No abstract

for pro matrix metalloproteinase activation. APMIS 1999;107:3844. The activation of pro matrix metalloproteinases (MMPs) by sequential proteolysis of the propeptide blocking the active site cleft is regarded as one of the key levels of regulation of these proteinases. Potential physiological mechanisms including cell-associated plasmin generation by urokinase-like plasminogen activator, or the action of cell surface MTI-MMPs appear to be involved in the initiation of cascades of pro M M P activation. Gelatinase A, collagenase 3 and gelatinase B may be activated by MT-MMP based mechanisms, as evidenced by both biochemical and cell based studies. Hence the regulation of MT-MMPs themselves becomes critical to the determination of M M P activity. This includes activation, assembly at the cell surfaces as TIMP-2 complexes and subsequent inactivation by proteolysis or TIMP inhibition.

Concanavalin A-stimulated fibroblasts expressing MT1-MMP and fibroblast-derived plasma membranes were able to process human procollagenase-3 via a M r 56,000 intermediate form to the final M r 48,000 active enzyme which, by analogy with progelatinase A activation, may represent a model system for in vivo activation. Inhibition experiments using tissue inhibitor of metalloproteinases, plasminogen activator inhibitor-2, or aprotinin demonstrated that activation in the cellular model system was due to MT1-MMP/gelatinase A and excluded the participation of serine proteinases such as plasmin during procollagenase-3 activation. We have established that progelatinase A can considerably potentiate the activation rate of procollagenase-3 by crude plasma membrane preparations from concanavalin Astimulated fibroblasts, thus confirming our results using purified progelatinase A and MT1-MMP. This new activation cascade may be significant in human breast cancer pathology, where all three enzymes have been implicated as playing important roles.Degradation of the extracellular matrix during tumor invasion is thought to result from a combined action of several proteolytic enzyme systems, including the collagenases and other matrix metalloproteinases (MMPs) 1 (1, 2) and serine proteases, such as plasmin generated by the urokinase pathway of plasminogen activation (3).Human collagenase-3 (MMP-13), a new member of the MMP family, is expressed by breast tumors and is likely to play a crucial role in the modulation of extracellular matrix degradation and cell-matrix interactions involved in metastasis (4). Procollagenase-3 comprises three distinct domains which include an 85-amino acid residue propeptide that is lost during activation (5), and in which the conserved sequence PRCGVPD is responsible for the latency of the MMPs (6). This sequence is followed by the catalytic domain containing the active site of the enzyme linked via a short hinge sequence motif to the third, C-terminal domain, that shows homology to vitronectin and which is essential for the collagenolytic activity of collagenase-3.2 Collagenase-3 is a powerful collagenolytic and gelatinolytic enzyme that preferentially cleaves type II collagen, and it can therefore be implied that this enzyme may play a considerable role in connective tissue turnover (5). One of the key events in the regulation of extracellular collagenolytic activity is the activation of procollagenase-3, but there are currently only limited data available on how this may occur in vivo. We have recently shown that procollagenase-3 can be directly activated by stromelysin (5); however, other mechanisms may be of physiological and pathophysiological significance.Increasing evidence is accumulating that the newly discovered membrane associated MMPs (MT-MMPs) act as cell surface activator(s) of progelatinase A (proMMP-2) under physiological or pathophysiological conditions (7-12). This mechanism was thought to be specific for progelatinase A, since other MMPs such as progelatinase B, fibroblast procollage...

Proteoglycans are key components of extracellular matrices, providing structural support as well as influencing cellular behaviour in physiological and pathological processes. The diversity of proteoglycan function reported in the literature is equally matched by diversity in proteoglycan structure. Members of the ADAMTS (A Disintegrin And Metalloproteinase with ThromboSpondin motifs) family of enzymes degrade proteoglycans and thereby have the potential to alter tissue architecture and regulate cellular function. In this review, we focus on ADAMTS enzymes that degrade the lectican and small leucine-rich repeat families of proteoglycans. We discuss the known ADAMTS cleavage sites and the consequences of cleavage at these sites. We illustrate our discussion with examples from the literature in which ADAMTS proteolysis of proteoglycans makes profound changes to tissue function.