O03 HPV8 leads to Lrig1+ keratinocyte stem cell expansion into the overlying epidermis

Abstract Actinic keratoses (AKs) represent the precursor skin lesions in the pathogenesis of up to 87% of cutaneous squamous cell carcinomas (cSCCs). However, current treatment of AK lesions, at best, lead to only a 25% reduction in cSCC and relies on therapies that target abnormal keratinocytes using topical chemotherapy, immune stimulants or surgical resection. We have previously shown that 44% of AK tissue sample histologies contain koilocytes, wherein genotyping universally identified human papillomavirus 8 (HPV8). To determine the role of HPV8 in the pathogenesis of AKs, we used the K14–HPV8 complete early region (HPV8tg) to generate triple cross-lineage tracing transgenic mice: HPV8:K5-CreERT2:R26R-LoxP-flanked-Brainbow2.1 (Confetti reporter); HPV8:Lrig1-CreERT2:R26R-LoxP-flanked-Brainbow2.1; and HPV8:K15-PGR:R26R-LoxP-flanked-Brainbow2.1. Upon Cre activation, progeny clones exhibit one of four fluorescent colours. Compared to wild-type mice, all HPV8tg mice exhibited an expansion of keratinocytes in the hair follicle infundibulum (77.09 mm3 and 253.43 ± 54.15 mm3) and overlying epidermis. Clones from the Lrig1, but not K15, keratinocyte stem cell population were responsible for keratinocyte expansion of both the hair follicle infundibulum and overlying epidermis. Compared with wild-type mice, HPV8tg mice exhibited greater colony-forming efficiency (1.75 ± 0.69% vs. 6.27 ± 2.41%; n = 3), and, consistent with keratinocyte stem cell expansion, ΔNp63 expression was increased 4.14 ± 2.10-fold (P < 0.05, n = 5). Flow-sorted epidermal clones from wild-type and HPV8tg mice were examined by RNA sequencing (n = 5). Warthin–Starry staining showed that the expanded population had no melanin ‘cap’ in our mouse models and human AK samples. In summary, expression of HPV8 early-region genes is associated with AK, wherein there is an expansion of the Lrig1, but not K15, keratinocyte stem cell population that results in epidermal thickening reminiscent of human AK pathology. These findings suggest that HPV8 results in translocation of hair follicle keratinocyte stem cells into the interfollicular epidermis without melanin production, making these cells susceptible to ultraviolet light transformation.