Removal of the propeptide is required for elevated tumor growth and lung colonization of EpC40 cells. (A) Schematic drawing of the interleukin-like epithelial-to-mesenchymal transition inducer (ILEI) protein and ILEI constructs used in this study. wt, Wild type. (B) ILEI and FLAG Western blot analysis of whole-cell lysates and conditioned medium (CM) of EpC40 cells overexpressing the ILEI constructs listed in (A). (C) and (D) Primary tumor growth capacity of EpC40 cells overexpressing empty vector or different ILEI forms was determined upon injection into the mammary gland fat pads of female nude mice (n = 5 per group). (C) Tumor growth rate by calculated tumor volume 41 days after injection (±SEM). (D) Tumor mass 41 days after injection (±SEM). (E) and (F) Lung colonization capacity of EpC40 cells overexpressing empty vector or different ILEI forms was determined upon intravenous injection of recultivated cells of mammary tumors into female nude mice (n = 5 per group). Lungs were dissected and analyzed for metastases 45 days after injection. (E) Hematoxylin and eosin–stained histological sections of representative lungs of each group. Scale bar, 2 mm. (F) The percentage of lung metastatic area of each group (±SEM).