ECRG2 inhibits cancer cell migration, invasion and metastasis through the down-regulation of uPA/plasmin activity

The esophageal cancer-related gene 2 (ECRG2) is a novel gene that shows sequence similarity to KAZAL-type serine protease inhibitor. In this study, the migration and invasion of PG cancer cells were inhibited by ectopic expression of ECRG2 in vitro, and metastases decreased after injecting PG/pcDNA3.1-ECRG2 cells into the tail veins of nude mice. Control mice were injected with PG/pcDNA3.1 cells. To test the hypothesis that ECRG2 interacts with proteases and inactivates extracellular matrix degradation, binding affinity and co-immunoprecipitation experiments were performed using serum-free conditioned medium. The results showed that ECRG2 bound to two species of urokinase-type plasminogen activator (uPA) with molecular weights of 55 and 33 kDa. Furthermore, analysis of the uPA/plasmin activity showed that expression of ECRG2 reduced proteolysis of the plasmin substrate D-Val-Phe-Lys-p-nitroanilide, which was seen by a decrease of absorbance at 405 nm. Taken together, these results suggested that ECRG2 inhibits aggressiveness of cancer cell, possibly through the down-regulation of uPA/plasmin activity.