High stearoyl-CoA desaturase protein and activity levels in simian virus 40 transformed-human lung fibroblasts

A Multimodal Drug-Diet-Immunotherapy Combination Restrains Melanoma Progression and Metastasis

The genetic landscape of cancer cells can lead to specific metabolic dependencies for tumor growth. Dietary interventions represent an attractive strategy to restrict the availability of key nutrients to tumors. In this study, we identified that growth of a subset of melanoma was severely restricted by a rationally designed combination therapy of a stearoyl-CoA desaturase (SCD) inhibitor with an isocaloric low-oleic acid diet. Despite its importance in oncogenesis, SCD underwent monoallelic codeletion along with PTEN on chromosome 10q in approximately 47.5% of melanoma, and the other SCD allele was methylated, resulting in very low-SCD expression. Although this SCD-deficient subset was refractory to SCD inhibitors, the subset of PTEN wild-type melanoma that retained SCD was sensitive. As dietary oleic acid could potentially blunt the effect of SCD inhibitors, a low oleic acid custom diet was combined with an SCD inhibitor. The combination reduced monounsaturated fatty acids and increased saturated fatty acids, inducing robust apoptosis and growth suppression and inhibiting lung metastasis with minimal toxicity in preclinical mouse models of PTEN wild-type melanoma. When combined with anti-PD1 immunotherapy, the SCD inhibitor improved T-cell functionality and further constrained melanoma growth in mice. Collectively, these results suggest that optimizing SCD inhibitors with diets low in oleic acid may offer a viable and efficacious therapeutic approach for improving melanoma treatment. Significance: Blockade of endogenous production of fatty acids essential for melanoma combined with restriction of dietary intake blocks tumor growth and enhances response to immunotherapy, providing a rational drug-diet treatment regimen for melanoma.

Fumonisin B1 protects against long-chained polyunsaturated fatty acid-induced cell death in HepG2 cells - implications for cancer promotion

Fumonisin B1 (FB1), a food-borne mycotoxin, is a cancer promoter in rodent liver and augments proliferation of initiated cells while inhibiting the growth of normal hepatocytes by disrupting lipid biosynthesis at various levels. HepG2 cancer cells exhibited resistance to FB1-induced toxic effects presumably due to their low content of polyunsaturated fatty acids (PUFA) even though FB1-typical lipid changes were observed, e.g. significantly increased phosphatidylethanolamine (PE), decreased sphingomyelin and cholesterol content, increased sphinganine (Sa) and sphinganine/sphingosine ratio, increased C18:1ω-9, decreased C20:4ω-6 content in PE and decreased C20:4ω-6_PC/PE ratio. Increasing PUFA content of HepG2 cells with phosphatidylcholine (PC) vesicles containing C20:4ω-6 (SAPC) or C22:6ω-3 (SDPC) disrupted cell survival, cellular redox status and induced oxidative stress and apoptosis. A partially protective effect of FB1 was evident in PUFA-enriched HepG2 cells which may be related to the FB1-induced reduction in oxidative stress and the disruption of key cell membrane constituents indicative of a resistant lipid phenotype. Interactions between different ω-6 and ω-3 PUFA, membrane constituents including cholesterol, and the glycerophospho- and sphingolipids and FB1 in this cell model provide further support for the resistant lipid phenotype and its role in the complex cellular effects underlying the cancer promoting potential of the fumonisins.

Death and the desaturase: implication of Stearoyl-CoA desaturase-1 in the mechanisms of cell stress, apoptosis, and ferroptosis

Growth and proliferation of normal and cancerous cells necessitate a finely-tuned regulation of lipid metabolic pathways to ensure the timely supply of structural, energetic, and signaling lipid molecules. The synthesis and remodeling of lipids containing fatty acids with an appropriate carbon length and insaturation level are required for supporting each phase of the mechanisms of cell replication and survival. Mammalian Stearoyl-CoA desaturases (SCD), particularly SCD1, play a crucial role in modulating the fatty acid composition of cellular lipids, converting saturated fatty acids (SFA) into monounsaturated fatty acids (MUFA) in the endoplasmic reticulum (ER). Extensive research has elucidated in great detail the participation of SCD1 in the molecular mechanisms that govern cell replication in normal and cancer cells. More recently, investigations have shed new light on the functional and regulatory role of the Δ9-desaturase in the processes of cell stress and cell death. This review will examine the latest findings on the involvement of SCD1 in the molecular pathways of cell survival, particularly on the mechanisms of ER stress and autophagy, as well in apoptotic and non-apoptotic cell death.

St. John's wort extract Ze 117 alters the membrane fluidity of C6 glioma cells by influencing cellular cholesterol metabolism

Chronic stress is associated with major depressive disorder (MDD). Increased glucocorticoid levels caused by uncontrolled release through the hypothalamic‒pituitary‒adrenal (HPA) axis can cause changes in the lipid content of the cellular plasma membrane. These changes are suspected to be involved in the development of depressive disorders. St. John's wort extract (SJW) Ze 117 has long been used as an alternative to synthetic antidepressants. Part of its effect may be due to an effect on the cellular lipid composition and thus on the properties of plasma membranes and receptor systems embedded therein. In this study, we investigated the effect of Ze 117 on that of dexamethasone and simvastatin. Dexamethasone increases the fluidity of C6 cell plasma membranes. This effect is counteracted by administration of Ze 117. Here we demonstrate that this is not due to a change in C16:1/16:0 and C18:1/18:0 ratios in C6 cell fatty acids. On the other hand, Ze 117 increased the cellular cholesterol content by 42.5%, whereas dexamethasone reduced cholesterol levels similarly to simvastatin. Lowering cholesterol levels by dexamethasone or simvastatin resulted in decreased β-arrestin 2 recruitment to the 5-HT1a receptor. This effect was counterbalanced by Ze 117, whereas the SJW extract had little effect on β-arrestin 2 recruitment in non-stressed cells. Taken together, in C6 cells, Ze 117 induces changes in membrane fluidity through its effect on cellular cholesterol metabolism rather than by affecting fatty acid saturation. This effect is reflected in an altered signal transduction of the 5-HT1a receptor under Ze 117 administration. The current in vitro results support the hypothesis that Ze 117 addresses relevant parts of the cellular lipid metabolism, possibly explaining some of the antidepressant actions of Ze 117.

White adipocyte dysfunction and obesity-associated pathologies in humans

The prevalence of obesity and associated chronic diseases continues to increase worldwide, negatively impacting on societies and economies. Whereas the association between excess body weight and increased risk for developing a multitude of diseases is well established, the initiating mechanisms by which weight gain impairs our metabolic health remain surprisingly contested. In order to better address the myriad of disease states associated with obesity, it is essential to understand adipose tissue dysfunction and develop strategies for reinforcing adipocyte health. In this Review we outline the diverse physiological functions and pathological roles of human white adipocytes, examining our current knowledge of why white adipocytes are vital for systemic metabolic control, yet poorly adapted to our current obesogenic environment.

Mechanism of SCD Participation in Lipid Droplet-Mediated Steroidogenesis in Goose Granulosa Cells

Stearoyl-CoA desaturase (SCD) is a key enzyme catalyzing the rate-limiting step in monounsaturated fatty acids (MUFAs) production. There may be a mechanism by which SCD is involved in lipid metabolism, which is assumed to be essential for goose follicular development. For this reason, a cellular model of SCD function in goose granulosa cells (GCs) via SCD overexpression and knockdown was used to determine the role of SCD in GC proliferation using flow cytometry. We found that SCD overexpression induced and SCD knockdown inhibited GCs proliferation. Furthermore, ELISA analysis showed that SCD overexpression increased the total cholesterol (TC), progesterone, and estrogen levels in GCs, while SCD knockdown decreased TC, progesterone, and estrogen levels (p < 0.05). Combining these results with those of related multi-omics reports, we proposed a mechanism of SCD regulating the key lipids and differentially expressed gene (DEGs) in glycerophospholipid and glycerolipid metabolism, which participate in steroidogenesis mediated by the lipid droplet deposition in goose GCs. These results add further insights into understanding the lipid metabolism mechanism of goose GCs.

Fatty acid binding protein 5 regulates lipogenesis and tumor growth in lung adenocarcinoma

AIMS

Lung cancer is the leading cause of cancer-related death. Unfortunately, targeted-therapies have been unsuccessful for most patients with lung adenocarcinoma (LUAD). Thus, new early biomarkers and treatment options are a pressing need. Fatty acid binding protein 5 (FABP5) has been associated with various types of cancers. Its contribution to LUAD onset, progression and metabolic reprogramming is, however, not fully understood. In this study we assessed the importance of FABP5 in LUAD and its role in cancer lipid metabolism.

MAIN METHODS

By radioactive labeling and metabolite quantification, we studied the function of FABP5 in fatty acid metabolism using genetic/pharmacologic inhibition and overexpression models in LUAD cell lines. Flow cytometry, heterologous transplantation and bioinformatic analysis were used, in combination with other methodologies, to assess the importance of FABP5 for cellular proliferation in vitro and in vivo and in patient survival.

KEY FINDINGS

We show that high expression of FABP5 is associated with poor prognosis in patients with LUAD. FABP5 regulates lipid metabolism, diverting fatty acids towards complex lipid synthesis, whereas it does not affect their catabolism in vitro. Moreover, FABP5 is required for de novo fatty acid synthesis and regulates the expression of enzymes involved in the pathway (including FASN and SCD1). Consistently with the changes in lipid metabolism, FABP5 is required for cell cycle progression, migration and in vivo tumor growth.

SIGNIFICANCE

Our results suggest that FABP5 is a regulatory hub of lipid metabolism and tumor progression in LUAD, placing it as a new putative therapeutic target for this disease.

Key signaling networks are dysregulated in patients with the adipose tissue disorder, lipedema

Objectives

Lipedema, a poorly understood chronic disease of adipose hyper-deposition, is often mistaken for obesity and causes significant impairment to mobility and quality-of-life. To identify molecular mechanisms underpinning lipedema, we employed comprehensive omics-based comparative analyses of whole tissue, adipocyte precursors (adipose-derived stem cells (ADSCs)), and adipocytes from patients with or without lipedema.

Methods

We compared whole-tissues, ADSCs, and adipocytes from body mass index–matched lipedema (n = 14) and unaffected (n = 10) patients using comprehensive global lipidomic and metabolomic analyses, transcriptional profiling, and functional assays.

Results

Transcriptional profiling revealed >4400 significant differences in lipedema tissue, with altered levels of mRNAs involved in critical signaling and cell function-regulating pathways (e.g., lipid metabolism and cell-cycle/proliferation). Functional assays showed accelerated ADSC proliferation and differentiation in lipedema. Profiling lipedema adipocytes revealed >900 changes in lipid composition and >600 differentially altered metabolites. Transcriptional profiling of lipedema ADSCs and non-lipedema ADSCs revealed significant differential expression of >3400 genes including some involved in extracellular matrix and cell-cycle/proliferation signaling pathways. One upregulated gene in lipedema ADSCs, Bub1, encodes a cell-cycle regulator, central to the kinetochore complex, which regulates several histone proteins involved in cell proliferation. Downstream signaling analysis of lipedema ADSCs demonstrated enhanced activation of histone H2A, a key cell proliferation driver and Bub1 target. Critically, hyperproliferation exhibited by lipedema ADSCs was inhibited by the small molecule Bub1 inhibitor 2OH-BNPP1 and by CRISPR/Cas9-mediated Bub1 gene depletion.

Conclusion

We found significant differences in gene expression, and lipid and metabolite profiles, in tissue, ADSCs, and adipocytes from lipedema patients compared to non-affected controls. Functional assays demonstrated that dysregulated Bub1 signaling drives increased proliferation of lipedema ADSCs, suggesting a potential mechanism for enhanced adipogenesis in lipedema. Importantly, our characterization of signaling networks driving lipedema identifies potential molecular targets, including Bub1, for novel lipedema therapeutics.

Modulation of SCD1 activity in hepatocyte cell lines: evaluation of genomic stability and proliferation

Stearoyl-CoA desaturase (SCD) is a central lipogenic enzyme for the synthesis of monounsaturated fatty acids (MUFA). SCD1 overexpression is associated with a genetic predisposition to hepatocarcinogenesis in mice and rats. This work hypothesized possible roles of SCD1 to genomic stability, lipogenesis, cell proliferation, and survival that contribute to the malignant transformation of non-tumorigenic liver cells. Therefore, HepG2 tumor cells were treated with the SCD1 inhibitor (CAY10566) to ensure a decrease in proliferation/survival, as confirmed by a lipidomic analysis that detected an efficient decrease in the concentration of MUFA. According to that, we switched to a model of normal hepatocytes, the HepaRG cell line, where we: (i) overexpressed SCD1 (HepaRG-SCD1 clones), (ii) inhibited the endogenous SCD1 activity with CAY10566, or (iii) treated with two monounsaturated (oleic OA and/or palmitoleic PA) fatty acids. SCD1 overexpression or MUFA stimulation increased cell proliferation, survival, and the levels of AKT, phospho-AKT(Ser473), and proliferating cell nuclear antigen (PCNA) proteins. By contrast, opposite molecular and cellular responses were observed in HepaRG cells treated with CAY10566. To assess genomic stability, HepaRG-SCD1 clones were treated with ionizing radiation (IR) and presented reduced levels of DNA damage and higher survival at doses of 5 Gy and 10 Gy compared to parental cells. In sum, this work suggests that modulation of SCD1 activity not only plays a role in cell proliferation and survival, but also in maintaining genomic stability, and therefore, contributes to a better understanding of this enzyme in molecular mechanisms of hepatocarcinogenesis projecting SCD1 as a potential translational target.

Lipid Metabolism in Cancer Cells

Metabolic reprogramming is one of the most critical hallmarks in cancer cells. In the past decades, mounting evidence has demonstrated that, besides the Warburg Effect, lipid metabolism dysregulation is also one of the essential characteristics of cancer cell metabolism. Lipids are water-insoluble molecules with diverse categories of phosphoglycerides, triacylglycerides, sphingolipids, sterols, etc. As the major utilization for energy storage, fatty acids are the primary building blocks for synthesizing triacylglycerides. And phosphoglycerides, sphingolipids, and sterols are the main components constructing biological membranes. More importantly, lipids play essential roles in signal transduction by functioning as second messengers or hormones. Much evidence has shown specific alterations of lipid metabolism in cancer cells. Consequently, the structural configuration of biological membranes, the energy homeostasis under nutrient stress, and the abundance of lipids in the intracellular signal transduction are affected by these alterations. Furthermore, lipid droplets accumulate in cancer cells and function adaptively to different types of harmful stress. This chapter reviews the regulation, functions, and therapeutic benefits of targeting lipid metabolism in cancer cells. Overall, this chapter highlights the significance of exploring more potential therapeutic strategies for malignant diseases by unscrambling lipid metabolism regulation in cancer cells.

Lipid metabolism in colon cancer: Role of Liver X Receptor (LXR) and Stearoyl-CoA Desaturase 1 (SCD1)

Colorectal cancer (CRC) is one of the most commonly occurring cancers worldwide. Although several genetic alterations have been associated with CRC onset and progression, nowadays the reprogramming of cellular metabolism has been recognized as a fundamental step of the carcinogenic process. Intestinal tumor cells frequently display an aberrant activation of lipid metabolism. Indeed, to satisfy the growing needs of a continuous proliferation, cancer cells can either increase the uptake of exogenous lipids or upregulate the endogenous lipogenesis and cholesterol synthesis. Therefore, strategies aimed at limiting lipid accumulation are now under development in order to counteract malignancies. Two major players of lipids metabolism have been so far identified for their contribution to CRC development: the nuclear receptor Liver X Receptor (LXRs) and the enzyme Stearoyl-CoA Desaturase 1 (SCD1). Whereas LXR is mainly recognized for its role as a cholesterol sensor, finally promoting the loss of cellular cholesterol and whole-body homeostasis, SCD1 acts as the major regulator of new fatty acids, finely tuning the monounsaturated fatty acids (MUFA) to saturated fatty acids (SFA) ratio. Intriguingly, SCD1 is directly regulated by LXRs. Despite LXRs agonists have elicited great interest as a promising therapeutic target for cancer, LXR's ability to induce SCD1 and new fatty acids synthesis represent a major obstacle in the development of new effective treatments. Thus, further investigations are required to fully dissect the concomitant modulation of both players, to develop specific therapies aimed at blocking intestinal cancer cells proliferation, eventually counteracting CRC progression.

The impact of PUFA on cell responses: Caution should be exercised when selecting PUFA concentrations in cell culture

Polyunsaturated fatty acids (PUFA) are important components of cellular membranes, serving both structural and signaling functions. Investigation of the functional responses of cells to various PUFA often involves cell culture experiments, which can then inform or guide subsequent in vivo and clinical investigations. In this study, human carcinoma and leukemia cell lines (MCF-7, HepG2, THP-1, Jurkat) were incubated for 3 days in the presence of up to 150 μM of exogenous arachidonic or eicosapentaenoic acids. At concentrations up to 20 μM these PUFA were enriched in cellular phospholipids, but at concentrations of 20 μM or higher cells accumulated large quantities of these PUFA and their elongation products into triglycerides. This coincided with decreased cell proliferation and enhanced apoptosis. Inhibition of DGAT1 but not DGAT2 enhanced the cytotoxic effect of exogenous PUFA suggesting a protective role of PUFA sequestration into TGs. Lower (10 μM) and higher (50 μM) exogenous PUFA concentrations also had different impacts on the expression of PUFA metabolizing enzymes. Overall, these results indicate that caution must be exercised when planning in vitro experiments since elevated concentrations of PUFA can lead to dysfunctional cellular responses that are not predictive of in vivo responses to dietary PUFA.

Antitumor effects of curcumin: A lipid perspective

Lipid metabolism plays an important role in cancer development due to the necessities of rapidly dividing cells to increase structural, energetic, and biosynthetic demands for cell proliferation. Basically, obesity, type 2 diabetes, and other related diseases, and cancer are associated with a common hyperactivated "lipogenic state." Recent evidence suggests that metabolic reprogramming and overproduction of enzymes involved in the synthesis of fatty acids are the new hallmarks of cancer, which occur in an early phase of tumorigenesis. As the first evidence to confirm dysregulated lipid metabolism in cancer cells, the overexpression of fatty acid synthase (FAS) was observed in breast cancer patients and demonstrated the role of FAS in cancer. Other enzymes of fatty acid synthesis have recently been found to be dysregulated in cancer, including ATP-dependent citrate lyase and acetyl-CoA carboxylase, which further underscores the connection of these metabolic pathways with cancer cell survival and proliferation. The degree of overexpression of lipogenic enzymes and elevated lipid utilization in tumors is closely associated with cancer progression. The question that arises is whether the progression of cancer can be suppressed, or at least decelerated, by modulating gene expression related to fatty acid metabolism. Curcumin, due to its effects on the regulation of lipogenic enzymes, might be able to suppress, or even cause regression of tumor growth. This review discusses recent evidence concerning the important role of lipogenic enzymes in the metabolism of cancer cells and whether the inhibitory effects of curcumin on lipogenic enzymes is therapeutically efficacious.

Stearoyl-CoA Desaturase 1 as a Therapeutic Target for the Treatment of Cancer

A distinctive feature of cancer cells of various origins involves alterations of the composition of lipids, with significant enrichment in monounsaturated fatty acids. These molecules, in addition to being structural components of newly formed cell membranes of intensely proliferating cancer cells, support tumorigenic signaling. An increase in the expression of stearoyl-CoA desaturase 1 (SCD1), the enzyme that converts saturated fatty acids to ∆9-monounsaturated fatty acids, has been observed in a wide range of cancer cells, and this increase is correlated with cancer aggressiveness and poor outcomes for patients. Studies have demonstrated the involvement of SCD1 in the promotion of cancer cell proliferation, migration, metastasis, and tumor growth. Many studies have reported a role for this lipogenic factor in maintaining the characteristics of cancer stem cells (i.e., the population of cells that contributes to cancer progression and resistance to chemotherapy). Importantly, both the products of SCD1 activity and its direct impact on tumorigenic pathways have been demonstrated. Based on these findings, SCD1 appears to be a significant player in the development of malignant disease and may be a promising target for anticancer therapy. Numerous chemical compounds that exert inhibitory effects on SCD1 have been developed and preclinically tested. The present review summarizes our current knowledge of the ways in which SCD1 contributes to the progression of cancer and discusses opportunities and challenges of using SCD1 inhibitors for the treatment of cancer.

Downregulation of CPT2 promotes tumorigenesis and chemoresistance to cisplatin in hepatocellular carcinoma

Background

Cancer cells often have characteristic changes in metabolism. Besides Warburg effect, abnormal lipid metabolism is also considered as one of the most typical metabolic symbols of cancer. Thus, understanding the mechanisms of cell metabolic reprogramming may provide a potential avenue for cancer treatment.

Materials and methods

In total, 41 pairs of matched samples of primary hepatocellular carcinoma (HCC) and adjacent non-cancerous liver tissues were collected. Afterward, we performed quantitative reverse transcriptase polymerase chain reaction to investigate carnitine palmitoyltransferase-2 (CPT2) expression and then systematically analyzed its relationship with clinicopathologic features. We further performed proliferation, colony formation, migration and invasion, drug resistance, and lipogenesis assays to determine the function of CPT2 in HCC.

Results

In this study, we have identified CPT2 which is the rate-limiting enzyme of fatty acid oxidation, downregulated in HCC and was significantly associated with tumor histological differentiation and venous invasion. In vitro studies demonstrated that knockdown of CPT2 remarkably enhanced the tumorigenic activity and metastatic potential of hepatoma cells. In addition, CPT2 silencing induced chemoresistance to cisplatin. Mechanistically, low expression of CPT2 promoted cancer cell lipogenesis via upregulation of stearoyl-CoA desaturase-1, the key enzyme involved in the synthesis of monounsaturated fatty acids, at both mRNA and protein levels in hepatoma cell line.

Conclusion

Altogether, our findings demonstrate that CPT2 has a critical role in HCC progression and chemoresistance and may potentially serve as a novel prognostic marker and therapeutic target for HCC treatment.

Insensitivity to atorvastatin is associated with increased accumulation of intracellular lipid droplets and fatty acid metabolism in breast cancer cells

Apart from the relevant lipid-lowering effects, statins have demonstrated significant, although heterogeneous, anti-tumor activities in preventing breast cancer (BC) progression. To characterize the critical pathways behind the diverse responses to therapy, we investigated statin-induced changes in regulation of lipid metabolism and abundance of neutral lipid-containing cytoplasmic lipid droplets (LDs) in BC cells displaying different sensitivity to atorvastatin. Following atorvastatin treatment, accumulated LD levels inversely mirrored the marginal anti-proliferative effects in a dose and time-dependent manner in the less-sensitive BC cells. Transcriptional profiling excluded dysregulation of lipid uptake and efflux as specific mechanisms associated with differences in LD accumulation and anti-proliferative effects of atorvastatin. Notably, significant upregulation of genes involved in unsaturated fatty acid metabolism [stearoyl-CoA desaturase (SCD)] and cholesterol biosynthesis [3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR)], were associated with atorvastatin insensitivity. Taken together, the increased ability to store neutral lipids in LDs as consequence of atorvastatin treatment likely confers a proliferative advantage to BC cells and may serve as potential biomarker of statin resistance in BC. Contributions of cholesterol biosynthesis and unsaturated fatty acid metabolism to LD formation should be thoroughly explored for better understanding of the molecular mechanisms underlying statin-induced effects against BC progression.

SCD1 is associated with tumor promotion, late stage and poor survival in lung adenocarcinoma

The discovery of Warburg effect opens a new era in anti-cancer therapy. Aerobic glycolysis is regarded as a hallmark of cancer cells and increasing literatures indicates that metabolic changes are critical for the maintenance and progression of cancer cells. Besides aerobic glycolysis, increased fatty acid synthesis is also required for the rapid growth of cancer cells, and is considered as one of the most typical metabolic symbols of cancer either. Thus, targeting fatty acid metabolism may provide a potential avenue for the diagnosis and therapeutic treatment of cancer. In this study, we have identified Sterol-CoA desaturase-1 (SCD1) which is the rate-limiting enzyme of unsaturated fatty acid synthesis, universally and highly expressed in lung adenocarcinoma and was required for the cell proliferation, migration and invasion. Both in vitro and in vivo studies demonstrated that high expression of SCD1 remarkably enhanced the ability of tumor formation and invasion, while knockdown of SCD1 significantly repressed tumorigenesis and induced cell apoptosis. Clinical association study suggested that high expression of SCD1 is more frequently observed in late stage patients and presents poor prognosis. Taken together, our results suggested that SCD1 is a potentially novel biomarker of lung adenocarcinoma, and targeting SCD1 may represent a new anti-cancer strategy.

EGFR modulates monounsaturated fatty acid synthesis through phosphorylation of SCD1 in lung cancer

Background

Epidermal growth factor receptor (EGFR), a well-known oncogenic driver, contributes to the initiation and progression of a wide range of cancer types. Aberrant lipid metabolism including highly produced monounsaturated fatty acids (MUFA) is recognized as a hallmark of cancer. However, how EGFR regulates MUFA synthesis in cancer remains elusive. This is the focus of our study.

Methods

The interaction between EGFR and stearoyl-CoA desaturase-1 (SCD1) was detected byco-immunoprecipitation. SCD1 protein expression, stability and phosphorylation were tested by western blot. The synthesis of MUFA was determined by liquid chromatography-mass spectrometry. The growth of lung cancer was detected by CCK-8 assay, Annexin V/PI staining, colony formation assay and subcutaneous xenograft assay. The expression of activated EGFR, phosphorylated and total SCD1 was tested by immunohistochemistry in 90 non-small cell lung cancersamples. The clinical correlations were analyzed by Chi-square test, Kaplan-Meier survival curve analysis and Cox regression.

Results

EGFR binds to and phosphorylates SCD1 at Y55. Phosphorylation of Y55 is required for maintaining SCD1 protein stability and thus increases MUFA level to facilitate lung cancer growth. Moreover, EGFR-stimulated cancer growth depends on SCD1 activity. Evaluation of non-small cell lung cancersamples reveals a positive correlation among EGFR activation, SCD1 Y55 phosphorylation and SCD1 protein expression. Furthermore, phospho-SCD1 Y55 can serve as an independent prognostic factor for poor patient survival.

Conclusions

Ourstudy demonstrates that EGFR stabilizes SCD1 through Y55 phosphorylation, thereby up-regulating MUFA synthesis to promote lung cancer growth. Thus, we provide the first evidence that SCD1 can be subtly controlled by tyrosine phosphorylation and uncover a previously unknown direct linkage between oncogenic receptor tyrosine kinase and lipid metabolism in lung cancer. We also propose SCD1 Y55 phosphorylation as a potential diagnostic marker for lung cancer.

Electronic supplementary material

The online version of this article (doi:10.1186/s12943-017-0704-x) contains supplementary material, which is available to authorized users.

Reprogramming of central carbon metabolism in cancer stem cells

Cancer metabolism has been studied for years and adopted in the clinic for monitoring disease progression and therapy response. Despite our growing knowledge of a distinctly altered metabolic behavior in cancer, drugs targeting cancer metabolism have remained less than promising. Recent efforts in cancer stem cell (CSC) biology suggest that a subpopulation of tumor-initiating cells within the tumor bulk represents the root of tumor recurrence and therapy resistance. In recent years, metabolic phenotype of CSCs of various tumor types has been identified. This breakthrough has shed light on the underlying mechanism by which CSCs maintain stemness, confer resistance to therapies and initiate tumor relapse. The distinct metabolic characteristics of CSCs compared to non-CSCs provide an opportunity to target CSCs more specifically and have become a major focus in cancer research in recent years with substantial efforts conducted towards discovering clinical targets. This perspective article summarizes the current knowledge of CSC metabolism in carcinogenesis and highlights the potential of targeting CSC metabolism for therapy.

Stearoyl CoA desaturase-1: New insights into a central regulator of cancer metabolism

The processes of cell proliferation, cell death and differentiation involve an intricate array of biochemical and morphological changes that require a finely tuned modulation of metabolic pathways, chiefly among them is fatty acid metabolism. The critical participation of stearoyl CoA desaturase-1 (SCD1), the fatty acyl Δ9-desaturing enzyme that converts saturated fatty acids (SFA) into monounsaturated fatty acids (MUFA), in the mechanisms of replication and survival of mammalian cells, as well as their implication in the biological alterations of cancer have been actively investigated in recent years. This review examines the growing body of evidence that argues for a role of SCD1 as a central regulator of the complex synchronization of metabolic and signaling events that control cellular metabolism, cell cycle progression, survival, differentiation and transformation to cancer.

O-GlcNAcylation and the Metabolic Shift in High-Proliferating Cells: All the Evidence Suggests that Sugars Dictate the Flux of Lipid Biogenesis in Tumor Processes

Cancer cells are characterized by their high capability to proliferate. This imposes an accelerated biosynthesis of membrane compounds to respond to the need for increasing the membrane surface of dividing cells and remodeling the structure of lipid microdomains. Recently, attention has been paid to the upregulation of O-GlcNAcylation processes observed in cancer cells. Although O-GlcNAcylation of lipogenic transcriptional regulators is described in the literature (e.g., FXR, LXR, ChREBP), little is known about the regulation of the enzymes that drive lipogenesis: acetyl co-enzyme A carboxylase and fatty acid synthase (FAS). The expression and catalytic activity of both FAS and O-GlcNAc transferase (OGT) are high in cancer cells but the reciprocal regulation of the two enzymes remains unexplored. In this perspective, we collected data linking FAS and OGT and, in so doing, pave the way for the exploration of the intricate functions of these two actors that play a central role in tumor growth.

17β-estradiol induces stearoyl-CoA desaturase-1 expression in estrogen receptor-positive breast cancer cells

Background

To sustain cell growth, cancer cells exhibit an altered metabolism characterized by increased lipogenesis. Stearoyl-CoA desaturase-1 (SCD-1) catalyzes the production of monounsaturated fatty acids that are essential for membrane biogenesis, and is required for cell proliferation in many cancer cell types. Although estrogen is required for the proliferation of many estrogen-sensitive breast carcinoma cells, it is also a repressor of SCD-1 expression in liver and adipose. The current study addresses this apparent paradox by investigating the impact of estrogen on SCD-1 expression in estrogen receptor-α-positive breast carcinoma cell lines.

Methods

MCF-7 and T47D mammary carcinomas cells and immortalized MCF-10A mammary epithelial cells were hormone-starved then treated or not with 17β-estradiol. SCD-1 activity was assessed by measuring cellular monounsaturated/saturated fatty acid (MUFA/SFA) ratios, and SCD-1 expression was measured by qPCR, immunoblot, and immunofluorescence analyses. The role of SCD-1 in cell proliferation was measured following treatment with the SCD-1 inhibitor A959372 and following SCD-1 silencing using siRNA. The involvement of IGF-1R on SCD-1 expression was measured using the IGF-1R antagonist AG1024. The expression of SREBP-1c, a transcription factor that regulates SCD-1, was measured by qPCR, and by immunoblot analyses.

Results

17β-estradiol significantly induced cell proliferation and SCD-1 activity in MCF-7 and T47D cells but not MCF-10A cells. Accordingly, 17β-estradiol significantly increased SCD-1 mRNA and protein expression in MCF-7 and T47D cells compared to untreated cells. Treatment of MCF-7 cells with 4-OH tamoxifen or siRNA silencing of estrogen receptor-α largely prevented 17β-estradiol-induced SCD-1 expression. 17β-estradiol increased SREBP-1c expression and induced the mature active 60 kDa form of SREBP-1. The selective SCD-1 inhibitor or siRNA silencing of SCD-1 blocked the 17β-estradiol-induced cell proliferation and increase in cellular MUFA/SFA ratios. IGF-1 also induced SCD-1 expression, but to a lesser extent than 17β-estradiol. The IGF-1R antagonist partially blocked 17β-estradiol-induced cell proliferation and SCD-1 expression, suggesting the impact of 17β-estradiol on SCD-1 expression is partially mediated though IGF-1R signaling.

Conclusions

This study illustrates for the first time that, in contrast to hepatic and adipose tissue, estrogen induces SCD-1 expression and activity in breast carcinoma cells. These results support SCD-1 as a therapeutic target in estrogen-sensitive breast cancer.

Betulinic acid induces a novel cell death pathway that depends on cardiolipin modification

Cancer is associated with strong changes in lipid metabolism. For instance, normal cells take up fatty acids (FAs) from the circulation, while tumour cells generate their own and become dependent on de novo FA synthesis, which could provide a vulnerability to target tumour cells. Betulinic acid (BetA) is a natural compound that selectively kills tumour cells through an ill-defined mechanism that is independent of BAX and BAK, but depends on mitochondrial permeability transition-pore opening. Here we unravel this pathway and show that BetA inhibits the activity of steroyl-CoA-desaturase (SCD-1). This enzyme is overexpressed in tumour cells and critically important for cells that utilize de novo FA synthesis as it converts newly synthesized saturated FAs to unsaturated FAs. Intriguingly, we find that inhibition of SCD-1 by BetA or, alternatively, with a specific SCD-1 inhibitor directly and rapidly impacts on the saturation level of cardiolipin (CL), a mitochondrial lipid that has important structural and metabolic functions and at the same time regulates mitochondria-dependent cell death. As a result of the enhanced CL saturation mitochondria of cancer cells, but not normal cells that do not depend on de novo FA synthesis, undergo ultrastructural changes, release cytochrome c and quickly induce cell death. Importantly, addition of unsaturated FAs circumvented the need for SCD-1 activity and thereby prevented BetA-induced CL saturation and subsequent cytotoxicity, supporting the importance of this novel pathway in the cytotoxicity induced by BetA.

Stearoyl-CoA desaturase 1 and paracrine diffusible signals have a major role in the promotion of breast cancer cell migration induced by cancer-associated fibroblasts

Background:

Despite the recognised contribution of the stroma to breast cancer development and progression, the effective targeting of the tumor microenvironment remains a challenge to be addressed. We previously reported that normal fibroblasts (NFs) and, notably, breast cancer-associated fibroblasts (CAFs) induced epithelial-to-mesenchymal transition and increases in cell membrane fluidity and migration in well- (MCF-7) and poorly-differentiated (MDA-MB-231) breast cancer cells. This study was designed to better define the role played, especially by CAFs, in promoting breast tumor cell migration.

Methods:

Fibroblast/breast cancer cell co-cultures were set up to investigate the influence of NFs and CAFs on gene and protein expression of Stearoyl-CoA desaturase 1 (SCD1), the main enzyme regulating membrane fluidity, as well as on the protein level and activity of its transcription factor, the sterol regulatory element-binding protein 1 (SREBP1), in MCF-7 and MDA-MB-231 cells. To assess the role of SREBP1 in the regulation of SCD1 expression, the desaturase levels were also determined in tumor cells treated with an SREBP1 inhibitor. Migration was evaluated by wound-healing assay in SCD1-inhibited (by small-interfering RNA (siRNA) or pharmacologically) cancer cells and the effect of CAF-conditioned medium was also assessed. To define the role of stroma-derived signals in cancer cell migration speed, cell-tracking analysis was performed in the presence of neutralising antibodies to hepatocyte growth factor, transforming growth factor-β or basic fibroblast growth factor.

Results:

A two to three fold increase in SCD1 mRNA and protein expression has been induced, particularly by CAFs, in the two cancer cell lines that appear to be dependent on SREBP1 activity in MCF-7 but not in MDA-MB-231 cells. Both siRNA-mediated and pharmacological inhibition of SCD1 impaired tumor cells migration, also when promoted by CAF-released soluble factors. Fibroblast-triggered increase in cancer cell migration speed was markedly reduced or abolished by neutralising the above growth factors.

Conclusion:

These results provide further insights in understanding the role of CAFs in promoting tumor cell migration, which may help to design new stroma-based therapeutic strategies.

Hypoxia induces a lipogenic cancer cell phenotype via HIF1α-dependent and -independent pathways

The biochemistry of cancer cells diverges significantly from normal cells as a result of a comprehensive reprogramming of metabolic pathways. A major factor influencing cancer metabolism is hypoxia, which is mediated by HIF1α and HIF2α. HIF1α represents one of the principal regulators of metabolism and energetic balance in cancer cells through its regulation of glycolysis, glycogen synthesis, Krebs cycle and the pentose phosphate shunt. However, less is known about the role of HIF1α in modulating lipid metabolism. Lipids serve cancer cells to provide molecules acting as oncogenic signals, energetic reserve, precursors for new membrane synthesis and to balance redox biological reactions. To study the role of HIF1α in these processes, we used HCT116 colorectal cancer cells expressing endogenous HIF1α and cells in which the hif1α gene was deleted to characterize HIF1α-dependent and independent effects on hypoxia regulated lipid metabolites. Untargeted metabolomics integrated with proteomics revealed that hypoxia induced many changes in lipids metabolites. Enzymatic steps in fatty acid synthesis and the Kennedy pathway were modified in a HIF1α-dependent fashion. Palmitate, stearate, PLD3 and PAFC16 were regulated in a HIF-independent manner. Our results demonstrate the impact of hypoxia on lipid metabolites, of which a distinct subset is regulated by HIF1α.

Thrombin inhibition with dabigatran protects against high-fat diet-induced fatty liver disease in mice

Nonalcoholic fatty liver disease (NAFLD) is the hepatic manifestation of obesity and metabolic syndrome. Robust coagulation cascade activation is common in obese patients with NAFLD. We identified a critical temporal relationship between thrombin generation and the manifestation of hepatic steatosis, inflammation, and injury in C57BL/6J mice fed a high-fat diet (HFD) for 1, 2, and 3 months. Mice fed a HFD exhibited dramatic increases in hepatocellular injury and inflammation over time. Hepatic fibrin deposition preceded an increase in serum alanine aminotransferase, and the most dramatic changes in liver histopathology occurred in conjunction with a detectable increase in plasma thrombin-antithrombin levels at 3 months. To directly determine whether thrombin activity promotes NAFLD pathogenesis, mice were fed a HFD and simultaneously treated with the direct thrombin inhibitor dabigatran etexilate for 3 months. Notably, dabigatran treatment significantly reduced hepatic fibrin deposition, hepatic inflammation, hepatocellular injury, and steatosis in mice fed a HFD. Of interest, dabigatran treatment also significantly attenuated HFD-induced body weight gain. Gene expression analysis suggested that thrombin potentially drives NAFLD pathogenesis by altering the expression of genes associated with lipid metabolism and bile acid synthesis. Collectively, the results suggest that thrombin activity is central to HFD-induced body weight gain, liver injury, and inflammation and provide the proof-of-principle evidence that pharmacological thrombin inhibition could be effective in limiting NAFLD and associated pathologies.

Lipogenesis in cancer progression (review)

In normal tissues, energy-providing lipids come principally from circulating lipids. However, in growing tumors, energy supply is mainly provided by lipids coming from de novo synthesis. It is not surprising to see elevated expression of several lipogenic genes in tumors from different origins. The role of lipogenic genes in the establishment of the primary tumor has been clearly established. A large number of studies demonstrate a role of fatty acid synthase in the activation of cell cycle and inhibition of apoptosis in tumor cells. Other lipogenic genes such as the acetyl CoA carboxylase (ACC) and the stearoyl CoA desaturase 1 (SCD1) are highly expressed in primary tumors and also appear to play a role in their development. However, the role of lipogenesis in the metastatic process is less clear. In the present review, we aim to present the most recent evidences for the key role of lipogenic enzymes in the metastatic process and in epithelial to mesenchymal transition.

Overexpression of stearoyl-CoA desaturase 1 in bone marrow mesenchymal stem cells enhance the expression of induced endothelial cells

Background

Bone marrow mesenchymal stem cells (BM-MSCs) are capable of differentiating into endothelial cells in vitro and acquire major characteristics of mature endothelial-like expression of vWF and CD31. SFAs and lipid oxidation products have been linked with postprandial endothelial dysfunction. Consumption of SFAs impairs arterial endothelial function, while a Mediterranean-type MUFA-diet has a beneficial effect on endothelial function by producing a decrease in levels of vWF, TFPI and PAI-1. Stearoyl-CoA desaturase 1 (SCD1), which converts SFA to MUFA, is involved in the cellular biosynthesis of MUFAs from SFA substrates. High expression of SCD1 is corresponded with low rates of fatty acid oxidation, therefore it might reduce inflammatory responses and be beneficial for the growth of induced endothelial cells. Overexpression of SCD1 in BM-MSCs might increase the growth of induced endothelial cells. The goal of this research is to study the relationship between overexpression of SCD1 and the expression of induced endothelial cells in BM-MSCs in vitro.

Methods

The gene SCD1 was integrated into a lentiviral vector, and then 293 T cells were transfected by the connected product to produce a packaged virus. BM-MSCs were infected by the packaged virus. Cell culture and endothelial induction were performed. Fluorescent quantitative PCR of CD31, vWF and VE-cad was performed after 1 week and 2 weeks to test the growth of induced endothelial cells.

Results

The mRNA amount of CD31, vWF and VE-cad of the SCD1 overexpressed group was statistically higher than that of the empty vector (EV) group and that of the normal group after 1 week and 2 weeks, respectively (p < 0.05). Immunocytochemical staining of CD31 or vWF was detected by visualizing red color.

Conclusions

This study suggested that overexpression of SCD1 in BM-MSCs could increase the expression of induced endothelial cells in vitro.

Hypoxia and metabolism in cancer

Interest in targeting metabolism has been renewed in recent years as research increases understanding of the altered metabolic profile of tumor cells compared with that of normal cells. Metabolic reprogramming allows cancer cells to survive and proliferate in the hostile tumor microenvironment. These metabolic changes support energy generation, anabolic processes, and the maintenance of redox potential, mechanisms that are all essential for the proliferation and survival of tumor cells. The metabolic switch in a number of key metabolic pathways is mainly regulated by genetic events, rendering cancer cells addicted to certain nutrients, such as glutamine. In addition, hypoxia is induced when highly proliferative tumor cells distance themselves from an oxygen supply. Hypoxia-inducible factor 1α is largely responsible for alterations in metabolism that support the survival of hypoxic tumor cells. Metabolic alterations and dependencies of cancer cells may be exploited to improve anticancer therapy. This chapter reviews the main aspects of altered metabolism in cancer cells, emphasizing recent advances in glucose, glutamine, and lipid metabolism.

Critical role of SCD1 in autophagy regulation via lipogenesis and lipid rafts-coupled AKT-FOXO1 signaling pathway

SCD1 (stearoyl-coenzyme A desaturase 1) is an endoplasmic reticulum-bound enzyme that catalyzes the formation of the first double bond at the cis-Δ9 position of saturated fatty acids (SFA) to form monounsaturated fatty acids (MUFA). Increasing evidence indicates that autophagy plays an important role in regulating lipid metabolism, while little is known about whether key enzymes of lipogenesis like SCD1 can regulate autophagy. In this study, we examined the role of SCD1 in autophagy using the tsc2(-/-) mouse embryonic fibroblasts (MEFs) possessing constitutively active MTORC1 as a cellular model. We found that mRNA and protein levels of SCD1 are significantly elevated in the tsc2(-/-) MEFs compared with Tsc2(+/+) MEFs, resulting in significant increases in levels of various lipid classes. Furthermore, inhibition of SCD1 activity by either a chemical inhibitor or genetic knockdown resulted in an increase of autophagic flux only in the tsc2(-/-) MEFs. Induction of autophagy was independent of MTOR as MTORC1 activity was not suppressed by SCD1 inhibition. Loss of phosphorylation on AKT Ser473 was observed upon SCD1 inhibition and such AKT inactivation was due to disruption of lipid raft formation, without affecting the formation and activity of MTORC2. Increased nuclear translocation of FOXO1 was observed following AKT inactivation, leading to increased transcription of genes involved in the autophagic process. The tsc2(-/-) MEFs were also more susceptible to apoptosis induced by SCD1 inhibition and blockage of autophagy sensitized the cell death response. These results revealed a novel function of SCD1 on regulation of autophagy via lipogenesis and the lipid rafts-AKT-FOXO1 pathway.

Fatty acid remodeling in cellular glycerophospholipids following the activation of human T cells

Changes in fatty acid (FA) and glycerophospholipid (GPL) metabolism associated with cell cycle entry are not fully understood. In this study FA-GPL remodeling was investigated in resting and proliferating primary human T cells. Significant changes were measured in the composition and distribution of FAs in GPLs following receptor activation of human T cells. The FA distribution of proliferating T cells was very similar to that of the human Jurkat T cell line and when the stimulus was removed from proliferating T cells, they stopped proliferating and the FA distribution largely reverted back to that of resting T cells. The cellular content of saturated and monounsaturated FAs was significantly increased in proliferating cells, which was associated with an induction of FA synthase and stearoyl-CoA desaturase-1 gene expression. Additionally, cellular arachidonate was redistributed in GPLs in a distinct pattern that was unlike any other FAs. This redistribution was associated with an induction of CoA-dependent and CoA-independent remodeling. Accordingly, significant changes in the expression of several acyl-CoA synthetases, lysophospholipid acyltransferases, and phospholipase A2 were measured. Overall, these results suggest that metabolic pathways are activated in proliferating T cells that may represent fundamental changes associated with human cell proliferation.

The role of phosphatidylcholine and choline metabolites to cell proliferation and survival

The reorganization of metabolic pathways in cancer facilitates the flux of carbon and reducing equivalents into anabolic pathways at the expense of oxidative phosphorylation. This provides rapidly dividing cells with the necessary precursors for membrane, protein and nucleic acid synthesis. A fundamental metabolic perturbation in cancer is the enhanced synthesis of fatty acids by channeling glucose and/or glutamine into cytosolic acetyl-CoA and upregulation of key biosynthetic genes. This lipogenic phenotype also extends to the production of complex lipids involved in membrane synthesis and lipid-based signaling. Cancer cells display sensitivity to ablation of fatty acid synthesis possibly as a result of diminished capacity to synthesize complex lipids involved in signaling or growth pathways. Evidence has accrued that phosphatidylcholine, the major phospholipid component of eukaryotic membranes, as well as choline metabolites derived from its synthesis and catabolism, contribute to both proliferative growth and programmed cell death. This review will detail our current understanding of how coordinated changes in substrate availability, gene expression and enzyme activity lead to altered phosphatidylcholine synthesis in cancer, and how these changes contribute directly or indirectly to malignant growth. Conversely, apoptosis targets key steps in phosphatidylcholine synthesis and degradation that are linked to disruption of cell cycle regulation, reinforcing the central role that phosphatidylcholine and its metabolites in determining cell fate.

Human breast cancer tissues contain abundant phosphatidylcholine(36∶1) with high stearoyl-CoA desaturase-1 expression

Breast cancer is the leading cause of cancer and mortality in women worldwide. Recent studies have argued that there is a close relationship between lipid synthesis and cancer progression because some enzymes related to lipid synthesis are overexpressed in breast cancer tissues. However, lipid distribution in breast cancer tissues has not been investigated. We aimed to visualize phosphatidylcholines (PCs) and lysoPCs (LPCs) in human breast cancer tissues by performing matrix assisted laser desorption/ionization-imaging mass spectrometry (MALDI-IMS), which is a novel technique that enables the visualization of molecules comprehensively. Twenty-nine breast tissue samples were obtained during surgery and subjected to MALDI-IMS analysis. We evaluated the heterogeneity of the distribution of PCs and LPCs on the tissues. Three species [PC(32∶1), PC(34∶1), and PC(36∶1)] of PCs with 1 mono-unsaturated fatty acid chain and 1 saturated fatty acid chain (MUFA-PCs) and one [PC(34∶0)] of PCs with 2 saturated fatty acid chains (SFA-PC) were relatively localized in cancerous areas rather than the rest of the sections (named reference area). In addition, the LPCs did not show any biased distribution. The relative amounts of PC(36∶1) compared to PC(36∶0) and that of PC(36∶1) to LPC(18∶0) were significantly higher in the cancerous areas. The protein expression of stearoyl-CoA desaturase-1 (SCD1), which is a synthetic enzyme of MUFA, showed accumulation in the cancerous areas as observed by the results of immunohistochemical staining. The ratios were further analyzed considering the differences in expressions of the estrogen receptor (ER), human epidermal growth factor receptor 2 (HER2), and Ki67. The ratios of the signal intensity of PC(36∶1) to that of PC(36∶0) was higher in the lesions with positive ER expression. The contribution of SCD1 and other enzymes to the formation of the observed phospholipid composition is discussed.

The role of membrane fatty acid remodeling in the antitumor mechanism of action of 2-hydroxyoleic acid

The synthetic fatty acid 2-hydroxyoleic acid (2OHOA) is a potent antitumor drug that we rationally designed to regulate the membrane lipid composition and structure. The lipid modifications caused by 2OHOA treatments induce important signaling changes that end up with cell death (Terés et al., 2012 [1]). One of these regulatory effects is restoration of sphingomyelin levels, which are markedly lower in cancer cells compared to normal cells (Barceló-Coblijn et al., 2011 [2]). In this study, we report another important regulatory effect of 2OHOA on cancer cell membrane composition: a large increase in 2OHOA levels, accounting for ~15% of the fatty acids present in membrane phospholipids, in human glioma (SF767 and U118) and lung cancer (A549) cells. Concomitantly, we observed marked reductions in oleic acid levels and inhibition of stearoyl-CoA desaturase. The impact of these changes on the biophysical properties of the lipid bilayer was evaluated in liposomes reconstituted from cancer cell membrane lipid extracts. Thus, 2OHOA increased the packing of ordered domains and decreased the global order of the membrane. The present results further support and extend the knowledge about the mechanism of action for 2OHOA, based on the regulation of the membrane lipid composition and structure and subsequent modulation of membrane protein-associated signaling.

High stearoyl-CoA desaturase 1 expression is associated with shorter survival in breast cancer patients

Stearoyl-CoA desaturase 1 (SCD1) is an essential regulator of fatty acid synthesis. We have previously shown that overexpression of SCD1 increases the growth of breast cancer cell lines. The purpose of this study was to determine the relationship between SCD1 expression level and clinical-pathologic characteristics and survival of patients with breast cancer. Fine-needle aspirates were collected from the primary tumors of 250 patients with stage I-III breast cancer. Demographic and clinical characteristics including patient age, ethnicity, and menopausal status and tumor clinical stage, grade, and subtype were reviewed. SCD1 expression was analyzed using reverse-phase protein arrays. Samples were divided into high or low SCD1 expression levels based on a cut-off determined from martingale residual plots and regression tree analysis. SCD1 levels were significantly higher in tumors from patients >50-years old compared to patients ≤50-years old and were lower in triple-negative (estrogen/progesterone receptor-negative and human epidermal growth factor receptor-2-negative) breast cancers than other tumor subtypes. After adjusting for patient age, tumor subtype, tumor grade, and clinical stage, we found that patients with primary breast cancers expressing high SCD1 levels had significantly shorter relapse-free survival (RFS) (P = 0.0140) and overall survival (OS) (P = 0.039) in multivariable analysis. We conclude that SCD1 expression varies by breast cancer subtype and that high levels of SCD1 expression are associated with significantly shorter RFS and OS in multivariable analysis. Future studies are needed to define the role of SCD1 in the malignant phenotype of breast cancer and to evaluate the potential for SCD1 as a therapeutic target.

Decreasing stearoyl-CoA desaturase-1 expression inhibits β-catenin signaling in breast cancer cells

Stearoyl-CoA desaturase-1 (SCD1) is an endoplasmic reticulum anchored enzyme catalyzing the synthesis of monounsaturated fatty acids, mainly palmytoleyl-CoA and oleyl-CoA. Recent studies have revealed a function for SCD1 in the modulation of signaling processes related to cell proliferation, survival and transformation to cancer. We used MCF7 and MDA-MB-231 cells to analyze the role of SCD1 in the metastatic acquisition of breast cancer cells. Silencing SCD1 expression in breast cancer cells has no effect on cell viability but the levels of cell proliferation, cell cycle genes' expressions and the phosphorylation state of ERK1/2 MAPK are significantly reduced. Decreasing SCD1 expression also reduces the level of GSK3 phosphorylation, indicating higher activity of the kinase. Using cells fractionation, immunofluorescence and a β-catenin/TCF-responsive reporter construct, we demonstrate that lowering SCD1 expression leads to a decrease of β-catenin amounts within the nucleus and to inhibition of its transactivation capacity. Moreover, MDA-MB-231 cells transfected with the SCD1 siRNA show a lower invasive potential than the control cells. Taken together, our data demonstrate that low SCD1 expression is associated with a decrease in the proliferation rate of breast cancer cells associated with a decrease in ERK1/2 activation. SCD1 silencing also inhibits GSK3 phosphorylation, lowering β-catenin translocation to the nucleus, and, subsequently, its transactivation capacity and the expression of its target genes. Finally, we show that silencing SCD1 impairs the epithelial to mesenchymal transition-like behavior of the cells, a characteristic of metastatic breast cancer.

Stearoyl-CoA desaturase activity modulates the activation of epidermal growth factor receptor in human lung cancer cells

Stearoyl-CoA desaturase-1 (SCD1), the main enzyme that converts saturated fatty acids into monounsaturated fatty acids, is a key factor in the mechanisms of cancer cell proliferation, survival and tumorigenesis. Evidence indicates that SCD1 activity regulates these events in part by targeting the phosphatidylinositol-3 phosphate kinase/Akt and Ras/extracellular signal-regulated kinase (ERK) pathways, but the molecular mechanisms remain unknown. We now show that in H460 lung cancer cells, the suppression of SCD activity with CVT-11127, a specific small molecule SCD inhibitor, impairs the ligand-induced phosphorylation of epidermal growth factor (EGF) receptor, causing the inactivation of its downstream targets Akt, ERK and mammalian target of rapamycin. Importantly, the mitogenic response to EGF was markedly defective in SCD-depleted cancer cells. The inactivation of EGF receptor (EGFR) promoted by SCD inhibition may be caused by perturbations in the lipid microenvironment surrounding the receptor, since we detected significant alterations in the lateral mobility of plasma lipid microdomains. Finally, incubation of lung cancer cells with SCD blockers potentiated the antigrowth effect of gefitinib, an EGFR inhibitor employed in cancer treatment. Altogether, our data indicate that SCD activity may control cancer cell metabolism, proliferation and survival by modulating the EGFR→Akt/ERK signaling platforms. Our studies also suggest a value for SCD inhibitors as novel pharmacological agents in lung cancer, one of the most common and lethal forms of cancer for which therapeutic options remain very limited.

Lipid metabolism in cancer

Lipids form a diverse group of water-insoluble molecules that include triacylglycerides, phosphoglycerides, sterols and sphingolipids. They play several important roles at cellular and organismal levels. Fatty acids are the major building blocks for the synthesis of triacylglycerides, which are mainly used for energy storage. Phosphoglycerides, together with sterols and sphingolipids, represent the major structural components of biological membranes. Lipids can also have important roles in signalling, functioning as second messengers and as hormones. There is increasing evidence that cancer cells show specific alterations in different aspects of lipid metabolism. These alterations can affect the availability of structural lipids for the synthesis of membranes, the synthesis and degradation of lipids that contribute to energy homeostasis and the abundance of lipids with signalling functions. Changes in lipid metabolism can affect numerous cellular processes, including cell growth, proliferation, differentiation and motility. This review will examine some of the alterations in lipid metabolism that have been reported in cancer, at both cellular and organismal levels, and discuss how they contribute to different aspects of tumourigenesis.

The role of stearoyl-CoA desaturase in obesity, insulin resistance, and inflammation

Stearoyl-CoA desaturase 1 (SCD1) is an essential lipogenic enzyme that has been shown to play an intrinsic role in the development of obesity and related conditions, such as insulin resistance. Through the generation of various mouse models of SCD1 deficiency, we have come to understand that SCD1 plays a role, directly or indirectly, in diverse metabolic processes, including lipogenesis, fatty acid oxidation, insulin signaling, thermogenesis, and inflammation. This review will address recent advances in our understanding of this key regulator of cellular metabolic processes, including the role of SCD1 in maintaining skin barrier integrity and the role of skin SCD1 in the metabolic phenotype elicited by global SCD1 deficiency.

Plasma phospholipid fatty acid concentrations and risk of gastric adenocarcinomas in the European Prospective Investigation into Cancer and Nutrition (EPIC-EURGAST)

BACKGROUND

Epidemiologic data suggest that diet is a risk factor in the etiology of gastric cancer. However, the role of dietary fatty acids, a modifiable risk factor, remains relatively unexplored.

OBJECTIVE

The objective of this study was to determine the association of plasma phospholipid fatty acid concentrations, as biomarkers of exogenous and endogenously derived fatty acids, with the risk of gastric adenocarcinoma in a case-control study nested within the European Prospective Investigation into Cancer and Nutrition-Europe Gastric Cancer (EPIC-EURGAST).

DESIGN

Fatty acids were measured by gas chromatography in prediagnostic plasma phospholipids from 238 cases matched to 626 controls by age, sex, study center, and date of blood donation. Conditional logistic regression models adjusted for Helicobacter pylori infection status, BMI, smoking, physical activity, education, and energy intake were used to estimate relative cancer risks.

RESULTS

Positive risk associations for gastric cancer were observed in the highest compared with the lowest quartiles of plasma oleic acid (OR: 1.72; 95% CI: 1.01, 2.94), di-homo-γ-linolenic acid (OR: 1.92; 95% CI: 1.10, 3.35), α-linolenic acid (OR: 3.20; 95% CI: 1.70, 6.06), and the ratio of MUFAs to saturated fatty acids, as an indicator of stearoyl-CoA desaturase-1 enzyme activity (OR: 1.40; 95% CI: 0.81, 2.43). An inverse risk association was observed with the ratio of linoleic to α-linolenic acid (OR: 0.37; 95% CI: 0.20, 0.66).

CONCLUSION

These data suggest that a specific prediagnostic plasma phospholipid fatty acid profile, characterized mainly by high concentrations of oleic acid, α-linolenic acid, and di-homo-γ-linolenic acid, which presumably reflect both a complex dietary pattern and altered fatty acid metabolism, may be related to increased gastric cancer risk.

Cancer cell dependence on unsaturated fatty acids implicates stearoyl-CoA desaturase as a target for cancer therapy

Emerging literature suggests that metabolic pathways play an important role in the maintenance and progression of human cancers. In particular, recent studies have implicated lipid biosynthesis and desaturation as a requirement for tumor cell survival. In the studies reported here, we aimed to understand whether tumor cells require the activity of either human isoform of stearoyl-CoA-desaturase (SCD1 or SCD5) for survival. Inhibition of SCD1 by siRNA or a small molecule antagonist results in strong induction of apoptosis and growth inhibition, when tumor cells are cultured in reduced (2%) serum conditions, but has little impact on cells cultured in 10% serum. Depletion of SCD5 had minimal effects on cell growth or apoptosis. Consistent with the observed dependence on SCD1, but not SCD5, levels of SCD1 protein increased in response to decreasing serum levels. Both induction of SCD1 protein and sensitivity to growth inhibition by SCD1 inhibition could be reversed by supplementing growth media with unsaturated fatty acids, the product of the enzymatic reaction catalyzed by SCD1. Transcription profiling of cells treated with an SCD inhibitor revealed strong induction of markers of endoplasmic reticulum stress. Underscoring its importance in cancer, SCD1 protein was found to be highly expressed in a large percentage of human cancer specimens. SCD inhibition resulted in tumor growth delay in a human gastric cancer xenograft model. Altogether, these results suggest that desaturated fatty acids are required for tumor cell survival and that SCD may represent a viable target for the development of novel agents for cancer therapy.

Roles of StearoylCoA Desaturase-1 in the Regulation of Cancer Cell Growth, Survival and Tumorigenesis

The development and maintenance of defining features of cancer, such as unremitting cell proliferation, evasion of programmed cell death, and the capacity for colonizing local tissues and distant organs, demand a massive production of structural, signaling and energy-storing lipid biomolecules of appropriate fatty acid composition. Due to constitutive activation of fatty acid biosynthesis, cancer cell lipids are enriched with saturated (SFA) and, in particular, monounsaturated fatty acids (MUFA), which are generated by StearoylCoA desaturase-1, the main enzyme that transforms SFA into MUFA. An increasing number of experimental and epidemiological studies suggest that high levels of SCD1 activity is a major factor in establishing the biochemical and metabolic perturbations that favors the oncogenic process. This review examines evidence that suggests the critical implication of SCD1 in the modulation of multiple biological mechanisms, specifically lipid biosynthesis and proliferation and survival signaling pathways that contribute to the development and progression of cancer.

Genistein downregulates de novo lipid synthesis and impairs cell proliferation in human lung cancer cells

Cancer cells require high levels of lipid synthesis to produce structural, signaling and energetic lipids to support continuous replication. We and others have reported that constitutively increased lipogenesis, mainly by the tandem activation of acetyl-CoA carboxylase, fatty acid synthase and stearoyl-CoA desaturase-1 (SCD1), is critical to sustain the biological features of cancer cells, making this metabolic pathway a potential anticancer target for nutritional and pharmacological interventions. Isoflavones are biologically potent botanical compounds that possess clear antilipogenic and anticancer properties; however, the regulatory effects of these nutraceutical agents on lipid biosynthesis in cancer cells are still not well understood. Here we show that genistein, an isoflavone abundant in soybeans, decreased the levels of SCD1 protein in H460 human lung adenocarcinoma cells, consequently reducing the rate of biosynthesis of oleic acid as well as its presence in cancer cell lipids. Moreover, genistein promoted a marked reduction in de novo synthesis of major phospholipids, triacylglycerol and cholesterolesters. Finally, cancer cells treated with genistein displayed a dramatic reduction in cell proliferation as a result of a blockade in cell cycle progression through G(2)/M phases. As a whole, our data suggest that, by globally downregulating lipid biosynthesis, genistein suppresses cancer cell growth, emphasizing the relevance of this botanical compound as a potential therapeutic agent against lung cancer, a disease for which therapeutic choices remain limited.