Histone demethylase that specifically demethylates 'Lys- 27' of histone H3, thereby playing a central role in histone code. Demethylates trimethylated and dimethylated H3 'Lys-27'. Plays a central role in regulation of posterior development, by regulating HOX gene expression. Involved in inflammatory response by participating in macrophage differentiation in case of inflammation by regulating gene expression and macrophage differentiation. Interacts with TLE1. Component of the MLL4 complex, at least composed of MLL4, ASH2L, RBBP5, WDR5, and KDM6B. By 12-O-tetradecanoylphorbol-13-acetate (TPA) in myeloid leukemia cells. Belongs to the UTX family. 2 isoforms of the human protein are produced by alternative splicing. Note: This description may include information from UniProtKB.