Data from Activation of Wnt Signaling Pathway by Human Papillomavirus E6 and E7 Oncogenes in HPV16-Positive Oropharyngeal Squamous Carcinoma Cells

Abstract

<div>Abstract<p>We sought to determine the role of human papillomavirus (HPV) <i>E6</i> and <i>E7</i> oncogenes in nuclear β-catenin accumulation, a hallmark of activated canonical Wnt signaling pathway. We used HPV16-positive oropharyngeal cancer cell lines 147T and 090, HPV-negative cell line 040T, and cervical cell lines SiHa (bearing integrated HPV16) and HeLa (bearing integrated HPV18) to measure the cytoplasmic and nuclear β-catenin levels and the β-catenin/Tcf transcriptional activity before and after <i>E6/E7</i> gene silencing. Repression of HPV <i>E6</i> and <i>E7</i> genes induced a substantial reduction in nuclear β-catenin levels. Luciferase assay showed that transcriptional activation of Tcf promoter by β-catenin was lower after silencing. The protein levels of <i>β</i>-catenin are tightly regulated by the ubiquitin/proteasome system. We therefore performed expression analysis of regulators of β-catenin degradation and nuclear transport and showed that seven in absentia homologue (Siah-1) mRNA and protein levels were substantially upregulated after <i>E6/E7</i> repression. Siah-1 protein promotes the degradation of <i>β</i>-catenin through the ubiquitin/proteasome system. To determine whether Siah-1 is important for the proteasomal degradation of <i>β</i>-catenin in HPV16-positive oropharyngeal cancer cells, we introduced a Siah-1 expression vector into 147T and 090 cells and found substantial reduction of endogenous <i>β</i>-catenin in these cells. Thus, <i>E6</i> and <i>E7</i> are involved in β-catenin nuclear accumulation and activation of Wnt signaling in HPV-induced cancers. In addition, we show the significance of the endogenous Siah-1–dependent ubiquitin/proteasome pathway for β-catenin degradation and its regulation by <i>E6/E7</i> viral oncoproteins in HPV16-positive oropharyngeal cancer cells. Mol Cancer Res; 8(3); 433–43</p></div>