Expressions of CCAAT/Enhancer-binding proteins beta and delta and their activities are intensified by cAMP signaling as well as Ca2+/calmodulin kinases activation in hippocampal neurons

Memory Takes Time

Memory is an adaptation to particular temporal properties of past events, such as the frequency of occurrence of a stimulus or the coincidence of multiple stimuli. In neurons, this adaptation can be understood in terms of a hierarchical system of molecular and cellular time windows, which collectively retain information from the past. We propose that this system makes various timescales of past experience simultaneously available for future adjustment of behavior. More generally, we propose that the ability to detect and respond to temporally structured information underlies the nervous system's capacity to encode and store a memory at molecular, cellular, synaptic, and circuit levels.

Upregulation of Runt-Related Transcription Factor-2 Through CCAAT Enhancer Binding Protein-β Signaling Pathway in Microglial BV-2 Cells Exposed to ATP

We have shown constitutive expression of the master regulator of osteoblastogenesis, runt-related transcription factor-2 (Runx2), by microglia cells outside bone. Here, we attempted to evaluate the pathological significance of Runx2 in microglial BV-2 cells exposed to ATP at a high concentration. Marked upregulation of Runx2 transcript and protein expression was seen in cells exposed to 1 mM ATP for a period longer than 30 min without inducing cytotoxicity. The Runx2 upregulation by ATP was prevented by extracellular and intracellular Ca(2+) chelators, while thapsigargin upregulated Runx2 expression alone without affecting the upregulation by ATP. A calmodulin antagonist prevented the upregulation by ATP, with calcineurin inhibitors being ineffective. Although ATP markedly increased nuclear levels of nuclear factor of activated T cell-2 (NFAT2), Runx2 promoter activity was not simulated by the introduction of either NFAT1 or NFAT2, but facilitated by that of CCAAT enhancer binding protein-α (C/EBPα), C/EBPβ and nuclear factor (erythroid-derived 2)-like-2 (Nrf2). Exposure to ATP up-regulated C/EBPβ and Nrf2, but not C/EBPα, expression, in addition to increasing nuclear levels of respective corresponding proteins. Runx2 upregulation by ATP was deteriorated by knockdown of C/EBPβ but not by that of Nrf2, however, while exposure to ATP up-regulated matrix metalloproteinase-13 (Mmp13) expression in a Runx2-dependent manner. Overexpression of Runx2 up-regulated Mmp13 expression with promoted incorporation of fluorescent beads into BV-2 cells without ATP. These results suggest that extracellular ATP up-regulates Runx2 expression through activation of the C/EBPβ signaling in a calmodulin-dependent manner to play a pivotal role in phagocytosis in microglial BV-2 cells.

C/EBPβ and C/EBPδ transcription factors: Basic biology and roles in the CNS

CCAAT/enhancer binding protein (C/EBP) β and C/EBPδ are transcription factors of the basic-leucine zipper class which share phylogenetic, structural and functional features. In this review we first describe in depth their basic molecular biology which includes fascinating aspects such as the regulated use of alternative initiation codons in the C/EBPβ mRNA. The physical interactions with multiple transcription factors which greatly opens the number of potentially regulated genes or the presence of at least five different types of post-translational modifications are also remarkable molecular mechanisms that modulate C/EBPβ and C/EBPδ function. In the second part, we review the present knowledge on the localization, expression changes and physiological roles of C/EBPβ and C/EBPδ in neurons, astrocytes and microglia. We conclude that C/EBPβ and C/EBPδ share two unique features related to their role in the CNS: whereas in neurons they participate in memory formation and synaptic plasticity, in glial cells they regulate the pro-inflammatory program. Because of their role in neuroinflammation, C/EBPβ and C/EBPδ in microglia are potential targets for treatment of neurodegenerative disorders. Any strategy to reduce C/EBPβ and C/EBPδ activity in neuroinflammation needs to take into account its potential side-effects in neurons. Therefore, cell-specific treatments will be required for the successful application of this strategy.

The transcription factor CCAAT enhancer-binding protein β protects rat cerebellar granule neurons from apoptosis through its transcription-activating isoforms

CCAAT enhancer-binding protein β is a transcription factor that is involved in many brain processes, although its role in neuronal survival/death remains unclear. By using primary cultures of rat cerebellar granule neurons, we have shown here that CCAAT enhancer-binding protein β is present as all of its isoforms: the transcriptional activators liver activator proteins 1 and 2, and the transcriptional inhibitor liver inhibitory protein. We have also shown that liver activator protein 1 undergoes post-translational modifications, such as phosphorylation and sumoylation. These isoforms have different subcellular localizations, liver activator protein 2 being found in the cytosolic fraction only, liver inhibitory protein in the nucleus only, and liver activator protein 1 in both fractions. Through neuronal apoptosis induction by shifting mature cerebellar granule neurons to low-potassium medium, we have demonstrated that nuclear liver activator protein 1 expression decreases and its phosphorylation disappears, whereas liver inhibitory protein levels increase in the nuclear fraction, suggesting a pro-survival role for liver activator protein transcriptional activation and a pro-apoptotic role for liver inhibitory protein transcriptional inhibition. To confirm this, we transfected cerebellar granule neurons with plasmids expressing liver activator protein 1, liver activator protein 2, or liver inhibitory protein respectively, and observed that both liver activator proteins, which increase CCAAT-dependent transcription, but not liver inhibitory protein, counteracted apoptosis, thus demonstrating the pro-survival role of liver activator proteins. These data significantly improve our current understanding of the role of CCAAT enhancer-binding protein β in neuronal survival/apoptosis.

CCAAT enhancer binding protein δ plays an essential role in memory consolidation and reconsolidation

A newly formed memory is temporarily fragile and becomes stable through a process known as consolidation. Stable memories may again become fragile if retrieved or reactivated, and undergo a process of reconsolidation to persist and strengthen. Both consolidation and reconsolidation require an initial phase of transcription and translation that lasts for several hours. The identification of the critical players of this gene expression is key for understanding long-term memory formation and persistence. In rats, the consolidation of inhibitory avoidance (IA) memory requires gene expression in both the hippocampus and amygdala, two brain regions that process contextual/spatial and emotional information, respectively; IA reconsolidation requires de novo gene expression in the amygdala. Here we report that, after IA learning, the levels of the transcription factor CCAAT enhancer binding protein δ (C/EBPδ) are significantly increased in both the hippocampus and amygdala. These increases are essential for long-term memory consolidation, as their blockade via antisense oligodeoxynucleotide-mediated knockdown leads to memory impairment. Furthermore, C/EBPδ is upregulated and required in the amygdala for IA memory reconsolidation. C/EBPδ is found in nuclear, somatic, and dendritic compartments, and a dendritic localization of C/EBPδ mRNA in hippocampal neuronal cultures suggests that this transcription factor may be translated at synapses. Finally, the induction of long-term potentiation at CA3-CA1 synapses by tetanic stimuli in acute slices, a cellular model of long-term memory, leads to an accumulation of C/EBPδ in the nucleus. We conclude that the transcription factor C/EBPδ plays a critical role in memory consolidation and reconsolidation.

CCAAT/enhancer binding protein δ regulates glial proinflammatory gene expression

The transcription factor CCAAT/enhancer binding protein δ (C/EBPδ) is expressed in activated astrocytes and microglia and can regulate the expression of potentially detrimental proinflammatory genes. The objective of this study was to determine the role of C/EBPδ in glial activation. To this end, glial activation was analyzed in primary glial cultures and in the central nervous system from wild type and C/EBPδ(-/-) mice. In vitro studies showed that the expression of proinflammatory genes nitric oxide (NO)synthase-2, cyclooxygenase-2, and interleukin (IL)-6 in glial cultures, and the neurotoxicity elicited by microglia in neuron-microglia cocultures, were decreased in the absence of C/EBPδ when cultures were treated with lipopolysaccharide (LPS) and interferon γ, but not with LPS alone. In C/EBPδ(-/-) mice, systemic LPS-induced brain expression of NO synthase-2, tumor necrosis factor-α, IL-1β, and IL-6 was attenuated. Finally, increased C/EBPδ nuclear expression was observed in microglial cells from amyotrophic lateral sclerosis patients and G93A-SOD1 mice spinal cord. These results demonstrate that C/EBPδ plays a key role in the regulation of proinflammatory gene expression in glial activation and suggest that C/EBPδ inhibition has potential for the treatment of neurodegenerative disorders, in particular, amyotrophic lateral sclerosis.

Lack of the transcription factor C/EBPδ impairs the intrinsic capacity of peripheral neurons for regeneration

Adult neurons of the peripheral nervous system (PNS), in contrast to those of the central nervous system, have a remarkable capacity to repair themselves after injury, yet the mechanisms underlying this regenerative propensity of peripheral neurons are far from completely understood. Here we show that the transcription factor CCAAT enhancer binding protein delta (C/EBPδ) is necessary for the efficient axonal regeneration of dorsal root ganglia (DRG) neurons after sciatic nerve crush injury. Loss of C/EBPδ substantially impairs axonal growth in dissociated cultured DRG neurons. In addition, lack of C/EPBδ causes a major reduction in the regenerative response of DRG neurons to a conditioning lesion, which is a well known paradigm of injury that enhances axonal growth due to a transcription-dependent cell body response. C/EBPδ is required for the induction of selected regeneration-associated genes. For example, the expression of SPRR1A (small proline-rich repeat protein 1A) is greatly reduced in DRG neurons of C/EBPδ knockout mice during axonal regeneration compared to those in wild-type mice, while the expression of GAP-43 (growth associated protein-43) and galanin is not affected. Nevertheless, the expected prompt recovery of sciatic nerve function after injury is severely impaired in C/EBPδ knockout mice, having a delay time of approximately 1 month for reaching the full function of recovering wild-type mice, suggesting that a transcription mechanism mediated by C/EBPδ is required for efficient axonal regeneration. Taken together, our results identify C/EBPδ as a crucial component of the transcriptional regulatory machinery which underlies the intrinsic capacity of peripheral neurons for axonal regeneration.

The role of CaMKII in regulating GLUT4 expression in skeletal muscle

Contractile activity during physical exercise induces an increase in GLUT4 expression in skeletal muscle, helping to improve glucose transport capacity and insulin sensitivity. An important mechanism by which exercise upregulates GLUT4 is through the activation of Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) in response to elevated levels of cytosolic Ca(2+) during muscle contraction. This review discusses the mechanism by which Ca(2+) activates CaMKII, explains research techniques currently used to alter CaMK activity in cells, and highlights various exercise models and pharmacological agents that have been used to provide evidence that CaMKII plays an important role in regulating GLUT4 expression. With regard to transcriptional mechanisms, the key research studies that identified myocyte enhancer factor 2 (MEF2) and GLUT4 enhancer factor as the major transcription factors regulating glut4 gene expression, together with their binding domains, are underlined. Experimental evidence showing that CaMK activation induces hyperacetylation of histones in the vicinity of the MEF2 domain and increases MEF2 binding to its cis element to influence MEF2-dependent Glut4 gene expression are also given along with data suggesting that p300 might be involved in acetylating histones on the Glut4 gene. Finally, an appraisal of the roles of other calcium- and non-calcium-dependent mechanisms, including the major HDAC kinases in GLUT4 expression, is also given.

Conditioning lesions before or after spinal cord injury recruit broad genetic mechanisms that sustain axonal regeneration: superiority to camp-mediated effects

Previous studies indicate that peripheral nerve conditioning lesions significantly enhance central axonal regeneration via modulation of cAMP-mediated mechanisms. To gain insight into the nature and temporal dependence of neural mechanisms underlying conditioning lesion effects on central axonal regeneration, we compared the efficacy of peripheral sciatic nerve crush lesions to cAMP elevations (in lumbar dorsal root ganglia) on central sensory axonal regeneration when administered either before or after cervical spinal cord lesions. We found significantly greater effects of conditioning lesions compared to cAMP elevations on central axonal regeneration when combined with cellular grafts at the lesion site and viral neurotrophin delivery; further, these effects persisted whether conditioning lesions were applied prior to or shortly after spinal cord injury. Indeed, conditioning lesions recruited extensively greater sets of genetic mechanisms of possible relevance to axonal regeneration compared to cAMP administration, and sustained these changes for significantly greater time periods through the post-lesion period. We conclude that cAMP-mediated mechanisms account for only a portion of the potency of conditioning lesions on central axonal regeneration, and that recruitment of broader genetic mechanisms can extend the effect and duration of cellular events that support axonal growth.

Role of C/EBPβ transcription factor in adult hippocampal neurogenesis

BACKGROUND

The dentate gyrus of the hippocampus is one of the regions in which neurogenesis takes place in the adult brain. We have previously demonstrated that CCAAT/enhancer binding protein β (C/EBPβ) is expressed in the granular layer of the dentate gyrus of the adult mouse hippocampus. Taking into account the important role of C/EBPβ in the consolidation of long term memory, the fact that newborn neurons in the hippocampus contribute to learning and memory processes, and the role of this transcription factor, previously demonstrated by our group, in regulating neuronal differentiation, we speculated that this transcription factor could regulate stem/progenitor cells in this region of the brain.

METHODOLOGY/PRINCIPAL FINDINGS

Here, we show, using C/EBPβ knockout mice, that C/EBPβ expression is observed in the subset of newborn cells that proliferate in the hippocampus of the adult brain. Mice lacking C/EBPβ present reduced survival of newborn cells in the hippocampus, a decrease in the number of these cells that differentiate into neurons and a diminished number of cells that are proliferating in the subgranular zone of the dentate gyrus. These results were further confirmed in vitro. Neurosphere cultures from adult mice deficient in C/EBPβ present less proliferation and neuronal differentiation than neurospheres derived from wild type mice.

CONCLUSIONS/SIGNIFICANCE

In summary, using in vivo and in vitro strategies, we have identified C/EBPβ as a key player in the proliferation and survival of the new neurons produced in the adult mouse hippocampus. Our results support a novel role of C/EBPβ in the processes of adult hippocampal neurogenesis, providing new insights into the mechanisms that control neurogenesis in this region of the brain.

Neuroadaptive changes in cerebellar neurons induced by chronic exposure to IL-6

IL-6 is an important signaling molecule in the CNS. CNS neurons express IL-6 receptors and their signal transduction molecules, consistent with a role for IL-6 in neuronal physiology. Research indicates that IL-6 levels are low in the normal brain but can be significantly elevated in CNS injury and disease. Relatively little is known about how the elevated levels of IL-6 affect neurons. In the current study we show that under conditions of chronic exposure, IL-6 induces alterations in the level of protein expression in developing CNS cells. Such changes may play a role in the altered CNS function observed in CNS conditions associated with elevated levels of IL-6 in the CNS.

CCAAT/enhancer binding protein β expression is increased in the brain during HIV-1-infection and contributes to regulation of astrocyte tissue inhibitor of metalloproteinase-1

Human immunodeficiency virus (HIV)-1-associated neurocognitive disorders (HAND) associated with infection and activation of mononuclear phagocytes (MP) in the brain, occur late in disease. Infected/activated MP initiate neuroinflammation activating glial cells and ultimately disrupting neuronal function. Astrocytes secrete tissue inhibitor of metalloproteinase (TIMP)-1 in response to neural injury. Altered TIMP-1 levels are implicated in several CNS diseases. CCAAT enhancer-binding protein β (C/EBPβ), a transcription factor, is expressed in rodent brains in response to neuroinflammation, implicating it in Alzheimer's, Parkinson's, and HAND. Here, we report that C/EBPβ mRNA levels are elevated and its isoforms differentially expressed in total brain tissue lysates of HIV-1-infected and HIV-1 encephalitis patients. In vitro, HAND-relevant stimuli additively induce C/EBPβ nuclear expression in human astrocytes through 7 days of treatment. Over-expression of C/EBPβ increases TIMP-1 promoter activity, mRNA, and protein levels in human astrocytes activated with interleukin-1β. Knockdown of C/EBPβ with siRNA decreases TIMP-1 mRNA and protein levels. These data suggest that C/EBPβ isoforms are involved in complex regulation of astrocyte TIMP-1 production during HIV-1 infection; however, further studies are required to completely understand their role during disease progression.

Spatiotemporal nuclear factor interleukin-6 expression in the rat brain during lipopolysaccharide-induced fever is linked to sustained hypothalamic inflammatory target gene induction

Rats injected with lipopolysaccharide (LPS) show brain-controlled sickness symptoms, including fever. In these animals, early genomic activation of brain cells was previously monitored by immunohistochemical detection of transcription factors such as nuclear factor (NF)-κB or signal transducer and activator of transcription (STAT)3 and was linked to the initiation or maintenance of the febrile response. To investigate whether NF-IL6 might be another important transcription factor implicated in this kind of immune-to-brain signaling, rats were injected with LPS (100 μg/kg, intraperitoneally) or phosphate-buffered saline, and brains were analyzed by immunohistochemistry, real-time PCR, or Western blot 4, 6, 8, and 10 hours later. Moderate to strong LPS-induced nuclear NF-IL6 immunoreactivity (IR) occurred in a time-dependent manner within circumventricular organs, namely, the vascular organ of the lamina terminalis, the subfornical organ, the area postrema, and the median eminence, brain structures with a leaky blood-brain barrier. Furthermore, nuclear NF-IL6-IR was observed in the pituitary gland, the choroid plexus, and the meninges as well as blood vessels throughout the entire brain. Endothelial, microglial, and ependymal cells, astrocytes, perivascular macrophages, and neurons exhibited LPS-induced nuclear NF-IL6-IR; mRNA levels of NF-IL6, responsive inflammatory genes, and NF-IL6 protein levels were significantly elevated. As opposed to observations on STAT3 or NFκB, the percentage of NF-IL6-reactive cells increased in parallel to late phases of the febrile response. In conclusion, these results suggest a potential role for NF-IL6 in the maintenance or possibly the termination of LPS-induced fever. Moreover, we propose NF-IL6 to be a delayed brain cell activation marker.

[Progress of transcription factor CCAAT enhancer binding protein β]

CCAAT enhancer binding protein β (C/EBP β) belongs to CCAAT enhancer binding protein (C/EBP) family, which is a subfamily of basic leucine zipper (bZIP) protein family. C/EBP family plays important roles in many processes such as cell differentiation, metabolism, and development. In this paper, the structure, expression regulation, and function of C/EBP β were reviewed.

Genome-wide gene expression and promoter binding analysis identifies NFIL3 as a repressor of C/EBP target genes in neuronal outgrowth

NFIL3 (nuclear factor IL-3 regulated) is a multifunctional transcription factor implicated in a wide range of physiological processes, including cellular survival, circadian gene expression and natural killer cell development. We recently demonstrated that NFIL3 acts as a repressor of CREB-induced gene expression underlying the regeneration of axotomized DRG sensory neurons. In this study we performed chromatin immunoprecipitation assays combined with microarray technology (ChIP-chip) to reveal direct NFIL3 and CREB target genes in an in vitro cell model for regenerating DRG neurons. We identified 505 promoter regions bound by NFIL3 and 924 promoter regions bound by CREB. Based on promoter analysis of NFIL3-bound genes, we were able to redefine the NFIL3 consensus-binding motif. Histone H3 acetylation profiling and gene expression microarray analysis subsequently indicated that a large fraction (>60%) of NFIL3 target genes were transcriptionally silent, whereas CREB target genes in general were transcriptionally active. Only a small subset of NFIL3 target genes also bound CREB. Computational analysis indicated that a substantial number of NFIL3 target genes share a C/EBP (CCAAT/Enhancer Binding Protein) DNA binding motif. ChIP analysis confirmed binding of C/EBPs to NFIL3 target genes, and knockdown of C/EBPα, C/EBPβ and C/EBPδ, but not C/EBPγ, significantly reduced neurite outgrowth in vitro. Together, our findings show that NFIL3 is a general feed-forward repressor of basic leucine zipper transcription factors that control neurite outgrowth.

Modulation of inducible nitric oxide synthase expression by sumoylation

BACKGROUND

In astrocytes, the inflammatory induction of Nitric Oxide Synthase type 2 (NOS2) is inhibited by noradrenaline (NA) at the transcriptional level however its effects on specific transcription factors are not fully known. Recent studies show that the activity of several transcription factors including C/EBPbeta, which is needed for maximal NOS2 expression, is modulated by conjugation of the small molecular weight protein SUMO. We examined whether the expression of SUMO Related Genes (SRGs: SUMO-1, the conjugating enzyme Ubc9, and the protease SENP1) are affected by inflammatory conditions or NA and whether SUMO-1 regulates NOS2 through interaction with C/EBPbeta.

METHODS

Bacterial endotoxin lipopolysaccharide (LPS) was used to induce inflammatory responses including NOS2 expression in primary astrocytes. The mRNA levels of SRGs were determined by QPCR. A functional role for SUMOylation was evaluated by determining effects of over-expressing SRGs on NOS2 promoter and NFkappaB binding-element reporter constructs. Interactions of SUMO-1 and C/EBPbeta with the NOS2 promoter were examined by chromatin immunoprecipitation assays. Interactions of SUMO-1 with C/EBPbeta were examined by immunoprecipitation and Western blot analysis and by fluorescence resonance energy transfer (FRET) assays.

RESULTS

LPS decreased mRNA levels of SUMO-1, Ubc9 and SENP1 in primary astrocytes and a similar decrease occurred during normal aging in brain. NA attenuated the LPS-induced reductions and increased SUMO-1 above basal levels. Over-expression of SUMO-1, Ubc9, or SENP1 reduced the activation of a NOS2 promoter, whereas activation of a 4 x NFkappaB binding-element reporter was only reduced by SUMO-1. ChIP studies revealed interactions of SUMO-1 and C/EBPbeta with C/EBP binding sites on the NOS2 promoter that were modulated by LPS and NA. SUMO-1 co-precipitated with C/EBPbeta and a close proximity was confirmed by FRET analysis.

CONCLUSION

Our results demonstrate that SUMOylation regulates NOS2 expression in astrocytes, and point to modification of C/EBPbeta as a possible mechanism of action. Targeting the SUMOylation pathway may therefore offer a novel means to regulate inflammatory NOS2 expression in neurological conditions and diseases.

Transcription factors in long-term memory and synaptic plasticity

Transcription is a molecular requisite for long-term synaptic plasticity and long-term memory formation. Thus, in the last several years, one main interest of molecular neuroscience has been the identification of families of transcription factors that are involved in both of these processes. Transcription is a highly regulated process that involves the combined interaction and function of chromatin and many other proteins, some of which are essential for the basal process of transcription, while others control the selective activation or repression of specific genes. These regulated interactions ultimately allow a sophisticated response to multiple environmental conditions, as well as control of spatial and temporal differences in gene expression. Evidence based on correlative changes in expression, genetic mutations, and targeted molecular inhibition of gene expression have shed light on the function of transcription in both synaptic plasticity and memory formation. This review provides a brief overview of experimental work showing that several families of transcription factors, including CREB, C/EBP, Egr, AP-1, and Rel, have essential functions in both processes. The results of this work suggest that patterns of transcription regulation represent the molecular signatures of long-term synaptic changes and memory formation.

Identification of neuronal target genes for CCAAT/enhancer binding proteins

CCAAT/Enhancer Binding Proteins (C/EBPs) play pivotal roles in the development and plasticity of the nervous system. Identification of the physiological targets of C/EBPs (C/EBP target genes) should therefore provide insight into the underlying biology of these processes. We used unbiased genome-wide mapping to identify 115 C/EBPbeta target genes in PC12 cells that include transcription factors, neurotransmitter receptors, ion channels, protein kinases and synaptic vesicle proteins. C/EBPbeta binding sites were located primarily within introns, suggesting novel regulatory functions, and were associated with binding sites for other developmentally important transcription factors. Experiments using dominant negatives showed C/EBPbeta to repress transcription of a subset of target genes. Target genes in rat brain were subsequently found to preferentially bind C/EBPalpha, beta and delta. Analysis of the hippocampal transcriptome of C/EBPbeta knockout mice revealed dysregulation of a high percentage of transcripts identified as C/EBP target genes. These results support the hypothesis that C/EBPs play non-redundant roles in the brain.

CCAAT/enhancer binding protein beta deficiency provides cerebral protection following excitotoxic injury

The CCAAT/enhancer-binding protein beta (C/EBPbeta, also known as CEBPB) was first identified as a regulator of differentiation and inflammatory processes in adipose tissue and liver. Although C/EBPbeta was initially implicated in synaptic plasticity, its function in the brain remains largely unknown. We have previously shown that C/EBPbeta regulates the expression of genes involved in inflammatory processes and brain injury. Here, we have demonstrated that the expression of C/EBPbeta is notably increased in the hippocampus in a murine model of excitotoxicity. Mice lacking C/EBPbeta showed a reduced inflammatory response after kainic acid injection, and exhibited a dramatic reduction in pyramidal cell loss in the CA1 and CA3 subfields of the hippocampus. These data reveal an essential function for C/EBPbeta in the pathways leading to excitotoxicity-mediated damage and suggest that inhibitors of this transcription factor should be evaluated as possible neuroprotective therapeutic agents.

Transthyretin: a key gene involved in the maintenance of memory capacities during aging

Aging is often associated with decline of memory function. Aged animals, like humans, can naturally develop memory impairments and thus represent a useful model to investigate genes involved in long-term memory formation that are differentially expressed between aged memory-impaired (AI) and aged memory-unimpaired (AU) animals following stimulation in a spatial memory task. We found that alterations in hippocampal gene expression of transthyretin (TTR), calcineurin, and NAD(P)H dehydrogenase quinone 2 (NQO2) were associated with memory deficits in aged animals. Decreased TTR gene expression could be attributed at least partially to diminish activity of C/EBP immediate-early gene cascade initiated by CREB since protein levels of C/EBP, a transcription factor regulating both TTR and NQO2 expression, was decreased in AI animals. Memory deficits were also found during aging in mice lacking TTR, a retinol transporter known to prevent amyloid-beta aggregation and plaque formation as seen in Alzheimer's disease. Treatment with retinoic acid reversed cognitive deficits in these knock-out mice as well as in aged rats. Our study provides genetic, behavioural and molecular evidence that TTR is involved in the maintenance of normal cognitive processes during aging by acting on the retinoid signalling pathway.

5'UTR of the neurogenic bHLH Nex1/MATH-2/NeuroD6 gene is regulated by two distinct promoters through CRE and C/EBP binding sites

Expression of the bHLH transcription factor Nex1/MATH-2/NeuroD6, a member of the NeuroD subfamily, parallels overt neuronal differentiation and synaptogenesis during brain development. Our previous studies have shown that Nex1 is a critical effector of the NGF pathway and promotes neuronal differentiation and survival of PC12 cells in the absence of growth factors. In this study, we investigated the transcriptional regulation of the Nex1 gene during NGF-induced neuronal differentiation. We found that Nex1 expression is under the control of two conserved promoters, Nex1-P1 and Nex1-P2, located in two distinct non-coding exons. Both promoters are TATA-less with multiple transcription start sites, and are activated on NGF or cAMP exposure. Luciferase-reporter assays showed that the Nex1-P2 promoter activity is stronger than the Nex1-P1 promoter activity, which supports the previously reported differential expression levels of Nex1 transcripts throughout brain development. Using a combination of DNaseI footprinting, EMSA assays, and site-directed mutagenesis, we identified the essential regulatory elements within the first 2 kb of the Nex1 5'UTR. The Nex1-P1 promoter is mainly regulated by a conserved CRE element, whereas the Nex1-P2 promoter is under the control of a conserved C/EBP binding site. Overexpression of wild-type C/EBPbeta resulted in increased Nex1-P2 promoter activity in NGF-differentiated PC12 cells. The fact that Nex1 is a target gene of C/EBPbeta provides new insight into the C/EBP transcriptional cascade known to promote neurogenesis, while repressing gliogenesis.

Identification and characterization of novel activity-dependent transcription factors in rat cortical neurons

Using gene chip analyses, we have identified novel neuronal activity-dependent genes. Application of 25 mM KCl to mature (14-day culture) rat cortical neurons resulted in more than 1.5-fold induction of 19 genes and reduction of 42 genes among 1200 neural genes. Changes in the overall gene expression profiles appeared to be related to the reduction of excitability and induction of cellular survival signals. Among the genes identified, three transcriptional modulators [encoding Cbp/p300-interacting transactivator with ED-rich tail 2 (CITED2), CCAAT/enhancer binding protein beta (C/EBPbeta) and neuronal orphan receptor-1, (NOR1)] were newly identified as activity-dependent transcription factors, and two of these (CITED2 and NOR1) were found to be influenced by electroconvulsive shock (ECS). NOR1 was induced in specific brain regions by behavioral activation, such as exposure to a novel environment. Because the brain regions that exhibited the induction of these newly identified neuronal activity-dependent transcriptional modulators were distinct from those showing the induction of previously identified activity-dependent genes such as c-fos, these genes might be useful markers for mapping neuronal activity in vivo.

C/EBPβ couples dopamine signalling to substance P precursor gene expression in striatal neurones

Dopamine-induced changes in striatal gene expression are thought to play an important role in drug addiction and compulsive behaviour. In this study we report that dopamine induces the expression of the transcription factor CCAAT/Enhancer Binding Protein beta (C/EBP)-beta in primary cultures of striatal neurones. We identified the preprotachykinin-A (PPT-A) gene coding for substance P and neurokinin-A as a potential target gene of C/EBPbeta. We demonstrated that C/EBPbeta physically interacts with an element of the PPT-A promoter, thereby facilitating substance P precursor gene transcription. The regulation of PPT-A gene by C/EBPbeta could subserve many important physiological processes involving substance P, such as nociception, neurogenic inflammation and addiction. Given that substance P is known to increase dopamine signalling in the striatum and, in turn, dopamine increases substance P expression in medium spiny neurones, our results implicate C/EBPbeta in a positive feedback loop, changes of which might contribute to the development of drug addiction.

CAAT/enhancer-binding protein delta and cAMP-response element-binding protein mediate inducible expression of the nerve growth factor gene in the central nervous system

Nerve growth factor (NGF) synthesis in the rat cerebral cortex is induced by the beta2-adrenergic receptor agonist clenbuterol (CLE). Because NGF is a crucial neurotrophic factor for basal forebrain cholinergic neurons, defining the mechanisms that regulate its transcription is important for developing therapeutic strategies to treat pathologies of these neurons. We previously showed that the transcription factor CCAAT/enhancer-binding protein delta (C/EBPdelta) contributes to NGF gene regulation. Here we have further defined the function of C/EBPdelta and identified a role for cAMP response element-binding protein (CREB) in NGF transcription. Inhibition of protein kinase A in C6-2B glioma cells suppressed CLE induction of an NGF promoter-reporter construct, whereas overexpression of protein kinase A increased NGF promoter activity, particularly in combination with C/EBPdelta. A CRE-like site that binds CREB was identified in the proximal NGF promoter, and C/EBPdelta and CREB were found to associate with the NGF promoter in vivo. Deletion of the CRE and/or C/EBP sites reduced CLE responsiveness of the promoter. In addition, ectopic expression of C/EBPdelta in combination with CLE treatment increased endogenous NGF mRNA levels in C6-2B cells. C/EBPdelta null mice showed complete loss of NGF induction in the cerebral cortex following CLE treatment, demonstrating a critical role for C/EBPdelta in regulating beta2-adrenergic receptor-mediated NGF expression in vivo. Thus, our findings demonstrate a critical role for C/EBPdelta in regional expression of NGF in the brain and implicate CREB in CLE-induced NGF gene transcription.

Inactivation of C/EBP transcription factors specifically affects the synaptic plasticity of a common snail neuron

Our previous studies showed that the acquisition of nociceptive sensitization in common snails is accompanied by long-term facilitation of synaptic transmission in defensive behavior command neuron LP11, this being dependent on translation and transcription processes. The characteristics of the neurochemical mechanisms of plasticity in the different sensory inputs of this nerve cell were identified. The mechanisms of induction of synaptic facilitation of the responses of neuron LP11 to chemical sensory stimulation of the snail's head involved NMDA glutamate receptors, serotonin receptors, cAMP, and serotonin-modulated transcription-regulating protein SMP-69. The mechanisms of induction of synaptic facilitation of another sensory input of the neuron--from tactile receptors on the head - involved protein kinase C. The present study addresses the involvement of C/EBP transcription factors (CCAAT-enhancer-binding protein) in the processes of synapse-specific plasticity of neuron LP11 during the acquisition of sensitization in snails. C/EBP was inactivated using oligonucleotides specifically binding to these proteins. The results showed that acquisition of sensitization during intracellular administration of oligonucleotides led to the selective suppression of synaptic facilitation in the responses of neuron LP11 to chemical sensory stimulation of the snail's head. Synaptic facilitation in the responses to tactile stimulation of the head or foot developed as in neurons in control sensitized snails. It is suggested that C/EBP transcription factor is selectively involved in the mechanisms of synapse-specific plasticity of the sensory input of neuron LP11 from chemoreceptors on the head during the acquisition of sensitization in snails.

Endothelin increases expression of exon III- and exon IV-containing brain-derived neurotrophic factor transcripts in cultured astrocytes and rat brain

The effects of endothelins (ETs) on brain-derived neurotrophic factor (BDNF) production in astrocytes were investigated. ET-1 (100 nM) increased the mRNA level and extracellular release of BDNF in cultured astrocytes. RT-PCR analyses using primer pairs that amplified exon-specific BDNF transcripts revealed that exon III- and exon IV-containing BDNF transcripts existed in cultured astrocytes, whereas exon I- and exon II-containing BDNF transcripts did not. ET-1 and Ala(1,3,11,15)-ET-1, an ET(B) receptor agonist, increased the expressions of the exon III and exon IV transcripts in cultured astrocytes. Intracerebroventricular administration of 500 pmol/day of Ala(1,3,11,15)-ET-1 increased exon III and exon IV BDNF transcripts in the rat striatum. In cultured astrocytes, Ca(2+)-chelation, W-7 (a calmodulin inhibitor), and KN93 (a Ca(2+)/calmodulin kinase inhibitor) inhibited the increases in exon IV BDNF mRNA and CCAAT enhancer-binding protein beta (C/EBPbeta) levels induced by ET-1. The ET-induced increases in exon III BDNF mRNA expression and phosphorylation of cAMP response element binding protein (CREB) were reduced by Ca(2+) chelation, W-7, KN93, PD98059 (a MEK inhibitor), and wortmannin (a phosphatidylinositol 3-kinase inhibitor). These results suggest that ETs stimulate the expressions of exon III and exon IV BDNF transcripts in astrocytes through CREB and C/EBPbeta-mediated mechanisms, respectively.

Gene expression profiling of experimental traumatic spinal cord injury as a function of distance from impact site and injury severity

Changes in gene expression contribute to pathophysiological alterations following spinal cord injury (SCI). We examined gene expression over time (4 h, 24 h, 7 days) at the impact site, as well as rostral and caudal regions, following mild, moderate, or severe contusion SCI in rats. High-density oligonucleotide microarrays were used that included approximately 27,000 genes/ESTs (Affymetrix RG-U34; A, B and C arrays), together with multiple analyses (MAS 5.0, dChip). Alterations after mild injury were relatively rapid (4 and 24 h), whereas they were delayed and prolonged after severe injury (24 h and 7 days). The number and magnitude of gene expression changes were greatest at the injury site after moderate injury and increased in rostral and caudal regions as a function of injury severity. Sham surgery resulted in expression changes that were similar to mild injury, suggesting the importance of using time-linked surgical controls as well as naive animals for these kinds of studies. Expression of many genes and ESTs was altered; these were classified functionally based on ontology. Overall representation of these functional classes varied with distance from the site of injury and injury severity, as did the individual genes that contributed to each functional class. Different clustering approaches were used to identify changes in neuronal-specific genes and several transcription factors that have not previously been associated with SCI. This study represents the most comprehensive evaluation of gene expression changes after SCI to date. The results underscore the power of microarray approaches to reveal global genomic responses as well as changes in particular gene clusters and/or families that may be important in the secondary injury cascade.

The effect of cyclosporin A on airway cell proinflammatory signaling and pneumonia

Cyclosporin A (CsA) blocks T cell activation by interfering with the Ca2+-dependent phosphatase, calcineurin. Proinflammatory responses to bacteria that are activated by Ca2+-fluxes in airway cells are a potential target for CsA. Although local immunosuppression may be advantageous to control airway inflammation, it could also increase susceptibility to bacterial pneumonia and invasive infection. As aerosolized CsA is currently under study in lung transplantation, we examined its direct effects on airway cells as well as in a murine model of pneumonia. Epithelial interleukin-6 production was very effectively inhibited by CsA, whereas CXCL8 production, the major PMN chemokine, was only modestly diminished. Responses to a TLR2 agonist Pam3Cys were more sensitive to CsA inhibition than those activated by Pseudomonas aeruginosa. CsA substantially blocked activation of nuclear factor of activated T cells and cAMP-responsive element-binding protein (P<0.001), inhibited CCAAT/enhancer-binding protein by 50% (P<0.05), and minimally blocked activator protein-1 and nuclear factor-kappaB responses to bacteria in epithelial cells. The in vitro effects were confirmed in a mouse model of P. aeruginosa infection with similar rates of PMN recruitment, pneumonia and mortality in CsA treated and control mice. These studies indicate that airway epithelial signaling is a potential target for CsA, and such local immunosuppression may not increase susceptibility to invasive infection.

Expression, hormonal regulation, and subcellular localization of CCAAT/enhancer-binding protein-beta in rat and human thyrocytes

The expression pattern of CCAAT/enhancer binding protein-beta (C/EBP-beta) was investigated in thyroid cells and tissues. Translation of C/EBP-beta mRNA results in the production of two isoforms, liver-enriched transcriptional activating protein (LAP) and liver-enriched transcriptional inhibitory protein (LIP), the latter lacking the transactivation domain. We found that LAP and LIP are expressed in the rat thyroid gland and in the FRTL-5 and PCCL3 rat thyroid cell lines. Thyrotropin (TSH), insulin, and serum withdrawal from cultures of thyroid cells induced downregulation of LAP and LIP expression. Subsequent activation of the cyclic adenosine monophosphate (cAMP) and insulin signaling pathways reinduced both isoforms. Vectors expressing rat LAP and LIP were constructed to study the effect of C/EBP-beta isoforms on the activity of the sodium iodide symporter (NIS) promoter in PCCL3 cells. The cAMP-stimulated activity of the NIS promoter was decreased by overexpression of LAP, whereas LIP had no significant effect. Expression of C/EBP-beta was studied by immunohistochemistry in normal human thyroid and papillary cancer tissues. C/EBP-beta immunostaining was always restricted to the nuclei of the normal thyrocytes. In contrast, C/EBP-beta was expressed mainly in the cytoplasm of thyroid papillary carcinoma cells. These data suggest that this factor may play important roles in the regulation of thyroidspecific genes and processes, and that its functions are altered in human thyroid carcinoma.

A bioinformatics analysis of memory consolidation reveals involvement of the transcription factor c-rel

Consolidation of long-term memory (LTM) is a complex process requiring synthesis of new mRNAs and proteins. Many studies have characterized the requirement for de novo mRNA and protein synthesis; however, few studies have comprehensively identified genes regulated during LTM consolidation. We show that consolidation of long-term contextual memory in the hippocampus triggers altered expression of numerous genes encompassing many aspects of neuronal function. Like contextual memory formation, this altered gene expression required NMDA receptor activation and was specific for situations in which the animal formed an association between a physical context and a sensory stimulus. Using a bioinformatics approach, we found that regulatory elements for several transcription factors are over-represented in the upstream region of genes regulated during consolidation of LTM. Using a knock-out mouse, we found that c-rel, one of the transcription factors identified in our bioinformatics study, is necessary for hippocampus-dependent long-term memory formation.

Microarray analysis supports a role for ccaat/enhancer-binding protein-beta in brain injury

CCAAT/enhancer-binding protein-beta (C/EBPbeta) is a transcription factor that plays an important role in regulating cell growth and differentiation. This protein plays a central role in lymphocyte and adipocyte differentiation and hepatic regeneration and in the control of inflammation and immunity in the liver and in cells of the myelomonocytic lineage. Our previous studies suggested that this protein could also have important functions in the brain. Therefore, we were interested in the identification of downstream targets of this transcription factor in cells of neural origin. We performed cDNA microarray analysis and found that a total of 48 genes were up-regulated in C/EBPbeta-overexpressing neuronal cells. Of the genes that displayed significant changes in expression, several were involved in inflammatory processes and brain injury. Northern blot analysis confirmed the up-regulation of ornithine decarboxylase, 24p3/LCN2, GRO1/KC, spermidine/spermine N(1)-acetyltransferase, xanthine dehydrogenase, histidine decarboxylase, decorin, and TM4SF1/L6. Using promoter-luciferase reporter transfection assays, we showed the ornithine decarboxylase and 24p3 genes to be biological downstream targets of C/EBPbeta in neuroblastoma cells. Moreover, the levels of C/EBPbeta protein were significantly induced after neuronal injury, which was accompanied by increased levels of cyclooxygenase-2 enzyme. This strongly supports the concept that C/EBPbeta may play an important role in brain injury.

Induction by staurosporine of hepatocyte growth factor production in human skin fibroblasts independent of protein kinase inhibition

Staurosporine is one of the most potent and well known inhibitors of protein kinases, and it is often used to study the involvement of protein kinases in signal transduction pathways. We now report that staurosporine can induce the production of hepatocyte growth factor (HGF) independently of protein kinase inhibition. Staurosporine markedly stimulated the production of HGF in various cell types, including human skin fibroblasts. Its effect was accompanied by up-regulation of HGF gene expression. The inhibition of protein kinases appears not to be involved in staurosporine-induced HGF production, because other protein kinase inhibitors, K-252a, H-7, GF 109203X and genistein, had no HGF-inducing activity. UCN-01, 7-hydroxystaurosporine, which differs from staurosporine only in its aglycone moiety, also showed HGF-inducing activity, and inactive K-252a differs from staurosporine only in its sugar moiety. These results indicate that the sugar moiety, a six-atom ring structure, is important in the HGF-inducing activity of staurosporine. Experiments were then carried out to determine whether the characteristics of staurosporine-induced HGF production have similarities to those of HGF production stimulated by other HGF inducers. The effect of staurosporine like that of 8-bromo-cAMP and that of cholera toxin was marked in human skin fibroblasts from all four different sources, whereas the effects of epidermal growth factor and phorbol 12-myristate 13-acetate were variable depending on cells. The net increase in HGF production induced by staurosporine was not reduced in protein kinase C-depleted human skin fibroblasts. Moreover, synergistic induction of HGF was detected between staurosporine and interferon-gamma as well as between 8-bromo-cAMP and interferon-gamma. Staurosporine, however, did not increase intracellular cAMP levels in human skin fibroblasts. These results indicate that staurosporine induced HGF in different cell types via a signaling pathway similar to the cAMP-mediated pathway without increasing cAMP levels.

CCAAT/enhancer-binding protein family members recruit the coactivator CREB-binding protein and trigger its phosphorylation

CCAAT/enhancer-binding protein (C/EBP) family members are transcription factors involved in important physiological processes, such as cellular proliferation and differentiation, regulation of energy homeostasis, inflammation, and hematopoiesis. Transcriptional activation by C/EBPalpha and C/EBPbeta involves the coactivators CREB-binding protein (CBP) and p300, which promote transcription by acetylating histones and recruiting basal transcription factors. In this study, we show that C/EBPdelta is also using CBP as a coactivator. Based on sequence homology with C/EBPalpha and -beta, we identify in C/EBPdelta two conserved amino acid segments that are necessary for the physical interaction with CBP. Using reporter gene assays, we demonstrate that mutation of these residues prevents CBP recruitment and diminishes the transactivating potential of C/EBPdelta. In addition, our results indicate that C/EBP family members not only recruit CBP but specifically induce its phosphorylation. We provide evidence that CBP phosphorylation depends on its interaction with C/EBPdelta and define point mutations within one of the two conserved amino acid segments of C/EBPdelta that abolish CBP phosphorylation as well as transcriptional activation, suggesting that this new mechanism could be important for C/EBP-mediated transcription.

Inducible enhancement of memory storage and synaptic plasticity in transgenic mice expressing an inhibitor of ATF4 (CREB-2) and C/EBP proteins

To examine the role of C/EBP-related transcription factors in long-term synaptic plasticity and memory storage, we have used the tetracycline-regulated system and expressed in the forebrain of mice a broad dominant-negative inhibitor of C/EBP (EGFP-AZIP), which preferentially interacts with several inhibiting isoforms of C/EBP. EGFP-AZIP also reduces the expression of ATF4, a distant member of the C/EBP family of transcription factors that is homologous to the Aplysia memory suppressor gene ApCREB-2. Consistent with the removal of inhibitory constraints on transcription, we find an increase in the pattern of gene transcripts in the hippocampus of EGFP-AZIP transgenic mice and both a reversibly enhanced hippocampal-based spatial memory and LTP. These results suggest that several proteins within the C/EBP family including ATF4 (CREB-2) act to constrain long-term synaptic changes and memory formation. Relief of this inhibition lowers the threshold for hippocampal-dependent long-term synaptic potentiation and memory storage in mice.

Calcium channel and NMDA receptor activities differentially regulate nuclear C/EBPbeta levels to control neuronal survival

Insulin-like growth factor-1 (IGF-1) promotes the survival of cerebellar granule neurons by enhancing calcium influx through L-type calcium channels, whereas NMDA receptor-mediated calcium influx can lead to excitotoxic death. Here we demonstrate that L and NMDA receptor channel activities differentially regulate the transcription factor C/EBPbeta to control neuronal survival. Specifically, we show that L channel-dependent calcium influx results in increased CaMKIV activity, which acts to decrease nuclear C/EBPbeta levels. Conversely, NMDA receptor-mediated influx rapidly elevates nuclear C/EBPbeta and induces excitotoxic death via activation of the calcium-dependent phosphatase, calcineurin. Moderate levels of AMPA receptor activity stimulate L channels to improve survival, whereas higher levels stimulate NMDA receptors and reduce neuronal survival, suggesting differential synaptic effects. Finally, N-type calcium channel activity reduces survival, potentially by increasing glutamate release. Together, these results show that the L-type calcium channel-dependent survival and NMDA receptor death pathways converge to regulate nuclear C/EBPbeta levels, which appears to be pivotal in these mechanisms.

C/EBPbeta regulation in lipopolysaccharide-stimulated macrophages

C/EBP family members contribute to the induction of the interleukin-12 p40 gene and the genes encoding several other mediators of inflammation. Here, we show by chromatin immunoprecipitation that C/EBPbeta binds the p40 promoter following lipopolysaccharide stimulation of peritoneal macrophages. However, three modes of C/EBPbeta regulation reported in other cell types were not detected, including alternative translation initiation, nuclear translocation, and increased DNA binding following posttranslational modification. In contrast, C/EBPbeta concentrations greatly increased following stimulation via MAP kinase-dependent induction of C/EBPbeta gene transcription. Increased C/EBPbeta concentrations were unimportant for p40 induction, however, as transcription of the p40 gene initiated before C/EBPbeta concentrations increased. Furthermore, disruption of C/EBPbeta upregulation by a MAP kinase inhibitor only slightly diminished p40 induction. Phosphopeptide mapping revealed that endogenous C/EBPbeta in macrophages is phosphorylated on only a single tryptic peptide containing 14 potential phosphoacceptors. This peptide was constitutively phosphorylated in primary and transformed macrophages, in contrast to its inducible phosphorylation in other cell types in response to Ras and growth hormone signaling. Altered-specificity experiments supported the hypothesis that C/EBPbeta activity in macrophages does not require an inducible posttranslational modification. These findings suggest that, although C/EBPbeta contributes to the induction of numerous proinflammatory genes, it is fully active in unstimulated macrophages and poised to stimulate transcription in conjunction with other factors whose activities are induced.

Synergism between calcium and cyclic GMP in cyclic AMP response element-dependent transcriptional regulation requires cooperation between CREB and C/EBP-beta

Calcium induces transcriptional activation of the fos promoter by activation of the cyclic AMP response element (CRE)-binding protein (CREB), and in some cells its effect is enhanced synergistically by cyclic GMP (cGMP) through an unknown mechanism. We observed calcium-cGMP synergism in neuronal and osteogenic cells which express type II cGMP-dependent protein kinase (G-kinase); the effect on the fos promoter was mediated by the CRE and proportional to G-kinase activity. Dominant negative transcription factors showed involvement of CREB- and C/EBP-related proteins but not of AP-1. Expression of C/EBP-beta but not C/EBP-alpha or -delta enhanced the effects of calcium and cGMP on a CRE-dependent reporter gene. The transactivation potential of full-length CREB fused to the DNA-binding domain of Gal4 was increased synergistically by calcium and cGMP, and overexpression of C/EBP-beta enhanced the effect, while a dominant negative C/EBP inhibited it. With a mammalian two-hybrid system, coimmunoprecipitation experiments, and in vitro binding studies, we demonstrated that C/EBP-beta and CREB interacted directly; this interaction involved the C terminus of C/EBP-beta but occurred independently of CREB's leucine zipper domain. CREB Ser(133) phosphorylation was stimulated by calcium but not by cGMP; in cGMP-treated cells, (32)PO(4) incorporation into C/EBP-beta was decreased and C/EBP-beta/CRE complexes were increased, suggesting regulation of C/EBP-beta functions by G-kinase-dependent dephosphorylation. C/EBP-beta and CREB associated with the fos promoter in intact cells, and the amount of promoter-associated C/EBP-beta was increased by calcium and cGMP. We conclude that calcium and cGMP transcriptional synergism requires cooperation of CREB and C/EBP-beta, with calcium and cGMP modulating the phosphorylation states of CREB and C/EBP-beta, respectively.

Different mechanisms for loss and recovery of binocularity in the visual cortex

Diverse molecular mechanisms have been discovered that mediate the loss of responses to the deprived eye during monocular deprivation. cAMP/Ca2+ response element-binding protein (CREB) function, in particular, is thought to be essential for ocular dominance plasticity during monocular deprivation. In contrast, we have very little information concerning the molecular mechanisms of recovery from the effects of monocular deprivation, even though this information is highly relevant for understanding cortical plasticity. To test the involvement of CREB activation in recovery of responses to the deprived eye, we used herpes simplex virus (HSV) to express in the primary visual cortex a dominant-negative form of CREB (HSV-mCREB) containing a single point mutation that prevents its activation. This mutant was used to suppress CREB function intracortically during the period when normal vision was restored in two protocols for recovery from monocular deprivation: reverse deprivation and binocular vision. In the reverse deprivation model, inhibition of CREB function prevented loss of responses to the newly deprived eye but did not prevent simultaneous recovery of responses to the previously deprived eye. Full recovery of cortical binocularity after restoration of binocular vision was similarly unaffected by HSV-mCREB treatment. The HSV-mCREB injections produced strong suppression of CREB function in the visual cortex, as ascertained by both DNA binding assays and immunoblot analysis showing a decrease in the expression of the transcription factor C/EBPbeta, which is regulated by CREB. These results show a mechanistic dichotomy between loss and recovery of neural function in visual cortex; CREB function is essential for loss but not for recovery of deprived eye responses.

NMDA receptor-dependent CREB activation in survival of cerebellar granule cells during in vivo and in vitro development

During both in vivo and in vitro development, cerebellar granule cells depend on the activity of the NMDA glutamate receptor subtype for survival and full differentiation. With the present results, we demonstrate that CREB activation, downstream of the NMDA receptor, is a necessary step to ensure survival of these neurons. The levels of CREB expression and activity increase progressively during the second week of postnatal cerebellar development and the phosphorylated form of CREB is localized selectively to cerebellar granule cells during the critical developmental stages examined. Chronically blocking the NMDA receptor through systemic administration of the competitive antagonist, CGP 39551, during the in vivo critical developmental period, between 7-11 postnatal days, results in increased apoptotic elimination of differentiating granule neurons in the cerebellum [Monti & Contestabile, Eur. J. Neurosci., 12, 3117-3123 (2000)]. We report here that this event is accompanied by a significant decrease of CREB phosphorylation in the cerebellum of treated rat pups. When cerebellar granule neurons are explanted and maintained in dissociated cultures, the levels of CREB phosphorylation increase with differentiation, similar to that which happens during in vivo development. When granule cells are kept in non-trophic conditions, their viability is affected and both CREB phosphorylation and transcriptional activity are decreased significantly. The neuronal viability and the deficiency of CREB activity, are both rescued by the pharmacological activation of the NMDA receptor. These results provide good circumstantial evidence for a functional link between the NMDA receptor and CREB activity in promoting neuronal survival during development.

Mood stabilizers, glycogen synthase kinase-3beta and cell survival

Glycogen synthase kinase-3beta (GSK3beta) is a central figure in many intracellular signaling systems and is directly regulated by lithium. Substantial evidence now indicates that an important property of the mood stabilizer, lithium, is to influence GSK3beta-linked signaling pathways. This raises the possibility that other mood stabilizers act in a similar manner, which may include modulation of signaling systems leading to GSK3beta, direct regulation of GSK3beta or regulation of signaling intermediates downstream of GSK3beta. Downstream targets of GSK3beta, and thus potential targets of mood stabilizers, are several key transcription factors, including beta-catenin, AP-1, cyclic AMP-response element binding protein, NFkappaB, Myc, heat shock factor-1, nuclear factor of activated T-cells and CCAAT/enhancer-binding proteins. GSK3beta also is an important modulator of cell death, which may be a consequence of its regulatory effects on transcription factor activities. GSK3beta facilitates apoptosis, and lithium's inhibition of GSK3beta supports cell survival. Thus, signaling systems determining cell fate appear to be important targets of mood stabilizers, and these may include signaling pathways encompassing GSK3beta, including transcription factors regulated by GSK3beta.

CCAAT/enhancer-binding proteins: structure, function and regulation

CCAAT/enhancer binding proteins (C/EBPs) are a family of transcription factors that all contain a highly conserved, basic-leucine zipper domain at the C-terminus that is involved in dimerization and DNA binding. At least six members of the family have been isolated and characterized to date (C/EBP alpha[bond]C/EBP zeta), with further diversity produced by the generation of different sized polypeptides, predominantly by differential use of translation initiation sites, and extensive protein-protein interactions both within the family and with other transcription factors. The function of the C/EBPs has recently been investigated by a number of approaches, including studies on mice that lack specific members, and has identified pivotal roles of the family in the control of cellular proliferation and differentiation, metabolism, inflammation and numerous other responses, particularly in hepatocytes, adipocytes and haematopoietic cells. The expression of the C/EBPs is regulated at multiple levels during several physiological and pathophysiological conditions through the action of a range of factors, including hormones, mitogens, cytokines, nutrients and certain toxins. The mechanisms through which the C/EBP members are regulated during such conditions have also been the focus of several recent studies and have revealed an immense complexity with the potential existence of cell/tissue- and species-specific differences. This review deals with the structure, biological function and the regulation of the C/EBP family.

Functional correction of established central nervous system deficits in an animal model of lysosomal storage disease with feline immunodeficiency virus-based vectors

Gene transfer vectors based on lentiviruses can transduce terminally differentiated cells in the brain; however, their ability to reverse established behavioral deficits in animal models of neurodegeneration has not previously been tested. When recombinant feline immunodeficiency virus (FIV)-based vectors expressing beta-glucuronidase were unilaterally injected into the striatum of adult beta-glucuronidase deficient [mucopolysaccharidosis type VII (MPS VII)] mice, an animal model of lysosomal storage disease, there was bihemispheric correction of the characteristic cellular pathology. Moreover, after the injection of FIV-based vectors expressing beta-glucuronidase into brains of beta-glucuronidase-deficient mice with established impairments in spatial learning and memory, there was dramatic recovery of behavioral function. Cognitive improvement resulting from expression of beta-glucuronidase was associated with alteration in expression of genes associated with neuronal plasticity. These data suggest that enzyme replacement to the MPS VII central nervous system goes beyond restoration of beta-glucuronidase activity in the lysosome, and imparts improvements in plasticity and spatial learning.

CCAAT/enhancer-binding protein beta plays a regulatory role in differentiation and apoptosis of neuroblastoma cells

The C/EBPbeta (CCAAT/enhancer-binding protein beta) is a transcription factor that belongs to basic region-leucine zipper class DNA-binding proteins. There is a significant body of evidence that suggests that this protein plays a central role in adipocytic and eosinophilic differentiation. However, there is no information available regarding the role of this transcription factor in the development of mammalian neuronal tissues. In this study, we have examined the effect of C/EBPbeta overexpression on the differentiation and survival of mouse Neuro2A cells. We found that C/EBPbeta induces neuronal differentiation and that this process is inhibited by transfection with the C/EBP homologous protein 10 (CHOP), strongly suggesting that the extension of neurites is indeed due to the C/EBPbeta transcriptional activity. As it has been suggested in adipocyte differentiation, here we show that C/EBPbeta induces the expression of the endogenous C/EBPalpha gene and that this protein by itself is also able to induce a differentiated phenotype in Neuro2A cells. Neuronal differentiation induced by C/EBPbeta requires activation of the phosphatidylinositol 3-kinase signaling pathway, whereas inhibition of the mitogen-activated protein kinase signaling does not have any effect. In addition, we show that C/EBPbeta is expressed in the brain of neonatal rats, suggesting that this protein could play an important role in neuronal maturation. Finally, cell death was also induced by C/EBPbeta through activation of the p53 protein and the cdk inhibitor p21.

The multifaceted roles of glycogen synthase kinase 3beta in cellular signaling

Glycogen synthase kinase-3beta (GSK3beta) is a fascinating enzyme with an astoundingly diverse number of actions in intracellular signaling systems. GSK3beta activity is regulated by serine (inhibitory) and tyrosine (stimulatory) phosphorylation, by protein complex formation, and by its intracellular localization. GSK3beta phosphorylates and thereby regulates the functions of many metabolic, signaling, and structural proteins. Notable among the signaling proteins regulated by GSK3beta are the many transcription factors, including activator protein-1, cyclic AMP response element binding protein, heat shock factor-1, nuclear factor of activated T cells, Myc, beta-catenin, CCAAT/enhancer binding protein, and NFkappaB. Lithium, the primary therapeutic agent for bipolar mood disorder, is a selective inhibitor of GSK3beta. This raises the possibility that dysregulation of GSK3beta and its inhibition by lithium may contribute to the disorder and its treatment, respectively. GSK3beta has been linked to all of the primary abnormalities associated with Alzheimer's disease. These include interactions between GSK3beta and components of the plaque-producing amyloid system, the participation of GSK3beta in phosphorylating the microtubule-binding protein tau that may contribute to the formation of neurofibrillary tangles, and interactions of GSK3beta with presenilin and other Alzheimer's disease-associated proteins. GSK3beta also regulates cell survival, as it facilitates a variety of apoptotic mechanisms, and lithium provides protection from many insults. Thus, GSK3beta has a central role regulating neuronal plasticity, gene expression, and cell survival, and may be a key component of certain psychiatric and neurodegenerative diseases.

Memory consolidation of Pavlovian fear conditioning: a cellular and molecular perspective

Pavlovian fear conditioning has emerged as a leading behavioral paradigm for studying the neurobiological basis of learning and memory. Although considerable progress has been made in understanding the neural substrates of fear conditioning at the systems level, until recently little has been learned about the underlying cellular and molecular mechanisms. The success of systems-level work aimed at defining the neuroanatomical pathways underlying fear conditioning, combined with the knowledge accumulated by studies of long-term potentiation (LTP), has recently given way to new insights into the cellular and molecular mechanisms that underlie acquisition and consolidation of fear memories. Collectively, these findings suggest that fear memory consolidation in the amygdala shares essential biochemical features with LTP, and hold promise for understanding the relationship between memory consolidation and synaptic plasticity in the mammalian brain.

Overexpression of and RNA interference with the CCAAT enhancer-binding protein on long-term facilitation of Aplysia sensory to motor synapses

In the marine mollusk Aplysia, the CCAAT/enhancer-binding protein, ApC/EBP, serves as an immediate early gene in the consolidation of long-term facilitation in the synaptic connection between the sensory and motor neurons of the gill-withdrawal reflex. To further examine the role of ApC/EBP as a molecular switch of a stable form of long-term memory, we cloned the full-length coding regions of two alternatively spliced forms, the short and long form of ApC/EBP. Overexpression of each isoform by DNA microinjection resulted in a l6-fold increase in the expression of the coinjected luciferase reporter gene driven by an ERE promoter. In addition, when we overexpressed ApC/EBP in Aplysia sensory neurons, we found that the application of a single pulse of 5-HT that normally induced only short-term facilitation now induced long-term facilitation. Conversely, when we attempted to block the synthesis of native ApC/EBP by microinjecting double-strand RNA or antisense RNA, we blocked long-term facilitation in a sequence-specific manner. These data support the idea that ApC/EBP is both necessary and sufficient to consolidate short-term memory into long-term memory. Furthermore, our results suggest that this double-strand RNA interference provides a powerful tool in the study of the genes functioning in learning and memory in Aplysia by specifically inhibiting both the constitutive and induced expression of the genes.

Ca(2+)/CaM-dependent kinases: from activation to function

Calmodulin (CaM) is an essential protein that serves as a ubiquitous intracellular receptor for Ca(2+). The Ca(2+)/CaM complex initiates a plethora of signaling cascades that culminate in alteration of cellular functions. Among the many Ca(2+)/CaM-binding proteins to be discovered, the multifunctional protein kinases CaMKI, II, and IV play pivotal roles. Our review focuses on this class of CaM kinases to illustrate the structural and biochemical basis for Ca(2+)/CaM interaction with and regulation of its target enzymes. Gene transcription has been chosen as the functional endpoint to illustrate the recent advances in Ca(2+)/CaM-mediated signal transduction mechanisms.

Interleukin-6-induced tethering of STAT3 to the LAP/C/EBPbeta promoter suggests a new mechanism of transcriptional regulation by STAT3

LAP/C/EBPbeta is a member of the C/EBP family of transcription factors and contributes to the regulation of the acute phase response in hepatocytes. Here we show that IL-6 controls LAP/C/EBPbeta gene transcription and identify an IL-6 responsive element in the LAP/C/EBPbeta promoter, which contains no STAT3 DNA binding motif. However, luciferase reporter gene assays showed that STAT3 activation through the gp130 signal transducer molecule is involved in mediating IL-6-dependent LAP/C/EBPbeta transcription. Southwestern analysis indicated that IL-6 induces binding of a 68-kDa protein to the recently characterized CRE-like elements in the LAP/C/EBPbeta promoter. Transfection experiments using promoter constructs with mutated CRE-like elements revealed that these sites confer IL-6 responsiveness. Further analysis using STAT1/STAT3 chimeras identified specific domains of the protein that are required for the IL-6-dependent increase in LAP/C/EBPbeta gene transcription. Overexpression of the amino-terminal domain of STAT3 blocked the IL-6-mediated response, suggesting that the STAT3 amino terminus has an important function in IL-6-mediated transcription of the LAP/C/EBPbeta gene. These data lead to a model of how tethering STAT3 to a DNA-bound complex contributes to IL-6-dependent LAP/C/EBPbeta gene transcription. Our analysis describes a new mechanism by which STAT3 controls gene transcription and which has direct implication for the acute phase response in liver cells.