Dataset Information

Functional Proteomic Analysis of Repressive Histone Methyltransferase Complexes Reveals ZNF518B as a G9A Regulator.

ABSTRACT: Cell-type specific gene silencing by histone H3 lysine 27 and lysine 9 methyltransferase complexes PRC2 and G9A-GLP is crucial both during development and to maintain cell identity. Although studying their interaction partners has yielded valuable insight into their functions, how these factors are regulated on a network level remains incompletely understood. Here, we present a new approach that combines quantitative interaction proteomics with global chromatin profiling to functionally characterize repressive chromatin modifying protein complexes in embryonic stem cells. We define binding stoichiometries of 9 new and 12 known interaction partners of PRC2 and 10 known and 29 new interaction partners of G9A-GLP, respectively. We demonstrate that PRC2 and G9A-GLP interact physically and share several interaction partners, including the zinc finger proteins ZNF518A and ZNF518B. Using global chromatin profiling by targeted mass spectrometry, we discover that even sub-stoichiometric binding partners such as ZNF518B can positively regulate global H3K9me2 levels. Biochemical analysis reveals that ZNF518B directly interacts with EZH2 and G9A. Our systematic analysis suggests that ZNF518B may mediate the structural association between PRC2 and G9A-GLP histone methyltransferases and additionally regulates the activity of G9A-GLP.

SUBMITTER: Maier VK

PROVIDER: S-EPMC4458711 | biostudies-literature | 2015 Jun

REPOSITORIES: biostudies-literature

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Functional Proteomic Analysis of Repressive Histone Methyltransferase Complexes Reveals ZNF518B as a G9A Regulator.

Maier Verena K VK Feeney Caitlin M CM Taylor Jordan E JE Creech Amanda L AL Qiao Jana W JW Szanto Attila A Das Partha P PP Chevrier Nicholas N Cifuentes-Rojas Catherine C Orkin Stuart H SH Carr Steven A SA Jaffe Jacob D JD Mertins Philipp P Lee Jeannie T JT

Molecular & cellular proteomics : MCP 20150213 6

Cell-type specific gene silencing by histone H3 lysine 27 and lysine 9 methyltransferase complexes PRC2 and G9A-GLP is crucial both during development and to maintain cell identity. Although studying their interaction partners has yielded valuable insight into their functions, how these factors are regulated on a network level remains incompletely understood. Here, we present a new approach that combines quantitative interaction proteomics with global chromatin profiling to functionally characte ...[more]

PMID: 25680957

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Project description:Methylation of lysine 9 (K9) in the N-terminus tail of histone H3 (H3) in chromatin is associated with transcriptionally silenced genes and is mediated by histone methyltransferases. Murine G9a is a 1263 amino acid H3-K9 methyltransferase that possesses characteristic SET domain and ANK repeats. In this paper, we have used a series of green fluorescent protein-tagged deletion constructs to identify two nuclear localization signals (NLS), the first NLS embedded between amino acids 24 and 109 and the second between amino acids 394 and 401 of murine G9a. Our data show that both long and short G9a isoforms were capable of entering the nucleus to methylate chromatin. Full-length or N-terminus-deleted G9a isoforms were also catalytically active enzymes that methylated recombinant H3 or synthetic peptides representing the N-terminus tail of H3. In vitro methylation reactions using N-terminus tail peptides resulted in tri-methylation of K9 that remained processive, even in G9a enzymes that lacked an N-terminus region by deletion. Co-expression of G9a and H3 resulted in di- and tri-methylation of H3-K9, while siRNA-mediated knockdown of G9a in HeLa cells resulted in reduction of global H3-K9 di- and tri-methylation. A recombinant deletion mutant enzyme fused with maltose-binding protein (MBP-G9aDelta634) was used for steady-state kinetic analysis with various substrates and was compared with full-length G9a (G9aFL). Turnover numbers of MBP-G9aDelta634 for various substrates was approximately 3-fold less compared with G9aFL, while their Michaelis constants (K(m)) for recombinant H3 were similar. The K(AdoMet)m for MBP-G9aDelta634 was approximately 2.3-2.65 microM with various substrates. Catalytic efficiencies (kcat/K(m)) for both MBP-G9aDelta634 and G9aFL were similar, suggesting that the N-terminus is not essential for catalysis. Furthermore, mutation of conserved amino acids R1097A, W1103A, Y1120A, Y1138A and R1162A, or the metal binding C1168A in the catalytic region, resulted in catalytically impaired enzymes, thereby confirming the involvement of the C-terminus of G9a in catalysis. Thus, distinct domains modulate nuclear targeting and catalytic functions of G9a.

Dataset Information

Functional Proteomic Analysis of Repressive Histone Methyltransferase Complexes Reveals ZNF518B as a G9A Regulator.

Publications

Functional Proteomic Analysis of Repressive Histone Methyltransferase Complexes Reveals ZNF518B as a G9A Regulator.

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