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Query: UNIPROT:P06889 (Mol)
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We investigated several indices involved in sphingomyelin metabolism in developing rat lung. The levels of sphingomyelin gradually increased during lung maturation, with highest levels observed postnatally. The content of sphingosine and ceramide, biologically active sphingomyelin degradation products, did not significantly change in microsomes during the prenatal period, but increased to peak levels in neonatal and adult lung, respectively. Sphingosine content increased 6-fold between the fetal (Day 21) and neonatal period. The developmental profiles of two enzymes involved in sphingomyelin synthesis, serine palmitoyltransferase and sphingomyelin synthase, were similar. Serine palmitoyltransferase activity increased progressively from the fetal to neonatal period, and plateaued at high levels in the adult lung. The activity of serine palmitoyltransferase correlated with the levels of endogenous sphingolipid in lung tissue. Sphingomyelin synthase activity also increased during fetal lung development, but attained highest levels at Day 21 gestation; postnatally, enzyme activity was detected at lower levels. The activities of the sphingolipid hydrolases, acid and neutral sphingomyelinase and acid and alkaline ceramidase, were elevated in fetal lung, thereafter declining to low levels after birth. Studies conducted in alveolar macrophages, fibroblasts, and alveolar type II epithelial cells revealed that these developmental changes in enzyme activities in lung tissue were also occuring globally at the cellular level and were not restricted to any specific cell population. These studies suggest that the developmental increase in lung sphingomyelin content is due to coordinate regulation of enzymes involved in the biosynthesis and degradation of sphingomyelin. These observations also suggest a regulatory role for serine palmitoyltransferase in the generation of long chain sphingoid bases.
Am J Respir Cell Mol Biol 1997 May
PMID:Sphingomyelin metabolism is developmentally regulated in rat lung. 916 Aug 43

p38 mitogen-activated protein kinase (MAPK) is known to be activated after exposure to endotoxin, osmotic and environmental stress, and, most recently, during ischemia/reperfusion. We investigated whether ischemic preconditioning also causes phosphorylation of the activation sites on p38 MAPK. Three groups of isolated rabbit hearts were studied. Control hearts experienced 30 min of ischemia only. The second group was preconditioned with 5 min of global ischemia and 10 min of reperfusion. Group 3 was also ischemically preconditioned, but in the presence of 100 microM 8-(p-sulfophenyl)theophylline (SPT). Transmural left ventricular biopsies were taken before and during the long ischemic period. Western blot analysis with either p38 MAPK or phospho-specific p38 MAPK (Tyr-182) antibodies showed a decreased phosphorylation during ischemia in non-preconditioned hearts, but phosphorylation was enhanced several fold after 10 and 20 min of ischemia in preconditioned hearts. Furthermore, when protection from ischemic preconditioning was blocked by SPT, increased phosphorylation of p38 MAPK during ischemia was not present. Therefore the phosphorylation of p38 MAPK at tyrosine 182, which is required for the kinase's activation, occurred during ischemia only when protection from preconditioning was evident. In a second study, changes in osmotic fragility were measured during simulated ischemia in rabbit cardiomyocytes. Reduced fragility in ischemically preconditioned myocytes could be completely abolished by the specific p38 MAPK inhibitor SB-203580. In contrast, anisomycin, an activator of p38 MAPK and JUN kinase pathways, was found to be as protective as ischemic preconditioning. We conclude that p38 MAPK phosphorylation correlates with preconditioning's protection, and that its activation may be an important step in the signal transduction cascade of ischemic preconditioning.
J Mol Cell Cardiol 1997 Sep
PMID:Phosphorylation of tyrosine 182 of p38 mitogen-activated protein kinase correlates with the protection of preconditioning in the rabbit heart. 929 62

While there is good evidence that both protein kinase C (PKC) and adenosine are involved in ischemic preconditioning, their sequence in the intracellular signaling cascade is in dispute. One hypothesis proposes that PKC activation causes release of adenosine which then protects the heart, while the other proposes that adenosine stimulates PKC which in turn causes protection. Accordingly, we studied the effects of specified sequences of pharmacologic triggers and blockers on the infarct-sparing effect of a preconditioning protocol. The combination of the adenosine receptor agonist R(-)N6-(2-phenylisopropyl) adenosine (PIA) and the PKC blocker chelerythrine would be protective only if the first hypothesis were correct. On the other hand, the combination of the adenosine receptor blocker 8-(p-sulfophenyl) theophylline (SPT) and a PKC activator would be protective only if the second hypothesis were correct. Isolated, Krebs-perfused rabbit hearts experienced 30 min of regional ischemia and 2 h of reperfusion. Infarct size was quantitated by triphenyltetrazolium chloride staining. In untreated control hearts, 30.0 +/- 2.7% of the risk zone infarcted. Fifty nmol/l PIA for 20 min starting 10 min prior to ischemia resulted in only 8.4 +/- 1.9% infarction (P<0.01), while the combination of PIA and 5 micromol/l chelerythrine resulted in large infarcts of 27.8 +/- 3.2%. This attenuation of the protective effect continued to be observed even when the PIA infusion was continued to the end of the reperfusion period. Conversely, 0.2 nmol of the PKC activator phorbol 12-myristate 13-acetate (PMA) infused during the 10-min interval prior to ischemia protected the hearts (6.5 +/- 1.3% infarction, P<0.01 v control). And protection persisted when PMA-treated hearts were also exposed to 100 microM SPT for 35 min starting 5 min prior to ischemia (9.5 +/- 1.9% infarction, P<0.01 v control). When PKC activation by the PKC-coupled agonist phenylephrine was continued to the end of ischemia and adenosine blockade was extended throughout the reperfusion period by prolonged infusion of SPT, protection was unaffected. The administration of either SPT or chelerythrine alone did not confer any protection (32.5 +/- 3.3 and 34.0 +/- 3.2% infarction, respectively). Thus, because the combination of PKC activation and adenosine receptor blockade was protective while that of adenosine receptor agonist and PKC blockade was not, adenosine receptors must be upstream of PKC in preconditioning.
J Mol Cell Cardiol 1998 Nov
PMID:The PKC activator PMA preconditions rabbit heart in the presence of adenosine receptor blockade: is 5'-nucleotidase important? 992 58

Mitogen-activated protein kinase (MAPK) is a conserved eukaryotic signaling factor that mediates various signals, cumulating in the activation of transcription factors. Extracellular signal-regulated kinase (ERK), a MAPK, is activated through phosphorylation by the kinase MAPK/ERK kinase (MEK). To elucidate the extent of the involvement of ERK in various aspects of animal development, we searched for a Drosophila mutant which responds to elevated MEK activity and herein identified a lace mutant. Mutants with mild lace alleles grow to become adults with multiple aberrant morphologies in the appendages, compound eye, and bristles. These aberrations were suppressed by elevated MEK activity. Structural and transgenic analyses of the lace cDNA have revealed that the lace gene product is a membrane protein similar to the yeast protein LCB2, a subunit of serine palmitoyltransferase (SPT), which catalyzes the first step of sphingolipid biosynthesis. In fact, SPT activity in the fly expressing epitope-tagged Lace was absorbed by epitope-specific antibody. The number of dead cells in various imaginal discs of a lace hypomorph was considerably increased, thereby ectopically activating c-Jun N-terminal kinase (JNK), another MAPK. These results account for the adult phenotypes of the lace mutant and suppression of the phenotypes by elevated MEK activity: we hypothesize that mutation of lace causes decreased de novo synthesis of sphingolipid metabolites, some of which are signaling molecules, and one or more of these changes activates JNK to elicit apoptosis. The ERK pathway may be antagonistic to the JNK pathway in the control of cell survival.
Mol Cell Biol 1999 Oct
PMID:De novo synthesis of sphingolipids is required for cell survival by down-regulating c-Jun N-terminal kinase in Drosophila imaginal discs. 1049 Jun 62

ISP-1 is a new type of immunosuppressant, the structure of which is homologous to that of sphingosine. In a previous study, ISP-1 was found to inhibit mammalian serine palmitoyltransferase, the primary enzyme involved in sphingolipid biosynthesis, and to reduce the intracellular pool of sphingolipids. ISP-1 induces the apoptosis of cytotoxic T cells, which is triggered by decreases in the intracellular levels of sphingolipids. In this study, the inhibition of yeast (Saccharomyces cerevisiae) proliferation by ISP-1 was observed. This ISP-1-induced growth inhibition was also triggered by decreases in the intracellular levels of sphingolipids. In addition, DNA duplication without cytokinesis was detected in ISP-1-treated yeast cells on flow cytometry analysis. We have cloned multicopy suppressor genes of yeast which overcome the lethal sphingolipid depletion induced by ISP-1. One of these genes, SLI2, is synonymous with YPK1, which encodes a serine/threonine kinase. Kinase-dead mutants of YPK1 did not show any resistance to ISP-1, leading us to predict that the kinase activity of the Ypk1 protein should be essential for this resistance to ISP-1. Ypk1 protein overexpression had no effect on sphingolipid biosynthesis by the yeast. Furthermore, both the phosphorylation and intracellular localization of the Ypk1 protein were regulated by the intracellular sphingolipid levels. These data suggest that the Ypk1 protein is a downstream kinase in the sphingolipid-mediated signaling pathway of yeast. The Ypk1 protein was reported to be a functional homologue of the mammalian protein kinase SGK, which is a downstream kinase of 3-phosphoinositide-dependent kinase 1 (PDK1). PDK1 phosphotidylinositol (PI) is regulated by PI-3,4,5-triphosphate and PI-3,4-bisphosphate through the pleckstrin homology (PH) domain. Overexpression of mammalian SGK also overcomes the sphingolipid depletion in yeast. Taking both the inability to produce PI-3,4, 5-triphosphate and PI-3,4-bisphosphate and the lack of a PH domain in the yeast homologue of PDK1, the Pkh1 protein, into account, these findings further suggest that yeast may use sphingolipids instead of inositol phospholipids as lipid mediators.
Mol Cell Biol 2000 Jun
PMID:Sli2 (Ypk1), a homologue of mammalian protein kinase SGK, is a downstream kinase in the sphingolipid-mediated signaling pathway of yeast. 1082 4

Transient glucose deprivation of the heart [GLU (-)] confers a preconditioning-like protection against subsequent ischemic/reperfusion (I/R). The mechanisms involved remain unclear. We hypothesized that GLU (-) would induce the classic ischemic preconditioning activated signaling cascade. Potential metabolic consequences and putative cell signaling events induced by transient glucose deprivation were evaluated as candidate mediators of this cardioprotection. Isolated glucose-perfused rat hearts were subjected to 30 min global ischemia followed by 30 min reperfusion (index I/R). Cardiac contractile recovery following I/R was used as the functional end-point in these studies. Metabolic preconditioning was stimulated by 15 min GLU (-) followed by 10 min glucose repletion prior to the index I/R. The potential metabolic consequences of GLU (-) were evaluated by using excess octanoate (11 mM OCT Hi) or 11 mM 2-deoxy-D-glucose (2-DG) in place of GLU (-) and by combining GLU (-) with fuels known to inhibit glycolysis supply (20 mM pyruvate or 1 mM octanoate, OCT Lo). The roles of alpha-adrenoceptors, beta-adrenoceptors, adenosine receptors, protein kinase C (PKC) and mitochondrial K(ATP) channels were investigated using inhibitors prazosin (10 microM), propranolol (10 microM), 8-(p-sulfophenyl) theophylline, (SPT 100 microM), chelerythrine (CHEL 10 microM) and 5-hydroxydecanoate (5 HD 100 microM) respectively. GLU (-) increased mechanical recovery (59.8 +/- 4.0 vs. 32.3 +/- 4.7%; p < 0.01). Protection was abolished by pyruvate 26.6 +/- 3.1; SPT 36.6 +/- 3.0; CHEL 35 +/- 4.8 or 5 HD 23.8 +/- 3.3%. In a separate set of experiments, the specificity of SPT in this model was tested by preconditioning with adenosine (100 microM) (34.7 +/- 4 vs. control 16.8 +/- 1.3%, p = 0.01) and blocking this protection with the same dose of SPT (16.3 +/- 1 .5%) used in the GLU (-) studies. Protection was unaltered by prazosin (50.2 +/- 3.3%), propranolol (55.5 +/- 4.0%), or OCT Lo (50.2 +/- 2.5%). Protection was not mimicked by OCT Hi (35.6 +/- 3.8%) or 2-DG (34 +/- 4.3%). Transient glucose deprivation does not seem to achieve preconditioning-like cardioprotection by decreased glycolysis. Rather, the signal system may involve enhanced adenosine release, PKC, and activation of the mitochondrial K(ATP) channel.
Mol Cell Biochem 2000 Aug
PMID:Mechanisms whereby glucose deprivation triggers metabolic preconditioning in the isolated rat heart. 1105 54

Adenosine accumulates to high levels in inflamed or ischemic tissues and activates A3 adenosine receptors (ARs) on mast cells to trigger degranulation. Here we show that stimulation of rat basophilic leukemia (RBL)-2H3 mast-like cells with the A3 AR agonists N6-(3-iodo)benzyl-5'-N-methylcarboxamidodoadenosine (IB-MECA; 10 nM) or inosine (10 microM) stimulates phosphorylation of protein kinase B (Akt). IB-MECA (1 microM) also causes a >50% reduction in apoptosis caused by exposure of RBL-2H3 cells to UV light. Akt phosphorylation is not stimulated by 100 nM N6-cyclopentyladenosine (A1-selective) or CGS21680 (A2A-selective) and is absent in cells pretreated with wortmannin or pertussis toxin. The KI values of the AR antagonists BW-1433 and 8-sulfophenyltheophylline (8-SPT) were determined in radioligand binding assays for all four subtypes of rat ARs: BW-1433 (A1, 5.8 +/- 1.0 nM; A2A, 240 +/- 37; A2B, 30 +/- 10; A3, 12,300 +/- 3, 700); 8-SPT (A1, 3.2 +/- 1.2 microM; A2A, 57 +/- 4; A2), 2.2 +/- 0.8; A3, >100). BW-1433 and the A3-selective antagonist MRS1523 (5 microM), but not 8-SPT (100 microM), block IB-MECA-induced protection from apoptosis, confirming the A3 AR as the mediator of the antiapoptotic response. The data suggest that adenosine and inosine activate Gi-coupled A3 ARs to protect mast cells from apoptosis by a pathway involving the betagamma subunits of Gi, phosphatidylinositol 3-kinase beta, and Akt. We speculate that activation of A3 ARs on mast cells or other cells that express A3 ARs (e.g., eosinophils) may facilitate their survival and accumulation in inflamed tissues.
Mol Pharmacol 2001 Jan
PMID:A3 adenosine receptor activation triggers phosphorylation of protein kinase B and protects rat basophilic leukemia 2H3 mast cells from apoptosis. 1112 27

Primary hyperoxaluria Type 1 (PH1) is caused by a functional deficiency of a liver enzyme, serine:pyruvate/alanine:glyoxylate aminotransferase (SPT/AGT), which catalyzes transamination between L-serine or l-alanine as an amino acid substrate and glyoxylate or pyruvate as an alpha-keto acid substrate. A high affinity for glyoxylate is a notable feature of this enzyme, suggesting a role in glyoxylate metabolism in vivo. Another conspicuous feature of SPT/AGT is its species-specific and food habit-dependent subcellular distribution. Thus, the enzyme is located in peroxisomes in herbivores and man, largely in mitochondria in carnivores, and in both the organelles in rodents. The mechanism of the species-specific dual organelle localization of SPT/AGT is either transcription of the gene from two different start sites or loss of the upstream translation initiation ATG codon by mutations. It appears that the mitochondrial versus peroxisomal distribution of SPT/AGT in different animal species is indispensable in meeting the metabolic needs caused by their respective food habits. As for the peroxisomal localization, glycolate is contained in plants much more than in animal tissues, and when ingested, it is converted to glyoxylate, an immediate precursor of oxalate, in liver peroxisomes. Therefore, peroxisomal localization of SPT/AGT may be indispensable for herbivores to convert the glyoxylate formed in peroxisomes into glycine in situ rather than forming oxalate. On the other hand, our recent studies showed that SPT/AGT contributed substantially to serine metabolism in rabbit, human, and dog livers; i.e., irrespective of its mitochondrial or peroxisomal localization. Thus, the mitochondrial localization of SPT/AGT was not a prerequisite for the metabolism of L-serine. Another source of glyoxylate is the metabolism of L-hydroxyproline, and in this case, the enzyme responsible for the glyoxylate formation has been reported to be a mitochondrial matrix enzyme. Collagen accounts for about 30% of total animal proteins and contains about 13% (w/w) hydroxyproline. It is therefore possible that both mitochondrial and peroxisomal SPT/AGT contribute to the metabolism of glyoxylate and serine, but the subcellular site for glyoxylate metabolism is different in herbivores and carnivores.
Mol Urol 2000
PMID:Oxalate synthesis in mammals: properties and subcellular distribution of serine:pyruvate/alanine:glyoxylate aminotransferase in the liver. 1115

Sphingolipids are major components of the plasma membrane of eukaryotic cells and were once thought of merely as structural components of the membrane. We have investigated effects of inhibiting sphingolipid biosynthesis, both in germinating spores and growing hyphae of Aspergillus nidulans. In germinating spores, genetic or pharmacological inactivation of inositol phosphorylceramide (IPC) synthase arrests the cell cycle in G(1) and also prevents polarized growth during spore germination. However, inactivation of IPC synthase not only eliminates sphingolipid biosynthesis but also leads to a marked accumulation of ceramide, its upstream intermediate. We therefore inactivated serine palmitoyltransferase, the first enzyme in the sphingolipid biosynthesis pathway, to determine effects of inhibiting sphingolipid biosynthesis without an accumulation of ceramide. This inactivation also prevented polarized growth but did not affect nuclear division of germinating spores. To see if sphingolipid biosynthesis is required to maintain polarized growth, and not just to establish polarity, we inhibited sphingolipid biosynthesis in cells in which polarity was already established. This inhibition rapidly abolished normal cell polarity and promoted cell tip branching, which normally never occurs. Cell tip branching was closely associated with dramatic changes in the normally highly polarized actin cytoskeleton and found to be dependent on actin function. The results indicate that sphingolipids are essential for the establishment and maintenance of cell polarity via control of the actin cytoskeleton and that accumulation of ceramide is likely responsible for arresting the cell cycle in G(1).
Mol Cell Biol 2001 Sep
PMID:Cell cycle progression and cell polarity require sphingolipid biosynthesis in Aspergillus nidulans. 1150 63

GCN5 is a histone acetyltransferase (HAT) originally identified in Saccharomyces cerevisiae and required for transcription of specific genes within chromatin as part of the SAGA (SPT-ADA-GCN5 acetylase) coactivator complex. Mammalian cells have two distinct GCN5 homologs (PCAF and GCN5L) that have been found in three different SAGA-like complexes (PCAF complex, TFTC [TATA-binding-protein-free TAF(II)-containing complex], and STAGA [SPT3-TAF(II)31-GCN5L acetylase]). The composition and roles of these mammalian HAT complexes are still poorly characterized. Here, we present the purification and characterization of the human STAGA complex. We show that STAGA contains homologs of most yeast SAGA components, including two novel human proteins with histone-like folds and sequence relationships to yeast SPT7 and ADA1. Furthermore, we demonstrate that STAGA has acetyl coenzyme A-dependent transcriptional coactivator functions from a chromatin-assembled template in vitro and associates in HeLa cells with spliceosome-associated protein 130 (SAP130) and DDB1, two structurally related proteins. SAP130 is a component of the splicing factor SF3b that associates with U2 snRNP and is recruited to prespliceosomal complexes. DDB1 (p127) is a UV-damaged-DNA-binding protein that is involved, as part of a complex with DDB2 (p48), in nucleotide excision repair and the hereditary disease xeroderma pigmentosum. Our results thus suggest cellular roles of STAGA in chromatin modification, transcription, and transcription-coupled processes through direct physical interactions with sequence-specific transcription activators and with components of the splicing and DNA repair machineries.
Mol Cell Biol 2001 Oct
PMID:Human STAGA complex is a chromatin-acetylating transcription coactivator that interacts with pre-mRNA splicing and DNA damage-binding factors in vivo. 1156 63


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