Abstract
UV-DDB, consisting of subunits DDB1 and DDB2, recognizes UV-induced photoproducts during global genome nucleotide excision repair (GG-NER). We recently demonstrated a noncanonical role of UV-DDB in stimulating base excision repair (BER) which raised several questions about the timing of UV-DDB arrival at 8-oxoguanine (8-oxoG), and the dependency of UV-DDB on the recruitment of downstream BER and NER proteins. Using two different approaches to introduce 8-oxoG in cells, we show that DDB2 is recruited to 8-oxoG immediately after damage and colocalizes with 8-oxoG glycosylase (OGG1) at sites of repair. 8-oxoG removal and OGG1 recruitment is significantly reduced in the absence of DDB2. NER proteins, XPA and XPC, also accumulate at 8-oxoG. While XPC recruitment is dependent on DDB2, XPA recruitment is DDB2-independent and transcription-coupled. Finally, DDB2 accumulation at 8-oxoG induces local chromatin unfolding. We propose that DDB2-mediated chromatin decompaction facilitates the recruitment of downstream BER proteins to 8-oxoG lesions.
Highlights
UV-damaged DNA binding protein (UV-DDB), consisting of subunits DDB1 and DDB2, recognizes UV-induced photoproducts during global genome nucleotide excision repair (GG-NER)
We propose a model for 8-oxoG processing that directly involves the NER proteins, DDB2, XPC, and XPA, where DDB2 binds 8-oxoG lesions to change the local chromatin environment facilitating the recruitment of downstream repair proteins
These results suggest that DDB2 is involved in 8-oxoG processing in cells maintained at 5% O2
Summary
UV-DDB, consisting of subunits DDB1 and DDB2, recognizes UV-induced photoproducts during global genome nucleotide excision repair (GG-NER). We recently demonstrated a noncanonical role of UV-DDB in stimulating base excision repair (BER) which raised several questions about the timing of UV-DDB arrival at 8-oxoguanine (8-oxoG), and the dependency of UV-DDB on the recruitment of downstream BER and NER proteins. Due to its low redox potential, guanine is the most readily oxidized base[2] leading to the formation of 8-oxoguanine (8-oxoG) This modification is one of the most abundant oxidative lesions in the genome, with an estimated steady-state level of about 1–2 lesions/106 guanines. AP (apurinic/apyrimidinic) lyase activity that cleaves the phosphate backbone and creates a single-strand break, leaving a free 5′ phosphate and a 3′-phospho-α, β-unsaturated aldehyde (3′PUA)[15,16]. This repair intermediate is processed by AP endonuclease (APE1), leaving a 3′OH and a deoxyribose-5′-phosphate (dRP). Cellular studies have suggested that the weak AP lyase activity of OGG1 might not function during BER, and instead APE1 cleaves the resulting abasic site[16,17]
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