Given the great diversity of HPV types and tropism to epithelial sites (with associated diseases ranging from mild skin lesions to cancer), they share general genome organization and life strategy for long term infection after initial disease regression. Persistent infected cells form a viral reservoir, causing disease occurrence and are particularly problematic during carcinogenesis development for high-risk types; therefore, understanding HPV-mediated epithelial homeostasis is essential for understanding disease progression.

In this study, I applied the multiplex high-content confocal imaging system to reveal the spatial heterogenicity of keratinocytes with and without exogenous HPV E6 expression. Two in vitro model systems were developed to mimick the basal/suprabasal layers of the epithelium and evaluate HPV E6 functions in modulating cellular environment based on either the expression of a real-time cell cycle indicator (FUCCI) and early differentiation marker (KRT10); or the competition between differently fluorescently labelled infected versus uninfected cells.

Here, it is presented that HPV16E6 expressing keratinocytes exhibited increased proliferation, delayed contact inhibition and commitment to differentiation compared with normal keratinocytes. When the two populations are cultured together, HPV16E6 expressing cells have growth advantage over the adjacent uninfected neighbours in colonising the basal layer of epithelium.

Functional-deficient mutants of HPV16E6 revealed PDZ-domain containing proteins contributes to the competition advantage independent of the p53-regulated cell cycle progression. Further RNAi on keratinocytes of established HPV16E6 PDZ targets suggested MAGI and hPAR3 are two important modulators in maintaining basal cell life span and facilitates the formation of viral reservoir.

Similar phenotypes are also observed when keratinocytes expressing the E6 protein from different genera (α-HPV11/16/27, β-HPV8, γ-HPV65 and µ-HPV1), suggesting E6 is a conserved basal epithelial modulator which co-evolved with different epithelial sites for the establishment of local persistent HPV infections.

These results provide new insights of the function diverted biology of HPV during disease development, which may fuel the understanding of basal epithelial homeostasis and the development of successful anti-viral therapies.