Degradation of hDlg and MAGIs by human papillomavirus E6 is E6-AP-independent

An important characteristic of the E6 proteins derived from cancer-associated human papillomaviruses (HPVs) is their ability to target cellular proteins for ubiquitin-mediated degradation. Degradation of the p53 tumour suppressor protein by E6 is known to involve the cellular ubiquitin ligase, E6-AP; however, it is presently not known how E6 targets the Drosophila discs large (Dlg) tumour suppressor and the membrane-associated guanylate kinase inverted (MAGI) family of proteins for degradation. By using an in vitro E6-AP immunodepletion assay, these targets were tested for degradation in a E6-AP-dependent manner. The data showed clearly that E6 can direct the degradation of Dlg and the MAGI family of proteins in the absence of E6-AP in this in vitro system. These results provide compelling evidence for the role of E6-associated ubiquitin ligases other than E6-AP in the degradation of certain E6 targets.