title: Mammalian ASH1L is a histone methyltransferase that occupies the transcribed region of active genes.
abstract: Histone lysine methylation regulates genomic functions, including gene transcription. Previous reports found various degrees of methylation at H3K4, H3K9, and H4K20 within the transcribed region of active mammalian genes. To identify the enzymes responsible for placing these modifications, we examined ASH1L, the mammalian homolog of the Drosophila melanogaster Trithorax group (TrxG) protein Ash1. Drosophila Ash1 has been reported to methylate H3K4, H3K9, and H4K20 at its target sites. Here we demonstrate that mammalian ASH1L associates with the transcribed region of all active genes examined, including Hox genes. The distribution of ASH1L in transcribed chromatin strongly resembles that of methylated H3K4 but not that of H3K9 or H4K20. Accordingly, the SET domain of ASH1L methylates H3K4 in vitro, and knockdown of ASH1L expression reduced H3K4 trimethylation at HoxA10 in vivo. Notably, prior methylation at H3K9 reduced ASH1L-mediated methylation at H3K4, suggesting cross-regulation among these marks. Drosophila ash1 and trithorax interact genetically, and the mammalian TrxG protein MLL1 and ASH1L display highly similar distributions and substrate specificities. However, by using MLL null cell lines we found that their recruitments occur independently of each other. Collectively, our data suggest that ASH1L occupies most, if not all, active genes and methylates histone H3 in a nonredundant fashion at a subset of genes.
authors.affiliation: Children's Hospital of Philadelphia, Division of Hematology, Philadelphia, Pennsylvania 19104, USA.
authors.forename: Gregory D
authors.initials: GD
authors.lastname: Gregory
authors.forename: Christopher R
authors.initials: CR
authors.lastname: Vakoc
authors.forename: Tanya
authors.initials: T
authors.lastname: Rozovskaia
authors.forename: Xingwu
authors.initials: X
authors.lastname: Zheng
authors.forename: Shetal
authors.initials: S
authors.lastname: Patel
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Nakamura
authors.forename: Eli
authors.initials: E
authors.lastname: Canaani
authors.forename: Gerd A
authors.initials: GA
authors.lastname: Blobel
mesh_terms: D000818:Animals; D001483:Base Sequence; D002843:Chromatin / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D005786:Gene Expression Regulation; D020043:Genes, Essential; D006367:HeLa Cells; D000076983:Histone Methyltransferases; D011495:Histone-Lysine N-Methyltransferase / Q000378:metabolism*; D006657:Histones / Q000378:metabolism; D018398:Homeodomain Proteins / Q000378:metabolism; D006801:Humans; D020014:K562 Cells; D008239:Lysine / Q000378:metabolism; D008322:Mammals / Q000378:metabolism*; D008745:Methylation; D051379:Mice; D051788:Myeloid-Lymphoid Leukemia Protein / Q000378:metabolism; D011485:Protein Binding; D011496:Protein Methyltransferases; D017434:Protein Structure, Tertiary; D014157:Transcription Factors / Q000737:chemistry / Q000378:metabolism*; D014158:Transcription, Genetic
chemical_list: D002843:Chromatin; D004268:DNA-Binding Proteins; D006657:Histones; D018398:Homeodomain Proteins; D014157:Transcription Factors; D051788:Myeloid-Lymphoid Leukemia Protein; D000076983:Histone Methyltransferases; D011496:Protein Methyltransferases; C490911:ASH1L protein, human; C000600280:Ash1l protein, mouse; D011495:Histone-Lysine N-Methyltransferase; D008239:Lysine