The plasminogen activator and matrix metalloproteinase systems in colorectal cancer: relationship to tumour pathology
Introduction
Extracellular matrix (ECM) degradation by proteinases occurs in both normal and pathological processes. In cancer, ECM degradation occurs at several stages of the metastatic cascade including local invasion, angiogenesis and extravasation. The proteinase systems primarily responsible for ECM degradation in vivo are matrix metalloproteinase (MMPs) and plasminogen activator (PA) systems; these proteinases have the combined ability to break down all ECM components.
The matrix metalloproteinase system consists of at least 20 human MMPs that are often divided into 5 groups based on their substrate specificity; gelatinases, collagenases, stromelysins, membrane type MMPs and other less well characterised MMPs 1, 2, 3 Each MMP breaks down several ECM components and therefore normally MMPs are tightly regulated. Levels of regulation include their activation, the presence of specific tissue inhibitors of metalloproteinases (TIMPs) and at the level of gene expression. The members and properties of the MMP system have been extensively reviewed 1, 2, 3. The plasminogen activator system (PAS) consists of two plasminogen activators (PAs), urokinase (uPA) and tissue type (tPA), which as their names suggest, activate plasminogen to the active serine proteinase plasmin. Plasmin can degrade ECM components directly, e.g. fibronectin and proteoglycans or indirectly by activating other proteinases, e.g. MMP-3. The other PAS components are a receptor for uPA (uPAR), which is thought to focus proteolysis in vivo and two plasminogen activator inhibitors PAI-1 and PAI-2. The PAS has also been reviewed elsewhere 4, 5.
Although many studies have determined the expression and involvement of various proteinases in colorectal and other cancers, the majority have involved small patient numbers 6, 7, 8, 9 and/or studied individuals 6, 9, 10, 11, 12, 13, 14, or a small number of proteinases and their inhibitors. 8, 9, 15, 16, 17, 18 No previous study has determined the detailed expression of two proteinase systems in colorectal cancer and related expression to tumour pathology. Therefore, the aim of our study was to determine the levels of proteinases and inhibitors from the MMP (MMP-1, 2, 3, 9; TIMP-1,-2) and PA (uPA, tPA, uPAR, PAI-1, PAI-2) proteinase systems in 101 paired colorectal tumour and normal tissue samples. The secondary aim was to determine whether a correlation existed between the tumour levels of each factor and the tumour pathology.
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Patient and tissue samples
101 paired colorectal tumour and normal mucosal tissue samples (taken at a site 10 cm or more from the primary tumour) were collected immediately after surgical resection (April 1998–September 2001). Each sample was finely diced with a scalpel, homogenised (Polytron PT 2,100; Kinematica) in phosphate-buffered saline (PBS) for 5 min and centrifuged for 15 min at 5000 rpm. The homogenate was pipetted off and stored at −80 °C until analysis. The total protein concentration of each tissue sample
Results
Of the 101 patients, there were 35 females and 66 males and their median age was 69 years with a range from 25 to 93 years old (males 70.5 years (34–86 years) and females 68 years (25–93 years)).
The pathology of the excised tumour was five adenomas, 19 Dukes’ A tumours, 36 Dukes’ B, 38 Dukes’ C, and 3 patients had distant metastatic disease (‘Dukes’ D'). For the 96 malignant tumours; 18 were described as being well differentiated, 63 moderately differentiated and 14 poorly differentiated; 25
Discussion
Several previous studies have determined the presence of individual proteinases/proteinase systems in colorectal and other human cancers, but only two studies have determined the simultaneous expression of components of both the MMP and PA proteinase systems in colorectal cancer. Saito and colleagues determined immunohistochemical staining of uPAR and MMP-9, and Inuzuka determined uPA, MMP-3 and MMP-9 expression. 17, 23 Therefore to our knowledge, this is the first study to determine the
Acknowledgements
We should like to thank Messrs Tabaqchali, Rosenberg and Hennessy of the University Hospital of North Tees for giving us permission to study patients in their care. We are also grateful to Drs Rettman, Hoffman and Geddy and staff in the Department of Pathology, University Hospital of North Tees for their histological data.
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