Enhancement of in vitro tumor-cell transcellular migration by tumor-cell-secreted endothelial-cell-retraction factor

To investigate the factors affecting endothelial-cell retraction, we have studied the interaction of tumor cells with endothelial cells in 2 human pancreatic cancer cell lines, PSN-1 and MiaPaca-2. The extent of endothelial-cell retraction measured by the amount of intercellular junctional transport of FITC-dextran through an endothelial monolayer was increased by the addition of a conditioned medium (CM) from both cell lines, while CM from PSN-1 cells was 2 to 3 times more potent than that from MiaPaca-2 cells. After the treatment of endothelial monolayer with CM of PSN-1 cells, the ability of both PSN-1 cells and MiaPaca cells to adhere to or invade the monolayer increased. The addition of CM from PSN-1 cells did not affect the growth rate of either the endothelial or the tumor cells. The activity in the CM was heat-stable and bound to heparin-Sepharose, but was inactivated when treated by 0.5% trypsin. Protease inhibitors did not influence the activity. Pre-treatment of PSN-1 cells by an inhibitor of protein synthesis, cycloheximide, or of protein processing, benzyl-N-acetyl-alpha-D-galactosaminide, reduced endothelial-cell-retraction activity in the CM. The active substance in the CM fractionated in the molecular-weight range of 10,000 to 50,000. These results suggest that PSN-1 cells produce and secrete (a) soluble factor(s) that can induce endothelial-cell retraction, thus facilitating tumor-cell invasion.