A Human Protein Complex Homologous to the Drosophila MSL Complex Is Responsible for the Majority of Histone H4 Acetylation at Lysine 16

Abstract

We describe a stable, multisubunit human histone acetyltransferase complex (hMSL) that contains homologs of the Drosophila dosage compensation proteins MOF, MSL1, MSL2, and MSL3. This complex shows strong specificity for histone H4 lysine 16 in chromatin in vitro, and RNA interference-mediated knockdown experiments reveal that it is responsible for the majority of H4 acetylation at lysine 16 in the cell. We also find that hMOF is a component of additional complexes, forming associations with host cell factor 1 and a protein distantly related to MSL1 (hMSL1v1). We find two versions of hMSL3 in the hMSL complex that differ by the presence of the chromodomain. Lastly, we find that reduction in the levels of hMSLs and acetylation of H4 at lysine 16 are correlated with reduced transcription of some genes and with a G 2 /M cell cycle arrest. This is of particular interest given the recent correlation of global loss of acetylation of lysine 16 in histone H4 with tumorigenesis.The dynamic regulation of chromatin structure can be brought about by a complex series of posttranslational modifications to histones, particularly on the amino-terminal histone tails (33,48). Among the lysines that can be acetylated, lysine 16 of histone H4 appears to be uniquely targeted in a number of organisms. Studies of telomeric silencing in Saccharomyces cerevisiae have shown that lysine 16-specific acetyltransferase and deacetylase activities determine the boundaries of silenced chromatin (32, 59). Furthermore, chromatin immunoprecipitation and site-directed mutagenesis in budding yeast clearly indicate that acetylation of H4 lysine 16 has an independent specific function in relation to gene transcription when compared to other histone acetylation sites (16,34). In Drosophila, lysine 16 acetylation is targeted to the hypertranscribed male X chromosome in the process of dosage compensation (8,35). Biochemical analysis of bulk histones in mammalian cells has indicated that most of the monoacetylated H4 is acetylated at lysine 16, as is most of the di-and triacetylated forms, leading to the suggestion that this is the first acetylation mark on H4 or possibly the last to be taken off (61, 69). One rationale for a special role for lysine 16 acetylation is that it is the only known site of acetylation in the basic patch of H4, a region from amino acids 16 to 20 that is implicated in the formation of higher-order chromatin structure (17). Recently, loss of acetylation at lysine 16 of histone H4 has been identified as a common hallmark of human cancer (22).In Drosophila, dosage compensation-the equalization of X-linked gene products in males and females-is achieved by enhancing the transcriptional level of X-linked genes in males.Five genes involved in this process were identified due to male-specific lethality when mutated (4,5,26). These genes are male-specific lethal 1 (msl1), msl2, msl3, maleless (mle), and males-absent on the first (mof). All five gene products form the MSL complex, which harbors histone acetyltransferase (HAT) activity with...

Structural and Biochemical Studies on the Chromo-barrel Domain of Male Specific Lethal 3 (MSL3) Reveal a Binding Preference for Mono- or Dimethyllysine 20 on Histone H4

“…A similar MOF-containing human MSL complex has also been identified, and although it contains homologous hMSL1, hMSL2, and hMSL3 subunits, it does not contain the MLE or RNA components, and has nothing to do with dosage compensation (3,4). However, the human MSL complex does function as a global histone H4K16 acetyltransferase (3)(4)(5).…”

“…However, the human MSL complex does function as a global histone H4K16 acetyltransferase (3)(4)(5). Human MOF (hMOF) and the hMSL proteins also play a role in cell-cycle progression and DNA repair (3)(4)(5).…”

“…The Drosophila and human MSL3 proteins contain a highly conserved N-terminal chromo-barrel domain (CBD) (residues 2-91; 50% identical) plus a conserved C-terminal MRG domain (residues 196 -512 in dMSL3; 25% identical to hMSL3) (3,4,(33)(34)(35). The CBD of Drosophila MSL3 is known to contribute to nucleic acid and nucleosome binding in the Drosophila MSL complex (18 -20), transcriptional up-regulation on the Drosophila male X-chromosome (18), and proper targeting and spreading of the dosage compensation complex in vivo (20).…”

“…MOF, a conserved member of the MYST (Moz, Ysb2, Sas2, Tip60) family of HAT enzymes, functions as the catalytic subunit in a number of distinct HAT complexes that target gene promoters (8), large contiguous domains of chromatin (3,4,14,15), or non-histone proteins such as p53 (5-7). The precise targeting and substrate specificity of MOF relies on the presence of components distinct from the catalytic subunit (3,4,7,8). Specifically, in the MOFcontaining Drosophila male specific lethal (MSL) complex, the MSL3 protein is required for chromatin targeting, nucleosome binding, histone tail substrate recognition, and maximal MOF HAT activity (16 -20).…”

“…Nuclear histone acetyltransferase (HAT) 3 enzymes are found in multiprotein complexes that acetylate specific lysine residues on the N-terminal tails of histone proteins, thereby regulating nucleosome structure, chromatin packaging, and gene expression (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15). MOF, a conserved member of the MYST (Moz, Ysb2, Sas2, Tip60) family of HAT enzymes, functions as the catalytic subunit in a number of distinct HAT complexes that target gene promoters (8), large contiguous domains of chromatin (3,4,14,15), or non-histone proteins such as p53 (5-7).…”