Preferential Dimethylation of Histone H4 Lysine 20 by Suv4-20

Abstract

Post-translational modifications of histone tails direct nuclear processes including transcription, DNA repair, and chromatin packaging. Lysine 20 of histone H4 is mono-, di-, or trimethylated in vivo, but the regulation and significance of these methylations is poorly understood. The SET domain proteins PRSet7 and Suv4-20 have been implicated in mono-and trimethylation, respectively; however, enzymes that dimethylate lysine 20 have not been identified. Here we report that Drosophila Suv4-20 is a mixed product specificity methyltransferase that dimethylates ϳ90% and trimethylates less than 5% of total H4 at lysine 20 in S2 cells. Trimethylation, but not dimethylation, is reduced in Drosophila larvae lacking HP1, suggesting that an interaction with HP1 regulates the product specificity of Suv4-20 and enrichment of trimethyllysine 20 within heterochromatin. Similar to the Drosophila enzyme, human Suv4-20h1/h2 enzymes generate di-and trimethyllysine 20. PR-Set7 and Suv4-20 are both required for normal levels of methylation, suggesting they have non-redundant functions. Alterations in the level of lysine 20 methylation following knock-down or overexpression of Suv4-20 did not affect lysine 16 acetylation, revealing that these two modifications are not competitive in vivo. Depletion of Suv4-20h1/h2 in HeLa cells impaired the formation of 53BP1 foci, suggesting dimethyllysine 20 is required for a proper DNA damage response. Collectively, the data indicate that Suv4-20 generates nearly ubiquitous dimethylation that facilitates the DNA damage response and selective trimethylation that is involved in heterochromatin formation.

Catalytic Function of the PR-Set7 Histone H4 Lysine 20 Monomethyltransferase Is Essential for Mitotic Entry and Genomic Stability

“…Trimethylated H4K20 is associated with repressed chromatin because it is targeted to constitutive heterochromatin, various repetitive elements, and imprinting control regions (16,18,19). Dimethylated H4K40 is more widely distributed within euchromatic regions in the genome, and recent findings suggest that it may function to recruit the 53BP1 repair protein to sites of DNA damage (17,20,21).…”

“…Trimethylated H4K20 is associated with repressed chromatin because it is targeted to constitutive heterochromatin, various repetitive elements, and imprinting control regions (16,18,19). Dimethylated H4K40 is more widely distributed within euchromatic regions in the genome, and recent findings suggest that it may function to recruit the 53BP1 repair protein to sites of DNA damage (17,20,21).The PR-Set7 enzyme is responsible for the bulk of H4K20 monomethylation (22)(23)(24)(25). Although original observations suggested that this modification was associated with repressed regions of the genome, recent findings have identified monomethylated H4K20 within actively transcribed genes (26,27).…”

“…For example, the mono-and dimethylation of histone H3 lysine 9 in humans is mediated by the G9a enzyme, whereas trimethylation is mediated by the SUV39H1 enzyme (14,15). Similarly, the Suv4 -20 enzymes are responsible for di-and trimethylation in mammals (16,17). Trimethylated H4K20 is associated with repressed chromatin because it is targeted to constitutive heterochromatin, various repetitive elements, and imprinting control regions (16,18,19).…”

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

“…The in vitro binding of H4K20Me 1 or H4K20Me 2 over H3K36Me 2 or other histone tail modifications associated with gene activation presented in this study strongly points to the N terminus of histone H4 being the likely in vivo binding target for the MSL3 and MRG15 CBDs. Supporting a role for H4K20Me 1 in the recruitment of the MSL complex, H4K20Me 1 is an abundant modification on histone tails in Drosophila and humans, and its presence correlates positively with the level of transcriptional activity along human genes, at least as well as for H3K36Me 3 (59,(62)(63)(64)(65)(66)(67). Furthermore, other studies have shown that H4K20Me 1 is found to be preferentially deposited on nucleosomes residing within exons (68,69), a pattern mirrored in the X-chromosome binding of the Drosophila MSL complex (30).…”

Chromatin dynamics coupled to DNA repair

“…54 In agreement with these results, it has very recently been shown that SUV420H1 and SUV420H2 are the enzymes responsible for the ubiquitous dimethylation of H4K20 in human and Drosophila melanogaster cells and that depletion of both SUV420H1 and SUV420H2 by siRNA decreases the number of 53BP1 foci in HeLa cells. 55 Another report describes the role of H4K20me during NHEJ in mammals, whereby during the process of XRCC4-dependent NHEJ, 53BP1 recruitment depends on its interaction with dimethylated H4K20 but not on H2AX. 23 The same study also found that, alternatively, MDC1 mediates efficient HR/SCR (sister-chromatid recombination) in a manner strictly dependent on its ability to recruit γH2AX and does not require recruitment of 53BP1 or BRCA1.…”