Transcriptional responses to growth factor and G protein-coupled receptors in PC12 cells: comparison of alpha(1)-adrenergic receptor subtypes

Endogenous N-terminal Domain Cleavage Modulates α1D-Adrenergic Receptor Pharmacodynamics

The α1D-adrenergic receptor (ADRA1D) is a key regulator of cardiovascular, prostate, and central nervous system functions. This clinically relevant G protein-coupled receptor has proven difficult to study, as it must form an obligate modular homodimer containing the PDZ proteins scribble and syntrophin or become retained in the endoplasmic reticulum as non-functional protein. We previously determined that targeted removal of the N-terminal (NT) 79 amino acids facilitates ADRA1D plasma membrane expression and agonist-stimulated functional responses. However, whether such an event occurs in physiological contexts was unknown. Herein, we report the ADRA1D is subjected to innate NT processing in cultured human cells. SNAP near-infrared imaging and tandem-affinity purification revealed the ADRA1D is expressed as both full-length and NT truncated forms in multiple human cell lines. Serial truncation mapping identified the cleavage site as Leu(90)/Val(91) in the 95-amino acid ADRA1D NT domain, suggesting human cells express a Δ1-91 ADRA1D species. Tandem-affinity purification MS/MS and co-immunoprecipitation analysis indicate NT processing of ADRA1D is not required to form scribble-syntrophin macromolecular complexes. Yet, label-free dynamic mass redistribution signaling assays demonstrate that Δ1-91 ADRA1D agonist responses were greater than WT ADRA1D. Mutagenesis of the cleavage site nullified the processing event, resulting in ADRA1D agonist responses less than the WT receptor. Thus, we propose that processing of the ADRA1D NT domain is a physiological mechanism employed by cells to generate a functional ADRA1D isoform with optimal pharmacodynamic properties.

Nerve growth factor enhances the CRE-dependent transcriptional activity activated by nobiletin in PC12 cells

Prevention and treatment of Alzheimer disease are urgent problems for elderly people in developed countries. We previously reported that nobiletin, a poly-methoxylated flavone from the citrus peel, improved the symptoms in various types of animal models of memory loss and activated the cAMP responsive element (CRE)-dependent transcription in PC12 cells. Nobiletin activated the cAMP/PKA/MEK/Erk/MAPK signaling pathway without using the TrkA signaling activated by nerve growth factor (NGF). Here, we examined the effect of combination of nobiletin and NGF on the CRE-dependent transcription in PC12 cells. Although NGF alone had little effect on the CRE-dependent transcription, NGF markedly enhanced the CRE-dependent transcription induced by nobiletin. The NGF-induced enhancement was neutralized by a TrkA antagonist, K252a. This effect of NGF was effective on the early signaling event elicited by nobiletin. These results suggested that there was crosstalk between NGF and nobiletin signaling in activating the CRE-dependent transcription in PC12 cells.

The stress of maternal separation causes misprogramming in the postnatal maturation of rat resistance arteries

We examined the effect of stress in the first 2 wk of life induced by brief periods of daily maternal separation on developmental programming of rat small resistance mesenteric arteries (MAs). In MAs of littermate controls, mRNAs encoding mediators of vasoconstriction, including the α1a-adrenergic receptor, smooth muscle myosin heavy chain, and CPI-17, the inhibitory subunit of myosin phosphatase, increased from after birth through sexual [postnatal day (PND) 35] and full maturity, up to ∼80-fold, as measured by quantitative PCR. This was commensurate with two- to fivefold increases in maximum force production to KCl depolarization, calcium, and the α-adrenergic agonist phenylephrine, and increasing systolic blood pressure. Rats exposed to maternal separation stress as neonates had markedly accelerated trajectories of maturation of arterial contractile gene expression and function measured at PND14 or PND21 (weaning), 1 wk after the end of the stress protocol. This was suppressed by the α-adrenergic receptor blocker terazosin (0.5 mg·kg ip(-1)·day(-1)), indicating dependence on stress activation of sympathetic signaling. Due to the continued maturation of MAs in control rats, by sexual maturity (PND35) and into adulthood, no differences were observed in arterial function or response to a second stressor in rats stressed as neonates. Thus early life stress misprograms resistance artery smooth muscle, increasing vasoconstrictor function and blood pressure. This effect wanes in later stages, suggesting plasticity during arterial maturation. Further studies are indicated to determine whether stress in different periods of arterial maturation may cause misprogramming persisting through maturity and the potential salutary effect of α-adrenergic blockade in suppression of this response.

Temporal Dissection of Rate Limiting Transcriptional Events Using Pol II ChIP and RNA Analysis of Adrenergic Stress Gene Activation

In mammals, increasing evidence supports mechanisms of co-transcriptional gene regulation and the generality of genetic control subsequent to RNA polymerase II (Pol II) recruitment. In this report, we use Pol II Chromatin Immunoprecipitation to investigate relationships between the mechanistic events controlling immediate early gene (IEG) activation following stimulation of the α_1a-Adrenergic Receptor expressed in rat-1 fibroblasts. We validate our Pol II ChIP assay by comparison to major transcriptional events assessable by microarray and PCR analysis of precursor and mature mRNA. Temporal analysis of Pol II density suggests that reduced proximal pausing often enhances gene expression and was essential for Nr4a3 expression. Nevertheless, for Nr4a3 and several other genes, proximal pausing delayed the time required for initiation of productive elongation, consistent with a role in ensuring transcriptional fidelity. Arrival of Pol II at the 3’ cleavage site usually correlated with increased polyadenylated mRNA; however, for Nfil3 and probably Gprc5a expression was delayed and accompanied by apparent pre-mRNA degradation. Intragenic pausing not associated with polyadenylation was also found to regulate and delay Gprc5a expression. Temporal analysis of Nr4a3, Dusp5 and Nfil3 shows that transcription of native IEG genes can proceed at velocities of 3.5 to 4 kilobases/min immediately after activation. Of note, all of the genes studied here also used increased Pol II recruitment as an important regulator of expression. Nevertheless, the generality of co-transcriptional regulation during IEG activation suggests temporal and integrated analysis will often be necessary to distinguish causative from potential rate limiting mechanisms.

Chemogenomic profiling of endogenous PARK2 expression using a genome-edited coincidence reporter

Parkin, an E3 ubiquitin ligase, is a central mediator of mitochondrial quality control and is linked to familial forms of Parkinson's disease (PD). Removal of dysfunctional mitochondria from the cell by Parkin is thought to be neuroprotective, and pharmacologically increasing Parkin levels may be a novel therapeutic approach. We used genome-editing to integrate a coincidence reporter into the PARK2 gene locus of a neuroblastoma-derived cell line and developed a quantitative high-throughput screening (qHTS) assay capable of accurately detecting subtle compound-mediated increases in endogenous PARK2 expression. Interrogation of a chemogenomic library revealed diverse chemical classes that up-regulate the PARK2 transcript, including epigenetic agents, drugs controlling cholesterol biosynthesis, and JNK inhibitors. Use of the coincidence reporter eliminated wasted time pursuing reporter-biased false positives accounting for ∼2/3 of the actives and, coupled with titration-based screening, greatly improves the efficiency of compound selection. This approach represents a strategy to revitalize reporter-gene assays for drug discovery.

Identification of two novel α1-AR agonists using a high-throughput screening model

α₁-Adrenoceptors (ARs; 1A, 1B, and 1D) have been determined to perform different prominent functions in the physiological responses of the sympathetic nervous system. A high-throughput screening assay (HTS) was set up to detect α₁-AR subtype-selective agonists by a dual-luciferase reporter assay in HEK293 cells. Using the HTS assay, two novel compounds, CHE3 and CHK3, were discovered as α₁-ARs agonists in α₁-ARs expressed in HEK293 cells. These compounds also showed moderate/weak anti-proliferative activities against tested cancer cell lines. The HTS assay proposed in this study represents a potential method for discovering more α₁-AR subtype-selective ligands.

Minimal NF-κB activity in neurons

Nuclear factor-kappa B (NF-κB) is a ubiquitous transcription factor that regulates immune and cell-survival signaling pathways. NF-κB has been reported to be present in neurons wherein it reportedly responds to immune and toxic stimuli, glutamate, and synaptic activity. However, because the brain contains many cell types, assays specifically measuring neuronal NF-κB activity are difficult to perform and interpret. To address this, we compared NF-κB activity in cultures of primary neocortical neurons, mixed brain cells, and liver cells, employing Western blot of NF-κB subunits, electrophoretic mobility shift assay (EMSA) of nuclear κB DNA binding, reporter assay of κB DNA binding, immunofluorescence of the NF-κB subunit protein p65, quantitative real-time polymerase chain reaction (PCR) of NF-κB-regulated gene expression, and enzyme-linked immunosorbent assay (ELISA) of produced proteins. Assay of p65 showed its constitutive presence in cytoplasm and nucleus of neurons at levels significantly lower than in mixed brain or liver cells. EMSA and reporter assays showed that constitutive NF-κB activity was nearly absent in neurons. Induced activity was minimal--many fold lower than in other cell types, as measured by phosphorylation and degradation of the inhibitor IκBα, nuclear accumulation of p65, binding to κB DNA consensus sites, NF-κB reporting, or induction of NF-κB-responsive genes. The most efficacious activating stimuli for neurons were the pro-inflammatory cytokines tumor necrosis factor α (TNFα) and interleukin-beta (IL-β). Neuronal NF-κB was not responsive to glutamate in most assays, and it was also unresponsive to hydrogen peroxide, lipopolysaccharide, norepinephrine, ATP, phorbol ester, and nerve growth factor. The chemokine gene transcripts CCL2, CXCL1, and CXCL10 were strongly induced via NF-κB activation by TNFα in neurons, but many candidate responsive genes were not, including the neuroprotective genes SOD2 and Bcl-xL. Importantly, the level of induced neuronal NF-κB activity in response to TNFα or any other stimulus was lower than the level of constitutive activity in non-neuronal cells, calling into question the functional significance of neuronal NF-κB activity.

NGF upregulates the plasminogen activation inhibitor-1 in neurons via the calcineurin/NFAT pathway and the Down syndrome-related proteins DYRK1A and RCAN1 attenuate this effect

BACKGROUND

Plasminogen activator inhibitor 1 (PAI-1) is a key regulator of the plasminogen activation system. Although several lines of evidence support a significant role of PAI-1 in the brain, the regulation of its expression in neurons is poorly understood. In the present study we tested the hypothesis that NGF induces the upregulation of PAI-1 via the calcineurin/nuclear factor of activated T cells (NFAT) pathway and analysed whether the overexpression of the Down syndrome-related proteins DYRK1A and RCAN1 modulated the effect of NGF on PAI-1 expression.

RESULTS

NGF upregulated PAI-1 mRNA levels in primary mouse hippocampal neurons cultured for 3 days in vitro and in the rat pheochromocytoma cell line PC12. Reporter gene assays revealed that NGF activated the calcineurin/NFAT pathway in PC12 cells. Induction of PAI-1 by NGF was sensitive to the calcineurin inhibitor FK506 and the specific inhibition of NFAT activation by the cell permeable VIVIT peptide. Activation of calcineurin/NFAT signalling through other stimuli resulted in a much weaker induction of PAI-1 expression, suggesting that other NGF-induced pathways are involved in PAI-1 upregulation. Overexpression of either DYRK1A or RCAN1 negatively regulated NFAT-dependent transcriptional activity and reduced the upregulation of PAI-1 levels by NGF.

CONCLUSION

The present results show that the calcineurin/NFAT pathway mediates the upregulation of PAI-1 by NGF. The negative effect of DYRK1A and RCAN1 overexpression on NGF signal transduction in neural cells may contribute to the altered neurodevelopment and brain function in Down syndrome.

Ephedrine induced thioredoxin-1 expression through β-adrenergic receptor/cyclic AMP/protein kinase A/dopamine- and cyclic AMP-regulated phosphoprotein signaling pathway

Ephedrine (Eph) is one of alkaloids that has been isolated from the ancient herb ephedra (ma huang) and is used as the treatment of asthma, hypotension and fatigue. However, its molecular mechanism remains unknown. Thioredoxin-1 (Trx-1) is a redox regulating protein, which has various biological activities, including regulating transcription factor DNA binding activity and neuroprotection. In this study, we found that Eph induced Trx-1 expression, which was inhibited by propranolol (β-adrenergic receptor inhibitor), but not by phenoxybenzamine (α-adrenergic receptor inhibitor) in rat pheochromocytoma PC12 cells. Moreover, the increase of Trx-1 expression was inhibited by SQ22536 (adenylyl cyclase inhibitor) and H-89 (protein kinase A inhibitor). Interestingly, the effect of Eph on dopamine- and cyclic AMP-regulated phosphoprotein (DARPP-32) was similar to Trx-1. Thus, the relationship between Trx-1 and DARPP-32 was further studied. The DARPP-32 siRNA significantly reduced Trx-1 expression, but Trx-1 siRNA did not exchange DARPP-32. These results suggested that Eph induced the Trx-1 expression through β-adrenergic receptor/cyclic AMP/PKA/DARPP-32 signaling pathway. Furthermore, Eph induced PKA-mediated cyclic AMP response element-binding protein (CREB) phosphorylation. Down-regulation of DARPP-32 expression decreased phosphorylated CREB. In addition, Eph had a significant effect on the viability of the rat pheochromocytoma PC12 cells through β-adrenergic receptors. Trx-1 may play an important role in the actions of Eph.

Norepinephrine promotes the β1-integrin-mediated adhesion of MDA-MB-231 cells to vascular endothelium by the induction of a GROα release

The migratory activity of tumor cells and their ability to extravasate from the blood stream through the vascular endothelium are important steps within the metastasis cascade. We have shown previously that norepinephrine is a potent inducer of the migration of MDA-MB-468 human breast carcinoma cells and therefore investigated herein, whether the interaction of these cells as well as MDA-MB-231 and MDA-MB-435S human breast carcinoma cells with the vascular endothelium is affected by this neurotransmitter as well. By means of a flow-through assay under physiologic flow conditions, we show that norepinephrine induces an increase of the adhesion of the MDA-MB-231 cells, but not of MDA-MB-468 and MDA-MB-435S cells to human pulmonary microvascular endothelial cells (HMVEC). The adhesion of MDA-MB-231 cells was based on a norepinephrine-mediated release of GROα from HMVECs. GROα caused a β1-integrin-mediated increase of the adhesion of MDA-MB-231 cells. Most interestingly, this effect of norepinephrine, similar to the aforementioned induction of migration in MDA-MB-468 cells, was mediated by β-adrenergic receptors and therefore abrogated by β-blockers. In conclusion, norepinephrine has cell line-specific effects with regard to certain steps of the metastasis cascade, which are conjointly inhibited by clinically established β-blockers. Therefore, these results may deliver a molecular explanation for our recently published retrospective data analysis of patients with breast cancer which shows that β-blockers significantly reduce the development of metastases.

Chromogranin B in heart failure: a putative cardiac biomarker expressed in the failing myocardium

BACKGROUND

Chromogranin B (CgB) is a member of the granin protein family. Because CgB is often colocalized with chromogranin A (CgA), a recently discovered cardiac biomarker, we hypothesized that CgB is regulated during heart failure (HF) development.

METHODS AND RESULTS

CgB regulation was investigated in patients with chronic HF and in a post-myocardial infarction HF mouse model. Animals were phenotypically characterized by echocardiography and euthanized 1 week after myocardial infarction. CgB mRNA levels were 5.2-fold increased in the noninfarcted part of the left ventricle of HF animals compared with sham-operated animals (P<0.001). CgB mRNA level in HF animals correlated closely with animal lung weight (r=0.74, P=0.04) but not with CgA mRNA levels (r=0.20, P=0.61). CgB protein levels were markedly increased in both the noninfarcted (110%) and the infarcted part of the left ventricle (70%) but unaltered in other tissues investigated. Myocardial CgB immunoreactivity was confined to cardiomyocytes. Norepinephrine, angiotensin II, and transforming growth factor-beta increased CgB gene expression in cardiomyocytes. Circulating CgB levels were increased in HF animals (median levels in HF animals versus sham, 1.23 [interquartile range, 1.03 to 1.93] versus 0.98 [0.90 to 1.04] nmol/L; P=0.003) and in HF patients (HF patients versus control, 1.66 [1.48 to 1.85] versus 1.47 [1.39 to 1.58] nmol/L; P=0.007), with levels increasing in proportion to New York Heart Association functional class (P=0.03 for trend). Circulating CgB levels were only modestly correlated with CgA (r=0.31, P=0.009) and B-type natriuretic peptide levels (r=0.27, P=0.014).

CONCLUSIONS

CgB production is increased and regulated in proportion to disease severity in the left ventricle and circulation during HF development.

DNA synthesis of rat bone marrow mesenchymal stem cells through alpha1-adrenergic receptors

Multipotential bone marrow mesenchymal stem cells (BMSCs) are important in maintaining the microenvironment of the bone marrow (BM). Sympathetic nerves histologically innervate the BM; however, their role remains unclear. In this study, the effects of norepinephrine on DNA synthesis and the related signaling molecules involved in rBMSCs were examined. mRNA levels of the alpha1-adrenergic receptor subtypes increased following norepinephrine stimulation (10(-5) M for 30 min). DNA synthesis increased in dose- and time-dependent manners as determined by [(3)H]thymidine incorporation. Intracellular Ca(2+) concentration and translocation of protein kinase C from the cytosol to the membrane were also found to be elevated in rBMSCs. Phentolamine was able to suppress translocation of PKC. Norepinephrine also induced phosphorylation of ERK1/2, which was prevented by staurosporine treatment. Pretreatment with PD98059 inhibited ERK1/2 phosphorylation and DNA synthesis in rBMSCs. These findings indicate that norepinephrine stimulates DNA synthesis via alpha1-adrenergic receptors and downstream Ca(2+)/PKC and ERK1/2 activation in rBMSCs.

Post-ischemic brain damage: NF-kappaB dimer heterogeneity as a molecular determinant of neuron vulnerability

Nuclear factor-kappaB (NF-kappaB) has been proposed to serve a dual function as a regulator of neuron survival in pathological conditions associated with neurodegeneration. NF-kappaB is a transcription family of factors comprising five different proteins, namely p50, RelA/p65, c-Rel, RelB and p52, which can combine differently to form active dimers in response to external stimuli. Recent research shows that diverse NF-kappaB dimers lead to cell death or cell survival in neurons exposed to ischemic injury. While the p50/p65 dimer participates in the pathogenesis of post-ischemic injury by inducing pro-apoptotic gene expression, c-Rel-containing dimers increase neuron resistance to ischemia by inducing anti-apoptotic gene transcription. We present, in this report, the latest findings and consider the therapeutic potential of targeting different NF-kappaB dimers to limit ischemia-associated neurodegeneration.

Blood pressure is regulated by an alpha1D-adrenergic receptor/dystrophin signalosome

Hypertension is a cardiovascular disease associated with increased plasma catecholamines, overactivation of the sympathetic nervous system, and increased vascular tone and total peripheral resistance. A key regulator of sympathetic nervous system function is the alpha(1D)-adrenergic receptor (AR), which belongs to the adrenergic family of G-protein-coupled receptors (GPCRs). Endogenous catecholamines norepinephrine and epinephrine activate alpha(1D)-ARs on vascular smooth muscle to stimulate vasoconstriction, which increases total peripheral resistance and mean arterial pressure. Indeed, alpha(1D)-AR KO mice display a hypotensive phenotype and are resistant to salt-induced hypertension. Unfortunately, little information exists about how this important GPCR functions because of an inability to obtain functional expression in vitro. Here, we identified the dystrophin proteins, syntrophin, dystrobrevin, and utrophin as essential GPCR-interacting proteins for alpha(1D)-ARs. We found that dystrophins complex with alpha(1D)-AR both in vitro and in vivo to ensure proper functional expression. More importantly, we demonstrate that knock-out of multiple syntrophin isoforms results in the complete loss of alpha(1D)-AR function in mouse aortic smooth muscle cells and abrogation of alpha(1D)-AR-mediated increases in blood pressure. Our findings demonstrate that syntrophin and utrophin associate with alpha(1D)-ARs to create a functional signalosome, which is essential for alpha(1D)-AR regulation of vascular tone and blood pressure.

Roles of c-Src in alpha1B-adrenoceptor phosphorylation and desensitization

1 The role of the protein tyrosine kinase, c-Src, on the function and phosphorylation of alpha1B-adrenoceptors (alpha1B-AR) and their association with G-protein-coupled receptor kinase (GRK) isozymes was studied. 2 Inhibitors of this kinase (PP2 and Src Inhibitor II) decreased ( approximately 50-75%) noradrenaline- (NA) and phorbol myristate acetate-mediated receptor phosphorylation. Expression of a dominant-negative mutant of c-Src similarly reduced receptor phosphorylation induced by the natural agonists, active phorbol esters and endothelin-1 (ET-1). 3 c-Src, GRK2, GRK3 and GRK5 coimmunoprecipitate with alpha1B-ARs in the basal state. In cells treated with NA or phorbol myristate acetate the amount of coimmunoprecipitated GRK2 and GRK3 increased ( approximately 2- to 3-fold), while treatment with ET-1 only augmented the amount of coimmunoprecipitated GRK2 ( approximately 2-fold). The Src inhibitor, PP2, markedly attenuated all these increases. 4 Cell pretreatment with PP2 amplified the increase in intracellular-free calcium observed with NA, in the basal state and after the stimulation (desensitization) induced by ET-1. 5 The data suggest a role of c-Src in alpha1B-AR desensitization/phosphorylation and in the interaction of these ARs with GRKs.

α2-Adrenergic receptors activate cyclic AMP-response element-binding protein through arachidonic acid metabolism and protein kinase A in a subtype-specific manner

On incubation with epinephrine, PC12 cells stably expressing alpha2-adrenergic receptor (alpha2-AR) undergo morphological and biochemical changes characteristic of neuron-like differentiation. The present study shows that alpha2-AR stimulation increases the phosphorylation of the transcription factor cAMP-response element-binding protein (CREB), the activity of a CRE-reporter plasmid and the expression of cyclin D1 with subtype-dependent efficiency (alpha2A approximately alpha2C >> alpha2B). The effects of epinephrine were mimicked by cell exposure to forskolin or to exogenous arachidonic acid (AA) and they were abrogated by prior treatment with the inhibitor of phospholipase C (PLC) (U73122) or the inhibitor of cytochrome P450-dependent epoxygenase, ketoconazole. On the other hand, treatment of the cells with epinephrine caused activation of protein kinase A (PKA), which was fully abolished by ketoconazole. Inhibition of PKA activity with H89 or ketoconazole abolished the effects of epinephrine on CREB, suggesting that activation of the cAMP/PKA pathway by AA epoxy-derivatives is responsible for CREB activation by alpha2-ARs. The effects of epinephrine were unaffected by LY294002. Furthermore, treatment with staurosporine, tyrphostin AG1478, PP1 or PD98059 did not change the extent of CREB phosphorylation but enhanced its transcriptional activity. Altogether, our results demonstrate that, in PC12 cells, the alpha2-AR subtypes cause phosphorylation and activation of CREB through a pathway involving stimulation of PLC, AA release, generation of epoxygenase derivative and increase of PKA activity. They also suggest attenuation of CREB transcriptional activity by mitogen-activated protein kinase, protein kinase C and Src kinases.

Epigenetic regulation of human alpha1d-adrenergic receptor gene expression: a role for DNA methylation in Sp1-dependent regulation

A growing body of evidence implicates alpha1-adrenergic receptors (alpha1ARs) as potent regulators of growth pathways. The three alpha1AR subtypes (alpha1aAR, alpha1bAR, alpha1dAR) display highly restricted tissue expression that undergoes subtype switching with many pathological stimuli, the mechanistic basis of which remains unknown. To gain insight into transcriptional pathways governing cell-specific regulation of the human alpha1dAR subtype, we cloned and characterized the alpha1dAR promoter region in two human cellular models that display disparate levels of endogenous alpha1dAR expression (SK-N-MC and DU145). Results reveal that alpha1dAR basal expression is regulated by Sp1-dependent binding of two promoter-proximal GC boxes, the mutation of which attenuates alpha1dAR promoter activity 10-fold. Mechanistically, chromatin immunoprecipitation data demonstrate that Sp1 binding correlates with expression of the endogenous gene in vivo, correlating highly with alpha1dAR promoter methylation-dependent silencing of both episomally expressed reporter constructs and the endogenous gene. Further, analysis of methylation status of proximal GC boxes using sodium bisulfite sequencing reveals differential methylation of proximal GC boxes in the two cell lines examined. Together, the data support a mechanism of methylation-dependent disruption of Sp1 binding in a cell-specific manner resulting in repression of basal alpha1dAR expression.

PC12 cells regulate inducible cyclic AMP (cAMP) element repressor expression to differentially control cAMP response element-dependent transcription in response to nerve growth factor and cAMP

Both cyclic AMP (cAMP) and nerve growth factor (NGF) have been shown to cause rapid activation of cAMP response element-binding protein (CREB) by phosphorylation of serine 133, but additional regulatory events contribute to CREB-targeted gene expression. Here, we have used stable transfection with a simple cAMP response element (CRE)-driven reporter to address the kinetics of CRE-dependent transcription during neuronal differentiation of PC12 cells. In naive cells, dibutyryl cAMP (dbcAMP) generated a rapid increase in CRE-driven luciferase activity by 5 h that returned to naive levels by 24 h. Luciferase induction after NGF treatment was delayed until 48 h when CRE-driven luciferase expression became TrkA dependent. Blocking histone deacetylase (HDAC) activity accelerated NGF-dependent CRE-driven luciferase expression by at least 24 h and resulted in a sustained cAMP-dependent expression of CRE-driven luciferase beyond 24 h. Inhibition of protein synthesis before stimulation with NGF or dbcAMP indicated that both stimuli induce expression of a transcriptional repressor that delays NGF-dependent and attenuates cAMP-dependent CRE-driven transcription. NGF caused a rapid but transient HDAC-dependent increase in inducible cAMP element repressor (ICER) expression, but ICER expression was sustained with increased cAMP. Depletion of ICER from PC12 cells indicated that HDAC-dependent ICER induction is responsible for the delay in CRE-dependent transcription after NGF treatment.

Selective upregulation of the ADP-ribosyl cyclases CD38 and CD157 by TNF but not by RANK-L reveals differences in downstream signaling

In macrophages and osteoclast precursors, the cytokines TNF and RANK-L induce similar downstream pathways and share some of the same adaptor molecules. However, despite these similarities, no defined signaling schematic has emerged to show how each cytokine favors particular pathways. In this report, we investigate whether TNF and RANK-L differentially regulate ADP-ribosyl cyclases-enzymes that are unique in being crucial for immunological function yet detrimental to osteoclastogenesis. TNF but not RANK-L led to the sustained upregulation of both CD38 and CD157 as demonstrated by real-time PCR and flow cytometry. Further investigation demonstrated that this upregulation was a result of continuous, direct TNF signaling and involved JNK, and more critically PKC and NF-κB. Using this approach allowed us to highlight the relative importance of the PKC, NF-κB, and JNK pathways in actualizing proper outcomes of TNF signaling. Albeit speculative, we believe that differences between TNF- and RANK-l-induced activation of downstream signaling pathways, in particular PKC, are crucial for determining whether progenitor cells become geared for immunity or bone resorption.

The neurotrophic effects of PACAP in PC12 cells: control by multiple transduction pathways

Pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal polypeptide (VIP) are closely related members of the secretin superfamily of neuropeptides expressed in both the brain and peripheral nervous system, and they exhibit neurotrophic and neurodevelopmental effects in vivo. Like the index member of the Trk receptor ligand family, nerve growth factor (NGF), PACAP promotes the differentiation of PC12 cells, a well-established cell culture model, to investigate neuronal differentiation, survival and function. Stimulation of catecholamine secretion and enhanced neuropeptide biosynthesis are effects exerted by PACAP at the adrenomedullary synapse in vivo and on PC12 cells in vitro through stimulation of the specific PAC1 receptor. Induction of neuritogenesis, growth arrest, and promotion of cell survival are effects of PACAP that occur in developing cerebellar, hippocampal and cortical neurons, as well as in the more tractable PC12 cell model. Study of the mechanisms through which PACAP exerts its various effects on cell growth, morphology, gene expression and survival, i.e. its actions as a neurotrophin, in PC12 cells is the subject of this review. The study of neurotrophic signalling by PACAP in PC12 cells reveals that multiple independent pathways are coordinated in the PACAP response, some activated by classical and some by novel or combinatorial signalling mechanisms.

Distinct roles of diverse nuclear factor-kappaB complexes in neuropathological mechanisms

The nuclear transcription factors kappaB (NF-kappaB) function as key regulators of physiological processes in the central nervous system. Aberrant regulation of NF-kappaB can underlie neurological disorders associated with neurodegeneration. A large number of studies have reported a dual role of NF-kappaB in regulating neuron survival in pathological conditions. A recent progress in understanding the mechanisms responsible for opposite effects elicited by NF-kappaB in brain dysfunctions arises from the identification of diverse NF-kappaB complexes specifically involved in the mechanism of neuronal cell death or cell survival. We here discuss the latest findings and consider the therapeutic potential of targeting distinct NF-kappaB complexes for the treatment of neurodegenerative disorders and memory dysfunctions.

Calcium-dependent expression of TNF-α in neural cells is mediated by the calcineurin/NFAT pathway

We report induction of TNF-alpha via the calcium/calcineurin/NFAT pathway in PC12 neural cells. In PC12, expression of TNF-alpha mRNA, protein and TNF-alpha gene promoter activity was induced by co-stimulation with phorbol ester and either calcium ionophore A23187 or the L-type Voltage Gated Calcium Channel agonist Bay K 8644. Pre-treatment with calcineurin inhibitors CsA or FK506 inhibited the dominant calcium-dependent component of this induction, limiting it to the level achieved with phorbol ester alone. Promoter activation by Bay was abolished by nifedipine, a specific inhibitor of L-type Voltage Gated Calcium Channels. Exogenous NFAT protein transactivated the TNF-alpha promoter, and the peptide VIVIT-a specific inhibitor of calcineurin/NFAT binding-blocked calcium-inducible transactivation of the TNF-alpha promoter. Given proposed functions of TNF-alpha in spatial learning, memory and the pathogenesis of neurodegenerative diseases, the data presented suggest an important role for calcineurin/NFAT signaling in these key neurological processes.

The zinc finger-only protein Zfp260 is a novel cardiac regulator and a nuclear effector of alpha1-adrenergic signaling

alpha1-Adrenergic receptors mediate several biological effects of catecholamines, including the regulation of myocyte growth and contractility and transcriptional regulation of the atrial natriuretic factor (ANF) gene whose promoter contains an alpha1-adrenergic response element. The nuclear pathways and effectors that link receptor activation to genetic changes remain poorly understood. Here, we describe the isolation by the yeast one-hybrid system of a cardiac cDNA encoding a novel nuclear zinc finger protein, Zfp260, belonging to the Krüppel family of transcriptional regulators. Zfp260 is highly expressed in the embryonic heart but is downregulated during postnatal development. Functional studies indicate that Zfp260 is a transcriptional activator of ANF and a cofactor for GATA-4, a key cardiac regulator. Knockdown of Zfp260 in cardiac cells decreases endogenous ANF gene expression and abrogates its response to alpha1-adrenergic stimulation. Interestingly, Zfp260 transcripts are induced by alpha1-adrenergic agonists and are elevated in genetic models of hypertension and cardiac hypertrophy. The data identify Zfp260 as a novel transcriptional regulator in normal and pathological heart development and a nuclear effector of alpha1-adrenergic signaling.

Subdivisions of human parietal area 5 revealed by quantitative receptor autoradiography: a parietal region between motor, somatosensory, and cingulate cortical areas

Brodmann's area (BA) 5 of the human superior parietal cortex occupies a central anatomical position between the primary motor (BA 4), somatosensory (area 3b and BA 2), cingulate (area 23c), and superior parietal association cortex (BA 7). We studied the regional and laminar distributions of the binding sites of 12 different neurotransmitter receptors (glutamatergic: AMPA, kainate, NMDA; GABAergic: GABAA, GABAB; cholinergic: muscarinic M2, nicotinic; adrenergic: alpha1, alpha2; serotoninergic: 5-HT1A, 5-HT2; dopaminergic: D1) in human postmortem brains by means of quantitative receptor autoradiography, since the structural and functional aspects of human BA 5 are widely unknown, and previous observations have demonstrated characteristic differences in receptor distribution between motor and somatosensory areas. Binding site densities were measured in the cytoarchitectonically defined BA 5 and surrounding regions. Similarities and differences of receptor distribution between cortical areas were studied by cluster analysis of mean binding site densities averaged over all cortical layers, univariate and multivariate statistics, and by density profiles representing laminar receptor distribution patterns. Based on regional heterogeneities of binding site densities and of the cytoarchitecture within BA 5, we suggest a subdivision into three subareas: medial area 5M, lateral area 5L, and area 5Ci in the region around the cingulate sulcus. BA 5 is therefore a heterogeneous cortical region, comprising three subareas showing receptor expression patterns similar to the adjoining higher order somatosensory, multimodal parietal, or cingulate regions. These findings suggest that human BA 5 constitutes a higher order cortical area, clearly distinct from the primary somatosensory and motor cortex.

The elusive alpha(1D)-adrenoceptor: molecular and cellular characteristics and integrative roles

alpha(1)-Adrenoceptors seem to play key roles in cardiovascular, genitourinary, and central nervous system functions. This review will be focused on alpha(1D)-adrenoceptors. These receptors have intrinsic activity, and many of the more commonly used antagonists are in reality inverse agonists. alpha(1D)-Adrenoceptors are phosphorylated in the basal state, and the natural agonists, adrenaline and noradrenaline, increase their phosphorylation; similar effects are induced by direct activation of protein kinase C and through activation of nonadrenergic receptors. Interestingly, a large proportion of alpha(1D)-adrenoceptors are located in intracellular vesicles. Such intracellular location can be changed to surface expression through the use of inverse agonists and coexpression of alpha(1B)-adrenoceptors, which seem to act as pharmacological chaperons for proper plasma membrane insertion. The alpha(1D)-adrenoceptor amino terminus seems to contain a signal that keeps the receptor intracellularly, but interaction with other proteins may also contribute. The precise relationship between the intrinsic activity, phosphorylation, and intracellular location is currently unknown. alpha(1D)-Adrenoceptor activation induces contraction in a variety of vessels, and a role in the control of blood pressure has been suggested. Studies using young prehypertensive and adult spontaneously hypertensive rats as well as knockout mice suggest that vascular alpha(1D)-adrenoceptors are involved in the genesis/maintenance of hypertension.

Gene deletion of dopamine β-hydroxylase and α1-adrenoceptors demonstrates involvement of catecholamines in vascular remodeling

In vitro studies have shown that stimulation of α1-adrenoceptors (ARs) directly induces proliferation, hypertrophy, and migration of arterial smooth muscle cells and adventitial fibroblasts. In vivo studies confirmed these findings and showed that catecholamine trophic activity becomes excessive after experimental balloon injury and contributes to neointimal growth, adventitial thickening, and lumen loss. However, past studies have been limited by selectivity of pharmacological agents. The aim of this study, in which mice devoid of norepinephrine and epinephrine synthesis [dopamine β-hydroxylase (DBH−/−)] or deficient in α1-AR subtypes expressed in murine carotid (α1B-AR−/− and α1D-AR−/−) were used, was to test the hypothesis that catecholamines contribute to wall hypertrophy after injury. At 3 wk after injury of wild-type mice, lumen area and carotid circumference increased significantly, and hypertrophy of media and adventitia was in excess of that needed to restore circumferential wall stress to normal. In DBH−/− and α1B-AR−/− mice, increases in lumen area, circumference, and hypertrophy of the media and adventitia were reduced by 50–91%, resulting in restoration of wall tension to nearly normal (DBH−/−) or normal (α1B-AR−/−). In contrast, in α1D-AR−/− mice, increases in lumen area, circumference, and wall hypertrophy were unaffected and wall thickening remained in excess of that required to return tension to normal. When examined 5 days after injury, proliferation and leukocyte infiltration were inhibited in DBH−/− mice. These studies suggest that the trophic effects of catecholamines are mediated primarily by α1B-ARs in mouse carotid and contribute to hypertrophic growth after vascular injury.

Transactivation of epidermal growth factor receptor mediates catecholamine-induced growth of vascular smooth muscle

Stimulation of alpha1-adrenoceptors induces proliferation of vascular smooth muscle cells (SMCs) and contributes to arterial remodeling. Although activation of NAD(P)H oxidase and generation of reactive oxygen species (ROS) are required, little is known about this pathway. In this study, we examined the hypothesis that epidermal growth factor receptor (EGFR) transactivation and extracellular regulated kinases (ERK) are involved in alpha1-adrenoceptor-mediated SMC growth. Phenylephrine increased protein synthesis in association with a rapid (< or =5 minutes) and sustained (> or =60 minutes) doubling of phosphorylation of EGFR and ERK1/2, but not p38 or JNK in the media of rat aorta maintained in organ culture. Antagonists of EGFR phosphotyrosine activity (AG-1478) and ERK phosphorylation (PD-98059, U-0126) abolished phenylephrine-induced protein synthesis, whereas antagonists of p38 or JNK phosphorylation had no specific effect. A competitive antagonist (P22) for heparin binding EGF-like growth factor (HB-EGF) blocked phenylephrine-induced protein synthesis, as did downregulation of pro-HB-EGF (CRM197). Phenylephrine-induced protein synthesis was inhibited by neutralizing antibody to HB-EGF and absent in HB-EGF-/- SMCs. Inhibitors of metalloproteinases (BiPS, KB-R7785) also blocked adrenergic growth. The neutralizing antibody against HB-EGF had no effect on the two-fold increase in ROS generation induced by phenylephrine (DCF fluorescence), suggesting that stimulation of NAD(P)H oxidase by alpha1-adrenoceptor occupation precedes HB-EGF release. Cell culture studies confirmed and extended these findings. These data suggest that alpha1-adrenoceptor-mediated SMC growth requires ROS-dependent shedding of HB-EGF, transactivation of EGFR, and activation of the MEK1/2-dependent MAP kinase pathway. This trophic pathway may link sympathetic activity to arterial wall growth in adaptive remodeling and hypertrophic disease.

Nuclear factor of activated T cells balances angiogenesis activation and inhibition

It has been demonstrated that vascular endothelial cell growth factor (VEGF) induction of angiogenesis requires activation of the nuclear factor of activated T cells (NFAT). We show that NFATc2 is also activated by basic fibroblast growth factor and blocked by the inhibitor of angiogenesis pigment epithelial–derived factor (PEDF). This suggests a pivotal role for this transcription factor as a convergence point between stimulatory and inhibitory signals in the regulation of angiogenesis.

We identified c-Jun NH₂-terminal kinases (JNKs) as essential upstream regulators of NFAT activity in angiogenesis. We distinguished JNK-2 as responsible for NFATc2 cytoplasmic retention by PEDF and JNK-1 and JNK-2 as mediators of PEDF-driven NFAT nuclear export.

We identified a novel NFAT target, caspase-8 inhibitor cellular Fas-associated death domain–like interleukin 1β–converting enzyme inhibitory protein (c-FLIP), whose expression was coregulated by VEGF and PEDF. Chromatin immunoprecipitation showed VEGF-dependent increase of NFATc2 binding to the c-FLIP promoter in vivo, which was attenuated by PEDF. We propose that one possible mechanism of concerted angiogenesis regulation by activators and inhibitors may be modulation of the endothelial cell apoptosis via c-FLIP controlled by NFAT and its upstream regulator JNK.

α1-Adrenergic receptor subtypes: non-identical triplets with different dancing partners?

Alpha(1)-adrenergic receptors are one of the three subfamilies of G protein coupled receptors activated by epinephrine and norepinephrine to control important functions in many target organs. Three human subtypes (alpha(1A), alpha(1B), alpha(1D)) are derived from separate genes and are highly homologous in their transmembrane domains but not in their amino or carboxyl termini. Recent advances in our understanding of these "non-identical triplets" include development of knockout mice lacking single or multiple subtypes, new insights into subcellular localization and trafficking, identification of allosteric modulators, and increasing evidence for an important role in brain function. Although all three subtypes activate the same G(q/11) signaling pathway, they also appear to interact with different protein binding partners. Recent evidence suggests they may also form dimers, and may initiate independent signals through pathways yet to be clearly elucidated. Thus, this subfamily represents a common phenomenon of a group of similar but non-identical receptor subtypes activated by the same neurotransmitter, whose individual functional roles remain to be clearly established.

Persistent TrkA activity is necessary to maintain transcription in neuronally differentiated PC12 cells

Neurotrophins are required for the differentiation and survival of several different neuronal subpopulations in the developing nervous system. The PC12 cell line responds to nerve growth factor (NGF) by withdrawing from the cell cycle and acquiring a sympathetic neuron-like phenotype. Previous studies have shown that the activation kinetics of the NGF receptor, TrkA, and downstream protein kinases appear rapid and seemingly transient after NGF treatment of naive PC12 cells. However, maintenance of the neuronal phenotype and survival of differentiated PC12 cells under serum-free conditions require constant NGF exposure. In this study we have addressed the mechanisms that NGF uses to maintain neuronal PC12 cells. We show that TrkA remains phosphorylated at a basal level throughout differentiation of the PC12 cells. The phospho-TrkA levels in the differentiated PC12 cells were diminished by both complete NGF withdrawal and pharmacological inhibition of Trk kinase activity. Intracellular sequestration of the majority of TrkA molecules (both phosphorylated and non-phosphorylated TrkA) and persistent dephosphorylation of the small pool of cell surface TrkA renders the persistent phospho-TrkA signal in the differentiated PC12 cells resistant to partial NGF withdrawal as well as exposure to additional NGF. NGF regulated both extracellular-regulated kinases 1/2 and Akt activity in the differentiated PC12 cells via sustained TrkA activity. Moreover, analysis of transcription using activating protein 1-, serum response element-, and cyclic AMP response element-Luc reporter constructs showed that NGF regulated these promoters through TrkA activity in differentiated PC12 cells. Interestingly, the initial response of the cyclic AMP response element promoter to NGF was delayed, becoming Trk-dependent well beyond the peaks in TrkA and downstream protein kinase signal transduction.

Regulation of glial glutamate transporter expression by growth factors

Injuries to the brain result in the decline of glial glutamate transporter expression within hours and a recovery after several days. One consequence of this disturbed expression seems to consist in the temporary accumulation of toxic extracellular glutamate levels followed by secondary neuronal cell death. Whereas evidence exists that the decline in glutamate transporter expression results from a loss of neuronal PACAP influences on astroglia, the mechanism(s) inducing the reexpression of glial glutamate transporters is presently unknown. We now demonstrate that the injury-induced growth factors EGF, TGFalpha, FGF-2, and PDGF all promote the expression of the glutamate transporters GLT-1 and/or GLAST in cultured cortical astroglia. In contrast, similar stimulatory influences were absent with GDNF and BDNF, growth factors not affected by brain injuries. The effects of EGF, TGFalpha, FGF-2, and PDGF on glial glutamate transport were only partly redundant and involved distinctly different signaling pathways. Unlike EGF, TGFalpha, and FGF-2, PDGF promoted GLT-1, but not GLAST expression and further failed to increase the maximal velocity of sodium-dependent glutamate uptake. Moreover, FGF-2 only affected glial glutamate transport when the RAF-MEK-ERK signaling pathway was concomitantly inhibited with PD98059. Depending on the extracellular growth factor and glutamate transporter subtype, the observed stimulatory effects required the activation of PKA, PKC, and/or AKT. We suggest that after brain injury, reactive processes may limit secondary neuronal cell death by promoting glial glutamate transport. The detailed knowledge of these compensatory mechanisms will eventually allow us to therapeutically interfere with glutamate-associated neuronal cell death in the brain.

Mutational uncoupling of alpha1A-adrenergic receptors from G proteins also uncouples mitogenic and transcriptional responses in PC12 cells

Activation of human alpha1A-adrenergic receptors in PC12 cells causes many second messenger, mitogenic, and transcriptional responses. We examined the role of G protein activation in these responses by uncoupling the receptor through deletion of the first three amino acids from the third intracellular loop (Delta208-210). Expression levels of retrovirus-transfected wild-type and Delta(208-210) alpha1A-adrenergic receptors in PC12 cells were similar and showed identical binding affinities for antagonists. However, the potency of the agonist norepinephrine was increased 9-fold by the Delta (208-210) mutation. In PC12 cells expressing the Delta (208-210) construct, calcium and inositol phosphate responses to norepinephrine were essentially abolished. The strong activation of mitogen-activated protein kinase pathways seen upon stimulation of wild-type alpha1A-adrenergic receptors in PC12 cells was abolished by the Delta (208-210) mutation, as was activation of the tyrosine kinase Pyk2. Norepinephrine also activates several transcriptional reporters through alpha1A-adrenergic receptors in PC12 cells, including reporters for activator protein 1, serum response element, cAMP response element, nuclear factor-kappaB, nuclear factor of activated T cells, gamma-interferon-activated sequence, and signal transducer and activator of transcription. All these transcriptional responses were abolished by the Delta (208-210) mutation. Overexpression of Galpha16 did not rescue any of these responses. These data suggest that known second messenger, mitogenic, and transcriptional effects of alpha1A-adrenergic receptors in PC12 cells all require G protein activation.

Subtype-specific neuronal differentiation of PC12 cells transfected with alpha2-adrenergic receptors

Cells of the PC12 rat pheochromocytoma cell line acquire characteristics of sympathetic neurons under appropriate treatment. Stably transfected PC12 cells expressing individual alpha2-adrenergic receptor (alpha2-AR) subtypes were used to assess the role of alpha2-ARs in neuronal differentiation and to characterise the signalling pathways activated by the alpha2-AR agonist epinephrine in these cells. The effects of alpha2-AR activation were compared with the differentiating action and the signalling mechanisms of nerve growth factor (NGF). Epinephrine induced neuronal differentiation of PC12alpha2 cells through alpha2-AR activation in a subtype-dependent manner, internalization of all human alpha2-AR subtypes, and activation of mitogen-activated protein kinase (MAPK) and the serine-threonine protein kinase Akt. Epinephrine and NGF showed synergism in their differentiating effects. The MAPK kinase (MEK-1) inhibitor PD 98059 abolished the differentiating effect of epinephrine indicating that the differentiation is dependent on MAPK activation. Activating protein-1 (AP-1) DNA-binding activity was increased after epinephrine treatment in all three PC12alpha2 subtype clones. Evaluation of the potential physiological consequences of these findings requires further studies on endogenously expressed alpha2-ARs in neuronal cells.

A novel pathway for adrenergic stimulation of cAMP-response-element-binding protein (CREB) phosphorylation: mediation via alpha1-adrenoceptors and protein kinase C activation

Because of the central role of adrenergic mechanisms in the expression of crucial genes during brown adipocyte differentiation, we examined the activation (phosphorylation) of CREB (cAMP-response-element-binding protein) in mouse brown adipocytes in primary culture. We found that noradrenaline ('norepinephrine') stimulated CREB phosphorylation rapidly (maximum effect in < or =5 min with slow decay) and efficiently (EC(50), 6 nM). The increase in CREB phosphorylation coincided with increased expression of an artificial cAMP-response-element-containing reporter construct. CREB phosphorylation was partly inhibitable, both by the beta-adrenergic antagonist propranolol and by the alpha(1)-adrenergic antagonist prazosin. Adenylate cyclase hyperactivation (by forskolin) could stimulate CREB phosphorylation to the same extent as noradrenaline. The alpha(1)-adrenergic agonist cirazoline also increased CREB phosphorylation. An increase in intracellular [Ca(2+)] had, however, no effect, but protein kinase C activation by PMA was a potent stimulator. The cirazoline-stimulated (alpha(1)-adrenergic) CREB phosphorylation was inhibited by a desensitizing pretreatment with PMA, demonstrating that the alpha(1)-stimulation was mediated via protein kinase C activation; neither Src nor extracellular-signal-regulated kinases 1 and 2 activation was involved in the signalling process. We conclude that CREB phosphorylation in brown adipocytes is mediated not only through the classical beta-adrenergic/cAMP pathway but also through a novel alpha(1)-adrenergic/protein kinase C/CREB pathway, which has not been described previously in any tissue.

NF kappa B and AP-1 mediate transcriptional responses to oxidative stress in skeletal muscle cells

The ability to induce cellular defense mechanisms in response to environmental challenges is a fundamental property of eukaryotic and prokaryotic cells. We have previously shown that oxidative challenges lead to an increase in antioxidant enzymes, particularly glutathione peroxidase (GPx) and catalase (CAT), in mouse skeletal muscle. The focus of the current studies is the transcriptional regulatory mechanisms responsible for these increases. Sequence analysis of the mouse GPx and CAT genes revealed putative binding motifs for NF kappa B and AP-1, transcriptional regulators that are activated in response to oxidative stress in various tissues. To test whether NF kappa B or AP-1 might be mediating the induction of GPx and CAT in muscle cells subjected to oxidative stress, we first characterized their activation by pro-oxidants. Electrophoretic mobility shift assays showed that oxidative stress led to increases in the DNA binding of NF kappa B in differentiated muscle cells. The NF kappa B complexes included a p50/p65 heterodimer, a p50 homodimer, and a p50/RelB heterodimer. AP-1 was also activated, but with slower kinetics than that of NF kappa B. The major component of the AP-1 complexes was a heterodimer composed of c-jun/fos. To test for redox regulation of NF kappa B- or AP-1-dependent transcriptional activation, muscle cells expressing either kappa B/luciferase or TRE/luciferase reporter constructs were subjected to oxidative stress. Pro-oxidant treatment resulted in increased luciferase activity in cells expressing either construct. To test whether NF kappa B mediates oxidant-induced increases of GPx and CAT expression, we transfected cells with either a transdominant inhibitor (I kappa B alpha) or a dominant-negative inhibitor (Delta SP) of NF kappa B. Both inhibitors blocked the induction of antioxidant gene expression by more than 50%. In summary, our results suggest that NF kappa B and AP-1 are important mediators of redox-responsive gene expression in skeletal muscle, and that at least NF kappa B is actively involved in the upregulation of the GPx and CAT in response to oxidative stress.

Nuclear translocation and activation of the transcription factor NFAT is blocked by herpes simplex virus infection

Transcription factors of the NFAT (nuclear factor of activated T cells) family are expressed in most immune system cells and in a range of other cell types. Signaling through NFAT is implicated in the regulation of transcription for the immune response and other processes, including differentiation and apoptosis. NFAT normally resides in the cytoplasm, and a key aspect of the NFAT activation pathway is the regulation of its nuclear import by the Ca(2+)/calmodulin-dependent phosphatase calcineurin. In a cell line stably expressing green fluorescent protein (GFP)-NFAT, this import can be triggered by elevation of intracellular calcium and visualized in live cells. Here we show that the inducible nuclear import of GFP-NFAT is efficiently blocked at early stages of herpes simplex virus (HSV) infection. This is a specific effect, since we observed abundant nuclear accumulation of a test viral protein and no impediment to general nuclear localization signal-dependent nuclear import and retention in infected cells. We show that virus binding at the cell surface is not itself sufficient to inhibit the signaling that induces NFAT nuclear translocation. Since the block occurs following infection in the presence of phosphonoacetic acid but not cycloheximide, we infer that the entry of the virion and early gene transcription are required but the effect is independent of DNA replication or late virus gene expression. A consequence of the block to GFP-NFAT import is a reduction in NFAT-dependent transcriptional activation from the interleukin-2 promoter in infected cells. This HSV-mediated repression of the NFAT pathway may constitute an immune evasion strategy or subversion of other NFAT-dependent cellular processes to promote viral replication.

Activation of NF-kappaB by the human herpesvirus 8 chemokine receptor ORF74: evidence for a paracrine model of Kaposi's sarcoma pathogenesis

Infection with human herpesvirus 8 (HHV-8), also known as Kaposi's sarcoma (KS)-associated herpesvirus, is necessary for the development of KS. The HHV-8 lytic-phase gene ORF74 is related to G protein-coupled receptors, particularly interleukin-8 (IL-8) receptors. ORF74 activates the inositol phosphate/phospholipase C pathway and the downstream mitogen-activated protein kinases, JNK/SAPK and p38. We show here that ORF74 also activates NF-kappaB independent of ligand when expressed in KS-derived HHV-8-negative endothelial cells or primary vascular endothelial cells. NF-kappaB activation was enhanced by the chemokine GROalpha, but not by IL-8. Mutation of Val to Asp in the ORF74 second cytoplasmic loop did not affect ligand-independent signaling activity, but it greatly increased the response to GROalpha. ORF74 upregulated the expression of NF-kappaB-dependent inflammatory cytokines (RANTES, IL-6, IL-8, and granulocyte-macrophage colony-stimulating factor) and adhesion molecules (VCAM-1, ICAM-1, and E-selectin). Supernatants from transfected KS cells activated NF-kappaB signaling in untransfected cells and elicited the chemotaxis of monocytoid and T-lymphoid cells. Expression of ORF74 conferred on primary endothelial cells a morphology that was strikingly similar to that of spindle cells present in KS lesions. Taken together, these data, demonstrating that ORF74 activates NF-kappaB and induces the expression of proangiogenic and proinflammatory factors, suggest that expression of ORF74 in a minority of cells in KS lesions could influence uninfected cells or latently infected cells via autocrine and paracrine mechanisms, thereby contributing to KS pathogenesis.

Inhibition of NF-kappaB-mediated gene transcription by the human A2B adenosine receptor in Chinese hamster ovary cells

NF-kappaB is a transcription factor that plays a vital role in regulating inducible gene expression in immune and inflammatory responses. In view of the well documented effects of adenosine on immune and inflammatory responses, we have explored whether adenosine A1, A2B and A3 receptors regulate NF-kappaB activity in transfected Chinese hamster ovary (CHO) cells using a luciferase reporter gene construct. No increases in NF-kappaB activity were observed in CHO-A1, -A2B and -A3 cells stimulated with the non-selective adenosine receptor agonist 5'-N-ethylcarboxamidoadenosine. Elevating intracellular cyclic AMP (cAMP) levels using forskolin (direct activator of adenylyl cyclase) and rolipram (type IV, cAMP-specific phosphodiesterase inhibitor), inhibited NF-kappaB activity in CHO cells. Adenosine A2B receptor stimulation also inhibited NF-kappaB activity, whereas adenosine A1 and A3 receptor activation had no effect. These data reflect the known coupling of adenosine A2B receptors to increases in cAMP. In conclusion, adenosine A1, A2B and A3 receptors do not directly activate NF-kappaB in CHO cells. However, adenosine A2B receptor activation significantly inhibited NF-kappaB activity. Inhibition of NF-kappaB activity by the adenosine A2B receptor may contribute to the anti-inflammatory effects of adenosine.

Kaposi's sarcoma-associated herpesvirus G protein-coupled receptor constitutively activates NF-kappa B and induces proinflammatory cytokine and chemokine production via a C-terminal signaling determinant

Kaposi's sarcoma-associated herpesvirus (KSHV) is believed to be the causative agent of Kaposi's sarcoma (KS), a multicentric growth factor-dependent tumor common in AIDS patients characterized histopathologically by spindle cell proliferation, angiogenesis, and leukocyte infiltration. Recently, open reading frame 74 of KSHV has been implicated as a major viral determinant of KS. Open reading frame 74 encodes KSHV G protein-coupled receptor (GPCR), a constitutively active chemokine receptor that directly transforms NIH 3T3 cells in vitro and induces multifocal KS-like lesions in KSHV-GPCR-transgenic mice. Interestingly, receptor-positive cells are very rare in lesions from these mice, implicating an indirect mechanism of tumorigenesis. In this regard, here we report that expression of KSHV-GPCR in transfected epithelial, monocytic, and T cell lines induced constitutive activation of the immunoregulatory transcription factors AP-1 and NF-kappaB. This was associated with constitutive induction of the proinflammatory NF-kappaB-dependent cytokines IL-1beta, IL-6, and TNF-alpha, and chemokines monocyte chemoattractant protein-1 and IL-8, as well as the AP-1-dependent basic fibroblast growth factor. In addition, IL-2 and IL-4 production was induced in transfected Jurkat T cells. Truncation of the final five amino acids in the cytoplasmic tail of KSHV-GPCR caused complete loss of its transforming and NF-kappaB-inducing activities, without affecting receptor expression or ligand binding. These data suggest that KS results in part from KSHV-GPCR induction of proinflammatory cytokine and growth factor gene expression, mediated by a signaling determinant within the last five amino acids of the C terminus, a domain that is also critical for direct cell transformation.

Molecular cloning and characterization of a novel type of histamine receptor preferentially expressed in leukocytes

Recently cDNA encoding the histamine H3 receptor was isolated after 15 years of considerable research. However, several studies have proposed heterogeneity of the H3 receptor. We report here the molecular cloning and characterization of a novel type of histamine receptor. A novel orphan G-protein-coupled receptor named GPRv53 was obtained through a search of the human genomic DNA data base and analyzed by rapid amplification of cDNA ends (RACE). GPRv53 possessed the features of biologic amine receptors and had the highest homology with H3 receptor among known G-protein-coupled receptors. Mammalian cells expressing GPRv53 were demonstrated to bind and respond to histamine in a concentration-dependent manner. In functional assays, not only an H3 receptor agonist, R-(alpha)-methylhistamine, but also a H3 receptor antagonist, clobenpropit, and a neuroleptic, clozapine, activated GPRv53-expressing cells. Tissue distribution analysis revealed that expression of GPRv53 is localized in the peripheral blood leukocytes, spleen, thymus, and colon, which was totally different from the H3 receptor, whose expression was restricted to the brain. The discovery of the GPRv53 receptor will open a new phase of research on the physiological role of histamine.

Activators and target genes of Rel/NF-kappaB transcription factors

The vertebrate transcription factor NF-kappaB is induced by over 150 different stimuli. Active NF-kappaB, in turn, participates in the control of transcription of over 150 target genes. Because a large variety of bacteria and viruses activate NF-kappaB and because the transcription factor regulates the expression of inflammatory cytokines, chemokines, immunoreceptors, and cell adhesion molecules, NF-kappaB has often been termed a 'central mediator of the human immune response'. This article contains a complete listing of all NF-kappaB inducers and target genes described to date. The collected data argue that NF-kappaB functions more generally as a central regulator of stress responses. In addition, NF-kappaB activation blocks apoptosis in several cell types. Coupling stress responsiveness and anti-apoptotic pathways through the use of a common transcription factor may result in increased cell survival following stress insults.