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Abstract
The protein kinase Akt is activated in a wide variety of cancers, and this activation results in enhanced resistance to apoptosis through multiple mechanisms. This article reviews the control of Akt activation by the opposing actions of the oncogene phosphoinositide 3-kinase (PI3-K) and the tumor suppressor phosphatase and tensin homolog deleted on chromosome 10. The activation of Akt by transforming mutations, such as the amplification of HER-2/neu in breast cancer and the formation of the BCR/ABL fusion gene in chronic myelogenous leukemia, seems to be essential for the transforming activity of these oncogenes. We discuss several of the proposed mechanisms for the antiapoptotic effect of activated Akt, including the inhibition of the proapoptotic protein Bad, downregulation of death receptors, and enhancement of the glycolytic rate. Increased glycolysis is seen in many malignancies and forms the basis for the increasing use of positron emission tomography imaging for diagnosis and staging. Finally, we discuss rapamycin and its analogs, which are now in trials as antineoplastic therapy; these agents show particular promise in tumors in which Akt has been activated.
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Affiliation(s)
- James E Thompson
- University of Pennsylvania, Abramson Family Cancer Research Institute, 421 Curie Blvd, Room 450 BRB II/III, Philadelphia, PA 19104-6160, USA
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102
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Colombaioni L, Garcia-Gil M. Sphingolipid metabolites in neural signalling and function. ACTA ACUST UNITED AC 2004; 46:328-55. [PMID: 15571774 DOI: 10.1016/j.brainresrev.2004.07.014] [Citation(s) in RCA: 90] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/26/2004] [Indexed: 11/20/2022]
Abstract
Sphingolipid metabolites, such as ceramide, sphingosine, sphingosine-1-phosphate (S1P) and complex sphingolipids (gangliosides), are recognized as molecules capable of regulating a variety of cellular processes. The role of sphingolipid metabolites has been studied mainly in non-neuronal tissues. These studies have underscored their importance as signals transducers, involved in control of proliferation, survival, differentiation and apoptosis. In this review, we will focus on studies performed over the last years in the nervous system, discussing the recent developments and the current perspectives in sphingolipid metabolism and functions.
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103
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Wadsworth TL, Carroll JM, Mallinson RA, Roberts CT, Roselli CE. Saw palmetto extract suppresses insulin-like growth factor-I signaling and induces stress-activated protein kinase/c-Jun N-terminal kinase phosphorylation in human prostate epithelial cells. Endocrinology 2004; 145:3205-14. [PMID: 15033918 DOI: 10.1210/en.2003-1716] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
A common alternative therapy for benign prostatic hyperplasia (BPH) is the extract from the fruit of saw palmetto (SPE). BPH is caused by nonmalignant growth of epithelial and stromal elements of the prostate. IGF action is important for prostate growth and development, and changes in the IGF system have been documented in BPH tissues. The main signaling pathways activated by the binding of IGF-I to the IGF-I receptor (IGF-IR) are the ERK arm of the MAPK cascade and the phosphoinositol-3-kinase (PI3K)/protein kinase B (PKB/Akt) cascade. We tested the hypothesis that SPE suppresses growth and induces apoptosis in the P69 prostate epithelial cell line by inhibiting IGF-I signaling. Treatment with 150 microg/ml SPE for 24 h decreased IGF-I-induced proliferation of P69 cells and induced cleavage of the enzyme poly(ADP-ribose)polymerase (PARP), an index of apoptosis. Treatment of serum-starved P69 cells with 150 microg/ml SPE for 6 h reduced IGF-I-induced phosphorylation of Akt (assessed by Western blot) and Akt activity (assessed by an Akt kinase assay). Western blot analysis showed that SPE reduced IGF-I-induced phosphorylation of the adapter protein insulin receptor substrate-1 and decreased downstream effects of Akt activation, including increased cyclin D1 levels and phosphorylation of glycogen synthase kinase-3 and p70(s6k). There was no effect on IGF-I-induced phosphorylation of MAPK, IGF-IR, or Shc. Treatment of starved cells with SPE alone induced phosphorylation the proapoptotic protein JNK. SPE treatment may relieve symptoms of BPH, in part, by inhibiting specific components of the IGF-I signaling pathway and inducing JNK activation, thus mediating antiproliferative and proapoptotic effects on prostate epithelia.
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Affiliation(s)
- Teri L Wadsworth
- Department of Physiology and Pharmacology L334, Oregon Health and Science University, 3181 Sam Jackson Park Road, Portland, Oregon 97239, USA
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104
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Stratford S, Hoehn KL, Liu F, Summers SA. Regulation of insulin action by ceramide: dual mechanisms linking ceramide accumulation to the inhibition of Akt/protein kinase B. J Biol Chem 2004; 279:36608-15. [PMID: 15220355 DOI: 10.1074/jbc.m406499200] [Citation(s) in RCA: 309] [Impact Index Per Article: 15.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
The sphingolipid ceramide negatively regulates insulin action by inhibiting Akt/protein kinase B (PKB), a serine/threonine kinase that is a central regulator of glucose uptake and anabolic metabolism. Despite considerable attention, the molecular mechanism accounting for this action of ceramide has remained both elusive and controversial. Herein we utilized deletion constructs encoding two different functional domains of Akt/PKB to identify which region of the enzyme conferred responsiveness to ceramide. Surprisingly the findings obtained with these separate domains reveal that ceramide blocks insulin stimulation of Akt/PKB by two independent mechanisms. First, using the isolated pleckstrin homology domain, we found that ceramide specifically blocks the translocation of Akt/PKB, but not its upstream activator phosphoinositide-dependent kinase-1, to the plasma membrane. Second, using a construct lacking this pleckstrin homology domain, which does not require translocation for activation, we found that ceramide stimulates the dephosphorylation of Akt/PKB by protein phosphatase 2A. Collectively these findings identify at least two independent mechanisms by which excessive ceramide accumulation in peripheral tissues could contribute to the development of insulin resistance. Moreover the results obtained provide a unifying theory to account for the numerous dissenting reports investigating the actions of ceramide toward Akt/PKB.
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Affiliation(s)
- Suzanne Stratford
- Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, CO 80523-1870, USA
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105
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Park IN, Cho IJ, Kim SG. Ceramide negatively regulates glutathione S-transferase gene transactivation via repression of hepatic nuclear factor-1 that is degraded by the ubiquitin proteasome system. Mol Pharmacol 2004; 65:1475-84. [PMID: 15155840 DOI: 10.1124/mol.65.6.1475] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The level of cellular ceramide, an apoptotic rheostat, is increased by sphingomyelinase or de novo synthesis. The expression of the glutathione S-transferase (GST) gene, whose induction accounts for cell viability, is regulated by activation of CCAAT/enhancer binding protein-beta (C/EBPbeta) and NF-E2-related factor-2 (Nrf2). Hepatic nuclear factor-1 (HNF1) is a transcription factor necessary for cell survival. This study investigated the role of HNF1 in GSTA2 gene transactivation, the ubiquitin proteasomal degradation of HNF1, and the inhibition of activating HNF1 by ceramide for GSTA2 repression. C2-ceramide (C2), a cell-permeable analog, repressed the GSTA2 expression in H4IIE cells, whereas dihydro-C2, an inactive analog, had no effect. Immunoblot, immunocytochemical, and gel shift analyses revealed that C2 decreased the level of nuclear HNF1 and protein binding to the HNF response element (HRE). Deletion of the HRE or the GSTA2 gene promoter region containing the HRE reduced luciferase reporter expression. Immunoprecipitation and immunoblot analyses showed that C2 decreased the level of ubiquitinated HNF1, which was reversed by treatment with MG132, a proteasome inhibitor. C2 suppressed GSTA2 induction by oltipraz via inhibition of inducible HNF1 DNA binding. The functional role of HRE for C2 repression of GSTA2 gene transactivation by oltipraz was verified by both the luciferase reporter gene expression and the transfection experiment with DeltaHNF-pGL-1651 lacking the HRE. C2 similarly repressed the induction of GSTA2 promoter-luciferase by tert-butylhydroquinone via HNF1 suppression, suggesting that constitutive HNF1 activation is required for GSTA2 induction. C2 also inhibited GSTA3/5 expression. In conclusion, the HRE in the GSTA2 promoter region is functionally active for the constitutive and inducible gene expression, and ceramide inhibits GST gene transactivation through decrease in nuclear HNF1, which is degraded by the ubiquitin proteasome system.
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Affiliation(s)
- I-Na Park
- National Research Laboratory, College of Pharmacy and Research Institute of Pharmaceutical Sciences, Seoul National University, Seoul, South Korea
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106
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Cui J, Engelman RM, Maulik N, Das DK. Role of ceramide in ischemic preconditioning. J Am Coll Surg 2004; 198:770-7. [PMID: 15110811 DOI: 10.1016/j.jamcollsurg.2003.12.016] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2003] [Accepted: 12/08/2003] [Indexed: 01/02/2023]
Abstract
BACKGROUND A recent study showed increased myocardial content of ceramide and sphingosine during preconditioning (PC). Because sphingosine-1-phosphate, a metabolite of ceramide, may function as an antiapoptotic factor, we hypothesized the increased ceramide during PC may be heart's effort to harness its own protection. STUDY DESIGN The isolated hearts were divided into five groups: 1) perfused for 3 hours 45 minutes with KHB buffer (control); 2) perfused with buffer for 45 minutes followed by 30 minutes of ischemia and 2 hours of reperfusion; 3) perfused for 15 minutes with desipramine followed by 30 minutes of perfusion with buffer, 30 minutes of ischemia, and 2 hours of reperfusion; 4) preconditioned followed by 30 minutes of ischemia and 2 hours of reperfusion; and 5) the same as 4), but preperfused for 15 minutes with desipramine. Myocardial preservation was assessed by examining left ventricular function, infarct size, and cardiomyocyte apoptosis. RESULTS Ischemia/reperfusion-mediated cardiac dysfunction was partially restored with desipramine. PC improved postischemic ventricular recovery and reduced myocardial infarct size and cardiomyocyte apoptosis. The cardioprotective abilities of PC were abolished with desipramine, which also downregulated a PC-mediated increase in antiapoptotic protein Bcl-2. The apparent paradoxical results of desipramine can be explained by the increase in proapoptotic ceramide content in the ischemic reperfused heart that was blocked with desipramine and an increase in antiapoptotic sphingosine-1-p content in the preconditioned heart that was inhibited with desipramine. CONCLUSIONS The results suggested for the first time that sphingolipid can induce the expression of Bcl-2 warranting its clinical use as a pharmacologic PC agent.
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Affiliation(s)
- Jianhua Cui
- Cardiovascular Research Center, School of Medicine, University of Connecticut Health Center, Farmington, CT 06030-1110, USA
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107
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Straczkowski M, Kowalska I, Nikolajuk A, Dzienis-Straczkowska S, Kinalska I, Baranowski M, Zendzian-Piotrowska M, Brzezinska Z, Gorski J. Relationship between insulin sensitivity and sphingomyelin signaling pathway in human skeletal muscle. Diabetes 2004; 53:1215-21. [PMID: 15111489 DOI: 10.2337/diabetes.53.5.1215] [Citation(s) in RCA: 195] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
In vitro studies revealed that insulin resistance might be associated with the intracellular formation of ceramide, the second messenger in the sphingomyelin signaling pathway. The aim of the present study was to examine the content and composition of fatty acids in ceramide and sphingomyelin in human muscle and to evaluate their relationships with insulin sensitivity. The study was conducted on 27 male subjects with normal glucose tolerance. Euglycemic-hyperinsulinemic clamps and biopsies of vastus lateralis muscle were performed. In 10 subjects, additional biopsies were taken after a 4-h clamp and after a clamp with concurrent Intralipid/heparin infusion. We identified 13 ceramides and sphingomyelins according to fatty acid residues. Insulin sensitivity was related to total ceramide content (r = -0.49, P = 0.01) and to ceramide consisting of palmitic (r = -0.48, P = 0.011), palmitoleic (r = -0.45, P = 0.019), mirystic (r = -0.42, P = 0.028), and nervonic acid (r = -0.39, P = 0.047). Hyperinsulinemia did not affect estimated muscle parameters. Intralipid/heparin infusion resulted in a 24.73% decrease in insulin sensitivity (P = 0.007) and a 47.81% increase in ceramide content (P = 0.005). These changes were significantly related to each other (r = -0.64, P = 0.046). A relationship with the decrease in insulin sensitivity was also observed for ceramides consisting of palmitic (r = -0.68, P = 0.03) and linoleic (r = -0.66, P = 0.038) acid. Our data indicate that the sphingomyelin signaling pathway in muscle might be an important factor determining the development of insulin resistance in humans.
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Affiliation(s)
- Marek Straczkowski
- Department of Endocrinology, Diabetology and Internal Medicine, Medical University Bialystok, M.C. Sklodowskiej 24a, 15-276 Bialystok, Poland.
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108
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Chalfant CE, Szulc Z, Roddy P, Bielawska A, Hannun YA. The structural requirements for ceramide activation of serine-threonine protein phosphatases. J Lipid Res 2004; 45:496-506. [PMID: 14657198 DOI: 10.1194/jlr.m300347-jlr200] [Citation(s) in RCA: 112] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The protein phosphatases1 (PP1) and 2A (PP2A) serve as ceramide-activated protein phosphatases (CAPP). In this study, the structural requirements for interaction between ceramide and CAPP were determined. D-erythro-C(6) ceramide activated the catalytic subunit of PP2A (PP2Ac) approximately 3-fold in a stereospecific manner. In contrast, saturation of the 4-5 double bond, producing D-erythro-dihydro C(6) ceramide, inhibited PP2Ac (IC(50) = 8.5 microM). Furthermore, phyto C(6) ceramide, D-erythro-dehydro C(6) ceramide, and D-erythro-cis-C(6) ceramide had no effect on PP2Ac activity. Modification of the sphingoid chain also abolished the ability of ceramide to activate PP2Ac. Further studies demonstrated the requirement for the amide group, the primary hydroxyl group, and the secondary hydroxyl group of the sphingoid backbone for activation of PP2Ac through the synthesis and evaluation of D-erythro-urea C(6) ceramide, L-erythro-urea C(6) ceramide, D-erythro-N-methyl C(6) ceramide, D-erythro-L-O-methyl C(6) ceramide, D-erythro-3-O-methyl C(6) ceramide, and (2S) 3-keto C(6) ceramide. None of these compounds induced significant activation of PP2Ac. Liposome binding studies were also conducted using analogs of D-erythro-C C(6) ceramide, and the results showed that the ability of ceramide analogs to influence CAPP (activation or inhibition) was associated with the ability of the analogs to bind to CAPP. This study demonstrates strict structural requirements for interaction of ceramide with CAPP, and disclose ceramide as a very specific regulator of CAPP. The studies also begin to define features that transform ceramide analogs into inhibitors of CAPP.
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Affiliation(s)
- Charles E Chalfant
- Department of Biochemistry & Molecular Biology, Medical University of South Carolina, and Ralph H Johnson Veterans Administration Mecial Center, Charleston, SC, USA.
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109
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Powell DJ, Hajduch E, Kular G, Hundal HS. Ceramide disables 3-phosphoinositide binding to the pleckstrin homology domain of protein kinase B (PKB)/Akt by a PKCzeta-dependent mechanism. Mol Cell Biol 2003; 23:7794-808. [PMID: 14560023 PMCID: PMC207567 DOI: 10.1128/mcb.23.21.7794-7808.2003] [Citation(s) in RCA: 276] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Ceramide is generated in response to numerous stress-inducing stimuli and has been implicated in the regulation of diverse cellular responses, including cell death, differentiation, and insulin sensitivity. Recent evidence indicates that ceramide may regulate these responses by inhibiting the stimulus-mediated activation of protein kinase B (PKB), a key determinant of cell fate and insulin action. Here we show that inhibition of this kinase involves atypical PKCzeta, which physically interacts with PKB in unstimulated cells. Insulin reduces the PKB-PKCzeta interaction and stimulates PKB. However, dissociation of the kinase complex and the attendant hormonal activation of PKB were prevented by ceramide. Under these circumstances, ceramide activated PKCzeta, leading to phosphorylation of the PKB-PH domain on Thr(34). This phosphorylation inhibited phosphatidylinositol 3,4,5-trisphosphate (PIP(3)) binding to PKB, thereby preventing activation of the kinase by insulin. In contrast, a PKB-PH domain with a T34A mutation retained the ability to bind PIP(3) even in the presence of a ceramide-activated PKCzeta and, as such, expression of PKB T34A mutant in L6 cells was resistant to inhibition by ceramide treatment. Inhibitors of PKCzeta and a kinase-dead PKCzeta both antagonized the inhibitory effect of ceramide on PKB. Since PKB confers a prosurvival signal and regulates numerous pathways in response to insulin, suppressing its activation by a PKCzeta-dependent process may be one mechanism by which ceramide promotes cell death and induces insulin resistance.
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Affiliation(s)
- Darren J Powell
- Division of Molecular Physiology, MRC Protein Phosphorylation Unit, MSI/WTB Complex, Faculty of Life Sciences, University of Dundee, Dundee DD1 5EH, United Kingdom
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110
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Kang JQ, Chong ZZ, Maiese K. Akt1 protects against inflammatory microglial activation through maintenance of membrane asymmetry and modulation of cysteine protease activity. J Neurosci Res 2003; 74:37-51. [PMID: 13130504 DOI: 10.1002/jnr.10740] [Citation(s) in RCA: 76] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
In several cell systems, protein kinase B (Akt1) can promote cell growth and development, but the "antiapoptotic" pathways of this kinase that may offer protection against cellular inflammatory demise have not been defined. Given that early cellular membrane phosphatidylserine exposure is a critical component of apoptosis, we investigated the role of Akt1 during neuronal apoptotic injury. By employing differentiated SH-SY5Y neuronal cells that overexpress a constitutively active form of Akt1 (myristoylated Akt1), free radical-induced cell injury was assessed through trypan blue dye exclusion, DNA fragmentation, membrane phosphatidylserine exposure, protein kinase B phosphorylation, cysteine protease activity, and mitochondrial membrane potential. Membrane phosphatidylserine exposure was both necessary and sufficient for microglial activation, insofar as cotreatment with an antiphosphatidylserine receptor-neutralizing antibody could prevent microglial activity following neuronal loss of membrane asymmetry. Furthermore, expression of myristoylated Akt1 not only prevented cell injury through the prevention of membrane phosphatidylserine exposure and genomic DNA fragmentation but also inhibited microglial activation and proliferation that required the inhibition of caspase 9-, caspase 3-, and caspase 1-like activities linked to cytochrome c release. Interestingly, Akt1 modulation of membrane phosphatidylserine exposure was primarily through caspase 1 activity. Removal of Akt1 activity abolished neuronal protection, suggesting that Akt1 functions as a critical pathway for the maintenance of cellular integrity and the prevention of phagocytic cellular removal during neurodegenerative insults.
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Affiliation(s)
- Jing-Qiong Kang
- Division of Cellular and Molecular Cerebral Ischemia, Wayne State University School of Medicine, Detroit, Michigan 48201, USA
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111
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Borgatti P, Martelli AM, Tabellini G, Bellacosa A, Capitani S, Neri LM. Threonine 308 phosphorylated form of Akt translocates to the nucleus of PC12 cells under nerve growth factor stimulation and associates with the nuclear matrix protein nucleolin. J Cell Physiol 2003; 196:79-88. [PMID: 12767043 DOI: 10.1002/jcp.10279] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
We have examined the issue of whether or not in PC12 cells it may be observed a nerve growth factor (NGF) nuclear translocation of an active (phosphorylated) Akt. Western blot analysis with antibodies to either total or phosphorylated Akt showed a maximal nuclear translocation after 15 min of NGF stimulation. NGF increased rapidly and transiently the enzymatic activity of immunoprecipitable nuclear Akt and after 45 min the values returned to a level close to the basal one. Enzyme translocation was blocked by the selective phosphoinositide 3-kinase inhibitor, LY294002. Confocal microscopy of samples stained with antibody to Akt showed an evident increase in immunostaining intensity in the nuclear interior after NGF treatment. Treatment of cells with inhibitors of protein phosphatase PP2A, calyculin A, or okadaic acid, maintained the phosphorylation levels of nuclear Akt. Immunoprecipitation experiments revealed an association between Akt and PP2A that was maximal when nuclear Akt activity was decreased. Both total and active Akt associated with the nuclear matrix and, in particular, with the protein nucleolin, with which Akt co-immunoprecipitated. These findings strongly suggest that the intranuclear translocation of active Akt is an important step in the signaling pathways elicited by the neurotrophin NGF and that the intranuclear control of Akt is achieved through the action of PP2A.
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Affiliation(s)
- Paola Borgatti
- Dipartimento di Morfologia ed Embriologia, Sezione di Anatomia Umana, Università di Ferrara, Ferrara, Italy
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112
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Chavez JA, Knotts TA, Wang LP, Li G, Dobrowsky RT, Florant GL, Summers SA. A role for ceramide, but not diacylglycerol, in the antagonism of insulin signal transduction by saturated fatty acids. J Biol Chem 2003; 278:10297-303. [PMID: 12525490 DOI: 10.1074/jbc.m212307200] [Citation(s) in RCA: 466] [Impact Index Per Article: 22.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Multiple studies suggest that lipid oversupply to skeletal muscle contributes to the development of insulin resistance, perhaps by promoting the accumulation of lipid metabolites capable of inhibiting signal transduction. Herein we demonstrate that exposing muscle cells to particular saturated free fatty acids (FFAs), but not mono-unsaturated FFAs, inhibits insulin stimulation of Akt/protein kinase B, a serine/threonine kinase that is a central mediator of insulin-stimulated anabolic metabolism. These saturated FFAs concomitantly induced the accumulation of ceramide and diacylglycerol, two products of fatty acyl-CoA that have been shown to accumulate in insulin-resistant tissues and to inhibit early steps in insulin signaling. Preventing de novo ceramide synthesis negated the antagonistic effect of saturated FFAs toward Akt/protein kinase B. Moreover, inducing ceramide buildup recapitulated and augmented the inhibitory effect of saturated FFAs. By contrast, diacylglycerol proved dispensable for these FFA effects. Collectively these results identify ceramide as a necessary and sufficient intermediate linking saturated fats to the inhibition of insulin signaling.
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Affiliation(s)
- Jose Antonio Chavez
- Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins 80523-1870, USA
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113
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Stoica BA, Movsesyan VA, Lea PM, Faden AI. Ceramide-induced neuronal apoptosis is associated with dephosphorylation of Akt, BAD, FKHR, GSK-3beta, and induction of the mitochondrial-dependent intrinsic caspase pathway. Mol Cell Neurosci 2003; 22:365-82. [PMID: 12691738 DOI: 10.1016/s1044-7431(02)00028-3] [Citation(s) in RCA: 130] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Neuronal apoptosis has been implicated as an important mechanism of cell death in acute and chronic neurodegenerative disorders. Ceramide is a product of sphingolipid metabolism which induces neuronal apoptosis in culture, and ceramide levels increase in neurons during various conditions associated with cell death. In this study we investigate the mechanism of ceramide-induced apoptosis in primary cortical neuronal cells. We show that ceramide treatment initiates a cascade of biochemical alterations associated with cell death: earliest signal transduction changes involve Akt dephosphorylation and inactivation followed by dephosphorylation of proapoptotic regulators such as BAD (proapoptotic Bcl-2 family member), Forkhead family transcription factors, glycogen synthase kinase 3-beta, mitochondrial depolarization and permeabilization, release of cytochrome c into the cytosol, and caspase-3 activation. Bongkrekic acid, an agent that inhibits mitochondrial depolarization, significantly reduces ceramide-induced cell death and correlated caspase-3 activation. Together, these data demonstrate the importance of the mitochondrial-dependent intrinsic pathway of caspase activation for ceramide-induced neuronal apoptosis.
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Affiliation(s)
- Bogdan A Stoica
- Department of Neuroscience, Georgetown University Medical Center, Washington, DC 20057, USA
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114
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Rölz W, Xin C, Ren S, Pfeilschifter J, Huwiler A. Interleukin-1beta inhibits ATP-induced protein kinase B activation in renal mesangial cells by two different mechanisms: the involvement of nitric oxide and ceramide. Br J Pharmacol 2003; 138:461-8. [PMID: 12569071 PMCID: PMC1573688 DOI: 10.1038/sj.bjp.0705064] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
1 Extracellular nucleotides, like ATP and UTP, have been shown to activate the protein kinase B (PKB) pathway in mesangial cells. In this study we report that the pro-inflammatory cytokine interleukin-1beta (IL-1beta) inhibits ATP-induced PKB activation. 2 Pretreatment of mesangial cells with IL-1beta leads to a time-dependent decrease of ATP-induced PKB phosphorylation. Maximal inhibition is seen after 6 h of pretreatment. Incubating cells with IL-1beta in the presence of the NO synthase inhibitor, N-monomethyl-L-arginine (L-NMMA), reversed the IL-1beta inhibition of PKB activity. A similar decrease in ATP-evoked PKB activation is obtained when cells were pretreated with the nitric oxide (NO) donor, (Z)-1-[2-Aminoethyl)-N-(2-ammonioethyl)amino]diazen-1-ium-1,2-diolate (Deta-NO), but not with the cell-permeable cGMP analogue, 8-bromo-cGMP. 3 The NO- and IL-1beta-mediated delayed inhibition of PKB activity is completely reversed by the phosphatase inhibitor calyculin A, but not by ocadaic acid, suggesting that NO upregulates a protein phosphatase activity, which most probably belongs to the group of protein phosphatases type 1. 4 In addition, IL-1beta also triggers a short-term and transient inhibitory effect on ATP-induced PKB activation which is maximal after 2-5 min of pre-incubation with IL-1beta. This effect occurs independently of NO generation, because no NO synthase is expressed at that time, and consequently, L-NMMA does not reverse the effect. Rather an involvement of the sphingolipid ceramide is likely, since IL-1beta triggers rapid ceramide formation and incubation of cells with the cell-permeable C6-ceramide blocked ATP-induced PKB phosphorylation. 5 In summary, our data show that IL-1beta exerts both short-term and long-term inhibitory effects on ATP-stimulated PKB activation, the short-term effect probably involves ceramide formation, whereas the long-term effect is due to inducible NO synthase induction and subsequent NO formation. These results reveal a further facet in the mechanisms of ceramide- and NO-induced cell death, i.e. by turning off the survival signal elicited by PKB.
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Affiliation(s)
- Waltraud Rölz
- Pharmazentrum Frankfurt, Klinikum der Johann Wolfgang Goethe-Universität, Theodor-Stern-Kai 7, D-60590 Frankfurt am Main, Germany
| | - Cuiyan Xin
- Pharmazentrum Frankfurt, Klinikum der Johann Wolfgang Goethe-Universität, Theodor-Stern-Kai 7, D-60590 Frankfurt am Main, Germany
| | - Shuyu Ren
- Pharmazentrum Frankfurt, Klinikum der Johann Wolfgang Goethe-Universität, Theodor-Stern-Kai 7, D-60590 Frankfurt am Main, Germany
| | - Josef Pfeilschifter
- Pharmazentrum Frankfurt, Klinikum der Johann Wolfgang Goethe-Universität, Theodor-Stern-Kai 7, D-60590 Frankfurt am Main, Germany
| | - Andrea Huwiler
- Pharmazentrum Frankfurt, Klinikum der Johann Wolfgang Goethe-Universität, Theodor-Stern-Kai 7, D-60590 Frankfurt am Main, Germany
- Author for correspondence:
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115
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van Blitterswijk WJ, van der Luit AH, Veldman RJ, Verheij M, Borst J. Ceramide: second messenger or modulator of membrane structure and dynamics? Biochem J 2003; 369:199-211. [PMID: 12408751 PMCID: PMC1223095 DOI: 10.1042/bj20021528] [Citation(s) in RCA: 335] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2002] [Revised: 10/30/2002] [Accepted: 10/31/2002] [Indexed: 12/18/2022]
Abstract
The physiological role of ceramide formation in response to cell stimulation remains controversial. Here, we emphasize that ceramide is not a priori an apoptotic signalling molecule. Recent work points out that the conversion of sphingomyelin into ceramide can play a membrane structural (physical) role, with consequences for membrane microdomain function, membrane vesiculation, fusion/fission and vesicular trafficking. These processes contribute to cellular signalling. At the Golgi, ceramide takes part in a metabolic flux towards sphingomyelin, diacylglycerol and glycosphingolipids, which drives lipid raft formation and vesicular transport towards the plasma membrane. At the cell surface, receptor clustering in lipid rafts and the formation of endosomes can be facilitated by transient ceramide formation. Also, signalling towards mitochondria may involve glycosphingolipid-containing vesicles. Ceramide may affect the permeability of the mitochondrial outer membrane and the release of cytochrome c. In the effector phase of apoptosis, the breakdown of plasma membrane sphingomyelin to ceramide is a consequence of lipid scrambling, and may regulate apoptotic body formation. Thus ceramide formation serves many different functions at distinct locations in the cell. Given the limited capacity for spontaneous intracellular diffusion or membrane flip-flop of natural ceramide species, the topology and membrane sidedness of ceramide generation are crucial determinants of its impact on cell biology.
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Affiliation(s)
- Wim J van Blitterswijk
- Division of Cellular Biochemistry, The Netherlands Cancer Institute, Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands.
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116
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Pettus BJ, Chalfant CE, Hannun YA. Ceramide in apoptosis: an overview and current perspectives. BIOCHIMICA ET BIOPHYSICA ACTA 2002; 1585:114-25. [PMID: 12531544 DOI: 10.1016/s1388-1981(02)00331-1] [Citation(s) in RCA: 579] [Impact Index Per Article: 26.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Recent years have witnessed significant advances in the understanding of the role of ceramide in apoptosis. This review summarizes these recent findings and discusses insights from studies of ceramide metabolism, topology, and effector actions. The recent identification of several genes for enzymes of ceramide metabolism, the development of mass spectrometric methods for ceramide analysis, and the increasing molecular and pharmacological tools to probe ceramide metabolism and function promise an accelerated phase in defining the molecular and biochemical details of the role of ceramide in apoptosis.
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Affiliation(s)
- Benjamin J Pettus
- Department of Biochemistry and Molecular Biology, Medical University of South Carolina, Charleston, SC, USA
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117
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Dawson G, Dawson SA, Marinzi C, Dawson PE. Anti-tumor promoting effects of palmitoyl: protein thioesterase inhibitors against a human neurotumor cell line. Cancer Lett 2002; 187:163-8. [PMID: 12359364 DOI: 10.1016/s0304-3835(02)00403-2] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Inhibiting the depalmitoylation of proteins disrupts cell survival signaling in tumor cells and leads to increased cell death. We chemically synthesized a non-hydrolyzable analog of the palmitoyl-cysteine thioester linkage (AcG-alpha-ketoamido-palmitoyl diamino propionate-VKIKK) (DAPKA) and showed that it inhibits palmitoyl:protein thioesterase (PPT1) in an in vitro assay using a specific fluorescent-based (4-methylumbelliferyl-beta-gluco-6-thiopalmitate) assay. We then showed that it killed cultured tumor cells and enhanced the killing of neurotumor cells by chemotherapeutic drugs such as etoposide and adriamycin. Overexpression of PPT1 protected against apoptosis induced by etoposide and the ketoamide and the inhibitory effect of the two was additive.
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Affiliation(s)
- Glyn Dawson
- Department of Pediatrics, University of Chicago, Chicago, IL 60637, USA.
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118
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Martin D, Salinas M, Fujita N, Tsuruo T, Cuadrado A. Ceramide and reactive oxygen species generated by H2O2 induce caspase-3-independent degradation of Akt/protein kinase B. J Biol Chem 2002; 277:42943-52. [PMID: 12213802 DOI: 10.1074/jbc.m201070200] [Citation(s) in RCA: 145] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
This study was designed to elucidate the mechanisms leading to down-regulation of the Akt/protein kinase B (PKB) survival pathway during H2O2-induced cell death. H2O2 produced early activation of Akt/PKB and also DNA damage that was followed by stabilization of p53 levels, formation of reactive oxygen species (ROS), and generation of ceramide through activation of a glutathione-sensitive neutral sphingomyelinase. These events correlated with long term dephosphorylation and subsequent degradation of Akt. A membrane-targeted active Akt version attenuated apoptosis but not necrosis induced by H2O2 and was more resistant to dephosphorylation and proteolysis induced by apoptotic concentrations of H2O2. Proteolysis of Akt was prevented by exogenous addition of glutathione, indicating a role of ROS and ceramide in Akt degradation. However, Akt was degraded similarly in cells transfected with wild type and dominant negative p53 mutant, indicating that degradation of Akt under oxidative injury may be p53-independent. Specific inhibitors of caspase groups I and III prevented proteolysis of Akt/PKB and poly(ADP-ribose) polymerase in cells submitted to apoptotic but not necrotic H2O2 concentrations. Surprisingly, in caspase-3-deficient MCF-7 cells Akt was more sensitive to H2O2-induced degradation than the caspase-3 substrate poly(ADP-ribose) polymerase. Moreover, the Akt/PKB double mutant Akt(D108A,D119A), which is not cleaved by caspase-3, and a triple mutant (D453A,D455A,D456A), which lacks the consensus sequence for caspase-3 cleavage, were also degraded in H2O2-treated cells. Our results suggest that strong oxidants generate intracellular ROS and ceramide which in term lead to down-regulation of Akt by dephosphorylation and caspase-3-independent proteolysis.
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Affiliation(s)
- Daniel Martin
- Departamento de Bioquimica and Instituto de Investigaciones Biomédicas Alberto Sols, Facultad de Medicina, Universidad Autónoma de Madrid, Madrid 28029, Spain
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119
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Neri LM, Borgatti P, Capitani S, Martelli AM. The nuclear phosphoinositide 3-kinase/AKT pathway: a new second messenger system. BIOCHIMICA ET BIOPHYSICA ACTA 2002; 1584:73-80. [PMID: 12385889 DOI: 10.1016/s1388-1981(02)00300-1] [Citation(s) in RCA: 133] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Lipid second messengers, particularly those derived from the polyphosphoinositide cycle, play a pivotal role in several cell signaling networks. Phosphoinositide 3-kinases (PI3Ks) generate specific inositol lipids that have been implicated in a plethora of cell functions. One of the best-characterized targets of PI3K lipid products is the serine/threonine protein kinase Akt. Recent findings have implicated Akt in cancer progression because it stimulates cell proliferation and suppresses apoptosis. Evidence accumulated over the past 15 years has highlighted the presence of an autonomous nuclear inositol lipid metabolism, and suggests that lipid molecules are important components of signaling pathways operating within the nucleus. PI3Ks, their lipid products, and Akt have also been identified at the nuclear level. In this review, we shall summarize the most updated findings about these molecules in relationship with the nuclear compartment and provide an overview of the possible mechanisms by which they regulate important cell functions.
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Affiliation(s)
- Luca M Neri
- Dipartimento di Morfologia ed Embriologia, Sezione di Anatomia Umana, Università di Ferrara, via Fossato di Mortara 66, 44100 Ferrara, Italy.
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120
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Gómez Del Pulgar T, De Ceballos ML, Guzmán M, Velasco G. Cannabinoids protect astrocytes from ceramide-induced apoptosis through the phosphatidylinositol 3-kinase/protein kinase B pathway. J Biol Chem 2002; 277:36527-33. [PMID: 12133838 DOI: 10.1074/jbc.m205797200] [Citation(s) in RCA: 127] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Cannabinoids, the active components of marijuana and their endogenous counterparts, exert many of their actions on the central nervous system by binding to the CB(1) cannabinoid receptor. Different studies have shown that cannabinoids can protect neural cells from different insults. However, those studies have been performed in neurons, whereas no attention has been focused on glial cells. Here we used the pro-apoptotic lipid ceramide to induce apoptosis in astrocytes, and we studied the protective effect exerted by cannabinoids. Results show the following: (i) cannabinoids rescue primary astrocytes from C(2)-ceramide-induced apoptosis in a dose- and time-dependent manner; (ii) triggering of this anti-apoptotic signal depends on the phosphatidylinositol 3-kinase/protein kinase B pathway; (iii) ERK and its downstream target p90 ribosomal S6 kinase might be also involved in the protective effect of cannabinoids; and (iv) cannabinoids protect astrocytes from the cytotoxic effects of focal C(2)-ceramide administration in vivo. In summary, results show that cannabinoids protect astrocytes from ceramide-induced apoptosis via stimulation of the phosphatidylinositol 3-kinase/protein kinase B pathway. These findings constitute the first evidence for an "astroprotective" role of cannabinoids.
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Affiliation(s)
- Teresa Gómez Del Pulgar
- Department of Biochemistry and Molecular Biology I, School of Biology, Complutense University, 28040 Madrid, Spain
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121
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Lou L, Urbani J, Ribeiro-Neto F, Altschuler DL. cAMP inhibition of Akt is mediated by activated and phosphorylated Rap1b. J Biol Chem 2002; 277:32799-806. [PMID: 12089143 DOI: 10.1074/jbc.m201491200] [Citation(s) in RCA: 70] [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
Rap1b has been implicated in the transduction of the cAMP mitogenic signal. Rap1b is phosphorylated and activated by cAMP, and its expression in cells where cAMP is mitogenic leads to an increase in G(1)/S phase entry and tumor formation. The PCCL3 thyroid follicular cells represent a differentiated and physiologically relevant system that requires thyrotropin (TSH), acting via cAMP, for a full mitogenic response. In this model system, cAMP stimulation of DNA synthesis requires activation and phosphorylation of Rap1b by the cAMP-dependent protein kinase A (PKA). This scenario presents the challenge of identifying biochemical processes involved in the phosphorylation-dependent Rap1b mitogenic action. In thyroid cells, Akt has been implicated in the stimulation of cell proliferation by TSH and cAMP. However, the mechanism(s) by which cAMP regulates Akt activity remains unclear. In this study we show that in PCCL3 cells 1) TSH inhibits Akt activity via cAMP and PKA; 2) Rap1b is required for cAMP inhibition of Akt; and 3) transduction of the cAMP signal into Akt requires activation as well as phosphorylation of Rap1b by PKA.
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Affiliation(s)
- Liguang Lou
- Department of Pharmacology, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, USA
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122
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Cui TX, Nakagami H, Nahmias C, Shiuchi T, Takeda-Matsubara Y, Li JM, Wu L, Iwai M, Horiuchi M. Angiotensin II subtype 2 receptor activation inhibits insulin-induced phosphoinositide 3-kinase and Akt and induces apoptosis in PC12W cells. Mol Endocrinol 2002; 16:2113-23. [PMID: 12198247 DOI: 10.1210/me.2001-0284] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
In the present study, we identified novel negative cross-talk between the angiotensin II subtype 2 (AT2) receptor and insulin receptor signaling in the regulation of phosphoinositide 3-kinase (PI3K), Akt, and apoptosis in rat pheochromocytoma cell line, PC12W cells, which exclusively express AT2 receptor. We demonstrated that insulin-mediated insulin receptor substrate (IRS)-2-associated PI3K activity was inhibited by AT2 receptor stimulation, whereas IRS-1-associated PI3K activity was not significantly influenced. AT2 receptor stimulation did not change insulin-induced tyrosine phosphorylation of IRS-2 or its association with the p85alpha subunit of PI3K, but led to a significant reduction of insulin-induced p85alpha phosphorylation. AT2 receptor stimulation increased the association of a protein tyrosine phosphatase, SHP-1, with IRS-2. Moreover, we demonstrated that AT2 receptor stimulation inhibited insulin-induced Akt phosphorylation and that insulin-mediated antiapoptotic effect was also blocked by AT2 receptor activation. Overexpression of a catalytically inactive dominant negative SHP-1 markedly attenuated the AT2 receptor- mediated inhibition of IRS-2-associated PI3K activity, Akt phosphorylation, and antiapoptotic effect induced by insulin. Taken together, these results indicate that AT2 receptor-mediated activation of SHP-1 and the consequent inhibition IRS-2-associated PI3K activity contributed at least partly to the inhibition of Akt phosphorylation, thereby inducing apoptosis.
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Affiliation(s)
- Tai-Xing Cui
- Department of Medical Biochemistry, Ehime University School of Medicine, Ehime 791-0295, Japan
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123
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Goswami R, Kilkus J, Scurlock B, Dawson G. CrmA protects against apoptosis and ceramide formation in PC12 cells. Neurochem Res 2002; 27:735-41. [PMID: 12374208 DOI: 10.1023/a:1020292504535] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
TNF-alpha activated caspase 8 and caspase 3 in PC12 cells, leading to cell death by apoptosis (DNA fragmentation). TNF-alpha caspase activation and cell killing were blocked by transfection and overexpression of the viral protein CrmA, which specifically inhibits caspase 8. CrmA was also able to block the TNF-alpha-induced increase in ceramide formation in PC12 cells. Conversely, if caspase 8 was activated by light-activated Rose Bengal, there was an increase in both ceramide and caspase 3-mediated apoptosis, which was blocked by CrmA overexpression. This suggested that caspase 8 increases ceramide either by increasing its synthesis or by activating sphingomyelinase. Since fumonisin B1 did not block and sphingomyelin decreased when ceramide increased, we concluded that activation of sphingomyelinase is the most likely mechanism. The Rose Bengal activation of caspase 8 and increased ceramide formation was blocked with IETD-CHO, to show that reactive oxygen species (also generated by Rose Bengal) were not responsible for the observed increase in ceramide. Thus in PC12 pheochromocytoma cells, ceramide appears to amplify the death signal and there appears to be a sequence of events: TNF; TRADD, pro-caspase 8, caspase 8, sphingomyelinase, ceramide, caspase 3, apoptosis.
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Affiliation(s)
- Raja Goswami
- Department of Pediatrics, University of Chicago, Illinois 60637, USA
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124
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el Bawab S, Mao C, Obeid LM, Hannun YA. Ceramidases in the regulation of ceramide levels and function. Subcell Biochem 2002; 36:187-205. [PMID: 12037981 DOI: 10.1007/0-306-47931-1_10] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Affiliation(s)
- Samer el Bawab
- Department of Biochemistry and Molecular Biology, Medical University of South Carolina, 114 Doughty Street, Charleston, SC 29425, USA
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125
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Kolesnick R. The therapeutic potential of modulating the ceramide/sphingomyelin pathway. J Clin Invest 2002. [DOI: 10.1172/jci0216127] [Citation(s) in RCA: 296] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
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126
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Kolesnick R. The therapeutic potential of modulating the ceramide/sphingomyelin pathway. J Clin Invest 2002; 110:3-8. [PMID: 12093880 PMCID: PMC151041 DOI: 10.1172/jci16127] [Citation(s) in RCA: 132] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Affiliation(s)
- Richard Kolesnick
- Laboratory of Signal Transduction, Sloan-Kettering Institute, Memorial Sloan-Kettering Cancer Center, 1275 York Avenue, New York, NY 10021, USA.
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127
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Abstract
Tumour necrosis factor-alpha (TNF alpha) is a multifunctional cytokine belonging to a family of ligands with an associated family of receptor proteins. The pleiotropic actions of TNF range from proliferative responses such as cell growth and differentiation, to inflammatory effects and the mediation of immune responses, to destructive cellular outcomes such as apoptotic and necrotic cell death mechanisms. Activated TNF receptors mediate the association of distinct adaptor proteins that regulate a variety of signalling processes including kinase or phosphatase activation, lipase stimulation, and protease induction. Moreover, the cytokine regulates the activities of transcription factors, heterotrimeric or monomeric G-proteins and calcium ion homeostasis in order to orchestrate its cellular functions. This review addresses the structural basis of TNF signalling, the pathways employed with their cellular consequences, and focuses on the specific role played by each of the two TNF receptor isotypes, TNFR1 and TNFR2.
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Affiliation(s)
- David J MacEwan
- Department of Biomedical Sciences, Institute of Medical Sciences, University of Aberdeen, Aberdeen AB25 2ZD, UK.
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128
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Abstract
Insulin resistance of skeletal muscle in humans, animals, and cells is often strongly correlated with increased lipid availability. The elevation of certain intracellular lipid species can lead to the activation of signal transduction pathways that inhibit normal insulin action. Thus, increased diacylglycerol levels in muscle are associated with the activation of one or more isoforms of the protein kinase C family, which is known to attenuate insulin signaling, especially at the level of IRS-1. In addition, de novo synthesis of ceramide can inhibit more distal sites by the activation of protein phosphatase 2A and hence promote the dephosphorylation and inactivation of protein kinase B. Such mechanisms may account at least in part for the reduced insulin sensitivity occurring in obesity and type 2 diabetes where lipid oversupply is a major factor.
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Affiliation(s)
- Carsten Schmitz-Peiffer
- Cell Signalling Group, Garvan Institute of Medical Research, Darlinghurst, NSW 2010, Australia.
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129
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Mora A, Sabio G, Risco AM, Cuenda A, Alonso JC, Soler G, Centeno F. Lithium blocks the PKB and GSK3 dephosphorylation induced by ceramide through protein phosphatase-2A. Cell Signal 2002; 14:557-62. [PMID: 11897496 DOI: 10.1016/s0898-6568(01)00282-0] [Citation(s) in RCA: 79] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The biochemical mechanism of apoptosis induced by ceramide remains still unclear, although it has been reported that dephosphorylation of PKB at Ser-473 may be a key event. In this article, we show that C(2)-ceramide (N-acetyl-sphingosine) induces the dephosphorylation of both protein kinase B (PKB) and glycogen synthase kinase-3 (GSK3) in cerebellar granule cells (CGC). We also show that lithium protects against the apoptosis induced by C(2)-ceramide by blocking the dephosphorylation of both kinases. Since lithium inhibits in vivo the observed protein phosphatase-2A (PP2A) activation induced by ceramide, we hypothesise that the neuroprotective action of lithium may be due to the inhibition of the PP2A activation by apoptotic stimuli.
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Affiliation(s)
- Alfonso Mora
- Departamento de Bioquímica y Biología Molecular, Facultad de Veterinaria, Universidad de Extremadura, Avenida Universidad s/n, 10071 Cáceres, Spain.
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130
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Kondo T, Kitano T, Iwai K, Watanabe M, Taguchi Y, Yabu T, Umehara H, Domae N, Uchiyama T, Okazaki T. Control of ceramide-induced apoptosis by IGF-1: involvement of PI-3 kinase, caspase-3 and catalase. Cell Death Differ 2002; 9:682-92. [PMID: 12032677 DOI: 10.1038/sj.cdd.4401019] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2001] [Revised: 12/07/2001] [Accepted: 01/07/2002] [Indexed: 11/09/2022] Open
Abstract
Insulin-like growth factor-1 (IGF-1) inhibited N-acetylsphingosine (C2-ceramide)-induced HL-60 cell apoptosis via relieving oxidative damage. This inhibitory action of IGF-1 was blocked by a phosphatidylinositol-3 (PI-3) kinase inhibitor wortmannin and enhanced by overexpression of the p110 catalytic subunit of PI-3 kinase. Either IGF-1 pretreatment or PI-3 kinase overexpression restored ceramide-depleted catalase function, and this restoration was inhibited by wortmannin. A catalase inhibitor 3-amino-1h-1, 2, 4-triazole (ATZ) blocked the inhibitory action of IGF-1 on ceramide-induced apoptosis, whereas exogenous purified catalase enhanced it. Ceramide-activated caspase-3 was inhibited by IGF-1/PI-3 kinase and enhanced by wortmannin, while the addition of a specific caspase-3 inhibitor DMQD-CHO significantly enhanced the restoration by IGF-1 of ceramide-depleted catalase function. Moreover, IGF-1 inhibited C2-ceramide-induced decrease of mitochondrial membrane potential, and increase of cytochrome c release, caspase-3 cleavage and caspase-3 activity as judged by PhiPhiLux cleaving method. In summary, these results suggest that IGF-1/PI-3 kinase inhibited C2-ceramide-induced apoptosis due to relieving oxidative damage, which resulted from the inhibition of catalase by activated caspase-3.
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Affiliation(s)
- T Kondo
- Department of Hematology and Oncology, Graduate School of Medicine, Kyoto University, 54 Syogoin-Kawaramachi, Sakyo-ku, Kyoto 606-8507, Japan
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131
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Toman RE, Movsesyan V, Murthy SK, Milstien S, Spiegel S, Faden AI. Ceramide-induced cell death in primary neuronal cultures: upregulation of ceramide levels during neuronal apoptosis. J Neurosci Res 2002; 68:323-30. [PMID: 12111862 DOI: 10.1002/jnr.10190] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Ceramide is a sphingolipid that has been implicated both in apoptosis and protection from cell death. We show that in both rat cerebellar granule cells and cortical neuronal cultures application of C(2)-ceramide causes cell death in a dose- and time-dependent manner. Similar effects were observed with the exogenous application of bacterial sphingomyelinase, which hydrolyzes sphingomyelin located on the outer leaflet of the plasma membrane and leads to endogenous ceramide accumulation. Furthermore, endogenous ceramide levels were increased during apoptosis induced by nutrient deprivation or etoposide treatment. These findings suggest that upregulation of ceramide levels, which may be generated through activation of sphingomyelinase, contributes to neuronal apoptosis.
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Affiliation(s)
- Rachelle E Toman
- Interdisciplinary Program in Neuroscience, Georgetown University Medical Center, Washington, DC, USA
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132
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Resjö S, Göransson O, Härndahl L, Zolnierowicz S, Manganiello V, Degerman E. Protein phosphatase 2A is the main phosphatase involved in the regulation of protein kinase B in rat adipocytes. Cell Signal 2002; 14:231-8. [PMID: 11812651 DOI: 10.1016/s0898-6568(01)00238-8] [Citation(s) in RCA: 115] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
In adipocytes, protein kinase B (PKB) has been suggested to be the enzyme that phosphorylates phosphodiesterase 3B (PDE3B), a key enzyme in insulin's antilipolytic signalling pathway. In order to screen for PKB phosphatases, adipocyte homogenates were fractionated using ion-exchange chromatography and analysed for PKB phosphatase activities. PKB phosphatase activity eluted as one main peak, which coeluted with serine/threonine phosphatases (PP)2A. In addition, adipocytes were incubated with inhibitors of PP. Incubation of adipocytes with 1 microM okadaic acid inhibited PP2A by 75% and PP1 activity by only 17%, while 1 microM tautomycin inhibited PP1 activity by 54% and PP2A by only 7%. Okadaic acid, but not tautomycin, induced the activation of both PKBalpha and PKBbeta. Finally, PP2A subunits were found in several subcellular compartments, including plasma membranes (PM) where the phosphorylation of PKB is thought to occur. In summary, our results suggest that PP2A is the principal phosphatase that dephosphorylates PKB in adipocytes.
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Affiliation(s)
- Svante Resjö
- Biomedical Center, C11, Lund University, SE-22184, Lund, Sweden.
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133
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Bourbon NA, Sandirasegarane L, Kester M. Ceramide-induced inhibition of Akt is mediated through protein kinase Czeta: implications for growth arrest. J Biol Chem 2002; 277:3286-92. [PMID: 11723139 DOI: 10.1074/jbc.m110541200] [Citation(s) in RCA: 188] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
We recently demonstrated that ceramide-coated balloon catheters limit vascular smooth muscle cell (VSMC) growth after stretch injury in vivo. In that study, inhibition of VSMC growth was correlated with a decrease in phosphorylation of the cell survival kinase Akt (protein kinase B). Utilizing cultured A7r5 VSMCs, we have now examined the mechanism by which ceramide inhibits Akt phosphorylation/activation. Our initial studies showed that ceramide-induced inhibition of Akt phosphorylation was not mediated through diminution in phosphoinositide 3-kinase activity. As we have previously demonstrated that protein kinase Czeta (PKCzeta) is a target of ceramide, we proposed an alternative signaling mechanism by which ceramide induces inhibition of Akt through activation of PKCzeta. We demonstrate that C(6)-ceramide (but not the inactive analog dihydro-C(6)-ceramide) induced PKCzeta activity and also caused a selective increase in the association between Akt and PKCzeta, without affecting PKCepsilon, in A7r5 cells. In addition, the ability of ceramide to significantly decrease platelet-derived growth factor-induced Akt phosphorylation or cell proliferation was abrogated in A7r5 cells overexpressing a dominant-negative mutant of PKCzeta. Taken together, these data suggest that ceramide-mediated activation of PKCzeta leads to diminished Akt activation and consequent growth arrest in VSMCs. The therapeutic potential for ceramide to limit dysregulated VSMC growth has direct applicability to vascular diseases such as restenosis and atherosclerosis.
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Affiliation(s)
- Nicole A Bourbon
- Department of Pharmacology, Penn State College of Medicine, Hershey, Pennsylvania 17033, USA
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134
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Göransson O, Resjö S, Rönnstrand L, Manganiello V, Degerman E. Ser-474 is the major target of insulin-mediated phosphorylation of protein kinase B beta in primary rat adipocytes. Cell Signal 2002; 14:175-82. [PMID: 11781143 DOI: 10.1016/s0898-6568(01)00242-x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The mechanism of activation for protein kinase B (PKB), an important target for insulin signaling, has been scarcely investigated in primary cells. In this study, we have characterized the insulin-induced phosphorylation and activation of PKB beta in primary rat adipocytes. Insulin stimulation resulted in a translocation of PKB beta from cytosol to membranes, and phosphorylation and activation of PKB beta. Phosphoamino acid analysis and phosphopeptide mapping demonstrated that the phosphorylation occurred mainly on serines, also when using calyculin A, and that these were localized within one major phosphopeptide. Radiosequencing showed that the radioactivity was released in Cycle No. 7. In addition, the peptide was specifically immunoprecipitated from a tryptic digest of PKB beta using the anti-phospho-PKB (Ser-473) antibody. Taken together, these results show that rat adipocyte PKB beta mainly is phosphorylated on Ser-474 in response to insulin stimulation, in contrast to previous studies in human embryonic kidney (HEK) 293 cells demonstrating, in addition, phosphorylation of Thr-309.
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Affiliation(s)
- Olga Göransson
- Section for Molecular Signalling, Department of Cell and Molecular Biology, Lund University, BMC, C11, S-221 84 Lund, Sweden.
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135
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Nam SY, Amoscato AA, Lee YJ. Low glucose-enhanced TRAIL cytotoxicity is mediated through the ceramide-Akt-FLIP pathway. Oncogene 2002; 21:337-46. [PMID: 11821946 DOI: 10.1038/sj.onc.1205068] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2001] [Revised: 10/05/2001] [Accepted: 10/12/2001] [Indexed: 01/24/2023]
Abstract
To examine whether the tumor microenvironment alters cytokine-induced cytotoxicity, human prostate adenocarcinoma DU-145 cells were exposed to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and/or glucose deprivation, a common characteristic of the tumor microenvironment. TRAIL alone reduced cell survival in a dose-dependent manner. Glucose deprivation alone induced no cytotoxicity within 4 h. However, the combination of TRAIL (50 ng/ml) and glucose deprivation for 4 h increased cell death and PARP cleavage by promoting activation of caspase-8 and caspase-3, relative to that of TRAIL alone. Similar results were observed in human colorectal carcinoma CX-1 cells. Data from immunoblotting analysis reveal that glucose deprivation-enhanced TRAIL cytotoxicity is inversely related to the intracellular level of FLICE inhibitory protein (FLIP) but not that of death receptor 5 (DR5). Results from mass spectrometry show that glucose deprivation elevates ceramide. The elevation of ceramide may cause dephosphorylation of Akt and maintain dephosphorylation of Akt in the presence of TRAIL and then subsequently down-regulate the expression of FLIP. Taken together, the present studies suggest that glucose deprivation enhances TRAIL-induced cytotoxicity through the ceramide-Akt-FLIP pathway.
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Affiliation(s)
- Seon Young Nam
- Department of Pharmacology and Cancer Institute, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, PA 15213, USA
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136
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Decraene C, Brugg B, Ruberg M, Eveno E, Matingou C, Tahi F, Mariani J, Auffray C, Pietu G. Identification of genes involved in ceramide-dependent neuronal apoptosis using cDNA arrays. Genome Biol 2002; 3:RESEARCH0042. [PMID: 12186649 PMCID: PMC126236 DOI: 10.1186/gb-2002-3-8-research0042] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2001] [Revised: 04/22/2002] [Accepted: 05/08/2002] [Indexed: 11/29/2022] Open
Abstract
BACKGROUND Ceramide is important in many cell responses, such as proliferation, differentiation, growth arrest and apoptosis. Elevated ceramide levels have been shown to induce apoptosis in primary neuronal cultures and neuronally differentiated PC 12 cells. RESULTS To investigate gene expression during ceramide-dependent apoptosis, we carried out a global study of gene expression in neuronally differentiated PC 12 cells treated with C2-ceramide using an array of 9,120 cDNA clones. Although the criteria adopted for differential hybridization were stringent, modulation of expression of 239 genes was identified during the effector phase of C2-ceramide-induced cell death. We have made an attempt at classifying these genes on the basis of their putative functions, first with respect to known effects of ceramide or ceramide-mediated transduction systems, and then with respect to regulation of cell growth and apoptosis. CONCLUSIONS Our cell-culture model has enabled us to establish a profile of gene expression during the effector phase of ceramide-mediated cell death. Of the 239 genes that met the criteria for differential hybridization, 10 correspond to genes previously involved in C2-ceramide or TNF-alpha signaling pathways and 20 in neuronal disorders, oncogenesis or more broadly in the regulation of proliferation. The remaining 209 genes, with or without known functions, constitute a pool of genes potentially implicated in the regulation of neuronal cell death.
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Affiliation(s)
- Charles Decraene
- Genexpress, CNRS FRE 2376, BP8, 94801 Villejuif, France
- CEA Service de Génomique Fonctionnelle, 2 rue Gaston Crémieux, 91057 Evry Cedex, France
| | - Bernard Brugg
- Neurobiologie des Processus Adaptatifs, UMR 7102 CNRS-UPMC, Université Pierre et Marie Curie, Paris, France
| | - Merle Ruberg
- INSERM U289, Hôpital de la Salpêtrière, 75013 Paris, France
| | - Eric Eveno
- Genexpress, CNRS FRE 2376, BP8, 94801 Villejuif, France
| | | | - Fariza Tahi
- Genexpress, CNRS FRE 2376, BP8, 94801 Villejuif, France
- Université d'Evry-Val d'Essonne, 91025 Evry, France
| | - Jean Mariani
- Neurobiologie des Processus Adaptatifs, UMR 7102 CNRS-UPMC, Université Pierre et Marie Curie, Paris, France
| | | | - Geneviève Pietu
- Genexpress, CNRS FRE 2376, BP8, 94801 Villejuif, France
- CEA Service de Génomique Fonctionnelle, 2 rue Gaston Crémieux, 91057 Evry Cedex, France
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137
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Teruel T, Hernandez R, Lorenzo M. Ceramide mediates insulin resistance by tumor necrosis factor-alpha in brown adipocytes by maintaining Akt in an inactive dephosphorylated state. Diabetes 2001; 50:2563-71. [PMID: 11679435 DOI: 10.2337/diabetes.50.11.2563] [Citation(s) in RCA: 174] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Tumor necrosis factor (TNF)-alpha causes insulin resistance on glucose uptake in fetal brown adipocytes. We explored the hypothesis that some effects of TNF-alpha could be mediated by the generation of ceramide, given that TNF-alpha treatment induced the production of ceramide in these primary cells. A short-chain ceramide analog, C2-ceramide, completely precluded insulin-stimulated glucose uptake and insulin-induced GLUT4 translocation to plasma membrane, as determined by Western blot or immunofluorescent localization of GLUT4. These effects were not produced in the presence of a biologically inactive ceramide analog, C2-dihydroceramide. Analysis of the phosphatidylinositol (PI) 3-kinase signaling pathway indicated that C2-ceramide precluded insulin stimulation of Akt kinase activity, but not of PI-3 kinase or protein kinase C-zeta activity. C2-ceramide completely abolished insulin-stimulated Akt/protein kinase B phosphorylation on regulatory residues Thr 308 and Ser 473, as did TNF-alpha, and inhibited insulin-induced mobility shift in Akt1 and Akt2 separated in PAGE. Moreover, C2-ceramide seemed to activate a protein phosphatase (PP) involved in dephosphorylating Akt because 1) PP2A activity was increased in C2-ceramide- and TNF-alpha-treated cells, 2) treatment with okadaic acid concomitantly with C2-ceramide completely restored Akt phosphorylation by insulin, and 3) transient transfection of a constitutively active form of Akt did not restore Akt activity. Our results indicate that ceramide produced by TNF-alpha induces insulin resistance in brown adipocytes by maintaining Akt in an inactive dephosphorylated state.
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Affiliation(s)
- T Teruel
- Departamento de Bioquimica y Biologia Molecular II, Facultad de Farmacia, Universidad Complutense, 28040, Madrid, Spain
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138
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Cazzolli R, Carpenter L, Biden TJ, Schmitz-Peiffer C. A role for protein phosphatase 2A-like activity, but not atypical protein kinase Czeta, in the inhibition of protein kinase B/Akt and glycogen synthesis by palmitate. Diabetes 2001; 50:2210-8. [PMID: 11574400 DOI: 10.2337/diabetes.50.10.2210] [Citation(s) in RCA: 114] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
We have shown previously that palmitate treatment of C2C12 skeletal muscle myotubes causes inhibition of the protein kinase B (PKB) pathway and hence reduces insulin-stimulated glycogen synthesis through the elevation of intracellular ceramide levels. Ceramide is known to activate both atypical protein kinase C (aPKC) zeta and protein phosphatase (PP) 2A, and each of these effectors has been reported to inhibit PKB. In the present study, palmitate pretreatment was found to elevate PP2A-like activity in myotubes and to prevent its inhibition by insulin. Incubation with the phosphatase inhibitor okadaic acid before insulin stimulation protected against the effect of the fatty acid on PKB phosphorylation. Palmitate was unable to inhibit PKB activity and glycogen synthesis in cells overexpressing the activated PKB mutant (T308D,S473D)-PKBalpha, which is unaffected by phosphatase. In contrast, PKB activity and glycogen synthesis were still inhibited by palmitate in cells overexpressing a membrane-targeted and, hence, activated PKB mutant that retains sensitivity to phosphatase. Although aPKC activity was also increased in palmitate-treated cells, overexpression of wild-type or kinase-dead aPKCzeta did not alter the inhibitory effects of the lipid on either stimulation of PKB or glycogen synthesis by insulin. We conclude that palmitate disrupts insulin signaling in C2C12 myotubes by promoting PP2A-like activity and, therefore, the dephosphorylation of PKB, which in turn reduces the stimulation of glycogen synthesis.
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Affiliation(s)
- R Cazzolli
- Garvan Institute of Medical Research, Sydney, Australia
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139
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Chen JK, Capdevila J, Harris RC. Cytochrome p450 epoxygenase metabolism of arachidonic acid inhibits apoptosis. Mol Cell Biol 2001; 21:6322-31. [PMID: 11509673 PMCID: PMC87364 DOI: 10.1128/mcb.21.18.6322-6331.2001] [Citation(s) in RCA: 131] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2001] [Accepted: 06/01/2001] [Indexed: 01/19/2023] Open
Abstract
The ubiquitous cytochrome P450 hemoproteins play important functional roles in the metabolism and detoxification of foreign chemicals. However, other than established roles in cholesterol catabolism and steroid hormone biosynthesis, their cellular and/or organ physiological functions remain to be fully characterized. Here we show that the cytochrome P450 epoxygenase arachidonic acid metabolite 14,15-epoxyeicosatrienoic acid (14,15-EET) inhibits apoptosis induced by serum withdrawal, H(2)O(2), etoposide, or excess free arachidonic acid (AA), as determined by DNA laddering, Hoechst staining, and fluorescein isothiocyanate-labeled annexin V binding. In the stable transfectants (BM3 cells) expressing a mutant bacterial P450 AA epoxygenase, F87V BM3, which was genetically engineered to metabolize arachidonic acid only to 14,15-EET, AA did not induce apoptosis and protected against agonist-induced apoptosis. Ceramide assays demonstrated increased AA-induced ceramide production within 1 h and elevated ceramide levels for up to 48 h, the longest time tested, in empty-vector-transfected cells (Vector cells) but not in BM3 cells. Inhibition of cytochrome P450 activity by 17-octadecynoic acid restored AA-induced ceramide production in BM3 cells. Exogenous C2-ceramide markedly increased apoptosis in quiescent Vector cells as well as BM3 cells, and apoptosis was prevented by pretreatment of Vector cells with exogenous 14,15-EET and by pretreatment of BM3 cells with AA. The ceramide synthase inhibitor fumonisin B1 did not affect AA-induced ceramide production and apoptosis; in contrast, these effects of AA were blocked by the neutral sphingomyelinase inhibitor scyphostatin. The pan-caspase inhibitor Z-VAD-fmk had no effect on AA-induced ceramide generation but abolished AA-induced apoptosis. The antiapoptotic effects of 14,15-EET were blocked by two mechanistically and structurally distinct phosphatidylinositol-3 (PI-3) kinase inhibitors, wortmannin and LY294002, but not by the specific mitogen-activated protein kinase kinase inhibitor PD98059. Immunoprecipitation followed by an in vitro kinase assay revealed activation of Akt kinase within 10 min after 14,15-EET addition, which was completely abolished by either wortmannin or LY294002 pretreatment. In summary, the present studies demonstrated that 14,15-EET inhibits apoptosis by activation of a PI-3 kinase-Akt signaling pathway. Furthermore, cytochrome P450 epoxygenase promotes cell survival both by production of 14,15-EET and by metabolism of unesterified AA, thereby preventing activation of the neutral sphingomyelinase pathway and proapoptotic ceramide formation.
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Affiliation(s)
- J K Chen
- Department of Medicine, Vanderbilt University, Nashville, Tennessee, USA
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140
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Martín D, Salinas M, López-Valdaliso R, Serrano E, Recuero M, Cuadrado A. Effect of the Alzheimer amyloid fragment Abeta(25-35) on Akt/PKB kinase and survival of PC12 cells. J Neurochem 2001; 78:1000-8. [PMID: 11553674 DOI: 10.1046/j.1471-4159.2001.00472.x] [Citation(s) in RCA: 121] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The phosphatidylinositol 3 kinase (PI3K)-Akt/PKB pathway protects neurons from apoptosis caused by diverse stress stimuli. However, its protective role against the amyloid beta peptide (Abeta), a major constituent of Alzheimer's disease plaques, has not been studied. We investigated the effect of the Abeta-derived Abeta(25-35) peptide on apoptosis and on the Akt survival pathway in PC12 cells. Cells submitted to micromolar concentrations of Abeta(25-35) exhibited increased production of reactive oxygen species (ROS) and morphological alterations consistent with apoptosis. Akt1 was activated shortly after incubation with Abeta(25-35) and Abeta(1-40) with a kinetics different to that of nerve-derived growth factor. Akt1 activation was blocked by the PI3K inhibitor wortmannin. We tested the hypothesis that Akt1 might modify the vulnerability of neural cells to apoptosis induced by Abeta(25-35). Overexpression of an active version of Akt1 attenuated the apoptotic effect of Abeta(25-35) as determined by flow cytometry. Moreover, PC12 cells overexpressing a membrane-targeted N-myristylated fusion protein of enhanced green fluorescence protein (EGFP) and mouse Akt1 exhibited lower levels of ROS than control EGFP-transfected cells. The present findings demonstrate that Akt1 is activated in response to Abeta(25-35) in a PI3K-dependent manner and that active Akt1 protects PC12 cells against the pro-apoptotic action of this peptide.
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Affiliation(s)
- D Martín
- Departamento de Bioquímica and Instituto de Investigaciones Biomédicas Alberto Sols UAM-CSIC, Facultad de Medicina, Universidad Autónoma de Madrid, Madrid, Spain
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141
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Egea J, Espinet C, Soler RM, Dolcet X, Yuste VJ, Encinas M, Iglesias M, Rocamora N, Comella JX. Neuronal survival induced by neurotrophins requires calmodulin. J Cell Biol 2001; 154:585-97. [PMID: 11489918 PMCID: PMC2196427 DOI: 10.1083/jcb.200101023] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
It has been reported that phosphoinositide 3-kinase (PI 3-kinase) and its downstream target, protein kinase B (PKB), play a central role in the signaling of cell survival triggered by neurotrophins (NTs). In this report, we have analyzed the involvement of Ca2+ and calmodulin (CaM) in the activation of the PKB induced by NTs. We have found that reduction of intracellular Ca2+ concentration or functional blockade of CaM abolished NGF-induced activation of PKB in PC12 cells. Similar results were obtained in cultures of chicken spinal cord motoneurons treated with brain-derived neurotrophic factor (BDNF). Moreover, CaM inhibition prevented the cell survival triggered by NGF or BDNF. This effect was counteracted by the transient expression of constitutive active forms of the PKB, indicating that CaM regulates NT-induced cell survival through the activation of the PKB. We have investigated the mechanisms whereby CaM regulates the activation of the PKB, and we have found that CaM was necessary for the proper generation and/or accumulation of the products of the PI 3-kinase in intact cells.
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Affiliation(s)
- J Egea
- Grup de Neurobiologia Molecular, Departament de Ciències Mèdiques Bàsiques, Facultat de Medicina, Universitat de Lleida, 25198 Lleida, Catalonia, Spain
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142
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Abstract
The sphingolipid ceramide is an important second signal molecule that regulates diverse signaling pathways involving apoptosis, cell senescence, the cell cycle, and differentiation. For the most part, ceramide's effects are antagonistic to growth and survival. Interestingly, ceramide and the pro-growth agonist, diacylglycerol (DAG) appear to be regulated simultaneously but in opposite directions in the sphingomyelin cycle. While ceramide stimulates signal transduction pathways that are associated with cell death or at least are inhibitory to cell growth (eg stress-activated protein kinase, SAPK, pathways), DAG activates the classical and novel isoforms of the protein kinase C (PKC) family. These PKC isoforms are associated with cell growth and cell survival. Furthermore, DAG activation of PKC stimulates other signal transduction pathways that support cell proliferation (eg mitogen-activated protein kinase, MAPK, pathways). Thus, ceramide and DAG generation may serve to monitor cellular homeostasis by inducing pro-death or pro-growth pathways, respectively. The production of ceramide is emerging as a fixture of programmed cell death. Ceramide levels are elevated in response to diverse stress challenges including chemotherapeutic drug treatment, irradiation, or treatment with pro-death ligands such as tumor necrosis factor alpha, TNF alpha. Consistent with this notion, ceramide itself is a potent apoptogenic agent. Ceramide activates stress-activated protein kinases like c-jun N-terminal kinase (JNK) and thus affects transcription pathways involving c-jun. Ceramide activates protein phosphatases such as protein phosphatase 1 (PP1) and protein phosphatase 2 (PP2A). Ceramide activation of protein phosphatases has been shown to promote inactivation of a number of pro-growth cellular regulators including the kinases PKC alpha and Akt, Bcl2 and the retinoblastoma protein. A new role has recently emerged for ceramide in the regulation of protein synthesis. Ceramide-induced activation of double-stranded RNA-dependent protein kinase (PKR), a protein kinase important in anti-viral host defense mechanisms and recently implicated in cellular stress pathways, results in the inhibition of protein synthesis as a prelude to cell death. Taken together, these properties of ceramide suggest that this important second-signal molecule may have useful properties as an anti-neoplastic agent. Thus, strategies to promote ceramide metabolism or use of ceramide analogs directly may one day become useful in the treatment of diseases like leukemia.
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Affiliation(s)
- P P Ruvolo
- University of Florida Shands Cancer Center and The Department of Medicine, Gainesville 32610-0232, USA
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143
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Monti B, Zanghellini P, Contestabile A. Characterization of ceramide-induced apoptotic death in cerebellar granule cells in culture. Neurochem Int 2001; 39:11-8. [PMID: 11311444 DOI: 10.1016/s0197-0186(01)00005-5] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Sphingomyelin signalling system has been involved in several examples of cell death through apoptosis. We have characterised the effect of exposure to the cell permeable ceramide analogue, C2-ceramide, on cultures of differentiated cerebellar granule cells. C(2)-ceramide was toxic to granule cells in a dose- and time-dependent way at concentrations higher than 10 microM. Ceramide exposure was accompanied by characteristic alterations of cell morphology, namely swollen cell bodies and punctuate appearance and arcuate direction of processes. The final outcome of ceramide exposure was a form of cell death largely apoptotic in nature. Hoechst stain, followed by counts of nuclei with normal appearance and size or with condensed chromatin and reduced size, revealed a large increase of the proportion of shrunken nuclei in treated cultures. In situ visualisation of fragmented DNA through the TUNEL technique, additionally marked cells undergoing apoptosis as a consequence of ceramide treatment. Accordingly, the DNA extracted from cultures exposed to C2-ceramide and subjected to agarose gel electrophoresis showed the peculiar ladder of fragmented low molecular weight DNA. Treatments with inhibitors of two caspases or of nitric oxide synthase were unable to rescue neurons exposed to ceramide, thus suggesting a neurotoxic action not primarily dependent on activation of death proteases or on nitric oxide production.
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Affiliation(s)
- B Monti
- Department of Biology, University of Bologna, Via Selmi 3, 40126, Bologna, Italy
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144
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Hernandez R, Teruel T, Lorenzo M. Akt mediates insulin induction of glucose uptake and up-regulation of GLUT4 gene expression in brown adipocytes. FEBS Lett 2001; 494:225-31. [PMID: 11311245 DOI: 10.1016/s0014-5793(01)02353-5] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Insulin acutely stimulated glucose uptake in rat primary brown adipocytes in a PI3-kinase-dependent but p70S6-kinase-independent manner. Since Akt represents an intermediate step between these kinases, this study investigated the contribution of Akt to insulin-induced glucose uptake by the use of a chemical compound, ML-9, as well as by transfection with a dominant-negative form of Akt (DeltaAkt). Pretreatment with ML-9 for 10 min completely inhibited insulin stimulation of (1) Akt kinase activity, (2) Akt phosphorylation on the regulatory residue Ser473 but not on Thr308, and (3) mobility shift in Akt1 and Akt2. However, ML-9 did not affect insulin-stimulated PI3-kinase nor PKCzeta activities. In consequence, ML-9 precluded insulin stimulation of glucose uptake and GLUT4 translocation to plasma membrane (determined by Western blot), without any effect on the basal glucose uptake. Moreover, DeltaAkt impaired insulin stimulation of glucose uptake and GFP-tagged GLUT4 translocation to plasma membrane in transiently transfected immortalised brown adipocytes and HeLa cells, respectively. Furthermore, ML-9 treatment for 6 h down-regulated insulin-induced GLUT4 mRNA accumulation, without affecting GLUT1 expression, in a similar fashion as LY294002. Indeed, co-transfection of brown adipocytes with DeltaAkt precluded the transactivation of GLUT4-CAT promoter by insulin in a similar fashion as a dominant-negative form of PI3-kinase. Our results indicate that activation of Akt may be an essential requirement for insulin regulation of glucose uptake and GLUT4 gene expression in brown adipocytes.
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Affiliation(s)
- R Hernandez
- Departamento de Bioquimica y Biologia Molecular II, Facultad de Farmacia, Universidad Complutense, 28040 Madrid, Spain
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145
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Moniakis J, Funamoto S, Fukuzawa M, Meisenhelder J, Araki T, Abe T, Meili R, Hunter T, Williams J, Firtel RA. An SH2-domain-containing kinase negatively regulates the phosphatidylinositol-3 kinase pathway. Genes Dev 2001; 15:687-98. [PMID: 11274054 PMCID: PMC312652 DOI: 10.1101/gad.871001] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
SHK1 is a novel dual-specificity kinase that contains an SH2 domain in its C-terminal region. We demonstrate that SHK1 is required for proper chemotaxis and phagocytosis. Mutant shk1 null cells lack polarity, move very slowly, and exhibit an elevated and temporally extended chemoattractant-mediated activation of the kinase Akt/PKB. GFP fusions of the PH domain of Akt/PKB or the PH-domain-containing protein CRAC, which become transiently associated with the plasma membrane after a global stimulation with a chemoattractant, remain associated with the plasma membrane for an extended period of time in shk1 null cells. These results suggest that SHK1 is a negative regulator of the PI3K (phosphatidylinositol-3 kinase) pathway. Furthermore, when a chemoattractant gradient is applied to a wild-type cell, these PH-domain-containing proteins and the F-actin-binding protein coronin localize to its leading edge, but in an shk1 null cell they become randomly associated with the plasma membrane and cortex, irrespective of the direction of the chemoattractant gradient, suggesting that SHK1 is required for the proper spatiotemporal control of F-actin levels in chemotaxing cells. Consistent with such functions, SHK1 is localized at the plasma membrane/cortex, and we show that its SH2 domain is required for this localization and the proper function of SHK1.
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Affiliation(s)
- J Moniakis
- Section of Cell and Developmental Biology and Center for Molecular Genetics, University of California, San Diego, La Jolla, California 92093-0634, USA
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146
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Stratford S, DeWald DB, Summers SA. Ceramide dissociates 3'-phosphoinositide production from pleckstrin homology domain translocation. Biochem J 2001; 354:359-68. [PMID: 11171115 PMCID: PMC1221664 DOI: 10.1042/0264-6021:3540359] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Numerous hormones, cytokines and transforming oncogenes activate phosphoinositide 3-kinase (PI-3K), a lipid kinase that initiates signal transduction cascades regulating cellular proliferation, survival, protein synthesis and glucose metabolism. PI-3K catalyses the production of the 3'-phosphoinositides PtdIns(3,4)P(2) and PtdIns(3,4,5)P(3), which recruit downstream effector enzymes to the membrane via their pleckstrin homology (PH) domains. Recent studies have indicated that another signalling lipid, the sphingolipid ceramide, inhibits several PI-3K-dependent events, including insulin-stimulated glucose uptake and growth-factor-stimulated cell survival. Here we show that ceramide analogues specifically prevent the recruitment of the PtdIns(3,4,5)P(3)-binding proteins Akt/protein kinase B (PKB) or the general receptor for phosphoinositides-1 (GRP1). Specifically, the short-chain ceramide derivative C2-ceramide inhibited the platelet-derived growth factor (PDGF)-stimulated translocation of full-length Akt/PKB, as well as truncated proteins encoding only the PH domains of Akt/PKB or GRP1. C2-ceramide did not alter the membrane localization of the PH domain for phospholipase Cdelta, which preferentially binds PtdIns(4,5)P(2), nor did it affect the PDGF-stimulated production of PtdIns(3,4)P(2) or PtdIns(3,4,5)P(3). Interestingly, a glucosylceramide synthase inhibitor, 1-phenyl-2-decanoylamino-3-morpholinopropan-1-ol (PDMP), shown previously to increase intracellular ceramide concentrations without affecting PI-3K [Rani, Abe, Chang, Rosenzweig, Saltiel, Radin and Shayman (1995) J. Biol. Chem. 270, 2859-2867], recapitulated the inhibitory effects of C2-ceramide on PDGF-stimulated Akt/PKB phosphorylation. These studies indicate that ceramide prevents the translocation of certain PtdIns(3,4,5)P(3)-binding proteins, despite the presence of a full complement of PtdIns(3,4)P(2) or PtdIns(3,4,5)P(3). Furthermore, these findings suggest a mechanism by which stimuli that induce ceramide synthesis could negate the fundamental signalling pathways initiated by PI-3K.
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Affiliation(s)
- S Stratford
- Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, CO 80523-1870, U.S.A
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147
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Zinda MJ, Vlahos CJ, Lai MT. Ceramide induces the dephosphorylation and inhibition of constitutively activated Akt in PTEN negative U87mg cells. Biochem Biophys Res Commun 2001; 280:1107-15. [PMID: 11162641 DOI: 10.1006/bbrc.2000.4248] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In the present study, treatment of the PTEN negative U87MG human glioblastoma cell line with C2-ceramide resulted in a dose- and time-dependent decrease in the constitutive phosphorylation of Akt at threonine 308 and serine 473. The C2-ceramide induced dephosphorylation of Akt correlated with a 90-95% reduction in the Akt kinase activity. Exposure to C2-ceramide did not affect the basal or PDGF activated levels PtdIns-3,4-P(2) and PtdIns-3,4,5-P(3), indicating PI3-K activity was not inhibited. Additionally, treatment of cells with the PI3-K inhibitor wortmannin and C2-ceramide resulted in an enhanced rate of Akt dephosphorylation versus either agent alone. Finally, treatment of cells with the phosphatase inhibitors okadaic acid or calyculin A prevented the C2-ceramide induced dephosphorylation and inhibition of Akt activity. These data demonstrate the ability of C2-ceramide to inhibit the constitutive phosphorylation and activity of Akt in U87MG cells and implicate the activation of ceramide activated protein phosphatase, rather than decreased PI3-K activity, as the mechanism of inhibition.
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Affiliation(s)
- M J Zinda
- Department of Cancer Research, Lilly Corporate Center, Indianapolis, Indiana, 46285, USA
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148
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Sée V, Koch B, Loeffler JP. C2-ceramide and reactive oxygen species inhibit pituitary adenylate cyclase activating polypeptide (PACAP)-induced cyclic-AMP-dependent signalling pathway. J Neurochem 2001; 76:778-88. [PMID: 11158249 DOI: 10.1046/j.1471-4159.2001.00106.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The pituitary adenylate cyclase activating polypeptide (PACAP) type I receptor, a seven-domain transmembrane receptor, is positively coupled to both adenylate cyclase and phospholipase C. PACAP exerts neurotrophic effects which are mainly mediated through the cAMP/protein kinase A pathway. Here we show that the cell-permeable C2-ceramide selectively blocks PACAP-activated cAMP production, without affecting phosphoinositide breakdown. Thus by blocking the neuroprotective cAMP signalling pathway, C2-ceramide will reinforce its direct death-inducing signalling. We found that a reactive oxygen species scavenger reversed the C2-ceramide effect and that H2O2 mimicked it. Together these data indicate that reactive oxygen species (ROS) mediates C2-ceramide-induced cAMP pathway uncoupling. This uncoupling did not involve ATP supply or Galphas protein function but rather adenylate cyclase function per se. Further, the tyrosine phosphatase inhibitors, but not the serine/threonine phosphatase inhibitors, prevent inhibition of cAMP production by ROS. This suggests that H2O2 requires a functional tyrosine phosphatase(s) to block PACAP-dependent cAMP production.
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Affiliation(s)
- V Sée
- Université Louis Pasteur, UMR 7519 CNRS, Strasbourg Cedex, France
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Salinas M, Martín D, Alvarez A, Cuadrado A. Akt1/PKBalpha protects PC12 cells against the parkinsonism-inducing neurotoxin 1-methyl-4-phenylpyridinium and reduces the levels of oxygen-free radicals. Mol Cell Neurosci 2001; 17:67-77. [PMID: 11161470 DOI: 10.1006/mcne.2000.0921] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
The phosphatidylinositol (PI)-3 kinase-Akt/PKB survival pathway protects neurons from apoptosis caused by diverse stress stimuli. However, its protective effect against neurotoxins that produce oxidative stress and neurodegeneration has not been investigated. We analyzed the effect of this pathway on the action of the parkinsonism-inducing neurotoxin 1-methyl-4-phenylpyridinium (MPP+). Overexpression of a membrane-targeted, N-myristylated fusion protein of enhanced green fluorescence protein (EGFP) and mouse Akt1 attenuated the apoptotic effect of the neurotoxin in PC12 cells. This effect was not due to protection of mitochondrial complex I activity or restoration of energy charge. Following MPP+-treatment, myr-EGFP-Akt1-transfected cells exhibited an unaltered mitochondrial membrane potential and lower ROS levels than control cells. These results provide a new site of action of Akt/PKB at the level of the oxidative detoxifying cell machinery and suggest that this effect may be responsible in part for the resistance of myr-EGFP-Akt1-expressing cells to oxidative stress and MPP+-induced apoptosis.
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Affiliation(s)
- M Salinas
- Departamento de Bioquímica, Instituto de Investigaciones Biomédicas Alberto Sols UAM-CSIC, Madrid, Spain
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150
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Wick MJ, Dong LQ, Riojas RA, Ramos FJ, Liu F. Mechanism of phosphorylation of protein kinase B/Akt by a constitutively active 3-phosphoinositide-dependent protein kinase-1. J Biol Chem 2000; 275:40400-6. [PMID: 11006271 DOI: 10.1074/jbc.m003937200] [Citation(s) in RCA: 107] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Phosphorylation of Thr(308) in the activation loop and Ser(473) at the carboxyl terminus is essential for protein kinase B (PKB/Akt) activation. However, the biochemical mechanism of the phosphorylation remains to be characterized. Here we show that expression of a constitutively active mutant of mouse 3-phosphoinositide-dependent protein kinase-1 (PDK1(A280V)) in Chinese hamster ovary cells overexpressing the insulin receptor was sufficient to induce PKB phosphorylation at Thr(308) to approximately the same extent as insulin stimulation. Phosphorylation of PKB by PDK1(A280V) was not affected by treatment of cells with inhibitors of phosphatidylinositol 3-kinase or by deletion of the pleckstrin homology (PH) domain of PKB. C(2)-ceramide, a cell-permeable, indirect inhibitor of PKB phosphorylation, did not inhibit PDK1(A280V)-catalyzed PKB phosphorylation in cells and had no effect on PDK1 activity in vitro. On the other hand, co-expression of full-length protein kinase C-related kinase-1 (PRK1/PKN) or 2 (PRK2) inhibited PDK1(A280V)-mediated PKB phosphorylation. Replacing alanine at position 280 with valine or deletion of the PH domain enhanced PDK1 autophosphorylation in vitro. However, deletion of the PH domain of PDK1(A280V) significantly reduced PDK1(A280V)-mediated phosphorylation of PKB in cells. In resting cells, PDK1(A280V) localized in the cytosol and at the plasma membrane. However, PDK1(A280V) lacking the PH domain localized predominantly in the cytosol. Taken together, our findings suggest that the wild-type PDK1 may not be constitutively active in cells. In addition, activation of PDK1 is sufficient to phosphorylate PKB at Thr(308) in the cytosol. Furthermore, the PH domain of PDK1 may play both positive and negative roles in regulating the in vivo function of the enzyme. Finally, unlike the carboxyl-terminal fragment of PRK2, which has been shown to bind PDK1 and allow the enzyme to phosphorylate PKB at both Thr(308) and Ser(473), full-length PRK2 and its related kinase PRK1/PKN may both play negative roles in PKB-mediated downstream biological events.
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Affiliation(s)
- M J Wick
- Departments of Pharmacology and Biochemistry, The University of Texas Health Science Center, San Antonio, Texas 78229, USA
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