HPV8 Field Cancerization in a Transgenic Mouse Model Is due to Lrig1+ Keratinocyte Stem Cell Expansion

Abstract

β-Human papillomaviruses (HPVs) cause near ubiquitous latent skin infection within long-lived hair follicle (HF) keratinocyte stem cells. In patients with epidermodysplasia verruciformis, β-HPV viral replication is associated with skin keratosis and cutaneous squamous cell carcinoma. To determine the role of HF keratinocyte stem cells in β-HPV-induced skin carcinogenesis, we utilized a transgenic mouse model in which the keratin 14 promoter drives expression of the entire HPV8 early region (HPV8tg). HPV8tg mice developed thicker skin in comparison with wild-type littermates consistent with a hyperproliferative epidermis. HF keratinocyte proliferation was evident within the Lrig1+ keratinocyte stem cell population (69 vs. 55%, P < 0.01, n = 7), and not in the CD34+, LGR5+, and LGR6+ keratinocyte stem cell populations. This was associated with a 2.8-fold expansion in Lrig1+ keratinocytes and 3.8-fold increased colony-forming efficiency. Consistent with this, we observed nuclear p63 expression throughout this population and the HF infundibulum and adjoining interfollicular epidermis, associated with a switch from p63 transcriptional activation isoforms to ΔNp63 isoforms in HPV8tg skin. Epidermodysplasia verruciformis keratosis and in some cases actinic keratoses demonstrated similar histology associated with β-HPV reactivation and nuclear p63 expression within the HF infundibulum and perifollicular epidermis. These findings would suggest that β-HPV field cancerization arises from the HF junctional zone and predispose to squamous cell carcinoma.

Molecular Mechanisms of Human Papillomavirus Induced Skin Carcinogenesis

“…In a very recent study, Marisa Gariglio and her team addressed the role of different hair follicle stem cells in HPV8-induced skin cancer development utilizing K14-HPV8-CER mice [ 52 ]. They identified the leucine rich repeats and immunoglobulin like domains 1 (Lrig1) positive stem cell population, residing in the hair follicle junctional zone [ 53 ], to be expanded in HPV8 transgenic animals.…”

“…They identified the leucine rich repeats and immunoglobulin like domains 1 (Lrig1) positive stem cell population, residing in the hair follicle junctional zone [ 53 ], to be expanded in HPV8 transgenic animals. Proliferation in these cells is induced by the overexpression of the p63 protein lacking the N-terminal domain (ΔNp63) that is accepted as an epidermal stemness marker [ 52 ]. At least for HPV8-E6, it is known to trigger ΔNp63 levels [ 54 , 55 ].…”

Regulating cellular plasticity to persist: a way for tumor viruses to triumph

“…For example, it was previously shown that the increased stem cell mobilization seen in transgenic animals is also concurrent with the expression of stem cell markers such as Keratin15 (K15) outside the typical stem cell niche [42]. The expression of early genes from the cutaneous HPV8 has also been shown to lead to an expansion of stem cell markers, specifically leucine-rich repeats and immunoglobulin-like domains 1 (Lrig1) [43].…”

Changing Stem Cell Dynamics during Papillomavirus Infection: Potential Roles for Cellular Plasticity in the Viral Lifecycle and Disease

“…While the effects of infection on tissue stem cell dynamics are less well understood in cutaneous and mucosal epithelia compared to the gut, studies investigating the expression of viral gene products on skin stem cell populations suggest that important changes occur. Compelling evidence regarding the changes in stem cell dynamics during papillomavirus infection comes from studies using transgenic animals for both mucosotropic [ 6 , 29 ] and cutaneous HPVs [ 30 ]. The available evidence for HPV16 converges towards a model where the expression of early gene products pushes the tissue stem cells towards a hybrid state: one which retains typical markers of stem cells (e.g., K15) [ 6 , 29 ], but also expresses atypical markers (e.g., P-cadherin) [ 6 ] and loses key functional characteristics such as quiescence.…”

“…The increased stem cell mobilization seen in transgenic animals is also concurrent with the expression of stem cell markers such as Keratin15 (K15) outside the typical stem cell niche [ 6 , 29 ]. The expression of early genes from the cutaneous HPV8 has also been shown to lead to an expansion of stem cell markers, specifically leucine-rich repeats and immunoglobulin-like domains 1 (Lrig1) [ 30 ] in a model expressing the early genes of HPV8 in the skin epithelium of mice. Interestingly similar Lrig1 expression pattern was also seen in biopsies from EV patients.…”