Characterization of the guinea pig lung membrane leukotriene D4 receptor solubilized in an active form. Association and dissociation with an islet-activating protein-sensitive guanine nucleotide-binding protein

A review of non-prostanoid, eicosanoid receptors: expression, characterization, regulation, and mechanism of action

Eicosanoid signaling controls a wide range of biological processes from blood pressure homeostasis to inflammation and resolution thereof to the perception of pain and to cell survival itself. Disruption of normal eicosanoid signaling is implicated in numerous disease states. Eicosanoid signaling is facilitated by G-protein-coupled, eicosanoid-specific receptors and the array of associated G-proteins. This review focuses on the expression, characterization, regulation, and mechanism of action of non-prostanoid, eicosanoid receptors.

Leukotriene receptors as potential therapeutic targets

Leukotrienes, a class of arachidonic acid-derived bioactive molecules, are known as mediators of allergic and inflammatory reactions and considered to be important drug targets. Although an inhibitor of leukotriene biosynthesis and antagonists of the cysteinyl leukotriene receptor are clinically used for bronchial asthma and allergic rhinitis, these medications were developed before the molecular identification of leukotriene receptors. Numerous studies using cloned leukotriene receptors and genetically engineered mice have unveiled new pathophysiological roles for leukotrienes. This Review covers the recent findings on leukotriene receptors to revisit them as new drug targets.

Modulation of leukotriene D4 attenuates the development of seizures in mice

The present study has been designed to pharmacologically investigate the effect of Montelukast sodium, a leukotriene D(4) receptor antagonist, and 1,2,3,4, tetrahydroisoquinoline, a leukotriene D(4) synthetic pathway inhibitor, on the pathophysiological progression of seizures using mouse models of kindled epilepsy and status epilepticus induced spontaneous recurrent seizures. Pentylenetetrazole (40 mg kg(-1)) (PTZ) administration every second day for a period of 15 d was used to elicit chemically induced kindled seizure activity in mice. In a separate set of groups, fifty consecutive electroshocks were delivered to mice using corneal electrodes with continuously increasing intensity with an inter-shock interval of 40s. Severity of kindled seizures was assessed in terms of a composite kindled seizure severity score (KSSS). Pilocarpine (100 mg kg(-1)) was injected every twenty minutes until the onset of status epilepticus. A spontaneous recurrent seizure severity score (SRSSS) was recorded as a measure of quantitative assessment of the progressive development of spontaneous recurrent seizures induced after pilocarpine status epilepticus. Sub-acute PTZ administration and electroshock induced the development of severe form of kindled seizures in mice. Severity of kindled seizures was assessed in terms of a composite kindled seizure severity score. Further, pharmacological status epilepticus elicited a progressive evolution of spontaneous recurrent seizures in the animals. However, Montelukast sodium, a leukotriene D(4) receptor antagonist, as well as 1,2,3,4, tetrahydroisoquinoline, a leukotriene D(4) synthetic pathway inhibitor, markedly and dose dependently suppressed the development of kindled seizures as well as pilocarpine induced spontaneous recurrent seizures. Therefore, leukotriene D(4) may be implicated in the pathogenesis of seizures.

International Union of Pharmacology XXXVII. Nomenclature for leukotriene and lipoxin receptors

The leukotrienes and lipoxins are biologically active metabolites derived from arachidonic acid. Their diverse and potent actions are associated with specific receptors. Recent molecular techniques have established the nucleotide and amino acid sequences and confirmed the evidence that suggested the existence of different G-protein-coupled receptors for these lipid mediators. The nomenclature for these receptors has now been established for the leukotrienes. BLT receptors are activated by leukotriene B(4) and related hydroxyacids and this class of receptors can be subdivided into BLT(1) and BLT(2). The cysteinyl-leukotrienes (LT) activate another group called CysLT receptors, which are referred to as CysLT(1) and CysLT(2). A provisional nomenclature for the lipoxin receptor has also been proposed. LXA(4) and LXB(4) activate the ALX receptor and LXB(4) may also activate another putative receptor. However this latter receptor has not been cloned. The aim of this review is to provide the molecular evidence as well as the properties and significance of the leukotriene and lipoxin receptors, which has lead to the present nomenclature.

Mrp2 modulates the activity of chloride channels in isolated hepatocytes

Adenosine triphosphate binding cassette family transport proteins are important organic ion transporters in hepatocytes but these molecules may also exhibit other functions. In the present study we have measured the effects of substrates of the canalicular organic ion transporter multidrug resistance associated protein 2 (Mrp2) on chloride channel activation and cell volume regulation. We found that substrates such as leukotriene D(4), 17-beta-estradiol glucuronide, and the leukotriene inhibitor MK-571 accelerated the activation of chloride channels by cell swelling and activated chloride channels in cytokine-pretreated hepatocytes. Two conjugated estrogens that are not Mrp2 substrates did not produce this effect. Hepatocytes derived from a strain of transport-deficient rats (TR(-)), which lack Mrp2 expression, showed none of these substrate effects. Coincident with their ability to activate channels, the Mrp2 substrates increased the rate of volume regulatory decrease by approximately 50% (P <.01), confirming that enhanced channel activation under this condition stimulated volume regulation. In TR-hepatocytes the Mrp2 substrate had no effect on volume regulation. In conclusion, Mrp2 plays a role in regulation of chloride channel function by reducing the lag time necessary for channel activation and consequently accelerating the process of cell volume regulation. Substrates of Mrp2 affect the ability of the protein to interact with chloride channels. These findings represent an alternative function of Mrp2 in hepatocytes.

Leukotriene D(4) activates MAPK through a Ras-independent but PKCepsilon-dependent pathway in intestinal epithelial cells

We have recently shown that leukotriene D(4) (LTD(4)) increases cell survival in intestinal epithelial cells. Here we report and explore the complementary finding that LTD(4) also enhances proliferation in these cells. This proliferative response was approximately half of that induced by epidermal growth factor (EGF) and its required activation of protein kinase C (PKC), Ras and the mitogen-activated protein kinase (MAPK) Erk-1/2. EGF also activated Erk-1/2 in these cells; however the EGF-receptor inhibitor PD153035 did not affect the LTD(4)-induced activation of Erk-1/2. In addition, LTD(4) did not induce phosphorylation of the EGF receptor, nor did pertussis toxin (PTX) block EGF-induced activation of Erk-1/2, thus refuting a possible crosstalk between the receptors. Furthermore, LTD(4)-induced, but not EGF-induced, activation of Erk-1/2 was sensitive to PTX, PKC inhibitors and downregulation of PKCepsilon. A definite role for PKCepsilon in LTD(4)-induced stimulation of Erk-1/2 was documented by the inability of LTD(4) to activate Erk-1/2 in cells transfected with either the regulatory domain of PKCepsilon (an isoform specific dominant-negative inhibitor) or a kinase-dead PKCepsilon. Although Ras and Raf-1 were both transiently activated by LTD(4), only Raf-1 activation was abolished by abrogation of the PKC signal. Furthermore, the LTD(4)-induced activation of Erk-1/2 was unaffected by transfection with dominant-negative N17 Ras but blocked by transfection with kinase-dead Raf-1. Consequently, LTD(4) regulates the proliferative response by a distinct Ras-independent, PKCepsilon-dependent activation of Erk-1/2 and a parallel Ras-dependent signaling pathway.

Leukotrienes as mediators of asthma

This review describes the aspects of leukotriene (LT) pharmacology and biology that are relevant to their important role in asthma. The biosynthesis and metabolism, including transcellular metabolism, of LTB4 and the cysteinyl-LTs (i.e. LTC4, LTD4 and LTE4) are described, and their transport is briefly outlined. The existence, distribution and pharmacological characterization of the receptors (BLT, CysLT1, CysLT2), as well as the transduction mechanisms triggered, are discussed in detail. We also describe their effects on airway smooth muscle tone, hyperresponsiveness and proliferation, on vascular tone and permeability, on mucus secretion, on neural fibers and inflammatory cell functions. Finally, the evidence supporting their role as asthma mediators is reviewed, including the effects of anti LT drugs (both biosynthesis inhibitors and receptor antagonists) in experimental and clinical asthma.

Leukotriene D(4) triggers an association between gbetagamma subunits and phospholipase C-gamma1 in intestinal epithelial cells

The proinflammatory mediator leukotriene D(4) (LTD(4)) binds to the seven-transmembrane receptor CYSLT(1). Although this leukotriene plays an important biological role, its intracellular signaling pathways are only partly known. In previous experiments, we found that LTD(4) induced tyrosine phosphorylation and translocation of phospholipase (PLC)-gamma1 to a plasma membrane fraction in a human epithelial cell line (Int 407). In the present study, we further examined these signaling events and found that LTD(4) induced a rapid interaction between Gbetagamma subunits and PLC-gamma1; results obtained with GST fusion proteins of PLC-gamma1 suggest that this interaction is mediated via the pleckstrin homology domain of PLC-gamma1. Moreover, LTD(4) induced an increased association of c-Src with PLC-gamma1, and the selective Src family tyrosine kinase inhibitor PP1 blocked both LTD(4)-induced tyrosine phosphorylation of PLC-gamma1 and the association of PLC-gamma1 with Gbetagamma subunits. The relevance of these observations in intracellular calcium signaling was investigated by microinjecting cells with anti-Gbeta, anti-PLC-gamma1, or anti-c-Src antibodies and by pretreatment with PP1. LTD(4)-induced calcium mobilization was blocked by each of the indicated antibodies (but not isotype-matched control antibodies) and by PP1. Our data suggest that Gbetagamma subunits can, directly or indirectly, serve as membrane-bound partners for PLC-gamma1 and c-Src and that each of these proteins is essential for LTD(4)-induced downstream PLC-gamma1 signaling.

Leukotriene D4 induces a rapid increase in cAMP in the human epithelial cell line, Int 407: a potential role for this signal in the regulation of calcium influx through the plasma membrane

Although the LTD4-induced Ca2+ influx in human epithelial cells has been shown to be regulated by a pertussis toxin-sensitive heterotrimeric G-protein, most likely a G alpha i3 protein [Adolfsson J.L.P., Ohd J.F., Sjölander A. Leukotriene D4-induced activation and translocation of the G-protein alpha i3-subunit in human epithelial cells. Biochem Biophys Res Commun 1996; 226: 413-419], the signalling pathway further downstream is still unclear. In the present study, we investigated the possible involvement of cAMP and protein kinase A activity in the LTD4-induced Ca2+ influx in the epithelial cell line Int 407. Stimulation with LTD4, but not with the calcium ionophore ionomycin, triggered a rapid increase (peak at 7 s) in the cellular cAMP level, an effect that was totally abolished by pertussis toxin. Furthermore, the LTD4-induced Ca2+ signal was reduced by 60% when cells that had been pre-incubated with the protein kinase A inhibitor Rp-cAMPS (50 microM for 30 min) were stimulated in a calcium containing medium. In contrast, Rp-cAMPS had no apparent effect on the LTD4-induced Ca2+ signal when the cells were stimulated in a calcium-depleted medium. The immediate LTD4-induced protein tyrosine phosphorylation (15 s), previously shown to be necessary for the subsequent Ca2+ influx, was abolished not only by pretreatment with pertussis toxin but also by exposure to Rp-cAMPS. Furthermore, direct activation of the cellular adenylyl cyclase activity by treatment with forskolin alone induced a prompt Ca2+ signal in the presence, but not in the absence, of extracellular Ca2+, identical results were obtained with the cell permeable cAMP analogue 8-bromo-cAMP. In addition, forskolin induced protein tyrosine phosphorylation similar to that seen with LTD4. These results suggest that protein kinase A activity participates in the regulation of the LTD4-induced Ca2+ influx at a site that is downstream of the activation of the pertussis toxin-sensitive G-protein but upstream of a LTD4-stimulated tyrosine kinase(s).

The inflammatory mediator leukotriene D4 triggers a rapid reorganisation of the actin cytoskeleton in human intestinal epithelial cells

Epithelial cells play an important role in maintaining the intestinal mucosa barrier, a barrier that is impaired in several inflammatory conditions. The mechanisms behind this impairment are not known, but it can be presumed that structural alterations of the epithelial cells are involved. In support of this notion, we here show the inflammatory mediator leukotriene D4 (LTD4) triggered first a rapid (10 s) increase and immediately thereafter (30 s) a sustained decrease in the cellular filamentous actin (F-actin) level in intestinal epithelial cells. The initial LTD4-induced increase in F-actin content was effectively blocked by preincubating the cells with either pertussis toxin or the tyrosine kinase inhibitor genistein. A possible involvement of the tyrosine kinase-dependent phosphatidylinositol-3-kinase (PI-3-kinase) in the polymerisation of actin was supported by the observations that LTD4 induced a translocation to a membrane fraction of PI-3-kinase and by the findings that wortmannin, a PI-3-kinase inhibitor, totally abolished both this translocation of PI-3-kinase as well as the initial LTD4-induced polymerisation of actin. In addition, pertussis toxin and genistein, both known to interfere with the LTD4-induced calcium signal, completely or partially reversed the actin-depolymerising effect of LTD4. The calcium ionophore ionomycin (30s) induced actin depolymerisation to the same extent as LTD4 (30 s) did, but lacked the initial effect on actin polymerisation. In cells loaded with the calcium chelator MAPT, LTD4 induced a normal actin polymerisation response but the subsequent depolymerisation was completely inhibited. Similar results were obtained when the cells were preincubated with the protein kinase A inhibitor Rp-cAMPS, which has been shown to impair the LTD4-induced calcium signal in these epithelial cells. The present results show that the inflammatory mediator LTD4 triggers a reorganisation of the actin network in intestinal epithelial cells that is likely to contribute to the impairment of the intestinal barrier function.

Leukotriene D4 activates mitogen-activated protein kinase through a protein kinase Calpha-Raf-1-dependent pathway in human monocytic leukemia THP-1 cells

Leukotriene D4 (LTD4) is a major lipid mediator involved in inflammatory and allergic disorders including bronchial asthma. Despite its potent biological activity, little is known about the receptor and intracellular signaling pathways. Here we analyzed the signal transduction mechanisms through LTD4 receptors using human monocytic leukemia THP-1 cells. When these cells were stimulated with LTD4, intracellular calcium concentration was increased and mitogen-activated protein kinase (MAP kinase) was activated severalfold. This activation was inhibited by staurosporine or GF109203X treatment or abolished by protein kinase C depletion. Cytosolic protein kinase Calpha was translocated to the membrane, and Raf-1 was activated by LTD4 treatment in a similar time course. LTD4-induced Raf-1 activation was diminished by protein kinase C depletion in the cells. A chemotactic response of THP-1 cells toward LTD4 was observed which was inhibited by pertussis toxin (PTX) pretreatment. Thus, LTD4 has at least two distinct signaling pathways in THP-1 cells, a PTX-insensitive mitogen-activated protein kinase activation through protein kinase Calpha and Raf-1 and a PTX-sensitive chemotactic response. This cellular signaling can explain in part the versatile activities of LTD4 in macrophages under inflammatory and allergic conditions.

Pharmacological characterization of the cysteinyl-leukotriene antagonists CGP 45715A (iralukast) and CGP 57698 in human airways in vitro

1. Cysteinyl-leukotrienes (cysteinyl-LTs) are important mediators in the pathogenesis of asthma. They cause bronchoconstriction, mucus hypersecretion, increase in microvascular permeability, plasma extravasation and eosinophil recruitment. 2. We investigated the pharmacological profile of the cysteinyl-LT antagonists CGP 45715A (iralukast), a structural analogue of LTD4 and CGP 57698, a quinoline type antagonist, in human airways in vitro, by performing binding studies on human lung parenchyma membranes and functional studies on human isolated bronchial strips. 3. Competition curves vs [3H]-LTD4 on human lung parenchyma membranes demonstrated that: (a) both antagonists were able to compete for the two sites labelled by [3H]-LTD4; (b) as in all the G-protein coupled receptors, iralukast and CGP 57698 did not discriminate between the high and the low affinity states of the CysLT receptor labelled by LTD4 (Ki1=Ki2= 16.6 nM+/-36% CV and Ki1= Ki2 = 5.7 nM+/-19% CV, respectively); (c) iralukast, but not CGP 57698, displayed a slow binding kinetic, because preincubation (15 min) increased its antagonist potency. 4. In functional studies: (a) iralukast and CGP 57698 antagonized LTD4-induced contraction of human bronchi, with pA2 values of 7.77+/-4.3% CV and 8.51+/-1.6% CV, respectively, and slopes not significantly different from unity; (b) the maximal LTD4 response in the presence of CGP 57698 was actually increased, thus clearly deviating from apparent simple competition. 5. Both antagonists significantly inhibited antigen-induced contraction of human isolated bronchial strips in a concentration-dependent manner, lowering the upper plateau of the anti-IgE curves. 6. In conclusion, the results of the present in vitro investigation indicate that iralukast and CGP 57698 are potent antagonists of LTD4 in human airways, with affinities in the nanomolar range, similar to those obtained for ICI 204,219 and ONO 1078, two of the most clinically advanced CysLT receptor antagonists. Thus, these compounds might be useful drugs for the therapy of asthma and other allergic diseases.

Effect of leukotriene D4 on tracheal mucociliary transport velocity in quails

We investigated the effect of leukotriene D4 (LTD4) on tracheal mucociliary transport in quails. Topical application of LTD4 (0.2-2 ng) to tracheal mucosa dose-dependently increased mucociliary transport velocity (MCTV) in 5 or 10 min after application. Forty minutes after application of 2 ng of LTD4, MCTV was decreased to about 84% of that in the control group. Both the transient increase and the subsequent decrease induced by 2 ng of LTD4 were blocked by ONO-1078 (Pranlukast: 4-oxo-8-[4-(4-phenylbutoxy)-benzoylamino]-2-(tetrazol-5-yl)- 4H- 1-benzopyran) (0.03-3 mg/kg, i.m.), a specific leukotriene antagonist. These results suggest that LTD4 possesses a biphasic effect on tracheal mucociliary transport through leukotriene receptors.

Subcellular localization of 12(S)-hydroxy-5,8,10,14-eicosatetraenoic acid binding sites in Lewis lung carcinoma cells

12(S)-Hydroxy-5,8,10,14-eicosatetraenoic acid (12(S)-HETE) stimulates both gene expression and cell surface expression of the heterodimeric integrin alpha IIb beta 3 in Lewis lung carcinoma cells. These cells contain high affinity binding sites which are specific for 12(S)-HETE. Analyses of the subcellular distribution and molecular size of these sites showed that cytosol was the fraction exhibiting the largest specific binding. On gel permeation chromatography the cytosolic 12(S)-HETE-binding component appeared to be slightly smaller than thyroglobulin (M(r) 669,000). The sedimentation coefficient (20.5 S, determined by sucrose density gradient centrifugation), on the other hand was 1 S unit higher than that of thyroglobulin. The radioactive material bound to the macromolecule was found to be unaltered 12(S)-HETE. Proteinase treatment disrupted the ligand/macromolecule complex, suggesting that a polypeptide component is essential. In addition to cytosol, mitochondria and nuclei also contained significant but lower amounts of specifically bound 12(S)-HETE. The biological significance of this is not clear, but the results are in agreement with observations that 12(S)-HETE exerts effects at several subcellular sites. Our results, to our knowledge for the first time, demonstrate a predominantly cytosolic localization of a recognition molecule for 12(S)-HETE. This localization is different from that of other eicosanoid receptors which are G-protein coupled plasma membrane proteins.

The regulation of leukotriene D4-induced calcium influx in human epithelial cells involves protein tyrosine phosphorylation

Leukotriene D4 (LTD4) has been found to induce calcium signalling in the intestinal epithelial cell line Int 407, and this action involves the activation of both different GTP-binding proteins (G-proteins) and phospholipase C of the gamma-subtype (PLC-gamma). With this knowledge as the incentive, we investigated the possible regulatory role of protein tyrosine kinase activities in the calcium signalling system of the LTD4 receptor. The tyrosine kinase inhibitors genistein and herbimycin. A both reduced the LTD4-induced calcium signal by 70% when Int 407 cells were stimulated in the presence of extracellular calcium, but had no effect on the signal when the cells were stimulated in a calcium-free medium. In accordance with these findings, pretreatment with a tyrosine kinase inhibitor also blocked thapsigargin-induced cellular influx of calcium. These inhibitors had no effect on the intracellular mobilisation of calcium, which was supported by the findings that LTD4 was able to induce an increase in the tyrosine phosphorylation of PLC-gamma even when one of the tyrosine kinase inhibitors was present. Of possible interest regarding the effect of genistein on LTD4-induced calcium influx is that two major tyrosine phosphorylated protein bands were detected in immunoprecipitates obtained with PLC-gamma antibodies from LTD4-stimulated cells. These proteins, which associate with PLC-gamma, have estimated molecular weights of 84 and 97 kD. Preincubation with genistein completely abolished the LTD4-induced increase in tyrosine phosphorylation of the major 97 kD band, whereas the 84 kD protein band, like the PLC-gamma band, still exhibited an increased phosphorylation of tyrosine residues in response to LTD4. Neither this effect nor any of the other effects of genistein were induced when cells were preincubated with daidzein, an inactive analogue of genistein. The present results suggest that LTD4-induced calcium signalling in epithelial cells involves not only tyrosine phosphorylation of PLC-gamma, but also a tyrosine kinase-dependent step which occurs downstream of PLC-gamma activation and is directly implicated in the regulation of agonist-mediated calcium influx.

Membrane mechanisms and intracellular signalling in cell volume regulation

Recent work on selected aspects of the cellular and molecular physiology of cell volume regulation is reviewed. First, the physiological significance of the regulation of cell volume is discussed. Membrane transporters involved in cell volume regulation are reviewed, including volume-sensitive K+ and Cl- channels, K+, Cl- and Na+, K+, 2Cl- cotransporters, and the Na+, H+, Cl-, HCO3-, and K+, H+ exchangers. The role of amino acids, particularly taurine, as cellular osmolytes is discussed. Possible mechanisms by which cells sense their volumes, along with the sensors of these signals, are discussed. The signals are mechanical changes in the membrane and changes in macromolecular crowding. Sensors of these signals include stretch-activated channels, the cytoskeleton, and specific membrane or cytoplasmic enzymes. Mechanisms for transduction of the signal from sensors to transporters are reviewed. These include the Ca(2+)-calmodulin system, phospholipases, polyphosphoinositide metabolism, eicosanoid metabolism, and protein kinases and phosphatases. A detailed model is presented for the swelling-initiated signal transduction pathway in Ehrlich ascites tumor cells. Finally, the coordinated control of volume-regulatory transport processes and changes in the expression of organic osmolyte transporters with long-term adaptation to osmotic stress are reviewed briefly.

Leukotriene D4-induced signal transduction

In a human epithelial cell line LTD4 induces a calcium signal that is dependent on both intracellular mobilization and influx of calcium. This calcium signal is generated via the activation of dual G protein pathways. Whereas the intracellular mobilization of calcium is regulated by a pertussis toxin-insensitive G protein, the subsequent influx of calcium is regulated by a pertussis toxin-sensitive G protein. Furthermore, a LTD4-induced cellular elevation of cAMP also participates in the regulation of this calcium signal. The increase in cAMP is directly related to the LTD4-induced influx of calcium, perhaps by an activation of protein kinase A and a subsequent phosphorylation of a plasma membrane channel. This model of the LTD4-induced signaling pathway in epithelial cells is outlined in Figure 2.

Characterization of prostaglandin F2 alpha receptor of mouse 3T3 fibroblasts and its functional expression in Xenopus laevis oocytes

Prostaglandin (PG) F2 alpha increased [3H]thymidine incorporation into quiescent NIH 3T3 cells, stimulated phosphoinositide breakdown, and raised intracellular Ca2+ concentration ([Ca2+]i) in a dose-dependent manner with ED50 values of 2.0 x 10(-8) M, 4.6 x 10(-8) M, and 7.5 x 10(-8) M, respectively. The increase in [3H]thymidine incorporation with PGF2 alpha was additive with that seen with epidermal growth factor (EGF) or insulin. The peak [Ca2+]i increase with PGF2 alpha was still obvious in the absence of extracellular Ca2+ and was insensitive to islet activating protein (IAP) pretreatment. Membranes prepared from NIH 3T3 cells exhibited a specific binding for PGF2 alpha, which was sensitive to GTP gamma S but not sensitive to IAP pretreatment. Xenopus laevis oocytes injected with NIH 3T3 cell mRNA between 18S and 28S rRNA fractionated by sucrose gradient, expressed a PGF2 alpha-specific Cl- current when examined by voltage clamp. This Cl- current was also insensitive to IAP pretreatment and not affected by extracellular Ca2+ concentration ([Ca2+]o). These results indicate 1) that the NIH 3T3 cells expressed a specific PGF2 alpha receptor which is linked to phosphoinositide-specific phospholipase C (PLC) activation and to mobilization of Ca2+ via an IAP-insensitive G-protein(s), 2) that this PGF2 alpha receptor may play an active role in the proliferation of NIH 3T3 cells, and 3) that this PGF2 alpha receptor can be expressed in the oocyte system.

Three types of Gi alpha protein of the guinea-pig lung: cDNA cloning and analysis of their tissue distribution

cDNA clones encoding three types of Gi alpha, the alpha subunit of GTP-binding protein (Gi1 alpha, Gi2 alpha, and Gi3 alpha), were isolated from a cDNA library of the guinea-pig lung. Nucleotide sequence analysis revealed a high degree of homology with other mammalian Gi alpha cDNAs. By RNA blot analysis, the expression pattern of Gi1 alpha was more tissue-specific than those of other types of Gi alphas in the guinea-pig tissues examined. While Gi2 alpha and Gi3 alpha mRNAs were ubiquitously expressed in all tissues examined, Gi1 alpha mRNA was mainly expressed in the brain, lung and kidney. These results suggest that each Gi alpha protein may have a different role.