Structure of the NGFI-A gene and detection of upstream sequences responsible for its transcriptional induction by nerve growth factor

Control by thyroid hormone of NGFI-A gene expression in lung: regulation of NGFI-A promoter activity

In previous studies, it was shown that the expression of the transcription factor NGFI-A is under thyroid hormone (T3) control in developing rat brain. Here, the effect of this hormone on the expression of this gene in lung, as well as the effect of T3 and NGFI-A protein on NGFI-A promoter activity, has been investigated. The results show that T3 regulates NGFI-A gene expression at a pretranslational level in neonatal and adult rat lung, but also at a translational and/or posttranslational level in 5-day-old neonates, since the NGFI-A protein content was decreased in hypothyroid animals without changes in mRNA. Transfection experiments showed an induction of NGFI-A promoter activity by thyroid hormone. NGFI-A protein blocked this stimulation, suggesting a negative interaction between NGFI-A protein and thyroid hormone receptor, which could explain the transient induction by T3 of this gene observed in the first 2-4 h.

Electroconvulsive shock does not induce c-fos and junB, but TIS1 and TIS8/zif-268, in neonatal rat hippocampus

The induction in the animal brain of immediate early genes (IEGs) is known to be age-dependent, and it was suggested that, during neonatal period, signaling pathways for the induction of IEGs are immature. In this study, we investigated the induction of various IEGs in neonatal rat hippocampus after electroconvulsive shock (ECS). ECS did not induce c-fos and junB in the hippocampus of 7-day-old rat, but these genes were weakly induced at postnatal 14 days and to an adult level at postnatal 21 days; two other IEGs, TIS1 (NGFI-B, nur77) and TIS8 (zif-268, Egr-1, Krox-24, NGFI-A), were induced at postnatal 7 days, however. Our results suggested that during the neonatal period, signaling pathways for TIS1 and TIS8 induction in rat hippocampus after ECS are complete, while those for c-fos and junB are immature.

Layer-specific differential regulation of transcription factors Zif268 and Jun-D in visual cortex V1 and V2 of macaque monkeys

To investigate intracellular mechanisms of cortical layer-specific gene regulation, we quantitatively examined the expression of two transcription factors, Zif268 and JunD, and compared their expression levels in each layer of the primary visual cortex (VI) and visual area 2 (V2) of macaque monkeys (Macaca fuscata). The brain sections were immunohistochemically stained for determination of the percentage of Zif268- or JunD-expressing neurons in the total neuronal population. We found area- and layer-specific expression of these transcription factors; Zif268 tended to be expressed at high levels in layers on the parvocellular pathway in V1, whereas JunD did not show such an expression pattern. In V1, many Zif268-immunopositive neurons were observed in layers II/III, IVC beta and VI. The percentage of Zif268-immunopositive neurons was highest in layer IVC beta and lowest in layer IVC alpha. JunD-immunopositive neurons were fewest in layer IVC beta and most abundant in layer VI. In V2, the level of expression of Zif268 was almost the same as that of JunD in layer II/II. However, layer IV of V2 tended to contain more Zif268-immunopositive neurons than JunD-immunopositive neurons, whereas layer VI contained more JunD-immunopositive neurons than Zif268-immunopositive neurons. Although it has been reported that the same extracellular signals induce both Zif268 and JunD, the present results indicate that the expression of these transcription factors is differentially controlled in each layer of the primate visual cortical areas. Furthermore, the present results suggest that these transcription factors contribute to area- and layer-specific gene regulation by mediating transmission of extracellular signals to the nucleus via different intracellular signalling pathways.

Hypotonicity increases transcription, expression, and action of Egr-1 in murine renal medullary mIMCD3 cells

In cells of the murine renal inner medullary collecting duct (mIMCD3) cell line, acute hypotonic shock (50% dilution of medium with sterile water but not with sterile 150 mM NaCl) increased Egr-1 mRNA abundance 2.5-fold at 6 h, as determined by Northern analysis. This increase was accompanied by increased Egr-1 transcription, as quantitated by luciferase reporter gene assay. Increased transcription was dose dependent, additive with other Egr-1 transcriptional activators, and occurred in the absence of overt cytotoxicity, as quantitated via a fluorometric viability assay. In addition, hypotonic stress increased Egr-1 protein abundance, which was accompanied by augmented Egr-1-specific DNA binding ability, as measured via electrophoretic mobility shift assay. Increased DNA binding was further associated with increased transactivation by Egr-1, demonstrated through transient transfection of mIMCD3 cells with a luciferase reporter gene driven by tandem repeats of the Egr-1 DNA consensus sequence. Taken together, these data indicate that hypotonic stress activates Egr-1 transcription, translation, DNA binding, and transactivation in renal medullary cells. This phenomenon might play a role in the acquisition of the adaptive phenotype in response to hypotonic stress in cells of the renal medulla in vivo.

Alpha2-adrenoreceptor agonist, dexmedetomidine, alters acute gene expression after global ischemia in gerbils

The effect of dexmedetomidine, a selective alpha2-adrenoreceptor agonist and neuroprotective agent on the expression of immediate early genes and heat shock protein hsp70, was studied using quantitative in situ hybridization in a global ischemia model. At the dose previously shown to be neuroprotective dexmedetomidine inhibited the expression of c-fos and hsp70 mRNA, did not affect jun-B mRNA, and enhanced the induction of NGFI-A mRNA in the postischemic gerbil hippocampus. The reduced gene expression of c-fos and hsp70 was detected in the CA1 pyramidal cells which are prone to ischemic degeneration, whereas the increased gene expression of NGFI-A was measured from the CA3 and dentate gyrus, areas relatively resistant to ischemia. These alterations in early gene expression possibly reflect the mechanisms mediating the neuroprotective effects of alpha2-adrenoreceptor agonists.

Calcium controls gene expression via three distinct pathways that can function independently of the Ras/mitogen-activated protein kinases (ERKs) signaling cascade

Calcium ions are the principal second messenger in the control of gene expression by electrical activation of neurons. However, the full complexity of calcium-signaling pathways leading to transcriptional activation and the cellular machinery involved are not known. Using the c-fos gene as a model system, we show here that the activity of its complex promoter is controlled by three independently operating signaling mechanisms and that their functional significance is cell type-dependent. The serum response element (SRE), which is composed of a ternary complex factor (TCF) and a serum response factor (SRF) binding site, integrates two calcium-signaling pathways. In PC12 cells, calcium-regulated transcription mediated by the SRE requires the TCF site and is not inhibited by expression of the dominant-negative Ras mutant, RasN17, nor by the MAP kinase kinase 1 inhibitor PD 98059. In contrast, TCF-dependent transcriptional regulation by nerve growth factor or epidermal growth factor is mediated by a Ras/MAP kinases (ERKs) pathway targeting the TCF Elk-1. In AtT20 cells and hippocampal neurons, calcium signals can stimulate transcription via a TCF-independent mechanism that requires the SRF binding site. The cyclic AMP response element (CRE), which cooperates with the TCF site in growth factor-regulated transcription, is a target of a third calcium-regulated pathway that is little affected by the expression of RasN17 or by PD 98059. Thus, calcium can stimulate gene expression via a TCF-, SRF-, and CRE-linked pathway that can operate independently of the Ras/MAP kinases (ERKs) signaling cascade in a cell type-dependent manner.

Calcium controls gene expression via three distinct pathways that can function independently of the Ras/mitogen-activated protein kinases (ERKs) signaling cascade

Calcium ions are the principal second messenger in the control of gene expression by electrical activation of neurons. However, the full complexity of calcium-signaling pathways leading to transcriptional activation and the cellular machinery involved are not known. Using the c-fos gene as a model system, we show here that the activity of its complex promoter is controlled by three independently operating signaling mechanisms and that their functional significance is cell type-dependent. The serum response element (SRE), which is composed of a ternary complex factor (TCF) and a serum response factor (SRF) binding site, integrates two calcium-signaling pathways. In PC12 cells, calcium-regulated transcription mediated by the SRE requires the TCF site and is not inhibited by expression of the dominant-negative Ras mutant, RasN17, nor by the MAP kinase kinase 1 inhibitor PD 98059. In contrast, TCF-dependent transcriptional regulation by nerve growth factor or epidermal growth factor is mediated by a Ras/MAP kinases (ERKs) pathway targeting the TCF Elk-1. In AtT20 cells and hippocampal neurons, calcium signals can stimulate transcription via a TCF-independent mechanism that requires the SRF binding site. The cyclic AMP response element (CRE), which cooperates with the TCF site in growth factor-regulated transcription, is a target of a third calcium-regulated pathway that is little affected by the expression of RasN17 or by PD 98059. Thus, calcium can stimulate gene expression via a TCF-, SRF-, and CRE-linked pathway that can operate independently of the Ras/MAP kinases (ERKs) signaling cascade in a cell type-dependent manner.

Mitogen-activated protein kinase cascades and the signaling of hyperosmotic stress to immediate early genes

Among prokaryotes and lower eukaryotes, the threat of exposure to hyperosmotic stress is ubiquitous. Among higher eukaryotes, in contrast, only specific tissues are routinely exposed to marked hypertonicity. The mammalian renal medulla, the prototypical example, is continually subjected to an elevated solute concentration as a consequence of the renal concentrating mechanism. Until recently, the investigative focus has concerned the effects of diverse solutes on the regulation of genes essential for the adaptive accumulation of osmotically active organic solutes. Recent and sweeping developments elucidating the molecular mechanisms underlying stress signaling to the nucleus have focused interest on earlier events in the response to hyperosmotic stress. Such events include the transcriptional activation and post-translational modification of transcriptional activating proteins, a large subset of which represent the protein products of so-called immediate early genes. This review highlights developments in the understanding of stress signaling in general and hypertonic stress signaling in particular in both yeast and higher eukaryotic models. The relationship between hyperosmotic stress signaling and the transcription and activation of immediate-early gene transcription factors is explored.

Early induction of mRNA for calbindin-D28k and BDNF but not NT-3 in rat hippocampus after kainic acid treatment

The influence of kainic acid (KA), which induces acute seizures, on expression of mRNA for the calcium-binding protein, calbindin-D28k, brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3) and early-response genes [c-fos, zif268 (NGFI-A), nur77 (NGFI-B)] was examined in rat hippocampus by Northern blot analysis. A significant increase (3.2-fold) in BDNF mRNA was observed 1 h after KA injection (12 mg/kg i.p.) and peak expression (9.4-fold) occurred 3 h after KA. The induction of BDNF mRNA was preceded by the induction of c-fos, mRNA (30 min after KA) and was followed by the induction of calbindin-D28k mRNA (3.5-fold 3 h after KA; a maximal response was at 3-6 h after KA). Region-specific changes, analyzed by immunocytochemistry and in situ hybridization, indicated that the most dramatic increases in calbindin protein and mRNA after KA treatment were in the dentate gyrus. Although calbindin-D28k and BDNF mRNAs were induced, a 3.4-3.8-fold decrease in NT-3 mRNA was observed by Northern analysis 3-24 h after KA treatment. Calbindin-D28k gene expression was also examined in rats with a chronic epileptic state characterized by recurrent seizures established with an episode of electrical stimulation-induced status epilepticus (SE). When these animals were examined 30 days post-SE, no changes in hippocampal calbindin-D28k mRNA were observed. Our findings suggest that the induction of calbindin-D28k mRNA (which may be interrelated to the induction of BDNF mRNA) is an early response which may not be related to enhanced neuronal activity or seizures per se, but rather to maintaining neuronal viability.

Apoptosis, neurotrophic factors and neurodegeneration

Apoptosis is an active process of cell death characterized by distinct morphological features, and is often the end result of a genetic programme of events, i.e. programmed cell death (PCD). There is growing evidence supporting a role for apoptosis in some neurodegenerative diseases. This conclusion is based on DNA fragmentation studies and findings of increased levels of pro-apoptotic genes in human brain and in in vivo and in vitro model systems. Additionally, there is some evidence for a loss of neurotrophin support in neurodegenerative diseases. In Alzheimer's disease, in particular, there is strong evidence from human brain studies, transgenic models and in vitro models to suggest that the mode of nerve cell death is apoptotic. In this review we describe the evidence implicating apoptosis in neurodegenerative diseases with a particular emphasis on Alzheimer's disease.

Visual sensitivities of nur77 (NGFI-B) and zif268 (NGFI-A) induction in the suprachiasmatic nucleus are dissociated from c-fos induction and behavioral phase-shifting responses

Mammalian circadian rhythms are regulated by a pacemaker in the suprachiasmatic nucleus of the hypothalamus. Recent work from several laboratories has shown that light induces the IEGs, c-fos and jun-B, in the rodent suprachiasmatic nucleus. In hamsters, there is a strong correlation between circadian entrainment and the induction of c-fos and jun-B in the suprachiasmatic nucleus by light. Previous work has shown that the IEGs, nur77 and zif268, both of which encode transcription factors, are also light-inducible in the rat suprachiasmatic nucleus [Rusak, B., McNaughton, L., Robertson, H.A. and Hunt, S.P., Circadian variation in photic regulation of IEG mRNAs in rat suprachiasmatic nucleus cells, Mol. Brain Res., 14 (1992) 124-130.; Sutin, E.L. and Kilduff, T.S., Circadian and light-induced expression of IEG mRNAs in the rat suprachiasmatic nucleus, Mol. Brain Res., 15 (1992) 281-290.]. To characterize the photic-regulation of these genes in the suprachiasmatic nucleus of golden hamsters, we used in situ hybridization to measure nur77 and zif268 mRNA levels with 33P-labeled complementary RNA probes. 5-min monochromatic light pulses at CT19 induced a dramatic increase in both nur77 and zif268 mRNA levels. Peak mRNA levels occurred 45-60 min after light onset for both nur77 and zif268. In addition, the induction of both nur77 and zif268 mRNA levels was gated by the circadian pacemaker. Light pulses during subjective day (CT3 and CT9), which do not cause behavioral phase-shifts, did not significantly alter mRNA levels of either nur77 or zif268; whereas light pulses during the subjective night (CT14 and CT19), which induce phase-shifts, dramatically increased both nur77 and zif268 mRNA levels. In contrast to c-fos induction, which has a photic threshold indistinguishable from that of the behavioral phase-shifting response, nur77 and zif268 mRNA induction were found to have visual sensitivities greater than the phase-shifting response by 1-2 log units (10-100-fold). Although light and circadian phase regulate nur77 and zif268 expression in the SCN, these results demonstrate that their induction is not rate-limiting for photic entrainment of the hamster circadian system.

Sensory regulation of immediate-early gene expression in mammalian visual cortex: implications for functional mapping and neural plasticity

The expression of immediate-early genes that code for transcription factors has been extensively studied in the brain with regard to imaging functional activity. The components of the AP-1 transcription factor--in particular, c-Fos--and Zif268 have been widely used for this purpose. However, the precise details by which they are induced after synaptic stimulation remain unknown. Furthermore, the roles of these two proteins in neurons remains speculative and include such varied functions as short-term maintenance of cellular homeostasis to long-term changes that guide cortical plasticity. Current efforts at elucidating the physiological roles of AP-1 and Zif268 rely on assessing their expression in response to different conditions of sensory and pharmacological stimulation. In this review, we have examined the expression patterns of these transcription factors in the mammalian visual cortex under different conditions, with particular emphasis on the constitutive levels and how they change after visual deprivation and stimulation. A synthesis of this information offers further insight into their likely functions and the extent to which transcription factors may represent patterns of neural activity as a possible prelude to plastic events.

Transcriptional regulation of neurofilament expression by protein kinase A

RN46A cells, a conditionally immortalized neuronal cell line derived from E12 rat medullary raphe nucleus, upregulate low M(r) (68 kDa, neurofilament [NF]-L) and medium M(r) (160 kDa, NF-M) neurofilament protein expression upon activation of protein kinase A (PKA). To examine possible transcriptional regulation of neurofilament protein expression by PKA, two cell lines were used; RN46A cells and C alpha EV6 cells, a cell line derived from RN46A cells that stably expresses the catalytic subunit of PKA under the control of the metallothionein promoter. Treatment of RN46A cells with dbcAMP resulted in an increase in the steady-state levels of both NF-L and NF-M, but not high M(r) (200 kDa, NF-H) neurofilament mRNA. These increases were both time and dose dependent and were sensitive to treatment with the protein synthesis inhibitor cycloheximide. In C alpha EV6 cells, activation of PKA by 80 microM ZnSO4 upregulated the expression of C alpha mRNA with maximal levels reached 8 hr post-treatment and maintained at 24 hr. Reporter gene assays in C alpha EV6 cells following transfection with increasing lengths of the NF-L promoter demonstrated that both a putative Sp1-like and a cAMP response (CRE), but not a NGFI-A, element were likely involved in PKA-dependent activation of the NF-L promoter. Electrophoretic mobility shift assays confirmed these results but showed that the nuclear proteins induced by PKA which bound to the NF-L promoter Sp1-like sequence were not Sp1. Collectively, these data suggest that constitutively expressed Sp1 may be involved in basal NF-L promoter activity, and newly synthesized, PKA-dependent nuclear proteins may synergistically activate the rat NF-L promoter.

Intrastriatally injected c-fos antisense oligonucleotide interferes with striatonigral but not striatopallidal gamma-aminobutyric acid transmission in the conscious rat

Antisense c-fos oligonucleotides injected into the neostriatum of conscious rats selectively inhibited c-fos expression associated with compensatory increases in striatal c-fos mRNA levels and also with increased expression of junB and NGFI-A mRNA, probably as a result of regulatory phenomena. Dual probe in vivo microdialysis was used to investigate gamma-aminobutyric acid (GABA) release in the substantia nigra and the globus pallidus, which represent the terminal sites of the dopamine D1 receptor regulated striatonigral and the dopamine D2 receptor regulated striatopallidal GABA pathways, respectively. Intrastriatal infusion of the c-fos antisense oligonucleotide profoundly decreased dialysate GABA levels in the ipsilateral substantia nigra within 60 min but did not influence the dialysate GABA levels in the globus pallidus compared with the sham and control oligonucleotide treated groups. The site of action of the antisense oligonucleotides was mainly restricted to striatal neurons as shown by the distribution of locally injected fluoresceine isothiocyanate and radiolabeled oligonucleotides. The findings demonstrate a facilitatory role for c-fos mediated gene regulation in striatonigral GABA transmission and strengthen the evidence that the regulation of neurotransmission is different in the striatonigral and striatopallidal GABA pathways.

Calcium influx via the NMDA receptor induces immediate early gene transcription by a MAP kinase/ERK-dependent mechanism

The regulation of gene expression by neurotransmitters is likely to play a key role in neuroplasticity both during development and in the adult animal. Therefore, it is important to determine the mechanisms of neuronal gene regulation to understand fully the mechanisms of learning, memory, and other long-term adaptive changes in neurons. The neurotransmitter glutamate stimulates rapid and transient induction of many genes, including the c-fos proto-oncogene. The c-fos promoter contains several critical regulatory elements, including the serum response element (SRE), that mediate glutamate-induced transcription in neurons; however, the mechanism by which the SRE functions in neurons has not been defined. In this study, we sought to identify transcription factors that mediate glutamate induction of transcription through the SRE in cortical neurons and to elucidate the mechanism(s) of transcriptional activation by these factors. To facilitate this analysis, we developed an improved calcium phosphate coprecipitation procedure to transiently introduce DNA into primary neurons, both efficiently and consistently. Using this protocol, we demonstrate that the transcription factors serum response factor (SRF) and Elk-1 can mediate glutamate induction of transcription through the SRE in cortical neurons. There are at least two distinct pathways by which glutamate signals through the SRE: an SRF-dependent pathway that can operate in the absence of Elk and an Elk-dependent pathway. Activation of the Elk-dependent pathway of transcription seems to require phosphorylation of Elk-1 by extracellular signal-regulated kinases (ERKs), providing evidence for a physiological function of ERKs in glutamate signaling in neurons. Taken together, these findings suggest that SRF, Elk, and ERKs may have important roles in neuroplasticity.

Transcription factor EGR-1 suppresses the growth and transformation of human HT-1080 fibrosarcoma cells by induction of transforming growth factor beta 1

The early growth response 1 (EGR-1) gene product is a transcription factor with role in differentiation and growth. We have previously shown that expression of exogenous EGR-1 in various human tumor cells unexpectedly and markedly reduces growth and tumorigenicity and, conversely, that suppression of endogenous Egr-1 expression by antisense RNA eliminates protein expression, enhances growth, and promotes phenotypic transformation. However, the mechanism of these effects remained unknown. The promoter of human transforming growth factor beta 1 (TGF-beta 1) contains two GC-rich EGR-1 binding sites. We show that expression of EGR-1 in human HT-1080 fibrosarcoma cells uses increased secretion of biologically active TGF-beta 1 in direct proportion (rPearson = 0.96) to the amount of EGR-1 expressed and addition of recombinant human TGF-beta 1 is strongly growth-suppressive for these cells. Addition of monoclonal anti-TGF-beta 1 antibodies to EGR-1-expressing HT-1080 cells completely reverses the growth inhibitory effects of EGR-1. Reporter constructs bearing the EGR-1 binding segment of the TGF-beta 1 promoter was activated 4- to 6-fold relative to a control reporter in either HT-1080 cells that stably expressed or parental cells cotransfected with an EGR-1 expression vector. Expression of delta EGR-1, a mutant that cannot interact with the corepressors, nerve growth factor-activated factor binding proteins NAB1 and NAB2, due to deletion of the repressor domain, exhibited enhanced transactivation of 2- to 3.5-fold over that of wild-type EGR-1 showing that the reporter construct reflected the appropriate in vivo regulatory context. The EGR-1-stimulated transactivation was inhibited by expression of the Wilms tumor suppressor, a known specific DNA-binding competitor. These results indicate that EGR-1 suppresses growth of human HT-1080 fibrosarcoma cells by induction of TGF-beta 1.

Calcium influx via the NMDA receptor induces immediate early gene transcription by a MAP kinase/ERK-dependent mechanism

The regulation of gene expression by neurotransmitters is likely to play a key role in neuroplasticity both during development and in the adult animal. Therefore, it is important to determine the mechanisms of neuronal gene regulation to understand fully the mechanisms of learning, memory, and other long-term adaptive changes in neurons. The neurotransmitter glutamate stimulates rapid and transient induction of many genes, including the c-fos proto-oncogene. The c-fos promoter contains several critical regulatory elements, including the serum response element (SRE), that mediate glutamate-induced transcription in neurons; however, the mechanism by which the SRE functions in neurons has not been defined. In this study, we sought to identify transcription factors that mediate glutamate induction of transcription through the SRE in cortical neurons and to elucidate the mechanism(s) of transcriptional activation by these factors. To facilitate this analysis, we developed an improved calcium phosphate coprecipitation procedure to transiently introduce DNA into primary neurons, both efficiently and consistently. Using this protocol, we demonstrate that the transcription factors serum response factor (SRF) and Elk-1 can mediate glutamate induction of transcription through the SRE in cortical neurons. There are at least two distinct pathways by which glutamate signals through the SRE: an SRF-dependent pathway that can operate in the absence of Elk and an Elk-dependent pathway. Activation of the Elk-dependent pathway of transcription seems to require phosphorylation of Elk-1 by extracellular signal-regulated kinases (ERKs), providing evidence for a physiological function of ERKs in glutamate signaling in neurons. Taken together, these findings suggest that SRF, Elk, and ERKs may have important roles in neuroplasticity.

Expression of the serum response factor gene is regulated by serum response factor binding sites

The serum response factor (SRF) is a ubiquitous transcription factor that plays a central role in the transcriptional response of mammalian cells to a variety of extracellular signals. Notably, SRF has been found to be a key regulator of members of a class of cellular response genes termed immediate-early genes (IEGs), many of which are believed to be involved in regulating cell growth and differentiation. The mechanism by which SRF activates transcription of IEGs in response to mitogenic agents has been extensively studied. Significantly less is known about how expression of the SRF gene itself is mediated. We and others have previously shown that the SRF gene is itself transiently induced by a variety of mitogenic agents and belongs to a class of "delayed" early response genes. We have cloned the SRF promoter and in the present study have analyzed the upstream regulatory sequences involved in mediating serum responsiveness of the SRF gene. Our analysis indicates that inducible SRF expression requires both SRF binding sites located within the first 63 nucleotides upstream from the start site of transcriptional initiation and an Sp1 site located 83 nucleotides upstream from the start site. Maximal transcriptional activity of the promoter also requires two CCAATT box sites located 90 and 123 nucleotides upstream of the start site.

NAB2, a corepressor of NGFI-A (Egr-1) and Krox20, is induced by proliferative and differentiative stimuli

Previous work had identified a corepressor, NAB1, which represses transcriptional activation mediated by NGFI-A (also known as Egr-1, zif268, and Krox24) and Krox20. These zinc finger transcription factors are encoded by immediate-early genes and have been implicated in a wide variety of proliferative and differentiative processes. We have isolated and characterized another corepressor, NAB2, which is highly related to NAB1 within two discrete domains. The first conserved domain of NAB2 mediates an interaction with the R1 domain of NGFI-A. NAB2 represses the activity of both NGFI-A and Krox20, and its expression is regulated by some of the same stimuli that induce NGFI-A expression, including serum stimulation of fibroblasts and nerve growth factor stimulation of PC12 cells. The human NAB2 gene has been localized to chromosome 12ql3.3-14.1, a region that is rearranged in several solid tumors, lipomas, uterine leiomyomata, and liposarcomas. Sequencing of the Caenorhabditis elegans genome has identified a gene that bears high homology to both NAB1 and NAB2, suggesting that NAB molecules fulfill an evolutionarily conserved role.

Functional and physical interactions between mammalian achaete-scute homolog 1 and myocyte enhancer factor 2A

The mammalian achaete-scute homolog 1 (MASH1) protein is required for the early development of the nervous system. However, the molecular and biochemical mechanism by which MASH1 acts to determine neurogenesis are still unknown. The myocyte enhancer factor 2A (MEF2A) is a MADS transcription factor that is essential for the specification and differentiation of the muscle lineage. Here we show that MEF2A and MASH1 are coordinately induced during the differentiation of the teratocarcinoma cell line P19 along a neuronal lineage and that in transient transfection assays, MEF2A and MASH1 cooperatively activate gene expression. This cooperativity appears to be due to a specific physical interaction between MEF2A and MASH1. Taken together, these findings suggest that MASH1 via a cooperative interaction with MEF2A may regulate the expression of specific genes that are critical for neuronal differentiation.

Urea inducibility of egr-1 in murine inner medullary collecting duct cells is mediated by the serum response element and adjacent Ets motifs

The renal medullary solute urea increases transcription and protein expression of the zinc finger-containing transcription factor Egr-1 in a renal epithelial cell-specific fashion. Transient transfection of mIMCD3 cells with a luciferase reporter gene driven by 1.2 kilobases of the murine egr-1 5'-flanking sequence showed 4-fold increase in reporter gene activity with 200 mM urea treatment. The effect of impermeant solutes such as NaCl was much less pronounced, whereas the permeant solute glycerol had no effect. In addition, this same sequence, minus the egr-1 minimal promoter, conferred urea responsiveness to a heterologous (thymidine kinase) promoter. Whereas deletion of two putative AP-1 sites from the sequence had no effect upon urea inducibility, elimination of the five putative serum response elements (SREs) abolished the urea effect. Progressive deletion of the SREs caused a corresponding diminution in urea effect. Two key tandem SREs (SRE-3 and SRE-4), in conjunction with their two adjacent clusters of Ets motifs, were sufficient to confer urea responsiveness to a reporter gene. This response was markedly attenuated in the absence of either cluster of Ets motifs and was abolished if both clusters were deleted. By electrophoretic mobility shift assay, formation of the ternary complex was constitutive and was demonstrable in vitro despite the presence of 200 mosm urea or NaCl. Therefore urea-inducible egr-1 transcription in renal medullary cells is mediated through the SRE and adjacent Ets motifs; ternary complex formation is not inhibited even in the presence of physiological hyperosmolality.

Urea signaling in cultured murine inner medullary collecting duct (mIMCD3) cells involves protein kinase C, inositol 1,4,5-trisphosphate (IP3), and a putative receptor tyrosine kinase

Urea, in concentrations unique to the renal medulla, increases transcription and protein expression of several immediate-early genes (IEGs) including the zinc finger-containing transcription factor, Egr-1. In the present study, the proximal 1.2 kb of the murine Egr-1 5' -flanking sequence conferred urea-responsiveness to a heterologous luciferase reporter gene when transiently transfected into renal medullary mIMCD3 cells,and this effect was comparable with that of the extremely potent immediate-early gene inducer, O-tetradecanoylphorbol 13-acetate (TPA). Urea inducibility of Egr-1 expression was protein kinase C (PKC)-dependent because staurosporine and calphostin C abrogated the urea effect, and down-regulation of PHC through chronic TPa treatment inhibited both urea-inducible Egr-1 protein expression and gene transcription. In addition, hyperosmotic urea increased inositol 1,4,5-trisphosphate (IP3) release from mIMCD3 cells and induced tyrosine phosphorylation of the receptor tyrosine kinase-specific phospholipase C (PLC) isoform, PLC-gamma. Importantly, urea-inducible Egr-1 expression was strongly genistein-sensitive, to a much greater extent than the comparable TPA-inducible Egr-1 expression. These data suggest that urea-inducible Egr-1 expression is a consequence of sequential PLC-gamma activation, IP3 release, and PKC activation. Urea-inducible PLC-gamma activation, in conjunction with the genistein-sensitivity of urea-inducible Egr-1 expression suggest the possibility of a cell surface or cytoplasmic urea-sensing receptor tyrosine kinase.

Ciliary neurotrophic factor-induced gene expression in human neuroblastoma cell lines

We have analyzed the response of the human neuroblastoma cell lines SK-N-SH (clone SY5Y) and SK-N-BE to the ciliary neurotrophic factor CNTF. In both cell lines CNTF induced the expression of the mRNA for two transcription factors, c-fos and NGF1A. The induction was rapid and transient reaching a maximum between 30 and 60 min after exposure to CNTF and subsequently declining. The level of induction of both c-fos and NGF1A mRNAs was much higher in SK-N-BE neuroblastoma cells compared to the SY5Y. Both cells express comparable levels of the transcript for the CNTF receptor-alpha. This mRNA was down regulated after 5 days of CNTF stimulation in both cell lines. CNTF also induced increased levels of the transcript for the growth cone associated protein GAP43 in SK-N-BE, but not in SY5Y cells. Induction followed a slower kinetic compared to that observed for c-fos and NGF1A. In fact, the GAP43 mRNA levels increased during 2 days of exposure to CNTF. Morphological analysis of CNTF treated cells showed that SK-N-BE undergo significant differentiation in response to CNTF (increased number of cells with neurites and increased neurite length) while SY5Y did not show appreciable morphological differentiation. These data shows that CNTF may elicit different response in neuroblastoma cell lines.

Characterization of the rat light neurofilament (NF-L) gene promoter and identification of NGF and cAMP responsive regions

We have isolated a genomic DNA clone covering the coding and 14 kb upstream region of the rat light neurofilament (NF-L) gene and sequenced 2.3 kb of its promoter. DNase I hypersensitive sites have been mapped in PC12 cells. For functional analysis of the NF-L promoter, constructs carrying 38, 97, 407, 564, 650, 1,099, 1,660, 2,003 base pairs (bp) upstream region in front of the chloramphenicol acetyltransferase (CAT) reporter gene were tested for their capability to direct CAT expression after transient transfection into various cell lines. Similar CAT activities were recorded both in rat pheochromocytoma (PC12) and mouse neuroblastoma N115 cells and also in several nonneural cell lines (HeLa, C127, NIH 3T3). Regions responsible for the basic promoter activity were located between -407 and +75 bp from the transcription initiation site. The NGF-responsive element was located between -38 and +75 bp, and sequence -97 to -38 was found to contain a functional cAMP-responsive element. In PC12 cells in which nerve growth factor (NGF) induces neurite outgrowth and NF-L transcription, NF-L promoter-driven CAT expression was stimulated up to 12-fold within three days of NGF treatment, whereas epidermal growth factor (EGF) had no effect. Rat NF-L promoter contained Sp1, AP-2 and CGCCCCCGC elements. In PC12 cells, NGF transiently induced the binding of transcription factors to the deoxyoligonucleotide probes containing the binding sites of these elements. The role of these factors in NF-L gene transcriptional induction by NGF in PC12 cells is discussed.

Zinc and the mitosis-inhibitory epidermal pentapeptide (EPP) form a stimulatory chelated dimer

A single intraperitoneal (i.p.) injection of picomolar doses of the epidermal pentapeptide (EPP), pGlu-Glu-Asp-Ser-GlyOH, is followed by a reversible inhibition of mouse epidermal cell proliferation. An equimolar mixture of zinc and EPP injected i.p. into hairless mice reversed the inhibitory activity, resulting in an immediate stimulation of epidermal G2-M cell flux. The stimulatory effect was strongest at the lowest dose (5 pmol). This effect was probably caused by a dizinc-dipentapeptide dimer, as shown by gel filtration and atomic emission spectrometry. When zinc was added in excess (EPP:Zn 1:9) no such dimer could be identified, and the mixture had no stimulatory effect. The results are discussed in terms of epidermal cell kinetics, and in relation to the use of zinc in dermatology.

Primary sequence and functional analysis of the bovine galanin gene promoter in human neuroblastoma cells

Galanin (GAL) is a biologically active neuropeptide that has been suggested to play a role in stress-induced inhibition of insulin secretion, in dementia of the Alzheimer's type, and in the regulation of growth hormone secretion. We report here the isolation of a bovine genomic clone containing more than 5-kb 5'-flanking sequences. Partial sequence analysis of the genomic clone revealed an atypical TATA-box in the promoter (ATAAATA) and several consensus sequences that typically bind transcription factors, including those that bind NF kappa B, Sp1, and AP-2. Primer extension and RNase protection analyses revealed that transcription is initiated at two sites, 28 and 31 bp, respectively, downstream from the TATA-box. To locate functionally active regulatory elements on the GAL gene, we first identified a neural crest-derived human neuroblastoma cell line, SK-N-SH subclone SH-SY5Y, that expressed easily detectable levels of endogenous GAL mRNA. We then constructed plasmids containing various lengths of bovine GAL 5'-flanking sequences and the first exon fused to a reporter plasmid encoding luciferase. Transfection of these plasmids into the SH-SY5Y cells and analysis by transient expression indicated that 131 bp of 5' gene sequence was sufficient to obtain maximal basal expression. Further, expression was suppressed 16-fold when 5 kb were included, suggesting the presence of a distal repressor element(s). In another set of experiments, we found that GAL mRNA levels could be induced more than 10-fold by 20-hr treatment with phorbol 12-myristate 13-acetate (PMA). In cells transfected with the same plasmids, luciferase activity was also induced by PMA, but the degree of induction did not significantly differ among the deletion constructions (varying from six- to eight-fold), suggesting that elements conferring PMA induction and/or RNA stabilization may be located within 131 bp of the transcriptional start site, in the first exon, or on gene sequences not studied here.

Diurnal expression of NGF1-A mRNA in retinal degeneration slow (rds) mutant mouse retina

The retinal degeneration slow (rds) mutant mouse is a model for studying the retinal dystrophy for human disease, retinitis pigmentosa (RP). To continue our effort towards a possible mechanism of photoreceptor cell death in retinal dystrophies, we have studied the impact of the rds mutation on diurnal expression of a 'zinc-finger' DNA-binding protein, NGF1-A mRNA in the isolated retinas of rds mutant mice compared to those of BALB/c mice. Background levels of NGF1-A mRNA were maintained during the subjective light period. Higher levels of NGF1-A mRNA were observed immediately after the light offset and peaked two hours into the light offset for both the BALB/c and the rds mutant retinas and remained higher for several hours in the dark. If the animals were left continuously in light during the subjective dark period, NGF1-A mRNA levels were not induced and remained lower. On the other hand NGF1-A mRNA levels were transiently induced during the transition of the dark-to-light phase. The data suggest that NGF1-A mRNA is differentially regulated by light and dark stimuli in the retina and an absence of rod outer segments in the rds mutant retina does not alter the normal diurnal cycle of NGF1-A mRNA expression.

A branched signaling pathway for nerve growth factor is revealed by Src-, Ras-, and Raf-mediated gene inductions

A myriad of gene induction events underlie nerve growth factor (NGF)-induced differentiation of PC12 cells. To dissect the signal transduction pathways which lead to NGF actions, we have assessed the relative roles of NGF receptor, Src, Ras, and Raf activities in mediating specific gene inductions. We have used the PC12 cell line as well as sublines which inducibly express activated forms of either Src, Ras, or Raf or a dominant inhibitory form of Ras (p21N17 Ras) to study the expression of multiple NGF-inducible mRNAs. The NGF induction of NGFI-A, transin, and VGF mRNAs was mimicked by activated forms of Src, Ras, or Raf and was blocked by p21N17 Ras. The NGF induction of SCG10 mRNA was mimicked only by activated Src and Ras and was blocked by p21N17 Ras, while the induction of Thy-1 mRNA was mimicked only by activated Src and was not blocked by p21N17 Ras. The NGF induction of mRNAs for two sodium channel types was neither mimicked by any activated oncoprotein nor blocked by p21N17 Ras. From these and previous results, we suggest a model in which a linear order of NGF receptor, Src, Ras, and Raf activities is used by NGF to elicit gene inductions. These signaling components define branchpoints in the pathway to specific gene induction events, providing a mechanism for generating a host of diverse NGF actions.

Characterization of the mouse gene that encodes the delta/YY1/NF-E1/UCRBP transcription factor

The mouse gene that encodes the delta transcription factor has been cloned and characterized. This gene spans 23 kb and is composed of five exons and four introns. The first exon consists of a long (431 bp), (C+G)-rich, untranslated segment and a 679-bp coding segment, which specifies the unusual tracts of consecutive acidic residues and histidines and the long alanine-glycine stretches. The sequence that encodes the four zinc-finger motifs of this protein is interrupted by two introns. Nuclease protection experiments revealed a major transcriptional start point and several additional start points distributed over a 28-bp segment. Transfection experiments with 5' and 3' deletion mutants localized the promoter to a (C+G)-rich region that is < 700 bp upstream and no more than 32 bp downstream of the major start point. An especially critical promoter element lies between -58 and -18 and contains a high-affinity Sp1 binding site, as demonstrated by electrophoretic mobility-shift experiments with nuclear extract and recombinant Sp1 proteins. Several striking similarities between the delta gene and genes encoding other transcription factors and regulatory proteins are noted and discussed with respect to their possible biological significance.

A branched signaling pathway for nerve growth factor is revealed by Src-, Ras-, and Raf-mediated gene inductions

A myriad of gene induction events underlie nerve growth factor (NGF)-induced differentiation of PC12 cells. To dissect the signal transduction pathways which lead to NGF actions, we have assessed the relative roles of NGF receptor, Src, Ras, and Raf activities in mediating specific gene inductions. We have used the PC12 cell line as well as sublines which inducibly express activated forms of either Src, Ras, or Raf or a dominant inhibitory form of Ras (p21N17 Ras) to study the expression of multiple NGF-inducible mRNAs. The NGF induction of NGFI-A, transin, and VGF mRNAs was mimicked by activated forms of Src, Ras, or Raf and was blocked by p21N17 Ras. The NGF induction of SCG10 mRNA was mimicked only by activated Src and Ras and was blocked by p21N17 Ras, while the induction of Thy-1 mRNA was mimicked only by activated Src and was not blocked by p21N17 Ras. The NGF induction of mRNAs for two sodium channel types was neither mimicked by any activated oncoprotein nor blocked by p21N17 Ras. From these and previous results, we suggest a model in which a linear order of NGF receptor, Src, Ras, and Raf activities is used by NGF to elicit gene inductions. These signaling components define branchpoints in the pathway to specific gene induction events, providing a mechanism for generating a host of diverse NGF actions.

Differential expression of immediate early genes in rubrospinal neurons following axotomy in rat

Many immediate early genes are rapidly and transiently expressed in the central nervous system following a variety of stimuli. Damage to the axons of peripheral and certain central neurons has been shown to result in a long-term increase in expression of c-Jun in the parent cell bodies. In the peripheral nervous system this increased expression of c-Jun protein and mRNA develops over 24 h following sciatic nerve section and is maintained if the damaged nerve is ligated, but returns to basal levels if the peripheral nerve is allowed to regenerate. Here, we report on the response of rubrospinal neurons to spinal cord hemisection at levels C3 and T10. c-Jun expression was first seen at 12 h post-lesion in a limited number of rubral neurons. The number of positively stained neurons increased up to 10 days post-lesion and then declined over the following weeks. By 7 weeks post-lesion there was still evidence of c-Jun immunoreactivity in both large and other clearly atrophic rubrospinal neurons. c-Fos immunoreactivity was seen only at 12-48 h in a small number of rubrospinal neurons. Evidence from retrograde tracing experiments following fluorogold application to the hemisected cord suggested that all c-Jun-positive neurons projected into the spinal cord. No c-Jun response was seen following a lesion at T10.(ABSTRACT TRUNCATED AT 250 WORDS)

Molecular analysis of the nerve growth factor inducible ornithine decarboxylase gene in PC12 cells

In an effort to understand molecular mechanisms by which nerve growth factor (NGF) regulates gene expression, we have isolated a full-length rat cDNA clone encoding ornithine decarboxylase (ODC) and utilized this probe to identify and examine the transcriptionally active, NGF inducible ODC gene in rat PC12 cells. This same gene is also responsive to epidermal growth factor, basic fibroblasts growth factor, and dibutyryl cAMP. Primer extension analysis demonstrates that both basal and NGF induced transcription of the ODC gene utilize the same major transcriptional start site, demonstrating that NGF acts to increase transcriptional activity at the basal start site as opposed to unmasking an alternative, stronger start site. Functional promoter analysis reveals the presence of a constitutive core promoter residing between positions -201 and +390, relative to the start site of transcription. Additional analyses reveal that sequences in the region -7800 to +2257 are insufficient to mediate NGF induced transcriptional activation, demonstrating that at least some of the regulatory sequences necessary for NGF mediated transcriptional induction of the ODC gene must reside at relatively enormous distances from the transcriptional start site. Such a long distance transcriptional regulatory mechanism is unique when compared with other NGF responsive genes that have been similarly analyzed.

Analysis of the DNA binding proteins interacting with specific upstream sequences of the S. purpuratus CyI actin gene

The CyI actin gene of the sea urchin, Strongylocentrotus purpuratus, is regulated temporally and spatially within the cells of the early embryo. In an effort to understand the molecular basis for the CyI actin pattern of expression, we have begun analyzing the protein-DNA interactions within regions previously shown to be of potential functional importance (Katula et al., 1987). Using DNase I footprinting, 10 protected regions were identified containing both conserved and apparently novel protein binding sites. Gel mobility shift competition assays confirmed the presence of multiple protein factors which specifically recognize CyI actin upstream sequences. Determination of a relative affinity constant value (Kr) indicated that most of the protein factors preferred their respective oligonucleotide sequences vs. a synthetic competitor DNA in a range of 10(4). The highest affinity binding was observed for proteins binding to the oligonucleotide probe containing the octamer element (Kr approximately 10(6)). Heterologous gel shift competition assays were carried out to investigate the interrelatedness of the protein factors. These studies, combined with other data, indicate there are both unique and redundant protein-DNA interactions in the region being examined. Possible alterations in CyI actin DNA binding proteins were investigated during the period of CyI transcriptional activation by gel mobility shift analysis. An increase in binding activity was observed for most of the factors, indicating that early transcriptional activity of CyI actin may involve a general increase in the amount or activity of specific transcription factors. In addition, qualitative changes, as seen by alterations in the shift patterns, were observed for some of the oligonucleotide probes.

Maximal serum stimulation of the c-fos serum response element requires both the serum response factor and a novel binding factor, SRE-binding protein

We have previously reported on the presence of a CArG motif at -100 in the Rous sarcoma virus long terminal repeat which binds an avian nuclear protein termed enhancer factor III (EFIII) (A. Boulden and L. Sealy, Virology 174:204-216, 1990). By all analyses, EFIII protein appears to be the avian homolog of the serum response factor (SRF). In this study, we identify a second CArG motif (EFIIIB) in the Rous sarcoma virus long terminal repeat enhancer at -162 and show only slightly lower binding affinity of the EFIII/SRF protein for this element in comparison with c-fos serum response element (SRE) and EFIII DNAs. Although all three elements bind the SRF with similar affinities, serum induction mediated by the c-fos SRE greatly exceeds that effected by the EFIII or EFIIIB sequence. We postulated that this difference in serum inducibility might result from binding of factors other than the SRF which occurs on the c-fos SRE but not on EFIII and EFIIIB sequences. Upon closer inspection of nuclear proteins which bind the c-fos SRE in chicken embryo fibroblast and NIH 3T3 nuclear extracts, we discovered another binding factor, SRE-binding protein (SRE BP), which fails to recognize EFIII DNA with high affinity. Competition analyses, methylation interference, and site-directed mutagenesis have determined that the SRE BP binding element overlaps and lies immediately 3' to the CArG box of the c-fos SRE. Mutation of the c-fos SRE so that it no longer binds SRE BP reduces serum inducibility to 33% of the wild-type level. Conversely, mutation of the EFIII sequence so that it binds SRE BP with high affinity results in a 400% increase in serum induction, with maximal stimulation equaling that of the c-fos SRE. We conclude that binding of both SRE BP and SRF is required for maximal serum induction. The SRE BP binding site coincides with the recently reported binding site for rNF-IL6 on the c-fos SRE. Nonetheless, we show that SRE BP is distinct from rNF-IL6, and identification of this novel factor is being pursued.

Maximal serum stimulation of the c-fos serum response element requires both the serum response factor and a novel binding factor, SRE-binding protein

We have previously reported on the presence of a CArG motif at -100 in the Rous sarcoma virus long terminal repeat which binds an avian nuclear protein termed enhancer factor III (EFIII) (A. Boulden and L. Sealy, Virology 174:204-216, 1990). By all analyses, EFIII protein appears to be the avian homolog of the serum response factor (SRF). In this study, we identify a second CArG motif (EFIIIB) in the Rous sarcoma virus long terminal repeat enhancer at -162 and show only slightly lower binding affinity of the EFIII/SRF protein for this element in comparison with c-fos serum response element (SRE) and EFIII DNAs. Although all three elements bind the SRF with similar affinities, serum induction mediated by the c-fos SRE greatly exceeds that effected by the EFIII or EFIIIB sequence. We postulated that this difference in serum inducibility might result from binding of factors other than the SRF which occurs on the c-fos SRE but not on EFIII and EFIIIB sequences. Upon closer inspection of nuclear proteins which bind the c-fos SRE in chicken embryo fibroblast and NIH 3T3 nuclear extracts, we discovered another binding factor, SRE-binding protein (SRE BP), which fails to recognize EFIII DNA with high affinity. Competition analyses, methylation interference, and site-directed mutagenesis have determined that the SRE BP binding element overlaps and lies immediately 3' to the CArG box of the c-fos SRE. Mutation of the c-fos SRE so that it no longer binds SRE BP reduces serum inducibility to 33% of the wild-type level. Conversely, mutation of the EFIII sequence so that it binds SRE BP with high affinity results in a 400% increase in serum induction, with maximal stimulation equaling that of the c-fos SRE. We conclude that binding of both SRE BP and SRF is required for maximal serum induction. The SRE BP binding site coincides with the recently reported binding site for rNF-IL6 on the c-fos SRE. Nonetheless, we show that SRE BP is distinct from rNF-IL6, and identification of this novel factor is being pursued.

Neural-specific expression, genomic structure, and chromosomal localization of the gene encoding the zinc-finger transcription factor NGFI-C

The nerve growth factor-induced clone C (NGFI-C) gene encodes a zinc-finger transcription factor that is rapidly induced by nerve growth factor in rat pheochromocytoma PC12 cells and by seizure in brain. NGFI-C is closely related to the previously described early response genes, nerve growth factor-induced clone A (NGFI-A or EGR1), EGR2, and EGR3. These four early response (immediate early) proteins all contain very similar zinc-finger DNA binding domains; in addition, analysis of the non-zinc-finger region revealed that they share an additional five highly homologous subdomains, four of which are within the amino terminus. The 5' flanking region of NGFI-C contains several cAMP response elements but does not contain any serum-response elements or CArG boxes [CC(A/T)6GG], cis-acting elements commonly involved in early response gene regulation. NGFI-C mRNA was detected in neural tissues of postnatal animals, but no expression was found in rat embryos. In situ hybridization demonstrated that NGFI-C is rapidly induced in the dentate gyrus of the hippocampus after seizure, but in contrast to NGFI-A, increases in NGFI-C mRNA were not detected in the overlying cortex. By using fluorescence in situ hybridization, NGFI-C was localized to human chromosome 2p13. This region contains a constitutive fragile site that is associated with chromosomal breakpoints and translocations characteristic of some chronic lymphocytic leukemias.

Analysis of the creA gene, a regulator of carbon catabolite repression in Aspergillus nidulans

The complete nucleotide sequence derived from a genomic clone and two cDNA clones of the creA gene of Aspergillus nidulans is presented. The gene contains no introns. The derived polypeptide of 415 amino acids contains two zinc fingers of the C2H2 class, frequent S(T)PXX motifs, and an alanine-rich region indicative of a DNA-binding repressor protein. The amino acid sequence of the zinc finger region has 84% similarity to the zinc finger region of Mig1, a protein involved in carbon catabolite repression in yeast cells, and it is related both to the mammalian Egr1 and Egr2 proteins and to the Wilms' tumor protein. A deletion removing the creA gene was obtained, by using in vitro techniques, in both a heterokaryon and a diploid strain but was unobtainable in a pure haploid condition. Evidence is presented suggesting that the phenotype of such a deletion, when not complemented by another creA allele, is leaky lethality allowing limited germination of the spore but not colony formation. This phenotype is far more extreme than that of any of the in vivo-generated mutations, and thus either the gene product may have an activator activity as well as a repressor function or some residual repressor function may be required for full viability.

Analysis of the creA gene, a regulator of carbon catabolite repression in Aspergillus nidulans

The complete nucleotide sequence derived from a genomic clone and two cDNA clones of the creA gene of Aspergillus nidulans is presented. The gene contains no introns. The derived polypeptide of 415 amino acids contains two zinc fingers of the C2H2 class, frequent S(T)PXX motifs, and an alanine-rich region indicative of a DNA-binding repressor protein. The amino acid sequence of the zinc finger region has 84% similarity to the zinc finger region of Mig1, a protein involved in carbon catabolite repression in yeast cells, and it is related both to the mammalian Egr1 and Egr2 proteins and to the Wilms' tumor protein. A deletion removing the creA gene was obtained, by using in vitro techniques, in both a heterokaryon and a diploid strain but was unobtainable in a pure haploid condition. Evidence is presented suggesting that the phenotype of such a deletion, when not complemented by another creA allele, is leaky lethality allowing limited germination of the spore but not colony formation. This phenotype is far more extreme than that of any of the in vivo-generated mutations, and thus either the gene product may have an activator activity as well as a repressor function or some residual repressor function may be required for full viability.

The ras-related gene rhoB is an immediate-early gene inducible by v-Fps, epidermal growth factor, and platelet-derived growth factor in rat fibroblasts

A set of genes is rapidly inducible when quiescent fibroblasts are stimulated by growth factors or by the activation of temperature-sensitive retroviral protein-tyrosine kinases. Most of these so-called immediate-early genes were cloned by differential cDNA hybridization. DNA sequence analysis identified many of them as putative members of the growth factor or of the transcription factor gene family, suggesting a role in signal transmission during the G0-to-G1 transition. In this study, we identified one of the genes that are rapidly inducible by the retroviral protein-tyrosine kinases v-Src and v-Fps of Rous sarcoma virus and Fujinami sarcoma virus, respectively, as the rhoB gene, a member of the ras gene superfamily whose products are GTP-binding proteins, rhoB is transiently activated at the transcriptional level by v-Fps and by epidermal growth factor. Its labile RNA is inducible in the presence of cycloheximide but not of actinomycin D. rhoB is strongly induced by epidermal growth factor and by platelet-derived growth factor both in subconfluent, serum-starved and in density-arrested Rat-2 fibroblasts. Fetal calf serum is a poor inducer, particularly in density-arrested cells, and phorbol esters do not increase rhoB expression at all. These data suggest that rhoB is inducible by protein-tyrosine kinases through a pathway not involving the activation of protein kinase C. Neither the closely related rhoC and rhoA genes nor the distantly related c-H-ras gene is rapidly inducible by mitogens. Thus, rhoB is the first known member of the small GTP-binding proteins among the immediate-early genes.

The ras-related gene rhoB is an immediate-early gene inducible by v-Fps, epidermal growth factor, and platelet-derived growth factor in rat fibroblasts

A set of genes is rapidly inducible when quiescent fibroblasts are stimulated by growth factors or by the activation of temperature-sensitive retroviral protein-tyrosine kinases. Most of these so-called immediate-early genes were cloned by differential cDNA hybridization. DNA sequence analysis identified many of them as putative members of the growth factor or of the transcription factor gene family, suggesting a role in signal transmission during the G0-to-G1 transition. In this study, we identified one of the genes that are rapidly inducible by the retroviral protein-tyrosine kinases v-Src and v-Fps of Rous sarcoma virus and Fujinami sarcoma virus, respectively, as the rhoB gene, a member of the ras gene superfamily whose products are GTP-binding proteins, rhoB is transiently activated at the transcriptional level by v-Fps and by epidermal growth factor. Its labile RNA is inducible in the presence of cycloheximide but not of actinomycin D. rhoB is strongly induced by epidermal growth factor and by platelet-derived growth factor both in subconfluent, serum-starved and in density-arrested Rat-2 fibroblasts. Fetal calf serum is a poor inducer, particularly in density-arrested cells, and phorbol esters do not increase rhoB expression at all. These data suggest that rhoB is inducible by protein-tyrosine kinases through a pathway not involving the activation of protein kinase C. Neither the closely related rhoC and rhoA genes nor the distantly related c-H-ras gene is rapidly inducible by mitogens. Thus, rhoB is the first known member of the small GTP-binding proteins among the immediate-early genes.

Promoter function and structure of the growth factor-inducible immediate early gene cyr61

cyr61 is an immediate early gene that is transcriptionally activated in 3T3 fibroblasts by serum, platelet-derived growth factor, fibroblast growth factor, and the tumor promoter TPA with kinetics similar to the induction of c-fos. cyr61 encodes a secreted protein that is associated with the cell surface and the extracellular matrix, and may play a role in cell-cell communication. We report here the complete nucleotide sequence of the mouse cyr61 gene, which contains four short introns. The transcription start site was mapped by S1 nuclease and primer extension analyses. A 2 kb 5' flanking DNA fragment functions as a serum-inducible promoter. This DNA fragment contains a poly(CA) sequence that can adopt the Z DNA form. In addition, it contains a sequence that resembles the serum response element (SRE) originally identified in the c-fos promoter. We show that deletion of the cry61 SRE-like sequence abrogates serum inducibility. Furthermore, this SRE-like sequence is sufficient to confer serum and growth factor inducibility when linked to a basal promoter, and binds the 67 kD serum response factor in vitro. We conclude that the cyr61 SRE functions as a serum response element and may account for the coordinate activation of cyr61 and c-fos.

The role of immediate early genes in the stabilization of long-term potentiation

Immediate early genes (IEGs) are a class of genes that show rapid and transient but protein synthesis-independent increases in expression to extracellular signals such as growth factors and neurotransmitters. Many IEGs code for transcription factors that have been suggested to govern the growth and differentiation of many cell types by regulating the expression of other genes. IEGs are expressed in adult neurons both constitutively and in response to afferent activity, and it has been suggested that during learning, IEGs may play a role in the signal cascade, resulting in the expression of genes critical for the consolidation of long-term memory. Long-term potentiation (LTP) is a persistent, activity-dependent form of synaptic plasticity that stands as a good candidate for the mechanism of associative memory. A number of IEGs coding for transcription factors have been shown to transiently increase transcription in the dentate gyrus of rats following LTP-inducing afferent stimulation. These include zif/268 (also termed NGFI-A, Krox-24, TIS-8, and egr-l), c-fos-related genes, c-jun, junB, and junD. Of these, zif/268 appears to be the most specifically related to LTP since it is evoked under virtually all LTP-inducing situations and shows a remarkably high correlation with the duration of LTP. There are a number of outstanding questions regarding the role of zif/268 and other IEGs in LTP, including which second messenger systems are important for activating them, which "late effector" genes are regulated by them, and the exact role these genes play, if any, in the stabilization and maintenance of LTP.

Retinoic acid increases zif268 early gene expression in rat preosteoblastic cells

In this study we demonstrate that retinoic acid (RA) increases the expression of transcription factor zif268 mRNA in primary cultures of fetal rat calvarial cells and in simian virus 40-immortalized clonal rat calvarial preosteoblastic cells (RCT-1), which differentiate in response to RA, but not in the more differentiated RCT-3 and ROS 17/2.8 cells. The increased expression of zif268 mRNA is rapid (maximal within 1 h), transient (returns to basal levels by 3 h), detectable at RA doses of 10(-12)M, and independent of protein synthesis. The relative stimulation of zif268 mRNA by RA was much larger than that of other early genes, including c-fos, c-jun, and junB. The rate of transcription of RA-stimulated RCT-1 cells, estimated by nuclear run-on assays, was elevated, suggesting that RA regulation of zif268 gene transcription was at least in part transcriptional. Moreover, RA stimulated the transcriptional activity of a Zif268CAT (chloramphenicol acetyltransferase) plasmid containing 632 bp of zif268 5' regulatory sequences in RCT-1 cells but not in the more differentiated RCT-3 cells. These in vitro data support the in vivo observations which localize zif268 and RA receptor-gamma transcripts to bone and cartilage during development, suggesting that both RA and zif268 may play a role in osteoblast differentiation.

Structure of the gene encoding VGF, a nervous system-specific mRNA that is rapidly and selectively induced by nerve growth factor in PC12 cells

Nerve growth factor (NGF) plays a critical role in the development and survival of neurons in the peripheral nervous system. Following treatment with NGF but not epidermal growth factor, rat pheochromocytoma (PC12) cells undergo neural differentiation. We have cloned a nervous system-specific mRNA, NGF33.1, that is rapidly and relatively selectively induced by treatment of PC12 cells with NGF and basic fibroblast growth factor in comparison with epidermal growth factor. Analysis of the nucleic acid and predicted amino acid sequences of the NGF33.1 cDNA clone suggested that this clone corresponded to the NGF-inducible mRNA called VGF (A. Levi, J. D. Eldridge, and B. M. Paterson, Science 229:393-395, 1985; R. Possenti, J. D. Eldridge, B. M. Paterson, A. Grasso, and A. Levi, EMBO J. 8:2217-2223, 1989). We have used the NGF33.1 cDNA clone to isolate and characterize the VGF gene, and in this paper we report the complete sequence of the VGF gene, including 853 bases of 5' flank revealed TATAA and CCAAT elements, several GC boxes, and a consensus cyclic AMP response element-binding protein binding site. The VGF promoter contains sequences homologous to other NGF-inducible, neuronal promoters. We further show that VGF mRNA is induced in PC12 cells to a greater extent by depolarization and by phorbol-12-myristate-13-acetate treatment than by 8-bromo-cyclic AMP treatment. By Northern (RNA) and RNase protection analysis, VGF mRNA is detectable in embryonic and postnatal central and peripheral nervous tissues but not in a number of nonneural tissues. In the cascade of events which ultimately leads to the neural differentiation of NGF-treated PC12 cells, the VGF gene encodes the most rapidly and selectively regulated, nervous-system specific mRNA yet identified.

Retinoic acid increases zif268 early gene expression in rat preosteoblastic cells

In this study we demonstrate that retinoic acid (RA) increases the expression of transcription factor zif268 mRNA in primary cultures of fetal rat calvarial cells and in simian virus 40-immortalized clonal rat calvarial preosteoblastic cells (RCT-1), which differentiate in response to RA, but not in the more differentiated RCT-3 and ROS 17/2.8 cells. The increased expression of zif268 mRNA is rapid (maximal within 1 h), transient (returns to basal levels by 3 h), detectable at RA doses of 10(-12)M, and independent of protein synthesis. The relative stimulation of zif268 mRNA by RA was much larger than that of other early genes, including c-fos, c-jun, and junB. The rate of transcription of RA-stimulated RCT-1 cells, estimated by nuclear run-on assays, was elevated, suggesting that RA regulation of zif268 gene transcription was at least in part transcriptional. Moreover, RA stimulated the transcriptional activity of a Zif268CAT (chloramphenicol acetyltransferase) plasmid containing 632 bp of zif268 5' regulatory sequences in RCT-1 cells but not in the more differentiated RCT-3 cells. These in vitro data support the in vivo observations which localize zif268 and RA receptor-gamma transcripts to bone and cartilage during development, suggesting that both RA and zif268 may play a role in osteoblast differentiation.