Heat shock factor 1 (HSF1), a master transcriptional regulator of the evolutionarily conserved proteotoxic stress response, preserves proteomic stability upon environmental insults. HSF1 is also a potent pro-oncogenic factor, suggesting that proteomic stability enables oncogenesis. AMP-activated protein kinase (AMPK), a key cellular metabolic sensor and downstream effector of the tumor suppressor LKB1, activates catabolic pathways but suppresses anabolic pathways, including fatty acid and cholesterol biosynthesis, thereby maintaining energy homeostasis. We previously showed that upon activation by metabolic stressors, AMPK interacts with and phosphorylates HSF1 to inactivate it and cause proteomic instability, leading to tumor suppression. Intriguingly, we also discovered that HSF1 suppresses AMPK and controls body fat mass. This study is to investigate the mechanisms by which HSF1 reciprocally suppresses AMPK and the roles of this suppression in lipid metabolism and tumorigenesis. By utilizing recombinant proteins, HSF1 peptide libraries and transcription-deficient HSF1 mutants, our in vitro studies reveal that through physical interactions HSF1 imposes multilayer regulations on AMPK, including blocking AMP binding to γ subunits, impairing LKB1-mediated Thr172 phosphorylation, promoting Thr172 de-phosphorylation by PP2A, and impeding ATP binding to catalytic α subunits. Results from circular dichroism spectroscopy reveal that HSF1 induces global AMPK conformational changes. Biologically, Hsf1 deficiency suppresses lipogenesis and decreases lipid content via AMPK activation. Moreover, Hsf1-deficient cells and mice display reduced cholesterol levels. Interestingly, this defect leads to impaired cholesteroylation of sonic hedgehog (SHH). Consequently, the oncogenic SHH signaling is impaired in HSF1-deficient cells. In vivo, Hsf1 deficiency reduces body fat mass in mice, which can be markedly rescued by either pharmacological or genetic inhibition of AMPK. Importantly, the transcription-deficient HSF1 mutant, through AMPK suppression, enhances the lipid content and SHH cholesteroylation, and promotes the in vivo growth of xenografted human melanomas. In conclusion, HSF1 is a direct AMPK antagonist. This transcription-independent interaction of HSF1 with AMPK epitomizes a reciprocal kinase-substrate regulation whereby lipid metabolism and proteomic stability intertwine and promotes cancer anabolism and oncogenesis.

Citation Format: Kuo-Hui Su, Siyuan Dai, Zijian Tang, Meng Xu, Chengkai Dai. Heat shock factor 1 directly suppresses AMP-activated protein kinase to promote tumorigenesis [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 293.