PCAF interacts with XBP-1S and mediates XBP-1S-dependent transcription

Lew, Qiao Jing; Chu, Kai Ling; Lee, Jialing; Koh, Poh Ling; Rajasegaran, Vikneswari; Teo, Jin Yuan; Chao, Sheng-Hao

Discovery of the involvement of PCAF in the transcriptional regulation of BiP and EDEM genes is novel. PCAF has been identified as a co-factor of ATF4 (or CREB2) for the expression of CHOP (38) . In response to amino acid starvation, ATF4 binds to the amino acid response element located in the CHOP promoter and recruits PCAF to the promoter, leading to the activation of CHOP transcription (38) . Besides PCAF, ATF4 also interacts with other HATs, including p300 and CBP, through its N-terminal transactivation domain (39, 40) . As shown in Figure 1 , XBP-1S shows more stringent protein binding than ATF4 and fails to associate with p300. Future study is required to investigate the interaction between XBP-1S and other HATs to further determine the binding specificity of the XBP-1S transactivation domain. Collectively, Figure 8 . Requirement of PCAF for the mediation of XBP-1S target genes under UPR. MCF7 cells were co-transfected with a non-specific (i.e. control) or PCAF shRNA, and incubated with 10 mg/ml Tm (A) or 300 nM Tg (B). Both Tm and Tg were dissolved in DMSO and the final concentration of DMSO in the culture was kept at 0.1%. Expression of endogenous BiP and CHOP genes was determined by QRT-PCR. Cells transfected with a control shRNA with 0.1% DMSO were served as a negative control. For quantitative ChIP assays, HEK293 cells were treated with 10 mg/ml Tm (C) or 300 nM Tg (D) and the bindings of XBP-1S and PCAF to the endogenous BiP and CHOP genes were analyzed by quantitative PCR. Cells incubated with 0.1% DMSO were used as a negative control. Fold changes were determined by comparing to the negative controls. *P < 0.05 versus negative controls. Figure 9 . Interaction between XBP-1S and PCAF under UPR. 293T cells were transiently transfected with a XBP-1S expression vector and incubated with 10 mg/ml Tm or 0.1% DMSO (i.e. the negative control) for 16 h. IP was performed using the cell lysates prepared from the transfected cells and the antibody against XBP-1. Normal IgG (IgG) was used as a negative control. The immunoprecipitated complexes and the protein inputs were analyzed by western blotting. the findings by our and other groups point out that PCAF may play an important role in transcriptional activation of CHOP through the XBP-1S-as well as ATF4-dependent pathways.