Invasion by esophageal cancer cells: functional contribution of the urokinase plasminogen activation system, and inhibition by antisense oligonucleotides to urokinase or urokinase receptor

Early metastasis contributes to the very poor prognosis of esophageal carci noma. The recent immunohistochemical finding that invasive esophageal carci nomas express elevated levels of urokinase (uPA) and urokinase receptor (uP A-R) in vivo suggest that the plasminogen activation system may contribute to metastasis in esophageal cancer. The aim of our study was to functionall y investigate, at the molecular level, the relative contribution of uPA and uPA-R to the invasiveness of esophageal cancer cells in vitro. The three e sophageal cancer cell lines, OC1-3, generated in our laboratory, were analy zed for uPA and uPA-R expression by RT-PCR, immunoenzymatic staining, and q uantitative ELISA. Invasiveness of all cell lines was quantified as percent age cellular invasiveness in a standardized Matrigel in vitro assay. OC1 an d OC3, which were found to coexpress both uPA and uPA-R, displayed stronger invasiveness (44% and 32.5% respectively) relative to OC2 (19%) which expr essed uPA-R but was negative for uPA. Transfection of OC2 cells with the uP A cDNA resulted in two variants, OC2. uPA1 and OC2. uPA2, stably expressing functional uPA. Both transfectants exhibited enhanced invasiveness (60% an d 50% respectively) relative to the parent uPA-negative OC2 cells (19%). An tisense oligonucleotide inhibition of either uPA or uPA-R expression result ed in a similar, marked reduction in invasiveness of esophageal tumor cells which normally coexpress both molecules (OC1, OC3 and the uPA-expressing O C2-transfectant clones). Neither antisense treatment altered the basal inva siveness of OC2, which expresses uPA-R but not uPA. In conclusion, coexpres sion of uPA with its receptor, uPA-R, is required for functional involvemen t of the urokinase system in invasion by esophageal carcinoma cells. Our re sults suggest that these synergistic mediators of invasiveness are quantita tively major contributors to the invasiveness of esophageal carcinoma.