A Molecular Analysis Provides Novel Insights into Androgen Receptor Signalling in Breast Cancer

Abstract

BackgroundAndrogen Receptor (AR) is an essential transcription factor for the development of secondary sex characteristics, spermatogenesis and carcinogenesis. Recently AR has been implicated in the development and progression of breast and prostate cancers. Although some of the functions of the AR are known but the mechanistic details of these divergent processes are still not clear. Therefore understanding the regulatory mechanisms of the functioning of the AR in ER-/AR+ breast cancer will provide many novel targets for the purpose of therapeutic intervention.Methods/ResultsUsing bioinformatics tools, we have identified 75 AR targets having prominent roles in cell cycle, apoptosis and metabolism. Herein, we validated 10 genes as AR targets by studying the regulation of these genes in MDA-MB-453 cell line on stimulation by androgens like 5α-dihydrotestosterone (DHT), using RT-qPCR and ChIP assay. It was observed that all the identified genes involved in cell cycle except MAD1L1 were found to be up regulated whereas expression of apoptosis related genes was decreased in response to DHT treatment. We performed an exhaustive, rigid-body docking between individual ARE and DNA binding domain (DBD) of the AR protein and it was found that novel residues K567, K588, K591 and R592 are involved in the process of DNA binding. To verify these specific DNA-protein interactions electrostatic energy term calculations for each residue was determined using the linearized Poisson–Boltzmann equation. Our experimental data showed that treatment of breast cancer cells with DHT promotes cell proliferation and decreases apoptosis. It was observed that bicalutamide treatment was able to reverse the effect of DHT.ConclusionTaken together, our results provide new insights into the mechanism by which AR promotes breast cancer progression. Moreover our work proposes to use bicalutamide along with taxanes as novel therapy for the treatment of TNBCs, which are positive for downstream AR signalling.

AR Signaling in Breast Cancer

“…Though there are advantages to the use of these classic cell line models, over time multiple cycles of cell cultures can select for certain subclones that can create variability in genetic and phenotypic expression across labs [183]. For example, in one study the cell line MDA-MB-453 notably had a homozygous deletion in TP53, a homozygous PTEN missense mutation and a PI3K mutation and it is unclear if these are preserved changes in the cell line or unique to the specific version from that particular lab [127]. Several studies do utilize cells fresh tumor samples to help corroborate their findings, but many do not and thus reproducibility of the findings is a question.…”

“…Another study aimed at understanding the interplay between the transcription factor ZEB1, which plays a role in cancer progression by regulating the epithelial to mesenchymal transition (i.e., increased tumor migration and invasion) in breast cancer, and AR signaling in TNBC noted that by inhibiting ZEB1, AR expression was decreased and perhaps more importantly, inhibition of AR signaling with bicalutamide suppressed ZEB1 expression [126]. Mehta and colleagues analyzed the TNBC cell line MDA-MB-453, which in addition to AR positivity, also has PTEN and p53 mutations [127]. They identified 10 genes as AR targets using RT-qPCR and ChIP sequencing techniques and found that androgens promote cell proliferation and decrease apoptosis via these gene targets.…”

“…Additionally, they hypothesized that the reason for poorer response to adjuvant or neoadjuvant chemotherapy in AR-positive TNBC was due to an AR-mediated resistance to apoptosis. The effects of paclitaxel, 5-fluorouracil and cyclophosphamide in AR-positive TNBC were studied and cells were found to have significant increases in cell survival and decreased apoptosis in the presence of androgen and that this could be reversed with the addition of bicalutamide [127]. As previously noted, patients with TNBC receiving neoadjuvant chemotherapy have been found to have lower pCR rates when AR-positive and this study provides rationale that perhaps targeting the AR pathway may help improve pCR rates [116].…”

Androgen Receptor Inhibitor Enhances the Antitumor Effect of PARP Inhibitor in Breast Cancer Cells by Modulating DNA Damage Response

“…About 50%-80% of invasive breast cancers (regardless of ER status) express AR and recent studies indicate AR expression is positively associated with a good prognosis. In addition, recent studies showed that AR-expressing triple-negative breast cancer (TNBC) is dependent on AR signaling; thus, targeting AR seems to improve outcomes in TNBC (1)(2)(3)(4)(5)(6)(7). Despite the prevalence and clinical significance of AR expression in breast cancer, preclinical evidence supporting the use of ARtargeting agents and potential biomarkers of response to AR inhibitors in breast cancer are lacking (4).…”

Interaction between APC and Fen1 during breast carcinogenesis

“…Detailed molecular and biochemical analysis of breast tumor tissues and cell lines have implicated defects in many different molecules, including BRAC1, BRAC2, c-Myc, c-erbB2, PTEN, LKB1, ATM, MSH2/MLH1, Chk2, BACH-1, Ki-67, cyclin D1, p53, estrogen, progesterone and androgen receptors in breast tumorigenesis [98–102]. Although there is less evidence of an association with defects in APC and Fen1 with breast cancer, it should be noted that in most studies these molecules have been analyzed independently and the focus has not been on protein/protein interactions.…”