Membrane depolarization and calcium induce c-fos transcription via phosphorylation of transcription factor CREB

Roles of mechano-sensitive ion channels, cytoskeleton, and contractile activity in stretch-induced immediate-early gene expression and hypertrophy of cardiac myocytes

Mechanical loading of cardiac and skeletal muscles in vivo and in vitro causes rapid activation of a number of immediate-early (IE) genes and hypertrophy of muscle cells. However, little is known as to how muscle cells sense mechanical load and transduce it into intracellular signals of gene regulation. We examined roles of putative cellular mechanotransducers, mechanosensitive ion channels, the cytoskeleton, and contractile activity in stretch-induced hypertrophy of cardiac myocytes grown on a deformable silicone sheet. Using the patch-clamp technique, we found a single class of stretch-activated cation channel that was completely blocked by gadolinium (Gd3+). Inhibition of this channel by Gd3+ did not affect either the stretch-induced expression of IE genes or the increase in protein synthesis. Neither disruption of microtubules with colchicine nor that of actin microfilaments by cytochalasin D prevented the stretch-induced IE gene expression and increase in protein synthesis. Arresting contractile activity of myocytes by high K+, tetrodotoxin, or Ba2+ did not affect the stretch-induced IE gene expression. Tetrodotoxin-arrested myocytes could increase protein synthesis in response to stretch. These results suggest that Gd(3+)-sensitive ion channels, microtubules, microfilaments, and contractile activity may not be necessary for transduction of mechanical stretch into the IE gene expression and hypertrophy. The stimulus of membrane stretch may be transmitted to the cell nucleus through some mechanisms other than electrical or direct mechanical transduction in cardiac myocytes.

Nuclear protein phosphorylation and growth control

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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.

Altered genetic response to beta-adrenergic receptor activation in late passage C6 glioma cells

Previous studies have demonstrated variability in the phenotype of rat C6 glioma cells. In the present study, we compared morphology, growth rate, and beta-adrenergic regulation of gene expression in early (P39-47) and late (P55-90) passage C6 cells. Morphological changes were observed in five independently derived, late passage populations. In four of the five, the untreated cells were more polygonal than the fibroblast-like parental cells, and only a small fraction exhibited process outgrowth after dbcAMP treatment. Untreated cells from the fifth late passage population had longer cytoplasmic processes than parental cells and responded to dbcAMP with further process outgrowth. All late passage populations had shorter generation times than the parental cells. In early passage cells, treatment with the beta-adrenergic agonist, isoproterenol (IPR), resulted in an increase in c-fos mRNA and a decrease in c-jun mRNA (Gu-bits RM, Yu H: J Neurosci Res, 30:625-630, 1991). Both of these immediate early gene responses were irreversibly lost between P50 and P55. Additional differences in basal or IPR-induced mRNA levels were observed for beta-APP, GFAP, NGF, and PPE, but not for a number of other mRNAs. These results are discussed in relationship to previously described differences in the ability of early and late passage C6 cells to accumulate cAMP (Mallorga P, et al.: Biochim Biophys Acta 678:221-229, 1981).

An ATF/CREB binding motif is required for aberrant constitutive expression of the MHC class II DR alpha promoter and activation by SV40 T-antigen

Constitutive expression of major histocompatibility complex class II (MHC II) antigens normally occurs in B-lymphocytes and antigen presenting cells of the monocyte/macrophage lineage. However, many malignant tumours and transformed cells express these proteins aberrantly. We demonstrate here that the MHC II DR alpha promoter is constitutively active both in the SV40 large T antigen transformed cell line, COS, and in CV1 cells from which they are derived. As an approach to understanding the molecular mechanisms underlying aberrant DR alpha expression we have examined the cis- and trans-acting requirements for DR alpha transcription in these cell types. Electrophoretic mobility shift assays showed that the region immediately 3' to the X-box was bound by a member of the ATF/CREB family of transcription factors. Using deletions and point mutations in the DR alpha promoter we demonstrate that, in contrast to B-cells, the octamer motif and conserved X- and Y-boxes make only a minor contribution to promoter function while single point mutations in the ATF/CREB motif reduced transcription up to 20-fold. In addition, we show that the DR alpha promoter is activated by SV40 large T-antigen and that activation requires an intact ATF/CREB motif. Similar data were obtained using B16 melanoma cells. These results suggest that the ATF/CREB motif may be a target for transcription deregulation in several transformed cell types.

A cyclic AMP-responsive element-binding transcriptional activator in Drosophila melanogaster, dCREB-A, is a member of the leucine zipper family

In this report, we describe the isolation and initial characterization of a Drosophila protein, dCREB-A, that can bind the somatostatin cyclic AMP (cAMP)-responsive element and is capable of activating transcription in cell culture. Sequence analysis demonstrates that this protein is a member of the leucine zipper family of transcription factors. dCREB-A is unusual in that it contains six hydrophobic residue iterations in the zipper domain rather than the four or five commonly found in this group of proteins. The DNA-binding domain is more closely related to mammalian CREB than to the AP-1 factors in both sequence homology and specificity of cAMP-responsive element binding. In embryos, dCREB-A is expressed in the developing salivary gland. A more complex pattern of expression is detected in the adult; transcripts are found in the brain and optic lobe cell bodies, salivary gland, and midgut epithelial cells of the cardia. In females, dCREB-A is expressed in the ovarian columnar follicle cells, and in males, dCREB-A RNA is seen in the seminal vesicle, ejaculatory duct, and ejaculatory bulb. These results suggest that the dCREB-A transcription factor may be involved in fertility and neurological functions.

Involvement of tyrosine kinase and protein kinase C in platelet-activating-factor-induced c-fos gene expression in A-431 cells

In A-431 cells, platelet-activating factor (PAF) induces the expression of c-fos and TIS-1 genes in both the absence and the presence of cycloheximide in a structurally specific and receptor-coupled manner. We have now investigated the molecular mechanisms of this response, particularly in relation to the role of protein kinases. Pretreatment of cells with genistein or methyl-2,5-dihydroxycinnamate (tyrosine kinase inhibitors) or staurosporine (a protein kinase C inhibitor) for 20 min abolished the c-fos expression induced by PAF. Interestingly, when genistein was added 90 s after addition of PAF, no inhibition was observed. Similarly, staurosporine did not inhibit c-fos expression when added 8 min after PAF addition to the cells. These inhibitions were dose-dependent (IC50 for staurosporine was 180 nM, and for genistein 50 microM). Simultaneous addition of PAF and phorbol 12-myristate 13-acetate (PMA) did not give a synergistic effect on c-fos expression. Pretreatment of cells with PMA had no effect on [3H]PAF binding, but abolished the PAF-induced gene expression. PAF-stimulated gene expression was desensitized if cells were pretreated with PAF. Interestingly, epidermal growth factor was able to stimulate c-fos expression in PAF-desensitized cells, and thus indicated involvement of distinct mechanisms for the two stimuli. Forskolin, an activator of adenylate cyclase, did not induce c-fos expression and had no effect on the PAF response. Exposure of cells to PAF for as little as 1 min, followed by its removal, was sufficient to activate the gene expression and demonstrated the rapidity and the exquisite nature of the signalling involved in this process. It is concluded that activation of PAF receptor (a proposed G-protein-coupled receptor) causes rapid production of signals which induce the expression of c-fos gene and that this is mediated via tyrosine kinase and protein kinase C.

The human T cell receptor gamma genes are transcribed from TATA-less promoters containing a conserved heptamer sequence

We have used the anchored polymerase chain reaction (A-PCR) to clone and compare the 5' upstream regions of the human T cell receptor gamma (TRG) genes. Whereas little homology was found among subgroups I, II, III and IV, sequence alignment of TRG subgroup I members revealed a high degree of homology in the 5' sequences. A conserved heptamer sequence (CTGCAGG), which was found upstream from the translation initiation site of all TRG genes in our analysis. Determination of the transcription initiation site located the conserved heptamer 65 base pairs upstream from the cap sites of V5. No TATA box or other cis-acting promoter sequences could be identified in any of the human TRG upstream sequences.

Intranuclear Ca2+ transients during neurite regeneration of an adult mammalian neuron

Depolarization-induced increases in cytoplasmic and intranuclear Ca2+ were visualized in adult mammalian dorsal root ganglion (DRG) neurons during different stages of neurite extension by using confocal laser scanning microscopy and the long-wavelength Ca2+ indicator dye fluo 3-AM (acetoxymethyl ester of fluo 3). In neurons beginning to extend neurites, depolarization led to pronounced increases in nuclear and nucleolar Ca2+ levels severalfold greater than corresponding increases in the cytoplasm. The nucleolar Ca2+ signal often exceeded that of the nucleus, indicating regional heterogeneity of the nucleus. The subcellular calcium transients were dependent on extracellular Ca2+ and the level of depolarization, indicating the importance of transmembrane Ca2+ fluxes in triggering the nuclear events. After neurite extension, the nuclear Ca2+ signals were attenuated and never exceeded cytoplasmic levels. These results indicate that activity-dependent modulation of intranuclear Ca2+ levels is greater in DRG neurons during early neurite extension. Given the importance of Ca2+ in gene expression, the results may be relevant to Ca(2+)-dependent nuclear events responsible for axonal regeneration.

A cyclic AMP-responsive element-binding transcriptional activator in Drosophila melanogaster, dCREB-A, is a member of the leucine zipper family

In this report, we describe the isolation and initial characterization of a Drosophila protein, dCREB-A, that can bind the somatostatin cyclic AMP (cAMP)-responsive element and is capable of activating transcription in cell culture. Sequence analysis demonstrates that this protein is a member of the leucine zipper family of transcription factors. dCREB-A is unusual in that it contains six hydrophobic residue iterations in the zipper domain rather than the four or five commonly found in this group of proteins. The DNA-binding domain is more closely related to mammalian CREB than to the AP-1 factors in both sequence homology and specificity of cAMP-responsive element binding. In embryos, dCREB-A is expressed in the developing salivary gland. A more complex pattern of expression is detected in the adult; transcripts are found in the brain and optic lobe cell bodies, salivary gland, and midgut epithelial cells of the cardia. In females, dCREB-A is expressed in the ovarian columnar follicle cells, and in males, dCREB-A RNA is seen in the seminal vesicle, ejaculatory duct, and ejaculatory bulb. These results suggest that the dCREB-A transcription factor may be involved in fertility and neurological functions.

The transcription factor CREB, but not immediate-early gene encoded proteins, is expressed in activated microglia of lumbar spinal cord following sciatic nerve transection in the rat

Expression of CREB, JUN, FOS and KROX-24 proteins was investigated in glial cells of the lumbar spinal cord. In untreated rats, CREB, c-JUN and JUN D were present in glial cells of the ventral and dorsal horn. Following sciatic nerve transection, the number of CREB immunoreactive glial cells increased in both the ipsilateral ventral and dorsal horns between 24 h and 48 h, reached a maximum after 5 days and returned to control levels after 20 days. Counterstaining with Cresyl violet, a general stain of cells, revealed that the increase of CREB positive glial cells was congruent with the increase of the number of glial cells. Staining with GFAP, a marker for astrocytes, showed an increase in intensity of labelling but no change in number of GFAP labelled cells. This indicates a constitutive expression of CREB in activated microglia. The number of glial cells labelled by c-JUN and JUN D did not change, and glial cells were not labelled by FOS and KROX-24 proteins following sciatic nerve transection. These findings demonstrate that proliferation and differentiation of glial cells in vivo can occur in absence of JUN, FOS and KROX proteins.

Regulation of gene expression in PC12 cells via an activator of dual second messengers: pituitary adenylate cyclase activating polypeptide

In this study we demonstrate that the activator protein-1 (AP-1) DNA motif, initially considered to be unresponsive to cyclic AMP (cAMP), does function as a cAMP-response element in PC12 cells. A luciferase reporter gene driven by the collagenase promoter that contains the AP-1 motif is responsive to cAMP as well as phorbol esters when transfected in PC12 cells. We have recently shown that pituitary adenylate cyclase activating peptide (PACAP) has neurotrophic properties and activates both adenylylcyclase and the inositol lipid cascade in PC12 cells. Consistent with these actions, we demonstrate that PACAP is an effective activator of luciferase reporter genes whose promoters bear the AP-1 motif, as well as the related DNA element that binds the protein CREB. Both the cAMP and inositol lipid pathways appear to play a role in the activation of these motifs by PACAP. Mutation of the AP-1 motif and its juxtaposition to a heterologous promoter proves that the AP-1 motif is a locus for response to cAMP and PACAP. The luciferase reporter genes bearing the AP-1 motif are not cAMP responsive in HeLa tk- cells, indicating that the mode of second-messenger responsiveness is cell-type specific.

Transient c-fos expression accompanies naturally occurring cell death in the developing interhemispheric cortex of the rat

We have searched for the possible correlation of naturally occurring cell death with spontaneously enhanced c-fos expression in the developing cerebral cortex of normal Wistar albino rats. During the late prenatal and early postnatal period, cells with irregular contours and intracytoplasmic electron-dense granules (granule-containing cells) were apparent in the interhemispheric cortex, including the anterior cingulate and the retrosplenial cortices. These cells were loosely packed within the cortical layers derived from the cortical plate. Having excluded the possibility that these cells could be phagocytes by immunocytochemical experiments, we propose that they are cells in different phases of a process of autophagic degeneration and death. Images of extreme nuclear pyknosis were also apparent in identical locations. Cells showing immunoreactivity for c-Fos protein appeared in the same cortical areas. The immunoreactive cells were very abundant in the retrosplenial cortex, but were also present in the anterior cingulate cortex. These cells showed markedly irregular contours and large, densely immunoreactive intracytoplasmic inclusions; these images were similar to those of granule-containing cells revealed by conventional stains. The immunoreactivity for c-Fos protein was ephemeral, occurring exclusively during embryonic days 20 and 21, but granule-containing cells were observed for a longer period. The present results provide evidence, albeit indirect, that c-fos expression may occur in certain neural cells at the onset of a process of death by autophagia, and suggest a possible involvement of the proto-oncogene c-fos in certain forms of naturally occurring neuronal death.

The transcription factors c-JUN, JUN D and CREB, but not FOS and KROX-24, are differentially regulated in axotomized neurons following transection of rat sciatic nerve

In adult rats, expression of c-JUN, JUN B, JUN D, c-FOS, FOS B, KROX-24 and CREB proteins was investigated by immunocytochemistry in L4 and L5 dorsal root ganglia and lumbar spinal cord for up to 300 days following transection of the left sciatic nerve. In dorsal root ganglia, expressions of c-JUN and JUN D were increased 10 h and 15 h after sciatic nerve transection, respectively. c-JUN was still at an elevated level after 300 days predominantly in small diameter neurons, whereas JUN D had declined to control levels after 100 days. In contrast to the JUN proteins, expression of CREB showed a delayed onset after 10 days and reached a maximum between 70 and 150 days. In motoneurons, expression of c-JUN and JUN D was increased 15 h and 25 h after sciatic nerve transection, respectively. Expression of c-JUN remained increased after 150 days, whereas JUN D had declined to control levels after 70 days. In contrast, expression of CREB declined within 30 h in axotomized motoneurons and remained on a reduced level for up to 150 days. JUN B, c-FOS, FOS B and KROX-24 were not induced either following axotomy or following a repeated nerve crush. Sciatic nerve transection including the surgical procedure transynaptically provoked a transient expression of all JUN, FOS and KROX-24 proteins in neurons of spinal dorsal horn which disappeared after 5 days except the expression of JUN D which lasted for up to 20 days. In contrast, CREB immunoreactivity was not at all altered in neurons of spinal dorsal horn. In untreated animals, CREB and to a lesser extent JUN D showed an ubiquitous expression in neurons and glia cells of spinal cord, whereas expression of c-JUN and a weak expression of FOS B were restricted to motoneurons. In neurons of the dorsal root ganglia, a basal expression was found for c-JUN, JUN D and CREB and, at a low level, for FOS B and KROX-24. c-JUN and JUN D were colocalized with CREB in many cells such as interneurons, motoneurons, dorsal root ganglion cells and glial cells indicating the possibility for both the control of c-jun and jun D expression by CREB and the competition of JUN and CREB proteins for CRE consensus sequences.

Stimulation of c-fos and c-jun gene expression and down-regulation of proenkephalin gene expression in C6 glioma cells by endothelin-1

The linkage between the transmembrane signal transduction system utilized by endothelin and alterations in gene expression has been investigated in C6 glioma cells. Treatment of C6 cells with endothelin-1 caused a rapid and transient 5-fold increase in c-fos and c-jun mRNA levels, followed by a decrease at 4 h. Dose-response studies indicated that 1 nM endothelin-1 caused half-maximal induction of c-fos mRNA 0.5 h after treatment and that maximal induction was elicited with a concentration of 10 nM. Actinomycin D totally abolished the rapid increase in c-fos mRNA caused by endothelin, indicating that the effect is at the transcriptional level. Endothelin-1 caused a decrease in proenkephalin mRNA to 50% of control levels at 4 h after treatment and had no effect on histone H4 mRNA over a 24 h period that was examined. These data indicate that receptor binding of endothelin-1 leads to rapid changes in the expression of immediate-early response genes which may cause more prolonged changes in the expression of AP-1 and/or CREB target genes in the nervous system.

The expression of the immediate-early genes c-fos, egr-1 and c-jun in the accessory olfactory bulb during the formation of an olfactory memory in mice

Female mice form a memory for the pheromones of the male with which they mate. It has been proposed that the site of the synaptic changes underlying this memory is the accessory olfactory bulb, at the first level of the accessory olfactory system. In this study we have examined the expression of the immediate-early genes c-fos, c-jun and egr-1 in the mitral and granule cells of the accessory olfactory bulb immediately after mating, during the period of memory formation. Transient increases were seen in the number of granule cell nuclei expressing c-fos and the number of granule and mitral cell nuclei expressing egr-1, during the period of memory formation. No changes were observed in the expression of c-jun during this period. The increase in the number of cells expressing c-fos and egr-1 required the association of mating and pheromonal exposure, conditions also required for memory formation. Large increases in the number of mitral and granule cell nuclei expressing c-fos and egr-1 were also observed following the infusion of the drug bicuculline into the accessory olfactory bulb in the absence of mating. This procedure has previously been shown to result in the formation of a nonspecific memory for male pheromones. These results associate the expression of c-fos and egr-1 in the accessory olfactory bulb with the conditions required for the formation of an olfactory memory for male pheromones.

Excitatory amino acid receptor activation produces a selective and long-lasting modulation of gene expression in hippocampal neurons

Activation of excitatory amino acid (EAA) receptors in cultured hippocampal neurons causes down-regulation of the protein ligatin, a receptor for phosphoglycoproteins and a marker protein for membrane-vesicle transport systems. This reduction occurs at both physiologic and excitotoxic levels of glutamate stimulation and is accompanied by a significant decrease in steady state levels of ligatin mRNA. Reduction in ligatin mRNA occurs within 60 min and persists 24 h later. Steady state levels of mRNAs encoding cyclophilin, an ubiquitous cytosolic protein, and neuron specific-enolase (N-SE) are not diminished by glutamate receptor activation, demonstrating that down-regulation of ligatin mRNA was not a result of general catabolism. Further, this reduction in ligatin mRNA occurred without induction of HSP 70. Pharmacological studies using selective antagonists and agonists indicate that this down-regulation of ligatin gene expression is predominantly mediated by the N-methyl-D-aspartate (NMDA) subclass of EAA receptors and that Ca2+ is required. This is the first report that EAA receptor activation in hippocampal neurons can pretranslationally down-regulate gene expression in a rapid and long-lasting manner under physiologic, as well as cytotoxic conditions. The data support the hypothesis that modulation of neuronal gene expression may represent a molecular mechanism mediating some of the long-lasting functional and pathophysiological effects of EAA on cell function.

Sequences that direct rat tyrosine hydroxylase gene expression

Investigation of neuroendocrine genes has revealed that transcription is regulated via multiple DNA binding sites, including the cyclic AMP response element (CRE). We show here that for the neuronal and chromaffin-specific gene tyrosine hydroxylase (TH), a 70-bp region (-229 to -160) lacking the CRE is sufficient, in either orientation, to confer levels of chloramphenicol acetyltransferase reporter expression equivalent to or greater than that conferred by 4.8 kb of the rat TH enhancer/promoter region. The 70-bp region contains potential binding sites for AP2, AP1, E2A/MyoD, and POU transcription factors, and functions when linked to the TH promoter, but not when joined to a heterologous RSV promoter. This demonstrates that promoter as well as enhancer elements are important for TH expression. In gel-shift assays, the 70-bp fragment forms a cell type-specific complex with nuclear extracts from TH-expressing cells. which is effectively competed by an oligonucleotide containing AP2, AP1, and E2A/MyoD (E box) sites, but not by one containing the POU site. These data suggest that the AP2, AP1, and/or E box sites may be involved in forming the cell-specific complex. Although it lacks an authentic CRE, the 70-bp region also mediated a twofold transcriptional response to forskolin, equivalent to that found with the endogenous gene. A different region (-60 to -29) bearing a consensus CRE mediated a sixfold increase in transcription in response to forskolin, but only minimally activated basal transcription from the TH promoter in the absence of forskolin.

Trans-synaptic regulation of gene expression

Neurotransmitters regulate gene expression through second messenger cascades that transmit the signal from the plasma membrane to the nucleus of the postsynaptic cell. Ca2+ and cAMP are two of the second messengers that regulate gene expression in response to neurotransmitters. The Ca2+ and cAMP signals induce expression of a class of genes, termed immediate early genes, within minutes of neurotransmitter receptor activation. Many of these genes encode transcription factors that regulate the expression of late response genes. The results of recent experiments have elucidated mechanisms by which neurotransmitter-induced Ca2+ and cAMP signals regulate immediate early gene expression.

The effect of stimulus duration on noxious-stimulus induced c-fos expression in the rodent spinal cord

C-fos is a proto-oncogene that is expressed within some neurons following depolarization. The protein product, fos, has been proposed as an anatomical marker for neuronal activity following noxious peripheral stimulation. However, the literature on noxious-stimulus induced fos expression contains several puzzling observations on the time course and laminar distribution of neuronal labeling within the spinal cord. This study has analyzed the effect of stimulus duration on the expression of fos-like immunoreactivity (FLI) within the spinal cord of anesthetized rats. In order to examine the time course of fos expression following brief periods of stimulation, we required a type of stimulus that was intense enough to activate nociceptors but that did not produce tissue damage. We have therefore employed pulsed, high intensity electrical stimulation, with stimulus durations ranging from 3 s to 24 h. The results indicate that stimulus duration has a profound effect upon the number of labeled cells, the intensity of neuronal labeling, the laminar pattern of FLI, and the time course of fos expression. Brief stimulation periods induce relatively few and relatively lightly labeled neurons, located predominantly within the most superficial laminae of the dorsal horn. Maximal immunoreactivity appears approximately 2 h after stimulation has ceased, and disappears within hours. Continuous stimulation produces many more labeled cells, darker labeling, and FLI within both dorsal and ventral laminar regions. Maximal FLI is seen after approximately 4.5 h of continuous stimulation, with reduction in the number of labeled cells thereafter. These data indicate that the results of any study employing c-fos as a marker for neuronal activity may be affected by the duration of the exciting stimulus.

Induction of D2 dopamine receptor mRNA synthesis in a 6-hydroxydopamine parkinsonian rat model

By injecting 6-hydroxydopamine into the pars compacta of the substantia nigra, we produced a hemiparkinsonian rat model in which there is almost complete destruction of the dopaminergic nigrostriatal pathway but sparing of the dopaminergic mesolimbic system. The lesion has been characterized by several criteria: a rotational behavior in response to apomorphine, a complete loss of tyrosine hydroxylase immunoreactivity in the lesioned substantia nigra, a near total depletion of dopamine and metabolites in the striatum ipsilateral to the lesion, and a supersensitivity of the dopamine D2 receptors in the ipsilateral striatum. Dopaminergic striatal deafferentation was accompanied by an increase of D2 receptor mRNA synthesis in the striatum ipsilateral to the lesion, suggesting that the increased D2 receptor density observed after the lesion is due to an increase of the synthesis of receptor molecules. This synthesis appears to be regulated at the transcriptional level.

The CREB family of transcription activators

A diverse family of transcription factors bind to the cAMP-response elements found in a variety of mammalian and viral gene promoters. One of the members of this family, CREB, is being intensively studied so as to elucidate the mechanisms by which second messenger signal transduction pathways act to positively and negatively regulate transcription.

Testing the in vivo role of protein kinase C and c-fos in neurite outgrowth by microinjection of antibodies into PC12 cells

To define the molecular bases of growth factor-induced signal transduction pathways, antibodies known to block the activity of either protein kinase C (PKC) or the fos protein were introduced into PC12 cells by microinjection. The antibody against PKC significantly inhibited neurite outgrowth when scored 24 h after microinjection and exposure to nerve growth factor (NGF). Microinjection of antibodies to fos significantly increased the percentage of neurite-bearing cells after exposure to either NGF or basic fibroblast growth factor (bFGF) but inhibited the stimulation of DNA synthesis by serum, suggesting that in PC12 cells, fos is involved in cellular proliferation. Thus, activation of PKC is involved in the induction of neurite outgrowth by NGF, but expression of the fos protein, which is induced by both NGF and bFGF, is not necessary and inhibits neurite outgrowth.

Regulation of cyclic AMP response element-binding protein (CREB) phosphorylation by acute and chronic morphine in the rat locus coeruleus

Previous studies have implicated adaptations in the cyclic AMP system in mechanisms of opiate tolerance, dependence, and withdrawal in the rat locus coeruleus. It has been speculated that such adaptations may occur at the level of gene expression. To understand better the mechanism by which opiates produce these intracellular adaptations, we studied morphine regulation of the state of phosphorylation of cyclic AMP response element-binding protein (CREB), a transcription factor that mediates some of the effects of the cyclic AMP system on gene expression. We show here, by use of a back phosphorylation and immunoprecipitation procedure, that acute morphine decreases the state of phosphorylation of CREB, an effect that becomes completely attenuated after chronic morphine administration. In contrast, acute precipitation of opiate withdrawal, via administration of an opiate receptor antagonist, increases the phosphorylation state of CREB. Such regulation of CREB phosphorylation could be part of the molecular pathway by which opiates produce changes in gene expression that lead to addiction.

C-fos immunoreactivity in the brain following unilateral electrical stimulation of the dorsal periaqueductal gray in freely moving rats

C-fos immunoreactivity was used to reveal brain areas in which neurons were influenced by electrical stimulations applied to the dorsal periaqueductal gray. These stimulations were applied in freely moving rats so that the resulting behaviors could be observed. Shortly afterwards, the brains of the rats were processed for C-fos immunoreactivity. In order to determine the specificity of the brain areas thus labeled, control stimulations were applied to the ventral tegmental area of other rats. Immunoreactive cells were found surrounding the tip of the stimulation electrode within a radius of 0.5 mm. This labeled area extended further along the rostro-caudal axis than along the medio-lateral or dorso-ventral axis in the periaqueductal gray. Distally, clusters of labeled cells were found ipsilaterally in the caudal periaqueductal gray extending to the nucleus cuneiformis, and bilaterally in the locus coeruleus and supramamillary decussation. More widespread labeling was found in most hypothalamic subareas and in the lateral habenula. The labeled brain areas following ventral tegmental area stimulations were totally distinct, and comprised the medial forebrain bundle, the nucleus accumbens, the vertical limb of the diagonal band and the medial septum. The pattern of labeling produced by periaqueductal gray stimulations was therefore specific, and provided information about brain structures involved in the motivational and behavioral effects of such stimulations.

Differential induction of the c-fos promoter through distinct PDGF receptor-mediated signaling pathways

The multiple isoforms of PDGF induce fibroblastic mitogenesis through two distinct PDGF receptors, alpha and beta. The molecular mechanisms by which these alpha and beta PDGF receptors regulate gene expression are poorly understood. We present data which indicates that differential induction of c-fos gene expression by PDGF isoforms occurs through distinct PDGF alpha and beta receptor-mediated signaling pathways. Comparison of PDGF-AA with PDGF-BB stimulation showed that PDGF-BB induced prolonged expression of the c-fos gene in BALB/c-3T3 cells, but that PDGF-AA induced more potent activation of the serum response element (SRE) in transient transfection assays. PDGF-AA, which binds alpha but not beta PDGF receptors, could only induce the SRE through a protein kinase C (PKC)-dependent pathway, whereas PDGF-BB, which binds both alpha and beta PDGF receptors, could also induce the SRE through a PKC-independent pathway. These results suggest that PDGF alpha receptors activate the PKC-dependent signaling pathway while PDGF beta receptors also activate a PKC-independent pathway. In addition, we found that PDGF-BB could induce another c-fos promoter element within the -90 to +10 region, suggesting that the more potent mitogenic effect and prolonged c-fos gene expression induced by PDGF-BB may result from cooperativity between more than one c-fos promoter elements.

From ligand binding to gene expression: new insights into the regulation of G-protein-coupled receptors

Transmembrane signaling systems relay information from the exterior to the interior of a cell, through a series of complex protein-protein interactions and second messenger cascades. One such system consists of the G-protein-coupled receptors, which interact with G proteins upon ligand binding, and in turn activate an effector molecule. The receptor is the first component in this signaling cascade and is subject to considerable regulation. Recent studies have shown that these regulatory events can occur at the levels of receptor protein modification and receptor gene expression. Interestingly, some of these processes appear to be mediated by the same second messenger systems that these receptors activate, which leads to various forms of positive and negative feedback regulation.

Glucocorticoid-mediated down regulation of c-fos mRNA in C6 glioma cells: lack of correlation with proenkephalin mRNA

We investigate the linkage between the transcriptional factor, c-fos, and expression of proenkephalin in rat C6 glioma cells. C6 cells contained abundant levels of c-fos mRNA. Treatment of cells with dexamethasone resulted in a 10-fold decline in c-fos transcripts and a small increase in proenkephalin mRNA. Combined exposure to dexamethasone and isoproterenol also induced a decrease in c-fos mRNA while proenkephalin mRNA increased 8-fold. Treatment of the C6 cells with phorbol 12-myristate 13-acetate caused a 13-fold increase in c-fos expression 0.5 h after administration and a decrease in proenkephalin mRNA. These data indicate that c-fos and proenkephalin mRNA are not regulated in a sequential, parallel manner, that newly synthesized c-fos is not the determining factor controlling proenkephalin gene regulation, and that c-fos expression is under negative control by glucocorticoids.

Long-term expression of the c-fos protein during the in vitro differentiation of cerebellar granule cells induced by potassium or NMDA

Levels of the c-fos protein were assayed in mouse cerebellar granule cells during their in vitro development under different culture conditions. When grown in media favoring both their survival and differentiation, i.e. in the presence of 30 mM K+ or 12.5 mM K+ plus 100 microM N-methyl-D-aspartate (NMDA), the c-fos protein becomes detectable in the nucleus of granule cells on and after 6 days and persists to high levels until the culture begins to decline. The protein c-fos appears therefore after the critical period described for the survival effect of K+ depolarization or NMDA receptor stimulation which corresponds to days 2-5 after plating. The c-fos protein remains however scarcely detectable or undetectable throughout the life-span of cells cultured under conditions providing poor survival and differentiation, i.e. in the presence of low K+ (5 or 12.5 mM) alone or when the effect of NMDA is blocked by the NMDA receptor antagonist MK-801. Interestingly, in cortical and striatal neurons, the survival and differentiation of which being not affected by depolarizing media, no c-fos protein is detected whatever the culture conditions tested at least during the first 18 days in vitro. This suggests that long-term expression of the c-fos gene might be related to some aspect of the late in vitro differentiation process of cerebellar granule cells.

Differential induction of immediate early genes by excitatory amino acid receptor types in primary cultures of cortical and striatal neurons

In primary cultures of neurons from cerebral cortex and striatum, 30 s stimulation with the excitatory amino acid glutamate elicited a 5 to 9-fold increase in immediate early gene (IEG) mRNAs. Glutamate increased c-fos, c-jun, jun-B, and NGFI-A (zif/268) mRNAs by binding to both alpha-amino-3-hydroxy-5-methylisoxazolepropionic acid (AMPA) and N-methyl-D-aspartate (NMDA) receptor types, and increased c-fos, jun-B, and NGFI-A mRNAs by binding to the metabotropic receptor. NMDA receptor activation elicited IEG expression by a transmembrane calcium influx; AMPA receptor-induced depolarization played a permissive role for the opening of the NMDA receptor channel. The protein kinase C (PKC) inhibitor H-7 (but not inhibitors of cyclic nucleotide-dependent and calcium/calmodulin-dependent protein kinases) partially blocked IEG expression induced by glutamate.

Attenuation of Fos-like immunoreactivity induced by a single electroconvulsive shock in brains of aging mice

c-fos is a proto-oncogene that encodes for a nuclear phosphoprotein with DNA binding properties and is presumed to have an important role in the long-term regulation of neuronal function. It is thought to act as a 'third messenger' molecule in signal transduction systems and its expression has been shown to be induced by a variety of exogenous and endogenous stimuli. This study examines the differential expression of the Fos protein in various brain regions after a single electroconvulsive shock (ECS) in 6-, 13-, and 28-month-old B6C3 mice. The animals received an acute electroconvulsive shock (90 V for 0.3 s), without prior anesthesia, through earclip electrodes and exhibited generalized tonic-clonic seizures lasting 20-36 s. Animals were anesthetized and perfused intracardially with 2.5% acrolein, 4% paraformaldehyde at 0.5, 1.0, 2.0 and 4.0 h postshock. The brains were Vibratome-sectioned (30 microns) and examined using a Fos antibody, directed against a conserved region of both mouse and human Fos by standard immunocytochemical methods. Systematic sampling of the total number of Fos immunostained neurons in amygdala, hippocampus and the cerebral cortex showed peak values at the 1-h time point followed by a steady decline thereafter in all age groups. In a second experiment, Fos-like immunoreactivity was compared 1 h after ECS in the hippocampus, amygdala and the cortex in all 3 age groups. There was increased expression of Fos-like immunoreactivity after ECS- compared to non-ECS-treated controls in all age groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Neuronal activity and tonotopy in the auditory system visualized by c-fos gene expression

Responsiveness in the cochlear nucleus complex and inferior colliculus of the mouse to tonal stimulation is labelled via immunocytochemically stained Fos protein that is expressed by c-fos gene activation in excited neurons. The locations of Fos-positive neurons closely reproduce the tonotopic maps in the dorsal cochlear nucleus and inferior colliculus. Thus, the c-fos method can demonstrate stimulus-related local neuronal activation on a single-cell level and may be useful to complement other mapping techniques such as electrophysiological recording or 2-deoxyglucose autoradiography.

Dual role for calcium in the control of spike duration in rat supraoptic neuroendocrine cells

Magnocellular neurosecretory cells (MNCs) display activity-dependent changes in spike duration to modulate Ca2+ influx both in their somata, and in their axon terminals in the neurohypophysis. This study reveals (i) that Ca2+ influx is required to mediate the expression of spike broadening, and (ii) that internal Ca2+ activates a delayed component of spike repolarization in MNCs of the rat supraoptic nucleus. This mechanism provides a rapid feedback control of spike-mediated Ca2+ influx in these neuroendocrine cells.

Uncoupling of Chlamydomonas flagellar gene expression and outgrowth from flagellar excision by manipulation of Ca2+

Chlamydomonas cells respond to certain environmental stimuli by shedding their flagella. Flagellar loss induces a rapid, transient increase in expression of a specific set of genes encoding flagellar proteins, and assembly of a new flagellar pair. While flagellar gene expression and initiation of flagellar outgrowth are normally tightly coupled to flagellar excision, our results demonstrate that these processes can be uncoupled by manipulating Ca2+ levels or calmodulin activity. In our experiments, wild-type cells were stimulated to excise their flagella using mechanical shearing, and at times after deflagellation, flagellar lengths were measured and flagellar mRNA abundance changes were determined by S1 nuclease protection analysis. When extracellular Ca2+ was lowered by addition of EGTA to cultures before excision, flagellar mRNA abundance changes and flagellar outgrowth were temporally uncoupled from flagellar excision. When extracellular Ca2+ was lowered immediately after excision or when calmodulin activity was inhibited with W-7, flagellar outgrowth was uncoupled from flagellar excision and flagellar mRNA abundance changes. Whenever events in the process of flagellar regeneration were temporally uncoupled, the magnitude of the flagellar mRNA abundance change was reduced. These results suggest that flagellar gene expression may be regulated by multiple signals generated from these events, and implicate Ca2+ as a factor in the mechanisms controlling flagellar regeneration.

Induction of somatostatin by kainic acid in pyramidal and granule cells of the rat hippocampus

Seizures were induced in rats by systemic administration of kainic acid and, 1.5-12 h after, expression of preprosomatostatin and c-fos mRNAs in 9 hippocampal areas and in the cerebral perirhinal cortex was investigated using in situ hybridization histochemistry. Immunohistochemistry was also performed to study somatostatin peptide. In the control animals preprosomatostatin mRNA was expressed in some cells in the dentate hilus, the stratum oriens and the stratum radiatum of Ammon's horn, the subiculum and the cortex. Starting 3 h after kainic acid administration preprosomatostatin mRNA was expressed in a subpopulation of granule and pyramidal cells which did not normally express it. Preprosomatostatin mRNA-positive cells were markedly increased in the subiculum. Immunohistochemical examination confirmed that preprosomatostatin mRNA in granule and pyramidal cells was translated into peptide. In contrast, c-fos mRNA was induced in most hippocampal and cortical neurons starting 1.5 h after the kainic acid injection. When diazepam was injected to suppress the generalized seizures, preprosomatostatin mRNA was still expressed in pyramidal and subicular cells but not in granule cells.

Synaptic regulation of immediate early gene expression in primary cultures of cortical neurons

Neuronal stimulation can rapidly activate several immediate early genes that code for transcription factors. We have used primary cortical cultures to study the regulation of four of these genes, c-fos, c-jun, jun-B, and zif268. Immunocytochemical studies with antibodies to Jun-B, c-Jun, and c-Fos demonstrate intense staining in the nuclei of a subset of cortical neurons in mature cultures (21-25 days in vitro) but not young cultures (3-7 days in vitro). To assess whether this immunoreactivity may be induced by spontaneous synaptic activity that develops with a similar profile, we examined the effects of agents that reduce this synaptic activity. Tetrodotoxin or N-methyl-D-aspartate receptor antagonists suppress basal immunoreactivity to Jun-B and c-Fos, but not c-Jun, indicating that the basal level of c-Jun expression is not dependent on electrical activity. Picrotoxin, an agent that increases synaptic excitation indirectly by blocking inhibitory synaptic currents mediated by gamma-aminobutyric acidA receptors, markedly increases the percentage of neurons displaying immunoreactivity to c-Fos, c-Jun, Jun-B, and Zif268. Northern analysis suggests that the increases in immunostaining induced by picrotoxin are secondary to a rapid increase in mRNA for these proteins. These findings provide evidence for rapid transcriptional regulation of immediate early genes in cortical neurons by synaptic activity.

Transcriptional regulation by cAMP

Cyclic AMP regulates a myriad of cellular processes through the cAMP-dependent protein kinase A. In many cases, activation of protein kinase A leads to altered patterns of gene transcription. Identification of the cAMP-response-element-binding-protein as a major nuclear substrate for protein kinase A accounts for many recent advances in understanding the signal transduction pathway. This review will focus on the role of cAMP-response-element-binding protein in coupling protein kinase A to the transcriptional machinery and the mechanisms that control cAMP signalling during mammalian development.

Electrical activation and c-fos mRNA expression in rat neurosecretory neurones after systemic administration of cholecystokinin

1. The expression of c-fos mRNA in the rat hypothalamus was examined by in situ hybridization following systemic administration of cholecystokinin (CCK), a procedure known to activate magnocellular oxytocin neurons but not magnocellular vasopressin neurones. 2. Conscious male rats were given a single I.P. injection of 50 micrograms/kg CCK, c-fos mRNA signal was apparent in the supraoptic and paraventricular nuclei in rats killed 10 min after injection but not in uninjected or saline-(vehicle) injected rats. The density of c-fos mRNA at both sites was further elevated in rats killed 30 min or 60 min following injection, and was absent in rats killed 4 h after injection. 3. In the paraventricular nucleus the most dense expression of c-fos mRNA following CCK administration was in the medial, mainly parvocellular portion of the nucleus, in an area corresponding to the distribution of corticotrophin-releasing factor mRNA determined by in situ hybridization in adjacent sections. 4. The I.P. injection of CCK increased plasma oxytocin concentrations, measured by specific radioimmunoassay from 13 +/- 5 pg/ml in control rats to 107 +/- 9 pg/ml in the rats killed 10 min after injection, a similar response to that observed previously in urethane-anaesthetized rats. 5. In each of six urethane-anaesthetized rats, recordings were made from single neurones in the supraoptic nucleus, identified antidronomically as projecting to the posterior pituitary and identified electrophysiologically as putative oxytocin neurones. Following I.P. injection of 50 micrograms/kg CCK, the neurones increased their firing rate by a mean of 1.3 +/- 0.2 spikes/s averaged over the 10 min following injection. 6. From the appearance of c-fos mRNA in supraoptic neurones following CCK administration we conclude that this message is expressed in magnocellular oxytocin neurones, since vasopressin neuronal activity and vasopressin release is known to be unaffected by this stimulus, and since the supraoptic nucleus contains essentially only oxytocin neurones and vasopressin neurones. 7. We conclude that c-fos mRNA expression can be induced in supraoptic oxytocin neurones following brief and modest episodes of electrical activation, suggesting that c-fos may be involved in the gene regulation of these neurones under physiological conditions.

Neural regulation of calmodulin in adult Xenopus leg muscle

Two Ca(2+)-binding proteins important in regulating muscle responses to Ca2+ flux are differentially expressed following denervation of Xenopus laevis gastrocnemius. Levels of parvalbumin (PV) RNA transcripts and proteins decrease in abundance, while calmodulin (CaM) transcript and protein levels increase. Our studies on PV kinetics in Xenopus follow a pattern observed in other species, however, our observation of a concomitant increase in CaM has not been documented in any system. Molecular analyses of the Xenopus CaM gene indicate that its structure and upstream sequences are highly conserved across several vertebrate species and implicate several transcription factors in the regulation of its expression.