mAM facilitates conversion by ESET of dimethyl to trimethyl lysine 9 of histone H3 to cause transcriptional repression.
ABSTRACT Methylation of histone tails plays an important role in chromatin structure and function. Previously, we reported that ESET/SETDB1 is a histone methyltransferase (HMTase). Here, we show that SETDB1 tightly associates with the human homolog of mAM, a murine ATFa-associated factor. Although recombinant ESET can methylate lysine 9 of histone H3 (H3-K9), its activity is severely compromised when compared to that of the ESET/mAM complex. mAM stimulates ESET enzymatic activity by increasing the Vmax and decreasing the Km. Importantly, mAM facilitates the ESET-dependent conversion of dimethyl H3-K9 to the trimethyl state both in vitro and in vivo. Chromatin-based transcription and ChIP analyses demonstrate that mAM enhances ESET-mediated transcriptional repression in a SAM-dependent manner, and this repression correlates with H3-K9 trimethylation at the promoter. Thus, our studies establish that promoter H3-K9 trimethylation is the cause of transcriptional repression and that mAM/hAM facilitates conversion of H3-K9 dimethyl to trimethyl by ESET/SETDB1.
SourceAvailable from: Tuempong Wongtawan01/2010, Degree: PhD, Supervisor: Ian Wilmut, Sari Pennings, Jane Taylor
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ABSTRACT: Retrotransposition of endogenous retroviruses (ERVs) poses a substantial threat to ge-nome stability. Transcriptional silencing of a subset of these parasitic elements in early mouse embryonic and germ cell development is dependent upon the lysine methyltransfer-ase SETDB1, which deposits H3K9 trimethylation (H3K9me3) and the co-repressor KAP1, which binds SETDB1 when SUMOylated. Here we identified the transcription co-factor hnRNP K as a novel binding partner of the SETDB1/KAP1 complex in mouse embryonic stem cells (mESCs) and show that hnRNP K is required for ERV silencing. RNAi-mediated knockdown of hnRNP K led to depletion of H3K9me3 at ERVs, concomitant with de-repres-sion of proviral reporter constructs and specific ERV subfamilies, as well as a cohort of germline-specific genes directly targeted by SETDB1. While hnRNP K recruitment to ERVs is dependent upon KAP1, SETDB1 binding at these elements requires hnRNP K. Furthermore, an intact SUMO conjugation pathway is necessary for SETDB1 recruitment to proviral chromatin and depletion of hnRNP K resulted in reduced SUMOylation at ERVs. Taken together, these findings reveal a novel regulatory hierarchy governing SETDB1 re-cruitment and in turn, transcriptional silencing in mESCs.PLoS Genetics 01/2015; DOI:10.1371/journal.pgen.1004933 · 8.52 Impact Factor
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ABSTRACT: Significance : Methylation of histone H3 on lysine 9 and 27 (H3K9 and H3K27) are two epigenetic modifications that have been linked to several crucial biological processes, among which transcriptional silencing and cell differentiation. Recent Advances : Deposition of these marks is catalyzed by H3K9 lysine methyltransferases (KMTs) and Polycomb Repressive Complex 2, respectively. Increasing evidences are emerging in favor of a functional crosstalk between these two major KMT families. Critical Issues: Here, we review the current knowledge on the mechanisms of action and function of these enzymes, with particular emphasis on their interplay in the regulation of chromatin states and biological processes. We outline their crucial roles played in tissue homeostasis, by controlling the fate of embryonic and tissue-specific stem cell, highlighting how their deregulation is often linked to the emergence of a number of malignancies and neurological disorders. Future Directions: Histone methyltransferares are starting to be tested as drug targets. A new generation of highly selective chemical inhibitors is starting to emerge. These hold great promise for a rapid translation of targeting epigenetic drugs into clinical practice for a number of aggressive cancers and neurological disorders.Antioxidants and Redox Signaling 11/2014; DOI:10.1089/ars.2014.6116 · 7.67 Impact Factor