Mammary lipogenic enzyme activity, trans fatty acids and conjugated linoleic acids are altered in lactating dairy cows fed a milk fat-depressing diet.
(57/1123)
The objectives of the present study were to examine the effect of a milk fat-depressing (MFD) diet on: 1) the activity of mammary acetyl-CoA carboxylase (ACC) and fatty acid synthase (FAS), 2) ACC mRNA relative abundance and 3) distributions of conjugated linoleic acids (CLA) and trans-18:1 fatty acids (tFA) in milk fat. Twelve lactating Holstein cows were used in a single reversal design. Two diets were fed: a control diet (60:40% forage/concentrate) and an MFD diet (25:70% forage/concentrate, supplemented with 5% soybean oil). The MFD diet decreased (P: < 0 0.001) milk fat by 43% and ACC and FAS activity by 61 and 44%, respectively. A reduced ACC mRNA relative abundance (P: < 0.001) corresponded with the lower ACC activity. The fatty acids synthesized de novo were decreased (P: < 0. 002), whereas tFA were increased from 1.9 to 15.6% due predominantly to a change in trans-10-18:1 isomer (P: < 0.001). With the MFD diet, the trans-7, cis-9 and trans-10, cis-12 CLA isomers were elevated (P: < 0.001), in contrast to the decrease in trans-11-18:1 (P: < 0. 001) and cis-9, trans-11-18:2. The data were consistent with a dietary effect on mammary de novo FA synthesis mediated through a reduction in ACC and FAS activity and in ACC mRNA abundance. The results were compatible with a role of trans-10, cis-12 CLA in milk fat depression, but alterations noted in tFA and other CLA isomers suggest that they also may be important during diet-induced milk fat depression. (+info)
Identification of a novel FAS/ER-alpha fusion transcript expressed in human cancer cells.
(58/1123)
A semi-nested reverse transcriptase-polymerase chain reaction (RT-PCR) was applied to evaluate the presence of estrogen receptor-alpha (ER-alpha) in human prostate cancer cells. Unexpectedly, a novel fatty acid synthase (FAS)/ER-alpha fusion transcript was identified, in which the N-terminus of FAS was fused in-frame with the C-terminus of ER-alpha. The existence of the FAS/ER-alpha transcript was further confirmed by RT-PCR analysis using various sets of amplification primers and different reverse-transcribed primers in the presence of dimethyl sulfoxide to eliminate the secondary structure of RNA. The predicted FAS/ER-alpha protein would contain largely domain I of FAS and the entire ligand binding domain of ER-alpha. The FAS/ER-alpha was expressed in a variety of human cancer cell lines including prostate, breast, cervical and bladder cancer cell lines. Our data suggest that the presence of FAS/ER-alpha may complicate the FAS and the ER-alpha signalling pathway. (+info)
The biology of somatotropin in adipose tissue growth and nutrient partitioning.
(59/1123)
During the past 20 years, much has been learned about how porcine somatotropin (pST) affects growth and nutrient partitioning in growing pigs. The development of techniques to produce large quantities of recombinantly derived pST enabled numerous long-term studies to be conducted in which the effects of daily pST administration could be evaluated. Collectively, these studies established that treatment of growing pigs with pST markedly stimulated muscle growth and, concurrently, reduced fat deposition. In growing pigs, maximally effective doses of pST increase average daily gain as much as 10-20%, improve feed efficiency 15-30%, decrease adipose tissue mass and lipid accretion rates by as much as 50-80% and concurrently increase protein deposition by 50%. These effects are associated with a decrease in feed intake of approximately 10-15%. These responses occur because pST has a wide array of biological effects that modulate nutrient partitioning between adipose tissue and skeletal muscle. The decrease in adipose tissue growth is due to a reduction in lipogenesis that is the consequence of pST blunting the effects of many insulin-dependent events. With respect to fatty acid synthase (FAS), a pace-setting enzyme in the lipogenic pathway, enzyme activity is markedly reduced by pST. This is the result of a pST-mediated decrease in FAS mRNA levels that occurs because FAS gene transcription is decreased. The consequence of the decrease in lipid synthesis is that adipocyte hypertrophy is impaired and, hence, tissue growth. This review will provide an overview of some of the biological effects of pST in adipose tissue and will discuss what is known about the underlying mechanisms that account for these effects. (+info)
Stimulation of tumor-associated fatty acid synthase expression by growth factor activation of the sterol regulatory element-binding protein pathway.
(60/1123)
Increased expression of fatty acid synthase (FAS) is observed in a clinically aggressive subset of various common cancers and interference with FAS offers promising opportunities for selective chemotherapeutic intervention. The mechanisms by which FAS expression is (up)-regulated in these tumors remain, however, largely unknown. Recently we demonstrated that in LNCaP prostate cancer cells FAS expression is markedly elevated by androgens via an indirect pathway involving sterol regulatory element-binding proteins (SREBPs). Here, we also show that growth factors such as EGF are able to stimulate FAS mRNA, protein and activity. Several observations also indicate that the effects of EGF on FAS expression are ultimately mediated by SREBPs. EGF stimulates SREBP-1c mRNA expression and induces an increase in mature nuclear SREBP-1. Moreover, in transient transfection studies EGF stimulates the transcriptional activity of a 178 bp FAS promoter fragment harboring a complex SREBP-binding site. Deletion or mutation of this binding site abolishes these effects and ectopic expression of dominant negative SREBP-1 inhibits FAS expression and induction in intact LNCaP cells. Given the frequent dysregulation of growth factor signaling in cancer and the key role of SREBP-1 in lipid homeostasis, growth factor-induced activation of the SREBP pathway is proposed as one of the mechanisms responsible for up-regulation of lipogenic gene expression in a subset of cancer cells. (+info)
Temperature-sensitive mutants of the yeast fatty-acid-synthetase complex.
(61/1123)
By genetic complementation analysis, 88 independently isolated temperature-sensitive fatty acid synthetase mutants have been assigned to the six different fas-complementation groups II (fas 1), III (fas 1), Vb (fas 1), VI (fas 2), VIII (fas 2) and IX (fas 2). The complementation groups Va, Vc, Vd, IV and VII observed among nonconditional fas-mutants have not been found among the temperature-sensitive strains studied. From the failure to detect pantetheine-deficient conditional fas-mutants it is concluded that the yease acyl-carrier protein has an exceptionally stable tertiary structure. Furthermore, the lack of temperature-sensitive mutants of complementation group IV possibly indicates that this group specifically represents only nonsense and frameshift mutations. Almost half of the temperature-sensitive fas 1 and fas 2 mutants studied exhigited non-complementing characteristics. These results confirm the existence of non-complementing fas1 and fas2 missense mutations. From this it is concluded that both fatty acid synthetase loci encode multifunctional polypeptide chains rather than several monofunctional component enzymes. The possible existence of an independent acyl-carrier protein, as suggested by the genetic data reported in this study, is discussed. With 10 different temperature-sensitive fas1 and fas2 mutants the dependence of cellular growth rates on growth temperature and fatty acid supplementation was determined. With all mutants studied fatty-acid-independent growth was completely suppressed at non-permissive temperatures (34 -37 degrees C). In fatty-acid-supplemented media, however, these mutants exhibited the same growth characteristics as wild-type yeast cells. In contrast to this, wild-type yeast growth was found to be fatty-acid-independent at all temperatures studied. Other than in vivo, the purified fatty acid synthetase isolated from five different temperature-sensitive fas1 and fas2 mutants exhibited in vitro no increased thermolability compared to the wild-type enzyme. From this it is concluded that the specific conformation of fatty acid synthetase subunits either forms only at the ribosomal level during translation, or that this conformation is stabilized by the assembly of subunits into the multienzyme complex structure. (+info)
Selection and properties of Escherichia coli mutants defective in the synthesis of cyclopropane fatty acids.
(62/1123)
Mutants of Escherichia coli K-12 defective in the synthesis of cyclopropane fatty acids (CFA) have been selected and isolated by a L-[methyl-3H]methionine suicide procedure. Two mutants were isolated. Stationary-phase cultures of both mutants contain less than 0.7% of the CFA content found in the parental strain. The CFA deficiency is attributed to a deficiency of CFA synthetase activity. Extracts of both mutants contain less than 10% of the CFA synthetase activity found in extracts of the parental strain. Experiments in which parental and mutant extracts were mixed indicate that the lack of activity in the mutant strains is not due to an inhibitor of CFA synthetase present in the mutant extracts. We have not yet detected a physiological phenotype for these mutants. These strains grow normally at various temperatures in a variety of media. We have tested survival (colony-forming ability) in response to (i) prolonged incubation in stationary phase, (ii) exposure to drying, and (iii) exposure to detergents, heavy metals, low pH, high salt concentration, and a variety of other environmental conditions. The survival of both mutants is identical to that of the parental strain under all conditions tested. The compositions (excepting the CFA deficiency) and metabolic turnover rates of the phospholipids of both mutant strains are indistinguishable from those of the wild-type strain. The transport of several amino acids also seems normal in these mutants. (+info)
Copper deficiency induces hepatic fatty acid synthase gene transcription in rats by increasing the nuclear content of mature sterol regulatory element binding protein 1.
(63/1123)
Dietary copper (Cu) deficiency results in an accelerated rate of hepatic fatty acid synthase gene transcription and an enhanced rate of hepatic lipid synthesis. Because the nuclear transcription factor sterol regulatory element binding protein-1 (SREBP-1) is a strong enhancer of fatty acid synthase promoter activity, it was hypothesized that Cu deficiency induces fatty acid synthase gene transcription by increasing the nuclear localization of mature SREBP-1. Male weanling rats were pair-fed a Cu-adequate (6.0 mg/kg) or Cu-deficient (0.6 mg/kg) diet (AIN-93) for 28 d. DNase I hypersensitivity site mapping of the hepatic fatty acid synthase gene revealed the presence of four major hypersensitivity sites located at -8700 to -8600, -7300 to -6900, -600 to -400 and -100 to +50. Although Cu deficiency did not change the hypersensitivity site pattern or intensity, in vitro footprinting of the region between -100 and +50 indicated that Cu deficiency enhanced DNA protein interactions within this region. The sequence between -68 and -58 contains the DNA recognition sequence for SREBP-1 and upstream stimulatory element-1 (USF-1). Western blot analysis revealed that the dietary Cu deficiency increased the hepatic nuclear content of mature SREBP-1 by 150% (P: < 0.05), and it concomitantly decreased the membrane content of precursor SREBP-1 by 45% (P: < 0.05). Changes in the hepatic distribution of SREBP-1 associated with Cu deficiency were not accompanied by changes in SREBP-1 mRNA. The nuclear content of USF-1 was unaffected by dietary Cu status. The hepatic increase in mature SREBP-1 of Cu-deficient rats was accompanied by a 400% increase and an 80% decrease in the abundance of fatty acid synthase and cholesterol 7-alpha hydroxylase mRNA, respectively. hepatic These data indicate that a Cu deficiency stimulates hepatic lipogenic gene expression by increasing the hepatic translocation of mature SREBP-1. (+info)
HIV protease inhibitors stimulate hepatic triglyceride synthesis.
(64/1123)
Hyperlipidemia may complicate the use of HIV protease inhibitors (PIs) in AIDS therapy. To determine the cause of hyperlipidemia, the effect of PIs on lipid metabolism was examined with HepG2 liver cells and AKR/J mice. In HepG2 cells, the PIs ABT-378, nelfinavir, ritonavir, and saquinavir stimulated triglyceride synthesis; ritonavir increased cholesterol synthesis; and amprenavir and indinavir had no effect. Moreover, nelfinavir increased mRNA expression of diacylglycerol acyltransferase and fatty acid synthase. The retinoid X receptor agonist LG100268, but not the antagonist LG100754, further increased PI-stimulated triglyceride synthesis and mRNA expression of fatty acid synthase in vitro. In fed mice, nelfinavir or ritonavir did not affect serum glucose and cholesterol, whereas triglyceride and fatty acids increased 57% to 108%. In fasted mice, ritonavir increased serum glucose by 29%, cholesterol by 40%, and triglyceride by 99%, whereas nelfinavir had no effect, suggesting these PIs have different effects on metabolism. Consistent with the in vitro results, nelfinavir and ritonavir increased triglyceride 2- to 3-fold in fasted mice injected with Triton WR-1339, an inhibitor of triglyceride clearance. We propose that PI-associated hyperlipidemia is due to increased hepatic triglyceride synthesis and suggest that retinoids or meal restriction influences the effects of select PIs on lipid metabolism. (+info)