Abstract 1322A: Computational study of the effects of non-synonymous mutations in human UBE3A gene present in virus-associated cancers
Authors: Machicado Claudia , Soto Maria Pia 
Published: August 2018

UBE3A gene encodes the ubiquitin ligase E6 associated protein (E6AP), an enzyme that catalyzes the high-risk human papilloma virus (HPV) E6-mediated ubiquitination of p53. Such modification in p53 contributes to the neoplastic progression of cells infected by HPV-16/18 that leads to cervical cancer (CC). The hijacking of E6AP also occurs by Hepatitis C virus (HCV) that targets Rb protein thus conducting to hepatocellular carcinoma (HCC). We hypothesized that certain non-synonymous (missense) mutations of E6AP drives to elevated degradation rates of either p53 or Rb by increasing its enzymatic activity. This study aimed to predict changes in: (i) functional activity in E6AP mutants, and (b) E6AP affinity to viral oncoproteins and p53/Rb. A subset of three virus-associated cancers including cervical carcinoma (CC), hepatocellular carcinoma (HCC) and oral squamous carcinoma (OSC) were analyzed. The Cancer Genome Atlas (TCGA) dataset as well as Biomuta were mined and missense mutations in human UBE3A gene were retrieved. To explore the impairment of protein function and stability across the UBE3A gene mutants, machine learning approaches (i.e. Polyphen, I-Mutant 3.0, Panther and Provean) and NetSurfP were applied. The 3D structures of E6AP variants were modelled and docking simulations with viral oncoproteins and p53/Rb were performed using PyDock. Our results showed 22 mutations in UBE3A gene that were present across CC, HCC and OSC, with most of variants (60%) appearing in HCC. UBE3A variants were different across the three tumor types analyzed. Seven of 22 UBE3A variants were predicted damaging or deleterious substitutions. Five damaging mutations affected the HECT domain responsible for the enzyme activity. Such corresponded to E743K and P850A, existing in CC, as well as M589L, E754K, and Q576*, found in HCC. Two predicted damaging mutations were located within the HCV binding site including G492V (found in CC) as well as F477C (present in OSC). No mutation involved the highly conserved LXXL domain implicated in E6 binding or the E6AP trimerization residues. The predicted E6AP-E6 complexes revealed that LXXLL domain in E6AP participates in E6 binding, both in wild-type and mutants. Interestingly, E6AP E743K mutant showed increased complex stability in comparison with wild-type. In conclusion, most of E6AP mutations (68%) existing in CC, HCC and OSC are likely to be neutral whereas some others (32%) are potentially damaging variants and likely to increase E6AP activity. E6AP-dependent ubiquitylation of p53 represents an important opportunity to discover novel entities that inhibit protein-protein interactions thus avoiding p53 degradation.

Citation Format: Claudia Machicado, Maria Pia Soto. Computational study of the effects of non-synonymous mutations in human UBE3A gene present in virus-associated cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1322A.