Gene Summary

Gene:APOE; apolipoprotein E
Aliases: AD2, LPG, APO-E, LDLCQ5
Summary:The protein encoded by this gene is a major apoprotein of the chylomicron. It binds to a specific liver and peripheral cell receptor, and is essential for the normal catabolism of triglyceride-rich lipoprotein constituents. This gene maps to chromosome 19 in a cluster with the related apolipoprotein C1 and C2 genes. Mutations in this gene result in familial dysbetalipoproteinemia, or type III hyperlipoproteinemia (HLP III), in which increased plasma cholesterol and triglycerides are the consequence of impaired clearance of chylomicron and VLDL remnants. Alternative splicing results in multiple transcript variants. [provided by RefSeq, Nov 2014]
Databases:OMIM, VEGA, HGNC, Ensembl, GeneCard, Gene
Protein:apolipoprotein E
Source:NCBIAccessed: 16 March, 2015


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 (1990-2015)
Graph generated 16 March 2015 using data from PubMed using criteria.

Literature Analysis

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Tag cloud generated 16 March, 2015 using data from PubMed, MeSH and CancerIndex

Specific Cancers (5)

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: APOE (cancer-related)

Correa DD, Satagopan J, Baser RE, et al.
APOE polymorphisms and cognitive functions in patients with brain tumors.
Neurology. 2014; 83(4):320-7 [PubMed] Article available free on PMC after 22/07/2015 Related Publications
OBJECTIVE: The goal of this study was to assess whether the APOE ε4 allele and other APOE single nucleotide polymorphisms (SNPs) influence neuropsychological and neuroimaging outcomes in patients with brain tumors.
METHODS: Two hundred eleven patients with brain tumors participated in the study. All patients completed standardized neuropsychological tests and provided a blood sample for APOE genotyping. Ratings of white matter abnormalities were performed on MRI scans. Patients were classified into 2 groups based on the presence (n = 50) or absence (n = 161) of at least one APOE ε4 allele. Additional APOE SNPs were genotyped in a subset of 150 patients.
RESULTS: Patients with at least one APOE ε4 allele had significantly lower scores in verbal learning and delayed recall, and marginally significant lower scores in executive function, in comparison to noncarriers of an ε4 allele. Patients with at least one ε4 allele and history of cigarette smoking had significantly higher scores in working memory and verbal learning than ε4 carriers who never smoked. Nine additional APOE SNPs were significantly associated with attention and executive and memory abilities. There were no significant differences between ε4 carriers and noncarriers on the extent of white matter abnormalities on MRI.
CONCLUSIONS: The findings suggest that patients with brain tumors who are carriers of the APOE ε4 allele may have increased vulnerability to developing memory and executive dysfunction, and that additional SNPs in the APOE gene may be associated with cognitive outcome.

Liu Y, Wang X, Li S, et al.
The role of von Willebrand factor as a biomarker of tumor development in hepatitis B virus-associated human hepatocellular carcinoma: a quantitative proteomic based study.
J Proteomics. 2014; 106:99-112 [PubMed] Related Publications
UNLABELLED: Chronic hepatitis B virus (HBV) infection is a major risk factor for hepatocellular carcinoma (HCC), the sixth most common cancer worldwide. To explore potential biomarkers for HCC, iTRAQ coupled with mass spectrometry was used to analyze proteins in plasma from individuals with HBV-associated HCC, nonmalignant cirrhosis, chronic hepatitis B, and healthy individuals. Twenty-one aberrantly expressed proteins were identified from HCC patients as compared with nontumor controls. Overexpression of von Willebrand factor (vWF) was confirmed by Western blotting, and immunohistochemical analysis from liver biopsies and ELISA from plasma samples revealed a correlation between vWF expression and HCC clinicopathologic staging. Furthermore, siRNA-induced vWF silencing reduced HBV replication by over two-fold via the interferon-signaling pathway and impaired the invasion and migration of HCC cells in vitro. These results indicate that vWF can serve as a biomarker, and perhaps an alternative target for therapeutic intervention of HCC progression and HBV viral infection.
BIOLOGICAL SIGNIFICANCE: We report comparative plasma proteome profiles of HBV-associated HCC and nonmalignant chronic liver diseases, including chronic hepatitis B and cirrhosis. The quantification of these datasets showed altered abundance of 21 proteins in HBV-related HCC and provides a reference point for future applied and basic research. In addition, we have demonstrated that the candidate protein vWF is involved in the pathogenesis of HBV infection and replication, and also associated with clinicopathologic staging of HCC patients with HBV infection. Overall these findings provide information on the mechanism of HCC development, which may assist in the development of novel cancer and HBV therapeutic drugs.

Papi A, De Carolis S, Bertoni S, et al.
PPARγ and RXR ligands disrupt the inflammatory cross-talk in the hypoxic breast cancer stem cells niche.
J Cell Physiol. 2014; 229(11):1595-606 [PubMed] Related Publications
Cancer stem cells (CSCs) are affected by the local micro-environment, the niche, in which inflammatory stimuli and hypoxia act as steering factors. Here, two nuclear receptors (NRs) agonists, i.e. pioglitazone (PGZ), a ligand of peroxisome proliferator activated receptor-γ, and 6-OH-11-O-hydroxyphenanthrene (IIF), a ligand of retinoid X receptors, were investigated for their capability to interference with the cross-talk between breast CSCs and the niche compartment. We found that IIF potentiates the ability of PGZ to hamper the mammospheres-forming capability of human breast tumours and MCF7 cancer cells, reducing the expression of CSCs regulatory genes (Notch3, Jagged1, SLUG, Interleukin-6, Apolipoprotein E, Hypoxia inducible factor-1α and Carbonic anhydrase IX). Notably, these effects are not observed in normal-MS obtained from human breast tissue. Importantly, NRs agonists abolish the capability of hypoxic MCF7 derived exosomes to induce a pro-inflammatory phenotype in mammary glands fibroblasts. Moreover, NRs agonist also directly acts on breast tumour associated fibroblasts to downregulate nuclear factor-κB pathway and metalloproteinases (MMP2 and MMP9) expression and activity. In conclusion, NRs agonists disrupt the inflammatory cross-talk of the hypoxic breast CSCs niche.

Pencheva N, Buss CG, Posada J, et al.
Broad-spectrum therapeutic suppression of metastatic melanoma through nuclear hormone receptor activation.
Cell. 2014; 156(5):986-1001 [PubMed] Related Publications
Melanoma metastasis is a devastating outcome lacking an effective preventative therapeutic. We provide pharmacologic, molecular, and genetic evidence establishing the liver-X nuclear hormone receptor (LXR) as a therapeutic target in melanoma. Oral administration of multiple LXR agonists suppressed melanoma invasion, angiogenesis, tumor progression, and metastasis. Molecular and genetic experiments revealed these effects to be mediated by LXRβ, which elicits these outcomes through transcriptional induction of tumoral and stromal apolipoprotein-E (ApoE). LXRβ agonism robustly suppressed tumor growth and metastasis across a diverse mutational spectrum of melanoma lines. LXRβ targeting significantly prolonged animal survival, suppressed the progression of established metastases, and inhibited brain metastatic colonization. Importantly, LXRβ activation displayed melanoma-suppressive cooperativity with the frontline regimens dacarbazine, B-Raf inhibition, and the anti-CTLA-4 antibody and robustly inhibited melanomas that had acquired resistance to B-Raf inhibition or dacarbazine. We present a promising therapeutic approach that uniquely acts by transcriptionally activating a metastasis suppressor gene.

Kulminski AM, Arbeev KG, Culminskaya I, et al.
Age, gender, and cancer but not neurodegenerative and cardiovascular diseases strongly modulate systemic effect of the Apolipoprotein E4 allele on lifespan.
PLoS Genet. 2014; 10(1):e1004141 [PubMed] Article available free on PMC after 22/07/2015 Related Publications
Enduring interest in the Apolipoprotein E (ApoE) polymorphism is ensured by its evolutionary-driven uniqueness in humans and its prominent role in geriatrics and gerontology. We use large samples of longitudinally followed populations from the Framingham Heart Study (FHS) original and offspring cohorts and the Long Life Family Study (LLFS) to investigate gender-specific effects of the ApoE4 allele on human survival in a wide range of ages from midlife to extreme old ages, and the sensitivity of these effects to cardiovascular disease (CVD), cancer, and neurodegenerative disorders (ND). The analyses show that women's lifespan is more sensitive to the e4 allele than men's in all these populations. A highly significant adverse effect of the e4 allele is limited to women with moderate lifespan of about 70 to 95 years in two FHS cohorts and the LLFS with relative risk of death RR = 1.48 (p = 3.6 × 10(-6)) in the FHS cohorts. Major human diseases including CVD, ND, and cancer, whose risks can be sensitive to the e4 allele, do not mediate the association of this allele with lifespan in large FHS samples. Non-skin cancer non-additively increases mortality of the FHS women with moderate lifespans increasing the risks of death of the e4 carriers with cancer two-fold compared to the non-e4 carriers, i.e., RR = 2.07 (p = 5.0 × 10(-7)). The results suggest a pivotal role of non-sex-specific cancer as a nonlinear modulator of survival in this sample that increases the risk of death of the ApoE4 carriers by 150% (p = 5.3 × 10(-8)) compared to the non-carriers. This risk explains the 4.2 year shorter life expectancy of the e4 carriers compared to the non-carriers in this sample. The analyses suggest the existence of age- and gender-sensitive systemic mechanisms linking the e4 allele to lifespan which can non-additively interfere with cancer-related mechanisms.

Ozen F, Polat F, Arslan S, Ozdemir O
Combined germline variations of thrombophilic genes promote genesis of lung cancer.
Asian Pac J Cancer Prev. 2013; 14(9):5449-54 [PubMed] Related Publications
BACKGROUND: A large variety of familiar and non-familiar lung carcinomas (LC) are caused by long term exposure to chemical carcinogens that are present in tobacco smoke. We aimed to investigate the prevalence of 5 thrombophilic germ-line mutations in patients with lung carcinomas.
MATERIALS AND METHODS: A total of 52 LC patients and 212 healthy controls from same population were analyzed for FV Leiden, factor V H1299R (R2), PAI-1, MTHFR C677T, MTHFR A1298C, ACE I/D, and Apo E genes and compared.
RESULTS: Overall, heterozygous and/or homozygous point mutations in FV Leiden Apo E2, PAI-1 and MTHFR C677T genes were associated with LC in the current cohort. There was no meaningful association between LC and ACE I/D gene markers.
CONCLUSIONS: The current results showed that LC is related to combined thrombophilic gene mutations and individuals with homozygosity of 4G in PAI-1 and MTHFR C677T genes and heterozygosity of FV Leiden, Apo E4 genes have a germ-line risk for LC tumorigenesis.

Kim HJ, Moon JH, Kim HM, et al.
The hypolipidemic effect of cilostazol can be mediated by regulation of hepatic low-density lipoprotein receptor-related protein 1 (LRP1) expression.
Metabolism. 2014; 63(1):112-9 [PubMed] Related Publications
OBJECTIVES: Cilostazol, a selective phosphodiesterase 3 (PDE3) inhibitor, is a vasodilator and an anti-thrombotic agent. The mechanism whereby cilostazol reduces plasma triglyceride is not completely understood. Here we investigated the effect of cilostazol on a remnant lipoprotein receptor, low-density lipoprotein receptor-related protein 1 (LRP1), which has been reported to play an essential role in clearance of circulating triglyceride in the liver.
MATERIALS/METHODS: Total cellular expression, and functional and transcriptional regulation of LRP1 were analyzed in human hepatocarcinoma cell lines incubated with cilostazol. Also, C57BL/6 mice were subjected to high-fat diet (60% kcal) and cilostazol (30 mg/kg) treatment for 10 weeks.
RESULTS: Cilostazol increased both mRNA and protein expression of LRP1 in HepG2 and Hep3B cells. In addition, enhanced transcriptional activity of the LRP1 promoter containing a peroxisome proliferator response element (PPRE) was observed after cilostazol exposure. Cilostazol treatment enhanced the uptake of lipidated apoE3, and this effect was abolished when LRP1 was silenced by siRNA knockdown. High-fat diet induced hyperglycemia with high level of plasma triglycerides, and reduced hepatic LRP1 expression in mice. Treatment with cilostazol for the same period of time, however, successfully prevented this down-regulation of LRP1 expression and reduced plasma triglycerides.
CONCLUSION: Taken together, our results demonstrated that cilostazol enhances LRP1 expression in liver by activating PPARγ through the PPRE in the LRP1 promoter. Increased hepatic LRP1 may be essential for the reduction of circulating triglycerides brought about by cilostazol.

Caselli RJ
Does an Alzheimer's disease susceptibility gene influence the cognitive effects of cancer therapy?
Pediatr Blood Cancer. 2014; 61(10):1739-42 [PubMed] Related Publications
The apolipoprotein E (APOE) e4 allele is the most prevalent genetic risk factor for Alzheimer's disease (AD). APOE e4 carriers suffer greater morbidity from head trauma, stroke, and carbon monoxide poisoning, yet possible interactions between APOE genotype and cancer therapy on cognition are unclear. Neuropathological and biomarker studies of young asymptomatic APOE e4 carriers that show elevated neocortical amyloid and medial temporal neurofibrillary tangles and longitudinal neuropsychological studies that show accelerated memory decline beginning around age 55-60 years define preclinical AD and have set the stage for assessing the potential adverse cognitive effects of cancer therapy in APOE e4 carriers.

Däumer C, Flachsbart F, Caliebe A, et al.
Adjustment for smoking does not alter the FOXO3A association with longevity.
Age (Dordr). 2014; 36(2):911-21 [PubMed] Article available free on PMC after 01/04/2015 Related Publications
Human longevity is a multifactorial phenotype influenced by both genetic and environmental factors. Despite its heritability of 25-32 %, the genetic background of longevity is as yet largely unexplained. Apart from APOE status, variation in the FOXO3A gene is the only confirmed genetic contributor to survival into old age. On the other hand, FOXO3A activity is known to be downregulated in various cancers, and the gene was recently identified as a novel deletion hotspot in human lung adenocarcinoma. In view of the strong association between smoking and lung cancer, we set out to explore whether smoking modifies the known association between FOXO3A variation and longevity. To this end, we conducted a case-control study in two different populations, drawing upon extensive collections of old-aged individuals and younger controls available to us (1,613 German centenarians/nonagenarians and 1,104 controls; 1,088 Danish nonagenarians and 736 controls). In the German sample, 21 single nucleotide polymorphisms (SNPs) from the FOXO3A gene region were genotyped, whereas 15 FOXO3A SNPs were analyzed in the Danish sample. Eight SNPs were typed in both populations. Logistic regression analysis revealed that adjustment for smoking does not systematically alter the association between FOXO3A variation and longevity in neither population. Our analysis therefore suggests that the said association is not largely due to the confounding effects of lung cancer.

Ifere GO, Desmond R, Demark-Wahnefried W, Nagy TR
Apolipoprotein E gene polymorphism influences aggressive behavior in prostate cancer cells by deregulating cholesterol homeostasis.
Int J Oncol. 2013; 43(4):1002-10 [PubMed] Article available free on PMC after 01/04/2015 Related Publications
High circulating cholesterol and its deregulated homeostasis may facilitate prostate cancer progression. Genetic polymorphism in Apolipoprotein (Apo) E, a key cholesterol regulatory protein may effect changes in systemic cholesterol levels. In this investigation, we determined whether variants of the Apo E gene can trigger defective intracellular cholesterol efflux, which could promote aggressive prostate cancer. ApoE genotypes of weakly (non-aggressive), moderate and highly tumorigenic (aggressive) prostate cancer cell lines were characterized, and we explored whether the ApoE variants were associated with tumor aggressiveness generated by intra-cellular cholesterol imbalance, using the expression of caveolin-1 (cav-1), a pro-malignancy surrogate of cholesterol overload. Restriction isotyping of ApoE isoforms revealed that the non-aggressive cell lines carried ApoE ε3/ε3 or ε3/ε4 alleles, while the aggressive cell lines carried the Apoε2/ε4 alleles. Our data suggest a contrast between the non-aggressive and the aggressive prostate cancer cell lines in the pattern of cholesterol efflux and cav-1 expression. Our exploratory results suggest a relationship between prostate aggressiveness, ApoE isoforms and cholesterol imbalance. Further investigation of this relationship may elucidate the molecular basis for considering cholesterol as a risk factor of aggressive prostate tumors, and underscore the potential of the dysfunctional ApoE2/E4 isoform as a biomarker of aggressive disease.

Gaibar M, Fernández G, Romero-Lorca A, et al.
Tamoxifen therapy in breast cancer: do apolipoprotein E genotype and menopausal state affect plasma lipid changes induced by the drug?
Int J Biol Markers. 2013 Oct-Dec; 28(4):e371-6 [PubMed] Related Publications
OBJECTIVE: This study examines the lipid profile change produced in response to tamoxifen (TAM) treatment, and its possible relationship with both apolipoprotein E genotype and menopausal state in patients with breast cancer.
METHODS: Blood samples were collected from 86 Spanish women with breast cancer before initiating TAM treatment and in the following 6, 12 and 18 months of treatment. Plasma lipid levels (total cholesterol, triglycerides, HDL-cholesterol and LDL-cholesterol) were determined using an automatic analyzer. Genotypes for apolipoprotein E (ApoE) were identified by PCR-RFLP using the HhaI enzyme.
RESULTS: In all patients, significant reductions in total cholesterol and LDL-cholesterol concentrations and a significant increase in triglyceride concentrations were observed after 6, 12, and 18 months of TAM treatment compared to baseline (p<0.01 for each time point). In the subset of APOE4-negative patients, triglyceride concentrations also significantly increased after 6, 12, and 18 months of treatment (p=0.019, p=0.045, p=0.001, respectively), while APOE4-positive patients showed no significant lipid changes at 12 and 18 months. However, after 18 months of TAM treatment the overall triglyceride concentrations had risen by 24.75% in APOE4-negative patients vs 29.9% in APOE4-positive patients. In postmenopausal women, significant reductions in total cholesterol, LDL-cholesterol and LDL/HDL ratios were observed at each time point (p<0.020 for each).
CONCLUSIONS: TAM treatment induced similar plasma triglyceride increases in patients with positive or negative APOE genotype. Compared to premenopausal patients, postmenopausal breast cancer patients showed a more beneficial lipid profile change in response to treatment.

Liu HW, Zhang F, Fan P, et al.
Effects of apolipoprotein E genotypes on metabolic profile and oxidative stress in southwest Chinese women with polycystic ovary syndrome.
Eur J Obstet Gynecol Reprod Biol. 2013; 170(1):146-51 [PubMed] Related Publications
OBJECTIVE: Apolipoprotein (APO) E genetic polymorphism plays an important role in lipid and lipoprotein metabolism, and has been shown to be associated with the risk of metabolic and cardio-cerebrovascular diseases and late-onset Alzheimer's disease. It is not clear, however, whether there are any relationships between the APOE genotypes and PCOS in Chinese women. The aim of this study was to investigate the relationship between APOE genotypes and the risk of polycystic ovary syndrome (PCOS) and to evaluate the effects of the genotypes on metabolic profile and oxidative stress in south-west Chinese women.
STUDY DESIGN: A total of 625 patients with PCOS based on the Rotterdam consensus criteria and 514 control women from a population of Chinese Han nationality in the Chengdu area were studied during 2006-2012. APOE genotypes were determined by PCR and restriction fragment length polymorphism analysis. Clinical and metabolic parameters, serum malondialdehyde concentration, and total antioxidant capacity were analyzed.
RESULTS: No significant differences were found in the frequencies of APOE genotypes (E2/2, E2/3, E2/4, E3/3, E3/4, E4/4) and alleles (ε2, ε3, ε4) between PCOS and control groups. Compared with ε3 homozygotes (APOE3/3), however, ε2 carriers (APOE2/2+APOE2/3+APOE2/4) had significantly higher body mass index, waist circumference and waist-to-hip ratio, a more adverse glucose and insulin metabolic profile, lower high density lipoprotein (HDL)-cholesterol (C) and APOA1 levels, higher triglyceride (TG)/HDL-C ratio and prevalence of metabolic syndrome (MS), whereas ε4 carriers (APOE3/4+APOE4/4) had higher total cholesterol (TC) and low density lipoprotein (LDL)-C levels in patients with PCOS.
CONCLUSIONS: In a cohort of south-west Chinese women, there were no significant associations between any APOE genotype and PCOS. The APOE ε2 allele seems to be related to abdominal obesity, insulin resistance and MS in PCOS women.

Sia KC, Huynh H, Chung AY, et al.
Preclinical evaluation of transcriptional targeting strategy for human hepatocellular carcinoma in an orthotopic xenograft mouse model.
Mol Cancer Ther. 2013; 12(8):1651-64 [PubMed] Related Publications
Gene regulation of many key cell-cycle players in S-, G(2) phase, and mitosis results from transcriptional repression in their respective promoter regions during the G(0) and G(1) phases of cell cycle. Within these promoter regions are phylogenetically conserved sequences known as the cell-cycle-dependent element (CDE) and cell-cycle genes homology regions (CHR) sites. Thus, we hypothesize that transcriptional regulation of cell-cycle regulation via the CDE/CHR region together with liver-specific apolipoprotein E (apoE)-hAAT promoter could bring about a selective transgene expression in proliferating human hepatocellular carcinoma. We show that the newly generated vector AH-6CC-L2C could mediate hepatocyte-targeted luciferase gene expression in tumor cells and freshly isolated short-term hepatocellular carcinoma cultures from patient biopsy. In contrast, normal murine and human hepatocytes infected with AH-6CC-L2C expressed minimal or low luciferase activities. In the presence of prodrug 5-fluorocytosine (5-FC), AH-6CC-L2C effectively suppressed the growth of orthotopic hepatocellular carcinoma patient-derived xenograft mouse model via the expression of yeast cytosine deaminase (yCD) that converts 5-FC to anticancer metabolite 5-fluoruracil. More importantly, we show that combination treatment of AH-6CC-L2C with an EZH2 inhibitor, DZNep, that targets EpCAM-positive hepatocellular carcinoma, can bring about a greater therapeutic efficacy compared with a single treatment of virus or inhibitor. Our study showed that targeting proliferating human hepatocellular carcinoma cells through the transcriptional control of therapeutic gene could represent a feasible approach against hepatocellular carcinoma.

Papi A, Storci G, Guarnieri T, et al.
Peroxisome proliferator activated receptor-α/hypoxia inducible factor-1α interplay sustains carbonic anhydrase IX and apoliprotein E expression in breast cancer stem cells.
PLoS One. 2013; 8(1):e54968 [PubMed] Article available free on PMC after 01/04/2015 Related Publications
AIMS: Cancer stem cell biology is tightly connected to the regulation of the pro-inflammatory cytokine network. The concept of cancer stem cells "inflammatory addiction" leads to envisage the potential role of anti-inflammatory molecules as new anti-cancer targets. Here we report on the relationship between nuclear receptors activity and the modulation of the pro-inflammatory phenotype in breast cancer stem cells.
METHODS: Breast cancer stem cells were expanded as mammospheres from normal and tumor human breast tissues and from tumorigenic (MCF7) and non tumorigenic (MCF10) human breast cell lines. Mammospheres were exposed to the supernatant of breast tumor and normal mammary gland tissue fibroblasts.
RESULTS: In mammospheres exposed to the breast tumor fibroblasts supernatant, autocrine tumor necrosis factor-α signalling engenders the functional interplay between peroxisome proliferator activated receptor-α and hypoxia inducible factor-1α (PPARα/HIF1α). The two proteins promote mammospheres formation and enhance each other expression via miRNA130b/miRNA17-5p-dependent mechanism which is antagonized by PPARγ. Further, the PPARα/HIF1α interplay regulates the expression of the pro-inflammatory cytokine interleukin-6, the hypoxia survival factor carbonic anhydrase IX and the plasma lipid carrier apolipoprotein E.
CONCLUSION: Our data demonstrate the importance of exploring the role of nuclear receptors (PPARα/PPARγ) in the regulation of pro-inflammatory pathways, with the aim to thwart breast cancer stem cells functioning.

Pencheva N, Tran H, Buss C, et al.
Convergent multi-miRNA targeting of ApoE drives LRP1/LRP8-dependent melanoma metastasis and angiogenesis.
Cell. 2012; 151(5):1068-82 [PubMed] Article available free on PMC after 01/04/2015 Related Publications
Through in vivo selection of human cancer cell populations, we uncover a convergent and cooperative miRNA network that drives melanoma metastasis. We identify miR-1908, miR-199a-5p, and miR-199a-3p as endogenous promoters of metastatic invasion, angiogenesis, and colonization in melanoma. These miRNAs convergently target apolipoprotein E (ApoE) and the heat shock factor DNAJA4. Cancer-secreted ApoE suppresses invasion and metastatic endothelial recruitment (MER) by engaging melanoma cell LRP1 and endothelial cell LRP8 receptors, respectively, while DNAJA4 promotes ApoE expression. Expression levels of these miRNAs and ApoE correlate with human metastatic progression outcomes. Treatment of cells with locked nucleic acids (LNAs) targeting these miRNAs inhibits metastasis to multiple organs, and therapeutic delivery of these LNAs strongly suppresses melanoma metastasis. We thus identify miRNAs with dual cell-intrinsic/cell-extrinsic roles in cancer, reveal convergent cooperativity in a metastatic miRNA network, identify ApoE as an anti-angiogenic and metastasis-suppressive factor, and uncover multiple prognostic miRNAs with synergistic combinatorial therapeutic potential in melanoma.

De Feo E, Simone B, Persiani R, et al.
A case-control study on the effect of Apolipoprotein E genotypes on gastric cancer risk and progression.
BMC Cancer. 2012; 12:494 [PubMed] Article available free on PMC after 01/04/2015 Related Publications
BACKGROUND: Apolipoprotein E (ApoE) is a multifunctional protein playing both a key role in the metabolism of cholesterol and triglycerides, and in tissue repair and inflammation. The ApoE gene (19q13.2) has three major isoforms encoded by ε2, ε3 and ε4 alleles with the ε4 allele associated with hypercholesterolemia and the ε2 allele with the opposite effect. An inverse relationship between cholesterol levels and gastric cancer (GC) has been previously reported, although the relationship between apoE genotypes and GC has not been explored so far.
METHODS: One hundred and fifty-six gastric cancer cases and 444 hospital controls were genotyped for apoE polymorphism (ε2, ε3, ε4 alleles). The relationship between GC and putative risk factors was measured using the adjusted odds ratios (ORs) and their 95% confidence intervals (CIs) from logistic regression analysis. A gene-environment interaction analysis was performed. The effect of the apoE genotypes on survival from GC was explored by a Kaplan-Meier analysis and Cox proportional hazard regression model.
RESULTS: Subjects carrying at least one apoE ε2 allele have a significant 60% decrease of GC risk (OR=0.40, 95% CI: 0.19 - 0.84) compared with ε3 homozygotes. No significant interaction emerged between the ε4 or ε2 allele and environmental exposures, nor ε2 or ε4 alleles affected the median survival times, even after correcting for age, gender and stadium.
CONCLUSIONS: Our study reports for the first time a protective effect of the ε2 allele against GC, that might be partly attributed to the higher antioxidant properties of ε2 compared with the ε3 or ε4 alleles. Given the study's sample size, further studies are required to confirm our findings.

Kulminski AM, Culminskaya I, Arbeev KG, et al.
Trade-off in the effect of the APOE gene on the ages at onset of cardiocascular disease and cancer across ages, gender, and human generations.
Rejuvenation Res. 2013; 16(1):28-34 [PubMed] Article available free on PMC after 01/04/2015 Related Publications
Decades of studies of candidate genes show their complex role in aging-related traits. We focus on apolipoprotein E e2/3/4 polymorphism and ages at onset of cardiovascular diseases (CVD) and cancer in the parental and offspring generations of the Framingham Heart Study participants to gain insights on the role of age and gender across generations in genetic trade-offs. The analyses show that the apolipoprotein E e4 allele carriers live longer lives without cancer than the non-e4 allele carriers in each generation. The role of the e4 allele in onset of CVD is age- and generation-specific, constituting two modes of sexually dimorphic genetic trade-offs. In offspring, the e4 allele confers risk of CVD primarily in women and can protect against cancer primarily in men of the same age. In the parental generation, genetic trade-off is seen in different age groups, with a protective role of the e4 allele against cancer in older men and its detrimental role in CVD in younger women. The puzzling complexity of genetic mechanisms working in different genders, ages, and environments calls for more detail and systemic analyses beyond those adapted in current large-scale genetic association studies.

Ahn SJ, Kim DK, Kim SS, et al.
Association between apolipoprotein E genotype, chronic liver disease, and hepatitis B virus.
Clin Mol Hepatol. 2012; 18(3):295-301 [PubMed] Article available free on PMC after 01/04/2015 Related Publications
BACKGROUND/AIMS: Apolipoprotein E (ApoE) plays an important role in regulating lipid and lipoprotein metabolism, and ApoE genotypes are known to affect plasma lipoprotein concentrations. We investigated whether ApoE genotype determines the disease outcome in hepatitis B virus (HBV)-infected individuals, and verified the association between ApoE genotype and the occurrence of hepatocellular carcinoma (HCC) in patients with chronic liver diseases of various etiologies.
METHODS: This hospital-based, case-controlled study enrolled 156 subjects (47 healthy controls, 50 HBV-related liver cirrhosis patients, and 59 HCC patients). ApoE genotypes were determined using PCR-based ApoE genotyping kits. The biological significance of ApoE genotype was verified by measuring serum ApoE levels using an ELISA kits.
RESULTS: The ε3 allele was the most common allele, with allele frequencies among the entire cohort of 5.8%, 84.3%, and 9.9% for the ε2, ε3, and ε4 alleles, respectively. Significantly more of those patients carrying the ε3/3 genotype had developed liver cirrhosis compared to the control subjects. Being an ApoE4 carrier was associated with a lower probability of developing liver cirrhosis. The allele frequencies and genotype distribution of ApoE did not differ significantly between the liver cirrhosis and HCC patients. The serum level of ApoE was significantly higher in patients with liver cirrhosis than in the healthy controls, but did not differ significantly with the ApoE genotype.
CONCLUSIONS: The ApoE ε3/3 genotype frequency was higher in patients with HBV-associated liver cirrhosis than in the controls.

Jiang X, Neapolitan RE
Mining pure, strict epistatic interactions from high-dimensional datasets: ameliorating the curse of dimensionality.
PLoS One. 2012; 7(10):e46771 [PubMed] Article available free on PMC after 01/04/2015 Related Publications
BACKGROUND: The interaction between loci to affect phenotype is called epistasis. It is strict epistasis if no proper subset of the interacting loci exhibits a marginal effect. For many diseases, it is likely that unknown epistatic interactions affect disease susceptibility. A difficulty when mining epistatic interactions from high-dimensional datasets concerns the curse of dimensionality. There are too many combinations of SNPs to perform an exhaustive search. A method that could locate strict epistasis without an exhaustive search can be considered the brass ring of methods for analyzing high-dimensional datasets.
METHODOLOGY/FINDINGS: A SNP pattern is a Bayesian network representing SNP-disease relationships. The Bayesian score for a SNP pattern is the probability of the data given the pattern, and has been used to learn SNP patterns. We identified a bound for the score of a SNP pattern. The bound provides an upper limit on the Bayesian score of any pattern that could be obtained by expanding a given pattern. We felt that the bound might enable the data to say something about the promise of expanding a 1-SNP pattern even when there are no marginal effects. We tested the bound using simulated datasets and semi-synthetic high-dimensional datasets obtained from GWAS datasets. We found that the bound was able to dramatically reduce the search time for strict epistasis. Using an Alzheimer's dataset, we showed that it is possible to discover an interaction involving the APOE gene based on its score because of its large marginal effect, but that the bound is most effective at discovering interactions without marginal effects.
CONCLUSIONS/SIGNIFICANCE: We conclude that the bound appears to ameliorate the curse of dimensionality in high-dimensional datasets. This is a very consequential result and could be pivotal in our efforts to reveal the dark matter of genetic disease risk from high-dimensional datasets.

Li Y, Graubard BI
Pseudo semiparametric maximum likelihood estimation exploiting gene environment independence for population-based case-control studies with complex samples.
Biostatistics. 2012; 13(4):711-23 [PubMed] Article available free on PMC after 01/04/2015 Related Publications
Advances in human genetics have led to epidemiological investigations not only of the effects of genes alone but also of gene-environment (G-E) interaction. A widely accepted design strategy in the study of how G-E relate to disease risks is the population-based case-control study (PBCCS). For simple random samples, semiparametric methods for testing G-E have been developed by Chatterjee and Carroll in 2005. The use of complex sampling in PBCCS that involve differential probabilities of sample selection of cases and controls and possibly cluster sampling is becoming more common. Two complexities, weighting for selection probabilities and intracluster correlation of observations, are induced by the complex sampling. We develop pseudo-semiparametric maximum likelihood estimators (pseudo-SPMLE) that apply to PBCCS with complex sampling. We study the finite sample performance of the pseudo-SPMLE using simulations and illustrate the pseudo-SPMLE with a US case-control study of kidney cancer.

Xue HY, Wong HL
Targeting megalin to enhance delivery of anti-clusterin small-interfering RNA nanomedicine to chemo-treated breast cancer.
Eur J Pharm Biopharm. 2012; 81(1):24-32 [PubMed] Related Publications
The goal of this study is to evaluate a new targeting strategy to improve nanomedicine delivery to breast cancer cells that survive prior exposure to chemotherapy. These cells are particularly difficult to treat because they often develop drug resistance by upregulation of chemoresistant factors such as clusterin and should be preferably eradicated before they further spread out. In this study, the surface endocytotic receptor megalin was studied for the first time for targeted delivery of anti-clusterin small-interfering RNAs (siRNAs) to these chemo-treated cells. Lipid-polyethylenimine hybrid nanocarriers decorated with apolipoprotein E (Ap-LPNs) were developed for this purpose. Using immunoblotting, we demonstrated induction of both megalin and clusterin in MCF-7 cells by previous paclitaxel treatment. The siRNA transfection of these megalin-rich chemo-treated cancer cells was improved by three-fold when the siRNAs were delivered by Ap-LPNs. This trend was translatable into enhanced clusterin knockdown and improved chemosensitization to subsequent paclitaxel treatment (both p<0.05 versus uncoated LPNs). This proof-of-principle study has validated a novel "chemoresistance-targeting" strategy for siRNA delivery to the cancer cell subpopulation that begins to acquire chemoresistance and is in strong need for chemosensitization.

Fu X, Rivera A, Tao L, et al.
Construction of an oncolytic herpes simplex virus that precisely targets hepatocellular carcinoma cells.
Mol Ther. 2012; 20(2):339-46 [PubMed] Article available free on PMC after 01/04/2015 Related Publications
Selective replication in tumor cells is a highly desirable feature for oncolytic viruses. Recent studies have shown that microRNAs (miRNAs) play important roles in controlling gene expression, and that certain tissue-specific miRNAs are frequently downregulated in malignant cells. miR-122 is a liver-specific microRNA. It is abundantly expressed in normal hepatocytes but is absent in many hepatocellular carcinoma (HCC) cells. We hypothesized that expression of an essential viral gene by a liver-specific promoter would initially restrict virus replication to cells of hepatic origin and that adding miR-122 complementary sequences to the viral gene would make the transcripts degradable by miR-122 in normal hepatocytes, thus further confining its replication to HCC. We have constructed such an oncolytic herpes simplex virus by linking the essential viral glycoprotein H gene with the liver-specific apolipoprotein E (apoE)-AAT promoter and by adding the miR-122a complimentary sequence to the 3' untranslated region (3'UTR). To further increase the safety of this virus, complementary sequences from miR-124a and let-7 were also engineered into the same 3'UTR. Designated liver-cancer specific oncolytic virus (LCSOV), it was highly selective in killing HCC cells and in shrinking HCC xenografts. We conclude that LCSOV is a highly specific oncolytic virus that can precisely target HCC.

Staquicini FI, Cardó-Vila M, Kolonin MG, et al.
Vascular ligand-receptor mapping by direct combinatorial selection in cancer patients.
Proc Natl Acad Sci U S A. 2011; 108(46):18637-42 [PubMed] Article available free on PMC after 01/04/2015 Related Publications
Molecules differentially expressed in blood vessels among organs or between damaged and normal tissues, are attractive therapy targets; however, their identification within the human vasculature is challenging. Here we screened a peptide library in cancer patients to uncover ligand-receptors common or specific to certain vascular beds. Surveying ~2.35 x 10(6) motifs recovered from biopsies yielded a nonrandom distribution, indicating that systemic tissue targeting is feasible. High-throughput analysis by similarity search, protein arrays, and affinity chromatography revealed four native ligand-receptors, three of which were previously unrecognized. Two are shared among multiple tissues (integrin α4/annexin A4 and cathepsin B/apolipoprotein E3) and the other two have a restricted and specific distribution in normal tissue (prohibitin/annexin A2 in white adipose tissue) or cancer (RAGE/leukocyte proteinase-3 in bone metastases). These findings provide vascular molecular markers for biotechnology and medical applications.

Fredericks WJ, McGarvey T, Wang H, et al.
The bladder tumor suppressor protein TERE1 (UBIAD1) modulates cell cholesterol: implications for tumor progression.
DNA Cell Biol. 2011; 30(11):851-64 [PubMed] Article available free on PMC after 01/04/2015 Related Publications
Convergent evidence implicates the TERE1 protein in human bladder tumor progression and lipid metabolism. Previously, reduced TERE1 expression was found in invasive urologic cancers and inhibited cell growth upon re-expression. A role in lipid metabolism was suggested by TERE1 binding to APOE, a cholesterol carrier, and to TBL2, a candidate protein in triglyceride disorders. Natural TERE1 mutations associate with Schnyder's corneal dystrophy, characterized by lipid accumulation. TERE1 catalyzes menaquinone synthesis, known to affect cholesterol homeostasis. To explore this relationship, we altered TERE1 and TBL2 dosage via ectopic expression and interfering RNA and measured cholesterol by Amplex red. Protein interactions of wild-type and mutant TERE1 with GST-APOE were evaluated by binding assays and molecular modeling. We conducted a bladder tumor microarray TERE1 expression analysis and assayed tumorigenicity of J82 cells ectopically expressing TERE1. TERE1 expression was reduced in a third of invasive specimens. Ectopic TERE1 expression in J82 bladder cancer cells dramatically inhibited nude mouse tumorigenesis. TERE1 and TBL2 proteins inversely modulated cellular cholesterol in HEK293 and bladder cancer cells from 20% to 50%. TERE1 point mutations affected APOE interactions, and resulted in cholesterol levels that differed from wild type. Elevated tumor cell cholesterol is known to affect apoptosis and growth signaling; thus, loss of TERE1 in invasive bladder cancer may represent a defect in menaquinone-mediated cholesterol homeostasis that contributes to progression.

Argyri L, Skamnaki V, Stratikos E, Chroni A
A simple approach for human recombinant apolipoprotein E4 expression and purification.
Protein Expr Purif. 2011; 79(2):251-7 [PubMed] Related Publications
We report a simple expression and purification procedure for the production of recombinant apolipoprotein E4 (apoE4), an important protein for the lipid homeostasis in humans that plays critical roles in the pathogenesis of cardiovascular and neurodegenerative diseases. Our approach is based on the expression of a thioredoxin-apoE4 fusion construct in bacterial cells and subsequent removal of the fused thioredoxin using the highly specific 3C protease, avoiding costly and laborious lipidation-delipidation steps used before. Our approach results in rapid, high-yield production of structurally and functionally competent apoE4 as evidenced by secondary structure measurements, thermal and chemical melting profiles and the kinetic profile of solubilization of dimyristoyl-phosphatidylcholine (DMPC) vesicles. This protocol is appropriate for laboratories with little experience in apolipoprotein biochemistry and will facilitate future studies on the role of apoE4 in the pathogenesis of cardiovascular disease and neurodegenerative diseases, including Alzheimer's disease.

Long G, Hiet MS, Windisch MP, et al.
Mouse hepatic cells support assembly of infectious hepatitis C virus particles.
Gastroenterology. 2011; 141(3):1057-66 [PubMed] Related Publications
BACKGROUND & AIMS: Hepatitis C virus (HCV) has a high propensity to establish persistence; better understanding of this process requires the development of a fully permissive and immunocompetent small animal model. Mouse cells can be engineered to express the human orthologs of the entry molecules CD81 and occludin to allow entry of HCV. However, RNA replication is poor in mouse cells, and it is not clear whether they support assembly and release of infectious HCV particles. We used a trans-complementation-based system to demonstrate HCV assembly competence of mouse liver cell lines.
METHODS: A panel of 3 mouse hepatoma cell lines that contain a stable subgenomic HCV replicon was used for ectopic expression of the HCV structural proteins, p7, nonstructural protein 2, and/or apolipoprotein E (apoE). Assembly and release of infectious HCV particles was determined by measuring viral RNA, proteins, and infectivity of virus released into the culture supernatant.
RESULTS: Mouse replicon cells released low amounts of HCV particles, but ectopic expression of apoE increased release of infectious HCV to levels observed in the human hepatoma cell line Huh7.5. Thus, apoE is the limiting factor for assembly of HCV in mouse hepatoma cells but probably not in primary mouse hepatocytes. Products of all 3 human alleles of apoE and mouse apoE support HCV assembly with comparable efficiency. Mouse and human cell-derived HCV particles have similar biophysical properties, dependency on entry factors, and levels of association with apoE.
CONCLUSIONS: Mouse hepatic cells permit HCV assembly and might be developed to create an immunocompetent and fully permissive mouse model of HCV infection.

Ritorto MS, Borlak J
Combined serum and tissue proteomic study applied to a c-Myc transgenic mouse model of hepatocellular carcinoma identified novel disease regulated proteins suitable for diagnosis and therapeutic intervention strategies.
J Proteome Res. 2011; 10(7):3012-30 [PubMed] Related Publications
Hepatocellular carcinoma (HCC) is the third leading cause of cancer death in the U.S. Notably, most HCCs display c-Myc hyperactivity but this transcription factor participates in the regulation of as many as 15-20% of genes of the human genome. To better understand its oncogenic activity, a mass spectrometry-based proteomic approach was employed to search for disease-regulated proteins in liver tissue and serum of c-Myc transgenic mice that specifically developed HCC. Overall, a total of 90 differentially expressed proteins were identified with retinol binding protein 4, transthyretin, major urinary protein family, apolipoprotein E, and glutathione peroxidase being regulated in common in tissue and serum of HCC mice. Importantly, this study identified n = 22 novel tumor tissue-regulated proteins to function in cell cycle and proliferation, nucleotide and ribosomal biogenesis, oxidative stress, and GSH metabolism, while bioinformatics revealed the coding sequences of regulated proteins to enharbour c-Myc binding sites. Translation of the findings to human disease was achieved by Western immunoblotting of serum proteins and by immunohistochemistry of human HCC. Taken collectively, our study helps to define a c-Myc proteome suitable for diagnostic and possible therapeutic intervention strategies.

Froklage FE, Reijneveld JC, Heimans JJ
Central neurotoxicity in cancer chemotherapy: pharmacogenetic insights.
Pharmacogenomics. 2011; 12(3):379-95 [PubMed] Related Publications
Central neurotoxicity of chemotherapy is likely to be multifactorial. There are two hypotheses regarding endogenous mechanisms that may be involved, namely the target and the blood-brain barrier transporter hypotheses. Here, we will review candidate genetic determinants for the risk of chemotherapy-induced neurotoxicity, such as polymorphisms involved in the target mechanism. These include polymorphisms in folate metabolizing enzymes and apolipoprotein E, as well as those in blood-brain barrier transporter genes. Currently, the exact role of pharmacogenetics in mechanisms that lead to central neurotoxicity of chemotherapy has not been fully unraveled. Larger, prospective, longitudinal and more uniform studies are needed, with prechemotherapy and follow-up measurements of neuropsychological performance, MRI, PET, genetic profiles and biomarkers relevant for the proposed target and transporter mechanisms.

Kulminski AM, Culminskaya I, Ukraintseva SV, et al.
Trade-off in the effects of the apolipoprotein E polymorphism on the ages at onset of CVD and cancer influences human lifespan.
Aging Cell. 2011; 10(3):533-41 [PubMed] Article available free on PMC after 01/04/2015 Related Publications
Progress in unraveling the genetic origins of healthy aging is tempered, in part, by a lack of replication of effects, which is often considered a signature of false-positive findings. We convincingly demonstrate that the lack of genetic effects on an aging-related trait can be because of trade-offs in the gene action. We focus on the well-studied apolipoprotein E (APOE) e2/3/4 polymorphism and on lifespan and ages at onset of cardiovascular diseases (CVD) and cancer, using data on 3924 participants of the Framingham Heart Study Offspring cohort. Kaplan-Meier estimates show that the e4 allele carriers live shorter lives than the non-e4 allele carriers (log rank = 0.016). The adverse effect was attributed to the poor survival of the e4 homozygotes, whereas the effect of the common e3/4 genotype was insignificant. The e3/4 genotype, however, was antagonistically associated with onsets of those diseases predisposing to an earlier onset of CVD and a later onset of cancer compared to the non-e4 allele genotypes. This trade-off explains the lack of a significant effect of the e3/4 genotype on survival; adjustment for it in the Cox regression model makes the detrimental effect of the e4 allele highly significant (P = 0.002). This trade-off is likely caused by the lipid-metabolism-related (for CVD) and nonrelated (for cancer) mechanisms. An evolutionary rationale suggests that genetic trade-offs should not be an exception in studies of aging-related traits. Deeper insights into biological mechanisms mediating gene action are critical for understanding the genetic regulation of a healthy lifespan and for personalizing medical care.

Rolyan H, Feike AC, Upadhaya AR, et al.
Amyloid-β protein modulates the perivascular clearance of neuronal apolipoprotein E in mouse models of Alzheimer's disease.
J Neural Transm. 2011; 118(5):699-712 [PubMed] Related Publications
The deposition of amyloid-β protein (Aβ) in the brain is a hallmark of Alzheimer's disease (AD). Apolipoprotein E (apoE) is involved in the clearance of Aβ from brain and the APOE ε4 allele is a major risk factor for sporadic AD. We have recently shown that apoE is drained into the perivascular space (PVS), where it co-localizes with Aβ. To further clarify the role of apoE in perivascular clearance of Aβ, we studied apoE-transgenic mice over-expressing human apoE4 either in astrocytes (GE4) or in neurons (TE4). These animals were crossbred with amyloid precursor protein (APP)-transgenic mice and with APP-presenilin-1 (APP-PS1) double transgenic mice. Using an antibody that specifically detects human apoE (h-apoE), we observed that astroglial expression of h-apoE in GE4 mice leads to its perivascular drainage, whereas neuronal expression in TE4 mice does not, indicating that neuron-derived apoE is usually not the subject of perivascular drainage. However, h-apoE was observed not only in the PVS of APP-GE4 and APP-PS1-GE4 mice, but also in that of APP-TE4 and APP-PS1-TE4 mice. In all these mouse lines, we found co-localization of neuron-derived h-apoE and Aβ in the PVS. Aβ and h-apoE were also found in the cytoplasm of perivascular astrocytes indicating that astrocytes take up the neuron-derived apoE bound to Aβ, presumably prior to its clearance into the PVS. The uptake of apoE-Aβ complexes into glial cells was further investigated in glioblastoma cells. It was mediated by α(2)macroglobulin receptor/low density lipoprotein receptor-related protein (LRP-1) and inhibited by adding receptor-associated protein (RAP). It results in endosomal Aβ accumulation within these cells. These results suggest that neuronal apoE-Aβ complexes, but not neuronal apoE alone, are substrates for LRP-1-mediated astroglial uptake, transcytosis, and subsequent perivascular drainage. Thus, the production of Aβ and its interaction with apoE lead to the pathological perivascular drainage of neuronal apoE and provide insight into the pathological interactions of Aβ with neuronal apoE metabolism.

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