Deletion of vitamin D receptor with calcium sensing receptor in keratinocytes promotes epidermal tumorigenesis by limiting dna repair and oxidative stress response genes.

The vitamin D receptor (Vdr) and calcium-sensing receptor (Casr) regulate epidermal proliferation and differentiation. Deletion of both Vdr and Casr from Krt14 expressing epidermal keratinocytes (DKO) causes alopecia and delays wound re-epithelialization. Here, we demonstrate that DKO mice spontaneously develop squamous cell carcinoma with aging. We investigated the molecular mechanisms by which loss of Vdr/Casr leads to epidermal tumorigenesis. Ingenuity Pathway Analysis (IPA) predicted oxidative stress as a major pathway driving the biological processes resulting from Vdr/Casr deficiency. DKO keratinocytes showed reduced expression of genes involved in oxidative stress responses in neonatal epidermis, occurring prior to tumor formation. Spatial transcriptomic (Xenium) analysis demonstrated that reactive oxygen-metabolizing enzymes were markedly decreased in the supra-basal epidermal layers at the skin surface, consistent with differentiation defects caused by Vdr/Casr loss. These reductions were also evident in cells from the lower portion of the hair follicle, the infundibulum, which may arise from epidermal fate transformation toward sebaceous cells. Expression of DNA repair genes, including Xpc and Gadd45a, both implicated in epidermal tumorigenesis, was also decreased following Vdr/Casr deletion. Consistently, DKO keratinocytes exhibited impaired oxidative stress responses and reduced DNA repair capacity. Vdr/Casr deficiency prolonged UVB-induced reactive oxygen species and delayed clearance of UV-induced pyrimidine (6-4) pyrimidone photoproducts. Together, these findings suggest that DKO predisposes supra-basal epidermal cells and infundibulum-derived hair follicle stem cells to malignant transformation by impairing their ability to mitigate oxidative stress and DNA repair process.