A histone H4 code regulates 53BP1-mediated responses to DNA damage

Hsiao, Kuei-Yang

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Description

Title

A histone H4 code regulates 53BP1-mediated responses to DNA damage

Author(s)

Hsiao, Kuei-Yang

Issue Date

2012-02-01T00:54:18Z

Director of Research (if dissertation) or Advisor (if thesis)

Mizzen, Craig A.

Committee Member(s)

• Bagchi, Milan K.
• Kemper, Byron W.
• Nardulli, Ann M.
• Spies, Maria

Department of Study

Molecular & Integrative Physl

Discipline

Molecular & Integrative Physi

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• DNA damage
• P53-binding protein 1 (53BP1)
• histone H4
• methylation
• acetylation
• deacetylation
• Deoxyribonucleic acid (DNA)

Abstract

Individual histone post-translational modifications have been implicated in regulating many cellular events. Modifications can occur at high densities in the N-terminal tail domains of core histones, enabling the possibility that combinations of modifications regulate chromatin processes differently than modifications occurring individually. However, surprisingly little is known about the nature and functions of multi-site histone modification. This study investigates functional interactions between acetylation of lysine 16 (K16ac) and methylation of lysine 20 (K20me), two modifications that frequently occur together on molecules of histone H4 (H4). Methylation state-specific binding of the P53-binding protein 1 (53BP1) to dimethyl K20 H4 (K20me2) and the formation of 53BP1 nuclear foci near double strand breaks are early events in DNA damage responses (DDR) that provide a platform for the assembly of downstream effectors. Since global levels of K20me2 are relatively stable and are established independently of DNA damage, we propose that reversible changes in the levels of K16ac co-modification act like a dynamic switch to modulate DDR responses mediated by K20me2. Analyses of the interaction of the K20me2 binding domain of 53BP1 with H4 peptides in vitro reveal that K16ac co-modification attenuates specific recognition of K20me1/2 (mono- and di-methylation) by 53BP1. The possibility that K16ac and K20me2 interact functionally in vivo is demonstrated by my finding that K16 deacetylation accompanies the induction of H2A.X phosphorylation, a well-known marker for DDR, following DNA damage by either UV irradiation, hydroxyurea or bleocin treatment. Moreover, the effects of expressing K16 mutants of H4 and inhibition of histone deacetylases on 53BP1 foci formation induced by DNA damage support the hypothesis that K16ac co-modification negatively regulates the formation of 53BP1 foci. The functional significance of these interactions is underscored by the finding that K16 hyperacetylation also hindered 53BP1-mediated nonhomologous end-joining as demonstrated by treatment of HDACi and overexpression of a H4 mutant mimicking acetylation at K16. DNA damage-induced deacetylation was associated with transcriptional repression, but was not linked to chromatin decondensation. Deregulated DDR mechanisms are frequently involved in the development and progression of cancer, and interruption of the DDR is used in chemotherapeutic treatments against cancer. Further investigation of the role of H4 modifications in DDR will enhance our understanding of how genome integrity is maintained in normal cells and may provide insights crucial for developing new cancer therapies.

Graduation Semester

2011-12

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Copyright 2011 Kuei-Yang Hsiao

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