A novel PAR-1-type thrombin receptor signaling pathway: cyclic AMP-independent activation of PKA in SNB-19 glioblastoma cells

Cellular effects of thrombin are mediated by members of a new subfamily of G protein-coupled receptors designated proteinase-activated receptors (PARs) with the prototype PAR-1. Investigation of PAR-1-induced signaling has been shown to be very important in clarifying thrombin's role in cell metabolism, differentiation, and growth. We evaluated connection of PAR-1 with the cAMP/PKA pathway in SNB-19 glioblastoma cells. Alpha-thrombin and the synthetic PAR-1 agonist SFLLRN stimulated PKA as shown by increased PKA activity and translocation of the catalytic PKA alpha subunits (PKA(cat)alpha) into the nucleus. However, no effect on cAMP could be observed. PKA(cat)alpha was found to be associated with nuclear factor-kappa B (NF-kappaB) p65 and its inhibitor protein IkappaB in SNB-19 cells. After PAR-1 stimulation, this association was markedly diminished. We conclude that PAR-1 mediates PKA activation without altering cAMP levels but includes NF-kappaB-associated PKA(cat)alpha in SNB-19 glioblastoma cells. This is the first evidence for a cAMP-independent PKA signaling by a G protein-coupled receptor.

Synthesis, characterization, and biological properties of cyanine-labeled somatostatin analogues as receptor-targeted fluorescent probes

We present the synthesis and characterization of the somatostatin receptor-specific peptide H(2)N-(D-Phe)-cyclo[Cys-Phe-(D-Trp)-Lys-Thr-Cys]-Thr-OH, which is labeled with a carboxylated indodicarbo- and an indotricarbocyanine dye at the N-terminal amino group. The preparation was performed by automated solid-phase synthesis, with subsequent attachment of the cyanine dye and cleavage of the entire conjugate from the resin. The compounds display high molar absorbance and fluorescence quantum yields typical for cyanine dyes and are thus suitable receptor-targeted contrast agents for molecular optical imaging. The ability of these agents to target the somatostatin receptor was demonstrated by flow cytometry in vitro, in which the indotricarbocyanine conjugate led to elevated cell-associated fluorescence on somatostatin receptor-expressing tumor cells. In contrast, the corresponding linearized derivative of the sequence H(2)N-(D-Phe)-Met-Phe-(D-Trp)-Lys-Thr-Met-Thr-OH produced only minimal cell fluorescence, hence confirming the specificity of the cyclic somatostatin analogue. Intracellular localization could be visualized by near-infrared (NIR) fluorescence microscopy. In conclusion, receptor-specific peptides are promising tools for designing site-directed optical contrast agents for use in molecular optical imaging.

Requirement of specific intrahelical interactions for stabilizing the inactive conformation of glycoprotein hormone receptors

Systematic analysis of structural changes induced by activating mutations has been frequently utilized to study activation mechanisms of G-protein-coupled receptors (GPCRs). In the thyrotropin receptor and the lutropin receptor (LHR), a large number of naturally occurring mutations leading to constitutive receptor activation were identified. Saturating mutagenesis studies of a highly conserved Asp in the junction of the third intracellular loop and transmembrane domain 6 suggested a participation of this anionic residue in a salt bridge stabilizing the inactive receptor conformation. However, substitution of all conserved cationic residues at the cytoplasmic receptor surface did not support this hypothesis. Asp/Glu residues are a common motif at the N-terminal ends of alpha-helices terminating and stabilizing the helical structure (helix capping). Since Asp/Glu residues in the third intracellular loop/transmembrane domain 6 junction are not only preserved in glycoprotein hormone receptors but also in other GPCRs we speculated that this residue probably participates in an N-terminal helix-capping structure. Poly-Ala stretches are known to form and stabilize alpha-helices. Herein, we show that the function of the highly conserved Asp can be mimicked by poly-Ala substitutions in the LHR and thyrotropin receptor. CD and NMR studies of peptides derived from the juxtamembrane portion of the LHR confirmed the helix extension by the poly-Ala substitution and provided further evidence for an involvement of Asp in a helix-capping structure. Our data implicate that in addition to well established interhelical interactions the inactive conformation of GPCRs is also stabilized by specific intrahelical structures.

Replacement of fetal calf serum in cell cultures by an egg yolk factor with cholecystokinin/gastrin-like immunoreactivity

The in vitro culture of various cell types is an important scientific tool and is becoming increasingly acceptable as a viable alternative to animal experiments. Fetal calf serum (FCS) is a supplement used in many cell culture media, and provides cells with growth factors and cytokines necessary for successful culture. In view of the animal welfare issues surrounding the production of FCS, an alternative agent allowing the replacement or reduction in the use of FCS is desirable. A yolk extract factor (EYF-X) obtained from chicken eggs is described, which facilitates the in vitro culture of a variety of cell types. When the extract was added to a culture medium used for in vitro fertilisation, the number of successful fertilisations was significantly increased. In a further in vitro model (permanent neuronal cell line N2A), the yolk extract significantly stimulated cell proliferation as well as the growth of cell processes. A set of specific antibodies against different parts of the prepro-cholecystokinin reacted with the extract. The intensity of the reaction depends on the age of the egg (time after the laying date). Analysis by gel chromatography recorded a main protein fraction with an apparent molecular mass of 20-30kDa. This fraction was labelled by Western blot with an antibody with specificity against CCK-octapeptide. These findings suggest that the yolk factor may be a CCK/gastrin-like molecule. Since CCK/gastrin-like molecules have also been detected in the spermatozoa of mammals, the influence on in vitro fertilisation could be explained by the yolk factor replacing the endogenous CCK/gastrin-like molecule destroyed in sperm freezing. The results of this study suggest that it might be possible to replace FCS with EYF-X. The application of the yolk factor to a broad spectrum of cell types remains to be investigated.

In vitro pharmacological activity of the tetrahydroisoquinoline salsolinol present in products from Theobroma cacao L. like cocoa and chocolate

Cocoa and chocolate contain the tetrahydroisoquinoline alkaloid salsolinol up to a concentration of 25 microg/g. Salsolinol is a dopaminergic active compound which binds to the D(2) receptor family, especially to the D(3) receptor with a K(i) of 0.48+/-0.021 micromol/l. It inhibits the formation of cyclic AMP and the release of beta-endorphin and ACTH in a pituitary cell system. Taking the detected concentration and the pharmacological properties into account, salsolinol seems to be one of the main psychoactive compounds present in cocoa and chocolate and might be included in chocolate addiction.

Functional and structural characterization of synthetic HIV-1 Vpr that transduces cells, localizes to the nucleus, and induces G2 cell cycle arrest

Human immunodeficiency virus (HIV) Vpr contributes to nuclear import of the viral pre-integration complex and induces G(2) cell cycle arrest. We describe the production of synthetic Vpr that permitted the first studies on the structure and folding of the full-length protein. Vpr is unstructured at neutral pH, whereas under acidic conditions or upon addition of trifluorethanol it adopts alpha-helical structures. Vpr forms dimers in aqueous trifluorethanol, whereas oligomers exist in pure water. (1)H NMR spectroscopy allows the signal assignment of N- and C-terminal amino acid residues; however, the central section of the molecule is obscured by self-association. These findings suggest that the in vivo folding of Vpr may require structure-stabilizing interacting factors such as previously described interacting cellular and viral proteins or nucleic acids. In biological studies we found that Vpr is efficiently taken up from the extracellular medium by cells in a process that occurs independent of other HIV-1 proteins and appears to be independent of cellular receptors. Following cellular uptake, Vpr is efficiently imported into the nucleus of transduced cells. Extracellular addition of Vpr induces G(2) cell cycle arrest in dividing cells. Together, these findings raise the possibility that circulating forms of Vpr observed in HIV-infected patients may exert biological effects on a broad range of host target cells.

Membrane interactions and alignment of structures within the HIV-1 Vpu cytoplasmic domain: effect of phosphorylation of serines 52 and 56

The cytoplasmic domain of the HIV-1 accessory protein Vpu is involved in the binding and degradation of the viral receptor CD4. In order to analyze previous structural models in the context of membrane environments, regions of Vpu(CYTO) incorporating particular conformational features have been synthesized and labelled with (15)N at selected backbone amides. Well-oriented proton-decoupled (15)N solid-state NMR spectra with (15)N chemical shifts at the most upfield position indicate that the amphipathic helix within [(15)N-Leu 45]-Vpu(27-57) strongly interacts with mechanically aligned POPC bilayers and adopts an orientation parallel to the membrane surface. No major changes in the topology of this membrane-associated amphipathic helix were observed upon phosphorylation of serine residues 52 and 56, although this modification regulates biological function of Vpu. In contrast, [(15)N-Ala 62]-Vpu(51-81) exhibits a pronounced (15)N chemical shift anisotropy.

Different signaling pathways are involved in CCK(B) receptor-mediated MAP kinase activation in COS-7 cells

Recently, the involvement of the MAP kinase ERK in mitogenic signaling of cholecystokininB (CCK(B)) receptors has been shown. However, the intracellular effector systems involved in this signaling pathway are poorly defined. In this study, we used COS-7 cells transiently transfected with the human CCK(B) receptor to investigate cholecystokinin-induced MAP kinase activation. CCK-8 induced activation of ERK2 which is associated with its phosphorylation and localization in the nucleus. The CCK-8-dependent ERK stimulation is sensitive to wortmannin an inhibitor of phosphoinositide 3-kinases (PI3Ks) indicating the involvement of PI3K activity. To identify the PI3K species involved in mitogenic signaling of the CCK(B) receptor several dominant-negative mutants of PI3K regulatory and catalytic subunits were transiently expressed. Surprisingly, different catalytically inactive mutants of the G protein-sensitive PI3Kgamma did not affect ERK stimulation induced by CCK, whereas a dominant-negative mutant of the regulatory p85 subunit induced significant inhibition of CCK-dependent ERK activity. These results indicate an involvement of PI3K class 1A species alpha, beta or/and delta in signal transduction via CCK(B) receptors. In addition, protein kinase C (PKC)-dependent signaling pathways contribute to CCK(B)-mediated MAP kinase signaling as shown by inhibition of CCK-8-induced ERK activation by the PKC inhibitor bisindolylmaleimide.

Comparison of the effects of 5- and 6-HOAt on model peptide coupling reactions relative to the cases for the 4- and 7-Isomers

Synthesis of 5- and 6-HOAt has completed the full set of the four HOAt isomers derived from HOBt by insertion of a single nitrogen atom in the benzenoid nucleus. Comparison of the reactivity of all four isomers in model peptide coupling reactions has confirmed the unique character of the 7-isomer in promoting selectivity and maintaining configuration at the reactive carboxylic acid residue.

Meizothrombin, an intermediate of prothrombin activation, stimulates human glioblastoma cells by interaction with PAR-1-type thrombin receptors

Thrombin induces well-characterized effects on normal and neoplastic brain cells by interaction with protease-activated receptor (PAR)-type thrombin receptors. However, nothing is known about the function of intermediate enzymes of prothrombin activation recently shown to evoke PAR-1-mediated signaling in smooth muscle cells. Therefore, we investigated the effect of recombinant human meizothrombin (rMT), one of thrombin's catalytically active precursor enzymes in the prothrombin cleavage cascade, on calcium mobilization in human SNB-19 glioblastoma cells. By using reverse-transcription polymerase chain reaction, immunofluorescence studies with a monoclonal anti-PAR-1 antibody and calcium measurements, SNB-19 cells were shown to express functional PAR-1-type thrombin receptors. PAR-1 is not only a receptor for thrombin in SNB-19 cells but was also activated by rMT very effectively. Under the conditions used in our experiments, SNB-19 cells stimulated with thrombin after rMT challenge were unable to elicit a new calcium response and vice versa. In addition, both rMT and thrombin induced no further calcium signal after that observed with the PAR-1-activating peptide SFLLRN. Therefore, rMT and thrombin seem to activate calcium signaling by similar mechanisms including PAR-1. Our results demonstrate rMT as a potent activator of PAR-1-type thrombin receptors in SNB-19 glioblastoma cells, suggesting a function of catalytically active thrombin precursor enzymes in cells of glial origin.

The two-receptor system PAR-1/PAR-4 mediates alpha-thrombin-induced [Ca(2+)](i) mobilization in human astrocytoma cells

The proteinase-activated receptor 1 (PAR-1) was characterized as a functional receptor for thrombin in cells from different brain tumor entities. Whether PAR-1 alone accounts for thrombin-induced effects in human cancer cells, or whether other PAR contribute is unknown. We established primary cultures from two neurosurgically removed human astrocytomas and investigated intracellular signaling roles of PAR-1 and PAR-4 by estimating the effect of alpha-thrombin and PAR-activating peptides on [Ca(2+)](i) mobilization in single astrocytoma cells. alpha-Thrombin or the PAR-1-activating peptide SFLLRN induced a transient calcium mobilization. This suggests the involvement of PAR-1 in alpha-thrombin-induced calcium signaling in human astrocytoma cells. In addition, a second, PAR-4-dependent, mechanism exists. This was deduced from the findings that a further calcium signal could be observed in human astrocytoma cells stimulated with alpha-thrombin after SFLLRN and the PAR-4-activating peptide GYPGQV also induced a calcium response. In addition, the observation that trypsin, known to activate both PAR-2 and PAR-4, but not the specifically PAR-2-activating peptide SLIGRL induced calcium signaling is a further indication of functional PAR-4-type thrombin receptors in human astrocytoma cells. This is the first report demonstrating a signaling role for a dual thrombin receptor system in human tumor cells.

Mutation of the fourth cytoplasmic loop of rhodopsin affects binding of transducin and peptides derived from the carboxyl-terminal sequences of transducin alpha and gamma subunits

The role of the putative fourth cytoplasmic loop of rhodopsin in the binding and catalytic activation of the heterotrimeric G protein, transducin (G(t)), is not well defined. We developed a novel assay to measure the ability of G(t), or G(t)-derived peptides, to inhibit the photoregeneration of rhodopsin from its active metarhodopsin II state. We show that a peptide corresponding to residues 340-350 of the alpha subunit of G(t), or a cysteinyl-thioetherfarnesyl peptide corresponding to residues 50-71 of the gamma subunit of G(t), are able to interact with metarhodopsin II and inhibit its photoconversion to rhodopsin. Alteration of the amino acid sequence of either peptide, or removal of the farnesyl group from the gamma-derived peptide, prevents inhibition. Mutation of the amino-terminal region of the fourth cytoplasmic loop of rhodopsin affects interaction with G(t) (Marin, E. P., Krishna, A. G., Zvyaga T. A., Isele, J., Siebert, F., and Sakmar, T. P. (2000) J. Biol. Chem. 275, 1930-1936). Here, we provide evidence that this segment of rhodopsin interacts with the carboxyl-terminal peptide of the alpha subunit of G(t). We propose that the amino-terminal region of the fourth cytoplasmic loop of rhodopsin is part of the binding site for the carboxyl terminus of the alpha subunit of G(t) and plays a role in the regulation of betagamma subunit binding.

A novel subgroup of class I G-protein-coupled receptors

Based on structural similarities of an expressed sequence tag with the platelet-activating factor (PAF) receptor a cDNA clone encoding a novel G-protein-coupled receptor (GPCR), named GPR34, was isolated from a human fetal brain cDNA library. Genomic DNA analyses revealed the receptor to be encoded by an intronless single-copy gene at Xp11. 3-11.4. The predicted 381-amino-acid protein disclosed all structural features characteristic of a member of the class I GPCR family. Except an obvious sequence homology in transmembrane domain 6, no further similarities to the PAF receptor or any other known GPCR were found. The corresponding mouse receptor DNA was isolated from a genomic P1 library displaying a 90% amino acid identity compared to the human receptor. Phylogenetic studies showed that GPR34 is preserved among vertebrates, and the existence of GPR34 subtypes was demonstrated. The receptor mRNA is abundantly expressed in human and mouse tissues. In addition to the major 2-kb transcript, a 4-kb transcript was found only in mouse liver and testis. Expression of the human GPR34 in COS-7 cells followed by Western blot studies revealed specific bands of a highly glycosylated protein between 75 and 90 kDa. A number of potential ligands including phospholipids, leukotrienes, hydroxy-eicosatetraenoic acids, nucleotides and peptides were tested in functional assays. Since none of the applied substances led to significant changes in second messenger levels (cAMP and inositol phosphates), the natural ligand and coupling profile of this novel GPCR subgroup remains unknown.

Solution structure and orientation of the transmembrane anchor domain of the HIV-1-encoded virus protein U by high-resolution and solid-state NMR spectroscopy

The structure of the membrane anchor domain (VpuMA) of the HIV-1-specific accessory protein Vpu has been investigated in solution and in lipid bilayers by homonuclear two-dimensional and solid-state nuclear magnetic resonance spectroscopy, respectively. Simulated annealing calculations, using the nuclear Overhauser enhancement data for the soluble synthetic peptide Vpu1-39 (positions Met-1-Asp-39) in an aqueous 2,2,2-trifluoroethanol (TFE) solution, afford a compact well-defined U-shaped structure comprised of an initial turn (residues 1-6) followed by a linker (7-9) and a short helix on the N-terminal side (10-16) and a further longer helix on the C-terminal side (22-36). The side chains of the two aromatic residues (Trp-22 and Tyr-29) in the longer helix are directed toward the center of the molecule around which the hydrophobic core of the folded VpuMA is positioned. As the observed solution structure is inconsistent with the formation of ion-conductive membrane pores defined previously for VpuMA in planar lipid bilayers, the isolated VpuMA domain as peptide Vpu1-27 was investigated in oriented phospholipid bilayers by proton-decoupled 15N cross polarization solid-state NMR spectroscopy. The line widths and chemical shift data of three selectively 15N-labeled peptides are consistent with a transmembrane alignment of a helical polypeptide. Chemical shift tensor calculations imply that the data sets are compatible with a model in which the nascent helices of the folded solution structure reassemble to form a more regular linear alpha-helix that lies parallel to the bilayer normal with a tilt angle of </=30 degrees. The arrangement of the membrane-associated structures described previously for the cytoplasmic domain and for the anchor domain of Vpu identified in this work is discussed.

PAR 1-type thrombin receptors are involved in thrombin-induced calcium signaling in human meningioma cells

Thrombin is known to play a role as regulator in tumor spreading and tumor growth. Proteinase-activated receptor 1 (PAR 1)-type thrombin receptors were identified in different cancer cells including human glioblastoma cells. Thus a function of PAR 1 in brain tumors may be suggested. In this study, the presence of PAR 1-type thrombin receptors was investigated in primary cell cultures established from operated human meningiomas from two 59- and 79-year-old women. Characterization of PAR 1 on binding level was performed using immunofluorescence studies with the monoclonal anti-PAR 1 antibody Mab 61-1 directed against a domain in the NH2-terminus of PAR 1. These binding sites constitute functional thrombin receptors that are involved in thrombin-induced signaling in human meningioma cells as demonstrated by investigation of alpha-thrombin- and PAR 1-activating hexapeptide (TRAP-6)-induced [Ca2+]i mobilization. To our knowledge, this is the first report demonstrating thrombin-induced intracellular signaling in human meningioma cells mediated by the PAR 1-type thrombin receptor.

Mimicry of beta II'-turns of proteins in cyclic pentapeptides with one and without D-amino acids

The solution structure of eight cyclic pentapeptides has been determined by two-dimensional 1H-NMR spectroscopy combined with spectra simulations and restrained molecular dynamic simulations. Six of the cyclic pentapeptides were derived from the C-terminal cholecystokinin fragment CCK-4 enlarged with Asp1 resulting in the sequence (Asp-Trp-Met-Asp-Phe), one L-amino acid after the other was substituted by its D-analog. In addition, two peptides, including an all-L-amino-acid-containing cyclic pentapeptide, cyclo(Asp-Phe-Lys-Ala-Thr) and cyclo(Asp-Phe-Lys-Ala-D-Thr) were investigated. All D-amino-acid-containing peptides show beta II'-turn conformations with the D-amino acid in the i + 1 position, excepting the D-aspartic-acid-containing peptides. These two peptides are characterized by the lack of beta-turns at pH values less than 4, suggesting that D-aspartic acid in the full-protonized state avoids the formation of beta-turns in these compounds. At pH values greater than 5, a conformational change into the beta II'-turn conformation was also observed for these peptides. Conformations without beta-turns are expected for cyclic all-L pentapeptides, but both cyclo(Asp-Phe-Lys-Ala-Thr) and the D-Thr analog cyclo(Asp-Phe-Lys-Ala-D-Thr) exhibit beta II'-turn conformations around Thr-Asp and D-Thr-Asp. Thus cyclic all-L pentapeptides and those with one D-amino acid are able to form similar structures preferably with a beta II'-turn. The beta-turn formation in cyclic pentapeptides containing a D-aspartic acid is dependent on the ionization state. The relevance of the work to the design of beta'-turn mimetics is discussed.

Solution structure of the cytoplasmic domain of the human CD4 glycoprotein by CD and 1H NMR spectroscopy: implications for biological functions

The human T cell receptor CD4 is a type I integral membrane glycoprotein that is involved in T cell activation and also acts as the primary coreceptor for human immunodeficiency viruses (HIV). Here the structure of a synthetic 38 amino acid peptide corresponding to the complete cytoplasmic domain of CD4 (CD4CYTO) has been investigated under a variety of solution conditions using a combination of circular dichroism and homonuclear two-dimensional 1H nuclear magnetic resonance spectroscopy. In the presence of the membrane mimetic 2,2,2-trifluoroethanol (TFE), a conformational change of CD4CYTO from a random coil to an alpha-helical structure was observed. In keeping with this, CD4CYTO has the potential to associate with membranes as demonstrated by binding studies of in vitro phosphorylated CD4CYTO with microsomal membranes. Both chemical shift and nuclear Overhauser enhancement data in 50% 2,2, 2-trifluoroethanol solution provide direct experimental evidence for the predominance of a short amphiphatic alpha-helix that is approximately 4 turns in length and extends from positions Arg-402 to Lys-417. The present data provide, for the first time, compelling experimental evidence that only a fraction of CD4CYTO has a propensity for adopting secondary structure under conditions that are assumed to exist at or near to the membrane surface and that this alpha-helical structure is located in the membrane-proximal region of CD4CYTO. The N-terminal residues, that link the alpha-helix to the transmembrane anchor of CD4, and a substantial C-terminal portion (14-18 residues) of CD4CYTO are unstructured under the solution conditions investigated. Correlation of our structural data with recent studies on the biological activity of CD4CYTO indicates that the alpha-helix is of crucial importance for the interaction of CD4 with Nef and Vpu in the process of HIV-mediated CD4 down-regulation.

Protein kinase C is involved in cholecystokinin octapeptide-induced proliferative action in rat glioma C6 cells

Chotecystoknin octapeptide (CCK-8) has been shown to stimulate DNA synthesis in rat glioma C6 cells by activation of CCKB type receptors. However, the signalling pathways contributing to this proliferative action in C6 cells have not been investigated thus far. This study demonstrated that stimulation of rat glioma C6 cells with CCK-8S resulted in activation of protein kinase C isozymes betaI, betaII, gamma and zeta. The participation of protein kinase C in the CCK-8S-induced effect on C6 cell growth was demonstrated by measurement of [3H]thymidine incorporation and estimation of cell number. The data indicate that CCK-8S stimulates growth in rat glioma C6 cells by a protein kinase C-dependent mechanism.

Cholecystokinin B-type receptor signaling is involved in human pancreatic cancer cell growth

Cholecystokinin (CCK) is known to stimulate pancreatic cancer cell growth, but no detailed CCK receptor subtype characterization and investigation of CCK receptor-mediated cellular responses in human pancreatic cancer cells have been reported thus far. In this study, CCK binding sites were identified in human pancreatic cancer cells (MIA-PaCa-2) using radioligand binding studies. Pharmacological characterization demonstrated a single class of high-affinity CCK sites on MIA-PaCa-2 cells (326 +/- 18 pM, receptor density 16.9 +/- 2.3 fmol/mg protein). These CCK binding sites displayed a typical CCKB binding profile as shown in competition studies by using different CCK-related compounds and non-peptide CCK antagonists discriminating between CCKA and CCKB sites. CCKB receptor-connected effector systems have been characterized in MIA-PaCA-2 cells, and their involvement in CCK-8S-induced proliferative effects on MIA-PaCa-2 cells has been demonstrated.

Actions of angiotensin and lisinopril on thalamic somatosensory neurons in normotensive, non-transgenic and hypertensive, transgenic rats

OBJECTIVE

To investigate the effects of angiotensin II on discharge rates of somatosensory thalamic neurons and whether these effects are altered in hypertensive transgenic rats [TGR(mREN-2)27] and by long-term treatment with the angiotensin converting enzyme inhibitor lisinopril.

DESIGN AND METHODS

Three strains of rats anesthetized with urethane were used (normotensive Wistar and Sprague-Dawley rats (SDR), and [TGR(mREN-2)27]). In addition, the effects of lisinopril treatment on SDR and transgenic animals were tested. The neuronal discharge frequency and the pattern were recorded extracellularly, and their behaviors in response to angiotensin and angiotensin antagonists administered iontophoretically were analyzed.

RESULTS

Angiotensin-sensitive neurons located in the ventral posteromedial and ventral posterolateral thalamic nuclei, and in the zona incerta were excited mainly by angiotensin II. The increase in the firing rates induced by administration of angiotensin II often coincided with an increase in the number of bursts of discharges. Effects induced by angiotensin II could be blocked by administration of specific antagonists (losartan, PD 123319). Long-term treatment with lisinopril reduced the neuronal responsiveness to angiotensin II in SDR significantly in comparison with that of untreated SDR controls. Lisinopril-treated SDR had a significantly lower responsiveness to angiotensin II than did hypertensive transgenic rats that had been treated with lisinopril.

CONCLUSION

The results show for the first time that administration of angiotensin II induced changes in discharge rates of somatosensory neurons, and that long-term administration of lisinopril caused a significant difference between the neuronal responsiveness to angiotensin of normotensive SDR and that of hypertensive transgenic rats.

Expression and subcellular localization of mouse 20S proteasome activator complex PA28

We have cloned the mouse PA28 proteasome activator cDNAs. Northern blot demonstrates high PA28 mRNA levels in liver, kidney and lung. mRNA levels are low in thymus, spleen and brain. In contrast, PA28 protein levels vary little between these tissues. Immunocytological analysis and cell fractionation experiments demonstrate that both subunits are almost equally distributed between the cytoplasm and the nucleus. Interestingly, PA28alpha spares nucleoli, while PA28beta is strongly enhanced in the nucleolus. This indicates for the first time that the PA28alpha and PA28beta subunits may serve nuclear functions which may be different from and independent of each other.

Neostriatal neurons of rats can be influenced by cholecystokinin-A receptor agonists

The present study investigated the effects of agonists of the neuropeptide cholecystokinin (CCK) on neostriatal neurons in order to confirm the existence of CCK-A receptors in the rat caudate-putamen. Single unit activity was recorded in rats anaesthetized with urethane. The CCK-A receptor agonists A-71378 (desamino-Tyr(SO3H)-Nle-Gly-Trp-Nle-(N-methyl)Asp-Phe-NH2), and A-71623 (Boc-Trp-Lys(epsilon-N-2-methylphenylamino-carbonyl)-Asp-(N-methyl )Phe-NH2, as well as the CCK-B receptor agonist Suc-CCK-4 (Suc-Trp-(N-methyl)Nle-Asp-Phe-NH2) were iontophoretically administered with multibarrel capillaries. About one-third of the neurons responded to the CCK-A receptor agonists. Excitatory effects predominated. The CCK-B receptor agonist also induced mainly increases in the neuronal firing. Several neurons were affected by both types of agonists. The results suggest that in the rat neostriatum not only CCK-B receptors, but also CCK-A receptors seem to mediate the effects of cholecystokinin.