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PubMed1984

Differential expression of c-fos in hematopoietic cells: correlation with differentiation of monomyelocytic cells in vitro.

Among various neonatal mouse tissues, elevated levels of c-fos transcripts have been detected in crude preparations of bone. Here, we show that c-fos expression originates in the bone marrow, and to a lesser extent in adherent cells (macrophages). High levels of c-fos expression were also detected in primary cultures of differentiated bone marrow-derived macrophages, but not in cell lines resembling immature hematopoietic cells. However, when the human promyelocytic cell line HL60 was induced in vitro to differentiate into macrophages, c-fos expression was readily detectable. These findings suggest that c-fos expression in mononuclear phagocytic cells is restricted to late stages of differentiation. This pattern of c-fos expression is in marked contrast to those of the c-myb and c-myc genes which are transcriptionally active predominantly in precursor cells. In the amnion, where c-fos expression increases to high levels at late stages of gestation, synthesis of c-fos protein occurs in cells that do not resemble macrophages. It thus appears that c-fos expression in several distinct cell types is correlated with differentiation processes.

Amnion↗

PubMed1986

Wounding a fibroblast monolayer results in the rapid induction of the c-fos proto-oncogene.

The c-fos gene has previously been shown to be transiently induced within minutes after the stimulation of mouse fibroblasts with growth factors. Induction of c-fos was observed specifically with competence factors (e.g., platelet-derived growth factor), not with progression factors (e.g., platelet-poor plasma), suggesting a role for c-fos in conferring competence on fibroblasts. To test this hypothesis we have analyzed c-fos expression in NIH 3T3 cells that were made competent in a different way, namely by wounding a confluent monolayer of cells. Using antibodies raised against either a synthetic fos peptide or a beta-galactosidase--fos fusion protein, we show in this study that in the majority of cells lining the wound c-fos protein is rapidly and transiently induced to high levels. No induction is observed in cells at a distance from the wound greater than approximately 5 cell layers. Induction is equally efficient in both serum-containing and serum-free medium, and is similar in cells that were deprived of fetal calf serum for 40 h prior to making the wound. Our observations support the hypothesis that c-fos may be involved in inducing the 'competent state' in fibroblasts and suggests an early role for c-fos in wound healing and tissue regeneration.

Animals↗

PubMed1987

Bombesin induction of c-fos and c-myc proto-oncogenes in Swiss 3T3 cells: significance for the mitogenic response.

Bombesin is a potent mitogen for Swiss 3T3 cells and acts synergistically with insulin and other growth factors. We show here that addition of bombesin to quiescent Swiss 3T3 cells causes a striking increase in the levels of c-fos and c-myc mRNAs. Enhanced expression of c-fos (122 +/- 14-fold) occurred within minutes of peptide addition followed by increased expression of c-myc (82 +/- 16-fold). The concentrations of peptide required for half-maximal increase in the levels of c-fos and c-myc mRNAs were 1.0 and 0.9 nM, respectively. The peptide [D-Arg1, D-Pro2, D-Trp7,9, Leu11] substance P which inhibits the binding of bombesin to its receptor and bombesin-stimulated DNA synthesis in Swiss 3T3 cells blocked the increase in c-fos and c-myc mRNA levels promoted by bombesin. Down-regulation of protein kinase C by long-term exposure to phorbol esters prevented c-fos and c-myc induction by bombesin. This and other results indicate that the induction of these proto-oncogenes by bombesin could be mediated by the coordinated effects of protein kinase C activation and Ca2+ mobilization. The marked synergistic effect between bombesin and insulin was used to assess whether the increase in the induction of c-fos and c-myc is an obligatory event in cell activation. In the presence of insulin, bombesin stimulated DNA synthesis at subnanomolar concentrations but had only a small effect on c-fos and c-myc mRNA levels. This apparent dissociation of mitogenesis from proto-oncogene induction was even more dramatic in 3T3 cells with down-regulated protein kinase C. In these cells bombesin stimulated DNA synthesis in the presence of insulin but failed to enhance c-fos and c-myc mRNA levels at comparable concentrations. Thus, the induction of c-fos and c-myc may be a necessary step in the mitogenic response initiated by ligands that act through activation of protein kinase C but the expression of these proto-oncogenes may not be an obligatory event in the stimulation of mitogenesis in 3T3 cells by mitogens that utilise other signalling pathways.

Animals↗

PubMed1986

The fos gene product undergoes extensive post-translational modification in eukaryotic but not in prokaryotic cells.

To investigate the properties of the fos oncogene, we have constructed bacterial and yeast vectors which express the entire fos-coded protein (Fos) and two C-terminal deletion products. In Escherichia coli, Fos proteins were expressed from the phage lambda pL promotor under the control of the temperature-sensitive lambda repressor. In vitro transcription/translation studies indicate that these vectors produce Fos proteins of the expected sizes. However, in vivo, Fos protein accumulation is observed only in hosts with the Lon- phenotype. In Saccharomyces cerevisiae, the fos gene was expressed from the PHO5 promoter which is induced under low-phosphate conditions. In contrast to the situation in E. coli, in which the heterologous proteins appeared as single major products when subjected to sodium dodecyl sulfate - polyacrylamide gel electrophoresis, the Fos proteins in S. cerevisiae displayed extensive Mr heterogeneity. Pulse-chase analyses indicated that this heterogeneity was a consequence of extensive post-translational modification. These modifications occurred to an equivalent extent on the products coded by the fos gene with C-terminal deletions and thus appear not to be controlled by the missing domain.

Animals↗

PubMed2002

Contribution of buried lysine residues to the oligomerization specificity and stability of the fos coiled coil.

Coiled coils comprise two or more helices characterized by a heptad repeat of amino acids denoted a through g. The buried a and d positions are usually occupied by hydrophobic residues. Fos dimerizes via a coiled coil (leucine zipper) with Jun family members to form the transcription factor AP-1. Fos homodimers are relatively unstable due to unfavorable interhelical electrostatic interactions within the Fos two-stranded coiled coil. The Fos coiled coil contains two polar position a Lys residues (Lys 16 and Lys 30 of Fos-p1, a peptide corresponding to the coiled-coil domain of v-Fos). Lys 16 and Lys 30 of Fos-p1 were replaced individually and together with the unnatural amino acid norleucine (2-aminohexanoic acid), which corresponds to a deletion of the Lys epsilon-amino group. The midpoint of thermal denaturation (T(m)) of Fos-p1 (10 microM) is 30 degrees C at pH 7. The Lys 16 --> Nle variant forms predominantly homodimers that are relatively unstable (T(m) = 46 degrees C). The Lys 30 --> Nle variant forms a stable homotetramer (T(m) = 60 degrees C). The Lys 16/Lys 30 --> Nle variant forms a very stable homotetramer (T(m) = 80 degrees C). The results show that (i) the effects of buried position a Lys residues on coiled-coil oligomerization are context dependent and (ii) electrostatic destabilization of the Fos homodimer can be mitigated by an oligomerization switch moderated by a single buried Lys residue.

Amino Acid Sequence↗

PubMed1986

Insulin and growth factor effects on c-fos expression in normal and protein kinase C-deficient 3T3-L1 fibroblasts and adipocytes.

We investigated the expression of the protooncogene c-fos in 3T3-L1 fibroblasts and adipocytes in response to a variety of growth-promoting agents in normal cells and in cells preincubated with phorbol esters to deplete them of protein kinase C. There was a rapid accumulation of c-fos mRNA in fibroblasts and adipocytes treated with phorbol 12-myristate 13-acetate, platelet-derived growth factor, fibroblast growth factor, fetal calf serum, bombesin, and insulin, especially in the adipocytes. Phorbol 12-myristate 13-acetate pretreatment abolished the increase in c-fos mRNA due to additional phorbol 12-myristate 13-acetate treatment and decreased but did not eliminate the ability of platelet-derived growth factor, fibroblast growth factor, fetal calf serum, bombesin, and insulin to stimulate c-fos mRNA. These data suggested that c-fos mRNA could be induced in serum-deprived 3T3-L1 fibroblasts and adipocytes by at least two separate pathways, one involving protein kinase C and the other independent of protein kinase C. In the very insulin-sensitive 3T3-L1 adipocytes, insulin rapidly and transiently increased c-fos expression (c-fos mRNA appeared by 15 min and disappeared after 60 min) via interaction with its own cellular receptor, rather than by interacting with receptors for one of the insulin-like growth factors. Cycloheximide treatment in combination with insulin or phorbol 12-myristate 13-acetate resulted in superinduction of c-fos mRNA. We conclude that insulin can rapidly stimulate c-fos mRNA accumulation in 3T3-L1 adipocytes and that part of the growth factor-stimulated increase in this mRNA that occurs in protein kinase C-deficient cells may be due to activation of a pathway similar or identical to that activated by insulin.

Adipose Tissue↗

PubMed1991

Nerve Growth Factor is Required for Induction of c-Fos Immunoreactivity by Serum, Depolarization, Cyclic AMP or Trauma in Cultured Rat Sympathetic Neurons.

Nerve growth factor (NGF) induces transient Fos-immunoreactivity (Fos-IR) independently of any other factor, both in newly isolated rat sympathetic neurons and in established cultures after NGF deprivation. The same proportion of neurons that express Fos-IR in response to NGF also survive. In addition to direct stimulation of Fos-IR expression, the presence or recent exposure to NGF is required to obtain Fos-IR expression by other stimuli. In newly isolated neurons no Fos-IR is detected in response to stimulation by serum alone and a response to depolarization or cyclic AMP is obtained only if neurons are stimulated within a short period after ganglion excision. In established cultures none of these stimuli, nor the trauma of cutting neurites or spiking cell bodies with a microinjection needle induce Fos-IR unless NGF is present or had been removed for <8 - 16 h. The lack of response is not due to a general decrease in the rate of protein or RNA synthesis. These findings show that in regenerating sympathetic neurons NGF induces c-Fos and suggest that NGF may activate a master trigger that is required for c-Fos expression to be induced by other stimuli.

Journal Article↗

PubMed1987

The chicken c-fos gene: cloning and nucleotide sequence analysis.

Using a DNA probe from an avian transforming virus, NK24, that contains the fos gene and that was newly isolated and characterized (M. Nishizawa, N. Goto, and S. Kawai, J. Virol. 61:3733-3740, 1987), we cloned and sequenced the chicken c-fos gene. Results showed that this gene, like the mouse or human c-fos gene, contains four exons encoding a predicted gene product of 367 amino acids which is about 79% homologous to p55c-fos (mouse), excluding several small insertions or gaps. The predicted gene product, however, contains two nonhomologous regions, as suggested by sequence analysis of the NK24 genome. About half the identical amino acids of these gene products are encoded by different codons, and the guanine-plus-cytosine content in the third letter of each codon used in the entire chicken c-fos coding region is high (93%). The 5'-flanking region of the TATA box contains a sequence that is homologous to a putative transcriptional regulatory sequence in the mouse or human c-fos gene. The 3'-noncoding region of chicken c-fos is strikingly homologous to that of mouse or human c-fos and covers a 67-base-pair adenine-plus-thymine-rich stretch which was previously reported to be essential for an inhibitory effect on the expression of the mouse c-fos gene.

Amino Acid Sequence↗

PubMed1988

Determinants that contribute to cytoplasmic stability of human c-fos and beta-globin mRNAs are located at several sites in each mRNA.

We have analyzed the contributions to cytoplasmic stability in an mRNA species with a very short half-life (human c-fos) and an mRNA species with a very long half-life (human beta-globin). When the human c-fos promoter was used to drive the expression of human c-fos, beta-globin, and chimeric DNAs between c-fos and beta-globin in transfected cells, a pulse of mRNA synthesis was obtained following induction of transcription by refeeding quiescent cells with medium containing 15% calf serum. The mRNA half-life was determined by using Northern (RNA) blot analysis of mRNAs prepared at various times following the pulse of transcription. Under these conditions human c-fos mRNA exhibited a half-life of 6.6 min and human beta-globin mRNA exhibited a half-life of 17.5 h. Replacement of the 3' end of the c-fos mRNA with the 3' end of the beta-globin mRNA increased the half-life of the resultant RNA from 6.6 to 34 min. The reciprocal chimera had a half-life of 34.6 min compared with the 17.5-h half-life of beta-globin mRNA. These results suggest that sequences which make a major contribution to mRNA stability reside in the 3' end of either or both molecules. A chimera in which the 5' untranslated region of globin was replaced by part of the 5' untranslated region of fos led to destabilization of the encoded mRNA. This construct produced an mRNA with a half-life of 6.8 h instead of the 17.5-h half-life of globin. This result suggests that additional determinants of stability reside in the 5' end of these mRNA molecules. Substitution of part of the 5' untranslated region of fos by the 5' untranslated region of beta-globin yielded an mRNA with stability similar to fos mRNA. These results suggest that interactions among sequences within each mRNA contribute to the stability of the respective molecules.

Animals↗

PubMed1987

Growth hormone-releasing factor induces c-fos expression in cultured primary pituitary cells.

GH-releasing factor (GRF) and somatostatin regulates the secretion and biosynthesis of GH as well as the proliferation of GH-producing cells. In order to further characterize the mitogenic effect of GRF, we studied the expression of the proto-oncogene c-fos in primary pituitary cells. Maximal induction of c-fos mRNA was observed 20-60 min after stimulation with 5 nM GRF, returning to basal levels after 2 h. Somatostatin-14 (5 nM) partially inhibited the GRF induced c-fos expression. Forskolin and phorbol 12, 13 dibutyrate induced c-fos gene in cultured primary pituitary cells with similar kinetics. Transcription of the fos gene was accompanied by biosynthesis of the fos protein. Indirect immunofluorescence using a fos specific antibody, showed exclusive nuclear localization of the fos protein. These data demonstrate that GRF and somatostatin, in addition to regulating GH secretion and somatotroph proliferation, can also regulate the expression of c-fos proto-oncogene in primary somatotrophs.

Animals↗

PubMed1999

c-Fos expression in the myenteric plexus, spinal cord and brainstem following injection of formalin in the rat colonic wall.

Fos expression induced by injection of dilute formalin (50 microl, 5% in physiological saline) into the colonic wall was examined in the myenteric plexus, lumbosacral spinal cord and brainstem of the rat. The aims of this study were (i) to determine whether neurons in these regions express Fos in response to the injection of formalin into the colon and (ii) to examine whether administration of an alpha 2 adrenoceptor agonist modulates Fos expression. Tissues were removed 2 h after the injection of saline or formalin. Saline injected in the colon induced Fos in enteric glia in the myenteric plexus. The number of Fos immunoreactive nuclei significantly increased in both myenteric neurons and enteric glia after the injection of formalin. Similarly, Fos immunoreactive neuronal nuclei were significantly increased in the spinal cord, area postrema and nucleus of the solitary tract after the injection of formalin. Pretreatment of rats with the alpha 2 adrenoceptor agonist xylazine (2, 4 and 8 mg/kg) 15 min before the injection of formalin, dose-dependently reduced the number of Fos immunoreactive neuronal and glial nuclei in the myenteric plexus, and neuronal nuclei in the spinal cord and brainstem. Simultaneous administration of xylazine (8 mg/kg) and the alpha 2 adrenoceptor antagonist yohimbine (1 mg/kg) reversed the effects of xylazine in the spinal cord and brainstem, but not in the myenteric plexus. These data show that injection of formalin in the colonic wall results in Fos expression in myenteric neurons and enteric glia, and neurons in the spinal cord and brainstem. This may be due to the direct chemical stimulation of the innervation of the colon and/or the subsequent acute colitis. The observed neuronal Fos expression can be modulated by an alpha 2 adrenoceptor agonist through noradrenergic pathways and/or reduction of the excitability of the enteric neural circuitry.

Journal Article↗

PubMed1990

Studies on the role of c-fos in TSH-stimulated thyroid cell proliferation.

TSH stimulates proliferation of FRTL5 rat thyroid cells, and also increases c-fos mRNA levels in these cells. We therefore investigated the role of c-fos in TSH-mediated FRTL5 cell proliferation. FRTL5 cells were stably transfected with plasmid constructs that transcribe, under the control of the dexamethasone-inducible MMTV promoter, a 5'-fragment (84 nucleotides) of c-fos mRNA, either in the sense or in the antisense orientation. Four c-fos antisense clones (A1, A2, A3, A4), one sense clone (S2), and wild-type (untransfected) FRTL5 cells were studied. Southern blot analysis indicated similar levels of transgenome in all transfected cell lines. Antisense clone A3 exhibited the greatest dexamethasone-induced growth inhibition, two times (59% vs. 30%) greater than that in control, sense c-fos-transfected or wild-type FRTL5, cells. Consistent with the degree of growth inhibition, northern blot analysis revealed that c-fos antisense clone A3 expressed the highest levels of c-fos antisense transcript. However, we did not observe dexamethasone induction of the antisense c-fos-beta globin hybrid mRNA in any clone, including clone A3. Taken together, our results provide circumstantial evidence that c-fos, at least in part, may play a role in TSH-mediated thyroid cell growth.

Animals↗

PubMed1988

c-sis but not c-fos gene expression is lineage specific in human myeloid cells.

Expression of both the c-fos and c-sis protooncogenes during myeloid differentiation has been detected in cells of the monocytic lineage. Since an increase in c-fos transcripts was not detected during dimethylsulfoxide induced HL-60 granulocytic differentiation, it was suggested that within the myeloid series c-fos gene expression might be lineage specific. In the present study, we have determined whether expression of the c-fos and c-sis genes is indeed specific for the monocytic pathway or rather common to both the granulocyte and monocyte pathways. C-fos and c-sis gene expression was analyzed in freshly isolated human granulocytes and monocytes, in human HL-60 promyelocytic leukemia cells induced to differentiate along the granulocytic or monocytic pathway, in myeloblasts from five patients with the M1 or M2 subtype of acute myeloblastic leukemia (AML) and in blasts from six patients with M4 myelomonocytic leukemia. The level of c-fos mRNA was fifteen times higher in granulocytes as compared with monocytes. An increase in c-fos expression was also found in HL-60 cells differentiated along the granulocytic pathway after exposure to hypoxanthine, hexamethylene bisacetamide, and the combination of retinoic acid and dibutyryl adenosine 3'5' cyclic monophosphate. Three of 5 M1 and M2 leukemic myeloblast preparations depleted of lymphoid and monocytic cells and all six M4 leukemic cells expressed c-fos transcripts. In contrast, c-sis gene transcripts were detectable in monocytes and during drug induced monocytic differentiation of the HL-60 cells but not in granulocytes during granulocytic differentiation of the HL-60 cells or in AML samples. Thus, in the myeloid series, c-sis gene expression is lineage specific while expression of the c-fos gene is found in both lineages and may be related to metabolic pathways common to both granulocytes and monocytes.

Actins↗

PubMed1986

Proto-oncogene fos: an inducible gene.

Proto-oncogene fos is a multifaceted gene, which is expressed during cell growth, cell differentiation, and development. The viral homologue, v-fos, was identified as the resident transforming gene of FBJ-murine osteosarcoma virus which induces bone tumors in mice. Due to an in-fram deletion during the biogenesis of the v-fos gene, the products of viral and cellular fos proteins differ at their C-termini. Despite different C-termini, both fas proteins are nuclear in their location, and can transform fibroblasts in vitro. However, transformation by c-fos gene requires removal of a 67 base pair sequence from the 3' non-coding domain. Proto-oncogene fos is a highly inducible gene in response to a variety of growth factors and differentiation-specific inducers. The transcriptional enhancer and the inducible element of the fos gene have been mapped along with sequences in the 3' non-coding domain which may influence the stability of the c-fos transcripts. The c-fos gene transcription is regulated by positively and negatively acting cellular factors.

Gene Expression Regulation↗

PubMed1996

Age-associated changes in basal c-fos transcription factor binding activity in rat hearts.

The early response proto-oncogene c-fos is expressed at very low levels in the mammalian heart at baseline. To further investigate the mechanism of altered c-fos expression with age, we studied in the basal state the binding of five transcription proteins to their cognate sites in the c-fos promoter/enhancer region, in adult and old F344 rats. Our results show a reduced binding of E2F and AP1 proteins to the c-fos promoter in aging hearts. The major calcium/cyclic AMP response element (CRE) and SP1 binding was unchanged. The only increase seen with age was in the serum response element (SRE) binding proteins. SRE is the point of convergence of different signal transduction pathways (via MAP kinases and the Rho family of GTPases) at the c-fos promoter. Increased SRE binding may reflect a compensation for a decreased binding of other transcription proteins to the c-fos promoter, alteration in the phosphorylation status of SRF, or a change in the ternary complex factors Elk 1 or SAP 1. Other possibilities include defects in the signal transduction pathways with aging, which combine to produce an overall negative balance in the function of the c-fos promoter despite the increased SRE binding activity. Both in vitro and in vivo experiments have shown decreased c-fos expression with age. This may be due partly to alterations in the basal levels of transcription factor binding.

Aging↗

PubMed2000

Luteinizing hormone-releasing hormone agonist triptorelin and antagonist cetrorelix inhibit EGF-induced c-fos expression in human gynecological cancers.

OBJECTIVES: Spontaneous and epidermal growth-factor-induced proliferation of human gynecological cancer cell lines is dose- and time-dependently reduced by treatment with the luteinizing hormone-releasing hormone (LHRH) agonist triptorelin and antagonist Cetrorelix. This antiproliferative activity is probably directly mediated through the LHRH receptors expressed by the tumor cells interacting with growth-factor-dependent mitogenic signal transduction. We have examined whether epidermal growth-factor (EGF)-induced expression of the early response gene c-fos is reduced by LHRH analogs. METHODS: Human endometrial (Ishikawa, Hec-1A), ovarian (EFO-21, EFO-27, SK-OV-3), and breast cancer cell lines (MCF-7) were rendered quiescent by incubation (72 h) in the absence of fetal calf serum and phenol red. This was followed by a 15-min incubation in the absence or presence of the LHRH agonist triptorelin (100 nM) or the antagonist Cetrorelix (100 nM) before the cells were stimulated for 10 min with EGF (100 nM). C-fos mRNA expression was determined by semi-quantitative RT-PCR using a synthetic DNA fragment as internal standard. C-Fos protein synthesis was determined by SDS-PAGE and semi-quantitative Western blotting. RESULTS: In cells derived from endometrial and ovarian cancer, maximal c-fos mRNA expression (seven- to ninefold over basal level) was obtained 30 min after EGF stimulation. In the breast cancer cell line MCF-7 this effect was obtained 60 min after EGF treatment. In all of the lines expressing LHRH receptor, EGF-induced c-fos mRNA expression as well as c-Fos protein synthesis was dose-dependently reduced by treatment with LHRH agonists and antagonists. At 100 nM concentrations of the LHRH analogs, c-fos expression was reduced to baseline levels. No effect of LHRH analogs on EGF-induced c-fos expression was observed in the ovarian cancer cell line SK-OV-3, which does not express the LHRH receptor. CONCLUSIONS: These results suggest that the binding of LHRH agonists and antagonists to their receptors inhibits the mitogenic signal transduction pathway of the EGF receptor in endometrial, ovarian, and breast cancer cell lines. The coupling of both signal transduction systems mediates the antiproliferative effect of LHRH analogs.

Antineoplastic Agents, Hormonal↗

PubMed1991

Intrastriatal grafts derived from fetal striatal primordia. III. Induction of modular patterns of fos-like immunoreactivity by cocaine.

Cocaine, a catecholamine agonist, has been shown to produce a transient induction of the immediate-early gene c-fos and its protein product Fos in the striatum of normal rats. In the present study we report that the expression of Fos can be induced by cocaine challenge in intrastriatal grafts derived from cell suspensions of embryonic striatal primordia. Fos-like immunoreactivity in the nuclei of grafted neurons was detected 2 hr after the injection of 50 mg/kg cocaine into the host rats. Neurons with Fos-immunoreactive nuclei tended to form clusters in the striatal grafts. The Fos-rich clusters were aligned with acetylcholinesterase (AChE)-rich and tyrosine hydroxylase (TH)-rich patches demonstrated in adjoining sections. Previous studies have shown that presynaptic and postsynaptic cellular markers of the dopaminergic system in the striatum, including immunostaining for TH and dopamine- and adenosine 3':5'-monophosphate-regulated phosphoprotein (DARPP-32), and binding for high affinity dopamine uptake sites and for dopamine D1 and D2 receptor sites, are all concentrated in the AChE-rich patch regions (P regions) of such embryonic striatal grafts. The preferential expression of Fos in neurons of the P regions of the grafts thus implies that the induction of Fos was cell-type specific in being concentrated in the parts of the grafts that express striatal phenotype and that are innervated by catecholamine-containing fibers.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholinesterase↗

PubMed1994

Double immunofluorescence staining of Fos and Jun in the hypothalamus of the rat.

The nuclear factor Fos participates in the transcriptional regulation of genes that contain a functional AP-1 binding site. Hyperosmotic stress induces Fos-like immunoreactivity in neurons of the hypothalamus. Fos appears to depend on the co-expression of the nuclear factor Jun, with which it dimerizes, to complete its regulatory role. The immunocytochemical co-localization of both peptides, however, has not been reported. The present study was designed to analyze the distribution of Fos and Jun by double immunofluorescence staining in Long-Evans rats that were osmotically challenged by a single intraperitoneal injection of 1.5 M NaCl. Non-injected and isotonic saline-injected animals were used as controls. Hypertonic saline injection induced Jun immunoreactivity in cell nuclei in the supraoptic nucleus, paraventricular nucleus, and median preoptic nucleus. The immunofluorescence for Jun was strong in the supraoptic and paraventricular nuclei, but weak in the median preoptic nucleus. The immunofluorescence for Fos in all 3 nuclei followed a similar pattern to that for Jun. Double immunofluorescence staining revealed co-localization of Jun with Fos in 87.4% of the cells of the supraoptic nucleus. Neither Jun nor Fos immunofluorescence was detected in control animals. The data support a role for Jun in transcriptional regulation of genes in hypothalamic neurons during acute hyperosmotic stress. Moreover, the findings are compatible with the suggestion that Fos and Jun act cooperatively in the regulation of gene transcription in neuroendocrine systems involved in the control of water balance during acute hyperosmotic stimulation.

Animals↗