101
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Bibel M, Barde YA. Neurotrophins: key regulators of cell fate and cell shape in the vertebrate nervous system. Genes Dev 2000; 14:2919-37. [PMID: 11114882 DOI: 10.1101/gad.841400] [Citation(s) in RCA: 789] [Impact Index Per Article: 32.9] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Affiliation(s)
- M Bibel
- Department of Neurobiochemistry, Max-Planck Institute of Neurobiology, 82152 Planegg-Martinsried, Germany
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102
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Sphingolipids and cholesterol modulate membrane susceptibility to cytosolic phospholipase A2. J Lipid Res 2000. [DOI: 10.1016/s0022-2275(20)32002-2] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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103
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Racké K, Hammermann R, Juergens UR. Potential role of EDG receptors and lysophospholipids as their endogenous ligands in the respiratory tract. Pulm Pharmacol Ther 2000; 13:99-114. [PMID: 10873548 DOI: 10.1006/pupt.2000.0241] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The role of lipid mediators derived from membrane glycerophospholipids and sphingolipids as intracellular messenger has been studied intensively during the last two decades, but with the recent discovery of high affinity G-protein coupled receptors for the lysophospholipids lysophosphatidic acid (LPA), sphingosine-1-phosphate (S1P) and sphingosylphosphorylcholine (SPC), increasing attention has been paid to the role of these lipid mediators as extracellular mediators. This review will summarize the biosynthesis and metabolism of lysophospholipids and describe the family of endothelial differentiation gene (EDG) receptors as high affinity receptors for lysophospholipids. Furthermore, an overview of the numerous biological effects of lysophospholipids which might be mediated by EDG receptors will be given together with an outlook on the potential role of such mechanisms in pulmonary physiology and pathophysiology.
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Affiliation(s)
- K Racké
- Institute of Pharmacology & Toxicology, University of Bonn, Reuterstrabetae 2b, Bonn, D-53113, Germany.
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104
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Kolesnick RN, Goñi FM, Alonso A. Compartmentalization of ceramide signaling: physical foundations and biological effects. J Cell Physiol 2000; 184:285-300. [PMID: 10911359 DOI: 10.1002/1097-4652(200009)184:3<285::aid-jcp2>3.0.co;2-3] [Citation(s) in RCA: 349] [Impact Index Per Article: 14.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Affiliation(s)
- R N Kolesnick
- Laboratory of Signal Transduction, Memorial Sloan-Kettering Cancer Center, New York, NY
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105
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Abstract
The recent recognition that the p75 neurotrophin receptor, p75((NTR)), can induce apoptotic signals has contributed to the perception that it acts primarily as a death receptor. Although the molecular mechanisms of p75(NTR) signaling remain to be fully characterized, many of the currently identified pathways activated by p75(NTR) may be generally characterized as stress response signals. This review describes recent advances in identifying the molecular components involved in p75(NTR) signal transduction and suggests that p75(NTR) signaling may more aptly serve as a general mechanism for the transduction and modulation of stress signals.
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Affiliation(s)
- R T Dobrowsky
- Department of Pharmacology and Toxicology, University of Kansas, Lawrence, Kansas, USA.
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106
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Prabhakar P, Cheng V, Michel T. A chimeric transmembrane domain directs endothelial nitric-oxide synthase palmitoylation and targeting to plasmalemmal caveolae. J Biol Chem 2000; 275:19416-21. [PMID: 10787410 DOI: 10.1074/jbc.m001952200] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
The endothelial nitric-oxide synthase (eNOS), a key signaling protein, undergoes a series of covalent modifications, including co-translational N-myristoylation at Gly(2), as well as post-translational thiopalmitoylation at Cys(15) and Cys(26). Myristoylation of eNOS is required for the subsequent palmitoylation of the enzyme, and both acylations are required for the efficient subcellular targeting of eNOS to plasmalemmal caveolae. We constructed chimeric cDNAs encoding proteins comprised of various acylation-deficient eNOS mutants fused at their N termini to the hydrophobic transmembrane domain of the glycoprotein CD8 and characterized these constructs in transient transfection experiments in COS-7 cells. One construct (termed CD8-myr(-)eNOS) encodes a fusion protein comprised of the eNOS myristoylation-deficient mutant coupled to the CD8 transmembrane domain. In biosynthetic labeling experiments using [(3)H]palmitic acid, we found that the CD8-myr(-)eNOS chimera undergoes palmitoylation. Subcellular fractionation showed that the CD8-myr(-)eNOS chimera is targeted to caveolae. We also constructed and characterized a cDNA encoding the CD8 transmembrane domain fused to the palmitoylation-deficient mutant eNOS (in which Cys(15) and Cys(26) are changed to serine). This chimera (termed CD8-myr(-).palm(-)eNOS) did not undergo palmitoylation, indicating that the palmitoylation seen with the CD8. myr(-)eNOS fusion protein occurs on the same residues as in the wild-type enzyme. Importantly, the CD8-myr(-).palm(-)eNOS fusion protein remained efficiently targeted to caveolae, in contrast to the palm(-)eNOS mutant lacking the CD8 transmembrane domain, which has nominal caveolar localization. A construct encoding the CD8 transmembrane domain alone was insufficient for selective targeting to caveolae. These results indicate that membrane targeting per se, but not necessarily myristoylation, is sufficient for eNOS palmitoylation and localization to plasmalemmal caveolae, and suggest further that sequences within eNOS itself, in addition to its palmitoylation sites, facilitate the selective localization of the enzyme within caveolae.
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Affiliation(s)
- P Prabhakar
- Cardiovascular Division, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA
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107
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Huwiler A, Kolter T, Pfeilschifter J, Sandhoff K. Physiology and pathophysiology of sphingolipid metabolism and signaling. BIOCHIMICA ET BIOPHYSICA ACTA 2000; 1485:63-99. [PMID: 10832090 DOI: 10.1016/s1388-1981(00)00042-1] [Citation(s) in RCA: 308] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Affiliation(s)
- A Huwiler
- Zentrum der Pharmakologie, Klinikum der Johann Wolfgang Goethe-Universität, Frankfurt, Germany.
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108
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Prinetti A, Chigorno V, Tettamanti G, Sonnino S. Sphingolipid-enriched membrane domains from rat cerebellar granule cells differentiated in culture. A compositional study. J Biol Chem 2000; 275:11658-65. [PMID: 10766784 DOI: 10.1074/jbc.275.16.11658] [Citation(s) in RCA: 119] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
Sphingolipid-enriched membrane domains, characterized by a particular protein and lipid composition, have been detected in a variety of cells. However, limited data are available concerning these domains in neuronal cells. We analyzed the lipid and protein composition of a sphingolipid-enriched membrane fraction prepared from primary rat cerebellar granule cells differentiated in culture. Although the protein content of this fraction was only 1.4% of total cellular protein, 60% of the gangliosides, 67% of the sphingomyelin, 50% of the ceramide, and 40% of the cholesterol were located in this fraction. The protein pattern of the sphingolipid-enriched domain fraction was dramatically different from that associated with the cell homogenate. This fraction contained 25% of the tyrosine-phosphorylated proteins and was enriched in two proteins with apparent molecular masses of 135 and 15 kDa. 12% of cellular glycerophospholipids were located in the fraction, with phosphatidylcholine having the highest enrichment. The molar ratio between proteins, glycerophospholipids, cholesterol, sphingomyelin, ceramide and gangliosides in cerebellar granule cells was 1.6:41.6:6. 1:1.3:0.3:1 in the cell homogenate and 0.04:8.3:4.0:1.4:0.2:1 in the sphingolipid-enriched membrane fraction. These data indicate that selected proteins segregate with sphingolipids in specialized domains in the membrane of cultured neurons.
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Affiliation(s)
- A Prinetti
- Study Center for the Functional Biochemistry of Brain Lipids, Department of Medical Chemistry and Biochemistry, Laboratorio Interdisciplenane Tecnologie Avanzate-Segrate, The Medical School, University of Milan, 20090 Milano, Italy
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109
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Abstract
In addition to its hypophysiotropic action, gonadotropin-releasing hormone (GnRH) can modify activity in extrapituitary organs and peripheral tumors. GnRH analogs are the preferred treatment for advanced and even metastatic or recurring carcinomas in vivo and in vitro. Hormone-responsive tumors undergo apoptosis with the appropriate stimulus; GnRH-induced tumor growth arrest may result from stimulated apoptotic cell death. The sensitivity of tumors and normal tissue to GnRH is strongly associated with the possession of receptors for GnRH as well as other hormonal control. Despite the lack of a precise apoptotic signaling cascade through GnRH receptors, biochemical events observed within a plasma membrane appear to constitute the most convincing evidence that the membrane event is primarily stimulated during cell activation by GnRH. GnRH receptors in tumors differ from those in pituitary gonadotrophs in some aspects, in particular with regard to the transmembrane signaling cascade. The intramembranous phenomena that occur independently of the contribution of other organelles upon tumoral GnRH receptor engagement include (i) activation of phosphotyrosine phosphatase and loss of phosphotyrosine from the endogenous membrane protein and (ii) phosphoinositide and perhaps sphingomyelin cleavage producing lipid-originated second messengers. GnRH has also been demonstrated to increase Fas ligand expression within plasma membrane, which is known to promote apoptotic cell death through attack on Fas-positive cells within tumors. The Fas-Fas ligand complex might, at least in part, account for the antiproliferative action of the hormone. An understanding of the relationship between the extracellular (hormonal) stimuli that leads to cell death and the intracellular events regulating growth arrest on GnRH action may fundamentally help clarify the therapeutic approach to all hormone-dependent carcinomas that respond to stimuli that lead to apoptosis. In this chapter, we review the recent literature and the results of our studies on GnRH-induced membrane events and summarize what is currently known about this promising antiproliferative function.
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Affiliation(s)
- A Imai
- Department of Obstetrics and Gynecology, Gifu University School of Medicine, Japan
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110
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Mutoh T, Hamano T, Tokuda A, Kuriyama M. Unglycosylated Trk protein does not co-localize nor associate with ganglioside GM1 in stable clone of PC12 cells overexpressing Trk (PCtrk cells). Glycoconj J 2000; 17:233-7. [PMID: 11201795 DOI: 10.1023/a:1026597408790] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Our previous studies have shown that acidic glycosphingolipid, ganglioside GM1 (GM1), is an endogenous regulator of high affinity nerve growth factor receptor, Trk, which is an essential factor for the normal development and differentiation of neuronal cells by forming a complex with Trk. GM1 is also known to be a major constituent of caveola or glycosphingolipid-enriched microdomain (GEM) of the plasma membrane. In order to study the effect of the glycosylation of Trk on the formation of GM1-Trk complex and subcellular distribution of this protein, we generated PC12 cells stably overexpressing Trk (PCtrk). Pretreatment of this stable clones with tunicamycin, a potent inhibitor of N-glycosylation, caused the appearance of unglycosylated Trk core protein. These unglycosylated Trk can hardly respond to its ligand, NGF. Sucrose density gradient analysis revealed that unglycosylated Trk core protein was recovered in high density fractions, whereas most of GM1 is present in low density fractions corresponding to caveola or GEM fractions. Moreover, these unglycosylated Trk proteins lose their ability to form a complex with GM1, although GM1 is present in the same high density fractions. These data strongly suggest that spatial segregation of GM1 from the Trk protein by the inhibition of the glycosylation of Trk might be an important molecular mechanism for the unresponsiveness to NGF. Moreover, the binding site of GM1 in the Trk protein might act as an important determinant for the normal trafficking of the Trk protein within the cells.
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Affiliation(s)
- T Mutoh
- The Second Department of Internal Medicine, Faculty of Medicine, Fukui Medical University, Japan.
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111
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Prinetti A, Marano N, Prioni S, Chigorno V, Mauri L, Casellato R, Tettamanti G, Sonnino S. Association of Src-family protein tyrosine kinases with sphingolipids in rat cerebellar granule cells differentiated in culture. Glycoconj J 2000; 17:223-32. [PMID: 11201794 DOI: 10.1023/a:1026545424720] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Src family kinases play a relevant role in the development and differentiation of neuronal cells. They are abundant in sphingolipid-enriched membrane domains of many cell types, and these domains are hypothesized to function in bringing together molecules important to signal transduction. We studied the association of Src family tyrosine kinases and their negative regulatory kinase, Csk, with sphingolipids in sphingolipid-enriched domains of rat cerebellar granule cells differentiated in culture. We find that c-Src, Lyn and Csk are enriched in the sphingolipid-enriched fraction prepared from these cells. Coimmunoprecipitation experiments show that these and sphingolipids are part of the same domain. Cross-linking experiments with a photoactivable, radioactive GD1b derivative show that c-Src and Lyn, which are anchored to the membrane via a myristoyl chain, associate directly with GD1b. Csk, which is not inserted in the hydrophobic core of the membrane, is not photolabeled by this ganglioside. These results suggest that lipid-lipid, lipid-protein, and protein-protein interactions cooperate to maintain domain structure. We hypothesize that such interactions might play a role in the process of neuronal differentiation.
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Affiliation(s)
- A Prinetti
- Department of Medical Chemistry and Biochemistry - LITA - Segrate, The Medical School, University of Milan, Milano, Italy
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112
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Dolo V, D'Ascenzo S, Sorice M, Pavan A, Sciannamblo M, Prinetti A, Chigorno V, Tettamanti G, Sonnino S. New approaches to the study of sphingolipid enriched membrane domains: the use of electron microscopic autoradiography to reveal metabolically tritium labeled sphingolipids in cell cultures. Glycoconj J 2000; 17:261-8. [PMID: 11201799 DOI: 10.1023/a:1026505710607] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
This paper is the first report on the use of the electron microscopy autoradiography technique to detect metabolically tritium labeled sphingolipids in intact cells in culture. To label cell sphingolipids, human fibroblasts in culture were fed by a 24 hours pulse, repeated 5 times, of 3 x 10(-7) M [1-(3)H]sphingosine. [1-(3)H]sphingosine was efficently taken up by the cells and very rapidly used for the biosynthesis of complex sphingolipids, including neutral glycolipids, gangliosides, ceramide and sphingomyelin. The treatment with [1-(3)H]sphingosine did not induce any morphological alteration of cell structures, and well preserved cells, plasma membranes, and intracellular organelles could be observed by microscopy. Ultrathin sections from metabolic radiolabeled cells were coated with autoradiographic emulsion. One to four weeks of exposition resulted in pictures where the location of radioactive sphingolipids was evidenced by the characteristic appearance of silver grains as irregular coiled ribbons of metallic silver. Radioactive sphingolipids were found at the level of the plasma membranes, on the endoplasmic reticulum and inside of cytoplasmic vesicles. Thus, electron microscopy autoradiography is a very useful technique to study sphingolipid-enriched membrane domain organization and biosynthesis.
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Affiliation(s)
- V Dolo
- Department of Experimental Medicine, University of L'Aquila, Italy
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113
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Abstract
Ceramide is a novel lipid mediator involved in regulating cell growth, cell differentiation and cell death. Many studies have focused on characterizing the stimulus-induced production of ceramide and identifying putative downstream molecular targets. However, little remains known about the localization of the regulated production of ceramide through sphingomyelin metabolism in the plasma membrane. Additionally, it is unclear whether a localized increase in ceramide concentration is necessary to facilitate downstream signalling events initiated by this lipid. Recent studies have suggested that detergent-insoluble plasma membrane domains may be highly localized sites for initiating signal transduction cascades by both tyrosine kinase and sphingolipid signalling pathways. These domains are typically enriched in both sphingolipids and cholesterol and have been proposed to form highly ordered lipid rafts floating in a sea of glycerophospholipids. Alternatively, upon integration of the cholesterol binding protein caveolin, these domains may also form small cave-like structures called caveolae. Emerging evidence suggests that the enhanced sphingomyelin content of these lipid domains make them potential substrate pools for sphingomyelinases to produce a high local concentration of ceramide. The subsequent formation of ceramide microdomains in the plasma membrane may be a critical factor in regulating downstream signalling through this lipid messenger.
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Affiliation(s)
- R T Dobrowsky
- Department of Pharmacology and Toxicology, University of Kansas, 5064 Malott Hall, Lawrence, KS 66045, USA.
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114
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Huang CS, Zhou J, Feng AK, Lynch CC, Klumperman J, DeArmond SJ, Mobley WC. Nerve growth factor signaling in caveolae-like domains at the plasma membrane. J Biol Chem 1999; 274:36707-14. [PMID: 10593976 DOI: 10.1074/jbc.274.51.36707] [Citation(s) in RCA: 110] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Nerve growth factor (NGF) binding to its receptors TrkA and p75(NTR) enhances the survival, differentiation, and maintenance of neurons. Recent studies have suggested that NGF receptor activation may occur in caveolae or caveolae-like membranes (CLM). This is an intriguing possibility because caveolae have been shown to contain many of the signaling intermediates in the TrkA signaling cascade. To examine the membrane localization of TrkA and p75(NTR), we isolated caveolae from 3T3-TrkA-p75 cells and CLM from PC12 cells. Immunoblot analysis showed that TrkA and p75(NTR) were enriched about 13- and 25-fold, respectively, in caveolae and CLM. Binding and cross-linking studies demonstrated that the NGF binding to both TrkA and p75(NTR) was considerably enriched in CLM and that about 90% of high affinity binding to TrkA was present in CLM. When PC12 cells were treated with NGF, virtually all activated (i.e. tyrosine phosphorylated) TrkA was found in the CLM. Remarkably, in NGF-treated cells, it was only in CLM that activated TrkA was coimmunoprecipitated with phosphorylated Shc and PLCgamma. These results document a signaling role for TrkA in CLM and suggest that both TrkA and p75(NTR) signaling are initiated from these membranes.
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Affiliation(s)
- C S Huang
- Departments of Neurology and Neurological Sciences and Pediatrics and the Program in Neuroscience, Stanford University, Stanford, California 94305, USA
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115
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Liu G, Kleine L, Hébert RL. Advances in the signal transduction of ceramide and related sphingolipids. Crit Rev Clin Lab Sci 1999; 36:511-73. [PMID: 10656539 DOI: 10.1080/10408369991239240] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Recently, the sphingolipid metabolites ceramide, sphingosine, ceramide 1-P, and sphingosine 1-P have been implicated as second messengers involved in many different cellular functions. Publications on this topic are appearing at a rapidly increasing rate and new developments in this field are also appearing rapidly. It is thus important to summarize the results obtained from many different laboratories and from different fields of research to obtain a clearer picture of the importance of sphingolipid metabolites. This article reviews the studies from the last few years and includes the effects of a variety of extracellular agents on sphingolipid signal transduction pathways in different tissues and cells and on the mechanisms of regulation. Sphingomyelin exists in a number of functionally distinct pools and is composed of distinct molecular species. Sphingomyelin metabolites may be formed by many different pathways. For example, the generation of ceramide from sphingomyelin can be catalyzed by at least five different sphingomyelinases. A large variety of stimuli can induce the generation of ceramide, leading to activation or inhibition of various cellular events such as proliferation, differentiation, apoptosis, and inflammation. The effect of ceramide on these physiological processes is due to its many different downstream targets. It can activate ceramide-activated protein kinases and ceramide-activated protein phosphatases. It also activates or inhibits PKCs, PLD, PLA2, PC-PLC, nitric oxide synthase, and the ERK and SAPK/JNK signaling cascades. Ceramide activates or inhibits transcription factors, modulates calcium homeostasis and interacts with the retinoblastoma protein to regulate cell cycle progression. Most of the work in this field has involved the study of ceramide effects, but the roles of the other three sphingomyelin metabolites is now attracting much attention. The complex interactions between signaling components and ceramide and the controls regulating these interactions are now being identified and are presented in this review.
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Affiliation(s)
- G Liu
- Department of Cellular and Molecular Medicine, University of Ottawa, Ontario, Canada
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116
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Affiliation(s)
- R T Dobrowsky
- Department of Pharmacology and Toxicology, University of Kansas, Lawrence 66045, USA
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117
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Abstract
Ceramide is considered to be an important signaling molecule in cellular processes such as cell growth, secretion, differentiation, and apoptosis. This implies that the molecule is able to move between cellular membranes. However, the ability of the molecule to undergo such exchange has been largely ignored despite the profound impact that this ability would have on its mechanism of action in signal-transduction cascades. With this in mind, the ability of a long-chain, radioactive ceramide, (14)C-C(16)-ceramide, to exchange between populations of lipid vesicles was evaluated. The rate of exchange of (14)C-C(16)-ceramide between lipid vesicles at lipid concentrations commonly found in cells (10-110 mM) was on the order of days (t(1/2) of 45-109 h). Simultaneous observations revealed negligible exchange of (3)H-cholesteryl oleate, which was included as a nontransferable marker to control for artifacts such as vesicle fusion and aggregation. In addition, all of the ceramide was exchangeable, and the exchange followed monoexponential kinetics, indicating that the ceramide underwent transbilayer movement at a rate faster than or equal to its rate of intervesicle exchange. Two conclusions can be drawn from these observations: (i) the spontaneous transfer of ceramide between cellular membranes is too slow to play a role in rapid, inter-membrane signaling phenomena and can only be a factor in cell functions that take place over days; and (ii) without the aid of an exchange protein, ceramide can only interact with target molecules that are located at the membrane where the ceramide is formed.
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Affiliation(s)
- C G Simon
- National Institute of Standards and Technology, Polymers Division, 100 Bureau Drive, Gaithersburg, Maryland 20899, USA
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118
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Smart EJ, Graf GA, McNiven MA, Sessa WC, Engelman JA, Scherer PE, Okamoto T, Lisanti MP. Caveolins, liquid-ordered domains, and signal transduction. Mol Cell Biol 1999; 19:7289-304. [PMID: 10523618 PMCID: PMC84723 DOI: 10.1128/mcb.19.11.7289] [Citation(s) in RCA: 782] [Impact Index Per Article: 31.3] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Affiliation(s)
- E J Smart
- University of Kentucky, Department of Physiology, Lexington, Kentucky 40536, USA
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119
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120
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Affiliation(s)
- Daniel D. Mikol
- Department of Neurology, University of Michigan, Ann Arbor, Michigan
| | - Hoylond L. Hong
- Department of Neurology, University of Michigan, Ann Arbor, Michigan
| | - Hsin‐Lin Cheng
- Department of Neurology, University of Michigan, Ann Arbor, Michigan
| | - Eva L. Feldman
- Department of Neurology, University of Michigan, Ann Arbor, Michigan
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121
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Vesper H, Schmelz EM, Nikolova-Karakashian MN, Dillehay DL, Lynch DV, Merrill AH. Sphingolipids in food and the emerging importance of sphingolipids to nutrition. J Nutr 1999; 129:1239-50. [PMID: 10395583 DOI: 10.1093/jn/129.7.1239] [Citation(s) in RCA: 371] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Eukaryotic organisms as well as some prokaryotes and viruses contain sphingolipids, which are defined by a common structural feature, i.e. , a "sphingoid base" backbone such as D-erythro-1,3-dihydroxy, 2-aminooctadec-4-ene (sphingosine). The sphingolipids of mammalian tissues, lipoproteins, and milk include ceramides, sphingomyelins, cerebrosides, gangliosides and sulfatides; plants, fungi and yeast have mainly cerebrosides and phosphoinositides. The total amounts of sphingolipids in food vary considerably, from a few micromoles per kilogram (fruits) to several millimoles per kilogram in rich sources such as dairy products, eggs and soybeans. With the use of the limited data available, per capita sphingolipid consumption in the United States can be estimated to be on the order of 150-180 mmol (approximately 115-140 g) per year, or 0.3-0.4 g/d. There is no known nutritional requirement for sphingolipids; nonetheless, they are hydrolyzed throughout the gastrointestinal tract to the same categories of metabolites (ceramides and sphingoid bases) that are used by cells to regulate growth, differentiation, apoptosis and other cellular functions. Studies with experimental animals have shown that feeding sphingolipids inhibits colon carcinogenesis, reduces serum LDL cholesterol and elevates HDL, suggesting that sphingolipids represent a "functional" constituent of food. Sphingolipid metabolism can also be modified by constituents of the diet, such as cholesterol, fatty acids and mycotoxins (fumonisins), with consequences for cell regulation and disease. Additional associations among diet, sphingolipids and health are certain to emerge as more is learned about these compounds.
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Affiliation(s)
- H Vesper
- Departments of Biochemistry and Pathology, and Division of Animal Resources, Emory University, Atlanta, GA 30322-3050, USA
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122
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Ko YG, Lee JS, Kang YS, Ahn JH, Seo JS. TNF-α-Mediated Apoptosis Is Initiated in Caveolae-Like Domains. THE JOURNAL OF IMMUNOLOGY 1999. [DOI: 10.4049/jimmunol.162.12.7217] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Abstract
Caveolae-like domains (CLDs) have been hypothesized to mediate apoptosis, since they contain sphingomyelin and initiate the conversion of sphingomyelin to ceramide. To address whether CLDs are directly involved in apoptosis, CLDs from U937 cells were isolated, taking advantage of their detergent insolubility and low density. The CLDs contained alkaline phosphatase as well as many signaling molecules, including Fyn, protein kinase Cα, Raf-1, phospholipase Cγ1, and tyrosine phosphoproteins. Immunoblotting and immunofluorescent data showed that TNF receptor 1 colocalized with CD36 in CLDs, suggesting that TNF-α-initiated apoptosis occurs in CLDs. When cells were incubated with lipoprotein-deficient medium, the cholesterol concentration was greatly decreased in CLDs but not in other fractions, implying that the CLDs were selectively disrupted. In the CLD-disrupted cells, the surface expression of TNF receptor 1 and CD36 was significantly reduced. Analysis of cellular morphology, percent DNA fragmentation, DNA laddering, and caspase-3 activity showed that TNF-α-mediated apoptosis was blocked in CLD-disrupted cells, whereas anti-Fas-mediated apoptosis was not. Since Fas was not found in CLDs of Jurkat cells, apoptosis by Fas ligation might not require CLDs. Taken together, these data strongly imply that TNF-α-mediated apoptosis is initiated in CLDs.
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Affiliation(s)
- Young-Gyu Ko
- Ilchun Molecular Medicine Institute Medical Research Center, Cancer Research Center, and Department of Biochemistry, Seoul National University College of Medicine, Seoul, Korea
| | - Jae-Seon Lee
- Ilchun Molecular Medicine Institute Medical Research Center, Cancer Research Center, and Department of Biochemistry, Seoul National University College of Medicine, Seoul, Korea
| | - Young-Sun Kang
- Ilchun Molecular Medicine Institute Medical Research Center, Cancer Research Center, and Department of Biochemistry, Seoul National University College of Medicine, Seoul, Korea
| | - Jung-Hyuck Ahn
- Ilchun Molecular Medicine Institute Medical Research Center, Cancer Research Center, and Department of Biochemistry, Seoul National University College of Medicine, Seoul, Korea
| | - Jeong-Sun Seo
- Ilchun Molecular Medicine Institute Medical Research Center, Cancer Research Center, and Department of Biochemistry, Seoul National University College of Medicine, Seoul, Korea
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123
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Abstract
Ionizing radiation activates not only signalling pathways in the nucleus as a result of DNA damage, but also signalling pathways initiated at the level of the plasma membrane. Proteins involved in DNA damage recognition include poly(ADP ribose) polymerase (PARP), DNA-dependent protein kinase, p53 and ataxia- telangiectasia mutated (ATM). Many of these proteins are inactivated by caspases during the execution phase of apoptosis. Signalling pathways outside the nucleus involve tyrosine kinases such as stress-activated protein kinase (SAPK)/c-Jun N-terminal kinase (JNK), protein kinase C, ceramide and reactive oxygen species. Recent evidence shows that tumour cells resistant to ionizing radiation-induced apoptosis have defective ceramide signalling. How these signalling pathways converge to activate the caspases is presently unknown, although in some cell types a role for calpain has been suggested.
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Affiliation(s)
- D Watters
- Cancer Research Unit, Queensland Institute of Medical Research, Brisbane, Queensland, Australia.
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124
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Separovic D, Pink JJ, Oleinick NA, Kester M, Boothman DA, McLoughlin M, Peña LA, Haimovitz-Friedman A. Niemann-Pick human lymphoblasts are resistant to phthalocyanine 4-photodynamic therapy-induced apoptosis. Biochem Biophys Res Commun 1999; 258:506-12. [PMID: 10329416 DOI: 10.1006/bbrc.1999.0670] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Stress-induced activation of sphingomyelinase (SMase) leading to generation of ceramide, a lipid mediator, has been associated with apoptosis in several malignant and nonmalignant cell lines. Photodynamic therapy (PDT), with the phthalocyanine photosensitizer Pc 4 [HOSiPcOSi(CH3)2(CH2)3N(CH3)2], is an oxidative stress associated with increased ceramide generation and subsequent induction of apoptosis in various cell types. We assessed the role of SMase in photocytotoxicity. Normal human lymphoblasts accumulated ceramide and underwent apoptosis after Pc 4-PDT. In contrast, Niemann-Pick disease (NPD) lymphoblasts, which are deficient in acid sphingomyelinase (ASMase) activity, failed to respond to Pc 4-PDT with ceramide accumulation and apoptosis, suggesting that ASMase may be a Pc 4-PDT target. NPD lymphoblasts were exposed to exogenous bacterial sphingomyelinase (bSMase) to test whether these defects are reversible. Treatment of NPD cells with bSMase itself led to elevated ceramide formation, which did not translate into induction of apoptosis. However, a combination of Pc 4-PDT + bSMase induced a significant apoptotic response. Thus, the combined treatment of Pc 4-PDT + bSMase, rather than bSMase alone, was required to restore apoptosis in NPD cells. These data support the hypothesis that SMase is a proapoptotic factor determining responsiveness of cells to Pc 4-PDT.
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Affiliation(s)
- D Separovic
- Department of Radiation Oncology, Case Western Reserve University School of Medicine, Cleveland, Ohio, 44106-4942, USA
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125
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Levade T, Jaffrézou JP. Signalling sphingomyelinases: which, where, how and why? BIOCHIMICA ET BIOPHYSICA ACTA 1999; 1438:1-17. [PMID: 10216276 DOI: 10.1016/s1388-1981(99)00038-4] [Citation(s) in RCA: 249] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
A major lipid signalling pathway in mammalian cells implicates the activation of sphingomyelinase (SMase), which upon cell stimulation hydrolyses the ubiquitous sphingophospholipid sphingomyelin to ceramide. This review summarizes our current knowledge on the nature and regulation of signalling SMase(s). Because of the controversy on the identity of this(these) phospholipase(s), the roles of various SMases in cell signalling are discussed. Special attention is also given to the subcellular site of action of signalling SMases and to the cellular factors that positively or negatively control their activity. These regulating agents include lipids (arachidonic acid, diacylglycerol and ceramide), kinases, proteases, glutathione and other proteins.
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Affiliation(s)
- T Levade
- INSERM Unit 466, Laboratoire de Biochimie, Maladies Métaboliques, Institut Louis Bugnard, Bât. L3, C.H.U. Rangueil, 1 Avenue Jean Poulhès, E 9910, Toulouse Cedex 4, France.
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126
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Hurlstone AF, Reid G, Reeves JR, Fraser J, Strathdee G, Rahilly M, Parkinson EK, Black DM. Analysis of the CAVEOLIN-1 gene at human chromosome 7q31.1 in primary tumours and tumour-derived cell lines. Oncogene 1999; 18:1881-90. [PMID: 10086342 DOI: 10.1038/sj.onc.1202491] [Citation(s) in RCA: 94] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
We identified CAVEOLIN-1 as a candidate for a tumour suppressor gene mapping to human chromosome 7q31.1. A number of studies suggest that caveolin could function as a tumour suppressor. Expression of caveolin, and in turn the number of caveolae within a cell, are inversely correlated with the transforming ability of numerous oncoproteins, including H-ras, v-abl, and bcr-abl, and caveolin is a major transformation-dependent substrate of v-src. Heterologous expression of caveolin has been shown to abrogate anchorage-independent growth and induce apoptosis in transformed fibroblasts and also to suppress anchorage-independent growth in human mammary carcinoma cells. We have analysed the status and expression of the human CAVEOLIN-1 gene in primary tumours and tumour-derived cell lines. We found no evidence for mutation of CAVEOLIN-1 in human cancers. Additionally, we found that while the first two exons of CAVEOLIN-1 are associated with a CpG island, this is not methylated in either primary tumours or in tumour-derived cell lines in which Caveolin-1 expression is low or undetectable. The level of expression of Caveolin-1 does not correlate with loss of heterozygosity at the CAVEOLIN-1 locus in these same cell lines. Contrary to other published studies, we have shown that CAVEOLIN-1 is not expressed in normal breast ductal epithelial cells in vivo. CAVEOLIN-1 is however highly expressed in breast myoepithelial cells and its expression is retained in tumours derived from breast myoepithelium. Together our data refute a role for CAVEOLIN-1 as a breast tumour suppressor gene in vivo.
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Affiliation(s)
- A F Hurlstone
- Beatson Institute for Cancer Research, CRC Beatson Laboratories, Bearsden, Glasgow, UK
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127
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Wang YM, Seibenhener ML, Vandenplas ML, Wooten MW. Atypical PKC zeta is activated by ceramide, resulting in coactivation of NF-kappaB/JNK kinase and cell survival. J Neurosci Res 1999; 55:293-302. [PMID: 10348660 DOI: 10.1002/(sici)1097-4547(19990201)55:3<293::aid-jnr4>3.0.co;2-9] [Citation(s) in RCA: 117] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Both protein kinase C (PKC) and ceramide play a critical role in cell signaling, but the relationship between PKC and ceramide is unclear. Low concentrations of ceramide were observed to transiently stimulate PKC zeta activity in vitro and in vivo, whereas high doses of ceramide lead to inhibition of PKC zeta. Inhibition of activity was accompanied by enhanced binding of the negative regulator, Par4 to PKC zeta. Treatment of PC12 cells with low doses of ceramide promoted survival in serum-free media and activation of nuclear factor-KB, whereas higher doses (>2.5 microM) resulted in cell death. Overexpression of either aPKC isoform, PKC zeta or iota, resulted in enhanced survival of PC12 cells at high doses of ceramide and in ceramide-stimulated Jun N-terminal kinase (JNK), without any apparent effect on mitogen-activated kinase. These findings support a role for ceramide-induced PKC zeta activity in the control of cell survival signaling via a pathway that also activates JNK kinase.
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Affiliation(s)
- Y M Wang
- Department of Zoology, Auburn University, Alabama, USA
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128
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MacKichan ML, DeFranco AL. Role of ceramide in lipopolysaccharide (LPS)-induced signaling. LPS increases ceramide rather than acting as a structural homolog. J Biol Chem 1999; 274:1767-75. [PMID: 9880559 DOI: 10.1074/jbc.274.3.1767] [Citation(s) in RCA: 81] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Ceramide and ceramide-activated enzymes have been implicated in responses to bacterial lipopolysaccharide (LPS) and the proinflammatory cytokines tumor necrosis factor-alpha (TNF) and interleukin-1beta (IL-1). Although TNF and IL-1 cause elevation of cellular ceramide, which is thought to act as a second messenger, LPS has been proposed to signal by virtue of structural similarity to ceramide. We have investigated the relationship between ceramide and LPS by comparing the effects of a cell-permeable ceramide analog (C2-ceramide) and LPS on murine macrophage cell lines and by measuring ceramide levels in macrophages exposed to LPS. We found that while both C2-ceramide and LPS activated c-Jun N-terminal kinase (JNK), only LPS also activated extracellular signal-regulated kinases (ERKs). C2-ceramide was also unable to activate NF-kappaB, a transcription factor important for LPS-induced gene expression. Upon measurement of cellular ceramide in macrophage lines, we observed a small but rapid rise in ceramide, similar to that seen upon IL-1 or TNF treatment, suggesting LPS induces an increase in ceramide rather than interacting directly with ceramide-responsive enzymes. We found that C2-ceramide activated JNK and induced growth arrest in macrophages cell lines from both normal mice (Lpsn) and mice genetically unresponsive to LPS (Lpsd), whereas only Lpsn macrophages made these responses to LPS. Surprisingly, LPS treatment of Lpsd macrophages induced a rise in ceramide similar to that observed in LPS-responsive cells. These results indicate that the wild type Lps allele is not required for LPS-induced ceramide generation and suggest that ceramide elevation alone is insufficent stimulus for most responses to LPS.
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Affiliation(s)
- M L MacKichan
- Department of Microbiology and Immunology and G. W. Hooper Foundation, University of California, San Francisco, California 94143-0552, USA
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129
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Bilderback TR, Gazula VR, Lisanti MP, Dobrowsky RT. Caveolin interacts with Trk A and p75(NTR) and regulates neurotrophin signaling pathways. J Biol Chem 1999; 274:257-63. [PMID: 9867838 DOI: 10.1074/jbc.274.1.257] [Citation(s) in RCA: 128] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Neurotrophins signal through Trk tyrosine kinase receptors and the low-affinity neurotrophin receptor p75(NTR). We have shown previously that activation of Trk A tyrosine kinase activity can inhibit p75(NTR)-dependent sphingomyelin hydrolysis, that caveolae are a localized site for p75(NTR) signaling, and that caveolin can directly interact with p75(NTR). The ability of caveolin to also interact with tyrosine kinase receptors and inhibit their activity led us to hypothesize that caveolin expression may modulate interactions between neurotrophin signaling pathways. PC12 cells were transfected with caveolin that was expressed efficiently and targeted to the appropriate membrane domains. Upon exposure to nerve growth factor (NGF), caveolin-PC12 cells were unable to develop extensive neuritic processes. Caveolin expression in PC12 cells was found to diminish the magnitude and duration of Trk A activation in vivo. This inhibition may be due to a direct interaction of caveolin with Trk A, because Trk A co-immunoprecipitated with caveolin from Cav-Trk A-PC12 cells, and a glutathione S-transferase-caveolin fusion protein bound to Trk A and inhibited NGF-induced autophosphorylation in vitro. Furthermore, the in vivo kinetics of the inhibition of Trk A tyrosine kinase activity by caveolin expression correlated with an increased ability of NGF to induce sphingomyelin hydrolysis through p75(NTR). In summary, our results suggest that the interaction of caveolin with neurotrophin receptors may have functional consequences in regulating signaling through p75(NTR) and Trk A in neuronal and glial cell populations.
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Affiliation(s)
- T R Bilderback
- Department of Pharmacology and Toxicology, University of Kansas, Lawrence, Kansas 66045, USA
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130
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Abstract
The sphingomyelin (SM) pathway is a ubiquitous, evolutionarily conserved signalling system analogous to conventional systems such as the cAMP and phosphoinositide pathways. Ceramide, which serves as second messenger in this pathway, is generated from SM by the action of a neutral or acidic SMase, or by de novo synthesis co-ordinated through the enzyme ceramide synthase. A number of direct targets for ceramide action have now been identified, including ceramide-activated protein kinase, ceramide-activated protein phosphatase and protein kinase Czeta, which couple the SM pathway to well defined intracellular signalling cascades. The SM pathway induces differentiation, proliferation or growth arrest, depending on the cell type. Very often, however, the outcome of signalling through this pathway is apoptosis. Mammalian systems respond to diverse stresses with ceramide generation, and recent studies show that yeast manifest a form of this response. Thus ceramide signalling is an older stress response system than the caspase/apoptotic death pathway, and hence these two pathways must have become linked later in evolution. Signalling of the stress response through ceramide appears to play a role in the development of human diseases, including ischaemia/reperfusion injury, insulin resistance and diabetes, atherogenesis, septic shock and ovarian failure. Further, ceramide signalling mediates the therapeutic effects of chemotherapy and radiation in some cells. An understanding of the mechanisms by which ceramide regulates physiological and pathological events in specific cells may provide new targets for pharmacological intervention.
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Affiliation(s)
- S Mathias
- Laboratory of Signal Transduction, Memorial Sloan-Kettering Cancer Center, 1275 York Ave., New York, NY 10021, USA
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131
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Shaul PW, Anderson RG. Role of plasmalemmal caveolae in signal transduction. THE AMERICAN JOURNAL OF PHYSIOLOGY 1998; 275:L843-51. [PMID: 9815100 DOI: 10.1152/ajplung.1998.275.5.l843] [Citation(s) in RCA: 211] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Caveolae are specialized plasmalemmal microdomains originally studied in numerous cell types for their involvement in the transcytosis of macromolecules. They are enriched in glycosphingolipids, cholesterol, sphingomyelin, and lipid-anchored membrane proteins, and they are characterized by a light buoyant density and resistance to solubilization by Triton X-100 at 4 degreesC. Once the identification of the marker protein caveolin made it possible to purify this specialized membrane domain, it was discovered that caveolae also contain a variety of signal transduction molecules. This includes G protein-coupled receptors, G proteins and adenylyl cyclase, molecules involved in the regulation of intracellular calcium homeostasis, and their effectors including the endothelial isoform of nitric oxide synthase, multiple components of the tyrosine kinase-mitogen-activated protein kinase pathway, and numerous lipid signaling molecules. More recent work has indicated that caveolae further serve to compartmentalize, modulate, and integrate signaling events at the cell surface. This specialized plasmalemmal domain warrants direct consideration in future investigations of both normal and pathological signal transduction in pulmonary cell types.
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Affiliation(s)
- P W Shaul
- Department of Pediatrics, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75235-9063, USA
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132
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Abstract
The cell biology of caveolae is a rapidly growing area of biomedical research. Caveolae are known primarily for their ability to transport molecules across endothelial cells, but modern cellular techniques have dramatically extended our view of caveolae. They form a unique endocytic and exocytic compartment at the surface of most cells and are capable of importing molecules and delivering them to specific locations within the cell, exporting molecules to extracellular space, and compartmentalizing a variety of signaling activities. They are not simply an endocytic device with a peculiar membrane shape but constitute an entire membrane system with multiple functions essential for the cell. Specific diseases attack this system: Pathogens have been identified that use it as a means of gaining entrance to the cell. Trying to understand the full range of functions of caveolae challenges our basic instincts about the cell.
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133
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Galbiati F, Volonte D, Gil O, Zanazzi G, Salzer JL, Sargiacomo M, Scherer PE, Engelman JA, Schlegel A, Parenti M, Okamoto T, Lisanti MP. Expression of caveolin-1 and -2 in differentiating PC12 cells and dorsal root ganglion neurons: caveolin-2 is up-regulated in response to cell injury. Proc Natl Acad Sci U S A 1998; 95:10257-62. [PMID: 9707634 PMCID: PMC21495 DOI: 10.1073/pnas.95.17.10257] [Citation(s) in RCA: 142] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
Caveolae are cholesterol/sphingolipid-rich microdomains of the plasma membrane that have been implicated in signal transduction and vesicular trafficking. Caveolins are a family of caveolae-associated integral membrane proteins. Caveolin-1 and -2 show the widest range of expression, whereas caveolin-3 expression is restricted to muscle cell types. It has been previously reported that little or no caveolin mRNA species are detectable in the brain by Northern blot analyses or in neuroblastoma cell lines. However, it remains unknown whether caveolins are expressed within neuronal cells. Here we demonstrate the expression of caveolin-1 and -2 in differentiating PC12 cells and dorsal root ganglion (DRG) neurons by using mono-specific antibody probes. In PC12 cells, caveolin-1 expression is up-regulated on day 4 of nerve growth factor (NGF) treatment, whereas caveolin-2 expression is transiently up-regulated early in the differentiation program and then rapidly down-regulated. Interestingly, caveolin-2 is up-regulated in response to the mechanical injury of differentiated PC12 cells; up-regulation of caveolin-2 under these conditions is strictly dependent on continued treatment with NGF. Robust expression of caveolin-1 and -2 is also observed along the entire cell surface of DRG neurons, including high levels on growth cones. These findings demonstrate that neuronal cells express caveolins.
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Affiliation(s)
- F Galbiati
- Department of Molecular Pharmacology, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461, USA
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134
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Waugh MG, Lawson D, Tan SK, Hsuan JJ. Phosphatidylinositol 4-phosphate synthesis in immunoisolated caveolae-like vesicles and low buoyant density non-caveolar membranes. J Biol Chem 1998; 273:17115-21. [PMID: 9642278 DOI: 10.1074/jbc.273.27.17115] [Citation(s) in RCA: 88] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
This study examined phosphatidylinositol 4-phosphate (PtdIns4P) synthesis in caveolae that have been suggested to be discrete signaling microdomains of the plasma membrane and are enriched in the marker protein caveolin. Caveolin-rich light membranes (CLMs) were isolated from A431 cells by detergent-free, discontinuous density-gradient centrifugation method. The CLM fraction was separated from the bulk of the cellular protein and was greatly enriched in PtdIns, PtdIns4P, and phosphatidylinositol 4, 5-bisphosphate (PtdIns(4,5)P2) and an adenosine-sensitive type II PtdIns 4-kinase activity. Preparation of CLMs by an OptiPrep-based cell fractionation procedure confirmed the co-localization of PtdIns 4-kinase and caveolin. Electron microscopy confirmed that an anti-caveolin antiserum immunopurified vesicles from CLMs that were within the size range described for caveolae in other systems. Co-immunoprecipitated PtdIns 4-kinase activity could utilize endogenous PtdIns, present within the caveolae-like vesicles, to produce PtdIns4P. The addition of recombinant phosphatidylinositol transfer protein increased PtdIns 4-kinase activity both in immunoisolated caveolae and CLMs. However, less than 1% of the total cellular PtdIns and PtdIns 4-kinase activity was present in caveolae-like vesicles, indicating that non-caveolar light membrane rafts are the main site for cellular PtdIns4P production.
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Affiliation(s)
- M G Waugh
- Ludwig Institute for Cancer Research, University College London Medical School, Courtauld Building, 91 Riding House Street, London W1P 8BT, United Kingdom
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135
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Abstract
The neurotrophins are a family of growth factors involved in the survival and differentiation of specific populations of neurons and glial cells. Many of the trophic signals elicited by neurotrophins are initiated by the binding of these molecules to various Trk tyrosine kinase receptors. In contrast, recent data suggest that neurotrophin-mediated death signals are generated through the interaction of nerve growth factor with the low-affinity neurotrophin receptor, p75NTR, Neurotrophins may signal through p75NTR by stimulating sphingomyelin hydrolysis and generating ceramide in primary cultures of neurons and glial cells as well as in fibroblasts heterologously expressing p75NTR. The biochemical characteristics of p75NTR-dependent ceramide generation are discussed relative to the role of ceramide in p75NTR-dependent apoptosis and the activation of NF-kappa B.
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Affiliation(s)
- R T Dobrowsky
- Department of Pharmacology and Toxicology, University of Kansas, Lawrence 66045, USA.
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136
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Lin X, Hengartner MO, Kolesnick R. Caenorhabditis elegans contains two distinct acid sphingomyelinases. J Biol Chem 1998; 273:14374-9. [PMID: 9603947 DOI: 10.1074/jbc.273.23.14374] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Mounting evidence supports a role for acid sphingomyelinase (ASM) in cellular stress signaling. Only murine and human sphingomyelinases have been defined at the molecular level. These enzymes are the products of a conserved gene and at the amino acid level share 82% identity. In this study, we show that the nematode Caenorhabditis elegans possesses two ASMs, termed ASM-1 and ASM-2 encoded by two distinct genes, but lacks detectable neutral sphingomyelinase activity. The C. elegans ASMs are about 30% identical with each other and with the human and murine enzymes. The conserved regions include a saposin-like domain, proline-rich domain, and a putative signal peptide. In addition, 16 cysteines distributed throughout the molecules, and selected glycosylation sites, are conserved. The expression of these genes in C. elegans is regulated during development. Asm-1 is preferentially expressed in the embryo, whereas asm-2 is predominantly expressed in postembryonic stages. When transfected as Flag-tagged proteins into COS-7 cells, ASM-1 is found almost entirely in a secreted form whereas only 20% of ASM-2 is secreted. Only the secreted forms display enzymatic activity. Furthermore, ASM-2 requires addition of Zn2+ to be fully active, whereas ASM-1 is active in the absence of cation. C. elegans is the first organism to display two ASMs. This finding suggests the existence of an ASM gene family.
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Affiliation(s)
- X Lin
- Laboratory of Signal Transduction, Memorial Sloan-Kettering Cancer Center, New York, New York 10021, USA
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137
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Affiliation(s)
- A Gómez-Muñoz
- Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias, Universidad del País Vasco, Apartado 644, Bilbao 48080, Spain.
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138
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Okamoto T, Schlegel A, Scherer PE, Lisanti MP. Caveolins, a family of scaffolding proteins for organizing "preassembled signaling complexes" at the plasma membrane. J Biol Chem 1998; 273:5419-22. [PMID: 9488658 DOI: 10.1074/jbc.273.10.5419] [Citation(s) in RCA: 1172] [Impact Index Per Article: 45.1] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Affiliation(s)
- T Okamoto
- Department of Neurosciences, Cleveland Clinic Foundation, Cleveland, Ohio 44195, USA
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139
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Ariga T, Jarvis WD, Yu RK. Role of sphingolipid-mediated cell death in neurodegenerative diseases. J Lipid Res 1998. [DOI: 10.1016/s0022-2275(20)34198-5] [Citation(s) in RCA: 138] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
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