Protein homeostasis is essential for life in eukaryotes. Organisms respond to proteotoxic stress by activating heat shock transcription factors (HSFs), which play important roles in cytoprotection, longevity and development. Of six human HSFs, HSF1 acts as a proteostasis guardian regulating stress-induced transcriptional responses, whereas HSF2 has a critical role in development, in particular of brain and reproductive organs. Unlike HSF1, that is a stable protein constitutively expressed, HSF2 is a labile protein and its expression varies in different tissues; however, the mechanisms regulating HSF2 expression remain poorly understood. Herein we demonstrate that the proteasome inhibitor anticancer drug bortezomib (Velcade), at clinically relevant concentrations, triggers de novo HSF2 mRNA transcription in different types of cancers via HSF1 activation. Similar results were obtained with next-generation proteasome inhibitors ixazomib and carfilzomib, indicating that induction of HSF2 expression is a general response to proteasome dysfunction. HSF2-promoter analysis, electrophoretic mobility shift assays, and chromatin immunoprecipitation studies unexpectedly revealed that HSF1 is recruited to a heat shock element located at 1.397 bp upstream from the transcription start site in the HSF2-promoter. More importantly, we found that HSF1 is critical for HSF2 gene transcription during proteasome dysfunction, representing an interesting example of transcription factor involved in controlling the expression of members of the same family. Moreover, bortezomib-induced HSF2 was found to localize in the nucleus, interact with HSF1, and participate in bortezomib-mediated control of cancer cell migration. The results shed light on HSF2-expression regulation, revealing a novel level of HSF1/HSF2 interplay that may lead to advances in pharmacological modulation of these fundamental transcription factors.

蛋白质稳态对于真核生物的生命至关重要。生物体通过激活热休克转录因子 (HSF) 来应对蛋白毒性应激，热休克转录因子在细胞保护、寿命和发育中发挥着重要作用。在六种人类 HSF 中，HSF1 作为蛋白质稳态守护者，调节应激诱导的转录反应，而 HSF2 在发育中发挥着关键作用，特别是在大脑和生殖器官的发育中。与HSF1不同，HSF1是一种稳定表达的蛋白质，HSF2是一种不稳定的蛋白质，其表达在不同组织中存在差异；然而，调节HSF2表达的机制仍然知之甚少。在此，我们证明蛋白酶体抑制剂抗癌药物硼替佐米 (Velcade) 在临床相关浓度下，可通过 HSF1 激活在不同类型的癌症中触发 HSF2 mRNA从头转录。下一代蛋白酶体抑制剂伊沙佐米和卡非佐米也获得了类似的结果，表明诱导 HSF2 表达是对蛋白酶体功能障碍的普遍反应。 HSF2 启动子分析、电泳迁移率变动分析和染色质免疫沉淀研究意外地揭示，HSF1 被招募到位于 HSF2 启动子转录起始位点上游 1.397 bp 的热休克元件中。更重要的是，我们发现HSF1在蛋白酶体功能障碍期间对于HSF2基因转录至关重要，这是参与控制同一家族成员表达的转录因子的一个有趣的例子。此外，硼替佐米诱导的HSF2被发现定位于细胞核，与HSF1相互作用，并参与硼替佐米介导的癌细胞迁移控制。 这些结果揭示了 HSF2 表达调控，揭示了 HSF1/HSF2 相互作用的新水平，可能导致这些基本转录因子的药理学调节取得进展。