脂肪酸从头合成代谢及其抑制剂在肿瘤中的研究进展

代谢重编程是肿瘤的重要特征之一.肿瘤细胞常会发生过度增殖、局部侵袭、转移、复发和耐药等.这些过程均需要大量的脂肪酸,用于合成肿瘤细胞所必需的生物膜和信号分子等.因此,研究脂肪酸从头合成代谢在肿瘤细胞发生发展过程中所发挥的重要作用有助于深入理解肿瘤的发病机制,为肿瘤的诊断和治疗提供新的思路.本文将对脂肪酸合成代谢在肿瘤中...     

Thermal modulation of fatty acid synthesis in Escherichia coli does not involve de novo enzyme synthesis.

An increased ratio of unsaturated to saturated fatty acids was synthesized within 30 s after shift of Escherichia coli K-12 from 42 degrees C to 24 degrees C. This was more than 10-fold faster than the induction of beta-galactosidase. Inhibition of ribonucleic acid or protein synthesis had no effect on the response of fatty acid synthesis to temperature shift.     

Role of fatty acid elongases in determination of de novo synthesized monounsaturated fatty acid species

Enhanced production of monounsaturated fatty acids (FA) derived from carbohydrate-enriched diets has been implicated in the development of obesity and insulin resistance. The FA elongases Elovl-5 and Elovl-6 are regulated by nutrient and hormone status, and have been shown using intact yeast and mammalian microsome fractions to be involved in the synthesis of monounsaturated FAs (MUFA). Herein, targeted knockdown and overexpression of Elovl-5 or Elovl-6 was used to determine their roles in de novo synthesis of specific MUFA species in mammalian cells. Treatment of rat insulinoma (INS)-1 cells with elevated glucose increased de novo FA synthesis and the ratio of MUFAs to saturated FAs. Elovl-5 knockdown decreased elongation of 16:1,n-7. Elovl-5 overexpression increased synthesis of 18:1,n-7; however, this increase was dependent on stearoyl-CoA desaturase–driven 16:1,n-7 availability. Knockdown of Elovl-6 decreased elongation of 16:0 and 16:1,n-7, resulting in accumulation of 16:1,n-7. Elovl-6 overexpression preferentially drove synthesis of 16:0 elongation products 18:0 and 18:1,n-9 but not 18:1,n-7. These findings demonstrate that coordinated induction of FA elongase and desaturase activity is required for balanced synthesis of specific n-7 versus n-9 MUFA species. Given the relative abundance of 16:0 to 16:1,n-7 and the specificity of Elovl-6 for 16:0, Elovl-6 is a major elongase for 18:1,n-9 production.     

De novo fatty acid synthesis in developing rat lung

The rate of de novo fatty acid synthesis in developing rat lung was measured by the rate of incorporation of 3H from 3H2O into fatty acids in lung slices and by the activity of acetyl-CoA carboxylase in fetal, neonatal and adult lung. Both tritium incorporation and acetyl-CoA carboxylase activity increased sharply during late gestation, peaked on the last fetal day, and declined by 50% 1 day after birth. In the adult, values were only one-half the peak fetal rates. In vitro regulation of acetyl-CoA carboxylase activity in fetal lung was similar to that described in adult non-pulmonary tissues: activation by citrate and inhibition by palmitoyl-CoA. Similarly, incubation conditions that favored enzyme phosphorylation inhibited acetyl-CoA carboxylase activity in lung while dephosphorylating conditions stimulated activity. Incorporation of [U-14 C]glucose into lung lipids during development was influenced heavily by incorporation into fatty acids, which generally paralleled the rate of tritium incorporation into fatty acids. The relative utilization of acetyl units from exogenous glucose for overall fatty acid synthesis was greater in adult lung than in fetal or neonatal lung, suggesting that other substrates may be important for fatty acid synthesis in developing lung. In fetal lung explants, de novo fatty acid synthesis was inhibited by exogenous palmitate. Taken together, these data suggest that de novo synthesis may be an important source of saturated fatty acids in fetal lung but of lesser importance in the neonatal period. Furthermore, the regulation of acetyl-CoA carboxylase activity and fatty acid synthesis in lung may be similar to non-pulmonary tissues.     

Epicatechin gallate prevents the de novo synthesis of fatty acid and the migration of prostate cancer cells

Lipid metabolism disorder caused by the upregulation of lipogenic genes is a typical feature of prostate cancer.The synthesis of fatty acids is enhanced to acce...     

Metabolic control analysis of de novo sunflower fatty acid biosynthesis

We have obtained a simulation of the final steps of de novo fatty acid biosynthesis in sunflower control line RHA-274. For this simulation, we have used data from the evolution of fatty acids during seed formation and from the biochemical characterization of beta-keto-acyl-ACP synthetase II (FASII), stearoyl-ACP desaturase (SAD) and acyl-ACP thioesterase activities and the program GEPASI (based on the metabolic control-analysis theory). When physiological data from high- and medium-stearic acid mutants seed development were used with this model the predicted changes in SAD and TE were very similar to those actually found in the biochemical characterization of these mutants. However, the model had to be modified when results from high-palmitic mutants, accumulating unusual fatty acids like palmitoleic, asclepic and palmitolinoleic acids, were used. The emerging model, that fits all of our results, predicts the existence of a dynamic channelling between the FASII complex and SAD, that channelling being responsible for the alternative pathway starting with the desaturation of palmitic acid by the stearoyl-ACP desaturase. This channelling is consistent with our previous results. For instance, the determination of SAD activity on sunflower seed crude extracts only rendered oleic acid when the stearic acid used as a substrate was obtained from a KASII assay, but not when the stearic acid came from in vitro synthesis using acyl-ACP synthetase from Escherichia coli. This theoretical approximation will be very useful in predicting the evolution of the system when introducing new or modified activities; similar approximations in other oil-seed crops could be of great interest.     

Identification of dicarboxylate carrier Slc25a10 as malate transporter in de novo fatty acid synthesis

Mitochondrial solute carrier family 25 member 10 (Slc25a10) transports dicarboxylates such as malate or succinate across the mitochondrial inner membrane. Although fatty acid synthesis in adipose tissue or the liver is initiated by citrate transport in exchange for malate across the mitochondrial membrane, the transporter responsible for supplying malate during citrate transport has not been identified. In the present study, we clarified the role of Slc25a10 in supplying malate for citrate transport and examined the effect of Slc25a10 suppression on the lipogenic pathway and lipid accumulation. We have reported an Slc25a10 increase in white adipose tissue in obese mouse models and a decrease in a fasted mouse model using expression profiles. Next, we examined the effect of Slc25a10 suppression by small interfering RNA on citrate transport in the lipogenic cell lines HepG2 and 3T3-L1. We observed that inhibition of malate transport by Slc25a10 suppression significantly reduced the citrate transport from the mitochondria to the cytosol. We also found that suppression of Slc25a10 down-regulated the lipogenic pathway, indicated by decreases in ACC1 expression and malonyl-CoA level. Furthermore, suppression of Slc25a10 decreased triglyceride lipid accumulation in adipose-differentiated 3T3-L1 cells. These results suggested that Slc25a10 plays an important role in supplying malate for citrate transport required for fatty acid synthesis and indicated that inhibition of Slc25a10 might effectively reduce lipid accumulation in adipose tissues.     

Mitochondrial protein lipoylation does not exclusively depend on the mtKAS pathway of de novo fatty acid synthesis in Arabidopsis

The photorespiratory Arabidopsis (Arabidopsis thaliana) mutant gld1 (now designated mtkas-1) is deficient in glycine decarboxylase (GDC) activity, but the exact nature of the genetic defect was not known. We have identified the mtkas-1 locus as gene At2g04540, which encodes beta-ketoacyl-[acyl carrier protein (ACP)] synthase (mtKAS), a key enzyme of the mitochondrial fatty acid synthetic system. One of its major products, octanoyl-ACP, is regarded as essential for the intramitochondrial lipoylation of several proteins including the H-protein subunit of GDC and the dihydrolipoamide acyltransferase (E2) subunits of two other essential multienzyme complexes, pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase. This view is in conflict with the fact that the mtkas-1 mutant and two allelic T-DNA knockout mutants grow well under nonphotorespiratory conditions. Although on a very low level, the mutants show residual lipoylation of H protein, indicating that the mutation does not lead to a full functional knockout of GDC. Lipoylation of the pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase E2 subunits is distinctly less reduced than that of H protein in leaves and remains unaffected from the mtKAS knockout in roots. These data suggest that mitochondrial protein lipoylation does not exclusively depend on the mtKAS pathway of lipoate biosynthesis in leaves and may occur independently of this pathway in roots.     

Pyrimidine de novo synthesis during the life cycle of the intraerythrocytic stage of Plasmodium falciparum

The 6 enzymes involved in de novo synthesis of pyrimidines were measured in Plasmodium falciparum isolated by saponin lysis from RBC's nonsynchronized and synchronized in vitro cultures. The total activities were found to be dependent on the stage of the P. falciparum cycle. In parasites isolated from synchronized cultures, the highest activities for all enzymes were found at about 27 hr after synchronization in the late trophozoite stage, or just before schizont formation. Merozoites and ring forms contained little de novo activity. The first enzyme of the pathway, carbamyl phosphate synthetase (CPS-II) preferentially utilized glutamine. Ammonia was a poor substrate. CPS-II was unstable in the absence of the cryoprotectants, dimethylsulfoxide and glycerol. The apparent Km for MgATP--was 3.8 +/- 0.7 mM and the enzyme in all morphological forms of P. falciparum (ring, mature trophozoites and schizonts) was inhibited by UTP. The activity of the fourth enzyme of the pathway, dihydroorotate dehydrogenase, appeared to be linked to the cell's respiratory chain; inhibitors of mammalian electron transport such as cyanide, amytal, antimycin A, thenoyltrifluoroacetone and ubiquinone analogs also inhibited the P. falciparum enzyme. The demonstration of the variation of activity of the pyrimidine enzymes correlates with the increased synthesis of nucleic acids in the late trophozoite stage. These observations provide a basis for the testing of the effectiveness of pyrimidine analogs as potential antimetabolites against various forms of the parasite.     

The de novo selection of drug-resistant malaria parasites

Antimalarial drug resistance emerges de novo predominantly in areas of low malaria transmission. Because of the logarithmic distribution of parasite numbers in human malaria infections, inadequately treated high biomass infections are a major source of de novo antimalarial resistance, whereas use of antimalarial prophylaxis provides a low resistance selection risk. Slowly eliminated antimalarials encourage resistance largely by providing a selective filter for resistant parasites acquired from others, and not by selecting resistance de novo. The de novo emergence of resistance can be prevented by use of antimalarial combinations. Artemisinin derivative combinations are particularly effective. Ensuring adequate treatment of the relatively few heavily infected patients would slow the emergence of resistance.     

Dynamic channelling during de novo fatty acid biosynthesis in Helianthus annuus seeds

We have obtained a simulation of the final intraplastidial steps of de novo fatty acid biosynthesis in sunflower (Helianthus annuus L.) seeds. For this simulation, we have used data from the fatty acid content of normal and high-saturated seed formation and from the enzymatic characterization of the stearoyl-ACP desaturase (SAD; EC 1.12.99.6), acyl-ACP thioesterase (TE; EC 3.1.2.14) and fatty acid synthase II complex (FAS II), and the program GEPASI (based on the metabolic control analysis theory). When developmental data from high-stearic acid mutant seeds were analysed and compared to those predicted with this model, the changes in SAD and TE actually found in the biochemical characterization of these mutants were very similar to the predictions. However, the model had to be modified when results from high-palmitic mutants, accumulating unusual fatty acids like palmitoleic, asclepic and palmitolinoleic acids, were used. The emerging model, consistent with all of our results, predicts the existence of a dynamic channelling between the FAS II complex and SAD, that channelling being responsible for an alternative pathway starting with the desaturation of palmitoyl-ACP by the SAD. For instance, the determination of SAD activity on crude extracts from sunflower seeds only rendered oleoyl-ACP when stearoyl-ACP used as a substrate was obtained from an FAS II assay but not when in vitro synthesized stearoyl-ACP was provided as a substrate. This theoretical approximation will be very useful in order to predict the evolution of the system when introducing new or modified activities; similar approximations in other oilseed crops could be of great interest.     

Coupling of the de novo fatty acid biosynthesis and lipoylation pathways in mammalian mitochondria

The objective of this study was to identify the products and possible role of a putative pathway for de novo fatty acid synthesis in mammalian mitochondria. Bovine heart mitochondrial matrix preparations were prepared free from contamination by proteins from other subcellular components and, using a combination of radioisotopic labeling and mass spectrometry, were shown to contain all of the enzymes required for the extension of a 2-carbon precursor by malonyl moieties to saturated acyl-ACP thioesters containing up to 14 carbon atoms. A major product was octanoyl-ACP and, in the presence of the apo-H-protein of the glycine cleavage complex, the newly synthesized octanoyl moieties were translocated to the lipoylation site on the acceptor protein. These studies demonstrate that one of the functions of the de novo fatty acid biosynthetic pathway in mammalian mitochondria is to provide the octanoyl precursor required for the essential protein lipoylation pathway.     

A novel acetyl-CoA carboxylase inhibitor reduces de novo fatty acid synthesis in HepG2 cells and rat primary hepatocytes

To identify the novel inhibitor of de novo lipogenesis in hepatocytes, we screened for inhibitory activity of triglyceride (TG) synthesis using [¹⁴C]acetate in the human hepatoma cell line, HepG2. Using this assay system we discovered the novel compound, benzofuranyl α-pyrone (TEI-B00422). TEI-B00422 also inhibited the incorporation of acetate into the triglyceride (TG) fraction in rat primary hepatocytes. In HepG2 cells, the incorporation of oleate into TG was unaffected. TEI-B00422 inhibited rat hepatic acetyl-CoA carboxylase (ACC), K_i = 3.3 μM, in a competitive manner with respect to acety-CoA but not fatty acid synthase and acyl-CoA transferase/diacylglycerol. Thus, these results suggest that the inhibition of TG synthesis by TEI-B00422 is based on the inhibitory action of ACC. The structure of TEI-B00422 is totally different from the known inhibitors of ACC and may be useful in the development of therapeutic agents to combat a number of metabolic disorders.     

Salicylic acid treatment of pea seeds induces its de novo synthesis

Salicylic acid (SA), which is known as a signal molecule in the induction of defense mechanisms in plants, could be a promising compound for the reduction of stress sensitivity. The aim of the present work was to investigate the distribution of SA in young pea (Pisum sativum L.) seedlings grown from seeds soaked in ³H-labeled SA solution before sowing, and to study the physiological changes induced by this seed treatment. The most pronounced changes in SA levels occurred in the epicotyl and the seeds. Radioactivity was detected only in the bound form of SA, the majority of which was localized in the seeds, and only a very low level of radioactivity was detected in the epicotyl. SA pre-treatment increased the expression of the chorismate synthase and isochorismate synthase genes in the epicotyl. Pre-soaking the seeds in SA increased the activities of some antioxidant enzymes, namely ascorbate peroxidase (EC 1.11.1.11) and guaiacol peroxidase (EC 1.11.1.7) and the level of ortho-hydroxycinnamic acid, but decreased the level of polyamines. These results suggest that the increased level of free and bound SA detected in plants growing from seeds soaked in SA solution before sowing is the product of de novo synthesis, rather than having been taken up and mobilized by the plants.     

GLP-1 stimulates glucose-derived de novo fatty acid synthesis and chain elongation during cell differentiation and insulin release

Glucagon-like peptide-1 (GLP-1, 7-36) is capable of restoring normal glucose tolerance in aging, glucose-intolerant Wistar rats and is a potent causal factor in differentiation of human islet duodenal homeobox-1-expressing cells into insulin-releasing beta cells. Here we report stable isotope-based dynamic metabolic profiles of rat pancreatic epithelial (ARIP) and human ductal tumor (PANC-1) cells responding to 10 nM GLP-1 treatment in 48 h cultures. Macromolecule synthesis patterns and substrate flow measurements using gas chromatography/mass spectrometry (MS) and the stable [1,2-13C2]glucose isotope as the tracer showed that GLP-1 induced a significant 20% and 60% increase in de novo fatty acid palmitate synthesis in ARIP and PANC-1 cells, respectively, and it also induced a significant increase in palmitate chain elongation into stearate utilizing glucose as the primary substrate. Distribution of 13C in other metabolites indicated no changes in the rates of nucleic acid ribose synthesis, glutamate oxidation, or lactate production. Tandem high-performance liquid chromatography-ion trap MS analysis of the culture media demonstrated mass insulin secretion by GLP-1-treated tumor cells. Metabolic profile changes in response to GLP-1-induced cell differentiation include selective increases in de novo fatty acid synthesis from glucose and consequent chain elongation, allowing increased membrane formation and greater insulin availability and release.