Activation of ATF6 and an ATF6 DNA binding site by the endoplasmic reticulum stress response

ATF6 is a member of the basic-leucine zipper family of transcription factor s. It contains a transmembrane domain and is located in membranes of the en doplasmic reticulum, ATF6 has been implicated in the endoplasmic reticulum (ER) stress response pathway since it can activate expression of GRP78 and other genes induced by the ER stress response. ER stress appears to activat e ATF6 by cleavage from the ER membrane and translocation to the nucleus, H owever, direct DNA binding by ATF6 had not been demonstrated. In this repor t, we have identified a consensus DNA binding sequence for ATF6. This site is related to but distinct from ATF1/CREB binding sites. The site was place d in a reporter gene and was specifically activated by ATF6 overexpression and was strongly induced by the ER stress response. A dominant negative for m of ATF6 blocked ER stress induction of both ATF6 site and GRP78 reporter genes. We further found that GAL4-ATF6 could be activated by ER stress. The se results demonstrate that ATF6 is a direct target of the ER stress respon se. A proximal sensor of the ER stress response, human IRE1 (hIRE1), was su fficient to activate the ATF6 reporter gene, while a dominant negative form of hIRE1 blocked ER stress activation, suggesting that: hIRE1 is upstream of ATF6 in the ER stress signaling pathway.