3 years ago

HPV-16, HPV-18 and HPV-31 E6 override the normal phospho-regulation of E6AP enzymatic activity.

Thatte J, Banks L
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 auto-ubiquitination and degradation. Recent studies identified an autism-linked mutation within E6AP at T485, which was identified as a PKA phospho-acceptor site and which could directly regulate E6AP ubiquitin ligase activity. In this study we have analysed 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 auto-degradation of E6AP, but does affect HPV-18 E6-induced auto-degradation of E6AP. In cells derived from cervical cancers, we find low levels of both phosphorylated and non-phosphorylated E6AP in the nucleus. However, ablation of E6 results in a dramatic accumulation of phospho-E6AP in the cytoplasm, whereas non-phosphorylated 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 phospho-regulation of E6AP, both in terms of its enzymatic activity and its sub-cellular distribution.Importance Recent reports demonstrate the importance of phospho-regulation of E6AP for its normal enzymatic activity. Here we show that HPV E6 is capable of overriding this regulation and can promote degradation of p53 and Dlg regardless of the phosphorylation status of E6AP. Furthermore, E6 interaction with E6AP also significantly alters how E6AP is subject to auto-degradation, and suggests that this is not a simple stimulation of an already-existing activity, but rather a re-direction of E6AP activity towards itself. Furthermore, E6 mediated regulation of the subcellular distribution of phospho-E6AP appears to be dependent, in part, upon the 14-3-3 family of proteins.

Publisher URL: https://www.ncbi.nlm.nih.gov/pubmed/28835500

DOI: PubMed:28835500

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