ATF-a0, a novel variant of the ATF/CREB transcription factor family, forms a dominant transcription inhibitor in ATF-a heterodimers

The regulatory role of activating transcription factor 2 in inflammation

Activating transcription factor 2 (ATF2) is a member of the leucine zipper family of DNA-binding proteins and is widely distributed in tissues including the liver, lung, spleen, and kidney. Like c-Jun and c-Fos, ATF2 responds to stress-related stimuli and may thereby influence cell proliferation, inflammation, apoptosis, oncogenesis, neurological development and function, and skeletal remodeling. Recent studies clarify the regulatory role of ATF2 in inflammation and describe potential inhibitors of this protein. In this paper, we summarize the properties and functions of ATF2 and explore potential applications of ATF2 inhibitors as tools for research and for the development of immunosuppressive and anti-inflammatory drugs.

The role of ATF-2 in oncogenesis

Activating Transcription Factor-2 is a sequence-specific DNA-binding protein that belongs to the bZIP family of proteins and plays diverse roles in the mammalian cells. In response to stress stimuli, it activates a variety of gene targets including cyclin A, cyclin D and c-jun, which are involved in oncogenesis in various tissue types. ATF-2 expression has been correlated with maintenance of a cancer cell phenotype. However, other studies demonstrate an antiproliferative or apoptotic role for ATF-2. In this review, we summarize the signaling pathways that activate ATF-2, as well as its downstream targets. We examine the role of ATF-2 in carcinogenesis with respect to other bZIP proteins, using data from studies in human cancer cell lines, human tumours and mouse models, and we propose a potential model for its function in carcinogenesis, as well as a theoretical basis for its utility in anticancer drug design.

Cloning and characterization of a novel member of the human ATF/CREB family: ATF2 deletion, a potential regulator of the human DNA polymerase beta promoter

The solitary cAMP response element (CRE)1 in the human DNA polymerase beta (beta-pol) core promoter plays a key role in both basal expression and the DNA-alkylating agent response of the promoter. To further understand the role of the CRE in the regulation of this promoter, we searched for novel CRE-binding proteins by using a 32P-labeled beta-pol CRE oligodeoxynucleotide and a human cDNA expression library constructed in phage lambda. A total of fourteen phage clones were isolated, corresponding to various members of the CRE-binding protein family. One of these clones, termed ATF2 deletion (ATF2d), encodes a novel ATF2 isoform and was chosen for further characterization in this study. Relative to ATF2 mRNA, this clone contains an internal 97-nt deletion and a unique 3' region. The 97-nt deletion causes a frame shift, resulting in a ATF2-like polypeptide of approximately 60 kDa. ATF2d retains the bZIP domain of ATF2, lacks the N-terminal zinc-finger region, and includes novel characteristics in its N- and C-terminal regions.

Prevention of human rhinovirus infection by multivalent fab molecules directed against ICAM-1

We have developed a technology for improving avidity by making bivalent, trivalent, or tetravalent recombinant polypeptides. We designed tripartite proteins consisting of the Fab fragment of an antibody fused with a hinge derived from human immunoglobulin D that was further linked to polymerization domains derived from human coiled-coil proteins. We report here on the application of this method with a Fab domain directed against the major human rhinovirus receptor, intercellular adhesion molecule 1 (ICAM-1). Multivalent anti-ICAM-1 molecules were produced in bacteria and purified as soluble preassembled homogeneous proteins at high yield. These proteins successfully blocked rhinovirus infection in vitro, with the efficiency increasing from monomer to dimer, trimer, and tetramer. The diminished dissociation rate of these multivalent antibodies and their improved efficacy in preventing rhinovirus infection provide a foundation for producing prophylactic and therapeutic molecules against human rhinovirus, the causative agent of the majority of common colds.

Repression of human fibroblast growth factor 2 by a novel transcription factor

Here we describe the cloning of the regulator of fibroblast growth factor 2 (FGF-2) transcription (RFT) using a yeast one-hybrid screening with a defined motif in FGF-2 promoter as a target sequence. Overexpression of human RFT (RFT-A) reduces FGF-2 RNA and protein levels in both normal and tumor cell lines. Its splice variants, RFT-A' and RFT-B, have deletions in the putative DNA binding domain and fail to bind FGF-2 promoter and repress FGF-2 gene expression. The ratios of RFT isoforms differ between normal and tumor cells, with the splice variants dominating in tumor cells. Overexpression of RFT-A induces glioma cell death. Our data suggest that regulation of FGF-2 by RFT is important for cellular functions and may be impaired in certain tumors.

Cytokine induction of monocyte chemoattractant protein-1 gene expression in human endothelial cells depends on the cooperative action of NF-kappa B and AP-1

Chemokines are potent mediators of cell migration and activation and therefore play an essential role in early events of inflammation. In conjunction with cell adhesion molecules, chemokines help to localize cells to a specific site and enhance the inflammatory reaction at the site. Clinically, elevated levels of chemokines have been found in a variety of inflammatory diseases. The prototype C-C chemokine is monocyte chemoattractant protein-1 (MCP-1) which is synthesized by variety of cell types including endothelial cells in response to a variety of stimuli. MCP-1 is a major chemoattractant for monocytes, T lymphocytes, and basophils. In the present study, we investigated the factors involved in cytokine-induced MCP-1 gene expression in human endothelial cells. We present evidence that the nuclear factor (NF)-kappa B-like binding site and the AP-1 binding site located 90 and 68 base pairs upstream of the transcriptional start site, respectively, are required for maximal induction of the human MCP-1 promoter by interleukin-(IL)-1 beta. Site-directed mutagenesis or deletion of the NF-kappa B-like site decreased the cytokine-induced activity of the promoter. Site-directed mutagenesis of the AP-1 binding site also decreased the cytokine-induced activity of the promoter. We show that the NF-kappa B-like site located at-90 in the MCP-1 promoter binds to the p50/p65 heterodimer of the NF-kappa B/Rel family in IL-1 beta-stimulated human endothelial cells. Overexpression of p65 results in the transactivation of the MCP-1 promoter as well. The data presented in this study suggest that cytokine-induced MCP-1 gene expression in human endothelial cells depends on the cooperative action of NF-kappa B and AP-1.

E-selectin gene expression in vascular smooth muscle cells. Evidence for a tissue-specific repressor protein

E-Selectin is an inducible, endothelium-specific, cell surface adhesion molecule that mediates inflammatory responses in the vasculature. Nonendothelial cell types such as cultured human aortic smooth muscle cells (HASMCs) lack the ability to express E-selectin. We tested the hypothesis that HASMCs express a negative regulatory factor that inhibits E-selectin gene expression. E-Selectin mRNA and gene transcription were not detected in HASMCs after treatment with tumor necrosis factor-alpha (TNF-alpha) by Northern and nuclear runoff analyses, respectively. However, both E-selectin mRNA and gene transcription were dramatically induced by TNF-alpha in the same cells pretreated with the protein synthesis inhibitor cycloheximide. Lipopolysaccharide demonstrated similar effects. Furthermore, E-selectin was detected on the cell surface of HASMCs after washing out of cycloheximide. Cycloheximide pretreatment enabled immortalized human dermal microvascular endothelial cells that have lost the ability to express E-selectin to induce both E-selectin mRNA and gene transcription in response to TNF-alpha. Induction of E-selectin mRNA by lipopolysaccharide or TNF-alpha in cycloheximide-treated HASMCs was inhibited by the antioxidant pyrrolidinedithiocarbamate and the serine protease inhibitor N alpha-L-tosyl-L-phenylalanine chloromethyl ketone, suggesting that a nuclear factor-kappa B-like mechanism may play an important role in E-selectin gene expression in HASMCs. These data strongly suggest that a labile repressor protein(s) plays an important role in inhibiting E-selectin gene expression in HASMCs likely at the level of gene transcription. Except for this repressor, HASMCs and endothelial cells may share similar regulatory mechanisms for controlling E-selectin expression.

Early activation signals in endothelial cells. Stimulation by cytokines

With limitation to the "proinflammatory program" induced in endothelial cells by exposure to interleukin-1, tumor necrosis factor, and interleukin-6, we review the available data on the signaling for these three cytokines, from receptor engagement to induction of gene transcription. Only a few molecular pathways have been characterized so far, and key issues in endothelial biology, such as endothelial specificity of gene expression and heterogeneity of different endothelial populations, remain largely unexplored.

Structure and expression of the ATFa gene

The human ATFa proteins belong to the ATF/CREB family of transcription factors. We have previously shown that they mediate the transcriptional activation by the largest E1a protein and can heterodimerize with members of the Jun/Fos family. ATFa proteins have also been found tightly associated with JNK2, a stress-activated kinase. We now report on the structure of the ATFa gene, which mapped to chromosome 12 (band 12q13). Sequence analysis revealed that ATFa isoforms are generated by alternative splice donor site usage. A minimal promoter region of approximately 200 base pairs was identified that retained nearly full transcriptional activity. Binding sites for potential transcription factors were delineated within a GC-rich segment by DNase I footprinting. Expression studies revealed that ATFa accumulates in the nuclei of transfected cells, and the nuclear localization signal was defined next to the leucine zipper domain. As revealed by hybridization with mouse ATFa sequences, low levels of ATFa mRNAs were ubiquitously distributed in fetal or adult mice, with enhanced expression in particular tissues, like squamous epithelia and specific brain cell layers. The possible significance of coexpression of ATFa, ATF-2, and Jun at similar sites in the brain is discussed.

The intron-exon structure of the porcine E-selectin-encoding gene

We have cloned and sequenced the gene encoding porcine E-selectin. The gene comprises 12 exons and 11 introns. Two pseudoexons are contained within intron 4 and intron 6. These sequences are similar to the corresponding exons in the human E-selectin sequence; however, they are not present in the porcine E-selectin-encoding cDNA. Transcription starts at position -498 relative to the translation initiation site. The first ATG is located within exon 2. Translation stops in exon 11 leaving exon 12 untranslated in its entirety.

Cold shock domain proteins repress transcription from the GM-CSF promoter

The human granulocyte-macrophage colony stimulating factor (GM-CSF) gene promoter binds a sequence-specific single-strand DNA binding protein termed NF-GMb. We previously demonstrated that the NF-GMb binding sites were required for repression of tumor necrosis factor-alpha (TNF-alpha) induction of the proximal GM-CSF promoter sequences in fibroblasts. We now describe the isolation of two different cDNA clones that encode cold shock domain (CSD) proteins with NF-GMb binding characteristics. One is identical to the previously reported CSD protein dbpB and the other is a previously unreported variant of the dbpA CSD factor. This is the first report of CSD factors binding to a cytokine gene. Nuclear NF-GMb and expressed CSD proteins have the same binding specificity for the GM-CSF promoter and other CSD binding sites. We present evidence that CSD factors are components of the nuclear NF-GMb complex. We also demonstrate that overexpression of the CSD proteins leads to complete repression of the proximal GM-CSF promoter containing the NF-GMb/CSD binding sites. Surprisingly, we show that CSD overexpression can also directly repress a region of the promoter which apparently lacks NF-GMb/CSD binding sites. NF-GMb/CSD factors may hence be acting by two different mechanisms. We discuss the potential importance of CSD factors in maintaining strict regulation of the GM-CSF gene.

Commonly used cat reporter vectors contain a cAMP-inducible, cryptic enhancer that co-operates with NF-kappa B-sites

Commercially available and widely used cat expression vectors were found to contain a forskolin (Fs)-inducible element capable of co-operation with NF-kappa B-sites in test promoters. An alternative NF-kappa B-dependent reporter system is presented that allows investigation of the effects of Fs and other agents that augment intracellular cyclic AMP.