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P Vernier

Publications and source records attributed to P Vernier.

At least 55 records · Page 3Linked to original sources
PubMed1995

Identification of a neural-specific cDNA, NPDC-1, able to down-regulate cell proliferation and to suppress transformation.

Immortalized neural precursor cell lines carrying the polyoma large tumor (T) gene have been shown previously to retain a clear-cut contact inhibition of growth and to differentiate in vitro. In the present study, we have identified and isolated cDNA clones corresponding to RNA expressed preferentially when these cells reach confluence. One of them, NPDC-1, is expressed specifically in the nervous system. The transfection of dividing cells with a NPDC-1 expression vector results in the inhibition of cell proliferation. In addition, the stable introduction of NPDC-1 into transformed cells, even of nonneural origin, leads to the suppression of transformed characteristics.

Amino Acid Sequence↗
PubMed1995

Sex steroid hormones change the differential distribution of the isoforms of the D2 dopamine receptor messenger RNA in the rat brain.

The two isoforms of the rat dopamine D2 receptor are generated by alternative splicing of the pre-messenger RNA and differ in the length of their third cytoplasmic loop involved in coupling to G-proteins. As quantified by polymerase chain reaction, the long isoform D2L is predominant in the pituitary gland, the striatum and to a lesser extend in the olfactory tubercle, whereas the short isoform D2S is relatively more abundant in the hypothalamus and the substantia nigra. Changes in circulating sex hormone levels modulated the splicing without affecting the total amount of D2 receptor messenger RNA. Castration of male rats increased the ratio D2L/D2S in the pituitary, hypothalamus and substantia nigra, and decreased it in the olfactory tubercle. Testosterone substitution reversed the effect of castration in the pituitary and olfactory tubercle but not in the substantia nigra. In castrated rats, 17beta-estradiol had a similar effect to that of testosterone in the olfactory tubercle, indicating that testosterone may act after aromatization of estradiol. In the hypothalamus, 17beta-estradiol alone reversed the effect of castration. In the striatum, neither castration nor hormonal treatments modified the splicing of the D2 receptor mRNA. Treatment of animals with specific androgen and estrogen receptor blockers confirmed that steroids were acting through their specific intracellular receptors. These observations suggest a molecular mechanism, physiologically relevant, by which circulating sex hormones could modulate dopamine transmission in areas implicated in reproductive and parental behaviours.

Animals↗
PubMed1995

An evolutionary view of drug-receptor interaction: the bioamine receptor family.

The large molecular diversity of receptors and their subtypes means that the pharmacologist is faced with many puzzling characterization questions. First, the molecular diversity of the receptors is deciphered only in part by a pharmacological approach, which precludes a satisfactory receptor classification based solely on pharmacological characteristics. Second, the physiological counterpart of the numerous subtypes of receptors specifically activated by single endogenous ligands remains unclear. Here, Philippe Vernier and colleagues use the example of the bioamine G protein-coupled receptors to show that many of the apparent inconsistencies that emerge from pharmacological and molecular characterizations of receptors can be better understood if the evolutionary history of the receptors is taken into account.

Amines↗
PubMed1994

SPARC and thrombospondin genes are repressed by the c-jun oncogene in rat embryo fibroblasts.

The sequence-specific transcription factor c-Jun displays oncogenic potential in mammalian cells either in cooperation with activated Ras in primary embryonic fibroblasts or alone in established cell lines. Although pathways for signal transduction leading to activation of c-Jun proteins have been extensively studied, little is known about the events downstream of c-Jun stimulation. We isolated cellular genes that are targets of c-Jun by differential screening of a cDNA library from primary rat embryo fibroblasts. Two transcripts with sequences similar to known genes were repressed following transitory expression of a c-Jun-encoding vector. They correspond to the SPARC and thrombospondin 1 (TS1) genes, encoding extracellular matrix proteins. These genes are tightly regulated during embryogenesis and in adult tissues and are involved in the control of cell growth. c-Jun transitory repression of these two genes was demonstrated both in primary cells and in FR3T3, an established fibroblast cell line. The repression was also detected in FR3T3 derivatives stably transformed by c-Jun or Ras. Although c-Jun regulation of the TS1 gene was found at the promoter level, preliminary results strongly suggest that repression of SPARC and TS1 gene expression are mediated by a secreted factor. In contrast, expression of these genes was unaffected by transformation with oncogenes from DNA viruses. Our results identify new, specific, probably indirect c-Jun target genes and suggest previously unsuspected regulatory roles for SPARC and thrombospondin in the control of cell growth.

Animals↗
PubMed1994

Structural organization and chromosomal localization of a human gene (HIP/PAP) encoding a C-type lectin overexpressed in primary liver cancer.

We previously identified, through differential screening of a human primary liver cancer library, a novel gene (named HIP) the expression of which is markedly increased in 25% of human primary liver cancers. HIP mRNA expression is tissue specific since it is restricted to pancreas and small intestine. HIP protein consists in a signal peptide linked to a carbohydrate-recognition domain (CRD), typical of C-type lectins without other binding domains. We have proposed that HIP and related proteins belong to a new family of C-type lectins. Drickamer [Drickamer, K. (1993) Curr. Opin. Struct. Biol. 3,393-400] included this group of proteins in his classification of C-type lectins as the free CRD (group VII) lectins. In the present report we describe the genomic organization and the chromosomal localization of HIP. We have shown that HIP is in fact the pancreatitis-associated protein (PAP) and provided a phylogenetic analysis of the free CRD lectins. Furthermore, the analysis of HIP/PAP gene indicates that the HIP/PAP CRD is encoded by four exons, a pattern shared with all members of this group of proteins. This common intron-exon organization indicates an ancient divergence of the free CRD-lectin group from other groups of C-type lectins. We provide evidence for the localization of HIP/PAP on chromosome 2, suggesting previous duplication of HIP/PAP and the related reg I alpha and reg I beta genes from the same ancestral gene. Finally, the sequence of the 5' upstream region of the HIP gene shows several potential regulatory elements which might account for the enhanced expression of the gene during pancreatic inflammation and liver carcinogenesis.

Amino Acid Sequence↗
PubMed1994

Transcription of the rat dopamine-D2-receptor gene from two promoters.

Modulation of the expression of the D2-dopamine receptor gene is involved in several pathological and developmental circumstances. The gene and the corresponding promoter regions of the rat D2 receptor were isolated and partly characterized to study its regulation. The rat D2-receptor gene spans at least 50 kb, and possesses eight exons; its organization was compared to those of the other dopamine-receptor genes in a phylogenetic perspective. The gene contains two transcription-start sites: the major one is located about 320 bp upstream from the 3' end of the first exon, and a minor site is 70 bp further upstream. Transient-expression assays with fusion constructs comprising fragments of the D2-promoter region and the luciferase reporter gene confirmed the existence of two independent, TATA-lacking promoters. Both promoters separately induced transcription of the luciferase gene in C6 glioma, primary fibroblasts, GH3 and MMQ pituitary cell lines, among which only the MMQ cells normally express the D2 receptor. Transcription is enhanced by the reunion of the two promoters, and modified by the addition of upstream sequences. Thus the 1-kb promoter region analysed does not contain all the elements necessary to confer tissue-specific expression of the gene, but does carry some positive and negative regulatory elements, which remain to be characterized.

Animals↗
PubMed1994

Rab3 proteins: key players in the control of exocytosis.

Although some mechanistic aspects of exocytosis, such as fusion events, have been well documented by the technique of time-resolved membrane-capacitance measurement, it was only recently that new insights into the molecular mechanisms involved in the traffic of secretory vesicles were provided by the convergence of different lines of research. In this review Lledo et al. present some of the recent findings concerning small GTPases of the Rab3 subfamily which regulate hormone release, triggered by entry of Ca2+, in endocrine and neuroendocrine cells. In view of these new results, Rab proteins might be considered as candidates for inhibition or stimulation of specific steps involved in vesicle traffic.

Animals↗
PubMed1993

Inhibition of Rab3B expression attenuates Ca(2+)-dependent exocytosis in rat anterior pituitary cells.

Low-molecular-weight GTP-binding proteins (small G proteins) of the Rab family have been proposed to act as central regulators of vesicular traffic, and proteins of the Rab3 subfamily (Rab3A, B, C and D) are thought to be associated with membrane vesicles or granules undergoing exocytotic fusion with the plasma membrane. Rab3A is highly expressed in brain, whereas Rab3B is the major form found in rat anterior pituitary gland. We report here that antisense oligonucleotides against Rab3B, introduced into pituitary cells using the whole-cell patch clamp technique, specifically and reversibly block expression of Rab3B. We find that calcium-dependent exocytosis is inhibited without affecting endocytosis. Antisense oligonucleotides directed against Rab3A have no effect. Our results indicate that Rab3B is likely to be a key intracellular signalling molecule which can control exocytosis downstream of other calcium-dependent processes in anterior pituitary cells.

Animals↗
PubMed1993

Bioamine receptors: evolutionary and functional variations of a structural leitmotiv.

Bioamines act as neurohormonal messengers through their binding to receptors which belong to the largest membrane protein family known so far: the seven spanning membrane receptors. This class of receptors transmits the effect of agonist binding to intracellular effectors by interacting with an intermediary G-protein. The diversity of receptor subtypes inside the protein family, observed in many animal species, is the result of a long evolutionary process. The tendency to protein diversification depends upon gene duplications and upon the continuous accumulation of mutations. The maintenance of vital functions in organisms, however, strictly requires enough structural conservation to ensure the functionality of the corresponding proteins. Both forces cooperate to ensure the adaptation of organisms to a changing environment. We have reviewed here the main conformational and functional constraints exerted on the structure of the bioamine receptors. They are mainly the transmembrane conformation of the receptors, their ability to bind ligands, to interact with G-proteins and to desensitize. The molecular basis of the biochemical and pharmacological differences used to classify the members of the receptor family have also been examined. Interestingly, this classification is very close to that obtained by the molecular phylogeny methods, used to elucidate the evolutionary relationships between bioamine receptors. However, this latter classification allows to accurately distinguish between different receptor subtypes (paralogous genes) and species homologous (orthologous genes). In addition, the calculation of phylogenetical distances reveals two main periods of diversification: the first one occurred before the separation of arthropods from vertebrates, in the Precambrian, and corresponds to the appearance of the main subtypes of the bioamine receptors. The second one, which occurred about 400 million years ago, might accompany the cephalization of the CNS in vertebrates.

Animals↗
PubMed1993

Hormonal control of neural function in the adult brain.

Although the mechanisms by which peripheral hormones modulate complex behaviors are far from being well understood, recent advances in deciphering the mechanisms of hormone action in the brain are promising. Current areas of interest include the molecular mechanisms of steroid receptor action, the steroid modulation of synaptic function, and the mediation of steroid-regulated neuronal and glial plasticity by growth factors or proteins associated with brain development.

Adult↗
PubMed1993

Haloperidol increases PPE mRNA levels in the caudal part of the nucleus accumbens in the rat.

Dopamine exerts a tonic inhibitory control in the regulation of mRNA encoding preproenkephalin (PPE), the precursor of enkephalin, in the dorsal part of the rat striatum. Less is known about the role of this amine in the regulation of PPE mRNA in the ventral part of the striatum which corresponds to the nucleus accumbens. In this study, the effects of an interruption of dopamine transmission by haloperidol (a dopaminergic receptor antagonist) were examined in the rat nucleus accumbens. The levels of PPE mRNA were analysed by in situ hybridization histochemistry by taking into account the complexity of the nucleus accumbens, i.e. by differentiating the rostro-caudal extension of the structure. It was found that PPE mRNA content was increased significantly only in the caudal part of the nucleus, indicating rostro-caudal differences in the haloperidol effects. The differential reactivity of PPE mRNA to dopaminergic receptor blockade and to a lesion of dopaminergic neurones along the rostrocaudal axis of the ventral striatum is discussed.

Animals↗
PubMed1993

Cloning and expression of a rat acetylcholinesterase subunit: generation of multiple molecular forms and complementarity with a Torpedo collagenic subunit.

We obtained a cDNA clone encoding one type of catalytic subunit of acetylcholinesterase (AChE) from rat brain (T subunit). The coding sequence shows a high frequency of (G+C) at the third position of the codons (66%), as already noted for several AChEs, in contrast with mammalian butyrylcholinesterase. The predicted primary sequence of rat AChE presents only 11 amino acid differences, including one in the signal peptide, from that of the mouse T subunit. In particular, four alanines in the mouse sequence are replaced by serine or threonine. In northern blots, a rat AChE probe indicates the presence of major 3.2- and 2.4-kb mRNAs, expressed in the CNS as well as in some peripheral tissues, including muscle and spleen. In vivo, we found that the proportions of G1, G2, and G4 forms are highly variable in different brain areas. We did not observe any glycolipid-anchored G2 form, which would be derived from an H subunit. We expressed the cloned rat AChE in COS cells: The transfected cells produce principally an amphiphilic G1a form, together with amphiphilic G2a and G4a forms, and a nonamphiphilic G4na form. The amphiphilic G1a and G2a forms correspond to type II forms, which are predominant in muscle and brain of higher vertebrates. The cells also release G4na, G2a, and G1a in the culture medium. These experiments show that all the forms observed in the CNS in vivo may be obtained from the T subunit. By co-transfecting COS cells with the rat T subunit and the Torpedo collagenic subunit, we obtained chimeric collagen-tailed forms. This cross-species complementarity demonstrates that the interaction domains of the catalytic and structural subunits are highly conserved during evolution.

Acetylcholinesterase↗
PubMed1993

D2-dopaminergic agonist quinpirole and 8-bromo-cAMP have opposite effects on Go alpha GTP-binding protein mRNA without changing D2 dopamine receptor mRNA levels in striatal neurones in primary culture.

Long-term coordinated regulations (during development or by agonists and second messenger molecules) of the expression of mRNAs encoding D2-dopamine (DA) receptors and D2 receptor-linked Go alpha proteins have been studied by Northern blot analysis in mouse embryonic striatal neurones in primary culture. During the course of the cell culture, the levels of both mRNAs increased, in conjunction with the maturation of the neurones. When the preparation was treated with the D2-DA agonist quinpirole (5-15 hrs, 10(-4) M), which decreases cAMP in these neurones, the levels of Go alpha mRNAs were enhanced whereas that of the D2 mRNA remained unchanged. Conversely, the Go alpha mRNAs, but not the D2 mRNA, decreased when the neurones were exposed to 8-bromo-cAMP (16 hrs, 10(-6) M). It is concluded that, in these experimental conditions where neurones have not yet established their connexions, the longterm regulation of the membrane transmission of D2-DA signal might implicate mainly the Go alpha encoding gene.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1993

[Coupling of metabotropic receptors to ionic channels. Role of G-proteins].

Besides channel receptors, there exist membrane receptors coupled to ionic channels by mean of proteins having GTPase activity. We show here as an example the dopamine receptor in the prolactin secreting cell in the anterior pituitary of the rat. The activation of D2 type receptors promotes varied effects on the electrophysiological properties of the cell membrane. They basically consist in a potassium dependent hyperpolarization and a decrease of excitability, linked to modifications of permeability of voltage-dependent potassium or calcium channels. By means of the patch-clamp technique associated to intracellular dialysis of antibodies or anti-sense oligonucleotides directed against the different G proteins alpha subunits, we have shown that the D2 receptor can activate different cellular effectors (potassium or calcium channels) by the mean of specific G proteins, thus accounting for the functional pleiotropy of the D2 receptor.

Animals↗
PubMed1993

[Calcium-dependent regulated secretion is controlled by GTPase Rab3 in neuroendocrine cells].

Changes in intracellular free calcium concentration ([Ca2+]i) play a fundamental role in the regulation of hormone secretion by endocrine and neuronal cells. The increase in [Ca2+]i is one of the principle events in stimulus-secretion coupling. Secretory phenomena are subjected to modulation via a large number of intracellular factors which can act on vesicular transport, exocytosis or endocytosis. Among these factors are proteins able to bind and hydrolyse the nucleotide GTP belonging to the ras superfamily of small GTPases (or superfamily of small G proteins). GTPases of the Sec4/Ypt1/Rab family have been implicated in the regulation of intracellular vesicle traffic. A role for Rab3 in regulating secretion was initially proposed because of its specific expression in the nervous and endocrine systems, and its association with secretory vesicles. The function of Rab3 has been studied in two types of neuroendocrine cells: the anterior pituitary lactotroph cells and the adrenal medulla chromaffin cells. Two techniques were combined: intracellular injection of antisense oligonucleotides and recombinant proteins, followed by membrane capacitance measurements. The inhibition of Rab3b synthesis in lactotroph cells by antisense oligonucleotides provokes an inhibition of exocytosis. On the other hand, injection of antisense oligonucleotides directed against rab3a into chromaffin cells led to a stimulation of the secretory response to successive depolarizations of the cell membrane. These results indicate that Rab3 proteins control the calcium-dependent secretory process in neuroendocrine cells. In lactotroph cells Rab3b seems to play a stimulatory role, whereas Rab3a acts as a negative regulator of catecholamine release in chromaffin cells.

Animals↗
PubMed1992

A novel gene (HIP) activated in human primary liver cancer.

Differential screening of a human hepatocellular carcinoma complementary DNA library using subtracted probes allowed us to identify a novel gene named HIP whose expression at the transcriptional level was elevated in liver tumors. The protein potentially encoded by the complementary DNA showed 68.5% identity with the bovine pancreatic thread protein and 49% identity with the human reg protein, which has been proposed as a pancreatic islet cell regenerating factor and is identical to the pancreatic stone or pancreatic thread protein. Sequence analysis suggests that the bovine pancreatic thread protein encoding gene is, in fact, the bovine homologue of the HIP gene. Furthermore, data base searches revealed a significant similarity of the HIP and pancreatic stone protein/pancreatic thread protein/reg sequences with the C-type lectin superfamily. The HIP sequence, like pancreatic stone protein/pancreatic thread protein/reg protein, consists of a single carbohydrate recognition domain linked to a signal peptide which would be involved in secretion of the protein. HIP mRNA was expressed at a high level in the tumors of seven of 29 hepatocellular carcinomas. In contrast, HIP mRNA was not detected in nontumorous adjacent areas or in normal adult and fetal liver, suggesting that HIP could be involved in liver cell proliferation or differentiation. HIP mRNA expression is tissue specific, since it is present in the normal small intestine and pancreas, while it could not be evidenced in colon, brain, kidney, or lung. In summary, our results show the existence of a novel family within the superfamily of C-type lectin which may be involved in liver, pancreatic, and intestinal cell proliferation or differentiation.

Amino Acid Sequence↗
PubMed1991

Parallel decrease of glutamic acid decarboxylase and preproenkephalin mRNA in the rat striatum following chronic treatment with a dopaminergic D1 antagonist and D2 agonist.

The levels of mRNA encoding glutamic acid decarboxylase (GAD) and preproenkephalin (PPE) were measured by Northern blot analysis, in the dorsal and the ventral part of the striatum, following long-term treatments with drugs acting selectively on D1 or D2 dopaminergic receptors. Chronic injection of the selective D1 antagonist SCH 23390 elicited a significant decrease in level of both GAD and PPE mRNA (-30%) in the dorsal striatum, whereas no significant change was observed in the ventral striatum. Chronic administration of both SCH 23390 and RU 24926, a D2 agonist, decreased the GAD and PPE mRNA levels in the dorsal (-38 and -57%, respectively) as well as in the ventral (-70 and -60%, respectively) striatum. In the ventral striatum the marked reduction of GAD mRNA levels was paralleled by a significant decrease of Vmax values of GAD enzymatic activity (-41%). These results suggest that the decrease in content of both GAD and PPE mRNA, promoted by the chronic blockade of D1 receptors, is mainly due to the action of dopamine acting on unaffected D2 receptors. Indeed, this decrease is further amplified when the D2 agonist and the D1 antagonist are administered together. Our results substantiate further the molecular mechanisms by which dopamine acts on different populations of GABAergic and enkephalinergic neurons in the two striatal regions examined.

Animals↗