DOWN-REGULATION OF FOCAL ADHESION KINASE, PP125(FAK), IN ENDOTHELIAL-CELL RETRACTION DURING TUMOR-CELL INVASION

Although endothelial cell retraction is required before tumor cell inv asion, its molecular mechanism still remains obscure. We previously de monstrated that conditioned medium (CRI) derived from a human pancreat ic cancer cell line, PSN-1, induced endothelial cell retraction and fa cilitated tumor cell invasion, To investigate the molecular change of events in the transduction of extracellular signals during endothelial cell retraction, we examined the effect of the CM derived from PSN-1 cells on the tyrosine phosphorylation in endothelial cells, Immunoblot analyses revealed that the PSN-1 CM decreased tyrosine phosphorylatio n of a 120-130 kD protein, and induced the concomitant down-regulation of focal adhesion kinase, pp125(FAk), during endothelial cell retract ion in time-and dose-dependent fashions, These changes preceded endoth elial cell retraction and were reversible after removal of the CM. Fur ther quantitative densitometric analyses demonstrated that the extent of decrease in tyrosine phosphorylated 120-130 kD protein during the e ndothelial cell retraction was likely to be proportional to that of th e down-regulation of pp125(FAK). A tyrosine phosphorylated 120-130 kD protein immunoprecipitated by anti-phosphotyrosine antibody immunoreac ted with anti-pp125(FAk) antibody, These results suggested that decrea sed amount of a tyrosine phosphorylated 120-130 kD protein probably du e to the down-regulation of pp125(FAK) might be associated with the si gnal transduction pathway in the endothelial cells during their retrac tion, Furthermore, these Endings were also observed in the Chi from an other four human cancer cell lines, suggesting the down-regulation of pp125(FAK) in endothelial cells during tumor cell invasion. (C) 1998 L ippincott-Raven Publishers.