The plasminogen activation system in tumor growth, invasion, and metastasis

Generation of the serine proteinase plasmin from the extracellular zymogen plasminogen can be catalyzed by either of two other serine proteinases, the urokinase- and tissue-type plasminogen activators (uPA and tPA). The plasminogen activation system also includes the serpins PAI-1 and PAI-2, and the uPA receptor (uPAR). Many findings, gathered over several decades, strongly suggest an important and causal role for uPA-catalyzed plasmin generation in cancer cell invasion through the extracellular matrix. Recent evidence suggests that the uPA system is also involved in cancer cell-directed tissue remodeling. Moreover, the system also supports cell migration and invasion by plasmin-independent mechanisms, including multiple interactions between uPA, uPAR, PAI-1, extracellular matrix proteins, integrins, endocytosis receptors, and growth factors. These interactions seem to allow temporal and spatial reorganizations of the system during cell migration and a selective degradation of extracellular matrix proteins during invasion. The increased knowledge about the plasminogen activation system may allow utilization of its components as targets for anti-invasive therapy.     

Messenger RNA differential display strategies in birds and amphibians

As an inroad to the discovery of genes involved in important biological activities, various techniques have been developed for detecting genes based on their expression levels. Arbitrary amplification of different messenger RNA (mRNA) populations and their comparison on display autoradiograms made mRNA differential display one of the most straightforward approaches to identification of differentially regulated mRNAs. Over the past decade this strategy has been employed in many in vitro and in vivo systems. The use of the method in bird and amphibian model systems is reviewed here, emphasizing several unique combinations of model system and design of differential display screen.     

Interleukin-12, a key cytokine in Th1-mediated autoimmune diseases

Interleukin 12 (IL-12) is a heterodimeric cytokine produced primarily by antigen-presenting cells (APCs) which plays a key role in promoting type 1 T helper cell (Th1) responses. The powerful activity of IL-12 requires tight control, which is exerted at various levels. Primary control is exerted on IL-12 production by APCs, a major factor driving the response towards the Th1 or Th2 phenotype. Another level of control regulates expression of the IL-12 receptor (IL-12R), which is composed of two subunits, β1 and β2. The IL-12R β2 subunit has signal-transducing capacity and modulation of its expression is central to the regulation of IL-12 responsiveness. Endogenous IL-12 plays an important role in host defense against infection by a variety of intracellular pathogens. Its Th1-promoting activity, however, also favors Th1-mediated immunopathology and, in particular, the induction of Th1-mediated autoimmune diseases. Received 15 January 1999; received after revision 11 March 1999; accepted 16 March 1999     

Novel aspects and new roles for the serine protease plasmin

The serine protease plasmin is distributed throughout the human body in the form of the zymogen plasminogen. The plasminogen activation system is mostly recognized for its fibrinolytic activity but is also upregulated in chronic inflammatory diseases, including atherosclerosis and arthritis. Plasmin can bind to a variety of cells, including monocytes, through low-affinity binding sites and triggers aggregation of neutrophils, platelet degranulation and arachidonate release from endothelial cells. In monocytes, plasmin elicits full-scale proinflammatory activation, including lipid mediator release, chemotaxis and cytokine expression, as well as induction of other proinflammatory genes. The effects of plasmin are specific, require the active catalytic center and can be antagonized by lysine analogues, implying binding of the plasmin molecule to the cell membrane through its lysine binding sites. In view of the upregulation of the fibrinolytic genes in chronic inflammatory diseases, cell activation by plasmin is likely to play a major pathophysiological role, a view that is further supported by data from transgenic mice.Received 9 September 2003; received after revision 4 October 2003; accepted 13 October 2003     

Regulation and interactions in the activation of cell-associated plasminogen

The main components in plasminogen activation include plasminogen, tissue plasminogen activator (tPA), urokinase plasminogen activator (uPA), urokinase plasminogen activator receptor (uPAR), and plasminogen activator inhibitors-1 and –2 (PAI-1, PAI-2). These components are subject to extensive regulation and interactions with for example, pericellular adhesion molecules. Although uPA and tPA are quite similar in structure and have common inhibitors and physiological substrates, their physiological roles are distinct. Traditionally, the role of tPA has been in fibrinolysis and that of uPA in cell migration, especially in cancer cells. Recently several targets for tPA/plasmin have been found in neuronal tissues. The functional role of the PAIs is no longer simply to inhibit overexpressed plasminogen activators, and PAI-2 has an unidentified role in the regulation of cell death.Received 2 June 2004; received after revision 30 June 2004; accepted 20 July 2004     

Dexamethasone enhances CTLA-4 expression during T cell activation

T cell activation is enhanced by the costimulatory interaction of B7 on antigen-presenting cells and CD28 on T cells, resulting in long-term T cell proliferation, differentiation and production of large amounts of cytokines, such as interleukin (IL)-2. CTLA-4 is a co-stimulation receptor that shares 31% homology with CD28 and binds B7 family members with higher affinity. CTLA-4 is transiently expressed intracellularly and on the cell surface following activation of T cells. We have studied the kinetics of CTLA-4 expression and the effects of dexamethasone on CTLA-4 expression during T cell activation in cultures of mouse spleen cells stimulated by a mixture of immobilized anti-CD3 and anti-CD28 monoclonal antibodies (anti-CD3/CD28 mAb) or concanavalin A (ConA). CTLA-4 expression peaked on day 2 and returned to background levels after 7 days. Dexamethasone was found to potentiate CTLA-4 expression in a dose-dependent manner with an EC₅₀ effective concentration 50%) of about 10⁻⁸ M. In contrast, other immunosuppressive agents, such as rapamycin or cyclosporin A had no or an inhibitory effect on CTLA-4 expression, respectively. Dexamethasone also stimulated CD28 expression, but inhibited IL-2R expression during anti-CD3/CD28 mAb-induced mouse splenic T cell activation. Western blot analyses of lysates of activated mouse T cells showed that dexamethasone increased CTLA-4 protein levels twofold during anti-CD3/CD28 mAb-induced activation. Dexamethasone also enhanced CTLA-4 messenger RNA twofold as quantified by ribonuclease protection assay. The effects of dexamethasone on CTLA-4 expression were glucocorticoid-specific and completely inhibited by the glucocorticoid receptor antagonist mifepristone (RU486), indicating that the effect of dexamethasone on CTLA-4 expression is mediated through the glucocorticoid receptor. In conclusion, the immunosuppressive agent dexamethasone actually stimulates CTLA-4 expression, which is involved in downregulation of T cell activation. Received 19 May 1999; received after revision 13 July 1999; accepted 13 July 1999     

The urokinase receptor and integrins in cancer progression

Enhanced levels of expression of urokinase receptor (uPAR) and certain integrins have been linked to cancer cell progression. This has classically been attributed to matrix degradation via the activation of the urokinase (uPA)/plasmin system and modulation of cell motility and survival through integrin engagement. More recently, uPAR has been shown to play multiple roles independent of protease activity. Specifically, uPAR has been shown to be intimately involved in the regulation of cell adhesion, migration and proliferation in part through interactions with other membrane partners, including integrins. The goal of this review is to summarize recent insights in the function of uPAR/integrin interactions, to provide a framework for understanding the importance of these interactions in the context of cancer, and to highlight its potential as a target for therapeutic intervention.     

Differential expression of genes for uncoupling proteins 1, 2 and 3 in brown and white adipose tissue depots during rat development

The different expression patterns of genes for uncoupling proteins (UCPs) 1, 2 and 3 (ucp1, ucp2 and ucp3) were studied in interscapular brown adipose tissue (BAT) and in four white adipose tissue (WAT) depots (epididymal, inguinal, mesenteric and retroperitoneal) in male rats of different ages (18 days-12 months). UCP mRNA expression levels were determined by Northern blotting. In BAT, there were high levels of expression of UCP1 and UCP3 mRNA, but no detectable levels of UCP2 mRNA. Both ucp1 and ucp3 followed a similar expression pattern with age, with high levels in suckling rats which decreased to 50% or less in rats just under 2 months old, declining thereafter until 5 months and then recovering with age. However, an additional peak of expression was observed for ucp3 at the age of 3 months. In WAT, ucp1 expression was rare: occasional expression was found for UCP1 mRNA in the retroperitoneal depot in suckling rats and in the epididymal and inguinal depots in suckling and mature adult rats. ucp2 and ucp3 had different developmental expression patterns, but these were similar for each gene in the different depots studied. UCP3 mRNA was highly expressed in rats soon after birth, it decreased until 3 months, and increased thereafter, except for the mesenteric WAT where ucp3 expression decreased until 7 months before recovering. The fact that changes with age of both ucp1 and ucp3 expression have a similar profile in BAT, which is also similar to the ucp3 and also ucp1 profiles in some WAT depots, might reflect a common regulatory pattern for the expression of these genes, and also a common function. In contrast to ucp1 and ucp3, ucp2 had a peak of expression at about 2 months, and lower expression at 3 months, suggesting different regulation and probably a different role for this UCP.     

Matriptase and its putative role in cancer

Tumor progression and metastasis are the pathologic effects of uncontrolled or deregulated invasive growth, a process in which proteases play a fundamental role. They mediate the degradation of extracellular matrix components and intercellular cohesive structures to allow migration of the cells into the extracellular environment and activate growth and angiogenic factors. In addition to metalloproteases and the plasminogen activation system, another protease, matriptase, contributes substantially to these processes. Matriptase is a type II transmembrane trypsin-like serine protease that is expressed by cells of epithelial origin and is overexpressed in a variety of human cancers. It has been suggested that this protease not only facilitates cellular invasiveness but may also activate oncogenic pathways. This review summarizes current knowledge about matriptase, its putative role in tumor initiation and progression, and its potential as a novel target in anti-cancer therapy. Received 29 June 2006; received after revision 1 August 2006; accepted 19 September 2006     

Anti-adipogenesis by 6-thioinosine is mediated by downregulation of PPAR γ through JNK-dependent upregulation of iNOS

Adipocyte dysfunction is associated with the development of obesity. This study shows that 6-thioinosine inhibits adipocyte differentiation. The mRNA levels of PPAR γ and C/EBPα, but not C/EBPβ and δ, were reduced by 6-thioinosine. Moreover, the mRNA levels of PPAR γ target genes (LPL, CD36, aP2, and LXRα) were down-regulated by 6-thioinosine. We also demonstrated that 6-thioinosine inhibits the transactivation activity and the mRNA level of PPAR γ. Additionally, attempts to elucidate a possible mechanism underlying the 6-thioinosine-mediated effects revealed that 6-thioinosine induced iNOS gene expression without impacting eNOS expression, and that this was mediated through activation of AP-1, especially, JNK. In addition, 6-thioinosine was found to operate upstream of MEKK-1 in JNK activation signaling. Taken together, these findings suggest that the inhibition of adipocyte differentiation by 6-thioinosine occurs primarily through the reduced expression of PPAR γ, which is mediated by upregulation of iNOS via the activation of JNK.     

The odd couple: signal transduction and endocytosis

Cell surface receptors are used to transmit extracellular information. The activation of cell surface receptors initiates signal transduction and receptor endocytosis. Signal transduction and the endosomal transport of activated receptors require precise regulation. New concepts for the integration of endocytosis and signaling arise from recent findings that suggest bidirectional interplay of these two processes. This review discusses the following questions: (i) do activated cell surface receptors modify the endosomal system to promote internalization and endosomal traffic, and (ii) do internalized cell surface receptors use specifically localized signaling complexes to generate specific biological signals?     

Spontaneous arterial dissection: phenotype and molecular pathogenesis

Arterial dissection (AD) is defined as the longitudinal splitting up of the arterial wall caused by intramural bleeding. It can occur as a spontaneous event in all large and medium sized arteries. The histological hallmark of AD is medial degeneration. Histological investigations, gene expression profiling and proteome studies of affected arteries reveal disturbances in many different biological processes including inflammation, proteolytic activity, cell proliferation, apoptosis and smooth muscle cell (SMC) contractile function. Medial degeneration can be caused by various rare dominant Mendelian disorders. Genetic linkage analysis lead to the identification of mutations in different disease-causing genes involved in the biosynthesis of the extracellular matrix (FBN1, COL3A1), in transforming growth factor (TGF) beta signaling (FBN1, TGFBR1, TGFBR2) and in the SMC contractile system (ACTA2, MYH11). Genome wide association studies suggest that the CDKN2A/CDKN2B locus plays a role in the etiology AD and other arterial diseases.