Induction of c-fos gene expression by interferons

Interferon-gamma-responsive neuronal sites in the normal rat brain: receptor protein distribution and cell activation revealed by Fos induction

Constitutive expression of the interferon-gamma receptor protein (IFN-gammaR), and the distribution of cells in which Fos, a marker of cell activation, is induced by intracerebroventricular administration of IFN-gamma, were studied in the rat brain by immunohistochemistry. IFN-gammaR immunopositivity was found in neuronal elements, which exhibited a selective distribution being concentrated in the piriform and entorhinal cortex, midline thalamus and medial hypothalamic structures, brainstem nociceptive relays (including the periaqueductal gray, the parabrachial nuclei and the caudal part of the spinal trigeminal nuclei), and circumventricular organs such as the median eminence and area postrema. IFN-gamma-induced Fos expression mostly corresponded to neuronal sites of receptor distribution. Because of its topographical distribution, it is suggested that activation of the IFN-gammaR in neurons may play a role to limit spread of infections in the brain and, in concert with other proinflammatory cytokines, to modulate adaptive responses to an antigen challenge mediated by the central nervous system.

A common nuclear signal transduction pathway activated by growth factor and cytokine receptors

Growth factors and cytokines act through cell surface receptors with different biochemical properties. Yet each type of receptor can elicit similar as well as distinct biological responses in target cells, suggesting that distinct classes of receptors activate common gene sets. Epidermal growth factor, interferon-gamma, and interleukin-6 all activated, through direct tyrosine phosphorylation, latent cytoplasmic transcription factors that recognized similar DNA elements. However, different ligands activated different patterns of factors with distinct DNA-binding specificities in the same and different cells. Thus, unrelated receptors may activate a common nuclear signal transduction pathway that, through differential use of latent cytoplasmic proteins, permits these receptors to regulate both common and unique sets of genes.

The expression of C-jun and junB mRNA in renal cell cancer and in vitro regulation by transforming growth factor beta 1 and tumor necrosis factor alpha 1

The proto-oncogene C-jun acts as a transcriptional activator or repressor for numerous cellular genes, and the overexpression of these genes may cause malignant transformation. JunB inhibits c-jun's transforming activities. We investigated the expression of jun genes in renal cell cancer (RCC) and their regulation by cytokines and transforming growth factor beta 1 (TGF-b1). The constitutive expression of c-jun was detected in 39 of 43 fresh frozen RCC, 5 of 10 normal kidneys, and the expression of junB detected in 28 of 34 RCC, 5 of 6 normal kidneys. C-jun was also found expressed in all 10 RCC tumor lines examined and junB was expressed at low levels in 6 of 10 renal tumor lines. TGF-b1 and tumor necrosis factor alpha (TNF-a) have been shown to alter the expression of jun genes in other tissue types. Additionally, TGF-b1, TNF-a, and gamma interferon (g-IFN) were shown to inhibit the growth of RCC. We found that TGF-b1 highly augmented the expression of junB (mean of 34 folds, p less than .05), but did not significantly alter the expression of c-jun, the transforming gene. In contrast, TNF-a significantly enhanced the expression of both c-jun (mean fold enhancement of 2.1, p less than .05) and junB (2.2 folds, p less than .05). Interleukin-2 (IL-2), interleukin-4 (IL-4) and g-IFN did not significantly alter jun expression. The findings presented suggest that c-jun may have a role in inducing malignant transformation in RCC and a novel mechanism by which TGF-b1 may exert its anti-tumor effects, via the activation of junB. Additionally, although TGF-b1, TNF-a, and g-IFN all have anti-proliferative actions on RCC in vitro, they were found to have different effects in altering jun expressions.

Interferon-alpha activates binding of nuclear factors to a sequence element in the c-fos proto-oncogene 5'-flanking region

Interferon-alpha (IFN-alpha) can regulate the expression of the c-fos proto-oncogene in different cell types. Here we show IFN-alpha-activated binding of murine and human fibroblast nuclear factors to a DNA sequence element located in the 5' upstream region (nucleotides -351/-337) of the c-fos gene. This element, like the conserved enhancer element, the IFN-stimulated response element (ISRE), that mediates transcriptional induction of IFN-alpha-inducible genes, also binds factors in response to platelet-derived growth factor (PDGF) and v-sis-conditioned medium (SCM). The IFN-inducible ISRE shares an 8-bp stretch of sequence homology with the IFN-responsive c-fos SCM element, and competes efficiently for binding of factors to the SCM. Protein-DNA cross-linking experiments with the SCM binding site identified an IFN-modulated nuclear protein of approximately 98 kD. This protein does not appear to be involved in transcription activation, since IFN-alpha failed to stimulate c-fos transcription in nuclear run-off assays, or the c-fos promoter in transient transcription assays of 3T3 fibroblasts. Our data nonetheless suggest the c-fos promoter may be an early target for signal transduction triggered by IFN alpha-receptor interaction.

Inducible overexpression of human protein kinase C alpha in NIH 3T3 fibroblasts results in growth abnormalities

We have stably overexpressed the human protein kinase C alpha (hPKC alpha) in NIH 3T3 fibroblasts under the control of the interferon (IFN) type I inducible murine Mx promoter. These cells showed a 10-fold increase in the transcription of hPKC alpha mRNA after induction with interferon alpha. The increase in the amount and activity of protein kinase C (PKC)-protein in these cells was only about 3-fold after induction with interferon alpha. Compared to control cells which were transfected with the vector only, the NIH 3T3 fibroblasts transfected with the hPKC alpha cDNA showed already a slightly increased PKC-activity and amount of PKC-protein in the absence of interferon alpha. The hPKC alpha overexpressing cells had an altered, "transformed-like" morphology, which was reversed by staurosporine, an increased growth rate and a higher saturation density. The growth rate was further increased by treating the cells with interferon alpha. The hPKC alpha overexpressing cells were able to grow in soft agarose after treatment with phorbol ester such as TPA (12-O-tetradecanoylphorbol 13-acetate). After phorbol ester and interferon treatment a stronger expression of the protooncogene c-jun was detectable in the hPKC alpha overexpressing cells, whereas expression of c-fos and c-myc was not affected. Since these cells show a specific response pattern due to induced PKC alpha expression they might be useful as an assay system for the development of PKC isozyme-specific inhibitors and activators.

c-fos mRNA expression in macrophages is downregulated by interferon-gamma at the posttranscriptional level

Treatment of macrophages with interferon-gamma (IFN gamma) strongly decreased the induction of c-fos mRNA by 12-O-tetradecanoylphorbol-13-acetate (TPA), lipopolysaccharide, or calcium ionophore A23187 in macrophages. Under the same experimental conditions, IFN gamma induced oligo(A) synthetase mRNA and did not affect the constitutive expression of transforming growth factor beta mRNA, indicating that IFN gamma did not induce general degradation of mRNAs. Run-on experiments indicated that c-fos was constitutively transcribed at low levels and that TPA augmented c-fos transcription. IFN gamma did not inhibit constitutive or TPA-induced c-fos transcription. However, IFN gamma decreased c-fos mRNA stability, as assessed by measuring the half-life of c-fos mRNA in actinomycin D-treated cells. These results indicated that IFN gamma inhibited c-fos mRNA induction by TPA at the posttranscriptional level.

c-fos mRNA expression in macrophages is downregulated by interferon-gamma at the posttranscriptional level

Treatment of macrophages with interferon-gamma (IFN gamma) strongly decreased the induction of c-fos mRNA by 12-O-tetradecanoylphorbol-13-acetate (TPA), lipopolysaccharide, or calcium ionophore A23187 in macrophages. Under the same experimental conditions, IFN gamma induced oligo(A) synthetase mRNA and did not affect the constitutive expression of transforming growth factor beta mRNA, indicating that IFN gamma did not induce general degradation of mRNAs. Run-on experiments indicated that c-fos was constitutively transcribed at low levels and that TPA augmented c-fos transcription. IFN gamma did not inhibit constitutive or TPA-induced c-fos transcription. However, IFN gamma decreased c-fos mRNA stability, as assessed by measuring the half-life of c-fos mRNA in actinomycin D-treated cells. These results indicated that IFN gamma inhibited c-fos mRNA induction by TPA at the posttranscriptional level.

Induction of c-Ha-ras gene expression by double-stranded RNA and interferon requirement

The addition of double-stranded RNA (dsRNA) to NIH 3T3 cells led to an increase in the RNA levels of c-Ha-ras. The double-stranded configuration was required for the increase in c-Ha-ras mRNA levels, as heat-denatured dsRNA and single-stranded RNA did not have any effect. Nuclear run-on transcription experiments indicated that the increase in c-Ha-ras mRNA levels stimulated by dsRNA was due to transcriptional activation of the gene. The induction of c-Ha-ras gene expression by dsRNA was inhibited by anti-beta interferon antibodies, suggesting that interferon might mediate the induction.

Induction of c-Ha-ras gene expression by double-stranded RNA and interferon requirement

The addition of double-stranded RNA (dsRNA) to NIH 3T3 cells led to an increase in the RNA levels of c-Ha-ras. The double-stranded configuration was required for the increase in c-Ha-ras mRNA levels, as heat-denatured dsRNA and single-stranded RNA did not have any effect. Nuclear run-on transcription experiments indicated that the increase in c-Ha-ras mRNA levels stimulated by dsRNA was due to transcriptional activation of the gene. The induction of c-Ha-ras gene expression by dsRNA was inhibited by anti-beta interferon antibodies, suggesting that interferon might mediate the induction.

Two interferon sensitive steps in the replication cycle of Rous sarcoma virus

De novo infection of Rous sarcoma virus (RSV) strains of receptor subgroups A, B, C, and D is inhibited by low doses of chick interferon. Adsorption and penetration into the cell are not marginally impaired by interferon treatment. Since the level of proviral DNA synthesis is strongly reduced in the interferon-treated cell it is concluded that uncoating or reverse transcription of the viral genome is inhibited. This inhibition of proviral DNA synthesis is not caused by an arrest of CEF in the stationary phase. Chronic infection of SR-RSV-A, -B, -C, but not SR-RSV-D is also sensitive to interferon. Chick interferon treatment (50 u/ml) also had no inhibitory effect on the amount of transcripts of the RSV-specific oncogene src or the cellular oncogenes src and myc.

K-252a inhibits the increase in c-fos transcription and the increase in intracellular calcium produced by nerve growth factor in PC12 cells

K-252a, a kinase inhibitor isolated from the culture broth of Nocardiopsis sp., selectively inhibits, in a dose- and time-dependent fashion, the increased transcription of the protooncogene c-fos induced by nerve growth factor in PC12 cells. Induction of c-fos by epidermal growth factor, A23187, dBcAMP, or TPA in the same cells is not affected. Pretreatment with K-252a for 30 min results in a complete inhibition of the nerve growth factor-induced increase in intracellular calcium. Increases in intracellular calcium induced by carbachol or by high K+ are not altered. K-252a derivatives selective for the inhibition of various known kinases were used to inhibit the nerve growth factor-dependent induction of c-fos mRNA, the nerve growth factor-dependent increase in intracellular calcium levels, and the nerve growth factor-dependent outgrowth of neurites. K-252a is the most effective inhibitor of all three of these actions of nerve growth factor. The possible mechanisms by which K-252a acts on PC12 cells are considered in the light of the characteristics of the inhibitions seen here.

Neonatal induction of a nuclear protein that binds to the c-fos enhancer

The expression of the c-fos gene is transiently induced at birth in most organs in the mouse. To study the basis of this induction we searched for a nuclear factor that binds to the 5' regulatory region of the c-fos gene. Gel mobility shift assays with tissue extracts revealed fast (band I) and slow (band III) migrating bands, which represent factor binding to the c-fos enhancer, termed the serum response element (SRE). Neonatal extracts preferentially elicited band I, with low or undetectable levels of band III, whereas fetal and adult extracts generated predominantly band III, with reduced levels of band I. These results indicate that the SRE-binding activity changes during perinatal development and that the appearance of band I, which coincides with diminution of band III, correlates with neonatal c-fos induction. Methylation interference and competition analyses showed that the neonatal factor (band I) binds to the SRE at a site different from the adult factor (band III). DNA-binding activity of the adult factor, but not the neonatal factor, was sensitive to phosphatase treatment. Furthermore, the adult factor, but not the neonatal factor, shared antigenic specificity with the human serum response factor (SRF) that is expressed in cultured cells irrespective of c-fos gene induction. We conclude that band I in neonates represents a SRE-binding factor that is distinct from the SRF, which may be responsible for the neonatal induction of the c-fos gene. The band III factor was indistinguishable from the SRF in all criteria tested.

c-fos antisense RNA blocks expression of c-fos gene in F9 embryonal carcinoma cells

To study the function of proto-oncogene c-fos, we prepared an antisense plasmid that expresses in mammalian cells c-fos antisense RNA which is complementary to the endogenous c-fos mRNA. Upon transfection into undifferentiated F9 EC cells, the antisense plasmid directed constitutive expression of a large amount of c-fos antisense RNA. These cells were very low in the basal level of c-fos message and were unable to induce c-fos message when stimulated with interferon or phorbol ester. The failure to induce c-fos message led to the blockade of c-fos protein expression in these cells. Thus, these cells represented a c-fos defective phenotype. The blockade of c-fos gene expression seen in antisense-cells could be caused by rapid degradation of the c-fos message, since c-fos mRNA expression was rescued in these cells when treated with protein synthesis inhibitor, cycloheximide. We found that expression of c-myc gene was down-regulated in c-fos antisense-cells: Although control undifferentiated F9 cells constitutively expressed a high level of c-myc message, the antisense cells had a much lower amount of c-myc mRNA. Since p53 and heat shock gene 70 were expressed at comparable levels in control and antisense cells, c-myc gene expression appears to be regulated by c-fos gene in F9 EC cells. Lastly, these antisense cells grew as rapidly as control F9 cells and underwent differentiation after retinoic acid treatment, indicating that c-fos expression is not a prerequisite for differentiation of F9 cells.

Constitutive expression of c-fos antisense RNA blocks c-fos gene induction by interferon and by phorbol ester and reduces c-myc expression in F9 embryonal carcinoma cells

To address the role of c-fos proto-oncogene we constructed a plasmid that allows constitutive expression of RNA complementary to c-fos mRNA, and stably introduced this plasmid into F9 embryonal carcinoma cells. Some F9 clones expressing c-fos antisense RNA had a reduced basal level of c-fos mRNA, and were unable to induce a c-fos mRNA as well as its protein when stimulated with phorbol ester or with interferon (IFN). Nevertheless, the ability to induce major histocompatibility class I genes following IFN treatment was not impaired in these clones. Clones expressing c-fos antisense RNA grew as rapidly as control F9 cells, and underwent differentiation after retinoic acid treatment. Unexpectedly, constitutive expression of c-myc mRNA was reduced on average by 10-fold in clones expressing c-fos antisense RNA. However, expression of the p53 gene and heat shock gene hsp 70 was not affected in these clones, indicating the existence of a specific regulatory linkage between c-fos and c-myc genes. Cycloheximide treatment led to induction of a large amount of c-fos mRNA in clones expressing c-fos antisense RNA as well as in control F9 clones. The amount of c-fos antisense RNA was also increased by cycloheximide treatment. We postulate that c-fos antisense RNA blocks expression of the endogenous c-fos gene by accelerating the degradation of c-fos mRNA and that cycloheximide treatment interferes with this degradation.