A novel hydrogen peroxide-induced phosphorylation and ubiquitination pathway leading to RNA polymerase II proteolysis

DNA damage-induced ubiquitination of the largest subunit of RNA polymerase II, Rpb1, has been implicated in transcription-coupled repair for years. The studies so far, however, have been limited to the use of bulky helix-distorting DNA damages caused by UV light and cisplatin, which are corrected by the nucleotide excision repair pathway. Non-bulky, non-helix-distorting damages are caused at high frequency by reactive oxygen species in cells and corrected by the base excision repair pathway. Contrary to a classic view, we recently found that the second type of DNA lesions also causes RNA polymerase II stalling in vitro. In this paper, we show that hydrogen peroxide (H2O2) causes significant ubiquitination and proteasomal degradation of Rpb1 by mechanisms that are distinct from those employed after UV irradiation. UV irradiation and H2O2 treatment cause characteristic changes in protein kinases phosphorylating the carboxyl-terminal domain at Ser-2 and -5. The H2O2-induced ubiquitination is likely dependent on unusual Ser-5 phosphorylation by ERK1/2. Moreover, the H2O2-induced ubiquitination occurs on transcriptionally engaged polymerases without the help of Cockayne syndrome A and B proteins and von Hippel-Lindau tumor suppressor proteins, which are all required for the UV-induced ubiquitination. These results suggest that stalled polymerases are recognized and ubiquitinated differentially depending on the types of DNA lesions. Our findings may have general implications in the basic mechanism of transcription-coupled nucleotide excision repair and base excision repair.