James E. Krause

Structure, expression, and some regulatory mechanisms of the rat preprotachykinin gene encoding substance P, neurokinin A, neuropeptide K, and neuropeptide gamma

The rat preprotachykinin (PPT) gene encoding the neuropeptides substance P (SP), neurokinin A (NKA), neuropeptide K (NPK), and neuropeptide gamma was isolated from a lambda Charon 4A genomic library. Two overlapping clones contained all of the exons present in beta-PPT, including some 7 and 9 kb 5′ and 3′ flanking sequence, respectively. The presence of 1 major and 2 minor transcription initiation sites was determined from primer extension and nuclease protection experiments. Analysis of the nucleotide sequence homology between the rat and bovine revealed the presence of highly conserved regions throughout the entire coding region and within the 5′ flanking sequences. Primer extension and nuclease protection experiments demonstrated that the primary transcript is differentially spliced primarily into gamma- and beta-PPT mRNA in all tissues examined in the adult rat where the gene is expressed. beta-PPT mRNA contains all of the exons, whereas gamma-PPT mRNA lacks exon 4, which encodes part of the N-terminus of NPK. The alpha-PPT mRNA, which lacks exon 6 (the sequence encoding NKA and processing sites), comprises about 1% of the total PPT mRNA. An RNA secondary structure model is proposed to account for these specific exon exclusion events in the RNA splicing process. These results are discussed with regard to the mechanisms regulating SP gene expression and the functional significance of differential RNA splicing in the rat.

Molecular cloning, structural characterization and functional expression of the human substance P receptor.

A cDNA encoding the human substance P receptor (SPR) was isolated and the primary structure of the protein was deduced by nucleotide sequence analysis. This SPR consists of 407 residues and is a member of the G-protein coupled receptor superfamily. Comparison of rat and human SPR sequences demonstrated a 94.5% identity. The receptor was expressed in a COS-7 cell line and displayed a Kd for Tyr-1-SP binding of 0.24 nM. Ligand displacement by naturally occurring tachykinin peptides was SP much greater than neurokinin A greater than neurokinin B. SP stimulation of transfected cells resulted in a rapid and transient inositol 1,4,5-trisphosphate response. RNA blot hybridization and solution hybridization demonstrated that SPR mRNA was about 4.5 Kb in size, and was expressed in IM-9 lymphoblast and U373-MG astrocytoma cells, as well as in spinal cord and lung but not in liver.

Neonatal and adult 6-hydroxydopamine-induced lesions differentially alter tachykinin and enkephalin gene expression

Abstract: The present investigation examined the effects of neonatal and adult 6‐hydroxydopamine (6‐OHDA)‐induced lesions of dopaminergic neurons on opioid and tachykinin peptides and their gene expression in the rat basal ganglia. This work was undertaken to determine if changes in these neuropeptide systems were contributing to the differing behavioral responses observed between neonatally and adult‐lesioned rats after dopamine agonist administration. [Met5]Enkephalin (ME) content was increased in striatal tissue from both 6‐OHDA‐lesioned groups when compared with unlesioned controls. Dynorphin‐A (1–8) content was not altered by the 6‐OHDA lesions. The tachykinin peptides substance P and neurokinin A were significantly decreased in level in the striatum and substantia nigra of neonatally lesioned rats, but not in the adult‐lesioned rats, when compared with unlesioned controls. Proenkephalin mRNA abundance (quantified by an RNA‐cDNA hybridization technique) and precursor level (as reflected by cryptic ME content) were increased in the striatum of both neonatally and adult‐lesioned rats. The abundance of preprotachykinin mRNA coding for the tachykinin peptides was markedly decreased in the neonatally lesioned rats, whereas only a small reduction was observed in the adult‐lesioned rats. These results suggest that destruction of dopamine‐containing terminals with 6‐OHDA elevates the level of ME by accelerating transcriptional and/or translational processes; conversely, the reduced content of tachykinins in neonatally lesioned rats may be due to a reduction in such processes. Thus, preproenkephalin‐A and preprotachykinin gene expression are differentially regulated after lesioning of catecholamine‐containing neurons, an observation suggesting a close functional relationship among these neurotransmitter systems. Furthermore, of the peptides studied, only levels of the tachykinin peptides were differentially altered in the striatum and substantia nigra of the neonatally lesioned rats compared with adult‐lesioned rats; therefore, these peptides may be associated with the distinctive behavioral differences between neonatally and adult 6‐OHDA‐lesioned rats given dopamine agonists.

Neurokinin-3 receptor distribution in rat and human brain: an immunohistochemical study

Autoradiographic and immunohistochemical studies have shown that the neurokinin-3 receptor is widely distributed in the rodent CNS. Expression of the neurokinin-3 receptor in human brain, however, has been debated. These conflicting findings, as well as the poor resolution of autoradiographic images, prompted us to develop a polyclonal antibody against an oligopeptide derived from the carboxy-terminus consensus sequence of both the rat and human neurokinin-3 receptor ([C]ASTTSSFISSPYTSVDEYS, amino acids 434-452 of the rat neurokinin-3 receptor). Western blot analysis of both human and rat brain tissue revealed a major band in the molecular weight range 65,000-67,000, the proposed molecular weight of the neurokinin-3 receptor based on its amino acid sequence and presumed glycosylation state. The distribution of selective high affinity neurokinin-3 receptor agonist [3H]senktide binding and neurokinin-3 receptor immunoreactivity were virtually identical in the brains of male Fischer 344 rats. The highest concentrations of neurokinin-3 receptors were observed in cortical layers IV-V; the basolateral amygdaloid nucleus; the hypothalamic paraventricular, perifornical and supraoptic nuclei; the zona incerta; and the entopeduncular and interpeduncular nuclei. [3H]senktide binding and neurokinin-3 receptor immunoreactivity were compared in homologous cortical areas of the human and rat brain. In contrast to the rat, autoradiographic analysis of normal control human brains (35-75 years) revealed a distinct and predominant superficial cortical labeling in the glia limitans and the cortical layer I. However, neurokinin-3 receptor immunoreactivity could be found not only in the superficial cortical layers, but also on pyramidal neurons and astrocytes in the neuropil and white matter. These findings suggest species differences in both the cellular and anatomical distribution of the neurokinin-3 receptor.

Localization of the tachykinin neurokinin B precursor peptide in rat brain by immunocytochemistry and in situ hybridization

Tachykinins exert a broad range of actions in the mammalian nervous system. While much is known about the localization of peptides derived from one of the two mammalian tachykinin genes (substance P- and neurokinin A-encoding preprotachykinin), little has been reported on the localization of peptides derived from a second tachykinin gene encoding neurokinin B. Using an antiserum raised against a 30-residue peptide fragment (Peptide 2) of the protein precursor to neurokinin B, we have mapped the distribution of Peptide 2 by immunocytochemistry. Peptide 2 antiserum specificity was determined by western blot analysis (which showed antibody cross-reactivity to a neurokinin B fusion protein from a cloned neurokinin B-encoding complementary DNA) and by the elimination of immunoreactive product in brain tissue sections upon preabsorption with a 10 microM concentration of Peptide 2 peptide. In addition, we report on the distribution of neurokinin B-messenger RNA with a full-length complementary RNA probe to localize cells that express the neurokinin B precursor. Peptide 2 immunoreactivity and neurokinin B-messenger RNA-positive cells were found, in some instances, paralleling the distribution of substance P and in other cases existing separately from substance P. Peptide 2 immunoreactivity as well as neurokinin B-messenger RNA-positive cells were found in the main olfactory bulb, cortex, olfactory tubercle, nucleus accumbens, hippocampus, bed nucleus of the stria terminalis, amygdala, medial habenula, periaqueductal gray, superior and inferior colliculus, and nucleus of the spinal trigeminal tract. Whereas substance P is found throughout the rat brain, neurokinin B appears to be partitioned more to forebrain than to brainstem structures. The marked differences in the distribution of both tachykinins in the rat central nervous system suggests that neurokinin B may play an important role in olfactory, gustatory, visceral, and neuroendocrine processing of information.

Regional distribution of neuropeptide γ and other tachykinin peptides derived from the substance P gene in the rat

Substance P (SP) and multiple neurokinin A (NKA)-related peptides can be derived from alpha-, beta- and/or gamma-preprotachykinin (PPT) mRNAs. In this study, the relative concentrations of the tachykinin peptides derived from the SP gene in rat brain, duodenum, jejunum, submandibular gland, parotid gland, urinary bladder and vas deferens was determined using high-performance liquid chromatography (HPLC) and radioimmunoassays (RIAs). In all tissues, SP levels were the highest. The relative abundance of NKA-related peptides was NKA greater than neuropeptide gamma (NP gamma) = neuropeptide K (NPK) greater than NKA(3-10). These results demonstrate that multiple tachykinin peptides are present in tissues where the SP gene is expressed, and that the NKA portion of the beta- and gamma-PPT precursors can be differentially processed posttranslationally in rat tissues into NKA, NPK, NP gamma and/or NKA(3-10).

Dialdehyde sesquiterpenes and other terpenoids as vanilloids

Selected naturally occurring unsaturated dialdehyde sesquiterpenes and related bioactive terpenoids were assayed for vanilloid-like activity. Out of the 25 compounds tested, eight inhibited completely the specific binding of [3H]resiniferatoxin by rat spinal cord membranes: binding affinities ranged from 0.6 microM for cinnamodial to 19.0 microM for hebelomic acid F. These values were comparable to the binding affinity of capsaicin (2.7 microM). With the exception of four ligands, compounds that inhibited resiniferatoxin binding to rat spinal cord membranes were also pungent on the human tongue where they showed cross-tachyphylaxis with capsaicin. As expected from their reactive nature, these compounds possess additional sites of action, as reflected in the complex behavior of the stimulation of calcium influx by cinnamodial and cinnamosmolide at high concentrations. This observation might explain the unexpectedly weak membrane depolarization by cinnamodial compared to capsaicin. We conclude that a range of sesquiterpene dialdehydes and related terpenoids, both pungent and non-pungent, may function as vanilloids. These compounds may represent a new chemical lead for the development of vanilloid drugs, structurally unrelated to either capsaicin or resiniferatoxin.

Resiniferatoxin‐type phorboid vanilloids display capsaicin‐like selectivity at native vanilloid receptors on rat DRG neurons and at the cloned vanilloid receptor VR1

Although the cloned rat vanilloid receptor VR1 appears to account for both receptor binding and calcium uptake, the identification of vanilloids selective for one or the other response is of importance because these ligands may induce distinct patterns of biological activities. Phorbol 12,13‐didecanoate 20‐homovanillate (PDDHV) evoked 45Ca2+‐uptake by rat dorsal root ganglion neurons (expressing native vanilloid receptors) in culture with an EC50 of 70 nM but inhibited [3H]‐resiniferatoxin (RTX) binding to rat dorsal root ganglion membranes with a much lower potency (Ki>10,000 nM). This difference in potencies represents a more than 100 fold selectivity for capsaicin‐type pharmacology. 45Ca2+ influx by PDDHV was fully inhibited by the competitive vanilloid receptor antagonist capsazepine, consistent with the calcium uptake occurring via vanilloid receptors. PDDHV induced calcium mobilization in CHO cells transfected with the cloned rat vanilloid receptor VR1 with an EC50 of 125 nM and inhibited [3H]‐RTX binding to these cells with an estimated Ki of 10,000 nM. By contrast, PDDHV failed to evoke a measurable calcium response in non‐transfected CHO cells, confirming its action through VR1. We conclude that PDDHV is two orders of magnitude more potent for inducing calcium uptake than for inhibiting RTX binding at vanilloid receptors, making this novel vanilloid a ligand selective for capsaicin‐type pharmacology. These results emphasize the importance of monitoring multiple endpoints for evaluation of vanilloid receptor structure‐activity relations. Furthermore, PDDHV now provides a tool to explore the biological correlates of capsaicin‐type vanilloid pharmacology.

Characterization of N-(adamantan-1-ylmethyl)-5-[(3R-amino-pyrrolidin-1-yl)methyl]-2-chloro-benzamide, a P2X7 antagonist in animal models of pain and inflammation.

Recent evidence suggests that the P2X7 receptor may play a role in the pathophysiology of preclinical models of pain and inflammation. Therefore, pharmacological agents that target this receptor may potentially have clinical utility as anti-inflammatory and analgesic therapy. We investigated and characterized the previously reported P2X7 antagonist N-(adamantan-1-ylmethyl)-5-[(3R-amino-pyrrolidin-1-yl)methyl]-2-chloro-benzamide, hydrochloride salt (AACBA; GSK314181A). In vitro, AACBA was a relatively potent inhibitor of both human P2X7-mediated calcium flux and quinolinium,4-[(3-methyl-2(3H)-benzoxazolylidene)methyl]-1-[3-(triemethylammonio)propyl]-diiodide (YO-PRO-1) uptake assays, with IC50 values of approximately 18 and 85 nM, respectively. Compared with the human receptor, AACBA was less potent at the rat P2X7 receptor, with IC50 values of 29 and 980 nM in the calcium flux and YO-PRO-1 assays, respectively. In acute in vivo models of pain and inflammation, AACBA dose-dependently reduced lipopolysaccharide-induced plasma interleukin-6 release and prevented or reversed carrageenan-induced paw edema and mechanical hypersensitivity. In chronic in vivo models of pain and inflammation, AACBA produced a prophylactic, but not therapeutic-like, prevention of the clinical signs and histopathological damage of collagen-induced arthritis. Finally, AACBA could not reverse L5 spinal nerve ligation-induced tactile allodynia when given therapeutically. Consistent with previous literature, these results suggest that P2X7 receptors do play a role in animal models of pain and inflammation. Further study of P2X7 antagonists both in preclinical and clinical studies will help elucidate the role of the P2X7 receptor in pain and inflammatory mechanisms and may help identify potential clinical benefits of such molecules.

Solution hybridization-nuclease protection assays for sensitive detection of differentially spliced substance P- and neurokinin A-encoding messenger ribonucleic acids

In this chapter we discussed methods that can be used for the sensitive detection and quantitation of differentially or alternatively spliced mRNAs as well as mRNAs of low abundance. Although mechanisms responsible for splicing (and differential splicing in particular) have not been fully determined, many RNAs derived from a variety of genes have been observed to undergo the process. The impact of splicing with regard to the expanded potential of gene expression emphasizes the usefulness of the solution hybridization-nuclease digestion technique described here, compared to Northern blot analysis. The use of radiolabeled cRNA(s) provides for an assay of both high specificity and high sensitivity. While end-labeled cDNA probes can be used, they do not have the sensitivity inherent in the assay performed with uniformly radiolabeled cRNAs. If multiple mRNAs are derived from a single gene as a result of differential or alternative precursor RNA splicing, however, the results with a cRNA probe may initially appear to be quite complicated, and end-labeled cDNAs may yield more easily interpretable results. Nonetheless, both types of probes are useful in the context of gene expression analysis, and it is clear that for routine purposes of quantitation cRNA probes in solution hybridization-nuclease protection assays are clearly more desirable than RNA blot analyses due to their truly quantitative nature as well as ease of assay.