Re: Skliris et al. Evaluation of seven oestrogen receptor beta antibodies for immunohistochemistry, western blotting, and flow cytometry in human breast tissue. J Pathol 2002; 196: 155-162

The Co-Expression of Estrogen Receptors ERα, ERβ, and GPER in Endometrial Cancer

Estrogens have important roles in endometrial cancer (EC) and exert biological effects through the classical estrogen receptors (ERs) ERα and ERβ, and the G-protein-coupled ER, GPER. So far, the co-expression of these three types of ERs has not been studied in EC. We investigated ERα, ERβ, GPER mRNA and protein levels, and their intracellular protein distributions in EC tissue and in adjacent control endometrial tissue. Compared to control endometrial tissue, immunoreactivity for ERα in EC tissue was weaker for nuclei with minor, but unchanged, cytoplasmic staining; mRNA and protein levels showed decreased patterns for ERα in EC tissue. For ERβ, across both tissue types, the immunoreactivity was unchanged for nuclei and cytoplasm, although EC tissues again showed lower mRNA and protein levels compared to adjacent control endometrial tissue. The immunoreactivity of GPER as well as mRNA levels of GPER were unchanged across cancer and control endometrial tissues, while protein levels were lower in EC tissue. Statistically significant correlations of estrogen receptor α (ESR1) versus estrogen receptor β (ESR2) and GPER variant 3,4 versus ESR1 and ESR2 was seen at the mRNA level. At the protein level studied with Western blotting, there was significant correlation of ERα versus GPER, and ERβ versus GPER. While in clinical practice the expression of ERα is routinely tested in EC tissue, ERβ and GPER need to be further studied to examine their potential as prognostic markers, provided that specific and validated antibodies are available.

Insufficient antibody validation challenges oestrogen receptor beta research

The discovery of oestrogen receptor β (ERβ/ESR2) was a landmark discovery. Its reported expression and homology with breast cancer pharmacological target ERα (ESR1) raised hopes for improved endocrine therapies. After 20 years of intense research, this has not materialized. We here perform a rigorous validation of 13 anti-ERβ antibodies, using well-characterized controls and a panel of validation methods. We conclude that only one antibody, the rarely used monoclonal PPZ0506, specifically targets ERβ in immunohistochemistry. Applying this antibody for protein expression profiling in 44 normal and 21 malignant human tissues, we detect ERβ protein in testis, ovary, lymphoid cells, granulosa cell tumours, and a subset of malignant melanoma and thyroid cancers. We do not find evidence of expression in normal or cancerous human breast. This expression pattern aligns well with RNA-seq data, but contradicts a multitude of studies. Our study highlights how inadequately validated antibodies can lead an exciting field astray.

A large body of work into the role of oestrogen receptor b (ERb) in breast cancer is contradictory, hindering future progress. Here the authors conduct extensive validation of anti-ERb antibodies , and show that normal and cancerous breast tissue do not express ERb, consistent with RNA-seq data.

Role of oestrogen receptors in bladder cancer development

Early studies documented the existence of sexual dimorphism in bladder cancer occurrence and progression, with a greater bladder cancer incidence in males than females. However, the progression of bladder cancer after diagnosis is much quicker in females than males. These findings can be explained by the effects of female hormones (predominantly oestrogens) and their binding receptors, including oestrogen receptor 1 (ESR1; also known as ERα), oestrogen receptor 2 (ESR2; also known as ERβ), and GPR30 protein on bladder cancer incidence and progression. Results from studies using various in vitro cell lines and in vivo mouse models demonstrate differential roles of oestrogen receptors in cancer initiation and progression. ERα suppresses bladder cancer initiation and invasion, whereas ERβ promotes bladder cancer initiation and progression. Mechanistic studies suggest that ERα and ERβ exert these effects via modulation of the AKT pathway and DNA replication complex, respectively. Targeting these signalling pathways--for example, with ERα agonists, ERβ antagonists, or selective oestrogen receptor modulators such as 4-[2-phenyl-5,7-bis(trifluoromethyl)pyrazolo[1,5-a]pyrimidin-3-yl]phenol (also known as PHTPP)--could lead to the development of new therapeutic approaches for controlling bladder cancer progression.

Wild-type oestrogen receptor beta (ERbeta1) mRNA and protein expression in Tamoxifen-treated post-menopausal breast cancers

This study has tested the hypothesis that comparison of protein and mRNA expression for ERα and ERβ1 by human breast cancers provides novel information relating to the clinical and pathological characteristics of human breast cancers. Expression of ERα and ERβ1 was identified in 167 invasive cancers from postmenopausal women treated only with endocrine therapy. The cohort included 143 cases receiving only adjuvant Tamoxifen following surgery. ERα and ERβ1 expression was analysed by immunohistochemistry and reverse transcription RT–PCR and compared with clinical progression of individual cancers. ERα protein was closely associated with the corresponding RNA detected by RT–PCR (Chi-square, P<0.001). In contrast, ERβ1 protein and mRNA were inconsistent. Although an association was identified between ERα and ERβ mRNAs (Chi-square, P<0.001) and between ERα protein and ERβ1 mRNA (Chi-square, P<0.027), no association was identified for the ERα and ERβ1 proteins detected by immunohistochemistry. ERβ1 was not associated with outcome. However, in the absence of ERα, ERβ1 protein expression was associated with elevated cell proliferation. There was a trend for the ERβ1 protein-positive cases to have a worse outcome, both within the group as a whole as well as within the ERα-positive Tamoxifen-treated cases. This study has confirmed the hypothesis that expression of ERα is an important determinant of breast cancer progression, and has further demonstrated that ERβ1 may play a role in the response of breast cancers to endocrine therapy.

Declining estrogen receptor-beta expression defines malignant progression of human breast neoplasia

It has been shown that the risk of breast cancer developing in certain morphologically identifiable benign breast lesions correlates with expression of estrogen receptor alpha (ER-alpha). Although ER-alpha and ER-beta genes share a large degree of homology, it is generally thought that their distribution and functions are substantially different in many tissues. Recent development of reliable antibodies to ER-beta has provided this first opportunity to test the hypothesis that the likelihood of malignant transformation in morphologically benign breast lesions can be accurately defined by the distribution and level of ER-beta expression relative to that of ER-alpha. Using a monoclonal antibody, ER-beta protein expression has been analyzed in 53 normal breasts and compared with a cohort of histologically distinct breast lesions of different prognostic risk (54 hyperplasia of usual type, 35 ductal carcinoma in situ, and 141 invasive cancers). All of these tissues were also assessed for ER-alpha. Expression of ER-beta protein was also analyzed in an additional spectrum of benign breast lesions with low or negligible risk of progression to malignancy. The median proportion of cells expressing ER-beta was highest in normal breast lobules (median 94.33%, interquartile range 78.25-99.00) but declined significantly through usual ductal hyperplasia (median 76.67, interquartile range 49.17-95.00, P = 0.002) and ductal carcinoma in situ (median 70.00, interquartile range 59.00-85.00, P = 0.009) to invasive cancer (median 60.00, interquartile range 50.00-80.00, P < 0.001). An appreciable proportion (33.81%) of ER-alpha-negative invasive cancers expressed ER-beta. A high but variable level of ER-beta expression occurred in the benign lesions. The data from the intact histologic tissues were evaluated with respect to the relative expression of ER-alpha and ER-beta in five mammary cell lines of different behavioral phenotype (MCF7, ZR-75, T47D, MDAMB231, HUMA121). The highly significant differences in expression and distinct tissue distributions of ER-alpha and ER-beta within the histologic lesions of defined risk, together with the data from the cell lines, support the original hypothesis that the tissue concentration, relative occurrence, and/or interaction of these two types of estrogen receptor may play an important role in modulating mammary tumorigenesis.