Multifunctional transcription factor in ER stress response. Plays an essential role in the response to a wide variety of cell stresses and induces cell cycle arrest and apoptosis in response to ER stress. Plays a dual role both as an inhibitor of CCAAT/enhancer-binding protein (C/EBP) function and as an activator of other genes. Acts as a dominant-negative regulator of C/EBP-induced transcription: dimerizes with members of the C/EBP family, impairs their association with C/EBP binding sites in the promoter regions, and inhibits the expression of C/EBP regulated genes. Positively regulates the transcription of TRIB3, IL6, IL8, IL23, TNFRSF10B/DR5, PPP1R15A/GADD34, BBC3/PUMA, BCL2L11/BIM and ERO1L. Negatively regulates; expression of BCL2 and MYOD1, ATF4-dependent transcriptional activation of asparagine synthetase (ASNS), CEBPA-dependent transcriptional activation of hepcidin (HAMP) and CEBPB-mediated expression of peroxisome proliferator-activated receptor gamma (PPARG). Inhibits the canonical Wnt signaling pathway by binding to TCF7L2/TCF4, impairing its DNA-binding properties and repressing its transcriptional activity. Plays a regulatory role in the inflammatory response through the induction of caspase-11 (CASP4/CASP11) which induces the activation of caspase-1 (CASP1) and both these caspases increase the activation of pro-IL1B to mature IL1B which is involved in the inflammatory response (By similarity). Heterodimer (By similarity). Interacts with TCF7L2/TCF4, EP300/P300, HDAC1, HDAC5 and HDAC6. Interacts with TRIB3 which blocks its association with EP300/P300. Interacts with FOXO3, CEBPB and ATF4 (By similarity). Present in the cytoplasm under non-stressed conditions and ER stress leads to its nuclear accumulation. The N-terminal region is necessary for its proteasomal degradation, transcriptional activity and interaction with EP300/P300. Ubiquitinated, leading to its degradation by the proteasome. Phosphorylation at serine residues by MAPK14 enhances its transcriptional activation activity while phosphorylation at serine residues by CK2 inhibits its transcriptional activation activity. Belongs to the bZIP family.