Retrospective on Cholesterol Homeostasis: The Central Role of Scap.

Scap is a polytopic membrane protein that functions as a molecular machine to control the cholesterol content of membranes in mammalian cells. In the 21 years since our laboratory discovered Scap, we have learned how it binds sterol regulatory element-binding proteins (SREBPs) and transports them from the endoplasmic reticulum (ER) to the Golgi for proteolytic processing. Proteolysis releases the SREBP transcription factor domains, which enter the nucleus to promote cholesterol synthesis and uptake. When cholesterol in ER membranes exceeds a threshold, the sterol binds to Scap, triggering several conformational changes that prevent the Scap-SREBP complex from leaving the ER. As a result, SREBPs are no longer processed, cholesterol synthesis and uptake are repressed, and cholesterol homeostasis is restored. This review focuses on the four domains of Scap that undergo concerted conformational changes in response to cholesterol binding. The data provide a molecular mechanism for the control of lipids in cell membranes.

Pseudorabies virus upregulates low-density lipoprotein receptors to facilitate viral entry.

Pseudorabies virus (PRV) is the causative agent of Aujeszky's disease in pigs. The low-density lipoprotein receptor (LDLR) is a transcriptional target of the sterol-regulatory element-binding proteins (SREBPs) and participates in the uptake of LDL-derived cholesterol. However, the involvement of LDLR in PRV infection has not been well characterized. We observed an increased expression level of LDLR mRNA in PRV-infected 3D4/21, PK-15, HeLa, RAW264.7, and L929 cells. The LDLR protein level was also upregulated by PRV infection in PK-15 cells and in murine lung and brain. The treatment of cells with the SREBP inhibitor, fatostatin, or with SREBP2-specific small interfering RNA prevented the PRV-induced upregulation of LDLR expression as well as viral protein expression and progeny virus production. This suggested that PRV activated SREBPs to induce LDLR expression. Furthermore, interference in LDLR expression affected PRV proliferation, while LDLR overexpression promoted it. This indicated that LDLR was involved in PRV infection. The study also demonstrated that LDLR participated in PRV invasions. The overexpression of LDLR or inhibition of proprotein convertase subtilisin/kexin type 9 (PCSK9), which binds to LDLR and targets it for lysosomal degradation, significantly enhanced PRV attachment and entry. Mechanistically, LDLR interacted with PRV on the plasma membrane, and pretreatment of cells with LDLR antibodies was able to neutralize viral entry. An in vivo study indicated that the treatment of mice with the PCSK9 inhibitor SBC-115076 promoted PRV proliferation. The data from the study indicate that PRV hijacks LDLR for viral entry through the activation of SREBPs.IMPORTANCEPseudorabies virus (PRV) is a herpesvirus that primarily manifests as fever, pruritus, and encephalomyelitis in various domestic and wild animals. Owing to its lifelong latent infection characteristics, PRV outbreaks have led to significant financial setbacks in the global pig industry. There is evidence that PRV variant strains can infect humans, thereby crossing the species barrier. Therefore, gaining deeper insights into PRV pathogenesis and developing updated strategies to contain its spread are critical. This study posits that the low-density lipoprotein receptor (LDLR) could be a co-receptor for PRV infection. Hence, strategies targeting LDLR may provide a promising avenue for the development of effective PRV vaccines and therapeutic interventions.

The role of KLF2 in regulating hepatic lipogenesis and blood cholesterol homeostasis via the SCAP/SREBP pathway.

Liver steatosis is a common metabolic disorder resulting from imbalanced lipid metabolism, which involves various processes such as de novo lipogenesis, fatty acid uptake, fatty acid oxidation, and VLDL secretion. In this study, we discovered that KLF2, a transcription factor, plays a crucial role in regulating lipid metabolism in the liver. Overexpression of KLF2 in the liver of db/db mice, C57BL/6J mice, and Cd36-/- mice fed on a normal diet resulted in increased lipid content in the liver. Additionally, transgenic mice (ALB-Klf2) that overexpressed Klf2 in the liver developed liver steatosis after being fed a normal diet. We found that KLF2 promotes lipogenesis by increasing the expression of SCAP, a chaperone that facilitates the activation of SREBP, the master transcription factor for lipogenic gene expression. Our mechanism studies revealed that KLF2 enhances lipogenesis in the liver by binding to the promoter of SCAP and increasing the expression of genes involved in fatty acid synthesis. Reduction of KLF2 expression led to a decrease in SCAP expression and a reduction in the expression of SREBP1 target genes involved in lipogenesis. Overexpression of KLF2 also increased the activation of SREBP2 and the mRNA levels of its downstream target SOAT1. In C57BL/6J mice fed a high-fat diet, overexpression of Klf2 increased blood VLDL secretion, while reducing its expression decreased blood cholesterol levels. Our study emphasizes the novelty that hepatic KLF2 plays a critical role in regulating lipid metabolism through the KLF2/SCAP/SREBPs pathway, which is essential for hepatic lipogenesis and maintaining blood cholesterol homeostasis.

SIRT1/SREBPs-mediated regulation of lipid metabolism.

Sirtuins, also called silent information regulator 2, are enzymes that rely on nicotinamide adenine dinucleotide (NAD+) to function as histone deacetylases. Further investigation is warranted to explore the advantageous impacts of Sirtuin 1 (SIRT1), a constituent of the sirtuin group, on lipid metabolism, in addition to its well-researched involvement in extending lifespan. The regulation of gene expression has been extensively linked to SIRT1. Sterol regulatory element-binding protein (SREBP) is a substrate of SIRT1 that has attracted significant interest due to its role in multiple cellular processes including cell cycle regulation, DNA damage repair, and metabolic functions. Hence, the objective of this analysis was to investigate and elucidate the correlation between SIRT1 and SREBPs, as well as assess the contribution of SIRT1/SREBPs in mitigating lipid metabolism dysfunction. The objective of this research was to investigate whether SIRT1 and SREBPs could be utilized as viable targets for therapeutic intervention in managing complications associated with diabetes.

Activation of the PERK-CHOP signaling pathway during endoplasmic reticulum stress contributes to olanzapine-induced dyslipidemia.

Olanzapine (OLZ) is a widely prescribed antipsychotic drug with a relatively ideal effect in the treatment of schizophrenia (SCZ). However, its severe metabolic side effects often deteriorate clinical therapeutic compliance and mental rehabilitation. The peripheral mechanism of OLZ-induced metabolic disorders remains abstruse for its muti-target activities. Endoplasmic reticulum (ER) stress is implicated in cellular energy metabolism and the progression of psychiatric disorders. In this study, we investigated the role of ER stress in the development of OLZ-induced dyslipidemia. A cohort of 146 SCZ patients receiving OLZ monotherapy was recruited, and blood samples and clinical data were collected at baseline, and in the 4th week, 12th week, and 24th week of the treatment. This case-control study revealed that OLZ treatment significantly elevated serum levels of endoplasmic reticulum (ER) stress markers GRP78, ATF4, and CHOP in SCZ patients with dyslipidemia. In HepG2 cells, treatment with OLZ (25, 50 µM) dose-dependently enhanced hepatic de novo lipogenesis accompanied by SREBPs activation, and simultaneously triggered ER stress. Inhibition of ER stress by tauroursodeoxycholate (TUDCA) and 4-phenyl butyric acid (4-PBA) attenuated OLZ-induced lipid dysregulation in vitro and in vivo. Moreover, we demonstrated that activation of PERK-CHOP signaling during ER stress was a major contributor to OLZ-triggered abnormal lipid metabolism in the liver, suggesting that PERK could be a potential target for ameliorating the development of OLZ-mediated lipid dysfunction. Taken together, ER stress inhibitors could be a potentially effective intervention against OLZ-induced dyslipidemia in SCZ.

Tri-ortho-cresyl phosphate induces hepatic steatosis by mTOR activation and ER stress induction.

Tri-ortho-cresyl phosphate (TOCP), an organophosphorus compound (OP), which is widely used as plasticizer, flame retardant and other industrial products, has been reported to cause multiple toxicities including neurotoxicity and reproductive toxicity. However, it remains to be elusive whether TOCP induces hepatotoxicity. The purpose of this study was to investigate the effect of TOCP on hepatocytes and the lipid metabolism in particular. The adult mice were given a single dose of TOCP (800 mg/kg, p.o.) and the histological changes in liver tissue and lipid content in serum were determined. The results showed that more vacuoles and lipid droplets were observed in the liver of the mice exposed to TOCP. And triglyceride concentrations in serum and liver tissue significantly increased. However, the histopathological changes of the liver and the elevated triglyceride levels in the exposed mice can be reversed by endoplasmic reticulum (ER) stress inhibitor 4-phenylbutyric acid and mTOR signal inhibitor rapamycin. It was also found that the changes of expression levels of the biomarkers of ER stress and mTOR signaling pathway, such as GRP78, CHOP, and p-mTOR, in the exposed mice were consistent with those observed in the cultured primary hepatocytes treated with the same chemicals. These results showed that TOCP activated mTOR signal and ER stress to induce de novo lipid synthesis, which led to the hepatic steatosis in mouse.

Rotavirus exploits SREBP pathway for hyper lipid biogenesis during replication.

Species A rotavirus (RVA) is one of the pathogens causing severe acute gastroenteritis in young children and animals worldwide. RVA replicates and assembles its immature particle within electron dense compartments known as viroplasm. Despite the importance of lipid droplet (LD) formation in the RVA viroplasm, the upstream molecules modulating LD formation have remained elusive. Here, we demonstrate that RVA infection reprogrammes sterol regulatory element binding proteins (SREBPs)-dependent lipogenic pathways in virus-infected cells. Interestingly, silencing of SREBPs significantly reduced RVA protein synthesis, genome replication and progeny virus production. Moreover, knockout of SREBP-1c gene conferred resistance to RVA-induced diarrhoea, reduction of RVA replication, and mitigation of small intestinal pathology in mice. This study identifies SREBPs-mediated lipogenic reprogramming in RVA-infected host cells for facilitating virus replication and SREBPs as a potential target for developing therapeutics against RVA infection.

[New eudesmane sesquiterpenoids from Atractylodis Macrocephalae Rhizoma and their inhibitory activities against SREBPs].

Three sesquiterpenoids were isolated and purified from the 95% ethanol extract of Atractylodis Macrocephalae Rhizoma by column chromatography on silica gel, Sephadex LH-20, ODS, and high-performance liquid chromatography(HPLC). Their chemical structures were identified on the basis of spectroscopic analysis and physiochemical properties as(7Z)-8ß,13-diacetoxy-eudesma-4(15),7(11)-diene(1), 7-oxo-7,8-secoeudesma-4(15),11-dien-8-oic acid(2), and guai-10(14)-en-11-ol(3). Compounds 1 and 2 are new compounds and compound 3 was obtained from Compositae family for the first time. Compounds 1, 2, and 3 showed weak inhibitory activities against sterol regulatory element-binding proteins(SREBPs).

Taurine prevents high-fat diet-induced-hepatic steatosis in rats by direct inhibition of hepatic sterol regulatory element-binding proteins and activation of AMPK.

This study investigated if the protective effect of taurine against high fat diet-induced hepatic steatosis involves modulating the hepatic activity of 5' AMP-activated protein kinase (AMPK) and levels/activity of the sterol regulatory element-binding proteins-1/2 (SREBP1/2). Rats were divided into four groups (n = 12/group) as (a) STD, fed standard diet (3.85 kcal/g); (b) STD + taurine (500 mg/kg); (c) HFD, fed HFD (4.73 kcal/g); and (d) HFD + taurine. All treatments were conducted for 12 weeks. Independent of food intake or modulating glucose or insulin levels, taurine administration to STD and HFD-fed rats significantly lowered weekly weight gain and the accumulation of the retroperitoneal, visceral and subcutaneous fats. In both groups, taurine also reduced serum and hepatic levels of triglycerides and cholesterol and reduced hepatic mRNA and protein levels of fatty acid synthase (FAS), acetyl CoA carboxylase-1 (ACC-1), HMG-CoA-reductase and HMG-CoA synthetase. In control rats only, taurine reduced hepatic levels of mature forms of sterol regulatory element-binding proteins (SREBP)-1/2. In HFD-fed rats, taurine reduced SREBP-1/2 precursor and mature forms in the livers of HFD-fed rats. Besides, taurine significantly increased levels of glutathione (GSH), the activity of superoxide dismutase (SOD), and the activity of AMPK and its downstream ß-oxidation genes including peroxisome proliferator-activated receptor-α (PPAR-α) and carnitine palmitoyltransferase (CPT-1) in the livers of both the control and HFD-fed rats. In conclusion, taurine protects against HFD-induced hepatic steatosis stimulating antioxidant levels, and concomitant stimulating hepatic ß-oxidation and suppressing lipid synthesis, mediated by activation of AMPK and suppression of SREBP-1.

SREBP-1a-stimulated lipid synthesis is required for macrophage phagocytosis downstream of TLR4-directed mTORC1.

There is a growing appreciation for a fundamental connection between lipid metabolism and the immune response. Macrophage phagocytosis is a signature innate immune response to pathogen exposure, and cytoplasmic membrane expansion is required to engulf the phagocytic target. The sterol regulatory element binding proteins (SREBPs) are key transcriptional regulatory proteins that sense the intracellular lipid environment and modulate expression of key genes of fatty acid and cholesterol metabolism to maintain lipid homeostasis. In this study, we show that TLR4-dependent stimulation of macrophage phagocytosis requires mTORC1-directed SREBP-1a-dependent lipid synthesis. We also show that the phagocytic defect in macrophages from SREBP-1a-deficient mice results from decreased interaction between membrane lipid rafts and the actin cytoskeleton, presumably due to reduced accumulation of newly synthesized fatty acyl chains within major membrane phospholipids. We show that mTORC1-deficient macrophages also have a phagocytic block downstream from TLR4 signaling, and, interestingly, the reduced level of phagocytosis in both SREBP-1a- and mTORC1-deficient macrophages can be restored by ectopic SREBP-1a expression. Taken together, these observations indicate SREBP-1a is a major downstream effector of TLR4-mTORC1 directed interactions between membrane lipid rafts and the actin cytoskeleton that are required for pathogen-stimulated phagocytosis in macrophages.

A functional interaction between Hippo-YAP signalling and SREBPs mediates hepatic steatosis in diabetic mice.

The Hippo pathway is an evolutionarily conserved regulator of organ size and tumorigenesis that negatively regulates cell growth and survival. Whether the Hippo pathway regulates cell metabolism is unknown. Here, we report that in the nucleus of hepatocytes, Yes-associated protein(YAP)-the terminal effector of the Hippo pathway-directly interacts with sterol regulatory element binding proteins (SREBP-1c and SREBP-2) on the promoters of the fatty acid synthase (FAS) and 30-hydroxylmethyl glutaryl coenzyme A reductase (HMGCR), thereby stimulating their transcription and promoting hepatocyte lipogenesis and cholesterol synthesis. In diet-induced diabetic mice, either Lats1 overexpression or YAP knockdown protects against hepatic steatosis and hyperlipidaemia through suppression of the interaction between YAP and SREBP-1c/SREBP-2. These results suggest that YAP is a nuclear co-factor of SREBPs and that the Hippo pathway negatively affects hepatocyte lipogenesis by inhibiting the function of YAP-SREBP complexes.

Functional diversification of sterol regulatory element binding proteins following gene duplication in a fungal species.

The sterol regulatory element binding proteins (SREBPs) are functionally well conserved and have been shown to regulate ergosterol synthesis in fungi. However, the distribution and evolution of the SREBPs in fungi, especially in the Pezizomycotina which comprised of a great many of animal and plant pathogens, are unexplored. In this study, we identified 641 SREBPs from 367 out of 530 fungi species. Reconstruction of their evolutionary history showed evidence of gene duplication and gene loss at multiple evolutionary scales. Especially, SREBPs undergo a gene duplication event in the common ancestor of Pezizomycotina, resulting in the formation of two clades of SREBPs. Besides, the conserved motifs in the bHLH domain of both clades within Eurotiomycetes are highly diverged. To better understand the evolutionary diversification of this biologically significant regulator, we performed a series of experiments using Penicillium digitatum, a member of the lineage of Eurotiomycetes, to investigate how the evolutionary process of gene duplication shaped its function. qRT-PCR analysis showed that although PdsreA and PdsreB can be induced by imazalil, they showed different expression pattern; the electrophoretic mobility shift assay showed that PdSreA but not PdSreB can directly bind to the PdMLE1 sequence, an element that leads to the increased resistance to demethylation inhibitors (DMI) fungicides in P. digitatum. These results demonstrated that functions of duplicated SREBPs have largely diverged in P. digitatum, which may be a major feature of the long-term adaptive evolution of a particular group of fungi.

Site-1 protease, a novel metabolic target for glioblastoma.

Sterol regulatory element binding proteins (SREBPs) are transcriptional regulators of lipids which promote glioblastoma growth. Here, we investigate the effect of inhibiting expression of SREBP target genes in human glioblastoma cells. This was achieved by using PF-429242 to inhibit site-1 protease (S1P), an enzyme required for SREBP activation. Treatment with PF-429242 decreased glioblastoma cell viability, induced apoptosis and downregulated steroid, isoprenoid and unsaturated fatty acid biosynthetic pathways. Several pro-inflammatory genes were upregulated. Collectively, these results demonstrate the potential of S1P as a target for glioblastoma therapy.

Chondroitin Sulfate-Rich Extract of Skate Cartilage Attenuates Lipopolysaccharide-Induced Liver Damage in Mice.

The protective effects of a chondroitin sulfate-rich extract (CSE) from skate cartilage against lipopolysaccharide (LPS)-induced hepatic damage were investigated, and its mechanism of action was compared with that of chondroitin sulfate (CS) from shark cartilage. ICR mice were orally administrated 200 mg/kg body weight (BW) of CS or 400 mg/kg BW of CSE for 3 consecutive days, followed by a one-time intraperitoneal injection of LPS (20 mg/kg BW). The experimental groups were vehicle treatment without LPS injection (NC group), vehicle treatment with LPS injection (LPS group), CS pretreatment with LPS injection (CS group), and CSE pretreatment with LPS injection (CSE group). Hepatic antioxidant enzyme expression levels in the CS and CSE groups were increased relative to those in the LPS group. In LPS-insulted hepatic tissue, inflammatory factors were augmented relative to those in the NC group, but were significantly suppressed by pretreatment with CS or CSE. Moreover, CS and CSE alleviated the LPS-induced apoptotic factors and mitogen-activated protein kinase (MAPK). In addition, CS and CSE effectively decreased the serum lipid concentrations and downregulated hepatic sterol regulatory element-binding proteins expression. In conclusion, the skate CSE could protect against LPS-induced hepatic dyslipidemia, oxidative stress, inflammation, and apoptosis, probably through the regulation of MAPK signaling.

Genetic effects of sterol regulatory element binding proteins and fatty acid-binding protein4 on the fatty acid composition of Korean cattle (Hanwoo).

OBJECTIVE: This study identifies single-nucleotide polymorphisms (SNP) or gene combinations that affect the flavor and quality of Korean cattle (Hanwoo) by using the SNP Harvester method. METHODS: Four economic traits (oleic acid [C18:1], saturated fatty acids), monounsaturated fatty acids, and marbling score) were adjusted for environmental factors in order to focus solely on genetic effects. The SNP Harvester method was used to investigate gene combinations (two-way gene interactions) associated with these economic traits. Further, a multifactor dimensionality reduction method was used to identify superior genotypes in gene combinations. RESULTS: Table 3 to 4 show the analysis results for differences between superior genotypes and others for selected major gene combinations using the multifactor dimensionality reduction method. Environmental factors were adjusted for in order to evaluate only the genetic effect. Table 5 shows the adjustment effect by comparing the accuracy before and after correction in two-way gene interactions. CONCLUSION: The g.3977-325 T>C and (g.2988 A>G, g.3977-325 T>C) combinations of fatty acid-binding protein4 were the superior gene, and the superior genotype combinations across all economic traits were the CC genotype at g.3977-325 T>C and the AACC, GACC, GGCC genotypes of (g.2988 A>G, g.3977-325 T>C).

Curcumin rescues high fat diet-induced obesity and insulin sensitivity in mice through regulating SREBP pathway.

Obesity and its major co-morbidity, type 2 diabetes, have reached an alarming epidemic prevalence without an effective treatment available. It has been demonstrated that inhibition of SREBP pathway may be a useful strategy to treat obesity with type 2 diabetes. Sterol regulatory element-binding proteins (SREBPs) are major transcription factors regulating the expression of genes involved in biosynthesis of cholesterol, fatty acid and triglyceride. In current study, we identified a small molecule, curcumin, inhibited the SREBP expression in vitro. The inhibition of SREBP by curcumin decreased the biosynthesis of cholesterol and fatty acid. In vivo, curcumin ameliorated HFD-induced body weight gain and fat accumulation in liver or adipose tissues, and improved serum lipid levels and insulin sensitivity in HFD-induced obese mice. Consistently, curcumin regulates SREBPs target genes and metabolism associated genes in liver or adipose tissues, which may directly contribute to the lower lipid level and improvement of insulin resistance. Take together, curcumin, a major active component of Curcuma longa could be a potential leading compound for development of drugs for the prevention of obesity and insulin resistance.

Schisandra polysaccharide inhibits hepatic lipid accumulation by downregulating expression of SREBPs in NAFLD mice.

BACKGROUND: Hepatoprotective effects of Chinese herbal medicine Schisandra Chinensis (Schisandra) have been widely investigated. However, most studies were focused on its lignan extracts. We investigated the effects of Schisandra polysaccharide (SCP) in a mouse model of non-alcoholic fatty liver disease (NAFLD), and studied its effect on sterol regulatory element binding proteins (SREBPs) and the related genes. METHODS: The mouse model of NAFLD was established by feeding mice with a high-fat diet for 16 weeks. Effect of SCP-treatment (100 mg/kg, once daily for 12 weeks) on biochemical parameters and liver histopathology was assessed. Relative levels of sterol regulatory element-binding proteins (SREBPs) and their gene expressions were determined by quantitative real-time polymerase chain reaction and Western Blot. RESULTS: SCP significantly reduced the liver index by 12.0%. Serum levels of triglycerides (TG), total cholesterol (TC), low-density lipoprotein cholesterol, alanine aminotransferase and aspartate aminotransferase were decreased by 31.3, 28.3, 42.8, 20.1 and 15.5%, respectively. Serum high-density lipoprotein cholesterol was increased by 26.9%. Further, SCP lowered hepatic TC and TG content by 27.0% and 28.3%, respectively, and alleviated fatty degeneration and necrosis of liver cells. A significant downregulation of mRNA and protein expressions of hepatic lipogenesis genes, SREBP-1c, fatty acid synthase and acetyl-CoA carboxylase, and the mRNA expression of liver X receptor α (LXRα) was observed in NAFLD mice treated with SCP. SCP also significantly reduced the hepatic expression of SREBP-2 and 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGCR). CONCLUSION: These findings demonstrate the hepatoprotective effects of SCP in a mouse model of NAFLD; the effects may be mediated via downregulation of LXRα/SREBP-1c/FAS/ACC and SREBP-2/HMGCR signaling pathways in the liver.

Berberine Alleviates Olanzapine-Induced Adipogenesis via the AMPKα-SREBP Pathway in 3T3-L1 Cells.

The aim of this study was to investigate the mechanisms underlying the inhibitory effects of berberine (BBR) on olanzapine (OLZ)-induced adipogenesis in a well-replicated 3T3-L1 cell model. Oil-Red-O (ORO) staining showed that BBR significantly decreased OLZ-induced adipogenesis. Co-treatment with OLZ and BBR decreased the accumulation of triglyceride (TG) and total cholesterol (TC) by 55.58% ± 3.65% and 49.84% ± 8.31%, respectively, in 3T3-L1 adipocytes accompanied by reduced expression of Sterol regulatory element binding proteins 1 (SREBP1), fatty acid synthase (FAS), peroxisome proliferator activated receptor-γ (PPARγ), SREBP2, low-density lipoprotein receptor (LDLR), and hydroxymethylglutaryl-coenzyme A reductase (HMGR) genes compared with OLZ alone. Consistently, the co-treatment downregulated protein levels of SREBP1, SREBP2, and LDLR by 57.71% ± 9.42%, 73.05% ± 11.82%, and 59.46% ± 9.91%, respectively. In addition, co-treatment reversed the phosphorylation level of AMP-activated protein kinase-α (AMPKα), which was reduced by OLZ, determined via the ratio of pAMPKα:AMPKα (94.1%) compared with OLZ alone. The results showed that BBR may prevent lipid metabolism disorders caused by OLZ by reversing the degree of SREBP pathway upregulated and the phosphorylation of AMPKα downregulated. Collectively, these results indicated that BBR could be used as a potential adjuvant to prevent dyslipidemia and obesity caused by the use of second-generation antipsychotic medication.

The epigenetic drug 5-azacytidine interferes with cholesterol and lipid metabolism.

DNA methylation and histone acetylation inhibitors are widely used to study the role of epigenetic marks in the regulation of gene expression. In addition, several of these molecules are being tested in clinical trials or already in use in the clinic. Antimetabolites, such as the DNA-hypomethylating agent 5-azacytidine (5-AzaC), have been shown to lower malignant progression to acute myeloid leukemia and to prolong survival in patients with myelodysplastic syndromes. Here we examined the effects of DNA methylation inhibitors on the expression of lipid biosynthetic and uptake genes. Our data demonstrate that, independently of DNA methylation, 5-AzaC selectively and very potently reduces expression of key genes involved in cholesterol and lipid metabolism (e.g. PCSK9, HMGCR, and FASN) in all tested cell lines and in vivo in mouse liver. Treatment with 5-AzaC disturbed subcellular cholesterol homeostasis, thereby impeding activation of sterol regulatory element-binding proteins (key regulators of lipid metabolism). Through inhibition of UMP synthase, 5-AzaC also strongly induced expression of 1-acylglycerol-3-phosphate O-acyltransferase 9 (AGPAT9) and promoted triacylglycerol synthesis and cytosolic lipid droplet formation. Remarkably, complete reversal was obtained by the co-addition of either UMP or cytidine. Therefore, this study provides the first evidence that inhibition of the de novo pyrimidine synthesis by 5-AzaC disturbs cholesterol and lipid homeostasis, probably through the glycerolipid biosynthesis pathway, which may contribute mechanistically to its beneficial cytostatic properties.

Managing lipid metabolism in proliferating cells: new perspective for metformin usage in cancer therapy.

Cancer cells metabolically adapt to undergo cellular proliferation. Lipids, besides their well-known role as energy storage, represent the major building blocks for the synthesis of neo-generated membranes. There is increasing evidence that cancer cells show specific alterations in different aspects of lipid metabolism. The changes of expression and activity of lipid metabolising enzymes are directly regulated by the activity of oncogenic signals. The dependence of tumour cells on the deregulated lipid metabolism suggests that proteins involved in this process could be excellent chemotherapeutic targets for cancer treatment. Due to its rare side effects in non-cancerous cells, metformin has been recently revaluated as a potential anti-tumourigenic drug, which negatively affects lipid biosynthetic pathways. In this review we summarised the emerging molecular events linking the anti-proliferative effect of metformin with lipid metabolism in cancer cells.