Co-localization of CD44 and urokinase-type plasminogen activator on the surface of human melanoma cells

Adhesion and proteolysis are basic reactions of tumor growth and metastasis. During these complex processes malignant cells change their adhesion behaviour and proteolytic capacity. Therefore, an extensive characterization of tumor cells is necessary if results of functional assays e.g., tests for tumor cell invasion are to be correlated with the presence of tumor antigens. This paper describes the detection of CD44 variant sequences, urokinase-type plasminogen activator (uPA) and uPA-receptor (uPAR) by immunoluminescence and activity measurements. For these investigations the melanoma cell line IGR 1 was used. The expression of CD44 (v5), uPA and uPAR on the cell surface was shown by indirect labelling with monoclonal antibodies (mAb). The marker enzyme horseradish peroxidase (HRP) of the secondary Ab was used to release luminescence and fluorescence with suitable substrates. The enhanced luminescent assay was superior to fluorescence analysis. uPA-activity in intact cells was examined with the substrates plasminogen, Z-Gly-Gly-Arg-AMC and Z-Lys-SBzl including selective inhibitors. The immunoluminescent assay can be alternatively used with well-tried immunofluorescent methods e.g. flow cytometry, for the detection of cellular cancer markers (1).