DGCR8 Phosphorylation is Required for the Repair of UV-induced DNA Lesions Independently of MicroRNA Processing

Abstract

Ultraviolet (UV) radiation generates toxic and mutagenic DNA lesions such as cyclobutane pyrimidine dimers (CPDs) and 6-4 pyrimidine-pyrimidone photoproducts (6-4PPs) and is a carcinogen. MicroRNAs have been implicated in cellular response to UV. However, mechanisms connecting the microRNA biogenesis machinery and UV response are unknown. Here we show a critical role of DGCR8, an RNA binding protein in the microRNA processing Drosha-DGCR8 complex, in repair of UV-induced DNA lesions. Treatment with UV (UV-C and UV-B) induced phosphorylation on Serine 153 (S153) of DGCR8 in human cells. DGCR8-deficient cells were hypersensitive to UV and deficient in removal of UV-induced CPDs and 6-4PPs. Phosphorylation of S153 was critical for removing CPDs and 6-4PPs and cellular resistance to UV, but not for microRNA expression. In contrast, the RNA-binding and the Drosha-binding activities of DGCR8 were not critical for UV resistance. DGCR8 depletion did not sensitize cells deficient in CSA, CSB or XPA, the genes involved in transcription-coupled nucleotide excision repair (TC-NER), to UV, while it sensitized wild-type or XPC-deficient cells to UV. DGCR8-depleted cells and S153A DGCR8 mutant cells showed delayed recovery of RNA synthesis after UV exposure, further suggesting that phosphorylation of S153 is involved in TC-NER. Interestingly, Drosha-depleted cells were UV sensitive, but proficient in repairing UV-induced DNA lesions. Thus, UV-inducible phosphorylation on S153 of DGCR8 mediates TC-NER of UV-induced DNA lesions in a manner independent of microRNA processing and Drosha. Our study revealed an unexpected role of DGCR8 in TC-NER and establishes a novel UV-response signaling pathway (the DGCR8-mediated UV response pathway) that connects the microRNA biogenesis machinery and DNA repair of UV-induced DNA damage. Since both the microRNA biogenesis machinery and DNA repair have been implicated in human diseases including cancer, these findings provide novel insights into our understanding of such diseases.