Repair of Bipyrimidine Photoproducts at Telomeres of Ultraviolet Light Irradiated Mammalian Cells
Year: 2014
Type: article
Abstract: Telomeres at chromosome ends promote genome stability, survival, and proliferation in cells, and prevent degenerative diseases and cancer in humans. Human telomeres are 10-15 kilobases long and consist of about 1500 tandem TTAGGG repeats. Six telomeric proteins form a shelterin complex that protects the telomeres from being recognized as a chromosome break, thereby preventing inappropriate repair and chromosome fusions. Telomeric DNA sequences are vulnerable to ultraviolet light (UV)-induced damage. UV creates primarily two types of photoproducts within DNA: cyclobutane pyrimidine dimers (CPDs) and 6-4 photoproducts (6-4 PPs). Unrepaired photoproducts can stall or block DNA replication and transcription, or if tolerated and bypassed, can introduce mutations that cause genomic instability which can drive carcinogenesis. In genomic DNA, these potentially harmful cellular effects are avoided through a specialized nucleotide excision repair (NER) pathway that removes photoproducts and restores normal DNA. This dissertation investigated if photoproducts also form at chromosome ends and if they are repaired over time by NER. We exposed skin fibroblasts BJ-hTERT (NER proficient) and XP-A (NER deficient) to 10 J/m2 UVC which induces CPD and 6-4 PP lesions. We then extracted genomic and telomeric DNA from these fibroblasts and measured the rate of lesion disappearance. Post UVC exposure, BJ-hTERT cells repaired all detectable telomeric 6-4 PPs by six hours and telomeric CPDs by two days. However, XP-A cells did not repair telomeric 6-4 PPs. We observed that unrepaired photoproducts inhibit telomere TRF1 protein binding to telomeric DNA in vitro, and that cellular UVC irradiation of NER deficient cells causes telomere aberrations. Our novel findings have uncovered the presence and importance of a major DNA repair pathway at telomeres and increase our understanding of how unrepaired bulky adducts at telomeres may impact telomere structure and function. Telomere maintenance is essential in protection against age-related diseases and cancer in humans. The public health relevance of our study thus, relates to its potential usefulness in developing biomarkers of toxicology for aging and cancer.
Author: Dhvani Parikh
Language: English
Topic: DNA Repair Mechanisms
Subfield: Molecular Biology
Domain: Life Sciences
Open Access status: green
Funder: Strong
OpenAlex ID: W575845765