Transcription factor that may act during endoplasmic reticulum stress by activating unfolded protein response target genes. Activated in response to cAMP stimulation. In vitro, binds to the cAMP response element (CRE) and box-B element. Activates transcription through box-B element. Activates transcription through CRE (By similarity). Seems to function synergistically with ATF6. In acute inflammatory response, may activate expression of acute phase response (APR) genes. May be involved in growth suppression.
The expression of liver-specific genes is regulated by unequivocally allocated transcription factors via proper responsible elements within their promoters. We identified a novel transcription factor, CREB-H, and found that its expression was restricted in the liver among 16 human tissues tested. A region of CREB-H exhibited significant homology to the basic leucine zipper (b-Zip) domain of members of the CREB/ATF family: mammalian LZIP and Drosophila BBF-2 that binds to box-B, a Drosophila enhancer modulating the fat-body-specific gene expression. CREB-H contained a hydrophobic region representing a putative transmembrane domain, like LZIP. Constructing a variety of CREB-H fusion proteins with the GAL4 DNA-binding domain disclosed that CREB-H functioned as a transcriptional activator and its N-terminal 149 amino acids accounted for the activation ability. Gel mobility sift assays revealed that CREB-H did not bind to the C/EBP, AP-1 and NF-kappaB elements but specifically bound to CRE and the box-B element. Luciferase reporter assays demonstrated that like BBF-2, CREB-H activated transcription via the box-B element and that a deletion of the putative transmembrane domain increased the activation of reporter expression significantly. Furthermore, a fusion protein of GFP and full-length CREB-H was localized in reticular structures surrounding the nucleus, whereas a fusion protein of GFP and a deletion mutant lacking the putative transmembrane domain was mainly in the nucleus. These findings suggest that CREB-H plays an important role in transcriptional regulation of genes specifically expressed in the liver, and that the putative transmembrane domain may be associated with modulation of its function as the transcriptional activator.
We have previously characterized transcription factor LZIP to be a growth suppressor targeted by hepatitis C virus oncoprotein. In search of proteins closely related to LZIP, we have identified a liver-enriched transcription factor CREB-H. LZIP and CREB-H represent a new subfamily of bZIP factors. CREB-H activates transcription by binding to cAMP responsive element, box B, and ATF6-binding element. Interestingly, CREB-H has a putative transmembrane (TM) domain and it localizes ambiently to the endoplasmic reticulum. Proteolytic cleavage that removes the TM domain leads to nuclear translocation and activation of CREB-H. CREB-H activates the promoter of hepatic gluconeogenic enzyme phosphoenolpyruvate carboxykinase. This activation can be further stimulated by cAMP and protein kinase A. CREB-H transcript is exclusively abundant in adult liver. In contrast, the expression of CREB-H mRNA is aberrantly reduced in hepatoma tissues and cells. The enforced expression of CREB-H suppresses the proliferation of cultured hepatoma cells. Taken together, our findings suggest that the liver-enriched bZIP transcription factor CREB-H is a growth suppressor that plays a role in hepatic physiology and pathology.
Regulated intramembrane proteolysis (RIP) of endoplasmic reticulum (ER) membrane-anchored transcription factors is known to maintain sterol homeostasis and to mediate the unfolded protein response (UPR). Here, we identified CREBH as a RIP-regulated liver-specific transcription factor that is cleaved upon ER stress and required to activate expression of acute phase response (APR) genes. Proinflammatory cytokines increase expression of ER membrane-anchored CREBH. In response to ER stress, CREBH is cleaved by site-1 and site-2 proteases to liberate an amino-terminal fragment that transits to the nucleus to activate transcription of the genes encoding serum amyloid P-component (SAP) and C-reactive protein (CRP). Proinflammatory cytokines and lipopolysaccharide activate the UPR and induce cleavage of CREBH in the liver in vivo. Together, our studies delineate a molecular mechanism for activation of an ER-localized transcription factor, CREBH, and reveal an unprecedented link by which ER stress initiates an acute inflammatory response.
Interacting selectively and non-covalently with any protein or protein complex (a complex of two or more proteins that may include other nonprotein molecules).
Evidence
1:
Inferred from Physical InteractionIntAct
Regulated intramembrane proteolysis (RIP) of endoplasmic reticulum (ER) membrane-anchored transcription factors is known to maintain sterol homeostasis and to mediate the unfolded protein response (UPR). Here, we identified CREBH as a RIP-regulated liver-specific transcription factor that is cleaved upon ER stress and required to activate expression of acute phase response (APR) genes. Proinflammatory cytokines increase expression of ER membrane-anchored CREBH. In response to ER stress, CREBH is cleaved by site-1 and site-2 proteases to liberate an amino-terminal fragment that transits to the nucleus to activate transcription of the genes encoding serum amyloid P-component (SAP) and C-reactive protein (CRP). Proinflammatory cytokines and lipopolysaccharide activate the UPR and induce cleavage of CREBH in the liver in vivo. Together, our studies delineate a molecular mechanism for activation of an ER-localized transcription factor, CREBH, and reveal an unprecedented link by which ER stress initiates an acute inflammatory response.
Interacting selectively and non-covalently with DNA of a specific nucleotide composition, e.g. GC-rich DNA binding, or with a specific sequence motif or type of DNA e.g. promotor binding or rDNA binding.
IEAInterPro 2 GO
Sequence-specific DNA binding transcription factor activitydefinition[GO:0003700]‹silver
Interacting selectively and non-covalently with a specific DNA sequence in order to modulate transcription. The transcription factor may or may not also interact selectively with a protein or macromolecular complex.
Any process that results in a change in state or activity of a cell or an organism (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of an unfolded protein stimulus.
Protein involved in the transfer of genetic information from DNA to messenger RNA (mRNA) by DNA-directed RNA polymerase. In the case of some RNA viruses, protein involved in the transfer of genetic information from RNA to messenger RNA (mRNA) by RNA-directed RNA polymerase.
Protein involved in the unfolded protein response. An accumulation of unfolded proteins in the ER lumen triggers a stress response, resulting in the transcriptional induction in the nucleus of a set of genes, whose products are involved in protein folding, assembly and modification as well as in phospholipid biosynthesis. The unfolded protein response (UPR) is the intracellular pathway that mediates signaling from the endoplasmic reticulum (ER) to the nucleus. UPR is also tightly linked to ER-associated protein degradation (ERAD). UPR is a ubiquitous mechanism observed in all eukaryotes from humans to yeast.
A reference proteome is a set of protein sequences derived from a complete proteome which constitutes a defined standard for a particular user community. Reference proteomes are manually defined according to a number of criteria. They cover the proteomes of well- studied model organisms and other proteomes of interest for biomedical and biotechnological research. Reference proteomes have been selected to provide broad coverage of the tree of life, and constitute a representative cross-section of the taxonomic diversity to be found within UniProtKB.
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