Abstract
We have examined the influence of fibroblasts on the invasive and migratory potential of highly metastatic melanoma B16‐BL6 and weakly metastatic B16‐FI cells in vitro. Co‐culture of B16‐BL6 cells with a fibroblast monolayer without cellular contact in a Transwell chamber more effectively induced tumor‐cell invasion into Matrigel basement membrane than co‐culture of B16‐FI cells with a fibroblast monolayer. The activity was closely correlated with the chemotactic migration of tumor cells toward the fibroblast monolayer. We also found that the conditioned medium (CM) from the co‐culture of fibroblasts with B16‐BL6 cells without cellular contact, i.e., CM (B16‐BL6/fibroblast), rather than from co‐culture with B16‐FI cells, could potentially promote the migration of tumor cells of both types. Tumor cells did not chemotactically migrate to the CM (B16‐BL6), CM (B16‐FI) or CM (fibroblast). Antibodies against TGF‐β1 or FN almost completely abolished the chemotactic migration of B16‐BL6 cells to the CM (B16‐BL6/fibroblast) or CM (TGF‐β1 ‐treated fibroblast) when these antibodies were c‐incubated with fibroblasts and either B16‐BL6 or TGF‐β1. In contrast, the anti‐EGF antibody did not show any inhibitory effects. Analysis of amounts of TGF‐β1 or FN in various CM using ELISA plates, and using their specific antibodies, revealed that the concentration of TGF‐β1 in the CM (B16‐BL6) was slightly higher than in the CM (B16‐FI), and the amount of FN in the CM (B16‐BL6/fibroblast) was twice as high as in the CM (B16‐FI /fibroblast). These results suggest that TGF‐β1 released from B16‐BL6 cells can stimulate fibroblasts to produce FN; consequently, the tumor cells were able to chemotactically migrate toward the released FN, and the differences in invasive and migratory activities towards fibroblasts in B16‐BL6 and B16‐FI cells may in part be due to the amounts of TGF‐β1 from tumor cells and of FN from TGF‐β1 ‐stimulated fibroblasts.