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

Abstract

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 F1TC‐dextran through an endothelial monolayer was increased by the addition of a conditioned medium (CM) from both cell lines, while CM from PSN‐I 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‐I cells by an inhibitor of protein synthesis, cyclohexi‐mide, or of protein processing, benzyl‐N‐acetyl‐a‐D‐galactos‐aminide, 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.