Project description:UV-induced DNA lesions are an important contributor to mutagenesis and cancer, but it is not fully understood how the chromosomal landscape influences UV lesion formation and repair. We have used a novel high-throughput sequencing method to precisely map UV-induced cyclobutane pyrimidine dimers (CPDs) at nucleotide resolution throughout the yeast genome. Analysis of CPD formation reveals that nucleosomal DNA having an inward rotational setting is protected from CPD lesions. In strongly positioned nucleosomes, this nucleosome 'photofootprint' overrides intrinsic dipyrimidine sequence preferences for CPD formation. CPD formation is also inhibited by DNA-bound transcription factors, in effect protecting important DNA elements from UV damage. Analysis of CPD repair revealed a clear signature of efficient transcription-coupled nucleotide excision repair. Repair was less efficient at translational positions near a nucleosome dyad and at heterochromatic regions in the yeast genome. These findings define the roles of nucleosomes and transcription factors in UV damage formation and repair. UV mapping data was analyzed for yeast cells irradiated with 125J/m2 and allowed to repair for 0hr (2 samples), 20 minutes, 1 hour, or 2 hours. Data is also included for naked DNA irradiated with UV 60 or 90 J/m2
Project description:UV-induced DNA lesions are an important contributor to mutagenesis and cancer, but it is not fully understood how the chromosomal landscape influences UV lesion formation and repair. We have used a novel high-throughput sequencing method to precisely map UV-induced cyclobutane pyrimidine dimers (CPDs) at nucleotide resolution throughout the yeast genome. Analysis of CPD formation reveals that nucleosomal DNA having an inward rotational setting is protected from CPD lesions. In strongly positioned nucleosomes, this nucleosome 'photofootprint' overrides intrinsic dipyrimidine sequence preferences for CPD formation. CPD formation is also inhibited by DNA-bound transcription factors, in effect protecting important DNA elements from UV damage. Analysis of CPD repair revealed a clear signature of efficient transcription-coupled nucleotide excision repair. Repair was less efficient at translational positions near a nucleosome dyad and at heterochromatic regions in the yeast genome. These findings define the roles of nucleosomes and transcription factors in UV damage formation and repair.
Project description:We used a high-throughput sequencing method known as CPD-seq to map the formation of UV-induced cyclobutane pyrimidine dimers (CPD) at single nucleotide resolution in UV-irradiated yeast genomic DNA (naked DNA) in the presence or absence of cytosine methylation at CpG sites by the methyltransferase M.SssI.
Project description:Noncoding mutation hotspots have been identified in melanoma and many of them occur at the binding sites of E26 transformation-specific (ETS) proteins; however, their formation mechanism and functional impacts are not fully understood. Here, we used UV damage sequencing data and analyzed cyclobutane pyrimidine dimer (CPD) formation, DNA repair, and CPD deamination in human cells at single-nucleotide resolution. Our data shows prominent CPD hotspots immediately after UV irradiation at ETS binding sites, particularly at sites with a conserved TTCCGG motif, which correlate with mutation hotspots identified in cutaneous melanoma. Additionally, CPDs are repaired slower at ETS binding sites than in flanking DNA. Cytosine deamination in CPDs to uracil is suggested as an important step for UV mutagenesis. However, we found that CPD deamination is significantly suppressed at ETS binding sites, particularly for the CPD hotspot on the 5’ side of the ETS motif, arguing against a role for CPD deamination in promoting ETS-associated UV mutations. Finally, we analyzed a subset of frequently mutated promoters, including the ribosomal protein genes RPL13A and RPS20, and found that mutations in the ETS motif can significantly reduce the promoter activity. Thus, our data identifies high UV damage and low repair, but not CPD deamination, as the main mechanism for ETS-associated mutations in melanoma and uncover new roles of often-overlooked mutation hotspots in perturbing gene transcription.
Project description:UV light is an initiating factor in the etiology of human melanoma due to its production of mutagenic DNA photoproducts, primarily cyclobutane pyrimidine dimers (CPDs) and 6-4 photoproducts. UV-induced mutations are heterogeneously distributed across melanoma genomes, being enriched, for example, in regions of compact heterochromatin and at active transcription factor binding sites (TFBS). Differential ability of nucleotide excision repair (NER) to remove UV-induced DNA lesions in these regions has been proposed as the primary factor establishing the observed regional differences in melanoma mutation density. However, it is not fully understood to what extent the binding of transcription factors and chromatin structure affect UV damage formation, nor how variations in initial damage levels contribute to mutagenesis. Here, we directly mapped sites of CPD formation across the genome in human cells, and show that variations in UV damage formation, due to primary chromatin structure and transcription factor binding, are strongly correlated with local differences in melanoma mutation density. Analysis of individual transcription factors revealed that the E26 transformation-specific (ETS) family is the major contributor to increased somatic mutation density at TFBS in melanoma, primarily because DNA binding by ETS family transcription factors stimulates the formation of CPD lesions, generating UV damage 'hotspots'. Moreover, many ETS binding sites, including those associated with known cancer genes, are recurrently mutated in human melanomas. These findings establish variable lesion formation as a key contributor to mutation heterogeneity in cancer.
Project description:Rad16 is required for global genomic nucleotide excision repair (GG-NER) of UV-induced CPD lesions. Here we have used a novel high-throughput sequencing method known as CPD-seq to map the repair of UV-induced cyclobutane pyrimidine dimers (CPDs) at single nucleotide resolution across the yeast genome in rad16 mutant cells. Analysis of CPD repair indicates that rad16 is generally required for CPD repair in the non-transcribed strand (NTS) of yeast genes and non-transcribed genomic regions.
Project description:UV-induced DNA damage is the major carcinogen of skin cancer. We developed HS-Damage-seq to map UV damage with unprecedented sensitivity and resolution in human cells. While the distribution of UV-induced damage are mainly determined by sequence context and essentially uniform throughout the genome, transcription factors can affect damage formation at specific positions. With time-course experiments, we observed changes in damage distribution at particular genomic loci and chromatin states, which reflects the nucleotide excision repair preferences and complements the repair maps by XR-seq. Our results demonstrated that while initial damage is uniformly distributed, they are heterogeneously repaired throughout the genome. The combination of damage and repair maps provides a holistic perspective of UV damage and repair in the human genome.
Project description:Nucleotide excision repair is a primary DNA repair mechanism that removes bulky DNA adducts such as UV-induced pyrimidine dimers. Correspondingly, genome-wide mapping of nucleotide excision repair with eXcision Repair sequencing (XR-seq), provides comprehensive profiling of DNA damage repair. A number of XR-seq experiments at a variety of conditions for different damage types revealed heterogenous repair in the human genome. Although human repair profiles were extensively studied, how repair maps vary between primates is yet to be investigated. Here, we characterized the genome-wide UV-induced damage repair maps of the grey mouse lemur,Microcebus murinus, in comparison with human. We derived fibroblast cell lines from mouse lemur and exposed them to UV irradiation. Following repair events were captured genome-wide by XR-seq protocol 1 hour and 5 minutes after irradiation for cyclobutane pyrimidine dimers (CPD) and 6-4 pyrimidine-pyrimidone photoproducts ([6-4]PP), respectively. Mouse lemur repair profiles were analyzed in comparison with the equivalent human fibroblast datasets. We found that transcription-coupled repair levels for CPD repair differs between two primates. Despite this, comparative analysis of human and mouse lemur fibroblasts revealed that genome-wide repair profiles of the homologous regions between the primates are highly correlated. This correlation is stronger for the highly expressed genes as well as the genes sharing high homology. With the inclusion of an additional XR-seq sample derived from another human cell line in the analysis, we found that fibroblasts between two primates repair lesions more similarly relative to two distinct cell lines from human. These results suggest that mouse lemurs and humans, and possibly primates in general, share similar repair mechanism as well as genomic variance distribution.