Plasminogen Activator Inhibitor-1 (PAI-1) Expression by Cultured Adenocarcinoma Cells

PAI-1 (plasminogen activator inhibitor-1) and its target protein uPA (urokinase plasminogen activator) are biomarkers used to manage therapy of cancer patients. High PAI-1 and uPA levels measured by ELISA in tumor biopsies are clinically-proven biomarkers of an invasive, metastatic phenotype in breast cancer. Prognostic biomarkers such as PAI-1 and uPA help to select the best treatment modality for each patient. PAI-1 and uPA are under study as biomarkers in other forms of cancer including oral cancer. Objectives: Determine whether PAI-1 levels are correlated with uPA levels in cultures of fibroblasts and three adenocarcinoma clonal cell lines that differ in metastatic potential in vivo. Methods: Secreted PAI-1 and uPA were measured by ELISA in serum-free conditioned media. Results: PAI-1 levels were not significantly different in media from normal mammary fibroblasts, non-metastatic MTC cells, or low metastatic potential MTLn2 cells (17±9, 5±2, 20±9 ng/mg protein), but PAI-1 was lower in media from highly-metastatic MTLn3 cells (0.9±0.4 ng/mg). In contrast, uPA levels were not significantly different in media from MTC and MTLn2 cells (22±7 and 10±4 ng/mg), but uPA was much higher in media from MTLn3 cells (193±38 ng/mg). uPA was not detected in fibroblast media. Conclusions: PAI-1 and uPA did not increase together in conditioned media from cultured adenocarcinoma cells, in contrast to results reported for tumor tissue. Instead, PAI-1 was lowest and uPA was highest in media from highly metastatic cells. The results suggest that the high levels of PAI-1 found in tumor tissue may be produced by stromal cells, including fibroblasts, endothelial cells, and inflammatory cells, rather than by cancer cells.

Supported by the UTHSC Dental Alumni Endowment Fund.