Regional Centre for Applied Molecular Oncology, Masaryk Memorial Cancer Institute, Brno, Czech Republic.
PLoS One. 2018 Aug 23;13(8):e0202758. doi: 10.1371/journal.pone.0202758. eCollection 2018.
Response of tumours to Hsp90 inhibitors is highly variable and their clinical effects are unpredictable, emphasising the need for a predictive marker. We postulated that sensitivity to Hsp90 inhibitors is connected to basal proteotoxic stress that makes cells dependent on Hsp90. Therefore, we assessed HSF1 as a general sensor of proteotoxic stress and correlated its activity with sensitivity to three separate small molecule Hsp90 inhibitors in seven breast cancer cell lines representing each of the different cancer subtypes. Flow cytometry was used to analyse the viability of breast cancer cell lines after Hsp90 inhibition. HSF1 activity was characterised by Ser326 phosphorylation and the transactivation capacity of HSF1 was determined by qPCR analysis of the ratios of HSF1-dependent (HOP, Hsp70) and HSF1-independent (CHIP) chaperones and cochaperone mRNAs. We show that the sensitivity of breast cancer cell lines to Hsp90 inhibition is highly variable. The basal levels of phosphorylated HSF1 also vary between cell lines and the magnitude of change in HSF1 phosphorylation after Hsp90 inhibition showed a negative correlation with sensitivity to Hsp90 inhibitors. Similarly, the basal transactivation capacity of HSF1, determined by the ratio of Hsp70 or HOP mRNA to CHIP mRNA level, is directly proportional to sensitivity to Hsp90 inhibitors. Increasing basal HSF1 activity by prior heat shock sensitised cells to Hsp90 inhibition. These results demonstrate that endogenous HSF1 activity varies between individual cancer cell lines and inversely reflects their sensitivity to Hsp90 inhibitors, suggesting that basal proteotoxic stress is an important and generalised predictor of response. Mechanistically, the data indicate that high endogenous proteotoxic stress levels sensitise to Hsp90 inhibition due to the inability to respond adequately to further proteotoxic stress. HSF1 activity therefore represents a potential biomarker for therapy with Hsp90 inhibitors, which may be useful for the rational design of future clinical studies.
肿瘤对 Hsp90 抑制剂的反应高度可变，其临床效果不可预测，这强调了需要预测标志物。我们假设对 Hsp90 抑制剂的敏感性与使细胞依赖 Hsp90 的基础蛋白毒性应激有关。因此，我们评估了 HSF1 作为蛋白毒性应激的一般传感器，并将其活性与七种乳腺癌细胞系中三种不同小分子 Hsp90 抑制剂的敏感性相关联，这些细胞系代表了不同的癌症亚型。流式细胞术用于分析 Hsp90 抑制后乳腺癌细胞系的活力。HSF1 活性通过 Ser326 磷酸化来表征，HSF1 的反式激活能力通过 qPCR 分析 HSF1 依赖性（HOP、Hsp70）和 HSF1 非依赖性（CHIP）伴侣和共伴侣 mRNA 的比率来确定。我们表明，乳腺癌细胞系对 Hsp90 抑制的敏感性高度可变。细胞系之间 HSF1 磷酸化的基础水平也有所不同，并且 Hsp90 抑制后 HSF1 磷酸化的变化幅度与对 Hsp90 抑制剂的敏感性呈负相关。同样，通过 Hsp70 或 HOP mRNA 与 CHIP mRNA 水平的比率确定的 HSF1 的基础反式激活能力与对 Hsp90 抑制剂的敏感性成正比。预先进行热休克会增加 HSF1 的基础活性，从而使细胞对 Hsp90 抑制敏感。这些结果表明，内源性 HSF1 活性在个体癌细胞系之间存在差异，并且与它们对 Hsp90 抑制剂的敏感性呈反比，这表明基础蛋白毒性应激是反应的一个重要和普遍的预测因子。从机制上讲，数据表明，由于无法对进一步的蛋白毒性应激做出适当反应，高水平的内源性蛋白毒性应激会使细胞对 Hsp90 抑制敏感。因此，HSF1 活性代表了 Hsp90 抑制剂治疗的潜在生物标志物，这可能对未来临床研究的合理设计有用。
