Endoglin (ENG), endothelial glycoprotein, also known as CD105, is a coreceptor of the transforming growth factor-β (TGFβ) family signaling complex, which is highly expressed on endothelial cells and plays a key role in angiogenesis. Endoglin contains an RGD tripeptide which is a key recognition structure in cellular adhesion,,suggesting a critical role for endoglin in the binding of endothelial cells to integrins and/or other RGD receptors. As a TGF-beta coreceptor, CD105/Endoglin activates SMAD transcription factors, participating in the TGF-beta/BMP signaling cascade.