DNA is the carrier of the genetic information that defines any living being. The genetic code fixed in DNA is crucial for processes on a subcellular scale up to the appearance and function of the organism as s whole. Nonetheless, DNA is constantly exposed to insults from endogenous sources such as hydrolysis, oxidation, alkylation, or replication errors. In addition, ionizing radiation, UV radiation, and a plethora of chemical reagents are external factors that threaten the integrity of DNA.
Unlike RNA and proteins, DNA is not being degraded and re-synthesized upon damage. Instead, various repair pathways are in existence to assure that the DNA remains intact. Francis Crick noted in 1974 that “we totally missed the possible role of enzymes in [DNA] repair. I later came to realize that DNA is so precious that probably many distinct mechanisms could exist.”
This presage holds true today: over a hundred genes have been characterized since that are involved in an intricate network of DNA repair pathways. DNA damage can be repaired via six different pathways depending on the nature of the lesion: chemical modifications, misincorporated nucleotides, and cross-links are reverted through direct reversal (DR), mismatch repair (MMR), and nucleotide excision repair mechanisms. DNA single strand breaks are being mended via base excision repair. Highly mutagenic DNA double strand breaks finally are repaired through a number of complex pathways that rely on homologous recombination (HR) with the sister chromatid (in the S or G2 phase of the cell cycle) or non-homologous end-joining (NHEJ) of both ends of the double strand break. The Fanconi Anemia pathway is or particular importance for the repair of DNA interstrand crosslinks. In case a DNA lesion cannot be repaired in time, specialized DNA polymerases enable trans-lesion synthesis (TLS) in order to prevent the DNA replication fork from stalling. Mutations that render components of these repair pathways non-functional lead to diseases such as xeroderma pigmentosum, ataxia telangiectasia, Fanconi anemia, and a predisposition for cancer.
Besides, these repair mechanisms are of high interest for current targeted genome editing approaches that typically take advantage of the cellular DNA repair machinery.
Aparacio T et al. DNA double-strand break repair pathway choice and cancer. DNA Repair (2014) PMID 24746645
Chatterjee N, Walker GC. Mechanisms of DNA damage, repair, and mutagenesis. Environ Mol Mutagen (2017) PMID 28485537
Chaudhuri AR, Nussenzweig A. The multifaceted roles of PARP1 in DNA repair and chromatin remodelling. Nat Rev Mol Cell Biol (2017) PMID 28676700
Bian L et al. MRE11-RAD50-NBS1 complex alterations and DNA damage response: implications for cancer treatment. Mol Cancer (2019) PMID 31767017
Fang C et al. Fanconi Anemia Pathway: Mechanisms of Breast Cancer Predisposition Development and Potential Therapeutic Targets. Front Cell Dev Biol (2020) PMID 32300589
Burgess JT et al. The Therapeutic Potential of DNA Damage Repair Pathways and Genomic Stability in Lung Cancer. Front Oncol (2020) PMID 32850380