Histone H3 K56 hyperacetylation perturbs replisomes and causes DNA damage

Area of Science:

• Molecular Biology
• Genetics
• Cell Biology

Background:

• Histone deacetylation, specifically of histone H3 K56, is regulated by sirtuins Hst3p and Hst4p.
• This process is crucial for maintaining genomic stability.
• The physiological impact of impaired H3 K56 deacetylation remains unclear.

Purpose of the Study:

• To investigate the consequences of lacking Hst3p and Hst4p, leading to constitutive H3 K56 hyperacetylation.
• To elucidate the role of H3 K56 deacetylation in DNA damage response and replication.
• To identify genetic interactions and pathways affected by H3 K56 hyperacetylation.

Main Methods:

• Analysis of DNA damage markers (Rad53p activation, DNA-damage inducible genes) in hst3 hst4 cells.
• Synthetic lethality screening with mutations in DNA replication and repair genes.
• Genetic suppression analysis using K56R mutations and altered clamp loader expression (Rfc1p, CTF18, RAD24, ELG1).
• Investigating the role of CTF4 in the H3 K56 acetylation pathway.

Main Results:

• Cells lacking Hst3p and Hst4p exhibit spontaneous DNA damage and activate DNA damage checkpoints.
• hst3 hst4 cells show synthetic lethality with mutations affecting DNA replication and double-strand break (DSB) repair.
• This synthetic lethality is largely dependent on H3 K56 hyperacetylation, as indicated by suppression via K56R mutation.
• Overexpression of Rfc1p or inactivation of alternative clamp loaders (CTF18, RAD24, ELG1) suppresses hst3 hst4 phenotypes.
• Loss of CTF4 also suppresses these phenotypes, suggesting its involvement in the H3 K56 acetylation pathway and replisome modulation.
• A balance between RFC complexes is critical, with nonreplicative RFC forms being detrimental in hyperacetylated cells.

Conclusions:

• Proper H3 K56 deacetylation by Hst3p and Hst4p is essential for preventing spontaneous DNA damage and maintaining genomic stability.
• The H3 K56 acetylation pathway, involving CTF4, converges on and modulates replisome function.
• Dysregulation of H3 K56 acetylation impacts DNA replication and repair, leading to synthetic lethality.
• A critical balance exists between replicative and nonreplicative RFC complexes, particularly under conditions of constitutive H3 K56 hyperacetylation.