Tax protein of human T-cell leukemia virus type I binds to the ankyrin motifs of inhibitory factor kappa B and induces nuclear translocation of transcription factor NF-kappa B proteins for transcriptional activation

Human T-cell leukemia virus type I causes adult T-cell leukemia and tropical spastic paraparesis, and its regulator protein Tax has been implicated in the pathogenic activity of human T-cell leukemia virus type I. Tax activates transcription of viral and cellular genes through specific enhancers: the 21-bp enhancer of human T-cell leukemia virus type I, the nuclear factor kappa B (NF-kappa B)-binding site of the interleukin 2 receptor alpha gene, and the serum-responsive element of c-fos. Tax binds to enhancer-binding proteins including cAMP-responsive element-binding protein, cAMP-responsive element modulator, transcription factor NF-kappa B p50 and p67SRF, and associates with each enhancer DNA indirectly. In addition to this mechanism, we report here that Tax binds to inhibitory factor kappa B gamma (I-kappa B) gamma, which forms a complex with NF-kappa B protein heterodimer p50-p65 or homodimer p50-p50 and retains them in the cytoplasm. Tax binding to I-kappa B gamma induces nuclear translocation of NF-kappa B p65. In association with this nuclear translocation of p65, transcription directed by the kappa B enhancer is strongly activated. Tax binds to the ankyrin motifs of I-kappa B gamma, suggesting its possible interaction with many other proteins carrying ankyrin motifs contributing to various regulatory processes. This is a different mechanism of transcriptional activation by the oncoprotein Tax and seems to be independent from the trans-activation through indirect binding to enhancer DNAs.

Novel isoforms of human cyclic AMP-responsive element modulator (hCREM) mRNA

The cyclic AMP-response element (CRE), a transcriptional enhancer, is regulated by CREB (CRE-binding protein) which is the leucine zipper protein phosphorylated by protein kinase A in response to cAMP signal. The highly homologous protein CREM (CRE-modulator) is thought to modulate CREB-stimulated transcription, and is also involved in transcriptional control during spermatogenesis. In this paper, we report two types of cDNAs of human CREM (hCREM), type 1 and type 2; type 1 is a group of human counterparts of the mouse CREM alpha and type 2 is a novel form having a distinct 5' exon which is unrelated to any species of the CREB and CREM isoforms so far described. This unique 5' region of type 2 hCREM may suggest its independent expression from type 1 CREM. The specific 5' region of type 2 hCREM consisted of 88 bp, containing an initiation codon for translation, but no possible phosphorylation site, suggesting different roles from type 1 CREM. Both type 1 and 2 hCREMs are expressed in lymphoid and non-lymphoid cell lines. Their excess expression by transfection induced suppression of cAMP-mediated activation of transcription, suggesting their negative regulation of CRE-mediated transcription.

[Mechanism of transcriptional activation by HTLV-1 Tax]

A trans-activator protein Tax of HTLV-1 activates the transcription of various cellular genes as well as viral promoter through the multiple enhancer elements and leads cells to the transformation. Tax protein interacts to enhancer DNA elements by associating with cellular enhancer binding proteins such as CREB, NF-kappa B and SRF. In addition, we found recently that Tax interacts with an I kappa B protein, the inhibitor of NF-kappa B, resulting in the enhancement of nuclear translocation of NF-kappa B molecules. Therefore, Tax seems to modulate the transcription by the interaction with multiple transcription factors in different modes of control.

Nucleotide sequence analysis of HTLV-I isolate from a Korean patient with HAM/TSP

Limited nucleotide sequences of human T-cell lymphotropic virus type I (HTLV-1) provirus isolated from the first case of a Korean patient with HTLV-I associated myelopathy and tropical spastic paraparesis (HAM/TSP) were analysed and compared with other isolates from different regions of the world. The sequences of the env, LTR regions (536bp, 690bp respectively) showed 98.7%, 99.3% homologies with the prototype HTLV-I, ATK-1, isolated from a Japanese Adult T-cell leukemia (ATL) patient. A comparison between other isolates from different geographical origins revealed that the Korean HTLV-I isolate is more closely related to Japanese isolates than to those from other geographical origins.

HTLV-I encoded Tax in association with NF-kappa B precursor p105 enhances nuclear localization of NF-kappa B p50 and p65 in transfected cells

NF-kappa B is a heterodimeric protein composed of two subunits, p50 and p65, and is sequestered in the cytoplasm as an inactive form through the association with an inhibitory protein, I kappa B. In the present study, the effect of HTLV-I encoded Tax on the exogenously expressed NF-kappa B p105, which encodes a precursor of p50, was investigated using a COS-7 expression system. When p105 was expressed in COS-7 cells, the precursor p105 and the processed p50 were retained in the cytosolic fraction by associating each other, and p50 was not detected in the nuclear fraction. In the cells co-expressing p105 and Tax, the p50/p105 ratio in the cytosolic fraction reduced with an induction of p50 in the nuclear fraction, which gave rise to a significant increase in NF-kappa B binding activity. Enhancement of NF-kappa B binding activity was not observed by adenovirus encoded E1A and bovine papilloma virus encoded E2, and correlated well with the ability of Tax to associate with p105. When p105 delta X which lacks the repeats of the ankyrin motif was expressed in this system, p105 delta X and processed p50 were detected in the nuclear fraction and p50/p105 delta X ratio was not affected by co-expression with Tax. In the same expression system, exogenously expressed NF-kappa B p65 was retained in the cytoplasm by p105 and further expression of Tax allowed entry of p65 in the nucleus. These results suggest that, in this model system, p105 acts as an I kappa B to sequester p50 and p65 in the cytoplasm and that Tax by inhibiting I kappa B activity of p105, enhances nuclear localization of p50 and p65. These findings raise a possibility for a novel mechanism for the induction of NF-kappa B in the nucleus by Tax.

Expression of a truncated guanylate cyclase (GC-C), a receptor for heat-stable enterotoxin of enterotoxigenic Escherichia coli, and its dimer formation in COS-7 cells

A fragment of guanylate cyclase C (GC-C) of about 1.7 k bp corresponding to amino acids 1-553 spanning the extracellular and transmembrane domains and a portion of the intracellular region was amplified using template cDNA prepared from rat intestinal cells by the polymerase chain reaction method. The cloned 1.7 k bp fragment was inserted into the mammalian expression vector pCGUT and the truncated GC-C expressed on the surface of COS-7 cells was demonstrated to bind heat-stable enterotoxin by photo affinity labeling with 125I-N-5-azidonitrobenzoyl-STh[5-19]. Analysis by sodium dodecyl sulfate-polyacrylamide disc gel electrophoresis showed that the truncated GC-C formed dimers on the surface of COS-7 cells. The intracellular region of GC-C was found not to be necessary for dimer formation by the GC-C. Comparison of the molecular weights of the truncated GC-C expressed in COS-7 cells and Escherichia coli suggested that the truncated GC-C was glycosylated in the mammalian expression system.

A new regulatory element that augments the Tax-dependent enhancer of human T-cell leukemia virus type 1 and cloning of cDNAs encoding its binding proteins

The Tax protein of human T-cell leukemia virus type 1 (HTLV-1) trans activates the 21-bp enhancer of HTLV-1. A sequence of more than two copies of the 21-bp enhancer is efficiently activated by Tax, but one copy is not activated extensively. Another sequence (TRE-2, positions -163 to -117) adjacent to the 21-bp enhancer in the long terminal repeat of HTLV-1 can enhance a single copy of the 21-bp enhancer activity in trans activation by Tax. This sequence contains motifs related to the Ets- and NF-kappa B-binding sequences, but mutations at these sites indicated that neither is responsive to cooperation with the 21-bp enhancer. A deletion mutation of TRE-2 identified 25 bases at positions -158 to -134 (TRE-2S) as an essential sequence, and TRE-2S was sufficient to give maximum cooperation with one copy of the 21-bp enhancer in trans activation by Tax protein. Using TRE-2S as a probe, we screened a cDNA library of HUT102 cells by the Southwestern (DNA-protein) procedure and isolated two cDNA clones, THP-1 and -2. These two clones encode TRE-2S-binding proteins, and they differ by only an extra 17 amino acids in THP-2. Both THP proteins contain five zinc finger motifs which are strikingly similar to those of the GLI family, an amplified gene product in glyoma cells. The binding site of THP-1 and -2 was GAACCACCCA in TRE-2S, which is highly homologous to the GLI-binding site. These results suggest that binding of THP to TRE-2S may be involved in cooperation with one copy of the 21-bp enhancer in responding to Tax trans activation.

A trans-activator Tax of human T-cell leukemia virus type 1 binds to NF-kappa B p50 and serum response factor (SRF) and associates with enhancer DNAs of the NF-kappa B site and CArG box

A transcriptional activator of human T-cell leukemia virus type 1 (HTLV-1) activates at least three distinct enhancers: the viral 21-bp enhancer, the NF-kappa B binding site of the IL-2R alpha gene and the CArG box of the c-fos gene. To understand the mechanisms of Tax transactivations of the NF-kappa B enhancer and CArG box, the interactions of Tax protein with their binding factors were analysed. Using a DNA affinity precipitation (DNAP) assay, we found here that Tax associates with the DNA sequences of the NF-kappa B site and CArG box. These Tax associations with enhancers were observed only in the presence of a nuclear factor(s) and were equal to the activating capacities of Tax mutants. To identify the nuclear factor(s), we defined conditions under which no Tax binding to the NF-kappa B binding site and CArG box was detected with a nuclear extract of 293T cells. Under these conditions, transfections with cDNAs of the NF-kappa B p50 and serum response factor (SRF) produced a factor(s) that mediated Tax binding to the NF-kappa B site and the CArG box respectively. Furthermore, purified Tax protein interacted with purified NF-kappa B p50 and purified SRF, indicating their direct bindings. These observations indicate that Tax protein associates with enhancer sequences of the NF-kappa B site and CArG box through NF-kappa B p50 and SRF respectively. Previously we demonstrated that Tax interacts with CREB and CREM proteins that bind to the 21-bp enhancer DNA. These results together suggest that indirect binding of Tax to DNA through each enhancer binding protein is a general mechanism for Tax transactivation of transcription.

A novel cAMP-dependent regulatory region including a sequence like the cAMP-responsive element, far upstream of the human CYP21A2 gene

Deletion mutants in the 5' upstream sequence of the human CYP21A2 gene demonstrated a novel regulatory DNA element responsible for cAMP-dependent expression of the gene in the transient expression system using Y-1 cells (mouse adrenocortical tumor cell line). This regulatory element (-2574 to -2489 bp) was also found to exhibit a strong enhancer activity through heterologous promoters in response to cAMP and to contain a sequence like the cAMP-responsive element (CRE) and a CAAT-like sequence. The CRE-like sequence has a five-base motif (5'-TGACG-3') of the palindromic CRE consensus (TGACGTCA). Competitive gel mobility shift assays using nuclear extracts of bovine adrenal cortex with sequences typical of the binding sites for the binding proteins of CRE and the CAAT-like sequence revealed that these binding proteins, or related factors, bound to their cognate DNA binding sites in the upstream enhancer region of the CYP21A2 gene. These two enhancer elements and their cognate binding factors cooperate with previously identified tissue-specific enhancers (adrenal-specific protein factor and Ad4-like sequences) and their binding factors to express a high level of cAMP-responsive expression of the CYP21A2 gene.

Limited sequence divergence of HTLV-I of Indian HAM/TSP patients from a prototype Japanese isolate

Nucleotide sequences of two HTLV-I proviruses isolated from Indian patients with HAM/TSP were analyzed. The sequence data of the env, pX, and LTR regions showed 98-99% homologies with the prototype HTLV-I, ATK-1, isolated from a Japanese ATL patient, indicating that HTLV-I isolates in India and Japan are similar, with minor variations. However, certain small sequences of noncoding regions in the pX and LTR showed differences of 6.1 and 7.2%, respectively, thus the conclusion could vary depending on the regions and length of the sequences used for comparison.

[A case of Buerger's disease solitary involved in the left subclavian and axillary artery]

A 26-year-old male with about a ten-year history of smoking was admitted to our hospital for evaluation of ischemic symptoms including numbness, easy fatigability on exercise and lack of pulse in his left arm. His left axillary, brachial and radial pulse could not be palpated and a needle reaction was negative on physical examination. Laboratory data showed no diabetes mellitus or hyperlipidemia. C-reactive protein, Wassermann's reaction, rheumatoid reaction, anti-nuclear factor, anti-DNA antibody, hypocomplementemia and circulating immune complex were negative. Invasive arteriography using contrast medium revealed segmental occlusion with multiple collateral arteries showing a typical "corkscrew" appearance at the left subclavian artery. However, no stenotic and aneurysm-like lesions suggesting aortitis syndrome, vasculo-Beçhet disease and giant arteritis were found on the aorta or other arteries including the pulmonary artery. Although no pathological study could be carried out, the angiographic and laboratory findings strongly suggested Buerger's disease as a possible cause of solitary stenosis of the left subclavian artery in this patient.

[A case of small cell undifferentiated carcinoma (SCUC) of the rectum treated with etoposide, cis-platinum and radiotherapy]

A 29-year-old-woman with recurrent cancer of rectum was treated with Etoposide, cis-platinum and external irradiation. Previous postoperative chemotherapies consisted of MMC, CPA, VCR and HCFU. Histologically, the tumor invaded in sheets and nests, and consisted of round to ovoid malignant cells with high nuclear/cytoplasmic and hyperchromatic nuclei with a coarse, clumped, or stippled chromatin pattern. Most cells demonstrated a positive reaction by Grimelius and NSE staining. Eight months after surgery, we switched to Etoposide cis-platinum and external irradiation, because of local recurrence. Etoposide (total 725 mg) and cis-platinum (total 100 mg) were injected into bilateral iliac artery and 60 Gy radiotherapy was performed. The patient showed a good response, and a complete response (CR) was evident for the following 42 months. Thus, Etoposide, Cis-platinum and radiotherapy are considered an effective combination therapy for a patient with small cell undifferentiated carcinoma.

Characterization of the promoter region of the src family gene lyn and its trans activation by human T-cell leukemia virus type I-encoded p40tax

The src family gene lyn is expressed preferentially in B lymphocytes but very little in normal T lymphocytes. Transcription of the lyn gene in T lymphocytes was shown to be induced by the p40tax protein encoded by human T-cell lymphotropic virus type I. For determination of the mechanism of p40tax-mediated trans activation, the transcriptional promoter region of the lyn gene was characterized. By endonuclease S1 mapping, the transcriptional initiation sites were identified within the 770-bp EcoRI-SacI fragment of the 5'-terminal portion of the human lyn gene. This fragment showed promoter activity when placed upstream of the bacterial chloramphenicol acetyltransferase gene and transfected into various cell lines. Nucleotide sequence analysis revealed that the lyn promoter region contained four GC box-like sequences but not a TATA or CCAAT box. In addition, it contained sequences characteristic of a cyclic AMP-responsive element, octamer-binding motif, PEA3-like motifs, and NF kappa B-binding motif-like sequence. Mutational analysis suggested that the octamer-binding motif sequence is of primary importance for the lyn promoter activity but that the other elements are not. Cotransfection of various chloramphenicol acetyltransferase constructs containing different length of the lyn promoter together with p40tax expression plasmids into Jurkat T cells showed that the sequence responsible for p40tax-induced transcription is present around the transcription initiation sites.

Transcriptional activator Tax of HTLV-1 binds to the NF-kappa B precursor p105

Human T-cell leukemia virus type 1 (HTLV-1) induces adult T-cell leukemia and also a neurological disease, tropical spastic paraparesis. Tax protein (p40tax) of HTLV-1 activates in trans its own transcriptional enhancer in the long terminal repeat and also those in some cellular genes such as interleukin 2 receptor alpha, granulocyte-macrophage colony-stimulating factor, Fos, Jun and MHC class I. Thus, Tax has been proposed to play a critical role in the pathogenesis induced by HTLV-1 infection. Here, we report formation of a complex of Tax protein with the precursor protein p105 of the NF-kappa B p50 subunit. p105 was co-immunoprecipitated with Tax protein from cells infected with HTLV-1 from cells transfected with the Tax expression plasmid, but not from cells transfected with inactive mutants of Tax. Furthermore, a GST-p105 fusion protein produced in Escherichia coli bound to Tax protein. These results strongly suggest that the trans-activator Tax protein forms a complex with precursor NF-kappa B p105 and plays a role in trans-activation of transcriptional initiation.

Frequent clonal proliferation of human T-cell leukemia virus type 1 (HTLV-1)-infected T cells in HTLV-1-associated myelopathy (HAM-TSP)

Human T-cell leukemia virus type 1 (HTLV-1) integrates its proviruses into random sites in host chromosomal DNA. Random integration of the proviruses was observed in asymptomatic HTLV-1 carriers and patients with HTLV-1-associated myelopathy (HAM/TSP). However, clonal integration has been reported in patients with adult T-cell leukemia (ATL), including that in the smoldering, chronic, and acute states, indicating clonal expansion of infected cells. In this study, we found that about 20% of HAM/TSP patients and their seropositive family members harbored subpopulation(s) of clonally proliferated cells infected with HTLV-1, although they still maintained randomly infected cells as a major population. These clones were stable during examination periods of 4 months to 3 years. However, these carriers or HAM/TSP patients did not show any significant indication of ATL. This extremely high frequency of clonal expansion of HTLV-1-infected cells indicates that some clones of HTLV-1-infected cells have a tendency to proliferate more efficiently than the other population without malignant transformation.

The indirect association of human T-cell leukemia virus tax protein with DNA results in transcriptional activation

trans-activator p40tax of human T-cell leukemia virus type I activates specific enhancers and stimulates transcription of the viral and some cellular genes but does not bind directly to the enhancer sequences. We demonstrated here that a fusion protein of p40tax and GAL4 DNA binding domain activated transcription dependent on the GAL4-binding site in the reporter plasmid. Mutants of p40tax were also tested in the fusion protein, and their activities were found to be in parallel with those of their free forms on the original target long terminal repeat. This activation with GAL4 fusion protein was interfered with by the free form of p40tax. These results suggest that p40tax associates with DNA through interaction with DNA binding protein(s) and also interacts with another transcription factor(s) to elicit the activation.

Cyclic AMP response element-binding protein, CRE-BP1, mediates the E1A-induced but not the Tax-induced trans-activation

The adenovirus E1A protein and tax protein (Tax) of human T-cell leukemia virus-1 (HTLV-1) are transcriptional regulators that do not bind to DNA directly. The ATF sites/CRE (cyclic AMP response element) of the adenovirus E4 promoter and the long terminal repeat of HTLV-1 have been shown to be required for E1A and Tax inducibility, respectively. Using the c-Myb-CRE-BP1 fusion protein, it was shown that CRE-BP1, which could bind to the ATF sites/CRE, mediated the E1A-induced trans-activation. For this activation, the N-terminal portion of CRE-BP1, which contained the putative metal finger structure, was essential but not sufficient. In contrast, the trans-activation induced by HTLV-1 Tax was not mediated by CRE-BP1. These results strongly suggested that E1A activates transcription through interaction with CRE-BP1, but another CRE-binding protein participates in the Tax-induced trans-activation.

Promoter region of the human CRE-BP1 gene encoding the transcriptional regulator binding to the cyclic AMP response element

Genomic clones containing the 5'-terminal portion of the human CRE-BP1 gene that encodes transcriptional regulator binding to the cyclic AMP response element (CRE) were isolated. Multiple transcriptional start sites in the promoter region were identified by nuclease S1 mapping and primer extension analysis. By DNase I footprinting with use of purified transcription factor Sp1 and nuclear extracts prepared from HeLa cells, 11 Sp1-binding sites, two CCAAT sequences, two CREs, and three unknown factor recognition elements were found. Transfection of chimeric chloramphenicol acetyltransferase plasmids containing various deletions of the promoter into CV-1 cells indicated that the region between nucleotides -50 and 90, which contained three Sp1-binding sites and one CRE, was sufficient for basal promoter activity. These results suggest that multiple sequence-specific DNA-binding proteins may control the expression of the CRE-BP1 gene, although Sp1 seems to be important for the basal promoter activity.

Multiple cDNA clones encoding nuclear proteins that bind to the tax-dependent enhancer of HTLV-1: all contain a leucine zipper structure and basic amino acid domain

A trans-activator protein, p40tax, of human T cell leukemia virus type 1 (HTLV-1) activates its own promoter and cellular promoters of IL-2, IL-2 receptor alpha and GM-CSF genes. We isolated three cDNA clones encoding cellular proteins that bind to the p40tax-dependent enhancer of HTLV-1 by screening a lambda gt11 cDNA library of an HTLV-1 infected cell line. All three proteins, TREB5, TREB7 and TREB36, contained a leucine zipper structure and basic amino acid domain, which are conserved in FOS, JUN and CREB, and also had multiple potential phosphorylation sites. The proteins expressed in Escherichia coli bound to the p40tax-dependent enhancer of the 21 bp sequence, but not to an inactive mutant carrying a mutation in the CRE region. In DNase I footprint analysis, all three proteins protected the 21 bp sequences in the LTR; however, the patterns were not identical to each other. TREB7 and TREB36 protected all three repeats of the 21 bp, but TREB5 protected only the second repeat. TREB7 and TREB36 protected the 5' and middle portions of the 21 bp which are essential for p40tax-mediated trans-activation, whereas TREB5 and CREB1 protected a narrower part of the middle region of the second 21 bp repeat containing the CRE consensus sequence. These structural features and DNA binding properties suggest that TREB proteins are members of a CREB protein family and that some of them (i.e., TREB7 and TREB36) may be involved in p40tax-mediated trans-activation.

Effect of tunicamycin on functions of PGE1 receptors from mouse mastocytoma P-815 cells

Prostaglandin E1 (PGE1) receptors from mouse mastocytoma P-815 cells were found to bind to a wheat germ agglutinin (WGA)-Agarose column, suggesting that the receptors are glycoproteins. To further elucidate the role of carbohydrate moieties in the PGE1 receptors for their binding activity to ligand, the P-815 cells were treated with tunicamycin, swainsonine or monensin. Tunicamycin, an inhibitor of N-glycosylation, dose- and time-dependently inhibited the binding of PGE1 to mastocytoma P-815 cells. Neither swainsonine, an inhibitor of Golgi mannosidase II, nor monensin, an inhibitor of processing beyond the high mannose stage, altered PGE1 binding properties of the cells. The inhibition of PGE1 binding by tunicamycin was observed when incorporation of [3H]glucosamine into macromolecules was inhibited. The inhibitory effect was not on their affinity but on their number of binding sites. Subcellular distributions of [3H]PGE1-binding activity showed that decreases in the binding activity by tunicamycin were highest in plasma membrane fractions. Treatment of membranes with various endo- and exoglycosidases did not affect PGE1 binding. PGE1-stimulated cyclic AMP accumulation in the cells was also inhibited by tunicamycin. These results suggest that PGE1 receptors of mastocytoma P-815 cells are glycoproteins and that inhibition of N-glycosylation of PGE1 receptors by tunicamycin results in the arrest of the translocation of newly synthesized receptors to the surface of mastocytoma P-815 cells.

A unique enhancer element for the trans activator (p40tax) of human T-cell leukemia virus type I that is distinct from cyclic AMP- and 12-O-tetradecanoylphorbol-13-acetate-responsive elements

The trans activator (p40tax) of human T-cell leukemia virus type I (HTLV-I) is a transcriptional factor that activates the long terminal repeat (LTR) of HTLV-I and interleukin-2 receptor alpha. We examined the HTLV-I enhancer responsible for tax-mediated trans activation and identified (A/T)(G/C)(G/C)CNNTGACG(T/A) as a plausible tax-responsive element (TRE). The putative TRE in the LTR was found to be different from the elements required for activation by cycle AMP and 12-O-tetradecanoylphorbol-13-acetate, although these elements overlapped each other. The TRE was also different from a binding site of an NF-kappa B-like factor that was identified in the interleukin-2 receptor alpha promoter and human immunodeficiency virus LTR as a TRE. The latter result was further demonstrated by the failure of the NF-kappa B sequence to compete with the TRE of the LTR in a protein-binding assay. These findings indicate that tax function and its cascade can modulate activities of various enhancer sequences, which are probably regulated by distinct DNA-binding factors.

Leucine zipper structure of the protein CRE-BP1 binding to the cyclic AMP response element in brain

By screening a lambda gt11 library with the multimerized sequence of the cAMP response element (CRE), we isolated human clones encoding the CRE binding protein, CRE-BP1, from a human brain cDNA library. CRE-BP1 expressed in Escherichia coli bound not only to the CRE element of the somatostatin and fibronectin genes, but also to the CRE element of the adenovirus E4 gene, suggesting that the protein was not distinguishable from the adenovirus transcription factor, ATF. The human CRE-BP1 clone encoded a 54.5 kd protein similar at its carboxy terminus to the leucine zipper motifs found in other enhancer binding proteins such as C/EBP and c-jun/AP-1. CRE-BP1 mRNA was expressed in all of the cells examined and was abundant in brain. The structure of CRE-BP1 and its recognition elements suggest that cellular response to extracellular stimuli is controlled by a family of transcription factors that bind to related cis-active elements and that contain several highly conserved domains.