Over the last 10 years, our knowledge ofextracellular proteolysis has progressed dramatically. Different enzymatic cascades cooperate to achieve extracellular matrix (ECM)I degradation, and a number of participant proteins have been characterized and cloned. Physiological inhibitors have been identified for most of these enzymes. Also, the concept of focused proteolysis, through binding of enzymes and inhibitors to specific regions ofthe extracellular milieu, has received broad experimental support. Finally, the biosynthesis of many of the relevant proteases and inhibitors has been shown to be under the control of hormones and growth factors. Plasminogen activators (PAs) and their inhibitors (PAIs) are thought to be key participants in the balance ofproteolytic and antiproteolytic activities that regulates matrix turnover. This article summarizes the evidence that supports this contention, discusses the role of PAspecific cell surface binding sites, and also draws attention to a number of instances in which the presence of PAs cannot be reconciled with an exclusive function in ECM degradation.The plasminogen activator/plasmin system ENZYMES PAs are serine proteases of tryptic specificity. Two enzymes, differing mostly in the domain organization and function of their noncatalytic regions, have been identified in mammals: urokinase-type PA (uPA) and tissue-type PA (tPA) (1). They are the products of distinct genes, and are secreted as singlechain (sc) proteins; whereas sc tPA is active, sc uPA is essentially inactive (pro-uPA) (2). Cleavage of pro-uPA by plasmin, kallikrein, Factor XIIa or cathepsin B (3) yields the disulfidelinked two-chain active enzyme. The two PAs have distinct targeting determinants in their noncatalytic regions: the "growth factor domain" of uPA directs the binding of the enzyme (and that ofpro-uPA) to a plasma membrane receptor (4,5), whereas other structural domains in tPA (the "finger" region and the "kringles") allow its binding to fibrin and other It is impossible to select a small set of references that would provide appropriate coverage of the entire field discussed. We have thus included references to reviews and to recent papers that can be used to trace back earlier work. We apologize to all our colleagues whose contributions are not adequately referenced, as well as to our readers.Receivedfor components of the ECM (6). These and perhaps additional interactions, for instance with heparinlike molecules, could have a dramatic effect on the focusing of PA-controlled proteolysis (7). The different extracellular addressing ofthe two PAs suggests that they play different biological roles.Plasminogen is the prefered substrate for PAs, but other molecules may also be cleaved by one or the other PA; for instance, avian uPA exerts a plasmin-independent effect on the morphology of chick fibroblasts (8). Plasminogen is present in plasma and extracellular fluids at a 1-2 AM concentration, in the range of the Km of the activation reaction. It can associate with fibrin and other proteins via lysi...

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Mutations in the p53 gene are implicated in the pathogenesis of half of all human tumors. We have developed a simple functional assay for p53 mutation in which human p53 expressed in Saccharomyces cerevisiae activates transcription of the ADE2 gene. Consequently, yeast colonies containing wild-type p53 are white and colonies containing mutant p53 are red. Since this assay tests the critical biological function of p53, it can distinguish inactivating mutations from functionally silent mutations. By combining this approach with gap repair techniques in which unpurified p53 reverse transcription-PCR products are cloned by homologous recombination in vivo it is possible to screen large numbers of samples and multiple clones per sample for biologically important mutations. This means that mutations can be detected in tumor specimens contaminated with large amounts of normal tissue. In addition, the assay detects temperature-sensitive mutants, which give pink colonies. We show here that this form of p53 functional assay can be used rapidly to detect germline mutations in blood samples, somatic mutations in tumors, and mutations in cell lines.

Half of elderly patients with breast cancer are undertreated, with strongly decreased specific survival as a consequence. Treatments need to be adapted to the patient's health status, but also should offer the best chance of cure.