Positional and temporal regulation of lipogenic gene expression in mouse liver

We have examined the dynamics of positional gene expression in mouse liver using the carbohydrate induction of lipogenic genes as a model. Using a protocol of fasting and refeeding a high-carbohydrate, no-fat diet to obtain maximal induction, we investigated the temporal expression and localization of malic enzyme (ME) and fatty acid synthase (FAS). In situ hybridization showed that both ME and FAS were expressed at low basal levels in all hepatocytes in livers of mice fed a control diet. Furthermore, dietary induction of ME and FAS mRNA occurred in periportal cells within 6 hours. After 12 hours, the portal cells were maximal; and after 24-36 hours, all cells showed high levels of message. This was coincident with expression of ME and FAS mRNAs, which appeared to be maximal between 24 and 36 hours. Both steady-state mRNA levels and pericentral localization then declined, until only periportal hepatocytes showed strong expression of ME and FAS. Nuclear transcription rates measured by run-on assay demonstrated that maximal transcription rates preceded maximum mRNA levels by peaking at 12 hours. Furthermore, run-on assays showed that the periportal induction by carbohydrates is primarily a transcriptional response for FAS, and both transcriptional and posttranscriptional for ME. These results indicate that lipogenic gene expression is a temporal response induced by carbohydrate feeding and is regulated by both positional and transcriptional mechanisms.

To complete its replication cycle, a shrimp virus changes the population of long chain fatty acids during infection via the PI3K-Akt-mTOR-HIF1α pathway

White spot syndrome virus (WSSV), the causative agent of white spot disease (WSD), is a serious and aggressive shrimp viral pathogen with a worldwide distribution. At the genome replication stage (12 hpi), WSSV induces a metabolic rerouting known as the invertebrate Warburg effect, which boosts the availability of energy and biosynthetic building blocks in the host cell. Here we show that unlike the lipogenesis that is seen in cancer cells that are undergoing the Warburg effect, at 12 hpi, all of the long chain fatty acids (LCFAs) were significantly decreased in the stomach cells of WSSV-infected shrimp. By means of this non-selective WSSV-induced lipolysis, the LCFAs were apparently diverted into β-oxidation and used to replenish the TCA cycle. Conversely, at 24 hpi, when the Warburg effect had ceased, most of the LCFAs were significantly up-regulated and the composition was also significantly altered. In crayfish these changes were in a direction that appeared to favor the formation of WSSV virion particles. We also found that, at 24 hpi, but not at 12 hpi, the PI3K-Akt-mTOR-HIF1α pathway induced the expression of fatty acid synthase (FAS), an enzyme which catalyzes the conversion of acetyl-CoA into LCFAs. WSSV virion formation was impaired in the presence of the FAS inhibitor C75, although viral gene and viral DNA levels were unaffected. WSSV therefore appears to use the PI3K-Akt-mTOR pathway to induce lipid biosynthesis at 24 hpi in order to support viral morphogenesis.

[Expression, purification and characterization of a novel fatty acid synthase from Rhodosporidium toruloides]

Fatty acid synthase (FAS) catalyses the reaction between acetyl-CoA and malonyl-CoA to produce fatty acids. It is one of the most important enzyme in lipid biosynthesis. FAS of the oleaginous yeast Rhodosporidium toruloides has two acyl carrier protein (ACP) domains and a distinct subunit composition compared with FASs of other species. As ACP is a protein cofactor crucial for fatty acid chain elongation, more ACPs in the FAS may facilitate the reaction. To study the biochemical and structural properties of this novel FAS from R. toruloides, plasmids were constructed and transformed into Escherichia coli BL21 (DE3). The strain ZWE06 harboring plasmids pET22b-FAS1 and pET24b-FAS2 could co-overexpress the two subunits. The recombinant FAS was purified by sequentially using ammonium sulphate precipitation, sucrose density gradient centrifugation and anion exchange chromatography. The specific activity of the recombinant FAS was 548 mU/mg. The purified complex would be used to study enzyme kinetics and protein structure of FAS, and heterogeneous expression and purification will facilitate revealing the mechanism of this novel FAS with double ACPs.

Morphotype transition and sexual reproduction are genetically associated in a ubiquitous environmental pathogen

Sexual reproduction in an environmental pathogen helps maximize its lineage fitness to changing environment and the host. For the fungal pathogen Cryptococcus neoformans, sexual reproduction is proposed to have yielded hyper virulent and drug resistant variants. The life cycle of this pathogen commences with mating, followed by the yeast-hypha transition and hyphal growth, and it concludes with fruiting body differentiation and sporulation. How these sequential differentiation events are orchestrated to ensure developmental continuality is enigmatic. Here we revealed the genetic network of the yeast-to-hypha transition in Cryptococcus by analyzing transcriptomes of populations with a homogeneous morphotype generated by an engineered strain. Among this network, we found that a Pumilio-family protein Pum1 and the matricellular signal Cfl1 represent two major parallel circuits directing the yeast-hypha transition. Interestingly, only Pum1 coordinates the sequential morphogenesis events during a-α bisexual and α unisexual reproduction. Pum1 initiates the yeast-to-hypha transition, partially through a novel filament-specific secretory protein Fas1; Pum1 is also required to sustain hyphal growth after the morphological switch. Furthermore, Pum1 directs subsequent differentiation of aerial hyphae into fruiting bodies in both laboratory and clinical isolates. Pum1 exerts its control on sexual reproduction partly through regulating the temporal expression of Dmc1, the meiosis-specific recombinase. Therefore, Pum1 serves a pivotal role in bridging post-mating morphological differentiation events with sexual reproduction in Cryptococcus. Our findings in Cryptococcus illustrate how an environmental pathogen can ensure the completion of its life cycle to safeguard its long-term lineage success.

Effects of short-term refeeding on the expression of genes involved in lipid metabolism in chicks (Gallus gallus)

The aim of this study was to analyze the expression patterns of key genes involved in lipid metabolism in response to feeding in chicks. A total of 18 thirteen day-old male chicks were fasted for 12h. The mRNA levels of the genes in the liver and white adipose tissue were analyzed after 0, 2, and 4h of refeeding. The mRNA levels of sterol regulatory element-binding protein (SREBP) 1, liver X receptor α, peroxisome proliferator-activated receptor (PPAR) γ, acetyl-CoA carboxylase α and fatty acid synthase were significantly increased after 2h of refeeding. In contrast, the mRNA levels of PPARα and carnitine palmitoyltransferase 1a were significantly decreased after 2h of refeeding. The mRNA level of acyl-CoA oxidase was significantly decreased after 4h of refeeding. The mRNA levels of cholesterol metabolism-related genes such as SREBP2 and 3-hydroxy-3-methylglutaryl-CoA reductase were significantly increased after 2h of refeeding. In the white adipose tissue, the mRNA level of PPARγ was significantly increased after 2h of refeeding, whereas the mRNA level of adipose triglyceride lipase was significantly decreased after 4h of refeeding. These results demonstrated that expression of lipid metabolism-related genes is regulated by short-term refeeding in chicks.

Proteomics using mammospheres as a model system to identify proteins deregulated in breast cancer stem cells

Breast cancer stem cells (BCSC) exist within many types of breast cancers, functioning to initiate tumorigenesis and augment its progression. The protein profile associated with BCSC has yet to be extensively studied. Mammospheres have been widely employed as a model system to study BCSC. We used proteomics on the MCF-7 breast cancer cell line to compare protein expression in mammosphere-derived cells to that of parental monolayer cells. We identified 34 differentially expressed proteins, seven of which were overexpressed, with the remaining downregulated in mammosphere-derived cells. These differentially expressed proteins include those involved in cell metabolism such as GAPDH and fatty acid synthase, stress response proteins like Hsp27 and FKBP4, and signal transduction related proteins like GIPC1. The expression of breast cancer tumorigenesis and progression-promoting proteins GAPDH and FKBP4 were validated through western blotting. These two proteins are especially recognized for their role in breast cancer resistance to current chemotherapies. The data generated by mammosphere proteomics suggest that this system can identify novel targets for breast cancer stem cells and may provide insights into novel therapy of breast cancer.

Early growth response 1 and fatty acid synthase expression is altered in tumor adjacent prostate tissue and indicates field cancerization

BACKGROUND

Field cancerization denotes the occurrence of molecular alterations in histologically normal tissues adjacent to tumors. In prostate cancer, identification of field cancerization has several potential clinical applications. However, prostate field cancerization remains ill defined. Our previous work has shown up-regulated mRNA of the transcription factor early growth response 1 (EGR-1) and the lipogenic enzyme fatty acid synthase (FAS) in tissues adjacent to prostate cancer.

METHODS

Immunofluorescence data were analyzed quantitatively by spectral imaging and linear unmixing to determine the protein expression levels of EGR-1 and FAS in human cancerous, histologically normal adjacent, and disease-free prostate tissues.

RESULTS

EGR-1 expression was elevated in both structurally intact tumor adjacent (1.6× on average) and in tumor (3.0× on average) tissues compared to disease-free tissues. In addition, the ratio of cytoplasmic versus nuclear EGR-1 expression was elevated in both tumor adjacent and tumor tissues. Similarly, FAS expression was elevated in both tumor adjacent (2.7× on average) and in tumor (2.5× on average) compared to disease-free tissues.

CONCLUSIONS

EGR-1 and FAS expression is similarly deregulated in tumor and structurally intact adjacent prostate tissues and defines field cancerization. In cases with high suspicion of prostate cancer but negative biopsy, identification of field cancerization could help clinicians target areas for repeat biopsy. Field cancerization at surgical margins on prostatectomy specimen should also be looked at as a predictor of cancer recurrence. EGR-1 and FAS could also serve as molecular targets for chemoprevention.

Immunohistochemical expressions of fatty acid synthase and phosphorylated c-Met in thyroid carcinomas of follicular origin

Thyroid carcinoma is the most common endocrine malignancy and the first cause of death among endocrine cancers. Fatty acid synthase (FASN) and c-Met are overexpressed in many types of human cancers. Recent studies have suggested a functional interaction between FASN and c-Met. However, their roles in thyroid carcinomas have not been fully investigated. In this study, we evaluated the expressions of FASN and phosphorylated (p)-c-Met by using immunohistochemistry in thyroid carcinomas of follicular origin, from 32 patients. The adjacent non-neoplastic thyroid tissue was also evaluated for comparison. Immunoreactive intensity and extensiveness were semi-quantified. The overexpression of FASN was observed in a subset of papillary thyroid carcinomas (PTC) including the classical type and tall cell, follicular, trabecular/insular and diffuse sclerosing variants, a subset of follicular thyroid carcinomas (FTC), and the PTC and FTC components in anaplastic thyroid carcinomas (ATC). No overexpression was observed in the ATCs per se and the columnar cell, solid, and cribriform variants of PTCs. All Hürthle cell variant FTCs and non-neoplastic Hürthle cells demonstrated positive staining for FASN while the non-neoplastic follicular cells without Hürthle cell change were negative. An association in overexpression between FASN and p-c-Met was observed in the majority of carcinomas as well as in the non-neoplastic Hürthle cells. In conclusion, overexpressions of FASN and p-c-Met were observed in a subset of thyroid carcinomas of follicular origin, which may be of values for targeted therapy and predicting prognosis while the positive immunostaining for these immunomarkers may be nonspecific for Hürthle cell thyroid carcinomas.

Effect of collagen I and aortic carboxypeptidase-like protein on 3T3-L1 adipocyte differentiation

Aortic carboxypeptidase-like protein (ACLP) is a secreted protein expressed in preadipocytes and down-regulated during adipogenesis. Results from previous studies on the influence of ACLP overexpression on adipogenesis vary from no effect to complete inhibition. We hypothesized that ACLP may modulate adipogenesis in the presence of collagen I, a protein to which it binds. We compared control (pLXSN) 3T3-L1 preadipocytes with 3T3-L1 preadipocytes stably overexpressing ACLP (pLXSN-ACLP) that were grown in standard vs collagen I-coated dishes. Aortic carboxypeptidase-like protein overexpression, via retroviral transduction, resulted in a 3.2-fold increase in ACLP cellular levels and a 2.1-fold increase in ACLP levels released into medium. Aortic carboxypeptidase-like protein overexpression did not inhibit differentiation in standard dishes. In collagen I-coated dishes compared with standard dishes, control preadipocytes, when induced to differentiate, exhibited the same increase in triacylglycerol accumulation, but showed a significantly higher induction of fatty acid synthase (1.6-fold more), peroxisome proliferator-activated receptor γ (1.4-fold more), and CCAAT/enhancer-binding protein α (1.4-fold more). Aortic carboxypeptidase-like protein overexpression significantly reduced this enhanced induction of fatty acid synthase, peroxisome proliferator-activated receptor γ, and CCAAT/enhancer-binding protein α by 65%, 59%, and 66%, respectively, but had no effect on the accumulation of triacylglycerol during differentiation. Finally, studies on proadipogenic insulin signaling in ACLP-overexpressing preadipocytes demonstrated that insulin-stimulated Akt phosphorylation was significantly decreased by 27% in cells cultured in collagen I-coated dishes vs standard dishes. Our data suggest that ACLP inhibits certain aspects of 3T3-L1 adipogenesis in a collagen I-rich environment.

Metformin blocks the stimulative effect of a high-energy diet on colon carcinoma growth in vivo and is associated with reduced expression of fatty acid synthase

The molecular mechanisms responsible for the association of obesity with adverse colon cancer outcomes are poorly understood. We investigated the effects of a high-energy diet on growth of an in vivo colon cancer model. Seventeen days following the injection of 5x10(5) MC38 colon carcinoma cells, tumors from mice on the high-energy diet were approximately twice the volume of those of mice on the control diet. These findings were correlated with the observation that the high-energy diet led to elevated insulin levels, phosphorylated AKT, and increased expression of fatty acid synthase (FASN) by the tumor cells. Metformin, an antidiabetic drug, leads to the activation of AMPK and is currently under investigation for its antineoplastic activity. We observed that metformin blocked the effect of the high-energy diet on tumor growth, reduced insulin levels, and attenuated the effect of diet on phosphorylation of AKT and expression of FASN. Furthermore, the administration of metformin led to the activation of AMPK, the inhibitory phosphorylation of acetyl-CoA carboxylase, the upregulation of BNIP3 and increased apoptosis as estimated by poly (ADP-ribose) polymerase (PARP) cleavage. Prior work showed that activating mutations of PI3K are associated with increased AKT activation and adverse outcome in colon cancer; our results demonstrate that the aggressive tumor behavior associated with a high-energy diet has similar effects on this signaling pathway. Furthermore, metformin is demonstrated to reverse the effects of the high-energy diet, thus suggesting a potential role for this agent in the management of a metabolically defined subset of colon cancers.

Expression of fatty acid synthase in nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is characterized by hepatic lipid accumulation which starts with simple hepatic steatosis and may progress toward inflammation (nonalcoholic steatohepatitis [NASH]). Fatty acid synthase (FASN) catalyzes the last step in fatty acid biosynthesis, and thus, it is believed to be a major determinant of the maximal hepatic capacity to generate fatty acids by de novo lipogenesis. The aim of this study was to analyze the correlation between hepatic steatosis and inflammation with FASN expression. In vitro incubation of primary human hepatocytes with fatty acids dose-dependently induced cellular lipid-accumulation and FASN expression, while stimulation with TNF did not affect FASN levels. Further, hepatic FASN expression was significantly increased in vivo in a murine model of hepatic steatosis without significant inflammation but not in a murine NASH model as compared to control mice. Also, FASN expression was not increased in mice subjected to bile duct ligation, an experimental model characterized by severe hepatocellular damage and inflammation. Furthermore, FASN expression was analyzed in 102 human control or NAFLD livers applying tissue micro array technology and immunohistochemistry, and correlated significantly with the degree of hepatic steatosis, but not with inflammation or ballooning of hepatocytes. Quantification of FASN mRNA expression in human liver samples confirmed significantly higher FASN levels in hepatic steatosis but not in NASH, and expression of SREBP1, which is the main transcriptional regulator of FASN, paralleled FASN expression levels in human and experimental NAFLD. In conclusion, the transcriptional induction of FASN expression in hepatic steatosis is impaired in NASH, while hepatic inflammation in the absence of steatosis does not affect FASN expression, suggesting that FASN may serve as a new diagnostic marker or therapeutic target for the progression of NAFLD.

In vivo and in vitro application of black soybean peptides in the amelioration of endoplasmic reticulum stress and improvement of insulin resistance

AIMS

Hepatic endoplasmic reticulum (ER) stress plays a key role in the development of obesity-induced insulin resistance. This study evaluated the effects of peptides from black soybean (BSP) on ER stress and insulin signaling in vitro and in vivo.

MAIN METHODS

Using C2C12 myotubes or HepG2 cells, we evaluated the effects of BSP on the expression of proteins involved in insulin signaling and in the ER stress response in insulin-sensitive or insulin-resistant cells. BSP was given orally to db/db mice for 5weeks to investigate its antidiabetic effects in vivo and the underlying mechanisms.

KEY FINDINGS

BSP increased GLUT4 translocation and glucose transport in myotubes and stimulated Akt-mediated glycogen synthase kinase-3beta (GSK-3beta) and Foxo1 phosphorylation in HepG2 cells. BSP significantly restored the suppression of insulin-mediated Akt phosphorylation in insulin-resistant cells. BSP significantly inhibited the activation of ER stress-responsive proteins by thapsigargin. BSP also significantly reduced blood glucose and improved glucose tolerance in db/db mice. The serum lipid profile (triglyceride and high-density lipoprotein concentrations) improved concomitantly with the BSP-induced downregulation of hepatic fatty acid synthase expression in db/db mice. Consistent with the results observed in HepG2 cells, BSP downregulated the elevated hepatic ER stress response in diabetic mice concomitantly with an increased expression of phospho-Foxo1.

SIGNIFICANCE

A peptide mixture, BSP, showed beneficial effects through multiple mechanisms involving the suppression of hepatic ER stress and restoration of insulin resistance, suggesting that it has potential as an antidiabetic agent.

Trophoblastic neoplasms express fatty acid synthase, which may be a therapeutic target via its inhibitor C93

Fatty acid synthase (FASN) is an emerging tumor-associated marker and a promising antitumor therapeutic target. In this study, we analyzed the expression of FASN in normal and molar placentas, as well as gestational trophoblastic neoplasia, and assessed the effects of a new FASN inhibitor, C93, on cellular proliferation and apoptosis in choriocarcinoma cells. Using a FASN-specific monoclonal antibody, we found that FASN immunoreactivity was detected in the cytotrophoblast and intermediate (extravillous) trophoblast of normal and molar placentas, as well as in placental site nodules. All choriocarcinomas (n = 33), 90% of epithelioid trophoblastic tumors (n = 20), and 60% of placental site trophoblastic tumors (n = 10) exhibited FASN positivity. FASN expression was further confirmed in vitro by Western blot and real-time PCR. Treatment of JEG3 and JAR cells with C93 induced significant apoptosis through the caspase-3/caspase-9/poly(ADP)ribose polymerase pathway. Cell cycle progression was not affected by the inhibitor. In summary, the data indicate that FASN is expressed in the majority of gestational trophoblastic neoplasias, and is essential for choriocarcinoma cells to survive and escape from apoptosis. FASN inhibitors such as C93 warrant further investigation as targeted therapeutic agents for metastatic and chemoresistant gestational trophoblastic neoplasia.

Comparison of insulin signaling gene expression in insulin sensitive tissues between cats and dogs

Diabetes mellitus (DM) is a common endocrine disease in cats and dogs with increasing prevalence. Type 1 DM appears to be the most common form of diabetes in dogs whereas Type 2 DM prevails for cats. Since insulin resistance is more frequently encountered in cats than dogs, our laboratory was interested in determining whether differences at the insulin signaling pathway level and differences in glucose and lipid metabolism could be observed between cats and dogs. Insulin resistance has been positively correlated to insulin signaling pathway abnormalities. As such, this study measured insulin receptor substrate-1 (IRS-1), insulin receptor substrate-2 (IRS-2), and phosphatidylinositol 3-kinase (PI3-K) P-85alpha mRNA expression levels in classical insulin-responsive sensitive tissues (liver, skeletal muscle, and abdominal fat) and peripheral leukocytes between cats and dogs by qRT-PCR. Different tissues were sampled because it is currently unknown where insulin-resistance arises from. In addition, enzymes involved in glucose and lipid metabolism, malate dehydrogenase (MDH), glucose-6-phosphate dehydrogenase (G6PDH) and fatty acid synthase (FAS) were also assessed since glucose and lipid metabolism differs between cats and dogs. Overall, IRS-1, IRS-2, PI3-K, MDH, G6DPH, and FAS mRNA tissue expression profiles demonstrated different levels of expression, in various tissues for both canines and felines, which was expected. No distinct expression pattern emerged; however, differences were noted between canines and felines. In addition, IRS-1, IRS-2, PI3-K, MDH, G6DPH, and FAS mRNA expression was significantly higher in canine versus feline tissues, including peripheral leukocytes. Remarkable differences in insulin signaling gene expression between felines and canines indicate that cats may have an underlying low insulin sensitivity level due to low IRS-1, IRS-2, and PI3-K P-85alpha mRNA expression levels which would predispose cats to develop insulin resistance. Moreover, differences in glucose and lipid metabolism related gene expression (MDH, G6DPH, and FAS) demonstrate that felines have an overall lower metabolic rate in various tissues which may be attributed to overall lower insulin signaling gene expression and a lack of physical activity as compared to canines. Therefore, a combination of genetic and environmental factors appears to make felines more prone to suffer from insulin resistance and type 2 DM than canines.

Proto-oncogene FBI-1 (Pokemon) and SREBP-1 synergistically activate transcription of fatty-acid synthase gene (FASN)

FBI-1 (Pokemon/ZBTB7A) is a proto-oncogenic transcription factor of the BTB/POZ (bric-à-brac, tramtrack, and broad complex and pox virus zinc finger) domain family. Recent evidence suggested that FBI-1 might be involved in adipogenic gene expression. Coincidentally, expression of FBI-1 and fatty-acid synthase (FASN) genes are often increased in cancer and immortalized cells. Both FBI-1 and FASN are important in cancer cell proliferation. SREBP-1 is a major regulator of many adipogenic genes, and FBI-1 and SREBP-1 (sterol-responsive element (SRE)-binding protein 1) interact with each other directly via their DNA binding domains. FBI-1 enhanced the transcriptional activation of SREBP-1 on responsive promoters, pGL2-6x(SRE)-Luc and FASN gene. FBI-1 and SREBP-1 synergistically activate transcription of the FASN gene by acting on the proximal GC-box and SRE/E-box. FBI-1, Sp1, and SREBP-1 can bind to all three SRE, GC-box, and SRE/E-box. Binding competition among the three transcription factors on the GC-box and SRE/E-box appears important in the transcription regulation. FBI-1 is apparently changing the binding pattern of Sp1 and SREBP-1 on the two elements in the presence of induced SREBP-1 and drives more Sp1 binding to the proximal promoter with less of an effect on SREBP-1 binding. The changes induced by FBI-1 appear critical in the synergistic transcription activation. The molecular mechanism revealed provides insight into how proto-oncogene FBI-1 may attack the cellular regulatory mechanism of FASN gene expression to provide more phospholipid membrane components needed for rapid cancer cell proliferation.

[Gene expression of H-FABP and FAS and its clinicopathological significance in breast infiltrating ductal carcinoma]

OBJECTIVE

To detect the expression of Heart or Muscle Fatty acid binding protein (H-FABP) and fatty acid synthase (FAS) in human breast cancer cells.

METHODS

The expression levels of FAS and H-FABP in 81 ductal infiltrating carcinoma (DIC) were detected by RT-PCR, immunohistochemistry and Western blot analysis. The possible associations of the expression of the two proteins with major clinicopathological factors were analyzed.

RESULTS

The expression of both H-FABP and FAS increased in DIC cells than in adjacent normal cells. But less H-FABP and FAS were found in grade III DIC than in grade I and grade II DIC (P < 0.05). There was a positive correlation between the expression of H-FABP and FAS. No correlations between the expressions of two genes with other clinicopathological factors were found.

CONCLUSION

The higher expression of H-FABP in grade I and II DIC suggests an early increased response to the over-expression of FAS. The parallel increase of H-FABP and FAS expressions marks increased breast cancer risk.

Selective binding of sterol regulatory element-binding protein isoforms and co-regulatory proteins to promoters for lipid metabolic genes in liver

Mice were subjected to different dietary manipulations to selectively alter expression of hepatic sterol regulatory element-binding protein 1 (SREBP-1) or SREBP-2. mRNA levels for key target genes were measured and compared with the direct binding of SREBP-1 and -2 to the associated promoters using isoform specific antibodies in chromatin immunoprecipitation studies. A diet supplemented with Zetia (ezetimibe) and lovastatin increased and decreased nuclear SREBP-2 and SREBP-1, respectively, whereas a fasting/refeeding protocol dramatically altered SREBP-1 but had modest effects on SREBP-2 levels. Binding of both SREBP-1 and -2 increased on promoters for 3-hydroxy-3-methylglutaryl-CoA reductase, fatty-acid synthase, and squalene synthase in livers of Zetia/lovastatin-treated mice despite the decline in total SREBP-1 protein. In contrast, only SREBP-2 binding was increased for the low density lipoprotein receptor promoter. Decreased SREBP-1 binding during fasting and a dramatic increase upon refeeding indicates that the lipogenic "overshoot" for fatty-acid synthase gene expression known to occur during high carbohydrate refeeding can be attributed to a similar overshoot in SREBP-1 binding. SREBP co-regulatory protein recruitment was also increased/decreased in parallel with associated changes in SREBP binding, and there were clear distinctions for different promoters in response to the dietary manipulations. Taken together, these studies reveal that there are alternative molecular mechanisms for activating SREBP target genes in response to the different dietary challenges of Zetia/lovastatin versus fasting/refeeding. This underscores the mechanistic flexibility that has evolved at the individual gene/promoter level to maintain metabolic homeostasis in response to shifting nutritional states and environmental fluctuations.

[Expression of epidermal fatty acid-binding protein and fatty acid synthase in infiltrating ductal breast carcinoma]

OBJECTIVE

To detect the expression of epidermal fatty acid-binding protein (E-FABP) and fatty acid synthase (FAS) in human breast cancer and identify the potential markers and therapeutic targets for breast cancer.

METHODS

FAS and E-FABP expressions were detected in 76 patients with infiltrating ductal breast carcinoma using RT-PCR, immunohistochemistry and Western blotting. The possible associations of the expression of the two proteins with the major clinicopathological factors were analyzed.

RESULTS

E-FABP and FAS expression levels were significantly decreased (P<0.05) in grade III as compared with grades I and II infiltrating ductal breast carcinoma. There was a positive correlation between E-FABP and FAS expressions, but their expressions were not correlated to the clinicopathological factors of the patients except for the tumor grades. High E-FABP expression level in grades I and II tumors were associated with an early increased responsiveness to FAS.

CONCLUSION

The variation of the E-FABP and FAS expressions in the lesions is associated with increase of the risk for breast cancer, and the results of this study provide evidence for developing new molecular markers of high-risk lesions and identifying new the targets for breast cancer therapy.

Effect of an enriched cholesterol diet during gestation on fatty acid synthase, HMG-CoA reductase and SREBP-1/2 expressions in rabbits

Pregnancy is associated with hyperlipidemia and hypercholesterolemia in humans. These changes take place to support fetal growth and development, and modifications of these maternal concentrations may influence lipids and cholesterol synthesis in the dam, fetus and placenta. Administration of a 0.2% enriched cholesterol diet (ECD) during rabbit gestation significantly increased cholesterol and triglyceride (TG) levels in maternal livers and decreased fetal weight by 15%. Here we used Western blot analysis to examine the impact of gestation and 0.2% ECD on the expression levels of fatty acid synthase (FAS), HMGR and SREBP-1/2, which are involved in either lipid or cholesterol synthesis. We confirmed that gestation modifies the hepatic and circulating lipid profile in the mother. Our data also suggest that the maternal liver mainly supports lipogenesis, while the placenta plays a key role in cholesterol synthesis. Thus, our data demonstrate a decrease in HMGR protein levels in dam livers by feeding an ECD. In the placenta, SREBPs are highly expressed, and the ECD supplementation increased nuclear SREBP-1/2 protein levels. In addition, our results show a decrease in FAS protein levels in non-pregnant liver and in the liver of offspring from ECD-treated animals. Finally, our data suggest that the placenta does not modify its own cholesterol synthesis in response to an increase in circulating cholesterol. However, the dam liver compensates for this increase by essentially decreasing the level of HMGR expression. Because HMGR and FAS expressions do not correlate with the circulating lipid profile, it would be interesting to find which genes are then targeted by SREBP-1/2 during gestation.

The human fatty acid synthase: a new therapeutic target for coxsackievirus B3-induced diseases?

Coxsackievirus is linked to a large variety of severe human and animal diseases such as myocarditis. The interplay between host factors and virus components is crucial for the fate of the infected cells. However, host proteins which may play a role in coxsackievirus-induced diseases are ill-defined. Two-dimensional gel electrophoresis of protein extracts obtained from coxsackievirus B3 (CVB3)-infected and uninfected HeLa or HepG2 cells combined with spot analysis revealed several proteins which are exclusively up-regulated in infected cells. One of these proteins was identified as the fatty acid synthase (FAS). By using cerulenin and C75, two known inhibitors of FAS we were able to significantly block CVB3 replication. FAS appears to be directly involved in CVB3-caused pathology and is therefore suitable as a therapeutic target in CVB3-induced diseases.

Up-regulation of acetyl-CoA carboxylase alpha and fatty acid synthase by human epidermal growth factor receptor 2 at the translational level in breast cancer cells

Expression of the HER2 oncogene is increased in approximately 30% of human breast carcinomas and is closely correlated with the expression of fatty acid synthase (FASN). In the present study, we determined the mechanism by which FASN and acetyl-CoA carboxylase alpha (ACCalpha) could be induced by HER2 overexpression. SK-BR-3 and BT-474 cells, breast cancer cells that overexpress HER2, expressed higher levels of FASN and ACCalpha compared with MCF-7 and MDA-MB-231 breast cancer cells in which HER2 expression is low. The induction of FASN and ACCalpha in BT474 cells were not mediated by the activation of SREBP-1. Exogenous HER2 expression in MDA-MB-231 cells induced the expression of FASN and ACCalpha, and the HER2-mediated increase in ACCalpha and FASN was inhibited by both LY294002, a phosphatidylinositol 3-kinase inhibitor, and rapamycin, a mammalian target of rapamycin (mTOR) inhibitor. In addition, the activation of mTOR by the overexpression of RHEB in MDA-MB-231 cells increased the synthetic rates of both FASN and ACCalpha. On the other hand, FASN and ACCalpha were reduced in BT-474 cells by a blockade of the mTOR signaling pathway. These changes observed in their protein levels were not accompanied by changes in their mRNA levels. The 5'- and 3'-untranslated regions of both FASN and ACCalpha mRNAs were involved in selective translational induction that was mediated by mTOR signal transduction. These results strongly suggest that the major mechanism of HER2-mediated induction of FASN and ACCalpha in the breast cancer cells used in this study is translational regulation primarily through the mTOR signaling pathway.

Immunohistochemical expression and prognostic significance of fatty acid synthase in pancreatic carcinoma

BACKGROUND

The aim of this study was to evaluate immunohistochemical markers in pancreatic cancer and to determine the association of their expression with clinicopathological features and prognosis.

PATIENTS AND METHODS

Thirty pancreatic adenocarcinoma patients were followed-up for an average period of 5 years. FAS, bcl-2, p53 and Ki-67 expression were detected immunohistochemically to determine their prognostic value.

RESULTS

FAS was statistically associated with p53 (p = 0.002), Ki-67 (p = 0.003), higher histological grade (p = 0.001 and recurrence and overall survival (p = 0.001).

CONCLUSION

The newly found overexpression of FAS in highly aggressive pancreatic carcinomas may help us stratify patients into different prognostic groups and indicate new therapeutic strategies.

Fatty acid synthase gene expression in human adipose tissue: association with obesity and type 2 diabetes

AIMS/HYPOTHESIS

Increased expression and activity of the lipogenic pathways in adipose tissue may contribute to the development of obesity. As a central enzyme in lipogenesis, the gene encoding fatty acid synthase (FASN) was identified as a candidate gene for determining body fat. In the present study we tested the hypothesis that increased FASN expression links metabolic alterations of excess energy intake, including hyperinsulinaemia, dyslipidaemia and altered adipokine profile to increased body fat mass.

SUBJECTS AND METHODS

In paired samples of visceral and subcutaneous adipose tissue from 196 participants (lean or obese), we investigated whether FASN mRNA expression (assessed by PCR) in adipose tissue is increased in obesity and related to visceral fat accumulation, measures of insulin sensitivity (euglycaemic-hyperinsulinaemic clamp) and glucose metabolism.

RESULTS

FASN mRNA expression was increased by 1.7-fold in visceral vs subcutaneous fat. Visceral adipose tissue FASN expression was correlated with FASN protein levels, subcutaneous FASN expression, visceral fat area, fasting plasma insulin, serum concentrations of IL-6, leptin and retinol-binding protein 4 (RBP4), and inversely with measures of insulin sensitivity, independently of age, sex and BMI. Moreover, we found significant correlations between FASN expression and markers of renal function, including serum creatinine and urinary albumin excretion.

CONCLUSIONS/INTERPRETATION

Increased FASN gene expression in adipose tissue is linked to visceral fat accumulation, impaired insulin sensitivity, increased circulating fasting insulin, IL-6, leptin and RBP4, suggesting an important role of lipogenic pathways in the causal relationship between consequences of excess energy intake and the development of obesity and type 2 diabetes.

An intervention study of the effects of calcium intake on faecal fat excretion, energy metabolism and adipose tissue mRNA expression of lipid-metabolism related proteins

CONTEXT

In various observational studies, an inverse relation between calcium intake and body weight has been observed. A possible explanation could be an increased calcium excretion through the faeces caused by an increased dietary calcium intake.

OBJECTIVE

To examine whether an increased calcium intake could lead to changes in faecal fat and energy excretion.

DESIGN

Four different isocaloric diets with various calcium contents (400, 1200 and 2500 mg from dairy and 1200 mg from calcium carbonate (1200S)) were administered in a crossover design for 7 days each.

SUBJECTS

Five healthy men and five healthy women (age=28+/-2, body mass index=24.1+/-0.4, body fat%=25.6+/-2.4) were recruited by local announcement.

MEASUREMENTS

At the end of every intervention period, faecal samples were collected for determination of fat, energy and calcium content, blood samples were obtained for determination of relevant blood parameters; and fat samples were obtained for measurement of the mRNA expression. Furthermore, resting energy expenditure and fat oxidation were measured with the ventilated-hood technique.

RESULTS

We observed a non-significant 56% increase in fat excretion (P=0.159) on the 2500 mg diet, compared to the 400 mg diet. The 2500 mg diet significantly reduced the expression of fatty acid synthase (FAS) mRNA (P<0.05) and the calcium content of the diets significantly affected calcium excretion. Furthermore, we saw a significant decrease of serum triglycerides on the 1200S diet (P<0.05).

CONCLUSION

In this study, we observed a trend towards a higher fat excretion on the high-calcium diet, but this difference failed to reach statistical significance. It is possible that the relatively high protein content of the experimental diets increased calcium absorption from the intestine, thus decreasing the amount of calcium available for binding to fat and eliminating possible effects of dietary calcium on fat excretion. Furthermore, we observed decreases in FAS mRNA expression and serum triglycerides as a result of a high calcium intake.

A key role for orphan nuclear receptor liver receptor homologue-1 in activation of fatty acid synthase promoter by liver X receptor

Liver X receptor (LXR) activates fatty acid synthase (FAS) gene expression through binding to a DR-4 element in the promoter. We show that a distinct nuclear receptor half-site 21 bases downstream of the DR-4 element is also critical for the response of FAS to LXR but is not involved in LXR binding to DNA. This half-site specifically binds liver receptor homologue-1 (LRH-1) in vitro and in vivo, and we show LRH-1 is required for maximal LXR responsiveness of the endogenous FAS gene as well as from promoter reporter constructs. We also demonstrate that LRH-1 stimulation of the FAS LXR response is blocked by the addition of small heterodimer partner (SHP) and that FAS mRNA is overexpressed in SHP knock-out animals, providing evidence that FAS is an in vivo target of SHP repression. Taken together, these findings identify the first direct lipogenic gene target of LRH-1/SHP repression and provide a mechanistic explanation for bile acid repression of FAS and lipogenesis recently reported by others.

Gender-specific programmed hepatic lipid dysregulation in intrauterine growth-restricted offspring

OBJECTIVE

Intrauterine growth restriction demonstrates increased risk of adult metabolic syndrome. The associated hyperlipidemia results from obesity or programmed metabolic abnormalities. Because lipid homeostasis is regulated by the liver, we hypothesized that hepatic structure and lipid content in intrauterine growth restriction would reflect a primary lipid dysfunction.

STUDY DESIGN

From 10 days to term gestation, control pregnant rats received ad libitum diet; study rats were 25% food-restricted (FR). All dams received ad libitum diet throughout lactation. At 3 weeks of age, hepatic lobule size and lipid profile of the pups were determined.

RESULTS

At 3 weeks of age, body and liver weights of the pups were comparable with controls, although with reduced hepatic lobule size. FR males had increased hepatic triglyceride and cholesterol content with elevated sterol regulatory element-binding protein-1c, fatty acid synthase, and lipoprotein lipase expression; FR females exhibited decreased hepatic cholesterol levels. Plasma lipid levels were unchanged in FR males and females.

CONCLUSION

Developmental programming results in sex-dependent altered lipid metabolism with increased risk in males.

Fatty acid synthase overexpression in colorectal cancer is associated with microsatellite instability, independent of CpG island methylator phenotype

Overexpression of fatty acid synthase (FASN), a key enzyme for de novo lipogenesis, is observed in many cancers including colorectal cancer and is associated with poor clinical outcomes. Cellular FASN expression is physiologically upregulated in a state of energy excess. Obesity and excess energy balance have been known to be risk factors for colorectal cancer. High degree of microsatellite instability (MSI-H) is a distinct phenotype in colorectal cancer, associated with CpG island methylator phenotype (CIMP). Previous data suggest that obesity or altered energy balance may potentially modify risks for MSI-H cancers and microsatellite stable (MSS) cancers differently. However, the relationship between MSI and FASN overexpression has not been investigated. Using 976 cases of population-based colorectal cancer samples from 2 large prospective cohort studies, we correlated FASN expression (by immunohistochemistry) with MSI, KRAS and BRAF mutations, p53 expression (by immunohistochemistry), and CIMP status [determined by MethyLight for 8 CIMP-specific gene promoters including CACNA1G, CDKN2A (p16), CRABP1, IGF2, MLH1, NEUROG1, RUNX3, and SOCS1]. Marked (2+) FASN overexpression was observed in 110 (11%) of the 976 tumors and was significantly more common in MSI-H tumors (21% [28/135]) than MSI-low (5.6% [4/72], P = .004) and MSS tumors (11% [72/678], P = .001). The association between FASN overexpression and MSI-H persisted even after stratification by CIMP status. In contrast, FASN overexpression was not correlated with CIMP after stratification by MSI status. Fatty acid synthase overexpression was not significantly correlated with sex, tumor location, p53, or KRAS/BRAF status. In conclusion, FASN overexpression in colorectal cancer is associated with MSI-H, independent of CIMP status.

Inhibition of Fatty Acid Synthase Induces Endoplasmic Reticulum Stress in Tumor Cells

Fatty acid synthase (FAS), the cellular enzyme that synthesizes palmitate, is expressed at high levels in tumor cells and is vital for their survival. Through the synthesis of palmitate, FAS primarily drives the synthesis of phospholipids in tumor cells. In this study, we tested the hypothesis that the FAS inhibitors induce endoplasmic reticulum (ER) stress in tumor cells. Treatment of tumor cells with FAS inhibitors induces robust PERK-dependent phosphorylation of the translation initiation factor eIF2alpha and concomitant inhibition of protein synthesis. PERK-deficient transformed mouse embryonic fibroblasts and HT-29 colon carcinoma cells that express a dominant negative PERK (DeltaC-PERK) are hypersensitive to FAS inhibitor-induced cell death. Pharmacologic inhibition of FAS also induces the processing of X-box binding protein-1, indicating that the IRE1 arm of the ER stress response is activated when FAS is inhibited. Induction of ER stress is further confirmed by the increased expression of the ER stress-regulated genes CHOP, ATF4, and GRP78. FAS inhibitor-induced ER stress is activated prior to the detection of caspase 3 and PARP cleavage, primary indicators of cell death, whereas orlistat-induced cell death is rescued by coincubation with the global translation inhibitor cycloheximide. Lastly, FAS inhibitors cooperate with the ER stress inducer thapsigargin to enhance tumor cell killing. These results provide the first evidence that FAS inhibitors induce ER stress and establish an important mechanistic link between FAS activity and ER function.

MRNA stability and overexpression of fatty acid synthase in human breast cancer cell lines

BACKGROUND

Elevation of fatty acid synthase (FAS) in human cancers is often associated with increased tumor aggression. The basic genetic mechanisms leading to increased enzyme content in cancer cells were investigated using cell lines derived from human metastatic breast carcinomas (T47D, Zr75 and SKBr3) and normal human breast epithelium (184A1).

MATERIALS AND METHODS

Western analysis, Northern blotting, [2-(14)C]malonyl-CoA incorporation assays, nuclear run-off transcription assays, mRNA decay assays, and poly(A) tail assays were used to measure and compare transcription rates of the FAS gene among the four cell lines.

RESULTS

By Western analysis, FAS levels in T47D were 2.6 times lower than ZR75 and SKBr3, but 6.7 times greater than non-neoplastic 184A1 cells. FAS mRNA levels and specific activity correlated with protein content. In contrast, relative rates of FAS gene transcription were significantly higher in non-neoplastic 184A1 cells than T47D, ZR75 and SKBr3. Stability of message was investigated to explain this discrepancy. The half-life of FAS mRNA in 184A1 cells was 5.6 h, or 4-5-fold less than ZR75 and SKBr3. Poly(A) tail assays showed that FAS mRNA species from 184A1 cells tended to be longer than those of breast cancer cell lines (500-1500 nt versus 500-800 nt, respectively).

CONCLUSION

Breast cancer cell lines contained significantly more FAS enzyme, message and activity than non-neoplastic 184A1 cells. Yet, 184A1 cells exhibited higher rates

Direct interaction between USF and SREBP-1c mediates synergistic activation of the fatty-acid synthase promoter

To understand the molecular mechanisms underlying transcriptional activation of fatty-acid synthase (FAS), we examined the relationship between upstream stimulatory factor (USF) and SREBP-1c, two transcription factors that we have shown previously to be critical for FAS induction by feeding/insulin. Here, by using a combination of tandem affinity purification and coimmunoprecipitation, we demonstrate, for the first time, that USF and SREBP-1 interact in vitro and in vivo. Glutathione S-transferase pulldown experiments with various USF and sterol regulatory element-binding protein (SREBP) deletion constructs indicate that the basic helix-loop-helix domain of USF interacts directly with the basic helix-loop-helix and an N-terminal region of SREBP-1c. Furthermore, cotransfection of USF and SREBP-1c with an FAS promoter-luciferase reporter construct in Drosophila SL2 cells results in highly synergistic activation of the FAS promoter. We also show similar cooperative activation of the mitochondrial glycerol-3-phosphate acyltransferase promoter by USF and SREBP-1c. Chromatin immunoprecipitation analysis of mouse liver demonstrates that USF binds constitutively to the mitochondrial glycerol 3-phosphate acyltransferase promoter during fasting/refeeding in vivo, whereas binding of SREBP-1 is observed only during refeeding, in a manner identical to that of the FAS promoter. In addition, we show that the synergy we have observed depends on the activation domains of both proteins and that mutated USF or SREBP lacking the N-terminal activation domain could inhibit the transactivation of the other. Closely positioned E-boxes and sterol regulatory elements found in the promoters of several lipogenic genes suggest a common mechanism of induction by feeding/insulin.

[Study on proliferation inhibiting and apoptosis inducing effects of cerulenin on multiple myeloma cells]

OBJECTIVE

To determine whether fatty acid synthase (FAS) is expressed in human multiple myeloma( MM) cells and investigate the proliferation inhibition effect of fatty acid synthase inhibitor cerulenin on multiple myeloma cell line U266 and its mechanism.

METHODS

FAS mRNA expression in human MM cell line U266, RPMI8226 cell was assayed by RT-PCR. The proliferation inhibition rate of U266 cells was assayed by MTr analysis. Cell apoptosis and cycle distribution were evaluated by flow cytometry (FCM).

RESULTS

FAS mRNA was highly expressed in human multiple myeloma cell lines as compared with healthy donor PBMNCs. After U266 cells were treated with cerulenin (the concentrations from 5 microg/ml to 640 microg/ ml) for 24 h, the cell proliferation was markedly inhibited with a dose related manner, while the inhibition rate of human skin fibroblast cells were all lower than 30%. When U266 cells were treated with 20 pjg/ml cerulenin for 12 h and 24 h, the early apoptosis rate revealed by Annexin V/PI were 56. 9% and 69. 3% respectively, being higher than that of the blank controls (4. 3% and 1.8%, P < 0. 01). Cell cycle analysis showed it was blocked in S phase. Conclusion FAS is highly expressed in human MM. Cerulenin could induce apoptosis and inhibit proliferation of U266 cells. FAS might be a new potential target for multiple myeloma treatment.

Acetyl-CoA carboxylase alpha is essential to breast cancer cell survival

Activation of de novo fatty acid synthesis is a characteristic feature of cancer cells. We have recently described an interaction between acetyl-CoA carboxylase alpha (ACCalpha), a key enzyme in fatty acid synthesis, and BRCA1, which indicates a possible connection between lipid synthesis and genetic factors involved in susceptibility to breast and ovarian cancers. For this reason, we explored the role of ACCalpha in breast cancer cell survival using an RNA interference (RNAi) approach. We show that specific silencing of either the ACCalpha or the fatty acid synthase (FAS) genes in cancer cells results in a major decrease in palmitic acid synthesis. Depletion of the cellular pool of palmitic acid is associated with induction of apoptosis concomitant with the formation of reactive oxygen species (ROS) and mitochondrial impairment. Expression of a small interfering RNA (siRNA)-resistant form of ACCalpha mRNA prevented the effect of ACCalpha-RNAi but failed to prevent the effect of FAS gene silencing. Furthermore, supplementation of the culture medium with palmitate or with the antioxidant vitamin E resulted in the complete rescue of cells from both ACCalpha and FAS siRNA-induced apoptosis. Finally, human mammary epithelial cells are resistant to RNAi against either ACCalpha or FAS. These data confirm the importance of lipogenesis in cancer cell survival and indicate that this pathway represents a key target for antineoplastic therapy that, however, might require specific dietary recommendation for full efficacy.

Tissue microarray analysis of FAS, Bcl-2, Bcl-x, ER, PgR, Hsp60, p53 and Her2-neu in breast carcinoma

BACKGROUND

The aim of this study was to detect immunohistochemical markers in breast carcinoma by means of tissue microarray analysis (TMA) and to associate their expressions with clinicopathological features and prognosis. Fatty acid synthase, bcl-2, bcl-x, p53, estrogen and progesterone receptors, heat shock protein 60 and Her2-neu (c-erbB-2) were evaluated in a group of 149 breast carcinoma patients with a 5-year follow-up period.

MATERIALS AND METHODS

TMA blocks were made by using duplicate 0.6-mm diameter tissue cores from each paraffin block.

RESULTS

Statistical analysis revealed that tumor stage (p=0.003) and node status (p=0.001) were the only two prognostic markers of disease-free survival. Moreover, FAS and bcl-x showed an independent effect on recurrence (p=0.005). The node status was the only marker of overall survival (p=0.05).

CONCLUSION

Our data confirmed recent reports associating the stage of disease, FAS and Bcl-x expressions with recurrence and outcome. These data demonstrated that TMA is an effective substitute for conventional histochemical-immunohistochemical techniques.

AICAR, an AMPK activator, has protective effects on alcohol-induced fatty liver in rats

BACKGROUND

Previous work with metformin has shown that this antidiabetic agent improves nonalcoholic fatty liver in ob/ob mice. AMP-activated protein kinase (AMPK) is one of the major cellular regulators of lipid and glucose metabolism, and reportedly mediates the beneficial metabolic effects of metformin. In this study, we examined the effects of 5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside (AICAR), an AMPK activator, on an experimental model of ethanol-induced hepatic steatosis.

METHODS

Rats were randomly divided into three groups: (A) rats fed ethanol-containing liquid diet for six weeks; (B) rats pair-fed ethanol-containing liquid diet for six weeks, during the last three weeks of which they were subcutaneously injected with 0.5 mg AICAR/g body weight per day; (C) rats pair-fed isocaloric liquid diet without ethanol for six weeks. At the end of the six-week period, the animals were sacrificed. Serum and liver specimens were analyzed using biochemical and histologic methods, as well as real-time PCR.

RESULTS

Chronic ethanol feeding resulted in fatty liver both histologically and biochemically, whereas AICAR administration attenuated the degree of change in the liver. AICAR also decreased the hepatic sterol regulatory factor binding protein-1c (SREBP-1c) and reduced fatty acid synthase (FAS) expression; these changes led to reduced triglyceride synthesis in rat livers. Furthermore, detection of 4-hydroxy-2-nonenal (4-HNE)-protein adducts showed that the AICAR treatment also decreased the products of lipid peroxidation.

CONCLUSION

In this preclinical rat model, AICAR, an AMPK activator, appears to protect the liver from fatty changes associated with chronic alcohol use. As such, AICAR may have a role in the treatment and prevention of alcohol-induced fatty liver.

Pu-erh Tea Supplementation Suppresses Fatty Acid Synthase Expression in the Rat Liver Through Downregulating Akt and JNK Signalings as Demonstrated in Human Hepatoma HepG2 Cells

Fatty acid synthase (FAS) is a key enzyme of lipogenesis. Overexpression of FAS is dominant in cancer cells and proliferative tissues. The expression of FAS in the livers of rats fed pu-erh tea leaves was significantly suppressed. The gains in body weight, levels of triacylglycerol, and total cholesterol were also suppressed in the tea-treated rats. FAS expression in hepatoma HepG2 cells was suppressed by the extracts of pu-erh tea at both the protein and mRNA levels. FAS expression in HepG2 cells was strongly inhibited by PI3K inhibitor LY294002 and JNK inhibitor II and slightly inhibited by p38 inhibitor SB203580 and MEK inhibitor PD98059, separately. Based on these findings, we suggest that the suppression of FAS in the livers of rats fed pu-erh tea leaves may occur through downregulation of the PI3K/AKt and JNK signaling pathways. The major components of tea that have been demonstrated to be responsible for the antiobesity and hypolipidemic effects are catechins, caffeine, and theanine. The compositions of catechins, caffeine, and theanine varied dramatically in pu-erh, black, oolong, and green teas. The active principles and molecular mechanisms that exerted these biological effects in pu-erh tea deserve future exploration.

Targeting fatty acid synthase: potential for therapeutic intervention in her-2/neu-overexpressing breast cancer

Fatty acid synthase (FAS)-catalyzed de novo fatty acid biosynthesis, an anabolic energy-storage pathway largely considered of minor importance in humans, actively contributes to the cancer phenotype by virtue of its ability to specifically regulate the expression and activity of Her-2/neu (erbB-2) oncogene. First, a positive correlation between high levels of FAS expression and/or activity and the amplification and/or overexpression of Her-2/neu oncogene exists in human breast cancer cell lines. Second, Her-2/neu overexpression stimulates the activity of FAS gene promoter and ultimately mediates increased endogenous fatty acid biosynthesis, while this Her-2/neu-induced upregulation of breast cancer-associated FAS is inhibitable by anti-Her-2/neu antibodies such as trastuzumab (Herceptin(TM)). Third, pharmacological inhibition of FAS activity negatively regulates the expression and tyrosine-kinase activity of Her-2/neu-coded p185(Her-2/neu) oncoprotein.

Fatty acid synthase and its mRNA concentrations are decreased at different times following Hoechst 33342-induced apoptosis in BC3H-1 myocytes

Fatty acid synthase (FAS) regulates the production of fatty acids and plays a role in regulating apoptosis. Hoechst 33342-induced apoptosis in BC3H-1 myocytes was used as a model to explore intracellular changes in FAS protein (Western blot) and FAS mRNA (RT-PCR). Total lipid and individual phospholipid synthesis was inhibited by a lethal dose of Hoechst 33342 (20 microg/ml) while total lipid and phospholipid degradation ([1-14C]-acetate pulse chase method) were not. Hoechst 33342 at 20 microg/ml reduced the concentration of FAS protein, which was followed more than 6 hr later by a reduction in FAS mRNA. In conclusion, the inhibition of fatty acid synthesis induced by 20 microg/ml of Hoechst 33342 is attributed to the degradation of FAS protein by activated caspases rather than by inhibition of FAS enzyme activity or FAS mRNA synthesis.

Potential role of leptin in increase of fatty acid synthase gene expression in chicken liver

Leptin is reported to have direct effects on lipogenesis in peripheral tissues that are independent of its central effects on food intake and body weight. These experiments have been mainly carried out in rodents (different models of obesity) in which lipogenesis occurs in both adipose tissue and liver. Such effects are unknown in birds in which lipogenesis occurs essentially in the liver. In this study, leptin gene expression and circulating leptin levels were examined in two chicken lines, selected for high (FL) or low (LL) abdominal fat pad size, at different nutritional states (fasted and fed state). In addition, effects of recombinant chicken leptin on liver metabolism were investigated. Hepatic leptin and fatty acid synthase (FAS) gene expression and plasma leptin levels were significantly higher in FL than in LL chickens (P < 0.05). In both lines, fasting significantly reduced hepatic leptin and FAS mRNA levels (P < 0.05). Continuous administration of recombinant chicken leptin (8 microg/kg/h) during 6 h significantly inhibited food intake (51%) and increased leptinemia (23-fold) compared to untreated group. Despite the decrease of food intake, leptin significantly induced the expression of FAS in chicken liver. These changes were accompanied by a significant down-regulation of leptin receptor gene expression, however SREBP-1, the main transcription factor of lipogenic genes, remained unchanged. This result suggests a local potential role of leptin in the regulation of avian hepatic lipogenesis, and explain, at least partly, the metabolic changes evolved during the divergent selection of FL and LL chickens.

Octanoate reduces very low-density lipoprotein secretion by decreasing the synthesis of apolipoprotein B in primary cultures of chicken hepatocytes

Fatty acids of varying lengths and saturation differentially affect plasma apolipoprotein B (apoB) levels. To identify the mechanisms underlying the effect of octanoate on very low-density lipoprotein (VLDL) secretion, chicken primary hepatocytes were incubated with either fatty acid-bovine serum albumin (BSA) complexes or BSA alone. Addition of octanoate to culture medium significantly reduced VLDL-triacylglycerol (TG), VLDL-cholesterol and apoB secretion from hepatocytes compared to both control cultures with BSA only and palmitate treatments, but did not modulate intracellular TG accumulation. However, no differences in cellular microsomal triglyceride transfer protein levels were observed in the cultures with saturated fatty acid. In pulse-chase studies, octanoate treatment resulted in reduced apoB-100 synthesis, in agreement with its promotion of secretion. This characteristic effect of octanoate was confirmed by addition of a protease inhibitor, N-acetyl-leucyl-leucyl-norleucinal (ALLN), to hepatocyte cultures. Analysis showed that the level of apoB mRNA was lower in cultures supplemented with octanoate than in the control cultures, but no significant changes were observed in the levels of apolipoprotein A-I, fatty acid synthase and 3-hydroxy-3-methylglutaryl-CoA reductase mRNA as a result of octanoate treatment. Time-course studies indicate that a 50% reduction in apoB mRNA levels requires 12 h of incubation with octanoate. We conclude that octanoate reduced VLDL secretion by the specific down-regulation of apoB gene expression and impairment of subsequent synthesis of apoB, not by the modulation of intracellular apoB degradation, which is known to be a major regulatory target of VLDL secretion of other fatty acids.

Polyunsaturated fatty acids suppress glycolytic and lipogenic genes through the inhibition of ChREBP nuclear protein translocation

Dietary polyunsaturated fatty acids (PUFAs) are potent inhibitors of hepatic glycolysis and lipogenesis. Recently, carbohydrate-responsive element-binding protein (ChREBP) was implicated in the regulation by glucose of glycolytic and lipogenic genes, including those encoding L-pyruvate kinase (L-PK) and fatty acid synthase (FAS). The aim of our study was to assess the role of ChREBP in the control of L-PK and FAS gene expression by PUFAs. We demonstrated in mice, both in vivo and in vitro, that PUFAs [linoleate (C18:2), eicosapentanoic acid (C20:5), and docosahexaenoic acid (C22:6)] suppressed ChREBP activity by increasing ChREBP mRNA decay and by altering ChREBP translocation from the cytosol to the nucleus, independently of an activation of the AMP-activated protein kinase, previously shown to regulate ChREBP activity. In contrast, saturated [stearate (C18)] and monounsaturated fatty acids [oleate (C18:1)] had no effect. Since glucose metabolism via the pentose phosphate pathway is determinant for ChREBP nuclear translocation, the decrease in xylulose 5-phosphate concentrations caused by a PUFA diet favors a PUFA-mediated inhibition of ChREBP translocation. In addition, overexpression of a constitutive nuclear ChREBP isoform in cultured hepatocytes significantly reduced the PUFA inhibition of both L-PK and FAS gene expression. Our results demonstrate that the suppressive effect of PUFAs on these genes is primarily caused by an alteration of ChREBP nuclear translocation. In conclusion, we describe a novel mechanism to explain the inhibitory effect of PUFAs on the genes encoding L-PK and FAS and demonstrate that ChREBP is a pivotal transcription factor responsible for coordinating the PUFA suppression of glycolytic and lipogenic genes.

Mode of leptin action in chicken hypothalamus

While there have been many studies in various species examining the mode of central leptin action on food intake, there is however a paucity of data in birds. We have, therefore, addressed this issue in broiler chickens because this strain was selected for high growth rate, hence high food intake. Continuous infusion of recombinant chicken leptin (8 microg/kg/h) during 6 h at a constant rate of 3 ml/h resulted in a significant reduction (49-57%) of food intake in 3-week-old broiler chickens (P < 0.05). The effect of leptin within the central nervous system (CNS) was mediated via selective hypothalamic neuropeptides. Leptin significantly decreased the expression of its receptor (Ob-R), neuropeptide Y (NPY), orexin (ORX), and orexin receptor (ORXR) (P < 0.05), but not that of agouti-related protein (AgRP) (anabolic/orexigenic effectors) in chicken hypothalamus. However, the catabolic/anorexigenic neuropeptides namely proopiomelanocortin (POMC) and corticotropin-releasing hormone (CRH) mRNA levels remained unchanged after leptin treatment. Despite the absence of leptin effect on AgRP (the antagonist of melanocortin receptor MCR) and POMC (the precursor of alpha-melanocyte stimulating hormone which is a potent agonist for MCR), leptin significantly decreased the expression of MCR-4/5 gene in chicken hypothalamus (P < 0.05) suggesting that leptin acts directly (as ligand) or indirectly (via other ligands) on MCRs to regulate food intake in birds. Additionally, leptin down-regulated the expression of fatty acid synthase (FAS) gene in chicken hypothalamus, indicating an additional pathway of leptin action on food intake such as described for FAS inhibitors. These findings provide new insight into the mechanism of leptin control of food intake in chickens.

Fatty acid synthase expression in cutaneous melanocytic neoplasms

Mammalian fatty acid synthase is a multifunctional enzyme complex involved in de novo synthesis of saturated fatty acids, and inhibitors of fatty acid synthase are being evaluated as potential therapeutic agents. Increased fatty acid synthase expression has been demonstrated in subsets of malignancies, including colon, breast, endometrium, prostate and ovarian carcinomas, and recently malignant melanomas. We evaluated the immunohistochemical expression of fatty acid synthase in 155 cutaneous melanocytic lesions. They included 30 congenital nevi, 19 compound nevi, 40 Spitz nevi, 48 primary melanomas, and 18 metastatic melanomas. Fatty acid synthase expression was stronger in malignant melanomas in comparison to conventional nevi and Spitz nevi, and was the highest for metastatic melanoma. Of the primary malignant melanomas, mean fatty acid synthase scores were significantly greater for Clark levels IV and V compared to Clark levels I and II (P<0.001). In addition, melanomas with Breslow thickness 0.75-1.50 mm and >1.50 mm showed significantly higher mean fatty acid synthase scores compared with those with Breslow thickness <0.75 mm (P=0.013 and <0.001, respectively). Of interest, congenital melanocytic nevi also showed strong fatty acid synthase expression, similar to that seen in metastatic melanoma. This may represent persistence of or regression to a fetal phenotype since normal fetal tissues are known to express high levels of fatty acid synthase.

Positive feedback regulation between AKT activation and fatty acid synthase expression in ovarian carcinoma cells

Activation of AKT and overexpression of fatty acid synthase (FAS) are frequently observed in human ovarian cancer. To explore a possible connection between AKT and FAS, immunohistochemical analyses were conducted on an ovarian cancer tissue microarray, which revealed a significant correlation between phosphorylated AKT (phospho-AKT) and expression of FAS. To investigate the relationship between phospho-AKT and FAS in vitro, a variety of experiments employing a specific phosphatidylinositol 3-OH kinase (PI3K) inhibitor (LY294002), inducible PTEN expression in PTEN-null cells, or AKT1 siRNA demonstrated that phosphatidylinositol-3 kinase (PI3K)/AKT signaling modulates FAS expression. In contrast, inhibition of FAS activity by the drug C75 resulted in downregulation of phospho-AKT and increased cell death. To explore the functional relationship between phospho-AKT and FAS, we used SKOV3, C200, and OVCAR10 ovarian carcinoma cells, which have constitutively active AKT, and OVCAR5 cells, which have very low basal phospho-AKT levels. Treatment with LY294002 abolished AKT activity and potentiated apoptosis induced by FAS inhibitors cerulenin or C75 only in cells with constitutively active AKT, suggesting that constitutive activation of AKT protects against FAS inhibitor-induced cell death. Furthermore, inhibition of FAS activity by cerulenin or C75 resulted in downregulation of phospho-AKT, which preceded the induction of apoptosis. To investigate the relationship between phospho-AKT and FAS in vivo, severe combined immunodeficient mice injected intraperitoneally with SKOV3 cells were treated with C75. Growth of SKOV3 xenografts was markedly inhibited by C75. Analysis of the levels of phospho-AKT and FAS in C75-treated tumors revealed concordant downregulation of phospho-AKT and FAS. Collectively, our findings are consistent with a working model in which AKT activation regulates FAS expression, at least in part, whereas FAS activity modulates AKT activation.

Insulin regulation of fatty acid synthase gene transcription: roles of USF and SREBP-1c

The transcriptional regulation of lipogenesis is a highly coordinated process occurring in concert with transcriptional as well as post-transcriptional regulation of enzymes involved in glycolysis and gluconeogenesis. Fatty acid synthase (FAS) plays a central role in de novo lipogenesis by converting acetyl-CoA and malonyl-CoA into the final end product, palmitate, which can subsequently be esterified into triacylglycerols and then stored in adipose tissue. Ultimately, this helps to prevent buildup of excess glucose in other types of cells and tissues, the effects of which can be readily observed in the pathophysiology of disease states such as Type-11 diabetes and obesity. Thus, elucidating the transcriptional mechanisms of lipogenic enzyme genes is important for understanding the normal regulation of lipogenesis and ultimately the dysregulation that may occur in certain metabolic disease. In this review, we discuss advances in our understanding of the regulation of lipogenesis at the genetic level, with a special emphasis on the common cis- and trans-acting factors involved in regulation of FAS. Two transcription factors, Upstream Stimulatory Factor (USF) and Sterol Regulatory Element Binding Protein-lc (SREBP-lc), seem to play a dominant and possibly cooperative role in regulating FAS transcription.

PPARgamma2 regulates lipogenesis and lipid accumulation in steatotic hepatocytes

Peroxisome proliferator-activated receptor-gamma (PPARgamma) is considered to be one of the master regulators of adipocyte differentiation. PPARgamma2 is abundantly expressed in mature adipocytes and is elevated in the livers of animals that develop fatty livers. The aim of this study was to determine the ability of PPARgamma2 to induce lipid accumulation in hepatocytes and to delineate molecular mechanisms driving this process. The hepatic cell line AML-12 was used to generate a cell line stably expressing PPARgamma2. Oil Red O staining revealed that PPARgamma2 induces lipid accumulation in hepatocytes. This phenotype is accompanied by a selective upregulation of several adipogenic and lipogenic genes including adipose differentiation-related protein (ADRP), adipocyte fatty acid-binding protein 4, sterol regulatory element-binding protein-1 (SREBP-1), fatty acid synthase (FAS), and acetyl-CoA carboxylase, genes whose expression levels are known to increase in steatotic livers of ob/ob mice. Furthermore, the PPARgamma2-regulated induction of both SREBP-1 and FAS parallels an increase in de novo triacylglycerol synthesis in hepatocytes. Triacylglycerol synthesis and lipid accumulation are further enhanced by culturing hepatocytes with troglitazone in the absence of exogenous lipids. These results correspond with an increase in the lipid droplet protein, ADRP, and the data demonstrate that ADRP functions to coat lipid droplets in hepatocytes as observed by confocal microscopy. Taken together, these observations propose a role for PPARgamma2 as an inducer of steatosis in hepatocytes and suggest that this phenomenon occurs through an induction of pathways regulating de novo lipid synthesis.

FAS expression inversely correlates with PTEN level in prostate cancer and a PI 3-kinase inhibitor synergizes with FAS siRNA to induce apoptosis

Fatty acid synthase (FAS), a key enzyme of the fatty acid biosynthetic pathway, has been shown to be overexpressed in various types of human cancer and is, therefore, considered to be an attractive target for anticancer therapy. However, the exact mechanism of overexpression of the FAS gene in tumor cells is not well understood. In this report, we demonstrate that the expression of the tumor suppressor gene PTEN has a significant inverse correlation with FAS expression in the case of prostate cancer in the clinical setting, and inhibition of the PTEN gene leads to the overexpression of FAS in vitro. We also found that the combination of the expression status of these two genes is a better prognostic marker than either gene alone. Furthermore, our results indicate that the specific inhibition of FAS gene by siRNA leads to apoptosis of prostate tumor cells, and inhibition of PI 3-kinase pathway synergizes with FAS siRNA to enhance tumor cell death. These results provide a strong rationale for exploring the therapeutic use of an inhibitor of the PTEN signaling pathway in conjunction with the FAS siRNA to inhibit prostate tumor growth.

"New" hepatic fat activates PPARalpha to maintain glucose, lipid, and cholesterol homeostasis

De novo lipogenesis is an energy-expensive process whose role in adult mammals is poorly understood. We generated mice with liver-specific inactivation of fatty-acid synthase (FAS), a key lipogenic enzyme. On a zero-fat diet, FASKOL (FAS knockout in liver) mice developed hypoglycemia and fatty liver, which were reversed with dietary fat. These phenotypes were also observed after prolonged fasting, similarly to fasted PPARalpha-deficiency mice. Hypoglycemia, fatty liver, and defects in expression of PPARalpha target genes in FASKOL mice were corrected with a PPARalpha agonist. On either zero-fat or chow diet, FASKOL mice had low serum and hepatic cholesterol levels with elevated SREBP-2, decreased HMG-CoA reductase expression, and decreased cholesterol biosynthesis; these were also corrected with a PPARalpha agonist. These results suggest that products of the FAS reaction regulate glucose, lipid, and cholesterol metabolism by serving as endogenous activators of distinct physiological pools of PPARalpha in adult liver.

A pilot study of fatty acid metabolism in oral squamous cell carcinoma

This study was undertaken to determine the characteristics of fatty acid synthesis in squamous carcinoma cells and to assess the possibility of exploiting this synthesis pathway in anticancer therapy. Incorporation of [(3)H]acetate into total lipids of the TCA-83 squamous carcinoma cell line and normal gingival fibroblasts was measured. The effects of cerulenin, a specific, potent, noncompetitive inhibitor of fatty acid synthase (FAS), on growth of TCA-83 cells and normal gingival fibroblasts was determined by the MTT method, and the effect of cerulenin on apoptosis was determined by electrophoresis of cellular DNA. Incorporation of [(3)H]acetate into total lipids was significantly higher in TCA-83 cells (68 +/- 12.7 cpm per 2 x 10(5) cells) than in normal gingival fibroblasts (13 +/- 4.2 cpm per 2 x 10(5) cells; P = 0.011). Cerulenin inhibited TCA-83 cell growth in a dose-dependent manner, even at 2.5 microg/ml, a concentration at which normal gingival fibroblasts were not inhibited. After exposure to cerulenin, TCA-83 cells showed typical apoptotic DNA ladders. These results indicate that cerulenin exerts selective cytotoxic effects on squamous carcinoma cells and can induce their apoptosis. These findings suggest that targeting of fatty acid synthesis may be useful in the treatment of squamous cell carcinomas.

Inhibition of tumor-associated fatty acid synthase activity enhances vinorelbine (Navelbine)-induced cytotoxicity and apoptotic cell death in human breast cancer cells

The lipogenic enzyme fatty acid synthase (FAS) is differentially overexpressed and hyperactivated in a biologically aggressive subset of breast carcinomas and minimally in most normal adult tissues, rendering it an interesting target for anti-neoplastic therapy development. Current trends in the treatment of human breast cancer are with drug combinations that result in improved responses as well as the ability to use less toxic concentrations of the drugs. Here, we envisioned that combinations of conventional chemotherapeutic agents with novel compounds directed against breast cancer-associated FAS hyperactivity may provide increased efficacy over existing therapy for human breast cancer. Specifically, we examined the ability of the mycotoxin cerulenin, a potent and non-competitive inhibitor of FAS activity, to enhance the cytotoxic effects of vinorelbine (Navelbine), a derivative of vinca alkaloid that interferes with tubulin assembly and exhibits activity against metastatic breast cancer. SK-Br3, MCF-7 and MDA-MB-231 human breast cancer cell lines were employed as models of high, moderate and low levels of FAS ('cerulenin-target'), respectively. Combinations of cerulenin with vinorelbine were tested for synergism, additivity or antagonism using the isobologram and the median-effect plot (Chou-Talalay) analyses. Breast cancer cells were either simultaneously exposed to cerulenin and vinorelbine for 24 h or sequentially to cerulenin for 24 h followed by vinorelbine for 24 h. Concurrent exposure to cerulenin and vinorelbine resulted in synergistic interactions in MCF-7 and MDA-MB-231 cell lines, while additivity was found in SK-Br3 cells. Sequencing cerulenin followed by vinorelbine resulted in synergism for SK-Br3 and MDA-MB-231 cells, whereas it showed additive effects in MCF-7 cells. FAS activity blockade was found to synergistically enhance apoptosis-inducing activity of vinorelbine, as determined by an enzyme-linked immunosorbent assay for histone-associated DNA fragments. To the best of our knowledge this is the first study demonstrating that breast cancer-associated FAS is playing an active role in human breast cancer chemosensitivity. We suggest that pharmacological inhibition of FAS activity is a novel molecular approach to enhance the cytotoxic effects of existing chemotherapeutic agents in human breast cancer.