Structure and mapping of the fosB gene. FosB downregulates the activity of the fosB promoter

Long-lasting expression of FosB/ΔFosB immunoreactivity following acute stress in the paraventricular and supraoptic nuclei of the rat hypothalamus

We examined expression profiles of FosB/∆FosB immunoreactivity and fosB gene transcripts in the paraventricular nucleus of the hypothalamus (PVH) and the supraoptic nucleus (SON) of rats following acute surgical stress (SS) and restraint stress (RS) and compared them with those of c-Fos immunoreactivity and c-fos mRNA. Following SS, the number of FosB/ΔFosB-ir cells markedly increased, the time course of which was slow-onset and long-lasting, in contrast with rapid-onset and short-lived c-Fos expression. Characteristically long-lasting FosB/ΔFosB expression was also observed following RS. On the other hand, fosB mRNA was short-lived, and its time course not much different from that of c-fos mRNA; thus, the long-lasting expression of FosB/∆FosB immunoreactivity may be attributed to the longer half-life of FosB proteins, and not to the persistent expression of fosB gene transcripts. Following SS, FosB/ΔFosB immunoreactivity was present mainly in PVH corticotropin-releasing factor (CRF) neurons and SON vasopressin (AVP) neurons, while c-Fos immunoreactivity in either PVH CRF neurons, or AVP and oxytocin neurons in PVH and SON. Following RS, FosB/ΔfosB- and c-Fos expression was almost restricted to PVH CRF neurons. The present study raises the possibility that FosB proteins in discrete populations of hypothalamic neuroendocrine neurons may play roles in forming adaptability to and/or resilience against stress, which takes longer than the acute phase response.

Effect of Gender on Chronic Intermittent Hypoxic Fosb Expression in Cardiorespiratory-Related Brain Structures in Mice

We aimed to delineate sex-based differences in neuroplasticity that may be associated with previously reported sex-based differences in physiological alterations caused by repetitive succession of hypoxemia-reoxygenation encountered during obstructive sleep apnea (OSA). We examined long-term changes in the activity of brainstem and diencephalic cardiorespiratory neuronal populations induced by chronic intermittent hypoxia (CIH) in male and female mice by analyzing Fosb expression. Whereas the overall baseline and CIH-induced Fosb expression in females was higher than in males, possibly reflecting different neuroplastic dynamics, in contrast, structures responded to CIH by Fosb upregulation in males only. There was a sex-based difference at the level of the rostral ventrolateral reticular nucleus of the medulla, with an increase in the number of FOSB/ΔFOSB-positive cells induced by CIH in males but not females. This structure contains neurons that generate the sympathetic tone and which are involved in CIH-induced sustained hypertension during waking hours. We suggest that the sex-based difference in neuroplasticity of this structure contributes to the reported sex-based difference in CIH-induced hypertension. Moreover, we highlighted a sex-based dimorphic phenomenon in serotoninergic systems induced by CIH, with increased serotoninergic immunoreactivity in the hypoglossal nucleus and a decreased number of serotoninergic cells in the dorsal raphe nucleus in male but not female mice. We suggest that this dimorphism in the neuroplasticity of serotoninergic systems predisposes males to a greater alteration of neuronal control of the upper respiratory tract associated with the greater collapsibility of upper airways described in male OSA subjects.

Activation of DREAM (downstream regulatory element antagonistic modulator), a calcium-binding protein, reduces L-DOPA-induced dyskinesias in mice

BACKGROUND

Previous studies have implicated the cyclic adenosine monophosphate/protein kinase A pathway as well as FosB and dynorphin-B expression mediated by dopamine D1 receptor stimulation in the development of 3,4-dihydroxyphenyl-L-alanine (L-DOPA)-induced dyskinesia. The magnitude of these molecular changes correlates with the intensity of dyskinesias. The calcium-binding protein downstream regulatory element antagonistic modulator (DREAM) binds to regulatory element sites called DRE in the DNA and represses transcription of target genes such as c-fos, fos-related antigen-2 (fra-2), and prodynorphin. This repression is released by calcium and protein kinase A activation. Dominant-active DREAM transgenic mice (daDREAM) and DREAM knockout mice (DREAM(-/-)) were used to define the involvement of DREAM in dyskinesias.

METHODS

Dyskinesias were evaluated twice a week in mice with 6-hydroxydopamine lesions during long-term L-DOPA (25 mg/kg) treatment. The impact of DREAM on L-DOPA efficacy was evaluated using the rotarod and the cylinder test after the establishment of dyskinesia and the molecular changes by immunohistochemistry and Western blot.

RESULTS

In daDREAM mice, L-DOPA-induced dyskinesia was decreased throughout the entire treatment. In correlation with these behavioral results, daDREAM mice showed a decrease in FosB, phosphoacetylated histone H3, dynorphin-B, and phosphorylated glutamate receptor subunit, type 1 expression. Conversely, genetic inactivation of DREAM potentiated the intensity of dyskinesia, and DREAM(-/-) mice exhibited an increase in expression of molecular markers associated with dyskinesias. The DREAM modifications did not affect the kinetic profile or antiparkinsonian efficacy of L-DOPA therapy.

CONCLUSIONS

The protein DREAM decreases development of L-DOPA-induced dyskinesia in mice and reduces L-DOPA-induced expression of FosB, phosphoacetylated histone H3, and dynorphin-B in the striatum. These data suggest that therapeutic approaches that activate DREAM may be useful to alleviate L-DOPA-induced dyskinesia without interfering with the therapeutic motor effects of L-DOPA.

The extraction of simple relationships in growth factor-specific multiple-input and multiple-output systems in cell-fate decisions by backward elimination PLS regression

Cells use common signaling molecules for the selective control of downstream gene expression and cell-fate decisions. The relationship between signaling molecules and downstream gene expression and cellular phenotypes is a multiple-input and multiple-output (MIMO) system and is difficult to understand due to its complexity. For example, it has been reported that, in PC12 cells, different types of growth factors activate MAP kinases (MAPKs) including ERK, JNK, and p38, and CREB, for selective protein expression of immediate early genes (IEGs) such as c-FOS, c-JUN, EGR1, JUNB, and FOSB, leading to cell differentiation, proliferation and cell death; however, how multiple-inputs such as MAPKs and CREB regulate multiple-outputs such as expression of the IEGs and cellular phenotypes remains unclear. To address this issue, we employed a statistical method called partial least squares (PLS) regression, which involves a reduction of the dimensionality of the inputs and outputs into latent variables and a linear regression between these latent variables. We measured 1,200 data points for MAPKs and CREB as the inputs and 1,900 data points for IEGs and cellular phenotypes as the outputs, and we constructed the PLS model from these data. The PLS model highlighted the complexity of the MIMO system and growth factor-specific input-output relationships of cell-fate decisions in PC12 cells. Furthermore, to reduce the complexity, we applied a backward elimination method to the PLS regression, in which 60 input variables were reduced to 5 variables, including the phosphorylation of ERK at 10 min, CREB at 5 min and 60 min, AKT at 5 min and JNK at 30 min. The simple PLS model with only 5 input variables demonstrated a predictive ability comparable to that of the full PLS model. The 5 input variables effectively extracted the growth factor-specific simple relationships within the MIMO system in cell-fate decisions in PC12 cells.

Drug experience epigenetically primes Fosb gene inducibility in rat nucleus accumbens

ΔFosB, a Fosb gene product, is induced in nucleus accumbens (NAc) and caudate-putamen (CPu) by repeated exposure to drugs of abuse such as cocaine. This induction contributes to aberrant patterns of gene expression and behavioral abnormalities seen with repeated drug exposure. Here, we assessed whether a remote history of cocaine exposure in rats might alter inducibility of the Fosb gene elicited by subsequent drug exposure. We show that prior chronic cocaine administration, followed by extended withdrawal, increases inducibility of Fosb in NAc, as evidenced by greater acute induction of ΔFosB mRNA and faster accumulation of ΔFosB protein after repeated cocaine reexposure. No such primed Fosb induction was observed in CPu; in fact, subsequent acute induction of ΔFosB mRNA was suppressed in CPu. These abnormal patterns of Fosb expression are associated with chromatin modifications at the Fosb gene promoter. Prior chronic cocaine administration induces a long-lasting increase in RNA polymerase II (Pol II) binding at the Fosb promoter in NAc only, suggesting that Pol II "stalling" primes Fosb for induction in this region upon reexposure to cocaine. A cocaine challenge then triggers the release of Pol II from the gene promoter, allowing for more rapid Fosb transcription. A cocaine challenge also decreases repressive histone modifications at the Fosb promoter in NAc, but increases such repressive marks and decreases activating marks in CPu. These results provide new insight into the chromatin dynamics at the Fosb promoter and reveal a novel mechanism for primed Fosb induction in NAc upon reexposure to cocaine.

Serum response factor and cAMP response element binding protein are both required for cocaine induction of ΔFosB

The molecular mechanism underlying induction by cocaine of ΔFosB, a transcription factor important for addiction, remains unknown. Here, we demonstrate a necessary role for two transcription factors, cAMP response element binding protein (CREB) and serum response factor (SRF), in mediating this induction within the mouse nucleus accumbens (NAc), a key brain reward region. CREB and SRF are both activated in NAc by cocaine and bind to the fosB gene promoter. Using viral-mediated Cre recombinase expression in the NAc of single- or double-floxed mice, we show that deletion of both transcription factors from this brain region completely blocks cocaine induction of ΔFosB in NAc, whereas deletion of either factor alone has no effect. Furthermore, deletion of both SRF and CREB from NAc renders animals less sensitive to the rewarding effects of moderate doses of cocaine when tested in the conditioned place preference (CPP) procedure and also blocks locomotor sensitization to higher doses of cocaine. Deletion of CREB alone has the opposite effect and enhances both cocaine CPP and locomotor sensitization. In contrast to ΔFosB induction by cocaine, ΔFosB induction in NAc by chronic social stress, which we have shown previously requires activation of SRF, is unaffected by the deletion of CREB alone. These surprising findings demonstrate the involvement of distinct transcriptional mechanisms in mediating ΔFosB induction within this same brain region by cocaine versus stress. Our results also establish a complex mode of regulation of ΔFosB induction in response to cocaine, which requires the concerted activities of both SRF and CREB.

Morphine activates the E twenty six-like transcription factor-1/serum response factor pathway via extracellular signal-regulated kinases 1/2 in F11 cells derived from dorsal root ganglia neurons

Morphine-induced signaling via opioid receptors (ORs) in dorsal root ganglia (DRG) neurons, the spinal cord, and various brain regions has been shown to modulate gene activity. Hitherto, little attention has been paid to extracellular signal-regulated kinases-1/2 (ERK-1/2)-mediated activation of the serum response factor (SRF) and ternary complex factors (TCFs) such as the E twenty six-like transcription factor-1 (ELK-1) in this context. Using TCF/SRF-dependent reporter gene constructs, a specific ERK-1/2 inhibitor and a dominant-negative ELK-1 mutant, we show herein that morphine activates ELK-1 via ERK-1/2 in DRG-derived F11 cells endogenously expressing μ and δ ORs. Previous studies with glioma cell lines such as NG108-15 cells attributed morphine-induced gene expression to the activation of the cAMP-responsive element binding protein (CREB). Thus, we also analyzed morphine-dependent activation of CREB in F11 and NG108-15 cells. In contrast to the CREB stimulation found in NG108-15 cells, we observed an inhibitory effect of morphine in F11 cells, indicating cell type-specific regulation of CREB by morphine. To obtain data about putative target genes of morphine-induced ELK-1/SRF activation, we analyzed mRNA levels of 15 ELK-1/SRF-dependent genes in cultured rat DRG neurons and F11 cells. We identified the early growth response protein-4 (EGR-4) as the strongest up-regulated gene in both cell types and observed ELK-1 activity-dependent activation of an EGR-4-driven reporter in F11 cells. Overall, we reveal an important role of ELK-1 for morphine-dependent gene induction in DRG-derived cells and propose that ELK-1 and EGR-4 contribute to the effects of morphine on neuronal plasticity.

Quantitative AP-1 gene regulation by oxidative stress in the human retinal pigment epithelium

The purpose of this study was to characterize the early molecular responses to quantified levels of oxidative stress (OS) in the human retinal pigment epithelium (RPE). Confluent ARPE-19 cells were cultured for 3 days in defined medium to stabilize gene expression. The cells were exposed to varying levels of OS (0-500 microM H(2)O(2)) for 1-8 h and gene expression was followed for up to 24-h after OS. Using real-time qPCR, we quantified the expression of immediate early genes from the AP-1 transcription factor family and other genes involved in regulating the redox status of the cells. Significant and quantitative changes were seen in the expression of six AP-1 transcription factor genes, FosB, c-Fos, Fra-1, c-Jun, JunB, and ATF3 from 1-8 h following OS. The peak level of induced transcription from OS varied from 2- to 128-fold over the first 4 h, depending on the gene and magnitude of OS. Increased transcription at higher levels of OS was also seen for up to 8-h for some of these genes. Protein translation was examined for 24-h following OS using Western blotting methods, and compared to the qPCR responses. We identified six AP-1 family genes that demonstrate quantitative upregulation of expression in response to OS. Two distinct types of quantifiable OS-specific responses were observed; dose-dependent responses, and threshold responses. Our studies show that different levels of OS can regulate the expression of AP-1 transcription factors quantitatively in the human RPE in vitro.

Kaposi's sarcoma-associated herpesvirus Lana-1 is a major activator of the serum response element and mitogen-activated protein kinase pathways via interactions with the Mediator complex

In cells infected with Kaposi's sarcoma-associated herpesvirus (KSHV), the activation of mitogen-activated protein kinase (MAPK) pathways plays a crucial role early after virus infection as well as during reactivation. In order to systematically identify viral proteins activating MAPK pathways in KSHV-infected cells, a clone collection of KSHV open reading frames (ORFs) was screened for induction of the serum response element (SRE), as SRE is induced by MAPKs. The strongest induction of the SRE was found with ORF73 (latency-associated nuclear antigen 1, or Lana-1), although weaker activation was also found with the kaposin B isoform, ORF54 (dUTPase) and ORF74 (G-protein-coupled receptor). The bipartite SRE is bound by a ternary complex consisting of serum response factor (SRF) and ternary complex factor. Lana-1 bound directly to SRF, but also to the MED25 (ARC92/ACID-1), MED15 (PCQAP) and MED23 (Sur-2) subunits of the Mediator complex, a multi-subunit transcriptional co-activator complex for RNA polymerase II. Lana-1-induced SRE activation was inhibited by the dominant-negative N-terminal domain of the MED25 mediator subunit, suggesting that this subunit mediates Lana-1-induced SRE activation. In summary, these data suggest a model in which Lana-1 acts as an adaptor between the transcription factor SRF and the basal transcriptional machinery.

Antagonistic regulation of cell-matrix adhesion by FosB and DeltaFosB/Delta2DeltaFosB encoded by alternatively spliced forms of fosB transcripts

Among fos family genes encoding components of activator protein-1 complex, only the fosB gene produces two forms of mature transcripts, namely fosB and DeltafosB mRNAs, by alternative splicing of an exonic intron. The former encodes full-length FosB. The latter encodes DeltaFosB and Delta2DeltaFosB by alternative translation initiation, and both of these lack the C-terminal transactivation domain of FosB. We established two mutant mouse embryonic stem (ES) cell lines carrying homozygous fosB-null alleles and fosB(d) alleles, the latter exclusively encoding DeltaFosB/Delta2DeltaFosB. Comparison of their gene expression profiles with that of the wild type revealed that more than 200 genes were up-regulated, whereas 19 genes were down-regulated in a DeltaFosB/Delta2DeltaFosB-dependent manner. We furthermore found that mRNAs for basement membrane proteins were significantly up-regulated in fosB(d/d) but not fosB-null mutant cells, whereas genes involved in the TGF-beta1 signaling pathway were up-regulated in both mutants. Cell-matrix adhesion was remarkably augmented in fosB(d/d) ES cells and to some extent in fosB-null cells. By analyzing ES cell lines carrying homozygous fosB(FN) alleles, which exclusively encode FosB, we confirmed that FosB negatively regulates cell-matrix adhesion and the TGF-beta1 signaling pathway. We thus concluded that FosB and DeltaFosB/Delta2DeltaFosB use this pathway to antagonistically regulate cell matrix adhesion.

B-cell receptor activation induces BIC/miR-155 expression through a conserved AP-1 element

microRNA-155 is an oncogenic microRNA that has been shown to be critical for B-cell maturation and immunoglobulin production in response to antigen. In line with its function in B-cell activation, miR-155, and its primary transcript, B-cell integration cluster (BIC), is induced by B-cell receptor (BCR) cross-linking. Using pharmacological inhibitors in the human B-cell line, Ramos, we show that activation of BIC and miR-155 expression by BCR signaling occurs through the extracellular signaling-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) pathways but not the p38 pathway. BCR activation results in the induction of c-Fos, FosB, and JunB, and expression of these are suppressed by ERK and JNK inhibitors. Reporter analysis established a key role for a conserved AP-1 site approximately 40 bp upstream from the site of initiation but not an upstream NF-kappaB site or a putative c-Ets located at the site of initiation. Lastly, chromatin immunoprecipitation analysis demonstrated the recruitment of FosB and JunB to the miR-155 promoter following BCR activation. These results identify key determinants of BCR-mediated signaling that lead to the induction of BIC/miR-155.

Spatiotemporal pattern of striatal ERK1/2 phosphorylation in a rat model of L-DOPA-induced dyskinesia and the role of dopamine D1 receptors

BACKGROUND

We examined the activation pattern of extracellular signal-regulated kinase 1 and 2 (ERK1/2) and its dependence on D1 versus D2 dopamine receptors in hemiparkinsonian rats treated with 3,4-dihydroxyphenyl-L-alanine (L-DOPA).

METHODS

6-Hydroxydopamine-lesioned rats were treated acutely or chronically with L-DOPA in combination with antagonists for D1 or D2 receptors. Development of dyskinesia was monitored in animals receiving chronic drug treatment. Phosphorylation of ERK1/2, mitogen- and stress-activated protein kinase-1 (MSK-1), and the levels of FosB/DeltaFosB expression were examined immunohistochemically.

RESULTS

L-DOPA treatment caused phosphorylation of ERK1/2 in the dopamine-denervated striatum after acute and chronic administration. Similar levels were observed in matrix and striosomes, and in enkephalin-positive and dynorphin-positive neurons. The severity of dyskinesia was positively correlated with phospho-ERK1/2 levels. Phosphorylation of ERK1/2 and MSK-1 was dose-dependently blocked by SCH23390, but not by raclopride. SCH23390 also inhibited the development of dyskinesia and the induction of FosB/DeltaFosB.

CONCLUSIONS

L-DOPA produces pronounced activation of ERK1/2 signaling in the dopamine-denervated striatum through a D1-receptor-dependent mechanism. This effect is associated with the development of dyskinesia. Phosphorylated ERK1/2 is localized to both dynorphinergic and enkephalinergic striatal neurons, suggesting a general role of ERK1/2 as a plasticity molecule during L-DOPA treatment.

Human T-cell leukemia virus type 1 Tax enhances serum response factor DNA binding and alters site selection

Human T-cell leukemia virus type I (HTLV-1) is the etiological agent of adult T-cell leukemia. The viral transforming protein Tax regulates the transcription of viral and cellular genes by interacting with cellular transcription factors and coactivators. The effects of Tax on cellular gene expression have an important impact on HTLV-1-mediated cellular transformation. Expression of the c-fos cellular oncogene is regulated by serum response factor (SRF), and Tax is known to induce c-fos gene expression by activating SRF-responsive transcription. SRF activates cellular gene expression by binding to a consensus DNA sequence (CArG box) located within a serum response element (SRE). Since SRF activates transcription of many growth regulatory genes, this pathway is likely to have a significant impact on Tax-mediated transformation. Here we demonstrate that Tax interacts with SRF and enhances the binding of SRF to SREs located in the c-fos, Nur77, and viral promoters. Also, we establish that in the presence of Tax, SRF selects more divergent CArG box sequences than in the absence of Tax, revealing a novel mechanism for regulating SRF-responsive gene expression. Finally, increased association of SRF with chromatin and specific promoters was observed in Tax-expressing cells, correlating with increased c-fos and Nur77 mRNA levels in Tax-expressing cells. These results suggest that Tax activates SRF-responsive transcription by enhancing its binding affinity to multiple different SRE sequences.

Serum response factor binding sites differ in three human cell types

The serum response factor (SRF) is essential for embryonic development and maintenance of muscle cells and neurons. The mechanism by which this factor controls these divergent pathways is unclear. Here we present a genome-wide view of occupancy of SRF at its binding sites with a focus on those that vary with cell type. We used chromatin immunoprecipitation (ChIP) in combination with human promoter microarrays to identify 216 putative SRF binding sites in the human genome. We performed independent quantitative PCR validation at over half of these sites that resulted in 146 sites we assert to be true binding sites at over 90% confidence. Nearly half of the sites are bound by SRF in only one of the three cell types we tested, providing strong evidence for the diverse roles for SRF in different cell types. We also explore possible mechanisms controlling differential binding of SRF in these cell types by assaying cofactor binding, DNA methylation, histone methylation, and histone acetylation at a subset of sites bound preferentially in smooth muscle cells. Although we did not see a strong correlation between SRF binding and epigenetics modifications, at these sites, we propose that SRF cofactors may play an important role in determining cell-dependent SRF binding sites. ELK4 (previously known as SAP-1 [SRF-associated protein-1]) is ubiquitously expressed. Therefore, we expected it to occupy sites where SRF binding is common in all cell types. Indeed, 90% of SRF sites also bound by ELK4 were common to all three cell types. Together, our data provide a more complete understanding of the regulatory network controlled by SRF.

Erratum to "Cellular mechanisms underlying acquired epilepsy: the calcium hypothesis of the induction and maintenance of epilepsy." [Pharmacol. Ther. 105(3) (2005) 229-266]

Epilepsy is one of the most common neurological disorders. Although epilepsy can be idiopathic, it is estimated that up to 50% of all epilepsy cases are initiated by neurological insults and are called acquired epilepsy (AE). AE develops in 3 phases: (1) the injury [central nervous system (CNS) insult]. (2) epileptogenesis (latency), and (3) the chronic epileptic (spontaneous recurrent seizure) phases. Status epilepticus (SE), stroke, and traumatic brain injury (TBI) are 3 major examples of common brain injuries that can lead to the development of AE. It is especially important to understand the molecular mechanisms that cause AE because it may lead to innovative strategies to prevent or cure this common condition. Recent studies have offered new insights into the cause of AE and indicate that injury-induced alterations in intracellular calcium concentration levels ([Ca(2+)](i)) and calcium homeostatic mechanisms play a role in the development and maintenance of AE. The injuries that cause AE are different, but the share a common molecular mechanism for producing brain damage--an increase in extracellular glutamate and are exposed to increased [Ca(2+)](i) are the cellular substrates to develop epilepsy because dead cells do not seize. The neurons that survive injury sustain permanent long-term plasticity changes in [Ca(2+)](i) and calcium homeostatic mechanisms that are permanent and are a prominent feature of the epileptic phenotype. In the last several years, evidence has accumulated indicating that the prolonged alteration in neuronal calcium dynamics plays an important role in the induction and maintenance of the prolonged neuroplasticity changes underlying the epileptic phenotype. Understanding the role of calcium as a second messenger in the induction and maintenance of epilepsy may provide novel insights into therapeutic advances that will prevent and even cure AE.

hnulp1, a basic helix-loop-helix protein with a novel transcriptional repressive domain, inhibits transcriptional activity of serum response factor

Many bHLH proteins are involved in cardiac development and cardiovascular diseases. Herein, we identified and characterized the human homologue (hnulp1) of mouse gene nulp1. The predicted protein contains a bHLH domain and a DUF654 domain in N-terminal and C-terminal, respectively. Northern blot analysis shows that a 2.3-kb transcript expressed broadly in early human embryonic and adult tissues, especially with a higher level in adult heart. hnulp1 is a transcription repressor when fused to GAL4 DNA-binding domain and co-transfected with VP-16, in which DUF654 motif represents the basal transcriptional repressive activity. Treatment of cells with trichostatin A can relieve this repression, suggesting that the DUF654 motif acts through increasing deacetylase activity at the GAL4-driven promoter. Overexpression of hnulp1 protein in COS-7 cells inhibits the transcriptional activity of serum response factor (SRF), suggesting that hnulp1 may act as a novel bHLH transcriptional repressor in SRF signaling pathway to mediate cellular functions.

Cyclic AMP response element-binding protein is required for normal maternal nurturing behavior

Analysis of mice with targeted disruptions of fosB or the gene encoding dopamine beta-hydroxylase suggests that FosB and adrenergic signaling play critical roles in maternal nurturing behavior. The majority of neonates born to null females from either mutation fail to thrive, and virgin mutant females of both lines exhibit impaired pup retrieval. Considering whether FosB and adrenergic signaling might share a signaling pathway important for maternal behavior, we examined the role of a potential intermediary, cyclic AMP response element-binding protein (CREB). Here we report that approximately 40% of neonates (all heterozygous) born to mice lacking the major isoforms of CREB (Creb-alphaDelta-/-) died within several days of birth. In contrast, heterozygotes born to Creb-alphaDelta+/- females thrived. Cross-fostering demonstrated that neonates born to Creb-alphaDelta(-/dagger/-) females thrived when reared by wild-type females, and that Creb-alphaDelta-/- females were capable of rearing neonates whose maternal care was initiated by wild-type females. Further, virgin Creb-alphaDelta-/- females were deficient in pup retrieval despite exhibiting normal investigation of pups and of novel objects. No maternal behavior phenotype was present in mice with a null mutation of the cyclic AMP response element modulator (Crem) gene. Interestingly, the number of cells immunostaining for phospho-CREB (on Ser(133)) in the medial preoptic area of the hypothalamus, a key region for the expression of maternal behavior, increased nearly three-fold in wild-type mice following exposure to pups but not to novel objects. On the other hand, basal expression and induction of FosB in response to pup exposure appeared to be independent of CREB because levels were equivalent between wild-type and Creb-alphaDelta-/- females. These results implicate CREB in maternal nurturing behavior and suggest that CREB is not critical for expression or induction of FosB in adult virgin female mice.

Cellular mechanisms underlying acquired epilepsy: the calcium hypothesis of the induction and maintainance of epilepsy

Epilepsy is one of the most common neurological disorders. Although epilepsy can be idiopathic, it is estimated that up to 50% of all epilepsy cases are initiated by neurological insults and are called acquired epilepsy (AE). AE develops in 3 phases: (1) the injury (central nervous system [CNS] insult), (2) epileptogenesis (latency), and (3) the chronic epileptic (spontaneous recurrent seizure) phases. Status epilepticus (SE), stroke, and traumatic brain injury (TBI) are 3 major examples of common brain injuries that can lead to the development of AE. It is especially important to understand the molecular mechanisms that cause AE because it may lead to innovative strategies to prevent or cure this common condition. Recent studies have offered new insights into the cause of AE and indicate that injury-induced alterations in intracellular calcium concentration levels [Ca(2+)](i) and calcium homeostatic mechanisms play a role in the development and maintenance of AE. The injuries that cause AE are different, but they share a common molecular mechanism for producing brain damage-an increase in extracellular glutamate concentration that causes increased intracellular neuronal calcium, leading to neuronal injury and/or death. Neurons that survive the injury induced by glutamate and are exposed to increased [Ca(2+)](i) are the cellular substrates to develop epilepsy because dead cells do not seize. The neurons that survive injury sustain permanent long-term plasticity changes in [Ca(2+)](i) and calcium homeostatic mechanisms that are permanent and are a prominent feature of the epileptic phenotype. In the last several years, evidence has accumulated indicating that the prolonged alteration in neuronal calcium dynamics plays an important role in the induction and maintenance of the prolonged neuroplasticity changes underlying the epileptic phenotype. Understanding the role of calcium as a second messenger in the induction and maintenance of epilepsy may provide novel insights into therapeutic advances that will prevent and even cure AE.

Transcriptional induction of FosB/DeltaFosB gene by mechanical stress in osteoblasts

Mechanical stress to bone plays a critical role in maintaining bone mass and strength. However, the molecular mechanism of mechanical stress-induced bone formation is not fully understood. In the present study, we demonstrate that FosB and its spliced variant DeltaFosB, which is known to increase bone mass by stimulating bone formation in vivo, is rapidly induced by mechanical loading in mouse hind limb bone in vivo and by fluid shear stress (FSS) in mouse calvarial osteoblasts in vitro both at the mRNA and protein levels. FSS induction of FosB/DeltaFosB gene expression was dependent on gadlinium-sensitive Ca(2+) influx and subsequent activation of ERK1/2. Analysis of the mouse FosB/DeltaFosB gene upstream regulatory region with luciferase reporter gene assays revealed that the FosB/DeltaFosB induction by FSS occurred at the transcriptional level and was conferred by a short fragment from -603 to -327. DNA precipitation assays and DNA decoy experiments indicated that ERK-dependent activation of CREB binding to a CRE/AP-1 like element (designated "CRE2") at the position of -413 largely contributed to the transcriptional effects of FSS. These results suggest that DeltaFosB participates in mechanical stress-induced intracellular signaling cascades that activate the osteogenic program in osteoblasts.

Mechanical stretch and progesterone differentially regulate activator protein-1 transcription factors in primary rat myometrial smooth muscle cells

During pregnancy, stretch of the uterus, imposed by the growing fetus, is an important signal for the induction of genes involved in the onset of labor. In this study, the expression of activator protein-1 (AP-1) family mRNAs in response to in vitro stretch was investigated in myometrial cells. Rat primary myometrial smooth muscle cells were plated onto collagen I-coated Flex I culture plates and subjected to 25% static stretch on day 4 of culture. Static stretch induced an increase in the expression of c-fos, fosB, fra-1, c-jun, and junB. The expression of both c-fos and junB was maximally induced at 30 min by static stretch. The peak induction for fosB and c-jun occurred at 1 h, whereas the peak of fra-1 induction occurred between 1 and 2 h after application of stretch. Treatment of myometrial cells with progesterone (100 nM, 400 nM, 1 microM) for 1 or 6 h before the application of static stretch did not affect the magnitude of the c-fos response. However, 24 h of progesterone exposure reduced the magnitude of c-fos and fosB stretch induction at both the 400 nM and 1 microM doses. These data indicate that several members of the AP-1 family are stretch-responsive genes in myometrial smooth muscle cells. This response can be attenuated by pretreatment with progesterone; however, the requirement for longer pretreatment times suggests that the inhibitory actions of progesterone do not occur through a direct action of the progesterone receptor within the promoter regions of AP-1 genes.

Quantitative PCR analysis of FosB mRNA expression after short duration oxygen and light stress

Quantitative polymerase chain reaction (QPCR) was used to examine changes in FosB mRNA expression in models of oxygen and light stress to the retina. C57BL/6 mice or Sprague-Dawley (SD) albino rats were subjected to several experimental paradigms: short-term light or oxygen stress, extended hyperoxia (75% oxygen), or a model of oxygen-induced retinopathy (OIR). Control animals were subjected to room air and 5 lux cyclic light. FosB expression dramatically increases in response to light stress as well as in a model of OIR, but not in response to sustained 75% oxygen. These data suggest that both hypoxia and light stress induce expression of FosB in the retina.

Identification of transcription factor binding sites upstream of human genes regulated by the phosphatidylinositol 3-kinase and MEK/ERK signaling pathways

We have taken an integrated approach in which expression profiling has been combined with the use of small molecule inhibitors and computational analysis of transcription factor binding sites to characterize regulatory sequences of genes that are targets of specific signaling pathways in growth factor-stimulated human cells. T98G cells were stimulated with platelet-derived growth factor (PDGF) and analyzed by DNA microarrays, which identified 74 immediate-early gene transcripts. Cells were then treated with inhibitors to identify subsets of genes that are targets of the phosphatidylinositol 3-kinase (PI3K) and MEK/ERK signaling pathways. Four groups of PDGF-induced genes were defined: independent of PI3K and MEK/ERK signaling, dependent on PI3K signaling, dependent on MEK/ERK signaling, and dependent on both pathways. The upstream regions of all genes in the four groups were scanned using TRANSFAC for putative cis-elements as compared with a background set of non-induced genes. Binding sites for 18 computationally predicted transcription factors were over-represented in the four groups of co-expressed genes compared with the background sequences (p < 0.01). Many of the cis-elements identified were conserved in orthologous mouse genes, and many of the predicted elements and their cognate transcription factors were consistent with previous experimental data. In addition, chromatin immunoprecipitation assays experimentally verified nine predicted SRF binding sites in T98G cells, including a previously unknown SRF site upstream of DUSP5. These results indicate that groups of human genes regulated by discrete intracellular signaling pathways share common cis-regulatory elements.

Role and regulation of activator protein-1 in toxicant-induced responses of the lung

Aberrant cell proliferation and differentiation after toxic injury to airway epithelium can lead to the development of various lung diseases including cancer. The activator protein-1 (AP-1) transcription factor, composed of mainly Jun-Jun and Jun-Fos protein dimers, acts as an environmental biosensor to various external toxic stimuli and regulates gene expression involved in various biological processes. Gene disruption studies indicate that the AP-1 family members c-jun, junB, and fra1 are essential for embryonic development, whereas junD, c-fos, and fosB are required for normal postnatal growth. However, broad or target-specific transgenic overexpression of the some of these proteins gives very distinct phenotype(s), including tumor formation. This implies that, although they are required for normal cellular processes, their abnormal activation after toxic injury can lead to the pathogenesis of the lung disease. Consistent with this view, various environmental toxicants and carcinogens differentially regulate Jun and Fos expression in cells of the lung both in vivo and in vitro. Moreover, Jun and Fos proteins distinctly bind to the promoter regions of a wide variety of genes to differentially regulate their expression in epithelial injury, repair, and differentiation. Importantly, lung tumors induced by various carcinogens display a sustained expression of certain AP-1 family members. Therefore a better understanding of the mechanisms of regulation and functional role(s), as well as identification of target genes of members of the AP-1 family in airway epithelial cells, will provide additional insight into toxicant-induced lung diseases. These studies might offer a unique opportunity to use AP-1 family members and transactivation as potential diagnostic markers or drug targets for early detection and/or prevention of various lung diseases.

Spatial and temporal profile of haloperidol-induced immediate-early gene expression and phosphoCREB binding in the dorsal and ventral striatum of amphetamine-sensitized rats

To determine if D(2) dopamine receptor-mediated nuclear signaling is altered during the development of amphetamine sensitization, we examined the expression of immediate-early gene (IEG) products, Fos, Jun, and Fos-related antigen (FRA), in both controls and amphetamine-sensitized rats after a challenge with the D(2) antagonist haloperidol. When chronic saline- or amphetamine (5 mg/kg, i.p. for 14 days)-treated rats were challenged with 2 mg/kg haloperidol at withdrawal day 3 (w3), more 35-kDa FRA was induced in the ventral striatum of the control group than in the amphetamine-treated rats. In contrast, more Jun and 35-kDa FRA were expressed in the ventral striatum of the amphetamine-treated group than in the controls when haloperidol was given at w10. Topographical analyses indicate that the decrease in FRA immunoreactive neuronal density in amphetamine-treated rats at w3 were located in the dorsolateral caudate/putamen and the nucleus accumbens shell and core subregions. Conversely, the increase in Jun-immunoreactive neurons in amphetamine-treated rats at w10 was observed in the dorsolateral caudate/putamen; in the case of the FRAs, the increase was observed in the nucleus accumbens shell. In addition, the time-dependent profile of IEG expression paralleled the activation of an upstream regulator, cAMP-response element binding protein, in the ventral striatum after haloperidol treatment. These neurochemical changes may be associated with behavioral plasticity, since amphetamine-treated rats displayed a lower amount of locomotor activity when exposed to a novel environment at w3, but had recovered at w10. Overall, the current study reveals that there is a distinct temporal and spatial profile of haloperidol-induced IEG expression and/or CREB phosphorylation in amphetamine-treated rats, suggesting that there is a critical transition between the early and late withdrawal periods.

MAPK-regulated transcription: a continuously variable gene switch?

Switching mechanisms that control genes could be viewed either as stable binary switches, in which genes exist in 'on' or 'off' states; or as quantitative rheostat-like switches, in which the rate of transcription is continuously variable and coupled directly to the strength of intracellular signalling events. Here, we discuss the biological need for quantitative gene regulation and, using mitogen-activated protein kinase (MAPK)-controlled transcription as a model, assess the evidence for its existence and postulate mechanisms by which it might occur.

Induction of 78 kD glucose-regulated protein (GRP78) expression and redox-regulated transcription factor activity by lead and mercury in C6 rat glioma cells

Lead (Pb) and mercury (Hg) are widespread environmental contaminants that induce prominent neural toxicity. Although the brain is not the major Pb and Hg depot in the body, these metals preferentially accumulate in astroglia to exert toxic effects. In this study, we examined the effects of Pb acetate and HgCl(2) on the expression of GRP78, a molecular chaperone in the endoplasmic reticulum (ER) that may provide cytoprotection in response to cellular stresses in the C6 rat glioma cell line. We also evaluated the DNA binding activities of several redox-regulated transcription factors in metal-treated cells. Our results showed that mRNA levels of GRP78 were up-regulated by Pb and Hg at 0.1 and 1 micro M, but down-regulated at higher concentrations (10 micro M). GRP78 protein levels increased in a concentration- and time-dependent manner in Pb and/or Hg-treated cells. Pb increased protein binding to the GST- Upsilon a antioxidant/electrophile response element (ARE/EpRE) and to the NF- kappaB consensus binding sequence of the cytomegalovirus 2 (CMB2) promoter, but decreased protein binding to the Ha-ras ARE/EpRE or to the c-fos 12-O-tetradecanoyl-phorbol-13-acetate (TPA) response element (TRE). In contrast, Hg activated DNA binding by all redox-regulated transcription factors. These studies shed some light on the molecular mechanisms of Pb and Hg toxicity in C6 rat glioma cells and suggest that GRP78 and oxidative stress may participate in the neurotoxic response to these metals.

High-throughput tissue microarray analysis of cyclin E gene amplification and overexpression in urinary bladder cancer

Studies by comparative genomic hybridization revealed that the 19q13 chromosomal region is frequently amplified in bladder cancer. The cyclin E gene (CCNE), coding for a regulatory subunit of cyclin-dependent kinase 2, has been mapped to 19q13. To investigate the role of cyclin E alterations in bladder cancer, a tissue microarray of 2,317 specimens from 1,842 bladder cancer patients was constructed and analyzed for CCNE amplification by fluorescence in situ hybridization and for cyclin-E protein overexpression by immunohistochemistry. Fluorescence in situ hybridization analysis showed amplification in only 30 of the 1,561 evaluable tumors (1.9%). Amplification was significantly associated with stage and grade (P: < 0.0005 each). Immunohistochemically detectable cyclin E expression was strong in 233 (12.4%), weak in 354 (18.9%), and negative in 1, 286 of the 1,873 interpretable tumors. The majority (62.1%) of CCNE-amplified tumors were strongly immunohistochemistry-positive (P: < 0.0001). The frequency of protein expression increased from stage pTa (22.2%) to pT1 (45.5%; P: < 0.0001) but then decreased for stage pT2-4 (29.4%; P: < 0.0001 for pT1 versus pT2-4). Low cyclin E expression was associated with poor overall survival in all patients (P: < 0.0001), but had no prognostic impact independent of stage. It is concluded that cyclin E overexpression is characteristic to a subset of bladder carcinomas, especially at the stage of early invasion. This analysis of the prognostic impact of CCNE gene amplification and protein expression in >1,500 arrayed bladder cancers was accomplished in a period of 2 weeks, illustrating how the tissue microarray technology remarkably facilitates the evaluation of the clinical relevance of molecular alterations in cancer.

Chronic DeltaFosB expression and increased AP-1 transcription factor binding are associated with the long term plasticity changes in epilepsy

NMDA receptor activation during status epilepticus (SE) has previously been shown to be required for epileptogenesis as well as the persistent upregulation of serum response factor (SRF) in the in vivo pilocarpine model of epilepsy. SRF is established as a regulator of the FosB gene which expresses FosB and DeltaFosB components of the AP-1 transcription factor complex. Therefore we investigated whether DeltaFosB expression and AP-1 DNA binding were also persistently elevated in pilocarpine-treated rats which chronically displayed spontaneous seizures. Using hippocampal nuclear extracts, DeltaFosB expression and AP-1 DNA binding were significantly elevated for up to one year in the epileptic animals. The expression of other fos and jun proteins was not persistently altered in epilepsy. Neuronal upregulation of DeltaFosB was correlated with regions of the brain that were involved in seizure generation and propagation. The increase in AP-1 DNA binding was shown to be dependent on NMDA receptor activation during SE. Hippocampal DeltaFosB immunostaining was seen predominately in the neuronal nuclei as opposed to other cell types. The data indicate that recurrent seizures which persistently occur in this model were not responsible for the increased DeltaFosB expression. Chronic DeltaFosB expression in epilepsy may be playing a role in the altered expression of other genes in this model and may be involved in some of the neuronal plasticity changes associated with epileptogenesis.

The temporal course of expression of c-Fos and Fos B within the medial preoptic area and other brain regions of postpartum female rats during prolonged mother--young interactions

Maternal behavior is associated with an increase in the expression of c-Fos and Fos B within neurons of the medial preoptic area (MPOA) and ventral bed nucleus of the stria terminalis (vBST). Whether this increase wanes as the duration of mother-young interaction increases is unknown. By varying the length of mother-young interactions in postpartum rats, the authors found that within the MPOA/vBST, the levels of both c-Fos and Fos B, once elevated, remained significantly above control levels through 47 hr of pup exposure. The persistence of c-Fos and Fos B within the MPOA/vBST of females that remained with pups was almost unique in that only one other neural area, the anterior magnocellular part of the paraventricular hypothalamic nucleus, showed such a response. Because MPOA/vBST neurons are essential for maternal behavior, the results suggest that c-Fos and Fos B expression within these regions may be necessary to maintain their normal functional activity.

Characterization of CArG-binding protein A initially identified by differential display

While investigating differences in the pattern of gene expression in functionally distinct areas of the rat caudate-putamen employing differential display, we identified a gene that is highly enriched in tissue adjacent to the lateral ventricle. To characterize the gene, a complementary DNA containing the complete coding sequence was obtained and sequenced. In addition, radiolabelled DNA and riboprobes were generated to examine the expression levels and anatomical distribution of the identified gene in the brain. The sequencing data suggests that the identified gene is a member of the heterogeneous nuclear ribonucleoprotein family and likely represents the rat homolog of CArG-binding protein A initially isolated from mouse C2 myogenic cells. CArG-binding protein A is widely distributed and moderately expressed in the rat brain and present within both neurons and astrocytes. Since the CArG box motif forms the core of the serum response element and the serum response element is involved in immediate early gene regulation, the expression level of CArG-binding protein A was examined following treatment of PC12 cells with nerve growth factor and correlated with changes in c-fos and zif268 expression. The results show that CArG-binding protein A is up-regulated following nerve growth factor treatment and that the up-regulation of CArG-binding protein A can be correlated with the down-regulation of c-fos and zif268. The results of the current study leads us to suggest that CArG-binding protein A may be involved in brain development and the regulation of the serum response element.

Expression pattern of the AP-1 family in breast cancer: association of fosB expression with a well-differentiated, receptor-positive tumor phenotype

In the present study, the expression of members of the AP-1 family of transcription factors in breast tumors (n = 53) was investigated by Western blot with antibodies specific for each of the AP-1 family members (c-jun, junB, junD and c-fos, fosB, fra1 and fra2). The tumors were characterized with regard to grading, staging, histology, steroid-receptor-expression status and c-erbB2/neu expression. For comparison, normal breast-tissue samples, human breast-cancer cell lines (T47D and MDA-MB231) and the transformed human breast epithelial cell line HBL100 were also analyzed. For c-jun, junB, c-fos and fra2, a relatively uniform expression pattern without significant differences among tumors was observed. junD-protein amounts varied strongly in the tumor specimens. fosB-expression levels also varied strongly in the tumors, weak/absent expression being found in 47%, while 45% exhibited strong/very strong levels of expression. While none of the other AP-1 family members showed significant correlations with clinico-pathological tumor parameters or receptor status, expression of fosB was found to correlate significantly with positive steroid-hormone-receptor status (in the tumors and the cell lines) and a more differentiated tumor phenotype. Expression of 2 fra-1-specific bands of 33 and 36.5 kDa showed significant negative correlation with fosB expression, as well as with estrogen-receptor status and differentiation. We conclude that strong differences in the expression pattern of AP-1 family members are present in breast tumors, and that certain members of this family, such as fosB and fra-1, might be involved in the pathogenesis of these tumors.

Persistent increased DNA-binding and expression of serum response factor occur with epilepsy-associated long-term plasticity changes

We have previously shown that NMDA receptor activation during status epilepticus (SE) is required to produce epilepsy in in vitro and in vivo models. As in human symptomatic epilepsy, the epilepsy in these models is permanent, suggesting that the pathological activation of NMDA receptors causes permanent plasticity changes in the brain. Ca(2+) influx through NMDA receptors is known to transiently activate a key transcription factor, serum response factor (SRF). Thus, we investigated whether this factor, in terms of its expression and ability to bind to the consensus serum response element, was altered long term in the pilocarpine model of epilepsy. In hippocampal nuclear extracts, SRF binding to DNA was significantly increased over saline-injected control rats at 24 hr and at 8 weeks after the onset of SE. This increase was shown to be the result of significantly elevated levels of SRF. DNA binding was also persistently increased in the cortical, but not in the cerebellar, extracts. Hippocampal expression of SRF was localized to neurons using immunohistochemistry. NMDA receptor activation during SE was required for these changes to take place, and the spontaneous seizures seen in epileptic rats did not appear to be responsible for the increase in SRF. The results demonstrate that SRF is persistently elevated after SE in the pilocarpine model of epilepsy and support the theory that long-term gene changes in this model occur and are associated with the long-lasting plasticity changes that are initiated during epileptogenesis.

Persistent increased DNA-binding and expression of serum response factor occur with epilepsy-associated long-term plasticity changes

We have previously shown that NMDA receptor activation during status epilepticus (SE) is required to produce epilepsy in in vitro and in vivo models. As in human symptomatic epilepsy, the epilepsy in these models is permanent, suggesting that the pathological activation of NMDA receptors causes permanent plasticity changes in the brain. Ca(2+) influx through NMDA receptors is known to transiently activate a key transcription factor, serum response factor (SRF). Thus, we investigated whether this factor, in terms of its expression and ability to bind to the consensus serum response element, was altered long term in the pilocarpine model of epilepsy. In hippocampal nuclear extracts, SRF binding to DNA was significantly increased over saline-injected control rats at 24 hr and at 8 weeks after the onset of SE. This increase was shown to be the result of significantly elevated levels of SRF. DNA binding was also persistently increased in the cortical, but not in the cerebellar, extracts. Hippocampal expression of SRF was localized to neurons using immunohistochemistry. NMDA receptor activation during SE was required for these changes to take place, and the spontaneous seizures seen in epileptic rats did not appear to be responsible for the increase in SRF. The results demonstrate that SRF is persistently elevated after SE in the pilocarpine model of epilepsy and support the theory that long-term gene changes in this model occur and are associated with the long-lasting plasticity changes that are initiated during epileptogenesis.

Functions of c-Jun in liver and heart development

Mice lacking the AP-1 transcription factor c-Jun die around embryonic day E13.0 but little is known about the cell types affected as well as the cause of embryonic lethality. Here we show that a fraction of mutant E13.0 fetal livers exhibits extensive apoptosis of both hematopoietic cells and hepatoblasts, whereas the expression of 15 mRNAs, including those of albumin, keratin 18, hepatocyte nuclear factor 1, beta-globin, and erythropoietin, some of which are putative AP-1 target genes, is not affected. Apoptosis of hematopoietic cells in mutant livers is most likely not due to a cell-autonomous defect, since c-jun-/- fetal liver cells are able to reconstitute all hematopoietic compartments of lethally irradiated recipient mice. A developmental analysis of chimeras showed contribution of c-jun-/- ES cell derivatives to fetal, but not to adult livers, suggesting a role of c-Jun in hepatocyte turnover. This is in agreement with the reduced mitotic and increased apoptotic rates found in primary liver cell cultures derived from c-jun-/- fetuses. Furthermore, a novel function for c-Jun was found in heart development. The heart outflow tract of c-jun-/- fetuses show malformations that resemble the human disease of a truncus arteriosus persistens. Therefore, the lethality of c-jun mutant fetuses is most likely due to pleiotropic defects reflecting the diversity of functions of c-Jun in development, such as a role in neural crest cell function, in the maintenance of hepatic hematopoiesis and in the regulation of apoptosis.

Specific regulation of fos family transcription factors in thymocytes at two developmental checkpoints

A central question in T cell development is what makes cortical thymocytes respond to stimulation in a qualitatively different way than any other thymocyte subset. Part of the answer is that AP-1 function changes drastically at two stages of T cell development. It undergoes striking down-regulation as thymocytes differentiate from immature, CD4(-)CD8(-) double-negative (DN) TCR- thymocytes to CD4(+)CD8(+) double-positive (DP) TCRlo cortical cells, and then returns in the cells that mature to TCRhigh, CD4(+)CD8(-) or CD4(-)CD8(+) single-positive (SP) thymocytes. At all three stages, the jun family mRNAs can be induced similarly. However, we demonstrate that DP cortical thymocytes are specifically impaired in c-fos and fosB mRNA induction, even when stimuli are used that optimize survival of the cells and a form of in vitro maturation. fra-2 expression is induction independent but much lower in DP cells than in the other subsets. Overall Fos family protein induction accordingly is severely decreased in DP cells. Defective c-Fos and FosB expression in cortical thymocytes is functionally significant, because antibody supershift experiments show that in activated immature and mature thymocytes, most detectable AP-1 DNA-binding complexes do contain c-Fos or FosB. Thus, defective c-Fos and FosB expression in cortical thymocytes qualitatively alters any AP-1 complexes they might express. The cortical thymocytes are not deficient in mRNA expression for any of the constitutive transcription factors that are known to be needed to drive c-Fos or FosB expression, so it is possible that the activity of these factors is developmentally regulated through a post-transcriptional mechanism.

Extracellular signal-regulated kinase 1/2-mediated phosphorylation of JunD and FosB is required for okadaic acid-induced activator protein 1 activation

Previously, we reported that in papilloma-producing 308 mouse keratinocytes, the tumor promoter okadaic acid, a serine-threonine phosphatase inhibitor, increased binding of activator protein 1 (AP-1) to a consensus 12-O-tetradecanoylphorbol-13-acetate-responsive element (Rosenberger, S. F., and Bowden, G. T. (1996) Oncogene 12, 2301-2308). In this study, we investigated the correlation between AP-1 DNA binding and transactivation and examined molecular mechanisms involved in this process. Using a luciferase reporter driven by region -74 to +63 of the human collagenase gene, we demonstrated induction of AP-1-mediated transcription following okadaic acid treatment. By performing in vitro kinase assays, we found elevated activities of extracellular signal-regulated kinase (ERK) 1/2, c-Jun N-terminal kinase, and p38 mitogen-activated protein kinase. The ERK-1/2-specific inhibitor PD 98059 completely abrogated okadaic acid-induced AP-1 transactivation without altering AP-1 expression, DNA binding, or complex composition. Phosphorylation analyses indicated that inhibition of ERK-1/2 decreased okadaic acid-elevated phosphorylation of JunD and FosB. To further examine the role of JunD and FosB in okadaic acid-induced AP-1 transactivation, we generated fusion proteins of the DNA-binding domain of the yeast transcription factor Gal4 and the transactivation domain of either JunD or FosB. Cotransfection experiments of these constructs with a Gal4-luciferase reporter demonstrated that both JunD and FosB are required for okadaic acid-induced transcription. Treatment with PD 98059 reduced JunD/FosB-dependent transactivation, suggesting that ERK-1/2-mediated phosphorylation is a critical component in this process.

E1A + cHa-ras transformed rat embryo fibroblast cells are characterized by high and constitutive DNA binding activities of AP-1 dimers with significantly altered composition

Transcription factors of the AP-1/ATF family, including c-Fos, c-Jun, and ATF-2, play an important role in the regulation of cell proliferation and differentiation, and changes in their levels and/or activities may contribute to oncogenesis. We analyzed the alterations of AP-1/ATF transcription factors upon immortalization and transformation in a panel of cell lines derived from rat embryo fibroblast (REF) cells. The tumorigenic E1A + cHa-ras cells are characterized by high and constitutive DNA binding activities of AP-1, in contrast to nontransformed cells and the E1A cells. The expression of c-fos and c-jun genes was affected differently by the oncogenic transformation. By using antibodies to c-Jun and c-Fos proteins in electrophoretic mobility shift assays (EMSA), we showed that E1A + cHa-ras transformants did not contain c-Fos under any condition of cell cultivation and growth factor stimulation, whereas c-Jun was constitutively upregulated. In the absence of c-fos gene expression, c-Fos protein appears to be replaced by proteins of Fos family (Fra-1) and ATF family (ATF-2 and ATFa). To determine the possible mechanisms of c-fos downregulation in E1A + cHa-ras transformants we have obtained populations of geneticin-resistant clones containing integrated reporter construct -711fos-CAT and its mutants in serum-responsive element (SRE) and cAMP-responsive element (CRE). Data obtained show that the mutations within the SRE lead to a manifold activation of fos-CAT expression. This allows to suggest that c-fos downregulation in E1A + cHa-ras transformants is provided by a negative control mediated through the SRE regulatory region. The profound differences in regulation and composition of transcription factors of the AP-1 family probably play a pivotal role in the transformation of REF cells by E1A and cHa-ras oncogenes.

Inducible and constitutive transcription factors in the mammalian nervous system: control of gene expression by Jun, Fos and Krox, and CREB/ATF proteins

This article reviews findings up to the end of 1997 about the inducible transcription factors (ITFs) c-Jun, JunB, JunD, c-Fos, FosB, Fra-1, Fra-2, Krox-20 (Egr-2) and Krox-24 (NGFI-A, Egr-1, Zif268); and the constitutive transcription factors (CTFs) CREB, CREM, ATF-2 and SRF as they pertain to gene expression in the mammalian nervous system. In the first part we consider basic facts about the expression and activity of these transcription factors: the organization of the encoding genes and their promoters, the second messenger cascades converging on their regulatory promoter sites, the control of their transcription, the binding to dimeric partners and to specific DNA sequences, their trans-activation potential, and their posttranslational modifications. In the second part we describe the expression and possible roles of these transcription factors in neural tissue: in the quiescent brain, during pre- and postnatal development, following sensory stimulation, nerve transection (axotomy), neurodegeneration and apoptosis, hypoxia-ischemia, generalized and limbic seizures, long-term potentiation and learning, drug dependence and withdrawal, and following stimulation by neurotransmitters, hormones and neurotrophins. We also describe their expression and possible roles in glial cells. Finally, we discuss the relevance of their expression for nervous system functioning under normal and patho-physiological conditions.

Fos family members induce cell cycle entry by activating cyclin D1

Expression of the fos family of transcription factors is stimulated by growth factors that induce quiescent cells to reenter the cell cycle, but the cellular targets of the Fos family that regulate cell cycle reentry have not been identified. To address this issue, mice that lack two members of the fos family, c-fos and fosB, were derived. The fosB-/- c-fos-/- mice are similar in phenotype to c-fos-/- mice but are 30% smaller. This decrease in size is consistent with an abnormality in cell proliferation. Fibroblasts derived from fosB-/- c-fos-/- mice were found to have a defect in proliferation that results at least in part from a failure to induce cyclin D1 following serum-stimulated cell cycle reentry. Although definitive evidence that c-Fos and FosB directly induce cyclin D1 transcription will require further analysis, these findings raise the possibility that c-Fos and FosB are either direct or indirect transcriptional regulators of the cyclin D1 gene and may function as a critical link between serum stimulation and cell cycle progression.

Expression of c-fos, fos B, and egr-1 in the medial preoptic area and bed nucleus of the stria terminalis during maternal behavior in rats

The spatial and temporal pattern of expression of the protein products of immediate early genes (IEGs) c-fos, fos B, and egr-1 were mapped in medial preoptic area (MPOA) and ventral bed nucleus of stria terminalis (VBST) during maternal behavior in rats. Immunocytochemical analysis indicated significant increases in the number of cells expressing c-Fos after 2 h of pup exposure, while Fos B levels showed a delayed response, reaching maximal levels after 6 h.

Differential time course of angiotensin-induced AP-1 and Krox proteins in the rat lamina terminalis and hypothalamus

We studied the time course of expression of the inducible transcription factors (ITF) c-Fos, FosB, c-Jun, JunB, JunD, Krox-20 and Krox-24, induced by a single intracerebroventricular injection of angiotensin II, in the subfornical organ (SFO), median preoptic nucleus (MnPO) paraventricular nucleus (PVN) and supraoptic nucleus (SON). c-Fos and Krox-24 were expressed rapidly in neurons of all four areas but completely disappeared after 4 h. FosB showed a delayed but persistent expression between 4 h and 24 h in the MnPO and PVN. c-Jun was induced in the MnPO, SFO and PVN after 1.5 h and in the SON after 4 h. JunB was selectively expressed in the MnPO and SFO and the level of JunD did not change. The expression of the pre-existing transcription factors SRF, CREB and ATF-2 which contribute to the transcriptional control of jun, fos and krox genes, was not affected by Ang II. Thus, we could show for the first time that an acute stimulation of AT receptors results in continual changes in ITF expression over 24 h.

Behavioural sensitization in 6-hydroxydopamine-lesioned rats is related to compositional changes of the AP-1 transcription factor: evidence for induction of FosB- and JunD-related proteins

Rats with unilateral dopamine denervation exhibit turning behaviour in response to the selective D1 agonist SKF 38393 only after a previous exposure to dopamine agonists. We demonstrate here that this 'priming' phenomenon is related to both an increased expression of the pre-existing AP-1 complex and the occurrence of novel AP-1 complexes which are formed by FosB- and JunD-related proteins. While the former protein is expressed as a consequence of the dopamine denervation, the latter is related to the first exposure to a dopamine agonist. Pre-treatment with MK-801, an antagonist for glutamatergic receptors, prevents both the priming development and the AP-1 compositional changes. Rotational behaviour induced by SKF 38393 closely correlates with the presence of the priming AP-1 complexes, regardless of the capability of the D1 agonist to induce the immediate-early gene cFos.

Changes in expression of delta FosB and the Fos family proteins following NMDA receptor activation in the rat striatum

Receptor-induced expression of transcription factors of the activator protein-1 (AP-1) family in neurons occurs in a unique temporal pattern which regulates subsequent downstream gene expression. We investigated the expression of the Fos family proteins following injection of the NMDA receptor agonist quinolinic acid (QA) into the rat striatum. The c-Fos protein is rapidly and transiently expressed, followed by the sequential and overlapping expression in the same striatal neurons of FosB, from 4 to 8 h post-lesion and delta FosB from 6 h to beyond 30 h post-lesion. Analysis confirms that mRNA transcripts of both fosB and alternatively spliced delta fosB are expressed in the striatum after QA lesion. The Fos-related antigens Fra-1 and Fra-2 and three previously uncharacterized c-Fos-related proteins were additionally found in the striatum which do not increase following lesion. These proteins are related to the highly conserved DNA-binding domain of c-Fos but are not immunologically related to the FosB protein as has been previously reported for proteins induced following chronic stimulation of the striatum. We additionally demonstrate that the c-Fos and delta FosB proteins expressed following QA lesion bind to the functional AP-1 site in the promoter of the nerve growth factor (NGF) gene, the regulation of which temporally and spatially coincides with the AP-1 protein increases in the QA-lesioned striatum. However, the levels of binding to the NGF AP-1 site do not increase throughout time following lesion despite the induced expression of Fos family proteins, suggesting that the regulation of the NGF gene in this paradigm does not simply involve increased binding to the AP-1 site in the NGF gene promoter.

Transcriptional activation and transformation by FosB protein require phosphorylation of the carboxyl-terminal activation domain

The transcription factor AP-1, composed of Fos-Jun dimers, mediates some aspects of the cellular response to growth factors. Transcriptional activation and neoplastic transformation by FosB, a member of the Fos family of proteins, require the presence of a potent C-terminal activation domain. Here we show by mutational analysis that the FosB C-terminal domain has a proline-based motif that is essential for both of these functions. Phosphopeptide mapping experiments show that the C terminus of FosB is phosphorylated within a cluster of functionally redundant serine residues that is adjacent to this proline-based motif. Mutation of these serine residues to alanine severely reduces the ability of this region to function as an activation domain and inhibits the ability of FosB protein to function as a transforming protein. Several observations suggest that the kinase responsible for phosphorylation of these sites is distinct from the mitogen-activation protein kinases and stress-activated protein kinases. Our results show that transcriptional activation and neoplastic transformation by the FosB protein are dependent on phosphorylation within the C terminus. This form of control may provide a potential mechanism of signal integration at the level of a single transcription factor.

Sequence analysis and expression in cultured lymphocytes of the human FOSB gene (G0S3)

G0S3 is a member of a set of putative G0/G1 switch regulatory genes (G0S genes) selected by screening cDNA libraries prepared from human blood mononuclear cells cultured for 2 hr with lectin and cycloheximide. The sequence shows high homology with the murine FOSB gene, which encodes a component of the AP1 transcriptional regulator. Comparison of cDNA and genomic sequences reveals a 4-exon structure characteristic of the FOS family of genes. Freshly isolated cells show high levels of FOSB/G0S3 and FOS/G0S7 mRNAs, which decline rapidly during incubation in culture medium. The kinetics of expression suggest that the high initial levels are caused by the isolation procedure, and do not reflect constitutive expression. In cells preincubated for a day, levels of FOS mRNA reach a maximum 20 min after the addition of lectin and decline to control levels over the next 3 hr. Levels of FOSB mRNA reach a maximum 40 min after the addition of lectin and decline to control levels over the next 6 hr. In freshly isolated cells, both FOS and FOSB mRNAs increase dramatically in response to the protein synthesis inhibitor cycloheximide. In preincubated cells, the cycloheximide response is decreased, especially in the case of FOSB. These differences in expression of FOS and FOSB suggest different roles and regulation. Regions of low base order-dependent stem-loop potential in the region of the gene are defined. These indicate where base order has been adapted for purposes other than stem-loop stability (e.g., encoding proteins or gene regulation). Regions of low potential in a 68.5-kb genomic segment containing the FOSB gene suggest that the potential may help locate genes in uncharted DNA sequences.

c-Fos expression in the rat intergeniculate leaflet: photic regulation, co-localization with Fos-B, and cellular identification

Ambient light alters the level of the transcriptional regulatory protein c-Fos in the suprachiasmatic nucleus, the site of an endogenous circadian clock in mammals, and in one other retino-recipient area, the intergeniculate leaflet of the lateral geniculate complex. Complementing previous work by ourselves and others on the photic and temporal regulation of c-Fos expression in the suprachiasmatic nucleus, the present studies investigated c-Fos regulation in the rat intergeniculate leaflet, revealing some important differences between the two brain regions. In the intergeniculate leaflet, the levels of c-fos mRNA (by in situ hybridization) and immunoreactive c-Fos protein (by immunohistochemistry) were elevated by light pulses administered either during the subjective day or subjective night. The regulation of immunoreactive Fos-B protein was similar to c-Fos, and 98% of Fos-B-expressing cells were also c-Fos-positive (by double-label immunofluorescence). By combining c-Fos immunofluorescence with stereotaxic injections of the retrograde tract tracer FluoroGold, we found photically-induced c-Fos in 15% of intergeniculate leaflet neurons projecting to the suprachiasmatic nucleus and in 34% of those projecting to the contralateral intergeniculate leaflet. Intergeniculate leaflet cells that express c-Fos after photic stimulation appear to represent a functionally-defined population that does not correspond to anatomically-defined categories based on connectivity or peptidergic phenotype.

FosB in the suprachiasmatic nucleus of the Syrian and Siberian hamster

The suprachiasmatic nucleus (SCN) generates circadian rhythms of behavior and hormone secretion in mammals, and integrates responses to light and nonphotic stimuli to synchronize such rhythms with the external environment. Previous studies have demonstrated a close association between the induction of the immediate early gene (IEG) c-fos in the SCN by light and phase shifts of circadian rhythms induced by light, but nonphotic stimuli (e.g., arousal), which also cause phase shifts, do not increase c-fos expression in the SCN. Because c-fos is now known to be a member of a large family of IEGs which can regulate transcription and thus cellular function, the aim of the current study was to determine whether induction of another member of this immediate early gene family, fosB, is associated with photic and nonphotic phase shifts. An antiserum that recognizes a unique peptide sequence derived from FosB was produced so that the expression of fosB could be investigated in cells within the SCN by immunocytochemical detection of its protein product. The regional distribution of FosB-immunoreactive (ir) cells in the SCN of Syrian and Siberian hamsters was broadly similar to that for c-Fos-ir cells. However, whereas c-fos expression in the SCN was constitutively low, but could be massively induced by light at particular circadian phases, FosB-ir cells were present at all circadian phases studied, irrespective of photic stimulation, and light only produced marginal increases in the number of FosB-ir cells compared with nonstimulated controls. Moreover, blockade of glutamatergic neurotransmission by pretreatment of hamsters with the NMDA receptor antagonist MK801 significantly reduced photic induction of c-Fos-ir cells, but did not influence the number of FosB-ir cells in the SCN. Finally, an arousing nonphotic stimulus known to cause phase advances in wheel-running behavior in Syrian hamsters did not alter significantly the number of FosB-ir cells in the SCN. These observations indicate that light and nonphotic stimuli are not potent regulators of fosB expression in the SCN. However, because fosB and c-fos can be present in the SCN at the same time after a light pulse, these studies indicate the potential for interactions with each other and with members of the Jun family in the regulation of the circadian timing system.

Promoter analysis of Zfp-36, the mitogen-inducible gene encoding the zinc finger protein tristetraprolin

The gene encoding the putative zinc finger protein tristetraprolin (TTP), Zfp-36, is rapidly induced by a variety of mitogens and growth factors. We show here that 77 base pairs 5' of the transcription start site are sufficient for full serum inducibility of the mouse Zfp-36 promoter. This region of the promoter includes consensus sequences for the binding of the transcription factors EGR-1, AP2, and Sp1. In addition, we have identified a previously undescribed element, TTP promoter element 1 (TPE1); this 10-base pair sequence includes a palindrome and is identical in the human, bovine, and mouse genes. Each of the three binding elements, EGR-1, AP2, and TPE1, contribute to the serum induction of Zfp-36 and can confer serum-inducible expression on a heterologous minimal promoter. Gel mobility shift assays demonstrated the formation of complexes consisting of this region of the promoter and cellular nuclear proteins and demonstrated that the extent of complex formation could be altered by treatment of the cells with serum or insulin. These results suggest that the response of Zfp-36 to serum and other mitogens is mediated by a series of cis-acting elements acting in concert to confer full inducible transcription of this gene.

Molecular characterization of a novel transcription factor that controls stromelysin expression

Stromelysins, which are the metalloproteinases with the widest substrate specificities, play a critical role in tumor invasion and metastasis. We have previously reported an element (SPRE) of the stromelysin promoter located between nucleotides -1221 and -1203 that is necessary and sufficient for the control of stromelysin gene expression by mitogenic activation, which induces a nuclear activity that binds to this sequence. Using a concatenated probe with several copies of this element to screen a lambda gt11 cDNA expression library from mouse Swiss 3T3 fibroblasts, we report here the molecular cloning of a cDNA coding for a novel protein (SPBP) of 937 amino acids that binds to this element and has several features of a transcription factor, such as a putative leucine zipper region, a nuclear localization signal, and a basic domain with homology to the DNA-binding domains of Fos and Jun. Evidence that SPBP is at least a critical component of the mitogen-induced SPRE nuclear binding activity is presented here. Furthermore, the transfection of an expression plasmid for SPBP transactivates reporter chloramphenicol acetyltransferase plasmids containing either the full-length stromelysin promoter or a single copy of the SPRE cloned upstream of the herpes simplex virus thymidine kinase minimal promoter. Therefore, the results presented here identify a novel transcription factor critically involved in the control of stromelysin expression.