Transcription factor involved in unfolded protein response (UPR). Binds the DNA consensus sequence 5'-GTGXGCXGC-3' (By similarity). In the absence of endoplasmic reticulum (ER) stress, inserted into ER membranes, with N-terminal DNA-binding and transcription activation domains oriented toward the cytosolic face of the membrane. In response to ER stress, transported to the Golgi, where it is cleaved in a site-specific manner by resident proteases S1P/MBTPS1 and S2P/MBTPS2. The released N-terminal cytosolic domain is translocated to the nucleus to effect transcription of specific target genes. Plays a critical role in bone formation through the transcription of COL1A1, and possibly COL1A2, and the secretion of bone matrix proteins. Directly binds to the UPR element (UPRE)-like sequence in an osteoblast-specific COL1A1 promoter region and induces its transcription. Does not regulate COL1A1 in other tissues, such as skin (PubMed:19767743). Required to protect astrocytes from ER stress-induced cell death. In astrocytes, binds to the cAMP response element (CRE) of the BiP/HSPA5 promoter and participate in its transcriptional activation (PubMed:15665855). Inhibits cell-cycle progression by binding to promoters and activating transcription of genes encoding cell-cycle inhibitors, such as p21/CDKN1A (By similarity). Required for TGFB1 to activate genes involved in the assembly of collagen extracellular matrix (By similarity). Interacts with SMAD4, the interaction takes place upon TGFB1 induction and SMAD4 acts as CREB3L1 coactivator to induce the expression of genes involved in assembly of collagen extracellular matrix. ER membrane resident protein. Upon ER stress, translocated to the Golgi apparatus where it is cleaved. The cytosolic N-terminal fragment (processed cyclic AMP-responsive element-binding protein 3-like protein 1) is transported into the nucleus. Upon ER stress, transported into the nucleus. Expressed in cortical and trabecular bones. Highly expressed in osteoblasts, but not detected in osteoclasts, nor in macrophages (PubMed:19767743). Expressed at relatively low levels in lung and kidney. Weakly expressed in brain and spleen. In the embryo, primarily expressed in the cartilage, tooth germs and salivary gland. Expressed in the inner enamel epithelium during the cap and bell stages (14.5 dpc - 18.5 dpc), in the preodontoblasts during differentiation stage (18.5 dpc - P0) and in the differentiating odontoblasts during the early secretory stage (P2.5-P4.5). After birth, at P14, detected at low levels in the cerebral cortex, hippocampus and thalamus. In the adult brain, expression becomes weaker. Up-regulated in astrocytes residing in or close to CNS lesions, such as cryo-injured cerebral cortex and stab-injured spinal cord (PubMed:12480185, PubMed:15665855). Up-regulated by ER stress in astrocytes (at protein level). This induction is accompanied by increased proteolytic cleavage that releases the N-terminal transcription factor domain (PubMed:15665855). Up-regulated by BMP2 and RUNX2 in calvaria osteoblasts. This induction at the transcript and protein levels is accompanied by increased proteolytic cleavage that releases the N-terminal transcription factor domain, possibly through mild ER stress (PubMed:19767743). Also induced by BMP2 in bone marrow stromal cells. N-glycosylated. Ubiquitinated by HRD1/SYVN1; undergoes 'Lys-48'-linked ubiquitination, followed by rapid proteasomal degradation under normal conditions. Upon ER stress, SYVN1 E3 ubiquitin-protein ligase dissociates from its substrate, ubiquitination does not occur and CREB3L1 is stabilized. Upon ER stress, translocated to the Golgi apparatus, where it is processed by regulated intramembrane proteolysis (RIP) to release the cytosol-facing N-terminal transcription factor domain (PubMed:19767743). The cleavage is performed sequentially by site-1 and site-2 proteases (S1P/MBTPS1 and S2P/MBTPS2). RIP is induced by TGFB1 and ceramide. Mutant mice are born at the expected Mendelian rate, but show growth retardation. They exhibit severe osteopenia, involving a decrease in type I collagen in the bone matrix and a decline in the activity of osteoblasts. Osteoblasts show abnormally expanded rough endoplasmic reticulum, containing of a large amount of bone matrix proteins, including COL1A1 and osteocalcin/BGLAP. Belongs to the bZIP family. ATF subfamily.