Nerve growth factor increases the transcriptional activity of the rat neuronal nicotinic acetylcholine receptor beta 4 subunit promoter in transfected PC12 cells

DDAH1 promotes neurogenesis and neural repair in cerebral ischemia

Choline acetyltransferase (ChAT)-positive neurons in neural stem cell (NSC) niches can evoke adult neurogenesis (AN) and restore impaired brain function after injury, such as acute ischemic stroke (AIS). However, the relevant mechanism by which ChAT+ neurons develop in NSC niches is poorly understood. Our RNA-seq analysis revealed that dimethylarginine dimethylaminohydrolase 1 (DDAH1), a hydrolase for asymmetric NG,NG-dimethylarginine (ADMA), regulated genes responsible for the synthesis and transportation of acetylcholine (ACh) (Chat, Slc5a7 and Slc18a3) after stroke insult. The dual-luciferase reporter assay further suggested that DDAH1 controlled the activity of ChAT, possibly through hypoxia-inducible factor 1α (HIF-1α). KC7F2, an inhibitor of HIF-1α, abolished DDAH1-induced ChAT expression and suppressed neurogenesis. As expected, DDAH1 was clinically elevated in the blood of AIS patients and was positively correlated with AIS severity. By comparing the results among Ddah1 general knockout (KO) mice, transgenic (TG) mice and wild-type (WT) mice, we discovered that DDAH1 upregulated the proliferation and neural differentiation of NSCs in the subgranular zone (SGZ) under ischemic insult. As a result, DDAH1 may promote cognitive and motor function recovery against stroke impairment, while these neuroprotective effects are dramatically suppressed by NSC conditional knockout of Ddah1 in mice.

Nicotinic Acetylcholine Receptors of PC12 Cells

Nicotinic acetylcholine receptors (nAChRs) have gained much attention in the scientific community since they play a significant role in multiple physiological and pathophysiological processes. Multiple approaches to study the receptors exist, with characterization of the receptors' functionality at a single cellular level using cell culturing being one of them. Derived from an adrenal medulla tumor, PC12 cells express nicotinic receptor subunits and form functional nicotinic receptors. Thus, the cells offer a convenient environment to address questions related to the functionality of the receptors. The review summarizes the findings on nicotinic receptors' expression and functions which were conducted using PC12 cells. Specific focus is given to α3-containing receptors as well as α7 receptor. Critical evaluation of findings is provided alongside insights into what can still be learned about nAChRs, using PC12 cells.

Bladder outlet obstruction causes up-regulation of nicotinic acetylcholine receptors in bladder-projecting pelvic ganglion neurons

Pelvic ganglion (PG) neurons relay sympathetic and parasympathetic signals to the lower urinary tract, comprising the urinary bladder and bladder outlet, and are thus essential for both storage and voiding reflexes. Autonomic transmission is mediated by activation of the nicotinic acetylcholine receptor (nAChR) in PG neurons. Previously, bladder outlet obstruction (BOO), secondary to benign prostatic hyperplasia, was found to increase soma sizes of bladder-projecting PG neurons. To date, however, it remains unknown whether these morphological changes are accompanied by functional plasticity in PG neurons. In the present study, we investigated whether BOO alters acetylcholine receptor (nAChR) transcript expression and current density in bladder PG neurons. Partial ligation of the rat urethra for six weeks induced detrusor overactivity (DO), as observed during cystometrical measurement. In rats exhibiting DO, membrane capacitance of parasympathetic bladder PG neurons was selectively increased. Real-time PCR analysis revealed that BOO enhanced the expression of the transcripts encoding the nAChR α3 and β4 subunits in PG neurons. Notably, BOO significantly increased ACh-evoked current density in parasympathetic bladder PG neurons, whereas no changes were observed in sympathetic bladder and parasympathetic penile PG neurons. In addition, other ligand-gated ionic currents were immune to BOO in bladder PG neurons. Taken together, these data suggest that BOO causes upregulation of nAChR in parasympathetic bladder PG neurons, which in turn may potentiate ganglionic transmission and contribute to the development of DO.

Alternative CHRNB4 3'-UTRs mediate the allelic effects of SNP rs1948 on gene expression

Common genetic factors strongly contribute to both nicotine, the main addictive component of tobacco, and alcohol use. Several lines of evidence suggest nicotinic acetylcholine receptors as common sites of action for nicotine and alcohol. Specifically, rs1948, a single-nucleotide polymorphism (SNP) located in the CHRNB4 3′-untranslated region (UTR), has been associated to early age of initiation for both alcohol and tobacco use. To determine the allelic effects of rs1948 on gene expression, two rs1948-containing sequences of different lengths corresponding to the CHRNB4 3′-UTR were cloned into pGL3-promoter luciferase reporter vectors. Data obtained showed that the allelic effects of SNP rs1948 on luciferase expression are mediated by the length and species of transcripts generated. In addition, it was found that miR-3157 increased the overall luciferase expression while miR-138, a microRNA known to play a role in neuroadaptation to drug abuse, decreased luciferase expression when compared to basal conditions. These findings demonstrate the importance of SNP rs1948 on the regulation of CHRNB4 expression and provide the first evidence of CHRNB4 down-regulation by miR-138.

Neuregulin 1 up-regulates the expression of nicotinic acetylcholine receptors through the ErbB2/ErbB3-PI3K-MAPK signaling cascade in adult autonomic ganglion neurons

We investigated effects of Neuregulin 1 (NRG1) on the expression of nicotinic acetylcholine receptor (nAChR) in major pelvic ganglion (MPG) from adult rat. MPG neurons were found to express transcripts for type I and III NRG1s as well as α and β-type epidermal growth factor (EGF)-like domains. Of the four ErbB receptor isoforms, ErbB1, ErbB2, and ErbB3 were expressed in MPG neurons. Treating MPG with NRG1β significantly increased the transcript and protein level of the nAChR α3 and β4 subunits. Consistent with these molecular data, nicotinic currents (I(ACh) ) were significantly up-regulated in NRG1β-treated sympathetic and parasympathetic MPG neurons. In contrast, the type III NRG1 and the α form of the NRG1 failed to alter the I(ACh) . Inhibition of the ErbB2 tyrosine kinase completely abolished the effects of NRG1β on the I(ACh) . Stimulation of the ErbB receptors by NRG1β activated the phosphatidylinositol-3-kinase (PI3K) and mitogen-activated protein kinase (MAPK). Immunoblot analysis revealed that PI3K-mediated activation of Akt preceded Erk1/2 activation in NRG1β-treated MPG neurons. Furthermore, specific PI3K inhibitors abrogated the phosphorylation of Erk1/2, while inhibition of MEK did not prevent the phosphorylation of Akt. Taken together, these findings suggest that NRG1 up-regulates nAChR expression via the ErbB2/ErbB3-PI3K-MAPK signaling cascade and may be involved in maintaining the ACh-mediated synaptic transmission in adult autonomic ganglia.

Temporally- and spatially-regulated transcriptional activity of the nicotinic acetylcholine receptor beta4 subunit gene promoter

Signaling through nicotinic acetylcholine (nACh) receptors underlies a diverse array of behaviors. In order for appropriate signaling to occur via nACh receptors, it is necessary for the genes encoding the receptor subunits to be expressed in a highly regulated temporal and spatial manner. Here we report a transgenic mouse approach to characterize the transcriptional regulation of the gene encoding the nACh receptor beta4 subunit. nACh receptors containing this subunit play critical roles in both the central and peripheral nervous systems. We demonstrate that a 2.3-kilobase pair fragment of the beta4 5'-flanking region is capable of directing reporter gene expression in transgenic animals. Importantly, the transcriptional activity of the promoter region is cell-type-specific and developmentally regulated and overlaps to a great extent with endogenous beta4 mRNA expression. These data indicate that the 2.3-kilobase pair fragment contains transcriptional regulatory elements critical for appropriate beta4 subunit gene expression.

The armadillo repeat-containing protein, ARMCX3, physically and functionally interacts with the developmental regulatory factor Sox10

Sox10 is a member of the group E Sox transcription factor family and plays key roles in neural crest development and subsequent cellular differentiation. Sox10 binds to regulatory sequences in target genes via its conserved high mobility group domain. In most cases, Sox10 exerts its transcriptional effects in concert with other DNA-binding factors, adaptor proteins, and nuclear import proteins. These interactions can lead to synergistic gene activation and can be cell type-specific. In earlier work, we demonstrated that Sox10 transactivates the nicotinic acetylcholine receptor alpha3 and beta4 subunit genes and does so only in neuronal-like cell lines, raising the possibility that Sox10 mediates its effects via interactions with co-regulatory factors. Here we describe the identification of the armadillo repeat-containing protein, ARMCX3, as a Sox10-interacting protein. Biochemical analyses indicate that ARMCX3 is an integral membrane protein of the mitochondrial outer membrane. Others have shown that Sox10 is a nucleocytoplasmic shuttling protein. We extend this observation and demonstrate that, in the cytoplasm, Sox10 is peripherally associated with the mitochondrial outer membrane. Both Sox10 and ARMCX3 are expressed in mouse brain and spinal cord as well as several cell lines. Overexpression of ARMCX3 increased the amount of mitochondrially associated Sox10. In addition, although ARMCX3 does not possess intrinsic transcriptional activity, it does enhance transactivation of the nicotinic acetylcholine receptor alpha3 and beta4 subunit gene promoters by Sox10. These results suggest that Sox10 is a membrane-associated factor whose transcriptional function is increased by direct interactions with ARMCX3 and raise the possibility of a signal transduction cascade between the nucleus and mitochondria through Sox10/ARMCX3 interactions.

Mammalian nicotinic acetylcholine receptors: from structure to function

The classical studies of nicotine by Langley at the turn of the 20th century introduced the concept of a "receptive substance," from which the idea of a "receptor" came to light. Subsequent studies aided by the Torpedo electric organ, a rich source of muscle-type nicotinic receptors (nAChRs), and the discovery of alpha-bungarotoxin, a snake toxin that binds pseudo-irreversibly to the muscle nAChR, resulted in the muscle nAChR being the best characterized ligand-gated ion channel hitherto. With the advancement of functional and genetic studies in the late 1980s, the existence of nAChRs in the mammalian brain was confirmed and the realization that the numerous nAChR subtypes contribute to the psychoactive properties of nicotine and other drugs of abuse and to the neuropathology of various diseases, including Alzheimer's, Parkinson's, and schizophrenia, has since emerged. This review provides a comprehensive overview of these findings and the more recent revelations of the impact that the rich diversity in function and expression of this receptor family has on neuronal and nonneuronal cells throughout the body. Despite these numerous developments, our understanding of the contributions of specific neuronal nAChR subtypes to the many facets of physiology throughout the body remains in its infancy.

Transcription factor assembly on the nicotinic receptor beta4 subunit gene promoter

Nicotinic acetylcholine receptors are involved in a plethora of fundamental biological processes ranging from muscle contraction to formation of memories. The receptors are pentameric proteins whose subunits are encoded by distinct genes. Subunit composition of a mature nicotinic receptor is governed in part by the transcriptional regulation of each subunit gene. Here, using chromatin immunoprecipitation assays, we report the interaction of the transcription factors Sp1, Sp3, c-Jun and Sox10 with the beta4 subunit gene promoter in neuronal-like cell lines and rodent brain tissue. Our results corroborate previous in-vitro data demonstrating that these transcription factors interact with the beta4 promoter. Taken together, these data suggest that Sp1, Sp3, c-Jun and Sox10 regulate expression of the beta4 subunit gene in the mammalian brain.

Axotomy and nerve growth factor regulate levels of neuronal nicotinic acetylcholine receptor alpha3 subunit protein in the rat superior cervical ganglion

Neuronal nicotinic acetylcholine receptors (nAChRs) play a significant role in sympathetic transmission in the superior cervical ganglia (SCG), with most of the signal carried by a nAChR containing an alpha3 subunit. Work has shown that transection of the postganglionic nerves (axotomy) of the SCG results in a decrease in mRNA transcripts for alpha3, alpha5, alpha7 and beta4 and in protein expression of alpha7 and beta4. To evaluate effects of axotomy on alpha3 protein in the SCG, quantitative immunoblotting was used to demonstrate a dramatic decrease (> 80%) in the levels of this subunit 4 days after axotomy. Similarly, immunocytochemistry showed a marked decline in the number and the intensity of stained neurons for the alpha3 subunit as well as tyrosine hydroxylase. Ganglia explanted into culture for 4 days also showed a substantial decrease in alpha3 subunit protein. This decrease was partially prevented by the addition of nerve growth factor (NGF) to the culture medium at the time of explantation. Additionally, this decrease was reversed by the addition of NGF to the culture medium following 4 days in culture in the absence of NGF. These findings suggest that the loss of alpha3 subunit contributes to the reported decrease in ganglionic synaptic transmission that follows axotomy, and that NGF plays an important role in regulating the expression of alpha3-containing nAChRs in the SCG.

The signal transduction pathway underlying ion channel gene regulation by SP1-C-Jun interactions

During neuronal differentiation, an exquisitely controlled program of signal transduction events takes place, leading to the temporally and spatially regulated expression of genes associated with the differentiated phenotype. A critical class of genes involved in this phenomenon is that made up of genes encoding neurotransmitter-gated ion channels that play a central role in signal generation and propagation within the nervous system. We used the well established PC12 cell line to investigate the molecular details underlying the expression of the neuronal nicotinic acetylcholine receptor class of ion channels. Neuronal differentiation of PC12 cells can be induced by nerve growth factor, leading to an increase in neuronal nicotinic acetylcholine receptor gene expression. Nerve growth factor initiates several signal transduction cascades. Here, we show that the Ras-dependent mitogen-activated protein kinase and phosphoinositide 3-kinase pathways are critical for the nerve growth factor-mediated increase in the transcriptional activity of a neuronal nicotinic acetylcholine receptor gene promoter. In addition, we show that a component of the Ras-dependent mitogen-activated protein kinase pathway, nerve growth factor-inducible c-Jun, exerts its effects on receptor gene promoter activity most likely through protein-protein interactions with Sp1. Finally, we demonstrate that the target for nerve growth factor signaling is an Sp1-binding site within the neuronal nicotinic acetylcholine receptor gene promoter.

Interactions between regulatory proteins that bind to the nicotinic receptor beta4 subunit gene promoter

The genes encoding the alpha3, alpha5 and beta4 subunits of nicotinic acetylcholine receptors are tightly clustered within the genome. As these three subunits constitute the predominant acetylcholine receptor subtype expressed in the peripheral nervous system, their genomic proximity suggests a regulatory mechanism ensuring their coordinate expression. We previously identified two transcriptional regulatory elements within the beta4 promoter. One of these elements, a CT box, interacts with the regulatory factors heterogeneous nuclear ribonucleoprotein K and Puralpha. Another element, a CA box, interacts with Sp1 and Sp3. The binding site for a fifth factor, Sox10, overlaps the CT and CA boxes. As the CT and CA boxes are adjacent, we postulated that the proteins that bind to the elements interact. Here we report that the CT box-binding factors interact with each other as do the CA box-binding factors. However, there are no direct associations between the two pairs of proteins. Interestingly though, Sox10 directly interacts with all four proteins, suggesting a central role in beta4 gene expression for this member of the Sox family of regulatory factors.

Cell type-specific activation of neuronal nicotinic acetylcholine receptor subunit genes by Sox10

The regulatory factor Sox10 is expressed in neural crest derivatives during development as well as in the adult CNS and peripheral nervous system. Mutations of the human Sox10 gene have been identified in patients with Waardenburg-Hirschsprung syndrome that is characterized by defects in neural crest development. Previous studies suggested that Sox10 might function as an important transcriptional regulator of neural crest development. No natural target genes of Sox10 have yet been identified. Although human Sox10 activates a synthetic promoter consisting of a TATA box and multiple Sox consensus sequences, no transcriptional activity of the rat Sox10 homolog has been detected. Here we report that the neuronal nicotinic acetylcholine receptor beta4 and alpha3 subunit gene promoters are transactivated by rat Sox10 in a cell type-specific manner. The alpha3 and beta4 subunits, in combination with the alpha5 subunit, make up the predominant nicotinic receptor subtype expressed in the peripheral nervous system. Transfections using Sox10 mutants indicate that the C-terminal region is dispensable for its ability to activate the beta4 and alpha3 promoters. Rat Sox10 was originally identified as an accessory protein of the POU domain protein Tst-1/Oct6/SCIP in glial cells. Tst-1/Oct6/SCIP was shown previously to activate the alpha3 promoter. We now demonstrate that it can transactivate the beta4 promoter as well. However, we were unable to detect any synergistic effects of Sox10 and Tst-1/Oct6/SCIP on beta4 or alpha3 promoter activity. Finally, we present data suggesting that recombinant Sox10 protein can directly interact with a previously characterized regulatory region of the beta4 gene.

Effects of nerve growth factor and nicotine on the expression of nicotinic acetylcholine receptor subunits in PC12 cells

The neuroprotective effect of nicotine via nicotinic acetylcholine receptor (nAChR) has been reported in differentiated PC12 cells. We examined the effects of nerve growth factor (NGF) and nicotine on the expressions of the nAChR subunits alpha3, alpha5, alpha7, beta2, beta3 and beta4, in PC12 cells using Northern blot analysis. NGF increased the transcriptions of alpha5 (1,4- to 2,3-fold), alpha7 (1.7- to 2.5-fold) and beta4 (1.9- to 3.0-fold) subunits, but changes in alpha3 and beta2 subunit levels were smaller than alpha5, alpha7, or beta4. Nicotine also increased the levels of mRNA encoding alpha5 and beta2 subunits. The pattern of subunit mRNA changes was different between NGF and nicotine treatment. No signal for beta3 subunit was detected. The results suggest that NGF changes the expression of nAChR in a subtype-specific manner over the course of the differentiation, and the disproportionate subunit expressions might be related to the neuroprotective effect exerted by nicotine.

beta43': An enhancer displaying neural-restricted activity is located in the 3'-untranslated exon of the rat nicotinic acetylcholine receptor beta4 gene

Members of a neuronal nicotinic acetylcholine receptor subunit gene cluster ordered beta4, alpha3, alpha5 in the vertebrate genome are expressed in highly restricted patterns in the PNS and CNS. Nothing is known, however, about the regulatory elements that control transcription of these genes in selected neuronal cell populations. We report here a novel enhancer, designated beta43', that is positioned in the beta4 3'-untranslated exon. It is composed of two nearly identical 37 bp direct repeats that are separated by 6 bp. Multimerization of the enhancer upstream of the alpha3 minimal promoter results in synergistic activation. Analysis in different cell types, including three neural lines and primary keratinocytes, shows that beta43' is preferentially active in the neural line PC12, which expresses all members of the cluster. Mobility shift assays reveal a cell-type-specific complex, which forms with the first repeat of the enhancer and PC12 extracts. Complexes co-migrating with the PC12 cell complex are not detected with extracts from other lines, which suggests that PC12 cells contain a differentially expressed factor that may be important for the restricted activity of beta43'. The cell-type-specific activity of the beta43' enhancer suggests that it is important for regulating restricted expression patterns of one or more clustered neuronal acetylcholine receptor genes. Its location within the beta4 gene may be a selective pressure for maintaining tight linkage of clustered neuronal nAchR genes.

Regulation of ion channel expression in neural cells by hormones and growth factors

Voltage-and ligand-gated ion channels are key players in synaptic transmission and neuron-glia communication in the nervous system. Expression of these proteins can be regulated at several levels (transcriptional, translational, or posttranslational) and by multiple extracellular factors in the developing and mature nervous system. A wide variety of hormones and growth factors have been identified as important in neural cell differentiation, which is a complex process involving the acquisition of cell-type-specific ion channel phenotypes. Much literature has already accumulated describing the structural and functional characteristics of ion channels, but relatively little is known about the factors that influence their synthesis and cell surface expression, although this area has generated considerable interest in the context of neural cell development. This article reviews several examples of regulated expression of these channels by cellular factors, namely peptide growth factors and steroid hormones, and discusses, where applicable, current understanding of molecular mechanisms underlying such regulation of voltage-and neurotransmitter-gated ion channels.

Differential effects of heterogeneous nuclear ribonucleoprotein K on Sp1- and Sp3-mediated transcriptional activation of a neuronal nicotinic acetylcholine receptor promoter

The neuronal nicotinic acetylcholine receptor gene family consists of 11 members, alpha2-alpha9 and beta2-beta4. Three of the genes, those encoding the alpha3, alpha5, and beta4 subunits, are clustered tightly within the genome. These three subunits constitute the predominant acetylcholine receptor subtype expressed in the peripheral nervous system. The genomic proximity of the three genes suggests a regulatory mechanism ensuring their coordinate expression. However, it is likely that gene-specific regulatory mechanisms are also functioning because the expression patterns of the three genes, although similar, are not identical. Previously we identified regulatory elements within the beta4 promoter region and demonstrated that these elements interact specifically with nuclear proteins. One of these elements, E1, interacts with the regulatory factor Puralpha as well as three other unidentified DNA-binding proteins with molecular masses of 31, 65, and 114 kDa. Another element, E2, interacts with Sp1 and Sp3. Because E1 and E2 are immediately adjacent to one another, we postulated that the proteins that bind to the elements interact to regulate beta4 gene expression. Here we report the identification of the 65-kDa E1-binding protein as heterogeneous nuclear ribonucleoprotein K and demonstrate that it affects the transactivation of beta4 promoter activity by Sp1 and Sp3 differentially.

Differential regulation of levels of nicotinic receptor subunit transcripts in adult sympathetic neurons after axotomy

Axotomy of adult peripheral neurons produces decreases in the levels of transcripts for a number of proteins involved in synaptic transmission. For example, tyrosine hydroxylase and neuropeptide Y mRNA decrease in axotomized sympathetic neurons in the superior cervical ganglion (SCG). In the present study, the effects of axotomy on the expression of nicotinic receptor subunit transcripts were examined in the SCG and the results were compared to those produced by deafferentation and explantation. Normally, neurons in the SCG express five different nicotinic subunits: alpha3, alpha5, alpha7, beta2, and beta4. Forty-eight hours after axotomy in vivo or explantation, dramatic decreases in these transcripts were seen, except for beta2, which increased. In contrast, deafferentation of the SCG had negligible effects on any of these transcripts. Both leukemia inhibitory factor (LIF) and nerve growth factor (NGF) have been shown to play a role in the decrease in neuropeptide Y mRNA expression after axotomy. In the cases of these nicotinic receptor transcripts, however, similar decreases were seen in wild-type and LIF knockout animals. Furthermore, administration of an antiserum to NGF in intact animals produced no changes in transcript levels. On the other hand, providing exogenous NGF to axotomized SCG in vivo or in explant cultures partially prevented the decreases in the transcripts for alpha3, alpha5, alpha7, and beta4. These data indicate that axotomy produces dramatic decreases in the expression of several nicotinic receptor subunit transcripts, and that the molecular signals underlying these changes differ from those previously shown to mediate the decrease in neuropeptide Y expression.

Human neuronal nicotinic receptors

Nicotine is a very widely used drug of abuse, which exerts a number of neurovegetative, behavioural and psychological effects by interacting with neuronal nicotinic acetylcholine receptors (NAChRs). These receptors are distributed widely in human brain and ganglia, and form a family of ACh-gated ion channels of different subtypes, each of which has a specific pharmacology and physiology. As human NAChRs have been implicated in a number of human central nervous system disorders (including the neurodegenerative Alzheimer's disease, schizophrenia and epilepsy), they are suitable potential targets for rational drug therapy. Much of our current knowledge about the structure and function of NAChRs comes from studies carried out in other species, such as rodents and chicks, and information concerning human nicotinic receptors is still incomplete and scattered in the literature. Nevertheless, it is already evident that there are a number of differences in the anatomical distribution, physiology, pharmacology, and expression regulation of certain subtypes between the nicotinic systems of humans and other species. This review will attempt to survey the major achievements reached in the study of the structure and function of NAChRs by examining the molecular basis of their functional diversity viewed mainly from pharmacological and biochemical perspectives. It will also summarize our current knowledge concerning the structure and function of the NAChRs expressed by other species, and the newly discovered drugs used to classify their numerous subtypes. Finally, the role of NAChRs in behaviour and pathology will be considered.

Nicotine regulates mRNA level of tyrosine hydroxylase gene but not that of nicotinic acetylcholine receptor genes in PC12 cells

To understand the molecular mechanism of nicotine addiction, we examined the mRNA level of the tyrosine hydroxylase (TH) gene and that of the nicotinic acetylcholine receptor (nAChR) genes by long-term nicotine treatment. The transcript levels of the four subunit genes of the nAChR (alpha3, alpha5, alpha7, and beta4) were down-regulated by the treatment with forskolin, whereas the mRNA levels of the TH gene was increased in PC12 cells. By long-term nicotine treatment, the mRNA level of the nAChR genes did not change, but transcript levels of alpha3, alpha5, alpha7, and beta4 nAChR genes were still negatively regulated by forskolin. However, the mRNA level of TH gene did not change by forskolin under long-term nicotine treatment. The TH gene may be regulated by a nicotine-related signaling pathway, whereas alpha3, alpha5, alpha7, and beta4 nAChR genes may be further regulated by a protein kinase A (PKA) pathway under long-term nicotine treatment.

Structural and functional characterization of the human alpha3 nicotinic subunit gene promoter

We describe the structural and functional features of the human alpha3 nicotinic receptor subunit promoter. A 0.35-kb region immediately upstream of the start codon was identified that when transfected in human neuroblastoma cells was able to drive the expression of the luciferase reporter gene with a strength comparable to that of the well-characterized simian virus 40 promoter/enhancer. This region displayed the features of a multistart-site, GC-rich, TATA-less, and CAAT-less promoter, containing many overlapping Sp1 and AP-2 putative binding sites. Further dissections of the 0.35-kb fragment revealed that its 3' region, specifying the 5' UT of the mRNA, plays a relevant positive effect in determining the strength of the promoter. This region contains putative cis-acting elements for AP-2, nuclear factor-kappaB, and the recently described multiple-start site element downstream-1. By mutation analysis, we showed that these sites are functional and when combined increase the promoter activity by 4-fold. The 0.35-kb promoter was found to be under the negative control of upstream sequences that include a modern Alu repeat. The alpha3 Alu repeat works as a composite region, containing both positive and negative elements that control the activity of the downstream promoter. Finally, we investigated the tissue-specific activity of the human alpha3 gene 5' regulatory sequences, showing that they are able to drive the expression of the reporter gene preferentially in neuronal cells.

Transcriptional analysis of acetylcholine receptor alpha 3 gene promoter motifs that bind Sp1 and AP2

In this study, we performed an analysis of the neuronal nicotinic acetylcholine receptor alpha 3 subunit gene promoter region, -238/+47, to identify cis and trans elements that are important for basal activity in PC12 cells. Sequence analyses of the alpha 3 promoter and footprint assays revealed an Sp1 binding site between -79 and -57 (termed the alpha 3 GA motif) and an AP2 binding site between -30 and -7. Using mobility shift analysis, we found that PC12 cell extracts contain proteins that specifically bind to the alpha 3 GA motif and are immunologically related to Sp1. Mutation of the alpha 3 GA motif, which prevented binding of Sp1, resulted in a 75% decrease in promoter activity. Mutation of the AP2 site resulted in only a minor loss of promoter activity, which is consistent with the lack of AP2 binding activity in PC12 extracts. In Drosophila Schneider line 2 (S2) cell cotransfection assays, Sp1 activated the alpha 3 promoter in a GA motif-dependent manner. Furthermore, multimerization of the GA motif upstream of the beta-globin TATA box conferred Sp1 responsiveness. Our results indicate that Sp1 can activate transcription through direct interaction with the alpha 3 GA motif and that this motif plays a major role in alpha 3 promoter basal activity in PC12 cells.

A novel regulatory element of a nicotinic acetylcholine receptor gene interacts with a DNA binding activity enriched in rat brain

Nicotinic acetylcholine receptors are ligand-gated ion channels that play a critical role in signal transmission in the nervous system. The genes encoding the various subunits that comprise functional acetylcholine receptors are expressed in distinct temporal and spatial patterns. Studies to understand the molecular mechanisms underlying the differential expression of the receptor subunit genes have led to the identification, in this report, of a 19-base pair cis-acting element that is required for transcriptional activation of the rat beta 4 subunit gene. Screening of computer data bases with the 19-base pair element revealed the sequence to be unique among known transcriptional regulatory elements. Loss of this element resulted in drastically reduced beta 4 promoter activity in transfected cholinergic SN17 cells. Furthermore, this element specifically interacts with nuclear proteins prepared from both SN17 cells and adult rat brain. UV cross-linking experiments indicated the presence, in SN17 nuclear extracts, of a prominent protein species (approximately 50 kDa) that interacts specifically with the 19-base pair element. These results lead us to hypothesize that interactions between the 50-kDa protein and the novel 19-base pair element are necessary for transcriptional activation of the beta 4 subunit gene.

Differential expression of sodium channels and nicotinic acetylcholine receptor channels in nnr variants of the PC12 pheochromocytoma cell line

An important component of neuronal differentiation is the tightly controlled expression of a spectrum of ion channel proteins. Ion channels play a critical role in the generation and propagation of action potentials as well as in the cellular response to neurotransmitters, and thus are central in the transfer and integration of information in the nervous system. A model system amenable to analysis of ion channel expression and neuronal differentiation is the rat pheochromocytoma (PC12) cell line. Here, we have used electrophysiological and molecular biological approaches to analyze the expression of voltage-dependent sodium (Na) channels and nicotinic acetylcholine receptors (nAChR) in mutagenized variants (nnr cells) of the PC12 cell line. Our data reveal striking differences in the expression of these channels when compared to wild-type PC12 cells. Even in the absence of nerve growth factor (NGF), nnr cells express functional Na channels and Na channel mRNA at levels exceeding those in wild-type PC12 cells differentiated with NGF. In contrast, acetylcholine-induced currents were evident in only a small proportion of cells, presumably due to the altered pattern of expression of mRNAs encoding individual nAChR subunits. The altered ion channel expression in these variants provides an avenue for analyzing Na channel and nAChR channel function, as well as for identifying mechanisms governing their expression.