The heat shock response is an evolutionally conserved adaptive response to high temperatures that controls proteostasis capacity and is regulated mainly by an ancient heat shock factor (HSF). However, the regulation of target genes by the stress-inducible HSF1 transcription complex has not yet been examined in detail in mammalian cells. In the present study, we demonstrated that HSF1 interacted with members of the ATF1/CREB family involved in metabolic homeostasis and recruited them on the HSP70 promoter in response to heat shock. The HSF1 transcription complex, including the chromatin-remodeling factor BRG1 and lysine acetyltransferases p300 and CREB-binding protein (CBP), was formed in a manner that was dependent on the phosphorylation of ATF1. ATF1-BRG1 promoted the establishment of an active chromatin state and HSP70 expression during heat shock, whereas ATF1-p300/CBP accelerated the shutdown of HSF1 DNA-binding activity during recovery from acute stress, possibly through the acetylation of HSF1. Furthermore, ATF1 markedly affected the resistance to heat shock. These results revealed the unanticipated complexity of the primitive heat shock response mechanism, which is connected to metabolic adaptation. Citation Takii R, Fujimoto M, Tan K, Takaki E, Hayashida N, Nakato R, Shirahige K, Nakai A. 2015. ATF1 modulates the heat shock response by regulating the stressinducible heat shock factor 1 transcription complex. Mol Cell Biol 35:11-25. on March 22, 2015 by TOKYO MEDICAL AND DENTAL UNIV http://mcb.asm.org/ Downloaded from FIG 2 The HSF1-ATF1 complex promoted HSP70 expression during heat shock. (A) Knockdown of mouse ATF1, CREB, and CREM. Immortalized MEF cells (stock no. 10) were infected for 72 h with adenovirus expressing shRNA against mATF1 (KD1, KD2), CREB (KD1, KD2), or CREM (KD1, KD2) or scrambled RNA (SCR). Cell extracts were prepared in NP-40 lysis buffer, and aliquots (120 g) were subjected to Western immunoblotting (IB) with rabbit antibody to ATF1/CREB or CREM or mouse antibody to -actin. Arrowheads indicate the positions of the proteins. The asterisk indicates nonspecific bands. (B) Knockdown of ATF1 and CREM reduced the mRNA expression of HSPs during heat shock. MEF cells that were infected with the adenovirus as described in panel A were treated without (Control) or with heat shock at 42°C for 30 min. The mRNA levels of HSPs, including HSP110, HSP70, and HSP40, and those of -actin were determined by RT-PCR. (C) Expression of HSP70 mRNA after the knockdown of ATF1/CREB members. ATF1, CREB, or CREM was knocked down in MEF cells and heat shocked at 42°C for 30 min (HS), MG132 for 3 h, AzC for 3 h, or As for 6 h. HSP70 mRNA levels were determined by RT-PCR and quantified. HSP70 mRNA levels relative to those in control Ad-sh-SCRinfected cells are shown (n ϭ 3). (D) Overexpression of ATF1 or CREM rescued the expression of HSP70 mRNA during heat shock in ATF1-null cells. GFP, HA-mATF1, HA-mCREB, or HA-mCREM was overexpressed in immortalized ATF1-null MEF cells. HSP70 mRNA levels during heat shock at 4...
