The promoter of the rat 3-hydroxy-3-methylglutaryl coenzyme A reductase gene contains a tissue-specific estrogen-responsive region

Evaluating the Effects of Perinatal Exposures to BPSIP on Hepatic Cholesterol Metabolism in Female and Male Offspring ICR Mice

BACKGROUND

A broad suite of bisphenol S (BPS) derivatives as alternatives for BPS have been identified in various human biological samples, including 4-hydroxyphenyl 4-isopropoxyphenylsulfone (BPSIP) detected in human umbilical cord plasma and breast milk. However, very little is known about the health outcomes of prenatal BPS derivative exposure to offspring.

OBJECTIVES

Our study aimed to investigate the response of hepatic cholesterol metabolism by sex in offspring of dams exposed to BPSIP.

METHODS

Pregnant ICR mice were exposed to 5 μ g / kg body weight (BW)/day of BPSIP, BPS, or E2 through drinking water from gestational day one until the pups were weaned. The concentration of BPSIP, BPS, or E2 in the plasma and liver of pups was determined by liquid chromatography-tandem mass spectrometry. Metabolic phenotypes were recorded, and histopathology was examined for liver impairment. Transcriptome analysis was employed to characterize the distribution and expression patterns of differentially expressed genes across sexes. The metabolic regulation was validated by quantitative real-time PCR, immunohistochemistry, and immunoblotting. The role of estrogen receptors (ERs) in mediating sex-dependent effects was investigated using animal models and liver organoids.

RESULTS

Pups of dams exposed to BPSIP showed a higher serum cholesterol level, and liver cholesterol levels were higher in females and lower in males than in the controls. BPSIP concentration in the male liver was 1.22 ± 0.25  ng / g and 0.69 ± 0.27  ng / g in the female liver. Histopathology analysis showed steatosis and lipid deposition in both male and female offspring. Transcriptome and gene expression analyses identified sex-specific differences in cholesterol biosynthesis, absorption, disposal, and efflux between pups of dams exposed to BPSIP and those in controls. In vivo, chromatin immunoprecipitation analysis revealed that the binding of ER α protein to key genes such as Hmgcr, Pcsk9, and Abcg5 was attenuated in BPSIP-exposed females compared to controls, while it was enhanced in males. In vitro, the liver organoid experiments demonstrated that restoration of differential expression induced by BPSIP in key genes, such as Hmgcr, Ldlr, and Cyp7a1, to levels comparable to the controls was only achieved when treated with a combination of ER α agonist and ER β agonist.

DISCUSSION

Findings from this study suggest that perinatal exposure to BPSIP disrupted cholesterol metabolism in a sex-specific manner in a mouse model, in which ER α played a crucial role both in vivo and in vitro. Therefore, it is crucial to systematically evaluate BPS derivatives to protect maternal health during pregnancy and prevent the transmission of metabolic disorders across generations. https://doi.org/10.1289/EHP14643.

Regulation of cholesterol metabolism: New players for an old physiological process

Identified more than two centuries ago, cholesterol plays a pivotal role in human physiology. Since cholesterol metabolism is a physiologically significant process, it is not surprising that its alterations are associated with several pathologies. The discovery of new molecular targets or compounds able to modulate this sophisticated metabolism has been capturing the attention of research groups worldwide since many years. Endogenous and exogenous compounds are known to regulate cellular cholesterol synthesis and uptake, or reduce cholesterol absorption at the intestinal level, thereby regulating cholesterol homeostasis. However, there is a great need of new modulators and diverse new pathways have been uncovered. Here, after illustrating cholesterol metabolism and its well-known regulators, some new players of this important physiological process are also described.

The human microglial surveillant phenotype is preserved by de novo neurosteroidogenesis through the control of cholesterol homeostasis: Crucial role of 18 kDa Translocator Protein

Neurodegenerative disease-associated microglia commonly exhibit harmful cholesterol accumulation that impairs their ability to resolve the neuroinflammatory response, contributing to disease onset and progression. Neurosteroids, whose levels have been often found significantly altered in brain diseases, are the most potent endogenous anti-inflammatory molecules exerting beneficial effects on activities of brain cells, including microglia. For the first time, the impact of neurosteroidogenesis on cholesterol homeostasis for the immune surveillance phenotype maintenance was investigated in a human microglia in vitro model. To enhance and inhibit neurosteroidogenesis, pharmacological stimulation and knock-down of 18 kDa Translocator Protein (TSPO), which is involved in the neurosteroidogenesis rate-limiting step, were used as experimental approaches, respectively. The obtained results point to an essential autocrine control of neurosteroidogenesis in orchestrating cholesterol trafficking in human microglia. TSPO pharmacological stimulation ensured cholesterol turnover by strengthening cholesterol efflux systems and preserving healthy immune surveillant phenotype. Conversely, TSPO knock-down induced an impairment of the controlled interplay among cholesterol synthesis, efflux, and metabolism mechanisms, leading to an excessive cholesterol accumulation and acquisition of a chronically activated dysfunctional phenotype. In this model, the exogenous neurosteroid administration restored proper the cholesterol clearance. The TSPO ability in promoting native neurosteroidogenesis opens the way to restore cholesterol homeostasis, and thus to maintain microglia proper functionality for the treatment of neuroinflammation-related brain diseases.

17β‑estradiol‑induced mitochondrial dysfunction and Warburg effect in cervical cancer cells allow cell survival under metabolic stress

Mitochondria from different types of cancer show bioenergetics and dysfunction that favor cell proliferation. The mechanistic understanding of estrogen in cervical cancer is poorly understood. Therefore, the objective of this study was to determine how 17β-estradiol (E2) affects mitochondrial function and the Warburg effect in SiHa, HeLa and C33A cervical cancer cells. Mitochondrial compromise was evaluated measuring changes in the membrane permeability by immunofluorescence, calcium concentration, redox status, iron and ferritin reserves. Glucose consumption and lactic acid assays were used to detect the metabolic activity. Results were confirmed at molecular level by analysis of the differential gene expression using RNA sequencing. E2 modified the mitochondrial permeability and produced an alteration in the calcium signaling pathway. In HeLa and SiHa, there was a significant decrease in nitric oxide levels and lipid peroxidation, and an increase in glucose consumption and lactic acid levels when stimulated with E2. Intracellular iron or ferritin reserves were not affected by the E2 treatment. Genes differentially modulated by E2 were involved in the mitochondrial electron transport chain, oxidative phosphorylation system, glycolysis, pentose phosphate pathway and the regulation of metabolic signaling pathways. Herein, we provide evidence for a primary effect of estrogen on mitochondrial function and the Warburg effect, favoring the metabolic adaptation of the cervical cancer cell lines and their survival.

Establishment and Characterization of a Novel Tissue-specific DNA Construct and Culture System with Potential for Avian Bioreactor Generation

Transgenic chickens are of great interest for the production of recombinant proteins in their eggs. However, the use of constitutive strong promoters or the tissue-specific ovalbumin promoter for the generation of the transgenic chickens have different drawbacks that have to be overcome in order to make chicken bioreactor an efficient production system. This prompted us to investigate the use of an alternative tissue-specific promoter, the vitellogenin promoter, which could overcome the difficulties currently found in the generation of chicken bioreactors. In the present work we establish and characterize a DNA construct consisting of a fragment of the 5´-flanking region of the chicken vitellogenin II gene cloned in a reporter vector. This construct is capable of showing the ability of the promoter to drive expression of a reporting gene in a tissue-specific manner and in a way that closely resembles physiologic regulation of vitellogenin, making it an ideal candidate to be used in the future for generation of avian bioreactors. Besides, we validate an in vitro culture system to test the performance of the DNA construct under study that could be used as a practical tool before generating any transgenic chicken. These results are important since they provide the proof of concept for the use of the vitellogenin promoter for future genetic modification of chickens bioreactors with improved characteristics in terms of quality of the recombinant protein produced.

Long noncoding RNA lncARSR promotes hepatic cholesterol biosynthesis via modulating Akt/SREBP-2/HMGCR pathway

AIMS

Disruption of cholesterol homeostasis has been identified as a major factor in the pathogenesis of atherosclerosis, myocardial infarction, and strokes. Long noncoding RNAs (lncRNAs) have emerged as critical players in cellular cholesterol metabolism, but their functions are still largely unknown.

MATERIALS AND METHODS

C57BL6/j mice were fed with high cholesterol diet (containing 4% cholesterol) or chow diet. Adenoviruses-lncARSR and lncARSR shRNA were used to overexpress or knockdown lncARSR expression.

KEY FINDINGS

The expression of lncARSR were increased both in patients with hypercholesterolemia and mice with high cholesterol diet feeding. Overexpression of lncARSR in mice resulted in elevated lipid levels in both serum and liver fragments. However, knockdown of lncARSR in mice fed with high cholesterol diet showed decreased lipid levels in serum and liver fragments compared with control mice. Furthermore, we found that the expression of HMG-CoA reductase (HMGCR), the rate-limiting enzyme of cholesterol synthesis was increased with lncARSR overexpression, which was accompanied with the increase of hepatic de novo cholesterol synthesis rate. Mechanistically, we found that lncARSR increased the expression of mature SREBP-2, which is a primary transcription factor of HMGCR. And lncARSR activated the PI3K/Akt pathway. When PI3K/Akt pathway was blocked by LY294002, the inhibitor of PI3K, the effect of lncARSR on SREBP-2 and HMGCR disappeared.

SIGNIFICANCE

Our data indicated upregulated lncARSR promotes hepatic cholesterol biosynthesis via modulating Akt/SREBP-2/HMGCR pathway, and implied that lncARSR may serve as a therapeutic target for cholesterol disorder.

A novel role for CRTC2 in hepatic cholesterol synthesis through SREBP-2

Cholesterol synthesis is regulated by the transcription factor sterol regulatory element binding protein 2 (SREBP-2) and its target gene 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR), which is the rate-limiting enzyme in cholesterol synthesis. Cyclic adenosine monophosphate-responsive element (CRE) binding protein-regulated transcription coactivator (CRTC) 2 is the master regulator of glucose metabolism. However, the effect of CRTC2 on cholesterol and its potential molecular mechanism remain unclear. Here, we demonstrated that CRTC2 expression and liver cholesterol content were increased in patients with high serum cholesterol levels who underwent resection of liver hemangiomas, as well as in mice fed a 4% cholesterol diet. Mice with adenovirus-mediated CRTC2 overexpression also showed elevated lipid levels in both serum and liver tissues. Intriguingly, hepatic de novo cholesterol synthesis was markedly increased under these conditions. In contrast, CRTC2 ablation in mice fed a 4% cholesterol diet (18 weeks) showed decreased lipid levels in serum and liver tissues compared with those in littermate wild-type mice. The expression of lipogenic genes (SREBP-2 and HMGCR) was consistent with hepatic CRTC2 levels. In vivo imaging showed enhanced adenovirus-mediated HMGCR-luciferase activity in adenovirus-mediated CRTC2 mouse livers; however, the activity was attenuated after mutation of CRE or sterol regulatory element sequences in the HMGCR reporter construct. The effect of CRTC2 on HMGCR in mouse livers was alleviated upon SREBP-2 knockdown. CRTC2 modulated SREBP-2 transcription by CRE binding protein, which recognizes the half-site CRE sequence in the SREBP-2 promoter. CRTC2 reduced the nuclear protein expression of forkhead box O1 and subsequently increased SREBP-2 transcription by binding insulin response element 1, rather than insulin response element 2, in the SREBP-2 promoter.

CONCLUSION

CRTC2 regulates the transcription of SREBP-2 by interfering with the recognition of insulin response element 1 in the SREBP-2 promoter by forkhead box O1, thus inducing SREBP-2/HMGCR signaling and subsequently facilitating hepatic cholesterol synthesis. (Hepatology 2017;66:481-497).

Role of Estrogens in the Regulation of Liver Lipid Metabolism

Before menopause, women are protected from atherosclerotic heart disease associated with obesity relative to men. Sex hormones have been proposed as a mechanism that differentiates this risk. In this review, we discuss the literature around how the endogenous sex hormones and hormone treatment approaches after menopause regulate fatty acid, triglyceride, and cholesterol metabolism to influence cardiovascular risk.The important regulatory functions of estrogen signaling pathways with regard to lipid metabolism have been in part obscured by clinical trials with hormone treatment of women after menopause, due to different formulations, routes of delivery, and pairings with progestins. Oral hormone treatment with several estrogen preparations increases VLDL triglyceride production. Progestins oppose this effect by stimulating VLDL clearance in both humans and animals. Transdermal estradiol preparations do not increase VLDL production or serum triglycerides.Many aspects of sex differences in atherosclerotic heart disease risk are influenced by the distributed actions of estrogens in the muscle, adipose, and liver. In humans, 17β-estradiol (E2) is the predominant circulating estrogen and signals through estrogen receptor alpha (ERα), estrogen receptor beta (ERβ), and G-protein-coupled estrogen receptor (GPER). Over 1000 human liver genes display a sex bias in their expression, and the top biological pathways are in lipid metabolism and genes related to cardiovascular disease. Many of these genes display variation depending on estrus cycling in the mouse. Future directions will likely rely on targeting estrogens to specific tissues or specific aspects of the signaling pathways in order to recapitulate the protective physiology of premenopause therapeutically after menopause.

Sex Hormones and Their Receptors Regulate Liver Energy Homeostasis

The liver is one of the most essential organs involved in the regulation of energy homeostasis. Hepatic steatosis, a major manifestation of metabolic syndrome, is associated with imbalance between lipid formation and breakdown, glucose production and catabolism, and cholesterol synthesis and secretion. Epidemiological studies show sex difference in the prevalence in fatty liver disease and suggest that sex hormones may play vital roles in regulating hepatic steatosis. In this review, we summarize current literature and discuss the role of estrogens and androgens and the mechanisms through which estrogen receptors and androgen receptors regulate lipid and glucose metabolism in the liver. In females, estradiol regulates liver metabolism via estrogen receptors by decreasing lipogenesis, gluconeogenesis, and fatty acid uptake, while enhancing lipolysis, cholesterol secretion, and glucose catabolism. In males, testosterone works via androgen receptors to increase insulin receptor expression and glycogen synthesis, decrease glucose uptake and lipogenesis, and promote cholesterol storage in the liver. These recent integrated concepts suggest that sex hormone receptors could be potential promising targets for the prevention of hepatic steatosis.

The effects of age and gender on the relationship between HMGCR promoter-911 SNP (rs33761740) and serum lipids in patients with coronary heart disease

BACKGROUND

Hydroxymethylglutaryl-Coenzyme A Reductase (HMGCR) catalyzes the rate-limiting step of cholesterol biosynthesis. This enzyme is the target of the widely available cholesterol lowering statins. In this population-based case-control study, the frequencies of -911 C>A polymorphism (rs3761740) of the HMGCR gene in patients with coronary heart disease (CHD) and healthy subjects were investigated and the correlations between the different genotypes and hypercholesterolemia with cardiovascular risk factors were analyzed.

METHODS

The HMGCR genotypes were determined in 365 patients with CHD and 365 controls by PCR-RFLP assay. Anthropometric measurements were measured in all participants.

RESULTS

There was no significant difference in the genotype frequencies of the HMGCR polymorphism between the male subjects of both patient and control groups, however, the HMGCR-CC genotype was found to be more frequent in female patients with CHD than female controls (p=0.002). The HMGCR-CC genotype showed higher total-cholesterol (TC) and LDL-cholesterol (LDL-C) levels than the CA+AA genotypes in male CHD patients (p=0.018). Due to this significant sex interaction, a multivariate analysis was conducted on the patient group. In the multivariate logistic regression analysis, the HMGCR-CC genotype was significantly associated with age<55 (OR=2.837, p=0.001) and TC ≥ 5.18 mmol/L (OR=1.970, p=0.027) in male subjects. However, this association was not observed in female patients (p>0.05). This analysis confirmed that the HMGCR-CC genotype was associated with elevated TC levels in male CHD patients with age<55 years.

CONCLUSION

These results suggest that age and sex modify the contribution of the HMGCR-911 polymorphism to fasting serum TC, LDL-C levels and risk of CHD.

Estrogen deficiency worsens steatohepatitis in mice fed high-fat and high-cholesterol diet

Recent studies indicate an accelerated progression of nonalcoholic steatohepatitis (NASH) in postmenopausal women. Hypercholesterolemia, an important risk factor for NASH progression, is often observed after menopause. This study examined the effects of estrogen on NASH in ovariectomized (OVX) mice fed a high-fat and high-cholesterol (HFHC) diet. To investigate the effects of estrogen deficiency, OVX mice and sham-operated (SO) mice were fed normal chow or HFHC diet for 6 wk. Next, to investigate the effects of exogenous estrogen replenishment, OVX mice fed with HFHC diet were treated with implanted hormone release pellets (containing 17β-estradiol or placebo vehicle) for 6 wk. OVX mice on the HFHC diet showed enhanced liver injury with increased liver macrophage infiltration and elevated serum cholesterol levels compared with SO-HFHC mice. Hepatocyte monocyte chemoattractant protein-1 (MCP1) protein expression in OVX-HFHC mice was also enhanced compared with SO-HFHC mice. In addition, hepatic inflammatory gene expressions, including monocytes chemokine (C-C motif) receptor 2 (CCR2), were significantly elevated in OVX-HFHC mice. Estrogen treatment improved serum cholesterol levels, liver injury, macrophage infiltration, and inflammatory gene expressions in OVX-HFHC mice. Moreover, the elevated expression of liver CCR2 and MCP1 were decreased by estrogen treatment in OVX-HFHC mice, whereas low-density lipoprotein dose dependently enhanced CCR2 expression in THP1 monocytes. Our study demonstrated that estrogen deficiency accelerated NASH progression in OVX mice fed HFHC diet and that this effect was improved by estrogen therapy. Hypercholesterolemia in postmenopausal women would be a potential risk factor for NASH progression.

The effect of retinoic acid receptor agonist acitretin on the production of bile and concentrations of some serum components in ovariectomized rats

OBJECTIVE

Acitretin is an oral retinoid that is approved for the treatment of psoriasis and in the chemoprevention of nonmelanoma skin cancer. The metabolism of acitretin occurs in the liver and may affect other metabolic processes in the liver, such as metabolism of bilirubin, bile acids, and lipids. These processes may be also affected by physiologic loss of estrogens in postmenopausal women. Therefore, the aim of this study was to examine the effect of acitretin on the secretion and composition of bile and the turnover of cholesterol in a model of estrogen deficiency in ovariectomized rats.

METHODS

The study was carried out on female Wistar rats divided into three groups: sham-operated control, ovariectomized control, and ovariectomized rats receiving acitretin. The studied group was administered acitretin (Neotigason capsules 25 mg, Roche; 7.1 mg/kg body weight per 24 h) for 28 days. Bile fractions and blood were collected for determinations of concentration of bile acids, total cholesterol, calcium ions, chloride ions, and direct bilirubin. In addition, low-density lipoprotein (LDL) cholesterol and high-density lipoprotein (HDL) cholesterol were assayed.

RESULTS

It was found that ovariectomy produced alterations in the process of secretion of bile and its principal components: cholesterol, bile acids, chloride ions, and bilirubin. The administration of acitretin decreased the secretion of bile and bile cholesterol, as well as serum levels of total, LDL, and HDL cholesterol, and moreover increased the proportion of bile acids to total cholesterol.

CONCLUSIONS

Acitretin may influence the hepatic metabolism of bile, bile acids, and lipids. This action is associated with a decrease in factors influencing the lithogenicity of bile, with reductions in the serum levels of total, LDL, and HDL cholesterol.

Estrogen signalling through amphiregulin may be implicated in human hepatocellular carcinoma

BACKGROUND

We investigated aromatase (Aro)-driven estrogen formation in non-tumoral and malignant liver tissues and cells, also in relation to expression of the estrogen receptors α and β (ERα and ERβ) and amphiregulin (AREG), aiming to gain insights into the potential role of estrogens in human hepatocellular carcinoma (HCC).

MATERIALS AND METHODS

Chromatographic and reverse transcriptase polymerase chain reaction (RT-PCR) analyses were used to assess activity and expression of the Aro enzyme and AREG as well as the expression of wild-type and variant ERs, both in vivo and in vitro.

RESULTS

Following 24 h and 72 h incubation of liver tissues or cells with testosterone, human HCC tissues and HepG2 hepatoma cells showed elevated Aro activity (estrogen formation, respectively, of 20% and 52%-99%). By contrast, no Aro activity could be detected in non-tumoral tissues and HA22T liver cancer cells. Cirrhotic samples and Huh7 cells exhibited intermediate enzyme activity, with estrogen formation of 4% and 34%, respectively. Markedly lower or undetectable Aro mRNA levels were observed in HA22T cells and non-tumoral liver tissues compared with HepG2 cells and HCC samples. Cirrhotic specimens displayed variable transcript levels. Interestingly, no or low expression of wild-type ERα and ERβ could be observed in liver cancer cells and malignant tissues. However, ubiquitous expression of the hERα46 variant and occasional expression of the hERβ2/Cx variant were observed in cancer tissues and cells.

CONCLUSIONS

It is noteworthy that the pattern of wild-type ERα was inversely related to Aro, whilst AREG expression was consistently associated with that of Aro. This combined evidence suggests that locally elevated Aro activity may increase malignant cell proliferation also through AREG signalling.

Functional promoter polymorphisms govern differential expression of HMG-CoA reductase gene in mouse models of essential hypertension

3-Hydroxy-3-methylglutaryl-coenzyme A [HMG-CoA] reductase gene (Hmgcr) is a susceptibility gene for essential hypertension. Sequencing of the Hmgcr locus in genetically hypertensive BPH (blood pressure high), genetically hypotensive BPL (blood pressure low) and genetically normotensive BPN (blood pressure normal) mice yielded a number of single nucleotide polymorphisms (SNPs). BPH/BPL/BPN Hmgcr promoter-luciferase reporter constructs were generated and transfected into liver HepG2, ovarian CHO, kidney HEK-293 and neuronal N2A cells for functional characterization of the promoter SNPs. The BPH-Hmgcr promoter showed significantly less activity than the BPL-Hmgcr promoter under basal as well as nicotine/cholesterol-treated conditions. This finding was consistent with lower endogenous Hmgcr expression in liver and lower plasma cholesterol in BPH mice. Transfection experiments using 5′-promoter deletion constructs (strategically made to assess the functional significance of each promoter SNP) and computational analysis predicted lower binding affinities of transcription factors c-Fos, n-Myc and Max with the BPH-promoter as compared to the BPL-promoter. Corroboratively, the BPH promoter-luciferase reporter construct co-transfected with expression plasmids of these transcription factors displayed less pronounced augmentation of luciferase activity than the BPL construct, particularly at lower amounts of transcription factor plasmids. Electrophoretic mobility shift assays also showed diminished interactions of the BPH promoter with HepG2 nuclear proteins. Taken together, this study provides mechanistic basis for the differential Hmgcr expression in these mouse models of human essential hypertension and have implications for better understanding the role of this gene in regulation of blood pressure.

Mechanisms of gender-linked ischemic brain injury

Biological sex is an important determinant of stroke risk and outcome. Women are protected from cerebrovascular disease relative to men, an observation commonly attributed to the protective effect of female sex hormones, estrogen and progesterone. However, sex differences in brain injury persist well beyond the menopause and can be found in the pediatric population, suggesting that the effects of reproductive steroids may not completely explain sexual dimorphism in stroke. We review recent advances in our understanding of sex steroids (estradiol, progesterone and testosterone) in the context of ischemic cell death and neuroprotection. Understanding the molecular and cell-based mechanisms underlying sex differences in ischemic brain injury will lead to a better understanding of basic mechanisms of brain cell death and is an important step toward designing more effective therapeutic interventions in stroke.

HMG-CoA reductase expression in breast cancer is associated with a less aggressive phenotype and influenced by anthropometric factors

Although several studies have reported on the anti-tumoural properties exerted by 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMG-CoAR) inhibitors (statins), the in vivo expression of HMG-CoAR in human cancer has been considerably less investigated. In our study, we examined the immunohistochemical expression of HMG-CoAR in 511 incident breast cancers within the Malmö Diet and Cancer Study in order to explore its relationship to established clinicopathological and tumour biological parameters. Furthermore, the potential influence of estrogen exposure on HMG-CoAR expression was assessed by performing Cox's proportional hazards analyses of the relationship between the use of hormone replacement therapy (HRT), obesity (waist circumference) and tumour-cell specific HMG-CoAR expression. We found that HMG-CoAR was present in various fractions and intensities in the cytoplasm, sometimes with a membranous pattern, but not in the tumour cell nuclei. The expression of HMG-CoAR was associated with a smaller tumour size (p = 0.02), low histological grade (p = 0.001), low Ki67 index (p = 0.004), ERalpha+ (p = 0.02), ERbeta+ (p = 0.005), and high p27 expression (p = <0.001). The incidence of tumours with a high HMG-CoAR-expression was increased among HRT-users, although this was not statistically significant in a heterogeneity analysis. Obesity was significantly associated with a high HMG-CoAR expression assessed both as a high (>50%) fraction of positive cells (relative risk: 2.06; 95% confidence interval: 1.20-3.51), and a strong staining intensity (2.33: 1.08-5.02). In summary, we demonstrate that HMG-CoAR is differentially expressed in breast cancer and that a high expression is associated with prognostically favourable tumour parameters. Moreover, estrogen related life-style and anthropometric factors might indeed regulate HMG-CoAR expression.

Transcriptional control of cholesterol biosynthesis in Schwann cells by axonal neuregulin 1

A characteristic feature of many vertebrate axons is their wrapping by a lamellar stack of glially derived membranes known as the myelin sheath. Myelin is a cholesterol-rich membrane that allows for rapid saltatory nerve impulse conduction. Axonal neuregulins instruct glial cells on when and how much myelin they should produce. However, how neuregulin regulates myelin sheath development and thickness is unknown. Here we show that neuregulin receptors are activated by drops in plasma membrane cholesterol, suggesting that they can sense sterol levels. In Schwann cells neuregulin-1 increases the transcription of the 3-hydroxy-3-methylglutarylcoenzyme A reductase, the rate-limiting enzyme for cholesterol biosynthesis. Neuregulin activity is mediated by the phosphatidylinositol 3-kinase pathway and a cAMP-response element located on the reductase promoter. We propose that by activating neuregulin receptors, neurons exploit a cholesterol homeostatic mechanism forcing Schwann cells to produce new membranes for the myelin sheath. We also show that a strong phylogenetic correlation exists between myelination and cholesterol biosynthesis, and we propose that the absence of the sterol branch of the mevalonate pathway in invertebrates precluded the myelination of their nervous system.

Farnesyl-transferase inhibitor R115,777 enhances tamoxifen inhibition of MCF-7 cell growth through estrogen receptor dependent and independent pathways

INTRODUCTION

We have previously shown that FTI-277, a farnesyl transferase inhibitor (FTI), enhances the efficacy of tamoxifen (Tam) in inhibiting the proliferation of the estrogen dependent MCF-7 cell line. As the cellular response to Tam is the result of an inhibition of both estrogen receptor-dependent and -independent pathways, we have used the estrogen receptor selective anti-estrogen ICI182,780 and N-pyrrolidine(-phenylmethyl-phenoxy)-ethanamine-HCl (PBPE), a selective ligand of anti-estrogen binding site (AEBS), to dissect out the mechanism(s) associated with the observed additivity resulting from combination treatment with FTI-277 and Tam. Moreover, for these studies, FTI-277 has been replaced by R115,777, a FTI currently in phase III clinical trials.

METHODS

The quantitative sulphorhodamine B (SRB) colorimetric assay was used to determine the growth inhibitory effect of agents on MCF-7 cells. Dose response interactions between R115,777-Tam, R115,777-ICI182,780 and R115,777-PBPE were evaluated, at the IC50 point, using the isobologram method. Apoptotic cell death (DNA fragmentation, nucleus condensation and cytokeratin 18 cleavage) and inhibition of the mevalonate pathway (western blot) were also determined.

RESULTS

Combinations of the specific FTI R115,777 with either ICI182,780 or PBPE exhibit a synergistic effect on MCF-7 cell growth inhibition, while its combination with Tam is additive, as previously reported for FTI-277. Apoptosis is detected after treatment with combinations of R115,777 with either Tam or PBPE but not with ICI182,780, suggesting that each combination inhibits cell proliferation by different mechanisms. Even though the ER pathway has not yet been deciphered, it is shown here that the AEBS pathway is able to interfere with the mevalonate pathway at the level of protein farnesylation.

CONCLUSION

Overall, this work reveals that combinations of R115,777 with either selective ER ligands or a selective AEBS ligand are able to induce large increases in their anti-proliferative activities on MCF-7 cells. Moreover, these results suggest that it may be of definite interest to evaluate combinations of R115,777 with different anti-estrogens in the treatment of ER positive breast tumours. Based on these experimental data, such combinations may prove beneficial in different clinical scenarios or when used in specific sequences; studying the combination of R115,777 with ICI182,780 for early treatment and reserving combinations with either Tam or a selective AEBS ligand, such as BMS-217380-01, for more resistant disease.

Identification of insulin-responsive regions in the HMG-CoA reductase promoter

An insulin-responsive line of rat hepatoma cells, H4IIE, was used to investigate the basis for insulin's transcriptional regulation of HMG-CoA reductase. Insulin addition to the media of these cells resulted in at least a 10-fold increase in levels of HMG-CoA reductase protein. Adding insulin to H4IIE cells transfected with pHMGR1 (containing the proximal reductase promoter from -270 to +20 ligated to luciferase) caused greater than 10-fold increases in luciferase activity. Transfections carried out with a series of deletion constructs identified insulin responsive regions between -203 and -130 (contains the SRE sequence) and between -85 and -105 (contains a CRE sequence). Mutation of the SRE in the -203 to -130 sequence did not decrease activation by insulin. In contrast, mutation of the C at -90 of the CRE completely eliminated the insulin response. The data suggest that insulin's activation of HMG-CoA reductase involves the CRE in the -85 to -105 region and the -203 to -130 region of the promoter exclusive of the SRE.

The low-density lipoprotein receptor is regulated by estrogen and forms a functional complex with the estrogen-regulated protein ezrin in pituitary GH3 somatolactotropes

Estrogen regulates the function, growth, and proliferation of lactotropes in the pituitary. We report here that low-density lipoprotein (LDL) receptor (LDLR) gene expression and LDL uptake are strongly up-regulated by estrogen in pituitary somatolactotropic GH(3) cells. The uptake of LDL was significantly inhibited by the F-actin-severing drug, swinholide A, indicating that LDL uptake is dependent on the integrity of the cortical actin cytoskeleton in GH(3) cells. We examined whether the estrogen-inducible cytoskeletal linker protein, ezrin, interacts with the LDLR. The LDLR coimmunoprecipitated with ezrin, and fluorescently labeled LDL bound to regions of the cell membrane that colocalized with the active, phosphorylated form of ezrin (phosphoezrin). Evidence for a functional interaction between ezrin and the LDLR was obtained by transient transfection experiments using ezrin-green fluorescent protein (GFP) expression constructs. We observed that transient transfection of GH(3) cells with an ezrin N terminus-GFP dominant-negative construct prevented the uptake of LDL particles, whereas expression of GFP alone or an ezrin C terminus-GFP construct had no effect on LDL uptake. Transfection with the ezrin N terminus dominant- negative construct had no effect on the endocytosis of transferrin. Thus, estrogen stimulates the expression of ezrin and the LDLR in GH(3) cells, which interact physically and functionally to facilitate the endocytosis of LDL. We propose that the up-regulation and interaction of ezrin and the LDLR serves to augment the delivery of cholesterol and other lipids in support of the hypertrophic and proliferative response of cells to estrogen.

Interplay between estrogen response element sequence and ligands controls in vivo binding of estrogen receptor to regulated genes

To examine the role of the estrogen response element (ERE) sequence in binding of liganded estrogen receptor (ER) to promoters, we analyzed in vivo interaction of liganded ER with the imperfect ERE in the pS2 gene and the composite estrogen-responsive unit (ERU) in the proteinase inhibitor 9 (PI-9) gene. In transient transfections of ER-positive HepG2-ER7 cells, PI-9 was strongly induced by estrogen, moxestrol (MOX), and 4-hydroxytamoxifen (OHT). PI-9 was not induced by raloxifene or ICI 182,780. Quantitative reverse transcriptase-PCR showed that moxestrol strongly induced cellular PI-9 and pS2 mRNAs, whereas OHT moderately induced PI-9 mRNA and weakly induced pS2 mRNA. Chromatin immunoprecipitation experiments demonstrated strong and similar association of 17beta-estradiol-hERalpha and MOX-hERalpha with the PI-9 ERU and with the pS2 ERE. Binding of MOX-hERalpha to the PI-9 ERU and the pS2 ERE was rapid and continuous. Although MOX-hERalpha bound strongly to the PI-9 ERU and less well to the pS2 ERE in chromatin immunoprecipitation, gel shift assays showed that estrogen-hERalpha binds with higher affinity to the deproteinized pS2 ERE than to the PI-9 ERU. Across a broad range of OHT concentrations, OHT-hERalpha associated strongly with the pS2 ERE and weakly with the PI-9 ERU. ICI-hERalpha bound poorly to the PI-9 ERU and effectively to the pS2 ERE. Raloxifene-hERalpha and MOX-hERalpha exhibited similar binding to the PI-9 ERU and the pS2 ERE. These studies demonstrate that ER ligand and ERE sequence work together to regulate in vivo binding of ER to estrogen-responsive promoters.

The aromatase knockout mouse presents with a sexually dimorphic disruption to cholesterol homeostasis

The aromatase knockout (ArKO) mouse cannot synthesize endogenous estrogens due to disruption of the Cyp19 gene. We have shown previously, that ArKO mice present with age-progressive obesity and hepatic steatosis, and by 1 yr of age both male and female ArKO mice develop hypercholesterolemia. In this present study 10- to 12-wk-old ArKO mice were challenged for 90 d with high cholesterol diets. Our results show a sexually dimorphic response to estrogen deficiency in terms of cholesterol homeostasis in the liver. ArKO females presented with elevated serum cholesterol; conversely, ArKO males had elevated hepatic cholesterol levels. In response to dietary cholesterol, 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase transcript levels were significantly reduced in females, whereas males showed more modest changes. Neither low density lipoprotein nor sterol regulatory element-binding protein expression levels were significantly altered by diet or genotype. The expression of Cyp7a, which encodes cholesterol 7 alpha-hydroxylase, was significantly reduced in ArKO females compared with wild-type females and was increased by cholesterol feeding. Cyp7a expression was significantly elevated in the wild-type males on the high cholesterol diet, although no difference was seen between genotypes on the control diet. The ATP-binding cassette G5 and ATP-binding cassette G8 transporters do not appear to be regulated by estrogen. The expression of acyl-coenzyme A:cholesterol acyltransferase 2 showed a sexually dimorphic response, where estrogen appeared to have a stimulatory effect in females, but not males. This study reveals a sexually dimorphic difference in mouse hepatic cholesterol homeostasis and roles for estrogen in the regulation of cholesterol uptake, biosynthesis, and catabolism in the female, but not in the male.

The aromatase knockout mouse presents with a sexually dimorphic disruption to cholesterol homeostasis

The aromatase knockout (ArKO) mouse cannot synthesize endogenous estrogens due to disruption of the Cyp19 gene. We have shown previously, that ArKO mice present with age-progressive obesity and hepatic steatosis, and by 1 yr of age both male and female ArKO mice develop hypercholesterolemia. In this present study 10- to 12-wk-old ArKO mice were challenged for 90 d with high cholesterol diets. Our results show a sexually dimorphic response to estrogen deficiency in terms of cholesterol homeostasis in the liver. ArKO females presented with elevated serum cholesterol; conversely, ArKO males had elevated hepatic cholesterol levels. In response to dietary cholesterol, 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase transcript levels were significantly reduced in females, whereas males showed more modest changes. Neither low density lipoprotein nor sterol regulatory element-binding protein expression levels were significantly altered by diet or genotype. The expression of Cyp7a, which encodes cholesterol 7 alpha-hydroxylase, was significantly reduced in ArKO females compared with wild-type females and was increased by cholesterol feeding. Cyp7a expression was significantly elevated in the wild-type males on the high cholesterol diet, although no difference was seen between genotypes on the control diet. The ATP-binding cassette G5 and ATP-binding cassette G8 transporters do not appear to be regulated by estrogen. The expression of acyl-coenzyme A:cholesterol acyltransferase 2 showed a sexually dimorphic response, where estrogen appeared to have a stimulatory effect in females, but not males. This study reveals a sexually dimorphic difference in mouse hepatic cholesterol homeostasis and roles for estrogen in the regulation of cholesterol uptake, biosynthesis, and catabolism in the female, but not in the male.

Estrogen and thyroid hormone receptor interactions: physiological flexibility by molecular specificity

The influence of thyroid hormone on estrogen actions has been demonstrated both in vivo and in vitro. In transient transfection assays, the effects of liganded thyroid hormone receptors (TR) on transcriptional facilitation by estrogens bound to estrogen receptors (ER) display specificity according to the following: 1) ER isoform, 2) TR isoform, 3) the promoter through which transcriptional facilitation occurs, and 4) cell type. Some of these molecular phenomena may be related to thyroid hormone signaling of seasonal limitations upon reproduction. The various combinations of these molecular interactions provide multiple and flexible opportunities for relations between two major hormonal systems important for neuroendocrine feedbacks and reproductive behaviors.

Distinct nongenomic signal transduction pathways controlled by 17beta-estradiol regulate DNA synthesis and cyclin D(1) gene transcription in HepG2 cells

Estrogens induce cell proliferation in target tissues by stimulating progression through the G1 phase of the cell cycle. Activation of cyclin D(1) gene expression is a critical feature of this hormonal action. The existence of rapid/nongenomic estradiol-regulated protein kinase C (PKC-alpha) and extracellular signal-regulated kinase (ERK) signal transduction pathways, their cross talk, and role played in DNA synthesis and cyclin D(1) gene transcription have been studied herein in human hepatoma HepG2 cells. 17Beta-estradiol was found to rapidly activate PKC-alpha translocation and ERK-2/mitogen-activated protein kinase phosphorylation in this cell line. These actions were independent of each other, preceding the increase of thymidine incorporation into DNA and cyclin D(1) expression, and did not involve DNA binding by estrogen receptor. The results obtained with specific inhibitors indicated that PKC-alpha pathway is necessary to mediate the estradiol-induced G1-S progression of HepG2 cells, but it does not exert any effect(s) on cyclin D(1) gene expression. On the contrary, ERK-2 cascade was strongly involved in both G1-S progression and cyclin D(1) gene transcription. Deletion of its activating protein-1 responsive element motif resulted in attenuation of cyclin D(1) promoter responsiveness to estrogen. These results indicate that estrogen-induced cyclin D(1) transcription can occur in HepG2 cells independently of the transcriptional activity of estrogen receptor, sustaining the pivotal role played by nongenomic pathways of estrogen action in hormone-induced proliferation.

Genome-wide analysis of changes in early gene expression induced by oestrogen

BACKGROUND

The sex hormone 17beta-oestradiol (E2) has profound effects on many aspects of reproduction, development, as well as behaviour. Although the oestrogen receptor is well characterized on a molecular level, relatively few genes affected by E2 have been identified, and the mechanisms underlying the physiological changes caused by E2 are largely unknown. In order to identify oestrogen-regulated genes in vivo, early uterine gene expression profiles were developed using DNA microarrays.

RESULTS

Ovariectomized mice were exposed to 17beta-oestradiol for 6 h, and mRNA expression analysis for 9977 genes was performed. Although a large number of genes was affected by oestrogen administration, the genes that showed higher reproducibility in repetitive experiments were selected and further examined. For most of the selected genes, expression was induced in a dose-dependent manner, and gene expression was not altered following oestrogen treatment in oestrogen receptor-alpha (ER(alpha))-deficient mice. In combination with the estimation of gene expression levels using quantitative PCR, it was revealed that multiple genes related to sterol biosynthesis, tRNA synthesis, RNA processing, and growth signalling were activated. Based on the microarray data, we selected additional genes related to sterol biosynthesis and tRNA synthesis and confirmed that these genes are also activated by oestrogen.

CONCLUSION

Genes suggesting a basis for the drastic uterotrophic effect observed several days following oestrogen administration were identified. These findings not only reveal the diverse effect of oestrogen signalling on transcript levels in vivo but also demonstrate the ability of DNA microarrays to identify cellular pathways affected by oestrogen.

Regulation of vascular endothelial growth factor (VEGF) gene transcription by estrogen receptors alpha and beta

Vascular endothelial growth factor (VEGF) mediates angiogenic activity in a variety of estrogen target tissues. To determine whether estrogen has a direct transcriptional effect on VEGF gene expression, we developed a model system by transiently transfecting human VEGF promoter-luciferase reporter constructs into primary human endometrial cells and into Ishikawa cells, derived from a well-differentiated human endometrial adenocarcinoma. In primary endometrial epithelial cells, treatment with 17beta-estradiol (E(2)) resulted in a 3.8-fold increase in luciferase activity, whereas a 3. 2-fold induction was demonstrated for stromal cells. Our Ishikawa cells had less than 100 functional estrogen receptors (ER)/cell and were therefore cotransfected with expression vectors encoding either the alpha- or the beta-form of the human ER. In cells cotransfected with ERalpha, E(2) induced 3.2-fold induction in VEGF-promoter luciferase activity. A 2.3-fold increase was observed in cells cotransfected with ERbeta. Through specific deletions, the E(2) response was restricted to a single 385-bp PvuII-SstI fragment in the 5' flanking DNA. Cotransfection of this upstream region with a DNA binding domain ER mutant, or site-directed mutagenesis of a variant ERE within this fragment, resulted in the loss of the E(2) response. Electromobility shift assays demonstrated that this same ERE sequence specifically binds estradiol-ER complexes. These studies demonstrate that E(2)-regulated VEGF gene transcription requires a variant ERE located 1.5 kb upstream from the transcriptional start site. Site-directed mutagenesis of this ERE abrogated E(2)-induced VEGF gene expression.