Sunlight is the main aetiological agent in the development of non melanoma skin cancer (NMSC), the most commonly diagnosed cancer in the fair skinned population. Mounting epidemiological and molecular data suggest that infection with cutaneous Human papillomavirus (HPV) may act as a co-factor in the early stages of NMSC development. The viral E6 protein can inhibit the apoptotic response to UV induced damage, partly through proteasomal degradation of the pro-apoptotic protein BAK. Upon UV damage, BAK undergoes a series of activating modifications that are linked to changes in phosphorylation status. BAK activation commits a cell to apoptosis through mitochondrial permeabilisation. The aim here was to elucidate the underlying mechanism of HPV5 E6-mediated BAK degradation. Mutation of lysine 113 in BAK and siRNA knockdown of a novel HPV5 E6 associated ubiquitin ligase, HERC1, prevented HPV5 E6 mediated-BAK degradation. A proximity ligation in situ assay showed an interaction between HERC1 and BAK in cells, which was dependent on the presence of the E6 protein and UV irradiation. Probing the BAK conformation and phosphorylation status suggests E6 targets a dephosphorylated BAK monomer before mitochondrial permeabilisation occurs, leading to the proposal of a mechanism for the interaction of BAK with HERC1 which depends on the activation status of BAK and a putative BH3 domain identified in HERC1. Additional work identifies β1-integrin as an interacting protein of a conserved YHDW amino acid motif at the C-terminus of certain β1 HPV E6 proteins. Only expression of E6 proteins with the YHDW motif (HPV5 and 8) in keratinocytes disrupted β1 integrin membrane localisation, altered expression of β1 integrin downstream effectors, such as focal adhesion kinase, and increased cell migration. Mutation of W157A in the HPV5 E6 YHDW motif reduced these effects. Together, this work furthers the understanding of mechanisms by which infection with HPV may promote the early stages of NMSC development.

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