1136 Xeroderma Pigmentosum: From disease modeling using CRISPR-Cas9 technology to the understanding of skin cancers pathophysiology

The sun's DNA-damaging ultraviolet (UV) radiation remains the major extrinsic risk factor for skin cancer development. Nevertheless, mammalian cells exploit the presence of the nucleotide excision repair (NER) pathway as a protective shield to eliminate the accumulation of photoproducts triggered by UV radiation. Xeroderma Pigmentosum C (XPC) is a key multifunctional protein implicated in the NER pathway acting as a key sensor for DNA lesions. Loss-of-function mutations in theXPC gene confer a photosensitive phenotype with the buildup of DNA damage without repair in XPC patients' cells and will tend to increase 10,000 folds the risk of skin cancer onset. To date, there is no relevant and reproducible cellular model that can mimic the course of human XPC disease. We carried out, for the first time, XPCgene editing in several human skin cells (keratinocytes, fibroblasts, and melanocytes) using CRISPR-Cas9 technology. Following disease phenotype characterization, WT and XPC knockout cellular models were used to map the proteomic signature of XPC KO cells at basal state and its modifications post UV irradiation. For this, total proteomes of WT and XPC KO cells subjected or not to UV irradiation were analysed by mass spectrometry-based quantitative proteomics. Surprisingly, a unique proteomic signature of 400 proteins was significantly (p=0.01, FDR 1%) and differentially altered in UV irradiated XPC KO versus WT cells. To better decipher the signaling pathways implicated, the kinases phosphorylation activity was also quantified post-UV irradiation. Following bioinformatic analysis for all the significant data, we identified a complete dysregulation of JAK/STAT signaling pathway from the upstream to the downstream effectors. JAK/STAT is a well-known inflammatory pathway, thus blocking it might be a key treasure to alleviate the photosensitive phenotype of XPC cells post-UV irradiation.