1
|
Abstract
Peptides derived from pro-opiomelanocortin, including alpha-MSH and ACTH, play important roles in the regulation of feeding. We investigated the central effect of ACTH 1-39 (ACTH) and peptides derived from the N-terminus (ACTH 1-10, Acetyl-ACTH 1-13-amide [alpha-MSH]) and C-terminus (ACTH 18-39 and ACTH 22-39) of this peptide on feeding in 16 hour-fasted or rats fed ad libitum. As expected, ACTH reduced feeding in fed and previously fasted rats, although this anorectic effect was more pronounced in fasted rats. The N-terminal-derived peptide alpha-MSH, but not ACTH 1-10, reduced cumulative food intake over 2 h after its injection intracerebroventricularly (icv) in 16 h-fasted, but not in fed rats. In contrast, the C-terminal fragments produced a long-lasting increase in feeding in fasted, but not in fed rats. The anorectic effects of N-terminal fragments of ACTH are recognised to be mediated via melanocortin MC4 receptors. However, the orexigenic effects of the C-terminal fragments do not appear to be conducted via MC4 receptors, since neither ACTH 18-39 nor ACTH 22-39 stimulated cAMP accumulation nor inhibited the ACTH-stimulated cAMP accumulation in HEK-293 cells transfected with the recombinant MC4 receptor.
Collapse
Affiliation(s)
- K A Al-Barazanji
- Department of Vascular Biology, GlaxoSmithKline, New Frontiers Science Park, Harlow, Essex, UK
| | | | | | | | | |
Collapse
|
2
|
Lochhead PA, Coghlan M, Rice SQ, Sutherland C. Inhibition of GSK-3 selectively reduces glucose-6-phosphatase and phosphatase and phosphoenolypyruvate carboxykinase gene expression. Diabetes 2001; 50:937-46. [PMID: 11334436 DOI: 10.2337/diabetes.50.5.937] [Citation(s) in RCA: 173] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
A major action of insulin is to regulate the transcription rate of specific genes. The expression of these genes is dramatically altered in type 2 diabetes. For example, the expression of two hepatic genes, glucose-6-phosphatase and PEPCK, is normally inhibited by insulin, but in type 2 diabetes, their expression is insensitive to insulin. An agent that mimics the effect of insulin on the expression of these genes would reduce gluconeogenesis and hepatic glucose output, even in the presence of insulin resistance. The repressive actions of insulin on these genes are dependent on phosphatidylinositol (PI) 3-kinase. However, the molecules that lie between this lipid kinase and the two gene promoters are unknown. Glycogen synthase kinase-3 (GSK-3) is inhibited following activation of PI 3-kinase and protein kinase B. In hepatoma cells, we find that selectively reducing GSK-3 activity strongly reduces the expression of both gluconeogenic genes. The effect is at the level of transcription and is observed with induced or basal gene expression. In addition, GSK-3 inhibition does not result in the subsequent activation of protein kinase B or inhibition of the transcription factor FKHR, which are candidate regulatory molecules for these promoters. Thus, GSK-3 activity is required for basal activity of each promoter. Inhibitors of GSK-3 should therefore reduce hepatic glucose output, as well as increase the synthesis of glycogen from L-glucose. These findings indicate that GSK-3 inhibitors may have greater therapeutic potential for lowering blood glucose levels and treating type 2 diabetes than previously realized.
Collapse
Affiliation(s)
- P A Lochhead
- Division of Cell Signalling, School of Life Sciences, University of Dundee, UK
| | | | | | | |
Collapse
|
3
|
Calver AR, Robbins MJ, Cosio C, Rice SQ, Babbs AJ, Hirst WD, Boyfield I, Wood MD, Russell RB, Price GW, Couve A, Moss SJ, Pangalos MN. The C-terminal domains of the GABA(b) receptor subunits mediate intracellular trafficking but are not required for receptor signaling. J Neurosci 2001; 21:1203-10. [PMID: 11160390 PMCID: PMC6762247] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/18/2023] Open
Abstract
GABA(B) receptors are G-protein-coupled receptors that mediate slow synaptic inhibition in the brain and spinal cord. These receptors are heterodimers assembled from GABA(B1) and GABA(B2) subunits, neither of which is capable of producing functional GABA(B) receptors on homomeric expression. GABA(B1,) although able to bind GABA, is retained within the endoplasmic reticulum (ER) when expressed alone. In contrast, GABA(B2) is able to access the cell surface when expressed alone but does not couple efficiently to the appropriate effector systems or produce any detectable GABA-binding sites. In the present study, we have constructed chimeric and truncated GABA(B1) and GABA(B2) subunits to explore further GABA(B) receptor signaling and assembly. Removal of the entire C-terminal intracellular domain of GABA(B1) results in plasma membrane expression without the production of a functional GABA(B) receptor. However, coexpression of this truncated GABA(B1) subunit with either GABA(B2) or a truncated GABA(B2) subunit in which the C terminal has also been removed is capable of functional signaling via G-proteins. In contrast, transferring the entire C-terminal tail of GABA(B1) to GABA(B2) leads to the ER retention of the GABA(B2) subunit when expressed alone. These results indicate that the C terminal of GABA(B1) mediates the ER retention of this protein and that neither of the C-terminal tails of GABA(B1) or GABA(B2) is an absolute requirement for functional coupling of heteromeric receptors. Furthermore although GABA(B1) is capable of producing GABA-binding sites, GABA(B2) is of central importance in the functional coupling of heteromeric GABA(B) receptors to G-proteins and the subsequent activation of effector systems.
Collapse
Affiliation(s)
- A R Calver
- Department of Neuroscience Research, SmithKline Beecham Pharmaceuticals, New Frontiers Science Park, Harlow, Essex CM19 5AW, United Kingdom.
| | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
4
|
Wood MD, Murkitt KL, Rice SQ, Testa T, Punia PK, Stammers M, Jenkins O, Elshourbagy NA, Shabon U, Taylor SJ, Gager TL, Minton J, Hirst WD, Price GW, Pangalos M. The human GABA(B1b) and GABA(B2) heterodimeric recombinant receptor shows low sensitivity to phaclofen and saclofen. Br J Pharmacol 2000; 131:1050-4. [PMID: 11082110 PMCID: PMC1572438 DOI: 10.1038/sj.bjp.0703682] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2000] [Accepted: 09/04/2000] [Indexed: 11/08/2022] Open
Abstract
1. The aim of this study was to characterize the pharmacological profile of the GABA(B1)/GABA(B2) heterodimeric receptor expressed in Chinese hamster ovary (CHO) cells. We have compared receptor binding affinity and functional activity for a series of agonists and antagonists. 2. The chimeric G-protein, G(qi5), was used to couple receptor activation to increases in intracellular calcium for functional studies on the Fluorimetric Imaging Plate Reader (FLIPR), using a stable GABA(B1)/GABA(B2)/G(qi5) CHO cell line. [(3)H]-CGP-54626 was used in radioligand binding studies in membranes prepared from the same cell line. 3. The pharmacological profile of the recombinant GABA(B1/B2) receptor was consistent with that of native GABA(B) receptors in that it was activated by GABA and baclofen and inhibited by CGP-54626A and SCH 50911. 4. Unlike native receptors, the GABA(B1)/GABA(B2)/G(qi5) response was not inhibited by high microMolar concentration of phaclofen, saclofen or CGP 35348. 5. This raises the possibility that the GABA(B1)/GABA(B2)/G(qi5) recombinant receptor may represent the previously described GABA(B) receptor subtype which is relatively resistant to inhibition by phaclofen.
Collapse
Affiliation(s)
- M D Wood
- Department of Neuroscience Research, SmithKline Beecham Pharmaceuticals, New Frontiers Science Park, Third Avenue, Harlow, Essex, CM19 5AW.
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
5
|
Häkkinen T, Luoma JS, Hiltunen MO, Macphee CH, Milliner KJ, Patel L, Rice SQ, Tew DG, Karkola K, Ylä-Herttuala S. Lipoprotein-associated phospholipase A(2), platelet-activating factor acetylhydrolase, is expressed by macrophages in human and rabbit atherosclerotic lesions. Arterioscler Thromb Vasc Biol 1999; 19:2909-17. [PMID: 10591668 DOI: 10.1161/01.atv.19.12.2909] [Citation(s) in RCA: 177] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
We studied the expression of lipoprotein-associated phospholipase A(2) (Lp-PLA(2)), an enzyme capable of hydrolyzing platelet-activating factor (PAF), PAF-like phospholipids, and polar-modified phosphatidylcholines, in human and rabbit atherosclerotic lesions. Oxidative modification of low-density lipoprotein, which plays an important role in atherogenesis, generates biologically active PAF-like modified phospholipid derivatives with polar fatty acid chains. PAF is known to have a potent proinflammatory activity and is inactivated by its hydrolysis. On the other hand, lysophosphatidylcholine and oxidized fatty acids released from oxidized low-density lipoprotein as a result of Lp-PLA(2) activity are thought to be involved in the progression of atherosclerosis. Using combined in situ hybridization and immunocytochemistry, we detected Lp-PLA(2) mRNA and protein in macrophages in both human and rabbit atherosclerotic lesions. Reverse transcriptase-polymerase chain reaction analysis indicated an increased expression of Lp-PLA(2) mRNA in human atherosclerotic lesions. In addition, approximately 6-fold higher Lp-PLA(2) activity was detected in atherosclerotic aortas of Watanabe heritable hyperlipidemic rabbits compared with normal aortas from control rabbits. It is concluded that (1) macrophages in both human and rabbit atherosclerotic lesions express Lp-PLA(2), which could cleave any oxidatively modified phosphatidylcholine present in the lesion area, and (2) modulation of Lp-PLA(2) activity could lead to antiatherogenic effects in the vessel wall.
Collapse
Affiliation(s)
- T Häkkinen
- A.I. Virtanen Institute, University of Kuopio, Kuopio, Finland
| | | | | | | | | | | | | | | | | | | |
Collapse
|
6
|
Carpenter D, Meadows HJ, Brough S, Chapman G, Clarke C, Coldwell M, Davis R, Harrison D, Meakin J, McHale M, Rice SQ, Tomlinson WJ, Wood M, Sanger GJ. Site-specific splice variation of the human P2X4 receptor. Neurosci Lett 1999; 273:183-6. [PMID: 10515189 DOI: 10.1016/s0304-3940(99)00653-9] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
P2X4 receptors are expressed in specific brain areas. We now describe site-specific splice variations of the human P2X4 receptor subunit, occurring at residue [YVIG / WVFV(W)] near the end of the first predicted transmembrane domain. p2X4(b) is formed by the insertion of an additional 16 amino acids. p2X4(C) is formed by deleting a cassette of 130 amino acids, including six of the 10 conserved extracellular cysteine residues. Transfection of P2X4(a), but not p2x4(c), formed functional channels in Xenopus oocytes and human 1321N1 cells. After transfection of p2X4(b) small, inconsistent ATP-evoked responses were detected only in the human cells, but when co-expressed, p2x4(b) may alter the function of P2X4(a) in oocytes. The distribution of splice variant RNA within human brain suggests regionally-dependent expression. These data indicate that the functions of the human P2X4 receptor may be altered by alternative splicing.
Collapse
Affiliation(s)
- D Carpenter
- Department of Information Management, SmithKline Beecham Pharmaceuticals, New Frontiers Science Park, Harlow, Essex, UK
| | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
7
|
Rice SQ, Southan C, Boyd HF, Terrett JA, MacPhee CH, Moores K, Gloger IS, Tew DG. Expression, purification and characterization of a human serine-dependent phospholipase A2 with high specificity for oxidized phospholipids and platelet activating factor. Biochem J 1998; 330 ( Pt 3):1309-15. [PMID: 9494101 PMCID: PMC1219277 DOI: 10.1042/bj3301309] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Using expressed sequence tag (EST) homology screening, a new human serine dependent phospholipase A2 (HSD-PLA2) was identified that has 40% amino acid identity with human low density lipoprotein-associated phospholipase A2 (LDL-PLA2). HSD-PLA2 has very recently been purified and cloned from brain tissue but named PAF-AH II. However, because the homology with LDL-PLA2 suggested a broader substrate specificity than simply platelet activating factor (PAF), we have further characterized this enzyme using baculovirus-expressed protein. The recombinant enzyme, which was purified 21-fold to homogeneity, had a molecular mass of 44kDa and possessed a specific activity of 35 micromol min-1 mg-1 when assayed against PAF. Activity could also be measured using 1-decanoyl-2-(4-nitrophenylglutaryl) phosphate (DNGP) as substrate. Like LDL-PLA2, HSD-PLA2 was able to hydrolyse oxidatively modified phosphatidylcholines when supplemented to human LDL prior to copper-stimulated oxidation. A GXSXG motif evident from sequence information and inhibition of its activity by 3,4, dichloroisocoumarin, diisopropyl fluorophosphate (DFP) and diethyl p-nitrophenyl phosphate (DENP) confirm that the enzyme is serine dependent. Moreover, sequence comparison indicates the HSD-PLA2 probable active site triad positions are shared with LDL-PLA2 and a C. elegans homologue, suggesting that these sequences comprise members of a new enzyme family. Although clearly structurally related with similar substrate specificities further work reported here shows HSD-PLA2 and LDL-PLA2 to be different with respect to chromosomal localization and tissue distribution.
Collapse
Affiliation(s)
- S Q Rice
- Department of Biopharmaceutical Research U.K., SmithKline Beecham Pharmaceuticals, New Frontiers Science Park North, Harlow, Essex, CM19 5AW, U.K
| | | | | | | | | | | | | | | |
Collapse
|
8
|
Bell R, Collier DA, Rice SQ, Roberts GW, MacPhee CH, Kerwin RW, Price J, Gloger IS. Systematic screening of the LDL-PLA2 gene for polymorphic variants and case-control analysis in schizophrenia. Biochem Biophys Res Commun 1997; 241:630-5. [PMID: 9434759 DOI: 10.1006/bbrc.1997.7741] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Systematic scans of the genome using microsatellite markers have identified chromosome 6p21.1 as a putative locus for schizophrenia in multiply affected families. There is also evidence from a series of studies for a role of abnormal phospholipid metabolism in schizophrenia. In light of these findings, and the role of platelet activating factor in neurotransmission and neurodevelopment, we have examined the LDL-PLA2 (plasma PAF acetylhydrolase, PAF-AH) gene, a serine dependent phospholipase that has been mapped by hybrid mapping to chromosome 6p21.1, as a positional candidate gene for schizophrenia. The gene was systematically screened using SSCP/HD analysis for polymorphisms associated with the disease. Four polymorphic variants were found within the gene and studied in a group of 200 schizophrenic patients and 100 controls. The variant in exon 7 (Iso195Thr) was found to be weakly associated with schizophrenia (p = 0.04) and the variant in exon 11 (Val379Ala) almost reached significance (p = 0.057). After correcting for multiple testing no significant associations were detected. Haplotype analysis combining pairs of polymorphisms also provided no evidence for association of this gene with schizophrenia in our sample of patients.
Collapse
Affiliation(s)
- R Bell
- Section of Genetics, Institute of Psychiatry, London, United Kingdom
| | | | | | | | | | | | | | | |
Collapse
|
9
|
Tew DG, Southan C, Rice SQ, Lawrence MP, Li H, Boyd HF, Moores K, Gloger IS, Macphee CH. Purification, properties, sequencing, and cloning of a lipoprotein-associated, serine-dependent phospholipase involved in the oxidative modification of low-density lipoproteins. Arterioscler Thromb Vasc Biol 1996; 16:591-9. [PMID: 8624782 DOI: 10.1161/01.atv.16.4.591] [Citation(s) in RCA: 125] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
A novel LDL-associated phospholipase A2 (LDL-PLA2) has been purified to homogeneity from human LDL obtained from plasma apheresis. This enzyme has activity toward both oxidized phosphatidylcholine and platelet activating factor (PAF). A simple purification procedure involving detergent solubilization and affinity and ion exchange chromatography has been devised. Vmax and Km for the purified enzyme are 170 micromol.min-1.mg-1 and 12 micromol/L, respectively. Extensive peptide sequence from LDL-PLA2 facilitated identification of an expressed sequence tag partial cDNA. This has led to cloning and expression of active protein in baculovirus. A lipase motif is also evident from sequence information, indicating that the enzyme is serine dependent. Inhibition by diethyl p-nitrophenyl phosphate and 3,4-dichloroisocoumarin and insensitivity to EDTA, Ca2+, and sulfhydryl reagents confirm that the enzyme is indeed a serine-dependent hydrolase. The protein is extensively glycosylated, and the glycosylation site has been identified. Antibodies to this LDL-PLA2 have been raised and used to show that this enzyme is responsible for >95% of the phospholipase activity associated with LDL. Inhibition of LDL-PLA2 before oxidation of LDL reduces both lysophosphatidylcholine content and monocyte chemoattractant ability of the resulting oxidized LDL. Lysophosphatidylcholine production and monocyte chemoattractant ability can be restored by addition of physiological quantities of pure LDL-PLA2.
Collapse
Affiliation(s)
- D G Tew
- Department of Mechanistic Enzymology, Welwyn, Hertfordshire, UK
| | | | | | | | | | | | | | | | | |
Collapse
|
10
|
Abstract
This study examined the production of an immunosuppressive factor by the KB and H191 human oral squamous carcinoma cell lines. Conditioned media (CM) from both cell lines markedly inhibited mitogen- and alloantigen-induced proliferation of normal human and rat peripheral blood lymphocytes. By contrast, the proliferation of an exponentially-growing fibroblast cell line remained unchanged by CM. The immunosuppressive factor appeared to act after lymphocyte commitment as indicated by continued blast cell formation, the failure of CM to suppress resting lymphocytes and the fact that CM caused maximum inhibition of lymphocyte proliferation 72 h after the addition of PHA. The addition of exogenous IL-2 did not counteract lymphocyte suppression. Inclusion of indomethacin and isoniazid during cell culture did not significantly alter the degree of suppressive activity. Mycoplasma contamination was absent and CM did not act directly with the thymidine or mitogen. The factor was heat stable at 50 degrees C, acid labile and had a molecular weight in excess of 300 kDa. The results demonstrate that human oral squamous carcinoma cell lines produce an immunosuppressive factor that may have a role in tumour evasion of the host immune response.
Collapse
Affiliation(s)
- S Q Rice
- University Department of Oral Medicine, Surgery and Pathology, Bristol Dental School and Hospital, UK
| | | | | | | |
Collapse
|
11
|
Crane IJ, Luker J, de Gay L, Rice SQ, Stone A, Scully C, Prime SS. Transformation of oral keratinocytes in vitro by 4-nitroquinoline N-oxide. Carcinogenesis 1988; 9:2251-6. [PMID: 2461265 DOI: 10.1093/carcin/9.12.2251] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Normal rat oral keratinocytes have been transformed with the carcinogen 4-nitroquinoline N-oxide (4NQO) in vitro. The morphology, growth characteristics, ability to grow without anchorage and tumorigenicity in athymic mice was examined in 12 selected cell lines. Each of the lines could be assigned to one of two general groups. The first group of cell lines although showing some morphological signs of transformation and the ability to be subcultured beyond passage 15 were not anchorage independent or able to form tumours in athymic mice. The second group of cell lines showed distinct signs of morphological transformation, could be serially subcultured without 3T3 feeder cells, were anchorage independent and tumorigenic in athymic mice. Anchorage independence was more common at higher passages and with increased 4NQO treatment and correlated well with a decreased reliance on 3T3 feeder cell support. The anchorage-independent phenotype was closely associated with the ability to form tumours in athymic mice. This same sequence of phenotypic changes has been demonstrated in rat oral keratinocytes after 4NQO treatment in vivo indicating that during carcinogenesis, cell populations progress through the same stages whether proliferation occurs in vitro or in vivo. There is some evidence to suggest, however, that the time interval between stages may be altered when carcinogenesis takes place in vitro.
Collapse
Affiliation(s)
- I J Crane
- University Department of Oral Medicine, Surgery and Pathology, University of Bristol Dental School, UK
| | | | | | | | | | | | | |
Collapse
|