The role of the PSD95/Dlg/ZO-1 (PDZ) binding motif of human papillomavirus type 18 E6 oncoprotein in the virus life cycle

Abstract

A PSD95/Dlg/ZO-1(PDZ)-binding motif (PBM) in the E6 protein of high-risk, cancer-causing human papillomaviruses (HPV) targets a subset of cellular PDZ domain-containing proteins involved in diverse regulatory processes including cell polarity and proliferation, for proteasome-mediated degradation. Interaction with this select group of PDZ domain-containing proteins is negatively regulated by cAMP-dependent protein kinase (PKA) mediated phosphorylation of the E6 PBM. This thesis has sought to address the hypothesis that the PBM of E6 plays an important role within the HPV life cycle. This study has shown that deletion of the E6 PBM from HPV18 genomes affects the morphology and growth of viral episome-containing human keratinocytes and furthermore links E6 PBM function to viral episome replication (maintenance replication and differentiation-dependent amplification). Loss of negative regulation of the E6 PBM by mutation of the PKA recognition motif was associated with increased cell growth and indeed the growth of wildtype HPV18 genome-containing cells responded to changes in PKA signalling. Constitutive E6 PBM function was also associated with invasion of cells suggesting that malignant progression of HPV-infected cells may be linked to changes in PKA signalling. Modulation of the E6 PBM function in the viral genome-containing cells was associated with a change in protein levels of the PDZ domain-containing protein discs large (hDlg) and changes in the non receptor protein phosphastase PTPN13 specific species