SREBF1

Gene Summary

Gene:SREBF1; sterol regulatory element binding transcription factor 1
Aliases: SREBP1, bHLHd1, SREBP1a, SREBP-1c
Location:17p11.2
Summary:This gene encodes a transcription factor that binds to the sterol regulatory element-1 (SRE1), which is a decamer flanking the low density lipoprotein receptor gene and some genes involved in sterol biosynthesis. The protein is synthesized as a precursor that is attached to the nuclear membrane and endoplasmic reticulum. Following cleavage, the mature protein translocates to the nucleus and activates transcription by binding to the SRE1. Sterols inhibit the cleavage of the precursor, and the mature nuclear form is rapidly catabolized, thereby reducing transcription. The protein is a member of the basic helix-loop-helix-leucine zipper (bHLH-Zip) transcription factor family. This gene is located within the Smith-Magenis syndrome region on chromosome 17. [provided by RefSeq, Mar 2016]
Databases:VEGA, OMIM, HGNC, Ensembl, GeneCard, Gene
Protein:sterol regulatory element-binding protein 1
Source:NCBIAccessed: 11 March, 2017

Ontology:

What does this gene/protein do?
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Pathways:What pathways are this gene/protein implicaed in?
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Cancer Overview

Research Indicators

Publications Per Year (1992-2017)
Graph generated 11 March 2017 using data from PubMed using criteria.

Literature Analysis

Mouse over the terms for more detail; many indicate links which you can click for dedicated pages about the topic.

  • Signal Transduction
  • Lipogenesis
  • Gene Expression Profiling
  • Cell Proliferation
  • Transcription Factors
  • Cancer Gene Expression Regulation
  • Transcriptional Activation
  • CCAAT-Enhancer-Binding Proteins
  • Western Blotting
  • DNA-Binding Proteins
  • Hepatocellular Carcinoma
  • Receptors, LDL
  • RTPCR
  • Chromosome 17
  • Promoter Regions
  • Sterol Regulatory Element Binding Protein 2
  • Oligonucleotide Array Sequence Analysis
  • Fatty Acids
  • Fatty Acid Synthase, Type I
  • Breast Cancer
  • Fatty Acid Synthases
  • Liver Cancer
  • Neoplasm Invasiveness
  • Cholesterol
  • Orphan Nuclear Receptors
  • Transfection
  • RNA Interference
  • Up-Regulation
  • Prostate Cancer
  • Sterol Regulatory Element Binding Protein 1
  • Liver X Receptors
  • Protein Binding
  • Apoptosis
  • Gene Expression
  • Cell Movement
  • siRNA
  • TOR Serine-Threonine Kinases
  • Lipid Metabolism
  • Liver
  • Messenger RNA
Tag cloud generated 11 March, 2017 using data from PubMed, MeSH and CancerIndex

Specific Cancers (3)

Data table showing topics related to specific cancers and associated disorders. Scope includes mutations and abnormal protein expression.

Note: list is not exhaustive. Number of papers are based on searches of PubMed (click on topic title for arbitrary criteria used).

Latest Publications: SREBF1 (cancer-related)

Bawazeer NA, Choudhry H, Zamzami MA, et al.
Role of hesperetin in LDL-receptor expression in hepatoma HepG2 cells.
BMC Complement Altern Med. 2016; 16:182 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: High plasma concentration of low-density lipoprotein cholesterol (LDL-c) plays a significant role in the incidence of atherosclerosis and coronary heart diseases. The aim of this study was to investigate the mechanism by which the citrus flavonoid, hesperetin, regulates the LDL receptor (LDLr) gene in the human liver using the human hepatoma cell line, HepG2.
METHODS: Luciferase reporter gene assays were performed (in the absence of lipoprotein) to measure the activity of the LDLr promoter and the promoters of the sterol regulatory element binding protein (SREBP) transcription factors that control the LDLr promoter.
RESULTS: Only SREBP-1 promoter activity was significantly increased 4 h after exposure to 200 μM hesperetin. However, after 24 h incubation with 200 μM hesperetin, the activities of all the promoter-constructs, SREBP-1a, -1c, -2 and LDLr, were significantly increased. The effects of 200 μM hesperetin on elevating LDLr mRNA levels were possibly due to regulation of LDLr gene transcription by SREBP-la and SREBP-2.
CONCLUSIONS: We conclude that 200 μM hesperetin was likely to have stimulated LDLr gene expression in human hepatoma HepG2 cells via increased phosphorylation of PI3K andERK1/2, which increased SREBP-1a and SREBP-2 mRNA levels and enhanced the maturation of the encoded proteins. This may lead to lower plasma LDL cholesterol; therefore, diets supplemented with hesperidin might provide cardio-protective effects and reduce mortality and morbidity from coronary heart diseases.

Li Y, Zhang J, He J, et al.
MicroRNA-132 cause apoptosis of glioma cells through blockade of the SREBP-1c metabolic pathway related to SIRT1.
Biomed Pharmacother. 2016; 78:177-84 [PubMed] Related Publications
BACKGROUND: The inhibition role of miRNA (microRNA or miR) on cancer signaling pathways has been used to prospective cancer treatment. SIRT1 might promote tumorigenesis in human glioma.
METHODS: Here, we investigated whether miR-132 regulate the expression of SIRT1 and its downstream SREBP (Sterol regulatory element-binding protein)-lipogenesis-cholesterogenesis metabolic pathway in human glioma cells. Furthermore, we studied the effect on biology function of glioma cell induced by miR-132.
RESULTS: MiR-132 inhibited SIRT1 and SREBP-1c expression and downregulated their targeted genes, including HMGCR and FASN. MiR-132 suppressed the cell growth, tumorigenicity, the invasion of glioma cells and migration as well as promoted their apoptosis. The pathways associated with cancer progression and tumorigenicity, and induce glioma cell apoptosis has been inhibited by miR-132 involving in a caspase-dependent apoptotic mechanism.
CONCLUSIONS: The recovery of miR-132 resulted in caspase-dependent apoptotic death in glioma cells. MiR-132 that was newly discovered represents a newly targeting mechanism in treatment for glioma.

Ravacci GR, Brentani MM, Tortelli TC, et al.
Docosahexaenoic Acid Modulates a HER2-Associated Lipogenic Phenotype, Induces Apoptosis, and Increases Trastuzumab Action in HER2-Overexpressing Breast Carcinoma Cells.
Biomed Res Int. 2015; 2015:838652 [PubMed] Free Access to Full Article Related Publications
In breast cancer, lipid metabolic alterations have been recognized as potential oncogenic stimuli that may promote malignancy. To investigate whether the oncogenic nature of lipogenesis closely depends on the overexpression of HER2 protooncogene, the normal breast cell line, HB4a, was transfected with HER2 cDNA to obtain HER2-overexpressing HB4aC5.2 cells. Both cell lines were treated with trastuzumab and docosahexaenoic acid. HER2 overexpression was accompanied by an increase in the expression of lipogenic genes involved in uptake (CD36), transport (FABP4), and storage (DGAT) of exogenous fatty acids (FA), as well as increased activation of "de novo" FA synthesis (FASN). We further investigate whether this lipogenesis reprogramming might be regulated by mTOR/PPARγ pathway. Inhibition of the mTORC1 pathway markers, p70S6 K1, SREBP1, and LIPIN1, as well as an increase in DEPTOR expression (the main inhibitor of the mTOR) was detected in HB4aC5.2. Based on these results, a PPARγ selective antagonist, GW9662, was used to treat both cells lines, and the lipogenic genes remained overexpressed in the HB4aC5.2 but not HB4a cells. DHA treatment inhibited all lipogenic genes (except for FABP4) in both cell lines yet only induced death in the HB4aC5.2 cells, mainly when associated with trastuzumab. Neither trastuzumab nor GW9662 alone was able to induce cell death. In conclusion, oncogenic transformation of breast cells by HER2 overexpression may require a reprogramming of lipogenic genetic that is independent of mTORC1 pathway and PPARγ activity. This reprogramming was inhibited by DHA.

Szydlowski M, Kiliszek P, Sewastianik T, et al.
FOXO1 activation is an effector of SYK and AKT inhibition in tonic BCR signal-dependent diffuse large B-cell lymphomas.
Blood. 2016; 127(6):739-48 [PubMed] Related Publications
Inhibition of spleen tyrosine kinase (SYK) in tonic B-cell receptor (BCR) signal-dependent diffuse large B-cell lymphomas (DLBCLs) inhibits cellular proliferation, decreases cholesterol biosynthesis, and triggers apoptosis, at least in part via a mechanism involving decreased activity of phosphatidylinositol 3-kinase/AKT axis. Because forkhead box O1 (FOXO1) is a major effector of this pathway, we investigated the role of FOXO1 in toxicity of BCR pathway inhibition. Inhibition of SYK in DLBCL cells with tonic BCR signaling decreased phospho-AKT and phospho-FOXO1 levels and triggered FOXO1-driven gene expression. Introduction of constitutively active FOXO1 mutant triggered cell cycle arrest and apoptosis, indicating that increased FOXO1 activity is toxic to these DLBCL cells. Depletion of FOXO1 with short hairpin RNA led to almost complete resistance to chemical SYK inhibitor R406, demonstrating that FOXO1 is also required for R406-induced cell death. FOXO1 in these cells is also involved in regulation of expression of the critical master regulator of cholesterol biosynthesis, SREBP1. Because HRK is the key effector of SYK inhibition, we characterized a mechanism linking FOXO1 activation and HRK induction that involves caspase-dependent cleavage of HRK's transcriptional repressor DREAM. Because AKT in lymphoma cells can be regulated by other signals than BCR, we assessed the combined effects of the AKT inhibitor MK-2206 with R406 and found markedly synergistic FOXO1-dependent toxicity. In primary DLBCLs, FOXO1 expression was present in 80% of tumors, correlated with SYK activity, and was associated with longer overall survival. These results demonstrate that FOXO1 is required for SYK and AKT inhibitor-induced toxicity.

Chakraborty PK, Xiong X, Mustafi SB, et al.
Role of cystathionine beta synthase in lipid metabolism in ovarian cancer.
Oncotarget. 2015; 6(35):37367-84 [PubMed] Free Access to Full Article Related Publications
Elevated lipid metabolism is implicated in poor survival in ovarian cancer (OC) and other cancers; however, current lipogenesis-targeting strategies lack cancer cell specificity. Here, we identify a novel role of cystathionine beta-synthase (CBS), a sulphur amino acid metabolizing enzyme highly expressed in several ovarian cancer cell lines, in driving deregulated lipid metabolism in OC. We examined the role of CBS in regulation of triglycerides, cholesterol and lipogenic enzymes via the lipogenic transcription factors SREBP1 and SREBP2. CBS silencing attenuated the expression of number of key enzymes involved in lipid synthesis (FASN and ACC1). Additionally CBS abrogates lipid uptake in OC cells. Gene silencing of CBS or SREBPs abrogated cellular migration and invasion in OC, while ectopic expression of SREBPs can rescue phenotypic effects of CBS silencing by restoring cell migration and invasion. Mechanistically, CBS represses SREBP1 and SREBP2 at the transcription levels by modulating the transcription factor Sp1. We further established the roles of both CBS and SREBPs in regulating ovarian tumor growth in vivo. In orthotopic tumor models, CBS or SREBP silencing resulted in reduced tumor cells proliferation, blood vessels formation and lipid content. Hence, cancer-selective disruption of the lipid metabolism pathway is possible by targeting CBS and, at least for OC, promises a profound benefit.

Li J, Huang Q, Long X, et al.
CD147 reprograms fatty acid metabolism in hepatocellular carcinoma cells through Akt/mTOR/SREBP1c and P38/PPARα pathways.
J Hepatol. 2015; 63(6):1378-89 [PubMed] Related Publications
BACKGROUND & AIMS: CD147 is a transmembrane glycoprotein which is highly expressed in various human cancers including hepatocellular carcinoma (HCC). A drug Licartin developed with (131)Iodine-labeled antibody against CD147 has been approved by the Chinese Food and Drug Administration (FDA) and enters into clinical use for HCC treatment. Increasing lines of evidence indicate that CD147 is implicated in the metabolism of cancer cells, especially glycolysis. However, the molecular mechanism underlying the relationship between CD147 and aberrant tumor lipid metabolism remains elusive.
METHODS: We systematically investigated the role of CD147 in the regulation of lipid metabolism, including de novo lipogenesis and fatty acid β-oxidation, in HCC cells and explored the underlying molecular mechanisms.
RESULTS: Bioinformatic analysis and experimental evidence demonstrated that CD147 significantly contributed to the reprogramming of fatty acid metabolism in HCC cells mainly through two mechanisms. On one hand, CD147 upregulated the expression of sterol regulatory element binding protein 1c (SREBP1c) by activating the Akt/mTOR signaling pathway, which in turn directly activated the transcription of major lipogenic genes FASN and ACC1 to promote de novo lipogenesis. On the other hand, CD147 downregulated peroxisome proliferator-activated receptor alpha (PPARα) and its transcriptional target genes CPT1A and ACOX1 by activating the p38 MAPK signaling pathway to inhibit fatty acid β-oxidation. Moreover, in vitro and in vivo assays indicated that the CD147-mediated reprogramming of fatty acid metabolism played a critical role in the proliferation and metastasis of HCC cells.
CONCLUSION: Our findings demonstrate that CD147 is a critical regulator of fatty acid metabolism, which provides a strong line of evidence for this molecule to be used as a drug target in cancer treatment.

Zhu Z, Zhao X, Zhao L, et al.
p54(nrb)/NONO regulates lipid metabolism and breast cancer growth through SREBP-1A.
Oncogene. 2016; 35(11):1399-410 [PubMed] Related Publications
Dysregulation of lipid metabolism is common in breast cancer. However, the underlying mechanisms remain elusive and the contribution of aberrant lipid metabolism to the malignant phenotypes of breast cancer is poorly understood. Here, we show that the nuclear protein p54(nrb)/Nono is highly expressed in breast cancer tissues as compared with the adjacent normal tissues in human patients. To determine the functions of p54(nrb) in breast cancer, we performed a biochemical screen and identified SREBP-1a, a master activator for genes involved in lipid biosynthesis, as a novel interacting protein of p54(nrb). In human breast cancer tissues, the levels of p54(nrb) and SREBP-1a proteins were positively correlated with each other. Our biochemical analyses showed that the conserved Y267 residue of p54(nrb) was required for its binding to the nuclear form of SREBP-1a. Interestingly, p54(nrb) binding to nuclear SREBP-1a caused an increase of nuclear SREBP-1a protein stability. As a result, p54(nrb) stimulates SREBP-1-meidated transcription of lipogenic genes and lipid production in breast cancer cells. Moreover, both p54(nrb) and SREBP-1a were required for breast cancer cell growth in vitro, and p54(nrb) binding to nuclear SREBP-1a was also critical for breast tumor development in vivo. Together, we conclude that p54(nrb) is a novel regulator of SREBP-1a in the nucleus, and our data suggest that p54(nrb) regulation of SREBP-1a supports the increased cellular demand of lipids for breast cancer growth. Thus, the SREBP pathway may represent a novel target for treating breast cancer.

Wang Y, Wang H, Zhao Q, et al.
PD-L1 induces epithelial-to-mesenchymal transition via activating SREBP-1c in renal cell carcinoma.
Med Oncol. 2015; 32(8):212 [PubMed] Related Publications
The incidence of kidney cancer has been increasing globally during the past two decades. Renal cell carcinoma (RCC) is the most aggressive subtype of kidney cancer, which usually deteriorates with epithelial-mesenchymal transition (EMT) that facilitates the migration and invasion of cancer cells. Till now, the underlying mechanism remains unclear. In this study, we demonstrated that programmed death ligand 1 (PD-L1/B7-H1/CD274) could induce EMT and enhance RCC cell cancer stemness through up-regulation of SREBP-1c. Furthermore, we found that PD-L1 is up-regulated in human RCC metastases. These results, taken together, provide evidence for a novel mechanism of PD-L1 in RCC progression, suggesting that there is a close relationship between EMT and immune escape signaling pathways in RCC.

Rueda-Rincon N, Bloch K, Derua R, et al.
p53 attenuates AKT signaling by modulating membrane phospholipid composition.
Oncotarget. 2015; 6(25):21240-54 [PubMed] Free Access to Full Article Related Publications
The p53 tumor suppressor is the central component of a complex network of signaling pathways that protect organisms against the propagation of cells carrying oncogenic mutations. Here we report a previously unrecognized role of p53 in membrane phospholipids composition. By repressing the expression of stearoyl-CoA desaturase 1, SCD, the enzyme that converts saturated to mono-unsaturated fatty acids, p53 causes a shift in the content of phospholipids with mono-unsaturated acyl chains towards more saturated phospholipid species, particularly of the phosphatidylinositol headgroup class. This shift affects levels of phosphatidylinositol phosphates, attenuates the oncogenic AKT pathway, and contributes to the p53-mediated control of cell survival. These findings expand the p53 network to phospholipid metabolism and uncover a new molecular pathway connecting p53 to AKT signaling.

Belkaid A, Duguay SR, Ouellette RJ, Surette ME
17β-estradiol induces stearoyl-CoA desaturase-1 expression in estrogen receptor-positive breast cancer cells.
BMC Cancer. 2015; 15:440 [PubMed] Free Access to Full Article Related Publications
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.

Cheng P, Li G, Yang SS, et al.
Tumor suppressor Menin acts as a corepressor of LXRα to inhibit hepatic lipogenesis.
FEBS Lett. 2015; 589(20 Pt B):3079-84 [PubMed] Related Publications
Menin, encoded by the MEN1 gene, was initially identified as a tumor suppressor for endocrine neoplasia. Our previous report showed that Menin enhances PPARα transactivity preventing triglyceride accumulation in the liver. Here, we further explore the role of Menin in liver steatosis. Transient transfection assays demonstrate that Menin inhibits the transcriptional activity of nuclear receptor liver X receptor α (LXRα). Accordingly, Menin overexpression results in reduced expression of LXRα target genes, such as lipogenic enzymes including SREBP-1c, FASN and SCD-1. Co-immunoprecipitation assays revealed physical interaction between Menin and LXRα. Collectively, our data suggest that Menin acts as a novel corepressor of LXRα and functions as a negative regulator of hepatic lipogenesis.

Li S, Oh YT, Yue P, et al.
Inhibition of mTOR complex 2 induces GSK3/FBXW7-dependent degradation of sterol regulatory element-binding protein 1 (SREBP1) and suppresses lipogenesis in cancer cells.
Oncogene. 2016; 35(5):642-50 [PubMed] Free Access to Full Article Related Publications
Cancer cells feature increased de novo lipogenesis. Sterol regulatory element-binding protein 1 (SREBP1), when presented in its mature form (mSREBP1), enhances lipogenesis by increasing transcription of several of its target genes. Mammalian target of rapamycin (mTOR) complexes, mTORC1 and mTORC2, are master regulators of cellular survival, growth and metabolism. A role for mTORC1 in the regulation of SREBP1 activity has been suggested; however, the connection between mTORC2 and SREBP1 has not been clearly established and hence is the focus of this study. mTOR kinase inhibitors (for example, INK128), which inhibit both mTORC1 and mTORC2, decreased mSREBP1 levels in various cancer cell lines. Knockdown of rictor, but not raptor, also decreased mSREBP1. Consistently, reduced mSREBP1 levels were detected in cells deficient in rictor or Sin1 compared with parent or rictor-deficient cells with re-expression of ectopic rictor. Hence it is mTORC2 inhibition that causes mSREBP1 reduction. As a result, expression of the mSREBP1 target genes acetyl-CoA carboxylase and fatty-acid synthase was suppressed, along with suppressed lipogenesis in cells exposed to INK128. Moreover, mSREBP1 stability was reduced in cells treated with INK128 or rictor knockdown. Inhibition of proteasome, GSK3 or the E3 ubiquitin ligase, FBXW7, prevented mSREBP1 reduction induced by mTORC2 inhibition. Thus mTORC2 inhibition clearly facilitates GSK3-dependent, FBXW7-mediated mSREBP1 degradation, leading to mSREBP1 reduction. Accordingly, we conclude that mTORC2 positively regulates mSREBP1 stability and lipogenesis. Our findings reveal a novel biological function of mTORC2 in the regulation of lipogenesis and warrant further study in this direction.

Guan M, Su L, Yuan YC, et al.
Nelfinavir and nelfinavir analogs block site-2 protease cleavage to inhibit castration-resistant prostate cancer.
Sci Rep. 2015; 5:9698 [PubMed] Free Access to Full Article Related Publications
Nelfinavir and its analogs inhibit proliferation and induce apoptosis of castration-resistant prostate cancer through inhibition of site-2 protease (S2P) activity, which leads to suppression of regulated intramembrane proteolysis. Western blotting in nelfinavir and its analog treated cells confirms accumulation of precursor SREBP-1 and ATF6. Nelfinavir and its analogs inhibit human homolog M. jannaschii S2P cleavage of an artificial protein substrate CED-9 in an in vitro proteolysis assay in a dose-dependent manner. Nelfinavir and its analogs are more potent inhibitors of S2P cleavage activity than 1,10-phenanthroline, a metalloprotease-specific inhibitor. Further, cluster analysis of gene expression from treated DU145 and PC3 cell lines demonstrate a close similarity of nelfinavir, its analogs, and 1,10-phenanthroline. These results show nelfinavir and its analogs inhibit castration-resistant prostate cancer proliferation by blocking regulated intramembrane proteolysis through suppression of S2P cleavage activity. This leads to accumulation of precursor SREBP-1 and ATF6, and development of insufficient reserves of their transcriptionally-active forms. The present results validate S2P and regulated intramembrane proteolysis as novel therapeutic targets for castration-resistant prostate cancer therapeutics. A clinical trial of nelfinavir or its analogs should be developed for castration-resistant prostate cancer.

Angelucci C, Maulucci G, Colabianchi A, et al.
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.
Br J Cancer. 2015; 112(10):1675-86 [PubMed] Free Access to Full Article Related Publications
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.

Li L, Yun JH, Ryoo JE, et al.
54G/C polymorphism of SREBF-1 gene is associated with polycystic ovary syndrome.
Eur J Obstet Gynecol Reprod Biol. 2015; 188:95-9 [PubMed] Related Publications
OBJECTIVE: A sterol regulatory element-binding protein (SREBF-1) transcription factor is a major regulator of lipid metabolism, carbohydrate, and plays a key role in energy homeostasis. The 54(G/C) polymorphism of SREBF-1 gene was reported that it is related with metabolic diseases including obesity, type 2 diabetes, and dyslipidemia. Among these, polycystic ovary syndrome (PCOS) is known as a common metabolic-endocrine disorder of women in reproductive ages.
STUDY DESIGN: Here, we performed a comparative study of 54(G/C) polymorphism of SREBF-1 gene with PCOS. The 54(G/C) polymorphism of SREBF-1 gene was analyzed by polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP) of total 286 PCOS patients and 149 matched controls of healthy women. Statistical analysis was performed using HapAnalyzer. A p-value under 0.05 was considered statistically significant.
RESULTS: There was a strong association between the 54(G/C) polymorphism of SREBF-1 gene and PCOS (OR: 0.65, 95% CI: 0.46-0.90, p: 0.0129). The genotype and allelic frequencies were in Hardy-Weinberg equilibrium (HWE).
CONCLUSION: This is the first study on the genetic variation of SREBF-1 gene and PCOS. We concluded that 54(G/C) polymorphism of SREBF-1 gene is associated with PCOS. Therefore, our results suggest that SREBF-1 gene may play a role in genetic predisposition to PCOS, which is helpful in understanding the etiology of PCOS.

Misra UK, Pizzo SV
Activated α2-macroglobulin binding to human prostate cancer cells triggers insulin-like responses.
J Biol Chem. 2015; 290(15):9571-87 [PubMed] Free Access to Full Article Related Publications
Ligation of cell surface GRP78 by activated α2-macroglobulin (α2M*) promotes cell proliferation and suppresses apoptosis. α2M*-treated human prostate cancer cells exhibit a 2-3-fold increase in glucose uptake and lactate secretion, an effect similar to insulin treatment. In both α2M* and insulin-treated cells, the mRNA levels of SREBP1-c, SREBP2, fatty-acid synthase, acetyl-CoA carboxylase, ATP citrate lyase, and Glut-1 were significantly increased together with their protein levels, except for SREBP2. Pretreatment of cells with α2M* antagonist antibody directed against the carboxyl-terminal domain of GRP78 blocks these α2M*-mediated effects, and silencing GRP78 expression by RNAi inhibits up-regulation of ATP citrate lyase and fatty-acid synthase. α2M* induces a 2-3-fold increase in lipogenesis as determined by 6-[(14)C]glucose or 1-[(14)C]acetate incorporation into free cholesterol, cholesterol esters, triglycerides, free fatty acids, and phosphatidylcholine, which is blocked by inhibitors of fatty-acid synthase, PI 3-kinase, mTORC, or an antibody against the carboxyl-terminal domain of GRP78. We also assessed the incorporation of [(14)CH3]choline into phosphatidylcholine and observed similar effects. Lipogenesis is significantly affected by pretreatment of prostate cancer cells with fatostatin A, which blocks sterol regulatory element-binding protein proteolytic cleavage and activation. This study demonstrates that α2M* functions as a growth factor, leading to proliferation of prostate cancer cells by promoting insulin-like responses. An antibody against the carboxyl-terminal domain of GRP78 may have important applications in prostate cancer therapy.

Lewis CA, Brault C, Peck B, et al.
SREBP maintains lipid biosynthesis and viability of cancer cells under lipid- and oxygen-deprived conditions and defines a gene signature associated with poor survival in glioblastoma multiforme.
Oncogene. 2015; 34(40):5128-40 [PubMed] Related Publications
Oxygen and nutrient limitation are common features of the tumor microenvironment and are associated with cancer progression and induction of metastasis. The inefficient vascularization of tumor tissue also limits the penetration of other serum-derived factors, such as lipids and lipoproteins, which can be rate limiting for cell proliferation and survival. Here we have investigated the effect of hypoxia and serum deprivation on sterol regulatory element-binding protein (SREBP) activity and the expression of lipid metabolism genes in human glioblastoma multiforme (GBM) cancer cells. We found that SREBP transcriptional activity was induced by serum depletion both in normoxic and hypoxic cells and that activation of SREBP was required to maintain the expression of fatty acid and cholesterol metabolism genes under hypoxic conditions. Moreover, expression of stearoyl-CoA desaturase, the enzyme required for the generation of mono-unsaturated fatty acids, and fatty acid-binding protein 7, a regulator of glioma stem cell function, was strongly dependent on SREBP function. Inhibition of SREBP function blocked lipid biosynthesis in hypoxic cancer cells and impaired cell survival under hypoxia and in a three-dimensional spheroid model. Finally, gene expression analysis revealed that SREBP defines a gene signature that is associated with poor survival in glioblastoma.

Sun Y, He W, Luo M, et al.
SREBP1 regulates tumorigenesis and prognosis of pancreatic cancer through targeting lipid metabolism.
Tumour Biol. 2015; 36(6):4133-41 [PubMed] Related Publications
Sterol regulatory element-binding protein 1 (SREBP1) is a known transcription factor of lipogenic genes, which plays important roles in regulating de novo lipogenesis. Accumulating evidences indicate SREBP1 is involved in tumorigenesis, yet its role in pancreatic cancer remains unclear. Here, we explored the expression characteristic and function of SREBP1 in pancreatic cancer. Analysis of 60 patients with pancreatic ducat cancer showed that SREBP1 level was significantly higher in pancreatic cancer than that in adjacent normal tissues. High expression of SREBP1 predicted poor prognosis in patients with pancreatic cancer. Multivariate analysis revealed that SREBP1 was an independent factor affecting overall survival. SREBP1 silencing resulted in proliferation inhibition and induction of apoptosis in pancreatic cancer cells. Mechanistically, lipogenic genes (acetyl-CoA carboxylase (ACC), fatty acid synthase (FASN), and stearoyl-CoA desaturase-1 (SCD1)) and de novo lipogenesis were promoted by SREBP1. Inhibition of lipogenic genes through specific inhibitors ablated SREBP1-mediated growth regulation. Furthermore, depletion of SREBP1 could suppress lipid metabolism and tumor growth in vivo. Our results indicate that SREBP1 had important role in tumor progression and appears to be a novel prognostic marker for pancreatic cancer.

Wan L, Tan HL, Thomas-Ahner JM, et al.
Dietary tomato and lycopene impact androgen signaling- and carcinogenesis-related gene expression during early TRAMP prostate carcinogenesis.
Cancer Prev Res (Phila). 2014; 7(12):1228-39 [PubMed] Free Access to Full Article Related Publications
Consumption of tomato products containing the carotenoid lycopene is associated with a reduced risk of prostate cancer. To identify gene expression patterns associated with early testosterone-driven prostate carcinogenesis, which are impacted by dietary tomato and lycopene, wild-type (WT) and transgenic adenocarcinoma of the mouse prostate (TRAMP) mice were fed control or tomato- or lycopene-containing diets from 4 to 10 weeks of age. Eight-week-old mice underwent sham surgery, castration, or castration followed by testosterone repletion (2.5 mg/kg/d initiated 1 week after castration). Ten-week-old intact TRAMP mice exhibit early multifocal prostatic intraepithelial neoplasia. Of the 200 prostate cancer-related genes measured by quantitative NanoString, 189 are detectable, 164 significantly differ by genotype, 179 by testosterone status, and 30 by diet type (P < 0.05). In TRAMP, expression of Birc5, Mki67, Aurkb, Ccnb2, Foxm1, and Ccne2 is greater compared with WT and is decreased by castration. In parallel, castration reduces Ki67-positive staining (P < 0.0001) compared with intact and testosterone-repleted TRAMP mice. Expression of genes involved in androgen metabolism/signaling pathways is reduced by lycopene feeding (Srd5a1) and by tomato feeding (Srd5a2, Pxn, and Srebf1). In addition, tomato feeding significantly reduced expression of genes associated with stem cell features, Aldh1a and Ly6a, whereas lycopene feeding significantly reduced expression of neuroendocrine differentiation-related genes, Ngfr and Syp. Collectively, these studies demonstrate a profile of testosterone-regulated genes associated with early prostate carcinogenesis that are potential mechanistic targets of dietary tomato components. Future studies on androgen signaling/metabolism, stem cell features, and neuroendocrine differentiation pathways may elucidate the mechanisms by which dietary tomato and lycopene impact prostate cancer risk.

Nambiar DK, Deep G, Singh RP, et al.
Silibinin inhibits aberrant lipid metabolism, proliferation and emergence of androgen-independence in prostate cancer cells via primarily targeting the sterol response element binding protein 1.
Oncotarget. 2014; 5(20):10017-33 [PubMed] Free Access to Full Article Related Publications
Prostate cancer (PCA) kills thousands of men every year, demanding additional approaches to better understand and target this malignancy. Recently, critical role of aberrant lipogenesis is highlighted in prostate carcinogenesis, offering a unique opportunity to target it to reduce PCA. Here, we evaluated efficacy and associated mechanisms of silibinin in inhibiting lipid metabolism in PCA cells. At physiologically achievable levels in human, silibinin strongly reduced lipid and cholesterol accumulation specifically in human PCA cells but not in non-neoplastic prostate epithelial PWR-1E cells. Silibinin also decreased nuclear protein levels of sterol regulatory element binding protein 1 and 2 (SREBP1/2) and their target genes only in PCA cells. Mechanistically, silibinin activated AMPK, thereby increasing SREBP1 phosphorylation and inhibiting its nuclear translocation; AMPK inhibition reversed silibinin-mediated decrease in nuclear SREBP1 and lipid accumulation. Additionally, specific SREBP inhibitor fatostatin and stable overexpression of SREBP1 further confirmed the central role of SREBP1 in silibinin-mediated inhibition of PCA cell proliferation and lipid accumulation and cell cycle arrest. Importantly, silibinin also inhibited synthetic androgen R1881-induced lipid accumulation and completely abrogated the development of androgen-independent LNCaP cell clones via targeting SREBP1/2. Together, these mechanistic studies suggest that silibinin would be effective against PCA by targeting critical aberrant lipogenesis.

Lin L, Zheng X, Qiu C, et al.
SIRT1 promotes endometrial tumor growth by targeting SREBP1 and lipogenesis.
Oncol Rep. 2014; 32(6):2831-5 [PubMed] Related Publications
Silent information regulator 1 (SIRT1) is involved in a number of cellular regulatory mechanisms affecting cellular life span, stress resistance, apoptosis and cellular metabolism. Recent studies have revealed that SIRT1 plays a dual role as a tumor suppressor and a tumor promoter in multiple stages of carcinogenesis. Increased lipogenesis has been found in cancer cells, sterol regulatory element binding protein 1 (SREBP1) are nuclear lipogenic transcription factors, which mainly regulate lipogenic processes by activating genes involved in fatty acid and triglyceride biosynthesis. In the present study, we detected expression of SIRT1 in endometrial cancer (EC) and illustrated the relationship between SIRT1 and SREBP1, which indicated that SIRT1 could stimulate endometrial tumor growth through the lipogenic pathway. Gene expression levels of SIRT1 were assayed using quantitative real-time PCR and protein expression levels were detected by western blotting. RNA interference was conducted in order to explore the subsequent effect on tumor cells and on the expression of SREBP1. Expression levels of SIRT1 in EC were found to be significantly higher than in normal endometrium. Knockdown of SIRT1 could downregulate expression of SREBP1 and suppress cell proliferation. These results demonstrated that SIRT1 may play a role as a tumor promoter in EC and can promote endometrial tumor growth by promoting lipogenesis. Our findings suggest that targeting SIRT1 may provide a theoretical basis for the management of EC.

Paland N, Gamliel-Lazarovich A, Coleman R, Fuhrman B
Urokinase-type plasminogen activator (uPA) stimulates triglyceride synthesis in Huh7 hepatoma cells via p38-dependent upregulation of DGAT2.
Atherosclerosis. 2014; 237(1):200-7 [PubMed] Related Publications
OBJECTIVE: The liver is the central organ of fatty acid and triglyceride metabolism. Oxidation and synthesis of fatty acids and triglycerides is under the control of peroxisome-proliferator-activated receptors (PPAR) α. Impairment of these receptors' function contributes to the accumulation of triglycerides in the liver resulting in non-alcoholic fatty liver disease. Urokinase-type plasminogen activator (uPA) was shown to regulate gene expression in the liver involving PPARγ transcriptional activity. In this study we questioned whether uPA modulates triglyceride metabolism in the liver, and investigated the mechanisms involved in the observed processes.
METHODS AND RESULTS: Huh7 hepatoma cells were incubated with increasing concentrations of uPA for 24 h uPA dose-dependently increased the cellular triglyceride mass, and this effect resulted from increased de novo triglyceride synthesis mediated by the enzyme diglyceride acyltransferase 2 (DGAT2). Also, the amount of free fatty acids was highly up regulated by uPA through activation of the transcription factor SREBP-1. Chemical activation of PPARα further increased uPA-stimulated triglyceride synthesis, whereas inhibition of p38, an upstream activator of PPARα, completely abolished the stimulatory effect of uPA on both triglyceride synthesis and DGAT2 upregulation. The effect of uPA on triglyceride synthesis in Huh7 cells was mediated via binding to its receptor, the uPAR. In vivo studies in uPAR(-/-) mice demonstrated that no lipid droplets were observed in their livers compared to C57BL/6 mice and the triglyceride levels were significantly lower.
CONCLUSION: This study presents a new biological function of the uPA/uPAR system in the metabolism of triglycerides and might present a new target for an early therapeutic intervention for NAFLD.

Zhu DQ, Lou YF, He ZG, Ji M
Nucleotidyl transferase TUT1 inhibits lipogenesis in osteosarcoma cells through regulation of microRNA-24 and microRNA-29a.
Tumour Biol. 2014; 35(12):11829-35 [PubMed] Related Publications
Osteosarcoma is the most common type of bone cancer. In the present study, by way of PCR-based microarrays, we found that TUT1, a nucleotidyl transferase, was significantly downregulated in osteosarcoma, compared with adjacent normal tissues. In the current study, we performed PCR-based microarrays using the cDNA prepared from osteosarcoma and adjacent normal tissues. The enforced expression of TUT1 was able to inhibit cell proliferation in U2OS and MG63 cells, while its knockdown using small interfering RNA (siRNA) oligos promoted cell proliferation. At the molecular level, we found that TUT1 could inhibit the expression levels of PPARgamma and SREBP-1c, two key regulators in lipogenesis, through upregulation of microRNA-24 and microRNA-29a. Therefore, our results suggest that TUT1 may act as a tumor suppressor for osteosarcoma, which might provide a novel mechanism for the tumor development.

Zhang H, Feng Z, Huang R, et al.
MicroRNA-449 suppresses proliferation of hepatoma cell lines through blockade lipid metabolic pathway related to SIRT1.
Int J Oncol. 2014; 45(5):2143-52 [PubMed] Related Publications
MicroRNA (miRNA or miR) inhibition of oncogenic related pathways has been shown to be a promising therapeutic approach for cancer. SIRT1 might be a promoter factor on tumorigenesis of hepatocellular carcinoma (HCC). However, the mechanism is unknown. We investigated whether miRNAs regulate the SIRT1 and its downstream SREBP-lipogenesis-cholesterogenesis metabolic pathway in hepatoma cells. Human hepatoma cells were transfected with miR-449 mimics and inhibitors, and the effects of miR-449 on cell proliferation was assessed. We identified the miRNAs, miR-449, that control lipogenesis and cholesterogenesis in hepatoma cells by inhibiting SIRT1 and SREBP-1c expression and downregulating their targeted genes, including fatty acid synthase (FASN) and 3-hydroxy-3-methylglutaryl CoA reductase (HMGCR). MiR-449 repressed DNA synthesis, mitotic entry and proliferation of hepatoma cells. Restoration of miR-449 led to suppression of SIRT1 expression and liver tumorigenesis. The newly identified miRNAs, miR-449 represents a novel targeting mechanism for HCC therapy.

Hamm R, Chen YR, Seo EJ, et al.
Induction of cholesterol biosynthesis by archazolid B in T24 bladder cancer cells.
Biochem Pharmacol. 2014; 91(1):18-30 [PubMed] Related Publications
BACKGROUND: Resistance of cancer cells towards chemotherapeutics represents a major cause of therapy failure. The objective of our study was to evaluate cellular defense strategies in response to the novel vacuolar H(+)-ATPase inhibitor, archazolid B.
EXPERIMENTAL APPROACH: The effects of archazolid B on T24 bladder carcinoma cells were investigated by combining "omics" technologies (transcriptomics (mRNA and miRNA) and proteomics). Free cholesterol distribution was determined by filipin staining using flow cytometry and fluorescence microscopy. Flow cytometry was performed for LDLR surface expression studies. Uptake of LDL cholesterol was visualized by confocal microscopy. SREBP activation was determined performing Western Blotting. The efficiency of archazolid B/fluvastatin combination was tested by cytotoxicity assays.
RESULTS: Archazolid B led to accumulation of free cholesterol within intracellular compartments and drastic disturbances in cholesterol homeostasis resulting in activation of SREBP-2 (sterol regulatory element-binding protein 2) and up-regulation of target genes including HMGCR (HMG-CoA reductase), the key enzyme of cholesterol biosynthesis. LDLR surface expression was reduced and LDL uptake was completely inhibited after 24h, indicating newly synthesized cholesterol to be the main source of cholesterol in archazolid B treated cells. By combining archazolid B with the HMGCR inhibitor fluvastatin, cholesterol was reduced and cell viability decreased by about 20% compared to archazolid B treatment alone.
CONCLUSIONS: Our study revealed cholesterol biosynthesis as an important resistance mechanism in T24 cells after archazolid B treatment. The combination of archazolid B with statins may be an attractive strategy to potentiate archazolid B induced cell killing by affecting cholesterol biosynthesis.

Li C, Yang W, Zhang J, et al.
SREBP-1 has a prognostic role and contributes to invasion and metastasis in human hepatocellular carcinoma.
Int J Mol Sci. 2014; 15(5):7124-38 [PubMed] Free Access to Full Article Related Publications
Sterol regulatory element-binding protein 1 (SREBP-1) is a well-known nuclear transcription factor involved in lipid synthesis. Recent studies have focused on its functions in tumor cell proliferation and apoptosis, but its role in cell migration and invasion, especially in hepatocellular carcinoma (HCC), is still unclear. In this study, we found that the expression of SREBP-1 in HCC tissues was significantly higher than those in matched tumor-adjacent tissues (p < 0.05). SREBP-1 was expressed at significantly higher levels in patients with large tumor size, high histological grade and advanced tumor-node-metastasis (TNM) stage (p < 0.05). The positive expression of SREBP-1 correlated with a worse 3-year overall and disease-free survival of HCC patients (p < 0.05). Additionally, SREBP-1 was an independent factor for predicting both 3-year overall and disease-free survival of HCC patients (p < 0.05). In vitro studies revealed that downregulation of SREBP-1 inhibited cell proliferation and induced apoptosis in both HepG2 and MHCC97L cells (p < 0.05). Furthermore, wound healing and transwell assays showed that SREBP-1 knockdown prominently inhibited cell migration and invasion in both HepG2 and MHCC97L cells (p < 0.05). These results suggest that SREBP-1 may serve as a prognostic marker in HCC and may promote tumor progression by promoting cell growth and metastasis.

Nakakuki M, Kawano H, Notsu T, et al.
A novel processing system of sterol regulatory element-binding protein-1c regulated by polyunsaturated fatty acid.
J Biochem. 2014; 155(5):301-13 [PubMed] Related Publications
The proteolytic cascade is the key step in transactivation of sterol regulatory element-binding proteins (SREBPs), a transcriptional factor of lipid synthesis. Proteolysis of SREBP-2 is strictly regulated by sterols, but that of SREBP-1c was not strongly sterol-regulated, but inhibited by polyunsaturated fatty acids (PUFAs). In this study, the proteolytic processing of SREBP-1 and -2 was examined by transfection studies of cDNA-encoding mutants in which all the known cleavage sites were disrupted. In cultured cells, sterol-regulated SREBP-2 processing was completely eliminated by mutation of cleavage sites. In contrast, the corresponding SREBP-1c mutants as well as wild type exhibited large amounts of cleaved products in the nuclear extracts from culture cells and murine liver in vivo. The nuclear form of the mutant SREBP-1c was induced by delipidated condition and suppressed by eicosapentaenoic acid, an n-3 PUFA, but not by sterols. This novel processing mechanism was affected by neither SREBP cleavage-activating protein (SCAP) nor insulin-induced gene (Insig)-1, unlike SREBP-2, but abolished by a serine protease inhibitor. Through analysis of deletion mutant, a site-2 protease recognition sequence (DRSR) was identified to be involved in this novel processing. These findings suggest that SREBP-1c cleavage could be subjected to a novel PUFA-regulated cleavage system in addition to the sterol-regulatory SCAP/Insig system.

Qiu CP, Lv QT, Dongol S, et al.
Single nucleotide polymorphism of SREBF-1 gene associated with an increased risk of endometrial cancer in Chinese women.
PLoS One. 2014; 9(3):e90491 [PubMed] Free Access to Full Article Related Publications
AIM: Elevated levels of sterol regulatory element-binding protein-1 (SREBP-1) have been found in endometrial cancer (EC), suggesting that it is essential to the development of EC. Obesity and diabetes have been established as known risk factors of EC, while SREBF-1 gene polymorphisms have also been found to be associated with obesity and type II diabetes. Therefore, we hypothesize that single nucleotide polymorphism (SNP) in SREBF-1 gene may be associated with increased risk of EC.
METHOD: We analyzed the sequence of SREBF-1 in tissue samples from 30 EC cases and 6 benign controls using high throughput method. Based on the primary results, we selected one SNP (rs2297508) as a genetic marker to conduct a hospital-based case-control study with 139 EC cases and 129 benign controls. The samples were examined under the microscope to determine their histopathology prior to the SNP analysis using RT-PCR.
RESULTS: Through sequence analysis, we found 10 SNPs of SREBF-1 associated with EC, including 3 new SNPs. Fourteen percent of EC showed the rs2297508 SNP with C allele, while only 7% had the C allele was present in benign controls (p = 0.027, OR = 1.983). Additionally, the C allele was associated with cancer differentiation (p<0.05) and the depth of myometrial invasion (p<0.05).
CONCLUSION: Our study indicates that SNP (rs2297508) of SREBF-1 may serve as a genetic predisposition factor for the development of EC and screening of such genetic marker may be helpful in its early detection.

Zhao F, Xie P, Jiang J, et al.
The effect and mechanism of tamoxifen-induced hepatocyte steatosis in vitro.
Int J Mol Sci. 2014; 15(3):4019-30 [PubMed] Free Access to Full Article Related Publications
The aim of this study was to determine the effect and mechanism of tamoxifen (TAM)-induced steatosis in vitro. HepG 2 (Human hepatocellular liver carcinoma cell line) cells were treated with different concentrations of TAM for 72 h. Steatosis of hepatocytes was determined after Oil Red O staining and measurement of triglyceride (TG) concentration. The expressions of genes in the TG homeostasis pathway, including sterol regulatory element-binding protein-1c (SREBP-1c), peroxisome proliferator-activated receptor γ (PPARγ), CCAAT/enhancer-binding protein α (C/EBPα), fatty acid synthase (FAS), acetyl-CoA carboxylase (ACC), stearoyl-CoA desaturase (SCD), carnitine palmitoyltransferase 1 (CPT1) and microsomal triglyceride transfer protein (MTP), were examined using quantitative real-time PCR and Western blot analysis. Cell proliferation was examined using the cell counting kit-8 (CCK-8) assay. We found that hepatocytes treated with TAM had: (1) induced hepatocyte steatosis and increased hepatocyte TG; (2) upregulation of SREBP-1c, FAS, ACC, SCD and MTP mRNA expressions (300%, 600%, 70%, 130% and 160%, respectively); (3) corresponding upregulation of protein expression; and (4) no difference in HepG 2 cell proliferation. Our results suggest that TAM can induce hepatocyte steatosis in vitro and that the enhancement of fatty acid synthesis through the upregulations of SREBP-1c and its downstream target genes (FAS, ACC and SCD) may be the key mechanism of TAM-induced hepatocyte steatosis.

Yun HJ, Kim JY, Kim G, Choi HS
Prolyl-isomerase Pin1 impairs trastuzumab sensitivity by up-regulating fatty acid synthase expression.
Anticancer Res. 2014; 34(3):1409-16 [PubMed] Related Publications
BACKGROUND/AIM: Clinical trials have shown efficacy of the anti-HER2 monoclonal antibody trastuzumab in metastatic breast cancer patients. The aim of the present study was to elucidate the mechanisms by which up-regulation of fatty acid synthase (FAS) expression confers resistance to trastuzumab in HER2-positive breast cancers.
MATERIALS AND METHODS: The expression of FAS as well as the cytotoxic effects of combinatorial treatment of trastuzumab and juglone was investigated by immunoblotting, BrdU incorporation, TUNEL assay, and soft agar assay.
RESULTS: Pin1 enhanced EGF-induced SREBP1c promoter activity, resulting in the induction of FAS expression in BT474 cells. In contrast, juglone, a potent Pin1 inhibitor, significantly enhanced trastuzumab-induced FAS down-regulation and cell death in BT474 cells. Furthermore, trastuzumab, when used in combination with gene silencing or chemical inhibition of Pin1, increased cleaved poly(ADP-ribose) polymerase and DNA fragmentation to increase trastuzumab sensitivity.
CONCLUSION: Pin1-mediated FAS overexpression is a major regulator of trastuzumab-resistant breast cancer growth and survival.

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