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Decreased expression of the c-Fos, but not Jun B, transcription factor in the auditory pathway of the rat after repetitive acoustic stimulation.

Between the 21st and 34th postnatal days, male rats received an acoustic stimulus every second day, and the expression of c-Fos and Jun B proteins was compared with rats that received only a single acoustic stimulus at postnatal day 34. For acoustic stimulation, 8-kHz pure-tone bursts (100 ms duration at a rate of 6.3 Hz) were applied for 5 min. The numbers of neurons immunoreactive to c-Fos and Jun B were studied 2 h after the last or acute stimulus, respectively, in the ventral cochlear nucleus (VCN), dorsal cochlear nucleus (DCN) and inferior colliculus (IC). Compared with the single stimulus, repetitive stimulation significantly reduced the number of c-Fos labeled neurons in the VCN by 51%, in the DCN by 75% and in the IC by 48%. In contrast to c-Fos, repetitive stimulation did not significantly lower the number of Jun-B-expressing neurons. These findings indicate that independent intraneuronal pathways terminate on the induction of c-Fos- and Jun-B-expressing genes during the juvenile maturation of the acoustic pathway and that chronic exposure of acoustic events alters the program of intraneuronal gene expression by reducing transcriptional activities with subsequent stabilization at the genetic level.

Acoustic Stimulation↗

Expression of Jun family members in human colorectal adenocarcinoma.

The products of the Jun family genes, c-Jun, JunB and JunD, are essential components of the activating protein-1 transcription factor complexes that are critically important in the control of cell growth, differentiation and neoplastic transformation. Although increased c-Jun expression has been reported in human colorectal tumors, expression of JunB and JunD in these tumors has not previously been characterized. In the current study, we examined 24 cases of human colorectal adenocarcinoma by western immunoblotting analysis and immunohistochemical staining for the expression of c-Jun, JunB and JunD proteins. Normal-appearing colonic mucosa distant from the tumors in the same colectomy specimens were used as a reference for comparison. The results showed that both c-Jun and JunB proteins were undetectable or barely detectable in normal mucosa but their expression levels were significantly increased in human colorectal adenocarcinomas. In contrast, JunD protein was present at high levels in normal mucosa and only showed a minimal increase in adenocarcinomas. These observations suggest that different Jun proteins may serve different roles in regulating colonic epithelial cell growth and in colorectal tumorigenesis.

Adenocarcinoma↗

Induction of highly proliferative phenotypes in cultured glomerular mesangial cells by benzo[a]pyrene alone or in combination with methoxamine.

Recent studies have suggested that aromatic hydrocarbons can initiate glomerular mesangial cell (GMC) injury and contribute to the onset of renal disease. The present studies were conducted to assess the impact of benzo[a]pyrene (BaP), a ubiquitous polycyclic aromatic hydrocarbon, on the proliferation of GMCs. Challenge of cultured GMCs with BaP (0.3-30 microM) for 24 h was associated with concentration-dependent decreases in DNA synthesis, a response mediated by selective interference with early G1 cell cycle progression. One cycle of sequential treatment with 3 microM BaP for 24 h followed by challenge with 10 microM methoxamine (MeoA), a growth-promoting alpha 1-adrenergic agonist, for an additional 24 h attenuated the inhibitory response elicited by BaP alone. Following three rounds of sequential treatment with BaP and MeoA, GMCs exposed to BaP alone or BaP/MeoA exhibited enhanced proliferation rates relative to controls. BaP/MeoA cells acquired the greatest proliferative enhancement and exhibited unregulated c-jun and c-fos gene expression under growth-arrested and serum-stimulated conditions. Marked increases in specific AP-1 binding to a synthetic oligonucleotide were observed upon serum stimulation of quiescent cultures of BaP/MeoA cells relative to controls or any of the other treatment groups. These data demonstrate that sequential treatment with BaP in combination with MeoA is associated with induction of highly proliferative phenotypes in GMCs characterized by differential expression of growth-related protooncogenes.

Adrenergic alpha-Agonists↗

v-Jun represses c-jun proto-oncogene expression in vivo through a 12-O-tetradecanoylphorbol-13-acetate-responsive element in the proximal gene promoter.

c-jun proto-oncogene expression is extinguished in cells transformed by v-Jun; however, the mechanistic basis of this phenomenon has not been elucidated. c-jun mRNA levels are greatly reduced in v-Jun-transformed cells, and we show that this reduction is associated with a similar decrease in the rate of c-jun transcription. Transcriptional down-regulation was also evident in functional assays in which the c-jun gene promoter was approximately 10-fold less active in v-Jun-transformed cells than it was in normal cells. This reduction was largely attributable to a conserved 12-O-tetradecanoylphorbol-13-acetate-responsive element (TRE)-like motif at position -72 (the proximal junTRE) that was essential for efficient basal expression in normal cells but that conferred little, if any, detectable transcriptional activity in v-Jun-transformed cells. DNA-binding analysis showed that this element was recognized by a mixture of c-Jun/Fra and cyclic AMP-responsive element-binding protein/activating transcription factor-like complexes in normal cells but that v-Jun/Fra heterodimers predominated in v-Jun-transformed cells. Furthermore, ectopic expression of v-Jun repressed c-jun promoter activity in normal cells through the proximal junTRE. Thus, the deficit in transcription mediated by the junTRE correlates with and is most likely attributable to binding of v-Jun to this element in vivo. We also find that the c-jun promoter is refractory to induction via the stress-activated protein kinase/c-jun NH2-terminal kinase pathway in v-Jun-transformed cells, suggesting that v-Jun interferes with signal-regulated gene expression. Therefore, c-jun is an example of a cellular gene, the transcription of which is regulated negatively by v-Jun in vivo.

Activating Transcription Factors↗

Oncoproteins and tumor suppressor proteins in congenital sacrococcygeal teratomas.

Congenital sacrococcygeal teratoma (SCT) is the most common germ cell tumor of infancy and childhood with a female preponderance. Most SCTs are diagnosed at birth, are benign, and consist of fully differentiated, mature tissues. Tumorigenesis of SCTs remains poorly understood. Almost nothing is known about possible oncogene activation or tumor suppressor inactivation in these rare tumors. We describe the presence of various oncoproteins and tumor suppressor proteins in eight cases of congenital SCT. The following oncogenes were examined: ras family (c-H-, c-N-, and c-K-ras), early genes (fos, jun), and tumor suppressor genes (p53 and nm23-H-I). There was no relationship between the intensity of expression of these oncoproteins and tumor suppressor genes and the following parameters: tumor size, age, and survival of the patients. We did not observe any difference, however, between the expression of the examined oncogenes and tumor suppressor genes nm23 and p53 in immature and mature teratomas. Our findings suggest that the ras family of oncogenes, fos and jun oncogenes, and nm23 and p53 tumor suppressor genes are present in congenital SCT, indicating a possible role in genesis and development of these tumors.

Child, Preschool↗

Transcriptional activation of C/EBPbeta gene by c-Jun and ATF2.

C/EBPbeta is one of the key transcription factors responsible for the induction of a wide array of genes. Like many proto-oncogenes and transcription factors, transcription of C/EBPbeta gene can be induced by multiple extracellular signals. Using nuclear extracts from lipopolysaccharide (LPS)-stimulated mouse liver, five trans-acting factor-binding motifs, URE1 (-376 to -352), URE2 (-253 to -223), URE3 (-220 to -190), URE4 (-123 to -103), and URE5 (-72 to -45) were identified by DNAse I footprinting assays. Competition and supershift analysis of the complexes formed at the URE2 and URE4 indicated that they contain CREB/ATF and AP-1 family factors. Furthermore, recombinant ATF2 and c-Jun proteins from mammalian and bacterial cells can bind to URE2 and URE4 but not URE1. Cotransfection experiments showed that ATF2 and c-Jun activate the C/EBPbeta gene expression cooperatively through URE2 and URE4, and this activation was greatly increased under the treatment of low concentration of anisomycin. During acute phase response, the phosphorylation of c-Jun and ATF2 was found to correlate with C/EBPbeta gene expression. Taken together, our results provide the evidences that both c-Jun and ATF2 are the regulators of C/EBPbeta gene.

Activating Transcription Factor 2↗

Conditional cell transformation by doxycycline-controlled expression of the ASV17 v-jun allele.

To investigate the molecular basis of oncogenesis induced by the v-jun oncogene of avian sarcoma virus 17 (ASV17), we developed a conditional cell transformation system in which transcription of the ASV17 v-jun allele is controlled by a doxycycline-sensitive transactivator (tTA) or a reverse (doxycycline-dependent) transactivator (rtTA), respectively. Permanent cell lines of quail embryo fibroblasts conditionally transformed by a doxycycline-controlled v-jun allele revert to the normal phenotype within 3 days and lose their ability to grow in soft agar, strictly dependent on the addition or removal of the drug, respectively. The reverted cells are rapidly retransformed on conditional activation of v-jun. While full-level synthesis of v-jun mRNA and v-Jun protein in these cells is established within 2 and 14 h, respectively, after switching to the permissive conditions, the first morphological alterations are observed after 24 h, and as early as 2 days later the morphology has changed entirely from flat cells resembling normal fibroblasts to spindle-shaped fusiform cells showing a typical jun-transformed phenotype. Kinetic expression analysis revealed that transcriptional activation of the direct jun target gene BKJ precisely coincides with the establishment of full-level v-Jun protein synthesis. Furthermore, we have analyzed the expression of a novel candidate v-jun target gene, termed JAC, which shows no sequence homology to known genes. Similar to BKJ, JAC is specifically activated in jun-transformed fibroblasts, and induction of JAC is tightly linked to the conditional expression of oncogenic v-Jun. These results demonstrate the high stringency of the doxycycline-controlled v-jun expression system, and they also indicate that expression of v-jun in these cells is indispensable for enhanced proliferation, cell transformation, and the induction of specific expression patterns of downstream target genes.

Alleles↗

Expression of stress response genes GADD153, c-jun, and heme oxygenase-1 in H2O2- and O2-resistant fibroblasts.

In the present study, the expression of the stress-inducible genes GADD153, c-jun, heme oxygenase-1 (HO-1), and HSP70 was compared among parental hamster diploid fibroblasts (HA-1), and cell lines isolated for resistance to either H2O2 (OC14) or O2 (O2R95). Both OC14 and O2R95 cell lines are known to have significantly augmented cellular antioxidant defenses, including increased glutathione content, as well as enhanced catalase, superoxide dismutase, and glutathione peroxidase activities. Northern analysis indicated that basal expression of HO-1 and c-jun is also elevated in these resistant cell lines. Relative to HA-1 values, basal GADD153 mRNA expression was approximately threefold higher in O2R95, but twofold lower in OC14 cells. HSP70 mRNA expression was comparable among parental and resistant cell lines. Both OC14 and O2R95 cells showed greatly enhanced survival following H2O2 exposure. The H2O2 doses that induced 50% toxicity in parental and resistant cells (3 vs. 30-60 x 10(-13) mol/cell, respectively) differed by more than an order of magnitude. Similarly, GADD153, c-jun, and HO-1 mRNA were elevated in control cells following exposure to doses of H2O2 an order of magnitude lower than is required for gene activation in resistant cell lines. Nonetheless, at equitoxic doses, the level of induction of GADD153 and HO-1 was greater in resistant than in parental cell lines. Taken together, our results suggest that alterations in the basal level of expression of certain stress-responsive genes, including HO-1, c-jun, and GADD153, may contribute to the H2O2-resistant phenotype in these fibroblast cell lines. Further, changes in the regulation of these genes in response to adverse stimuli may provide an additional mechanism for enhanced cell survival following oxidative stress.

Animals↗

Ionizing radiation regulates expression of the c-jun protooncogene.

There is little known about the regulation of gene expression by ionizing radiation exposure. The present studies demonstrate transcriptional activation of a mammalian gene, the c-jun protooncogene, by x-rays. The c-jun gene encodes a component of the AP-1 protein complex and is important in early signaling events involved in various cellular functions. The increase in c-jun transcripts by ionizing radiation was time- and dose-dependent as determined by Northern blot analysis. Transcriptional run-on analysis demonstrated that ionizing radiation stimulates the rate of c-jun gene transcription. Furthermore, the half-life of c-jun RNA was prolonged in the absence of protein synthesis. These findings indicate that the increase in c-jun RNA observed after irradiation is regulated by transcriptional and posttranscriptional mechanisms. Moreover, the induction of c-jun by ionizing radiation was associated with an inverse dose rate effect in that decreasing the dose rate resulted in increased c-jun expression. The present results similarly demonstrate that ionizing radiation increases levels of c-fos transcripts as well as that of jun-B, another member of the jun family. Taken together, these results suggest a role for induction of early response genes in the pathophysiologic effects of ionizing radiation.

Blotting, Northern↗

Effects of dexamethasone on cytokine and phorbol ester stimulated c-Fos and c-Jun DNA binding and gene expression in human lung.

Glucocorticosteroids have a wide variety of effects which result in the long-term dampening of inflammatory responses. An important site of steroid action may be on the control of the activator protein-1 (AP-1) binding to deoxyribonucleic acid (DNA). AP-1 is a proinflammatory transcription factor composed of a heterodimer of Fos and Jun proto-oncogenes, which can be induced by phorbol esters and various cytokines. We have examined the hypothesis that dexamethasone may inhibit inflammation via an effect on AP-1 activation in human lung tissue. The effect of dexamethasone on the phorbol ester and cytokine activation of AP-1 and its monomers was examined in human lung tissue obtained from transplantation donors. AP-1 activation was measured by its ability to bind DNA, its localization in the nucleus by Western blotting, and the levels of fos and jun messenger ribonucleic acids (mRNAs) using Northern blotting. The phorbol ester, phorbol myristate acetate (PMA), caused a significant 2-3 fold increase in AP-1 DNA binding, which was sustained for 24 h and completely attenuated by co-incubation with dexamethasone. Dexamethasone alone caused a 40% decrease in AP-1 DNA binding. Dexamethasone modulated the expression of both c-jun and c-fos mRNA and produced long-term (24 h) 40% reduction in both mRNAs when compared to control tissues. PMA induced a rapid and prolonged increase in c-Fos and c-Jun nuclear localization, which was not attenuated by co-incubation with dexamethasone.(ABSTRACT TRUNCATED AT 250 WORDS)

Blotting, Northern↗

HIV-1 gp120 induces the activation of both c-fos and c-jun immediate-early genes in HEL megakaryocytic cells.

We have previously demonstrated that the addition in culture of recombinant HIV-1 IIIB envelope gp120 affects the survival/growth of pluripotent haemopoietic progenitors, and, in particular, of those committed towards the megakaryocytic lineage. To characterize some of the molecular mechanisms involved in this phenomenon, we investigated the expression of members of the activating protein-1 (AP-1) complex in the HEL megakaryoblastic cell line. Following the treatment of HEL cells with recombinant IIIB envelope gp120, we noticed: (i) increased levels of endogenous c-fos and c-jun mRNA and proteins, (ii) activation of both c-fos and c-jun promoters, and (iii) a very rapid stimulation of a MAPK/ERK pathway.

Cell Line↗

[Pressure-induced expression of immediate-early gene product c-Jun of the common carotid arteries in rats].

In order to investigate the mechanism of mechanical stress-mediated arterial remodeling, we studied the pressure-induced expression of immediate-early response gene product c-Jun in common carotid arteries in rats. The common carotid arteries were perfused with both high pressure (160 mmHg) and normal pressure (80 mmHg) for 0.5, 1, 3 and 6 hours. Expression of immediate-early response gene product c-Jun in the arteries was examined by immunohistochemistry and computer image processing. c-Jun was weakly expressed at 1 h, then increased at 3 h and 6 h after exposure of the arteries to normal pressure. Positive immunohistochemical product of c-Jun appeared in the arteries at 0.5 h after the onset of high pressure, then it increased markedly till 6 h. There was significant difference between the two groups. These results indicate that expression of c-Jun of the arteries can be induced by pressure, which may play an important role in mechanical stress-mediated arterial remodeling.

Animals↗

Gastrin and glycine-extended progastrin processing intermediates induce different programs of early gene activation.

We recently reported that gastrin and glycine-extended progastrin processing intermediates (G-Gly) exert growth-promoting effects on AR4-2J cells (derived from rat pancreas) via interaction with distinct receptors. In this study we sought to investigate the mechanisms by which gastrin and G-Gly stimulate cell proliferation. While gastrin increased [Ca2+]i in AR4-2J cells, G-Gly had no effect. Similarly, G-Gly had no effect either on basal and 10(-7) M vasoactive intestinal polypeptide-stimulated cAMP generation, although gastrin is known to inhibit cAMP generation. Gastrin dose dependently stimulated AR4-2J cell mRNA content of both c-fos and c-jun, two genes known to function in regulating cell proliferation, but G-Gly had no effect. Gastrin also induced the expression of luciferase in AR4-2J cells transfected with a construct consisting of a luciferase reporter gene coupled to the serum response element of the c-fos gene promoter. In similar fashion, gastrin stimulated the activity of mitogen-activated protein kinase, an enzyme known to mediate the induction of the c-fos serum response element in response to growth factor stimulation. Although G-Gly had none of these effects of gastrin in AR4-2J cells, it stimulated activity of c-Jun amino-terminal kinase, an enzyme known to phosphorylate and transcriptionally activate c-Jun. These data support the notion that gastrin stimulates cell proliferation by inducing c-fos and c-jun gene expression, while G-Gly acts by post-translationally regulating early gene transcriptional activation. Our studies represent a novel model in which both the precursor and the product of a key processing reaction, peptide alpha-amidation, act cooperatively to stimulate cell proliferation via distinct receptors linked to different signal transduction pathways.

Animals↗

Regulation of fos and jun immediate-early genes by redox or metabolic stress in cardiac myocytes.

We have previously demonstrated coordinate inductions of c-fos, c-jun, jun B, and jun D in cardiac myocytes exposed to hypoxia for 2 to 4 hours. Induction of these transcripts occurred before any significant loss of intracellular ATP. In the present study, the origin of the signal(s) that regulates immediate-early gene induction was investigated by comparing the effects of hypoxia with those of the metabolic inhibitors cyanide, deoxyglucose and cyanide combined, and iodoacetic acid. Cyanide, an inhibitor of oxidative metabolism, closely mimicked the metabolic effects of hypoxia, with elimination of oxygen consumption, increased lactate production, and minimal decline in ATP levels under both conditions. Compared with hypoxia, cyanide mediated small transient inductions of fos and jun transcripts that followed a different time course. The combination of cyanide and deoxyglucose resulted in inhibition of lactate production as well as respiration, and ATP dropped rapidly to 20% of control levels. The loss of intracellular ATP was followed by fourfold inductions of c-fos and c-jun with minor changes in jun B and jun D transcript levels. Similarly, iodoacetic acid caused a major (90%) loss of ATP and irreversible cell damage as measured by leakage of creatine phosphokinase enzyme and loss of membrane arachidonic acid; ATP loss was followed by fivefold to sevenfold inductions of c-fos, c-jun and jun B transcripts.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

Mutation of a phosphorylation site in the DNA-binding domain is required for redox-independent transactivation of AP1-dependent genes by v-Jun.

The ability of the nuclear oncoprotein Jun to activate transcription is controlled both by level of DNA binding and by the activity of its transactivation domain. Control of DNA binding is achieved by two mechanisms: phosphorylation and redox regulation. Mutation of Ser-226 inhibits phosphorylation of the DNA binding, resulting in enhanced DNA-binding and transactivation activity of Jun. In contrast, mutation of Cys-252, which is the target for repression of DNA-binding activity under oxidative conditions, results in a strong decrease of Jun-specific activation of transcription. However, transactivation by c-Jun-Cys-252 is fully restored upon mutation of Ser-226. Both mutations are also found in the oncogenic counterpart of c-Jun, v-Jun, and are the only differences between these proteins in the DNA-binding domain, suggesting that v-Jun escapes down-modulation of DNA binding by both mechanisms. However, inhibition of phosphorylation of Ser-226 is absolutely required for the ability of v-Jun to activate transcription of AP-1-dependent genes in a redox-independent manner.

Animals↗

Stress-induced transcriptional activation mediated by YAP1 and YAP2 genes that encode the Jun family of transcriptional activators in Saccharomyces cerevisiae.

The Saccharomyces cerevisiae YAP2 gene encoding an AP-1-like transcriptional activator protein was cloned by selection for genes that confer pleiotropic drug resistance when present in high copy number. The novel YAP2 gene encodes a protein of 45827 daltons and is homologous in part to a known transcriptional activator protein encoded by YAP1/PDR4/SNQ3/PAR1. Homology was found only in both terminal regions. The N-terminal portion contains a region rich in basic amino acids, followed by a "leucine zipper" motif. Overexpression of YAP2 led to the induction of expression of an AP-1 recognition element (ARE)-dependent promoter. The yap1 disruptant has been shown to be sensitive to H2O2. In this study, we demonstrated that the yap1 disruptant is also unable to grow in medium containing 150 microM cadmium, whereas the yap2 disruptant exhibited no significant phenotypes. However, YAP2 in high copy number did suppress cadmium sensitivity, but not H2O2 sensitivity of the yap1 disruptant. YAP1 was able to mediate both cadmium- and H2O2-induced transcriptional activation of an ARE-dependent promoter. A high-copy-number plasmid bearing YAP2 mediated cadmium-induced transcriptional activation of this promoter. The inductions were prevented by the antioxidant N-acetyl-L-cysteine.

Acetylcysteine↗

Histone modifications in kainate-induced status epilepticus.

To understand the molecular actions of status epilepticus at the chromatin level, we studied the effects of kainate-induced status epilepticus on two different histone modifications at amino terminal tails: histone H3 phosphorylation at serine 10 and histone H4 acetylation. In addition to induction of c-fos and c-jun immediate early genes (IEGs) expression in mouse hippocampus, we also found the upregulation of acetylation and phosphorylation of histones, coupled with status epilepticus after kainate administration. c-fos and c-jun mRNA were sequentially induced in response to kainate, in different hippocampal subpopulations, starting from the dentate gyrus (DG) and spreading to the cornus ammonis regions. Immunohistochemical analysis showed that the spatio-temporal distribution of histone H4 hyperacetylation after kainate treatment was well correlated with the expression of c-fos and c-jun genes. Additionally, there was a transient appearance of phosphorylated histone H3 specifically in the DG region. CREB-binding protein or CBP, a well-known transcriptional co-activator with histone acetyltransferase (HAT) activity, was also induced by kainate and its expression pattern well correlated with histone H4 hyperacetylation in the hippocampus. Chromatin immunoprecipitation analysis showed that both histone modifications were associated with c-fos gene promoter after kainate stimulation, but only histone acetylation with c-jun gene. Pretreatment with curcumin, which has a HAT inhibitory activity specific for CBP/p300, attenuated histone modifications, IEGs expression and also the severity of status epilepticus after kainate treatment. Our findings suggest the involvement of histone modifications induced by kainate not only in IEGs expression but also in the development of epilepsy.

Animals↗

Divergent regulation of the human atrial natriuretic peptide gene by c-jun and c-fos.

Employing transient transfection analysis in neonatal rat cardiocytes, we have demonstrated that overexpression of c-jun results in a dose-dependent induction of the human atrial natriuretic peptide (hANP) gene promoter. Studies using a series of mutations in the hANP gene promoter identified a TRE-like, cis-acting regulatory sequence which conferred c-jun sensitivity. This same region was shown to interact with the c-jun/c-fos complex in an in vitro gel mobility shift assay. Selective mutation of this site suppressed basal activity of the hANP promoter and significantly reduced c-jun-dependent activation. Overexpression of c-fos had a biphasic effect on hANP gene promoter activity. At low levels, in concert with c-jun, it activated, while at higher levels it suppressed, transcription from the hANP gene promoter. This inhibition was both cell and promoter specific. hANP gene promoter sequences which mediate c-fos-dependent inhibition appear to be separable from those responsible for the induction. In addition, the protein domains on c-fos responsible for transcriptional activation and repression can be segregated topographically, with the inhibitory activity being localized to the carboxy-terminal domain. Thus, c-fos can activate or repress hANP gene expression through two separate functional domains that act on distinct regulatory elements in the hANP gene promoter. These data imply that the ANP gene may be a physiological target for c-fos- and c-jun-dependent activity in the heart and suggest a potential mechanism linking environmental stimuli to its expression.

Animals↗