Phosphorylation-dependent transcription factor that stimulates transcription upon binding to the DNA cAMP response element (CRE), a sequence present in many viral and cellular promoters. Transcription activation is enhanced by the TORC coactivators which act independently of Ser-119 phosphorylation. Involved in different cellular processes including the synchronization of circadian rhythmicity and the differentiation of adipose cells. Interacts with PPRC1. Binds DNA as a dimer. This dimer is stabilized by magnesium ions. Interacts, through the bZIP domain, with the coactivators TORC1/CRTC1, TORC2/CRTC2 and TORC3/CRTC3. When phosphorylated on Ser-119, binds CREBBP (By similarity). Interacts with CREBL2; regulates CREB1 phosphorylation, stability and transcriptional activity (By similarity). Interacts (phosphorylated form) with TOX3. Interacts with ARRB1. Binds to HIPK2. Interacts with SGK1. Interacts with TSSK4; this interaction facilitates phosphorylation on Ser-119 (PubMed:15964553). Forms a complex with KMT2A and CREBBP (PubMed:23651431, PubMed:14506290, PubMed:14536081, PubMed:15454081, PubMed:15733869, PubMed:15964553, PubMed:16325578, PubMed:16908542, PubMed:20573984, PubMed:21172805) (By similarity). Interacts with TOX4; CREB1 is required for full induction of TOX4-dependent activity and the interaction is increased by cAMP and inhibited by insulin (By similarity). (Microbial infection) Interacts with hepatitis B virus/HBV protein X. (Microbial infection) Interacts with HTLV-1 protein Tax. Stimulated by phosphorylation. Phosphorylation of both Ser-119 and Ser-128 in the SCN regulates the activity of CREB and participates in circadian rhythm generation. Phosphorylation of Ser-119 allows CREBBP binding. In liver, phosphorylation is induced by fasting or glucagon in a circadian fashion (By similarity). CREBL2 positively regulates phosphorylation at Ser-119 thereby stimulating CREB1 transcriptional activity (By similarity). Phosphorylated upon calcium influx by CaMK4 and CaMK2 on Ser-119. CaMK4 is much more potent than CaMK2 in activating CREB. Phosphorylated by CaMK2 on Ser-128. Phosphorylation of Ser-128 blocks CREB-mediated transcription even when Ser-119 is phosphorylated. Phosphorylated by CaMK1 (By similarity). Phosphorylation of Ser-257 by HIPK2 in response to genotoxic stress promotes CREB1 activity, facilitating the recruitment of the coactivator CBP. Phosphorylated at Ser-119 by RPS6KA3, RPS6KA4 and RPS6KA5 in response to mitogenic or stress stimuli. Phosphorylated by TSSK4 on Ser-119 (PubMed:15964553). Sumoylated with SUMO1. Sumoylation on Lys-290, but not on Lys-271, is required for nuclear localization of this protein. Sumoylation is enhanced under hypoxia, promoting nuclear localization and stabilization. The gene represented in this entry may be involved in disease pathogenesis. A chromosomal aberration involving CREB1 is found in a patient with angiomatoid fibrous histiocytoma. Translocation t(2;22)(q33;q12) with CREB1 generates a EWSR1/CREB1 fusion gene that is most common genetic abnormality in this tumor type. A CREB1 mutation has been found in a patient with multiple congenital anomalies consisting of agenesis of the corpus callosum, cerebellar hypoplasia, severe neonatal respiratory distress refractory to surfactant, thymus hypoplasia, and thyroid follicular hypoplasia. Highly expressed in adult testis and sperm. Belongs to the bZIP family.