Ormanns Steffen, Neumann Jens, Horst David, Kirchner Thomas, Jung Andreas
Institute of Pathology, Ludwig Maximilians Universität, Munich, Germany.
Oncotarget. 2014 May 30;5(10):2999-3011. doi: 10.18632/oncotarget.1626.
We determined whether active PI3K signaling together with nuclear accumulation of β-Catenin is necessary to fully activate canonical WNT signaling and examined the association of both signaling pathways with colon cancer progression. Using reporter gene assays we examined the activation of β-Catenin mediated transcription upon PI3K inhibition with or without β-Catenin nuclear accumulation. Ectopically induced as well as constitutively active WNT signaling strictly required PI3K activity whereas PI3K inhibition had no effect on β-Catenin subcellular localization but impaired β-Catenin binding to WNT target gene promoters and decreased WNT target gene expression. Transcriptional activity of nuclear β-Catenin depended on active PI3K signaling as nuclear accumulation of β-Catenin failed to induce WNT reporter gene transcription upon PI3K inhibition. PI3K dependend transcriptional transactivation of β-Catenin relies on events beyond phosphorylation at the AKT target site serine 552, as S552D-phosphomimetic β-Catenin mutants were unable to restore WNT signaling when inhibiting PI3K. To study the prognostic value of PI3K pathway activation (activating PIK3CA mutations or loss of PTEN expression) and nuclear β-Catenin expression, both variables were determined in 55 matched pairs of primary right sided colon cancer cases with or without distant metastasis. Activating mutations in the PIK3CA gene or loss of PTEN expression did not correlate with distant metastasis while high nuclear β-Catenin expression combined with activation of the PI3K pathway identified cases in which distant metastasis had occurred. Activation of the PI3K pathway was not associated with nuclear β-Catenin expression. We conclude that the transcriptional activity of nuclear β-Catenin depends on PI3K activity. However, PI3K on its own does not affect β-Catenin subcellular localization. Both factors synergize for full WNT signaling activity and are associated with distant metastasis in colon cancer. Thus, the detection of high nuclear β-Catenin expression and simultaneous PI3K pathway activation identifies colon cancer patients with a high risk for distant metastasis.
我们确定了活性PI3K信号传导与β-连环蛋白的核积累共同作用对于完全激活经典WNT信号传导是否必要，并研究了这两种信号通路与结肠癌进展的关联。我们使用报告基因检测法，在有或没有β-连环蛋白核积累的情况下，检测了PI3K抑制后β-连环蛋白介导的转录激活情况。异位诱导的以及组成型激活的WNT信号传导严格依赖PI3K活性，而PI3K抑制对β-连环蛋白的亚细胞定位没有影响，但损害了β-连环蛋白与WNT靶基因启动子的结合，并降低了WNT靶基因的表达。核β-连环蛋白的转录活性依赖于活性PI3K信号传导，因为在PI3K抑制后，β-连环蛋白的核积累未能诱导WNT报告基因转录。PI3K依赖的β-连环蛋白转录反式激活依赖于AKT靶位点丝氨酸552磷酸化以外的事件，因为当抑制PI3K时，S552D磷酸模拟β-连环蛋白突变体无法恢复WNT信号传导。为了研究PI3K通路激活（激活PIK3CA突变或PTEN表达缺失）和核β-连环蛋白表达的预后价值，在55对匹配的原发性右半结肠癌病例（有或没有远处转移）中测定了这两个变量。PIK3CA基因的激活突变或PTEN表达缺失与远处转移无关，而高核β-连环蛋白表达与PI3K通路激活相结合可识别出已发生远处转移的病例。PI3K通路的激活与核β-连环蛋白表达无关。我们得出结论，核β-连环蛋白的转录活性依赖于PI3K活性。然而，PI3K自身并不影响β-连环蛋白的亚细胞定位。这两个因素协同作用以实现完整的WNT信号传导活性，并与结肠癌的远处转移相关。因此，检测到高核β-连环蛋白表达并同时激活PI3K通路可识别出远处转移风险高的结肠癌患者。
