Tommasi, C; (2017) Investigation into common mechanisms of virus replication and propagation in skin. Doctoral thesis , UCL (University College London).

Text final submission PhD thesis Cristina Tommasi .pdf Access restricted to UCL open access staff until 1 August 2025. Download (8MB)

Abstract

The skin is a common route of infection for many viruses, but is a mechanically tough tissue resistant to environmental insults and therefore refractory to viral propagation. Varicella Zoster Virus (VZV) and Human Papilloma Virus (HPV) are skin-tropic viruses causing chickenpox and warts respectively. This thesis shows that although divergent, these viruses exploit a common pathway to hijack epidermal terminal differentiation. Both viruses degrade the structural protein keratin 10 (K10). I show this was achieved by the up-regulation of the protease Kallikrein 6 (KLK6), which caused up-regulation of the E3 ubiquitin ligase MDM2. MDM2 bound and ubiquitinated K10 targeting K10 for degradation. In VZV infection, inhibition of MDM2/K10 binding by Nutlin-3 prevented K10 degradation and was sufficient to reduce viral growth and cell-host damage in VZV-infected epithelial cells and prevent blister formation in VZV-infected skin explants. Genes that were dysregulated in response to VZV infection and restored by Nutlin-3 were identified. One of these, the nuclear receptor subfamily 4, group A, member 1 (NR4A1) was up-regulated in keratinocytes expressing low levels of K10. In NR4A1 knockdown keratinocytes VZV growth was reduced and the autophagy marker LC3 was down-regulated, while the lysosomal marker LAMP2 was up-regulated, indicating that NR4A1 induces autophagy while also blocking the late stages of the autophagic flux. We postulate that autophagy is exploited by VZV to form autophagy-based viral factories for viral replication. This thesis also shows that NR4A1 is not up-regulated in HPV infection whereas it is up-regulated in a model of HSV-1 infected organotypic epidermis. KLK6 and MDM2 are up-regulated and K10 down-regulated in this model of HSV-1 infection. This thesis therefore describes a novel pathway, readily inhibited by small molecule inhibitors, used by highly diverse skin-tropic viruses to promote viral propagation and also identifies in NR4A1 the point where this pathway diverges between alphaherpesviruses and cutaneous HPVs.

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