Heat shock factor 1 (HSF1) cooperates with estrogen receptor α (ERα) in the regulation of estrogen action in breast cancer cells

Abstract

Heat shock factor 1 (HSF1), a key regulator of transcriptional responses to proteotoxic stress, was linked to estrogen (E2) signaling through estrogen receptor α (ERα). We found that an HSF1 deficiency may decrease ERα level, attenuate the mitogenic action of E2, counteract E2-stimulated cell scattering, and reduce adhesion to collagens and cell motility in ER-positive breast cancer cells. The stimulatory effect of E2 on the transcriptome is largely weaker in HSF1-deficient cells, in part due to the higher basal expression of E2-dependent genes, which correlates with the enhanced binding of unliganded ERα to chromatin in such cells. HSF1 and ERα can cooperate directly in E2-stimulated regulation of transcription, and HSF1 potentiates the action of ERα through a mechanism involving chromatin reorganization. Furthermore, HSF1 deficiency may increase the sensitivity to hormonal therapy (4-hydroxytamoxifen) or CDK4/6 inhibitors (palbociclib). Analyses of data from the TCGA database indicate that HSF1 increases the transcriptome disparity in ER-positive breast cancer and can enhance the genomic action of ERα. Moreover, only in ER-positive cancers, an elevated HSF1 level is associated with metastatic disease.

HSF1 Can Prevent Inflammation following Heat Shock by Inhibiting the Excessive Activation of the ATF3 and JUN&FOS Genes

“…Especially, HSPB8 , a known target of both HSF1 and ERα, but also other known HSF1 targets ( HSPD1 , HSPA4L ) were not upregulated in ER−/HSF1 high breast cancers ( Figure 6 A; see also Figure S8 showing the correlation analyses between HSF1 and HSPs expression). This is in agreement with the recent report on the cooperation of HSF1 with the estrogen receptor [ 17 ], and on the other hand, indicates that MCF7 cells are a good model cell line for ER-positive breast cancer. Other typical HSF1 targets upregulated by heat shock (e.g., HSPA1A , HSPA1B , HSP90AB1 ) showed higher expression levels in all HSF1 high breast cancers.…”

“…To investigate how cancer cells deal with cellular stress in the case of HSF1 deficiency, we analyzed the global gene expression profiles in breast adenocarcinoma MCF7 cells with decreased HSF1 levels (HSF1-deficient, HSF1 def ) and corresponding control cells with normal HSF1 levels (HSF1-proficient, HSF1 prof ) (cell model described previously in [ 17 ]). HSF1 silencing or functional knockout ( Figure S1A ) inhibited activation of HSP genes after heat shock, although full inhibition was only seen in some genes and in the complete absence of HSF1 ( Figure S1B,C ).…”

“…Some differences between cell lines were observed in the case of ATF3 , CHAC1 , CLCF1 , DDIT3 , FOSB , TIPARP , VEGFA , and WEE1 , indicating that their regulation after heat shock can be cell-type specific. For validation at the protein level, we have chosen ATF3 (which in HAP1 cells showed a weaker transcriptional response in HSF1− than in HSF1+ cells) and EGR3 (since we previously found its dependence on HSF1 in response to estrogen treatment; [ 17 ]). Western blot analyses up to 24 h of recovery from heat shock confirmed the higher levels or delayed upregulation of EGR3 and ATF3 in stressed HSF1− cells (for details see Figure 2 B).…”

“…MCF7 cells with downregulated HSF1 using shRNA (stably transduced with lentiviruses) or HSF1 CRISPR/Cas9-mediated functional knockout (two individual clones) and corresponding control cell variants were obtained as described in detail previously [ 17 ] (collectively referred to herein as HSF1 def cells). For validation experiments, MCF7 and RKO (colon carcinoma) knockout cells created using a DNA-free CRISPR/Cas9 system described previously were used [ 10 , 17 ]. Six individual unaffected clones (HSF1+) or with the HSF1 functional knockout (HSF1−) were pooled each time before analysis.…”

“…Total RNA was isolated and processed from HSF1-proficient (SCR, MIX, WT) and HSF1-deficient (shHSF1, KO#1, KO#2) MCF7 cell variants, untreated, and two hours after one-hour heat shock at 43 °C, as described in [ 17 ]. In shHSF1 cells, the level of HSF1 was stably decreased by 90% by HSF1-specific shRNA ( Figure S1A ).…”