Cloning,expression and characterization of serine palmitoyltransferase(SPT)-like gene subunit(LCB2) from marine Emiliania huxleyi virus(Coccolithovirus)

The authors have isolated and characterized a novel serine palmitoyltransferase （SPT）-like gene in marine Emiliania huxleyi virus （EhV-99B1）. The open-reading frame （ORF） of EhV99BI-SPT encoded a protein of 496 amino acids with a calculated molecular mass of 96 kDa and Ip 6.01. The results of sequence analysis showed that there was about 31% 45% identity in amino acid sequence with other organisms. The maximum likelihood phylogenetic tree suggested that the EhV99B1-SPT gene possibly horizontally transferred from the eukaryote. Hydrophobic profiles of deduced amino acid sequences suggested a hydrophobic, globular and membrane-associated protein with five transmembrane domains （TMDs） motifs. Several potential N-linked glycosylation sites were presented in SPT. These results suggested that EhV99BI-SPT was an integral endoplasmic reticulum membrane protein. Despite lower sequence identity, the secondary and three-dimensional structures predicted showed that the “pocket” structure element composed of 2a-helices and 4β- sheets was the catalytic center of this enzyme, with a typical conserved “TFTKSFG” active site in the N-terminal region and was very close to those of prokaryotic organisms. However, the N-terminal domain of EhV99B1-SPT most closely resembled the LCB2 catalysis subunit and the C-terminal domain most closely resembled the LCBI regulatory subunit of other organisms which together formed a spherical molecule. This “chimera” was highly similar to the prokaryotic homologous SPT. For a functional identification, the EhV99B1-LCB2 subunit gene was expressed in Escherichia coli, which resulted in significant accumulation of new sphingolipid in E. coli cells.

Transformation of coccolithophorid Emiliania huxleyi harboring a marine virus(Coccolithoviruses)serine palmitoyltransferase(SPT)gene by electroporation

Emiliania huxleyi is the most prominent modern coccolithophore,a group of marine unicellular eukaryotes that play a critical role in ocean biogeochemistry.Coccolithoviruses are large double stranded DNA viruses,which is responsible for the demise of large oceanic blooms formed by E.huxleyi.E.huxleyi virus(EhVs)acquired a series of enzyme-coding genes predicted to be involved in the sphingolipid biosynthesis by horizontal gene transfer between virus-host.Currently,there is limited experimental validation identifying the functions of these genes in EhV.Genetic transformation of eukaryotic cells is a powerful tool to get an insight into gene functions of the studied organisms.Serine palmitoyltransferase(SPT)catalyzes the first committed step in de novo sphingolipid biosynthetic pathway.Here,a novel vector system for the transformation of E.huxleyi was designed.It contained fragments of promoter and terminator sequences of E.huxleyi endogenic fucoxanthin chlorophyll a/c-binding protein gene“fcp”and harbored EhV-99B1 spt gene.The resultant recombinant transformation vectors pEhux-I-spt and pEhux-II were co-transferred into E.huxleyi BOF92 by electroporation.Transformants were obtained upon glufosinate-ammonium selection,and confirmed by Southern hybridization,genome PCR,qRT-PCR and Western blot screening of spt gene,which indicated that spt gene was integrated into the nuclear genome and was expressed at the mRNA and protein levels.The expression of the viral spt gene led to differences in lipid compositions analyzed using thin-layer chromatography(TLC).The results present the genetic transformation system for E.huxleyi,providing additional genetic resource with potential for exploring basic biological questions such as the virus-host interactions.

A palmitoyltransferase Approximated gene Bm-app regulates wing development in Bombyx mori

The silkworm Bombyx mori is an important lepidopteran model insect in which many kinds of natural mutants have been identified.However,molecular mechanisms of most of these mutants remain to be explored.Here we report the identification of a gene Bm-app is responsible for the silkworm minute wing(mw)mutation which exhibits exceedingly small wings during pupal and adult stages.Compared with the wild type silkworm,relative messenger RNA expression of Bm-app is significantly decreased in the ul 1 mutant strain which shows mw phenotype.A 10 bp insertion in the putative promoter region of the Bm-app gene in mw mutant strain was identified and the dual luciferase assay revealed that this insertion decreased Bm-app promoter activity.Furthermore,clustered regularly interspaced short palindromic repeats/RNA-guided Cas9 nucleases-mediated depletion of the Bm-app induced similar wing defects which appeared in the mw mutant,demonstrating that Bm-app controls wing development in B.mori.Bm-app encodes a palmitoyltransferase and is responsible for the palmitoylation of selected cytoplasmic proteins,indicating that it is required for cell mitosis and growth during wing development.We also discuss the possibility that Bm-app regulates wing development through the Hippo signaling pathway in B.mori.

Acylcarnitine: Useful biomarker for early diagnosis of hepatocellular carcinoma in non-steatohepatitis patients

BACKGROUND Early diagnosis of hepatocellular carcinoma(HCC)is necessary to improve the prognosis of patients.However,the currently available tumor biomarkers are insufficient for the early detection of HCC.Acylcarnitine is essential in fatty acid metabolic pathways.A recent study reported that a high level of acylcarnitine may serve as a useful biomarker for the early diagnosis of HCC in steatohepatitis(SH)patients.In contrast,another study reported that the level of acetylcarnitine(AC2)-one of the acylcarnitine species-in non-SH patients with HCC was decreased vs that reported in those without HCC.AIM To investigate the usefulness of acylcarnitine as a biomarker for the early diagnosis of HCC in non-SH patients.METHODS Thirty-three non-SH patients(14 with HCC and 19 without HCC)were enrolled in this study.Blood samples were obtained from patients at the time of admission.The levels of acylcarnitine and AC2 in the serum were determined through tandem mass spectrometry.The levels of vascular endothelial growth factor(VEGF)and VEGF receptor 2(VEGFR-2)were determined by enzymelinked immunosorbent assay.Univariate and multivariate analyses were used to determine early diagnostic factors of HCC.RESULTS The level of acylcarnitine was significantly lower in non-SH patients with HCC vs those without HCC(P<0.05).In contrast,the level of lens culinaris agglutininreactive fraction ofα-fetoprotein(AFP)-AFP-L3%-was significantly higher in non-SH patients with HCC vs those without HCC(P<0.05).However,the levels of total carnitine,free carnitine,AFP,des-γ-carboxy prothrombin,VEGF,and VEGFR-2 were not different between patients with and without HCC.The multivariate analysis showed that a low level of acylcarnitine was the only independent factor for the early diagnosis of HCC.The patients with a low level of AC2 had a significantly higher level of VEGF vs those with a high level of AC2(P<0.05).CONCLUSION The metabolic pathways of fatty acids may differ between SH HCC and non-SH HCC.Further studies are warranted to investigate these differences.

The effect of 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR) on fatty acid oxidation in hepatocytes isolated from neonatal piglets

In the present study, the effect of 5-aminoimidazole-4-carboxamide ribonucleoside （AICAR） on long-chain fatty acid oxidation by hepatocytes isolated from suckled neonatal pig liver （a low ketogenic and lipogenic tissue） was tested Incubation of hepatocytes with AICAR （0.5 raM） in the presence of ] mM of carnitine and 10 mM of glucose for 1 hour at 37℃ had no significant effect on total [1-14C]-palrnitate （0.5 mM） oxidation （14CO2 and 14C-Acid soluble products （ASP））. Consistent with the fatty acid oxidation, carnitine palmitoyltransferase I activity and inhibition of its activity by malonyI-CoA （10 MM） assayed in cell homogenate also remained constant. However, addition of AICAR to the hepatocytes decreased 14CO2 production by 18% compared to control （p 〈 0.06）. The reduction of labeled carboxylic carbon accumulated in C02 caused a significant difference in distribution of oxidative products between 14C02 and 14C-ASP （p 〈 0.03） compared with the control. It was also noticed that acetyI-CoA carboxylase （ACC） was increased by AICAR （p 〈 0.03）, indicating that ACC might drive acetyI-CoA toward fatty acid synthesis pathway and induce an increase in distribution of fatty acid carbon to 14C-ASP. Addition of insulin to hepatocyte incubations with AICAR did not change the oxidative product distribution between CO2 and ASP, but further promoted ACC activity. The increased ACC activity was 70% higher than in the control group when citrate was absent in the reaction medium and was 30% higher when citrate was present in the medium. Our results suggest that AICAR may affect the distribution of metabolic products from fatty acid oxidation by changing ACC activity in hepatocyte isolated from suckled neonatal piglets; however, the basis for the increase in ACC activity elicited by AICAR is not apparent.

Concluding Step in Cell Restitution Cycle: ER Transport Vesicles with Sphingolipids in the Outer Leaflet of the Membrane Restore Lysosomes

Restitution of the cell organelles and the membrane implicates serine palmitoyltransferase (SPT) in signal-specific and selective assembly of the transport vesicles. Here, we reveal that SPT, embedded in the outer leaflet (OL) of endoplasmic reticulum (ER), is engaged in the synthesis of ER transport vesicles that recondition cell organelles, and the inner leaflet (IL) SPT in the restitution of the cell membrane. The OL SPT impacts assembly of sphingomyelinase (SMase)—susceptible ER vesicles but not the SMase-resistant and sphingolipid (SPhL) core—carrying vesicles that refurbish the cell membrane. The investigation of the SPT-initiated differences in the placement of SPhL in vesicular membranes by utilizing ER depleted of OL SPT, allows us to conclude that the restitution of endosomal and lysosomal membranes is achieved with the involvement of OL SPT, whereas the IL SPT is involved in formation of the lipid core for glycosphingolipids (GSL) and sphingomyelin (SM) of the apical and basolateral cell membrane. These findings along with our previously published report (Slomiany and Slomiany, Advances in Biological Chemistry, 2013, 3, 275-287), provide a clear distinction between the processes that renovate cell membrane and its organelles from that of the endocytotic cell debridement, and show that vesicles are navigated to the specific organelles and the cell membrane by the biomembrane constituents programmed in ER.

Carnitine palmitoyl transferase 1C regulates tumor cell senescence

OBJECTIVE Passage-dependent cel ular senescence is a complex process limiting the proliferative lifespan of tumor cells but the mechanism of this process is not understood.METHODS Replicative senescenceof pancreatic carcinoma-derived PANC-1 cells wasanalyzed.Metabolomics and transcriptomic analyses were performed to find endogenous metabolites changed andassociated genes.Mitochondrial function,cell survival andtumorigenesis of replicative senescent PANC-1 cellswere analyzed.PANC-1 cells were transfected with RNAi CPT1C to specifically knockdown CPT1C expressions,then mitochondrial function,cellular senescence,cell survival and tumorigenesis were investigated.MDA-MB-231,HCT116,A549,MCF7,and He Lacells werealso transfected with si RNA CPT1C and cellular senescence were monitored.RESULTS Replicative senescenceof PANC-1 cells was confirmed.Metabolomic and transcriptomicanalyses revealed that acylcarnitines and their upstream regulator carnitine palmitoyltransferase 1C(CPT1C),an enzyme that catalyzes the initiating step of fatty acidβ-oxidation,were markedly decreased in senescent PANC-1 cells.Furthermore,low CPT1C expression caused abnormal energy metabolism and mitochondrial dysfunction of PANC-1 cells,resulting in decreased cell survival and a suppressed tumorigenesis.Most importantly,loss of CPT1C triggered mitochondrial dysfunction,leading to senescence-like growth suppression and cellular senescence,suppressed cell survival under metabolic stress,and lower tumorigenesis in a mouse xenograft model.Silencing of CPT1C also induced cellular senescence in five other tumor cell lines.CONCLUSION Low CPT1C expression is a novel biomarker and key regulator of cellular senescence in tumor cell lines.Inhibition of CPT1C may be a new cancer therapeutic target impacting cellular senescence and tumorigenesis through modulation of mitochondrial function.

Berberine alleviates non-alcoholic hepatic steatosis partially by promoting SIRT1 deacetylation of CPT1A in mice

Background:Berberine effectively alleviates non-alcoholic fatty liver disease(NAFLD).Nevertheless,the mechanism is incompletely comprehended.It has been reported that SIRT1 mediates lipid metabolism in liver and berberine promotes the expression of SIRT1 in hepatocytes.We hypothesized that SIRT1 mediated the effect of berberine on NAFLD.Methods:The effects of berberine on NAFLD were evaluated in C57BL/6J mice fed a high-fat diet(HFD)and in mouse primary hepatocytes and cell lines exposed to palmitate.The change of fatty acid oxidation(FAO)and the activity of CPT1A were observed in HepG2 cells.Quantitative real-time polymerase chain reaction and Western blot were employed to observe the expression of SIRT1 and lipid metabolism-related molecules.The interaction between SIRT1 and CPT1A was investigated by using co-immunoprecipitation assay in HEK293T cells.Results:Berberine treatment attenuated hepatic steatosis,reduced triglyceride(190.1611.2 lmol/g liver vs 113.667.6 lmol/g liver,P<0.001)and cholesterol(11.362.5 lmol/g liver vs 6.360.4 lmol/g liver,P<0.001)concentration in the liver,and improved lipid and glucose metabolism disorders compared with the HFD group.The expression of SIRT1 was reduced in the liver of NAFLD patients and mouse models.Berberine increased the expression of SIRT1 and promoted the protein level of CPT1A and its activity in HepG2 cells.SIRT1 overexpression mimicked the effect of berberine on reducing triglyceride levels in HepG2 cells,whereas SIRT1 knock-down attenuated the effect of berberine.Mechanistically,berberine increased the expression of SIRT1.SIRT1 deacetylated CPT1A at the Lys675 site,which suppressed its ubiquitin-dependent degradation,thereby promoting FAO and alleviating non-alcoholic liver steatosis.Conclusions:Berberine promoted SIRT1 deacetylation of CPT1A at the Lys675 site,which reduced the ubiquitin-dependent degradation of CPT1A and ameliorated non-alcoholic liver steatosis.