No abstract

Nucleotide Excision Repair (NER) eliminates highly-genotoxic solar UV-induced DNA photoproducts that otherwise stimulate malignant melanoma development. Here, a genome-wide CRISPR/Cas9 screen was exploited to uncover novel genes required for efficient NER in human cells. The screen identified Dyrk1A, a dual specificity kinase that phosphorylates the cell cycle regulator and proto-oncoprotein cyclin D1 on threonine 286 (T286), which in turn promotes its timely cytoplasmic relocalization and proteasomal degradation. Failure to modify cyclin D1 on T286 leads to nuclear accumulation of the protein, premature S phase entry, and enhanced cellular proliferation that drives tumourigenesis. We now demonstrate that Dyrk1A knockdown in UV-exposed cells causes significant inhibition of NER uniquely in S phase and reduced cell survival; moreover, both of these aberrant phenotypes were rescued upon concomitant depletion of cyclin D1. Additionally, we show (i) that expression of nonphosphorylatable cyclin D1 (T286A) interferes with NER specifically during S in a CDK-independent manner, and (ii) that this repair defect depends upon co-stabilization/upregulation of the CDK inhibitor p21waf1cip1. Our data indicate that inhibition of NER during S phase might represent a heretofore unappreciated mechanism by which oncogenic nuclear cyclin D1 fosters melanomagenesis.