SEARCH · Search PubMed

Results for “Fos”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 757 records · Page 42Linked to original sources

PubMed1989

fos-jun Conspiracy: implications for the cell.

Two nuclear oncoproteins, fos and jun (AP-1), cooperate in forming a very stable heterodimeric complex that binds to the AP-1 site with increased affinity. The 'leucine zipper' domain of both fos and jun is necessary for the formation of this heterodimer. Mutations of single residues within the leucine zipper domain had no effect on protein complex formation. However, mutagenesis of the first leucine of the heptad repeat in either fos or jun basic regions and alteration of the spacing between the basic and leucine zipper domains indicate that the basic region of fos has a crucial role in determining the DNA binding affinity of the transcriptional complex. Mutations of the basic amino acids in fos protein prevent binding to TPA (phorbol ester)-responsive element (TRE) in the presence of wild-type jun protein. Thus fos protein appears to be dominant in jun-fos binding to DNA, even though fos alone cannot bind to TRE. Mutants in the basic regions of fos and jun can be exploited as dominant-negative mutants to ablate their normal cellular function.

Amino Acid Sequence↗

PubMed1995

Conditioned fear-induced changes in behavior and in the expression of the immediate early gene c-fos: with and without diazepam pretreatment.

The synthesis of Fos, the protein product of the immediate early gene c-fos, was used to map metabolically some of the neural substrates of conditioned fear in the rat. Analysis of the behaviors emitted by the rats during the test session provided strong evidence that the conditioning procedure was effective. Exposure to the environment in which they had previously received footshock significantly increased the number of Fos-like immunoreactive neurons in nearly 50 brain regions, both cortical and subcortical. Among the structures showing the most dramatic increases in fear-induced c-fos expression were the cingulate, piriform, infralimbic, and retrosplenial cortices, the anterior olfactory nucleus, claustrum, endopiriform nucleus, nucleus accumbens shell, lateral septal nucleus, various amygdalar nuclei, paraventricular thalamic nucleus, ventral lateral geniculate nucleus, the ventromedial, lateral, and dorsal hypothalamic nuclei, the ventral tegmental area, and the supramammillary area. These data demonstrate that a relatively simple classical conditioning procedure activates a large number of widely dispersed cortical and subcortical structures. Some of the structures showing increased c-fos expression have important autonomic functions and may therefore have reflected centrally mediated changes in blood pressure and respiration produced by the anxiogenic stimuli. In a second experiment, the effects of pretreatment with the anxiolytic drug diazepam (2.5, 5.0, or 10 mg/kg) were evaluated. The benzodiazepine produced dose-related decreases in the frequency of crouching (freezing) elicited by the aversively conditioned contextual cues. Diazepam also produced dose-related decreases in conditioned stress-induced c-fos expression in all but one structure, the effects being statistically significant in 38 of 60 sampled structures. Diazepam dose dependently increased fear-induced c-fos expression in the central nucleus of the amygdala. There was considerable regional variability with respect to sensitivity to diazepam, the retrosplenial cortex and the supramammillary area being the only two structures to show decreases after the lowest dose of diazepam. In contrast, the entorhinal cortex, nucleus accumbens core, ventromedial and posterior hypothalamic nuclei, median raphe, and locus coeruleus were particularly resistant to diazepam, all failing to show statistically significant decreases in conditioned fear-induced c-fos expression even at the highest dose. The extent to which diazepam decreased conditioned stress-induced c-fos expression was unrelated to previous estimates of benzodiazepine receptor density in the sampled structures.

Animals↗

PubMed1994

Arachidonic acid increases c-fos and Egr-1 mRNA in 3T3 fibroblasts by formation of prostaglandin E2 and activation of protein kinase C.

Studying Swiss 3T3 fibroblasts, we report that arachidonic acid strongly stimulates mRNA levels of the growth-associated immediate early genes c-fos and Egr-1. Structurally related compounds like arachidonic acid methyl ester, arachidonyl alcohol, or eicosatetraynoic acid are ineffective, indicating a specific role of free unesterified arachidonic acid or an arachidonic acid metabolite in c-fos and Egr-1 mRNA accumulation. Blocking the conversion of arachidonic acid to prostaglandins by inhibiting cyclooxygenase abolishes arachidonic acid-induced accumulation of c-fos and Egr-1 mRNA. Inhibition of the lipoxygenase or cytochrome P-450 epoxygenase pathways has no significant effect on arachidonic acid-induced c-fos and Egr-1 mRNA levels, indicating that prostaglandin synthesis is necessary for the increase in c-fos and Egr-1 mRNA. Reversed phase high performance liquid chromatography revealed prostaglandin E2 (PGE2) as the major arachidonic acid metabolite in Swiss 3T3 fibroblasts. When added to the cells, PGE2 stimulates c-fos and Egr-1 mRNA levels to the same degree as arachidonic acid. Also, the inhibition of arachidonic acid-stimulated c-fos and Egr-1 mRNA accumulation by indomethacin is reversed by PGE2. Contrary to reports that PGE2 caused an increase in cAMP levels in Swiss 3T3 fibroblasts, we found that arachidonic acid and PGE2 only minimally increase cAMP levels as compared with untreated cells. In contrast, inhibition of protein kinase C by calphostin C and chelerythrine or down-regulation with phorbol 12-myristate 13-acetate drastically reduces PGE2 and arachidonic acid-induced c-fos and Egr-1 mRNA levels. These data indicate that arachidonic acid exerts its stimulatory effect on c-fos and Egr-1 mRNA via synthesis of PGE2 and subsequent activation of protein kinase C, probably through a PGE2 receptor coupled to phospholipase C.

3T3 Cells↗

PubMed1994

beta Adrenergic control of c-fos protooncogene expression in developing rat brain regions.

The protooncogene c-fos encodes a nuclear protein that acts as a powerful enhancer of gene transcription, and shares the same general patterns of reactivity to stimulation as ornithine decarboxylase, an essential enzyme in cell replication and differentiation; c-fos enhances expression of proteins whose genes possess the AP-1 consensus sequence, which include ornithine decarboxylase. In the current study, we examined the regulation of c-fos during early postnatal development of the rat central nervous system. Regional profiles of basal c-fos mRNA paralleled the ontogenetic profiles of cell replication and differentiation; in the earliest developing region (midbrain + brainstem) c-fos was low by birth and did not change over the first 2 postnatal weeks; in the forebrain, where replication and differentiation peak somewhat later, c-fos levels were higher during the first postnatal week than in the second; in the latest developing region (cerebellum), basal c-fos expression was low at birth and increased markedly during the second postnatal week, coincidentally with the increase in neuronal cell replication/differentiation. The resemblance of these patterns to those of ornithine decarboxylase, which is regulated in part by beta adrenergic input, led us to evaluate the potential role of beta receptors in the ontogenetic control of c-fos. In the forebrain of 2-day-old rats, intracisternal administration of isoproterenol, a beta adrenergic agonist, produced > 20-fold stimulation of c-fos within 10 min of drug administration. The induction was mediated through the beta receptor, as confirmed by studies with selective adrenergic blocking agents, and could be reproduced by administration of cAMP analogs.(ABSTRACT TRUNCATED AT 250 WORDS)

Age Factors↗

PubMed1993

Transcriptional activation and transformation by chimaeric Fos-estrogen receptor proteins: altered properties as a consequence of gene fusion.

We have generated a series of conditionally active Fos and FosB proteins by fusion with a C-terminal fragment of the human estrogen receptor (ER) which harbours the ligand binding site and the overlapping hormone-inducible transactivation domain TAF-2. The chimaeric Fos-ER proteins showed estrogen-inducible activation of TRE (TPA-responsive element)-directed transcription and hormone-dependent transformation of fibroblasts. These properties of the fusion proteins were independent of the transregulatory and transforming properties of their normal non-fused counterparts c-Fos, v-Fos, FosB-L and FosB-S. Thus c-Fos-ER and FosB-S-ER were strong transforming proteins in the presence of hormone, although c-Fos and FosB-S possess only marginal oncogenic properties. In addition, all fusion proteins showed increased transactivation in the presence of estrogen, again most noticeable in the case of c-Fos-ER and FosB-S-ER. The ER-fusion thus basically eliminated the differences in the transactivating potential seen among the various native Fos proteins. Our data therefore provide evidence: (i) that the hormone binding domain of the human estrogen receptor, apart from delivering hormonal control to a heterologous protein, can have profound effects on the activity of certain transcription factors, particularly on proteins with weak oncogenic and/or transregulatory potential, and (ii) that the transforming potential of c-Fos and FosB-S can be dramatically elevated by increasing their transactivating properties.

3T3 Cells↗

PubMed1993

Induction of c-fos mRNA by kindled seizures: complex relationship with neuronal burst firing.

Expression of the immediate-early gene c-fos has been advanced as a marker of neuronal activity in the adult nervous system. We sought to test the validity of c-fos mRNA expression as a marker of neuronal activity during seizures and to elucidate specific neurotransmitter receptors whose activation was necessary for seizure-evoked c-fos mRNA expression. We correlated c-fos mRNA expression, measured with in situ hybridization, with kindled seizure-induced firing of hippocampal dentate granule cells or substantia nigra pars compacta and pars reticulata neurons. We found that the occurrence of seizure-evoked synchronous action potentials during the seizure exhibited a perfect qualitative correlation with the presence of c-fos mRNA expression in the granule cells 30 min following the seizure (Fisher's exact test, p = 0.002). However, there was no quantitative correlation between the number of seizure-induced population action potentials and the magnitude of c-fos mRNA expression in the granule cells. In the substantia nigra, where neuronal populations have previously been demonstrated to exhibit synchronous firing during kindled seizures, no induction of c-fos mRNA was detected in either pars compacta or pars reticulata. Pretreatment with antagonists of the NMDA subtype of glutamate receptor selectively and markedly decreased seizure-induced c-fos mRNA expression in the dentate granule cells, despite increasing the number of granule cell population action potentials. These findings illustrate the complexity of the relationship between c-fos induction and neuronal burst firing during kindled seizures.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1995

The c Fos immunoreactivities in the developing and adult rat cerebella.

c Fos immunoreactivities were studied by immunohistochemistry in the developing and adult rat cerebella. c Fos immunoreactivities were observed in purkinje cells early in postnatal development (P26 d) and reached a peak by P40-P60 d, followed by a decline in the 3-month-old adult. The granule cells revealed c Fos immunoreactivities by P26 d but declined until P50 d. Then c Fos immunoreactivities increased in the granule layer by P50-P60 d and decreased again in the adult. The deep nuclei showed c Fos immunoreactivities by P40 d and persisted in the adult. In spite of the difference in the patterns of location in c Fos immunoreactivities from the early postnatal period to adulthood, no decrease in the amount of c Fos immunoreactivity was evident from immunoblotting studies. Thus, it is concluded that c Fos immunoreactivities change from development to adult, but this does not affect the total amount of c Fos protein expression in the cerebellum.

Age Factors↗

PubMed1996

Expression of c-fos and c-jun proteins and AP-1 binding activity during cell cycle progression of HL60 cells and phytohemagglutinin-stimulated lymphocytes.

The protein products of the c-fos (p62c-fos) and c-jun (p39c-jun) genes are members of the AP-1 transcription factor family and are thought to play important roles in the regulation of gene expression during the cell cycle. Most studies on the expression of these proteins in relation to the cell cycle have been performed at the mRNA level, and therefore do not give direct information about the presence of the proteins during the cell cycle. We have used Western blotting to investigate the presence of these proteins during the cell cycles of two different cellular systems: a continuously growing myeloid leukemic cell line, HL60, and normal cells stimulated into cycle, phyto- hemagglutinin (PHA)-stimulated normal human peripheral blood lymphocytes (PBL). The binding activity of transcription factor AP-1, which consists of dimers of Fos and Jun family proteins, was also studied using a gel shift assay. We found nuclear p62c-fos, p39c-jun, and AP-1 binding activity throughout the cell cycle both in HL60 cells and in PHA-stimulated PBL, and we postulate that these proteins are required throughout the cell cycle and not transiently in the G0 to G1 transition as previous mRNA studies have indicated. We demonstrated an uncoupling of AP-1 binding activity from p62c-fos, and p39c-jun AP-1 activity was expressed more strongly in the G1- and G2/M-phase enriched samples than in the S-phase enriched samples of HL60 cells, while levels of nuclear p62c-fos and p39c-jun were constant. Nuclei of unstimulated PBL from different donors expressed p62c-fos and p39c-jun, but AP-1 was not detected in the majority of samples. Following PHA stimulation of PBL, the increase in AP-1 activity was delayed with respect to the augmentation of p39c-jun expression. We also observed that cytoplasmic p62c-fos and p39c-jun were present in HL60 cells and PHA-stimulated PBL. However, no cytoplasmic p62c-fos was detected in unstimulated PBL, although in some cases cytoplasmic p39c-jun was detected, suggesting that subcellular compartmentalization of these proteins may occur under certain circumstances.

Base Sequence↗

PubMed1996

Apoptosis and delayed expression of c-jun and c-fos after gamma irradiation of Jurkat T cells.

The purpose of this study was to determine the role of radiation-induced expression of c-jun and c-fos in radiation-induced apoptosis of cells of the Jurkat T-cell line. Doses of 10-20 Gy caused a massive number of cells to undergo apoptosis within the first 24 h. This was accompanied by extensive increases in c-jun mRNA levels and moderate increases in c-fos levels, both occurring at the time of onset of internucleosomal DNA fragmentation. Increased c-jun and c-fos expression was maximum at 8 h after irradiation with a 10-fold increase in c-jun and a 2-fold increase in c-fos mRNA levels. In comparison, stimulation of the Jurkat cells with PMA resulted in rapid induction of c-jun and c-fos within 1 h. The late induction of c-jun and c-fos was not preceded by induction of tumor necrosis factor-alpha (TNF-alpha) or the bifunctional repair endonuclease and nuclear redox factor Ref-1; rather a slow decrease in Ref-1 mRNA levels was found over the first 24 h. Our results showed that radiation-induced c-jun and c-fos expression is a late response in Jurkat cells, and is most likely a secondary effect not necessary for radiation-induced apoptosis. Furthermore, apoptosis was induced by the RNA synthesis inhibitor actinomycin D, which does not induce c-jun or c-fos expression. This demonstrates that massive late induction of c-jun and c-fos is not a general requirement for apoptosis in Jurkat cells.

Apoptosis↗

PubMed1996

To what extent do spinal interactions between an alpha-2 adrenoceptor agonist and a mu opioid agonist influence noxiously evoked c-Fos expression in the rat? A pharmacological study.

Three hours after the intraplantar injection of carrageenin (6 mg/150 microliters of saline) Fos-like immunoreactivity (Fos-LI) was observed in both superficial and deep laminae of the dorsal horn segments L4 and L5 of the spinal cord. Systemic medetomidine, an alpha-2 adrenoceptor agonist (12.5, 25 or 75 micrograms/kg i.v.), dose-dependently reduced the number of superficial and deep Fos-LI neurons; 75 micrograms/kg produced a 66 +/- 4% and a 90 +/- 4% reduction of superficial and deep Fos-LI neurons, respectively, P < .0001 for both. In addition, systemic medetomidine dose-relatedly reduced the carrageenin-evoked paw and ankle edema; medetomidine 75 micrograms/kg resulted in a 70 +/- 3% reduction of paw edema and in a blockade of the development of ankle edema. The effects of medetomidine were blocked by systemic atipamezole (75 micrograms/kg, i.v.), which, when injected alone, had no effect on the number of Fos-LI neurons or the peripheral edema. Co-administration of a low dose of medetomidine (12.5 micrograms/kg i.v.) with an ineffective dose of morphine (1.5 micrograms/kg i.v.) strongly decreased the number of superficial and deep Fos-LI neurons (40 +/- 5%, P < .0001 and 62 +/- 11%, P < .0001 reduction as compared with control group) without altering the effects of medetomidine on the peripheral edema. Both atipamezole and a combined injection of atipamezole and naloxone blocked the effects of medetomidine plus morphine on both the total number of Fos-LI neurons (86 +/- 11% and 86 +/- 6% of control, respectively) and carrageenin inflammation (87 +/- 6%, P < .05 and 84 +/- 3%, P < .05 of control for the paw edema; 75 +/- 8%, P < .01 and 81 +/- 7%, P < .05 of control for the ankle edema, respectively). Naloxone alone blocked the effects of the co-administered agonists on the total number of Fos-Li neurons (91 +/- 6% of the control carrageenin group) without influencing the effect on the peripheral edema. Our results demonstrate, for the first time, that co-administration of alpha-2 adrenoceptor and mu opioid agonists substantially reduces inflammatory evoked expression of c-Fos, one of the long-term consequences of sustained nociceptive processing.

Adrenergic alpha-2 Receptor Agonists↗

PubMed1996

Competitive and non-competitive NMDA receptor antagonists induce c-Fos expression in the rat anterior, cingulate cortex.

In the present study we tried to find out whether the competitive NMDA receptor antagonist CGP 40116 was capable of inducing c-Fos expression in the rat cingulate cortex in a manner similar to that described previously for the non-competitive NMDA receptor antagonist MK-801. Induction of fast early genes by MK-801, especially in the rat cortex, has recently been linked with the neurotoxic effects of non-competitive NMDA receptor antagonists on cortical neurones, hence it was of interest to extend those studies to another class of NMDA receptors antagonists i.e., competitive one. It was found that CGP 40116 (2.5 and 5 mg/kg) induced c-Fos expression in the rat anterior cingulate cortex. That effect was dose-dependent and was shown as an increase in the number of cells expressing the c-Fos immunoreactivity. A qualitatively similar, but quantitatively stronger, effect was observed after administration of MK-801 (0.2 and 0.4 mg/kg), which also caused a dose-dependent increase in the number of c-Fos positive neurones. The described dose-dependent effects of CGP 40116 and MK-801 are shown as an increase in the number of c-Fos-positive neurones, but not as an increase in the optical density of c-Fos immunostaining in c-Fos positive neurones. In control, vehicle-injected rats, the constitutive c-Fos immunoreactivity was not found in the rat anterior cingulate cortex. The obtained data indicate that both competitive and non-competitive NMDA receptor antagonists may induce similar effects on the c-Fos immunoreactivity in the rat anterior cingulate cortex, and that their administration may lead to similar functional consequences resulting form activation of fast, early genes.

2-Amino-5-phosphonovalerate↗

PubMed1996

Temporal expression of c-fos mRNA following balloon injury in the rat common carotid artery.

OBJECTIVE: Restenosis is a common problem which limits the effectiveness of percutaneous transluminal coronary angioplasty (PTCA). The cellular mechanisms of restenosis appear to involve smooth muscle cell (SMC) migration to the neointima in response to mitogens and growth factors, resulting in proliferation and deposition of cells in the lumen of the vessel. An antibody directed against PDGF attenuates this response in the rat. Thus, signaling cascades induced by growth factors including PDGF may be important targets for therapeutic intervention. METHODS: Since a number of growth factors activate c-fos via the p21-ras signaling pathway, we examined c-fos expression in a time course experiment involving restenotic lesions in rat carotid arteries. Sections of arteries collected at 1, 3, 7, 14 and 28 days following balloon injury were hybridized using a fluorescein-labeled RNA probe to c-fos. Immunohistochemistry was performed with antibodies to proliferating cell nuclear antigen (PCNA) and alpha-smc actin to characterize cellular constituents of the neointima, and detect any correlation between fos expression and PCNA localization. RESULTS: Expression of c-fos was low at day 1. By day 3, the media and adventitia were positively stained. At days 7 and 14, most cells in the neointima were labeled. By day 28, c-fos was expressed mainly in scattered cells along the luminal surface. Control sections revealed little labeling and confirmed specific staining by the antisense strand, PCNA localization and c-fos expression were similar at days 1, 3, 7 and 28, but at day 14 c-fos was expressed throughout the lesion, with PCNA localized mainly along the luminal edge. The majority of the cells making up the neointima stained rather intensely for alpha-smc actin, identifying them as SMCs. CONCLUSIONS: Results of these experiments indicate that, while c-fos expression correlates with lesion formation, it may be associated with a cellular process distinct from proliferation in this model.

Animals↗

PubMed1999

Suppression of postischemic hippocampal nerve growth factor expression by a c-fos antisense oligodeoxynucleotide.

We examined the uptake and distribution of an antisense phosphorothioated oligodeoxynucleotide (s-ODN) to c-fos, rncfosr115, infused into the left cerebral ventricle of male Long-Evans rats and the effect of this s-ODN on subsequent Fos, NGF, neurotrophin-3 (NT-3), and actin expression. To establish the uptake and turnover of s-ODN in the brain, we studied the copurification of the immunoreactivity of biotin with biotinylated s-ODN that was recovered from different regions of the brain. A time-dependent diffusion and the localization of s-ODN were further demonstrated by labeling the 3'-OH terminus of s-ODN in situ with digoxigenin-dUTP using terminal transferase and detection using anti-digoxigenin IgG-FITC. Cellular uptake of the s-ODN was evident in both the hippocampal and cortical regions, consistent with a gradient originating at the ventricular surface. Degradation of the s-ODN was observed beginning 48 hr after delivery. The effectiveness of c-fos antisense s-ODN was demonstrated by its suppression of postischemic Fos expression, which was accompanied by an inhibition of ischemia-induced NGF mRNA expression in the dentate gyrus. Infusion of saline, the sense s-ODN, or a mismatch antisense s-ODN did not suppress Fos expression. That this effect of c-fos antisense s-ODN was specific to NGF was demonstrated by its lack of effect on the postischemic expression of the NT-3 and beta-actin genes. Our results demonstrate that c-fos antisense s-ODN blocks selected downstream events and support the contention that postischemic Fos regulates the subsequent expression of the NGF gene and that Fos expression may have a functional component in neuroregeneration after focal cerebral ischemia-reperfusion.

Actins↗

PubMedDate not supplied

Degradation of cellular and viral Fos proteins.

c-Fos proto-oncoprotein is a short-lived transcription factor with oncogenic potential. We have shown that it is massively degraded by the proteasome in vivo under various experimental conditions. Other proteolytic systems including lysosomes and calpains, might, however, also marginally operate on it. Although there is evidence that c-Fos can be ubiquitinylated in vitro, the unambiguous demonstration that ubiquitinylation is necessary for its addressing to the proteasome in vivo is still lacking. c-Jun, one of the main dimerization partners of c-Fos within the AP-1 transcription complex, is also an unstable protein. Its degradation is clearly proteasome- and ubiquitin-dependent in vivo. Interestingly, several lines of evidence indicate that the addressing of c-Fos and c-Jun to the proteasome is, at least in part, governed by different mechanisms. c-Fos has been transduced by two murine osteosarcomatogenic retroviruses under mutated forms which are more stable and more oncogenic. The stabilization is not simply accounted for by simple deletion of c-Fos main destabilizer but, rather, by a complex balance between opposing destabilizing and stabilizing mutations. Though mutations in viral Fos proteins confer full resistance to proteasomal degradation, stabilization is limited because mutations also entail sensitivity to an unidentified proteolytic system. This observation is consistent with the idea that Fos-expressing viruses have evolved to ensure control protein levels to avoid high protein accumulation-linked apoptosis. In conclusion, the unveiling of the complex mechanism network responsible for the degradation of AP-1 family members is still at its beginning and a number of issues regarding the regulation of this process and the addressing to the proteasome are still unresolved.

Animals↗

PubMed1998

Apoptosis during castration-induced regression of the prostate is Fos dependent.

Apoptotic cell death was shown to be accompanied or preceded by an elevated expression of the c-fos protooncogene and DNA binding activity of transcription factor AP-1. We used Fos-deficient mice to study the role of c-Fos during programmed cell death in the prostate. In normal mice apoptosis is induced in the prostate within 2-4 days after castration. Histological features of reduced secretory activity and morphological signs of programmed cell death become obvious. No apparent decrease in secretory activity and no epithelial cell death were observed in Fos-deficient animals after castration. Fragmentation of nuclear DNA was measured by in situ terminal transferase reaction. DNA fragmentation was observed in the prostate epithelium of control mice after castration whereas no similar fragmentation was found in Fos-deficient animals. After castration an AP-1 complex accumulated in the prostate of Fos deficient mice which mainly consists of FosB, Fra-2 and JunD whereas in control animals the AP-1 complex in addition contained c-Fos. Our data strongly suggest that c-Fos is required for programmed cell death of prostate epithelial cells.

Animals↗

PubMed1999

The repertoire of fos and jun proteins expressed during the G1 phase of the cell cycle is determined by the duration of mitogen-activated protein kinase activation.

In Rat-1 fibroblasts nonmitogenic doses of lysophosphatidic acid (LPA) stimulate a transient activation of mitogen-activated protein kinase (MAPK), whereas mitogenic doses elicit a sustained response. This sustained phase of MAPK activation regulates cell fate decisions such as proliferation or differentiation, presumably by inducing a program of gene expression which is not observed in response to transient MAPK activation. We have examined the expression of members of the AP-1 transcription factor complex in response to stimulation with different doses of LPA. c-Fos, c-Jun, and JunB are induced rapidly in response to LPA stimulation, whereas Fra-1 and Fra-2 are induced after a significant lag. The expression of c-Fos is transient, whereas the expression of c-Jun, JunB, Fra-1, and Fra-2 is sustained. The early expression of c-Fos can be reconstituted with nonmitogenic doses of LPA, but the response is transient compared to that observed with mitogenic doses. In contrast, expression of Fra-1, Fra-2, and JunB and optimal expression of c-Jun are observed only with doses of LPA which induce sustained MAPK activation and DNA synthesis. LPA-stimulated expression of c-Fos, Fra-1, Fra-2, c-Jun, and JunB is inhibited by the MEK1 inhibitor PD098059, indicating that the Raf-MEK-MAPK cascade is required for their expression. In cells expressing a conditionally active form of Raf-1 (DeltaRaf-1:ER), we observed that selective, sustained activation of Raf-MEK-MAPK was sufficient to induce expression of Fra-1, Fra-2, and JunB but, interestingly, induced little or no c-Fos or c-Jun. The induction of c-Fos observed in response to LPA was strongly inhibited by buffering the intracellular [Ca2+]. Moreover, although Raf activation or calcium ionophores induced little c-Fos expression, we observed a synergistic induction in response to the combination of DeltaRaf-1:ER and ionomycin. These results suggest that kinetically distinct phases of MAPK activation serve to regulate the expression of distinct AP-1 components such that sustained MAPK activation is required for the induced expression of Fra-1, Fra-2, c-Jun, and JunB. However, in contrast to the case for Fra-1, Fra-2, and JunB, activation of the MAPK cascade alone is not sufficient to induce c-Fos expression, which rather requires cooperation with other signals such as Ca2+ mobilization. Finally, the identification of the Fra-1, Fra-2, c-Jun, and JunB genes as genes which are selectively regulated by sustained MAPK activation or in response to activated Raf suggests that they are candidates to mediate certain of the effects of Ras proteins in oncogenic transformation.

3T3 Cells↗

PubMed2000

Fos family members: regulation, structure and role in oncogenic transformation.

The members of the Fos protein family might be subdivided in two groups, according to their ability to transform rodent fibroblasts, transforming (c-Fos and FosB) and non-transforming (Fra-1 and Fra-2) proteins. Members of these groups are differently activated in response to external stimuli and possess different structural features. Importantly, whilst c-Fos and FosB contain multiple transactivation modules in their N- and C-terminal parts, transactivation domains are absent in the non-transforming Fos proteins. As a result, Fra-1 and Fra-2 though efficiently form dimers with the Jun proteins, are weak transcriptional activators and inhibit the c-Fos-dependent activation in transient transfection assay. The numerous experiments performed with the different Fos mutant proteins with impaired transforming ability, as well as with chimeric proteins revealed the importance of the transactivation function for transformation. Fra-1 and Fra-2 proteins albeit ineffectively triggering oncogenic transformation, are abundant in ras- and src-transformed murine and chicken fibroblasts, in neoplastic thyroid cells and in highly malignant mouse adenocarcinoma cells, which underwent mesenchymal transition. The abundance of the non-transforming Fos proteins in these systems might be mediated by a positive AP-l-dependent feedback mechanism, as well as by wnt signals. Furthermore, the manipulation of the Fra-1 expression level in thyroid and mammary tumor cells modulated the transcription of several tumor progression markers and affected cell morphology and invasiveness. These recent data demonstrate a novel function of non-transforming Fos proteins in the maintenance and progression of the transformed state. Interestingly, this function is independent of the documented invalidity of the Fra-1 and Fra-2 proteins as transcriptional activators in rodent fibroblasts.

Animals↗

PubMed2006

Jun and Fos family protein expression in human breast cancer: correlation of protein expression and clinicopathological parameters.

OBJECTIVES: The activator protein-1 (AP-1) is a dimeric transcription factor formed by members of the Jun and Fos protein family. AP-1 plays a role in a variety of physiological functions including cell proliferation and differentiation, although both c-Jun and c-Fos have also been implicated in oncogenic transformation and tumor progression. To further elucidate the role of AP-1 in breast cancer, we have investigated the expression of the AP-1 proteins c-Jun, JunB, JunD, phosphorylated c-Jun, c-Fos, Fral, Fra2 and the tumor supressor protein p53. METHODS: Protein expression was evaluated on a breast cancer tissue microarray with 58 lymph node positive or negative breast cancer specimens, 29 corresponding lymph node metastases, and 11 tissue samples from surrounding tumor-free tissue, each cored as triplicate. Jun and Fos protein family expression was evaluated by immunohistochemistry and was correlated with clinicopathological parameters. RESULTS: High expression levels were observed for c-Jun, JunD, c-Fos and Fra2, whereas JunB and Fral exhibited lower staining. c-Jun protein expression was correlated to Fral staining (p = 0.007, Kendall's Tau) and Fral was further associated with c-Fos (p < 0.001), JunD (p = 0.001) and Fra2 (p = 0.011) expression. JunD expression correlated with c-Fos (p < 0.001), JunB (p = 0.035) and c-Jun (p = 0.05). Activated c-Jun correlated with c-Fos expression (p = 0.041). JunB was negatively correlated to tumor stage, (p = 0.093, corr coeff. = -0.293, Spearman's correlation) but was significantly increased in nodal negative tumors (p = 0.004, Mann Whitney test). In addition, increased Fral expression showed a trend towards an increased overall survival (p = 0.077, RR = 0.534, Cox regression). CONCLUSION: Our results suggest an important role for JunB and Fral in the biological behavior of malignant breast tumors.

Biomarkers, Tumor↗