Cloning and characterization of hGMEB1, a novel glucocorticoid modulatory element binding protein

Lipotoxicity-induced circGlis3 impairs beta cell function and is transmitted by exosomes to promote islet endothelial cell dysfunction

AIMS/HYPOTHESIS

Lipotoxicity constitutes the major driving force for type 2 diabetes. Circular RNAs (circRNAs) play important roles in regulating beta cell function and exosomes are essential mediators of intercellular communication. The role of exosomal circRNAs in type 2 diabetes remains largely unknown. We aimed to examine whether lipotoxicity induces dysregulation of circRNAs in beta cell-derived exosomes and to determine the contribution of exosomal circRNAs to the development of type 2 diabetes.

METHODS

Exosomes were extracted from MIN6 cells treated with palmitate or BSA, and RNA sequencing was performed. CircGlis3 (Gli-similar 3) expression level was validated by qPCR. The impact of circGlis3 on beta cell function and the deleterious effects of exosomal circGlis3 on islet endothelial cells (islet ECs) were investigated in vitro and in vivo in human and mouse models by gain or loss of function assays. The molecular mechanism of circGlis3 was explored by RNA pull-down and immunoprecipitation assays.

RESULTS

Beta cell-derived exosomal circGlis3 was significantly upregulated under lipotoxic conditions, and exosomal circGlis3 levels were also elevated in the serum of mouse models of diabetes and participants with type 2 diabetes. CircGlis3 participated in lipotoxicity-induced beta cell dysfunction in vitro and in vivo. Moreover, beta cell-derived exosomal circGlis3 could be transferred to islet ECs and reduce the cell viability, cell migration and angiogenesis of islet ECs. Mechanistically, circGlis3 promoted the degradation of glucocorticoid modulatory element-binding protein 1 (GMEB1) by facilitating the interaction between GMEB1 and mindbomb E3 ubiquitin protein ligase 2 (MIB2), thus suppressing the phosphorylation of heat shock protein 27 (HSP27).

CONCLUSIONS/INTERPRETATION

Our study points to the involvement of circGlis3 in diabetes development, and exosomal circGlis3 transfer as a communication mode between beta cells and islet ECs, suggesting that circGlis3 might be a potential biomarker and therapeutic target for type 2 diabetes.

DATA AVAILABILITY

The RNA-sequencing data have been deposited in the NCBI Sequence Read Archive (SRA) database, with accession number PRJNA689673. Mass spectrometry data are available via ProteomeXchange with identifier PXD024693.

Glucocorticoid modulatory element-binding protein 1 (GMEB1) interacts with the de-ubiquitinase USP40 to stabilize CFLARL and inhibit apoptosis in human non-small cell lung cancer cells

Background

GMEB1 was originally identified via its interaction with GMEB2, which binds to the promoter region of the tyrosine aminotransferase (TAT) gene and modulates transactivation of the glucocorticoid receptor gene. In the cytosol, GMEB1 interacts with and inhibits CASP8, but the molecular mechanism is currently unknown.

Methods

Human non-small cell lung cancer cells and 293FT cells were used to investigate the function of GMEB1/USP40/CFLAR_L complex by WB, GST Pull-Down Assay, Immunoprecipitation, Immunofluorescence and Flow cytometry analysis. A549 cells overexpressing green fluorescent protein and GMEB1 shRNA were used for tumor xenograft using female athymic nu/nu 4-week-old mice.

Results

We found GMEB1 interacted with CFLAR_L (also known as c-FLIP_L) in the cytosol and promoted its stability. USP40 targeted CFLAR_L for K48-linked de-ubiquitination. GMEB1 promoted the binding of USP40 to CFLAR_L. USP40 knockdown did not increase CFLAR_L protein level despite GMEB1 overexpression, suggesting GMEB1 promotes CFLAR_L stability via USP40. Additionally, GMEB1 inhibited the activation of pro-caspase 8 and apoptosis in non-small cell lung cancer (NSCLC) cell via CFLAR_L stabilization. Also, GMEB1 inhibited the formation of DISC upon TRAIL activation. CFLAR_L enhanced the binding of GMEB1 and CASP8. Downregulation of GMEB1 inhibited A549 xenograft tumor growth in vivo.

Conclusions

Our findings show the de-ubiquitinase USP40 regulates the ubiquitination and degradation of CFLAR_L; and GMEB1 acts as a bridge protein for USP40 and CFLAR_L. Mechanistically, we found GMEB1 inhibits the activation of CASP8 by modulating ubiquitination and degradation of CFLAR_L. These findings suggest a novel strategy to induce apoptosis through CFLAR_L targeting in human NSCLC cells.

Electronic supplementary material

The online version of this article (10.1186/s13046-019-1182-3) contains supplementary material, which is available to authorized users.

SPE-44 implements sperm cell fate

The sperm/oocyte decision in the hermaphrodite germline of Caenorhabditis elegans provides a powerful model for the characterization of stem cell fate specification and differentiation. The germline sex determination program that governs gamete fate has been well studied, but direct mediators of cell-type-specific transcription are largely unknown. We report the identification of spe-44 as a critical regulator of sperm gene expression. Deletion of spe-44 causes sperm-specific defects in cytokinesis, cell cycle progression, and organelle assembly resulting in sterility. Expression of spe-44 correlates precisely with spermatogenesis and is regulated by the germline sex determination pathway. spe-44 is required for the appropriate expression of several hundred sperm-enriched genes. The SPE-44 protein is restricted to the sperm-producing germline, where it localizes to the autosomes (which contain sperm genes) but is excluded from the transcriptionally silent X chromosome (which does not). The orthologous gene in other Caenorhabditis species is similarly expressed in a sex-biased manner, and the protein likewise exhibits autosome-specific localization in developing sperm, strongly suggestive of an evolutionarily conserved role in sperm gene expression. Our analysis represents the first identification of a transcriptional regulator whose primary function is the control of gamete-type-specific transcription in this system.

Stem cells give rise to the variety of specialized cell types within an organism. The decision to adopt a particular cell fate, a process known as specification or determination, requires the coordinated expression of all of the genes needed for that specialized cell to develop and function properly. Understanding the mechanisms that govern these patterns of gene expression is critical to our understanding of stem cell fate specification. We study this process in a nematode species that makes both sperm and eggs from the same stem cell population. We have identified a gene, named spe-44, that is required for the proper expression of sperm genes (but not egg genes). Mutation in spe-44 produces sterile sperm with developmental defects. spe-44 is controlled by factors that govern the sperm/egg decision, and its function in controlling sperm gene expression appears to be conserved in other nematode species.

Glucocorticoid modulatory element-binding protein 1 binds to initiator procaspases and inhibits ischemia-induced apoptosis and neuronal injury

Caspases are divided into two classes: initiator caspases, which include caspase-8 and -9 and possess long prodomains, and effector caspases, which include caspase-3 and -7 and possess short prodomains. Recently, we demonstrated that glucocorticoid modulatory element-binding protein 1 (GMEB1) interacts with the prodomain of procaspase-2, thereby disrupting its autoactivation and the induction of apoptosis. Here we show that GMEB1 is also capable of binding to procaspase-8 and -9. GMEB1 attenuated the Fas-mediated activation of these caspases and the subsequent apoptosis. The knockdown of endogenous GMEB1 using RNA interference revealed that cells with decreased GMEB1 expression are more sensitive to stress and undergo accelerated apoptosis. Transgenic mice expressing a neurospecific GMEB1 had smaller cerebral infarcts and less brain swelling than wild-type mice in response to transient focal ischemia. These results suggest that GMEB1 is an endogenous regulator that selectively binds to initiator procaspases and inhibits caspase-induced apoptosis.

Mapping DNA-binding domains of the autoimmune regulator protein

The human autoimmune regulator (AIRE) gene encodes a putative DNA-binding protein, which is mutated in patients affected by the autoimmune polyglandular syndrome type 1 or autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy. We have recently reported that AIRE can bind to two different DNA sequence motifs, suggesting the existence of at least two DNA-binding domains in the AIRE protein. By expressing a series of recombinant AIRE protein fragments, we demonstrate here that the two well-known plant homeodomains (PHD) domains in AIRE can bind to the ATTGGTTA sequence motif. The first ATTGGTTA-binding domain is mapped to amino acids 299-355 and the second ATTGGTTA-binding domain to amino acids 434-475. Furthermore, the SAND domain of AIRE is shown to bind to TTATTA motif. Results presented herein show that the residues at position 189-196 of AIRE (QRAVAMSS) are required for its binding to the TTATTA motif. The required sequence for DNA binding in the SAND domain of AIRE is remarkably different from other SAND-containing proteins such as Sp-100b and NUDR. Data presented in this paper indicate that the two PHD domains contained in AIRE, in addition to the SAND domain, can bind to specific DNA sequence motifs.

Regulation of procaspase-2 by glucocorticoid modulatory element-binding protein 1 through the interaction with caspase recruitment domain

Caspases are the primary executioners of apoptosis. Although procaspases believe to exist as inactive forms in cells, the detailed regulatory system remains unclear. Here we show that glucocorticoid modulatory element-binding protein 1 (GMEB1) is capable of binding to the prodomain of caspase-2. We found that this molecule inhibits the autoproteolytic activation of procaspase-2 by oligomerization on a chemical compound-dependent system. These findings indicated that GMEB1 might be an endogenous inhibitory protein that selectively interacts with prodomain of caspase-2 to disrupt the autoactivation.

The multiassembly problem: reconstructing multiple transcript isoforms from EST fragment mixtures

Recent evidence of abundant transcript variation (e.g., alternative splicing, alternative initiation, alternative polyadenylation) in complex genomes indicates that cataloging the complete set of transcripts from an organism is an important project. One challenge is the fact that most high-throughput experimental methods for characterizing transcripts (such as EST sequencing) give highly detailed information about short fragments of transcripts or protein products, instead of a complete characterization of a full-length form. We analyze this "multiassembly problem"-reconstructing the most likely set of full-length isoform sequences from a mixture of EST fragment data-and present a graph-based algorithm for solving it. In a variety of tests, we demonstrate that this algorithm deals appropriately with coupling of distinct alternative splicing events, increasing fragmentation of the input data and different types of transcript variation (such as alternative splicing, initiation, polyadenylation, and intron retention). To test the method's performance on pure fragment (EST) data, we removed all mRNA sequences, and found it produced no errors in 40 cases tested. Using this algorithm, we have constructed an Alternatively Spliced Proteins database (ASP) from analysis of human expressed and genomic sequences, consisting of 13,384 protein isoforms of 4422 genes, yielding an average of 3.0 protein isoforms per gene.

Structure/Activity Relationships for GMEB-2: The Second Member of the Glucocorticoid Modulatory Element-Binding Complex

The position of the dose-response curve of agonist complexes of glucocorticoid receptors (GRs), and the partial agonist activity of GR-antagonist complexes, can be modulated by two proteins (GMEB-1 and -2), which bind as oligomers to a DNA element that is called a glucocorticoid modulatory element, or GME. This element is active when located upstream of the glucocorticoid response element that controls the expression of a reporter gene. Here, we report the structure/activity relationships of GMEB-2 and compare them to our previous findings for GMEB-1. Most of the activities of GMEB-2, such as homo- and heterooligomerization, binding to GR and to CBP, DNA binding, and modulation of the above GR transcriptional properties, require large regions of the protein. Only the intrinsic transactivation activity could be localized to a small region of the protein. These studies shed light on the mechanism of action of GMEB-2 and further support our previous conclusion that the ability of factors to modulate the position of the dose-response curve, and the partial agonist activity, of GR complexes is unrelated to effects on the total levels of GR-induced gene expression. These studies also identify regions of GMEB-2 possessing yet unidentified properties that are critical for several activities. Finally, as the domain organization of GMEB-2 and -1 is extremely similar, we conclude that the quantitative differences in activities derive from variations in amino acid sequence rather than more global features of protein structure.

The identity of proteins associated with a small heat shock protein during heat stress in vivo indicates that these chaperones protect a wide range of cellular functions

The small heat shock proteins (sHSPs) are a ubiquitous class of ATP-independent chaperones believed to prevent irreversible protein aggregation and to facilitate subsequent protein renaturation in cooperation with ATP-dependent chaperones. Although sHSP chaperone activity has been studied extensively in vitro, understanding the mechanism of sHSP function requires identification of proteins that are sHSP substrates in vivo. We have used both immunoprecipitation and affinity chromatography to recover 42 proteins that specifically interact with Synechocystis Hsp16.6 in vivo during heat treatment. These proteins can all be released from Hsp16.6 by the ATP-dependent activity of DnaK and co-chaperones and are heat-labile. Thirteen of the putative substrate proteins were identified by mass spectrometry and reveal the potential for sHSPs to protect cellular functions as diverse as transcription, translation, cell signaling, and secondary metabolism. One of the putative substrates, serine esterase, was purified and tested directly for interaction with purified Hsp16.6. Hsp16.6 effectively formed soluble complexes with serine esterase in a heat-dependent fashion, thereby preventing formation of insoluble serine esterase aggregates. These data offer critical insights into the characteristics of native sHSP substrates and extend and provide in vivo support for the chaperone model of sHSP function.

Striated muscle cytoarchitecture: an intricate web of form and function

Striated muscle is an intricate, efficient, and precise machine that contains complex interconnected cytoskeletal networks critical for its contractile activity. The individual units of the sarcomere, the basic contractile unit of myofibrils, include the thin, thick, titin, and nebulin filaments. These filament systems have been investigated intensely for some time, but the details of their functions, as well as how they are connected to other cytoskeletal elements, are just beginning to be elucidated. These investigations have advanced significantly in recent years through the identification of novel sarcomeric and sarcomeric-associated proteins and their subsequent functional analyses in model systems. Mutations in these cytoskeletal components account for a large percentage of human myopathies, and thus insight into the normal functions of these proteins has provided a much needed mechanistic understanding of these disorders. In this review, we highlight the components of striated muscle cytoarchitecture with respect to their interactions, dynamics, links to signaling pathways, and functions. The exciting conclusion is that the striated muscle cytoskeleton, an exquisitely tuned, dynamic molecular machine, is capable of responding to subtle changes in cellular physiology.

Structure/activity elements of the multifunctional protein, GMEB-1. Characterization of domains relevant for the modulation of glucocorticoid receptor transactivation properties

GMEB-1 was initially described as a component of a 550-kDa heteromeric DNA binding complex that is involved in the modulation of two properties of glucocorticoid receptor (GR) transactivation, the dose-response curve of agonists and the partial agonist activity of antagonists. Subsequently, GMEB-1 was also found to bind to hsp27, to associate with the coactivator TIF2 in yeast cells, and to participate in Parvovirus replication. To understand these multiple activities of GMEB-1 at a molecular level, we have now determined which regions are associated with the various activities associated with the modulation of GR transactivation properties. These activities include, homooligomerization, heterooligomerization, DNA binding, binding to GR and the transcriptional cofactor CBP, and GR modulation. Complex activities such as DNA binding and GR modulation, are found to require the physical combination of those domains that would be predicted from the involved biochemical processes. We have previously documented that GMEB-1 possesses both GR modulatory and intrinsic transactivation activity. However, the domains for these two activities of GMEB-1 are found not to overlap. This separation of activities provides a structural basis for our prior biological observations that the modulation of the dose-response curve and partial agonist activity of GR complexes is independent of the total levels of gene activation by the same GR complexes.

DEAF-1 function is essential for the early embryonic development of Drosophila

The Drosophila protein DEAF-1 is a sequence-specific DNA binding protein that was isolated as a putative cofactor of the Hox protein Deformed (Dfd). In this study, we analyze the effects of loss or gain of DEAF-1 function on Drosophila development. Maternal/zygotic mutations of DEAF-1 largely result in early embryonic arrest prior to the expression of zygotic segmentation genes, although a few embryos develop into larvae with segmentation defects of variable severity. Overexpression of DEAF-1 protein in embryos can induce defects in migration/closure of the dorsal epidermis, and overexpression in adult primordia can strongly disrupt the development of eye or wing. The DEAF-1 protein associates with many discrete sites on polytene chromosomes, suggesting that DEAF-1 is a rather general regulator of gene expression.

Muscle-specific RING finger-1 interacts with titin to regulate sarcomeric M-line and thick filament structure and may have nuclear functions via its interaction with glucocorticoid modulatory element binding protein-1

The COOH-terminal A168-170 region of the giant sarcomeric protein titin interacts with muscle-specific RING finger-1 (MURF-1). To investigate the functional significance of this interaction, we expressed green fluorescent protein fusion constructs encoding defined fragments of titin's M-line region and MURF-1 in cardiac myocytes. Upon expression of MURF-1 or its central region (containing its titin-binding site), the integrity of titin's M-line region was dramatically disrupted. Disruption of titin's M-line region also resulted in a perturbation of thick filament components, but, surprisingly, not of the NH2-terminal or I-band regions of titin, the Z-lines, or the thin filaments. This specific phenotype also was caused by the expression of titin A168-170. These data suggest that the interaction of titin with MURF-1 is important for the stability of the sarcomeric M-line region.MURF-1 also binds to ubiquitin-conjugating enzyme-9 and isopeptidase T-3, enzymes involved in small ubiquitin-related modifier-mediated nuclear import, and with glucocorticoid modulatory element binding protein-1 (GMEB-1), a transcriptional regulator. Consistent with our in vitro binding data implicating MURF-1 with nuclear functions, endogenous MURF-1 also was detected in the nuclei of some myocytes. The dual interactions of MURF-1 with titin and GMEB-1 may link myofibril signaling pathways (perhaps including titin's kinase domain) with muscle gene expression.

A consensus DNA recognition motif for two KDWK transcription factors identifies flexible-length, CpG-methylation sensitive cognate binding sites in the majority of human promoters

Parvovirus initiation factor (PIF), identified in HeLa cells as a host factor essential for parvoviral DNA replication, is a ubiquitous heterodimeric cellular transcription factor. This protein complex was simultaneously identified as glucocorticoid modulatory element binding protein (GMEB) by its ability to bind to the glucocorticoid modulating element (GME) upstream of the tyrosine transaminase promoter. Here, we show that the two PIF/GMEB subunits form site-specific DNA-binding heterodimers when co-expressed from recombinant baculoviruses and homodimers when expressed separately. Degenerate oligonucleotide selection experiments, combined with analysis of dissociation rates, established that the three complexes bind to flexibly spaced tetranucleotide half-sites that conform to the consensus ACGPy N(1-9) PuCGPy, with an optimum of N=6. Binding of all three complexes is extremely sensitive to methylation of the cytosine residues in the invariant CpG half-site core, suggesting a means by which PIF/GMEB binding could be regulated in vivo. Because CpG dinucleotides are suppressed in eukaryotic genomes, such binding sites would be expected to be very rare. However, analysis of 100 human promoters showed that over half of them contained at least one site conforming to the consensus, a significant deviation from the expected random distribution. In many of these, the binding site is within 100 nucleotides of the transcriptional start site, indicating that PIF/GMEB may be involved in regulation of these genes. Oligonucleotides corresponding to five of these sequences, chosen to represent the range of half-site separations identified by the consensus, were tested for PIF/GMEB binding by mobility shift assay. All five probes bound the heterodimer efficiently and, in each case, binding was completely abrogated by 5-methylation of the C residues in the CpGs of the putative half-sites.

Interferon-induced antiviral Mx1 GTPase is associated with components of the SUMO-1 system and promyelocytic leukemia protein nuclear bodies

Mx proteins are interferon-induced large GTPases, some of which have antiviral activity against a variety of viruses. The murine Mx1 protein accumulates in the nucleus of interferon-treated cells and is active against members of the Orthomyxoviridae family, such as the influenza viruses and Thogoto virus. The mechanism by which Mx1 exerts its antiviral action is still unclear, but an involvement of undefined nuclear factors has been postulated. Using the yeast two-hybrid system, we identified cellular proteins that interact with Mx1 protein. The Mx1 interactors were mainly nuclear proteins. They included Sp100, Daxx, and Bloom's syndrome protein (BLM), all of which are known to localize to specific subnuclear domains called promyelocytic leukemia protein nuclear bodies (PML NBs). In addition, components of the SUMO-1 protein modification system were identified as Mx1-interacting proteins, namely the small ubiquitin-like modifier SUMO-1 and SAE2, which represents subunit 2 of the SUMO-1 activating enzyme. Analysis of the subcellular localization of Mx1 and some of these interacting proteins by confocal microscopy revealed a close spatial association of Mx1 with PML NBs. This suggests a role of PML NBs and SUMO-1 in the antiviral action of Mx1 and may allow us to discover novel functions of this large GTPase.

Adenovirus E4 open reading frame 4-induced apoptosis involves dysregulation of Src family kinases

The adenoviral early region 4 open reading frame 4 (E4orf4) death factor induces p53-independent apoptosis in many cell types and appears to kill selectively transformed cells. Here we show that expression of E4orf4 in transformed epithelial cells results in early caspase-independent membrane blebbing, associated with changes in the organization of focal adhesions and actin cytoskeleton. Evidence that E4orf4 can associate with and modulate Src family kinase activity, inhibiting Src-dependent phosphorylation of focal adhesion kinase (FAK) and paxillin while increasing phosphorylation of cortactin and some other cellular proteins, is presented. Furthermore, E4orf4 dramatically inhibited the ability of FAK and c-src to cooperate in induction of tyrosine phosphorylation of cellular substrates, suggesting that E4orf4 can interfere with the formation of a signaling complex at focal adhesion sites. Consistent with a functional role for E4orf4-Src interaction, overexpression of activated c-src dramatically potentiated E4orf4-induced membrane blebbing and apoptosis, whereas kinase dead c-src constructs inhibited E4orf4 effects on cell morphology and death. Moreover treatment of E4orf4-expressing cells with PP2, a selective Src kinase inhibitor, led to inhibition of E4orf4-dependent membrane blebbing and later to a marked decrease in E4orf4-induced nuclear condensation. Taken together, these observations indicate that expression of adenovirus 2 E4orf4 can initiate caspase-independent extranuclear manifestations of apoptosis through a modulation of Src family kinases and that these are involved in signaling E4orf4-dependent apoptosis. This study also suggests that Src family kinases are likely to play a role in the cytoplasmic execution of apoptotic programs.

Properties of the glucocorticoid modulatory element binding proteins GMEB-1 and -2: potential new modifiers of glucocorticoid receptor transactivation and members of the family of KDWK proteins

An important component of glucocorticoid steroid induction of tyrosine aminotransferase (TAT) gene expression is the glucocorticoid modulatory element (GME), which is located at -3.6 kb of the rat TAT gene. The GME both mediates a greater sensitivity to hormone, due to a left shift in the dose-response curve of agonists, and increases the partial agonist activity of antiglucocorticoids. These properties of the GME are intimately related to the binding of a heteromeric complex of two proteins (GMEB-1 and -2). We previously cloned the rat GMEB-2 as a 67-kDa protein. We now report the cloning of the other member of the GME binding complex, the 88-kDa human GMEB-1, and various properties of both proteins. GMEB-1 and -2 each possess an intrinsic transactivation activity in mammalian one-hybrid assays, consistent with our proposed model in which they modify glucocorticoid receptor (GR)-regulated gene induction. This hypothesis is supported by interactions between GR and both GMEB-1 and -2 in mammalian two-hybrid and in pull-down assays. Furthermore, overexpression of GMEB-1 and -2, either alone or in combination, results in a reversible right shift in the dose-response curve, and decreased agonist activity of antisteroids, as expected from the squelching of other limiting factors. Additional mechanistic details that are compatible with the model of GME action are suggested by the interactions in a two-hybrid assay of both GMEBs with CREB-binding protein (CBP) and the absence of histone acetyl transferase (HAT) activity in both proteins. GMEB-1 and -2 share a sequence of 90 amino acids that is 80% identical. This region also displays homology to several other proteins containing a core sequence of KDWK. Thus, the GMEBs may be members of a new family of factors with interesting transcriptional properties.

Genomic organization of human GMEB-1 and rat GMEB-2: structural conservation of two multifunctional proteins

The glucocorticoid modulatory element binding proteins 1 and 2 (GMEB-1 and GMEB-2) are of interest both for their multiple activities (e.g. modulation of transactivation by the glucocorticoid receptor and initiation of parvovirus replication) and their membership in the emerging family of KDWK proteins. The genomic sequence of these proteins was desired in order to begin studies on the control of GMEB expression and to pursue previous evidence for significant homologies between the GMEBs. We now report the genomic sequence of human GMEB-1 and rat GMEB-2. The structure of both genes, including portions of the introns, is highly conserved. However, GMEB-1 and GMEB-2 were found to reside on chromosomes 1 and 20, respectively, demonstrating that they are encoded by distinctly different genes. Several isoforms of the GMEBs have been reported or detected in this study, and the splicing patterns were determined. The tissue distribution of each GMEB is not the same and is highest in fetal and developing tissues, consistent with previous suggestions that both homo- and hetero-oligomers may possess biological activity. The promoter region of both genes has been identified and both display high levels of transcription activity in transiently transfected cells when fused upstream of a promoterless reporter. These results indicate that the GMEBs are proteins that evolved from a single parent gene, have been highly conserved since the divergence of rats and humans and probably play important roles in development and differentiation.

Cloning of a mouse glucocorticoid modulatory element binding protein, a new member of the KDWK family

A mouse cDNA that encodes a nuclear DNA binding protein was identified by yeast two-hybrid screening using the activation domain 2 of the nuclear receptor coactivator TIF2 as a bait. BLAST analysis revealed that the identified cDNA encodes a KDWK domain and contains sequences almost identical to three tryptic peptides of rat GMEB-1 which together with the GMEB-2 heterodimeric partner binds to the GME/CRE sequence (glucocorticoid modulatory element) of the tyrosine aminotransferase (TAT) promoter. Mouse GMEB-1 is ubiquitously expressed in all the tissues examined. In vitro translated mGMEB-1 bound specifically to GME oligonucleotides, either alone or as a heterodimer with rGMEB-2. Transient transfection experiments with TAT promoter reporter genes suggest a potential role for mGMEB-1 as a transcriptional regulator of the TAT promoter.