Glioblastoma (GBM) is the most aggressive type of glioma. Temozolomide (TMZ) is currently the drug of choice used for post-operative chemotherapy of GBM. However, the presence of intrinsic and acquired resistance hinders the success of chemotherapy. To understand the TMZ resistant mechanisms in glioma, we investigated the alterations in cellular signaling pathways by performing transcriptome analysis of TMZ treated glioma cells. Gene Set Enrichment Analysis (GSEA) indicated a significant enrichment of Wnt/β-catenin signaling besides many other pathways in TMZ treated cells. Further, we demonstrate that TMZ treatment increased the activity from TOPflash reporter, (a Wnt responsive reporter), enhanced the levels of pGSK-3β (S9) and reduced the levels of p-β-catenin (S33/37/T41) with a concomitant increase in transcript and protein levels of Wnt targets in a concentration and time-dependent manner. While TMZ treated cells did not show alteration in any of the Wnt ligands, PI3K inhibitor (LY294002) treatment repressed Akt activation and abolished the TMZ–mediated induction of Wnt/β-catenin pathway. In addition, we show that Wnt/β-catenin signaling activation by TMZ is independent of ATM/Chk2 pathway. Further, we also demonstrate the activation of mTOR pathway after TMZ treatment. Thus, our results demonstrate that activation of Wnt/β-catenin pathway involves an ATM/Chk2- independent PI3K/Akt/GSK-3 cascade in TMZ treated cells and further provides mechanistic basis for the chemoresistance of glioma to TMZ.

中文翻译：

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替莫唑胺通过 PI3K/Akt 通路诱导胶质瘤细胞中 Wnt/β-catenin 信号的激活：对胶质瘤治疗的影响。

胶质母细胞瘤 (GBM) 是最具侵袭性的胶质瘤类型。替莫唑胺（TMZ）是目前GBM术后化疗的首选药物。然而，内在和获得性耐药的存在阻碍了化疗的成功。为了了解胶质瘤中的 TMZ 抗性机制，我们通过对 TMZ 处理的胶质瘤细胞进行转录组分析来研究细胞信号通路的改变。基因集富集分析 (GSEA) 表明，除了 TMZ 处理的细胞中的许多其他途径外，Wnt/β-连环蛋白信号传导显着富集。此外，我们证明 TMZ 治疗增加了 TOPflash 记者（Wnt 响应记者）的活动，提高 pGSK-3β (S9) 的水平并降低 p-β-连环蛋白 (S33/37/T41) 的水平，同时以浓度和时间依赖性方式增加 Wnt 靶标的转录物和蛋白质水平。虽然 TMZ 处理的细胞没有显示出任何 Wnt 配体的改变，但 PI3K 抑制剂 (LY294002) 处理抑制了 Akt 活化并消除了 TMZ 介导的 Wnt/β-连环蛋白通路诱导。此外，我们表明 TMZ 对 Wnt/β-连环蛋白信号的激活独立于 ATM/Chk2 途径。此外，我们还证明了 TMZ 治疗后 mTOR 通路的激活。因此，我们的结果表明 Wnt/β-catenin 通路的激活涉及 TMZ 处理的细胞中不依赖 ATM/Chk2 的 PI3K/Akt/GSK-3 级联反应，并进一步为胶质瘤对 TMZ 的化学抗性提供机制基础。