Involvement of fibronectin in the regulation of urokinase production and binding in murine mammary tumor cells

Tumor invasion and metastasis development is a multistep process involving adhesion molecules as well as tumor proteases, It has been reported that tu mor cells lacking fibronectin (FN) expression and engineered to re-express FN showed a marked reduction in metastatic ability. Besides its effects on cell adhesion and migration, FN could be modulating other cellular events a ssociated with the metastatic cascade. To test this hypothesis, we analyzed the production of urokinase-type plasminogen activator (uPA), and its rece ptor (uPAR), 2 molecules involved in the invasive phenotype, in cells overe xpressing RGD wild-type FN (FNwt clones) or RGD-mutated FN (FN RGD-minus cl ones). Secreted uPA activity and antigen were significantly up-regulated in FN-expressing clones, although RGD-minus cells secreted approximately 50% less uPA than the FNwt ones. Interestingly, while control and FN RGD-minus clones were able to readily bind uPA to their surface, FNwt clones exhibite d impaired uPA binding, Furthermore, treatment of the parental cell line as well as the control and FN-expressing clones with exogenous purified FN or RGD peptides induced up-regulation of uPA production and the reduction of uPA membrane binding, which was associated with lower expression of uPAR. T his modulation by FN was found to be dependent on RGD sequence and PI integ rin, These results strongly suggest a novel activity for the multifunctiona l glycoprotein FN regarding the regulation of uPA production as well as the capacity of tumor cells to bind uPA, Int. J, Cancer 82:748-753, 1999, (C) 1999 Wiley-Liss, Inc.