Identification of responsible amino acid residues in Staphylococcal superantigen-like 12 for the activation of mast cells

Staphylococcal superantigen-like 12 (SSL12) is reported to evoke the degranulation in murine mast cells. The allelic variant of SSL12 in the genome of reference strain NCTC8325 induced the degranulation of murine mast cells, that of MRSA252 strain did not, nevertheless relatively high sequence similarity (82%). To identify responsible amino acid residues of SSL12 for mast cell activation, we created a series of domain swap mutants and amino acid substitution mutants between the active and inactive variants. The mutants that harbored oligonucleotide/oligosaccharide binding (OB)-fold domain of the active variant activated mast cells. The replacement at position 56 (L56F) in the OB-fold domain diminished the mast cell stimulatory activity, and the combinatorial substitutions L56F/K92E, L56F/D95S, and L56F/S100V abolished the stimulatory activities of the mutant that harbored OB-fold domain of the active variant and the intact active variant. These indicate that the responsive elements of SSL12 for mast cell activation are in the OB-fold of SSL12, and L56 would be an essential amino acid residue for the activation of mast cells. The findings would contribute to the understanding of the molecular mechanism of SSL12 for mast cell activation and the development of toxoids preventing allergic inflammations associated with S. aureus. This article is protected by copyright. All rights reserved.

Proton Shell Evolution below ^{132}Sn: First Measurement of Low-Lying β-Emitting Isomers in ^{123,125}Ag

The β-delayed γ-ray spectroscopy of neutron-rich ^{123,125}Ag isotopes is investigated at the Radioactive Isotope Beam Factory of RIKEN, and the long-predicted 1/2^{-} β-emitting isomers in ^{123,125}Ag are identified for the first time. With the new experimental results, the systematic trend of energy spacing between the lowest 9/2^{+} and 1/2^{-} levels is extended in Ag isotopes up to N=78, providing a clear signal for the reduction of the Z=40 subshell gap in Ag towards N=82. Shell-model calculations with the state-of-the-art V_{MU} plus M3Y spin-orbit interaction give a satisfactory description of the low-lying states in ^{123,125}Ag. The tensor force is found to play a crucial role in the evolution of the size of the Z=40 subshell gap. The observed inversion of the single-particle levels around ^{123}Ag can be well interpreted in terms of the monopole shift of the π1g_{9/2} orbitals mainly caused by the increasing occupation of ν1h_{11/2} orbitals.

β-Decay Half-Lives of 110 Neutron-Rich Nuclei across the N=82 Shell Gap: Implications for the Mechanism and Universality of the Astrophysical r Process

The β-decay half-lives of 110 neutron-rich isotopes of the elements from _{37}Rb to _{50}Sn were measured at the Radioactive Isotope Beam Factory. The 40 new half-lives follow robust systematics and highlight the persistence of shell effects. The new data have direct implications for r-process calculations and reinforce the notion that the second (A≈130) and the rare-earth-element (A≈160) abundance peaks may result from the freeze-out of an (n,γ)⇄(γ,n) equilibrium. In such an equilibrium, the new half-lives are important factors determining the abundance of rare-earth elements, and allow for a more reliable discussion of the r process universality. It is anticipated that universality may not extend to the elements Sn, Sb, I, and Cs, making the detection of these elements in metal-poor stars of the utmost importance to determine the exact conditions of individual r-process events.

Quantitative analysis of computed tomography images and early detection of cerebral edema for pediatric traumatic brain injury patients: retrospective study

BACKGROUND

The purpose of this study was to identify whether the distribution of Hounsfield Unit (HU) values across the intracranial area in computed tomography (CT) images can be used as an effective diagnostic tool for determining the severity of cerebral edema in pediatric traumatic brain injury (TBI) patients.

METHODS

CT images, medical records and radiology reports on 70 pediatric patients were collected. Based on radiology reports and the Marshall classification, the patients were grouped as mild edema patients (n=37) or severe edema patients (n=33). Automated quantitative analysis using unenhanced CT images was applied to eliminate artifacts and identify the difference in HU value distribution across the intracranial area between these groups.

RESULTS

The proportion of pixels with HU=17 to 24 was highly correlated with the existence of severe cerebral edema (P<0.01). This proportion was also able to differentiate patients who developed delayed cerebral edema from mild TBI patients. A significant difference between deceased patients and surviving patients in terms of the HU distribution came from the proportion of pixels with HU=19 to HU=23 (P<0.01).

CONCLUSIONS

The proportion of pixels with an HU value of 17 to 24 in the entire cerebral area of a non-enhanced CT image can be an effective basis for evaluating the severity of cerebral edema. Based on this result, we propose a novel approach for the early detection of severe cerebral edema.

Yrast 6⁺ seniority isomers of (136,138)Sn

Delayed γ-ray cascades, originating from the decay of (6⁺) isomeric states, in the very neutron-rich, semimagic isotopes (136,138)Sn have been observed following the projectile fission of a ²³⁸U beam at RIBF, RIKEN. The wave functions of these isomeric states are proposed to be predominantly a fully aligned pair of f(7/2) neutrons. Shell-model calculations, performed using a realistic effective interaction, reproduce well the energies of the excited states of these nuclei and the measured transition rates, with the exception of the B(E2;6⁺→4⁺) rate of ¹³⁶Sn, which deviates from a simple seniority scheme. Empirically reducing the νf(7/2)(2) orbit matrix elements produces a 4₁⁺ state with almost equal seniority 2 and 4 components, correctly reproducing the experimental B(E2;6⁺→4⁺) rate of ¹³⁶Sn. These data provide a key benchmark for shell-model interactions far from stability.

Monopole-driven shell evolution below the doubly magic nucleus 132Sn explored with the long-lived isomer in 126Pd

A new isomer with a half-life of 23.0(8) ms has been identified at 2406 keV in (126)Pd and is proposed to have a spin and parity of 10(+) with a maximally aligned configuration comprising two neutron holes in the 1h(11/2) orbit. In addition to an internal-decay branch through a hindered electric octupole transition, β decay from the long-lived isomer was observed to populate excited states at high spins in (126)Ag. The smaller energy difference between the 10(+) and 7(-) isomers in (126)Pd than in the heavier N=80 isotones can be interpreted as being ascribed to the monopole shift of the 1h(11/2) neutron orbit. The effects of the monopole interaction on the evolution of single-neutron energies below (132)Sn are discussed in terms of the central and tensor forces.

Comparison of live performance and meat quality parameter of cross bred (korean native black pig and landrace) pigs with different coat colors

Five hundred and forty crossbred (Korean native black pig×Landrace) F₂ were selected at a commercial pig farm and then divided into six different coat color groups: (A: Black, B: White, C: Red, D: White spot in black, E: Black spot in white, F: Black spot in red). Birth weight, 21st d weight, 140th d weight and carcass weight varied among the different coat color groups. D group (white spot in black coat) showed a significantly higher body weight at each weigh (birth weight, 140th d weight and carcass weight) than did the other groups, whereas the C group (red coat color) showed a significantly lower body weight at finishing stage (140th d weight and carcass weight) compared to other groups. Meat quality characteristics, shear force, cooking loss and meat color were not significantly different among the different coat color groups, whereas drip loss was significantly higher in F than in other groups. Most blood characteristics were not significantly different among the different groups, except for the red blood cells.

1p3/2 proton-hole state in 132Sn and the shell structure along N = 82

A low-lying state in 131In82, the one-proton hole nucleus with respect to double magic 132Sn, was observed by its γ decay to the Iπ=1/2- β-emitting isomer. We identify the new state at an excitation energy of Ex=1353  keV, which was populated both in the β decay of 131Cd83 and after β-delayed neutron emission from 132Cd84, as the previously unknown πp3/2 single-hole state with respect to the 132Sn core. Exploiting this crucial new experimental information, shell-model calculations were performed to study the structure of experimentally inaccessible N=82 isotones below 132Sn. The results evidence a surprising absence of proton subshell closures along the chain of N=82 isotones. The consequences of this finding for the evolution of the N=82 shell gap along the r-process path are discussed.

Isomers in 128Pd and 126Pd: evidence for a robust shell closure at the neutron magic number 82 in exotic palladium isotopes

The level structures of the very neutron-rich nuclei 128Pd and 126Pd have been investigated for the first time. In the r-process waiting-point nucleus 128Pd, a new isomer with a half-life of 5.8(8) μs is proposed to have a spin and parity of 8(+) and is associated with a maximally aligned configuration arising from the g(9/2) proton subshell with seniority υ=2. For 126Pd, two new isomers have been identified with half-lives of 0.33(4) and 0.44(3) μs. The yrast 2(+) energy is much higher in 128Pd than in 126Pd, while the level sequence below the 8(+) isomer in 128Pd is similar to that in the N=82 isotone 130Cd. The electric quadrupole transition that depopulates the 8(+) isomer in 128Pd is more hindered than the corresponding transition in 130Cd, as expected in the seniority scheme for a semimagic, spherical nucleus. These experimental findings indicate that the shell closure at the neutron number N=82 is fairly robust in the neutron-rich Pd isotopes.

Effect of enzymatic pretreatment on solubilization and volatile fatty acid production in fermentation of food waste

Food waste can be a valuable carbon source in biological nutrient removal (BNR) systems because of the high C/N and C/P ratio. However, pretreatment is necessary to promote hydrolysis of food waste because of the high concentration of volatile solids associated with organic matter. The influence of the enzymatic pretreatment on acid fermentation of food waste was investigated in this study. Solubilization of particulate matter in food waste was carried out using commercial enzymes. The acidification efficiency and the volatile fatty acid (VFA) production potential of enzymatically pretreated food waste were examined. The highest volatile suspended solid (VSS) reduction was obtained with an enzyme mixture ratio of 1:2:1 for carbohydrase: protease: lipase. An optimum enzyme dosage for solubilization of food waste was 0.1% (V/V) with the enzyme mixture ratio of 1:2:1. In the acid fermentation of enzymatically pretreated food waste, the maximum VFA production and the highest VFA fraction in soluble COD (SCOD) were also achieved at 0.1% (V/N) of total enzyme dosage. Increase in VFA production at this level of enzyme dosage was over 300% compared with the control fermenter. The major form of VFA produced by fermentation was n-butyrate followed by acetate.

Sensing of ionizing radiation-induced DNA damage by ATM through interaction with histone deacetylase

The ATM gene is mutated in individuals with ataxia telangiectasia, a human genetic disease characterized by extreme sensitivity to radiation. The ATM protein acts as a sensor of radiation-induced cellular damage and contributes to cell cycle regulation, signal transduction, and DNA repair; however, the mechanisms underlying these functions of ATM remain largely unknown. Binding and immunoprecipitation assays have now shown that ATM interacts with the histone deacetylase HDAC1 both in vitro and in vivo, and that the extent of this association is increased after exposure of MRC5CV1 human fibroblasts to ionizing radiation. Histone deacetylase activity was also detected in immunoprecipitates prepared from these cells with antibodies to ATM, and this activity was blocked by the histone deacetylase inhibitor trichostatin A. These results suggest a previously unanticipated role for ATM in the modification of chromatin components in response to ionizing radiation.

Agonist-induced internalization of the G protein G11alpha and thyrotropin-releasing hormone receptors proceed on different time scales

Using a combination of confocal immunofluorescence microscopy and subcellular fractionation, we demonstrate for the first time active internalization, trafficking, and down-regulation of a G protein alpha subunit subsequent to agonist occupation of a receptor. This proceeds on a much slower time scale than internalization of the corresponding receptor. In intact E2M11 HEK293 cells that express high levels of murine G11alpha and the rat thyrotropin-releasing hormone (TRH) receptor, the immunofluorescence signal of G11alpha was restricted almost exclusively to the plasma membrane. Exposure to TRH (10 microM) resulted first in partial relocation of G11alpha to discrete, segregated patches within the plasma membrane (10-60 min). Further exposure to TRH caused internalization of G11alpha to discrete, punctate, intracellular bodies (2-4 h) and subsequently to a virtually complete loss of G11alpha from plasma membranes and the cells (8-16 h). Short-term treatment with TRH followed by wash-out of the ligand allowed G11alpha immunofluorescence to be restored to the plasma membrane within 12 h. In subcellular membrane fractions, G11alpha was centered on plasma membranes, and this was not altered by up to 1-2 h of incubation with TRH. Further exposure to TRH (2-4 h) resulted in transfer of a significant portion of G11alpha to light-vesicular and cytosol fractions. At longer time intervals (4-16 h), an overall decrease in G11alpha content was observed.

Implementation of a low-cost PACS/CR for clinical use in Yonsei Cardiovascular Center

The PACS/CR for clinical use in Yonsei Cardiovascular Center has been designed and implemented. Our system is open architecture to comply with emerging standards such as DICOM. database SQL, TCP/IP and to reduce operational and maintenance costs, PC-based low cost workstations running Microsoft Windows, database as Microsoft SQL based on Client/Server, Long-term storage using CD-ROM Jukebox are developed. Also, auto routing and image pre-fetching are implemented.

CCAAT/enhancer binding protein epsilon is preferentially up-regulated during granulocytic differentiation and its functional versatility is determined by alternative use of promoters and differential splicing

CCAAT/enhancer binding protein (C/EBP) epsilon is a recently cloned member of the C/EBP family of transcription factors and is expressed exclusively in cells of hematopoietic origin. The human C/EBPepsilon gene is transcribed by two alternative promoters, Palpha and Pbeta. A combination of differential splicing and alternative use of promoters generates four mRNA isoforms, of 2.6 kb and 1.3-1.5 kb in size. These transcripts can encode three proteins of calculated molecular mass 32.2 kDa, 27.8 kDa, and 14.3 kDa. Accordingly, Western blots with antibodies specific for the DNA-binding domain, that is common to all forms, identify multiple proteins. C/EBPepsilon mRNA was greatly induced during in vitro granulocytic differentiation of human primary CD34(+) cells. Retinoic acid treatment of HL60 promyelocytic leukemia cells for 24 hr induced C/EBPepsilon mRNA levels by 4-fold, while prolonged treatment gradually reduced mRNA expression to pretreatment levels. Transient transfection experiments with expression vectors for two of the isoforms demonstrated that the 32.2-kDa protein is an activator of transcription of granulocyte colony-stimulating factor receptor promoter, while the 14.3-kDa protein is not. Thus, C/EBPepsilon is regulated in a complex fashion and may play a role in the regulation of genes involved in myeloid differentiation.

Agonist regulation of adenylate cyclase activity in neuroblastoma x glioma hybrid NG108-15 cells transfected to co-express adenylate cyclase type II and the beta 2-adrenoceptor. Evidence that adenylate cyclase is the limiting component for receptor-mediated stimulation of adenylate cyclase activity

Stable cell lines, derived from NG108-15 cells and transfected to express both the beta 2-adrenoceptor and adenylate cyclase type II, were produced and examined. The absence of adenylate cyclase type II in the parental cells and its presence in these clones was demonstrated by reverse transcriptase-PCR. Total cellular levels of adenylate cyclase were increased in a number of clones between 3- and 8-fold, as assessed by guanine nucleotide-stimulated specific high-affinity binding of [3H]forskolin to cellular membranes. Basal adenylate cyclase activity was markedly elevated compared with a clone expressing similar levels of the beta 2-adrenoceptor in the absence of adenylate cyclase type II. Each of NaF, forskolin and guanosine 5'-[beta, gamma-imido]triphosphate (a poorly hydrolysed analogue of GTP) produced substantially higher levels of adenylate cyclase activity in membranes of the clones positive for expression of adenylate cyclase type II than was achieved with the parental cells. Both isoprenaline, acting at the introduced beta 2-adrenoceptor, and iloprost, acting at the endogenously expressed IP prostanoid receptor, stimulated adenylate cyclase activity to much higher levels in the clones expressing adenylate cyclase type II compared with the clone lacking this adenylate cyclase; however, the concentration-effect curves for adenylate cyclase stimulation by these two agonists were not different between parental cells and clones over-expressing adenylate cyclase type II. A maximally effective concentration of the beta-adrenoceptor partial agonist ephedrine displayed similar intrinsic activity and potency to stimulate adenylate cyclase in membranes of clones both with and without adenylate cyclase type II. Both secretin and 5'-N-ethylcarbox-amidoadenosine (acting at an endogenous A2 adenosine receptor) were also able to produce substantially greater maximal activations of adenylate cyclase in the clones expressing excess adenylate cyclase type II, without alterations in agonist intrinsic activity or potency. These results demonstrate that the maximal output of the stimulatory arm of the adenylate cyclase cascade can be increased by increasing total levels of adenylate cyclase in the genetic background of NG108-15 cells.

Thyrotropin-releasing hormone-induced subcellular redistribution and down-regulation of G11alpha: analysis of agonist regulation of coexpressed G11alpha species variants

Human embryonic kidney 293 cells that had been transfected to express the long isoform of the rat thyrotropin-releasing hormone (TRH) receptor (clone E2) were further transfected with a cDNA encoding the murine version of G11alpha. A clone was isolated (clone E2M11) that stably expressed murine as well as the endogenous human G11alpha. Subcellular fractionation demonstrated identical cellular distribution of the two species variants of this G protein. Sustained exposure of clone E2M11 cells to TRH resulted in substantial cellular redistribution and reduction in total cellular levels of G11alpha immunoreactivity. Fractions of both the exogenously introduced murine and endogenously expressed human isoforms of G11alpha were transferred from plasma membranes to low density membranes (detected as a shift from middle to low density regions on sucrose density gradients) and cytosol fractions. The plasma membrane redistribution to low density membrane was accompanied by a parallel redistribution of G protein beta subunits; however, there was no increase in beta subunits in the cytosol. The total cellular amount of G11alpha subunits was decreased to 21% and 59% for human and murine isoforms, respectively, and beta subunits were decreased to 68% after sustained treatment with TRH compared with controls (100%). Such data are consistent with the notion that the agonist-occupied long isoform of the rat TRH receptor may be able to partially differentiate between the endogenous (human) and exogenous (murine) G11alpha. This was not a reflection that the murine G protein was expressed but incorrectly folded as both species variants of G11alpha were solubilized equally from E2M11 membranes by sodium cholate. Using this system, we demonstrate both agonist-induced subcellular redistribution and down-regulation of G11alpha and beta subunit proteins in response to activation of a phospholipase C coupled receptor.

Regulation of cellular Gs alpha levels and basal adenylyl cyclase activity by expression of the beta 2-adrenoceptor in neuroblastoma cell lines

Mouse neuroblastoma x rat glioma hybrid NG 108-15 and mouse neuroblastoma x embryonic hamster brain NCB20 cells were transfected with a construct containing a human beta 2 adrenoceptor cDNA under the control of the beta actin promoter. Clones were selected on the basis of resistance to geneticin sulphate and those expressing a range of levels of the receptor expanded for further study. Membranes from a clone of NG108-15 cells expressing high levels of the receptor (beta N22) but not one expressing only low levels of the receptor (beta N17) exhibited a markedly elevated adenylyl cyclase activity when measured in the presence of Mg2+ compared to wild type cells. This was not due to elevated levels of the adenylyl cyclase catalytic moiety however as there was no difference in these membranes when the adenylyl cyclase activity was measured in the presence of Mn2+. The elevated basal activity was partially reversed by addition of the beta-adrenoceptor antagonist propranolol. Agonist activation of beta N22 but not beta N17 cells led to a large selective down-regulation of cellular Gs alpha levels which was independent of the generation of cyclic AMP. Isoprenaline stimulation of adenylyl cyclase activity and of the specific high affinity binding of [3H] forskolin was achieved with substantially greater potency (some 30 fold) in beta N22 cell membranes than in beta N17. By contrast agonist activation of the endogenously expressed IP prostanoid receptor caused stimulation of adenylyl cyclase and stimulation of high affinity [3H] forskolin binding which was equipotent in each of beta N22, beta N17 and wild type NG108-15 cells. Agonist activation of the IP prostanoid receptor caused an equivalent degree of Gs alpha down-regulation in each cell type. Expression of an epitope tagged variant of Gs alpha in NG108-15 cells resulted in prostanoid agonist-induced down-regulation of this polypeptide in a manner indistinguishable from that of wild type Gs alpha. Isolation of clones of NCB20 cells expressing high levels of the beta 2 adrenoceptor also resulted in a specific agonist-induced down-regulation of Gs alpha.

Analysis of the role of receptor number in defining the intrinsic activity and potency of partial agonists in neuroblastoma x glioma hybrid NG108-15 cells transfected to express differing levels of the human beta 2-adrenoceptor

Many agonist ligands are known experimentally to display a range of efficacies and potencies in different tissues and preparations. To analyze the role of the levels of receptor expression and availability in the intrinsic activities and potencies of agonists, the function of a number of beta-adrenoceptor ligands was examined in clones of neuroblastoma x glioma hybrid NG108-15 cells transfected to express differing levels of the human beta 2-adrenoceptor, as well as after treatment of these cell lines with the irreversible beta-adrenoceptor antagonist bromoacetyl alprenolol menthane (BAAM). Clone beta N22 expressed approximately 10-fold higher levels of the receptor than did clone beta N17. In measurements of agonist stimulation of adenylyl cyclase activity in membranes of these cells or agonist stimulation of the formation of the complex of Gs alpha and adenylyl cyclase, which acts as the high affinity binding site for [3H]forskolin in whole cells, a series of beta-adrenoceptor agonists, including dichloroisoprenaline, ephedrine, dobutamine, and salbutamol, displayed higher intrinsic activity and showed concentration-response curves that were substantially to the left (lower EC50 values) in clone beta N22, compared with clone beta N17. Treatment of clone beta N22 cells with varying concentrations of BAAM reduced the intrinsic activity of these ligands and shifted the concentration-response curves for these agents to the right. In clone beta N22 cells and membranes, reduction in the observed intrinsic activity for ephedrine required elimination of a smaller fraction of the beta 2-adrenoceptor reserve than for salbutamol and reduction in the effect of the full agonists isoprenaline and epinephrine was noted only with high fractional elimination of the receptor pool. The effect of isoprenaline was substantially reduced, however, by BAAM treatment of clone beta N17 cells, where the beta 2-adrenoceptor number approached extremely low levels. Analysis of the data using the formalisms of Whaley et al. [Mol. Pharmacol. 45:481-489 (1994)] showed that prediction of alterations in agonist potency with receptor number for full agonists can be adequately extended to partial agonists.

Detection and analysis of agonist-induced formation of the complex of the stimulatory guanine nucleotide-binding protein with adenylate cyclase in intact wild-type and beta 2-adrenoceptor-expressing NG108-15 cells

Neuroblastoma x glioma hybrid, NG108-15, cells appear to express the alpha-subunit of the guanine nucleotide-binding protein Gs in a substantial molar excess over its effector adenylate cyclase [Kim, Adie and Milligan (1994) Eur. J. Biochem. 219, 135-143]. Addition of the IP prostanoid receptor agonist iloprost to intact NG108-15 cells resulted in a dose-dependent increase in formation of the complex between Gs alpha and adenylate cyclase (GSAC) as measured by specific high-affinity binding of [3H]forskolin. NG108-15 cells transfected to express either relatively high (clone beta N22) or low (clone beta N17) levels of beta 2-adrenoceptor both showed dose-dependent increases in specific [3H]forskolin binding in response to the beta-adrenoceptor agonist isoprenaline, and maximally effective concentrations of isoprenaline resulted in the generation of similar numbers of GSAC complexes in both clones. The dose-effect curve for clone beta N22, however, was some 15-fold to the left of that for clone beta N17, which is similar to that noted for isoprenaline-mediated stimulation of adenylate cyclase activity [Adie and Milligan (1994) Biochem. J. 303, 803-808]. In contrast, dose-effect curves for iloprost stimulation of [3H]forskolin binding were not different in clones beta N22 and beta N17. Basal specific [3H]forskolin binding in the absence of agonist was significantly greater in cells of clone beta N22 than clone beta N17. This was not a reflection of higher immunological levels of adenylate cyclase, indicating that the higher basal formation of GSAC probably reflects empty-receptor activation of Gs. This higher basal specific [3H]forskolin binding was partially reversed by propranolol. The addition of the opioid peptide D-Ala-D-Leu-enkephalin to NG108-15 cells did not reduce iloprost-stimulated [3H]forskolin binding even though this peptide inhibits stimulated adenylate cyclase activity by activation of a delta opioid receptor.

Receptor availability defines the extent of agonist-mediated G-protein down-regulation in neuroblastoma x glioma hybrid cells transfected to express the beta 2-adrenoceptor

Sustained exposure of neuroblastoma x glioma hybrid, NG108-15, cells transfected to express the human beta 2-adrenoceptor (clone beta N22) to isoprenaline or iloprost (an agonist at the endogenously expressed IP prostanoid receptor) resulted in a substantial and selective down-regulation of the alpha subunit of the G-protein Gs. Treatment of these cells with the irreversible beta-adrenoceptor antagonist bromoacetyl alprenolol menthane diminished both the potency and the maximal ability of isoprenaline but not of iloprost to cause Gs alpha down-regulation. These results demonstrate that the extent of agonist-mediated Gs alpha down-regulation is dependent upon the availability of receptor to agonist.

The long isoform of the rat thyrotropin-releasing hormone receptor down-regulates Gq proteins

A cDNA encoding the long isoform of the rat thyrotropin releasing hormone (TRH) receptor was expressed stably in HEK-293 cells. Polymerase chain reaction analysis confirmed expression of mRNA encoding only the long and not the short isoform. Activation of this receptor with TRH caused a large stimulation in production of inositol phosphates but did not produce either activation of basal or inhibition of forskolin-amplified adenylyl cyclase activity. Sustained exposure of these transfected cells to TRH resulted in a substantial reduction in cellular levels of Gq alpha-like immunoreactivity from some 12 to 5 pmol/mg of membrane protein without significant alterations in cellular levels of the alpha subunits of Gs, Gi1, Gi2, Gi3, or Go. Equivalent experiments in GH3 cells also indicated a marked down-regulation of Gq alpha/G11 alpha. Dose-response curves indicated that 20 nM TRH produced half-maximal down-regulation of cellular Gq-like immunoreactivity in the transfected HEK-293 cells and that half-maximal loss was produced within 3-4 h. Separation of the transfected HEK-293 cell membranes in SDS-polyacrylamide gel electrophoresis conditions able to resolve individual members of the Gq family of G-proteins demonstrated the presence of two related G-proteins. Both of the expressed Gq-like G-proteins were observed to be down-regulated in parallel by TRH. The similarity of dose-response curves and time-courses for loss of the two G-proteins indicates that the long isoform of the rat TRH receptor does not functionally select between these two transducer proteins. In GH3 cells both Gq alpha and G11 alpha, which are expressed at similar levels, were observed to be down-regulated equivalently by treatment with TRH.

Concurrent specific immunological detection of both primate and rodent forms of the guanine nucleotide binding protein G11 alpha following their coexpression

The phosphoinositidase C-linked G proteins Gq alpha and G11 alpha are highly similar and comigrate in 10% (w/v) acrylamide SDS-PAGE. Antisera generated against regions common between these G proteins thus detect a composite of the two polypeptides following resolution in such gels. Using SDS-PAGE conditions which allow resolution of Gq alpha and G11 alpha in rodent brain and neuroblastoma cell lines it was observed that primate frontal cortex and neuroblastoma cell lines did not express a polypeptide which comigrated with rodent G11 alpha. Species diversity in G-protein sequences is extremely limited; however, immunoblotting primate cells and frontal cortex with a G11 alpha-specific antiserum demonstrated this to be due to a difference in mobility of rodent and primate G11 alpha under these conditions rather than lack of expression of G11 alpha by primates. A cDNA encoding mouse G11 alpha was transiently expressed in monkey COS-1 cells and membranes from these cells were immunoblotted with antisera able to identify primate and rodent G11 alpha equally, following SDS-PAGE under the resolving conditions. Both mouse and monkey G11 alpha could be detected concurrently and unambiguously following transfection. This is the first demonstration that species variants of the same G protein expressed in a single cell can be detected simultaneously.

Muscarinic M-current inhibition via G alpha q/11 and alpha-adrenoceptor inhibition of Ca2+ current via G alpha o in rat sympathetic neurones

1. Microinjection of selective antibodies into superior cervical ganglion (SCG) neurones has identified the G-protein alpha-subunits mediating muscarinic receptor inhibition of M-type K+ current (IK(M)) and alpha-adrenoceptor inhibition of Ca2+ current (ICa). 2. Antibodies specific for G alpha q/11, but not those for G alpha o, reduced M-current inhibition by the muscarinic agonist oxotremorine-M, whereas anti-G alpha o antibodies, but not anti-G alpha q/11 or anti-G alpha i1-3 antibodies, reduced calcium current inhibition by noradrenaline. 3. Immunoblots with specific anti-G-protein antibodies demonstrated the presence of both G alpha q and G alpha 11, while G alpha o1 (but virtually no G alpha o2) was present. 4. We conclude that M1 muscarinic receptor inhibition of IK(M) is transduced by G alpha q and/or G alpha 11, and that G alpha o transduces alpha-adrenoceptor inhibition of ICa.

Quantitative stoichiometry of the proteins of the stimulatory arm of the adenylyl cyclase cascade in neuroblastoma x glioma hybrid, NG108-15 cells

To understand the details of regulation of guanine-nucleotide-binding-protein-linked transmembrane cellular-signalling cascades, it is important to know the absolute levels of each polypeptide component and the stoichiometry of their interactions. Amounts of the IP prostanoid receptor, the stimulatory G protein of the adenylyl cyclase cascade (Gs alpha) and the functional complex of Gs alpha with adenylyl cyclase, which acts as the cyclic AMP generator, were measured in membranes of neuroblastoma x glioma hybrid, NG108-15, cells. As measured by the specific binding of [3H]prostaglandin E1, the IP prostanoid receptor was present in some 100,000 copies/cell. Gs alpha assessed by quantitative immunoblotting with recombinantly expressed protein, was present in considerably higher levels (1,250,000 copies/cell). However, the maximal formation of a complex of Gs alpha and adenylyl cyclase represented only some 17,500 copies/cell. The previously established 8:1 stoichiometry of concurrent downregulation of Gs alpha and the IP prostanoid receptor in these cells [Adie, E. J., Mullaney, I., McKenzie, F. R. & Milligan, G. (1992) Biochem. J. 285, 529-536] indicates that full-agonist occupation of the receptor should be able to activate some 65% of the expressed Gs. Despite the potential 70-fold excess of Gs alpha over the Gs alpha/adenylyl cyclase complex, IP prostanoid-receptor-agonist-mediated reduction of Gs alpha levels by some 35% resulted in a 25% reduction in the maximal formation of the Gs alpha/adenylyl cyclase complex. Such results demonstrate that adenylyl cyclase is quantitatively the least highly expressed component of this signalling cascade and suggests that much of the cellular Gs alpha may not have access to adenylyl cyclase.