G alpha i RNA antisense expression demonstrates the exclusive coupling of peptide YY receptors to G(i)2 proteins in renal proximal tubule cells

Construction of antisense RNA expression vectors and correction of splicing defect in human beta-globin gene (IVS-2-654 C-->T mutant) in HeLa cells

The antisense fragments, which were available in in vitro system, were cloned into the mammalian expression vector pcDNA3, and were transfected into H654 cells, a mammalian cell line stably expressing the thalassaemic (IVS-2-654 C-->T) human beta-globin gene. In these transfected cells, the level of correctly spliced beta-globin mRNA in total beta-globin mRNA (beta/(beta + beta*)) was improved from 0.07 (0 d) to 0.22 (3 d), and this effect persisted for up to 15 d post transfection. All the results demonstrated that antisense RNAs were able to be transcribed from the antisense fragment expression vectors stably and effectively suppressed aberrant splicing pattern of the mutated beta-globin gene (IVS-2-654 C-->T) and restored correct splicing pathway. This work provided a novel approach with potential clinical significance to gene therapy of this kind of splicing mutants including beta-thalassaemia (IVS-2-654 C-->T) by antisense RNAs.

Coexpression of Y1, Y2, and Y4 receptors in smooth muscle coupled to distinct signaling pathways

Coexpression of Y1, Y2, and Y4 receptors on smooth muscle cells was determined by reverse transcription-polymerase chain reaction, and the receptors were characterized by radioligand binding, selective receptor protection, and functional analysis of signaling pathways. 125I-peptide YY (PYY) binding was completely inhibited by neuropeptide Y (NPY) and PYY, and partially inhibited by the Y1 agonist [Leu31, Pro34]NPY or the Y2 agonist NPY13-36. In cells where Y1 receptors were preserved by selective receptor protection, 125I-PYY binding was selectively inhibited by the Y1 agonist or antagonist BIBP 3226 [(R)-N2-(diphenylacetyl)-N-[(4-hydroxyphenyl)methyl]-D-arginine-amide]. Conversely, in cells where Y2 receptors were preserved, 125I-PYY binding was selectively inhibited by the Y2 agonist or antagonist BIIE 0246 [(S)N2-[1-[2-[4-[(R,S)-5,11-dihydro-6(66H)-oxodibenz[b,e]azepin-11-y]-1piperazinyl]-2-oxoethyl]cyclopentyl]acetyl]-N-[2-[1,2-dihydro-35(4H)-dioxo-1,2-diphenyl-3H-1,2,4-triazol-4-yl]ethyl]-argininamide]. All Y receptors activated preferentially Gi2, but only Y2 and Y4 receptors activated Gq. Consequently, Y2 agonists (NPY, PYY, and NPY13-36) and the Y4 agonist (pancreatic polypeptide) induced concentration-dependent contraction, inositol 1,4,5-trisphosphate (IP3) formation, and increase in cytosolic free Ca2+. Contraction induced by Y2 and Y4 agonists was not affected by 0 Ca2+, Ca2+ channel blockers, or pertussis toxin (PTx), but it was abolished by thapsigargin, U73122 [1-(6-(17beta-3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-25-dione], or the myosin light chain kinase inhibitor ML-9 [1-(5-chloronaphthalene-1-sulfonyl)homopiperazine, HCl]. Y2-mediated contraction was inhibited by the selective Y2 antagonist BIIE 0246. Insensitivity to PTx implied that the coupling to Gi did not initiate (Y1) or contribute (Y2 and Y4) to contraction. All Y receptor agonists inhibited cAMP formation in a PTx-sensitive manner. The patterns of contraction and inhibition of cAMP by various Y receptors were corroborated by selective receptor protection. The study demonstrates coexpression of Y1, Y2, and Y4 receptors on smooth muscle negatively coupled to adenylyl cyclase via Gi2. Coupling of Y2 and Y4 receptors to Gq determines their ability to induce IP3-dependent Ca2+ release and initiate contraction.

Reversal of aberrant splicing of beta-thalassaemia allele (IVS-2-654 C-->T) by antisense RNA expression vector in cultured human erythroid cells

The antisense fragment targeting the aberrant splice sites of the beta-thalassaemia allele, IVS-2-654 C-->T (beta654), pretranscript was cloned into the mammalian expression vector, pcDNA3. The recombinant construct, pCMVA, was then used to repair the defective splicing of the beta654 mutant pretranscript in cultured beta654 erythroid cells by the lipofectin-mediated DNA transfection method. The total RNA was extracted at given time points after transfection and the effect of antisense RNA was studied by reverse transcription polymerase chain reaction (RT-PCR)-mediated mRNA quantitative assay, as well as globin chain microbiosynthesis. The antisense fragment transcribed from pCMVA effectively improved the beta654 splicing pattern in cultured erythroid cells. The level of correctly spliced transcript increased from 0.19 (day 0 after transfection) to 0.58 (day 8) in beta654/beta654 homozygous erythroid cells, and from 0.45 (day 0) to 0.83 (day 8) in beta654/betaA heterozygous erythroid cells, as determined by the ratio of normally spliced beta-globin transcript over total beta-globin transcript. Correspondingly, the ratios of globin chain biosynthesis (beta/alpha) increased from 0.16 (day 0) to 0.52 (day 8) in beta654/beta654 erythroid cells, and from 0.39 (day 0) to 0.84 (day 8) in beta654/betaA erythroid cells. Antisense RNA had no significant effect on the splicing pattern in betaA/betaA erythroid cells. The splicing pattern in transfected cells with pCMVA showed significant changes compared with that in untransfected cells and that in transfected cells with the control antisense fragment (human SRY gene sequence). In addition, we did not observe side-effects on cytological features after the introduction of pCMVA. All these results indicated that the antisense RNA transcribed from the mammalian expression vector pCMVA could efficiently and specifically suppress the aberrant splicing pattern of beta654 mutant pretranscript and restore the correct splicing pathway in vivo, leading to the improvement of globin chain biosynthesis in thalassaemic cells.

Immortalized kidney cells derived from transgenic mice harboring L-type pyruvate kinase and vimentin promoters

Targeted oncogenesis in transgenic mice, where an oncogene is placed under the control of the regulatory sequences of a cell-specific gene, has been used to derive several new types of differentiated nonepithelial and epithelial cell lines. This review summarizes the properties of cell lines derived from proximal, distal and collecting duct cells. The cells were obtained from kidneys of transgenic mice harboring the 5' regulatory sequences of the L-type pyruvate kinase or vimentin genes controlling the expression of either the large T and little t antigens or the temperature-sensitive large T antigen.

Characterization of Y1, Y2 and Y5 subtypes of the neuropeptide Y (NPY) receptor in rabbit kidney. Sensitivity of ligand binding to guanine nucleotides and phospholipase C inhibitors

The binding of two peptide YY/neuropeptide Y analogues selective for major subtypes of neuropeptide Y (NPY) receptors was compared in particulates from rabbit kidney cortex employing modulators of activity of G-proteins, phospholipase enzymes, and ion channels. The binding of (Leu31,Pro34)human peptide YY resembled the patterns observed previously for the brain tissue Y1 receptor, exhibiting a high sensitivity to monovalent cations, disulfide disruptors, guanosine polyphosphates and phospholipase C inhibitors. However, this binding was bimodal in response to human pancreatic polypeptide and to peptides selective for the Y2 subtype of the NPY receptor, displaying a large component pharmacologically similar to the brain Y5 receptor. This kidney Y5-like binding largely shared the sensitivity to monovalent cations, guanine nucleotides and phospholipase C inhibitors found for either the kidney or the brain Y1 receptor, and also was activated by Ca2+ ion. Both Y1- and Y5-like binding in the kidney displayed a uniformly low reactivity to a nonpeptidic Y1 antagonist, BIBP-3226, and to a receptor peptide mimetic, mastoparan analogue MAS-7. The kidney Y2 binding shared the low sensitivity to ionic environment observed for the brain Y2 subtype, and was only partially sensitive to guanine nucleotides or to MAS-7. The Y2 liganding had a sensitivity to phospholipase C inhibitors similar to the Y1/Y5 binding. This reactivity was retained in the fraction of the Y2 receptor persisting detergent solubilization in a high-affinity form, which, however, was activated rather than inhibited by G-protein agonists.

Identification and distribution of mRNA encoding the Y1, Y2, Y4, and Y5 receptors for peptides of the PP-fold family in the rat intestine and colon

Peptide YY (PYY), neuropeptide Y (NPY) and pancreatic polypeptide (PP) are structurally related peptides which have potent antisecretory effects in small and/or large intestines. Receptors mediating these effects are still unknown with the exception of a PYY-preferring receptor expressed in small intestinal crypts. In the present study, expression of recently cloned Y1, Y2, and Y5 receptors which have similar affinity for PYY and NPY and Y4 receptors which have a high affinity for PP was investigated in gut by RT-PCR analysis. The data show that all Y receptors are expressed in small intestine and/or colon but with specific distributions. Y1 receptors are only expressed in nonepithelial colonic tissue, whereas Y2 and Y4 receptors are present in both epithelial and nonepithelial tissue of the small or large intestine. In contrast, Y5 receptor expression appears to be restricted to epithelial crypts of the small intestine and nonepithelial tissue of colon. Sequencing of PCR products showed 100% identity with the corresponding sequences of the cloned Y1, Y4, or Y5 receptors. The PCR product obtained with Y2 primers from rat crypt cells showed 84% identity with the cloned human Y2 receptor. These data indicate a wide distribution of Y receptors in small intestine and colon. They also suggest that Y1, Y2, Y4, and Y5 receptors may be responsible for still unexplained effects of PYY, NPY, or PP on secretion in small and large intestines.

Concomitant regulation of Ca2+ mobilization and G13 expression in human erythroleukemia cells

In human erythroleukemia (HEL) cells, stimulation of alpha2-adrenoceptors by adrenaline or neuropeptide Y Y1 receptors by neuropeptide Y, concomitantly inhibit cAMP accumulation and stimulate mobilization of Ca2+ from intracellular stores via pertussis toxin-sensitive G-proteins. Treatment of HEL cells in chemically-defined, serum-free medium with 1.25% dimethylsulfoxide (DMSO) for 4 days, increased alpha2-adrenoceptor number by 120%, while the neuropeptide Y receptor number was not significantly changed. In DMSO-treated HEL cells, Ca2+ elevations by adrenaline or neuropeptide Y were significantly reduced by 28% and 57%, respectively, while basal Ca2+ and elevations by thrombin or thapsigargin were not significantly altered. Adrenaline and neuropeptide Y-induced inhibition of forskolin-stimulated cAMP accumulation was not significantly altered upon DMSO treatment. While immunodetectable alpha-subunits of Gi2 were not significantly changed by DMSO treatment, those of Gi3 were reduced by 27%. Inactivation of pertussis toxin substrates by pertussis toxin treatment and inhibition of adrenaline or neuropeptide Y stimulated Ca2+ elevations were linearly correlated. These data are compatible with the idea that, in HEL cells, alpha2-adrenoceptors and neuropeptide Y receptors couple to inhibition of adenylyl cyclase via Gi2 while they couple to Ca2+ elevations via Gi3.

Functional coupling of Gi subtype with GABAB receptor/adenylyl cyclase system: analysis using a reconstituted system with purified GTP-binding protein from bovine cerebral cortex

A single molecular species of GTP-binding protein (G protein) has been purified from the bovine cerebral cortex. The immunoblot analysis indicated that the isolated G protein might be Gi1 or Gi2 but not Go, since it was reacted by specific antibodies, anti-Gi alpha 1-2 and anti-Gi alpha 1-1, but not anti-Go alpha. When the Gi protein was reconstituted into phospholipid vesicles with partially purified GABAB receptor and adenylyl cyclase, the stimulation of GABAB receptor by its agonists induced the inhibition of forskolin-stimulated cAMP accumulation. This GABA-induced inhibition was abolished by CGP 55845A, an antagonist of GABAB receptor. These results suggest that a Gi subtype, which was suggested to correspond to Gi1 or Gi2 may be functionally coupled with GABAB receptor/adenylyl cyclase system.

An evaluation of strategies available for the identification of GTP-binding proteins required in intracellular signalling pathways

Strategies which can be used to elucidate the nature of a GTP-binding regulatory protein (G-protein) involved in an intracellular pathway of interest in the complex environment of the cell are described and evaluated. A desirable strategy is considered to be one in which the first stage indicates a requirement for one or more G-proteins, provides information on whether a monomeric, trimeric or other type of G-protein is involved, and gives some idea of the G-protein sub-class. In the second stage the specific G-protein involved is identified. Approaches available for investigations in the first stage include the use of analogues of GTP and GDP, AlF4-, inhibitors of G-protein isoprenylation, bacterial toxins which covalently modify G-proteins, and the introduction of a purified GDP dissociation inhibitor, GDP exchange and/or GTP-ase activating protein. Identification of the specific G-protein in the second stage can be achieved using anti G-protein antibodies, G-protein-or receptor-derived peptides, antisense G-protein RNA and over-expressed, constitutively-active or dominant-negative G-protein mutants. The correct interpretation of results obtained with GTP and GDP analogues and AlF4- in the first stage is complex and often difficult, and requires a thorough understanding of the functions and mechanisms of activation of G-proteins. Nevertheless, it is important to reach the correct conclusion at this stage since considerable time and expense are usually required for investigations in the second stage.

The P2U purinoceptor obligatorily engages the heterotrimeric G protein G16 to mobilize intracellular Ca2+ in human erythroleukemia cells

To assess the role of G16, a trimeric G protein exclusively expressed in hematopoietic cells, Galpha16 antisense RNA was stably expressed in human erythroleukemia (HEL) cells. Western blot analysis showed that in transfected cell lines, the expression of endogenous Galpha16 protein was suppressed, but the expression of Galphaq/11, Galphai2, and Galphai3 remained unaffected. Suppression of Galpha16 in transfected HEL cells did not interfere with transient elevations of intracellular free Ca2+ concentrations induced by prostaglandin E1 (PGE1), platelet-activating factor, or thrombin. In parental HEL cells, UTP and ATP mobilized Ca2+ from intracellular stores with half-maximum effective concentrations of 3. 6 +/- 0.7 and 4.7 +/- 1.6 microM, respectively, apparently by stimulating P2U purinoceptors. By contrast, Ca2+ mobilization by UTP or ATP was completely abrogated in Galpha16-suppressed cells, indicating specific coupling of G16 to P2U purinoceptors. Pertussis toxin inhibited the effect of UTP in parental HEL cells by 57.6 +/- 4.9%. These data indicate that signaling by the P2U purinoceptor obligatorily requires G16 but may be modulated further by activation of Gi. Priming of HEL cells with UTP or ATP prior to stimulation with PGE1 markedly enhanced the PGE1-induced intracellular Ca2+ release. This indirect, potentiating effect of UTP and ATP was not impaired in Galpha16-suppressed cells but was inhibited by pertussis toxin, indicating that functional P2U purinoceptors are present on these cells and that the potentiating effect primarily depends on Gi. The data demonstrate (i) that Galpha16 antisense RNA selectively inhibits endogenous Galpha16 protein expression in HEL cells; (ii) that stimulation of endogenous P2U (P2Y2) purinoceptors leads to the mobilization of intracellular Ca2+ by a mechanism that strictly depends on Galpha16; and (iii) that P2U purinoceptors in HEL cells can communicate with two distinct signaling pathways diverging at the G protein level.

Selective reconstitution of gastrin-releasing peptide receptor with G alpha q

Identification of the molecular mechanisms that determine specificity of coupling interactions between gastrin-releasing peptide receptors (GRPrs) and their cognate heterotrimeric GTP-binding proteins is a fundamental step in understanding the signal transduction cascade initiated by receptor-ligand interaction. To explore these mechanisms in greater detail, we have developed an in situ reconstitution assay in chaotrope-extracted membranes from mouse fibroblasts expressing the GRPr, and we have used it to measure GRPr-catalyzed binding of GTP gamma S to purified G protein alpha subunits. Binding studies with 125I-labeled [D-Tyr6]bombesin(6-13) methyl ester (125I-Tyr-ME), a GRPr specific antagonist, show a single binding site with a Kd = 1.4 nM +/- 0.4 (mean +/- SD, n = 3) and capacity of 15-22 pmol of receptor per mg of protein in the extracted membrane preparations, representing a 2- to 3-fold enrichment of binding sites compared with the membranes before extraction. Quantitative ligand displacement analysis using various unlabeled GRPr agonists shows a rank order of potency characteristic of the GRPr: bombesin > or = GRP > > neuromedin B. Reconstitution of urea extracted membranes with a purified G alpha q showed that receptor-catalyzed binding of GTP gamma S was dependent on agonist (GRP) and G beta gamma subunits. The EC50 for GRP was 3.5 nM, which correlates well with the reported Kd of 3.1 nM for GRP binding to GRPr expressed in mouse fibroblasts [Benya, R. V., et al. (1994) Mol. Pharmacol. 46, 235-245]. The apparent Kd for bovine brain G beta gamma in this assay was 60 nM, and the Km for squid retinal G alpha q was 90 nM. The GRPr-catalyzed binding of GTP gamma S is selective for G alpha q, since we did not detect receptor-catalyzed exchange using either G alpha i/o or G alpha t. These data demonstrate that GRPr can functionally couple to G alpha q but not to the pertussis toxin-sensitive G alpha i/o or retinal specific G alpha t. This in situ receptor reconstitution method will allow molecular characterization of G protein coupling to other heptahelical receptors.

Stimulated secretion of lysosomal enzymes induced by drugs in transimmortalized proximal tubule mouse kidney cells

We summarize the results of study of the properties of two models of transimmortalized proximal tubule epithelial cells derived from the kidneys of transgenic mice harboring the SV40 large T and little t antigens/L-pyruvate kinase hybrid gene. The two cell lines, referred to as PKSV-PCT and PKSV-PR cells, maintained for long-term passages the main biochemical and functional properties from the convoluted and terminal parts of the proximal tubule, respectively, from which they were derived. In PKSV-PCT cells, gentamicin induced lysosomal alkalinization, decreased the cellular N-acetyl-beta-D-glucuronidase, and stimulated its secretion in a dose-dependent manner. The results indicate that these models of mouse proximal cultured cells could be suitable models for the study of the cellular action of drugs.

Guanine nucleotide exchange on heterotrimeric Gi3 protein controls autophagic sequestration in HT-29 cells

Recent results have shown that autophagic sequestration in the human colon cancer cell line HT-29 is controlled by the pertussis toxin-sensitive heterotrimeric Gi3 protein. Here we show that transfection of an antisense oligodeoxynucleotide to the alphai3-subunit markedly inhibits autophagic sequestration, whereas transfection of an antisense oligodeoxynucleotide to the alphai2-subunit does not change the rate of autophagy in HT-29 cells. Autophagic sequestration was arrested in cells transfected with a mutant of the alphai3-subunit (Q204L) that is restricted to the GTP-bound form. In Q204L-expressing cells, 3-methyladenine-sensitive degradation of long lived [14C]valine-labeled proteins was severely impaired and could not be stimulated by nutrient deprivation. Autophagy was also reduced when dissociation of the betagamma dimer from the GTP-bound alphai3-subunit was impaired in cells transfected with the G203A mutant. In contrast, a high rate of pertussis toxin-sensitive autophagy was observed in cells transfected with an alphai3-subunit mutant (S47N) which has an increased guanine nucleotide exchange rate and increased preference for GDP over GTP. Cells that express pertussis toxin-insensitive mutants of either wild-type alphai3-subunit (C351S) or S47N alphai3-subunit (S47N/C351S) exhibit a high rate of autophagy.

Vasoactive intestinal peptide (VIP)1 receptor. Three nonadjacent amino acids are responsible for species selectivity with respect to recognition of peptide histidine isoleucineamide

Vasoactive intestinal peptide (VIP)1 receptors in rats and humans recognize peptide histidine isoleucineamide (PHI) with high and low affinity, respectively. We took advantage of this phenotypic difference to identify the domain responsible for the selective recognition of PHI by rat and human receptors which display >80% sequence identity. After transfection of human and rat receptors in COS cells, the ratio of IC50 for PHI/IC50 for VIP (referred to as P/V) in inhibiting 125I-VIP binding was shown to be >1,000 and <40, respectively. Construction of eight rat/human receptor chimerae by overlap polymerase chain reaction and determination of their P/V ratios demonstrated that the critical domain for PHI recognition is present within a sequence comprising part of the first extracellular loop and third transmembrane domain. This domain contains three different amino acids numbered according to human and rat sequences, respectively, e.g. Gln207 (human) versus His208 (rat), Gly211 versus Ala212 and Met219 versus Val220. Site-directed mutagenesis introducing individual, double, or triple mutations in a chimeric construct revealed that all three amino acids were involved in the recognition of PHI. Triple mutations were then introduced in the wild-type receptors i.e. Q207H, G211A, M219V human VIP1 receptor and H208Q, A212G, V220M rat VIP1 receptor, resulting in a complete change in their phenotype from human to rat and from rat to human, respectively. The results demonstrate that three nonadjacent amino acids are responsible for the selective recognition of PHI by human and rat VIP1 receptors.