Site Of Phospholipid Synthesis Research Articles

2-Hydroxyglutarate-Mediated Autophagy of the Endoplasmic Reticulum Leads to an Unusual Downregulation of Phospholipid Biosynthesis in Mutant IDH1 Gliomas.

Tumor metabolism is reprogrammed to meet the demands of proliferating cancer cells. In particular, cancer cells upregulate synthesis of the membrane phospholipids phosphatidylcholine (PtdCho) and phosphatidylethanolamine (PtdE) in order to allow for rapid membrane turnover. Nonetheless, we show here that, in mutant isocitrate dehydrogenase 1 (IDHmut) gliomas, which produce the oncometabolite 2-hydroxyglutarate (2-HG), PtdCho and PtdE biosynthesis is downregulated and results in lower levels of both phospholipids when compared with wild-type IDH1 cells. 2-HG inhibited collagen-4-prolyl hydroxylase activity, leading to accumulation of misfolded procollagen-IV in the endoplasmic reticulum (ER) of both genetically engineered and patient-derived IDHmut glioma models. The resulting ER stress triggered increased expression of FAM134b, which mediated autophagic degradation of the ER (ER-phagy) and a reduction in the ER area. Because the ER is the site of phospholipid synthesis, ER-phagy led to reduced PtdCho and PtdE biosynthesis. Inhibition of ER-phagy via pharmacological or molecular approaches restored phospholipid biosynthesis in IDHmut glioma cells, triggered apoptotic cell death, inhibited tumor growth, and prolonged the survival of orthotopic IDHmut glioma-bearing mice, pointing to a potential therapeutic opportunity. Glioma patient biopsies also exhibited increased ER-phagy and downregulation of PtdCho and PtdE levels in IDHmut samples compared with wild-type, clinically validating our observations. Collectively, this study provides detailed and clinically relevant insights into the functional link between oncometabolite-driven ER-phagy and phospholipid biosynthesis in IDHmut gliomas.Significance: Downregulation of phospholipid biosynthesis via ER-phagy is essential for proliferation and clonogenicity of mutant IDH1 gliomas, a finding with immediate therapeutic implications. Cancer Res; 78(9); 2290-304. ©2018 AACR.

Biochemical analyses of phospholipid in normal and sympathectomized lungs

The phospholipid component of the surfactant system has been under investigation since it was described by Klaus et ul. in 1961 [13]. Increased interest in this subject developed when a surfactant disorder was implicated in the etiology of the infant and adult respiratory distress syndromes [3, 111. Today it is generally agreed that the main component of surfactant is lipid (80% of which is phospholipid [ 121). The major phospholipid is dipalmityl lecithin, which has been localized within the granular II pneumocyte, as well as in the alveolar lining layer [l]. Preliminary studies indicate some type of neural control of phospholipid production and distribution within the lung. Using pilocarpine injections, it is possible to decrease the number of lamellated bodies in the granular II pneumocyte and increase the amount of phospholipid in the lung lavage. Similar findings were produced with isoproterenol [15]. These stimulatory effects of cholinergic and adrenergic agents can be blocked by their respective antagonists [6, 10, 161. In an earlier study, we demonstrated that chemical sympathectomy alters the ultrastructural appearance of the granular II pneumocyte [7], particularly the lamellated bodies, which may be the site of phospholipid synthesis [2, 141. Phospholipid staining indicated that sympathectomy affects the distribution of phospholipids, both within the granular II pneumocyte and along the alveolus [7]. Although morphologic evidence suggests a significant role of the sympathetics on the production and distribution of pulmonary phospholipid, little biochemical data exist supporting such a role for the sympathetic nervous system. The purpose of this investigation was to analyze pulmonary phospholipids following sympathectomy, and to substantiate biochemically the previous morphologic data.

Studies on the biogenesis of smooth endoplasmic reticulum membranes in hepatocytes of phenobarbital-treated rats. II. The site of phospholipid synthesis in the initial phase of membrane proliferation.

The specific activity of the acyltransferases of smooth microsomes of rat liver rose threefold by 12 h after injection of phenobarbital, while the activity of the acyltransferases of the rough microsomes rose slightly to peak at 3-4 h, and subsequently fell. The latter rise was abolished by treatment of the animal with actinomycin D or puromycin, while that of the smooth microsomes was unaffected. Incorporation of [(14)C]glycerol into phospholipid of smooth microsomes was elevated 100% by phenobarbital, while that of the rough microsomes was elevated 15%, and this could be accounted for by exchange between the microsomal phospholipids. The phospholipid/protein ratio of the smooth microsomes rose 1.5 times 3-4 h after injection of phenobarbital, while that of the rough microsomes fell slightly. The specific activity of NADPH cytochrome c reductase and NADPH diaphorase rose first in the rough microsomes, and subsequently in the smooth microsomes at a time coinciding with the return of the phospholipid/protein ratio to the control level. The rise in phospholipid/protein ratio was unaffected by actinomycin D or puromycin. These results indicate that the proliferating smooth membranes are the site of phospholipid synthesis, and that the phospholipid/protein ratio of these membranes may change independently.

Renewal of glycerol in the visual cells and pigment epithelium of the frog retina.

The renewal of glycerol in the visual cells and pigment epithelium of the frog retina was studied by autoradiographic analysis of animals injected with [2-(3)H]glycerol. Assay of chloroform:methanol extracts showed that the labeled precursor was used mainly in lipid synthesis, although there was also some utilization in the formation of protein. Radioactive glycerol was initially concentrated in the myoid portion of rods and cones, indicating that this is the site of phospholipid synthesis in visual cells. The glycogen bodies (paraboloids) of accessory cones were also heavily labeled, suggesting the diversion of some glycerol into glycogenic pathways. In the pigment epithelium, only the oil droplets became significantly radioactive. The outer plexiform layer (which contains the visual cell synaptic bodies) and the cone oil droplets gradually accumulated considerable amounts of labeled material. Within 1-4 h, labeled molecules began to appear in the visual cell outer segments, evidently having been transported there from the myoid portion of the inner segment. Most of these were phospholipid molecules which became distributed throughout the outer segments, presumably replacing comparable constituents in existing membranes. In rods only, there was also an aggregation of labeled material at the base of the outer segment due to membrane biogenesis. These highly radioactive membranes, containing labeled molecules of lipid and protein, were subsequently displaced along the rod outer segments due to repeated membrane assembly at the base. The distribution of radioactivity supported the conclusion that membrane renewal by molecular replacement is more rapid for lipid than it is for protein.

Enzymes of phospholipid metabolism: Localization in the cytoplasmic and outer membrane of the cell envelope of Escherichia coli and Salmonella typhimurium

The phospholipid biosynthetic enzymes of the cell envelope of Escherichia coli and Salmonella typhimurium had highest specific activities in the cytoplasmic membrane fraction and lowest specific activities in the outer membrane fraction obtained by isopycnic sucrose density gradient centrifugation of the total membrane fraction of lysozyme-EDTA spheroplasts. This finding suggests that the site of phospholipid synthesis is the cytoplasmic membrane. Several degradative enzymes of phospholipid metabolism had highest specific activities in the outer membrane fraction and lowest specific activities in the cytoplasmic membrane. These data suggest an intracellular separation of the degradative and biosynthetic enzymes of phospholipid metabolism.