.033) after adjustments for age, cardiorespiratory fitness, body mass index, smoking, LDL cholesterol, and systolic blood pressure and for sonographers. The 5A/6A polymorphism independently explained 7% of the variance in carotid bifurcation IMT. The IL-6 polymorphism was also significantly associated (P:=0. 036) with increased IMT, with men homozygous for the G allele having IMT that was 11% greater than men homozygous for the C allele. Men who were homozygous for both the 6A and G alleles had an covariate adjusted IMT that was 36% greater than men who were homozygous for neither allele (P:<0.003). These data suggest that genetic factors that predispose to reduced matrix remodeling (stromelysin 6A allele) and to increased inflammation (IL-6 G allele) combine to increase susceptibility for intima-media thickening in the carotid bifurcation, a predilection site for atherosclerosis.

Matrix metalloproteinases: pro- and anti-angiogenic activities

Matrix metalloproteinases (MMP) are a family of structurally related proteinases most widely recognized for their ability to degrade extracellular matrix, although recent investigations have demonstrated other biologic functions for these enzymes. MMP are typically not constitutively expressed, but are regulated by: (1) cytokines, growth factors, and cell-cell and cell-matrix interactions that control gene expression; (2) activation of their proenzyme form; and (3) the presence of MMP inhibitors [tissue inhibitors of metalloproteinases, (TIMP)]. MMP have important roles in normal processes including development, wound healing, mammary gland, and uterine involution, but are also involved in angiogenesis, tumor growth, and metastasis. Angiogenesis, characteristically defined as the establishment of new vessels from pre-existing vasculature, is required for biologic processes such as wound healing and pathologic processes such as arthritis, tumor growth, and metastasis. Blocking of MMP activity has been studied for potential therapeutic efficacy in controlling such pathologic processes. Synthetic MMP inhibitors, most notably the hydroxymates, have been engineered for this purpose and are presently in clinical trial. These inhibitors may have broad versus specific MMP inhibitory activity. As increased non-matrix degrading capabilities of MMP are recognized, however, i.e., cytokine activation, processing of proteins to molecules of distinct biologic function, it becomes less clear whether the nonselective inhibition of MMP activity for all pathologic processes involving MMP is appropriate. This review focuses upon the contribution of MMP to the process of tumor invasion and angiogenesis, and discusses the design and use of MMP inhibitors as therapeutic agents in these processes.

Structural characterization of the catalytic active site in the latent and active natural gelatinase B from human neutrophils

Matrix metalloproteinases are endopeptidases that have a leading role in the catabolism of the macromolecular components of the extracellular matrix in a variety of normal and pathological processes. Human gelatinase B is a zinc-dependent proteinase and a member of the matrix metalloproteinase family that is involved in inflammation, tissue remodeling, and cancer. We have conducted x-ray absorption spectroscopy, atomic emission, and quantum mechanics studies of natural and activated human gelatinase B. Our results show that the natural enzyme contains one catalytic zinc ion that is central to catalysis. In addition, upon enzyme activation, the catalytic zinc site exhibits a conformation change that results in the expansion of the bond distances around the zinc ion and the replacement of one sulfur with oxygen. Interestingly, quantum mechanics calculations show that oxygen ligation at the catalytic zinc ion exhibits a greater affinity to the binding of an oxygen from an amino acid residue rather than from an external water molecule. These results suggest that the catalytic zinc ion plays a key role in both substrate binding and catalysis.

TIMP-3 binds to sulfated glycosaminoglycans of the extracellular matrix

Of the four known tissue inhibitors of metalloproteinases (TIMPs), TIMP-3 is distinguished by its tighter binding to the extracellular matrix. The present results show that glycosaminoglycans such as heparin, heparan sulfate, chondroitin sulfates A, B, and C, and sulfated compounds such as suramin and pentosan efficiently extract TIMP-3 from the postpartum rat uterus. Enzymatic treatment by heparinase III or chondroitinase ABC also releases TIMP-3, but neither one alone gives complete release. Confocal microscopy shows colocalization of heparan sulfate and TIMP-3 in the endometrium subjacent to the lumen of the uterus. Immunostaining of TIMP-3 is lost upon digestion of tissue sections with heparinase III and chondroitinase ABC. The N-terminal domain of human TIMP-3 was expressed and found to bind to heparin with affinity similar to that of full-length mouse TIMP-3. The A and B beta-strands of the N-terminal domain of TIMP-3 contain two potential heparin-binding sequences rich in lysine and arginine; these strands should form a double track on the outer surface of TIMP-3. Synthetic peptides corresponding to segments of these two strands compete for heparin in the DNase II binding assay. TIMP-3 binding may be important for the cellular regulation of activity of the matrix metalloproteinases.

Elevated expression of membrane type 1 metalloproteinase (MT1-MMP) in reactive astrocytes following neurodegeneration in mouse central nervous system

Reactive astrocytes occurring in response to neurodegeneration are thought to play an important role in neuronal regeneration by upregulating the expression of extracellular matrix (ECM) components as well as the ECM degrading metalloproteinases (MMPs). We examined the mRNA levels and cellular distribution of membrane type matrix metalloproteinase 1 (MT1-MMP) and tissue inhibitors 1-4 of MMPs (TIMPs) in brain stem and spinal cord of wobbler (WR) mutant mice affected by progressive neurodegeneration and astrogliosis. MT1-MMP, TIMP-1 and TIMP-3 mRNA levels were elevated, whereas TIMP-2 and TIMP-4 expression was not affected. MT1-MMP was expressed in reactive astrocytes of WR. In primary astrocyte cultures, MT1-MMP mRNA was upregulated by exogeneous tumor necrosis factor alpha. Increased plasma membrane and secreted MMP activities were found in primary WR astrocytes.

A novel double-headed proteinaceous inhibitor for metalloproteinase and serine proteinase

A novel proteinaceous inhibitor for the metalloproteinase of Streptomyces caespitosus has been isolated from the culture supernatant of Streptomyces sp. I-355. It was named ScNPI (Streptomyces caespitosus neutral proteinase inhibitor). ScNPI exhibited strong inhibitory activity toward ScNP with a K(i) value of 1.6 nm. In addition, ScNPI was capable of inhibiting subtilisin BPN' (K(i) = 1.4 nm) (EC ). The scnpi gene consists of two regions, a signal peptide (28 amino acid residues) and a mature region (113 amino acid residues, M(r) = 11,857). The deduced amino acid sequence of scnpi showed high similarity to those of Streptomyces subtilisin inhibitor (SSI) and its homologues. The reactive site of ScNPI for inhibition of subtilisin BPN' was identified to be Met(71)-Tyr(72) bond by specific cleavage. To identify the reactive site for ScNP, Tyr(33) and Tyr(72), which are not conserved among other SSI family inhibitors but are preferable amino acid residues for ScNP, were replaced separately by Ala. The Y33A mutant retained inhibitory activity toward subtilisin BPN' but did not show any inhibitory activity toward ScNP. Moreover, a dimer of ternary complexes among ScNPI, ScNP, and subtilisin BPN' was formed to give the 2:2:2 stoichiometry. These results strongly indicate that ScNPI is a double-headed inhibitor that has individual reactive sites for ScNP and subtilisin BPN'.

Tissue inhibitor of metalloproteinases-1 undergoes microsecond to millisecond motions at sites of matrix metalloproteinase-induced fit

The N-terminal, matrix metalloproteinase (MMP)-inhibitory fragment of recombinant, human tissue inhibitor of metalloproteinases (TIMP-1) exhibits varied backbone dynamics and rigidity. Most striking is the presence of chemical exchange in the MMP-binding ridge reported to undergo conformational change upon MMP binding. Conformational exchange fluctuations in microseconds to milliseconds map to the sites of MMP-induced fit at residues Val29 through Leu34 of the AB loop and to the Ala65 and Cys70 "hinges" of the CD loop of TIMP-1. Slow chemical exchange is also present at the type I turn of the EF loop at the base of the MMP-binding ridge. These functional slow motions and other fast internal motions are evident from backbone (15)N spin relaxation at 500 and 750 MHz, whether interpreted by the model-free formalism with axial diffusion anisotropy or by the reduced spectral density approach. The conformational exchange is confirmed by its deviation from the trend between R(2) and the cross-correlation rate eta. The magnetic field-dependence indicates that the chemical exchange broadening in the AB and CD loops is fast on the time-scale of chemical shift differences. The conformational exchange rates for most of these exchanging residues, which can closely approach MMP, appear to be a few thousand to several thousand per second. The slow dynamics of the TIMP-1 AB loop contrast the picosecond to nanosecond dynamics reported in the longer TIMP-2 AB loop.

Expression of human membrane type 1 matrix metalloproteinase in Pichia pastoris

A soluble, C-terminal truncated form of human membrane type 1 matrix metalloproteinase (MT1-MMP) containing the hemopexin-like domain was expressed in Pichia pastoris strain KM71. High levels of secreted protein were detected. Although the c-DNA for the proenzyme (Ala(21)-Glu(523) called DeltaTM-MT1-MMP) was cloned, almost only active MT1-MMP (Tyr(112)-Glu(523)) with identical N-terminus as described for the wild-type enzyme was isolated. This active enzyme was highly purified and characterized with respect to its biochemical properties. The recombinant protein showed high stability against autolysis and proteolysis by yeast proteases, although the calculated in vivo half-life is rather low. The biochemical properties of this new MT1-MMP species were compared with the well-characterized catalytic domain (Ile(114)-Ile(318)) of MT1-MMP. The novel form of MT1-MMP exhibited a higher stability against autolysis than the isolated catalytic domain (Ile(114)-Ile(318)).

Expression of matrix metalloproteinases and related tissue inhibitors in the cyst fluids of ovarian mucinous neoplasms

OBJECTIVES AND METHODS

The growth of an ovarian cystic neoplasm often involves its invasion into and destruction of the extracellular matrix. We examined neoplastic cysts of ovarian mucinous tumors for the presence of matrix metalloproteinases (MMPs) and tissue inhibitors of MMPs (TIMPs) using zymography (in situ zymography, gelatin zymography, and casein zymography) and enzyme-linked immunosorbent assay.

RESULTS

Matriolytic activity was detected within the cystic contents and cytoplasm of the lining epithelial cells of the cyst by in situ zymography. This intracystic matriolytic activity was thought to originate mainly in the epithelial cells. The activated form of MMP-9 was seen in all carcinoma and borderline fluids and in 7 of 15 adenomas. The concentration of MMP-9 was higher in carcinoma fluids than in borderline and adenoma fluids (P < 0.05). TIMP-1, which specifically binds to MMP-9, was also higher in carcinoma and borderline fluids than in adenoma fluids (P < 0.05). MMP-2 activity was nearly ubiquitously present in all cyst fluids, irrespective of the fluid's histologic category. The amount of MMP-2 was highest in the carcinoma category, although not to a statistically significant degree. TIMP-2, a specific inhibitor for MMP-2, was significantly lower in the borderline category than in the adenoma category. The molar ratios of TIMP-1/MMP-9 (not significant) and TIMP-2/MMP-2 (P < 0.05) were higher in the adenoma category. Expressions of trypsin, MMP-7, and MMP-9 were generally higher in carcinoma and borderline fluids than in adenoma fluids.

CONCLUSIONS

These observations indicate the importance of ovarian cystic fluids for analyzing tumor-associated matriolytic activities. The findings suggest that these matriolytic enzymes, together with the presence of their inhibitors, play an important role in the growth of ovarian mucinous tumors.

Distal recognition site for classical pathway convertase located in the C345C/netrin module of complement component C5

Previous studies focused on indels in the complement C345 protein family identified a number of potential protein-protein interaction sites in components C3 and C5. Here, one of these sites in C5, near the alpha-chain C terminus, was examined by alanine-scanning mutagenesis at 16 of the 18 non-alanine residues in the sequence KEALQIKYNFSF RYIYPLD. Alanine substitutions affected activities in the highly variable manner characteristic of binding sites. Substitutions at the lysine or either phenylalanine residue in the central KYNFSF sequence had the greatest effects, yielding mutants with <20% of the normal activity. These three mutants were also resistant to the classical pathway (CP) C5 convertase, with sensitivities roughly proportional to their hemolytic activities, but had normal susceptibilities to the cobra venom factor (CVF)-dependent convertase. Synthetic peptide MGKEALQIKYNFS-NH2 was found similarly to inhibit CP but not CVF convertase activation, and the effects of alanine substitutions in this peptide largely reflected those of the equivalent mutations in C5. These results indicate that residues KYNFSF form a novel, distal binding site for the CP, but not CVF convertase. This site lies approximately 880 residues downstream of the convertase cleavage site within a module that has been independently named C345C and NTR; this module is found in diverse proteins including netrins and tissue inhibitors of metalloproteinases.

Compromise and accommodation in ecotin, a dimeric macromolecular inhibitor of serine proteases

Ecotin is a dimeric serine protease inhibitor from Escherichia coli which binds proteases to form a hetero-tetramer with three distinct interfaces: an ecotin-ecotin dimer interface, a larger primary ecotin-protease interface, and a smaller secondary ecotin-protease interface. The contributions of these interfaces to binding and inhibition are unequal. To investigate the contribution and adaptability of each interface, we have solved the structure of two mutant ecotin-trypsin complexes and compared them to the structure of the previously determined wild-type ecotin-trypsin complex. Wild-type ecotin has an affinity of 1 nM for trypsin, while the optimized mutant, ecotin Y69F, D70P, which was found using phage display technologies, inhibits rat trypsin with a K(i) value of 0.08 nM. Ecotin 67-70A, M84R which has four alanine substitutions in the ecotin-trypsin secondary binding site, along with the M84R mutation at the primary site, has a K(i) value against rat trypsin of 0.2 nM. The structure of the ecotin Y69F, D70P-trypsin complex shows minor structural changes in the ecotin-trypsin tetramer. The structure of the ecotin 67-70A, M84R mutant bound to trypsin shows large deviations in the tertiary and quaternary structure of the complex. The trypsin structure shows no significant changes, but the conformation of several loop regions of ecotin are altered, resulting in the secondary site releasing its hold on trypsin. The structure of several regions previously considered to be rigid is also significantly modified. The inherent flexibility of ecotin allows it to accommodate these mutations and still maintain tight binding through the compromises of the protein-protein interfaces in the ecotin-trypsin tetramer. A comparison with two recently described ecotin-like genes from other bacteria suggests that these structural and functional features are conserved in otherwise distant bacterial lineages.

Interactions between tumour cells and stromal cells and proteolytic modification of the extracellular matrix by metalloproteinases in cancer

Over the last few years a growing number of matrix degrading metalloproteinases have been implicated in cancer. These include in particular the matrix metalloproteinases (MMPs) which have been shown to be associated with a large variety of human malignancies, and the metalloproteinases with a disintegrin domain (ADAMs) whose potential role in cancer has begun to be examined. The expression of MMPs in human cancer is the result of a complex interaction between tumour cells and non-malignant stromal cells including fibroblasts, endothelial cells and inflammatory cells which all actively participate in the production of MMPs in tumour tissue. The proteolytic modification of the extracellular matrix by these proteases does more than allow malignant cells to locally invade and form distant metastasis. It significantly alters the tumour micro-environment and modifies the contacts between tumour cells and extracellular matrix proteins. These changes can affect essential cellular functions such as growth, survival, migration and even drug resistance. As our understanding of the nature of the contacts between tumour cells and a proteolytically modified extracellular matrix continues to progress, it is likely that novel therapeutic approaches to modify tumour cell behaviour will be identified.

Structural differences of matrix metalloproteinases. Homology modeling and energy minimization of enzyme-substrate complexes

Matrix metalloproteinases are extracellular enzymes taking part in the remodeling of extracellular matrix. The structures of the catalytic domain of MMP1, MMP3, MMP7 and MMP8 are known, but structures of enzymes belonging to this family still remain to be determined. A general approach to the homology modeling of matrix metalloproteinases, exemplified by the modeling of MMP2, MMP9, MMP12 and MMP14 is described. The models were refined using an energy minimization procedure developed for matrix metalloproteinases. This procedure includes incorporation of parameters for zinc and calcium ions in the AMBER 4.1 force field, applying a non-bonded approach and a full ion charge representation. Energy minimization of the apoenzymes yielded structures with distorted active sites, while reliable three-dimensional structures of the enzymes containing a substrate in active site were obtained. The structural differences between the eight enzyme-substrate complexes were studied with particular emphasis on the active site, and possible sites for obtaining selectivity among the MMP's are discussed. Differences in the P1' pocket are well-documented and have been extensively exploited in inhibitor design. The present work indicates that selectivity could be further improved by considering the P2 pocket as well.

Expression, characterization and structure determination of an active site mutant (Glu202-Gln) of mini-stromelysin-1

Human stromelysin-1 is a member of the matrix metalloproteinase (MMP) family of enzymes. The active site glutamic acid of the MMPs is conserved throughout the family and plays a pivotal role in the catalytic mechanism. The structural and functional consequences of a glutamate to glutamine substitution in the active site of stromelysin-1 were investigated in this study. In contrast to the wild-type enzyme, the glutamine-substituted mutant was not active in a zymogram assay where gelatin was the substrate, was not activated by organomercurials and showed no activity against a peptide substrate. The glutamine-substituted mutant did, however, bind to TIMP-1, the tissue inhibitor of metalloproteinases, after cleavage of the propeptide with trypsin. A second construct containing the glutamine substitution but lacking the propeptide was also inactive in the proteolysis assays and capable of TIMP-1 binding. X-ray structures of the wild-type and mutant proteins complexed with the propeptide-based inhibitor Ro-26-2812 were solved and in both structures the inhibitor binds in an orientation the reverse of that of the propeptide in the pro-form of the enzyme. The inhibitor makes no specific interactions with the active site glutamate and a comparison of the wild-type and mutant structures revealed no major structural changes resulting from the glutamate to glutamine substitution.

Biochemical characterization of the catalytic domain of human matrix metalloproteinase 19. Evidence for a role as a potent basement membrane degrading enzyme

We have recently cloned MMP-19, a novel matrix metalloproteinase, which, due to unique structural features, was proposed to represent the first member of a new MMP subfamily (Pendás, A. M., Knäuper, V. , Puente, X. S., Llano, E., Mattei, M. G., Apte, S., Murphy, G., and López-Otin, C. (1997) J. Biol. Chem. 272, 4281-4286). A recombinant COOH-terminal deletion mutant of MMP-19 (proDelta(260-508)MMP-19), comprising the propeptide and the catalytic domain, was expressed in Escherichia coli, refolded, and purified. Interestingly, we found that proDelta(260-508)MMP-19 has the tendency to autoactivate, whereby the Lys(97)-Tyr(98) peptide bond is hydrolyzed, resulting in free catalytic domain. Mutation of two residues (Glu(88) --> Pro and Pro(90) --> Val) within the propeptide latency motif did not prevent autoactivation but the autolysis rate was somewhat reduced. Analysis of the substrate specificity revealed that the catalytic domain of MMP-19 was able to hydrolyze the general MMP substrate Mca-Pro-Leu-Gly-Dpa-Ala-Arg-NH(2) and, with higher efficiency, the stromelysin substrate Mca-Pro-Leu-Ala-Nva-Dpa-Ala-Arg-NH(2). Kinetic analysis of the interactions of the catalytic domain of MMP-19 with the natural MMP inhibitors, the tissue inhibitors of metalloproteinases (TIMPs), showed strong inhibition using TIMP-2, TIMP-3, and TIMP-4, while TIMP-1 was less efficient. We also demonstrated that synthetic hydroxamic acid-based compounds efficiently inhibited the enzyme. The catalytic domain of MMP-19 was able to hydrolyze the basement membrane components type IV collagen, laminin, and nidogen, as well as the large tenascin-C isoform, fibronectin, and type I gelatin in vitro, suggesting that MMP-19 is a potent proteinase capable of hydrolyzing a broad range of extracellular matrix components. Neither the catalytic domain nor the full-length MMP-19 was able to degrade triple-helical collagen. Finally, and in contrast to studies with other MMPs, MMP-19 catalytic domain was not able to activate any of the latent MMPs tested in vitro.

Target molecules for anti-angiogenic therapy: from basic research to clinical trials

There is growing evidence that anti-angiogenic drugs will improve future therapies of diseases like cancer, rheumatoid arthritis and ocular neovascularisation. However, it is still uncertain which kind of substance, out of the large number of angiogenesis inhibitors, will prove to be a suitable agent to treat these human diseases. There are currently more than 30 angiogenesis inhibitors in clinical trials and a multitude of promising new candidates are under investigation in vitro and in animal models. Important therapeutic strategies are: suppression of activity of the major angiogenic regulators like vascular endothelial growth factor (VEGF) and fibroblast growth factor (FGF); inhibition of function of alphav-integrins and matrix metalloproteinases (MMPs); the exploitation of endogenous anti-angiogenic molecules like angiostatin, endostatin or thrombospondin. Given the wide spectrum of diseases which could be treated by anti-angiogenic compounds, it is important for today's clinicians to understand their essential mode of action at a cellular and molecular level. Here we give an in-depth overview of the basic pathophysiological mechanisms underlying the different anti-angiogenic approaches used to date based on the most recent fundamental and clinical research data. The angiogenesis inhibitors in clinical trials are presented and promising future drug candidates are discussed.

Structural basis of the endoproteinase-protein inhibitor interaction

Proteolytic enzymes are potentially hazardous to their protein environment, so that their activity must be carefully controlled. Living organisms use protein inhibitors as a major tool to regulate the proteolytic activity of proteinases. Most of the inhibitors for which 3D structures are available are directed towards serine proteinases, interacting with the active sites in a 'canonical' i.e. substrate-like manner via an exposed reactive site loop of conserved conformation. More recently, some non-canonically binding serine proteinase inhibitors directed against coagulation factors, in particular thrombin, a few cysteine proteinase inhibitors inhibitory towards papain-like proteinases, and three zinc endopeptidase inhibitors directed against metzincins and thermolysin have been characterised in the free and complexed state, displaying novel mechanisms of inhibition with their target proteinases. These different interaction modes are presented and briefly discussed with respect to the different strategies applied by nature.

Tissue inhibitors of metalloproteinases: evolution, structure and function

The matrix metalloproteinases (MMPs) play a key role in the normal physiology of connective tissue during development, morphogenesis and wound healing, but their unregulated activity has been implicated in numerous disease processes including arthritis, tumor cell metastasis and atherosclerosis. An important mechanism for the regulation of the activity of MMPs is via binding to a family of homologous proteins referred to as the tissue inhibitors of metalloproteinases (TIMP-1 to TIMP-4). The two-domain TIMPs are of relatively small size, yet have been found to exhibit several biochemical and physiological/biological functions, including inhibition of active MMPs, proMMP activation, cell growth promotion, matrix binding, inhibition of angiogenesis and the induction of apoptosis. Mutations in TIMP-3 are the cause of Sorsby's fundus dystrophy in humans, a disease that results in early onset macular degeneration. This review highlights the evolution of TIMPs, the recently elucidated high-resolution structures of TIMPs and their complexes with metalloproteinases, and the results of mutational and other studies of structure-function relationships that have enhanced our understanding of the mechanism and specificity of the inhibition of MMPs by TIMPs. Several intriguing questions, such as the basis of the multiple biological functions of TIMPs, the kinetics of TIMP-MMP interactions and the differences in binding in some TIMP-metalloproteinase pairs are discussed which, though not fully resolved, serve to illustrate the kind of issues that are important for a full understanding of the interactions between families of molecules.

An overview of collagenase-3 expression in malignant tumors and analysis of its potential value as a target in antitumor therapies

Collagenase-3 (MMP-13) is a member of the matrix metalloproteinase family of endopeptidases that is characterized by a potent degrading activity against a wide spectrum of substrates. This enzyme was first detected in breast carcinomas but it is also overexpressed in a variety of malignant tumors including head and neck carcinomas, chondrosarcomas, skin carcinomas, and carcinomas of the female genital tract. Clinical studies have revealed that in all these tumors collagenase-3 expression is associated with invasive and metastatic tumors. Analysis of the molecular mechanisms underlying its marked overexpression in malignant tumors has allowed to identify different cytokines, growth factors and tumor promoters with ability to up-regulate collagenase-3 expression in tumor cells, or in stromal fibroblasts surrounding epithelial tumor cells. The first strategies designed to target this enzyme are being developed, and are mainly directed to prepare synthetic inhibitors with ability to selectively block the collagenase-3 proteolytic activity. Alternatively, inhibitors of the signal transduction pathways mediating the expression of this enzyme by tumor cells may also be useful for collagenase-3 targeting. These studies together with those performed on other enzymes associated with tumor processes may lead to the development of novel therapeutic strategies to control the progression and metastatic capacity of neoplastic cells.

Recognition and catabolism of synthetic heterotrimeric collagen peptides by matrix metalloproteinases

BACKGROUND

The general consensus is that interstitial collagens are digested by collagenases and denatured collagen by gelatinases, although processing of fibrillar and acetic-acid-soluble collagen by gelatinase A has also been reported. One of the main difficulties in studying the mechanism of action of these matrix metalloproteinases (MMPs) derives from the physicochemical properties of the natural triple-helical collagen, which makes it difficult to handle.

RESULTS

Synthetic heterotrimeric collagenous peptides that contain the collagenase cleavage site of human collagen type I and differ in the thermal stability of the triple-helical fold were used to mimic natural collagen and gelatin, respectively. Results from digestion of these substrates by fibroblast and neutrophil collagenases (MMP-1 and MMP-8), as well as by gelatinase A (MMP-2), confirmed that the two classes of enzymes operate within the context of strong conformational dependency of the substrates. It was also found that gelatinases and collagenases exhibit two distinct proteolytic mechanisms: gelatinase digests the gelatin-like heterotrimer rapidly in individual steps with intermediate releases of partially processed substrate into the medium, whereas collagenases degrade the triple-helical heterotrimer by trapping it until scission through all three alpha chains is achieved.

CONCLUSIONS

The results confirm the usefulness of synthetic heterotrimeric collagenous peptides in the folded and unfolded state as mimics of the natural substrates collagen and gelatin, respectively, to gain a better a insight into the proteolytic mechanisms of matrix metalloproteinases.

Increased concentration of pro-matrix metalloproteinase 9 in term fetal membranes overlying the cervix before labor: implications for membrane remodeling and rupture

OBJECTIVES

Regional structural alterations that develop before labor are important in the mechanisms of both physiologic and pathologic membrane rupture, because they are also detected in preterm prelabor rupture of the fetal membranes, the most common cause of preterm birth (as great as 60%). Matrix metalloproteinases are located in the fetal membranes and are the main mediators of extracellular matrix degradation. The objective of this study was to examine whether gelatinases (matrix metalloproteinases 2 and 9) could be involved in the development of these regional structural changes seen at term before labor.

STUDY DESIGN

Fetal membranes from patients undergoing elective cesarean delivery were regionally sampled from over the cervix (cervical membranes) and midway between this area and the placental edge (midzone). Fetal membranes obtained after spontaneous labor and delivery at term were also regionally sampled. Matrix metalloproteinase 2 and 9 activities were assessed by gelatin zymography, whereas total matrix metalloproteinase 9 protein was determined by enzyme-linked immunosorbent assay.

RESULTS

Zymography only detected activity corresponding to the pro-matrix metalloproteinase 2 (72 kd) and 9 (92 kd) forms in prelabor fetal membranes. Although the levels of pro-matrix metalloproteinase 2 showed no regional differences, the pro-matrix metalloproteinase 9 level was higher in the cervical area than in the midzone (2.5 +/- 0.98 vs 0.76 +/- 0.28 optical density units/20 microg protein; P <.01). The concentration of pro-matrix metalloproteinase 9 protein in the cervical area was also significantly higher than that in the midzone (6.69 +/- 4.8 vs 1.58 +/- 1.14 ng/mg protein; P <.01). After delivery both pro-matrix metalloproteinase 2 and 9 activities were elevated, whereas pro-matrix metalloproteinase 9 protein activity showed no regional difference between the rupture site and midzone (23.47 +/- 4.5 vs 25. 3 +/- 6.2 ng/mg protein). Active bands of matrix metalloproteinases 2 (66 kd) and 9 (83 kd) were also detected after delivery.

CONCLUSION

This study suggests that a specific regional induction of pro-matrix metalloproteinase 9 occurs in the cervical area before labor and may play a role in "programming" this area for subsequent rupture after activation during labor.

NMR structure of tissue inhibitor of metalloproteinases-1 implicates localized induced fit in recognition of matrix metalloproteinases

A high quality solution structure of the matrix metalloproteinase inhibitory N-terminal domain of recombinant human tissue inhibitor of metalloproteinases-1 (N-TIMP-1) has been determined. For the rigidly packed residues, the average RMSD to the mean structure is 0. 57 A for the backbone atoms and 1.00 A for all heavy atoms. Comparison of the solution structure of free N-TIMP-1 with the crystal structure of TIMP-1 bound to the catalytic domain of MMP-3 ( Gomis-R]uth et al., 1997 ) shows that the structural core of the beta barrel flanked by helices is nearly unchanged by the association with MMP-3, evident from a backbone RMSD of 1.15 A. However, clear differences in the conformation of the MMP-binding ridge of free and MMP-bound TIMP-1 suggest induced fit throughout the ridge. The MMP-dependent conformational changes in the ridge include a dramatic bending of AB loop residues Glu28 through Leu34, moderate hinge bending of the CD-loop about residues Ala65 and Cys70, and modest bending of the Cys1 through Pro6 segment. A large number of interresidue Nuclear Overhauser enhancements (NOEs) augmented by stereospecific assignments, torsion restraints, and dipolar couplings (an average of 18 non-trivial restraints per residue) engender confidence in these structural inferences. A tight cluster of three lysine residues and one arginine residue atop beta-strands A and B, and identical among TIMP sequences, form the heart of a highly conserved electropositive patch that may interact with anionic components of the extracellular matrix.

Post-translational proteolytic processing of procollagen C-terminal proteinase enhancer releases a metalloproteinase inhibitor

Activity of matrix metalloproteinases (MMP) is regulated by a family of proteins called tissue inhibitors of metalloproteinases (TIMP). Four TIMPs have been cloned, and their molecular weights range from 29,000 to 20,000. By reverse zymography, we have observed a metalloproteinase inhibitor with an apparent molecular weight of 16, 500 from medium conditioned by human brain tumor cells. Antibodies directed against TIMPs failed to react with the 16,500 molecular weight inhibitor, indicating that it was not a truncated form of a known TIMP. The inhibitor was isolated from conditioned medium using affinity and ion exchange chromatography. N-terminal sequences of the inhibitor matched amino acid sequences within the C-terminal domain of a protein known as procollagen C-terminal proteinase enhancer (PCPE). Thus, the inhibitor was named CT-PCPE. Comparison of the N-terminal domain of TIMP with CT-PCPE revealed that both contained six cysteine residues. As in the case of TIMP, reduction and alkylation abolished the inhibitory activity of CT-PCPE. Purified CT-PCPE inhibited MMP-2 with an IC(50) value much greater than that of TIMP-2. This implies that MMPs may not be the physiologic targets for CT-PCPE inhibition. However, these results suggest that CT-PCPE may constitute a new class of metalloproteinase inhibitor.

The effect of matrix metalloproteinase complex formation on the conformational mobility of tissue inhibitor of metalloproteinases-2 (TIMP-2)

The backbone mobility of the N-terminal domain of tissue inhibitor of metalloproteinases-2 (N-TIMP-2) was determined both for the free protein and when bound to the catalytic domain of matrix metalloproteinase-3 (N-MMP-3). Regions of the protein with internal motion were identified by comparison of the T(1) and T(2) relaxation times and (1)H-(15)N nuclear Overhauser effect values for the backbone amide (15)N signals for each residue in the sequence. This analysis revealed rapid internal motion on the picosecond to nanosecond time scale for several regions of free N-TIMP-2, including the extended beta-hairpin between beta-strands A and B, which forms part of the MMP binding site. Evidence of relatively slow motion indicative of exchange between two or more local conformations on a microsecond to millisecond time scale was also found in the free protein, including two other regions of the MMP binding site (the CD and EF loops). On formation of a tight N-TIMP-2. N-MMP-3 complex, the rapid internal motion of the AB beta-hairpin was largely abolished, a change consistent with tight binding of this region to the MMP-3 catalytic domain. The extended AB beta-hairpin is not a feature of all members of the TIMP family; therefore, the binding of this highly mobile region to a site distant from the catalytic cleft of the MMPs suggests a key role in TIMP-2 binding specificity.

Catalytic activities and substrate specificity of the human membrane type 4 matrix metalloproteinase catalytic domain

Membrane type (MT) matrix metalloproteinases (MMPs) are recently recognized members of the family of Zn(2+)- and Ca(2+)-dependent MMPs. To investigate the proteolytic capabilities of human MT4-MMP (i.e. MMP-17), we have cloned DNA encoding its catalytic domain (CD) from a breast carcinoma cDNA library. Human membrane type 4 MMP CD (MT4-MMPCD) protein, expressed as inclusion bodies in Escherichia coli, was purified to homogeneity and refolded in the presence of Zn(2+) and Ca(2+). While MT4-MMPCD cleaved synthetic MMP substrates Ac-PLG-[2-mercapto-4-methylpentanoyl]-LG-OEt and Mca-PLGL-Dpa-AR-NH(2) with modest efficiency, it catalyzed with much higher efficiency the hydrolysis of a pro-tumor necrosis factor-alpha converting enzyme synthetic substrate, Mca-PLAQAV-Dpa-RSSSR-NH(2). Catalytic efficiency with the pro-tumor necrosis factor-alpha converting enzyme substrate was maximal at pH 7.4 and was modulated by three ionizable enzyme groups (pK(a3) = 6.2, pK(a2) = 8.3, and pK(a1) = 10.6). MT4-MMPCD cleaved gelatin but was inactive toward type I collagen, type IV collagen, fibronectin, and laminin. Like all known MT-MMPs, MT4-MMPCD was also able to activate 72-kDa progelatinase A to its 68-kDa form. EDTA, 1,10-phenanthroline, reference hydroxamic acid MMP inhibitors, tissue inhibitor of metalloproteinases-1, and tissue inhibitor of metalloproteinases-2 all potently blocked MT4-MMPCD enzymatic activity. MT4-MMP is, therefore, a competent Zn(2+)-dependent MMP with unique specificity among synthetic substrates and the capability to both degrade gelatin and activate progelatinase A.

The second type II module from human matrix metalloproteinase 2: structure, function and dynamics

BACKGROUND

Matrix metalloproteinase 2 (MMP-2, gelatinase A, 72 kDa type IV collagenase) has an important role in extracellular matrix degradation during cell migration and tissue remodeling. It is involved in development, inflammation, wound healing, tumor invasion, metastasis and other physiological and pathological processes. The enzyme cleaves several types of collagen, elastin, fibronectin and laminin. Binding to collagen is mediated by three repeats homologous to fibronectin type II modules, which are inserted in the catalytic domain in proximity to the active site.

RESULTS

We have determined the NMR solution structure of the second type II module from human MMP-2 (col-2). The module exhibits a typical type II fold with two short double-stranded antiparallel beta sheets and three large loops packed around a cluster of conserved aromatic residues. Backbone amide dynamics, derived from (15)N relaxation experiments, correlate well with solvent accessibility and intramolecular hydrogen bonding. A synthetic peptide with the collagen consensus sequence, (Pro-Pro-Gly)(6), is shown to interact with the module.

CONCLUSIONS

Spectral perturbations induced by (Pro-Pro-Gly)(6) binding reveal the region involved in the interaction of col-2 with collagen. The binding surface comprises exposed aromatic residues Phe21, Tyr38, Trp40, Tyr47, Tyr53 and Phe55, and the neighboring Gly33-Gly37 segment.

Effect of matrix metalloproteinase inhibitors on rat embryo development in vitro

Matrix metalloproteinases appear to play a role in cell migration and tissue remodeling and are postulated to be important in the development of embryos. We hypothesized that inhibition of these proteinases with the synthetic inhibitor batimastat or with endogenous tissue inhibitor of metalloproteinases (TIMP) would alter in vitro development of day 9 rat embryos. Batimastat had a dose-related effect on embryo growth and viability following 48 h in culture, with significant inhibition at 1.0 microM concentration. Dying cells were observed in many organs of living embryos. TIMP-2 at 3.0 microg/ml had a similar effect on embryo growth. TIMP-1 alone or used in combination with TIMP-2 had no obvious effect. No focal malformations were observed. The effective concentrations are comparable to those which inhibit enzyme activity in cell culture. We conclude that matrix metalloproteinases are probably important in mammalian embryo development.

Effect of species differences on stromelysin-1 (MMP-3) inhibitor potency. An explanation of inhibitor selectivity using homology modeling and chimeric proteins

For an animal model to predict a compound's potential for treating human disease, inhibitor interactions with the cognate enzymes of separate species must be comparable. Rabbit and human isoforms of stromelysin-1 are highly homologous, yet there are clear and significant compound-specific differences in inhibitor potencies between these two enzymes. Using crystal structures of discordant inhibitors complexed with the human enzyme, we generated a rabbit enzyme homology model that was used to identify two unmatched residues near the active site that could explain the observed disparities. To test these observations, we designed and synthesized three chimeric mutants of the human enzyme containing the single (H224N and L226F) and double (H224N/L226F) mutations. A comparison of inhibitor potencies among the mutant and wild-type enzymes shows that the mutation of a single amino acid in the human enzyme, histidine 224 to asparagine, is sufficient to change the selectivity profile of the mutant to that of the rabbit isoform. These studies emphasize the importance of considering species differences, which can result from even minor protein sequence variations, for the critical enzymes in an animal disease model. Homology modeling provides a tool to identify key differences in isoforms that can significantly affect native enzyme activity.

Gelatinase B (MMP-9), but not its inhibitor (TIMP-1), dictates the growth rate of experimental thymic lymphoma

Dysregulation of metalloproteinase production at tumor sites contributes to the modification of local stromal tissue necessary for tumor development. Gelatinase B (matrix metalloproteinase-9, MMP-9) is one of the key enzymes that have been associated with the progression of several tumors. Paradoxically, MMP-9 expression by tumor cells, most notably by lymphoma cells, is concomitant with the expression of its physiological inhibitor, TIMP-1. Not only are both genes often co-expressed in the most aggressive forms of lymphomas but also both are up-regulated upon contact with stromal cells. Since TIMP-1 is known to regulate growth in several cell types and some aggressive lymphoma cells express TIMP-1 constitutively without MMP-9, it is unclear whether the over-expression of MMP-9 is counterbalanced by TIMP-1 and whether TIMP-1 expression alone could favor the development of lymphoma. To gain further insight into the respective roles of MMP-9 and TIMP-1 in lymphoma, we generated lymphoma cell lines expressing constitutively high levels of MMP-9 or TIMP-1 and compared these cells for the ability to form thymic lymphoma in vivo. Moreover, we generated lymphoma cell lines expressing constitutively high levels of both MMP-9 and TIMP-1 to reproduce the net physiological balance resulting from the expression of both genes simultaneously and to determine which gene overrides the other. Our results show that mice injected with lymphoma cells expressing MMP-9 constitutively developed thymic lymphoma more rapidly than those injected with control lymphoma cells. Over-expression of TIMP-1 alone did not significantly influence tumor progression of lymphoma nor did it delay the capacity of MMP-9 to accelerate the development of thymic lymphoma.

The NTR module: domains of netrins, secreted frizzled related proteins, and type I procollagen C-proteinase enhancer protein are homologous with tissue inhibitors of metalloproteases

Using homology search, structure prediction, and structural characterization methods we show that the C-terminal domains of (1) netrins, (2) complement proteins C3, C4, C5, (3) secreted frizzled-related proteins, and (4) type I procollagen C-proteinase enhancer proteins (PCOLCEs) are homologous with the N-terminal domains of (5) tissue inhibitors of metalloproteinases (TIMPs). The proteins harboring this netrin module (NTR module) fulfill diverse biological roles ranging from axon guidance, regulation of Wnt signaling, to the control of the activity of metalloproteases. With the exception of TIMPs, it is not known at present what role the NTR modules play in these processes. In view of the fact that the NTR modules of TIMPs are involved in the inhibition of matrixin-type metalloproteases and that the NTR module of PCOLCEs is involved in the control of the activity of the astacin-type metalloprotease BMP1, it seems possible that interaction with metzincins could be a shared property of NTR modules and could be critical for the biological roles of the host proteins.

Biophysical and functional characterization of full-length, recombinant human tissue inhibitor of metalloproteinases-2 (TIMP-2) produced in Escherichia coli. Comparison of wild type and amino-terminal alanine appended variant with implications for the mechanism of TIMP functions

Matrix metalloproteinases (MMPs) function in the remodeling of the extracellular matrix that is integral for many normal and pathological processes. The tissue inhibitor of metalloproteinases family, including tissue inhibitor of metalloproteinases-2 (TIMP-2), regulates the activity of these multifunctional metalloproteinases. TIMP family members are proteinase inhibitors that contain six conserved disulfide bonds, one involving an amino-terminal cysteine residue that is critical for MMP inhibitor activity. TIMP-2 has been expressed in Escherichia coli, folded from insoluble protein, and functionally characterized. The wild type protein inhibited gelatinase A (MMP-2), whereas a variant with an alanine appended to the amino terminus (Ala+TIMP-2) was inactive. Removal of amino-terminal alanine by exopeptidase digestion restored protease inhibitor activity. This confirms the mechanistic importance of the amino-terminal amino group in the metalloproteinase inhibitory activity, as originally suggested from the x-ray structure of a complex of MMP-3 with TIMP-1 and a complex of TIMP-2 with MT-1-MMP. The Ala+TIMP-2 variant exhibited conformational, pro-MMP-2 complex formation and fibroblast growth modulating properties of the wild type protein. These findings demonstrate that Ala+TIMP-2 is an excellent biochemical tool for examining the specific role of MMP inhibition in the multiple functions ascribed to TIMPs.

The specificity of TIMP-2 for matrix metalloproteinases can be modified by single amino acid mutations

Residues 1-127 of human TIMP-2 (N-TIMP-2), comprising three of the disulfide-bonded loops of the TIMP-2 molecule, is a discrete protein domain that folds independently of the C-terminal domain. This domain has been shown to be necessary and sufficient for metalloproteinase inhibition and contains the major sites of interaction with the catalytic N-terminal domain of active matrix metalloproteinases (MMPs). Residues identified as being involved in the interaction with MMPs by NMR chemical shift perturbation studies and TIMP/MMP crystal structures have been altered by site-directed mutagenesis. We show, by measurement of association rates and apparent inhibition constants, that the specificity of these N-TIMP-2 mutants for a range of MMPs can be altered by single site mutations in either the TIMP "ridge" (Cys1-Cys3 and Ser68-Cys72) or the flexible AB loop (Ser31-Ile41). This work demonstrates that it is possible to engineer TIMPs with altered specificity and suggests that this form of protein engineering may be useful in the treatment of diseases such as arthritis and cancer where the selective inhibition of key MMPs is desirable.

Ca(2+) and Zn(2+) binding properties of peptide substrates of vertebrate collagenase, MMP-1

To understand the role of Ca(2+) in vertebrate in the structure and action of collagenase, we have examined peptides that interact with recombinant human fibroblast collagenase for their affinities towards Ca(2+) and Zn(2+) in a non-polar solvent. Two of the peptides, GPQGIAGQ and GNVGLAGA, had sequences in collagen which are, respectively, cleaved and not cleaved by collagenase. A third peptide, PSYFLNAG, had a collagenase-cleaved sequence in ovostatin, a globular protein substrate. Peptides TVGCEECTV and CLPREPGL were derived from TIMP-1; the former competitively inhibits collagenase while the latter does not. The relative rates of hydrolysis of the peptides by collagenase had the order GPQGIAGQ>PSYFLNAG>GNVGLAGA. Circular dichroism spectral data in trifluoroethanol showed that while the TIMP control peptide, CLPREPGL, bound only Zn(2+), the other four peptides bound both Ca(2+) and Zn(2+) with definite stoichiometries. Ca(2+) could displace Zn(2+) in the substrate peptides while Zn(2+) displaced Ca(2+) in the TIMP peptide. GPQGIAGQ, PSYFLNAG and TVGCEECTV formed peptide:Ca(2+):Zn(2+) ternary complexes. Our results suggest that both collagen and globular protein substrates of collagenase may bind Ca(2+) and Zn(2+) in the enzyme's active site. This, in turn, may account for the known importance of the non-catalytic Ca(2+) and Zn(2+) in collagenase activity.

The rationale and future potential of angiogenesis inhibitors in neoplasia

Malignant tumours are angiogenesis-dependent diseases. Several experimental studies suggest that primary tumour growth, invasiveness and metastasis require neovascularisation. Tumour-associated angiogenesis is a complex multistep process under the control of positive and negative soluble factors. A mutual stimulation occurs between tumour and endothelial cells by paracrine mechanisms. Angiogenesis is necessary, but not sufficient, as the single event for tumour growth. There is, however, compelling evidence that acquisition of the angiogenic phenotype is a common pathway for tumour progression, and that active angiogenesis is associated with other molecular mechanisms leading to tumour progression. Experimental research suggests that it is possible to block angiogenesis by specific inhibitory agents, and that modulation of angiogenic activity is associated with tumour regression in animals with different types of neoplasia. The more promising angiosuppressive agents for clinical testing are: naturally occurring inhibitors of angiogenesis (angiostatin, endostatin, platelet factor-4 and others), specific inhibitors of endothelial cell growth (TNP-470, thalidomide, interleukin-12 and others), agents neutralising angiogenic peptides (antibodies to fibroblast growth factor or vascular endothelial growth factor, suramin and analogues, tecogalan and others) or their receptors, agents that interfere with vascular basement membrane and extracellular matrix [metalloprotease (MMP) inhibitors, angiostatic steroids and others], antiadhesion molecules antibodies such as antiintegrin alpha v beta 3, and miscellaneous drugs that modulate angiogenesis by diverse mechanisms of action. Antiangiogenic therapy is to be distinguished from vascular targeting. Gene therapy aimed to block neovascularisation is also a feasible anticancer strategy in animals bearing experimental tumours. Antiangiogenic therapy represents one of the more promising new approaches to anticancer therapy and it is already in early clinical trials. Because angiosuppressive therapy is aimed at blocking tumour growth indirectly, through modulation of neovascularisation, antiangiogenic agents need to be developed and evaluated as biological response modifiers. Therefore, adequate and well designed clinical trials should be performed for a proper evaluation of antiangiogenic agents, by determination and monitoring of surrogate markers of angiogenic activity.

Engineering of selective TIMPs

Differences in proteinase susceptibility between free TIMP-1 and the TIMP-1-MMP-3 complex and mutagenesis studies suggested that the residues around the disulfide bond between Cys1 and Cys70 in TIMP-1 may interact with MMPs. The crystal structure of the complex between TIMP-1 and the catalytic domain of MMP-3 has revealed that the alpha-amino group of Cys1 bidentately chelates the catalytic zinc of MMP-3 and the Thr2 side chain occupies the S1' pocket. Generation of the N-terminal domain of TIMP-1 (N-TIMP-1) variants with 15 different amino acid substitutions for Thr2 has indicated that the nature of the side chain of residue 2 has a major effect on the affinity of N-TIMP-1 for three different MMPs (MMPs-1, -2 and -3). The results also demonstrate that the mode of binding of N-TIMP-1 residue 2 differs from the binding of the P1' residue of a peptide substrate.

Tissue inhibitors of matrix metalloproteinases in cancer

Tissue inhibitors of metalloproteinases (TIMPs) play a key regulatory role in the homeostasis of the extracellular matrix (ECM) by controlling the activity of matrix metalloproteinases (MMPs). Some TIMPs have a second function as well, unrelated to their antiMMP activity, which affects cell proliferation and survival. The role of these inhibitors in cancer has been the subject of extensive investigations that have examined their biological activity in tumor growth, invasion, metastasis and angiogenesis, as well as their potential use in the diagnosis and treatment of human cancer.

Insights into MMP-TIMP interactions

The proteolytic activity of the matrix metalloproteinases (MMPs) involved in extracellular matrix degradation must be precisely regulated by their endogenous protein inhibitors, the tissue inhibitors of metalloproteinases (TIMPs). Disruption of this balance can result in serious diseases such as arthritis and tumor growth and metastasis. Knowledge of the tertiary structures of the proteins involved in such processes is crucial for understanding their functional properties and to interfere with associated dysfunctions. Within the last few years, several three-dimensional structures have been determined showing the domain organization, the polypeptide fold, and the main specificity determinants of the MMPs. Complexes of the catalytic MMP domains with various synthetic inhibitors enabled the structure-based design and improvement of high-affinity ligands, which might be elaborated into drugs. Very recently, structural information also became available for some TIMP structures and MMP-TIMP complexes, and these new data elucidated important structural features that govern the enzyme-inhibitor interaction.

Matrix metalloproteinase inhibition. From the Jurassic to the third millennium

A brief historical introduction to the matrix metalloproteinase (MMP) field, which began in 1962, is followed by an overview of the inhibition of these proteases by natural inhibitors such as alpha 2 macroglobulin and the TIMPs (tissue inhibitors of metalloproteinases) and by synthetic inhibitors, which are largely chelating agents. The latter include thiol, alkylcarbonyl, phosponamidate and hydroxamate compounds, as well as the tetracyclines. A review of the most recent progress concludes with prognostications as to where the field may be going next.

Picking the S1, S1' and S2' pockets of matrix metalloproteinases. A niche for potent acyclic sulfonamide inhibitors

A series of acyclic hydroxamic acids harboring strategically placed alpha-arylsulfonamido and thioether groups was synthesized and found to be potent inhibitors of various MMPs. An unprecedented cleavage of t-butyl hydroxamates to hydroxamic acids was found.

Human tissue inhibitor of metalloproteinases 3 interacts with both the N- and C-terminal domains of gelatinases A and B. Regulation by polyanions

We compared the association constants of tissue inhibitor of metalloproteinases (TIMP)-3 with various matrix metalloproteinases with those for TIMP-1 and TIMP-2 using a continuous assay. TIMP-3 behaved more like TIMP-2 than TIMP-1, showing rapid association with gelatinases A and B. Experiments with the N-terminal domain of gelatinase A, the isolated C-terminal domain, or an inactive progelatinase A mutant showed that the hemopexin domain of gelatinase A makes an important contribution to the interaction with TIMP-3. The exchange of portions of the gelatinase A hemopexin domain with that of stromelysin revealed that residues 568-631 of gelatinase A were required for rapid association with TIMP-3. The N-terminal domain of gelatinase B alone also showed slower association with TIMP-3, again implying significant C-domain interactions. The isolation of complexes between TIMP-3 and progelatinases A and B on gelatin-agarose demonstrated that TIMP-3 binds to both proenzymes. We analyzed the effect of various polyanions on the inhibitory activity of TIMP-3 in our soluble assay. The association rate was increased by dextran sulfate, heparin, and heparan sulfate, but not by dermatan sulfate or hyaluronic acid. Because TIMP-3 is sequestered in the extracellular matrix, the presence of certain heparan sulfate proteoglycans could enhance its inhibitory capacity.