101
|
Bate C, Tayebi M, Williams A. Sequestration of free cholesterol in cell membranes by prions correlates with cytoplasmic phospholipase A2 activation. BMC Biol 2008; 6:8. [PMID: 18269734 PMCID: PMC2270799 DOI: 10.1186/1741-7007-6-8] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2007] [Accepted: 02/12/2008] [Indexed: 12/03/2022] Open
Abstract
Background The transmissible spongiform encephalopathies (TSEs), otherwise known as the prion diseases, occur following the conversion of the normal cellular prion protein (PrPC) to an alternatively folded isoform (PrPSc). The accumulation of PrPSc within the brain leads to neurodegeneration through an unidentified mechanism. Since many neurodegenerative disorders including prion, Parkinson's and Alzheimer's diseases may be modified by cholesterol synthesis inhibitors, the effects of prion infection on the cholesterol balance within neuronal cells were examined. Results We report the novel observation that prion infection altered the membrane composition and significantly increased total cholesterol levels in two neuronal cell lines (ScGT1 and ScN2a cells). There was a significant correlation between the concentration of free cholesterol in ScGT1 cells and the amounts of PrPSc. This increase was entirely a result of increased amounts of free cholesterol, as prion infection reduced the amounts of cholesterol esters in cells. These effects were reproduced in primary cortical neurons by the addition of partially purified PrPSc, but not by PrPC. Crucially, the effects of prion infection were not a result of increased cholesterol synthesis. Stimulating cholesterol synthesis via the addition of mevalonate, or adding exogenous cholesterol, had the opposite effect to prion infection on the cholesterol balance. It did not affect the amounts of free cholesterol within neurons; rather, it significantly increased the amounts of cholesterol esters. Immunoprecipitation studies have shown that cytoplasmic phospholipase A2 (cPLA2) co-precipitated with PrPSc in ScGT1 cells. Furthermore, prion infection greatly increased both the phosphorylation of cPLA2 and prostaglandin E2 production. Conclusion Prion infection, or the addition of PrPSc, increased the free cholesterol content of cells, a process that could not be replicated by the stimulation of cholesterol synthesis. The presence of PrPSc increased solubilisation of free cholesterol in cell membranes and affected their function. It increased activation of the PLA2 pathway, previously implicated in PrPSc formation and in PrPSc-mediated neurotoxicity. These observations suggest that the neuropathogenesis of prion diseases results from PrPSc altering cholesterol-sensitive processes. Furthermore, they raise the possibility that disturbances in membrane cholesterol are major triggering events in neurodegenerative diseases.
Collapse
Affiliation(s)
- Clive Bate
- Department of Pathology and Infectious Diseases, Royal Veterinary College, Hawkshead Lane, North Mymms, Herts, AL9 7TA, UK.
| | | | | |
Collapse
|
102
|
Adamson RH, Ly JC, Sarai RK, Lenz JF, Altangerel A, Drenckhahn D, Curry FE. Epac/Rap1 pathway regulates microvascular hyperpermeability induced by PAF in rat mesentery. Am J Physiol Heart Circ Physiol 2008; 294:H1188-96. [PMID: 18178724 DOI: 10.1152/ajpheart.00937.2007] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Experiments in cultured endothelial cell monolayers demonstrate that increased intracellular cAMP strongly inhibits the acute permeability responses by both protein kinase A (PKA)-dependent and -independent pathways. The contribution of the PKA-independent pathways to the anti-inflammatory mechanisms of cAMP in intact mammalian microvessels has not been systematically investigated. We evaluated the role of the cAMP-dependent activation of the exchange protein activated by cAMP (Epac), a guanine nucleotide exchange factor for the small GTPase Rap1, in rat venular microvessels exposed to the platelet-activating factor (PAF). The cAMP analog 8-pCPT-2'-O-methyl-cAMP (O-Me-cAMP), which stimulates the Epac/Rap1 pathway but has no effect on PKA, significantly attenuated the PAF increase in microvessel permeability as measured by hydraulic conductivity (Lp). We also demonstrated that PAF induced a rearrangement of vascular endothelial (VE)-cadherin seen as numerous lateral spikes and frequent short breaks in the otherwise continuous peripheral immunofluorescent label. Pretreatment with O-Me-cAMP completely prevented the PAF-induced rearrangement of VE-cadherin. We conclude that the action of the Epac/Rap1 pathway to stabilize cell-cell adhesion is a significant component of the activity of cAMP to attenuate an acute increase in vascular permeability. Our results indicate that increased permeability in intact microvessels by acute inflammatory agents such as PAF is the result of the decreased effectiveness of the Epac/Rap1 pathway modulation of cell-cell adhesion.
Collapse
Affiliation(s)
- R H Adamson
- Physiology and Membrane Biology, School of Medicine, University of California at Davis, Davis, CA 95616, USA.
| | | | | | | | | | | | | |
Collapse
|
103
|
Andersson KE, Uckert S, Stief C, Hedlund P. Phosphodiesterases (PDEs) and PDE inhibitors for treatment of LUTS. Neurourol Urodyn 2008; 26:928-33. [PMID: 17806124 DOI: 10.1002/nau.20485] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Lower urinary tract (LUT) smooth muscle can be relaxed by drugs that increase intracellular concentrations of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP). Both of these substances are degraded by phosphodiesterases (PDEs), which play a central role in the regulation of smooth muscle tone. The distribution and functional significance of PDE enzymes vary in different tissues of the LUT. Targeting specific PDE isoenzymes should thus allow organ selectivity. PDE 4 and 5 appear to predominate in the prostate, PDE 1 and 4 are thought to influence detrusor smooth muscle function, and PDE 5 may be functionally important in the urethra and vasculature. Studies on the use of PDE inhibitors to treat various LUT symptoms (LUTS), have yielded favorable results. Thus, positive effects of the PDE 5 inhibitors sildenafil and tadalafil on symptoms and quality of life in men with LUTS, erectile dysfunction, and BPH have also been demonstrated. These effects may be due to effects on cGMP signaling and/or modification of afferent input from bladder, urethral, and prostate tissue. This review gives an update on the distribution of PDEs in structures relevant for LUT function, and discusses how inhibition of these enzymes can contribute to beneficial effects on LUTS. Information for the review was obtained from searches of the PubMed database, and from the authors' files.
Collapse
Affiliation(s)
- Karl-Erik Andersson
- Wake Forest Institute for Regenerative Medicine, Wake Forest University School of Medicine, Winston Salem, North Carolina 27157, USA.
| | | | | | | |
Collapse
|
104
|
Baragli A, Grieco ML, Trieu P, Villeneuve LR, Hébert TE. Heterodimers of adenylyl cyclases 2 and 5 show enhanced functional responses in the presence of Galpha s. Cell Signal 2007; 20:480-92. [PMID: 18164588 DOI: 10.1016/j.cellsig.2007.10.033] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2007] [Accepted: 10/30/2007] [Indexed: 12/22/2022]
Abstract
Recent studies have demonstrated that adenylyl cyclase isoforms can form both homo- and heterodimers and that this may be the basic functional unit of these enzymes (see Cooper, D.M.F. and Crossthwaite, A.J. (2006) Trends. Pharmacol. Sci. 8:426-431). Here, we show that adenylyl cyclases 2 and 5 can form a functional heterodimeric complex in HEK293 cells using a combination of BRET, confocal imaging, co-immunoprecipitation and assays of adenylyl cyclase activity. The AC2/5 complex is formed constitutively and is stable in the presence of receptor or forskolin stimulation. The complex formed by AC2/5 is also much more sensitive to the presence of Galpha(s) and forskolin than either of the parent AC isoforms themselves. Finally, we also show that this complex can be detected in native tissues as AC2 and AC5 were localized to the same structures in adult mouse ventricular myocytes and neonatal mouse cardiac fibroblasts and could be co-immunoprecipitated from lysates of mouse heart.
Collapse
Affiliation(s)
- Alessandra Baragli
- Department of Pharmacology and Therapeutics, McGill University, Montréal, Quebec, Canada
| | | | | | | | | |
Collapse
|
105
|
Raymond DR, Wilson LS, Carter RL, Maurice DH. Numerous distinct PKA-, or EPAC-based, signalling complexes allow selective phosphodiesterase 3 and phosphodiesterase 4 coordination of cell adhesion. Cell Signal 2007; 19:2507-18. [PMID: 17884339 DOI: 10.1016/j.cellsig.2007.08.005] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2007] [Accepted: 08/06/2007] [Indexed: 11/23/2022]
Abstract
By activating two distinct classes of effector enzymes, namely Protein Kinases A [PKA] or Exchange Proteins Activated by cAMP [EPAC], the ubiquitous second messenger cAMP selectively coordinates numerous events simultaneously in virtually all cells. Studies focused on dissecting the manner by which cAMP simultaneously regulates multiple cellular events have shown that cAMP activates its effectors non-uniformly in cells and that this localized cAMP-mediated signalling is made possible, at least in part, by anchoring of cAMP effectors to selected subcellular structures. In the work described here, we report that HEK293T cells ["293T"] contain several PKA- and EPAC1-based signalling complexes. Interestingly, our data do not identify signalling complexes in which both PKA and EPAC are each present but rather are consistent with the idea that these two effectors operate in distinct complexes in these cells. Similarly, we report that while individual PKA- or EPAC-containing complexes can contain either phosphodiesterase 3B, [PDE3B] or phosphodiesterase 4D [PDE4D], they do not contain both these phosphodiesterases. Indeed, although PDE4D enzymes were identified in both PKA- and EPAC-based complexes, PDE3B was largely identified in EPAC-based complexes. Using a combination of approaches, we identified that integration of PDE3B into EPAC-based complexes occurred through its amino terminal fragment [PDE3B(AT)]. Consistent with the idea that integration of PDE3B within EPAC-based complexes was dynamic and regulated PDE3 inhibitor-mediated effects on cellular functions, expression of PDE3B(AT) competed with endogenous PDE3B for integration into EPAC-based complexes and antagonized PDE3 inhibitor-based cell adhesion. Our data support the concept that cells can contain several non-overlapping PKA- and EPAC-based signalling complexes and that these complexes may also represent sites within cells were the effects of family-selective PDE inhibitors could be integrated to affect cell functions, including adhesion.
Collapse
Affiliation(s)
- Daniel R Raymond
- Department of Pharmacology & Toxicology, Queen's University, Kingston, ON, Canada K7L 3N6
| | | | | | | |
Collapse
|
106
|
Hull JJ, Kajigaya R, Imai K, Matsumoto S. The Bombyx mori sex pheromone biosynthetic pathway is not mediated by cAMP. JOURNAL OF INSECT PHYSIOLOGY 2007; 53:782-93. [PMID: 17449058 DOI: 10.1016/j.jinsphys.2007.02.013] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/16/2006] [Revised: 02/17/2007] [Accepted: 02/19/2007] [Indexed: 05/15/2023]
Abstract
In most moths, sex pheromone production is regulated by pheromone biosynthesis-activating neuropeptide (PBAN). How the extracellular PBAN signal is turned into a biological response has been the focus of numerous studies. In the classical scheme of signal transduction, activated G proteins relay the extracellular signal to downstream effector molecules such as calcium channels and adenylyl cyclase. The role of calcium in PBAN signaling has been clearly demonstrated, but the possible involvement of cAMP is not as straightforward. While cAMP has been shown to be necessary for PBAN signaling in most heliothine species, there has been no definitive demonstration of its role in Bombyx mori. To address this question, we used degenerate RT-PCR to clone two Gs subunits, designated P50Gs1 and P50Gs2, from B. mori pheromone gland (PG) cDNAs. The two Gs proteins were expressed in all tissues examined and were not up-regulated in accordance with adult eclosion. Even though two bands corresponding to the approximate molecular weights of P50Gs1 and P50Gs2 were detected in PG homogenates, the Gs antagonist, NF449, had no effect on sex pheromone production. Furthermore, no changes in the intracellular cAMP levels were detected following PBAN stimulation.
Collapse
Affiliation(s)
- J Joe Hull
- Molecular Entomology Laboratory, RIKEN, Hirosawa 2-1, Wako, Saitama 351-0198, Japan.
| | | | | | | |
Collapse
|
107
|
Willoughby D, Cooper DMF. Organization and Ca2+Regulation of Adenylyl Cyclases in cAMP Microdomains. Physiol Rev 2007; 87:965-1010. [PMID: 17615394 DOI: 10.1152/physrev.00049.2006] [Citation(s) in RCA: 327] [Impact Index Per Article: 19.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
The adenylyl cyclases are variously regulated by G protein subunits, a number of serine/threonine and tyrosine protein kinases, and Ca2+. In some physiological situations, this regulation can be readily incorporated into a hormonal cascade, controlling processes such as cardiac contractility or neurotransmitter release. However, the significance of some modes of regulation is obscure and is likely only to be apparent in explicit cellular contexts (or stages of the cell cycle). The regulation of many of the ACs by the ubiquitous second messenger Ca2+provides an overarching mechanism for integrating the activities of these two major signaling systems. Elaborate devices have been evolved to ensure that this interaction occurs, to guarantee the fidelity of the interaction, and to insulate the microenvironment in which it occurs. Subcellular targeting, as well as a variety of scaffolding devices, is used to promote interaction of the ACs with specific signaling proteins and regulatory factors to generate privileged domains for cAMP signaling. A direct consequence of this organization is that cAMP will exhibit distinct kinetics in discrete cellular domains. A variety of means are now available to study cAMP in these domains and to dissect their components in real time in live cells. These topics are explored within the present review.
Collapse
Affiliation(s)
- Debbie Willoughby
- Department of Pharmacology, University of Cambridge, Cambridge, United Kingdom
| | | |
Collapse
|
108
|
Feldman RD, Gros R. New insights into the regulation of cAMP synthesis beyond GPCR/G protein activation: implications in cardiovascular regulation. Life Sci 2007; 81:267-71. [PMID: 17604058 DOI: 10.1016/j.lfs.2007.05.015] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2007] [Revised: 04/12/2007] [Accepted: 05/19/2007] [Indexed: 11/25/2022]
Abstract
Regulation of intracellular concentrations of cyclic AMP is one of the most ubiquitous mechanisms for regulating cellular functions. Further, the manner in which cAMP production is regulated via G proteins at the level of adenylyl cyclase activation has been studied extensively. This review focuses instead on the recently identified mechanisms and roles for regulation of adenylyl cyclase functions beyond G protein activation. These mechanisms include: a) the coupling of particular isoforms of adenylyl cyclase to function within a single cell type b) regulation of membrane trafficking of higher order enzyme aggregates and c) raf kinase-dependent phosphorylation and sensitization of adenylyl cyclases--an important pathway for crosstalk between tyrosine kinase signaling cascades with regulation of cAMP-mediated responses.
Collapse
Affiliation(s)
- Ross D Feldman
- Cell Biology and Vascular Biology Research Groups, Robarts Research Institute, London, Ontario, Canada.
| | | |
Collapse
|
109
|
Fischmeister R, Castro LRV, Abi-Gerges A, Rochais F, Jurevicius J, Leroy J, Vandecasteele G. Compartmentation of cyclic nucleotide signaling in the heart: the role of cyclic nucleotide phosphodiesterases. Circ Res 2006; 99:816-28. [PMID: 17038651 DOI: 10.1161/01.res.0000246118.98832.04] [Citation(s) in RCA: 302] [Impact Index Per Article: 16.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
A current challenge in cellular signaling is to decipher the complex intracellular spatiotemporal organization that any given cell type has developed to discriminate among different external stimuli acting via a common signaling pathway. This obviously applies to cAMP and cGMP signaling in the heart, where these cyclic nucleotides determine the regulation of cardiac function by many hormones and neuromediators. Recent studies have identified cyclic nucleotide phosphodiesterases as key actors in limiting the spread of cAMP and cGMP, and in shaping and organizing intracellular signaling microdomains. With this new role, phosphodiesterases have been promoted from the rank of a housekeeping attendant to that of an executive officer.
Collapse
Affiliation(s)
- Rodolphe Fischmeister
- INSERM U769, Université Paris-Sud 11, Faculté de Pharmacie, 5, Rue J.-B. Clément, F-92296 Châtenay-Malabry Cedex, France.
| | | | | | | | | | | | | |
Collapse
|
110
|
Kamenetsky M, Middelhaufe S, Bank EM, Levin LR, Buck J, Steegborn C. Molecular details of cAMP generation in mammalian cells: a tale of two systems. J Mol Biol 2006; 362:623-39. [PMID: 16934836 PMCID: PMC3662476 DOI: 10.1016/j.jmb.2006.07.045] [Citation(s) in RCA: 241] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2006] [Revised: 07/15/2006] [Accepted: 07/20/2006] [Indexed: 01/05/2023]
Abstract
The second messenger cAMP has been extensively studied for half a century, but the plethora of regulatory mechanisms controlling cAMP synthesis in mammalian cells is just beginning to be revealed. In mammalian cells, cAMP is produced by two evolutionary related families of adenylyl cyclases, soluble adenylyl cyclases (sAC) and transmembrane adenylyl cyclases (tmAC). These two enzyme families serve distinct physiological functions. They share a conserved overall architecture in their catalytic domains and a common catalytic mechanism, but they differ in their sub-cellular localizations and responses to various regulators. The major regulators of tmACs are heterotrimeric G proteins, which transduce extracellular signals via G protein-coupled receptors. sAC enzymes, in contrast, are regulated by the intracellular signaling molecules bicarbonate and calcium. Here, we discuss and compare the biochemical, structural and regulatory characteristics of the two mammalian AC families. This comparison reveals the mechanisms underlying their different properties but also illustrates many unifying themes for these evolutionary related signaling enzymes.
Collapse
Affiliation(s)
- Margarita Kamenetsky
- Department of Pharmacology, Joan and Sanford I. Weill Medical College of Cornell University, New York, NY 10021, USA
| | - Sabine Middelhaufe
- Department of Physiological Chemistry, Ruhr-University, Bochum, Universitätsstraße
| | - Erin M. Bank
- Department of Pharmacology, Joan and Sanford I. Weill Medical College of Cornell University, New York, NY 10021, USA
| | - Lonny R. Levin
- Department of Pharmacology, Joan and Sanford I. Weill Medical College of Cornell University, New York, NY 10021, USA
- Corresponding authors: ;
| | - Jochen Buck
- Department of Pharmacology, Joan and Sanford I. Weill Medical College of Cornell University, New York, NY 10021, USA
| | - Clemens Steegborn
- Department of Physiological Chemistry, Ruhr-University, Bochum, Universitätsstraße
- Corresponding authors: ;
| |
Collapse
|