[PREPARATION OF HUMAN TISSUE PROTEIN EXTRACTS ENRICHED WITH THE SPHINGOMYELIN SYNTHASE 1]

Sphingomyelin synthase 1 (SMS 1) catalyzes sphingomyelin biosynthesis in eukaryotic cells. We previously studied the structure of the human SGMS1 gene, which encodes the enzyme and its numerous transcripts. The tissue-specific expression of the transcripts was also described. Analysis of the SMS1 protein expression in human tissues using immunoblotting of tissue extracts prepared in the RIPA (Radio Immuno-Precipitation Assay) buffer revealed a weak signal in renal cortex, testis, lung, and no signal in placenta and lymphatic node. In this work, a new method of preparation of the tissue protein extracts enriched with SMS1 was suggested. The method based on the consecutive extraction with a buffer containing 0.05 and 1 mg/ml of the Quillaja saponaria saponin allowed SMS1 to be detected in all tissues tested. The SMS1 content in the saponin extract of kidney cortex is about 12-fold higher compared to the RIPA extraction procedure.

Cardiolipin-mediated mitochondrial dynamics and stress response in Arabidopsis

Mitochondria are essential and dynamic organelles in eukaryotes. Cardiolipin (CL) is a key phospholipid in mitochondrial membranes, playing important roles in maintaining the functional integrity and dynamics of mitochondria in animals and yeasts. However, CL's role in plants is just beginning to be elucidated. In this study, we used Arabidopsis thaliana to examine the subcellular distribution of CL and CARDIOLIPIN SYNTHASE (CLS) and analyzed loss-of-function cls mutants for defects in mitochondrial morphogenesis and stress response. We show that CL localizes to mitochondria and is enriched at specific domains, and CLS targets to the inner membrane of mitochondria with its C terminus in the intermembrane space. Furthermore, cls mutants exhibit significantly impaired growth as well as altered structural integrity and morphogenesis of mitochondria. In contrast to animals and yeasts, in which CL's effect on mitochondrial fusion is more profound, Arabidopsis CL plays a dominant role in mitochondrial fission and exerts this function, at least in part, through stabilizing the protein complex of the major mitochondrial fission factor, DYNAMIN-RELATED PROTEIN3. CL also plays a role in plant responses to heat and extended darkness, stresses that induce programmed cell death. Our study has uncovered conserved and plant-specific aspects of CL biology in mitochondrial dynamics and the organism response to environmental stresses.

Evaluation of Analgesic, Antipyretic Activity and Toxicity Study ofBryonia laciniosain Mice and Rats

Analgesic, antipyretic activity and toxicity study of the leaves of Bryonia laciniosa Linn. (Family: Cucurbitaceae) was evaluated in the standard animal models. The methanol extract of Bryonia laciniosa (MEBL) was evaluated by hot plate and acetic acid-induced writhing methods to assess analgesic activity. The antipyretic activity of the extract was also evaluated by normal body temperature and yeast-induced hyperpyrexia. The extract showed significant analgesic and antipyretic activity. The MEBL was further evaluated for toxicity at the doses of 125 and 250 mg/kg administered orally for 14 days in rats. At the end of experiments, the blood, liver function and kidney metabolism were observed. The hematological profile and different biochemical parameters such as SGOT, SGPT and ALP were estimated. The present study revealed that MEBL exhibited significant analgesic and antipyretic activity in the tested experimental animal models. The toxicity study indicates that the extract is not toxic at the tested doses.

Cellular localization of sphingomyelin synthase 2 in the seminiferous epithelium of adult rat testes

Sphingomyelin synthase 2 (SMS2) is an enzyme that catalyzes the conversion of phosphatidylcholine and ceramide to sphingomyelin and diacylglycerol, and it is crucial to cellular lipid metabolism. Using the technique of subtraction hybridization, we have isolated a full-length cDNA encoding SMS2 from rat testes, which shared 93 and 87% identity at the nucleotide level with SMS2 in mice and humans respectively. A specific polyclonal antibody was prepared against a 20 amino acid peptide of NH(2)-FSWPLSWPPGCFKSSCKKYS-COOH near the C-terminus of SMS2. Studies by RT-PCR and immunoblotting have shown that the expression of SMS2 was limited to late round spermatids and elongating spermatids, but it was not detected in late elongate spermatids and Sertoli cells. Furthermore, SMS2 was shown to associate with the developing acrosome beginning in late round spermatid through elongating spermatids (but not late elongate spermatids) and the cell membrane in studies using fluorescent microscopy and immunohistochemistry. These data were further confirmed by studies using immunogold electron microscopy. The expression of SMS2 in the seminiferous epithelium is stage-specific with its highest expression detected in the acrosome region in late round spermatids from stages VIII-IX, and also in the acrosome in elongating spermatids with diminished intensity in stages X-V; however, it was not found in the acrosome in elongate spermatids in stages VI-VIII. Collectively, these results suggest that SMS2 may play a crucial role in the lipid metabolism in acrosome formation and the plasma membrane restructuring from late round spermatids to early elongating spermatids.

Missense mutation in the N-acetylglucosamine-1-phosphotransferase gene (GNPTA) in a patient with mucolipidosis II induces changes in the size and cellular distribution of GNPTG

Mucolipidosis type II (ML II; I-cell disease) and mucolipidosis III (ML III; pseudo Hurler polydystrophy) are autosomal recessively inherited disorders caused by a defective N-acetylglucosamine 1-phosphotransferase (phosphotransferase). The formation of mannose 6-phosphate markers in soluble lysosomal enzymes is impeded leading to their increased excretion into the serum, to cellular deficiency of multiple hydrolases, and lysosomal storage of non-digested material. Phosphotransferase deficiency is caused by mutations in GNPTA and GNPTG encoding phosphotransferase subunits. Here we report on an adolescent with progressive joint contractions and other signs of mucolipidosis II who survived to the age of 14 years. Impaired trafficking of lysosomal enzymes cathepsin D and -hexosaminidase in metabolically labeled fibroblasts was documented. Mutations in the GNPTG gene and alterations in the GNPTG mRNA level were not detected. A different electrophoretic mobility of the 97 kDa GNPTG dimer suggested posttranslational modification abrogating the compartmentalization of GNPTG in the Golgi apparatus. A nucleotide substitution in the GNPTA gene (c.3707A>T) was identified altering the predicted C-terminal transmembrane anchor of the phosphotransferase subunit. The data demonstrate that defective GNPTA not only impairs lysosomal enzyme targeting but also the availability of intact GNPTG required for phosphotransferase activity and assembly of subunits.

On the mechanism of the increase in cardiolipin biosynthesis and resynthesis in hepatocytes during rat liver regeneration

CL (cardiolipin) is a major mitochondrial membrane phospholipid important for the regulation of mitochondrial function. We examined CL de novo biosynthesis and its resynthesis in isolated rat liver hepatocytes prepared 48 h subsequent to two-thirds PHx (partial hepatectomy). The pool size of CL and its de novo biosynthesis from [1,3-(3)H]glycerol were increased 3.3-fold (P<0.05) and 3.1-fold (P<0.05) respectively in hepatocytes prepared from PHx rats compared with sham-operated controls. The reason for the increased CL biosynthesis was a 65% increase (P<0.05) in enzymic activity in PGP-S (phosphatidylglycerolphosphate synthase), a key enzyme in de novo CL biosynthesis. The increase in PGP-S activity was due to a 3-fold increase (P<0.05) of hepatic PGP-S mRNA expression. The increase in de novo CL biosynthesis and pool size corresponded to a 2.3-fold increase (P<0.05) in the amount of [1-14C]linoleic acid incorporated into CL of hepatocytes prepared from PHx rats compared with sham-operated controls, indicating an increase in CL resynthesis. The activity of MLCL-AT (monolysocardiolipin acyltransferase), a rate-limiting enzyme of CL resynthesis, was increased by 43% (P<0.05) in hepatocytes prepared from PHx rats compared with sham-operated controls; this result would explain the increase in [1-14C]linoleic acid incorporation into CL. The increase in MLCL-AT activity was due to an increase in hepatic MLCL-AT protein expression. The results show that CL de novo biosynthesis and its resynthesis are increased during liver regeneration.

Astroglial expression of ceramide in Alzheimer's disease brains: a role during neuronal apoptosis

Accumulating evidences indicate that ceramide is closely involved in apoptotic cell death in neurodegenerative disorders and aging. We examined ceramide levels in the cerebrospinal fluid (CSF) or brain tissues from patients with neurodegenerative disorders and the mechanism of how intra- and extracellular ceramide was regulated during neuronal apoptosis. We screened the ceramide levels in the CSF of patients with neurodegenerative disorders, and found that ceramide was significantly increased in patients with Alzheimer's disease (AD) than in patients with age-matched amyotrophic lateral sclerosis (ALS) and other neurological controls. With immunohistochemistry in AD brains, ceramide was aberrantly expressed in astroglia in the frontal cortices, but not detected in ALS and control brains. To explore for the regulation of ceramide in astroglia in Alzheimer's disease brains, we examined the metabolism of ceramide during neuronal apoptosis. In retinoic acid (RA)-induced neuronal apoptosis, RA slightly increased de novo synthesis of ceramide, but interestingly, RA dramatically inhibited conversion of [14C] ceramide to glucosylceramide (GlcCer), suggesting that the increase of ceramide mass is mainly due to inhibition of the ceramide-metabolizing enzyme GlcCer synthase. In addition, a significant increase of the [14C] ceramide level in the culture medium was detected by chasing and turnover experiments without alteration of extracellular [14C] sphingomyelin levels. A 2.5-fold increase of ceramide mass in the supernatant was also detected after 48 h of treatment with RA. These results suggest a regulatory mechanism of intracellular ceramide through inhibition of GlcCer synthase and a possible role of ceramide as an extracellular/intercellular mediator for neuronal apoptosis. The increased ceramide level in the CSF from AD patients, which may be derived from astroglia, raises a possibility of neuronal apoptosis by the response to intercellular ceramide in AD.

Chromatin-associated sphingomyelin: metabolism in relation to cell function

After the first histochemical demonstration by Chayen and Gahan of the presence of phospholipids and especially of sphingomyelin in chromatin, this became the object of long debate and of contradictory results. The general conclusion was that the presence of phospholipids may due to contamination during the isolation of chromatin. More recently the existence of a phospholipid chromatin fraction was confirmed by demonstrating that isolated hepatocyte nuclei, labelled by saturated and unsaturated radioiodination method, showed the presence of radioactivity only in the membrane and not in the isolated chromatin. The phospholipid composition showed an enrichment in sphingomyelin which increased during hepatocyte maturation or erythroleukemic cell differentiation induced by DMSO. A decrease in sphingomyelin was observed at the beginning of the S-phase in regenerating liver or in cultured proliferating cells. These changes were due to the presence of sphingomyelinase and sphingomyelin synthase in the chromatin, the activity of which paralleled the variation in sphingomyelin content. The sphingomyelin was co-localized with RNA as shown by biochemical and electron microscopy methods. Using bromo-uridine it was demonstrated that labelled RNA and sphingomyelin were present in actively transcribing nuclear regions. Isolated nuclear complexes after DNase and RNase digestion contained not only protein, but also RNA and sphingomyelin. After hydrolysis of sphingomyelin the RNAse-resistant RNA becomes RNAse sensitive. It can therefore be concluded that sphingomyelin and the related enzymes are present in the chromatin; sphingomyelin may have a role in RNA transcription protecting RNA by RNAse digestion before its transfer to the cytoplasm.

Effect of pulp and paper mill effluent (BKME) on physiological parameters of roach (Rutilus rutilus) infected by the digenean Rhipidocotyle fennica

Physiological parameters were measured after experimental infection of roach (Rutilus rutilus L.) with Rhipidocotyle fennica Gibson, Valtonen et Taskinen, 1992 (Digenea) cercariae. The fish were caught from two lakes: a eutrophic bleached kraft mill effluent (BKME)-contaminated lake and an oligotrophic unpolluted lake. The intensity of infection was followed up to 10 days post infection (p.i.) and physiological parameters indicating non-specific stress responses and the condition of fish were examined simultaneously. The mean abundance, the number of parasites per fish, of R. fennica was significantly higher in the fish from the contaminated water during the first two days p.i., probably reflecting the decreased resistance of these fish to infection. The decrease of leukocrit, as well as the increase of the activity of transaminases (GOT and GPT) in infected fish of both groups are suggestive of pathological processes caused by cercariae penetrating the fish. A significantly lower leukocrit value, as well as higher alkaline phosphatase activity and plasma chloride levels were noted in fish originating from the contaminated lake compared to those from the unpolluted lake. No significant differences were noted in haematocrit, plasma protein and calcium values between the fish from the uncontaminated and contaminated lakes, or between the infected and uninfected control fish.

The lysis protein E of phi X174 is a specific inhibitor of the MraY-catalyzed step in peptidoglycan synthesis

Coliphage phi X174 encodes a single lysis protein, E, a 91-amino acid membrane protein. Dominant mutations have been isolated in the host gene mraY that confer E resistance. mraY encodes translocase I, which catalyzes the formation of the first lipid intermediate in bacterial cell wall synthesis, suggesting a model in which E inhibits MraY and promotes cell lysis in a manner analogous to cell wall synthesis inhibitors like penicillin. To test this model biochemically, we monitored the effect of E on cell wall synthesis in vivo and in vitro. We find that expression of Emyc, encoding an epitope-tagged E protein, from a multicopy plasmid inhibits the incorporation of [(3)H]diaminopimelic acid into cell wall and leads to a profile of labeled precursors consistent with MraY inhibition. Moreover, we find that membranes isolated after Emyc expression are drastically reduced in MraY activity, whereas the activity of Rfe, an enzyme in the same superfamily, was unaffected. We therefore conclude that E is indeed a cell wall synthesis inhibitor and that this inhibition results from a specific block at the MraY-catalyzed step in the pathway.

Deficient platelet-activating factor and related enzymes in hemimegalencephaly

Platelet-activating factor (PAF) may influence neuronal migration, and gyral anomaly in hemimegalencephaly is believed to result from a neuronal disorder. A 7-month-old girl with hemimegalencephaly presented with intractable seizures, for which graded hemispherectomy was performed. In the resected specimen, we could not detect PAF, and related enzyme activities were low. These results suggest a role of PAF in neuronal migration.

Preparation of Golgi subfractions with free-solution isotachophoresis: analysis of sphingomyelin synthesis in Golgi subfractions from rat liver

A new displacement electrophoresis technique, termed free-solution isotachophoresis (FS-ITP) was used for the analysis of sphingolipid metabolism in Golgi subfractions. The discontinuous electrolyte system enables tissue-derived membrane vesicles to be separated and purified due to their polarity patterns in a mobility gradient. In this study total Golgi apparatus obtained from rat liver by discontinuous density gradient centrifugation was subfractionated by preparative FS-ITP, yielding enzymatically active cis-, medial-, and trans-Golgi subfractions. These membrane vesicles were assayed by the following established enzyme marker activities: NADH cytochrome c reductase (cis-Golgi), NADP phosphatase (medial-Golgi), and thiamine pyrophosphatase (trans-Golgi). The activity of phosphatidylcholine:ceramide phosphocholine transferase, a sphingomyelin synthesizing enzyme, is attributed to the cis- and medial-Golgi-derived subfractions. Analysis of Golgi lipids revealed a decline in membranous ceramide along the cis- to trans-Golgi polarity axis. Furthermore, significant amounts of newly synthesized sphingomyelin and diacylglycerol are transferred from the medial/cis- to the trans-Golgi compartment. The FS-ITP system is well suited for micropreparative experimental applications, as demonstrated by studies on phosphatidylcholine:ceramide phosphocholine transferase activity in Golgi membrane vesicles of rat liver obtained by FS-ITP.

Characterization of multiple transcripts of the hamster dolichol-P-dependent N-acetylglucosamine-1-P transferase suggests functionally complex expression

The evolutionarily conserved dolichol-P-dependent N-acetylglucosamine-1-P transferase gene, ALG7, functions by initiating the dolichol pathway of protein N-glycosylation. In yeast, ALG7 has a complex expression pattern and plays a critical role in diverse cellular functions, including proliferation and morphological response. In Chinese hamster ovary cells (CHO), ALG7 gives rise to three mRNAs of 1.5, 1.9 and 2.2 kb. We report results of RNA blotting assays, ribonuclease protection, PCR-amplification and sequencing of the CHO ALG7 transcripts 5' and 3' ends which suggest that the 1.5 and 1.9 kb transcripts are produced as a consequence of initiation at 2 distinct start sites, 350-379 bp apart. The transcriptional start site for the 1.5 kb mRNA is positioned between the first two in frame ATGs, while that of the 1.9 kb species is located upstream of these two in-frame ATGs. In order to test the translational competence of the 1.5 and 1.9 kb mRNAs, we constructed DNA templates specifying these transcripts and used them for in vitro transcription/translation. Our data show that the 1.9 kb mRNA served in the synthesis of 36 and 24 kDa species, as well as a low-abundance 32 kDa protein. The 1.5 kb transcript gave rise to a translation product of 32 kDa. The latter is synthesized in CHO cells and hamster submandibular glands. These results suggest the possibility that the 1.5 and 1.9 kb transcripts give rise to related protein isoforms with different lengths of their NH2-terminal regions.

Spontaneous mucolipidosis in a cat: an animal model of human I-cell disease

A 7-month-old female cat was seen for abnormal facial features and abnormality of gait. Facial dysmorphism, large paws in relation to body size, dysostosis multiplex, and poor growth were noted, and mucopolysaccharidosis was suspected. A negative urine test for sulfated glycosaminoglycans and extreme stiffness of skin indicated a mucolipidosis hitherto unknown in animals. Deficiency of UDP-N-acetylglucosamine: lysosomal enzyme N-acetylglucosamine-1-phosphotransferase (GlcNAc-phosphotransferase, EC 2.7.8.17) activity was demonstrated in leukocytes and cultured fibroblasts, which had the appearance of inclusion cells (I-cells). Activities of a set of lysosomal hydrolases were abnormally low in fibroblasts and excessive in blood plasma. Postmortem morphology revealed lysosomal inclusions predominantly in fibroblasts but also in endothelial cells and chondrocytes, i.e., in cells of mesenchymal origin. Storage lysosomes contained oligosaccharides, mucopolysaccharides, and lipids. Tissues most affected were bones, cartilage, skin, and other connective tissues such as those in heart valves, aortic wall, and vocal cords. Parenchymal cells of liver and kidney were unaffected, as was skeletal muscle. Only a few of the cerebral cortical neurons had lipid inclusions; in sciatic nerve some axons were affected, but other peripheral nerves were normal. There were striking clinical, biochemical, and morphologic similarities between the disorder in this cat and the human I-cell disease.

Rod outer segment-associated N-acetylgalactosaminylphosphotransferase

PURPOSE

To determine the exact location of a cell surface glycosyltransferase (N-acetylgalactosaminylphosphotransferase, (GalNAcPTase) immunochemically identified in mammalian rod outer segments (ROS), to determine whether anti-GalNAcPTase antibody recognizes retinal molecules that possess transferase activity and to characterize ROS transferase enzyme activity and acceptors. The GalNAcPTase is known to be associated with the adhesion molecule N-cadherin in embryonic avian retinas and with E-cadherin in mammalian pancreatic islet cells.

METHODS

Purified, fixed ROS were reacted with anti-chick GalNAcPTase antibody followed by secondary antibody conjugated to colloidal gold and were examined by electron microscopy. Fractions of retinal and ROS proteins enriched in the transferase were obtained through batch adsorption on Sepharose, separated by gel electrophoresis, transferred to nitrocellulose, and either reacted with anti-GalNAcPTase antibody or assayed for transferase activity. Interphotoreceptor matrix (IPM) was examined for the presence of immunoreactive GalNAcPTase by gel electrophoresis and immunoblot. The kinetics and endogenous acceptors of the cow ROS transferase were characterized.

RESULTS

ROS are specifically labeled by anti-GalNAcPTase antibody at the cell surface. The immunogold label was associated with the cell surface and with flocculent material adherent to the cell surface. In addition, soluble and particulate fractions of the IPM showed GalNAcPTase-like immunoreactivity. The transferase appears as single immunoreactive band at or near 220 kd. Transferase enzyme activity was present at this position on Western transfers of retinal and ROS proteins. In whole ROS, transferase activity was directed toward endogenous acceptors of very high molecular mass.

CONCLUSIONS

The GalNAcPTase is localized on ROS in association with the cell surface and with components of the IPM. The molecule recognized by the anti-GalNAcPTase antibody possesses transferase activity toward itself and a few other proteins, but mostly toward very large molecules that may be IPM proteoglycans. It is not yet known whether the enzyme of the adult retina specifically transfers sugar or sugar-phosphate groups to its acceptors. It is proposed that the ROS GalNAcPTase is involved in the modulation of adhesive phenomena between or within photoreceptors or between photoreceptors and the interphotoreceptor matrix.

Intracellular processes associated with vesicular transport from endoplasmic reticulum to Golgi and exocytosis: ethanol-induced changes in membrane biogenesis

Membrane biogenesis, expressed in endoplasmic reticulum (ER) by formation of transport vesicles, was studied in the liver of ethanol-fed and pair-fed rats. In ER of ethanol-fed animals, the endogenous synthesis of phosphatidylcholine (PC) and its contribution to ER transport vesicles were reduced by 50%, as compared to that in pair-fed controls. Reduction of PC synthesis and of its presence in ER-transport vesicles was also observed in pair-fed controls when the native cytosol was replaced with that from ethanol-fed animals. In contrast, preincubation of ER membranes from ethanol-fed animals with cytosol from controls led to the stimulation of PC synthesis in ER and its contribution to ER-transport vesicles. Analysis of water soluble metabolites of [methyl-14C]choline phosphate revealed the accumulation of CDP-choline precursor in samples derived from ethanol-fed rats. Concomitantly, the endogenous synthesis of phosphatidylinositol (PI) in the ER of ethanol-fed animals was stimulated up to 400-500%, but declined when the cytosol from ethanol-fed rats was replaced with that from the controls. The restoration of PC synthesis, the normalization of PI synthase activity, and, similar to control, the contribution of PC to ER-transport vesicles in ethanol-fed animals was achieved when ER membranes were preincubated with diglycerides or the cytosol was treated with ethylene glycol bis (beta-aminoethyl ether) N,N'-tetraacetic acid (EGTA). Conversely, addition of CaCl2-EGTA buffer containing 3 microM free Ca2+ to control samples, led to a reduction in PC synthesis. The studies on the effect of free Ca2+ on PI synthase and phosphatidic acid (PA) phosphatase activity established that in the presence of 1-3 microM free Ca2+, PI synthase activity remained constant, whereas that of PA phosphatase was reduced by 40% at 1 microM Ca2+, and no activity was detected when free Ca2+ was adjusted to 3 microM. The results suggest that modified membrane biogenesis in the liver of ethanol-fed rats is connected to the elevated free Ca2+ in the cytosol, which appears to regulate phosphatase activity. Accumulation of CDP-choline, decreased activity of PA phosphatase, and increased contribution of PI lipids to ER-transport vesicle membrane suggest that in ethanol-fed animals diglycerides are depleted and PA is utilized in a CDP-diacylglycerol pathway, thus leading to the generation of a different group of phospholipids and consequently modified ER-transport vesicle membrane.