Prolonged activation of protein kinase C induces transcription and expression of the alpha 1B adrenergic receptor gene in DDT1 MF-2 cells

Modulation of the beta-adrenergic receptor system of vascular smooth muscle cells in vitro and in vivo by chronically elevated endothelin-1 levels

Endothelin-1 (ET-1) levels are chronically elevated in several cardiovascular diseases and correlate with an increased mortality. However, in contrast to acute biological activities such as vasoconstriction, little is known about long-term effects of ET-1. In this study we determined the effects of ET-1 on the beta(2)-adrenergic receptor (AR) system. Incubation of smooth muscle cells with ET-1 for 72 hr led to increased beta(2)AR density as determined by radioligand binding. Experiments with inhibitors of protein and RNA synthesis as well as RT-PCR revealed that beta(2)AR upregulation required de novo synthesis. In addition, protein kinase C but neither NO nor prostaglandin metabolism were involved in this effect. The enhanced expression of beta(2)AR was associated with an increased expression of its stimulatory G-protein and the receptor's ability to stimulate adenylyl cyclase. To study chronic effects of ET-1 in vivo, rats were infused with ET-1 for 3 weeks. Similarly as in cultured cells, prolonged ET-1 exposure led to increased betaAR expression in vivo. As a consequence, beta(2)AR-induced vasodilatation was increased in aortic rings from ET-1-treated animals. Our results therefore suggest that chronically elevated ET-1 levels in vitro and in vivo induce counterregulatory mechanisms by increasing betaARs that attenuate the vasoconstrictive effects of ET-1.

The simian virus 40 core C enhancer-like element is a positive regulator in the rat alpha1B adrenergic receptor gene proximal promoter

Transcription of the rat alpha1B adrenergic receptor (alpha1B AR) gene is controlled by three promoters (P1, P2, and P3), which generate 2.3-, 2.7-, and 3.3-kb transcripts, respectively. The expression of the 2.3-kb mRNA species is tissue-specific. To explore the underlying mechanism, the P1 promoter was analyzed. DNase I footprinting of the P1 promoter yielded three protected regions: Plfl(-49 to -62); P1f2 (-73 to -90), and P1f3 (-95 to -115). Sequence analysis of P1f3 revealed the presence of an SV40 core C enhancer-like element. In gel mobility shift assays, P1f3 was found to bind a sequence specific protein, which was competed away by a SV40 core C enhancer consensus oligonucleotide. Mutations of this enhancer-like core sequence within P1f3 significantly reduced specific protein binding to P1f3 and inhibited P1 promoter activity. The distribution of the protein which binds to P1f3 is restricted. These findings suggest that the P1 promoter is controlled by a cell-type-specific transcription factor, which may account for the tissue-specific expression of 2.3-kb rat alpha1B AR mRNA species.

Protein kinase C-mediated down-regulation of beta1-adrenergic receptor gene expression in rat C6 glioma cells

In the current study, we investigated the mechanism by which protein kinase C (PKC) regulates the expression of beta1-adrenergic receptor (beta1AR) mRNA in rat C6 glioma cells. Exposure of the cells to 4beta-phorbol-12-myristate-13-acetate (PMA), an activator PKC, resulted in a down-regulation of both beta1AR binding sites and mRNA levels in a time- and concentration-dependent manner. This effect was not observed with phorbol esters that do not activate PKC and was blocked by bisindolylmaleimide, a specific PKC inhibitor. Activation of PKC did not reduce the half-life of beta1AR mRNA but significantly decreased the activity of the beta1AR promoter, as determined by reporter analysis. A putative response element, with partial homology to a consensus cAMP response element, was identified by mutation analysis of the promoter at positions -343 to -336, relative to the translational start site. Mutation of this putative regulatory element, referred to as a beta1AR-PKC response element, completely blocked the PKC-mediated down-regulation of beta1AR promoter activity. Gel mobility shift analysis detected two specific bands when C6 cell extracts were incubated with a labeled DNA probe containing the beta1AR-PKC response element sequence. Formation of one of these bands was inhibited by an oligonucleotide probe containing a consensus CRE and disrupted by an antibody for cAMP response element binding protein. Based on these studies, we propose that the PKC-induced down-regulation of beta1AR gene transcription in C6 cells is mediated in part by a cAMP response element binding protein-dependent mechanism acting on a novel response element.

Both the cyclic AMP response element and the activator protein 2 binding site mediate basal and cyclic AMP-induced transcription from the dominant promoter of the rat alpha 1B-adrenergic receptor gene in DDT1MF-2 cells

cAMP markedly increases alpha 1B adrenergic receptor (alpha 1B-AR) expression in FRTL-5 and PC C13 rat thyroid cells, DDT1MF-2 smooth muscle cells, primary rat hepatocytes, and K9 rat liver cells. Here, we used DDT1MF-2 cells to evaluate further the mechanisms by which cAMP stimulates alpha 1B-AR expression. Receptor binding assays, Northern blotting, and nuclear run-on analyses demonstrated that forskolin (1 microM) in the presence of isobutylmethylxanthine (0.25 mM) increased alpha 1B-AR numbers, mRNA level, and gene transcription rate by 2.3 +/- 0.2-, 2.5 +/- 0.3-, and 3.5 +/- 0.2-fold over control, respectively. Dibutyryl cAMP (1 mM) plus isobutylmethylxanthine (0.25 mM) also enhanced alpha 1B-AR density by 2.7 +/- 0.1-fold over control. Further experiments demonstrated that the induction of alpha 1B-AR by forskolin requires new protein synthesis and is protein kinase A dependent. In DDT1MF-2 cells transfected with alpha 1B-AR gene P2 promoter/CAT constructs, both forskolin and dibutyryl cAMP significantly increased P2 promoter activity. The P2 promoter region of the rat alpha 1B-AR gene (-813 to -432) contains a cAMP response element (CRE) (-444 to -437) and an AP2 binding site (-647 to -638). Mutations in either one of these elements alone led to a decrease in both basal and cAMP-induced P2 promoter activity. Mutations in both elements caused a further inhibition of basal transcription and a complete block of cAMP-induced P2 promoter activity. Direct binding of purified activator protein 2 (AP2) to the AP2 element in the P2 promoter was reported previously. Gel mobility shift and super-shift assays using liver nuclear extracts from either rat liver or DDT1MF-2 cells demonstrated that the CRE in the alpha 1B-AR gene bound CRE binding protein. These data indicate that both the CRE and the AP2 element in the P2 promoter contribute to basal as well as cAMP-induced transcription of the alpha 1B-AR gene in DDT1MF-2 cells.

Alpha-adrenoceptors and vascular regulation: molecular, pharmacologic and clinical correlates

This manuscript is intended to provide a comprehensive review of the alpha-adrenoceptors (ARs) and their role in vascular regulation. The historical development of the concept of receptors and the division of the alpha-ARs into alpha 1 and alpha 2 subtypes is traced. Emphasis will be placed on current understanding of the specific contribution of discrete alpha 1- and alpha 2-AR subtypes in the regulation of the vasculature, selective agonists and antagonists for these receptors, the second messengers utilized by these receptors, the myoplasmic calcium pathways activated to initiate smooth muscle contraction, as well as the clinical uses of agonists and antagonists that work at these receptors. New information is presented that deals with the molecular aspects of ligand interactions with specific subdomains of these receptors, as well as mRNA distribution and the regulation of alpha 1- and alpha 2-AR gene transcription and translation.

Sp1-mediated transcriptional activation from the dominant promoter of the rat alpha1B adrenergic receptor gene in DDT1MF-2 cells

In the rat liver, NF1 and CP1 bind to the major P2 promoter of the alpha1B adrenergic receptor gene to generate footprint II. Here we show that, in DDT1MF-2 smooth muscle cells, the major protein bound to footprint II is not NF1 but Sp1, which binds to the 5'-portion of the footprint II sequence (footprint IIb). Mutational analyses demonstrate that the CCCGCG sequence in footprint IIb is critical for Sp1 binding and P2 promoter activity. A second GC box in the P2 promoter also binds the Sp1 protein and contributes to the P2 promoter activity. Gel shift assays indicate that footprint II can bind Sp1, NF1, and CP1, and that the binding of these 3 proteins is mutually exclusive. This is also indicated by the results of functional cotransfection experiments, where transient overexpression of NF1 and Sp1 together caused a similar increase in the activity of a P2/CAT reporter construct as overexpression of either Sp1 or NF1 alone, indicating lack of additivity. The preferential interaction of footprint II with Sp1 in DDT1MF-2 cells and NF1 in liver appears to be due to low levels of NF1 expression in DDT1MF-2 cells and low levels of Sp1 in liver. These observations suggest that NF1 and Sp1 are the major transcription factors involved in controlling the P2 promoter in liver versus DDT1MF-2 cells, respectively, which may be one of the mechanisms responsible for the complex tissue-specific regulation of the expression of the alpha1B adrenergic receptor gene.

Characterization of the alpha1B-adrenergic receptor gene promoter region and hypoxia regulatory elements in vascular smooth muscle

We previously demonstrated that alpha1B-adrenergic receptor (AR) gene transcription, mRNA, and functionally coupled receptors increase during 3% O2 exposure in aorta, but not in vena cava smooth muscle cells (SMC). We report here that alpha1BAR mRNA also increases during hypoxia in liver and lung, but not heart and kidney. A single 2.7-kb alpha1BAR mRNA was detected in aorta and vena cava during normoxia and hypoxia. The alpha1BAR 5' flanking region was sequenced to -2,460 (relative to ATG +1). Transient transfection experiments identify the minimal promoter region between -270 and -143 and sequence between -270 and -248 that are required for transcription of the alpha1BAR gene in aorta and vena cava SMC during normoxia and hypoxia. An ATTAAA motif within this sequence specifically binds aorta, vena cava, and DDT1MF-2 nuclear proteins, and transcription primarily initiates downstream of this motif at approximately -160 in aorta SMC. Sequence between -837 and -273 conferred strong hypoxic induction of transcription in aorta, but not in vena cava SMC, whereas the cis-element for the transcription factor, hypoxia-inducible factor 1, conferred hypoxia-induced transcription in both aorta and vena cava SMC. These data identify sequence required for transcription of the alpha1BAR gene in vascular SMC and suggest the atypical TATA-box, ATTAAA, may mediate this transcription. Hypoxia-sensitive regions of the alpha1BAR gene also were identified that may confer the differential hypoxic increase in alpha1BAR gene transcription in aorta, but not in vena cava SMC.

Mechanical load opposes angiotensin-mediated decrease in vascular alpha 1-adrenoceptors

alpha 1-Adrenergic receptor contraction of vascular smooth muscle is augmented by increases in angiotensin II and also in several forms of hypertension. Whether angiotensin directly modulates alpha 1-adrenoceptor subtype expression to contribute to this effect is unknown. In a previous study, we demonstrated that increased mechanical load (pressure) per se does not alter expression of alpha 1B- and alpha 1D-adrenoceptors in rat aortic smooth muscle in cell culture, in vitro or in vivo. However, findings in aortic coarctation hypertension suggested that a humoral factor, possibly angiotensin, selectively reduces alpha 1B-adrenoceptors and that increased mechanical load opposes this decrease. The present study examined this hypothesis by determining the effect of angiotensin alone and in the presence of mechanical loading on the expression of alpha 1D- and alpha 1B-adrenergic receptor mRNAs and alpha 1-receptor density in cultured aortic smooth muscle cells. alpha 1D mRNA content, per smooth muscle cell, concentration-dependently decreased after 3 hours of exposure to 0.3 nmol/L to 1 mumol/L angiotensin but by 24 hours had returned to control levels. In contrast, alpha 1B mRNA concentration-dependently declined at a later time (24 hours) and remained decreased at 48 hours to 27 +/- 6% of control with 1 mumol/L angiotensin. Angiotensin also decreased alpha 1-adrenoceptor density in a dose-dependent manner. Angiotensin had no effect on cell number in these confluent, quiescent cells but did increase cell protein and total RNA. This cellular hypertrophy and the decreases in alpha 1-adrenoceptor mRNAs were blocked by the angiotensin type 1 receptor antagonist losartan. Cyclic mechanical loading of smooth muscle cells opposed the angiotensin-mediated hypertrophy and decrease in alpha 1B mRNA expression and alpha 1-adrenergic receptor density. These data suggest that angiotensin and intravascular pressure interact to affect cell growth and expression of alpha 1B-adrenergic receptors by vascular smooth muscle.

Neurotensin agonist induces differential regulation of neurotensin receptor mRNA. Identification of distinct transcriptional and post-transcriptional mechanisms

The binding of neurotensin (NT) to specific receptors triggers the multiple functions that NT exerts in both periphery and brain. By studying the effect of the concentration and time of NT agonist exposure, two separate regulatory mechanisms were detected for the neurotensin receptor (NTR) gene in human colonic adenocarcinoma cells (HT-29). The incubation of cells for 6 h with the NT agonist, JMV 449, resulted in an increase of 270% in NTR mRNA levels. These changes were the direct result of new NTR gene transcription, as indicated by run-on and half-life experiments. In addition, the transcriptional activation of the NTR gene was dependent on NT-receptor complex internalization and de novo protein synthesis. A second response was detected with prolonged exposure to JMV 449. In this case, a decrease of 70% was detected in NTR mRNA levels. Unlike the initial phase, this change was mediated by a post-transcriptional event as the half-life of NTR mRNA from treated cells decreased by 50% as compared with control cells. NT agonist appears to regulate the synthesis of NTR mRNA. In HT-29 cells, this feedback is exerted by a biphasic response. These phases are apparently independent and mediated by two separate mechanisms.

Regulation of pineal alpha1B-adrenergic receptor mRNA: day/night rhythm and beta-adrenergic receptor/cyclic AMP control

Mammalian pineal function is regulated by norepinephrine acting through alpha1beta- and beta1-adrenergic receptors (ARs). Noradrenergic stimulation of alpha1beta-ARs potentiates the beta1-AR-driven increase in cAMP, serotonin N-acetyltransferase, and melatonin production. In the present study, we describe a 3-fold daily rhythm in mRNA-encoding alpha1beta-ARs in the pineal gland, with a peak at midnight. Pharmacological studies indicate that this increase in alpha1beta-AR mRNA is due to activation of beta-ARs. Second messenger studies indicate that alpha1beta-AR mRNA is increased by agents that increase cAMP, including dibutyryl cAMP, cholera toxin, forskolin, or vasoactive intestinal peptide. These observations indicate that alpha1beta-AR mRNA can be physiologically regulated by a beta-AR-dependent enhancement of cAMP. It also was observed that in vivo and in vitro changes in alpha1beta-AR mRNA are not accompanied by similar changes in alpha1beta-AR binding, indicating that turnover of alpha1beta-AR protein is significantly slower than that of alpha1beta-AR mRNA and that post-transcriptional mechanisms play an important role in regulating alpha1beta-AR binding.

Recent advances in the molecular pharmacology of the alpha 1-adrenergic receptors

This review is intended to discuss recent developments in the molecular pharmacology of the alpha 1-adrenergic receptor (alpha 1-AR) subtypes. After a brief historical development, we will focus on the more contemporary issues having to do with this receptor family. Emphasis will be put on recent data regarding the cloning, nomenclature, signalling mechanisms, and genomic organization of the alpha 1-AR subtypes. We will also highlight recent mutational studies that identify key amino acid residues involved in ligand binding, as well as the role of the alpha 1-AR subtypes in regulating physiologic processes.

Regulation of hamster alpha 1B-adrenoceptors expressed in Chinese hamster ovary cells

Chinese hamster ovary (CHO) cells were stably transfected to express the hamster alpha 1B-adrenoeceptor, and the function and agonist-induced regulation of the binding properties of these receptors were characterized. The cells expressed approximately 230,000 receptors per cell, with a KD for [3H]prazosin of 140 pM. In assays of competition by epinephrine for [3H]prazosin binding to receptors on intact cells, 88% of the receptors were in a low affinity form. The protein kinase C activator phorbol 12-myristate, 13-acetate (PMA) did not further increase the fraction in the low affinity form, but the protein kinase C inhibitor staurosporine reduced the low affinity fraction to 51%. In sucrose density gradient centrifugation assays of receptor internalization, the percentage of receptors in the light vesicle fraction was 25% for control cells, 53% for epinephrine-pretreated cells, 44% for PMA-pretreated cells, and 53% for cells pretreated with epinephrine plus PMA. Staurosporine completely blocked PMA-induced internalization, but only partially inhibited epinephrine-induced internalization. These results suggest a relationship between low affinity binding and internalization for alpha 1B-adrenoceptors and the involvement of protein kinase C in both processes. Longer-term (24 h) exposure of cells to epinephrine induced an unexpected up-regulation of receptor density of approximately 2-fold that was accompanied by an increase in maximal agonist-stimulated phosphoinositide turnover. These studies document several regulatory differences between alpha 1B-adrenoceptors expressed in transfected CHO cells and those natively expressed in DDT1 MF-2 hamster smooth muscle cells, and they provide additional information on the molecular mechanisms involved in agonist-induced regulation of alpha 1B-adrenoceptors.

Regulation of vascular smooth muscle growth by alpha 1-adrenoreceptor subtypes in vitro and in situ

Rat aorta smooth muscle cells which express all three alpha 1-adrenoreceptors (alpha 1A, alpha 1B and alpha 1D) were used to determine the effect of stimulation of alpha 1-adrenergic receptor subtypes on cell growth. "Combined" alpha 1-adrenoreceptor subtype stimulation with norepinephrine alone caused a concentration-dependent, prazosin-sensitive increase in protein content and synthesis: 48 h of stimulation at 1 microM increased cell protein to 216 +/- 40% of time-matched controls (p = 0.008) and RNA to 140 +/- 13% (p = 0.03); protein synthesis increased to 167 +/- 13% (p < 0.01) after 24 h. Stimulation with norepinephrine plus the selective alpha 1A/alpha 1D antagonist 5-methylurapidil produced greater increases in alpha-actin mRNA (270 +/- 40% at 8 h; p = 0.007), total cell protein (220 +/- 45% at 24 h; p = 0.004), and RNA (135 +/- 8% at 24 h; p = 0.01). These effects were prevented by pretreatment with the selective alpha 1B antagonist chloroethylclonidine. Comparable results were obtained for intact aortae. Stimulation with norepinephrine plus 5-methylurapidil increased (p < 0.05) tissue protein, RNA, dry weight, and alpha-actin mRNA; and as in culture cells, combined stimulation with norepinephrine alone attenuated these responses. By comparison, adventitia (fibroblasts) was unaffected. Removal of endothelial cells had no effect. alpha 1B mRNA decreased by 42 +/- 12% (p = 0.01) in cultured cells during combined alpha 1-adrenoreceptor stimulation and by 23 +/- 8% (p = 0.03) for intact aorta. alpha 1D and beta-actin mRNA were unchanged in cultured cells, aorta media, and adventitia. These findings suggest that prolonged stimulation of chloroethylclonidine-sensitive, possibly alpha 1B-adrenoceptors induces hypertrophy of arterial smooth muscle cells and that stimulation of 5-methylurapidil-sensitive, non-alpha 1B-adrenoreceptors attenuates this growth response.

Does ischemic preconditioning trigger translocation of protein kinase C in the canine model?

BACKGROUND

Brief episodes of ischemia protect or "precondition" the heart and reduce the size of infarcts caused by subsequent sustained coronary artery occlusion, yet the mechanisms responsible for this cardioprotection remain unresolved. We tested the theory that translocation of protein kinase C (PKC) to the myocyte membranes, initiated in response to brief preconditioning ischemia and manifest during the initial minutes of the sustained occlusion, mediates this phenomenon by attempting to (1) blunt the cardioprotective effects of preconditioning by administration of the PKC inhibitors H-7 and polymyxin B, (2) visualize by fluorescence staining and confocal microscopy changes in the amount or location of PKC, and (3) quantify by incorporation of 32P into PKC-specific peptide changes in the subcellular distribution of PKC in preconditioned versus control hearts.

METHODS AND RESULTS

In the first three limbs of this study, anesthetized open-chest dogs underwent four 5-minute episodes of preconditioning ischemia or a comparable control period before 1 hour of sustained occlusion and 4 to 5 hours of reperfusion. Collateral blood flow was assessed with radioactive microspheres; area at risk (AR) was delineated by injection of blue dye; and the area of necrosis (AN) was measured by tetrazolium staining. AN/AR was smaller in preconditioned versus control dogs that received no treatment (6 +/- 2% versus 19 +/- 3%, P < .01), H-7 (2 +/- 2% versus 14 +/- 5%, P < .02), or polymyxin B (10 +/- 3% versus 29 +/- 5%, P < .01) during the preconditioning or control period. Additional dogs underwent four 5-minute episodes of ischemia, with biopsies obtained at baseline and after the first and fourth occlusions. Frozen sections were stained with a fluorescent probe for active PKC and viewed with confocal microscopy. No differences in the intensity or distribution of fluorescence staining were observed after brief ischemia compared with baseline. Finally, myocardial samples were obtained from dogs subjected to four 5-minute episodes of preconditioning ischemia and time-matched sham-operated controls. Incorporation of 32P into PKC-specific peptide revealed no quantitative difference in the subcellular distribution of PKC between control and preconditioned cohorts.

CONCLUSIONS

H-7 and polymyxin B did not blunt the reduction in infant size achieved with ischemic preconditioning. Neither fluorescence staining and confocal microscopy nor biochemical quantification revealed evidence of preconditioning-induced translocation of PKC to the cell membranes. These results fail to support the hypothesis that translocation of PKC, triggered by preconditioning ischemia, is an important mechanism for the reduction in infarct size seen with preconditioning in the dog model.

The rat alpha 1B adrenergic receptor gene middle promoter contains multiple binding sites for sequence-specific proteins including a novel ubiquitous transcription factor

Transcription of the rat alpha 1B adrenergic receptor (alpha 1BAR) gene in the liver is controlled by three promoters that generate three mRNAs. The middle promoter (P2), located between -432 and -813 base pairs upstream from the translation start codon and lacking a TATA box, is responsible for generating the major, 2.7-kilobase mRNA-species expressed in many tissues (Gao, B., and Kunos, G. (1994) J. Biol. Chem. 269, 15762-15767). DNase I footprinting using rat liver nuclear extracts identified three protected regions in P2: footprint I (-432 to -452), footprint II (-490 to -540), and footprint III (-609 to -690). Putative response elements in footprints I and III were not analyzed except the AP2 binding site in footprint III, which could be protected by purified AP2 protein. Footprint II contains four sites corresponding to half of the NF-I consensus sequence, but DNA mobility shift assays indicate that this footprint binds two proteins distinct from NF-I: a ubiquitous CP1-related factor and another novel factor, termed alpha-Adrenergic Receptor Transcription Factor (alpha ARTF), which binds to two separate sites in this region. The alpha ARTF is widely distributed, with the highest amounts found in brain, followed by liver, kidney, lung, and spleen, but no detectable activity in heart. Deletions of alpha ARTF binding sites nearly abolished P2 promoter activity, which suggests that the alpha ARTF is essential for the transcription of the alpha 1BAR gene in most tissues.

Regulation of alpha 1B-adrenergic receptor half-life: protein synthesis dependence and effect of norepinephrine

Agonist-mediated down-regulation of alpha 1B-adrenergic receptors (AAR) may involve a decrease in synthesis, an increase in degradation, or a combination of the two mechanisms. Norepinephrine (NE) causes downregulation of AAR in rabbit aortic smooth muscle cells (RbSMC). To study the role of receptor degradation in this phenomenon, we studied the half-life (t1/2) of the AAR under basal conditions and during exposure to NE. We first determined the disappearance rate of AAR in the presence of cycloheximide, a commonly used method for measuring receptor t1/2. By this approach, the basal t1/2 was surprisingly long, 172 +/- 20 h. In contrast, the t1/2 in NE-treated cells was 11.8 +/- 0.3 h, suggesting that either NE decreased the t1/2 of AAR or cycloheximide increased the basal t1/2. To distinguish these possibilities, basal receptor t1/2 was determined by a second, independent method based on the repopulation of AAR after irreversible alkylation with chloroethylclonidine. This approach indicated a basal t1/2 (7.4 +/- 0.2 h) that was similar to the t1/2 with NE but more than 20-fold shorter than the t1/2 with cycloheximide. We conclude that in RbSMC NE-induced downregulation of AAR occurs without a decrease in receptor t1/2. The unexpected finding that cycloheximide markedly increases the basal t1/2 of the AAR further indicates that the t1/2 of the AAR is regulated, at least in part, by a short-lived protein that may regulate and/or mediate receptor degradation.

Enhanced transcription of the human alpha 2A-adrenergic receptor gene by cAMP: evidence for multiple cAMP responsive sequences in the promoter region of this gene

Expression of the human alpha 2A-adrenergic receptor gene is induced by cAMP. The present studies were designed to define potential cAMP-responsive enhancer elements (CREs) in the promoter region of this gene. Regions from the 5'-flanking sequences of the gene were placed in a promoterless vector with a chloramphenicol acetyltransferase (CAT) reporter gene, and cAMP-stimulated CAT activity was assayed in transfected JEG-3 placental carcinoma cells. Enhancer activity responsive to cAMP was located in DNA sequences both upstream and downstream from the endogenous promoter region. Within the upstream sequences there is a putative "core sequence" homologous to the eight base CRE consensus palindrome, but this region did not function independently as a CRE enhancer; additional upstream sequences were required to provide significant enhancer activity in response to cAMP. Regulation of expression of the alpha 2A-adrenergic gene by cAMP is complex and involves multiple and likely novel DNA sequences.