37. A previous study showed that BMP4 promoted proliferation and DNA synthesis of human Sertoli cells via activating Smad1/5 phosphorylation and enhancing the expression of Id2/3 25. Recently, a study revealed that BMP4 enhanced hepatocellular carcinoma proliferation by promoting cell cycle progression through upregulating the expression of Id2 38. In line with these results, the data presented in this study showed that BMP4 promoted the mRNA expression of Id2 in ICP1 cells. Here, BMP4 is linked to hepatocellular carcinoma.