Extracellular signals, transcriptional responses and cellular specificity

Morphological Study of the Cortical and Thalamic Glutamatergic Synaptic Inputs of Striatal Parvalbumin Interneurons in Rats

Parvalbumin-immunoreactive (Parv+) interneurons is an important component of striatal GABAergic microcircuits, which receive excitatory inputs from the cortex and thalamus, and then target striatal projection neurons. The present study aimed to examine ultrastructural synaptic connection features of Parv+ neruons with cortical and thalamic input, and striatal projection neurons by using immuno-electron microscopy (immuno-EM) and immunofluorescence techniques. Our results showed that both Parv+ somas and dendrites received numerous asymmetric synaptic inputs, and Parv+ terminals formed symmetric synapses with Parv- somas, dendrites and spine bases. Most interestingly, spine bases targeted by Parv+ terminals simultaneously received excitatory inputs at their heads. Electrical stimulation of the motor cortex (M1) induced higher proportion of striatal Parv+ neurons express c-Jun than stimulation of the parafascicular nucleus (PFN), and indicated that cortical- and thalamic-inputs differentially modulate Parv+ neurons. Consistent with that, both Parv + soma and dendrites received more VGlut1+ than VGlut2+ terminals. However, the proportion of VGlut1+ terminal targeting onto Parv+ proximal and distal dendrites was not different, but VGlut2+ terminals tended to target Parv+ somas and proximal dendrites than distal dendrites. These functional and morphological results suggested excitatory cortical and thalamic glutamatergic inputs differently modulate Parv+ interneurons, which provided inhibition inputs onto striatal projection neurons. To maintain the balance between the cortex and thalamus onto Parv+ interneurons may be an important therapeutic target for neurological disorders.

Distinct gene regulatory programs define the inhibitory effects of liver X receptors and PPARG on cancer cell proliferation

Background

The liver X receptors (LXRs, NR1H2 and NR1H3) and peroxisome proliferator-activated receptor gamma (PPARG, NR1C3) nuclear receptor transcription factors (TFs) are master regulators of energy homeostasis. Intriguingly, recent studies suggest that these metabolic regulators also impact tumor cell proliferation. However, a comprehensive temporal molecular characterization of the LXR and PPARG gene regulatory responses in tumor cells is still lacking.

Methods

To better define the underlying molecular processes governing the genetic control of cellular growth in response to extracellular metabolic signals, we performed a comprehensive, genome-wide characterization of the temporal regulatory cascades mediated by LXR and PPARG signaling in HT29 colorectal cancer cells. For this analysis, we applied a multi-tiered approach that incorporated cellular phenotypic assays, gene expression profiles, chromatin state dynamics, and nuclear receptor binding patterns.

Results

Our results illustrate that the activation of both nuclear receptors inhibited cell proliferation and further decreased glutathione levels, consistent with increased cellular oxidative stress. Despite a common metabolic reprogramming, the gene regulatory network programs initiated by these nuclear receptors were widely distinct. PPARG generated a rapid and short-term response while maintaining a gene activator role. By contrast, LXR signaling was prolonged, with initial, predominantly activating functions that transitioned to repressive gene regulatory activities at late time points.

Conclusions

Through the use of a multi-tiered strategy that integrated various genomic datasets, our data illustrate that distinct gene regulatory programs elicit common phenotypic effects, highlighting the complexity of the genome. These results further provide a detailed molecular map of metabolic reprogramming in cancer cells through LXR and PPARG activation. As ligand-inducible TFs, these nuclear receptors can potentially serve as attractive therapeutic targets for the treatment of various cancers.

Electronic supplementary material

The online version of this article (doi:10.1186/s13073-016-0328-6) contains supplementary material, which is available to authorized users.

Effect of Sevoflurane postconditioning on gene expression in brain tissue of the middle cerebral artery occlusion rat model

Ischemic postconditioning has been described in both heart and brain. The first aim of this study was to evaluate the effects of Sevoflurane postconditioning (SP) on brain biochemical parameters, Bcl-2, Bax, c-Fos and Caspase-3 protein levels and Bcl-2, Bax, TNF-α and Caspase-3 mRNA expression in the middle cerebral artery occlusion model. Results showed that SP markedly decreased cerebral oxidative injury and improved immunity activity. In addition, SP significantly enhanced cerebral Bcl-2, c-Fos and decreased Bax, Caspase-3 proteins positive expression. Reverse transcription polymerase chain reaction analysis showed that SP markedly enhanced Bcl-2, and decreased Bax, TNF-α and Caspase-3 mRNA expression. Our results confirm that SP can play the protective action against cerebral ischemia reperfusion-induced brain injury by regulating cerebral antioxidant enzymes activities, Bcl-2, Bax, c-Fos and Caspase-3 protein positive expression levels and Bcl-2, Bax, TNF-α and Caspase-3 mRNA expression.

Selection for stress-induced analgesia affects the mouse hippocampal transcriptome

Stress responsiveness, including pain sensitivity and stress-induced analgesia (SIA), depends on genotype and, partially, is mediated by hippocampus. The present study examined differences in constitutive gene expression in hippocampus in lines of mice bred for high (HA) and low (LA) swim SIA. Between the lines, we found 1.5-fold or greater differences in expression of 205 genes in the hippocampus in nonstressed animals. The identity of these genes indicates that selective breeding for swim SIA affected many aspects of hippocampal neurons physiology, including metabolism, structural changes, and cellular signaling. Genes involved in calcium signaling pathway, including Slc8a1, Slc8a2, Prkcc, and Ptk2b, were upregulated in LA mice. In HA mice, robust upregulation of genes coding some transcription factors (Klf5) or receptors for neurotensin (Ntsr2) and GABA (Gabard) suggests the genetic basis for a novel mechanism of the non-opioid type of SIA in HA animals. Additional groups of differentially expressed genes represented functional networks involved in carbohydrate metabolism, gene expression regulation, and molecular transport. Our data indicate that selection for a single and very specific stress response trait, swim SIA, alters hippocampal gene expression. The results suggest that individual stress responsiveness may be associated with characteristics of the constitutive hippocampal transcriptome.

Exposure of the dorsal root ganglion in rats to pulsed radiofrequency currents activates dorsal horn lamina I and II neurons

OBJECTIVE

Application of pulsed radiofrequency (RF) currents to the dorsal ganglion has been reported to produce long-term relief of spinal pain without causing thermal ablation. The present study was undertaken to identify spinal cord neurons activated by exposure of the dorsal ganglion to pulsed RF currents in rats.

METHODS

Left-sided hemilaminectomy was performed in adult Sprague-Dawley rats to expose the C6 dorsal root ganglion. An RF electrode (0.5 mm diameter) with a thermocouple for temperature monitoring was positioned on the exposed ganglion, and rats were assigned to one of three treatment groups: pulsed RF treatment (20 ms of 500-kHz RF pulses delivered at a rate of 2 Hz for 120 s to produce tissue heated to 38 degrees C), continuous RF (continuous RF currents for 120 s to produce tissue heated to 38 degrees C), or sham treatment (no RF current; electrode maintained in contact with ganglion for 120 s).

RESULTS

Treatment with pulsed RF but not continuous RF was associated with a significant increase in the number of cFOS-immunoreactive neurons in the superficial laminae of the dorsal horn as observed 3 hours after treatment.

CONCLUSION

Exposure of the dorsal ganglion to pulsed RF currents activates pain-processing neurons in the dorsal horn. This effect is not mediated by tissue heating.

Granulocyte colony-stimulating factor induces Egr-1 up-regulation through interaction of serum response element-binding proteins

Granulocyte colony-stimulating factor (G-CSF) stimulates the proliferation and maturation of myeloid progenitor cells both in vitro and in vivo. We showed that G-CSF rapidly and transiently induces expression of egr-1 in the NFS60 myeloid cell line. Transient transfections of NFS60 cells with recombinant constructs containing various deletions of the human egr-1 promoter identified the serum response element (SRE) between nucleotides (nt) -418 and -391 as a critical G-CSF-responsive sequence. The SRE (SRE-1) contains a CArG box, the binding site for the serum response factor (SRF), which is flanked at either side by an ETS protein binding site. We demonstrated that a single copy of the wild-type SRE-1 in the minimal promoter plasmid, pTE2, is sufficient to induce transcriptional activation in response to G-CSF and that both the ETS protein binding site and the CArG box are required for maximal transcriptional activation of the pTE2-SRE-1 construct. In electromobility shift assays using NFS60 nuclear extracts, we identified SRF and the ETS protein Fli-1 as proteins that bind the SRE-1. We also demonstrated through electrophoretic mobility shift assays, using an SRE-1 probe containing a CArG mutation, that Fli-1 binds the SRE-1 independently of SRF. Our data suggest that SRE-binding proteins potentially play a role in G-CSF-induced egr-1 expression in myeloid cells.

Neonatal capsaicin treatment prevents the normal postnatal withdrawal of A fibres from lamina II without affecting fos responses to innocuous peripheral stimulation

The development of spinal cord sensory pathways has been investigated in postnatal day (P) 21 rat pups following neonatal capsaicin treatment. Capsaicin-induced destruction of C fibres was confirmed by 62% loss of Isolectin B4 (IB4)-binding and an 86% loss of calcitonin gene-related peptide (CGRP)-immunoreactive small diameter dorsal root ganglion cells. Neonatal capsaicin treatment prevented the normal withdrawal of choleragenoid-horseradish peroxidase (B-HRP)-labelled A fibres from lamina II (substantia gelatinosa) to deeper laminae postnatally. A fibre terminals projected more dorsally, extending into 43% of lamina II compared to vehicle-treated littermates. A small cell loss in, and/or shrinkage of, substantia gelatinosa cannot account for this. These support the concept of a competitive interaction between A and C fibre afferents to establish final terminal fields. However the continued exuberant A fibre termination in capsaicin-treated rats did not lead to continued c-fos induction in the superficial dorsal horn by innocuous stimulation. In normal development, exuberant A fibre terminals coincide with c-fos activation in lamina II by innocuous skin stimulation [23]. Despite the continued presence of exuberant A fibre terminals, c-fos was not induced by innocuous peripheral stimulation in P21 capsaicin-treated rats implying that these superficial terminals do not activate lamina II neurons in the same way as in the neonate.

Large-scale identification of differentially expressed genes during neurogenesis

We report here a modified mRNA differential display method and its application for the analysis of differential gene expression in NGF-treated PC12 cells and in embryonic rat spinal cord. The optimized protocol is based on low fidelity priming of multiple cDNAs followed by high fidelity amplification. In PC12 cells induction by nerve growth factor (NGF) altered the expression of 4% of the 466 transcripts evaluated. During neurogenesis of the spinal cord we found that 30% of the 288 examined products changed. The differential expression of the characterized genes was confirmed by independent quantitative PCR. We conclude this method is suitable for the identification of increases and decreases of mRNA levels and allows the discovery of differentially expressed unknown transcripts.

Genomic organization and identification of an enhancer element containing binding sites for multiple proteins in rat pituitary tumor-transforming gene

The rat pituitary tumor transforming gene (PTTG) genomic structure was characterized in this study. Northern blot analysis showed that PTTG mRNA is highly expressed in testicular cell lines. Transfection of testicular cell lines with fusion constructs containing various portions of PTTG 5'-flanking sequences linked to luciferase showed that at least 745 base-pair (bp(s)) 5'-flanking sequences are required for PTTG transcriptional activation. DNaseI footprinting assays indicated that nuclear protein(s) from testicular cell lines interacts with PTTG 5'-flanking sequence between -509 and -624 bp, including two consensus Sp1 binding sites. Western and Southwestern blot analysis showed that three nuclear proteins in addition to Sp1 protein specifically interact with this DNA sequence and that two of these proteins are testicular cell-specific. Deletion of this 115-bp sequence from PTTG promoter resulted in complete loss of promoter function. Site-directed mutagenesis within the Sp1 consensus sequences indicated that the Sp1 binding sites are not critical components of the enhancer sequence for PTTG trancriptional activation in testicular cell lines. Finally, the 115-bp enhancer sequence was shown to be able to activate transcription from a heterologous promoter. These results suggest that PTTG transcriptional activation in testicular cell lines involves interactions of multiple nuclear factors with the PTTG 5' enhancer sequence.

C-fos can be induced in the neonatal rat spinal cord by both noxious and innocuous peripheral stimulation

The development of spinal cord nociceptive pathways has been investigated in neonatal rat pups using the expression of Fos immunoreactivity in laminae I and II cells produced by high and low intensity skin stimulation. Noxious pinch of the hindpaw evoked a clear response in the newborn rat pup, which was not significantly different from that seen at postnatal day (P) 21. Low intensity touch stimulation also produced a significant fos response in laminae I and II cells at P3 which was 60% that of the pinch response. This was reduced to 27% of the pinch response by P10 and was gone by P21. Electrical stimulation through percutaneous electrodes showed that A beta fibre stimulation also produced a fos response at P3 that was not significantly different from that produced by C fibre stimulation. By P21 and P30 the response to C fibre stimulation was much greater and the response to A fibre stimulation was not significantly above background. The results suggest that in the neonatal spinal cord, low threshold A fibres are able to activate pathways in lamina I and II of the dorsal horn that in the adult are predominantly nociceptive.

Immediate early-gene induction in rat osteoblastic cells after mechanical deformation

Previous studies have reported changes in proliferation, second-messenger generation and activation of various cellular processes when osteoblasts have been mechanically stimulated. Recent evidence suggests that mechanical loading of long bones induces immediate early-gene expression. Immediate early genes, such as Egr-1, are genes that control cell proliferation, are involved in signal transduction, and share properties of transcription factors. The purpose of this study was to examine how mechanical deformation of osteoblasts affects cellular proliferation and Egr-1 mRNA induction. Osteoblasts were isolated from collagenase digestion of newborn rat calvariae, cultured in Petri dishes with flexible bottoms and then constantly stretched, producing an increase of 3 or 7% in surface area. A mechanical stretch of 7% for 0.5 or 24 h resulted in a doubling of [3H]thymidine incorporation, while 50 nM of epidermal growth factor resulted in a 4-fold increase. A time-course experiment showed that a 7% stretch induced Egr-1 mRNA as early as 15 mm, reaching maximum levels by 60 min and returning to baseline by 120 min. Epidermal growth factor at 50 nM for 60 min resulted in a 3.8-fold Egr-1 mRNA induction. A mechanical stretch of 3% for 30 min also produced an Egr-1 mRNA induction. No induction of Egr-1 mRNA was seen in osteoblasts that were exposed to conditioned media from deformed cells. It is concluded that the immediate early gene, Egr-1, may be directly involved in the signal-transduction pathway of mechanical stimuli in osteoblasts.

Basal and touch-evoked fos-like immunoreactivity during experimental inflammation in the rat

Fos-immunoreactivity can readily be induced in spinal cord neurones by noxious, but to a much more limited extent, by innocuous peripheral stimuli. The present study has investigated whether low intensity stimuli and electrical stimulation of A beta afferents elicit greater c-fos expression during the behavioural sensory hypersensitivity generated by experimental peripheral inflammation. We have examined the time-course of c-fos expression after inflammation produced by either an intra-plantar injection of the irritant turpentine oil or of complete Freund's adjuvant (CFA). In the former case, a significant initial expression in all dorsal horn laminae was followed by a gradual decrease, whereas after CFA injection, an initial expression limited to the superficial laminae subsequently extended into the deep laminae, with a decrease at 24 h and an increase in labelling at later times. Low intensity touch stimuli repeated for 10 min, when applied at 24 h and 48 h after CFA injection, elicited a significant increase in the number of Fos-immunoreactive neurons in both the superficial and deep laminae of the dorsal horn compared to non-inflamed animals. Electrical stimulation of the sciatic nerve 24 h post-CFA injection, at a strength sufficient only to activate A beta-afferents fibres (100 microA, 50 microseconds, 10 min), also elicited a significant increase in labelling relative to the same stimuli applied in control animals, especially in laminae V-VI. The present results demonstrate that low intensity cutaneous stimuli elicit a significantly greater increase in c-fos expression in dorsal horn neurons during peripheral inflammation and that A beta-afferent input contributes to this, a finding that may relate to the allodynia experienced during inflammation.

Effect of hypothalamic-hypophysary inhibitory factor on mesangial cell activation

We examined the effect of a sodium pump inhibitor isolated from bovine hypothalamus and pituitary tissues on contraction, proliferation, and calcium mobilization in primary cultures of rat mesangial cells. Hypothalamic-hypophysary inhibitory factor (HHIF) inhibited rubidium uptake in a concentration-dependent manner (0.2 U/mL: 56.8 +/- 6.3% inhibition). It also induced a concentration- and time-dependent decrease in planar cell surface area. Maximal contraction (25 +/- 5% reduction in cell size) was reached at 60 minutes with a concentration of 0.2 U/mL. This effect was inhibited by both verapamil and TMB-8 (10(-5) mol/L). HHIF was also observed to increase DNA synthesis (0.2 U/mL: 4361 +/- 168 versus 2129 +/- 162 cpm per well under control conditions) and cell proliferation (0.2 U/mL: 52,290 +/- 1931 versus 10,512 +/- 121 cells per well under control conditions). Both effects were also inhibited by verapamil and TMB-8. Moreover, HHIF induced the expression of immediate early genes c-fos and c-jun mRNA. HHIF-induced effects were accompanied by an increase in cytosolic free calcium (203 +/- 58 versus 101 +/- 2 nmol/L under control conditions), which was inhibited by verapamil and TMB-8. In summary, HHIF induces mesangial cell contraction and proliferation; these effects seem to be mediated by an increase in cytosolic free calcium levels.

Blood pressure regulates platelet-derived growth factor A-chain gene expression in vascular smooth muscle cells in vivo. An autocrine mechanism promoting hypertensive vascular hypertrophy

To clarify the role of PDGF A-chain in hypertensive vascular hypertrophy of spontaneously hypertensive rats (SHRs), we studied levels of PDGF A-chain gene expression and transcription factors related to the gene in vascular smooth muscle cells (VSMCs) of SHRs in vivo. RNase protection assay and in situ hybridization showed that PDGF A-chain mRNA levels in VSMCs of SHRs were twofold higher than in those of normotensive Wistar-Kyoto rats. Gel retardation assays showed that levels of Sp1 and AP-2 in VSMCs of SHRs were twofold more abundant than in those of Wistar-Kyoto rats. Treatment with four pharmacologically different species of antihypertensive drugs for 2 wk decreased the levels of both PDGF A-chain mRNA and Sp1, but not AP-2 level in VSMCs of SHRs with regression of aortic hypertrophy, indicating that increases in levels of both PDGF A-chain mRNA and Sp1 in VSMCs of SHRs were associated with high blood pressure. These results suggest that high blood pressure is a stimulus which upregulates PDGF A-chain gene expression in VSMCs of SHRs, resulting in an autocrine enhancement in hypertensive vascular hypertrophy, and that the activation of the gene may be mediated through increases in Sp1 in these cells.

Two closely related isoforms of protein kinase C produce reciprocal effects on the growth of rat fibroblasts. Possible molecular mechanisms

We have previously reported that two closely related protein kinase C (PKC) isoforms, PKC alpha and PKC beta I, had divergent effects on the growth and transformation of the same parental R6 rat embryo fibroblast cell line (Housey, G. M., Johnson, M. D., Hsiao, W.-L. W. O'Brian, C. A., Murphey, J. P., Kirschmeier, P., and Weinstein, I. B. (1988) Cell 52, 343-354; Borner, C., Filipuzzi, I., Weinstein, I. B., and Imber, R. (1991) Nature 353, 78-80). Whereas cells that overexpress PKC beta I lost anchorage dependence, grew to higher saturation densities, and generated small tumors when injected into nude mice, none of these properties were seen with cells that overexpress PKC alpha. In fact, the latter cells grew even slower and to lower saturation densities as compared to control cells. Here we investigate possible molecular mechanisms underlying the reciprocal effects of PKC alpha and PKC beta I. Overexpression of both isoforms enhanced 12-O-tetradecanoyl phorbol-13 acetate-induced expression of the growth regulatory genes c-jun, c-myc, and collagenase and enhanced feedback inhibition of epidermal growth factor receptor binding and cellular levels of diacylglycerol. However, the cells overexpressing PKC beta I differed from those overexpressing PKC alpha by displaying a decreased requirement for growth factors and by the production of a mitogenic factor. Thus, the basis for enhanced growth and transformation of cells overexpressing PKC beta I may be the establishment of an autocrine growth factor loop. These findings may be relevant to the roles of specific isoforms of PKC in carcinogenesis and tumor growth.

Expression of a growth arrest specific gene (gas-6) during liver regeneration: molecular mechanisms and signalling pathways

A set of growth arrest-specific (gas) genes negatively regulated by serum has been identified. To define the role of gas genes in a model of cell proliferation in vivo we analyzed the expression of one of these genes (gas-6) during liver regeneration after partial hepatectomy (PH). We found that gas-6 mRNA was down-regulated 4 hours after PH, within the G0 to G1 transition. Later on, gas-6 mRNA increased over the level found in normal liver with a peak at 16 hours, before the onset of DNA synthesis. This surge was probably triggered by an inflammatory response caused by the surgical trauma, because an increase of similar extent occurring with the same time course was present in livers of sham-operated and turpentine-treated rats. Comparison of mRNA steady state levels with nuclear transcription rates indicated that gas-6 expression is post-transcriptionally regulated. As we found that down-regulation of gas-6 expression was prevented by treatment with Actinomycin D, a labile protein might be involved in the determination of gas-6 mRNA stability. To investigate the mitogenic signals controlling gas-6 expression during liver regeneration we treated hepatectomized rats with a specific alpha-1-adrenoceptor blocker (prazosin) as well as with drugs which modify intracellular calcium levels. The decrease of gas-6 mRNA 4 hours after PH was prevented by prazosin and by neomycin, an inhibitor of calcium release from endogenous stores. These findings suggest that down-regulation of gas-6 expression during hepatic regeneration is triggered by catecholamines interaction with alpha-1-adrenergic receptors and by subsequent calcium release. In addition we found that the rise of gas-6 gene expression occurring at 16 hours after PH was not affected by prazosin but was inhibited by trifluoperazine. Therefore, we suggest that up-regulation of gas-6 gene expression is mediated by the interaction of calcium with calmodulin, independently of catecholamines.

Differential induction of ‘metabolic genes’ after mitogen stimulation and during normal cell cycle progression

Mitogenic stimulation of quiescent cells not only triggers the cell division cycle but also induces an increase in cell volume, associated with an activation of cellular metabolism. It is therefore likely that genes encoding enzymes and other proteins involved in energy metabolism and biosynthetic pathways represent a major class of mitogen-induced genes. In the present study, we investigated in the non-established human fibroblast line WI-38 the induction by mitogens of 17 genes whose products play a role in different metabolic processes. We show that these genes fall into 4 different categories, i.e. non-induced genes, immediate early (IE) primary genes, delayed early (DE) secondary genes and late genes reaching peak levels in S-phase. In addition, we have analysed the regulation of these genes during normal cell cycle progression, using HL-60 cells separated by counterflow elutriation. A clear cell cycle regulation was seen with those genes that are induced in S-phase, i.e. thymidine kinase, thymidylate synthase and dihydrofolate reductase. In addition, two DE genes showed a cell cycle dependent expression. Ornithine decarboxylase mRNA increased around mid-G1, reaching maximum levels in S/G2, while hexokinase mRNA expression was highest in early G1. In contrast, the expression of other DE and IE genes did not fluctuate during the cell cycle, a result that was confirmed with elutriated WI-38 and serum-stimulated HL-60 cells. These observations suggest that G0-->S and G1-->S transition are distinct processes, exhibiting characteristic programmes of gene regulation, and merging around S-phase entry.

Direct transcriptional stimulation of the ornithine decarboxylase gene by Fos in PC12 cells but not in fibroblasts

We have established rat PC12 pheochromocytoma cell lines stably expressing the estrogen-activatable transcription factor FosER to identify genes that can be regulated by c-Fos in this neuronal cell type. Induction of ectopic c-Fos activity in PC12 cells increased the mRNA levels of the ornithine decarboxylase (ODC) and tyrosine hydroxylase genes with similar kinetics and to the same maximal level as nerve growth factor treatment. In both cases the rate of transcription initiation was increased. Induction of the ODC gene occurred even in the absence of protein synthesis, indicating direct regulation by FosER. ODC expression, however, was not induced by a mutant FosER protein containing a proline insertion in the basic region of the c-Fos moiety, demonstrating the requirement for a functional DNA-binding domain. These data show that FosER, and by extrapolation c-Fos, can directly activate transcription of the endogenous ODC gene in PC12 cells by binding to cis-regulatory sequences. Activation of the ODC gene was unexpectedly transient, as transcripts returned to the basal level after prolonged exposure of PC12 cells to FosER activity. Furthermore, ODC transcription was not at all induced by FosER in rat fibroblasts. To account for this cell-specific action of FosER, we propose that stimulation of the ODC gene by FosER requires either (i) cooperation with another transcription factor(s) or (ii) a specific pattern of modification which is present in PC12 cells but not in otherwise unstimulated fibroblasts. One or both of these mechanisms may be employed by cells to achieve selective gene activation in response to apparently stereotyped induction of c-fos.

Phorbol ester induction of early response gene expression in lymphocytic leukemia and normal human B-cells

The spectrum of early response genes induced following phorbol ester (phorbol 12-myristate 13-acetate-PMA) stimulation of B-chronic lymphocytic leukemia cells was compared with that in normal tonsillar B-cells by using a panel of 20 gene probes. Of these, 2 (fos-B and Fra-1) were not expressed in either cell type; 11 displayed a comparable pattern and magnitude of induction in both the cell types, and one anonymous gene (5L3) that was inducible in leukemic cells was not detectably expressed in normal B-cells. Four further anonymous cDNAs (1R21, 10A, 1R19 and 3L11) detected transcripts that were constitutively expressed in normal B-cells with a concomitant reduction in inducibility compared with leukemic B-cells, whilst jun-B and jun-D, which were both inducible in normal B-cells, were constitutively expressed and only marginally PMA-inducible in leukemic B-cells. These data demonstrate clear differences in the PMA-activated early response gene regulatory pathways between normal and lymphocytic leukemia B-cells, which may reflect perturbations in signal transduction pathways that manifest in the differentiation arrest characteristic of these malignant B-cells.

Direct transcriptional stimulation of the ornithine decarboxylase gene by Fos in PC12 cells but not in fibroblasts

We have established rat PC12 pheochromocytoma cell lines stably expressing the estrogen-activatable transcription factor FosER to identify genes that can be regulated by c-Fos in this neuronal cell type. Induction of ectopic c-Fos activity in PC12 cells increased the mRNA levels of the ornithine decarboxylase (ODC) and tyrosine hydroxylase genes with similar kinetics and to the same maximal level as nerve growth factor treatment. In both cases the rate of transcription initiation was increased. Induction of the ODC gene occurred even in the absence of protein synthesis, indicating direct regulation by FosER. ODC expression, however, was not induced by a mutant FosER protein containing a proline insertion in the basic region of the c-Fos moiety, demonstrating the requirement for a functional DNA-binding domain. These data show that FosER, and by extrapolation c-Fos, can directly activate transcription of the endogenous ODC gene in PC12 cells by binding to cis-regulatory sequences. Activation of the ODC gene was unexpectedly transient, as transcripts returned to the basal level after prolonged exposure of PC12 cells to FosER activity. Furthermore, ODC transcription was not at all induced by FosER in rat fibroblasts. To account for this cell-specific action of FosER, we propose that stimulation of the ODC gene by FosER requires either (i) cooperation with another transcription factor(s) or (ii) a specific pattern of modification which is present in PC12 cells but not in otherwise unstimulated fibroblasts. One or both of these mechanisms may be employed by cells to achieve selective gene activation in response to apparently stereotyped induction of c-fos.

Acrylamide induces immediate-early gene expression in rat brain

Northern blot analysis was used to study the effects of acrylamide, a potent neurotoxin, on the induction of c-fos and c-jun mRNA in rat brain. Male Sprague-Dawley rats (10-12 weeks old) treated with acrylamide as a single dose (100 mg/kg, i.p.) or via drinking water (0.03% w/v) for 4 weeks, were used to study acute and chronic effects on immediate-early gene expression, respectively. Acute administration of acrylamide caused a statistically significant increase in the expression of c-fos (approx. 37%) and c-jun (approx. 17%) mRNA in rat brain. By contrast, the level of c-fos mRNA in chronic acrylamide treatment was not altered significantly, but the expression of c-jun mRNA was increased almost 100% as compared to control. These data show that the neurotoxin acrylamide induces immediate-early gene expression in the brain. The effects appear to be related to the route of administration, dose and duration of acrylamide treatment.

Induction of primary response genes by excitatory amino acid receptor agonists in primary astroglial cultures

We have characterized the genomic response of astroglial cells to excitatory amino acids by using selective agonists and antagonists for the various receptor subtypes and by analyzing different primary response genes, such as members of the Fos (c-fos and fosB) and Jun (c-jun, junB, and junD) families, zif/268, and c-myc. A rapid and transient elevation of mRNA levels for c-fos, fosB, c-jun, junB, and zif/268 was observed after addition of glutamate to cultured astrocytes, whereas junD and c-myc expression was not affected. The level of AP-1 DNA binding activity, as measured by the electrophoretic mobility shift assay, also increased after addition of glutamate to cultured astrocytes. Glutamate-induced c-fos expression was not affected by the N-methyl-D-aspartate receptor antagonists MK-801 and D-2-amino-5-phosphonopentanoate, by the kainate/alpha-amino-3-hydroxy-5- methylisoxazole-4-propionate (AMPA) receptor antagonist 6,7-dinitroquinoxaline-2,3-dione (DNQX), or by the broad-spectrum antagonist kynurenate. Kainate and AMPA were also effective in inducing primary response gene expression, and their actions were antagonized by kynurenate and DNQX but not by MK-801. 1S,3R-1-Aminocyclopentane-1,3-dicarboxylic acid, a selective agonist for the metabotropic glutamate receptor, induced primary response gene expression, but its action was not antagonized by different glutamate antagonists, including L-2-amino-3-phosphonopropionate. In conclusion, our data suggest that cultured astrocytes express both kainate/AMPA ionotropic receptors and metabotropic receptors coupled to the rapid and coordinated activation of different classes of transcriptional factor genes.

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

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

Differential intracellular mechanisms mediate the co-ordinate induction of c-fos and jun-B in the rat pineal gland

In the rat pineal gland the immediate early genes c-fos and jun-B are co-ordinately induced in vivo following the onset of darkness, and in vitro following treatment with adrenergic drugs. An extensive in vitro analysis of the mechanisms which regulate the induction of these two genes has revealed that, although there are common pathways of control, c-fos and jun-B exhibit differential regulation by adrenoceptor types, second messenger pathways and protein kinase C. The presence of differential intracellular mechanisms of regulation provides precise control over the expression pattern of immediate early genes, a pattern which is crucial for cellular response since the combinatorial actions of the products of these genes are a determinant of target gene activation. The pineal gland is a unique experimental model in which the molecular pharmacology of immediate early gene regulation can be investigated.

Endothelins stimulate c-fos and nerve growth factor expression in astrocytes and astrocytoma

Endothelin receptors have been identified on astrocytes and astrocytoma, but their physiological significance has remained elusive. It is shown here that endothelins induce c-fos in primary cultures of mouse embryo astrocytes, as well as in two subclones of rat astrocytoma C6 cells, although with different kinetics. In addition, nerve growth factor expression is stimulated, as seen by mRNA accumulation and protein secretion, in primary astrocytes and one of the two C6 subclones, with an apparent correlation with the transience of c-fos induction. The activation of protein kinase C appears as an obligatory step during these processes, because (a) inhibition of protein kinase C by staurosporine blocks the induction by endothelin or phorbol esters of both c-fos and nerve growth factor, and (b) phorbol ester-evoked down-regulation of protein kinase C completely abolishes the c-fos induction by endothelin, but not that by the beta-adrenergic agonist isoproterenol, a known activator of the cyclic AMP-dependent pathway. Our results support the hypothesis that c-fos product might be implicated in nerve growth factor expression by astrocytes, and also suggest that endothelins may participate in vivo in the modulation of the glial neurotrophic activity during brain development or wound healing.

Excitable membranes, lipid messengers, and immediate-early genes. Alteration of signal transduction in neuromodulation and neurotrauma

The physical nature of neuronal cells, particularly in the functional and morphological segregation of synapse, soma, and dendrites, imparts special importance on the integrity of their cell membranes for the localization of function, generation of intrinsic second messengers, and plasticity required for adaptation and repair. The component phospholipids of neural membranes are important sources of bioactive mediators that participate in such diverse phenomena as memory formation and cellular damage following trauma. A common role for PAF in these processes is established through the suppressive effects of its antagonists. Furthermore, being both an extracellular and intracellular agonist of phospholipase activation, in addition to being a product of phospholipase activity, PAF assumes a centralized role in the cellular metabolism following neural stimulation. The linkage of PAF to neural immediate-early gene expression, both in vitro and in vivo, suggests that its effects are initiating to long-term formative and reparative processes. Such a common link between destructive and plastic responses provides an important view of cellular and tissue maintenance in the nervous system.

Expression of a growth arrest specific gene (gas-1) in transformed cells

A set of growth arrest-specific (gas) genes negatively regulated by serum has been identified. We report the analysis of the expression of one of them (gas-1) in transformed cells. We found a down regulation of gas-1 expression in NIH 3T3 cells transfected in vitro with an activated Ha-ras oncogene. In five chemically-induced mouse tumours grown in vivo the amounts of gas-1 mRNA were largely different but not related to the proliferating activity (evaluated by both H3 histone expression and 3H-thymidine incorporation into DNA). The amount of gas-1 mRNA in the tumours was in general higher than in normal tissues. Expression of c-myc was also evaluated and found to be high in tumours which exhibited low gas-1 expression. Two fibrosarcomas, CA-2 and CB-20, with similar phenotype, similar growth rate, different expression of c-myc and 100-fold difference in gas-1 expression were further investigated and gas-1 expression was found to be correlated with the expression of a differentiated function (as judged from collagen expression). Cell lines derived from CA-2 and CB-20 and maintained under different culture conditions showed that the cell cycle regulation and serum response of gas-1 expression were lost in CA-2. The higher steady state level of gas-1 mRNA in spite of a shorter mRNA half life suggests that in CB-20 cells the gas-1 gene is transcribed faster than in CA-2 cells indicating that transcriptional regulation is the major determinant of gas-1 gene expression in tumour cells. The finding of gas-1 expression in tumour cells suggests that its expression is not sufficient to maintain cells into quiescence, however, as a marker specific for the G0 phase, it could be useful, in conjunction with other growth related genes, to define the cell cycle distribution of a cell population.

Regulation of C-myc protooncogene expression in osteoblastic cells by arachidonic acid metabolites: relationship to proliferation

Prostaglandin E2 and leukotriene B4 are metabolites of arachidonic acid with well-characterized effects on osteoblastic cells. Prostaglandin E2 has been shown to be a potent bone-resorbing agent and to stimulate as well as inhibit osteoblastic cell proliferation. Leukotriene B4 has also been demonstrated to stimulate or inhibit osteoblastic cell proliferation, depending on the cell type tested. In the present study, the potential relationship of the effects of prostaglandin E2 and leukotriene B4 on osteoblastic cell proliferation to c-myc protooncogene expression was investigated. Prostaglandin E2 has been shown previously to inhibit normal rat osteoblastic cell proliferation. The present studies show that prostaglandin E2 at 10(-6) M decreased c-myc expression in these cells. In the human osteoblastic osteosarcoma cell line, G292, prostaglandin E2 increased c-myc expression and inhibited proliferation. In contrast, epidermal growth factor increased DNA synthesis as well as c-myc expression. Prostaglandin E2 also inhibited proliferation of another human osteoblastic osteosarcoma cell line, Saos-2, but it did not produce any changes in c-myc expression. In these cells, epidermal growth factor did not affect either DNA synthesis or c-myc expression. Leukotriene B4 did not show any effects on c-myc expression in any of the osteoblastic cells tested.

c-fos protein-like immunoreactivity: distribution in the human brain and over-expression in the hippocampus of patients with Alzheimer's disease

c-fos protein-like immunoreactivity was investigated in the human brain post mortem, using a polyclonal antiserum raised against the N-terminal conserved peptide of c-fos protein. Immunostaining was found in the cerebral cortex, hippocampus, striatum, thalamus and cerebellum but not in the upper brainstem and the adrenal gland. c-fos-like immunoreactivity predominated in neuronal elements, but was also observed in neuropil and glial cells. In addition to a nuclear localization, the staining could be seen in neuronal dendrites (i.e. in the pyramidal cells of hippocampus or in some cortical areas). In order to analyse the effect of brain injury on c-fos expression, the characteristics of the immunostaining were analysed in the hippocampus of patients deceased with Alzheimer's disease known to be associated with a preferential vulnerability of the pyramidal neurons. No staining was observed in the senile plaques or in neurofibrillary tangles, the histopathological stigmata of the disease. Densitometric measurement of the intensity of c-fos-like staining revealed a significant increase in the hilus, the fimbria and the CA1 field of the pyramidal layer in brains of patients with Alzheimer's disease compared to controls. These modifications may result from a suffering stage of hippocampal cells or from a compensatory mechanism in the still surviving neurons not yet affected by the pathological process.

Differential induction of 12-O-tetradecanoylphorbol-13-acetate sequence gene expression in murine melanocytes and melanoma cells

We previously showed that growth of the nontumorigenic, immortal murine melanocyte line Mel-ab correlates with the depletion of protein kinase C (PKC), whereas quiescence is associated with elevated levels of this enzyme (Brooks G, et al., Cancer Res 51: 3281-3288, 1991). Here we report responses that occur in these cells downstream of PKC activation or downregulation. We examined induction of 12-O-tetradecanoylphorbol-13-acetate (TPA)-inducible sequence (TIS) gene expression in Mel-ab melanocytes and in their transformed counterparts, B16 melanoma cells. Exposure of quiescent Mel-ab cells to the PKC-activating phorbol esters TPA or sapintoxin A at 81 nM for 2 h increased levels of mRNA for six of seven TIS genes examined (twofold to 80-fold increase in steady-state RNA levels for TIS 1, 7, 8, 11, 21, and 28 (c-fos); TIS 10 expression was not affected). No induction of TIS gene expression was observed either in growing Mel-ab cells maintained in 324 nM phorbol 12,13-dibutyrate or in B16 cells previously unexposed to phorbol esters, in which normal PKC levels were endogenously depressed. The cAMP-elevating agents choleratoxin (10 nM) and dibutyryl cyclic AMP (2.5 mM) increased levels of TIS mRNA (with the exception of TIS 10) in both proliferating Mel-ab and B16 cells, suggesting that downregulation of the PKC pathway is specific and not a consequence of a general inhibition of all signalling pathways.

Platelet-activating factor and polyunsaturated fatty acids in cerebral ischemia or convulsions: intracellular PAF-binding sites and activation of a fos/jun/AP-1 transcriptional signaling system

Platelet-activating factor (PAF) is a lipid mediator formed in the early response of the central nervous system to ischemia or convulsions. Free polyunsaturated fatty acids and arachidonic and docosahexaenoic acids are accumulated along with PAF. Antagonists of PAF have been found to improve cerebral blood flow and partially block the rise in free fatty acids, an effect that may arise by way of inhibition of PAF receptors or stimulation of the reacylation of free fatty acids released upon insult. Three intracellular PAF-binding sites have been identified in rat cerebral cortex. These very high-affinity binding sites are inhibited by PAF antagonists, with certain antagonists exhibiting specificity for a particular binding site. This specificity indicates heterogeneity in these binding sites. Ischemia or stimulation also leads to protooncogene transcriptional activation. Here, we discuss studies with cells in culture showing that PAF promotes transcriptional activation of immediate-early genes. PAF activates the transcription of the immediate-early genes fos and jun, whose gene products are regulators of the transcription of other genes. Transcription of fos is also activated by convulsion or ischemia in the central nervous system. The activation of these genes by PAF can be inhibited by PAF antagonists, and is apparently accomplished by way of an AP-1 transcription regulatory sequence in the promoter region of the target genes. Studies with deletion mutants show that PAF can also exert its activating properties by way of cyclic adenosine-3',5'-monophosphate-(cAMP) and Ca(2+)-responsive elements, and suggest that PAF is involved in an interconnected network of cell signaling that may coordinate short-term and long-term responses of cells to stimulus and injury.

The plasmacytoma J558L lacks constitutively active NF-kappa B and is deficient in early response gene activation

In mature B cells the nuclear factor NF-kappa B which binds within the kappa enhancer is constitutively present in the nucleus. However, the lambda light chain producing myeloma J558L has been found to lack constitutively functional NF-kappa B. Deoxycholate released functional NF-kappa B from cytoplasmic extracts and functional NF-kappa B was present in J558L following cycloheximide but not phorbol ester treatment. J558L was also unable to respond to phorbol ester stimulation with synthesis of mRNA from the early response gene TIS11. J558L differs from S107, another myeloma which was found to be deficient in the synthesis of NF-kappa B but not in the activation of TIS11. Somatic cell hybrids were used to further define the defect in J558L; hybrids were made with the myelomas S107 and S194 and the pre-B cell line 70Z/3. In general, complementation of the defect in J558L was observed; however there was not a direct correlation between the levels of TIS11 mRNA and NF-kappa B expression in the somatic cell hybrids, suggesting that the pathways of activation of these genes, while possibly sharing common elements, are not identical. The defect in J558L was surprising given that it has frequently been used for the expression of transfected light chain genes.

Zinc transfer from transcription factor IIIA fingers to thionein clusters

The rapid induction of thionein (apometallothionein) by many endogenous stimuli such as steroid hormones, cytokines, and second messengers suggests that this cysteine-rich, metal binding protein participates in an as yet undefined role in cellular regulatory processes. This study demonstrates with DNA and RNA binding assays and in vitro transcription measurements that thionein suppresses the binding of the Xenopus laevis zinc finger transcription factor IIIA (TFIIIA) to 5S RNA and to the 5S RNA gene and abrogates the capacity of TFIIIA to initiate the RNA polymerase III-catalyzed synthesis of 5S RNA. The effect is reversed by the addition of zinc and is not observed in the TFIIIA-independent transcription of a tRNA gene by the same RNA polymerase. In view of the strong tendency of thionein to complex posttransition metals such as zinc, one effect of its enhanced synthesis in vivo could be to reduce the intracellular disposability of zinc and thus modulate the actions of zinc-dependent enzymes and proteins, most notably those of the zinc finger transcription factors.

Transcriptional repression mediated by the WT1 Wilms tumor gene product

The wt1 gene, a putative tumor suppressor gene located at the Wilms tumor (WT) locus on chromosome 11p13, encodes a zinc finger-containing protein that binds to the same DNA sequence as EGR-1, a mitogen-inducible immediate-early gene product that activates transcription. The transcriptional regulatory potential of WT1 has not been demonstrated. In transient transfection assays, the WT1 protein functioned as a repressor of transcription when bound to the EGR-1 site. The repression function was mapped to the glutamine- and proline-rich NH2-terminus of WT1; fusion of this domain to the zinc finger region of EGR-1 converted EGR-1 into a transcriptional repressor.

Differential effects of transforming growth factor-beta 1 and phorbol myristate acetate on cardiac fibroblasts. Regulation of fibrillar collagen mRNAs and expression of early transcription factors

Cardiac fibroblasts are responsible for synthesis and deposition of fibrillar collagen types I and III. Transforming growth factor-beta 1 (TGF-beta 1) has been proved to increase collagen biosynthesis in various systems, both in vivo and in vitro. We have investigated the effect of TGF-beta 1 on collagen gene expression in cultured cardiac fibroblasts and have compared this effect with that of a mitogenic agent, phorbol myristate acetate (PMA). The regulation of collagen types I and III gene expression was examined by using cDNA probes to rat alpha 2 (I) and mouse alpha 1 (III) procollagens. Quiescent cultured cardiac fibroblasts from rabbit heart were treated with TGF-beta 1 (10-15 ng/ml) and PMA (200 ng/ml). After 24 hours of treatment with TGF-beta 1, the abundance of mRNA for pro-alpha 2 (I) and pro-alpha 1 (III) collagens was increased by 112% (p less than 0.001) and 97% (p = 0.05), respectively, in treated fibroblasts compared with untreated cells. However, PMA-treated cells showed an opposite response: a 42% (p = 0.01) decrease in mRNA levels for pro-alpha 2 (I) collagen was observed. Immunofluorescent staining of cardiac fibroblasts in culture with anti-type I collagen antibody showed that alterations in mRNA levels led to altered collagen synthesis: cellular collagen was relatively increased in TGF-beta 1-treated cells and significantly diminished in PMA-treated cells. The abundance of mRNA for pro-alpha 1 (III) collagen was not affected by PMA treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Differences in induction of c-fos transcription by cholera toxin-derived cyclic AMP and Ca2+ signals in astrocytes and 3T3 fibroblasts

The B subunit of cholera toxin, a protein which binds specifically to membrane ganglioside GM1, is known to affect cell growth and differentiation. To investigate the mechanism of these cellular responses at the nuclear level, we used the induction of c-fos in astrocytes and 3T3 fibroblasts as a model. Northern blot analysis showed that treatment with B subunit provokes a rapid and transient expression of c-fos mRNA, independent of a measurable increase in cyclic AMP. The B subunit signal, which is mediated by Ca2+, was compared to cholera toxin and other agents which increase intracellular cyclic AMP levels. In transient transfection assays of astrocytes and fibroblasts, functional analysis of c-fos promoter deletions was used to identify the elements involved in transcriptional activation by B subunit. In astrocytes, the DNA region including the serum response element and the cyclic AMP response element (CRE) are equally required, whereas 3T3 cells require only the CRE for maximal induction. A synergistic effect of signal transduction was mediated by calcium and cyclic AMP on the CRE, being positive in 3T3 cells and negative in astrocytes. Diverse regulatory elements may be thus involved in responses of different cell types to the same extracellular signal. Furthermore, a single regulatory element (CRE) can integrate both calcium and cyclic AMP signals in the control of gene expression.

Differences in "primary response" gene expression in renal compensatory hypertrophy and hyperplasia

The induction of a family of primary response genes (ie, genes whose transcription is not dependent on new protein synthesis) occurs within minutes after stimulation of quiescent 3T3 cells by phorbol esters and growth factors. A similar pattern of gene expression is seen in PC-12 pheochromocytoma cells induced to differentiate by nerve growth factor (NGF), suggesting that a common set of activating signals occur in different forms of cell growth. To determine whether the same "activation" process occurs in renal hypertrophy, we measured mRNA levels in mice subjected to uninephrectomy (UNX) or sham operation. Regenerative renal hyperplasia was induced by intraperitoneal folic acid (FA) injection with vehicle as control. Northern blots showed induction of these genes by FA with elevated mRNA levels persisting for up to 24 to 48 hours. UNX and sham operation demonstrated a slight and transient elevation of mRNA levels, with a prompt return to basal levels by 60 minutes.

The Egr family of nuclear signal transducers

Extracellular ligands regulate the induction of several genes without the need for de novo protein synthesis. A subset of these so-called immediate-early response genes (IEG) encode transcription factors. This report focuses on the Egr group of zinc finger transcription factors. Their characterization should provide important insights into how cells respond to diverse extracellular signals.

Requirement of the adenovirus E1A transformation domain 1 for inhibition of PC12 cell neuronal differentiation

Expression of the adenovirus early gene E1A inhibits the nerve growth factor (NGF)-induced differentiation of PC12 pheochromocytoma cells. Expression of the 12S form of E1A, which lacks the transcription activation region, also inhibited PC12 cell differentiation in a manner similar to the wild-type gene. Three cellular proteins--the retinoblastoma susceptibility gene product referred to as 105(Rb)-, 107-, and 300-kDa proteins--stably interacted with the different E1A polypeptides. Analysis of the association of these cellular proteins with mutant E1A polypeptides demonstrated that a functional domain 1, which is minimally involved in the association of the 300-kDa protein with E1A, was sufficient to inhibit neuronal differentiation. Deletion of transformation domain 2, which encodes sequences necessary for the binding of the 105(Rb)- and 107-kDa proteins, did not influence the ability of the mutant E1A polypeptide to inhibit PC12 cell differentiation. E1A was also shown to alter the expression of mRNAs for the early response genes c-fos, c-myc, egr-1, and c-jun and their regulation in response to NGF. In clones expressing either 12S or 13S E1A, NGF stimulation of c-fos and c-myc was repressed. In contrast, basal mRNA levels for c-jun and egr-1 were constitutively elevated and not significantly affected further by challenge with NGF. Simply expressing c-jun by gene transfer, however, did not mimic the action of E1A because constitutively expressing c-jun clones differentiated in response to NGF. Thus, expression of the E1A polypeptide disrupts NGF control of early transcription events that have been shown to be critical for PC12 cell neuronal differentiation.