Mutually dependent response elements in the cis-regulatory region of the neurotensin/neuromedin N gene integrate environmental stimuli in PC12 cells

The potential use of the neurotensin high affinity receptor 1 as a biomarker for cancer progression and as a component of personalized medicine in selective cancers

A growing challenge in medicine today, is the need to improve the suitability of drug treatments for cancer patients. In this field, biomarkers have become the "flags" to provide additional information in tumor biology. They are a relay between the patient and practitioner and consequently, aid in the diagnosis, providing information for prognosis, or in some cases predicting the response to specific therapies. In addition to being markers, these tumor "flags" can also be major participants in the process of carcinogenesis. Neurotensin receptor 1 (NTSR1) was recently identified as a prognosis marker in breast, lung, and head and neck squamous carcinomas. Neurotensin (NTS) was also shown to exert numerous oncogenic effects involved in tumor growth and metastatic spread. These effects were mostly mediated by NTSR1, making the NTS/NTSR1 complex an actor in cancer progression. In this review, we gather information on the oncogenic effects of the NTS/NTSR1 complex and its associated signaling pathways in order to illuminate its significant role in tumor progression and its potential as a biomarker and a therapeutic target in some tumors.

mTORC1 inhibition increases neurotensin secretion and gene expression through activation of the MEK/ERK/c-Jun pathway in the human endocrine cell line BON

The mammalian target of rapamycin (mTOR) signaling exists in two complexes: mTORC1 and mTORC2. Neurotensin (NT), an intestinal hormone secreted by enteroendocrine (N) cells in the small bowel, has important physiological effects in the gastrointestinal tract. The human endocrine cell line BON abundantly expresses the NT gene and synthesizes and secretes NT in a manner analogous to that of N cells. Here, we demonstrate that the inhibition of mTORC1 by rapamycin (mTORC1 inhibitor), torin1 (both mTORC1 and mTORC2 inhibitor) or short hairpin RNA-mediated knockdown of mTOR, regulatory associated protein of mTOR (RAPTOR), and p70 S6 kinase (p70S6K) increased basal NT release via upregulating NT gene expression in BON cells. c-Jun activity was increased by rapamycin or torin1 or p70S6K knockdown. c-Jun overexpression dramatically increased NT promoter activity, which was blocked by PD98059, an mitogen-activated protein kinase kinase (MEK) inhibitor. Furthermore, overexpression of MEK1 or extracellular signal-regulated kinase 1 (ERK1) increased c-Jun expression and NT promoter activity. More importantly, PD98059 blocked rapamycin- or torin1-enhanced NT secretion. Consistently, rapamycin and torin1 also increased NT gene expression in Hep3B cells, a human hepatoma cell line that, similar to BON, expresses high levels of NT. Phosphorylation of c-Jun and ERK1/2 was also increased by rapamycin and torin1 in Hep3B cells. Finally, we showed activation of mTOR in BON cells treated with amino acids, high glucose, or serum and, concurrently, the attenuation of ERK1/2 and c-Jun phosphorylation and NT secretion. Together, mTORC1, as a nutrient sensor, negatively regulates NT secretion via the MEK/ERK/c-Jun signaling pathway. Our results identify a physiological link between mTORC1 and MEK/ERK signaling in controlling intestinal hormone gene expression and secretion.

Characterization of promoter elements regulating the expression of the human neurotensin/neuromedin N gene

Expression of the gene encoding neurotensin/neuromedin N (NT/N) is mostly limited to the brain and specialized enteroendocrine N cells in the distal small intestine. We have identified key regulatory elements in the promoter region that are involved in human NT/N (hNT/N) gene expression in the novel human endocrine cell line, BON, which resembles intestinal N cells in several important aspects including NT/N precursor protein processing, ratios of different NT/N mRNA isoforms, and high levels of constitutive expression of the NT/N gene. In this study, we demonstrated multiple cis-regulatory elements including a proximal region containing a cAMP-responsive element (CRE)/AP-1-like element that binds both the AP-1 and CRE-binding protein (CREB)/ATF proteins (c-Jun, ATF-1, ATF-2, JunD, and CREB). Similar to the rat NT/N gene, this region is critical for constitutive hNT/N gene expression. Moreover, we identified a novel region that binds the orphan hormone receptor, NR2F2. We have demonstrated that the C terminus of NR2F2 strongly represses hNT/N transcription, whereas an N-terminal domain antagonizes this repressive effect. Regulation of NT/N expression by NR2F2 may have important consequences for lipid metabolism. We speculate that a complex interplay between the proximal CRE/AP-1-like motif and NR2F2 binding region exists to regulate hNT/N expression, which is critical for the high level of constitutive expression of NT/N in enteroendocrine cells. Finally, the BON cell line provides a unique model to characterize the factors regulating expression of the hNT/N gene and to better understand the mechanisms responsible for terminal differentiation of the N cell lineage in the gut.

Neurotensin and neuromedin N are differentially processed from a common precursor by prohormone convertases in tissues and cell lines

Neurotensin (NT) is synthesized as part of a larger precursor that also contains neuromedin N (NN), a six amino acid NT-like peptide. NT and NN are located in the C-terminal region of the precursor (pro-NT/NN) where they are flanked and separated by three Lys-Arg sequences. A fourth dibasic sequence is present in the middle of the precursor. Dibasics are the consensus sites recognized and cleaved by specialized endoproteases that belong to the family of proprotein convertases (PCs). In tissues that express pro-NT/NN, the three C-terminal Lys-Arg sites are differentially processed, whereas the middle dibasic is poorly cleaved. Processing gives rise mainly to NT and NN in the brain, NT and a large peptide with a C-terminal NN moiety (large NN) in the gut, and NT, large NN, and a large peptide with a C-terminal NT moiety (large NT) in the adrenals. Recent evidence indicates that PC1, PC2, and PC5-A are the prohormone convertases responsible for the processing patterns observed in the gut, brain, and adrenals, respectively. As NT, NN, large NT, and large NN are all endowed with biological activity, the evidence reviewed here supports the idea that posttranslational processing of pro-NT/NN in tissues may generate biological diversity of pathophysiological relevance.

Involvement of NTS2 receptors in stress-induced analgesia

Stress activates multiple neural systems that suppress pain sensation. This adaptive phenomenon referred as stress-induced analgesia (SIA) is mediated by the activation of endogenous pain inhibitory systems. Both opioid and non-opioid forms of SIA have been elicited in rodents according to stressor parameters and duration. There is accumulating evidence that the endogenous neurotensin (NT) system plays an important role in SIA. Especially, NT-deficient mice were shown to exhibit reduced SIA following water avoidance or restraint stress. Since central NT produces naloxone-insensitive analgesic effects by acting on spinal and supraspinal NTS2 receptors, we hypothesized that NT might mediate non-opioid SIA through NTS2 activation. Here, we evaluated the influence of an opioid-independent severe stress produced by a cold-water swim for 3 min at 15 degrees C on rodent offspring's pain perception. Our results demonstrated that mice lacking NTS2 exhibit significantly reduced SIA following cold-water swim stress. Indeed, NTS2 knockout mice submitted to both acute (plantar test) and tonic (formalin test) pain stimuli show a greater sensitivity to pain in comparison to wild-type littermates. Accordingly, pretreatment with the NT receptor antagonist SR142948A results in a hyperalgesic response to stress induced by cold-water swim. Endogenous NT regulates hypothalamic-pituitary-adrenal axis activity in stress condition by increasing corticosterone plasma levels. Accordingly, the plasma levels of corticosterone measured by radioimmunoassay are significantly reduced in non-stressed and stressed NTS2-deficient mice in comparison with wild-type mice. To further investigate the site of action of NT in mediating SIA, we microinjected NTS2 agonists in lumbar spinal cord and quantified post-stress sensitivity to pain in rats using the plantar test. Exogenously administered NTS2 analogs, JMV-431, beta-lactotensin and NT69L markedly enhance the magnitude and duration of stress antinociception in both 25- and 60-day-old rats. In sum, by using genetic and pharmacological approaches, we demonstrated here that NTS2 receptors mediate non-opioid SIA. Our results also revealed that the release of endogenous NT in response to stress requires the presence of NTS2 to stimulate corticotropin-releasing factor (CRF)-induced elevation of plasma corticosterone, and that NTS2 receptors localized at the lumbar spinal cord participate to the disinhibition of descending pain control pathways. Therefore, these data highlight the significance of NTS2 as a novel target for the treatment of pain and stress-related disorders.

Neurotensin inversely modulates maternal aggression

Neurotensin (NT) is a versatile neuropeptide involved in analgesia, hypothermia, and schizophrenia. Although NT is released from and acts upon brain regions involved in social behaviors, it has not been linked to a social behavior. We previously selected mice for high maternal aggression (maternal defense), an important social behavior that protects offspring, and found significantly lower NT expression in the CNS of highly protective females. Our current study directly tested NT's role in maternal defense. Intracerebroventricular (i.c.v.) injections of NT significantly impaired defense in terms of time aggressive and number of attacks at all doses tested (0.05, 0.1, 1.0, and 3.0 microg). Other maternal behaviors, including pup retrieval, were unaltered following NT injections (0.05 microg) relative to vehicle, suggesting specificity of NT action on defense. Further, i.c.v. injections of the NT receptor 1 (NT1) antagonist, SR 48692 (30 microg), significantly elevated maternal aggression in terms of time aggressive and attack number. To understand where NT may regulate aggression, we examined Fos following injection of either 0.1 microg NT or vehicle. Thirteen of 26 brain regions examined exhibited significant Fos increases with NT, including regions expressing NT1 and previously implicated in maternal aggression, such as lateral septum, bed nucleus of stria terminalis, paraventricular nucleus, and central amygdala. Together, our results indicate that NT inversely regulates maternal aggression and provide the first direct evidence that lowering of NT signaling can be a mechanism for maternal aggression. To our knowledge, this is the first study to directly link NT to a social behavior.

Rapid and preferential activation of Fos protein in hypocretin/orexin neurons following the reversal of dehydration-anorexia

Dehydration (DE)-anorexia is stimulated by chronic consumption of hypertonic saline. Spontaneous nocturnal food intake is markedly reduced with this treatment but is rapidly reversed upon the return of drinking water. Here we examined the neurons in the lateral hypothalamic area (LHA) of chronically dehydrated rats for their peptidergic phenotype, colocalization, and activation profiles following the rapid reversal of anorexia. To do this, we used double-labeling combinations of Fos immunocytochemistry and radioisotopic- and digoxigenin-labeled in situ hybridization. We found that lateral hypothalamic corticotropin-releasing hormone (CRH) neurons show extensive coexpression with neurotensin mRNA, but they are distinct from hypocretin/orexin and melanin-concentrating hormone (MCH) neurons. Chronic dehydration increases Fos-ir in large numbers of neurons in dorsal regions of the LHA. Some of these LHA neurons also show increased CRH, but not hypocretin/orexin or MCH gene expression, as dehydration-anorexia develops. Furthermore, the behavioral sequence of eating and increased activity exhibited by DE animals in the minutes following water drinking is accompanied by a further increase in the number of Fos-ir nuclei in the LHA. Increased Fos activation occurs in a significant number of LHA hypocretin/orexin neurons, but not CRH or MCH neurons, in the LHA. Together these data implicate CRH but not hypocretin/orexin or MCH neurons in the LHA in the motor events associated with dehydration. However, when water is returned, contributions to the network controlling responses evidently come from hypocretin/orexin, but not CRH or MCH, neurons in the LHA.

Neurotensin receptor mechanisms and its modulation of glutamate transmission in the brain: relevance for neurodegenerative diseases and their treatment

The extracellular accumulation of glutamate and the excessive activation of glutamate receptors, in particular N-methyl-D-aspartate (NMDA) receptors, have been postulated to contribute to the neuronal cell death associated with chronic neurodegenerative disorders such as Parkinson's disease. Findings are reviewed indicating that the tridecaptide neurotensin (NT) via activation of NT receptor subtype 1 (NTS1) promotes and reinforces endogenous glutamate signalling in discrete brain regions. The increase of striatal, nigral and cortical glutamate outflow by NT and the enhancement of NMDA receptor function by a NTS1/NMDA interaction that involves the activation of protein kinase C may favour the depolarization of NTS1 containing neurons and the entry of calcium. These results strengthen the hypothesis that NT may be involved in the amplification of glutamate-induced neurotoxicity in mesencephalic dopamine and cortical neurons. The mechanisms involved may include also antagonistic NTS1/D2 interactions in the cortico-striatal glutamate terminals and in the nigral DA cell bodies and dendrites as well as in the nigro-striatal DA terminals. The possible increase in NT levels in the basal ganglia under pathological conditions leading to the NTS1 enhancement of glutamate signalling may contribute to the neurodegeneration of the nigro-striatal dopaminergic neurons found in Parkinson's disease, especially in view of the high density of NTS1 receptors in these neurons. The use of selective NTS1 antagonists together with conventional drug treatments could provide a novel therapeutic approach for treatment of Parkinson's disease.

Leptin signaling in neurotensin neurons involves STAT, MAP kinases ERK1/2, and p38 through c‐Fos and ATF1

The adipokine leptin signals energy status to the hypothalamus, which triggers a network of neuropeptide responses. Each hypothalamic cell type expresses a unique complement of neuropeptides, receptors, and second messengers; thus each likely responds specifically to peripheral hormones. We describe here the analysis of leptin signaling in a clonal population of mouse neurotensin (NT) -expressing hypothalamic neurons, N-39. Leptin induced phosphorylation of STAT3 and MAPK ERK1/2, but not the downstream effector of PI3K, Akt, and also induced c-Fos protein. We found activation of p38 MAPK by leptin, accompanied by phosphorylation of its downstream effector ATF-1. Phosphorylation of ATF-1 is blocked by the p38 MAPK inhibitor SB 203580. We linked this signaling directly to NT transcription. Protein binding analysis indicates that both ATF-1 and c-Fos are capable of binding to the mouse NT/N gene predominantly at physiological or high concentrations of leptin. The evidence indicates activation of distinct leptin signal transduction pathways that directly result in changes in NT gene expression and links these specific neurons to the control of energy homeostasis.

Brain neurotensin, psychostimulants, and stress--emphasis on neuroanatomical substrates

Neurotensin (NT) is a peptide that is widely distributed throughout the brain. NT is involved in locomotion, reward, stress and pain modulation, and in the pathophysiology of drug addiction and depression. In its first part this review brings together relevant literature about the neuroanatomy of NT and its receptors. The second part focuses on functional-anatomical interactions between NT, the mesotelencephalic dopamine system and structures targeted by dopaminergic projections. Finally, recent data about the actions of NT in processes underlying behavioral sensitization to psychostimulant drugs and the involvement of NT in the regulation of the hypothalamo-pituitary-adrenal gland axis are considered.

Differential processing of pro-neurotensin/neuromedin N and relationship to pro-hormone convertases

Neurotensin (NT) is synthesized as part of a larger precursor that also contains neuromedin N (NN), a six amino acid neurotensin-like peptide. NT and NN are located in the C-terminal region of the precursor (pro-NT/NN) where they are flanked and separated by three Lys-Arg sequences. A fourth dibasic sequence is present in the middle of the precursor. Dibasics are the consensus sites recognized and cleaved by endoproteases that belong to the recently identified family of pro-protein convertases (PCs). In tissues that express pro-NT/NN, the three C-terminal Lys-Arg sites are differentially processed, whereas the middle dibasic is poorly cleaved. Pro-NT/NN processing gives rise mainly to NT and NN in the brain, to NT and a large peptide ending with the NN sequence at its C-terminus (large NN) in the gut and to NT, large NN and a large peptide ending with the NT sequence (large NT) in the adrenals. Recent evidence indicates that PC1, PC2 and PC5-A are the pro-hormone convertases responsible for the processing patterns observed in the gut, brain and adrenals, respectively. As NT, NN, large NT and large NN are all endowed with biological activity, the evidence reviewed here supports the idea that post-translational processing of pro-NT/NN in tissues may generate biological diversity.

Prohormone convertases differentially process pro-neurotensin/neuromedin N in tissues and cell lines

Neurotensin (NT) is synthesized as part of a larger precursor that also contains neuromedin N (NN), a six-amino acid neurotensin-like peptide. NT and NN are located in the C-terminal region of the precursor (pro-NT/NN) where they are flanked and separated by three Lys-Arg sequences. A fourth dibasic sequence is present in the middle of the precursor. Dibasics are the consensus sites recognized and cleaved by specialized endoproteases that belong to the family of proprotein convertases (PCs). In tissues that express pro-NT/NN, the three C-terminal Lys-Arg sites are differentially processed, whereas the middle dibasic is poorly cleaved. Processing gives rise mainly to NT and NN in the brain, to NT and a large peptide with a C-terminal NN moiety (large NN) in the gut, and to NT, large NN, and a large peptide with a C-terminal NT moiety (large NT) in the adrenals. Recent evidence indicates that PC1, PC2, and PC5-A are the prohormone convertases responsible for the processing patterns observed in the gut, brain, and adrenals, respectively. As NT, NN, large NT, and large NN are all endowed with biological activity, the evidence reviewed in this paper supports the idea that posttranslational processing of pro-NT/NN in tissues may generate biological diversity of pathophysiological relevance.

Induction patterns of transcription factors of the nur family (nurr1, nur77, and nor-1) by typical and atypical antipsychotics in the mouse brain: implication for their mechanism of action

Monitoring gene expression has been intensively used to identify neurobiological and neuroanatomical substrates associated with administration of antipsychotic drugs. Transcription factors of the Nur family (Nurr1, Nur77, and Nor-1) are orphan nuclear receptors that have been recently associated with dopamine neurotransmission. Nurr1 is involved in midbrain dopamine neuron development. Nur77 and Nor-1 are expressed in dopaminoceptive areas such as the striatum, nucleus accumbens, and prefrontal cortex. To better understand the relationship between Nur and antipsychotic drug effects, we conducted a comprehensive evaluation of the effect of various typical and atypical antipsychotic drugs on the modulation of Nur mRNA levels. We show that differential patterns of Nur expression can be obtained with typical and atypical antipsychotic drugs. Modulation of Nur77 and Nor-1 mRNA expression by antipsychotics can be used to calculate an index that is predictive of the typical or atypical profile of antipsychotic drugs. Inductions of Nur by anti-psychotic drugs are correlated with dopamine D2 receptor in the striatum and D2 and D3 receptor subtypes in the nucleus accumbens. The 5-hydroxytryptamine 2A/D2 affinity ratio of antipsychotics can also predict these patterns of inductions. In addition to classical gene patterns induced in the striatal complex (striatum, accumbens) and cortex, most antipsychotic drugs tested strongly induced Nur77, Nor-1, and increased Nurr1 mRNA levels in the substantia nigra and ventral tegmental area. These data suggest that typical and atypical antipsychotic drugs might induce in multiple brain regions distinct Nur-dependent transcriptional activities, which may contribute to their pharmacological effects.

Endogenous neurotensin attenuates dopamine-dependent locomotion and stereotypy

The neuropeptide neurotensin (NT) is highly sensitive to changes in dopaminergic signaling in the striatum, and is thought to modulate dopamine-mediated behaviors. To explore the interaction of NT with the dopamine system, we utilized mice with a targeted deletion of dopamine synthesis specifically in dopaminergic neurons. Dopamine levels in dopamine-deficient (DD) mice are less than 1% of control mice, and they require daily administration of the dopamine precursor L-dihydroxyphenylalanine (L-DOPA) for survival. DD mice are supersensitive to the effects of dopamine, becoming hyperactive relative to control mice in the presence of L-DOPA. We show that 24 h after L-DOPA treatment, when DD mice are in a "dopamine-depleted" state, Nt mRNA levels in the striatum of DD mice are similar to those in control mice. Administration of L-DOPA or L-DOPA plus the L-amino acid decarboxylase inhibitor, carbidopa, (C/L-DOPA) induced Nt expression in the striatum of DD mice. The dopamine D1 receptor antagonist, SCH23390, blocked C/L-DOPA-induced Nt. To test the hypothesis that this striatal Nt expression modulated dopamine-mediated behavior in DD mice, we administered SR 48692, an antagonist of the high affinity NT receptor, together with L-DOPA or C/L-DOPA. L-DOPA-induced hyperlocomotion and C/L-DOPA-induced stereotypy were potentiated by peripheral administration of SR 48692. Furthermore, intrastriatal microinjections of SR 48692 augmented L-DOPA-induced hyperlocomotion. These results demonstrate a dynamic regulation of striatal Nt expression by dopamine via D1 receptors in DD mice, and point to a physiological role for endogenous striatal NT in counteracting motor behaviors induced by an overactive dopamine system.

Expression of adrenomedullin and proadrenomedullin N-terminal 20 peptide in PC12 cells after exposure to nerve growth factor

Adrenomedullin (AM) and proadrenomedullin N-terminal 20 peptide (PAMP) are multi-functional peptides derived from the same precursor, proadrenomedullin. We have studied the regulatory mechanism of expression of these peptides during neuronal differentiation of rat pheochromocytoma PC12 cells by nerve growth factor (NGF). The cellular levels of the peptides increased slightly, and then progressively decreased below the control by NGF. Immunoreactive (ir)-AM in the medium was transiently increased by NGF. Cytochemical staining showed that ir-AM and ir-PAMP were abundantly present in cytoplasm in the undifferentiated cells, and were decreased during culture with NGF. There was no preferential localization of ir-AM or ir-PAMP in neurites in comparison with in cytoplasm in the differentiated cells. Northern blot analysis showed that mRNA encoding these peptides, as detected as a band of 1.6 kb, increased more than three-fold at 1 h after the addition of NGF and then progressively decreased to one fifth of the control during 72 h. Degradation rate of the mRNA was slowed by NGF even when mRNA level is decreased after 72 h of NGF treatment. The transcription rate of their gene increased transiently and then decreased by the long-term treatment with NGF. These results demonstrate that expression of AM and PAMP is regulated by NGF along with time-dependent differentiation: AM gene transcription is transiently activated by NGF, whereas it was suppressed during neuronal differentiation of the cells.

Differential regulation of gene expression of neurotensin and prohormone convertases PC1 and PC2 in the bovine ocular ciliary epithelium: possible implications on neurotensin processing

Prohormone convertases PC1 and PC2 are enzymes involved in the intracellular processing of pro-neurotensin/neuromedin N (pro-NT/NN) through the regulated secretory pathway. In this study, we present evidence of the differential gene expression of pro-NT/NN, pro-PC1 and pro-PC2 in two cell lines established from the neuroendocrine ocular ciliary epithelium. Dexamethasone and forskolin were found to synergistically up-regulate NT/NN mRNA expression in both cell types. The pigmented cells released NT, and this release was enhanced by agents that induced its biosynthesis. In contrast, nonpigmented cells exhibited a significantly reduced neurotensin secretion in response to inducers, leading to an accumulation of the peptide. PC1 and PC2 mRNA expression was induced in a cell-specific manner by the same agents that enhanced pro-NT/NN biosynthesis. These results demonstrate cell-specific processing of pro-NT/NN by the ciliary epithelium.

Point mutants of EHEC intimin that diminish Tir recognition and actin pedestal formation highlight a putative Tir binding pocket

Attachment to host cells by enterohaemorrhagic Escherichia coli (EHEC) is associated with the formation of a highly organized cytoskeletal structure containing filamentous actin, termed an attaching and effacing (AE) lesion. Intimin, an outer membrane protein of EHEC, is required for the formation of AE lesions, as is Tir, a bacterial protein that is translocated into the host cell to function as a receptor for intimin. We established a yeast two-hybrid assay for intimin-Tir interaction and, after random mutagenesis, isolated 24 point mutants in intimin, which disrupted Tir recognition in this system. Analysis of 11 point mutants revealed a correlation between recognition of recombinant Tir and the ability to trigger AE lesions. Many of the mutations fell within a 50-residue region near the C-terminus of intimin. Alanine-scanning mutagenesis of this region revealed four residues (Ser890, Thr909, Asn916 and Asn927) that are critical for Tir recognition. Mapping the sequences of EHEC intimin and Tir onto the crystal structure of the intimin-Tir complex of enteropathogenic E. coli predicts that each of these four intimin residues lies at the intimin-Tir interface and contributes to a pocket that interacts with Ile298 of EHEC Tir. Thus, this genetic approach to intimin function both identified residues critical for Tir binding and demonstrated a correlation between the ability to bind Tir and the ability to trigger actin focusing.

Regulation of the Y1 neuropeptide Y receptor gene expression in PC12 cells

The Y1 receptor for neuropeptide Y (NPY-Y1) is constitutively expressed in PC12 cells. In this study, we examined the role of nerve growth factor (NGF), pituitary adenylyl cyclase activating polypeptide (PACAP) and dexamethasone on the expression of the gene encoding the rat NPY-Y1 receptor in PC12 cells. A fusion gene (pY1-Luc) was constructed where the reporter enzyme firefly luciferase was placed under the control of 700 bp of the promoter region of the rat NPY-Y1 receptor gene. This promoter region contains recognition consensus sequences for various transcription factors, including one activation protein-1 (AP-1) site, two cyclic AMP responsive element sites, one estrogen receptor element site and four glucocorticoid receptor element sites. NGF increased luciferase activity in a concentration dependent manner. This increase was inhibited by K-252a, a trk A receptor inhibitor, and calphostin C, a PKC inhibitor. PACAP-38 increased luciferase activity in a concentration dependent manner. This activation was inhibited by H-89. Dexamethasone increased transcription of NPY-Y1 gene in PC12 cells. These results indicate that differentiation of PC12 cells into endocrine-like phenotype by dexamethasone and into a neuronal-like phenotype by either NGF or PACAP-38 increases the transcriptional activity of the NPY-Y1 receptor gene in PC12 cells.

Site-specific DNA methylation contributes to neurotensin/neuromedin N expression in colon cancers

The neurotensin/neuromedin N (NT/N) gene is expressed in fetal colon, repressed in newborn and adult colon, and reexpressed in approximately 25% of colon cancers. Our purpose was to determine the effect of gene methylation on NT/N silencing in colon cancers. We found that the NT/N gene was expressed in human colon cancer cell line KM12C but not in KM20 colon cancer cells. Bisulfite genomic sequencing demonstrated that all CpG dinucleotides in the region from -373 to +100 of the NT/N promoter, including a CpG site in a distal consensus AP-1 site, were methylated in KM20 but unmethylated in KM12C cells. Treatment of KM20 cells with demethylating agent 5-azacytidine induced NT/N expression, suggesting a role for DNA methylation in silencing of NT/N in colon cancers. To better elucidate the mechanisms responsible for NT/N repression by DNA methylation, we performed gel shift assays using an oligonucleotide probe corresponding to the distal AP-1 consensus sequence of the NT/N promoter. Methylation of the oligonucleotide probe inhibited protein binding to the distal AP-1 site of the NT/N promoter, suggesting a potential mechanism of NT/N gene repression in colon cancers. We show that DNA methylation plays a role in NT/N gene silencing in the human colon cancer KM20 and that NT/N expression in KM12C cells is associated with demethylation of the CpG sites. DNA methylation likely contributes to NT/N gene expression noted in human colon cancers.

Contrasting patterns and cellular specificity of transcriptional regulation of the nuclear receptor nerve growth factor-inducible B by haloperidol and clozapine in the rat forebrain

This study was designed to investigate the possible involvement of members of the nuclear receptor family of transcription factors in the effects of antipsychotic drugs used in the treatment of schizophrenia. We have identified, using RT-PCR screening, an important modulation of nerve growth factor-inducible B (NGFI-B) mRNA levels by typical and atypical neuroleptics in the rat forebrain. NGFI-B, a member of the nuclear receptor family, can be observed in target structures of dopaminergic pathways. Using in situ hybridization, we also demonstrate that typical and atypical antipsychotics induced contrasting patterns of expression of NGFI-B after both acute and chronic administration. An acute treatment with clozapine or haloperidol induces high NGFI-B mRNA levels in the prefrontal and cingulate cortices and in the nucleus accumbens shell. However, haloperidol, but not clozapine, dramatically increases NGFI-B expression in the dorsolateral striatum. In contrast, chronic treatment with clozapine reduces NGFI-B expression below basal levels in the rat forebrain, whereas haloperidol still induces high NGFI-B mRNA levels in the dorsolateral striatum. Finally, using a double in situ hybridization technique, we show that acute administration of both neuroleptics increases NGFI-B expression in neurotensin-containing neurons in the nucleus accumbens shell, whereas the effects of haloperidol in the dorsolateral striatum are mainly observed in enkephalin-containing neurons. These results are the first demonstration that members of the nuclear receptor family of transcription factors could play an important role in the effects of antipsychotic drugs.

Changes in CArG-binding protein A expression levels following injection(s) of the D1-dopamine agonist SKF-82958 in the intact and 6-hydroxydopamine-lesioned rat

We recently characterized the rat brain homolog of mouse muscle CArG-binding protein A initially identified in C2 myogenic cells and showed an inverse temporal correlation between increased expression levels of this messenger RNA, c-fos and zif268 messenger RNA levels following the addition of nerve growth factor to PC12 cells. In addition, we found an inverse correlation between c-Fos protein and CArG-binding protein A messenger RNA levels in the lateral caudate-putamen of rats treated acutely and chronically with the D2 receptor antagonist fluphenazine (phenothiozine typical psychotic). To determine whether D1 receptor stimulation is also capable of inducing CArG-binding protein A up-regulation, drug naive or dopamine-depleted (i.e. 6-hydroxydopamine-lesioned) D1 hypersensitized rats (i.e. rats given repeated daily injections of SKF-82958 for 14days) were acutely injected with the D1 agonist SKF-82958 and examined using a combination of in situ hybridization for CArG binding protein A and immunocytochemistry for c-Fos. Both acutely treated animals and dopamine-depleted hypersensitized animals showed increases in CArG-binding protein A. Moderate increases were found in the medial caudate-putamen and nucleus accumbens core and shell regions following acute treatment whereas large increases in CArG-binding protein A expression levels were found in the medial and lateral caudate-putamen and the shell and core of the nucleus accumbens following hypersensitization. No change in CArG-binding protein A expression level was found in the dopamine-depleted, drug naive animals relative to controls. Regions of the basal ganglia where increases in CArG-binding protein A were detected following each treatment correlated perfectly with c-Fos protein induction. The results demonstrate that CArG-binding protein A responds to SKF-82958 and that the changes in CArG-binding protein A match perfectly with the pattern of c-Fos induction induced by the D1 agonist.

The Tir-binding region of enterohaemorrhagic Escherichia coli intimin is sufficient to trigger actin condensation after bacterial-induced host cell signalling

Enterohaemorrhagic Escherichia coli (EHEC) has emerged as an important agent of diarrhoeal disease. Attachment to host cells, an essential step during intestinal colonization by EHEC, is associated with the formation of a highly organized cytoskeletal structure containing filamentous actin, termed an attaching and effacing (A/E) lesion, directly beneath bound bacteria. The outer membrane protein intimin is required for the formation of this structure, as is Tir, a bacterial protein that is translocated into the host cell and is thought to function as a receptor for intimin. To understand intimin function better, we fused EHEC intimin to a homologous protein, Yersinia pseudotuberculosis invasin, or to maltose-binding protein. The N-terminal 539 amino acids of intimin were sufficient to promote outer membrane localization of the C-terminus of invasin and, conversely, the N-terminal 489 amino acids of invasin were sufficient to promote the localization of the C-terminus of intimin. The C-terminal 181 residues of intimin were sufficient to bind mammalian cells that had been preinfected with an enteropathogenic E. coli strain that expresses Tir but not intimin. Binding of intimin derivatives to preinfected cells correlated with binding to recombinant Tir protein. Finally, the 181-residue minimal Tir-binding region of intimin, when purified and immobilized on latex beads, was sufficient to trigger A/E lesions on preinfected mammalian cells.

Distinct patterns of neuropeptide gene expression in the lateral hypothalamic area and arcuate nucleus are associated with dehydration-induced anorexia

We have investigated the hormonal and hypothalamic neuropeptidergic substrates of dehydration-associated anorexia. In situ hybridization and hormone analyses of anorexic and paired food-restricted rats revealed two distinct profiles. First, both groups had the characteristic gene expression and endocrine signatures usually associated with starvation: increased neuropeptide Y and decreased proopiomelanocortin and neurotensin mRNAs in the arcuate nucleus (ARH); increased circulating glucocorticoid but reduced leptin and insulin. Dehydrated animals are strongly anorexic despite these attributes, showing that the output of leptin- and insulin-sensitive ARH neurons that ordinarily stimulate eating must be inhibited. The second pattern occurred only in anorexic animals and had two components: (1) reduced corticotropin-releasing hormone (CRH) mRNA in the neuroendocrine paraventricular nucleus (PVH) and (2) increased CRH and neurotensin mRNAs in the lateral hypothalamic (LHA) and retrochiasmatic areas. However, neither corticosterone nor suppressed PVH CRH gene expression is required for anorexia after dehydration because PVH CRH mRNA in dehydrated adrenalectomized animals is unchanged from euhydrated adrenalectomized controls. We also showed that LHA CRH mRNA was strongly correlated with the intensity of anorexia, increased LHA CRH gene expression preceded the onset of anorexia, and dehydrated adrenalectomized animals (which also develop anorexia) had elevated LHA CRH gene expression with a distribution pattern similar to intact animals. Finally, we identified specific efferents from the CRH-containing region of the LHA to the PVH, thereby providing a neuroanatomical framework for the integration by the PVH of neuropeptidergic signals from the ARH and the LHA. Together, these observations suggest that CRH and neurotensin neurons in the LHA constitute a novel anatomical substrate for their well known anorexic effects.

Transcriptional effects of estrogen on neuronal neurotensin gene expression involve cAMP/protein kinase A-dependent signaling mechanisms

Steroid hormones exert dramatic effects on neuronal expression of genes that encode neuropeptides. Expression of the neurotensin/neuromedin (NT/N) gene in preoptic area neurons is dramatically enhanced by estrogen in vivo, even though its promoter lacks palindromic estrogen response elements. We report here that estrogen promotes transcription of this gene by interactions with the cAMP cascade in a neuronal cell line, SK-N-SH, and in a mouse model. In neuroblastoma cells, estrogen increases cAMP and the phosphorylation of the cAMP response element-binding protein in a time frame that precedes induction of NT/N gene transcription. Interference with the cAMP/protein kinase A signal transduction cascade blocks the ability of estrogen to elicit increases in transcription of this gene. Furthermore, in studies performed in vivo using mice deficient in protein kinase A, estrogen fails to induce increases in NT/N mRNA but retains its ability to promote estrogen response element-dependent progesterone receptor gene transcription. These data represent the first report of a nonclassical effect of estrogen on the expression of an endogenous estrogen-regulated neuropeptide gene through cAMP-mediated mechanisms both in a neuroblastoma cell line and in hypothalamic neurons. More importantly, this "cross-talk" may represent a more generalized mechanism by which steroid hormones act through other signal transduction cascades to regulate the expression of other genes in the brain.

DNA methylation contributes to expression of the human neurotensin/neuromedin N gene

The gut and liver share a common embryological origin. The gene encoding the gut hormone neurotensin/neuromedin N (NT/N) is expressed in the adult small bowel, and NT/N is transiently expressed in the fetal liver, suppressed in the adult liver, and reexpressed in certain liver cancers. In our present study, we found that the NT/N gene was expressed at high levels in the human hepatoma cell line Hep 3B but was not expressed in Hep G2 cells. To further determine the mechanisms regulating NT/N expression, we performed Southern blotting and gene cloning techniques. Neither alteration nor mutation of the NT/N gene was responsible for this differential NT/N expression pattern. Human NT/N promoter constructs were transfected into either Hep 3B or Hep G2. Both cell lines supported NT/N transcription, indicating that the absence of NT/N expression in Hep G2 cells was due to mechanisms other than the absence of positive transcription factors. The role of DNA methylation was next assessed. Methylation of NT/N promoter constructs in vitro resulted in a 67-fold reduction in promoter activity, whereas treatment with the demethylating agent 5-azacytidine induced NT/N expression in Hep G2 cells, thus suggesting that DNA methylation plays a role in the expression of the gut endocrine gene NT/N. Defining the mechanisms regulating NT/N expression in these hepatic-derived cell lines will provide not only a better understanding of cell-specific and developmental regulation of a gut endocrine gene but also possible insight into liver cell lineage patterns and the derivation of certain hepatocellular cancers.

Lithium increases melanin-concentrating hormone mRNA stability and inhibits tyrosine hydroxylase gene expression in PC12 cells

Melanin-concentrating hormone (MCH) is a cyclic peptide involved in the regulation of food-intake behaviour and stress response in mammals. Expression of the MCH gene predominates in hypothalamic neurons. Mechanisms governing the regulation of expression of MCH gene in established cell lines were not explored yet. Here, we analysed the actions of nerve growth factor (NGF), dexamethasone, forskolin and lithium on MCH mRNA levels in the PC12 pheochromocytoma cell line. We compared them with those observed on tyrosine hydroxylase (TH) mRNA, constitutively expressed in PC12 cells, and neurotensin (NT) mRNA, taken as a control. In untreated cells, MCH RNA species of high molecular weight were found. Exposure of cells at a combination of NGF and lithium resulted in decreased expression of these MCH RNAs and in the transient production of mature MCH mRNA. Strikingly, after short exposure of PC12 cells to NGF, lithium per se elicited a marked increase in MCH mRNA levels whilst it exerted a potent inhibitory action on TH mRNA expression. Detailed investigations revealed that lithium enhanced MCH mRNA expression through post-transcriptional mechanisms whereas it regulated TH gene expression mainly at the level of transcription. These results demonstrate that lithium, an agent widely used for treatment of manic depressive illness, can exert an opposite effect on MCH and TH mRNA production in PC12 cells. The MCH gene system in NGF-treated PC12 cells provides a good opportunity for studying the effect of lithium on gene expression at post-transcriptional levels in a neuron-like cellular model.

Loss of haloperidol induced gene expression and catalepsy in protein kinase A-deficient mice

The antipsychotic drug, haloperidol, elicits the expression of neurotensin and c-fos mRNA in the dorsal lateral region of the striatum and produces an acute cataleptic response in rodents that correlates with the motor side effects of haloperidol in humans. Mice harboring a targeted disruption of the RIIbeta subunit of protein kinase A have a profound deficit in cAMP-stimulated kinase activity in the striatum. When treated with haloperidol, RIIbeta mutant mice fail to induce either c-fos or neurotensin mRNA and the acute cataleptic response is blocked. However, both wild-type and mutant mice become cataleptic when neurotensin peptide is directly injected into the lateral ventricle, demonstrating that the kinase deficiency does not interfere with the action of neurotensin but rather its synthesis and release. These results establish a direct role for protein kinase A as a mediator of haloperidol induced gene induction and cataleptic behavior.

Involvement of a c-fos-dependent mechanism in caffeine-induced expression of the preprotachykinin A and neurotensin/neuromedin N genes in rat striatum

Striatal c-fos induction was blocked by local administration of phosphorothioated c-fos antisense oligonucleotides (AS-ODN) to examine the possible role of caffeine-induced c-fos expression in transcriptional regulation of striatal preproenkephalin, prodynorphin, preprotachykinin A and neurotensin/neuromedin N. Caffeine (100 mg/kg i.p.) induced both c-fos mRNA and Fos-protein, and this induction was significantly attenuated by intrastriatal injection of 4 (but not 1) nmol c-fos AS-ODN. This suggests that, in addition to translational arrest, other mechanisms may be involved in the mediation of antisense action. The action of the AS-ODN was sequence specific. The antisense blockade of c-fos reduced the effect of caffeine on the expression of mRNAs for preprotachykinin A and neurotensin/neuromedin N in the ventrolateral caudate-putamen. Levels of preproenkephalin and prodynorphin transcripts were unaffected. Thus caffeine induction of striatal preprotachykinin A mRNA and neurotensin/neuromedin N mRNA, but not of preproenkephalin mRNA or prodynorphin mRNA, may at least in part be mediated by a pathway involving Fos protein. The findings illustrate the utility of blockade of gene expression with antisense oligonucleotides for in vivo studies of drug actions.

Haloperidol regulates neurotensin gene expression in striatum of c-fos-deficient mice

The immediate-early gene c-fos has been proposed to play a role in induction of neurotensin/neuromedin N (NT/N) gene expression in the striatum following acute haloperidol (HAL) treatment. We utilized mice with targeted disruption of the c-fos gene to directly test this hypothesis. A robust increase in NT/N gene expression was observed in the dorsolateral striatum (DLSt) in both wild-type (WT) and c-fos-deficient mice 4-6 h after a single injection of HAL (1 or 4 mg/kg) indicating that products of the c-fos gene are not absolutely required for induction of NT/N mRNA. The basal expression of preprotachykinin, preproenkephalin and preprocholecystokinin mRNAs did not differ between WT and c-fos knockout mice. HAL treatment first increased striatal NT/N mRNA on postnatal day (PD) 10. HAL-induced NT/N mRNA levels were significantly lower in c-fos knockout mice than in WT mice on PD 10 and 15. These findings indicate that reliance on c-fos may be greater earlier in development and that redundant molecular pathways can lead to induction of NT/N mRNA in mouse striatum.

Neurotensin and neuroendocrine regulation

More than two decades of research indicate that the peptide neurotensin (NT) and its cognate receptors participate to a remarkable extent in the regulation of mammalian neuroendocrine systems, potentially at multiple levels in a given system. NT-synthesizing neurons appear to exert a direct or indirect stimulatory influence on neurosecretory cells that synthesize gonadotropin-releasing hormone, dopamine (DA), somatostatin, and corticotropin-releasing hormone (CRH). In addition, context-specific synthesis of NT occurs in hypothalamic neurosecretory cells located in the arcuate nucleus and parvocellular paraventricular nucleus, including distinct subsets of cells which release DA, CRH, or growth hormone-releasing hormone into the hypophysial portal circulation. At the level of the anterior pituitary, NT stimulates secretion of prolactin and occurs in subsets of gonadotropes and thyrotropes. Moreover, circulating hormones influence NT synthesis in the hypothalamus and anterior pituitary, raising the possibility that NT mediates certain feedback effects of the hormones on neuroendocrine cells. Gonadal steroids alter NT levels in the preoptic area, arcuate nucleus, and anterior pituitary; adrenal steroids alter NT levels in the hypothalamic periventricular nucleus and arcuate nucleus; and thyroid hormones alter NT levels in the hypothalamus and anterior pituitary. Finally, clarification of the specific neuroendocrine roles subserved by NT should be greatly facilitated by the use of newly developed agonists and antagonists of the peptide.

Atypical and typical neuroleptic treatments induce distinct programs of transcription factor expression in the striatum

Atypical and typical neuroleptics, when administered chronically, can bring about profound but contrasting changes in schizophrenic symptoms and motor activation and dramatically modulate brain neurochemistry. To explore the transcriptional events that might be involved in this neurochemical regulation, we used immunohistochemistry and immunoblotting to examine the expression patterns of two bZip transcription factors, c-Fos and FosB, in the striatum of rats treated acutely and chronically with neuroleptic drugs of different classes. Typical and atypical neuroleptic drugs produced contrasting regulatory effects on a FosB-like protein of ca. 36-39 kDa, the molecular weight of truncated FosB (delta FosB). Chronic treatments with two typical neuroleptics, haloperidol and metoclopramide, but not with the atypical neuroleptic clozapine, led to markedly enhanced FosB-like immunoreactivity in the caudoputamen. Further, c-Fos-like protein in the striatum, considered a marker for the induction of antipsychotic actions by neuroleptic treatments, was downregulated by chronic treatment with the two potent antipsychotic drugs tested, but not by chronic treatment with metoclopramide, which has low antipsychotic efficacy but induces extrapyramidal side effects. These results suggest that chronic treatments with neuroleptics having different effects on cognitive and motor behavior induce different long-term changes in transcription factor expression in the striatum. Nevertheless, we found that neuroleptics of both classes regulated transcription factor expression in overlapping populations of striatal neurons expressing enkephalin or DARPP-32. Contrasting patterns of transcriptional regulation in these neurons may thus contribute to the distinct neurochemical and behavioral effects that characterize neuroleptics of different classes.

Evidence that PC2 is the endogenous pro-neurotensin convertase in rMTC 6-23 cells and that PC1- and PC2-transfected PC12 cells differentially process pro-neurotensin

The neuropeptide precursor proneurotensin/neuromedin N (pro-NT/NN) is mainly expressed and differentially processed in the brain and in the small intestine. We showed previously that rMTC 6-23 cells process pro-NT/NN with a pattern similar to brain tissue and increase pro-NT/NN expression in response to dexamethasone, and that PC12 cells also produce pro-NT/NN but are virtually unable to process it. In addition, PC12 cells were reported to be devoid of the prohormone convertases PC1 and PC2. The present study was designed to identify the proprotein convertase(s) (PC) involved in pro-NT/NN processing in rMTC 6-23 cells and to compare PC1- and PC2-transfected PC12 cells for their ability to process pro-NT/NN. rMTC 6-23 cells were devoid of PC1, PC4, and PC5 but expressed furin and PC2. Stable expression of antisense PC2 RNA in rMTC 6-23 cells led to a 90% decrease in PC2 protein levels that correlated with a > 80% reduction of pro-NT/NN processing. PC2 expression was stimulated by dexamethasone in a time- and concentration-dependent manner. Stable PC12/PC2 transfectants processed pro-NT/NN with a pattern similar to that observed in the brain and in rMTC 6-23 cells. In contrast, stable PC12/PC1 transfectants reproduced the pro-NT/NN processing pattern seen in the gut. We conclude that (i) PC2 is the major pro-NT/NN convertase in rMTC 6-23 cells; (ii) its expression is coregulated with that of pro-NT/NN in this cell line; and (iii) PC2 and PC1 differentially process pro-NT/NN with brain and intestinal phenotype, respectively.

Characterization of promoter elements required for cell-specific expression of the neurotensin/neuromedin N gene in a human endocrine cell line

Expression of the gene encoding neurotensin/neuromedin N (NT/N) is mostly limited to the brain and specialized enteroendocrine cells (N cells) of the distal small intestine. We have analyzed the NT/N DNA sequences upstream of the RNA start site that direct cell-specific expression using a novel human endocrine cell line, BON, that resembles intestinal N cells in several important aspects, including NT/N precursor protein processing, ratios of different NT/N mRNA forms, and high levels of constitutive expression of the NT/N gene. Transient transfection assays with plasmids with progressive 5' deletions of the rat NT/N promoter identified the proximal 216 bp of 5' flanking sequences as essential for high-level constitutive NT/N expression in BON cells. In addition, a detailed mutational analysis defined multiple regions within the proximal 216 bp that contribute to cell-specific NT/N expression. These elements include a proximal cyclic AMP response element (CRE)/AP-1-like motif (TGACATCA) that binds c-Jun, JunD, CRE-binding (CREB), and ATF proteins, a near-consensus glucocorticoid response element, and a distal consensus AP-1 site that binds c-Fos, Fra-1, and JunD. In addition, elements contained within two 21-bp imperfect direct repeats play an important role in NT/N expression in BON cells and may bind novel factors that act as positive regulators of NT/N expression. DNase I footprinting and gel shift analyses demonstrate that the sites identified by mutational analysis, and at least one additional site, specifically bind BON cell nuclear proteins in vitro. We speculate that a complex pattern of regulation requiring interaction between a proximal CRE/AP-1-like motif and other upstream control elements play an important role in the high-level constitutive expression of NT/N in the human endocrine cell line BON. In addition, the BON cell line provides a unique model to further characterize the factors regulating cell-specific NT/N expression and to better understand the mechanisms responsible for the terminal differentiation of the N-cell lineage in the gut.

C-fos mediates antipsychotic-induced neurotensin gene expression in the rodent striatum

The ubiquitous inducibility of the immediate-early gene c-fos in the central nervous system has led to the search for downstream genes which are regulated by its product, Fos. Recent evidence suggests that c-fos induction by a single injection of the classical antipsychotic haloperidol may contribute to the subsequent increase in neurotensin gene expression in the rodent striatum. Consistent with this proposal, in the present study haloperidol-induced Fos-like immunoreactivity and neurotensin/neuromedin N messenger RNA were found to be expressed by the same population of striatal neurons. Moreover, inhibition of haloperidol-induced c-fos expression by intrastriatal injection of antisense phosphorothioate oligodeoxynucleotides complimentary either to bases 109-126 or 127-144 of c-fos attenuated the subsequent increase in neurotensin/neuromedin N messenger RNA. However, injection of a sense phosphorothioate oligodeoxynucleotide corresponding to bases 127-144 of c-fos did not reduce haloperidol-induced c-fos or neurotensin/neuromedin N expression. Furthermore, constitutive expression of Jun-like immunoreactivity in the striatum was not reduced by either the sense or antisense phosphorothioate oligodeoxynucleotides. Similarly, the sense and antisense phosphorothioate oligodeoxynucleotide failed to reduce proenkephalin messenger RNA, which is located in the same striatal neurons that express haloperidol-induced neurotensin/neuromedin N messenger RNA, which is located in the same striatal neurons that express haloperidol-induced neurotensin/neuromedin N messenger RNA. Lastly, haloperidol-induced increases in nerve growth factor I-A-, JunB- and FosB-like immunoreactivity and fosB messenger RNA were not decreased by intrastriatal injection of either the sense or antisense phosphorothioate oligodeoxynucleotides. These results indicate that the antisense phosphorothioate oligodeoxynucleotides attenuated haloperidol-induced neurotensin/neuromedin N expression by selectively reducing c-fos expression and emphasize the potential importance of immediate-early gene induction in the mechanism of action of this antipsychotic drug.

The neurotensin gene is a downstream target for Ras activation

Ras regulates novel patterns of gene expression and the differentiation of various eukaryotic cell types. Stable transfection of Ha-ras into the human colon cancer line CaCo2 results in the morphologic differentiation to a small bowel phenotype. The purpose of our study was to determine whether the Ras regulatory pathway plays a role in the expression of the neurotensin gene (NT/N), a terminally differentiated endocrine product specifically localized in the gastrointestinal tract to the adult small bowel. We found that CaCo2-ras cells, but not parental CaCo2, express high levels of the human NT/N gene and, moreover, that this increase in gene expression is regulated at the level of transcription. Transfection experiments using NT/N-CAT mutation constructs identify the proximal 200 bp of NT/N flanking sequence as sufficient for maximal Ras-mediated NT/N reporter gene induction. Furthermore, a proximal AP-1/CRE motif is crucial for this Ras-mediated NT/N activation. Wild-type Ha-ras induces NT/N gene expression, albeit at lower levels than activated Ras; a dominant-negative Raf blocks this NT/N induction, suggesting that Raf lies down-stream of Ras in this pathway. In addition, postconfluent cultures of CaCo2 cells, which are differentiated to a small bowel phenotype, express the NT/N gene by 6 d after reaching confluency; this increase of NT/N expression is associated with concomitant increases of cellular p21ras protein. We conclude that Ras (both wild-type and activated) enhances expression of the NT/N gene in the gut-derived CaCo2 cell line, suggesting an important role for the Ras signaling pathway in NT/N gene transcription. Our results underscore the possibility that tissue-specific genes (such as NT/N) expressed in distinct subpopulations of the gut may be subject to Ras regulation. Finally, we speculate that the NT/N gene and the CaCo2 and CaCo2-ras cell systems will provide unique models to further define the cellular mechanisms leading to mammalian intestinal differentiation.

Region-specific regulation of neuropeptide mRNAs in rat limbic forebrain neurones by aldosterone and corticosterone

1. We have determined in adrenalectomized male rats the effects of clamping plasma corticosterone and aldosterone at various concentrations on corticotropin-releasing hormone (CRH), neurotensin/neuromedin N (NT/N) and proenkephalin (pENK) mRNAs in the hypothalamus and amygdala using semi-quantitative in situ hybridization. 2. Corticosterone differentially regulated the levels of CRH and NT/N but not pENK mRNA. These effects were cell specific. CRH mRNA was reduced in the hypothalamic paraventricular nucleus (PVH), but increased in the central nucleus of the amygdala and bed nuclei of the stria terminalis. NT/N mRNA was never seen in the PVH, whereas levels increased in the central nucleus of the amygdala, but were unaffected in the lateral hypothalamic area. In those regions expressing pENK mRNA, levels were unaffected in all treatment groups. 3. CRH mRNA in both the central nucleus of the amygdala and PVH, and NT/N mRNA in the central nucleus of the amygdala were most sensitive to plasma corticosterone concentrations of less than 120 ng ml-1, i.e. those seen away from the peak of the diurnal rhythm. In adrenalectomized animals CRH mRNA in both the central nucleus of the amygdala and PVH could be set at levels usually seen in intact animals by the same plasma concentration of corticosterone. 4. The levels of CRH mRNA in the PVH and the central nucleus of the amygdala were closely correlated, while CRH and NT/N mRNA levels were similarly correlated in the central nucleus of the amygdala suggesting the existence of a common regulatory mechanism. The ED50 of their responses to corticosterone and correlations with thymus weight suggested the operation of glucocorticoid (type II) receptor mechanisms. 5. In the absence of corticosterone, aldosterone increased CRH and NT/N mRNA accumulation in the central nucleus of the amygdala, and increased CRH but not NT/N mRNA accumulation in the PVH. Aldosterone also blunted the dose-response effects of corticosterone on CRH and NT/N mRNA levels in the central nucleus of the amygdala, but not in the PVH. 6. These results suggest that, in intact animals, adrenal steroids play a major role in maintaining the levels of neuropeptide mRNAs in the PVH, bed nuclei of the stria terminalis and central nucleus of the amygdala. The results underscore the importance of cell-specific mechanisms operating to regulate the expression of neuropeptide genes in different cell types in response to diverse physiological conditions.

Treatment of PC12 cells by nerve growth factor, dexamethasone, and forskolin. Effects on cell morphology and expression of neurotensin and tyrosine hydroxylase

Several lines of anatomical, neurochemical, electrophysiological, and behavioral evidence suggest the existence of physiological interactions between neurotensin (NT) and the brain dopaminergic systems. Thus, NT has been shown to exert a neuroleptic-like action and could be implicated in the pathogenesis and treatment of schizophrenia. It is thus of particular importance to develop in vitro cell culture systems as models to study such interactions. Rat adrenal pheochromocytoma PC12 cells, which expressed high levels of tyrosine hydroxylase, were used in the present study. In contrast to rat brain cells in primary cultures, PC12 cells did not express functional NT receptors. However, they were able to express both NTmRNA and NT in response to NGF, forskolin, and dexamethasone. Those neurochemical modifications furthermore may be related to changes in the morphology of the PC12 cells in response to NGF, forskolin, and dexamethasone alone or in combination. These data suggest that PC12 cells may provide a useful model to study in vitro the regulation of both catecholamine and neurotensin phenotypes.

Synergistic induction of neurotensin gene transcription in PC12 cells parallels changes in AP-1 activity

A consensus AP-1 site in the promoter of the rat neurotensin/neuromedin N (NT/N) gene is a critical regulatory element required for synergistic regulation by combinations of nerve growth factor (NGF), lithium, glucocorticoids, and adenylate cyclase activators. A rapid RNase protection assay was developed to examine the kinetics of NT/N gene activation and to determine whether activation requires newly synthesized proteins. Either NGF or lithium in combination with dexamethasone and forskolin transiently activated NT/N gene expression, but with distinct kinetics. Protein synthesis was not required for activation when NGF was used as the permissive inducer, but was required for the rapid down-regulation of the response. In contrast, lithium responses were attenuated in the absence of protein synthesis, consistent with a requirement for newly synthesized AP-1 complexes in activation. In all cases, increases in NT/N gene expression closely paralleled increases in AP-1 binding activity. Lithium in combination with other inducers caused delayed increases in both AP-1 binding activity and c-jun, c-fos and fra-1 gene expression. These results indicate that NGF and lithium exert their effects on NT/N gene expression through distinct pathways. The lithium pathway is active in neuronally-differentiated PC12 cells and could potentially be involved in the regulation of NT/N gene expression in the nervous system.

BON cells display the intestinal pattern of neurotensin/neuromedin N precursor processing

Antisera towards the bioactive peptides, neurotensin (NT, 13 residues) and neuromedin N (NMN, 6 residues), as well as towards three regions of their 147-residue canine precursor were used to identify and to quantitate precursor-derived peptides in extracts of human BON cells. This cell-line, which was obtained from a human pancreatic carcinoid tumor, constitutively expresses NT/NMN mRNA and secretes NT. Quantitation of seven precursor-derived peptides led us to conclude that BON cells display the intestinal pattern of NT/NMN precursor processing, which is primarily characterized by the production of a large molecular (125 amino acid) form of NMN. Four large molecular components, identified by immunochemical analyses and Western blotting, displayed physico-chemical properties which, for the most part, were consistent with the structures predicted from the partially-known human mRNA sequence. However, as shown previously for these peptides in canine gut, the empirically determined M(r) and pI values were slightly higher than those predicted solely from the amino acid content, perhaps due to the presence of additional substituents. These results suggest that BON cells may provide a good in vitro model in which to study the regulation of intestinal NT/NMN precursor processing and the nature of the enzyme(s) involved.

Opposing roles for dopamine D2 and D3 receptors on neurotensin mRNA expression in nucleus accumbens

Using in situ hybridization histochemistry in rat nucleus accumbens, we show that the dopamine D3 receptor mRNA is expressed in the ventromedial part of the shell subdivision, where its gross distribution matches that of neurotensin mRNA. In addition, hybridization studies at the cellular level show that a large fraction of the neurotensin neurons co-express the D3 receptor mRNA in this restricted area. In contrast, the dopamine D2 receptor mRNA is expressed mainly in the core and marginally in the shell, at the level of the cone. In rats treated by haloperidol and sulpiride, two D2-like receptor antagonists, but not by SCH 23390, a D1-like receptor antagonist, proneurotensin mRNA was increased in the D2 receptor mRNA-rich areas but decreased in the D3 receptor mRNA-rich areas. This suggests that the D2 and D3 receptors control neurotensin mRNA expression negatively and positively, respectively.

Coexpression of neurotensin and c-fos mRNAs in rat neostriatal neurons following acute haloperidol

Our previous studies have shown several fold induction of neurotensin/neuromedin N (NT/N) primary transcripts and mature cytosolic mRNA in the dorsolateral region of the rat neostriatum (DLSt) following a single dose of the neuroleptic, haloperidol. The apparent enhancement of NT/N gene transcription by haloperidol is preceded by increases in the expression of c-fos mRNA in the same region. The present study used double-labeling in situ hybridization technique to study cellular localization of NT/N and c-fos mRNA following acute haloperidol treatment. Simultaneous detection of NT mRNA and c-fos mRNA was achieved using cRNA probes synthesized in vitro with digoxigenin- and 35S-labeled UTP, respectively. Interestingly, approximately 75% of DLSt neurons expressing NT/N mRNA also displayed c-fos mRNA in rats treated with haloperidol (1 mg/kg, i.p.) for 1 h. Colocalization of c-fos mRNA in haloperidol-responsive NT neurons in the DLSt suggests that haloperidol's induction of NT/N gene transcription may involve participation of the transcription factor Fos and the AP-1 consensus sequence in regulatory region of the NT/N gene.

Long-term action of lithium: a role for transcriptional and posttranscriptional factors regulated by protein kinase C

Lithium, a simple monovalent cation, represents one of psychiatry's most important treatments and is the most effective treatment for reducing both the frequency and severity of recurrent affective episodes. Despite extensive research, the underlying biologic basis for the therapeutic efficacy this drug remains unknown, and in recent years, research has focused on signal transduction pathways to explain lithium's efficacy in treating both poles of manic-depressive illness. Critical to attributions of therapeutic relevance to any observed biochemical effect, however, is the observation that the characteristic prophylactic action of lithium in stabilizing the profound mood cycling of bipolar disorder requires a lag period for onset and is not immediately reversed upon discontinuation of treatment. Biochemical changes requiring such prolonged administration of a drug suggest alterations at the genomic level but, until recently, little has been known about the transcriptional and posttranscriptional factors regulated by chronic drug treatment, although long-term changes in neuronal synaptic function are known to be dependent upon the selective regulation of gene expression. In this paper, we will present evidence to show that chronic lithium exerts significant transcriptional and posttranscriptional effects, and that these actions of lithium may be mediated via protein kinase C (PKC)-induced alterations in nuclear transcription regulatory factors responsible for modulating the expression of proteins involved in long-term neural plasticity and cellular response. Such target sites for chronic lithium may help unravel the processes by which a simple monovalent cation can produce a long-term stabilization of mood in individuals vulnerable to bipolar illness.

Induction of the neurotensin (NT) gene in PC12 cells gives rise to NT precursor (approximately 88%), NT(3-13)-like peptide (approximately 10%), and NT (approximately 2%)

Neurotensin (NT) is coexpressed with catecholamines in sympathetic neurons and adrenal chromaffin cells. A pheochromocytoma PC12 cell line can also be induced to express the NT gene and produce immunoreactive NT. In the present study, NT mRNA was quantified under various hormonal conditions and NT precursor synthesis rates were determined by pulse labeling and immunoprecipitation. In addition, NT precursor and NT-related products were measured using RIA and were characterized using HPLC and Sephadex chromatography. Neurotensin mRNA, NT precursor synthesis, and NT precursor/product levels were correlated. Surprisingly, NT appeared to be a minor product, both in cells and media: NT precursor (approximately 88%), NT(3-13)-like peptide (approximately 10%), and NT (approximately 2%). Neurotensin added to cultures was not converted to NT(3-13). Treatment of cells with 60 mM KCl or various secretagogues induced Ca(2+)-dependent release of NT precursor, NT(3-13), and NT in proportion to their cellular contents. These results suggest a) that NT precursor processing in induced PC12 cells was much slower than NT precursor synthesis, b) that NT(3-13) was a major product and NT a minor one, and c) that NT precursor and its products were stored within secretory vesicles.

PC12 cells can be induced to produce, but do not process, the neurotensin/neuromedin N precursor

Neurotensin and neuromedin N are two biologically active, related peptides that are encoded in the same precursor molecule. In the rat, the precursor consists of a 169-residue polypeptide containing in its C-terminal region one copy each of neurotensin and neuromedin N. Four Lys-Arg sequences, which are thought to represent putative processing sites, occur in the precursor molecule. Studies by others have shown that rat pheochromocytoma PC12 cells produced neurotensin and dramatically increased their neurotensin/neuromedin N precursor mRNA content in response to a combination of nerve growth factor, dexamethasone, forskolin, and Li+. Here, we investigated the effects of this combination of inducers on the posttranslational processing of the neurotensin/neuromedin N precursor in PC12 cells. Radioimmunoassays coupled to HPLC and arginine-directed tryptic cleavage of cell extracts were performed with five antisera specific for precursor sequences adjacent to basic doublets. Thus, mature neurotensin and neuromedin N represented less than 1% of the total precursor content in PC12 cells. The PC12 cell line may represent an interesting model with which one could transfect the recently cloned prohormone convertases PC1 and PC2, thereby allowing the study of the role of these enzymes in the processing of the neurotensin/neuromedin N precursor.

Direct transcriptional stimulation of the ornithine decarboxylase gene by Fos in PC12 cells but not in fibroblasts

We have established rat PC12 pheochromocytoma cell lines stably expressing the estrogen-activatable transcription factor FosER to identify genes that can be regulated by c-Fos in this neuronal cell type. Induction of ectopic c-Fos activity in PC12 cells increased the mRNA levels of the ornithine decarboxylase (ODC) and tyrosine hydroxylase genes with similar kinetics and to the same maximal level as nerve growth factor treatment. In both cases the rate of transcription initiation was increased. Induction of the ODC gene occurred even in the absence of protein synthesis, indicating direct regulation by FosER. ODC expression, however, was not induced by a mutant FosER protein containing a proline insertion in the basic region of the c-Fos moiety, demonstrating the requirement for a functional DNA-binding domain. These data show that FosER, and by extrapolation c-Fos, can directly activate transcription of the endogenous ODC gene in PC12 cells by binding to cis-regulatory sequences. Activation of the ODC gene was unexpectedly transient, as transcripts returned to the basal level after prolonged exposure of PC12 cells to FosER activity. Furthermore, ODC transcription was not at all induced by FosER in rat fibroblasts. To account for this cell-specific action of FosER, we propose that stimulation of the ODC gene by FosER requires either (i) cooperation with another transcription factor(s) or (ii) a specific pattern of modification which is present in PC12 cells but not in otherwise unstimulated fibroblasts. One or both of these mechanisms may be employed by cells to achieve selective gene activation in response to apparently stereotyped induction of c-fos.

Direct transcriptional stimulation of the ornithine decarboxylase gene by Fos in PC12 cells but not in fibroblasts

We have established rat PC12 pheochromocytoma cell lines stably expressing the estrogen-activatable transcription factor FosER to identify genes that can be regulated by c-Fos in this neuronal cell type. Induction of ectopic c-Fos activity in PC12 cells increased the mRNA levels of the ornithine decarboxylase (ODC) and tyrosine hydroxylase genes with similar kinetics and to the same maximal level as nerve growth factor treatment. In both cases the rate of transcription initiation was increased. Induction of the ODC gene occurred even in the absence of protein synthesis, indicating direct regulation by FosER. ODC expression, however, was not induced by a mutant FosER protein containing a proline insertion in the basic region of the c-Fos moiety, demonstrating the requirement for a functional DNA-binding domain. These data show that FosER, and by extrapolation c-Fos, can directly activate transcription of the endogenous ODC gene in PC12 cells by binding to cis-regulatory sequences. Activation of the ODC gene was unexpectedly transient, as transcripts returned to the basal level after prolonged exposure of PC12 cells to FosER activity. Furthermore, ODC transcription was not at all induced by FosER in rat fibroblasts. To account for this cell-specific action of FosER, we propose that stimulation of the ODC gene by FosER requires either (i) cooperation with another transcription factor(s) or (ii) a specific pattern of modification which is present in PC12 cells but not in otherwise unstimulated fibroblasts. One or both of these mechanisms may be employed by cells to achieve selective gene activation in response to apparently stereotyped induction of c-fos.

Blunting of the neurotensin mRNA response to haloperidol in the striatum of aging rats: possible relationship to decline in dopamine D2 receptor expression

Neuroleptic drugs such as haloperidol (H) induce a rapid increase in neurotensin/neuromedin N (NT/N) gene expression in the dorsolateral striatum (DLSt) and nucleus accumbens (NA) in young adult rats. This effect may be mediated by post-receptor effectors that are activated by dopamine D2 receptor antagonism. The regional pattern of induction of neurotensin gene expression correlates with the side effect profile of particular neuroleptics. As motor side effects of H differ in aged animals, we hypothesized that the regional expression of the neurotensin gene may differ between young and old animals. We administered H or saline acutely to 3, 14, and 25 month-old Fischer 344 rats, followed by in situ hybridization and quantitative autoradiography for NT/N mRNA. There was a significant age effect on the H-induced NT/N mRNA response in the DLSt, but not the NA, of older animals. In addition to the blunted NT/N mRNA response, significant decreases in D2 receptor mRNA were observed in the lateral striatum of another group of young, middle-aged, and aged rats. Age-related blunting of the NT/N mRNA response to H in the DLSt may be due in part to a decrease in D2 receptors in this structure.