Chimaeric HPV E6 proteins allow dissection of the proteolytic pathways regulating different E6 cellular target proteins

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Abstract
The ability of HPV E6 oncoproteins to induce the degradation of PDZ domain-containing MAGUK proteins correlates with their malignant potential. We previously showed that the HPV-6 E6 protein, when provided with the PDZ-binding domain from HPV-18 E6, acquires the ability to bind the Discs Large (Dlg) tumour suppressor and target it for degradation. Based on this finding we have extended this analysis to E6 proteins from a variety of different papillomavirus types. Cloning a PDZ-binding sequence onto the C-terminus of E6 proteins derived from low-risk mucosal, and low and high-risk cutaneous papillomavirus types, enables them to bind Dlg and a second MAGUK family member, MAGI-1. This renders the mucosally-derived low-risk chimaeric HPV E6 proteins capable of targeting Dlg for degradation, but they are unable to induce significant levels of degradation of MAGI-1. In contrast, none of the E6 proteins derived from cutaneous papillomavirus types induce significant degradation of either MAGI-1 or Dlg when provided with a PDZ-binding domain. These results demonstrate significant differences, both between mucosal and cutaneous HPV E6 proteins and in the pathways required for Dlg and MAGI-1 degradation.