George Kuiper

Comparison of the ligand binding specificity and transcript tissue distribution of estrogen receptors alpha and beta

The rat estrogen receptor (ER) exists as two subtypes, ERα and ERβ, which differ in the C-terminal ligand binding domain and in the N-terminal transactivation domain. In this study we investigated the messenger RNA expression of both ER subtypes in rat tissues by RT-PCR and compared the ligand binding specificity of the ER subtypes. Saturation ligand binding analysis of in vitro synthesized human ERα and rat ERβ protein revealed a single binding component for 16α-iodo-17β-estradiol with high affinity[ dissociation constant (Kd) = 0.1 nm for ERα protein and 0.4 nm for ERβ protein]. Most estrogenic substances or estrogenic antagonists compete with 16α-[125I]iodo-17β-estradiol for binding to both ER subtypes in a very similar preference and degree; that is, diethylstilbestrol > hexestrol > dienestrol > 4-OH-tamoxifen > 17β-estradiol > coumestrol, ICI-164384 > estrone, 17α-estradiol > nafoxidine, moxestrol > clomifene > estriol, 4-OH-estradiol > tamoxifen, 2-OH-estradiol, 5-androstene-3β,17β-diol, genistein f...

The Estrogen Receptor β Subtype: A Novel Mediator of Estrogen Action in Neuroendocrine Systems☆

The recent discovery that an additional estrogen receptor (ERbeta) subtype is present in many rat, mouse, and human tissues has advanced our understanding of the mechanisms underlying estrogen signalling. Ligand-binding experiments have shown specific binding of 17beta-estradiol by ERbeta with an affinity similar to that of ERalpha. The rat tissue distribution and/or the relative level of ERalpha and ERbeta expression seems to be quite different, i.e., moderate to high expression in uterus, testis, pituitary, ovary, kidney, epididymis, and adrenal for ERalpha and prostate, ovary, lung, bladder, brain, bone, uterus, and testis for ERbeta. Within the same organ it often appears that the ER subtypes are expressed in different cell types, supporting the hypothesis that the ERs may have different biological functions. The cell type-specific expression of ERalpha and ERbeta in rat prostate, testis, uterus, ovary, and brain and the distribution of ERbeta mRNA in the ERalpha knock-out mouse brain are discussed. The discovery of ERbeta suggests the existence of two previously unrecognized pathways of estrogen signalling; via the ERbeta subtype in tissues exclusively expressing this subtype and via the formation of heterodimers in tissues expressing both ER subtypes. The existence of two ER subtypes, their differential expression pattern, and different actions on certain response elements could provide explanations for the striking species-, cell-, and promoter-specific actions of estrogens and antiestrogens. The challenge for the future is to unravel the detailed physiological role of each subtype and to use this knowledge to develop the next generation of ER-targeted drugs with improved therapeutic profiles in the treatment or prevention of osteoporosis, cardiovascular system disorders, Alzheimers disease, breast cancer, and disorders of the urogenital tract.

The novel estrogen receptor-β subtype: potential role in the cell- and promoter-specific actions of estrogens and anti-estrogens

The recent discovery that an additional estrogen receptor (ER) subtype is present in various rat, mouse and human tissues has advanced our understanding of the mechanisms underlying estrogen signalling. The discovery of a second ER subtype (ERβ) suggests the existence of two previously unrecognised pathways of estrogen signalling: via the ERβ subtype in tissues exclusively expressing this subtype and via the formation of heterodimers in tissues expressing both ER subtypes. Various models have been suggested as explanations for the striking cell‐ and promoter‐specific effects of estrogens and anti‐estrogens, all on the basis of the assumption that only a single ER gene exists. This minireview describes several of these models and focuses on the potential role which the novel ERβ subtype might have in this regard.

Differential distribution and regulation of estrogen receptor-α and -β mRNA within the female rat brain

Abstract In the present study, estrogen receptor (ER)α and ERβ genes were found to be differentially expressed in discrete subregions of the rat amygdaloid complex. The amygdala nuclei showing predominant ERα mRNA expression included the posterolateral cortical nucleus, amygdala hippocampal area, and lateral dorsolateral nucleus, whereas the amygdala areas with predominant ERβ mRNA expression were the medial anterodorsal and central nuclei. Both ERα and ERβ mRNAs were highly expressed in the medial posterodorsal nucleus. In addition to the discrete anatomical expression patterns, there appeared to be a differential regulation by estradiol of the ERα and ERβ mRNAs. Two weeks of estradiol (170 μg total) treatment decreased ERα mRNA expression levels in the arcuate, ventromedial hypothalamus, and posterolateral cortical amygdala nucleus, but increased ERβ mRNA in the arcuate. In the medial amygdala nuclei, only ERβ mRNA levels were altered (reduced) by estradiol treatment. These results suggest that estrogen can modulate behaviors and functions mediated by the amygdala and hypothalamus via differentially regulated ER subtypes.

Increased Expression of Estrogen Receptor-β mRNA in Male Blood Vessels After Vascular Injury

Estrogen exerts direct effects on vascular endothelial and smooth muscle cells that are important for vascular protection. Estrogen receptor-alpha (ERalpha) is expressed in vascular cells from males and females and may mediate some of the effects of estrogen on vascular tissue. However, we recently found that estrogen is able to protect against vascular injury in ovariectomized female ERalpha knockout mice. These mice express the newly described estrogen receptor-beta (ERbeta) in their aortas, suggesting that ERbeta may also mediate some of the direct effects of estrogen on the vasculature. In this study, the level of expression of ERalpha and ERbeta mRNA in male rat aortas was examined before and after vascular injury using en face (Häutchen) preparations and in situ hybridization. Little or no change in ERalpha expression was observed after vascular injury in either vascular endothelial or smooth muscle cells at any time point. In contrast, ERbeta mRNA was found to be expressed markedly after balloon injury. In endothelial cells, ERbeta was increased by 2 days after injury, and high levels of expression were maintained at 8 and 14 days. Furthermore, ERbeta expression was high in luminal smooth muscle cells at 8 and 14 days after injury and had decreased to low levels by 28 days after injury. These data demonstrate the presence of ERbeta in male vascular tissues and the induction of ERbeta mRNA expression after vascular injury, supporting a role for ERbeta in the direct vascular effects of estrogen.

Differential Expression of Estrogen Receptors α and β mRNA During Differentiation of Human Osteoblast SV-HFO Cells

Estrogens have been shown to be essential for maintaining a sufficiently high bone mineral density and ER alpha expression has been demonstrated in bone cells. Recently, a novel estrogen receptor, estrogen receptor beta (ERbeta) has been identified. Here we demonstrate that also ERbeta is expressed in human osteoblasts, and that ER alpha and ERbeta are differentially expressed during human osteoblast differentiation. ERbeta mRNA expression increased gradually during osteoblast culture, resulting in an average increase of 9.9+/-5.3 fold (mean+/-S.D., n=3) at day 21 (mineralization phase) as compared to day 6 (proliferation phase). In contrast, ER alpha mRNA expression levels increased only slightly until day 10 (2.3+/-1.7 fold) and then remained constant. The observed differential regulation of ER alpha and beta is suggestive for an additional functional role of ERbeta to ER alpha in bone metabolism.

Differential expression of estrogen receptors α and β in adult rat accessory sex glands and lower urinary tract

Abstract Estrogens induce pronounced structural and functional changes in male accessory sex glands and the lower urinary tract in both sexes, but the exact mechanisms of estrogen action are not fully understood. This study was undertaken to localise the tissue cell types that express estrogen receptor in adult rats, and to determine the receptor subtype (ERα and ERβ) in order to identify sites that may respond directly to estrogens. In the male accessory sex glands (seminal vesicles, prostatic lobes and ampullary glands), ERβ mRNA and protein were strongly expressed in the epithelium but not in the stroma, while ERα mRNA was present only in the fibromuscular tissue surrounding the prostatic collecting ducts in the posterior periurethral region and in ampullary gland stroma. In the epithelium of the urinary bladder and urethra of both sexes, high level of ERβ mRNA and protein, but no ERα mRNA, was detected. The connective tissue in urinary bladder of both males and females, as well as that in prostatic urethra in males expressed ERα mRNA. The neural cells in the autonomic ganglia of the prostatic plexus were strongly positive for ERβ mRNA, but were completely devoid of ERα. We conclude that ERβ is the predominant ER subtype in the epithelium of adult male rat accessory sex glands and the lower urinary tract of both males and females, as well as in the prostatic neural plexus regulating the function of the lower urinary tract in males, while ERα is present only in the stromal compartment of distinct sites. These results indicate that in these tissues in intact adults there are multiple targets for direct estrogen action. Furthermore, the differential or complementary expression of the two ER subtypes suggests that they may have specific functions, and may explain the complex structural and functional changes induced by estrogens.

Expression of estrogen receptor alpha and beta during mouse embryogenesis.

In adult mammals numerous target tissues and organs for estrogens exist. Little is known about possible target organs during embryogenesis other than the reproductive tract and the gonads. This is the first report on the expression of estrogen receptor beta (ERbeta) in comparison with ERalpha mRNA during mouse embryogenesis. We found expression of estrogen receptor mRNA in the reproductive tract, but also in the atrial wall, brain, kidney, urethra, bladder neck, mammary gland primordium, midgut, cartilage primordia and perichondria.

ERβ a Novel Estrogen Receptor Offers the Potential for New Drug Development

There is increasing interest in developing better drugs for improving the health of women. Because of the multiple target organs for estrogens and the occurrence of both beneficial and unwanted effects during treatment, the key to improvement in drug therapy is the development of estrogen receptor modulators with better tissue selectivity. The recent discovery that there are not one but two estrogen receptors, ERalpha and ERbeta, each with its unique tissue distribution and with differing and sometimes opposing actions on certain genes, promises new hope for the development of novel, tissue-selective estrogens. Our present knowledge of the tissue distribution of ERalpha and ERbeta suggests that development of selective therapies for treatment and/or prevention of menopausal symptoms, osteoporosis, cardiovascular disease, type II diabetes, Alzheimers disease and urinary incontinence is an achievable goal in the foreseeable future. Furthermore, it is possible that future estrogen therapy might be beneficial for men.

Erratum to “Differential expression of estrogen receptors α and β in adult rat accessory sex glands and lower urinary tract”[Mol. Cell. Endocrinol. 164 (2000) 109–116]

Estrogens induce pronounced structural and functional changes in male accessory sex glands and the lower urinary tract in both sexes, but the exact mechanisms of estrogen action are not fully understood. This study was undertaken to localise the tissue cell types that express estrogen receptor in adult rats, and to determine the receptor subtype (ERa and ERb) in order to identify sites that may respond directly to estrogens. In the male accessory sex glands (seminal vesicles, prostatic lobes and ampullary glands), ERb mRNA and protein were strongly expressed in the epithelium but not in the stroma, while ERa mRNA was present only in the fibromuscular tissue surrounding the prostatic collecting ducts in the posterior periurethral region and in ampullary gland stroma. In the epithelium of the urinary bladder and urethra of both sexes, high level of ERb mRNA and protein, but no ERa mRNA, was detected. The connective tissue in urinary bladder of both males and females, as well as that in prostatic urethra in males expressed ERa mRNA. The neural cells in the autonomic ganglia of the prostatic plexus were strongly positive for ERb mRNA, but were completely devoid of ERa. We conclude that ERb is the predominant ER subtype in the epithelium of adult male rat accessory sex glands and the lower urinary tract of both males and females, as well as in the prostatic neural plexus regulating the function of the lower urinary tract in males, while ERa is present only in the stromal compartment of distinct sites. These results indicate that in these tissues in intact adults there are multiple targets for direct estrogen action. Furthermore, the differential or complementary expression of the two ER subtypes suggests that they may have specific functions, and may explain the complex structural and functional changes induced by estrogens.