Human Papillomavirus 16 (HPV-16), HPV-18, and HPV-31 E6 Override the Normal Phosphoregulation of E6AP Enzymatic Activity.

The human papillomavirus (HPV) E6 oncoproteins recruit the cellular ubiquitin ligase E6AP/UBE3A to target cellular substrates for proteasome-mediated degradation, and one consequence of this activity is the E6 stimulation of E6AP autoubiquitination and degradation. Recent studies identified an autism-linked mutation within E6AP at T485, which was identified as a protein kinase A phosphoacceptor site and which could directly regulate E6AP ubiquitin ligase activity. In this study, we have analyzed how T485-mediated regulation of E6AP might affect E6 targeting of some of its known substrates. We show that modulation of T485 has no effect on the ability of E6 to direct either p53 or Dlg for degradation. Furthermore, T485 regulation has no effect on HPV-16 or HPV-31 E6-induced autodegradation of E6AP but does affect HPV-18 E6-induced autodegradation of E6AP. In cells derived from cervical cancers, we find low levels of both phosphorylated and nonphosphorylated E6AP in the nucleus. However, ablation of E6 results in a dramatic accumulation of phospho-E6AP in the cytoplasm, whereas nonphosphorylated E6AP accumulates primarily in the nucleus. Interestingly, E6AP phosphorylation at T485 confers association with 14-3-3 proteins, and this interaction seems to be important, in part, for the ability of E6 to recruit phospho-E6AP into the nucleus. These results demonstrate that HPV E6 overrides the normal phosphoregulation of E6AP, both in terms of its enzymatic activity and its subcellular distribution.