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

It has been reported that p300 is recruited to the endogenous BiP promoter in the Tg-treated cells by ChIP assays (41) . Co-overexpression of p300, YY1 and ATF6 showed synergistic activation of luciferase expression driven by the BiP promoter, suggesting that p300 might be required for YY1-/ATF6-mediated activation of BiP (41) . Similar cell-based reporter assays (i.e. using the BiP-Luc reporter plasmid) were performed to determine the requirement of p300 for XBP-1S-mediated transactivation. Neither overexpression nor knockdown of p300 showed any significant effects on XBP-1S-dependent luciferase expression (Figures 3 and 4) , suggesting that p300 might function in a XBP-1S-independent manner. These results were further supported by Co-IP data, in which no interaction between p300 and XBP-1S was detected ( Figure 1C ). Furthermore, we assessed the requirement of p300 for transcriptional activation of BiP and CHOP genes under UPR. In contrast to the report by Baumeister et al. (41) , our results obtained from the quantitative ChIP analyses did not show any increased p300 binding to either BiP or CHOP promoters in the Tm-or Tg-stressed cells (data not shown), raising the questions regarding to the involvement of p300 in the regulation of XBP-1S target genes.