Acts as a negative regulator of the endoplasmic reticulum stress response or unfolded protein response (UPR). Represses the transcriptional activity of CREB3 during the UPR. Recruits CREB3 into nuclear foci. Interacts (via leucine-zipper domain) with CREB3 (via leucine-zipper domain); the interaction promotes CREB3 degradation. Colocalizes with CREB3 in nuclear foci. Up-regulated by endoplasmic reticulum stress. Probably degraded by the proteasome. Belongs to the bZIP family. CREBRF subfamily.