Transcription factor that may act during endoplasmic reticulum stress by activating unfolded protein response target genes. Activated in response to cAMP stimulation. Binds the cAMP response element (CRE). Activates transcription through box-B element and CRE. Seems to function synergistically with ATF6. In acute inflammatory response, may activate expression of acute phase response (APR) genes (By similarity). May be involved in growth suppression. Regulates FGF21 transcription (By similarity). Plays a crucial role in the regulation of triglyceride metabolism and is required for the maintenance of normal plasma triglyceride concentrations (By similarity). Binds DNA as a dimer. May form homodimers (By similarity). Interacts with ATF6 (By similarity). Interacts with SYNV1/HRD1; this interaction leads to CREB3L3 ubiquitination and proteasomal degradation (By similarity). Under ER stress the cleaved N-terminal cytoplasmic domain translocates into the nucleus. Controlled by regulated intramembrane proteolysis (RIP). Following ER stress a fragment containing the cytoplasmic transcription factor domain is released by proteolysis. The cleavage seems to be performed sequentially by site-1 and site-2 proteases (PS1 and PS2) (By similarity). N-glycosylation is required for optimal proteolytic activation. Ubiquitinated at Lys-290 by SYNV1/HRD1 via 'Lys-27'-linked ubiquitin. Belongs to the bZIP family. ATF subfamily.