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Query: UNIPROT:P05412 (c-Jun)
 11,453 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The proto-oncogene c-jun encodes the major component of the transcription factor AP-1 and is thought to have important functions in cell proliferation and differentiation as well as in the cellular response to a variety of external stimuli. To investigate directly the role of c-jun in growth, differentiation and tumorigenicity we generated mouse embryonic stem (ES) cell lines in which both copies of the c-jun gene have been inactivated by homologous recombination. The disruption of both copies of the c-jun gene had no apparent effect on ES cell viability, growth rate and in vitro differentiation potential. Transcriptional activation of the c-jun, junB and c-fos genes following TPA/serum induction was unaffected and efficient transactivation of AP-1 reporter constructs was demonstrated in these cells. Remarkably, subcutaneous injection of ES cells lacking c-Jun into syngeneic mice led to a drastic reduction in the formation of teratocarcinomas. We propose that whereas most of the functions of c-Jun in ES cells appear to be complemented by other Jun proteins in vitro, functional c-Jun protein is essential for efficient tumor growth in vivo.
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PMID:Embryonic stem (ES) cells lacking functional c-jun: consequences for growth and differentiation, AP-1 activity and tumorigenicity. 128 2

Cytokine modulation of elastin gene expression was examined by assay of elastin mRNA abundance and by transient transfections of cultured human skin fibroblasts and rat aortic smooth muscle cells with elastin promoter/reporter gene (chloramphenicol acetyltransferase, CAT) constructs. Incubation of cells with human recombinant tumor necrosis factor-alpha (TNF-alpha) markedly suppressed the elastin mRNA levels in a time- and dose-dependent manner by up to 91%. TNF-alpha also suppressed the expression of the elastin promoter/CAT construct by up to 70% in transiently transfected cells, indicating regulation at the transcriptional level. This suppression was temporally preceded by rapid and transient up-regulation of c-jun and c-fos genes. The down-regulatory effect of TNF-alpha on elastin promoter activity was abolished by co-transfections with a synthetic double-stranded AP-1 oligomer. Furthermore, co-transfection of the elastin promoter construct with c-jun and c-fos expression plasmids resulted in a marked decrease in the promoter activity. Elucidation of the cis-regulatory elements in the elastin promoter by 5' deletion construct analysis implicated a region -290 to -198 containing one AP-1 binding site. The functional role of this AP-1 site was further tested by gel retardation assays which indicated formation of a DNA-protein complex specific for TNF-alpha treated cells. This complex could be partially dissociated by a competing oligomer containing the consensus AP-1 binding site. These observations suggest that the inhibitory effects of TNF-alpha on elastin gene expression involve the transcription factor AP-1. Interferon-gamma also suppressed the elastin gene expression at the mRNA level by approximately 52%, but it had no effect on the elastin promoter activity, suggesting post-transcriptional mechanisms. These results indicate that mediators released from inflammatory cells can modulate elastin gene expression, and such modulation may play a role in diseases characterized by altered accumulation of elastic fibers in tissues.
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PMID:Tumor necrosis factor-alpha down-regulates human elastin gene expression. Evidence for the role of AP-1 in the suppression of promoter activity. 128 83

c-Fos is a major component of the transcription factor AP-1 which has been implicated in the control of cell proliferation and differentiation as well as in transformation. In order to identify Fos target genes involved in these processes, we have taken advantage of the regulatory properties of the hormone-binding domain of the human estrogen receptor to develop transcriptional and post-translational induction systems, both of which allow selective elevation of Fos activity within a cell. Using this approach we have searched for Fos-responsive genes in rat fibroblasts and PC12 cells. Here we describe the identification and regulation of five Fos-responsive genes encoding a transcription factor (Fra-1), a secreted protein (Fit-1), a biosynthetic enzyme (ODC) and two membrane-associated proteins (annexin II and V), respectively. The post-translational induction system was also used to study the Fos-mediated block of neuronal differentiation of PC12 cells. These experiments demonstrate that Fos activity is dominant over NGF function and interferes with the expression of late NGF-inducible genes.
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PMID:Identification of Fos target genes by the use of selective induction systems. 129 55

The viral Jun protein (v-Jun) transforms chicken embryo fibroblasts (CEF) more effectively than its cellular counterpart (c-Jun). In certain cell types v-Jun is also a stronger transcriptional activator than c-Jun. These functional differences between v-Jun and c-Jun result from a deletion in v-Jun (referred to as "delta deletion") that seems to weaken the interaction of Jun with a negative cellular regulator molecule. These observations suggested that the oncogenicity of v-Jun may be due to an enhanced ability to activate transcription of target genes. To test this hypothesis, we constructed several deletions in the delta domain of chicken c-Jun and determined their transforming and transactivating properties. Surprisingly, we found an inverse correlation between the ability of the mutants to transform CEF and to transactivate the collagenase and transin promoters in CEF. In contrast, there was no significant effect of the delta mutations in c-Jun on transactivation in F9 murine embryonal carcinoma cells. The function of the delta region is therefore cell-type specific. The inverse correlation between transformation and transactivation in CEF suggests that the strong growth-promoting effect of v-Jun may be related to a failure to activate the transcription of growth attenuating genes.
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PMID:Mutations in the Jun delta region suggest an inverse correlation between transformation and transcriptional activation. 130 52

To extend our analysis of the regulation of human cytomegalovirus (HCMV) early gene expression, we examined a transcription unit located in the terminal repeats of the long segment of the viral genome. This region encodes a major 1.2-kb RNA which is induced at early times in infection but undergoes its largest increase in abundance after the onset of viral DNA replication. To identify the important cis-acting regulatory elements for this gene, two constructs were prepared for use in transient expression assays. One contained 413 bp of the upstream sequence and 43 bp of the leader sequence fused to the gene for chloramphenicol acetyltransferase (CAT). The second construct included 1,722 bp upstream of the start site of the 1.2-kb RNA, the entire transcribed region with an additional 166-bp insert derived from the CAT gene as an assayable marker, and 2,393 bp downstream of the polyadenylation signal. Both constructs were individually transfected into human fibroblast cells, and the cells were infected with HCMV. RNA specified by the hybrid construct was initiated at the correct position and accumulated with the same kinetics as the authentic viral transcript at early times in the infection but did not undergo the increase in abundance at late at late times. By 5'-end-deletion analysis, we determined that the promoter for the 1.2-kb RNA contains a number of cis-acting elements, the most significant of which are the TATA-like sequence CATAAA at -30 and a sequence corresponding to the binding site for the transcription factor AP-1 at -75. Using extracts prepared from HeLa cells as well as from infected and uninfected fibroblasts in gel retardation assays, we obtained evidence for the specific interaction of a cellular factor(s) with the AP-1 binding site. The pattern of binding differed in the HeLa and fibroblast cells but did not change as a function of the HCMV infection. However, the functional importance of the AP-1 binding site and its key role in the regulation of the 1.2-kb RNA was supported by analysis of constructs containing specific point mutations at this site in gel retardation and transient expression assays. Site-specific mutations in the AP-1 consensus sequence, which resulted in the complete loss of binding to cellular factors, eliminated the basal activity and reduced the inducible promoter activity by eightfold.
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PMID:An AP-1 binding site is the predominant cis-acting regulatory element in the 1.2-kilobase early RNA promoter of human cytomegalovirus. 131 36

Myogenin and MyoD belong to a family of muscle-specific helix-loop-helix (HLH) proteins that have the potential to activate muscle-specific genes in nonmyogenic cells. Peptide growth factors can block the ability of myogenin and MyoD to activate their target genes. Here, we show that the growth factor-inducible proto-oncogenes c-fos, c-jun, and junB mimic the effects of exogenous growth factors and suppress trans-activation of the muscle creatine kinase (MCK) enhancer by myogenin and MyoD. In contrast, JunD, which shares DNA-binding specificity with JunB and c-Jun but is expressed constitutively in muscle cells, is an inefficient inhibitor of the trans-activating capacity of myogenin and MyoD. Transcriptional repression by Fos and Jun is specific to myogenic HLH proteins and is not observed with the widely expressed HLH protein E47, which recognizes the same DNA sequence. Repression of the MCK enhancer by Fos and Jun is targeted at the myogenin and MyoD DNA recognition sequence and can be mediated by the amino terminus of c-Jun. Comparison of several myogenin mutants for their responsiveness to Fos and Jun shows that repression is directed at the basic-HLH region. These results indicate that members of the Jun family can be distinguished on the basis of their effects on muscle-specific transcription and suggest there is cross talk between transcription factors that control myogenesis and those involved in cell proliferation.
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PMID:Fos and Jun repress transcriptional activation by myogenin and MyoD: the amino terminus of Jun can mediate repression. 131 72

Rat 1a fibroblasts transformed by the Gi2 oncogene, gip2, exhibit a constitutively elevated mitogen-activated protein (MAP) kinase activity that correlates with enhanced tyrosine phosphorylation of the p42 MAP kinase polypeptide. The MAP kinase activity in gip2 transformed cells is 50-60% of the pertussis toxin-sensitive, thrombin-stimulated activity observed in wild-type Rat 1a cells. A similar activation of MAP kinase is observed in src but not ras or raf transformed Rat 1a cells, indicating that the persistent MAP kinase activity results from the action of the specific oncoprotein and is not the consequence of cellular transformation. The enhanced transactivation function of c-Jun characteristic of the transformed phenotype, measured using a collagenase promoter-CAT reporter gene, is observed in gip2, src, ras, and raf transformed Rat 1a cells. The regulatory networks controlled by the four transforming oncogenes therefore alter the activity of specific transcription factors, but only gip2 and src constitutively activate MAP kinase. The findings demonstrate that the catalytic activity of growth factor-regulated cytoplasmic kinases are selectively and stably activated as a consequence of specific oncogene expression.
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PMID:MAP kinase is constitutively activated in gip2 and src transformed rat 1a fibroblasts. 131 14

Okadaic acid, a protein phosphatase inhibitor, is a strong tumor promoter which activates protein phosphorylation. Because another activator of protein phosphorylation, phorbol esters, stimulates hematopoietic differentiation, we sought to determine whether okadaic acid could also induce the differentiation of the human leukemic cell line U937. Differentiation was assessed by measuring changes in the following: mRNA levels, cell growth, morphology, cell surface markers, and the ability to induce superoxide. We found that okadaic acid treatment of U937 cells induces immediate increases in total cellular levels of both c-jun and c-fos mRNAs. Nuclear run-on experiments demonstrate that initial increases are secondary to increases in transcription, whereas latter changes may be secondary to mRNA stabilization. Like phorbol esters, okadaic acid treatment also activates AP-1 enhancer activity and induces the phosphorylation of c-Jun protein. Approximately 6-12 hours after treatment with okadaic acid, mRNA levels of c-myc, p34cdc2, and p58GTA, two cell cycle regulated protein kinases, decrease. Okadaic acid inhibits the growth of U937 cells, induces changes in nuclear morphology, stimulates increases in Mac-1 and Leu 11 surface antigens, and induces these cells to produce superoxide. These changes, taken together, suggest that U937 cells have been induced by okadaic acid to differentiate towards a more mature cell type.
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PMID:Induction of differentiation and c-jun expression in human leukemic cells by okadaic acid, an inhibitor of protein phosphatases. 131 24

The origins of DNA replication (ori) in simian virus 40 (SV40) and polyomavirus (Py) contain an auxiliary component (aux-2) composed of multiple transcription factor binding sites. To determine whether this component stimulated replication by binding specific transcription factors, aux-2 was replaced by synthetic oligonucleotides that bound a single transcription factor. Sp1 and T-antigen (T-ag) sites, which exist in the natural SV40 aux-2 sequence, provided approximately 75 and approximately 20%, respectively, of aux-2 activity when transfected into monkey cells. In cell extracts, only T-ag sites were active. AP1 binding sites could replace completely either SV40 or Py aux-2. Mutations that eliminated AP1 binding also eliminated AP1 stimulation of replication. Yeast GAL4 binding sites that strongly stimulated transcription in the presence of GAL4 proteins failed to stimulate SV40 DNA replication, although they did partially replace Py aux-2. Stimulation required the presence of proteins consisting of the GAL4 DNA binding domain fused to specific activation domains such as VP16 or c-Jun. These data demonstrate a clear role for transcription factors with specific activation domains in activating both SV40 and Py ori. However, no correlation was observed between the ability of specific proteins to stimulate promoter activity and their ability to stimulate origin activity. We propose that only transcription factors whose specific activation domains can interact with the T-ag initiation complex can stimulate SV40 and Py ori-core activity.
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PMID:Specific transcription factors stimulate simian virus 40 and polyomavirus origins of DNA replication. 131 5

Phorbol esters stimulate and glucocorticoid hormones down-regulate a variety of promoters such as that of the collagenase gene through the transcription factor AP-1 (Fos/Jun). We now show by genomic footprinting of the collagenase promoter that phorbol ester treatment of cells results in the binding of AP-1 to its cognate DNA binding site in vivo. The DNA-protein contacts obtained in living cells are also found in vitro using cloned DNA and purified AP-1. Although in vitro synthesized glucocorticoid receptor can disturb the DNA binding of Jun homodimers, it does not interfere with the binding of Fos-Jun heterodimers or of purified AP-1 in vitro. Consistently, fully inhibitory doses of glucocorticoid hormone cause no change in apparent occupation of the AP-1 binding site in vivo. The hormone receptor acts without itself binding to DNA.
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PMID:Interference between pathway-specific transcription factors: glucocorticoids antagonize phorbol ester-induced AP-1 activity without altering AP-1 site occupation in vivo. 131 96


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