Functions of RING1B and ZRF1 in ubiquitin-mediated regulation of nucleotide excision repair
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Summary
DNA damage is repaired by a plethora of various DNA repair pathways. Nucleotide Excision Repair (NER) is specifically evolved to deal with helix-distortive DNA damage, arising for example from exposure of cells to UV-light. DNA damage binding proteins DDB2 and XPC are initiating the process of the lesion recognition. Various factors, such as posttranslational modifications of the NER factors as well as the histone at the chromatin region, surrounding the damage site, contribute in the regulation of this process. Ubiquitination of XPC and DDB2 as well as core histones by the ubiquitin E3 ligase DDB2-DDB1-CUL4-RBX1 (UV-CUL4) are accompanying the recognition of the DNA damage in NER. However, little is known about the molecular orchestration of this process.
Ubiquitin E3 ligase RING1B was previously described to be involved the transcriptional repression of genes by monoubiquitination of histone H2A at lysine 119 (H2A-ubiquitin). This activity can be reversed by tethering of the ubiquitin-binding protein ZRF1 which facilitates further removal of ubiquitin from H2A. Previous reports have linked RING1B to the DNA-damage dependent H2A ubiquitination. In this project we have addressed the role of RING1B and ZRF1 in the regulation of NER.
We show that after UV-irradiation H2A is monoubiquitinated by a novel ubiquitin E3 ligase complex, containing RING1B together with DDB proteins and adaptor protein CUL4B (UV-RING1B). This histone modification serves as a recruitment platform ZRF1. ZRF1 is a noverly described factor in NER and it functions by displacing CUL4B and RING1B from UV-RING1B E3 ligase complex and promotes formation of the UV-CUL4 E3 ligase complex which acts downstream. Additionally we demonstrate that ZRF1 may contribute in the proteasomal degradation of the NER proteins, and potentially act in other DNA repair pathways.
Our data expands our understanding of the ubiquitination processes, regulating early steps of the NER pathway as well as the contribution of the chromatin context in this process.