Type I Interferon Signaling Defines a Novel Disease Signature in Xeroderma Pigmentosum C Human Keratinocytes

Xeroderma Pigmentosum C (XPC) is a DNA damage recognition protein central to the global genome nucleotide excision repair (GG-NER) pathway, where it acts as a primary sensor of UV-induced DNA lesions. Loss-of-function mutations in the XPC gene lead to a photosensitive phenotype, with marked accumulation of unrepaired DNA damage and a dramatically elevated risk (10,000-fold) of skin cancer. However, understanding the molecular signaling mechanisms associated with XP-C has been hindered by the lack of reproducible disease models. Here, we overcome this challenge using our genetically engineered human XPC knockout (KO) keratinocytes, the predominant cell type affected by UV radiation. To uncover upstream signaling changes associated with the absence of XPC expression, we quantified protein tyrosine kinase (PTK) activity one-hour post-UVB exposure. XPC KO keratinocytes showed significant dysregulation of PTK activity on ∼100 phosphosites compared to controls. Complementary mass spectrometry (MS)-based quantitative proteomic analysis performed 24 hours post-UVB exposure identified a downstream signature comprising 791 differentially expressed proteins in XPC KO cells irradiated compared to non-irradiated counterparts. An integrative bioinformatic assessment of the kinase activity and proteomic data revealed a significant perturbation in type I interferon signaling via the JAK/STAT pathway in XPC-deficient keratinocytes, which is further exacerbated by UVB exposure. These findings were validated by western blot analysis, establishing a novel disease-associated molecular signature. Given the central role played by JAK/STAT signaling in inflammatory processes, our results implicate this pathway as a key mediator of XP-C’s hypersensitivity, thereby highlighting its potential as a therapeutic target to alleviate the disease pathology.