XPC loss-of-function triggers melanomagenesis through CDKN2A downregulation

We identified a novel XPC variant, c.2420+5G>A (XPCvar), in siblings with multiple melanomas, inherited alongside c.779+1G>T, which results in an absent or disrupted protein. However, they did not exhibit significantly higher nucleotide excision repair (NER) deficits compared to their unaffected parents, suggesting an NER-independent tumor suppressor function for XPC. XPC knockdown increased cell proliferation and tumorigenicity in vitro without affecting NER. Single-cell RNA sequencing revealed lower Cdkn2a in Xpcvar/var mouse melanocytes. Additionally, XPC knockdown downregulated CDKN2A in vitro. Furthermore, patient fibroblasts showed decreased p16INK4a, which was rescued by XPC overexpression. ChIP-PCR and luciferase assays confirmed XPC binding to the CDKN2A promoter, initiating transcription. Premature stop codon read-through, with gentamicin, restored XPC and p16INK4A in patient fibroblasts. These suggest that XPC regulates CDKN2A and XPC loss might promote melanomagenesis by downregulating CDKN2A, independent of its NER function. We provide preclinical evidence for potential preventive and/or therapeutic strategies for similarly affected individuals. STATEMENT OF SIGNIFICANCECharacterizing a novel XPC variant identified in patients with melanoma revealed a non-canonical role for XPC in regulating CDKN2A transcription. XPC binding to the CDKN2A promoter is crucial for CDKN2A expression and might suppress melanomagenesis. This expands our understanding of melanomagenesis and suggests potential therapies targeting XPC-mediated regulation of CDKN2A.