Oncogene dependent requirement of fatty acid synthase in hepatocellular carcinoma

Hepatocellular carcinoma (HCC), the most frequent primary tumor of the liver, is an aggressive cancer type with limited treatment options. Cumulating evidence underlines a crucial role of aberrant lipid biosynthesis (a process known as de novo lipogenesis) along carcinogenesis. Previous studies showed that suppression of fatty acid synthase (FASN), the major enzyme responsible for de novo lipogenesis, is highly detrimental for the in vitro growth of HCC cell lines. To assess whether de novo lipogenesis is required for liver carcinogenesis, we have generated various mouse models of liver cancer by stably overexpressing candidate oncogenes in the mouse liver via hydrodynamic gene delivery. We found that overexpression of FASN in the mouse liver is unable to malignantly transform hepatocytes. However, genetic deletion of FASN totally suppresses hepatocarcinogenesis driven by AKT and AKT/c-Met protooncogenes in mice. On the other hand, liver tumor development is completely unaffected by FASN depletion in mice co-expressing β-catenin and c-Met. Our data indicate that tumors might be either addicted to or independent from de novo lipogenesis for their growth depending on the oncogenes involved. Additional investigation is required to unravel the molecular mechanisms whereby some oncogenes render cancer cells resistant to inhibition of de novo lipogenesis.     

Determination of Fatty Acid Oxidation and Lipogenesis in Mouse Primary Hepatocytes

Lipid metabolism in liver is complex. In addition to importing and exporting lipid via lipoproteins, hepatocytes can oxidize lipid via fatty acid oxidation, or alternatively, synthesize new lipid via de novo lipogenesis. The net sum of these pathways is dictated by a number of factors, which in certain disease states leads to fatty liver disease. Excess hepatic lipid accumulation is associated with whole body insulin resistance and coronary heart disease. Tools to study lipid metabolism in hepatocytes are useful to understand the role of hepatic lipid metabolism in certain metabolic disorders.In the liver, hepatocytes regulate the breakdown and synthesis of fatty acids via β-fatty oxidation and de novo lipogenesis, respectively. Quantifying metabolism in these pathways provides insight into hepatic lipid handling. Unlike in vitro quantification, using primary hepatocytes, making measurements in vivo is technically challenging and resource intensive. Hence, quantifying β-fatty acid oxidation and de novo lipogenesis in cultured mouse hepatocytes provides a straight forward method to assess hepatocyte lipid handling. Here we describe a method for the isolation of primary mouse hepatocytes, and we demonstrate quantification of β-fatty acid oxidation and de novo lipogenesis, using radiolabeled substrates.     

Fat mass and obesity-associated protein regulates lipogenesis via m6A modification in fatty acid synthase mRNA

As the first identified N⁶-methyladenosine (m⁶A) demethylase, fat mass and obesity-associated (FTO) protein is associated with fatty acid synthase (FASN) and lipid accumulation. However, little is known about the regulatory role of FTO in the expression of FASN and de novo lipogenesis through m⁶A modification. In this study, we used FTO small interfering RNA to explore the effects of FTO knockdown on hepatic lipogenesis and its underlying epigenetic mechanism in HepG2 cells. We found that knockdown of FTO increased m⁶A levels in total RNA and enhanced the expression of YTH domain family member 2 which serves as the m⁶A-binding protein. The de novo lipogenic enzymes and intracellular lipid content were significantly decreased under FTO knockdown. Mechanistically, knockdown of FTO dramatically enhanced m⁶A levels in FASN messenger RNA (mRNA), leading to the reduced expression of FASN mRNA through m⁶A-mediated mRNA decay. The protein expressions of FASN along with acetyl CoA carboxylase and ATP-citrate lyase were further decreased, which inhibited de novo lipogenesis, thereby resulting in the deficiency of lipid accumulation in HepG2 cells and the induction of cellular apoptosis. The results reveal that FTO regulates hepatic lipogenesis via FTO-dependent m⁶A demethylation in FASN mRNA and indicate the critical role of FTO-mediated lipid metabolism in the survival of HepG2 cells. This study provides novel insights into a unique RNA epigenetic mechanism by which FTO mediates hepatic lipid accumulation through m⁶A modification and indicates that FTO could be a potential target for obesity-related diseases and cancer.     

Glucose-dependent de Novo Lipogenesis in B Lymphocytes: A REQUIREMENT FOR ATP-CITRATE LYASE IN LIPOPOLYSACCHARIDE-INDUCED DIFFERENTIATION*

Bacterially derived lipopolysaccharide (LPS) stimulates naive B lymphocytes to differentiate into immunoglobulin (Ig)-secreting plasma cells. Differentiation of B lymphocytes is characterized by a proliferative phase followed by expansion of the intracellular membrane secretory network to support Ig production. A key question in lymphocyte biology is how naive B cells reprogram metabolism to support de novo lipogenesis necessary for proliferation and expansion of the endomembrane network in response to LPS. We report that extracellularly acquired glucose is metabolized, in part, to support de novo lipogenesis in response to LPS stimulation of splenic B lymphocytes. LPS stimulation leads to increased levels of endogenous ATP-citrate lyase (ACLY), and this is accompanied by increased ACLY enzymatic activity. ACLY produces cytosolic acetyl-CoA from mitochondrially derived citrate. Inhibition of ACLY activity in LPS-stimulated B cells with the selective inhibitor 2-hydroxy-N-arylbenzenesulfonamide (compound-9; C-9) blocks glucose incorporation into de novo lipid biosynthesis, including cholesterol, free fatty acids, and neutral and acidic phospholipids. Moreover, inhibition of ACLY activity in splenic B cells results in inhibition of proliferation and defective endomembrane expansion and reduced expression of CD138 and Blimp-1, markers for plasma-like B cell differentiation. ACLY activity is also required for LPS-induced IgM production in CH12 B lymphoma cells. These data demonstrate that ACLY mediates glucose-dependent de novo lipogenesis in response to LPS signaling and identify a role for ACLY in several phenotypic changes that define plasma cell differentiation.     

The Selective Target of Capsaicin on FASN Expression and De Novo Fatty Acid Synthesis Mediated through ROS Generation Triggers Apoptosis in HepG2 Cells

The inhibition of the mammalian de novo synthesis of long-chain saturated fatty acids (LCFAs) by blocking the fatty acid synthase (FASN) enzyme activity in tumor cells that overexpress FASN can promote apoptosis, without apparent cytotoxic to non-tumor cells. The present study aimed to focus on the potent inhibitory effect of capsaicin on the fatty acid synthesis pathway inducing apoptosis of capsaicin in HepG2 cells. The use of capsaicin as a source for a new FASN inhibitor will provide new insight into its possible application as a selective anti-cancer therapy. The present findings showed that capsaicin promoted apoptosis as well as cell cycle arrest in the G0/G1 phase. The onset of apoptosis was correlated with a dissipation of mitochondrial membrane potential (ΔΨm). Apoptotic induction by capsaicin was mediated by inhibition of FASN protein expression which was accompanied by decreasing its activity on the de novo fatty acid synthesis. The expression of FASN was higher in HepG2 cells than in normal hepatocytes that were resistant to undergoing apoptosis following capsaicin administration. Moreover, the inhibitory effect of capsaicin on FASN expression and activity was found to be mediated by an increase of intracellular reactive oxygen species (ROS) generation. Treatment of HepG2 cells with capsaicin failed to alter ACC and ACLY protein expression, suggesting ACC and ACLY might not be the specific targets of capsaicin to induce apoptosis. An accumulation of malonyl-CoA level following FASN inhibition represented a major cause of mitochondrial-dependent apoptotic induction instead of deprivation of fatty acid per se. Here, we also obtained similar results with C75 that exhibited apoptosis induction by reducing the levels of fatty acid without any change in the abundance of FASN expression along with increasing ROS production. Collectively, our results provide novel evidence that capsaicin exhibits a potent anti-cancer property by targeting FASN protein in HepG2 cells.     

Futile cycle of β-oxidation and de novo lipogenesis are associated with essential fatty acids depletion in lipoatrophy

Total absence of adipose tissue (lipoatrophy) is associated with the development of severe metabolic disorders including hepatomegaly and fatty liver. Here, we sought to investigate the impact of severe lipoatrophy induced by deletion of peroxisome proliferator-activated receptor gamma (PPARγ) exclusively in adipocytes on lipid metabolism in mice. Untargeted lipidomics of plasma, gastrocnemius and liver uncovered a systemic depletion of the essential linoleic (LA) and α-linolenic (ALA) fatty acids from several lipid classes (storage lipids, glycerophospholipids, free fatty acids) in lipoatrophic mice. Our data revealed that such essential fatty acid depletion was linked to increased: 1) capacity for liver mitochondrial fatty acid β-oxidation (FAO), 2) citrate synthase activity and coenzyme Q content in the liver, 3) whole-body oxygen consumption and reduced respiratory exchange rate in the dark period, and 4) de novo lipogenesis and carbon flux in the TCA cycle. The key role of de novo lipogenesis in hepatic steatosis was evidenced by an accumulation of stearic, oleic, sapienic and mead acids in liver. Our results thus indicate that the simultaneous activation of the antagonic processes FAO and de novo lipogenesis in liver may create a futile metabolic cycle leading to a preferential depletion of LA and ALA. Noteworthy, this previously unrecognized cycle may also explain the increased energy expenditure displayed by lipoatrophic mice, adding a new piece to the metabolic regulation puzzle in lipoatrophies.     

Fine-tuning the lipogenic/lipolytic balance to optimize the metabolic requirements of cancer cell growth: Molecular mechanisms and therapeutic perspectives

Evolving evidence suggest that metabolic requirements for cell proliferation are identical in all normal and cancer cells. HER2 oncogene-overexpressors, a highly aggressive subtype of human cancer cells, constitute one of the best examples of how malignant cells maximize their ability to acquire and metabolize nutrients in a manner conductive to proliferation rather than efficient ATP production. HER2-overexpressors optimize their requirements of rapid cancer cell growth by fine-tuning a double [lipogenic/lipolytic]-edged metabolic sword. On the one edge, HER2 oncogene overexpression triggers redundant signaling cascades to ensure that all the major enzymes involved in de novo fatty acid (FA) synthesis will facilitate aerobic glycolysis instead of oxidative phosphorylation for energy production (Warburg effect). HER2 also establishes a positive bidirectional relationship with the key lipogenic enzyme Fatty Acid Synthase (FASN) that rapidly senses and respond to any disturbance in the flux of lipogenic substrates (e.g. NADPH and acetyl-CoA) and lipogenesis end-products (i.e. palmitate). On the other edge, HER2 overexpression arranges detoxifying mechanisms by upregulating PPARγ, a well established positive regulator role of adipogenesis and lipid storage in cell types with active lipid metabolism. PPARγ establishes a lipogenesis/lipolysis joining-point that enables HER2-positive cancer cells to avoid endogenous palmitate toxicity while securing palmitate into fat stores to avoid palmitate feedback on FASN functioning. The ability of HER2 to supercharge lipogenesis (by activating regulatory circuits that activate and fuel the lipogenic enzyme FASN) while averting lipotoxicity (by promoting conversion and storage of excess FAs to triglycerides in a PPARγ-dependent manner) supports the notion that best adapted cancer phenotypes are addicted to oncogenic lipid metabolism for cell proliferation and survival. It is conceptually attractive to assume that we can crash HER2-driven rapid cell proliferation by inhibiting “motor refueling” (upon blockade of lipogenic enzymes), by losing the “lipolytic brake” (upon blockade of PPARγ) and/or by sticking the “lipogenic gas pedal” (upon supplementation with dietary FAs).     

Liver Clock Protein BMAL1 Promotes de Novo Lipogenesis through Insulin-mTORC2-AKT Signaling

The clock protein BMAL1 (brain and muscle Arnt-like protein 1) participates in circadian regulation of lipid metabolism, but its contribution to insulin AKT-regulated hepatic lipid synthesis is unclear. Here we used both Bmal1^−/− and acute liver-specific Bmal1-depleted mice to study the role of BMAL1 in refeeding-induced de novo lipogenesis in the liver. Both global deficiency and acute hepatic depletion of Bmal1 reduced lipogenic gene expression in the liver upon refeeding. Conversely, Bmal1 overexpression in mouse liver by adenovirus was sufficient to elevate the levels of mRNA of lipogenic enzymes. Bmal1^−/− primary mouse hepatocytes displayed decreased levels of de novo lipogenesis and lipogenic enzymes, supporting the notion that BMAL1 regulates lipid synthesis in hepatocytes in a cell-autonomous manner. Both refed mouse liver and insulin-treated primary mouse hepatocytes showed impaired AKT activation in the case of either Bmal1 deficiency or Bmal1 depletion by adenoviral shRNA. Restoring AKT activity by a constitutively active mutant of AKT nearly normalized de novo lipogenesis in Bmal1^−/− hepatocytes. Finally, Bmal1 deficiency or knockdown decreased the protein abundance of RICTOR, the key component of the mTORC2 complex, without affecting the gene expression of key factors of insulin signaling. Thus, our study uncovered a novel metabolic function of hepatic BMAL1 that promotes de novo lipogenesis via the insulin-mTORC2-AKT signaling during refeeding.     

Isocaloric manipulation of macronutrients within a high-carbohydrate/moderate-fat diet induces unique effects on hepatic lipogenesis,steatosis and liver injury

Diets containing excess carbohydrate and fat promote hepatic steatosis and steatohepatitis in mice. Little is known, however, about the impact of specific carbohydrate/fat combinations on liver outcome. This study was designed to determine whether high-energy diets with identical caloric density but different carbohydrate and fat composition have unique effects on the liver. Four experimental diets were formulated with 60% kcal carbohydrate and 20% kcal fat, each in nearly pure form from a single source: starch-oleate, starch-palmitate, sucrose-oleate and sucrose-palmitate. The diets were fed to mice for 3 or 12 weeks for analysis of lipid metabolism and liver injury. All mice developed hepatic steatosis over 12 weeks, but mice fed the sucrose-palmitate diet accumulated more hepatic lipid than those in the other three experimental groups. The exaggerated lipid accumulation in sucrose-palmitate-fed mice was attributable to a disproportionate rise in hepatic de novo lipogenesis. These mice accrued more hepatic palmitate and exhibited more evidence of liver injury than any of the other experimental groups. Interestingly, lipogenic gene expression in mice fed the custom diets did not correlate with actual de novo lipogenesis. In addition, de novo lipogenesis rose in all mice between 3 and 12 weeks, without feedback inhibition from hepatic steatosis. The pairing of simple sugar (sucrose) and saturated fat (palmitate) in a high-carbohydrate/moderate-fat diet induces more de novo lipogenesis and liver injury than other carbohydrate/fat combinations. Diet-induced liver injury correlates positively with hepatic de novo lipogenesis and is not predictable by isolated analysis of lipogenic gene expression.     

Glucose-mediated de novo lipogenesis in photoreceptors drives early diabetic retinopathy

Diabetic retinopathy (DR) is an increasingly frequent cause of blindness across populations; however, the events that initiate pathophysiology of DR remain elusive. Strong preclinical and clinical evidence suggests that abnormalities in retinal lipid metabolism caused by diabetes may account for the origin of this disease. A major arm of lipid metabolism, de novo biosynthesis, is driven by elevation in available glucose, a common thread binding all forms of vision loss in diabetes. Therefore, we hypothesized that aberrant retinal lipid biogenesis is an important promoter of early DR. In murine models, we observed elevations of diabetes-associated retinal de novo lipogenesis ∼70% over control levels. This shift was primarily because of activation of fatty acid synthase (FAS), a rate-limiting enzyme in the biogenic pathway. Activation of FAS was driven by canonical glucose-mediated disinhibition of acetyl-CoA carboxylase, a major upstream regulatory enzyme. Mutant mice expressing gain-of-function FAS demonstrated increased vulnerability to DR, whereas those with FAS deletion in rod photoreceptors maintained preserved visual responses upon induction of diabetes. Excess retinal de novo lipogenesis—either because of diabetes or because of FAS gain of function—was associated with modestly increased levels of palmitate-containing phosphatidylcholine species in synaptic membranes, a finding with as yet uncertain significance. These findings implicate glucose-dependent increases in photoreceptor de novo lipogenesis in the early pathogenesis of DR, although the mechanism of deleterious action of this pathway remains unclear.     

High Fat Feeding Induces Hepatic Fatty Acid Elongation in Mice

Background

High-fat diets promote hepatic lipid accumulation. Paradoxically, these diets also induce lipogenic gene expression in rodent liver. Whether high expression of these genes actually results in an increased flux through the de novo lipogenic pathway in vivo has not been demonstrated.

Methodology/Principal Findings

To interrogate this apparent paradox, we have quantified de novo lipogenesis in C57Bl/6J mice fed either chow, a high-fat or a n-3 polyunsaturated fatty acid (PUFA)-enriched high-fat diet. A novel approach based on mass isotopomer distribution analysis (MIDA) following 1-¹³C acetate infusion was applied to simultaneously determine de novo lipogenesis, fatty acid elongation as well as cholesterol synthesis. Furthermore, we measured very low density lipoprotein-triglyceride (VLDL-TG) production rates. High-fat feeding promoted hepatic lipid accumulation and induced the expression of lipogenic and cholesterogenic genes compared to chow-fed mice: induction of gene expression was found to translate into increased oleate synthesis. Interestingly, this higher lipogenic flux (+74 µg/g/h for oleic acid) in mice fed the high-fat diet was mainly due to an increased hepatic elongation of unlabeled palmitate (+66 µg/g/h) rather than to elongation of de novo synthesized palmitate. In addition, fractional cholesterol synthesis was increased, i.e. 5.8±0.4% vs. 8.1±0.6% for control and high fat-fed animals, respectively. Hepatic VLDL-TG production was not affected by high-fat feeding. Partial replacement of saturated fat by fish oil completely reversed the lipogenic effects of high-fat feeding: hepatic lipogenic and cholesterogenic gene expression levels as well as fatty acid and cholesterol synthesis rates were normalized.

Conclusions/Significance

High-fat feeding induces hepatic fatty acid synthesis in mice, by chain elongation and subsequent desaturation rather than de novo synthesis, while VLDL-TG output remains unaffected. Suppression of lipogenic fluxes by fish oil prevents from high fat diet-induced hepatic steatosis in mice.     

Cancer Cells Differentially Activate and Thrive on De Novo Lipid Synthesis Pathways in a Low-Lipid Environment

Increased lipogenesis is a hallmark of a wide variety of cancers and is under intense investigation as potential antineoplastic target. Although brisk lipogenesis is observed in the presence of exogenous lipids, evidence is mounting that these lipids may adversely affect the efficacy of inhibitors of lipogenic pathways. Therefore, to fully exploit the therapeutic potential of lipid synthesis inhibitors, a better understanding of the interrelationship between de novo lipid synthesis and exogenous lipids and their respective role in cancer cell proliferation and therapeutic response to lipogenesis inhibitors is of critical importance. Here, we show that the proliferation of various cancer cell lines (PC3M, HepG2, HOP62 and T24) is attenuated when cultured in lipid-reduced conditions in a cell line-dependent manner, with PC3M being the least affected. Interestingly, all cell lines - lipogenic (PC3M, HepG2, HOP62) as well as non-lipogenic (T24) - raised their lipogenic activity in these conditions, albeit to a different degree. Cells that attained the highest lipogenic activity under these conditions were best able to cope with lipid reduction in term of proliferative capacity. Supplementation of the medium with very low density lipoproteins, free fatty acids and cholesterol reversed this activation, indicating that the mere lack of lipids is sufficient to activate de novo lipogenesis in cancer cells. Consequently, cancer cells grown in lipid-reduced conditions became more dependent on de novo lipid synthesis pathways and were more sensitive to inhibitors of lipogenic pathways, like Soraphen A and Simvastatin. Collectively, these data indicate that limitation of access to exogenous lipids, as may occur in intact tumors, activates de novo lipogenesis is cancer cells, helps them to thrive under these conditions and makes them more vulnerable to lipogenesis inhibitors. These observations have important implications for the design of new antineoplastic strategies targeting the cancer cell''s lipid metabolism.     

Maternal Obesity Reduces Milk Lipid Production in Lactating Mice by Inhibiting Acetyl-CoA Carboxylase and Impairing Fatty Acid Synthesis

Maternal metabolic and nutrient trafficking adaptations to lactation differ among lean and obese mice fed a high fat (HF) diet. Obesity is thought to impair milk lipid production, in part, by decreasing trafficking of dietary and de novo synthesized lipids to the mammary gland. Here, we report that de novo lipogenesis regulatory mechanisms are disrupted in mammary glands of lactating HF-fed obese (HF-Ob) mice. HF feeding decreased the total levels of acetyl-CoA carboxylase-1 (ACC), and this effect was exacerbated in obese mice. The relative levels of phosphorylated (inactive) ACC, were elevated in the epithelium, and decreased in the adipose stroma, of mammary tissue from HF-Ob mice compared to those of HF-fed lean (HF-Ln) mice. Mammary gland levels of AMP-activated protein kinase (AMPK), which catalyzes formation of inactive ACC, were also selectively elevated in mammary glands of HF-Ob relative to HF-Ln dams or to low fat fed dams. These responses correlated with evidence of increased lipid retention in mammary adipose, and decreased lipid levels in mammary epithelial cells, of HF-Ob dams. Collectively, our data suggests that maternal obesity impairs milk lipid production, in part, by disrupting the balance of de novo lipid synthesis in the epithelial and adipose stromal compartments of mammary tissue through processes that appear to be related to increased mammary gland AMPK activity, ACC inhibition, and decreased fatty acid synthesis.     

Aging shifts mitochondrial dynamics toward fission to promote germline stem cell loss

Changes in mitochondrial dynamics (fusion and fission) are known to occur during stem cell differentiation; however, the role of this phenomenon in tissue aging remains unclear. Here, we report that mitochondrial dynamics are shifted toward fission during aging of Drosophila ovarian germline stem cells (GSCs), and this shift contributes to aging‐related GSC loss. We found that as GSCs age, mitochondrial fragmentation and expression of the mitochondrial fission regulator, Dynamin‐related protein (Drp1), are both increased, while mitochondrial membrane potential is reduced. Moreover, preventing mitochondrial fusion in GSCs results in highly fragmented depolarized mitochondria, decreased BMP stemness signaling, impaired fatty acid metabolism, and GSC loss. Conversely, forcing mitochondrial elongation promotes GSC attachment to the niche. Importantly, maintenance of aging GSCs can be enhanced by suppressing Drp1 expression to prevent mitochondrial fission or treating with rapamycin, which is known to promote autophagy via TOR inhibition. Overall, our results show that mitochondrial dynamics are altered during physiological aging, affecting stem cell homeostasis via coordinated changes in stemness signaling, niche contact, and cellular metabolism. Such effects may also be highly relevant to other stem cell types and aging‐induced tissue degeneration.     

n-3 PUFAs protect against adiposity and fatty liver by promoting browning in postnatally overfed male rats: a role for NRG4

Early-life nutrition plays an important role in regulating adult metabolism. This study evaluated the effects of early nutrition during the suckling and postweaning periods on expression of the adipocytokine Neuregulin 4 (Nrg4) and its relationship with nonalcoholic fatty liver disease (NAFLD) in adulthood. In vivo, male rats were adjusted to litter sizes of three (small litter, SL) or ten (normal litter, NL) on postnatal day 3. Pups were fed control chow (NL and SL groups) or a high-fat diet (NL-HF and SL-HF groups), and SL pups specifically were fed a fish oil diet rich in n-3 polyunsaturated fatty acids (n-3 PUFAs) (SL-FO group), from postnatal weeks 3 to 13. The results demonstrated that postnatal overnutrition increased weight, hepatic de novo lipogenesis (DNL) gene expression and NAFLD and decreased body temperature and Nrg4, Ucp1 and Pgc1a mRNA expression in adipose tissues in SL, SL-HF and NL-HF rats compared to NL rats in adulthood. The opposite trends were observed in SL-FO rats. Moreover, in vitro, recombinant NRG4 protein reduced lipid accumulation by inhibiting DNL gene expression in fatty HepG2 cells stimulated with sodium oleate. In HPAs, eicosapentaenoic acid (EPA) treatment elevated NRG4 production and caused adipocyte browning, and these effects were abrogated by PPARG antagonism. In conclusion, a postweaning n-3 PUFA diet enhanced Nrg4 expression in adipose tissues, associated with attenuation of NAFLD induced by SL rearing. Additionally, external NRG4 reduced lipogenesis in steatotic hepatocytes. Thus, white adipose tissue browning induced by n-3 PUFAs may promote NRG4 production through the PPARG pathway.     

Cancer cells incorporate and remodel exogenous palmitate into structural and oncogenic signaling lipids

De novo lipogenesis is considered the primary source of fatty acids for lipid synthesis in cancer cells, even in the presence of exogenous fatty acids. Here, we have used an isotopic fatty acid labeling strategy coupled with metabolomic profiling platforms to comprehensively map palmitic acid incorporation into complex lipids in cancer cells. We show that cancer cells and tumors robustly incorporate and remodel exogenous palmitate into structural and oncogenic glycerophospholipids, sphingolipids, and ether lipids. We also find that fatty acid incorporation into oxidative pathways is reduced in aggressive human cancer cells, and instead shunted into pathways for generating structural and signaling lipids. Our results demonstrate that cancer cells do not solely rely on de novo lipogenesis, but also utilize exogenous fatty acids for generating lipids required for proliferation and protumorigenic lipid signaling. This article is part of a special issue entitled Lipid Metabolism in Cancer.     

Expression of Lipid Metabolism-Related Proteins in Metastatic Breast Cancer

Purpose

The tumor biology of metastatic breast cancers differ according to the metastatic sites, and the features of cancer metabolism may also be different. The aim of this study is to investigate the expression of lipid metabolism-related proteins in metastatic breast cancer according to metastatic site and discuss the clinical significance thereof.

Methods

Immunohistochemical staining for lipid metabolism-related proteins [fatty acid synthase (FASN), hormone-sensitive lipase (HSL), carnitine palmitoyltransferase IA (CPT-1A), acyl-CoA oxidase 1 (ACOX1), fatty acid binding protein 4 (FABP4,) and perilipin 1 (PLIN1)] was performed using a tissue microarray of 149 cases of metastatic breast cancer (bone metastasis = 39, brain metastasis = 37, liver metastasis = 21, and lung metastasis = 52).

Results

The expression levels of ACOX1 (p = 0.009) and FASN (p = 0.007) varied significantly according to metastatic site, with the highest expression in brain metastasis and the lowest expression in liver metastasis. ACOX1 positivity (p = 0.005) and FASN positivity (p = 0.003) correlated with HER-2 positivity. The expression of FASN was significantly higher in HER-2 type breast cancer, and lower in luminal A and TNBC type breast cancer (p<0.001). Among lipid metabolism-related proteins, PLIN1 positivity was found to be an independent poor prognostic factor on multivariate analysis (Hazard ratio: 4.979, 95% CI: 1.054–22.59, p = 0.043).

Conclusion

Different expression levels of lipid metabolism-related proteins were observed according to metastatic site. The expression of ACOX1 and FASN was highest in brain metastasis. These results suggest that the metastatic site should be considered when using lipid metabolism inhibitors for targeted therapy.