ERβ SNPs in African Americans and disease susceptibility 5.1
Compared to white Americans, African-Americans have poor outcome of certain diseases such as breast cancer and prostate cancer. The mortality rate of breast cancer is three times higher in African American than other populations. Notably, the prevalence of TNBC is highest in premenopausal African American women [145]. It was reported that 39% of premenopausal African American breast cancer patients was diagnosed with TNBC [146]. The prevalence of TNBC among non- African American is around 15% and the difference was not seen in other breast cancer subtype groups [146]. We speculate that African-specific genetic variants may be associated with the susceptibility to specific subtypes of cancer. One recent report found that the SNP rs10069690 in the TERT gene was significantly associated with TNBC in an African ancestry population [147]. We are one of the very few groups studying polymorphisms of ERβ genes in African populations. We screened the ERβ gene in an African population for polymorphisms. The identified polymorphism, particularly a functional polymorphism, would constitute important tools for further disease association studies in this population. Future studies should address the frequency of the two identified polymorphisms that change the amino acid sequence of the ERβ protein in a much larger cohort. It would also be interesting to investigate if these SNPs are present, and their frequency, in other populations. Finally, further functional studies of these variants could involve generating mice strains with the corresponding SNPs in ERβ.
Rodent ERβ2; considerations when performing animal studies using ER 5.2
agonists and antagonists
Our studies showed that the binding affinity of E2 was mERβ1 selective while raloxifene was mERβ2 selective. mERβ2 required 10-fold greater E2 concentrations compared to mERβ1 to reach the maximal transactivity, whereas raloxifene was more potent in antagonizing E2-induced gene expression via mERβ2 than mERβ1.
Mouse and rat are commonly used animal models to study ER function in vivo. Furthermore, disease models in mouse and rat are used to evaluate the effect of compounds with estrogenic or anti-estrogenic properties to improve the disease condition. As humans do not have mERβ2, this isoform-dependent ligand selectivity, reported for the two rodent ERβs in this study, needs to be considered when novel compounds are tested in animal studies. A further complication arises from the fact that the relative levels of mERβ1 and mERβ2 likely vary between tissues. The development of mice strains lacking expression of mERβ2 would be an important development. However, humanized mice, in which the mouse ERβ LBD was replaced by human ERβ LBD showed embryo lethality (Per Antonson, personal communication).
Estrogen signaling, cell proliferation and invasion 5.3
Estrogens promotes epithelial cell proliferation in both normal and neoplastic breast [148] and ER signaling is associated with tumorigenesis, metastasis and therapeutic resistance.
In our study we showed that hERβ2 is the predominant endogenously expressed ER in a TNBC cell line BT549 and promotes cell proliferation and invasion in this cell line. We demonstrate that the invasive phenotype associated with hERβ2 expression could potentially be via repressing expression of PHD3 followed by up-regulation of the HIF-1α-MET pathway or direct regulation of MET.
tumor-protective functions and to inhibit tumor growth in pancreatic cancer. Our study contributes to the understanding of the molecular mechanism of hERβ2 regulation of cell proliferation and invasion. Future studies should focus on how hERβ2 regulates PHD3 and ultimately cell proliferation and invasion. It will be important to identify additional cell lines expressing hERβ2 in the absence of other ERs to investigate the generality of the observations, both TNBC cell lines and cell lines of different origin, including regulation of PHD3 and the HIF-1a-MET pathway. Furthermore, it will be important to pursue similar studies in cell lines expressing hERβ2 in the presence of ERα and/or hERβ1. The correlation of hERβ2 with PHD3 or components of the HIF-1α-MET pathway in clinical samples will provide evidence for the clinical relevance of our findings. Although, in this thesis, we focus on hERβ2 regulation of PHD3 and the HIF-1α-MET pathway, other potential mechanisms should be explored. These could be derived from a more careful examination of the global gene expression profiling data already obtained. Furthermore, the global gene expression profiling data is derived from a single time point following inhibition of hERβ2 with siRNA. Performing global gene expression profiling at additional time points following siRNA transfection might reveal alternative potential targets responsible for the observed phenotypes. Such studies could also include identification hERβ2 regulated miRNAs and other non- coding RNAs. Finally, although hERβ2 does not bind tested ER ligands, it is possible that compounds that inhibit its function or target genes can be identified, thus providing potential therapeutic agents for breast cancers that express hERβ2.