Estrogen receptor-alpha mRNA variants in murine and human tissues

DNA methylation patterns of steroid receptor genes ESR1, ESR2 and PGR in deep endometriosis compromising the rectum

Endometriosis is characterized by the presence of endometrial-like tissue located outside the uterine cavity. Recent evidence suggests that endometriosis may be an epigenetic disease, as well as an estrogen-dependent disease. Based on the unique steroid hormone receptor expression profile observed in endometriotic lesions as compared to eutopic endometrium, the present study aimed to gain further insight into the DNA methylation patterns of alternative promoters of the steroid receptor genes ESR1, ESR2 and PGR in intestinal deep endometriosis, one of the most aggressive forms of endometriosis. The DNA methylation patterns were evaluated by methylation-specific polymerase chain reaction (MS-PCR) after bisulfite modification in 44 endometriotic tissues as well as in 7 matched eutopic endometrium. No differences in the DNA methylation were observed for the ESR1 and ESR2 genes. Methylation of the PGR gene was observed in 39% (17 out of 44) and 19% (7 out of 37) of the cases in the promoter regions B (PGRB) and A (PGRA), respectively. Both PGR promoter regions were methylated in 3 cases. PGRB methylated alleles were detected exclusively in the endometriotic lesions when compared to the eutopic endometrium obtained from the same patient. The effect of DNA methylation in inhibiting the PGR gene expression was corroborated by immuno-staining for PgR protein in a subset of tissue samples. The present study demonstrated that epigenetic changes occur in both promoter regions of the PGR gene in intestinal endometriosis. Since eutopic and ectopic tissues do not respond sufficiently to progesterone in women with endometriosis, further study is necessary to evaluate the effect of epigenetic alterations in progesterone-resistance in this enigmatic disease.

Estrogen stimulates Th2 cytokine production and regulates the compartmentalisation of eosinophils during allergen challenge in a mouse model of asthma

BACKGROUND

The observation that asthma becomes more prevalent following puberty in females suggests estrogen potentiates the development of this disease. However, most studies examining the role of estrogen in rodent models of asthma are complicated by their reliance on ovariectomised mice in which hormones other than estrogen are also attenuated.

METHODS

We aimed to understand the influence of estrogen on allergic airway disease by using type I (tamoxifen) or type II (ICI 182,780) antagonists in female mice or delivering estradiol to male mice during aeroallergen challenge.

RESULTS

The antagonists showed that estrogen promoted both the mobilisation of bone marrow eosinophils and egression of eosinophils to the airway lumen. These findings were corroborated in male mice treated with estradiol, which increased eosinophil numbers in both blood and airways. Estrogen stimulated goblet cell hyperplasia and baseline lung resistance, but had little effect on the number of eosinophils in the bronchial submucosa or methacholine-induced airway hyperreactivity. Estrogen receptor α was expressed by CD4+ T cells from allergic mice, and estrogen promoted the production of IL-5 and IL-13, and suppressed the production of the eicosanoid 12-HETE by mediastinal lymph node cells.

CONCLUSIONS

These data show that during aeroallergen challenge, estrogen stimulates Th2 cytokine production, which may be linked to its ability to suppress 12-HETE. Lung resistance at baseline, goblet cell hyperplasia and the compartmentalisation of eosinophils was also influenced by estrogen. However, estrogen does not play a major role in stimulating enhanced sensitivity to methacholine-induced lung resistance.

Oestrogen receptor splice variants in the pathogenesis of disease

The full-length oestrogen receptor (ER) exists in most vertebrates as two separately encoded isoforms. ER splice variants represent truncated or otherwise modified versions of the full-length alpha or beta isoforms of the parent receptor. ERalpha is found on chromosome 6q and encodes a 595 amino acid protein, while ERbeta is found on chromosome 14q and encodes a 530 amino acid protein. These receptors possess differing ligand affinities, are differentially expressed in a tissue-specific fashion and may act antagonistically. Their altered expression has been implicated in the pathophysiology of a diverse range of conditions from cancer progression in hormone-responsive tissues to neurodegenerative disease. Variously co-expressed with full-length ERs, ER splice variants may have a positive or negative influence on transcription either by modifying the effect of the parent receptor or through their own intrinsic activity. To date, the vast majority of studies have used generic primers or antibodies against the full-length receptors and would not distinguish ER-mediated effects associated with various splice variants. Thus the evidence base of the influence of ER splice variants in normal developmental physiology and in the pathogenesis of disease is weak and greater understanding of their role will undoubtedly lead to new therapeutic strategies for disease intervention and treatment. This review aims to compile the current evidence for the presence of ER splice variants in humans, their physiological roles and clinical sequelae.

Estrogen receptor-alpha and -beta immunoreactive neurons in the brainstem and spinal cord of male and female mice: relationships to monoaminergic, cholinergic, and spinal projection systems

For many populations of estrogen-sensitive neurons it remains unknown how they are associated with central nervous system circuitries that mediate estrogen-induced modulation of behavioral components. With the use of double-labeling immunohistochemistry and tracing techniques, the relationships of estrogen receptor (ER)-alpha- and ER-beta-immunoreactive (IR) neurons in the mouse brainstem and spinal cord to monoaminergic, cholinergic, and spinal projection systems are explored. Similar distributions of ER-IR neurons were present in females and males, with differences in labeling intensity of ER-alpha immunoreactivity among males and estrogen-, and oil-treated females. Barrington's nucleus, the ventrolateral medulla, and the nucleus of the solitary tract contained spinal-projecting ER-alpha-IR neurons, whereas ER-alpha-IR neurons in the periaqueductal gray, parabrachial nucleus, and catecholaminergic A1 cell group received spinal input. Numerous tyrosine hydroxylase (TH)-IR ER-alpha-IR neurons were present in the ventral periaqueductal gray, nucleus of the solitary tract, A1 cell group, and lumbosacral cord. The dorsal raphe nucleus contained ER-alpha-IR and ER-beta-IR neurons that colocalized with serotonin (5HT), and the reticulotegmental nucleus contained 5HT-IR ER-alpha-IR neurons. Fibers IR for vesicular acetylcholine transporter (VAChT), TH, and 5HT were located among ER-alpha-IR neurons in the dorsal horn and spinal autonomic regions. Robust staining for TH and VAChT, but not 5HT, was present among ER-alpha-IR neurons in the lumbosacral lateral collateral pathway. Possible modulatory actions of estrogen on each of these ER-IR populations are discussed in the context of their specific function, including micturition, sexual behavior, ejaculation, cardiovascular and respiratory control, tactile and nociceptive sensory processing, anti-nociception, endocrine regulation, and feeding.

Full-length sequence and expression analysis of estrogen receptor alpha mRNA in feline mammary tumors

We report here on the isolation and sequencing of feline estrogen receptor alpha (ER-alpha) mRNA. Feline ER-alpha showed three alternative 5' untranslated exons and a common transcript of 6183 base pairs (bp). The putative coding sequence (1788 bp) and the unusually long 3' untranslated (3'-UTR) region (4305 bp) displayed high sequence similarity with human ER-alpha. A highly conserved sequence block was found in the 3'-UTR corresponding to a putative regulatory element for mRNA stability. In addition to wild-type ER-alpha mRNA, several exon-deleted splicing variants (ERDeltaE2, ERDeltaE3, ERDeltaE4, ERDeltaE5, ERDeltaE6, ERDeltaE7) were found in various feline tissues. This is similar to what observed in human tissues and opposite to the near absence of exon-deleted isoforms in rodents. Expression analysis of exon-deleted variants was also conducted on 24 samples of feline mammary carcinoma (FMC) and 15 normal mammary gland (NMG) controls, using a "splice targeted approach". The prevalence of some variants was similar for human and feline ER-alpha, while other isoforms were expressed at different frequencies in the two species. Two of the most frequent isoforms (ERDeltaE4, ERDeltaE7) were significantly less frequent in FMCs than in NMGs, likely as a consequence of decreased expression of ER-alpha in FMCs.

Expression of estrogen receptor alpha exon-deleted mRNA variants in the human and non-human primate frontal cortex

Although estrogen receptor alpha (ERalpha) mRNA has been detected in the primate frontal cortex, the types of ERalpha transcripts expressed, including exon-deleted variants (Delta), have not been determined in the monkey or human frontal cortex. Because the types of ERalpha mRNA expressed in brain could define neuronal responses to estrogens, we examined the transcript pool of ERalpha mRNAs expressed in normal adult and developing human and macaque frontal cortex. We reverse transcribed total RNA from the postmortem frontal cortex of 29 normal adult humans, 12 rhesus macaques, and 19 people ranging from infants to adults and employed two rounds of nested polymerase chain reaction (PCR) to generate ERalpha products spanning the coding domain. In a third nested PCR, we used primers specific for novel sequences of exon-exon junctions created when whole exons are missing. By sequencing PCR products, we detected 60 instances of 12 distinct DeltaERalpha mRNAs in adult humans and 94 instances of 13 distinct DeltaERalpha mRNAs in monkeys in differing patterns from one individual to another. In adult humans, 83% of individuals expressed at least 1 DeltaERalpha mRNA variant, and 100% of the monkeys expressed at least 1 DeltaERalpha mRNA variant. The single Delta2, Delta5, and Delta7 variants were frequently expressed in both human and monkey frontal cortex, Delta3 variants were rare in both species, and Delta6 variants were more frequently expressed in monkeys. In both species, we detected double, triple and quadruple Deltas, but these were less common than single Deltas. The pattern of human variant expression did not appear to change dramatically as a function of age. These findings imply the potential to produce different ERalpha proteins in frontal cortex, possibly with altered structure and function which may have physiological relevance for gene transcription by virtue of altered functional interactions with each other, other steroid hormone receptors, and genomic DNA.

Occludin TM4-: an isoform of the tight junction protein present in primates lacking the fourth transmembrane domain

The tight junction protein occludin possesses four transmembrane domains,two extracellular loops, and cytoplasmic N- and C-termini. Reverse transcription-PCR analysis of human tissues, embryos and cells using primers spanning the fourth transmembrane domain (TM4) and adjacent C-terminal region revealed two products. The larger and predominant product corresponded in sequence to canonical occludin (TM4+), while the smaller product exhibited a 162 bp deletion encoding the entire TM4 and immediate C-terminal flanking region (TM4-). Examination of the genomic occludin sequence identified that the 162 bp sequence deleted in TM4-coincided precisely with occludin exon 4, strongly suggesting that TM4- is an alternative splice isoform generated by skipping of exon 4. Indeed, the reading frame of downstream exons is not affected by exclusion of exon 4. The presence of both TM4+ and TM4- occludin isoforms was also identified in monkey epithelial cells but TM4-was undetected in murine and canine tissue and cells, indicating a late evolutionary origin for this alternative splicing event. Conceptual translation of TM4- isoform predicts extracellular localisation of the C-terminus. Immunocytochemical processing of living human Caco-2 cells using a C-terminal occludin antibody revealed weak, discontinuous staining restricted to the periphery of subconfluent islands of cells, or islands generated by wounding confluent layers. In occludin immunoblots, a weak band at ∼58 kDa, smaller than the predominant band at 65 kDa and corresponding to the predicted mass of TM4- isoform, is evident and upregulated in subconfluent cells. These data suggest that the TM4- isoform may be translated at low levels in specific conditions and may contribute to regulation of occludin function.

Estrogen receptor beta. Potential functional significance of a variety of mRNA isoforms

Recent cloning of estrogen receptor beta (ERbeta) was followed by the discovery of a variety of its isoforms. This review describes the complexity of ERbeta mRNAs in various species for which most data have been gathered so far. The most surprising finding is the great variation in isoform structure among various mammalian species. This may reflect either the fact that only a very limited number of isoforms have been described so far or between-species specificity, especially as common elements in closely related species could still be noted. Isoform variations, as detected mainly at the mRNA sequence level, should result in profound functional differences at the level of proteins as already shown in selected cases. Thus, it is proposed that the diversity of ERbeta isoforms implies a functional role of this phenomenon in cellular physiology and pathology of estrogen response.

Genomic structure and identification of a truncated variant message of the mouse estrogen receptor alpha gene

Estrogen receptor alpha (ERalpha) is a ligand-dependent transcription factor that directs the transcription of a wide number of estrogen-regulated genes. ERalpha mediates the effects of 17-beta-estradiol in both males and females, and was the first estrogen receptor identified. Despite the cloning of the mouse ERalpha cDNA over 15 years ago, the precise genomic organization of the mouse ERalpha gene has not yet been elucidated. In order to determine the structure of this gene, overlapping BAC and P1 clones containing partial genomic sequences of the mouse ERalpha cDNA were obtained from a mouse ES cell genomic library. Using standard restriction fragment analysis followed by Southern blotting, the mouse ERalpha gene was determined to be greater than 220 kb in length. The introns vary widely in size, from 1.8 to 60 kb in length. Sequencing of intron-exon boundaries shows that these boundaries are highly conserved between the human and mouse ERalpha genes. Additionally, we have identified a splice variant message of mouse ERalpha arising from a failure to properly splice at the 3' end of exon 4; the resulting message is predicted to produce a protein lacking the ligand-binding domain. Variant message was detected by RT-PCR in several tissues, including uterus, ovary, mammary gland, placenta and testis.

Selective estrogen receptor modulators and coronary heart disease

The vasculature has been recognized as an important target of estrogen action through rapid non-genomic effects and/or via the classic pathway (genomic effects) involving estrogen receptors (ER-alpha and ER-beta). Multiple mechanisms participate in the regulation of different estrogen-controlled genes, providing a wide spectrum of possibilities for development of drugs, including pure agonists or antagonists or mixed agonists/antagonists, the so-called selective estrogen receptor modulators (SERM). In theory, an ideal SERM should reduce the risks of coronary heart disease (CHD) and preserve bone density, without or with very low incidences of breast and endometrial neoplasms or venous thromboembolism (VTE). The precise mechanism for the protective effects of estrogens and their receptors on cardiovascular diseases is not yet fully established. In this review, we summarize the recent advances in understanding the action of ERs/ligands, the therapeutic implications for CHD, and highlight the recent progress of both clinical and basic studies on the protection issue. Finally, a number of newly developed SERMs and their clinical applications as well as the laboratory investigations are discussed.

Expression and regulation of estrogen receptors in mesangial cells: influence on matrix metalloproteinase-9

Diabetic glomerulosclerosis is characterized by the accumulation of extracellular matrix (ECM) in the mesangium. Estrogens seem to retard whereas estrogen deficiency seems to accelerate progressive glomerulosclerosis. Thus, mesangial cells (MC) may be a target for estrogens. Estrogen action is mediated via estrogen receptor (ER) subtypes ERalpha and ERbeta. Both ER subtypes were expressed in human and mouse MC. Using an estrogen-responsive reporter construct in transfection assays, it also was demonstrated that the nuclear ER were transcriptionally active. In the presence of 17beta-estradiol (E2; 10(-10) to 10(-8) M), there was a progressive increase in the mRNA levels of both ERalpha (approximately 1.8-fold and approximately 2.7-fold after 24 and 72 h, respectively) and ERbeta (approximately 1.3-fold and approximately 2.2-fold after 24 and 72 h, respectively). ERalpha protein levels increased approximately 2.5-fold after 24 h (10(-10) M, E2) and up to approximately 5.4-fold after 72 h (10(-9) M, E2). ERbeta protein levels increased approximately 2.1-fold in the presence of E(2) (10(-9) M) after 24 h. Thus, estrogens positively regulate the expression of the ER subtypes, thereby maintaining or increasing MC responsiveness to estrogens. Because diabetic glomerulosclerosis may be due partly to a decrease in ECM degradation, the effects of estrogens on matrix metalloproteinases (MMP) were studied. It was found that E2 (10(-10) to 10(-8) M) increased both MMP-9 mRNA and MMP-9 activity in MC. This may be an important mechanism by which estrogens influence ECM turnover and protect against progression of diabetic glomerulosclerosis.

Estrogen blocks inducible nitric oxide synthase accumulation in LPS-activated microglia cells

Estrogens are thought to play a protective role against neurodegeneration through a variety of mechanisms including the activation of growth factors and neurotransmitter synthesis, the control of synaptic plasticity and functions, and the blockade of oxidative reactions. We here propose a novel mechanism to explain the neuroprotective effects of estradiol by showing that estrogens may antagonize nitric oxide synthase activity and reduce the accumulation of nitrites and nitrates consequent to various inflammatory stimuli. The potential anti-inflammatory activity of estradiol is analyzed in vitro in cells in culture including primary cultures of microglia and in vivo in a well-known model of inflammation.

Tissue-specific expression of multiple mRNA variants of the mouse estrogen receptor alpha gene

The isolation of five new mouse estrogen receptor alpha mRNA variants (mERalpha A, B, F1, F2 and H) is described. All of these transcripts are generated by alternative splicing and all encode the 66 kDa ERalpha protein that the previously identified mRNA C variant generates. However, these transcripts differ in their 5' untranslated regions. RT-PCR and S1 nuclease protection assays revealed a tissue- and sex-specific expression pattern of all variants. The C and F mRNA variants are the predominantly expressed mERalpha variants in mouse. The expression of mERalpha H mRNA is restricted to liver, although female mice produce around a five fold higher level of this transcript than males. Our results show that the mERalpha gene is a complex genomic unit in mice that exhibits alternative splicing which is regulated in a tissue-specific manner.