SMAD6 and hepatocellular carcinoma: Conversely, the decreased levels of p‐Smad1/5/8 and Smad6 following the increased level of p‐Smad3 were abolished in the HUVECs pre‐incubated with BMP9‐overexpressing HBV‐infected hepatoma cells (Figure 5C, Supporting Information Figure S4A).