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Estrogen deprivation alters epigenetic modifications in breast cancer cells - HOXC10 loss in endocrine resistance

ABSTRACT: Postmenopausal breast cancer patients benefit from aromatase inhibitors (AIs) that reduce the levels of estrogens critical for the growth of estrogen receptor (ER)-positive tumors. Unfortunately, many tumors are resistant to AI, and we are only beginning to understand the complex mechanisms underlying treatment resistance. Here we set out to determine whether epigenetic changes could contribute to therapy resistance. For AI-resistance models, we used previously established MCF-7 cell clones, termed C4-12 and long-term estrogen deprivation (LTED), that were isolated after being cultured in estrogen-free media for 9 months and 18–24 months, respectively. Methyl CpG Binding Domain (MBD) - pull down followed by affymetrix promoter array was used to detect promoter methylation patterns in these cell lines. These studies identified widespread genomic hyper- and hypomethylation events, with a significant enrichment of promoter hypermethylation of development-associated genes in both cell lines. A developmentally regulated gene that was heavily methylated and lost expression in both cell-line systems was HOXC10. Moreover, we found that HOXC10 is an estrogen-regulated gene and lack of ER regulation is associated with progressive epigenetic silencing through EZH2/H3K27me3 and DNA hypermethylation. Stable knockdown of HOXC10 in MCF-7 cells resulted in increased cell growth, reduced cell apoptosis, and increased cell motility. A preliminary study using AI-treated breast tumors did not show significant associations, however, the numbers were small. We identified HOXC10 methylation as a novel determinant of endocrine resistance. Also, we revealed that epigenetic reprogramming of genes involved in development may be a fundamental phenomenon in hormone resistance. Therefore, our study might provide the basis for the expansion of clinical markers for endocrine resistance and future clinical trials such as combination of endocrine and epigenetic therapies.

ORGANISM(S): Homo sapiens

PROVIDER: GSE39783 | GEO | 2014/05/01

SECONDARY ACCESSION(S): PRJNA171707

REPOSITORIES: GEO

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Project description:Postmenopausal breast cancer patients benefit from aromatase inhibitors (AIs) that reduce the levels of estrogens critical for the growth of estrogen receptor (ER)-positive tumors. Unfortunately, many tumors are resistant to AI, and we are only beginning to understand the complex mechanisms underlying treatment resistance. Here we set out to determine whether epigenetic changes could contribute to therapy resistance. For AI-resistance models, we used previously established MCF-7 cell clones, termed C4-12 and long-term estrogen deprivation (LTED), that were isolated after being cultured in estrogen-free media for 9 months and 18M-bM-^@M-^S24 months, respectively. Methyl CpG Binding Domain (MBD) - pull down followed by affymetrix promoter array was used to detect promoter methylation patterns in these cell lines. These studies identified widespread genomic hyper- and hypomethylation events, with a significant enrichment of promoter hypermethylation of development-associated genes in both cell lines. A developmentally regulated gene that was heavily methylated and lost expression in both cell-line systems was HOXC10. Moreover, we found that HOXC10 is an estrogen-regulated gene and lack of ER regulation is associated with progressive epigenetic silencing through EZH2/H3K27me3 and DNA hypermethylation. Stable knockdown of HOXC10 in MCF-7 cells resulted in increased cell growth, reduced cell apoptosis, and increased cell motility. A preliminary study using AI-treated breast tumors did not show significant associations, however, the numbers were small. We identified HOXC10 methylation as a novel determinant of endocrine resistance. Also, we revealed that epigenetic reprogramming of genes involved in development may be a fundamental phenomenon in hormone resistance. Therefore, our study might provide the basis for the expansion of clinical markers for endocrine resistance and future clinical trials such as combination of endocrine and epigenetic therapies. Long-term estrogen deprived previously established MCF-7 cell clones termed C4-12 and LTED genomic DNA subjected to Methyl CpG Binding Domain (MBD) - pull down followed by affymetrix promoter array to detect promoter methylation patterns

Project description:Despite the success of the aromatase inhibitors (AIs) in treating estrogen receptor positive breast cancer, 15-20% of patients receiving adjuvant AIs will relapse within 5-10 years of treatment initiation. Long term estrogen deprivation (LTED) of breast cancer cells in culture has been successfully used to mimic AI-induced estrogen depletion to dissect mechanisms of AI resistance. However, we hypothesized that a subset of patients receiving AI therapy may maintain low circulating concentrations of estrogens that influence the development of endocrine resistance. We sought to expand established LTED models to account for these observations. MCF-7 cells were grown in medium with charcoal stripped serum supplemented with defined concentrations of E2 or the estrogenic androgen metabolite 3βAdiol. Cells were selected in the EC10 and EC90 of E2 or 3βAdiol, or estrogen deprived. Estrogen-independence was evaluated during selection by assessing cell growth in the absence or presence of E2 or 3βAdiol. Following >7 months of selection, estrogen-independence developed in estrogen-deprived cells and cells maintained in low concentrations of steroid hormone. Functional analyses demonstrated that estrogen-deprived and low-steroid selected cells developed estrogen-independence via unique mechanisms, independent and dependent of ERα, respectively. Estrogen-independent growth in low-steroid selected cells could be blocked by kinase inhibitors. However, these cells were completely resistant to kinase inhibition in the presence of low steroid hormone concentrations. These data offer a novel perspective on the development of resistance to AI therapy, and may yield novel approaches to treat AI-resistant tumors. MCF-7 cells were selected for >7months in IMEM+10% Charcoal Stripped FBS, supplmented with defined steroid hormone conditions. Following outgrowth of estrogen-independent cells, cell lines were grown in estrogen-free conditions and gene expression analysis was performed to identify drivers of estrogen-independent growth. Cells were assessed in biological triplicates.

Project description:Resistance to endocrine therapy agents has presented a clinical obstacle in the treatment of hormone-dependent breast cancer. Our laboratory has initiated a study of microRNA regulation of signaling pathways that may result in breast cancer progression on aromatase inhibitors (AI). Microarray analysis of microRNA expression identified 115 significantly regulated microRNAs, of which 49 microRNAs were believed to be hormone-responsive. Within the AI-resistant cells, microRNAs were differentially expressed between the steroidal and non-steroidal AI-resistant lines. Also, a group of microRNAs were inversely expressed in the AI-resistant lines versus LTEDaro and tamoxifen-resistant. We focused our work on hsa-miR-128a which was hormone-responsive and up-regulated in the letrozole-resistant cell lines. Human miR-128a was shown to negatively target TGFBRI protein expression by binding to the 3âUTR region of the gene. Loss of TGFBRI resulted in compromised sensitivity to the growth inhibitory effects of TGFB in the letrozole-resistant lines. Inhibition of endogenous miR-128a resulted in re-sensitization of the letrozole-resistant lines to TGFB growth inhibitory effects. This data suggests that the hormone-responsive miR-128a can modulate TGFB signaling and survival of the letrozole-resistant cell lines. To our knowledge, this is the first study to address the role of microRNA regulation as well as TGFB signaling in AI-resistant breast cancer cell lines. We believe that in addition to estrogen-modulation of gene expression, hormone-regulated microRNAs may provide an additional level of post-transcriptional regulation of signaling pathways critically involved in breast cancer progression and AI-resistance. To look at microRNA expression profiles of breast cancer cell lines derived from MCF-7 cells that are resistant to endocrine therapy agents. MCF-7 cells that overexpress aromatase (MCF-7aro) were cultured long-term in the presence of endocrine therapy agents until cells acquired resistance. Three different aromatase inhibitors (letrozole, anastrozole or exemestane) were used, as well as the ER antagonist tamoxifen, or the hormone-free long-term estrogen deprived cells (LTED). Three replicates of the control cells (MCF-7aro) and all resistant cells were used for microarray experiments. Total of 23 samples were analyzed by microarray.

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Estrogen deprivation alters epigenetic modifications in breast cancer cells - HOXC10 loss in endocrine resistance

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