Work

Nucleotide Excision Repair and Transcription-coupled DNA Repair Abrogate the Impact of DNA Damage on Transcription

Year: 2015

Type: article

Abstract: DNA adducts derived from carcinogenic polycyclic aromatic hydrocarbons like benzo[a]pyrene (B[a]P) and benzo[c]phenanthrene (B[c]Ph) impede replication and transcription, resulting in aberrant cell division and gene expression. Global nucleotide excision repair (NER) and transcription-coupled DNA repair (TCR) are among the DNA repair pathways that evolved to maintain genome integrity by removing DNA damage. The interplay between global NER and TCR in repairing the polycyclic aromatic hydrocarbon-derived DNA adducts (؉)-trans-anti-B[a]P-N6 -dA, which is subject to NER and blocks transcription in vitro, and (؉)-trans-anti-B[c]Ph-N 6 -dA, which is a poor substrate for NER but also blocks transcription in vitro, was tested.The results show that both adducts inhibit transcription in human cells that lack both NER and TCR.The (؉)-trans-anti-B[a]P-N 6 -dA lesion exhibited no detectable effect on transcription in cells proficient in NER but lacking TCR, indicating that NER can remove the lesion in the absence of TCR, which is consistent with in vitro data.In primary human cells lacking NER, (؉)-trans-anti-B[a]P-N 6 -dA exhibited a deleterious effect on transcription that was less severe than in cells lacking both pathways, suggesting that TCR can repair the adduct but not as effectively as global NER.In contrast, (؉)-trans-anti-B[c]Ph-N 6 -dA dramatically reduces transcript production in cells proficient in global NER but lacking TCR, indicating that TCR is necessary for the removal of this adduct, which is consistent with in vitro data showing that it is a poor substrate for NER.Hence, both global NER and TCR enhance the recovery of gene expression following DNA damage, and TCR plays an important role in removing DNA damage that is refractory to NER.Chemicals and radiation can damage DNA, resulting in structural alterations to the nitrogenous bases, deletions of genetic material, and breaks in chromosomes (1-4).The resulting damage often disrupts fundamental cellular processes, including replication and transcription.During replication, DNA damage interferes with DNA synthesis, introduces genetic errors, and increases genomic instability, events often associated with cancer (5, 6).During transcription, damaged DNA can disrupt RNA synthesis, resulting in truncated transcripts, or introduce errors into the products during elongation (7).Although the effects of DNA damage on replication have been well characterized, less is known about its influence on gene expression in cells.There is considerable biochemical evidence that DNA damage profoundly affects the progression of RNA polymerases during RNA synthesis (8).A DNA lesion situated on the transcribed strand often stalls or strongly impedes RNA polymerase translocation, resulting in altered transcripts that can be truncated, contain deletions or insertions, or harbor misincorporated bases (9 -11).In fact, alterations to mRNA generated during transcription, an event referred to as transcriptional mutagenesis, can result in changes to protein function following translation (12).For example, O 6 -methylguanine, a DNA lesion formed by methylating agents, partially blocks transcription elongation of human RNA polymerase and frequently directs insertion of a uridine nucleotide rather than a cytidine nucleotide into RNA (13, 14).To minimize the adverse consequences of DNA damage, genome maintenance pathways have evolved in cells (15-17).Among them is nucleotide excision repair (NER) 3 that has two branches, global NER and transcription-coupled DNA repair (TCR), each of which is germane to the work reported here.Global NER is executed via a complex set of coordinated events.The pathway requires over 30 proteins, including the XPA through XPG proteins, that are defective in patients with the disease xeroderma pigmentosum (XP).The first step in global NER, which distinguishes it from TCR, is DNA damage * This work was supported by National Institutes of Health Grant ES-010581 (to D. A.

Source: Journal of Biological Chemistry

DOI: 10.1074/jbc.m115.685271