The impact of HPV8 E6 on Lrig1+ hair follicle stem cell populations

Despite epidermal turnover, the skin is host to a complex array of microbes including viruses, such as the human papillomavirus (HPV), which must infect and manipulate skin keratinocyte stem cells (KSC) to survive. This crosstalk between the virome and KSC populations remains largely unknown. Here, we investigated the effect of HPV8 on KSCs using various mouse models. We observed that the HPV8 early region gene E6 specifically caused Lrig1+hair follicle junctional zone KSC proliferation and expansion, which would facilitate viral transmission. Within Lrig1+KSCs specifically, HPV8 E6 bound intracellular p300 to phosphorylate the STAT3 transcriptional regulatory node. This induces a transcriptional switch from TAp63 to ΔNp63 expression, resulting in expansion of KSC into the overlying epidermis. HPV8 was associated with 70% of human actinic keratoses (AK). Together these results redefine human AK as an expansion of KSC, which lack protecting melanosomes and are thus susceptible to sun-light-induced malignant transformation. To determine whether HPV8 E6-driven Lrig1+ hair follicle junctional zone keratinocyte stem cell proliferation was sufficient to cause expansion into the overlying epidermis by lineage tracing we generated Lrig1CreERT2:R26RConfetti:HPV8-E6tg and Lrig1CreERT2:R26RConfetti:WT mice. Confetti labeled cells were isolated by flow-cytometry, enabling us to simultaneously identify Lrig1+ cells by antibody labeling, such that we could isolate flow-sorted Lrig1+ confetti+ and their Lrig1- confetti+ progeny. Lrig1+ confetti+ and their Lrig1- confetti+ progeny from both HPV8-E6tg and WT mice were sequenced by RNA-seq and gene expression profiling analysis was performed on the dataset.