Fisetin, a dietary flavonoid, induces apoptosis of cancer cells by inhibiting HSF1 activity through blocking its binding to the hsp70 promoter

• Published in: Carcinogenesis (New York) 2015-06, Vol.36 (6), p.696-706
• Main Authors: Kim, Joo Ae, Lee, Somyoung, Kim, Da-Eun, Kim, Moonil, Kwon, Byoung-Mog, Han, Dong Cho
• Format: Article
• Language: English
• Subjects: Adaptor Proteins, Signal Transducing - biosynthesis; Animals; Antineoplastic Agents - pharmacology; Apoptosis - genetics; Apoptosis Regulatory Proteins - biosynthesis; bcl-X Protein - biosynthesis; Binding Sites; Cell Line, Tumor; Cell Proliferation - drug effects; DNA-Binding Proteins - antagonists & inhibitors; DNA-Binding Proteins - genetics; DNA-Binding Proteins - metabolism; Female; Flavonoids - pharmacology; HCT116 Cells; Heat Shock Transcription Factors; HSP27 Heat-Shock Proteins - biosynthesis; HSP70 Heat-Shock Proteins - biosynthesis; HSP70 Heat-Shock Proteins - genetics; Humans; Mice; Mice, Inbred BALB C; Mice, Nude; Myeloid Cell Leukemia Sequence 1 Protein - biosynthesis; Neoplasms - drug therapy; Neoplasms - genetics; Promoter Regions, Genetic - genetics; Protein Binding; Proto-Oncogene Proteins c-bcl-2 - biosynthesis; Transcription Factors - antagonists & inhibitors; Transcription Factors - genetics; Transcription Factors - metabolism
• ISSN: 0143-3334; 1460-2180
• DOI: 10.1093/carcin/bgv045

Heat shock factor 1 (HSF1) is a transcription factor for heat shock proteins (HSPs) expression that enhances the survival of cancer cells exposed to various stresses. HSF1 knockout suppresses carcinogen-induced cancer induction in mice. Therefore, HSF1 is a promising therapeutic and chemopreventive target. We performed cell-based screening with a natural compound collection and identified fisetin, a dietary flavonoid, as a HSF1 inhibitor. Fisetin abolished heat shock-induced luciferase activity with an IC50 of 14 μM in HCT-116 cancer cells. The treatment of HCT-116 with fisetin inhibited proliferation with a GI50 of 23 μM. When the cells were exposed to heat shock in the presence of fisetin, the induction of HSF1 target proteins, such as HSP70, HSP27 and BAG3 (Bcl-2-associated athanogene domain 3), were inhibited. HSP70/BAG3 complexes protect cancer cells from apoptosis by stabilizing anti-apoptotic Bcl-2 family proteins. The downregulation of HSP70/BAG3 by fisetin significantly reduced the amounts of Bcl-2, Bcl-xL and Mcl-1 proteins, subsequently inducing apoptotic cell death. Chromatin immunoprecipitation assays showed that fisetin inhibited HSF1 activity by blocking the binding of HSF1 to the hsp70 promoter. Intraperitoneal treatment of nude mice with fisetin at 30mg/kg resulted in a 35.7% (P < 0.001) inhibition of tumor growth.