Molecular mechanisms of protease-mediated tumor invasiveness

Interleukin-4 improves the migration of human myogenic precursor cells in vitro and in vivo

Different molecules are available to recruit new neighboring myogenic cells to the site of regeneration. Formerly called B cell stimulatory factor-1, IL-4 can now be included in the list of motogenic factors. The present report demonstrates that human IL-4 is not required for fusion between mononucleated myoblasts but is required for myotube maturation. In identifying IL-4 as a pro-migratory agent for myogenic cells, these results provide a mechanism which partly explains IL-4 demonstrated activity during differentiation. Among the different mechanisms by which IL-4 might enhance myoblast migration processes, our results indicate that there are implications of some integrins and of three major components of the fibrinolytic system. Indeed, increases in the amount of active urokinase plasminogen activator and its receptor were observed following an IL-4 treatment, while the plasminogen activator inhibitor-1 decreased. Finally, IL-4 did not modify the amount of cell surface alpha5 integrin but increased the presence of beta3 and beta1 integrins. This integrin modulation might favor myogenic cell migration and its interaction with newly formed myotubes. Therefore, IL-4 co-injection with transplanted myoblasts might be an approach to enhance the migration of transplanted cells for the treatment of a damaged myocardium or of a Duchenne Muscular Dystrophy patient.

The emerging role of proteases in retinal ganglion cell death

Retinal ganglion cell (RGC) death is an important issue in Primary Open Angle-Glaucoma (POAG) in terms of both vision loss and health care costs. Yet, the pathophysiology underlying RGC death in glaucoma is unclear. A growing body of evidence indicates that proteases that modulate the extracellular matrix (ECM) milieu in the retina, either directly or indirectly, play an important role in dictating the fate of RGCs. Recent evidence indicates that proteases, in addition to ECM-remodeling, have broader functional roles in glutamate receptor processing and predisposing RGCs to secondary damage. This review is focused on discussing the role of two groups of proteases, the matrix metalloproteinases (MMPs) and the plasminogen activators (PAs), in RGC death. In a long-run, a better understanding of the mechanisms involved in the regulation of proteases may lead to the development of adjunctive treatment options to attenuate RGC death and improve vision loss in glaucoma.

Thrombospondin-1 up-regulates tumor cell invasion through the urokinase plasminogen activator receptor in head and neck cancer cells

BACKGROUND

We have previously demonstrated that thrombospondin-1 (TSP-1) is expressed in squamous cell carcinomas of the head and neck. We have also shown that TSP-1 promotes tumor cell invasion through up-regulation of the urokinase plasminogen activator receptor (uPAR), in adenocarcinoma models. We now determined the role of TSP-1 in the regulation of uPAR expression and tumor cell invasion in squamous cell carcinoma of the head and neck cells.

MATERIALS AND METHODS

KB squamous cell carcinoma of the head and neck cells were used. The effect of TSP-1 on uPAR and its ligand, urokinase plasminogen activator (uPA), expression were determined by ELISA. The effect of TSP-1 on KB tumor cell invasion was determined in a modified Boyden chamber collagen invasion assay. To determine the role of uPAR on TSP-1-mediated KB tumor cell invasion, we used the three following different strategies: (a). blocking uPAR or its ligand, uPA, with neutralizing antibodies; (b). enzymatic cleavage of uPAR with glycosylphosphatidylinositol (GPI)-specific phospholipase C; and (c). inhibition of plasminogen binding by using epsilon-aminocaproic acid.

RESULTS

TSP-I up-regulated uPAR and uPA expression 3- and 4-fold, respectively. TSP-1 up-regulated KB tumor cell invasion 5-fold. Inhibition of uPAR blocked the TSP-1-mediated up-regulation of KB tumor cell invasion.

CONCLUSIONS

Our data support a central role for TSP-1 in the regulation of uPAR and tumor cell invasion in squamous cell carcinomas of the head and neck cells. Furthermore, uPAR seems to play a crucial role in TSP-1-mediated squamous cell carcinoma of the head and neck tumor cell invasion.

Binding of plasminogen to Pseudomonas aeruginosa results in formation of surface-associated plasmin and enhanced bacterial invasiveness

The interaction of Pseudomonas aeruginosa with plasminogen (Plg) is herein reported. Plg bound similarly to laboratory and clinical P. aeruginosa isolates from blood of septicemic patients and stools of asymptomatic carriers. No difference in Plg capture was detected between the piliated PAK strain and its isogenic nonpiliated mutant. Western immunoblotting results suggested that low molecular weight nonpilus adhesins from the bacterial outer membranes accounted for the Plg capture. Bacteria-bound Plg was converted to bioactive plasmin in the presence of exogenous urokinase-type Plg activator. The presence of surface-bound plasmin enhanced significantly the P. aeruginosa capability to invade fibrin gels and a reconstituted basement membrane matrix. These findings support the concept that Plg capture by P. aeruginosa may represent a mechanism which offers advantages to bacterial invasiveness through tissue barriers.

HGF, MET, and matrix-related proteases in hepatocellular carcinoma, fibrolamellar variant, cirrhotic and normal liver

Fibrolamellar variant is an uncommon subcategory of hepatocellular carcinoma with a better prognostic outcome. Proteinases and growth factors that are involved in the remodeling of extracellular matrix may influence the behavior of cancers. To determine whether these factors contribute to the distinct etiologies of fibrolamellar hepatocellular carcinoma and traditional hepatocellular carcinoma, we assayed hepatocyte growth factor, the hepatocyte growth factor receptor, and two hepatocyte growth factor activators, hepatocyte growth factor activator and urokinase-type plasminogen activator, in hepatocellular carcinoma, fibrolamellar hepatocellular carcinoma, cirrhotic liver and normal liver. In addition, we examined the urokinase-type plasminogen activator receptor, the type 1 plasminogen activator inhibitor, plasmin, fibrinogen, and the type IV matrix metalloproteinases. Eighteen hepatocellular carcinomas and 11 fibrolamellar hepatocellular carcinomas were obtained as paraffin embedded sections from the University of Pittsburgh Department of Pathology. Frozen tissues from a subset of cases (9 hepatocellular carcinomas, 4 fibrolamellar hepatocellular carcinomas, 12 cirrhotic livers and 2 normal livers) were also available for analysis. Antibodies against urokinase-type plasminogen activator, urokinase-type plasminogen activator receptor, hepatocyte growth factor and hepatocyte growth factor receptor were used to analyze immunoperoxidase stained slides from the paraffin blocks. Western blot analyses using antibodies against hepatocyte growth factor, hepatocyte growth factor receptor, phosphotyrosine, hepatocyte growth factor activator, urokinase-type plasminogen activator receptor, urokinase-type plasminogen activator, plasminogen activator inhibitor-1, fibrinogen and plasmin were performed on membrane-enriched fractions from the frozen tissue, as was collagen zymography for matrix metalloproteinase-2 and matrix metalloproteinase-9. The most notable findings are as follows: hepatocyte growth factor activator was only detected in malignant tissue but not cirrhotic liver or normal liver. Although hepatocyte growth factor was detected in most samples, it was significantly elevated in 5/9 hepatocellular carcinomas. Furthermore, 8/9 fibrolamellar hepatocellular carcinomas demonstrated hepatocyte growth factor receptor levels similar to normal, whereas 8/9 hepatocellular carcinomas and 11/12 cirrhotic livers exhibited either an increase or decrease. In contrast, active matrix metalloproteinase-2, which was absent in normal liver, was elevated in fibrolamellar hepatocellular carcinoma as compared to cirrhotic liver and conventional hepatocellular carcinoma. Surprisingly, 10/12 cirrhotic livers and 2/4 fibrolamellar hepatocellular carcinomas but only 1/9 hepatocellular carcinomas were enriched for plasmin. The combined data suggest that the hepatocyte growth factor and plasmin systems tend to be operative in hepatocellular carcinoma and cirrhotic liver, more than fibrolamellar hepatocellular carcinoma. Furthermore, matrix turnover appears to be a more prominent feature of fibrolamellar hepatocellular carcinoma. These findings provide insight into the behavioral differences between hepatocellular carcinoma and the fibrolamellar variant.

Proteases in gastrointestinal neoplastic diseases

Cysteine and serine proteases are involved in cancer invasion and metastasis. In the past few years we investigated the tissue levels of these proteases in gastric cancer (GC), gastric precancerous changes (CAG), colorectal cancer (CRC) and the plasma and serum levels of proteases in several gastrointestinal tumours, using ELISA methods. Significantly higher antigen levels were found not only in GC tissue but also in CAG with respect to the levels found normal tissue; with respect to CAG, patients with dysplasia had higher levels than patients without dysplasia. The same findings were obtained in CRC. In general protease levels correlated with the major histomorphological parameters, such as grading and histotype in GC as well as in CRC. Tissue protease levels had a strong prognostic impact in GC, in which UPA was singled out by multivariate analysis as the major prognostic factor, and CRC. The plasma levels of urokinase-type plasminogen activator (UPA) and the serum levels of cathepsin B were significantly increased in patients with gastrointestinal tumours. In conclusions, cysteine and serine proteases may have a part not only in GC and CRC invasion and metastasis, but also in the progression of gastric precancerous changes into cancer. They are strong prognostic factors in GC and CRC. These proteases may also have a role as tumour markers in the early diagnosis of gastrointestinal tract tumours.

Role of urokinase plasminogen activator receptor in thrombospondin 1-mediated tumor cell invasion

We previously showed that thrombospondin 1 (TSP-1) upregulates the plasminogen/plasmin system and promotes breast tumor cell invasion. Preliminary data from our laboratory using neutralizing antibodies suggested that the upregulation in breast tumor cell invasion seen in response to TSP-1 involved the urokinase plasminogen activator receptor (uPAR). To confirm these findings in MDA-MB-231 breast cancer cells, we developed three other strategies to study the role of uPAR in tumor cell adhesion and TSP-1-mediated tumor cell invasion: (a) enzymatic cleavage of uPAR with glycosylphosphatidylinositol-specific phospholipase C; (b) inhibition at the mRNA level with a uPAR antisense construct (cells named LKAS-MDA); (c) inhibition of plasminogen binding with the lysine analogue epsilon-aminocaproic acid. Adhesion to laminin and type I and type IV collagen with and without the addition of epsilon-aminocaproic acid was studied. Tumor cell invasion was studied in a modified Boyden chamber collagen invasion assay. Antisense uPAR inhibition decreased uPAR expression by 48-66% and cell-associated urokinase plasminogen activator (uPA) by 30-68%. Additionally, antisense uPAR inhibition induced a 68-70% reduction in uPA and plasmin activities. Antisense uPAR transfection increased tumor cell adhesion by 46-53%. A similar effect was observed in epsilon-aminocaproic acid-treated MDA-MB-231 cells. TSP-1-mediated tumor cell invasion was almost completely inhibited by either antisense uPAR inhibition or treatment with phospholipase C or epsilon-aminocaproic acid. We conclude that uPAR plays a crucial role in the regulation of tumor cell adhesion and TSP-1-mediated tumor cell invasion.

Persistent activation of mitogen-activated protein kinases p42 and p44 and ets-2 phosphorylation in response to colony-stimulating factor 1/c-fms signaling

An antibody that specifically recognized phosphothreonine 72 in ets-2 was used to determine the phosphorylation status of endogenous ets-2 in response to colony-stimulating factor 1 (CSF-1)/c-fms signaling. Phosphorylation of ets-2 was detected in primary macrophages, cells that normally express c-fms, and in fibroblasts engineered to express human c-fms. In the former cells, ets-2 was a CSF-1 immediate-early response gene, and phosphorylated ets-2 was detected after 2 to 4 h, coincident with expression of ets-2 protein. In fibroblasts, ets-2 was constitutively expressed and rapidly became phosphorylated in response to CSF-1. In both cell systems, ets-2 phosphorylation was persistent, with maximal phosphorylation detected 8 to 24 h after CSF-1 stimulation, and was correlated with activation of the CSF-1 target urokinase plasminogen activator (uPA) gene. Kinase assays that used recombinant ets-2 protein as a substrate demonstrated that mitogen-activated protein (MAP) kinases p42 and p44 were constitutively activated in both cell types in response to CSF-1. Immune depletion experiments and the use of the MAP kinase kinase inhibitor PD98059 indicate that these two MAP kinases are the major ets-2 kinases activated in response to CSF-1/c-fms signaling. In the macrophage cell line RAW264, conditional expression of raf kinase induced ets-2 expression and phosphorylation, as well as uPA mRNA expression. Transient assays mapped ets/AP-1 response elements as critical for basal and CSF-1-stimulated uPA reporter gene activity. These results indicate that persistent activation of the raf/MAP kinase pathway by CSF-1 is necessary for both ets-2 expression and posttranslational activation in macrophages.

TSG-6: an IL-1/TNF-inducible protein with anti-inflammatory activity

The pro-inflammatory cytokines IL-1 and TNF-alpha are primary mediators of the acute phase response, the complex reaction of the mammalian organism to infection and injury. Among the genes activated by TNF-alpha and IL-1 in a variety of cells is TNF-stimulated gene 6 (TSG-6). The TSG-6 cDNA encodes a secreted 35 kDa glycoprotein which is abundant in synovial fluids of patients with various forms of arthritis and detectable in serum of patients with different inflammatory or autoimmune disorders. TSG-6 protein consists of two structural domains: a hyaluronan-binding link module, the characteristic domain of the hyaladherin family of proteins, and a C-terminal CUB domain, present in a variety of diverse proteins. TSG-6 forms a stable complex with components of the plasma protein inter-alpha-inhibitor (I[alpha]I), a Kunitz-type serine protease inhibitor. TSG-6 and I(alpha)I synergize to inhibit plasmin, a serine protease involved in the activation of matrix metalloproteinases which are part of the proteolytic cascade associated with inflammation. Recombinant human TSG-6 protein exerts a potent anti-inflammatory effect in a murine model of acute inflammation. Modulation of the proteolytic network associated with inflammatory processes may be a mechanism whereby TSG-6, in cooperation with I(alpha)I, inhibits inflammation. Activation of the TSG-6 gene by pro-inflammatory cytokines, presence of TSG-6 protein in inflammatory lesions and its anti-inflammatory effect suggest a role for TSG-6 in a negative feed-back control of the inflammatory response.

The metastatic phenotype--prognostic implications

Strong efforts are being made in order to better understand the molecular mechanisms underlying cancer dissemination. We have attempted to summarise some of the findings in this area. A large number of differences in gene expression have been described in metastatic and non-metastatic cells. In the mouse B16 melanoma system, more than 50 different markers have been described. It is likely that many of these differences reflect the same genetic alteration (i.e. a mutation in a regulatory gene alters the expression of a set of co-regulated target genes). One could argue that it is more effective to study mutations in regulatory as opposed to expression of down-stream target genes. However, we feel that proto-oncogenes are less suitable as markers compared to target genes, since it is difficult to screen for mutations at multiple levels in regulatory pathways. In contrast, measuring the expression of a small number of target genes (i.e. one of the targets in Fig. 1), the expression of which are stimulated by upstream regulators, is accomplished more easily. It is anticipated that the future of optimised panels of independent markers will sharpen cancer diagnosis and lead to individualised therapy.

Antithrombotic and fibrinolytic factors. A review

Excessive or nonphysiologic thrombogenesis and fibrinolysis accompanies many diseases. Several specific proteins involved in the physiologic regulation and maintenance of blood in a fluid state are reviewed in this article. Assays for these proteins or evidence of their function (antithrombin III, protein C, protein S, plasminogen/plasmin, tissue plasminogen activator, plasminogen activator inhibitor I, fibrinogen/fibrin degradation products, and thrombin/antithrombin complexes) are described. Principles, general methodology, and application in veterinary medicine are discussed. Although most of the investigative work and knowledge concerning these proteins and assays has been in human beings, their use and application in veterinary medicine is becoming more available in research laboratories at referral centers and some larger commercial veterinary laboratories. Use and interpretation of these assays will help clinicians and researchers better understand pathophysiologic processes occurring in various diseases associated with thrombogenesis and excessive fibrinolysis.

Plasminogen activators in oesophageal carcinoma

The expression of components of the plasminogen activator system was investigated in patients with oesophageal carcinoma. Tumour and normal mucosa were obtained from resected oesophageal carcinomas and antigens were measured by enzyme-linked immunosorbent assay. Median levels of urokinase plasminogen activator (uPA) and the uPA receptor were higher in carcinoma than in matched normal mucosa (squamous cell carcinoma: uPA 4.05 versus 0.66 ng antigen per mg protein, uPA receptor 1.95 versus 0.50 ng/mg, n = 10, P < 0.05; adenocarcinoma: uPA 2.16 versus 0.61 ng/mg, uPA receptor 2.01 versus 0.49 ng/mg, n = 8, P < 0.05). Tissue plasminogen activator (tPA) level was lower than control values in squamous cell carcinoma but not in adenocarcinoma (1.97 versus 4.70 ng/mg, P < 0.05). There was no difference in plasminogen activator inhibitor (PAI) 1 level between carcinoma and normal mucosa. The PAI-2 level was lower than that in normals in adenocarcinoma only (6.0 versus 64.77 ng/mg, P < 0.05). These data support the hypothesis that membrane-bound uPA has a role in the breakdown of extracellular matrix in invasive oesophageal carcinoma.