Presence of urokinase plasminogen activator, its inhibitor and receptor in small cell lung cancer and non-small cell lung cancer

Spreading of cancer cells is dependent on the combined action of several proteolytic enzymes, such as serine proteases, comprising the urokinase pathway of plasminogen activation. Previous studies of lung cancer indicate that expression, localization and prognostic impact of the components of the plasminogen activation system differ in the different non-small cell lung cancer (NSCLC) types, whereas the expression of the components in small cell lung cancer (SCLC) has only sparingly been investigated. In the present study we investigate the presence of the components of the plasminogen activation system, and compare the levels of uPA, PAI-1 and uPAR in extracts of NSCLC-tissue and SCLC-tissue. A statistically significant difference, P = 0.037, was found between uPA-levels in NSCLC-patients (n = 75) and SCLC-patients (n = 8), the highest levels being found in NSCLC. No such difference was found for the two other components investigated, although a trend towards increased uPAR-levels was observed in SCLC, P = 0.055. The relationship between the levels of each of the components and other known clinical parameters was also analysed. No relationship was found between any of the components and the clinical parameters. This is the first report of a study using a quantitative method to compare levels of the components of the plasminogen activation system in tissue extracts from the two major lung cancer groups. The study shows that uPA, PAI-1 and uPAR are present in SCLC-tissue, suggesting that the plasminogen activation system could play a role in this type of cancer during invasion. In addition a difference in the levels of the components of the plasminogen activation system in NSCLC and SCLC is found, which could contribute to the differences in biology.