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

UPR induces the generation of XBP-1S which up-regulates its target genes required for secretory pathway, membrane synthesis, protein folding and ER-associated degradation (1). The involvement of PCAF for XBP-1S activation during UPR was studied by examining the expression BiP and CHOP genes. Cells were transfected with a control or PCAF shRNA followed by the treatment of Tm to induce UPR. The mRNAs isolated from the cells were analyzed by QRT-PCR. The mRNA levels of BiP and CHOP increased 4-and 14-fold, respectively, after Tm incubation ( Figure 8A ). Knockdown of PCAF only led to minor inhibition on the transcription of the two genes ( Figure 8A ). An identical set of assays was performed using Tg as the UPR inducing reagent. Little or no significant effects on BiP and CHOP mRNAs were detected in the PCAF shRNA-transfected cells ( Figure 8B) . We further carried out quantitative ChIP to examine the distribution of XBP-1S and PCAF on BiP and CHOP genes during UPR. Incubation of Tm resulted in 15-and 5-fold increases in XBP-1S binding to BiP and CHOP promoters, respectively, while only 3-and 1.7-fold increases in PCAF associating with the two genes ( Figure 8C ). In another set of experiments with Tg treatment, <2-fold increases in PCAF binding to endogenous BiP and CHOP genes were detected, while more than 20-(BiP) and 5-fold (CHOP) enhancement in XBP-1S binding ( Figure 8D) . Taken together the QRT-PCR and quantitative ChIP analyses suggest the limited involvement of PCAF in the mediation of XBP-1S target genes during UPR.