The UV-damaged DNA binding protein mediates efficient targeting of the nucleotide excision repair complex to UV-induced photo lesions

Previous studies point to the XPC-hHR23B complex as the principal initiator of global genome nucleotide excision repair (NER) pathway, responsible for the repair of UV-induced cyclobutane pyrimidine dimers (CPD) and 6-4 photoproducts (6-4PP) in human cells. However, the UV-damaged DNA binding protein (UV-DDB) has also been proposed as a damage recognition factor involved in repair of UV-photoproducts, especially CPD. Here, we show in human XP-E cells (UV-DDB deficient) that the incision complex formation at UV-induced lesions was severely diminished in locally damaged nuclear spots. Repair kinetics of CPD and 6-4PP in locally and globally UV-irradiated normal human and XP-E cells demonstrate that UV-DDB can mediate efficient targeting of XPC-hHR23B and other NER factors to 6-4PP. The data is consistent with a mechanism in which UV-DDB forms a stable complex when bound to a 6-4PP, allowing subsequent repair proteins - starting with XPC-hHR23B - to accumulate, and verify the lesion, resulting in efficient 6-4PP repair. These findings suggest that (i) UV-DDB accelerates repair of 6-4PP, and at later time points also CPD, (ii) the fraction of 6-4PP that can be bound by UV-DDB is limited due to its low cellular quantity and fast UV dependent degradation, and (iii) in the absence of UV-DDB a slow XPC-hHR23B dependent pathway is capable to repair 6-4PP, and to some extent also CPD.