(A) Morphological change in 2H11 endothelial cells from EC to EC-OSB hybrid cells following BMP4 (100 ng/mL) treatment for 48 h. In this and subsequent experiments, 2H11 cells treated for 48 h with BMP4 are designated as EC-OSB hybrid cells. (B) Alkaline phosphatase activity and osteocalcin mRNA levels in 2H11 cells treated as in (A). (C-E) C4-2B4 or PC3-mm2 PCa cells were treated with conditioned medium (CM) from 2H11 or EC-OSB hybrid cells, or directly with BMP4 alone. The effects of these treatments on (C) migration, (D) invasion, and (E) anchorage-independent growth were measured. P values are from Student’s t-test. (F) Graphical summary. BMP4-mediated EC-to-OSB transition generates EC-OSB hybrid cells that secrete factors, which increase the migration, invasion and anchorage-independent growth of PCa cells. BMP4 alone does not elicit these activities in PCa cells.