SPECIFIC SEQUENCES OF FIBRONECTIN ACTIVATE THE PROTEIN-KINASE-C SIGNAL-TRANSDUCTION PATHWAY IN INVASIVE BLADDER-CANCER

The mechanism of human bladder cancer cell invasion is not clear, but it appears that extracellular matrix components, such as fibronectin, may be involved. To investigate the role of fibronectin in tumor cell invasion and progression, we used an in vitro invasion assay to define the motility stimulating fragment of fibronectin for invasive human b ladder cancer T24 cells. Using a modified Boyden chamber assay and pur ified fragments of fibronectin, we demonstrated that both the 120 kDa chymotrypsin generated fragment of fibronectin (containing the cell at tachment RGD motif and additional sequences towards the carboxyl-termi nal heparin binding domain), as well as the trypsin generated 60 kDa f ragment of fibronectin (containing the carboxyl-terminal heparin bindi ng domain and additional sequences towards the cell attachment RGD mot if), were able to stimulate the migration of invasive human bladder ca ncer T24 cells. Control fragments containing only the amino-terminal g elatin binding region of fibronectin did not stimulate the motility of the human bladder cancer T24 cells. To determine the molecular mechan ism in which these fragments may stimulate the migration of the T24 ce lls, we assayed for intracellular signal transduction pathway protein kinase C (PKC). We demonstrated that both the 120 kDa and the 60 kDa f ragments were able to stimulate the activation of protein kinase C. No n-motility stimulating fragments of fibronectin were not able to activ ate protein kinase C. We conclude that the PKC signal transduction pat hway may be involved in matrix mediated motility, and suggest that the inhibition of such pathway(s) may alter the malignant phenotype of hu man bladder cancer.