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R K Mishra

Publications and source records attributed to R K Mishra.

At least 19 recordsLinked to original sources
PubMed1998

Selective inhibition of cell-free translation by oligonucleotides targeted to a mRNA hairpin structure.

Using an in vitro selection approach we have previously isolated oligodeoxy aptamers that can bind to a DNA hairpin structure without disrupting the double-stranded stem. We report here that these oligomers can bind to the RNA version of this hairpin, mostly through pairing with a designed 6 nt anchor. The part of the aptamer selected against the DNA hairpin did not increase stability of the RNA-aptamer complex. However, it contributed to the binding site for Escherichia coli RNase H, leading to very efficient cleavage of the target RNA. In addition, a 2'- O -methyloligoribonucleotide analogue of one selected sequence selectively blocked in vitro translation of luciferase in wheat germ extract by binding to the hairpin region inserted upstream of the initiation codon of the reporter gene. Therefore, non-complementary oligomers can exhibit antisense properties following hybridization with the target RNA. Our study also suggests that in vitro selection might provide a means to extend the repertoire of sequences that can be targetted by antisense oligonucleotides to structured RNA motifs of biological importance.

Binding Sites↗
PubMed1998

Chromatin domain boundaries in the Bithorax complex.

Eukaryotic chromosomes are thought to be organized into a series of discrete higher-order chromatin domains. This organization is believed to be important not only in the compaction of the chromatin fibre, but also in the utilization of genetic information. Critical to this model are the domain boundaries that delimit and segregate the chromosomes into units of independent gene activity. In Drosophila, such domain boundaries have been identified through two different approaches. On the one hand, elements like scs/scs' and the reiterated binding site for the SU(HW) protein have been characterized through their activity of impeding enhancer-promoter interactions when intercalated between them. Their role of chromatin insulators can protect transgenes from genomic position effects, thereby establishing independent functional domains within the chromosome. On the other hand, domain boundaries of the Bithorax complex (BX-C) like Fab-7 and Mcp have been identified through mutational analysis. Mcp and Fab-7, however, may represent a specific class of boundary elements; instead of separating adjacent domains that contain separate structural genes. Mcp and Fab-7 delimit adjacent cis-regulatory domains, each of which interacts independently with their target promoters. In this article, we review the genetic and molecular characteristics of the domain boundaries of the BX-C. We describe how Fab-7 functions to confine activating as well as repressive signals to the flanking regulatory domains. Although the mechanisms by which Fab-7 works as a domain boundary remain an open issue, we provide preliminary evidence that Fab-7 is not a mere insulator like scs or the reiterated binding site for the SU(HW) protein.

Animals↗
PubMed1998

Protection against MPTP treatment by an analog of Pro-Leu-Gly-NH2 (PLG, MIF-1)

3(R)-[(2(S)-Pyrrolidinyl-carbonyl)amino]-2-oxo-1-pyrrolidineacetamide (PAOPA) is a peptidomimetic analog of Pro-Leu-Gly-NH2 (PLG or MIF-1) that has previously been demonstrated to be more potent and efficacious that MIF-1 in enhancing dopamine receptor activity. Given the ability of MIF-1 to protect against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) lesioning in C57 BL/6 mice, the present study was undertaken to evaluate the neuroprotective effect of PAOPA in this model. PAOPA was found to be more potent and efficacious that MIF-1 in sparing dopamine and its metabolite levels following 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine administration. Whether the enhanced neuroprotective effect of PAOPA is due to dopamine receptor stimulation, or a result of reduced oxidative stress through normalization of dopamine turnover, remains to be determined.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1997

Design, synthesis, and dopamine receptor modulating activity of diketopiperazine peptidomimetics of L-prolyl-L-leucylglycinamide.

The diketopiperazine "C5" conformational mimic has been incorporated into the L-prolyl-L-leucylglycinamide (PLG, 1) structure and into the bicyclic lactam PLG peptidomimetic structure 3 to give compounds 5 and 6, respectively. These analogues were designed to explore the idea that the N-terminal "C5" conformation, which was found in the crystal structure of 2 and which was mimicked in 4 by the diketopiperazine function, was a factor in the high potency of these two agents. Through the use of the [3H]spiroperidol/N-propylnorapomorphine (NPA) D2 receptor competitive binding assay, both 5 and 6 were found to increase the affinity of the dopamine receptor for agonists and both were found to increase the percentage of D2 receptors which existed in the high-affinity state. These effects were observed when Gpp(NH)p was either absent or present, and they were analogous to the effects observed previously for PLG and the PLG peptidomimetics 2 and 4. However, the potency seen with 5 and 6 was less than that seen for 2 and 4, suggesting that while the N-terminal "C5" conformation may play a role in the potency of the gamma-lactam peptidomimetics of PLG, it does not appear to be the primary factor. In the 6-hydroxydopamine-lesioned animal model of Parkinson's disease, 5 altered apomorphine-induced rotational behavior in a dose-dependent manner. The maximum effect occurred at a dose of 0.01 mg/kg i.p. and resulted in a 52.27 +/- 13.96% (p < 0.001, n = 7) increase in rotations compared to apomorphine administered alone.

Animals↗
PubMed1997

Three small nucleolar RNAs that are involved in ribosomal RNA precursor processing.

Three small nucleolar RNAs (snoRNAs), E1, E2 and E3, have been described that have unique sequences and interact directly with unique segments of pre-rRNA in vivo. In this report, injection of antisense oligodeoxynucleotides into Xenopus laevis oocytes was used to target the specific degradation of these snoRNAs. Specific disruptions of pre-rRNA processing were then observed, which were reversed by injection of the corresponding in vitro-synthesized snoRNA. Degradation of each of these three snoRNAs produced a unique rRNA maturation phenotype. E1 RNA depletion shut down 18 rRNA formation, without overaccumulation of 20S pre-rRNA. After E2 RNA degradation, production of 18S rRNA and 36S pre-rRNA stopped, and 38S pre-rRNA accumulated, without overaccumulation of 20S pre-rRNA. E3 RNA depletion induced the accumulation of 36S pre-rRNA. This suggests that each of these snoRNAs plays a different role in pre-rRNA processing and indicates that E1 and E2 RNAs are essential for 18S rRNA formation. The available data support the proposal that these snoRNAs are at least involved in pre-rRNA processing at the following pre-rRNA cleavage sites: E1 at the 5' end and E2 at the 3' end of 18S rRNA, and E3 at or near the 5' end of 5.8S rRNA.

Animals↗
PubMed1997

Modulation of dopamine receptor agonist-induced rotational behavior in 6-OHDA-lesioned rats by a peptidomimetic analogue of Pro-Leu-Gly-NH2 (PLG).

The present study was undertaken to determine if the previously reported in vitro interactions of the Pro-Leu-Gly-NH2 (PLG) peptidomimetic analogue 3(R)-[(2(S)-pyrrolidinylcarbonyl)amino]-2-oxo-1-pyrrolidineacet amide (PAOPA) with the dopaminergic system could be exhibited in an in vivo animal model using 6-hydroxydopamine (6-OHDA)-lesioned rats. In this model, PAOPA was found to potentiate the contralateral rotational behavior induced by either apomorphine or L-DOPA. PAOPA was 100-fold more potent than PLG, and produced a fourfold greater response than PLG when administered i.p. PAOPA also potentiated contralateral rotations induced by SKF-38393 and quinpirole. In summary, the results of this study indicate that PAOPA, a conformationally constrained peptidomimetic analogue of PLG, can modulate dopaminergic activity in vivo with higher potency and efficacy than PLG.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗
PubMed1996

NMDA and dopamine D2L receptor interaction in human neuroblastoma SH-SY5Y cells involves tyrosine kinase and phosphatase.

Blockade of N-methyl-D-aspartate (NMDA) receptors by the specific antagonists dizocilpine and (+/-)-3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid on human neuroblastoma SH-SY5Y cells expressing human D21 receptors resulted in a significant increase in the density of D2L receptors. In order to understand the mechanism of dopamine D2L receptor induction following NMDA receptor blockade we used specific protein tyrosine kinase and phosphatase inhibitors to demonstrate their involvement in this interaction. The induction of dopamine D2L receptor was measured by radioreceptor binding assay. The density of the dopamine D2L receptor was increased to 109% by the inhibition of protein tyrosine kinase and prevented by the inhibition of phosphatase 1 or 2A. Inactivation of NMDA receptors might effect the phosphorylation-dephosphorylation states of the regulatory proteins and lead to the induction of the D2L receptor gene.

Cell Line↗
PubMed1996

Modulation of dopaminergic neurotransmission in the 6-hydroxydopamine lesioned rotational model by peptidomimetic analogues of L-prolyl-L-leucyl-glycinamide.

Melanocyte stimulating hormone release inhibiting factor (MIF-1), also known as L-prolyl-L-leucyl-glycinamide (PLG), has previously been found to have the ability to modulate dopamine D2-receptor agonist binding both in the striatum and limbic regions. In the present study the 6-hydroxydopamine unilateral lesion model of apomorphine-induced rotational behaviour, in Wistar rats, was used to assess the dopaminergic modulatory activity of PLG and two novel analogues, L-prolyl-L-prolyl-L-prolinamide (analogue A) and (2S, 5R, 7R)-1-Aza-7[3'(S)-1-(2',5'-dioxo-pyrrolidino[2,1-c]piperazino++ +)] -8-oxo-4-thiabicyclo[3.30]octane-2-carboxamide (analogue B). PLG and the two novel analogues showed a bell-shaped dose-response relationship, suggesting that analogue A, B and PLG all manifest their effect through a similar mechanism and exhibit a window of therapeutic efficacy. Analogue A was a 100 times, while analogue B was 10 times, more potent than PLG in increasing the contralateral rotational response when given in combination with apomorphine. Analogue A was also more efficacious than PLG or analogue B at increasing apomorphine-induced contralateral rotations. Intrastriatal administration of either analogue A or B resulted in a greater increase in apomorphine-induced rotations than the most efficacious intraperitoneally delivered dose. The results of the present study suggest that PLG and its two novel analogues are able to modulate dopamine receptor activity and may be possible therapeutic agents for the treatment of Parkinsonian symptoms as well as tardive dyskinesia.

Animals↗
PubMed1996

Targeting nucleic acid secondary structures by antisense oligonucleotides designed through in vitro selection.

Using an in vitro selection approach, we have isolated oligonucleotides that can bind to a DNA hairpin structure. Complex formation of these oligonucleotides with the target hairpin involves some type of triple-stranded structure with noncanonical interaction, as indicated by bandshift assays and footprinting studies. The selected oligomers can block restriction endonuclease cleavage of the target hairpin in a sequence-specific manner. We demonstrate that in vitro selection can extend the antisense approach to functional targeting of secondary structure motifs. This could provide a basis for interfering with regulatory processes mediated by a variety of nucleic acid structures.

Binding Sites↗
PubMed1996

Modulation of brain catecholamine absorbing proteins by dopaminergic agents.

Catecholamine absorbing proteins (CATNAPs) are localized in the brain and thus far have no known biochemical and pharmacological characteristics consistent with other receptor proteins or metabolic enzymes in the central nervous system. The oxidative metabolism of catecholamines in the brain, especially the catabolism of dopamine and its conjugation with metabolic brain proteins, results in the production of highly toxic free radicals. Since such processes are implicated in the pathophysiology of various neurodegenerative diseases, including parkinsonism, and since CATNAPs bind catecholamines with high affinity, there is a need to further investigate if these novel proteins could play a protective role against these harmful catecholamine metabolites. In this study, we demonstrate the purification, pharmacological characterization and modulation of CATNAPs, as the first steps necessary to elucidate the function of these proteins in the brain. First, CATNAPs were identified from tissues using [3H]N-n-propylnorapomorphine (a specific dopamine receptor agonist) and [125I]6-hydroxy-5-iodo[N(N-2,4-dinitro-phenyl)- aminopropyl]1,2,3,4-tetrahydronaphthalene ([125I]DATN; a highly specific ligand synthesized in our laboratory). Three proteins, with molecular masses of 47, 40 and 26 kDa, were identified and purified, which allowed for the subsequent production of antibodies against each of these CATNAPs. The effects of in vivo chronic administration of several dopaminergic agents on CATNAPs were also examined by Western immunoblotting. L-3,4-Dihydroxyphenylalanine (L-DOPA) treatment in rats resulted in the increase of all of the three proteins, as compared to controls. Treatment in rats with the dopamine depleting agent, reserpine, produced a significant decrease in all of the three CATNAPs. In addition, the effects of direct administration of apomorphine, dopamine, epinephrine, isopropylnorepinephrine, norepinephrine, N-n-propylnorapomorphine and 6-hydroxydopamine on CATNAP levels in rats were examined. Interestingly, we observed an increase (as compared to control) of the 47, 40 and 26 kDa proteins in animals treated with dopamine, norepinephrine, N-n-propylnorapomorphine and apomorphine. In contrast, animals treated with 6-hydroxydopamine showed significant decreases in the levels of all three proteins. It is evident that as the concentration of catecholamines increases, there is a corresponding increase in the levels of CATNAPs in the brain. These results clearly demonstrate the pharmacological modulation of CATNAPs by dopaminergic agents and suggest their possible role in the cytoprotection against damage caused by free radicals generated by oxidative stress.

Adrenergic Uptake Inhibitors↗
PubMed1996

Interaction of NMDA and dopamine D2L receptors in human neuroblastoma SH-SY5Y cells.

To understand the mechanism of interaction of the dopamine D2L receptors with NMDA receptors, we have developed a model by transfecting human neuroblastoma SH-SY5Y cells with the human dopamine D2L receptor gene. In vitro blockade of NMDA receptors by the specific antagonists MK-801 and (+/-)-3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP) on human neuroblastoma SH-SY5Y cells expressing human dopamine D2L receptors resulted in a significant increase in the density of D2L receptors without a significant change in receptor affinity. Moreover, the dopamine receptor mRNA level increased by approximately 50% by the blockade of NMDA with MK-801. These results suggest a possible interaction of NMDA and dopamine D2L receptors in neuroblastoma SH-SY5Y cells. This system would serve as an excellent model to study the molecular mechanisms involved in the interaction of these two receptors.

Base Sequence↗
PubMed1996

A neurochemical basis for the antipsychotic activity of loxapine: interactions with dopamine D1, D2, D4 and serotonin 5-HT2 receptor subtypes.

Loxapine is a typical neuroleptic that shows great structural and functional homology to the atypical antipsychotic clozapine. Chronic loxapine treatment is usually associated with extrapyramidal symptoms (EPS), whereas clozapine treatment is not. Conversely, loxapine does not produce the agranulocytosis that often results from protracted clozapine treatment. Earlier studies of loxapine have usually implicated D2 receptor blockade as the cause of the tardive dyskinesia that occurs with chronic treatment. More recently, loxapine's ability to potentiate serotonergic neurotransmission has also been implicated. In this study, the pharmacological affinities of loxapine for the dopamine D1, D2, D4, as well as serotonin-2 (5-HT2) and NMDA receptor subtypes, were investigated through direct radioreceptor assays. The findings indicate that loxapine displays an extremely strong binding affinity for dopamine D4 and serotonin 5-HT2 receptors, which suggests that both serotonergic and dopaminergic mechanisms contribute to the antipsychotic drug action and EPS associated with loxapine in the treatment of schizophrenia.

Antipsychotic Agents↗
PubMed1995

Ontogenic development of dopamine D4 receptor in rat brain.

The postnatal development of rat brain dopamine D4 receptor gene expression was studied in animals 1 day to 1 year old, using the polymerase chain reaction technique. The level of expression of the D4 mRNA was appreciable at birth (day 1), increased to maximum at day 3, and showed declines at day 28. D4 mRNA expression remained unchanged at the ages of 6 months to 1 year. The mRNA expression at day 1 is about 50% of that observed on day 3, and declines approximately 50% by day 28. In contrast, the dopamine D2 mRNA expression was maximum at day 28, which is consistent with the reported studies.

Animals↗
PubMed1995

Improved leishmanicidal effect of phosphorotioate antisense oligonucleotides by LDL-mediated delivery.

We have designed antisense oligonucleotides that can interact with lipoproteins in order to use them as vectors to facilitate the uptake by those cells expressing the corresponding receptor. Phosphorothioate (PS) oligonucleotides were linked at the 5' end to a palmityl group giving rise to PSPal conjugates. Such a modification enables the oligonucleotide to form a stable non-covalent complex with low density lipoproteins (LDL) through hydrophobic interactions. The antisense effect of LDL-oligonucleotide complexes was assayed by targeting the mini-exon sequence of Leishmania amazonensis in infected mouse peritoneal macrophages. A 16-mer antisense PSPal oligonucleotide/LDL complex exerted a more pronounced sequence-specific effect than the free oligomer: about 25% and 10% of infected macrophages were cured by a 48 h incubation in the presence of 2.5 microM of the complexed and the free oligomer, respectively. When oxidized LDL was used instead of the native one for complexation, a further 2-fold increase in the antisense effect was observed suggesting that alternative (unregulated) scavenger receptor can be used for more efficient delivery of antisense oligonucleotides into macrophages. In addition, a significant reduction of the parasitic load was observed in those cells that were not fully cured.

Animals↗
PubMed1995

Modulation of N-methyl-D-aspartate (NMDA) antagonist-induced darting behaviour by the peptidomimetic PAMTA.

The N-Methyl-D-Aspartate (NMDA) receptor has attracted much attention in recent years due to its involvement in both the functions and dysfunctions of CNS neurotransmission. The existence of multiple sites by which NMDA receptor channel function can be pharmacologically modified and the interaction between glutamate and other neurotransmitter systems such as dopamine, provide exciting therapeutic avenues for related CNS disorders. In the present study, a novel synthetic analogue of the endogenous brain peptide L-prolyl-L-leucyl glycinamide (PLG) has demonstrated a significant modulatory action on the NMDA receptor. On the basis of radioligand binding studies, the novel synthetic peptide 5-[1(S)-(2(S)-pyrrolidinylcarbonyl)amino-3-methylbutyl]-2- tetrazolylacetamide (PAMTA) has been suggested to act at a polyamine site on the NMDA receptor complex. Scatchard analysis of [3H]MK-801 binding revealed that in the presence of 100 microM PAMTA, a single binding site was obtained with the Kd being increased from 2.5 +/- 0.2 nM to 6.2 +/- 0.1 nM. The ability of PAMTA to inhibit the binding of [3H]MK-801 was sensitive to the presence of both spermidine (polyamine agonist) and arcaine (polyamine antagonist). Analyses of the binding profiles of various NMDA receptor antagonists support PAMTA's interaction with the polyamine site on this receptor complex. Furthermore, we have investigated the behavioural profile of the peptidomimetic PAMTA, by studying its effect on stereotypic behaviours induced by the NMDA receptor antagonist, CPP (3(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid). Male Sprague-Dawley rats cannulated bilaterally into the medial prefrontal cortex were injected with PAMTA, CPP, a CPP/PAMTA combination, or a saline control.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Covalent affinity labeling of brain catecholamine-absorbing proteins using a high-specific-activity substituted tetrahydronaphthalene.

The recently described catecholamine-absorbing proteins (CATNAPs) are expressed within the CNS and have been shown to participate in neurochemical processes involving dopamine and several structurally related catecholamines. Specifically, CATNAPs have been implicated in participating directly in oxidative mechanisms involving reactive species (such as free radicals) derived from these compounds. Toxic free radicals generated from endogenous catecholamines have been identified as a major cause of neuronal tissue injury and are implicated in several disease processes. CATNAPs were first identified by their ability to react covalently with tritiated dopaminergic compounds, incorporating low levels of radioactivity under appropriate reaction conditions. The biochemical characterization of CATNAPs has until now been hampered by the lack of a suitable high-specific-activity probe to allow the rapid detection of these proteins. We describe here the synthesis and labeling characteristics of a high-specific-activity substituted tetrahydronaphthalene derivative (6-hydroxy-[125I]iodo-[N-(N-2',4'- dinitrophenyl)aminopropyl]-2-amino-1,2,3,4-tetrahydronaphthalene), which covalently incorporates into CATNAPs with the same tissue distribution, molecular weight patterns, and pharmacology as observed for the previously studied tritiated catecholamines. This compound greatly enhances the detection of CATNAPs and will facilitate further biochemical characterization of these proteins.

Absorption↗