The NuA4 histone acetyltransferase complex is required for gene regulation, cell cycle progression, and DNA repair. Dissection of the 13-subunit complex reveals that the Eaf7 subunit bridges Eaf5 with Eaf3, a H3K36me3-binding chromodomain protein, and this Eaf5/7/3 trimer is anchored to NuA4 through Eaf5. This trimeric subcomplex represents a functional module, and a large portion exists in a native form outside the NuA4 complex. Gene-specific and genome-wide location analyses indicate that Eaf5/7/3 correlates with transcription activity and is enriched over the coding region. In agreement with a role in transcription elongation, the Eaf5/7/3 trimer interacts with phosphorylated RNA polymerase II and helps its progression. Loss of Eaf5/7/3 partially suppresses intragenic cryptic transcription arising in set2 mutants, supporting a role in nucleosome destabilization. On the other hand, loss of the trimer leads to an increase of replicationindependent histone exchange over the coding region of transcribed genes. Taken together, these results lead to a model where Eaf5/7/3 associates with elongating polymerase to promote the disruption of nucleosomes in its path, but also their refolding in its wake.

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SummaryPOU3F2 is a POU-Homeodomain transcription factor expressed in neurons and melanoma cells. In melanoma lesions, cells expressing high levels of POU3F2 show enhanced invasive and metastatic capacity that can in part be explained by repression of Micropthalmia-associated Transcription Factor (MITF) expression via POU3F2 binding to its promoter. To identify other POU3F2 target genes that may be involved in modulating the properties of melanoma cells, we performed ChIP-chip experiments in 501Mel melanoma cells. 2108 binding loci located in the regulatory regions of 1700 potential target genes were identified. Bioinformatic and experimental assays showed the presence of known POU3F2-binding motifs, but also many AT-rich sequences with only partial similarity to the known motifs at the occupied loci. Functional analysis indicates that POU3F2 regulates the stem cell factor (Kit ligand, Kitl) promoter via a cluster of four closely spaced binding sites located in the proximal promoter. Our results suggest that POU3F2 may regulate the properties of melanoma cells via autocrine KIT ligand signalling.

Cellular processes and homeostasis control in eukaryotic cells is achieved by the action of regulatory proteins such as protein kinase A (PKA). Although the outbound signals from PKA directed to processes such as metabolism, growth, and aging have been well charted, what regulates this conserved regulator remains to be systematically identified to understand how it coordinates biological processes. Using a yeast PKA reporter assay, we identified genes that influence PKA activity by measuring proteinprotein interactions between the regulatory and the two catalytic subunits of the PKA complex in 3,726 yeast genetic-deletion backgrounds grown on two carbon sources. Overall, nearly 500 genes were found to be connected directly or indirectly to PKA regulation, including 80 core regulators, denoting a wide diversity of signals regulating PKA, within and beyond the described upstream linear pathways. PKA regulators span multiple processes, including the antagonistic autophagy and methionine biosynthesis pathways. Our results converge toward mechanisms of PKA posttranslational regulation by lysine acetylation, which is conserved between yeast and humans and that, we show, regulates protein complex formation in mammals and carbohydrate storage and aging in yeast. Taken together, these results show that the extent of PKA input matches with its output, because this kinase receives information from upstream and downstream processes, and highlight how biological processes are interconnected and coordinated by PKA.Ras/cAMP/PKA pathway | acetylation | methionine | autophagy | TOR

e Recognition of histone marks by reader modules is thought to be at the heart of epigenetic mechanisms. These protein domains are considered to function by targeting regulators to chromosomal loci carrying specific histone modifications. This is important for proper gene regulation as well as propagation of epigenetic information. The NuA4 acetyltransferase complex contains two of these reader modules, an H3K4me3-specific plant homeodomain (PHD) within the Yng2 subunit and an H3K36me2/3-specific chromodomain in the Eaf3 subunit. While each domain showed a close functional interaction with the respective histone mark that it recognizes, at the biochemical level, genetic level (as assessed with epistatic miniarray profile screens), and phenotypic level, cells with the combined loss of both readers showed greatly enhanced phenotypes. Chromatin immunoprecipitation coupled with next-generation sequencing experiments demonstrated that the Yng2 PHD specifically directs H4 acetylation near the transcription start site of highly expressed genes, while Eaf3 is important downstream on the body of the genes. Strikingly, the recruitment of the NuA4 complex to these loci was not significantly affected. Furthermore, RNA polymerase II occupancy was decreased only under conditions where both PHD and chromodomains were lost, generally in the second half of the gene coding regions. Altogether, these results argue that methylated histone reader modules in NuA4 are not responsible for its recruitment to the promoter or coding regions but, rather, are required to orient its acetyltransferase catalytic site to the methylated histone 3-bearing nucleosomes in the surrounding chromatin, cooperating to allow proper transition from transcription initiation to elongation. Chromatin is a dynamic nucleoprotein structure that compacts the long DNA molecule into the small nuclear space, simultaneously creating a mechanism to regulate DNA access to machineries implicated in essential nuclear processes, namely, transcription, DNA replication, DNA repair, and meiotic recombination. Modulation of the chromatin structure is highly regulated by four broad classes of nuclear factors: chromatin remodelers, histone chaperones, histone variants, and histone modifiers. These players essentially target nucleosomes, basic units of chromatin consisting of 146 bp of DNA wrapped around an octamer of histone proteins. Histone modifiers catalyze posttranslational modifications (PTM), including acetylation, phosphorylation, and methylation, that can directly affect DNA-histone contacts (e.g., acetylation) and/or create a binding platform for PTM readers (1, 2). These readers correspond to proteins/complexes containing distinct domains/modules that can bind specific modified histone residues. Such motifs include bromodomains that recognize acetylated residues; chromodomains (CHD); PWWP, Tudor, and MBT domains for methylated residues; BRCT, BIR, and 14-3-3 domains for phosphorylated histones; and plant homeodomain (PHD) fingers that can bind different modification...

Conserved from yeast to humans, the NuA4 histone acetyltransferase is a large multisubunit complex essential for cell viability through the regulation of gene expression, genome maintenance, metabolism, and cell fate during development and stress. How the different NuA4 subunits work in concert with one another to perform these diverse functions remains unclear, and addressing this central question requires a comprehensive understanding of NuA4's molecular architecture and subunit organization. We have determined the structure of fully assembled native yeast NuA4 by single-particle electron microscopy. Our data revealed that NuA4 adopts a trilobal overall architecture, with each of the three lobes constituted by one or two functional modules. By performing cross-linking coupled to mass spectrometry analysis and protein interaction studies, we further mapped novel intermolecular interfaces within NuA4. Finally, we combined these new data with other known structural information of NuA4 subunits and subassemblies to construct a multiscale model to illustrate how the different NuA4 subunits and modules are spatially arranged. This model shows that the multiple chromatin reader domains are clustered together around the catalytic core, suggesting that NuA4's multimodular architecture enables it to engage in multivalent interactions with its nucleosome substrate.

Significance Recent proteomic studies have revealed that lysine acetylation is a global and ubiquitous posttranslational modification. However, in the vast majority of cases the lysine acetyltransferases (KATs) responsible for individual modifications remain unknown. Here we present a unique methodology that connects KATs to their substrates. To validate the methodology, we use the yeast KAT nucleosome acetyltransferase of histone H4 (NuA4) and identify both protein interactions and acetylation targets. Importantly, this methodology can be applied to any KAT and should aid in the linking of KATs to their cellular targets.

f MITF-M and PAX3 are proteins central to the establishment and transformation of the melanocyte lineage. They control various cellular mechanisms, including migration and proliferation. BRN2 is a POU domain transcription factor expressed in melanoma cell lines and is involved in proliferation and invasion, at least in part by regulating the expression of MITF-M and PAX3. The T361 and S362 residues of BRN2, both in the POU domain, are conserved throughout the POU protein family and are targets for phosphorylation, but their roles in vivo remain unknown. To examine the role of this phosphorylation, we generated mutant BRN2 in which these two residues were replaced with alanines (BRN2TS¡BRN2AA). When expressed in melanocytes in vitro or in the melanocyte lineage in transgenic mice, BRN2TS induced proliferation and repressed migration, whereas BRN2AA repressed both proliferation and migration. BRN2TS and BRN2AA bound and repressed the MITF-M promoter, whereas PAX3 transcription was induced by BRN2TS but repressed by BRN2AA. Expression of the BRN2AA transgene in a Mitf heterozygous background and in a Pax3 mutant background enhanced the coat color phenotype. Our findings show that melanocyte migration and proliferation are controlled both through the regulation of PAX3 by nonphosphorylated BRN2 and through the regulation of MITF-M by the overall BRN2 level. POU family transcription factors are expressed in a wide variety of cell types. They are involved in diverse functions, such as cell type determination, proliferation, renewal, invasion, and migration. The members of the POU domain family of transcription factors share the POU DNA-binding domain (DBD) called the POU domain. The POU domain consists of two DNA-binding units (POUs for POU specific and POUh for POU homeodomain) connected by a flexible linker (3). This molecular structure allows POU proteins to recognize a large set of DNA targets and also to bind different transactivator proteins, depending on the spacing and the positioning adopted by the two subdomains of the POU DBD (50).POU transcription factor function can be modulated by posttranslational modifications, including sumoylation, oxidation, ubiquitinylation, glycosylation, and particularly phosphorylation (5,20,32). Two residues in the DBD domain, a threonine and a serine, are conserved in all mammalian POU domains (see Table S1 at http://umr3347.curie.fr/fr/quipes-de -recherche/d-veloppement-normal-et-pathologie-des-m-lanocytes /differential-function-non-pho). These serine and/or threonine residues in Oct-1, Pit-1, and BRN2 are phosphorylated by protein kinase A (PKA) (31,46,55).Several lines of evidence suggest that PKA is involved in melanocyte lineage proliferation. Forskolin stimulates the proliferation of human melanocytes (54). Proliferation of human melanocytes is induced in a dose-dependent manner by alphamelanocyte-stimulating hormone (1,57,58). Dibutyryl adenosine cyclic AMP induces the proliferation of epidermal melanocytes in culture (29). PKA phosphorylates claudin-1 and allows its tr...