Repair of ribosomal DNA (rDNA) is a very important nuclear process due to the most active transcription of ribosomal genes. Proper repair of rDNA is required for physiological biogenesis of ribosomes. Here, we analyzed the epigenetics of the DNA damage response in a nucleolar compartment, thus in the ribosomal genes studied in nonirradiated and UVA-irradiated mouse embryonic fibroblasts (MEFs). We found that the promoter of ribosomal genes is not abundant on H4K20me2, but it is densely occupied by H4K20me3. Ribosomal genes, regulated via UBF1/2 proteins, were characterized by an interaction between UBF1/2 and H4K20me2/me3. This interaction was strengthened by UVA irradiation that additionally causes a focal accumulation of H4K20me3 in the nucleolus. No interaction has been found between UBF1/2 and H3K9me3. Interestingly, UVA irradiation decreases the levels of H3K9me3 and H4K20me3 at 28S rDNA. Altogether, the UVA light affects the epigenetic status of ribosomal genes at 28S rDNA and strengthens an interaction between UBF1/2 proteins and H4K20me2/me3.

• Keywords
• DNA damage response, DNA repair, Nucleolus, UBF, UVA irradiation,
• MeSH
• Cell Nucleolus metabolism   MeSH
• Cell Nucleus metabolism   MeSH
• Chromatin Immunoprecipitation MeSH
• DNA-Binding Proteins MeSH
• Epigenesis, Genetic radiation effects   MeSH
• Fluorescent Antibody Technique MeSH
• Histones metabolism   MeSH
• Methylation MeSH
• Mice MeSH
• Promoter Regions, Genetic MeSH
• Gene Expression Regulation radiation effects   MeSH
• DNA, Ribosomal genetics   MeSH
• Pol1 Transcription Initiation Complex Proteins metabolism   MeSH
• Ultraviolet Rays * MeSH
• Protein Binding MeSH
• High-Throughput Nucleotide Sequencing MeSH
• Animals MeSH
• Check Tag
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• DNA-Binding Proteins MeSH
• Histones MeSH
• DNA, Ribosomal MeSH
• transcription factor UBF MeSH Browser
• Pol1 Transcription Initiation Complex Proteins MeSH

Methylation of histones H4 at lysine 20 position (H4K20me), which is functional in DNA repair, represents a binding site for the 53BP1 protein. Here, we show a radiation-induced increase in the level of H4K20me3 while the levels of H4K20me1 and H4K20me2 remained intact. H4K20me3 was significantly pronounced at DNA lesions in only the G1 phase of the cycle, while this histone mark was reduced in very late S and G2 phases when PCNA was recruited to locally micro-irradiated chromatin. H4K20me3 was diminished in locally irradiated Suv39h1/h2 double knockout (dn) fibroblasts, and the same phenomenon was observed for H3K9me3 and its binding partner, the HP1β protein. Immunoprecipitation showed the existence of an interaction between H3K9me3-53BP1 and H4K20me3-53BP1; however, HP1β did not interact with 53BP1. Together, H3K9me3 and H4K20me3 represent epigenetic markers that are important for the function of the 53BP1 protein in non-homologous end joining (NHEJ) repair. The very late S phase represents the cell cycle breakpoint when a DDR function of the H4K20me3-53BP1 complex is abrogated due to recruitment of the PCNA protein and other DNA repair factors of homologous recombination to DNA lesions.

• Keywords
• DNA damage, H3K9me3, H4K20me1/me2/me3, Suv39h1/h2, epigenetics,
• MeSH
• Tumor Suppressor p53-Binding Protein 1 genetics   metabolism   MeSH
• Cell Nucleus genetics   metabolism   radiation effects   MeSH
• Cell Line MeSH
• Cell Cycle MeSH
• Chromosomal Proteins, Non-Histone metabolism   MeSH
• Epigenesis, Genetic * radiation effects   MeSH
• Histones metabolism   MeSH
• Chromobox Protein Homolog 5 MeSH
• Humans MeSH
• DNA Methylation * radiation effects   MeSH
• Methylation MeSH
• Mice MeSH
• DNA End-Joining Repair * MeSH
• DNA Damage * MeSH
• Proliferating Cell Nuclear Antigen metabolism   MeSH
• Chromatin Assembly and Disassembly MeSH
• Protein Binding MeSH
• Binding Sites MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Tumor Suppressor p53-Binding Protein 1 MeSH
• CBX1 protein, human MeSH Browser
• Cbx1 protein, mouse MeSH Browser
• Chromosomal Proteins, Non-Histone MeSH
• Histones MeSH
• Chromobox Protein Homolog 5 MeSH
• PCNA protein, human MeSH Browser
• Proliferating Cell Nuclear Antigen MeSH
• TP53BP1 protein, human MeSH Browser
• Trp53bp1 protein, mouse MeSH Browser