Cellular Concentrations of DDB2 Regulate Dynamic Binding of DDB1 at UV-Induced DNA Damage

Abstract

Nucleotide excision repair (NER) is the principal pathway for counteracting cytotoxic and mutagenic effects of UV irradiation. To provide insight into the in vivo regulation of the DNA damage recognition step of global genome NER (GG-NER), we constructed cell lines expressing fluorescently tagged damaged DNA binding protein 1 (DDB1). DDB1 is a core subunit of a number of cullin 4-RING ubiquitin ligase complexes. UV-activated DDB1-DDB2-CUL4A-ROC1 ubiquitin ligase participates in the initiation of GG-NER and triggers the UV-dependent degradation of its subunit DDB2. We found that DDB1 rapidly accumulates on DNA damage sites. However, its binding to damaged DNA is not static, since DDB1 constantly dissociates from and binds to DNA lesions. DDB2, but not CUL4A, was indispensable for binding of DDB1 to DNA damage sites. The residence time of DDB1 on the damage site is independent of the main damage-recognizing protein of GG-NER, XPC, as well as of UV-induced proteolysis of DDB2. The amount of DDB1 that is temporally immobilized on damaged DNA critically depends on DDB2 levels in the cell. We propose a model in which UV-dependent degradation of DDB2 is important for the release of DDB1 from continuous association to unrepaired DNA and makes DDB1 available for its other DNA damage response functions.

ACKNOWLEDGMENTS

S.A. was financed by the European Science Foundation, EuroDYNA program 03-DYNA-F-18 (Spatio-temporal Organization of Genome Surveillance in Live Cells). A.P. was financed by an FP6-EU grant (DNA Repair; LSHG-CT-2005-512113). M.S.L., A.B.H., and W.V. were supported by grants from The Netherlands Organization for Health Research and Development (ZonMW; grants 912-03-012, 917-46-371, and 917-46-364), P.-O.M. and H.L. were supported by grants from the Association for International Cancer Research (AICR 07-0129 and AICR 08-045), and H.L. was also supported by the Human Frontiers Science Program Organization (RGP0007/2004). G.G.-M. was supported by an Erasmus University Fellowship.