Fig. 3. BMP-9 binds to endogenous receptors in non-endothelial cells. (A-C) Autoradiography of crosslinked complexes of [¹²⁵I]BMP-9 with cell surface receptors in C2C12 myoblasts (A), XTH-1 breast cancer cells (B), and T98G glioblastoma cells (C). Ligand-receptor complexes were immunoprecipitated with specific antisera as indicated in the figure and subjected to SDS-PAGE. BMP-9 binds to ALK2 in all cell lines, to ALK1 in glioblastoma cells and to endoglin in breast cancer and glioblastoma cells.