Breast cancer oestrogen independence mediated by BCAR1 or BCAR3 genes is transmitted through mechanisms distinct from the oestrogen receptor signalling pathway or the epidermal growth factor receptor signalling pathway

Abstract

IntroductionTamoxifen is effective for endocrine treatment of oestrogen receptor-positive breast cancers but ultimately fails due to the development of resistance. A functional screen in human breast cancer cells identified two BCAR genes causing oestrogen-independent proliferation. The BCAR1 and BCAR3 genes both encode components of intracellular signal transduction, but their direct effect on breast cancer cell proliferation is not known. The aim of this study was to investigate the growth control mediated by these BCAR genes by gene expression profiling.MethodsWe have measured the expression changes induced by overexpression of the BCAR1 or BCAR3 gene in ZR-75-1 cells and have made direct comparisons with the expression changes after cell stimulation with oestrogen or epidermal growth factor (EGF). A comparison with published gene expression data of cell models and breast tumours is made.ResultsRelatively few changes in gene expression were detected in the BCAR-transfected cells, in comparison with the extensive and distinct differences in gene expression induced by oestrogen or EGF. Both BCAR1 and BCAR3 regulate discrete sets of genes in these ZR-75-1-derived cells, indicating that the proliferation signalling proceeds along distinct pathways. Oestrogen-regulated genes in our cell model showed general concordance with reported data of cell models and gene expression association with oestrogen receptor status of breast tumours.ConclusionsThe direct comparison of the expression profiles of BCAR transfectants and oestrogen or EGF-stimulated cells strongly suggests that anti-oestrogen-resistant cell proliferation is not caused by alternative activation of the oestrogen receptor or by the epidermal growth factor receptor signalling pathway.

Functional identification of genes causing estrogen independence of human breast cancer cells

“…The proliferation capacity of the transfectant cells with overexpression of various genes (AKT1, BCAR1, BCAR3, and EGFR) was retained in the presence of a pure anti-estrogen as well, indicating that growth was not stimulated by tamoxifen through the ER [15,19,24]. The list of (candidate) target genes of retrovirus insertion mutagenesis causing estrogen independence comprises several functional categories of cellular signaling, i.e.…”

Functional Screen for Genes Responsible for Tamoxifen Resistance in Human Breast Cancer Cells

“…16 and this article). Four of these genes are expressed at extremely low levels (EGFR) or are undetectable (PDGFRA, PDGFRB, and LOC400500/BCAR4) in the parental ZR-75-1 cells (17). 4 Thus, the infected cells acquired a novel function essential for tamoxifen-resistant proliferation.…”

Downregulation of SIAH2, an ubiquitin E3 ligase, is associated with resistance to endocrine therapy in breast cancer

“…An Assay-on-Demand kit (Hs00192581_m1; Applied Biosystems) was used to measure SIAH2 mRNA levels. Primer sequences for ER, PgR, EGFR, HER2, and reference genes PBGD, HPRT and B2 M have been described [14,16,17]. About 40 rounds of amplification were performed to generate Cycle threshold (Ct) values and to calculate mRNA expression levels.…”

“…MCF7, estrogen sensitive, was cultured in RPMI 1640 containing 10% foetal calf serum. The estrogen-dependent ZR-75-1 and its EGFR-transfectant, ZR/HERc, were maintained in RPMI 1640, 10% bovine calf serum and 1 nM 17 b-estradiol as described previously [17]. Cell lines were grown in different culture conditions in short-(2, 4 and 6 h) and long-term (96, 168 and 192 h) experiments.…”

“…Charcoal treated serum and phenol red-free medium were used to obtain E2-depleted culture conditions. Medium was supplemented with previously described compounds [17]: E2 (10 nM), ICI164,384 (100 nM), EGF (10 ng/ml) or a combination, or with ethanol vehicle alone as indicated in the legends. In vitro, to evaluate only pure anti-E2 effects, the selective estrogen receptor degrader (SERD) ICI164,384 was used instead of tamoxifen.…”