Identification of ERSE-II, a new cis-acting element responsible for the ATF6-dependent mammalian unfolded protein response

Abstract

Herp is a 54-kDa membrane protein in the endoplasmic reticulum (ER). The mRNA expression level of Herp is increased by the accumulation of unfolded proteins in the ER. Transcriptional changes designed to deal with this type of ER stress is called the unfolded protein response (UPR). Most mammalian UPR-target genes encode ER-resident molecular chaperones: GRP78, GRP94, and calreticulin. The promoter regions of these genes contain a cis-acting ER stress response element, ERSE, with the consensus sequence of CCAAT-N(9)-CCACG. Under conditions of ER stress, p50ATF6 (the active form of the transcription factor, ATF6) binds to CCACG when CCAAT is bound by the general transcription factor, NF-Y/CBF. Here, we report the genomic structure of human Herp and the presence of a new ER stress response element, ERSE-II, in its promoter region. The gene for Herp consists of eight exons, localized to chromosome 16q12.2-13. The promoter region contains a single ERSE-like sequence. In reporter gene assays, disruption of this cis-element resulted in a partial reduction of the transcriptional response to ER stress, suggesting that the element is functional for the UPR. These results also suggest the involvement of additional elements in the UPR. Further analysis, using an optimized plasmid containing an mRNA-destabilizing sequence, revealed ERSE-II (ATTGG-N-CCACG) as the second ER stress response element. Interestingly, ERSE-II was also dependent on p50ATF6, in a manner similar to that of ERSE, despite the disparate structure. The strong induction of Herp mRNA by ER stress would be achieved by the cooperation of ERSE and ERSE-II.