A silencing pathway to induce H3-K9 and H4-K20 trimethylation at constitutive heterochromatin

Abstract

Histone lysine methylation is a central modification to mark functionally distinct chromatin regions. In particular, H3-K9 trimethylation has emerged as a hallmark of pericentric heterochromatin in mammals. Here we show that H4-K20 trimethylation is also focally enriched at pericentric heterochromatin. Intriguingly, H3-K9 trimethylation by the Suv39h HMTases is required for the induction of H4-K20 trimethylation, although the H4 Lys 20 position is not an intrinsic substrate for these enzymes. By using a candidate approach, we identified Suv4-20h1 and Suv4-20h2 as two novel SET domain HMTases that localize to pericentric heterochromatin and specifically act as nucleosomal H4-K20 trimethylating enzymes. Interaction of the Suv4-20h enzymes with HP1 isoforms suggests a sequential mechanism to establish H3-K9 and H4-K20 trimethylation at pericentric heterochromatin. Heterochromatic H4-K20 trimethylation is evolutionarily conserved, and in Drosophila, the Suv4-20 homolog is a novel PEV modifier to regulate position-effect variegation. Together, our data indicate a function for H4-K20 trimethylation in gene silencing and further suggest H3-K9 and H4-K20 trimethylation as important components of a repressive pathway that can index pericentric heterochromatin.[Keywords: Histone code; histone H4 Lys 20; mono-, di-, trimethylation; Suv4-20h HMTases; heterochromatin; combinatorial histone methyl marks] Supplemental material is available at http://www.genesdev.org.

Epigenetic regulation of the human p53 gene promoter by the CTCF transcription factor in transformed cell lines

“…Using immunofluorescence assays, we compared the nuclear distribution of different histone covalent modifications in HeLa and HeLa-kd-CTCF cell lines (Supplementary Figure 4). In HeLa cells we observed an enrichment of the speckled-like pattern of H3K9me3, H3K27me3 and H4K20me3 distribution that could correspond to different heterochromatic genomic regions (Schotta et al, 2004). However, in the CTCF knockdown cellular context, we observed a clear redistribution of heterochromatin foci.…”

H3K9 methylation and RNA interference regulate nucleolar organization and repeated DNA stability

“…Interestingly, loss of the SUV4-20 H4K20 methyltransferase did not produce multiple nucleoli; this result demonstrates that H3K9 methylation is the primary histone modification responsible for maintaining repeated DNA integrity, and not H4K20 trimethylation by SUV4-20, which requires H3K9me2 (ref. 31). In addition, Drosophila sir2 mutants did not contain multiple nucleoli, despite SIR2 repression of ecc rDNA formation in S. cerevisiae 14 .…”

Histone H4 lysine 20 monomethylation promotes transcriptional repression by L3MBTL1

“…Significantly, expression of a catalytically dead form of PR-SET7 (R265G mutation; DBD-PR-SET7-R265G) with L3MBTL1 did not repress luciferase expression. Furthermore, neither DBD-SUV420H1 (an H4K20 trimethyltransferase (Schotta et al, 2004)) nor DBD-G9a (an H3K9 mono-/dimethyltransferase (Rice et al, 2003)) caused significant repression when coexpressed with L3MBTL1 ( Figure 5b). Although the L3MBTL1-DMBT mutant localizes to chromatin, it did not synergize with DBD-PR-SET7 (Figure 5c), nor did the L3MBTL1-D355N mutant (Figure 5d).…”

“…H4K20me1 is associated with facultative heterochromatin (Fang et al, 2002;Martens et al, 2005;Sims et al, 2006), and the inactive X chromosome (Kohlmaier et al, 2004). In contrast, H4K20me3 marks constitutive heterochromatin (Schotta et al, 2004;Mikkelsen et al, 2007).…”