Structure of the m1 muscarinic acetylcholine receptor gene and its promoter

Loss of Cholinergic Receptor Muscarinic 1 (CHRM1) Protein in the Hippocampus and Temporal Cortex of a Subset of Individuals with Alzheimer’s Disease, Parkinson’s Disease, or Frontotemporal Dementia: Implications for Patient Survival

Background: Dysfunction of cholinergic neurotransmission is a hallmark of Alzheimer’s disease (AD); forming the basis for using acetylcholine (ACh) esterase (AChE) inhibitors to mitigate symptoms of ACh deficiency in AD. The Cholinergic Receptor Muscarinic 1 (CHRM1) is highly expressed in brain regions impaired by AD. Previous analyses of postmortem AD brains revealed unaltered CHRM1 mRNA expression compared to normal brains. However, the CHRM1 protein level in AD and other forms of dementia has not been extensively studied. Reduced expression of CHRM1 in AD patients may explain the limited clinical efficacy of AChE inhibitors. Objective: To quantify CHRM1 protein in the postmortem hippocampus and temporal cortex of AD, Parkinson’s disease (PD), and frontotemporal dementia (FTD) patients. Methods: Western blotting was performed on postmortem hippocampus (N = 19/73/7/9: unaffected/AD/FTD/PD) and temporal cortex (N = 9/74/27: unaffected/AD/PD) using a validated anti-CHRM1 antibody. Results: Quantification based on immunoblotting using a validated anti-CHRM1 antibody revealed a significant loss of CHRM1 protein level (<50%) in the hippocampi (78% AD, 66% PD, and 85% FTD) and temporal cortices (56% AD and 42% PD) of dementia patients. Loss of CHRM1 in the temporal cortex was significantly associated with early death (<65–75 years) for both AD and PD patients. Conclusion: Severe reduction of CHRM1 in a subset of AD and PD patients can explain the reported low efficacy of AChE inhibitors as a mitigating treatment for dementia patients. Based on this study, it can be suggested that future research should prioritize therapeutic restoration of CHRM1 protein levels in cholinergic neurons.

Inactivation of JAK2/STAT3 signaling axis and downregulation of M1 mAChR cause cognitive impairment in klotho mutant mice, a genetic model of aging

We previously reported cognitive dysfunction in klotho mutant mice. In the present study, we further examined novel mechanisms involved in cognitive impairment in these mice. Significantly decreased janus kinase 2 (JAK2) and signal transducer and activator of transcription3 (STAT3) phosphorylation were observed in the hippocampus of klotho mutant mice. A selective decrease in protein expression and binding density of the M1 muscarinic cholinergic receptor (M1 mAChR) was observed in these mice. Cholinergic parameters (ie, acetylcholine (ACh), choline acetyltransferase (ChAT), and acetylcholinesterase (AChE)) and NMDAR-dependent long-term potentiation (LTP) were significantly impaired in klotho mutant mice. McN-A-343 (McN), an M1 mAChR agonist, significantly attenuated these impairments. AG490 (AG), a JAK2 inhibitor, counteracted the attenuating effects of McN, although AG did not significantly alter the McN-induced effect on AChE. Furthermore, AG significantly inhibited the attenuating effects of McN on decreased NMDAR-dependent LTP, protein kinase C βII, p-ERK, p-CREB, BDNF, and p-JAK2/p-STAT3-expression in klotho mutant mice. In addition, k252a, a BDNF receptor tyrosine kinase B (TrkB) inhibitor, significantly counteracted McN effects on decreased ChAT, ACh, and M1 mAChR and p-JAK2/p-STAT3 expression. McN-induced effects on cognitive impairment in klotho mutant mice were consistently counteracted by either AG or k252a. Our results suggest that inactivation of the JAK2/STAT3 signaling axis and M1 mAChR downregulation play a critical role in cognitive impairment observed in klotho mutant mice.

Role of CREB in the regulatory action of sarsasapogenin on muscarinic M1 receptor density during cell aging

This work studied the role of cyclic AMP responsive element binding protein (CREB) in the up-regulation of M(1) muscarinic acetylcholine receptor (M(1) receptor) density by sarsasapogenin (ZMS) in CHO cells transfected with M(1) receptor gene (CHOm1 cells). During cell aging, sarsasapogenin elevated M(1) receptor density as well as CREB and phosphor-CREB (pCREB) levels. CREB peaked earliest, followed by pCREB and M(1) receptor density peaked last. When CREB synthesis was blocked by antisense oligonucleotides, the elevation effect of sarsasapogenin on M(1) receptor density was abolished. These results suggest that sarsasapogenin up-regulates M(1) receptor density in aged cells by promoting CREB production and phosphorylation. Furthermore, the results support the hypothesis that pCREB regulates M(1) receptor gene expression through heterodimer formation.

Regulatory elements of the melanocortin 1 receptor

Among more than 120 genes that are now known to regulate mammalian pigmentation, one of the key genes is MC1R, which encodes the melanocortin 1 receptor, a seven transmembrane G protein-coupled receptor expressed on the surface of melanocytes. Since the monoexonic sequence of the gene was cloned and characterized more than a decade ago, tremendous efforts have been dedicated to the extensive genotyping of mostly red-haired populations all around the world, thus providing allelic variants that may or may not account for melanoma susceptibility in the presence or absence of ultraviolet (UV) exposure. Soluble factors, such as proopiomelanocortin (POMC) derivatives, agouti signal protein (ASP) and others, regulate MC1R expression, leading to improved photoprotection via increased eumelanin synthesis or in contrast, inducing the switch to pheomelanin. However, there is an obvious lack of knowledge regarding the numerous and complex regulatory mechanisms that govern the expression of MC1R at the intra-cellular level, from gene transcription in response to an external stimulus to the expression of the mature receptor on the melanocyte surface.

Up-regulation of M1 muscarinic receptors expressed in CHOm1 cells by panaxynol via cAMP pathway

Loss of cholinergic neurons along with muscarinic acetylcholine receptors (mAChRs) in cerebral cortex and hippocampus is closely associated with Alzheimer's disease (AD). Recent drug development for AD treatment focuses heavily on identifying M(1) receptor agonists. However, mAChRs undergo down-regulation in response to agonist-induced sustained activation. Therefore, therapeutic effectiveness wanes during continuous use. Thus, another potentially effective approach, which overcomes this drawback is to develop compounds, which instead up-regulate M(1) receptor expression. In the present study, we took this alternative approach and contrasted in Chinese hamster ovary cells transfected with human m(1) subtype gene (CHOm(1) cells) changes of M(1) receptor expression levels caused by muscarinic agonists and upregulators of its expression. The muscarinic agonists carbachol and pilocarpine reduced M(1) receptor number in CHOm(1) cells by 29 and 46%, respectively, at 100muM, whereas panaxynol, a polyacetylene compound isolated from the lipophilic fraction of Panax notoginseng, concentration-dependently up-regulated the M(1) receptor number after pre-incubation with CHOm(1) cells for 48 h, reaching a plateau at 1 microM, and was accompanied by enhanced M(1) mRNA levels. Moreover, the protein kinase A (PKA) inhibitor RP-adenosine-3',5'-cyclic mono-phosphoro-thioate triethylamine salt (RP-cAMPs) 5 microM completely prevented panaxynol-induced up-regulation of M(1) receptors. Panaxynol (1muM) caused a significant and consistent stimulation of cAMP accumulation (27% increase above basal at 40 min). These results suggest that in CHOm(1) cells panaxynol up-regulates M(1) receptor number through cAMP pathway-mediated stimulation of gene transcription.

Molecular biology of gonadotropin-releasing hormone (GnRH)-I, GnRH-II, and their receptors in humans

In human beings, two forms of GnRH, termed GnRH-I and GnRH-II, encoded by separate genes have been identified. Although these hormones share comparable cDNA and genomic structures, their tissue distribution and regulation of gene expression are significantly dissimilar. The actions of GnRH are mediated by the GnRH receptor, which belongs to a member of the rhodopsin-like G protein-coupled receptor superfamily. However, to date, only one conventional GnRH receptor subtype (type I GnRH receptor) uniquely lacking a carboxyl-terminal tail has been found in the human body. Studies on the transcriptional regulation of the human GnRH receptor gene have indicated that tissue-specific gene expression is mediated by differential promoter usage in various cell types. Functionally, there is growing evidence showing that both GnRH-I and GnRH-II are potentially important autocrine and/or paracrine regulators in some extrapituitary compartments. Recent cloning of a second GnRH receptor subtype (type II GnRH receptor) in nonhuman primates revealed that it is structurally and functionally distinct from the mammalian type I receptor. However, the human type II receptor gene homolog carries a frameshift and a premature stop codon, suggesting that a full-length type II receptor does not exist in humans.

Historical review: a brief history and personal retrospective of seven-transmembrane receptors

Pharmacologists have studied receptors for more than a century but a molecular understanding of their properties has emerged only during the past 30-35 years. In this article, I provide a personal retrospective of how developments and discoveries primarily during the 1970s and 1980s led to current concepts about the largest group of receptors, the superfamily of seven-transmembrane (7TM) receptors [also known as G-protein-coupled receptors (GPCRs)]. Significant technical advances such as the development of methods for radioligand binding, solubilization and purification of the beta(2)-adrenoceptor and other adrenoceptors led to the cloning of receptor genes and the discovery of their 7TM architecture and homology with rhodopsin. A universal mechanism of receptor regulation by G-protein-coupled receptor kinases (GRKs) and arrestins, originally discovered as a means of "desensitizing" G-protein-mediated second-messenger generation, was subsequently found to mediate both receptor endocytosis and activation of a growing list of signaling pathways such as those involving mitogen-activated protein kinases. Numerous opportunities for novel therapeutics should emerge from current and future research on 7TM receptor biology.

Multiple promoters drive tissue-specific expression of the human M2 muscarinic acetylcholine receptor gene

Despite the wealth of information on the functional and pharmacological properties of the M2 muscarinic receptor, we know relatively little of structure and regulation of the M2 receptor gene. Here, we describe the organisation of the human M2 gene and its promoters. Four exons are present in the 5' untranslated region of the human M2 mRNA distributed over 146 kb on chromosome 7 which produce eight different splice variants in the IMR-32 neuroblastoma cell line. The unexpectedly large size of this gene indicates that transcription initiates much further upstream of the coding region than earlier studies had indicated. We present evidence that there are three distinct human M2 promoters. Analysis of endogenous transcripts revealed that promoter 2 is preferentially used in neuroblastoma cells, whereas promoter 1 in cardiac cells. All promoters are highly conserved across human, mouse, rat and pig. They contain multiple start sites and none possess a TATA-box. In addition, we describe another M2 promoter that is specific for rat. We show that GATA-4 transcription factor binds to two sites within the regulatory regions of the M2 gene using reporter gene assays, electromobility shift assays and mutational analysis.

Effects of estrogen on muscarinic acetylcholine receptors in the rat hippocampus

The aim of the present study was to investigate whether different estrogen manipulations have effects on the expression of muscarinic acetylcholine receptors (mAChRs) in the adult female rat hippocampus. Hippocampus was obtained from rats in proestrus (control), ovariectomized for 2, 10 and 15 days, ovariectomized for 15 days and treated with 17beta-estradiol for 7 days, and treated with 17beta-estradiol immediately after ovariectomy for 21 days. Rats' estrogen status was monitored by measuring estradiol plasma levels and uterus relative weight. [3H]quinuclidinyl benzilate ([3H]QNB) binding studies indicated that ovariectomy time-dependently increases the number of mAChRs in hippocampus when compared to those obtained from control rats. Estradiol treatments for 21 days avoid the effect of ovariectomy. However, the estradiol treatments for 7 days after 15 days of ovariectomy slightly change the number of mAChRs. In conclusion, these results showed that ovariectomy time-dependently increases mAChRs number in the rat hippocampus. In addition, these data suggest that treatment with estradiol initiated within a specific period of time after the loss of ovarian function may be effective at preventing specific effects of hormone deprivation on hippocampus.

Transcription of the M1 muscarinic receptor gene in neurons and neuronal progenitors of the embryonic rat forebrain

Development of the nervous system is accompanied by expansion and differentiation of the neuronal progenitors within the embryonic neuroepithelium. Although the role of growth factors in this process is well documented, there is increasing evidence for a role of neurotransmitters. Acetylcholine is known to exert many actions on developing neural cells, but its potential role in neurogenesis is unclear. Here, we show that the M1 muscarinic acetylcholine receptor is expressed in the neuroepithelium of the rat forebrain, where it is found on both nestin+ progenitor cells and TuJ1+ newly differentiated neurons. Furthermore, transcription is governed, at least in part, by regulatory cis elements that are also responsible for driving transcription in neuroblastoma cells. This represents the first demonstration of M1 receptors on neuronal progenitor cells and supports the notion that M1 muscarinic receptors may play a role in development of the nervous system prior to the onset of synaptogenesis and their subsequent role in neurotransmission.

Structure and transcription of the human m3 muscarinic receptor gene

We have isolated and characterized the human m3 muscarinic receptor gene and its promoter. Using 5' rapid amplification of cDNA ends (RACE), internal polymerase chain reaction (PCR), and homology searching to identify EST clones, we determined that the cDNA encoding the m3 receptor comprises 4,559 bp in 8 exons, which are alternatively spliced to exclude exons 2, 4, 6, and/or 7; the receptor coding sequence occurs within exon 8. Analysis of P1 artificial chromosome (PAC) and bacterial artificial chromosome (BAC) clones and of PCR- amplified genomic DNA, and homology searching of human chromosome 1 sequence provided from the Sanger Centre (Hinxton, Cambridge, UK) revealed that the m3 muscarinic receptor gene spans at least 285 kb. A promoter fragment containing bp -1240 to +101 (relative to the most 5' transcription start site) exhibited considerable transcriptional activity during transient transfection in cultured subconfluent, serum-fed canine tracheal myocytes, and 5' deletion analysis of promoter function revealed the presence of positive transcriptional regulatory elements between bp -526 and -269. Sequence analysis disclosed three potential AP-2 binding sites in this region; five more AP-2 consensus binding motifs occur between bp -269 and +101. Cotransfection with a plasmid expressing human AP-2alpha substantially increased transcription from m3 receptor promoter constructs containing 526 or 269 bp of 5' flanking DNA. Furthermore, m3 receptor promoter activity was enhanced by long-term serum deprivation of canine tracheal myocytes, a treatment that is known to increase AP-2 transcription-promoting activity in these cells. Together, these data suggest that expression of the human m3 muscarinic receptor gene is regulated in part by AP-2 in airway smooth muscle.

The basic helix-loop-helix domain of the E47 transcription factor requires other protein regions for full DNA binding activity

Most transcription factors are believed to be composed of independently functioning modules [A. D. Frankel and P. S. Kim (1991) Cell 65, 717-719]. Basic helix-loop-helix (bHLH) transcription factors appear to fit this model, with the HLH domains mediating dimerization, the basic regions mediating DNA binding, and other modules controlling other functions such as transcriptional activation. We tested predictions of this model using forced dimers of bHLH proteins including E47 homodimers and MyoD:E47 heterodimers and found that protein dimers containing complete bHLH domains but lacking other regions of E47 have only 20% of the DNA binding ability and transcriptional transactivation activity of wild-type dimers. These results demonstrate that the bHLH domains do not function as completely independent DNA binding modules. In addition, these results demonstrate that the transcriptional activation domains from a single bHLH protein are sufficient to activate transcription.

Structure of the human M(2) muscarinic acetylcholine receptor gene and its promoter

The M(2) muscarinic receptor inhibits the release of acetylcholine from cholinergic fibers in the lungs and elsewhere. In airway parasympathetic neurons, M(2) receptor expression is decreased by viral infections and by interferon-gamma, increasing actylcholine release. Dexamethasone increases M(2) receptor expression, decreasing acetylcholine release. We carried out 5' rapid amplification of cDNA ends beginning with mRNA from human heart and IMR32 human neuroblastoma cells. This demonstrated a 5' UTR of 100 BP, corresponding to two sequences on chromosome 7, separated by a 22.6 kB intron. The splice acceptor site is at -45 relative to the initiating atg. The 3000 BP upstream of 5' RACE product were subcloned into a pGL3 luciferase reporter vector. Deletional constructs were expressed in IMR32 cells. These demonstrated that 412 BP provided full expression of the reporter gene, and suggested a repressor element between -1848 and -1510.

The basic helix-loop-helix protein, sharp-1, represses transcription by a histone deacetylase-dependent and histone deacetylase-independent mechanism

Many aspects of neurogenesis and neuronal differentiation are controlled by basic helix-loop-helix (bHLH) proteins. One such factor is SHARP-1, initially identified on the basis of its sequence similarity to hairy. Unlike hairy, and atypically for bHLHs, SHARP-1 is expressed late in development, suggestive of a role in terminal aspects of differentiation. Nevertheless, the role of SHARP-1 and the identity of its target genes remain unknown. During the course of a one-hybrid screen for transcription factors that bind to regulatory domains of the M1 muscarinic acetylcholine receptor gene, we isolated the bHLH transcription factor SHARP-1. In this study, we investigated the functional role of SHARP-1 in regulating transcription. Fusion proteins of SHARP-1 tethered to the gal4 DNA binding domain repress both basal and activated transcription when recruited to either a TATA-containing or a TATAless promoter. Furthermore, we identified two independent repression domains that operate via distinct mechanisms. Repression by a domain in the C terminus is sensitive to the histone deacetylase inhibitor trichostatin A, whereas repression by the bHLH domain is insensitive to TSA. Furthermore, overexpression of SHARP-1 represses transcription from the M(1) promoter. This study represents the first report to assign a function to, and to identify a target gene for, the bHLH transcription factor SHARP-1.

Multiplex semi-quantitative reverse transcriptase-polymerase chain reaction of low abundance neuronal mRNAs

The sequential use of reverse transcriptase and the polymerase chain reaction (RT-PCR) has provided molecular biology research with an exquisitely sensitive and fast technique for studying gene expression. This method is particularly useful to study transcripts in the nervous system, which are on average present at low levels and the amount of tissue or cells to be analyzed is often limited. Here, we describe a RT-PCR assay which allows the simultaneous detection and semi-quantitation of several transcripts (multiplex). Multiple PCR primer pairs are used to detect different target transcripts in a single reaction, together with a pair of primers able to amplify the hypoxantine-phosphoribosyl-transferase (HPRT), a gene constitutively expressed at low levels throughout the nervous system. HPRT levels remain constant also during neurogenesis and it is thus apt to be used in developmental neurobiology. This internal standard is the mRNA of reference to evaluate sample variation in RT and PCR reactions and to monitor the degradation and recovery of RNAs. Normalization with respect to HPRT cDNA allows to estimate the relative abundance of each target mRNA.

Reporter gene technology: the future looks bright

Reporter gene technology is widely used to monitor the cellular events associated with signal transduction and gene expression. Based upon the splicing of transcriptional control elements to a variety of reporter genes (with easily measurable phenotypes), it "reports" the effects of a cascade of signalling events on gene expression inside cells. The principal advantage of these assays is their high sensitivity, reliability, convenience, and adaptability to large-scale measurements. This review summarises the current status of reporter gene technology including its role in monitoring gene transfer and expression and its development as a biological screen. With the advances in this technology and in detection methods, it is likely that luciferase and green fluorescent protein will become increasingly popular for the non-invasive monitoring of gene expression in living tissues and cells. Such techniques will be important in defining the molecular events associated with gene transcription, which has implications for our understanding of the molecular basis of disease and will influence our approach to gene therapy and drug development.

Characterization of the promoter region of the human melanocortin-1 receptor (MC1R) gene

We sequenced 3201 bp upstream from the ATG translation start codon of the human melanocortin-1 receptor (MC1R). A number of transcriptional initiation sites were detected over a region of approximately 600 base pairs upstream of the receptor coding region. These consist of GC-rich regions, each including SP-1 consensus binding motifs. Neither a TATA nor a CAAT box was found in this region. The 5'-flanking region also contains the consensus regulatory elements for AP-1, AP-2, and several E-boxes. Gel shift assays targeting the three GC boxes confirmed binding of SP-1. A promoter assay revealed that the minimal region exhibiting promoter activity was located between nucleotides -517 and -282 in human melanoma SK-Mel-2 cells. Further deletion from -517 to -447, which removed an SP-1 site, completely abolished luciferase activity. In conclusion, the MC1R promoter shares the characteristics of many other GPCR promoters. These characteristics include GC-rich sequence, lack of a TATA box, and binding of SP-1.

Control elements of muscarinic receptor gene expression

Studies describing the structures of the M1, M2 and M4 muscarinic acetylcholine receptors (mAChR) genes and the genetic elements that control their expression are reviewed. In particular, we focus on the role of the neuron-restrictive silencer element/restriction element-1 (NRSE/RE-1) in the regulation of the M4 mAChR gene. The NRSE/RE-1 was first identified as a genetic control element that prevents the expression of the SCG-10 and type II sodium channel (NaII) genes in non-neuronal cells in culture. The NRSE/RE-1 inhibits gene expression by binding the repressor/silencer protein NRSF/REST, which is present in many non-neuronal cell lines and tissues. Our studies show that although the expression of the M4 mAChR gene is inhibited by NRSF/REST, this inhibition is not always complete. Rather, the efficiency of silencing by NRSF/REST is different in different cells. A plausible explanation for this differential silencing is that the NRSF/RE-1 interacts with distinct sets of promoter binding proteins in different types of cells. We hypothesize that modulation of NRSF/REST silencing activity by these proteins contributes to the cell-specific pattern of expression of the M4 mAChR in neuronal and non-neuronal cells. Recent studies that suggest a more complex role for the NRSE/RE-1 in regulating gene expression are also discussed.

Repression and activation of muscarinic receptor genes

The specific cellular response to muscarinic receptor activation is dependent upon appropriate expression of each of the five muscarinic receptor genes by individual cells. Here we summarise recent work describing some of the genomic regulatory elements and transcriptional mechanisms that control expression of the M1 and M4 genes.

Identification and characterization of the rat M1 muscarinic receptor promoter

Five subtypes of the muscarinic receptor have been cloned from both the rat and human genomes. Although all five genes have the coding sequences in a single exon, their structures 5' of the initiation codon are largely uncharacterized, except for the M4 receptor. In the brain, muscarinic receptors mediate motor and memory function by interaction with their ligand acetylcholine. In addition, the M1 muscarinic subtype has been implicated in behavior, stress-adaptive cardiovascular reflexes, and blood pressure regulation. In the current study the M1 muscarinic receptor noncoding 5'-flanking region has been identified and characterized, including the promoter and two 5' noncoding exons located approximately 13-14 kb from the coding exon. Similar to the M4 muscarinic receptor gene the M1 promoter is GC-rich, contains no TATA box, but has two potential CAAT boxes and several putative binding sites for transcription factors such as SP1 and AP-1-3. The transcription initiation site was identified by RNase protection and primer extension. Promoter activity was confirmed in transient expression assays, using luciferase reporter constructs. A 0.89-kb fragment consisting of 480 bp of the promoter, exon 1, and part of intron 1 expressed luciferase activity in two M1 receptor-expressing cell lines (CCL-107 and CCL-147), whereas a longer fragment (1.5 kb) that extends into intron 2 demonstrated significantly increased luciferase activity. The constructs exhibited responses indicating the presence of functional glucocorticoid-, acute-phase-, and heat shock-responsive elements.

Nerve growth factor regulation of m4 muscarinic receptor mRNA stability but not gene transcription requires mitogen-activated protein kinase activity

Nerve growth factor (NGF) up-regulated steady-state levels of m4 muscarinic acetylcholine receptor (mAChR) mRNA in PC12 cells. Up-regulation of mRNA levels was associated with a corresponding increase in mAChR binding sites. Two other growth factors, basic fibroblast growth factor (bFGF) and epidermal growth factor (EGF), up-regulated m4 mRNA and mAChR binding sites. Treatment of PC12 cells with NGF and bFGF, but not EGF, has previously been demonstrated to result in sustained activation of mitogen-activated protein kinase (MAPK). Analogously, NGF and bFGF, but not EGF, increased the stability of m4 mRNA in PC12 cells. In HER-PC12 cells, a clonal PC12 cell transfectant overexpressing EGF receptors and displaying sustained MAPK activation upon receptor stimulation, EGF treatment stabilized the m4 transcript. A synthetic inhibitor of MAPK kinase, PD98059, inhibited growth factor-induced stabilization of the m4 transcript in both PC12 and HER-PC12 cells. These findings demonstrate that the MAPK pathway is involved in transcript stabilization. Cycloheximide pretreatment abolished the post-transcriptional effect of NGF, indicating that de novo protein synthesis was required for the observed increase in m4 mRNA stability. By contrast, cycloheximide had no discernible post-transcriptional effect if added after NGF treatment, suggesting that an inducible yet stable protein factor was involved in m4 mRNA decay. An unusually well conserved 137 nucleotides of m4 3'-untranslated region has been identified by sequence comparison with other mRNAs that are post-transcriptionally regulated by NGF. In PC12 cells that heterologously overexpress this region, we demonstrate that NGF no longer stabilizes endogenous m4 mRNA. This conserved region probably represents an NGF-responsive element involved in mRNA stability regulation. Finally, transcription of the m4 gene can be induced by all three growth factors but is not dependent on MAPK activity, unlike growth factor-induced m4 mRNA stabilization.

Regulation of the expression and function of the M2 muscarinic receptor

Since the cloning and expression of many of the G protein-coupled receptors during the 1980s, there has been a massive increase in our understanding of many aspects of their function. The use of molecular biology to engineer and express mutant receptors has made it possible to determine key amino acids involved in receptor function. Although advances in molecular biology have contributed greatly to our understanding of the pharmacology and structure of the five subtypes of muscarinic receptor, much remains to be learned about the factors that regulate their expression and function. This review by El-Bdaoui Haddad and Jonathan Rousell describes the current state of awareness and highlights recent advances made in the elucidation of the mechanisms involved in muscarinic receptor regulation. Because most is known about the regulation of expression of the M2 receptor subtype, particular attention will be paid to it. Furthermore, this receptor subtype plays an important role in regulating acetylcholine output from airway cholinergic nerves, and there is substantial evidence from studies both in vivo and in vitro in human and animal models that these receptors are dysfunctional in asthma.

GATA factor-dependent regulation of cardiac m2 muscarinic acetylcholine gene transcription

The m2 subtype is the predominant muscarinic acetylcholine receptor subtype expressed in heart and regulates the rate and force of cardiac contraction. We have previously reported the isolation of the promoter region for the chick m2 receptor gene and defined a region of the chick m2 promoter sufficient for high level expression in cardiac primary cultures. In this manuscript we demonstrate transactivation of cm2 promoter by the GATA family of transcription factors. In addition, we define the GATA-responsive element in the chick m2 promoter and demonstrate that this element is required for expression in cardiac primary cultures. Finally, we demonstrate specific binding of both a chick heart nuclear protein and of cloned chick GATA-4, -5, and -6 to the GATA-responsive element.