Lin Yi-Te, Chao Chuck C-K
Graduate Institute of Biomedical Sciences, College of Medicine, Chang Gung University, Taoyuan 33302, Taiwan, Republic of China.
Department of Biochemistry and Molecular Biology, College of Medicine, Chang Gung University, Taoyuan 33302, Taiwan, Republic of China.
Oncotarget. 2015 Nov 17;6(36):38999-9017. doi: 10.18632/oncotarget.5738.
Sorafenib is a kinase inhibitor used as anticancer drug against various human tumors, including advanced hepatocellular carcinoma (HCC). β-Catenin and prothymosin alpha (PTMA) are overexpressed in HCC and other tumors. Previous studies have shown that PTMA expression modulates the response of HCC cells to sorafenib. However, the underlying mechanism of PTMA activity in this context remains unclear. We show here that sorafenib inhibits both β-catenin and PTMA in a dose-dependent manner. Silencing β-catenin reduces PTMA level and sensitizes HCC cells to sorafenib. In contrast, ectopic expression of β-catenin induces PTMA expression and cell resistance to the drug. Sorafenib inhibits PTMA expression at the transcriptional level by inhibiting the β-catenin pathway. Nucleotide deletion analysis of the PTMA gene promoter reveals that a DNA segment lying 1,500-1,600 bp upstream of the PTMA transcription start site represents an AP-1-binding site that is critical for β-catenin modulation of gene transcription in response to sorafenib. In addition, chemical inhibitors that target JNK abrogate β-catenin/AP-1 binding to the endogenous PTMA gene and reduces PTMA transcription and protein expression. Silencing of β-catenin or c-Fos induces similar effects on gene regulation and these are reversed by ectopic expression of β-catenin. Mutations in the PTMA promoter at the predicted β-catenin/AP-1 binding site partly abrogate sorafenib's effects on PTMA transcription. These results indicate that PTMA is induced by the oncoprotein β-catenin and protects HCC cells against sorafenib-induced cell death. The β-catenin/JNK/PTMA axis may thus represent a novel target for chemotherapy against HCC.
索拉非尼是一种激酶抑制剂，用作针对包括晚期肝细胞癌（HCC）在内的多种人类肿瘤的抗癌药物。β-连环蛋白和前胸腺素α（PTMA）在HCC和其他肿瘤中过表达。先前的研究表明，PTMA表达调节HCC细胞对索拉非尼的反应。然而，在此背景下PTMA活性的潜在机制仍不清楚。我们在此表明，索拉非尼以剂量依赖性方式抑制β-连环蛋白和PTMA。沉默β-连环蛋白可降低PTMA水平并使HCC细胞对索拉非尼敏感。相反，β-连环蛋白的异位表达诱导PTMA表达并使细胞对该药物产生抗性。索拉非尼通过抑制β-连环蛋白途径在转录水平上抑制PTMA表达。PTMA基因启动子的核苷酸缺失分析表明，位于PTMA转录起始位点上游1500-1600 bp的DNA片段代表一个AP-1结合位点，该位点对于β-连环蛋白响应索拉非尼调节基因转录至关重要。此外，靶向JNK的化学抑制剂消除β-连环蛋白/AP-1与内源性PTMA基因的结合，并降低PTMA转录和蛋白质表达。沉默β-连环蛋白或c-Fos对基因调控产生类似影响，而β-连环蛋白的异位表达可逆转这些影响。PTMA启动子在预测的β-连环蛋白/AP-1结合位点的突变部分消除了索拉非尼对PTMA转录的影响。这些结果表明，PTMA由癌蛋白β-连环蛋白诱导，并保护HCC细胞免受索拉非尼诱导的细胞死亡。因此，β-连环蛋白/JNK/PTMA轴可能代表针对HCC化疗的新靶点。
