GlcNAcylation of a histone methyltransferase in retinoic-acid-induced granulopoiesis

The post-translational modifications of histone tails generate a ‘histone code’ that defines local and global chromatin states 1 . The resultant regulation of gene function is thought to govern cell fate, proliferation and differentiation 2 . Reversible histone modifications such as methylation are under mutual controls to organize chromosomal events 3 , 4 . Among the histone modifications, methylation of specific lysine and arginine residues seems to be critical for chromatin configuration and control of gene expression 5 . Methylation of histone H3 lysine 4 (H3K4) changes chromatin into a transcriptionally active state 6 . Reversible modification of proteins by β- N -acetylglucosamine ( O -GlcNAc) in response to serum glucose levels regulates diverse cellular processes 7 , 8 , 9 . However, the epigenetic impact of protein GlcNAcylation is unknown. Here we report that nuclear GlcNAcylation of a histone lysine methyltransferase (HKMT), MLL5, by O -GlcNAc transferase facilitates retinoic-acid-induced granulopoiesis in human HL60 promyelocytes through methylation of H3K4. MLL5 is biochemically identified in a GlcNAcylation-dependent multi-subunit complex associating with nuclear retinoic acid receptor RARα (also known as RARA), serving as a mono- and di-methyl transferase to H3K4. GlcNAcylation at Thr440 in the MLL5 SET domain evokes its H3K4 HKMT activity and co-activates RARα in target gene promoters. Increased nuclear GlcNAcylation by means of O -GlcNAc transferase potentiates retinoic-acid-induced HL60 granulopoiesis and restores the retinoic acid response in the retinoic-acid-resistant HL60-R2 cell line. Thus, nuclear MLL5 GlcNAcylation triggers cell lineage determination of HL60 through activation of its HKMT activity.