HDAC9 and hepatocellular carcinoma: Upregulation of miR‐22 promotes tumor metastasis by directly down‐regulating members of the TET gene family, which include methylcytosine dioxygenases.[20] Oncomine analysis showed that TET2 is downregulated in two independent HCC libraries (TCGA and Guichard liver libraries) (Figure S4J, Supporting Information); but upon ATRA treatment combined with HDAC inhibitor induced TET2 protein (Figure6A left, B,C).