Histone H4 Lysine 20 (H4K20) Methylation, Expanding the Signaling Potential of the Proteome One Methyl Moiety at a Time
2015; Elsevier BV; Volume: 15; Issue: 3 Linguagem: Inglês
10.1074/mcp.r115.054742
ISSN1535-9484
Autores Tópico(s)RNA modifications and cancer
ResumoCovalent post-translational modifications (PTMs) of proteins can regulate the structural and functional state of a protein in the absence of primary changes in the underlying sequence. Common PTMs include phosphorylation, acetylation, and methylation. Histone proteins are critical regulators of the genome and are subject to a highly abundant and diverse array of PTMs. To highlight the functional complexity added to the proteome by lysine methylation signaling, here we will focus on lysine methylation of histone proteins, an important modification in the regulation of chromatin and epigenetic processes. We review the signaling pathways and functions associated with a single residue, H4K20, as a model chromatin and clinically important mark that regulates biological processes ranging from the DNA damage response and DNA replication to gene expression and silencing. Covalent post-translational modifications (PTMs) of proteins can regulate the structural and functional state of a protein in the absence of primary changes in the underlying sequence. Common PTMs include phosphorylation, acetylation, and methylation. Histone proteins are critical regulators of the genome and are subject to a highly abundant and diverse array of PTMs. To highlight the functional complexity added to the proteome by lysine methylation signaling, here we will focus on lysine methylation of histone proteins, an important modification in the regulation of chromatin and epigenetic processes. We review the signaling pathways and functions associated with a single residue, H4K20, as a model chromatin and clinically important mark that regulates biological processes ranging from the DNA damage response and DNA replication to gene expression and silencing. The human genome consists of greater than 20,000 protein-coding genes (1.International Human Genome Sequencing Consortium Finishing the euchromatic sequence of the human genome.Nature. 2004; 431: 931-945Crossref PubMed Scopus (3498) Google Scholar). Additionally, most genes give rise to multiple isoforms due to alternative splicing (2.Pan Q. Shai O. Lee L.J. Frey B.J. Blencowe B.J. Deep surveying of alternative splicing complexity in the human transcriptome by high-throughput sequencing.Nat. Genet. 2008; 40: 1413-1415Crossref PubMed Scopus (2542) Google Scholar). Further complexity of the proteome is achieved by the reversible covalent post-translational modifications (PTMs) 1The abbreviations used are:PTMpost-translational modificationPCNAproliferating cell nuclear antigenORIorigins of replicationBAHbromo-adjacent homologyORCorigin of replication complexMEFmouse embryonic fibroblastMGSMeier-Gorlin syndrome. of proteins by chemical moieties such as phosphorylation, acetylation, and methylation. These covalent modifications occur largely on the side chains of distinct amino acid residues and regulate protein function by diverse mechanisms that together greatly expands the complexity of the proteome (3.Minguez P. Parca L. Diella F. Mende D.R. Kumar R. Helmer-Citterich M. Gavin A.C. van Noort V. Bork P. Deciphering a global network of functionally associated post-translational modifications.Mol. Syst. Biol. 2012; 8: 599Crossref PubMed Scopus (179) Google Scholar). post-translational modification proliferating cell nuclear antigen origins of replication bromo-adjacent homology origin of replication complex mouse embryonic fibroblast Meier-Gorlin syndrome. Histones are some of the most abundant proteins in eukaryotic cells. Two copies of histone H2A, H2B, H3, and H4 form an octameric structure that is wrapped by ∼147 bp of double-stranded DNA (dsDNA) to form the nucleosome, the core structural unit of chromatin and the first step in packaging of the genome (4.Luger K. Mäder A.W. Richmond R.K. Sargent D.F. Richmond T.J. Crystal structure of the nucleosome core particle at 2.8 A resolution.Nature. 1997; 389: 251-260Crossref PubMed Scopus (6884) Google Scholar). Histone proteins are highly modified with the majority of PTMs occurring within the highly charged and unstructured N- and C-terminal histone tail regions (5.Kouzarides T. Chromatin modifications and their function.Cell. 2007; 128: 693-705Abstract Full Text Full Text PDF PubMed Scopus (8034) Google Scholar). Here we will focus on lysine methylation of histone proteins, an important modification that was first identified on histones in the 1960s and is now appreciated to fundamentally regulate chromatin dynamics (6.Black J.C. Van Rechem C. Whetstine J.R. Histone lysine methylation dynamics: establishment, regulation, and biological impact.Mol. Cell. 2012; 48: 491-507Abstract Full Text Full Text PDF PubMed Scopus (765) Google Scholar). Proteins are reversibly methylated on the nitrogen side chain of lysine residues (Fig. 1). This reaction, although subtly changing the primary structure of the modified peptide, greatly increases the information encoded within the molecule. Lysine residues can accept up to three methyl groups, forming mono-, di-, and tri-methylated derivatives (referred to here as Kme1, Kme2, and Kme3, respectively; Fig. 1), with unique activities frequently being coupled to the specific extent of methylation on the lysine residue (5.Kouzarides T. Chromatin modifications and their function.Cell. 2007; 128: 693-705Abstract Full Text Full Text PDF PubMed Scopus (8034) Google Scholar, 7.Suganuma T. Workman J.L. Signals and combinatorial functions of histone modifications.Annu. Rev. Biochem. 2011; 80: 473-499Crossref PubMed Scopus (383) Google Scholar, 8.Taverna S.D. Li H. Ruthenburg A.J. Allis C.D. Patel D.J. How chromatin-binding modules interpret histone modifications: lessons from professional pocket pickers.Nat. Struct. Mol. Biol. 2007; 14: 1025-1040Crossref PubMed Scopus (1169) Google Scholar). Here, when referring to sites of histone methylation, we will use nomenclature in which the histone, residue and number, and type of methylation are sequentially denoted (9.Turner B.M. Reading signals on the nucleosome with a new nomenclature for modified histones.Nat. Struct. Mol. Biol. 2005; 12: 110-112Crossref PubMed Scopus (190) Google Scholar). For example, me1 of histone H3 at lysine 4 will be referred to H3K4me1. In humans, the canonical lysine methylation sites on the core histones are H3K4, H3K9, H3K27, H3K36, H3K79, and H4K20 (10.Moore K.E. Gozani O. An unexpected journey: lysine methylation across the proteome.Biochim. Biophys. Acta. 2014; 1839: 1395-1403Crossref PubMed Scopus (74) Google Scholar). Here, to highlight the functional complexity that can be added to the proteome via lysine methylation, we focus on the signaling pathways and functions associated with methylation of a single residue, H4K20, as a model chromatin and clinically important mark that regulates diverse biological processes ranging from the DNA damage response and DNA replication to gene expression and silencing. For more detailed and comprehensive reviews of H4K20 methylation biology, we refer the reader to two excellent reviews, Refs. 11.Beck D.B. Oda H. Shen S.S. Reinberg D. PR-Set7 and H4K20me1: at the crossroads of genome integrity, cell cycle, chromosome condensation, and transcription.Genes Dev. 2012; 26: 325-337Crossref PubMed Scopus (218) Google Scholar, 12.Jørgensen S. Schotta G. Sørensen C.S. Histone H4 lysine 20 methylation: key player in epigenetic regulation of genomic integrity.Nucleic Acids Res. 2013; 41: 2797-2806Crossref PubMed Scopus (244) Google Scholar. Lysine 20 is the major site of methylation on histone H4. Depending on the cell type, up to ∼80% of H4 molecules can be di-methylated, whereas H4K20me1 and H4K20me3 are generally less abundant, for example being present on 10 and 5% of nucleosomes in asynchronous HeLa cells, respectively, with similar ratios observed in mouse embryonic fibroblasts (MEFs) and other cell types (13.Schotta G. Sengupta R. Kubicek S. Malin S. Kauer M. Callén E. Celeste A. Pagani M. Opravil S. De La Rosa-Velazquez I.A. Espejo A. Bedford M.T. Nussenzweig A. Busslinger M. Jenuwein T. A chromatin-wide transition to H4K20 monomethylation impairs genome integrity and programmed DNA rearrangements in the mouse.Genes Dev. 2008; 22: 2048-2061Crossref PubMed Scopus (317) Google Scholar, 14.Leroy G. Dimaggio P.A. Chan E.Y. Zee B.M. Blanco M.A. Bryant B. Flaniken I.Z. Liu S. Kang Y. Trojer P. Garcia B.A. A quantitative atlas of histone modification signatures from human cancer cells.Epigenetics Chromatin. 2013; 6: 20Crossref PubMed Scopus (93) Google Scholar, 15.Pesavento J.J. Yang H. Kelleher N.L. Mizzen C.A. Certain and progressive methylation of histone H4 at lysine 20 during the cell cycle.Mol. Cell. Biol. 2008; 28: 468-486Crossref PubMed Scopus (223) Google Scholar, 16.Evertts A.G. Manning A.L. Wang X. Dyson N.J. Garcia B.A. Coller H.A. H4K20 methylation regulates quiescence and chromatin compaction.Mol. Biol. Cell. 2013; 24: 3025-3037Crossref PubMed Scopus (93) Google Scholar). Three distinct SET domains containing lysine (K) methyltransferase (KMT) enzymes, SETD8 (SET8, PR-SET7), SUV4-20H1, and SUV4-20H2, are responsible for the generation of the three different methyl states of H4K20 (17.Nishioka K. Rice J.C. Sarma K. Erdjument-Bromage H. Werner J. Wang Y. Chuikov S. Valenzuela P. Tempst P. Steward R. Lis J.T. Allis C.D. Reinberg D. PR-Set7 is a nucleosome-specific methyltransferase that modifies lysine 20 of histone H4 and is associated with silent chromatin.Mol. Cell. 2002; 9: 1201-1213Abstract Full Text Full Text PDF PubMed Scopus (462) Google Scholar, 18.Fang J. Feng Q. Ketel C.S. Wang H. Cao R. Xia L. Erdjument-Bromage H. Tempst P. Simon J.A. Zhang Y. Purification and functional characterization of SET8, a nucleosomal histone H4-lysine 20-specific methyltransferase.Curr. Biol. 2002; 12: 1086-1099Abstract Full Text Full Text PDF PubMed Scopus (267) Google Scholar, 19.Pannetier M. Julien E. Schotta G. Tardat M. Sardet C. Jenuwein T. Feil R. PR-SET7 and SUV4-20H regulate H4 lysine-20 methylation at imprinting control regions in the mouse.EMBO Rep. 2008; 9: 998-1005Crossref PubMed Scopus (58) Google Scholar, 20.Schotta G. Lachner M. Sarma K. Ebert A. Sengupta R. Reuter G. Reinberg D. Jenuwein T. A silencing pathway to induce H3-K9 and H4-K20 trimethylation at constitutive heterochromatin.Genes Dev. 2004; 18: 1251-1262Crossref PubMed Scopus (846) Google Scholar). SETD8 was identified as the first KMT for H4K20, and genetic ablation of Setd8 in flies completely abolished all three methylation states, initially suggesting that it might catalyze mono-, di-, and tri-methylation (17.Nishioka K. Rice J.C. Sarma K. Erdjument-Bromage H. Werner J. Wang Y. Chuikov S. Valenzuela P. Tempst P. Steward R. Lis J.T. Allis C.D. Reinberg D. PR-Set7 is a nucleosome-specific methyltransferase that modifies lysine 20 of histone H4 and is associated with silent chromatin.Mol. Cell. 2002; 9: 1201-1213Abstract Full Text Full Text PDF PubMed Scopus (462) Google Scholar, 18.Fang J. Feng Q. Ketel C.S. Wang H. Cao R. Xia L. Erdjument-Bromage H. Tempst P. Simon J.A. Zhang Y. Purification and functional characterization of SET8, a nucleosomal histone H4-lysine 20-specific methyltransferase.Curr. Biol. 2002; 12: 1086-1099Abstract Full Text Full Text PDF PubMed Scopus (267) Google Scholar). However, biochemical analysis showed that SETD8 only catalyzed the addition of one methyl moiety, converting unmodified H4K20 to H4K20me1. Structural studies provided the molecular basis for this specificity, demonstrating that the active site of SETD8 is not able to accommodate a lysine carrying more than a single methyl group (21.Couture J.F. Collazo E. Brunzelle J.S. Trievel R.C. Structural and functional analysis of SET8, a histone H4 Lys-20 methyltransferase.Genes Dev. 2005; 19: 1455-1465Crossref PubMed Scopus (190) Google Scholar, 22.Xiao B. Jing C. Kelly G. Walker P.A. Muskett F.W. Frenkiel T.A. Martin S.R. Sarma K. Reinberg D. Gamblin S.J. Wilson J.R. Specificity and mechanism of the histone methyltransferase Pr-Set7.Genes Dev. 2005; 19: 1444-1454Crossref PubMed Scopus (154) Google Scholar). Two related enzymes, SUV4-20H1 and SUV4-20H2, also methylate H4K20 and are the enzymes responsible for the conversion of SETD8-generated H4K20me1 into H4K20me2 and H4K20me3 (20.Schotta G. Lachner M. Sarma K. Ebert A. Sengupta R. Reuter G. Reinberg D. Jenuwein T. A silencing pathway to induce H3-K9 and H4-K20 trimethylation at constitutive heterochromatin.Genes Dev. 2004; 18: 1251-1262Crossref PubMed Scopus (846) Google Scholar). Indeed, the deletion of both enzymes in MEFs led to a dramatic and specific loss of H4K20me2 and H4K20me3 levels and a concomitant increase in the levels of H4K20me1 (19.Pannetier M. Julien E. Schotta G. Tardat M. Sardet C. Jenuwein T. Feil R. PR-SET7 and SUV4-20H regulate H4 lysine-20 methylation at imprinting control regions in the mouse.EMBO Rep. 2008; 9: 998-1005Crossref PubMed Scopus (58) Google Scholar); these results suggested that the accumulation of H4K20me1 was a result of failure in the Suv4-20h1/Suv4h2 double knock-out cells to convert H4K20me1 to the higher methylated states. Similar results were observed upon depletion of the two homologous proteins, suv420h1/h2 in the zebrafish Danio rerio (23.Kuo A.J. Song J. Cheung P. Ishibe-Murakami S. Yamazoe S. Chen J.K. Patel D.J. Gozani O. The BAH domain of ORC1 links H4K20me2 to DNA replication licensing and Meier-Gorlin syndrome.Nature. 2012; 484: 115-119Crossref PubMed Scopus (252) Google Scholar). There are reports of other KMTs such as NSD2/MMSET/WHSC1 having activity on H4K20 (24.Pei H. Zhang L. Luo K. Qin Y. Chesi M. Fei F. Bergsagel P.L. Wang L. You Z. Lou Z. MMSET regulates histone H4K20 methylation and 53BP1 accumulation at DNA damage sites.Nature. 2011; 470: 124-128Crossref PubMed Scopus (331) Google Scholar); however, careful analysis of NSD2-methylated histones demonstrated that this enzyme has absolutely no activity on H4K20 (25.Li Y. Trojer P. Xu C.F. Cheung P. Kuo A. Drury 3rd, W.J. Qiao Q. Neubert T.A. Xu R.M. Gozani O. Reinberg D. The target of the NSD family of histone lysine methyltransferases depends on the nature of the substrate.J. Biol. Chem. 2009; 284: 34283-34295Abstract Full Text Full Text PDF PubMed Scopus (211) Google Scholar, 26.Kuo A.J. Cheung P. Chen K. Zee B.M. Kioi M. Lauring J. Xi Y. Park B.H. Shi X. Garcia B.A. Li W. Gozani O. NSD2 links dimethylation of histone H3 at lysine 36 to oncogenic programming.Mol. Cell. 2011; 44: 609-620Abstract Full Text Full Text PDF PubMed Scopus (298) Google Scholar), and similar analyses have ruled out several other putative H4K20 methyltransferases (25.Li Y. Trojer P. Xu C.F. Cheung P. Kuo A. Drury 3rd, W.J. Qiao Q. Neubert T.A. Xu R.M. Gozani O. Reinberg D. The target of the NSD family of histone lysine methyltransferases depends on the nature of the substrate.J. Biol. Chem. 2009; 284: 34283-34295Abstract Full Text Full Text PDF PubMed Scopus (211) Google Scholar, 26.Kuo A.J. Cheung P. Chen K. Zee B.M. Kioi M. Lauring J. Xi Y. Park B.H. Shi X. Garcia B.A. Li W. Gozani O. NSD2 links dimethylation of histone H3 at lysine 36 to oncogenic programming.Mol. Cell. 2011; 44: 609-620Abstract Full Text Full Text PDF PubMed Scopus (298) Google Scholar, 27.Van Aller G.S. Reynoird N. Barbash O. Huddleston M. Liu S. Zmoos A.F. McDevitt P. Sinnamon R. Le B. Mas G. Annan R. Sage J. Garcia B.A. Tummino P.J. Gozani O. Kruger R.G. Smyd3 regulates cancer cell phenotypes and catalyzes histone H4 lysine 5 methylation.Epigenetics. 2012; 7: 340-343Crossref PubMed Scopus (135) Google Scholar, 28.Kudithipudi S. Kusevic D. Weirich S. Jeltsch A. Specificity analysis of protein lysine methyltransferases using SPOT peptide arrays.J. Vis. Exp. 2014; 93: e52203Google Scholar, 29.Kudithipudi S. Lungu C. Rathert P. Happel N. Jeltsch A. Substrate specificity analysis and novel substrates of the protein lysine methyltransferase NSD1.Chem. Biol. 2014; 21: 226-237Abstract Full Text Full Text PDF PubMed Scopus (42) Google Scholar). 2O. Gozani, unpublished observations. Thus, in higher eukaryotes, SETD8 appears to be the sole mono-methyltransferase for H4K20, and successive methylation of H4K20me1 by SUV4-20H1 and SUV4-20H2 generates the preponderance of global H4K20me2 and H4K20me3. SUV4-20H1 and SUV4-20H2 share a high degree of sequence similarity in their catalytic SET domain (20.Schotta G. Lachner M. Sarma K. Ebert A. Sengupta R. Reuter G. Reinberg D. Jenuwein T. A silencing pathway to induce H3-K9 and H4-K20 trimethylation at constitutive heterochromatin.Genes Dev. 2004; 18: 1251-1262Crossref PubMed Scopus (846) Google Scholar), and consistent with the cellular studies (13.Schotta G. Sengupta R. Kubicek S. Malin S. Kauer M. Callén E. Celeste A. Pagani M. Opravil S. De La Rosa-Velazquez I.A. Espejo A. Bedford M.T. Nussenzweig A. Busslinger M. Jenuwein T. A chromatin-wide transition to H4K20 monomethylation impairs genome integrity and programmed DNA rearrangements in the mouse.Genes Dev. 2008; 22: 2048-2061Crossref PubMed Scopus (317) Google Scholar), in vitro methylation assays using recombinant SUV4-20H1 and SUV4-20H2 indicate that both proteins catalyze H4K20me2 with similar kinetics and that these enzymes are more active on H4K20me1 as substrate than on unmethylated H4K20 (20.Schotta G. Lachner M. Sarma K. Ebert A. Sengupta R. Reuter G. Reinberg D. Jenuwein T. A silencing pathway to induce H3-K9 and H4-K20 trimethylation at constitutive heterochromatin.Genes Dev. 2004; 18: 1251-1262Crossref PubMed Scopus (846) Google Scholar, 30.Yang H. Pesavento J.J. Starnes T.W. Cryderman D.E. Wallrath L.L. Kelleher N.L. Mizzen C.A. Preferential dimethylation of histone H4 lysine 20 by Suv4-20.J. Biol. Chem. 2008; 283: 12085-12092Abstract Full Text Full Text PDF PubMed Scopus (106) Google Scholar, 31.Southall S.M. Cronin N.B. Wilson J.R. A novel route to product specificity in the Suv4-20 family of histone H4K20 methyltransferases.Nucleic Acids Res. 2014; 42: 661-671Crossref PubMed Scopus (27) Google Scholar, 32.Wu H. Siarheyeva A. Zeng H. Lam R. Dong A. Wu X.H. Li Y. Schapira M. Vedadi M. Min J. Crystal structures of the human histone H4K20 methyltransferases SUV420H1 and SUV420H2.FEBS Lett. 2013; 587: 3859-3868Crossref PubMed Scopus (34) Google Scholar). Nonetheless, deletion of the individual enzymes in MEFs showed clear differences with respect to H4K20 methylation as Suv4-20h1 deletion resulted in an ∼60% decrease in H4K20me2 levels without affecting H4K20me3. In contrast, genetic ablation of Suv4-20h2 largely eradicated H4K20me3 but did not have an impact on global levels of H4K20me2 (13.Schotta G. Sengupta R. Kubicek S. Malin S. Kauer M. Callén E. Celeste A. Pagani M. Opravil S. De La Rosa-Velazquez I.A. Espejo A. Bedford M.T. Nussenzweig A. Busslinger M. Jenuwein T. A chromatin-wide transition to H4K20 monomethylation impairs genome integrity and programmed DNA rearrangements in the mouse.Genes Dev. 2008; 22: 2048-2061Crossref PubMed Scopus (317) Google Scholar). It is worth noting that both Suv4-20h1 and Suv4-20h2 are capable of mono-methylation but with a 3-fold lower activity compared with their activity on mono-methylated peptides and a 250-fold lower activity relative to SETD8. The molecular basis for this specificity was revealed in structural studies on the SET domain of mouse SUV4-20H2, which showed that a single methyl group on the substrate lysine helps to lock the lysine in place in the active site (31.Southall S.M. Cronin N.B. Wilson J.R. A novel route to product specificity in the Suv4-20 family of histone H4K20 methyltransferases.Nucleic Acids Res. 2014; 42: 661-671Crossref PubMed Scopus (27) Google Scholar, 32.Wu H. Siarheyeva A. Zeng H. Lam R. Dong A. Wu X.H. Li Y. Schapira M. Vedadi M. Min J. Crystal structures of the human histone H4K20 methyltransferases SUV420H1 and SUV420H2.FEBS Lett. 2013; 587: 3859-3868Crossref PubMed Scopus (34) Google Scholar). Peptides containing an unmodified lysine would therefore be oriented in a less optimal position rendering mono-methylation inefficient (31.Southall S.M. Cronin N.B. Wilson J.R. A novel route to product specificity in the Suv4-20 family of histone H4K20 methyltransferases.Nucleic Acids Res. 2014; 42: 661-671Crossref PubMed Scopus (27) Google Scholar, 32.Wu H. Siarheyeva A. Zeng H. Lam R. Dong A. Wu X.H. Li Y. Schapira M. Vedadi M. Min J. Crystal structures of the human histone H4K20 methyltransferases SUV420H1 and SUV420H2.FEBS Lett. 2013; 587: 3859-3868Crossref PubMed Scopus (34) Google Scholar). With respect to tri-methylation, a significant structural rearrangement of the active site has to take place in order to accommodate an H4K20me3 peptide, which is energetically unfavorable, potentially explaining why this activity is difficult to detect in vitro when utilizing the SET domains of SUV4-20H1 and SUV4-20H2 (31.Southall S.M. Cronin N.B. Wilson J.R. A novel route to product specificity in the Suv4-20 family of histone H4K20 methyltransferases.Nucleic Acids Res. 2014; 42: 661-671Crossref PubMed Scopus (27) Google Scholar, 32.Wu H. Siarheyeva A. Zeng H. Lam R. Dong A. Wu X.H. Li Y. Schapira M. Vedadi M. Min J. Crystal structures of the human histone H4K20 methyltransferases SUV420H1 and SUV420H2.FEBS Lett. 2013; 587: 3859-3868Crossref PubMed Scopus (34) Google Scholar). The discrepancy between the in vitro and in vivo data argues that catalytic specificity of the SUV4-20H1 and SUV4-20H2 does not solely come from the SET domain and is also influenced by domains outside the SET domain and/or differential interacting proteins. Thus, SUV4-20H1 and SUV4-20H2 are both di-methyltransferases in vitro, but we have much to learn in order to understand how H4K20me3 is regulated by SUV4-20H1 and SUV4-20H2 in vivo. In multicellular organisms, H4K20 methylation appears to be important for development and organismal viability. Specifically, knock-out Setd8 mouse embryos die before they reach the 8-cell stage, and flies lacking Setd8 have developmental defects and only make it into the late larval stage (17.Nishioka K. Rice J.C. Sarma K. Erdjument-Bromage H. Werner J. Wang Y. Chuikov S. Valenzuela P. Tempst P. Steward R. Lis J.T. Allis C.D. Reinberg D. PR-Set7 is a nucleosome-specific methyltransferase that modifies lysine 20 of histone H4 and is associated with silent chromatin.Mol. Cell. 2002; 9: 1201-1213Abstract Full Text Full Text PDF PubMed Scopus (462) Google Scholar, 18.Fang J. Feng Q. Ketel C.S. Wang H. Cao R. Xia L. Erdjument-Bromage H. Tempst P. Simon J.A. Zhang Y. Purification and functional characterization of SET8, a nucleosomal histone H4-lysine 20-specific methyltransferase.Curr. Biol. 2002; 12: 1086-1099Abstract Full Text Full Text PDF PubMed Scopus (267) Google Scholar, 33.Oda H. Okamoto I. Murphy N. Chu J. Price S.M. Shen M.M. Torres-Padilla M.E. Heard E. Reinberg D. Monomethylation of histone H4-lysine 20 is involved in chromosome structure and stability and is essential for mouse development.Mol. Cell. Biol. 2009; 29: 2278-22795Crossref PubMed Scopus (239) Google Scholar). However, it is worth noting that SETD8 has non-histone substrates that may contribute to the knock-out phenotype (see below). Indeed, flies expressing H4 that contains a K20A substitution display significant developmental delay (24–48 h) and have significant death at the larval stage (46%), but overall they have a less severe phenotype than the Setd8 knock-out flies, in which 100% death at the larval stage is observed (17.Nishioka K. Rice J.C. Sarma K. Erdjument-Bromage H. Werner J. Wang Y. Chuikov S. Valenzuela P. Tempst P. Steward R. Lis J.T. Allis C.D. Reinberg D. PR-Set7 is a nucleosome-specific methyltransferase that modifies lysine 20 of histone H4 and is associated with silent chromatin.Mol. Cell. 2002; 9: 1201-1213Abstract Full Text Full Text PDF PubMed Scopus (462) Google Scholar, 18.Fang J. Feng Q. Ketel C.S. Wang H. Cao R. Xia L. Erdjument-Bromage H. Tempst P. Simon J.A. Zhang Y. Purification and functional characterization of SET8, a nucleosomal histone H4-lysine 20-specific methyltransferase.Curr. Biol. 2002; 12: 1086-1099Abstract Full Text Full Text PDF PubMed Scopus (267) Google Scholar, 34.McKay D.J. Klusza S. Penke T.J. Meers M.P. Curry K.P. McDaniel S.L. Malek P.Y. Cooper S.W. Tatomer D.C. Lieb J.D. Strahl B.D. Duronio R.J. Matera A.G. Interrogating the function of metazoan histones using engineered gene clusters.Dev. Cell. 2015; 32: 373-386Abstract Full Text Full Text PDF PubMed Scopus (88) Google Scholar). Suv4-20h1/Suv4-20h2 double knock-out mice are born at sub-Mendelian ratios, have significant perinatal death, and upon birth are noticeably smaller than control littermates (13.Schotta G. Sengupta R. Kubicek S. Malin S. Kauer M. Callén E. Celeste A. Pagani M. Opravil S. De La Rosa-Velazquez I.A. Espejo A. Bedford M.T. Nussenzweig A. Busslinger M. Jenuwein T. A chromatin-wide transition to H4K20 monomethylation impairs genome integrity and programmed DNA rearrangements in the mouse.Genes Dev. 2008; 22: 2048-2061Crossref PubMed Scopus (317) Google Scholar). A similar phenotype has been described for the single deletion of Suv4-20h1. However, Suv4-20h2 deletion alone is compatible with life, and the mice seem to develop normally (13.Schotta G. Sengupta R. Kubicek S. Malin S. Kauer M. Callén E. Celeste A. Pagani M. Opravil S. De La Rosa-Velazquez I.A. Espejo A. Bedford M.T. Nussenzweig A. Busslinger M. Jenuwein T. A chromatin-wide transition to H4K20 monomethylation impairs genome integrity and programmed DNA rearrangements in the mouse.Genes Dev. 2008; 22: 2048-2061Crossref PubMed Scopus (317) Google Scholar). This striking difference may in part be attributed to the more restricted expression pattern of SUV4-20H2 in the mouse embryo relative to SUV4-20H1, which is ubiquitously expressed throughout the embryo (13.Schotta G. Sengupta R. Kubicek S. Malin S. Kauer M. Callén E. Celeste A. Pagani M. Opravil S. De La Rosa-Velazquez I.A. Espejo A. Bedford M.T. Nussenzweig A. Busslinger M. Jenuwein T. A chromatin-wide transition to H4K20 monomethylation impairs genome integrity and programmed DNA rearrangements in the mouse.Genes Dev. 2008; 22: 2048-2061Crossref PubMed Scopus (317) Google Scholar). Taken together, the data in higher eukaryotes support the notion that establishing a proper H4K20me pattern is important for development, yet the non-essential role for SUV4-20H2 in this process requires additional studies as does separating the function of the individual KMTs versus the specific methylation event on H4. In mice, the deletion of Setd8 gives a much more severe phenotype as compared with the double deletion of Suv4-20h1 and Suv4-20h2 (13.Schotta G. Sengupta R. Kubicek S. Malin S. Kauer M. Callén E. Celeste A. Pagani M. Opravil S. De La Rosa-Velazquez I.A. Espejo A. Bedford M.T. Nussenzweig A. Busslinger M. Jenuwein T. A chromatin-wide transition to H4K20 monomethylation impairs genome integrity and programmed DNA rearrangements in the mouse.Genes Dev. 2008; 22: 2048-2061Crossref PubMed Scopus (317) Google Scholar, 33.Oda H. Okamoto I. Murphy N. Chu J. Price S.M. Shen M.M. Torres-Padilla M.E. Heard E. Reinberg D. Monomethylation of histone H4-lysine 20 is involved in chromosome structure and stability and is essential for mouse development.Mol. Cell. Biol. 2009; 29: 2278-22795Crossref PubMed Scopus (239) Google Scholar). This suggests that loss of all methylation states on H4K20 is more detrimental than the loss of only H4K20me2 and H4K20me3. At the same time, SETD8 has also been shown to methylate non-histone substrates such as the tumor suppressor p53 (35.Shi X. Kachirskaia I. Yamaguchi H. West L.E. Wen H. Wang E.W. Dutta S. Appella E. Gozani O. Modulation of p53 function by SET8-mediated methylation at lysine 382.Mol. Cell. 2007; 27: 636-646Abstract Full Text Full Text PDF PubMed Scopus (336) Google Scholar), the protein NUMB (36.Dhami G.K. Liu H. Galka M. Voss C. Wei R. Muranko K. Kaneko T. Cregan S.P. Li L. Li S.S. Dynamic methylation of Numb by Set8 regulates its binding to p53 and apoptosis.Mol. Cell. 2013; 50: 565-576Abstract Full Text Full Text PDF PubMed Scopus (78) Google Scholar), and proliferating cell nuclear antigen (PCNA) (37.Takawa M. Cho H.S. Hayami S. Toyokawa G. Kogure M. Yamane Y. Iwai Y. Maejima K. Ueda K. Masuda A. Dohmae N. Field H.I. Tsunoda T. Kobayashi T. Akasu T. Sugiyama M. Ohnuma S. Atomi Y. Ponder B.A. Nakamura Y. Hamamoto R. Histone lysine methyltransferase SETD8 promotes carcinogenesis by deregulating PCNA expression.Cancer Res. 2012; 72: 3217-3227Crossref PubMed Scopus (150) Google Scholar). To date, a non-histone target for SUV4-20H1 and SUV4-20H2 has yet to been identified. SETD8 mono-methylates p53 on lysine 382 to suppress p53-mediated transcriptional activation of highly responsive target genes (35.Shi X. Kachirskaia I. Yamaguchi H. West L.E. Wen H. Wang E.W. Dutta S. Appella E. Gozani O. Modulation of p53 function by SET8-mediated methylation at lysine 382.Mol. Cell. 2007; 27: 636-646Abstract Full Text Full Text PDF PubMed Scopus (336) Google Scholar). In addition to p53, SETD8 methylates PCNA, which is reported to stabilize PCNA, and promotes its function in DNA replication and DNA damage (37.Takawa M. Cho H.S. Hayami S. Toyokawa G. Kogure M. Yamane Y. Iwai Y. Maejima K. Ueda K. Masuda A. Dohmae N. Field H.I. Tsunoda T. Kobayashi T. Akasu T. Sugiyama M. Ohnuma S. Atomi Y. Ponder B.A. Nakamura Y. Hamamoto R. Histone lysine methyltransferase SETD8 promotes carcinogenesis by deregulating PCNA expression.Cancer Res. 2012; 72: 3217-3227Crossref PubMed Scopus (150) Google Scholar). SETD8 methylation of NUMB also impacts p53 functions, suggesting SETD8 integrates multiple pathways to regulate the key tumor suppressor p53. Together, these studies indicate that SETD8 deletion phenotypes are likely due to a combination in the absence of H4K20 methylation as well as SETD8 functions in non-histone methyl-lysine signaling pathways. Lysine methylation, although a relatively
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