Matrix metalloproteinases (MMPs) have long been associated with cancer-cell invasion and metastasis. This provided the rationale for clinical trials of MMP inhibitors, unfortunately with disappointing results. We now know, however, that the MMPs have functions other than promotion of invasion, have substrates other than components of the extracellular matrix, and that they function before invasion in the development of cancer. With this knowledge in hand, can we rethink the use of MMP inhibitors in the clinic?

New functions for the matrix metalloproteinases in cancer progression

Inefficient vascular supply and the resultant reduction in tissue oxygen tension often lead to neovascularization in order to satisfy the needs of the tissue. Examples include the compensatory development of collateral blood vessels in ischaemic tissues that are otherwise quiescent for angiogenesis and angiogenesis associated with the healing of hypoxic wounds. But the presumptive hypoxia-induced angiogenic factors that mediate this feedback response have not been identified. Here we show that vascular endothelial growth factor (VEGF; also known as vascular permeability factor) probably functions as a hypoxia-inducible angiogenic factor. VEGF messenger RNA levels are dramatically increased within a few hours of exposing different cell cultures to hypoxia and return to background when normal oxygen supply is resumed. In situ analysis of tumour specimens undergoing neovascularization show that the production of VEGF is specifically induced in a subset of glioblastoma cells distinguished by their immediate proximity to necrotic foci (presumably hypoxic regions) and the clustering of capillaries alongside VEGF-producing cells.

Vascular endothelial growth factor induced by hypoxia may mediate hypoxia-initiated angiogenesis.

Matrix metalloproteinases (MMPs), also designated matrixins, hydrolyze components of the extracellular matrix. These proteinases play a central role in many biological processes, such as embryogenesis, normal tissue remodeling, wound healing, and angiogenesis, and in diseases such as atheroma, arthritis, cancer, and tissue ulceration. Currently 23 MMP genes have been identified in humans, and most are multidomain proteins. This review describes the members of the matrixin family and discusses substrate specificity, domain structure and function, the activation of proMMPs, the regulation of matrixin activity by tissue inhibitors of metalloproteinases, and their pathophysiological implication.

Matrix metalloproteinases and tissue inhibitors of metalloproteinases: structure, function, and biochemistry.

▪ Abstract The matrix metalloproteinases (MMPs) constitute a multigene family of over 25 secreted and cell surface enzymes that process or degrade numerous pericellular substrates. Their targets include other proteinases, proteinase inhibitors, clotting factors, chemotactic molecules, latent growth factors, growth factor–binding proteins, cell surface receptors, cell-cell adhesion molecules, and virtually all structural extracellular matrix proteins. Thus MMPs are able to regulate many biologic processes and are closely regulated themselves. We review recent advances that help to explain how MMPs work, how they are controlled, and how they influence biologic behavior. These advances shed light on how the structure and function of the MMPs are related and on how their transcription, secretion, activation, inhibition, localization, and clearance are controlled. MMPs participate in numerous normal and abnormal processes, and there are new insights into the key substrates and mechanisms responsible for regula...

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How Matrix Metalloproteinases Regulate Cell Behavior

Background Retinal ischemia induces intraocular neovascularization, which often leads to glaucoma, vitreous hemorrhage, and retinal detachment, presumably by stimulating the release of angiogenic molecules. Vascular endothelial growth factor (VEGF) is an endothelial-cell-specific angiogenic factor whose production is increased by hypoxia. Methods We measured the concentration of VEGF in 210 specimens of ocular fluid obtained from 164 patients undergoing intraocular surgery, using both radioimmunoassays and radioreceptor assays. Vitreous proliferative potential was measured with in vitro assays of the growth of retinal endothelial cells and with VEGF-neutralizing antibody. Results VEGF was detected in 69 of 136 ocular-fluid samples from patients with diabetic retinopathy, 29 of 38 samples from patients with neovascularization of the iris, and 3 of 4 samples from patients with ischemic occlusion of the central retinal vein, as compared with 2 of 31 samples from patients with no neovascular disorders (P<0.00...

https://www.nejm.org/doi/pdf/10.1056/NEJM199412013312203

Vascular Endothelial Growth Factor in Ocular Fluid of Patients with Diabetic Retinopathy and Other Retinal Disorders

Bovine aortic and corneal endothelial cells synthesize a growth factor that remains mostly cell-associated but can also be extracted from the subendothelial extracellular matrix (ECM) deposited by these cells. The endothelial cell-derived growth factors extracted from cell lysates and from the extracellular matrix appear to be structurally related to basic fibroblast growth factor by the criteria that they bind to heparin-Sepharose and are eluted at 1.4-1.6 M NaCl, have a molecular weight of about 18,400, cross-react with anti-basic fibroblast growth factor antibodies when analyzed by electrophoretic blotting and immunoprecipitation, and are potent mitogens for bovine aortic and capillary endothelial cells. It is suggested that endothelium can store growth factors capable of autocrine growth promotion in two ways: by sequestering growth factor within the cell and by incorporating it into the underlying extracellular matrix.

https://www.pnas.org/content/pnas/84/8/2292.full.pdf

Endothelial cell-derived basic fibroblast growth factor: synthesis and deposition into subendothelial extracellular matrix

A comprehensive sequence alignment of 64 members of the family of matrix metalloproteinases (MMPs) for the entire sequences, and subsequently the catalytic and the hemopexin-like domains, have been performed. The 64 MMPs were selected from plants, invertebrates, and vertebrates. The analyses disclosed that as many as 23 distinct subfamilies of these proteins are known to exist. Information from the sequence alignments was correlated with structures, both crystallographic as well as computational, of the catalytic domains for the 23 representative members of the MMP family. A survey of the metal binding sites and two loops containing variable sequences of amino acids, which are important for substrate interactions, are discussed. The collective data support the proposal that the assembly of the domains into multidomain enzymes was likely to be an early evolutionary event. This was followed by diversification, perhaps in parallel among the MMPs, in a subsequent evolutionary time scale. Analysis indicates that a retrograde structure simplification may have accounted for the evolution of MMPs with simple domain constituents, such as matrilysin, from the larger and more elaborate enzymes.

Matrix metalloproteinases: structures, evolution, and diversification

Neuronal cell death occurs during many neurodegenerative disorders and stroke. The aberrant, excessive activity of matrix metalloproteinases (MMPs), especially MMP-9, contributes directly to neuron apoptosis and brain damage (Rosenberg et al., 1996; Asahi et al., 2001; Gu et al., 2002; Horstmann et al., 2003). We determined that MMP-9 degrades the extracellular matrix protein laminin and that this degradation induces neuronal apoptosis in a transient focal cerebral ischemia model in mice. We also determined that the highly specific thiirane gelatinase inhibitor SB-3CT blocks MMP-9 activity, including MMP-9-mediated laminin cleavage, thus rescuing neurons from apoptosis. We conclude that MMP-9 is a highly promising drug target and that SB-3CT derivatives have significant therapeutic potential in stroke patients.

https://www.jneurosci.org/content/jneuro/25/27/6401.full.pdf

A Highly Specific Inhibitor of Matrix Metalloproteinase-9 Rescues Laminin from Proteolysis and Neurons from Apoptosis in Transient Focal Cerebral Ischemia

Gelatin zymography is a simple yet powerful method to detect proteolytic enzymes capable of degrading gelatin from various biological sources. It is particularly useful for the assessment of two key members of the matrix metalloproteinase family, MMP-2 (gelatinase A) and MMP-9 (gelatinase B), due to their potent gelatin-degrading activity. This polyacrylamide gel electrophoresis-based method can provide a reliable assessment of the type of gelatinase, relative amount, and activation status (latent, compared with active enzyme forms) in cultured cells, tissues, and biological fluids. The method can be used to investigate factors that regulate gelatinase expression and modulate zymogen activation in experimental systems. The system provides information on the pattern of gelatinase expression and activation in human cancer tissues and how this relates to cancer progression. Interpretation of the data obtained in gelatin zymography requires a thorough understanding of the principles and pitfalls of the technique; this is particularly important when evaluating enzyme levels and the presence of active gelatinase species. If properly used, gelatin zymography is an excellent tool for the study of gelatinases in biological systems.

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Assessment of gelatinases (MMP-2 and MMP-9) by gelatin zymography.

Recent studies have demonstrated the existence of a soluble fibroblast growth factor (FGF) receptor type 1 (FGFR1) extracellular domain in the circulation and in vascular basement membranes. However, the process of FGFR1 ectodomain release from the plasma membrane is not known. Here we report that the 72-kDa gelatinase A (matrix metalloproteinase type 2, MMP2) can hydrolyze the Val368-Met369 peptide bond of the FGFR1 ectodomain, eight amino acids upstream of the transmembrane domain, thus releasing the entire extracellular domain. Similar results were obtained regardless of whether FGF was first bound to the receptor or not. The action of MMP2 abolished binding of FGF to an immobilized recombinant FGFR1 ectodomain fusion protein and to Chinese hamster ovary cells overexpressing FGFR1 The released recombinant FGFR1 ectodomain was able to bind FGF after MMP2 cleavage, suggesting that the cleaved soluble receptor maintained its FGF binding capacity. The activity of MMP2 could not be reproduced by the 92-kDa gelatinase B (MMP9) and was inhibited by tissue inhibitor of metalloproteinase type 2. These studies demonstrate that FGFR1 may be a specific target for MMP2 on the cell surface, yielding a soluble FGF receptor that may modulate the mitogenic and angiogenic activities of FGF.

https://www.pnas.org/content/pnas/93/14/7069.full.pdf

Rafael Fridman

Papers

Endothelial cell-derived basic fibroblast growth factor: synthesis and deposition into subendothelial extracellular matrix

Matrix metalloproteinases: structures, evolution, and diversification

A Highly Specific Inhibitor of Matrix Metalloproteinase-9 Rescues Laminin from Proteolysis and Neurons from Apoptosis in Transient Focal Cerebral Ischemia

Assessment of gelatinases (MMP-2 and MMP-9) by gelatin zymography.

Matrix metalloproteinase 2 releases active soluble ectodomain of fibroblast growth factor receptor 1.