APOBEC3 dysregulation by the beta papillomaviruses, a key step for non-melanoma skin carcinogenesis?

Abstract

Background: The beta-HPVs are part of the skin commensal flora. Numerous research state an association between those viruses and several skin cancers, although it is still debated. The cytidine deaminases APOBEC3s are members of the innate immune response and target numerous exogenous viruses by introducing mutations in their genome. APOBEC3s are notably known to restrict alpha-HPVs, accountable for the development and the maintenance of many cancers in mucosal tissues. Importantly, the alpha-HPV oncoproteins E6 and E7 have been shown to trigger APOBEC3A and APOBEC3B expression. Their overexpression contributes to HPV restriction but also to introduce mutations in the cellular genome. Indeed, the majority of the mutations in the genome of alpha-HPV positive cancers is introduced by the APOBEC3 editing activity.
Aim: Since the alpha and beta-HPVs are highly similar, our aim is to investigate the process by which beta-HPVs could participate to skin cancer development, more precisely if the process is similar as the one in alpha HPVs-induced cancers. Therefore, this project will point out if beta-HPVs promote the expression of APOBEC3A and APOBEC3B in human primary keratinocytes.
Methods: Firstly, E6 and E7 expression after doxycycline induction in N/TERT-1 was confirmed by RT-qPCR. Then, the impact of these oncoproteins on the levels of A3A and A3B transcripts and proteins was tested in basal condition and upon IFN treatment, using RT-qPCR and western blot. Because differentiation of HPV16-infected keratinocytes induces A3A and A3B expression, we evaluated the impact of differentiation on our E6/E7 expressing N/TERT-1. Hence, A3A and A3B expression were analyzed in 2D and 3D differentiated N/TERT-1 expressing or not the oncogenes, by western blot.
Results: The transduced cells highly express the oncogenes when induced with doxycycline, except for the alpha-HPV 16 cells. Those oncoproteins induce a slight increase in the mRNA expression of A3B. However, this effect is not visible at the protein level by western blots, nor in basal condition neither upon IFN treatment. The expression of the A3B protein does not change in differentiated cells or not, and the oncoproteins of the beta HPV 38 and 49 do not impact the expression of A3B in 2D and 3D differentiated N/TERT-1.
Conclusion: This project did not achieve to demonstrate an induction of the APOBEC3A and APOBEC3B expression by the beta-HPV oncoproteins E6 and E7. However, many opportunities to study this subject in greater depth exit.

Date of Award	18 Jan 2021
Original language	English
Awarding Institution	University of Namur
Supervisor	Nicolas Gillet (Supervisor)