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Stepwise transformation of rat embryo fibroblasts: c-Jun, JunB, or JunD can cooperate with Ras for focus formation, but a c-Jun-containing heterodimer is required for immortalization.

Among the Jun family of transcription factors, only c-Jun displays full transforming potential in cooperation with activated c-Ha-Ras in primary rat embryo fibroblasts. c-Jun in combination with Ras can both induce foci of transformed cells from rat embryo fibroblast monolayers and promote the establishment of these foci as tumoral cell lines. JunB can also cooperate with Ras to induce foci but is unable to promote immortalization. We report here that JunD, in cooperation with Ras, induces foci with an efficiency similar to that of JunB. Artificial Jun/eb1 derivatives from each of the three Jun proteins were also analyzed. These constructs carry a heterologous homodimerization domain from the viral EB1 transcription factor and are thought to form only homodimers in the cell. We show here that these Jun/eb1 chimeras are potent transactivators of AP1 sites and that they can cooperate with c-Ha-Ras to induce foci. However, among all the Ras-Jun and Ras-Jun/eb1 combinations tested, only foci from Ras-c-Jun can be efficiently expanded and maintained as long-term growing cultures. Therefore, we suggest that a heterodimer containing c-Jun might be required for in vitro establishment of these primary mammalian cells.

Animals↗

Adenovirus E1A negatively and positively modulates transcription of AP-1 dependent genes by dimer-specific regulation of the DNA binding and transactivation activities of Jun.

Adenovirus E1A proteins inhibit expression of the collagenase gene but activate expression of the c-jun gene. Both effects are mediated by TPA-responsive elements (TREs), the binding sites for members of the AP-1 transcription factor family. By a process that is independent of the retinoblastoma gene product, E1A distinguishes between different AP-1 factors: in vivo binding of Jun/Jun homodimers and Jun/Fos heterodimers to the collagenase TRE is totally blocked by E1A while, in contrast, there is no inhibition of Jun/ATF-2 binding to the TRE sequences in the c-jun promoter. Altered phosphorylation of the DNA binding domain of cJun is not involved in the inhibition of cJun/cJun and cJun/cFos binding. E1A does, however, cause hyperphosphorylation of the transactivation domain of cJun, which is likely to be responsible for the enhanced c-jun transcription by E1A mediated through cJun/ATF-2 heterodimers.

Activating Transcription Factors↗

BCR/ABL confers growth factor independence upon a murine myeloid cell line.

The BCR/ABL oncogene in chronic myelogenous leukemia produces an activated tyrosine kinase fusion protein (p210). Like other tyrosine kinase oncogenes, BCR/ABL can abrogate the interleukin-3 (IL-3) dependence of lymphoid cell lines. To investigate the ability of BCR/ABL to generate growth factor independence in myeloid cells, the IL-3 dependent myeloid cell line NFS/N1.H7 (H7) was transfected with the p210BCR/ABL-containing plasmid, pGD210. Stable clones A54 and A74 were capable of IL-3 independent growth and tumor formation in syngeneic mice. Relief of growth factor dependence was not mediated by autocrine release of IL-3. The baseline proliferation rate of the BCR/ABL transformed cells was greater than that of the parental H7 cells maximally stimulated by IL-3. Abundant constitutive expression of c-myc, c-jun, and c-fos was observed in the p210BCR/ABL transfectants even in low serum conditions. In contrast, c-myc expression in H7 cells was dependent upon IL-3 stimulation, and neither c-jun nor c-fos was highly expressed following IL-3 stimulation in H7 cells. Thus, BCR/ABL transformation and relief of IL-3 dependence involve not only pathways that can substitute for IL-3 induced growth via tyrosine kinase mediated signals, but also pathways that recruit constitutive c-jun and c-fos expression.

Animals↗

Oncogene interaction in basal cell carcinomas of human skin.

The expression of the p53 protein (p53) was compared with those of several oncogenes including c-fos (Fos), c-jun (Jun), and epidermal growth factor receptor (EGFR1) using immunohistochemistry in frozen and paraffin-embedded sections of 25 basal cell carcinomas (BCCs) to find out any correlation between p53 and oncogenes in the pathogenesis of human BCC. In normal skin, positive reactions were obtained for EGFR1 and Fos, while p53 and Jun were negative in all cases. In the lesions, EGFR1 was observed in all cases and p53 was positive in 9 of 25 (36%). Fos was expressed in 21 of 25 (84%) and four negative cases were all p53-positive; this negative correlation between p53 and Fos staining was statistically significant (P < 0.01). Jun was detected in 14 of 20 (70%) and no significant relationship was observed between the expression of Jun and Fos or p53. These data suggest the possibility of down regulation of Fos expression by high levels of p53 protein. Further work is necessary to determine the mechanism of this interaction.

Aged↗

Induction of c-fos and c-jun mRNA expression by basic fibroblast growth factor in cultured rat Müller cells.

PURPOSE: Exogenous basic fibroblast growth factor (bFGF) induces bFGF gene expression in cultured rat Müller cells. To elucidate the mechanism that links exogenous bFGF to transcriptional regulation of bFGF gene expression in these cells, the authors examined mRNA expression of the proto-oncogenes c-fos and c-jun in response to exogenous bFGF in cultured rat Müller cells. METHODS: Müller cells from 1- to 3-day-old Sprague-Dawley rats were isolated and cultured in essential modified Eagle's medium + 10% fetal calf serum. Cultured cells were identified by immunocytochemical analysis using antibodies against vimentin, carbonic anhydrase C, and glutamine synthetase. Cells of passages 1 through 4 were treated with bFGF (0.01, 0.1, 1, 10, and 100 ng/ml), either the protein kinase C (PKC) inhibitors H-7 (30 microM) and GF109203X (1 microM) or the PKC activator phorbol 12-myristate 13-acetate (PMA; 1, 10, 100, 500 nM), and either adenylate cyclase activator forskolin (5 microM) or adenylate cyclase inhibitor SQ22536 (100 microM). Northern blot analysis was performed to determine the mRNA expression of c-fos, c-jun, and bFGF. RESULTS: Addition of bFGF to culture medium induced c-fos and c-jun mRNA expression in a dose- and time-dependent manner. Induction of c-fos mRNA was observed as early as 10 minutes (9.6-fold) after exposure to bFGF at a dose of 10 ng/ml. It reached a maximum of 17.4-fold by 30 minutes. A rapid decline of c-fos mRNA level was observed after 45 minutes of bFGF treatment. The temporal pattern of c-jun gene expression was similar to that of c-fos, whereas a maximum induction of c-jun mRNA (8.2-fold) was seen after 45 minutes of treatment. Induction of c-fos and c-jun gene expression started at a bFGF concentration of 0.1 ng/ml. It reached peak levels of 15-fold for c-fos and 7.6-fold for c-jun mRNA at 10 ng/ml. A dose-dependent upregulation of c-fos and c-jun gene expression by the PKC activator PMA was also observed. A maximum induction was seen at 100 nM PMA. The induction of c-fos and c-jun gene expression by bFGF or by PMA was blocked by the PKC inhibitors H-7 (30 microM) or GF109203X (1 microM). SQ22536 (100 microM), an adenylate cyclase inhibitor, did not inhibit bFGF-induced c-fos and c-jun gene expression, whereas forskolin (5 microM), an adenylate cyclase activator, upregulated the expression. CONCLUSIONS: These results indicate that exogenous bFGF induces c-fos and c-jun gene expression in cultured rat Müller cells through PKC activation. The proto-oncogenes c-fos and c-jun may play a role in the regulation of bFGF gene expression in response to exogenous bFGF in retinal Müller cells. These findings provide further insight into the roles of Müller cells and exogenous bFGF in protecting against photoreceptor degeneration.

Adenylyl Cyclases↗

Neurotransmitter-stimulated immediate-early gene responses are organized through differential post-synaptic receptor mechanisms.

The products of the cellular immediate-early genes (IEGs) are thought to act as messengers in the coupling of trans-synaptic stimuli with altered neuronal gene expression. However, the manner in which neurotransmission specifies particular responses through the IEGs is undefined. In this report, mRNA and transcription analysis of a precisely-timed, physiological IEG response illustrates how an IEG signal may be organized through differential neurotransmitter receptor activation. The nocturnal pattern of IEG expression in the rat pineal gland has been shown to be differentially regulated through post-synaptic adrenergic receptors. Induction of the c-fos gene is primarily mediated through alpha 1-receptors, whereas the coordinately regulated jun-B gene exhibits dual regulation through alpha 1- and beta-receptors. A simultaneous repression of c-jun expression is partly mediated through a beta-receptor mechanism. In vitro analysis of IEGs in cultured pineal glands has confirmed the receptor-specific link between adrenergic neurotransmission and IEG induction. The pineal is a unique neuroendocrine model in which the characteristics and function of the IEG third messenger system may be defined.

Animals↗

Identification of promoters bound by c-Jun/ATF2 during rapid large-scale gene activation following genotoxic stress.

The NH2-terminal Jun kinases (JNKs) function in diverse roles through phosphorylation and activation of AP-1 components including ATF2 and c-Jun. However, the genes that mediate these processes are poorly understood. A model phenotype characterized by rapid activation of Jun kinase and enhanced DNA repair following cisplatin treatment was examined using chromatin immunoprecipitation with antibodies against ATF2 and c-Jun or their phosphorylated forms and hybridization to promoter arrays. Following genotoxic stress, we identified 269 genes whose promoters are bound upon phosphorylation of ATF2 and c-Jun. Binding did not occur following treatment with transplatin or the JNK inhibitor SP600125 or JNK-specific siRNA. Of 89 known DNA repair genes represented on the array, 23 are specifically activated by cisplatin treatment within 3-6 hr. Thus, the genotoxic stress response occurs at least partly via activation of ATF2 and c-Jun, leading to large-scale coordinate gene expression dominated by genes of DNA repair.

Activating Transcription Factor 2↗

The product of a novel growth factor activated gene, fos B, interacts with JUN proteins enhancing their DNA binding activity.

We have identified a gene, fos B, encoding a nuclear protein of 338 amino acids presenting a 70% homology with c-fos, whose expression is activated during G0/G1 transition. Growth factor stimulation of quiescent cells leads to a rapid and transient accumulation of fos B mRNA, with kinetics similar to those of c-fos. The induction of fos B mRNA levels is in part due to a dramatic increase in the transcription of the gene. The half-life of fos B mRNA is in the order of 10-15 min. Both transcriptional activation and mRNA stability are substantially increased in the presence of protein synthesis inhibitors. Immunoprecipitation studies showed that fos B as c-fos protein, forms a complex in vitro with c-jun and jun B proteins in the absence of a target binding sequence. Gel retardation assays demonstrated that fos B protein positively influences the binding of c-jun and jun B proteins to an AP-1 binding consensus sequence, suggesting that fos B protein plays a role in control of gene expression.

Amino Acid Sequence↗

Docosahexaenoic acid-containing phosphatidylethanolamine enhances HL-60 cell differentiation by regulation of c-jun and c-myc expression.

18:1/docosahexaenoic acid (DHA)-containing phosphatidylethanolamine (PE) enhanced cell differentiation and growth inhibition of HL-60 induced by dibutyryl cAMP (dbcAMP) in a dose-dependent manner. The combined treatment of 200 microM dbcAMP and 50 microM 18:1/DHA-PE increased the NBT reducing activity, which is as an indicator of cell differentiation, to more than 75% from 40% of cells treated with 200 microM dbcAMP alone. In HL-60 cells treated with 50 microM 18:1/DHA-PE and 200 microM dbcAMP for 24 h, the expression level of c-jun mRNA and c-Jun protein were remarkably elevated compared to cells treated with dbcAMP alone. In contrast, there was no difference in the expression levels of c-fos mRNA and c-Fos protein between the combination of 18:1/DHA-PE + dbcAMP or dbcAMP alone. On the other hand, the combine treatment of 18:1/DHA-PE and dbcAMP markedly reduced the expression level of c-myc oncogene during 48 h incubation. The decreases of c-myc mRNA by 18:1/DHA-PE and/or dbcAMP was correlated with growth inhibition effect. Thus, 18:1/DHA-PE might enhance dbcAMP-induced HL-60 cell differentiation and growth inhibition by regulation of c-jun and c-myc mRNA and their products.

Bucladesine↗

Transforming growth factor-beta-induced expression of the apolipoprotein E gene requires c-Jun N-terminal kinase, p38 kinase, and casein kinase 2.

OBJECTIVE: The cytokine transforming growth factor-beta (TGF-beta) and apolipoprotein E (apoE) play potent antiatherogenic roles. Despite such importance, the mechanisms underlying the regulation of apoE expression by TGF-beta have not been characterized and were therefore investigated. METHODS AND RESULTS: Using THP-1 cell line as a model system, with key findings confirmed in primary cultures, we show that TGF-beta induces the expression of apoE, and this is prevented by pharmacological inhibitors of c-Jun N-terminal kinase (JNK), p38 kinase, and casein kinase 2 (CK2). In support for an important role for these pathways, TGF-beta activates JNK, p38 kinase, and CK2, and dominant-negative (DN) forms of these proteins inhibit the cytokine-induced apoE expression. TGF-beta also increases the phosphorylation and expression of c-Jun, a downstream target for JNK action and a component of activator protein-1 (AP-1), and DN c-Jun inhibits the induction of apoE expression in response to the cytokine. AP-1 DNA binding was also induced by TGF-beta, and the action of p38 kinase, JNK, and CK2 converged on the activation of c-Jun/AP-1. CONCLUSIONS: These studies reveal a novel role for JNK, p38 kinase, CK2, and c-Jun/AP-1 in the TGF-beta-induced expression of apoE.

Apolipoproteins E↗

The defective transforming phenotype of c-Jun Ala(63/73) is rescued by mutation of the C-terminal phosphorylation site.

Cotransfection of primary rat embryo fibroblasts (REF) with c-Jun and activated Ras leads to oncogenic transformation and this process requires the phosphorylation of the N-terminal domain of c-Jun. Ras augments this phosphorylation and, consequently activates the c-Jun transactivation property of TRE (TPA Responsive Element)-dependent promoters. To analyse the role of the c-Jun C-terminal phosphorylation site in oncogenic cooperation we tested the activities of N-terminal c-Jun Ala(63/73) (named Nt), C-terminal c-Jun Ala(234/242/246/252) (named Ct) and (Nt+Ct)-with both mutations-non-phosphorylatable c-Jun mutants. In cooperation with Ras, the Ct mutant and wt c-Jun display similar oncogenic properties whereas the Nt form was defective in transforming REF cells. Unexpectedly, the Nt+Ct mutant exhibited identical oncogenic properties to wt c-Jun, demonstrating that the Ct mutation rescues in cis the Nt mutation. The transcriptional activity and the capacity to bind the c-Jun coactivator CREB Binding Protein (CBP) were enhanced by Ras for the wt and Ct proteins but not for the Nt mutant. Interestingly, the Nt+Ct mutant presents identical transactivation and CBP binding activities to wt c-Jun. Therefore the rescue in cis of the defective Nt mutation by the Ct mutation seems to be due to the recovery of CBP binding. Our results revealed that the process of oncogenic cooperation can occur between Ras and the Nt+Ct non-phosphorylatable c-Jun protein.

Alanine↗

Differential expression of immediate early genes after hippocampal long-term potentiation in awake rats.

The pattern of expression of fos and jun family immediate early genes following the induction of long-term potentiation (LTP) was investigated in the dentate gyrus of awake rats. Rapid, transient increases in the levels of c-jun and jun-B mRNA and protein, and in the levels of Fos-related proteins (FRAs), occurred in the dentate gyrus after LTP-inducing tetanization of the perforant path. A delayed, and more prolonged induction occurred for jun-D mRNA and protein. The induction of c-Jun, Jun-B, Jun-D and Fos-related proteins was prevented by administration of an N-methyl-D-aspartate receptor antagonist, which also blocked LTP induction, and by pentobarbital, which reduced but did not block LTP. These findings show that differential expression of fos and jun gene family members occurs in a distinct pattern following LTP in awake rats. The responsive genes may participate in the biochemical cascade leading to the long-term stabilization of synaptic modifications.

Animals↗

Synergistic activation of neurotensin/neuromedin N gene expression by c-Jun and glucocorticoids: novel effects of Fos family proteins.

The cis-regulatory region of the neurotensin/neuromedin N (NT/N) gene integrates diverse environmental signals in the neuroendocrine PC12 cell line, resulting in remarkable synergistic regulation. An AP-1 site appears to play a pivotal role in cooperative NT/N gene activation, as mutations in this site decrease responses to all inducer combinations by at least an order of magnitude. Here we report that c-Jun acts synergistically with glucocorticoids to activate the NT/N promoter, and that Fos family proteins have novel regulatory effects on this interaction. Cotransfection of individual pCMV-AP-1 expression plasmids revealed that c-Jun most potently activates the NT/N promoter and that costimulation with dexamethasone results in a further 6- to 12-fold increase in expression. Unlike its general inhibitory effects on glucocorticoid regulation in other systems, c-Fos potentiated activation by glucocorticoids when coexpressed with c-Jun, and Fos B had a similar, but more limited, positive effect. In contrast, Fra-1 reversed the direction of glucocorticoid regulation, and Fra-2 abolished synergism. AP-1, cAMP response element, and glucocorticoid response element motifs are required for full cooperative activation by either c-Jun or c-Jun/c-Fos and glucocorticoids. These results indicate that NT/N promoter activation involves synergistic interactions between specific AP-1 complexes and ligand-activated glucocorticoid receptor, and similar mechanisms may regulate NT/N gene expression in central neurons.

Animals↗

DNA damage, apoptosis and C-myc, C-fos, and C-jun overexpression induced by selenium in rat hepatocytes.

OBJECTIVE: To study the effects of selenium on DNA damage, apoptosis and c-myc, c-fos, and c-jun expression in rat hepatocytes. METHODS: Sodium selenite at the doses of 5, 10, and 20 micromol/kg was given to rats by i.p. and there were 5 male SD rats in each group. Hepatocellular DNA damage was detected by single cell gel electrophoresis (or comet assay). Hepatocellular apoptosis was determined by TUNEL (TdT-mediated dUTP nick end labelling) and flow cytometry. C-myc, c-fos, and c-jun expression in rat hepatocytes were assayed by Northern dot hybridization. C-myc, c-fos, and c-jun protein were detected by immunohistochemical method. RESULTS: At the doses of 5, 10, and 20 micromol/kg, DNA damage was induced by sodium selenite in rat hepatocytes and the rates of comet cells were 34.40%, 74.80%, and 91.40% respectively. Results also showed an obvious dose-response relationship between the rates of comet cells and the doses of sodium selenite (r=0.9501, P<0.01). Sodium selenite at the doses of 5, 10, and 20 micromol/kg caused c-myc, c-fos, and c-jun overexpression obviously. The positive brown-yellow signal for proteins of c-myc, c-fos, and c-jun was mainly located in the cytoplasm of hepatocytes with immunohistochemical method. TUNEL-positive cells were detected in selenium-treated rat livers. Apoptotic rates (%) of selenium-treated liver cells at the doses of 5, 10, and 20 micromol/kg were (3.72 +/- 1.76), (5.82 +/- 1.42), and (11.76 +/- 1.87) respectively, being much higher than those in the control. Besides an obvious dose-response relationship between apoptotic rates and the doses of sodium selenite (r=0.9897, P<0.01), these results displayed a close relationship between DNA damage rates and apoptotic rates, and the relative coefficient was 0.9021, P<0.01. CONCLUSION: Selenium at 5-20 micromol/kg can induce DNA damage, apoptosis, and overexpression of c-myc, c-fos, and c-jun in rat hepatocytes.

Animals↗

In vivo response of hepatocytes to growth factors requires an initial priming stimulus.

Although growth factor effects have been studied in cultured hepatocytes, little information exists as to whether these factors can trigger hepatocyte replication in vivo. In this study we infused epidermal growth factor, transforming growth factor-alpha and hepatocyte growth factor directly into the portal vein of rats for 24 hr to see whether they could induce DNA synthesis in normal livers or in livers subjected to one-third hepatectomy. Infusion of transforming growth factor-alpha or epidermal growth factor at doses up to 80 micrograms/24 hr had little effect on hepatic DNA synthesis in normal liver, whereas the monomeric and heterodimeric forms of hepatocyte growth factor generally produced increases of less than threefold in hepatic DNA synthesis. In contrast, after one-third hepatectomy infusion of epidermal growth factor, transforming growth factor-alpha or hepatocyte growth factor produced dose-dependent increases in hepatic DNA synthesis. At a dose of 40 micrograms/24 hr, epidermal growth factor increased DNA synthesis threefold, whereas transforming growth factor-alpha or hepatocyte growth factor increased DNA synthesis to greater than six times that in rats that had undergone hepatectomy alone. Furthermore, infusion of these growth factors, with or without one third-hepatectomy, induced the expression of transforming growth factor-alpha mRNA in the liver. The pattern of protooncogene expression induced by one-third hepatectomy was studied to determine the effect of this procedure in sensitizing the liver to the growth factors. Compared with the well-characterized two-thirds hepatectomy system, there was a similar but smaller increase in c-myc expression but no induction of c-jun expression.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

Tissue differences in the expression of mRNAs of Ha-ras, c-myc, fos and jun in human uterine endometrium, myometrium and leiomyoma under the influence of estrogen/progesterone.

Ha-ras expression level in uterine endometrium (EM) in the proliferative phase (PP) was significantly higher than that in the secretory phase (SP). c-myc expressions were detected in EM, uterine myometrium (MM) and uterine leiomyoma (LM) without any cyclic change; fos expressions in LM, MM, and EM were detectable in PP, but not in SP. jun expression level in LM was significantly higher than that in MM and EM in PP, but did not alter during the menstrual cycle. Estrogen elevated the levels of Ha-ras and fos mRNAs in the three tissues, jun mRNA in MM and EM, and c-myc mRNA in LM and MM. These results suggest that there is a tissue difference in the expression of Ha-ras, c-myc, fos and jun among EM, MM and LM, under the influence of estrogen/progesterone.

Adult↗

Augmentation of c-fos and c-jun expression in transgenic mice carrying the human T-cell leukemia virus type-I tax gene.

To analyze the effect of human T-cell leukemia virus type I (HTLV-I) on cellular gene expression and its relation to tumorigenesis, two lines of transgenic mice carrying the long terminal repeat (LTR)-env-pX-LTR regions of the HTLV-I genome were produced. The transgene was expressed in many organs, including the brain, salivary gland, spleen, thymus, skin, muscle, and mammary gland. We found that the expression of the c-fos and c-jun genes, but not of the lyn and c-myc genes, was augmented 2- to 20-fold in histologically normal skin and muscle of these mice. The augmentation was tissue specific, suggesting the involvement of a cellular factor in the transgene action. In these mice, a three to seven times higher incidence of tumors was seen as compared with the control mice. These tumors included mesenchymal tumors, such as fibrosarcoma, neurofibroma, and lipoma, and adenocarcinomas of the mammary gland, salivary gland, and lung. The c-fos and c-jun genes were also activated in these tumors. The possible roles of elevated c-fos and c-jun gene expression in tumorigensis are discussed.

Animals↗

Opposing actions of Fos and Jun on transcription of the phosphoenolpyruvate carboxykinase (GTP) gene. Dominant negative regulation by Fos.

Jun homodimers and Fos/Jun heterodimers bind to the gene for phosphoenolpyruvate carboxykinase (GTP) (EC 4.1.1.32) (PEPCK) at three sites within the first 350 base pairs of the promoter. These include CRE-1 (-82 to -90), and P3(II) and P4 (-252 to -258 and -268 to -285, respectively). Over-expression of Jun in HepG2 cells resulted in a 10-15-fold increase in the level of transcription of a chimeric PEPCK (-490 to +73)-CAT gene, while expression of Fos decreased transcription and blocked the induction of transcription from the PEPCK promoter by Jun. The action of Fos and Jun on PEPCK gene transcription involved each of the Fos/Jun-binding sites and was modulated by additional transcriptional regulatory elements within the PEPCK promoter. The ability of Fos to inhibit PEPCK transcription was dependent upon P3(I), a region of the promoter which does not bind Fos/Jun heterodimers, but does bind members of the C/EBP family of transcription factors. Stimulation of PEPCK transcription by 8-Br-cAMP or by overexpression of the catalytic subunit of protein kinase A was inhibited by Fos expression. The inhibitory effects of phorbol esters and protein kinase C on PEPCK gene expression may be mediated through the action of Fos and Jun.

Binding Sites↗