FOXO3 and hepatocellular carcinoma: In this study, we demonstrates that FOXO3a functions as a growth factor in serum-deprived HCC cells and serotonin promotes the proliferation of serum-deprived HCC cells via upregulation of FOXO3a, in the presence of sufficient levels of the serotonin receptor 5-HT2BR. Knockdown of FOXO3a enhanced the sensitivity of HCC cells to serum withdraw and inhibited cell growth.