histone modifications
DESCRIPTION
Histone Modifications. Outline. Overview of histone modifications: Types of modifications and modifiers General roles of modifications Techniques used to study histone modifications Specific modifications (acetylation, methylation, etc ): Residues/positions that are frequently modified - PowerPoint PPT PresentationTRANSCRIPT
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Histone Modifications
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Outline
1. Overview of histone modifications:a. Types of modifications and modifiersb. General roles of modificationsc. Techniques used to study histone modifications
2. Specific modifications (acetylation, methylation, etc):a. Residues/positions that are frequently modifiedb. Enzymes that add/remove the modificationc. Biological roles
3. Cross-talk between histone modifications
4. Summary
5. A histone code?
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Quick Overview
• Modifications and modifiers• General roles• Techniques
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Bhaumik, Smith, and Shilatifard, 2007.
Types of Histone Modifications
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• Covalently attached groups (usually to histone tails)
• Reversible and Dynamic– Enzymes that add/remove modification– Signals
• Have diverse biological functions
Cell, 111:285-91, Nov. 1, 2002
Methyl Acetyl Phospho Ubiquitin SUMO
Features of Histone Modifications
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• Small vs. Large groups
• One or up to three groups per residue
Features of Histone Modifications
Jason L J M et al. J. Biol. Chem. 2005
Ub = ~8.5 kDaH4 = 14 kDa
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• Writers: enzymes that add a mark
• Readers: proteins that bind to and “interpret” the mark
• Erasers: enzymes that remove a mark
Tarakhovsky, A., Nature Immunology, 2010.
Histone Modifications and Modifers
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• Others: Sumoylation (Lysine), ADP Ribosylation (Glutamate)
Histone Modifications and Modifers
Residue Modification Modiying Enzyme
Lysine AcetylationDeacetylation
HAT HDAC
Lysine MethylationDemethylation
HMT HDM
Lysine UbiquitylationDeubiquitylation
Ub ligaseUb protease
Serine/Threonine PhosphorylationDephosphorylation
KinasePhosphatase
Arginine MethylationDemethylation
PRMTDeiminase/
Demethylase
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Histone Modifiers
• Do not bind to DNA themselves– Can be recruited by:
• Histone modifications (through chromodomains, bromodomains, etc.)
• Transcription factors• RNA (fission yeast, mammals, plants)• DNA damage
• Act as transcriptional co-regulators
• Enhance activities of transcriptional repressors or activators– Co-repressor: ex. HDACs– Co-activator: ex. HATs
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General Roles of Histone Modifications• Intrinsic
– Single nucleosome changes– Example: histone variant specific modifications (H2AX)
• Extrinsic – Chromatin organization: nucleosome/nucleosome interactions– Alter chromatin packaging, electrostatic charge– Example: H4 acetylation
• Effector-mediated – Recruitment of other proteins to the chromatin via
• Bromodomains bind acetylation• Chromo-like royal domains (chromo, tudor, MBT) and PHD bind methylation• 14-3-3 proteins bind phosphorylation
Kouzarides, Cell 2007
- Prevent binding: H3S10P prevents Heterochromatin Protein 1 binding
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General Roles of Histone Modifications
Wade P A Hum. Mol. Genet. 2001.
Gene Regulation
Moggs and Orphanides, Toxicological Sciences, 2004.
DNA Damage
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General Roles of Histone Modifications
Chromatin Condensation Spermatogenesis
Kruhlak M J et al. J. Biol. Chem. 2001.
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Techniques to Study Histone Modifications
• Chromatin immunoprecipitation (ChIP): Strategy for localizing histone marks
• ChIP-qPCR: if you know the target gene
• ChIP-chip, ChIP-seq, or other genome-wide techniques: unbiased
• Limitations: » Antibody specificity» Inherent biases of localization methods
• Mass Spectrometry:• Requires digestion of histones
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ChIP-chip
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Massively parallel sequencing
Local amplification
ChIP-seq
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ChIP-seq
Genome
“Depth”: the number of mapped sequence tags
“Coverage”: how much of the genome the reads can be mapped to
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ChIP-seq vs. ChIP-chip
Mikkelsen et al., 2007
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Outline
1. Overview of histone modifications:a. Types of modifications and modifiersb. General roles of modificationsc. Techniques used to study histone modifications
2. Specific modifications (acetylation, methylation, etc):a. Residues/positions that are frequently modifiedb. Enzymes that add/remove the modificationc. Biological roles
3. Cross-talk between histone modifications
4. Summary
5. A histone code?
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Specific Histone Modifications
• Positions that are modified• Modifying enzymes• Functions of the modification
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Lysine Acetylation
Bhaumik, Smith, and Shilatifard, 2007.
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Acetylation
• Many lysine residues can be acetylated• mainly on histone tails (sometimes in core)
• Can be part of large acetylation domains
• Modifying enzymes: • often multi-enzyme complexes • can modify multiple residues
• Well correlated with transcriptional activation
• Other roles (chromatin assembly, DNA repair, etc.)
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• Two general types:• Type B: cytoplasmic (newly synthesized histones)
• HAT1
Kouzarides, Cell, 2007.
Histone Acetyl Transferases (HATs/KATs)
Type B
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1. GNAT
2. MYST
3. P300/CBP (metazoan)
Other HATs exist as well:e.g. associated with nuclear receptors or Pol III
4. Rtt109 (fungal)
HAT SuperfamiliesType A: nuclear
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Marmorstein and Trievel, 2009
GNAT MYST P300/CBP Rtt109
HAT Superfamilies
• Similarities• Structurally conserved central core• Can acetylate non-histone proteins
• Differences• Sequence divergence• Catalytic mechanisms• Interacting proteins (regulate specificity)
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• Multi-enzyme complexes
• Targeted by transcriptional repressors
• Deactylate histone tails
Histone Deacetylases (HDACs)
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• Class I HDACs• RPD3-like (HDAC 1, 2, 3)• most cell types• in nucleus
• Class II HDACs• HDA1- like (HDAC 4, 5, 6, 7, 9, 10)• HDAC and N-term repressor motif• restricted expression • shuttle in/out nucleus
• Class III HDACs• Sir-2 (NAD-dependent)• sirtuins
HDAC Superfamilies
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HDACs are in Complexes
Butler and Bates, Nature Reviews Neuroscience, 2006.
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1. Opens up chromatin: – Reduces charge interactions of histones with DNA
(K has a positive charge)– Prevents chromatin compaction (H4K16ac
prevents 30nm fiber formation)
2. Recruits chromatin proteins with bromodomains (SWI/SNF, HATs: GCN5, p300)
3. May occur at same residues as methylation with repressive effect (competitive antagonism)
Roles of Acetylation
Robinson et al., J. Mol. Biol., 2008.
Mujtaba et al., Oncogene, 2007.
PCAF
Yang and Chen, Cell Research, 2011.
H3K27ac
H3K27me3
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4. Highly correlated with active transcription i.e. enriched at TSS of actively transcribed genes
Roles of Acetylation -- Continued
Expression: P1<P2<P3<P4
Heintzman N et al., Nature Genetics, 2007.
Roles of Acetylation
H4Ac H3Ac H3 RNAPII
208 TSS investigated
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5. Correlated with binding of activating transcription factors i.e. enriched at promoters and enhancers
Roles of Acetylation
Heintzman N et al., Nature Genetics, 2007.
H4Ac H3Ac p300
Expression: E1<E2<E3 74 enhancers
(distal p300 binding sites)
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Lysine Methylation
Bhaumik, Smith, and Shilatifard, 2007.
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Lysine Methylation
• Many lysine residues can be methylated• Mainly on histone tails (sometimes in core)• Can be mono-, di-, or tri-methylated
• Depending on residue and number of methyl groups, can be associated with active or repressive transcription
• Other roles• Transcriptional elongation• Pericentromeric heterochromatin• X chromosome inactivation
Liu et. al, Annu. Rev. Plant Biol., 2010.
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• Enzymes very specific• Target a certain lysine on a certain histone
• Put on mono, di, and/or tri methyl (me, me2, me3)• Many contain SET domains (me-transferase)• ‘Readout’ is very specific
• Ex. H3K4me1 vs. H3K4me3
Lysine Methyltransferases: KMTs
Xiao et al., Nature, 2003.
Only room for one methyl
group
Set7/9
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H3K4me: trithorax/Set1, KMT2
H3K9me: Suv3-9, KMT1
H3K27me: polycomb Group (E(z)), KMT6
H3K36me: Set2, KMT3
H3K79me: Dot1 (nonSET) KMT4
H4K20me: Suv4-20, KMT5
KMTs
***Most contain SET Domains
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1. Recruitment of other chromatin proteins through specific domains:
Chromodomain (CHD ATPases, HP1, PC)Tudor (some histone demethylases)PhD (many chromatin regulators BPTF, ING2)MBT (in some polycomb proteins)
WD-40 (WDR5)
Roles of Lysine methylation
Chromo-like(Royal)
Roles of Lysine Methylation
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Bannister and Kouzarides Cell Research 2011
Roles of Lysine Methylation
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Roles of Lysine Methylation
Liu et. al, Annu. Rev. Plant Biol., 2010.
2. Different readout depending on level of methylation
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Roles of Lysine Methylation
2. Different readout depending on level of methylation
– Methylation status of H3K4 is recognized by different domains• H3K4me1: chromodomain in CHD1 (ATPase) = transcription activation• H3K4me2: WD-40 domain in WDR5 in MLL (Trx) = transcription activation• H3K4me3: PhD domain of BPTF in NURF (ISWI) = transcription activation• H3K4me3: PhD ING2 recognizes during DNA damage and shuts down
active transcription through mSin3a-HDAC1
Promoters Enhancers
Heintzman N et al., Nature Genetics, 2007.
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Li et al., Cell, 2007.
Roles of Lysine Methylation
3. Transcriptional activation– H3K4me3: euchromatin promoter, 5’ end activates transcription (Set1)– H3K36me3: in gene (ORF), transcriptional elongation (Set2)
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3. Transcriptional activation– H3K36me3 marks actively transcribed genes
Guenther et al., Cell 2007
H3K36me3
Roles of Lysine Methylation
PolII
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4. Transcriptional repression• H3K9me (Suv39H1)• In promoter, represses transcription• In larger domains, heterochromatin formation• H3K27me (EZH2)• Repression of transcription • Polycomb group silencing• H4K20me (Suv420H1)• Some forms of silencing and repression of gene expression• In repetitive elements, similar localization as H3K9me3 in ES cells
Li et al., Cell, 2007.
Roles of Lysine Methylation
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Co-occurrence of activating and repressivelysine methylation
Bivalency marks “poised” genes
Mikkelsen et al., Nature 2007
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Position of histone modifications
Mikkelsen et al., Nature, 2007.
H3K9me3 and H4K20me3 can occur in actively transcribed genes
Thought to prevent access to cryptic transcription initiation
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Wysocka et al., Cell, 2005.
Jumonji family: H3K9(JHDM2A:me1 and me2)
LSD1: H3K4
JHDM1A demethylase: H3K36 me1 and me2
Lysine Demethylation
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Lysine Demethylation
• LSD1 – first histone demethylase– amine oxidase– only me1 and me2 can serve as substrates
• Different domain structure from other demethylase• Complex determines specificity (H3K4me vs. H3K9me)
Stavropoulos et al., NSMB, 2006.
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• JmjC– JmjC-domain containing oxygenases– 27 family members– Catalytic JmjC domain can accommodate me3 as substrate
Lysine Demethylation
Wolf et al., EMBO Reports, 2007.
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Lysine Methylation/Demethylation
Shi, Nature Reviews, 2007.
Individual lysines can be targeted by different methyltransferases/demethylases
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Kouzarides, Cell, 2007.
Other Histone Modifications
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Arginine Methylation
Bhaumik et al., NSMB, 2007.
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Arginine Methylation
Can be symmetric or asymmetric
Zhang et al., EMBO Journal, 2000.
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Protein Arginine Methyltransferases (PRMTs)
Arginine methylation can be activating or repressive
Kouzarides, Curr. Opin. G&D, 2002.
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Arginine demethylation:1. different amino acid
Involves a different mechanism than Lysine demethylation
Lysine demethylation:removal of methyl groups
Arginine Demethylation
Bannister and Kouzarides, Nature, 2005.
2. Also possible simple de-methylationJMJD6, H3R2 and H4R3
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Serine/Threonine Phosphorylation
Bhaumik et al., NSMB, 2007.
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Serine/Threonine Phosphorylation
• Kinases phosphorylate
• Phosphatases remove
example H3S10P during mitosisKinases: Aurora BPhosphatase: PP1
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Roles of Ser/Thr Phosphorylation
Cheung et al., Cell, 2000.
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Hirota et al., Nature, 2005.
Fernandez-Capetilly et al., JEM, 2004.
H2AX-pDAPI
Laser
UV
Roles of Ser/Thr Phosphorylation
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Histone Ubiquitination
• Ubiquitination– H2A K119:
• Function: Polycomb repression (Ring1a, PCG)– H2B K123: activation (Rad6+Bre yeast; RNF20/RNF40 and UbcH6 in mam)
• Function: FACT recruitment, transcriptional elongation– H3 and H4: DNA repair (CUL4)
• De-ubiquitination– H2A: Dub (PCAF)
• Function: counteract Polycomb– H2B: Ubp8 (SAGA)
• Function: transcription elongation
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Outline
1. Overview of histone modifications:a. Types of modifications and modifiersb. General roles of modificationsc. Techniques used to study histone modifications
2. Specific modifications (acetylation, methylation, etc):a. Residues/positions that are frequently modifiedb. Enzymes that add/remove the modificationc. Biological roles
3. Cross-talk between histone modifications
4. Summary
5. A histone code?
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Crosstalk among Modifications
Bannister and Kouzarides, Cell Research, 2011.
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Crosstalk among Modifications
• Mutually exclusive: a position can be modified either with an activating or repressive mark (competitive antagonism)– H3K9ac vs. H3K9me
• One modification recruits a modifying enzyme that places/removes another modification on the same/different histone tail– H3S10P GCN5 H3K14ac
In cis In trans
Lee et. al, Cell, 2010.
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Crosstalk among Modifications
• Mutually exclusive: a position can be modified either with an activating or repressive mark (competitive antagonism)– H3K9ac vs. H3K9me
• One modification recruits a modifying enzyme that places/removes another modification on the same/different histone tail– H3S10P GCN5 H3K14ac
• The binding of a protein may be disrupted by modification of an adjacent position – HP1 (binds to H3K9me) by H3S10P : “phospho switch”
Badia et al., Curr. Med. Chem., 2007.
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Crosstalk among Modifications
• Mutually exclusive: a position can be modified either with an activating or repressive mark – H3K9ac vs. H3K9me
• One modification recruits a modifying enzyme that places/removes another modification on the same/different histone tail– H3S10P GCN5 H3K14ac
• The binding of a protein may be disrupted by modification of an adjacent position – HP1 (binds to H3K9me) by H3S10P
• Cooperative recruitmentPHF8 binds H3K4me3 most strongly if H3K9ac and H3K14ac
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One complex may contain both demethylase and methyltransferasetargeting different residues with opposing functions
Crosstalk among Modifications
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Crosstalk among Modifications
One modification affects the generation of another
Schotta et al., Genes and Dev., 2004.
Pericentric heterochromatin
H3K9me3
H4K20me
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Summary: Histone PTMs
• Covalent and reversible • Usually occur on histone tails• Modifying enzymes:
• Redundancy: A single position can be modified by multiple different enzymes
• Specificity: Some enzymes (like HMTs) can target only one residue and some (like HATs) can target many
• Histone PTMs recruit other proteins to DNA via specific domains• Bromo (Ac)• Chromo/PHD (Me)• 14-3-3 (Ph)
• Participate in regulation of many processes– transcription– DNA repair– chromatin assembly – long-range packaging (heterochromatin formation, silencing)
• Readout frequently depends on the context
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So…is there a histone code?
Kharchenko et al., Nature, 2011.
Euchromatin
Heterochromatin
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So…is there a histone code?
Iwase et al., NSMB, 2011.
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• Discuss.
So…is there a histone code?
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1. Type of modification– Which amino-acid– Number of modifications (me)
2. Position in genome– Promoter: H3K36me, H3K9me are repressive– Coding region: H3K36me, H3K9me are activating and prevent cryptic initiation of transcription in ORF
3. Other histone modifications– combinatorial (occur together)– H3K4me + H3K9me: transcriptional activation– H4K20me + H3K9me: heterochromatin formation– H3K27me + H3K4me: “bivalent” mark in stem cells
4. Size of histone modification domain– large: heritable (can be copied more easily)
• H3K27me can recruit PRC2 has H3K27me3 activity• H3K4me recruits WDR5 (MLL thrithorax): H3K4me
5. Cycles of modifications– H2Bub H2B required for transcriptional elongation
Summary: Histone PTMs and readout