Importantly, treatment of EECs with either BMP4 or BMP7 induced phosphorylation of SMAD5 (Figure 4C, left panel), one of the central receptor‐regulated R‐SMAD proteins that act as transcription factors for a broad variety of target genes upon BMP‐receptor interaction.18, 19, 25, 26 As a control, treatment of the hepatocellular carcinoma cell line HepG2 resulted in comparable BMP‐mediated SMAD5 phosphorylation, confirming the results obtained with the primary EEC cultures (Figure 4C, right panel). This evidence concerns the gene SMAD5 and hepatocellular carcinoma.