IntroductionMetalloproteinases (MPs) play key roles in the responses of cells to their microenvironment. By effecting proteolytic degradation or activation of cell surface and extracellular matrix (ECM) proteins they can modulate both cell-cell and cell-ECM interactions, which influence cell differentiation, migration, proliferation and survival. Both secreted and membranebound forms of metalloproteinases have been implicated in pericellular proteolysis, including the matrix metalloproteinases (MMPs), the adamalysin-like proteinases with both metalloproteinase and disintegrin-like domains (ADAMs and their counterparts that have a thrombospondin-1-like domain, ADAM-TSs) and the astacins (Werb, 1997). Cells use various strategies to regulate extracellular proteinases: transcriptional regulation, trafficking of membrane-bound forms (secretion and endocytosis), activation of latent proenzyme forms, extracellular binding proteins and the action of endogenous inhibitors. Here we will discuss the role of metalloproteinase inhibitors, from the well-known tissue inhibitors of metalloproteinases (TIMPs) and α2-macroglobulin through to newer and less well-understood putative inhibitors (Fig. 1). We look at the available evidence that their other roles in cell biology do not all relate to their metalloproteinase inhibitory activity. Finally, we discuss the potential for use of such natural metalloproteinase inhibitors as therapeutic agents. Tissue inhibitors of metalloproteinases (TIMPs):basic structure and activity Four mammalian TIMPs have been cloned, purified and characterised. These secreted proteins are thought to regulate MMP activity during tisssue remodelling. One TIMP gene has been identified in Drosophila, and its ablation generates a phenotype similar to that of integrin mutants, which indicates that it has a role in ECM function (Godenschwege et al., 2000). All four mammalian TIMPs have many basic similarities, but they exhibit distinctive structural features, biochemical properties and expression patterns (Table 1). This suggests that each TIMP has specific roles in vivo. As in Drosophila, the mammalian TIMP genes are embedded intragenically in intron 5 of synapsin genes (Edwards, 2000).The TIMPs have molecular weights of ~21 kDa and are variably glycosylated (Table 1). They have six disulphide bonds and comprise a three-loop N-terminal domain and an interacting three-loop C-subdomain. Most of the biological functions of these proteins discovered thus far are attributable to sequences within the N-terminal domain, although the Csubdomains mediate interactions with the catalytic domains of some MMPs and with the hemopexin domains of MMP-2 and MMP-9 . The TIMPs are secreted proteins, but may be found at the cell surface in association with membrane-bound proteins; for example, TIMP-2, TIMP-3 and Many of these MMP inhibitors, including the TIMPs, possess other biological activities which may not be related to their inhibitory capacities. These need to be thoroughly characterized in order to allow informed develop...

Adenoviruses are used extensively as gene transfer agents, both experimentally and clinically. However, targeting of liver cells by adenoviruses compromises their potential efficacy. In cell culture, the adenovirus serotype 5 fiber protein engages the coxsackievirus and adenovirus receptor (CAR) to bind cells. Paradoxically, following intravascular delivery, CAR is not used for liver transduction, implicating alternate pathways. Recently, we demonstrated that coagulation factor (F)X directly binds adenovirus leading to liver infection. Here, we show that FX binds to the Ad5 hexon, not fiber, via an interaction between the FX Gla domain and hypervariable regions of the hexon surface. Binding occurs in multiple human adenovirus serotypes. Liver infection by the FX-Ad5 complex is mediated through a heparin-binding exosite in the FX serine protease domain. This study reveals an unanticipated function for hexon in mediating liver gene transfer in vivo.

Cardiac rupture is a fatal complication of acute myocardial infarction lacking treatment. Here, acute myocardial infarction resulted in rupture in wild-type mice and in mice lacking tissue-type plasminogen activator, urokinase receptor, matrix metalloproteinase stromelysin-1 or metalloelastase. Instead, deficiency of urokinase-type plasminogen activator (u-PA-/-) completely protected against rupture, whereas lack of gelatinase-B partially protected against rupture. However, u-PA-/- mice showed impaired scar formation and infarct revascularization, even after treatment with vascular endothelial growth factor, and died of cardiac failure due to depressed contractility, arrhythmias and ischemia. Temporary administration of PA inhibitor-1 or the matrix metalloproteinase-inhibitor TIMP-1 completely protected wild-type mice against rupture but did not abort infarct healing, thus constituting a new approach to prevent cardiac rupture after acute myocardial infarction.