HDAC9 and cancer: Histone deacetylases (HDACs) are a family of enzymes that typically deacetylate histone and non-histone substrates to regulate gene transcriptions that are essential for cancer cell proliferation, motility, etc. So far 18 different deacetylases have been reported that can be divided into two major classes of enzymes: Zn2+ dependent (HDAC) or NAD+ dependent (Sirtuins).