RESUMO
BACKGROUND: Activating transcription factor-2 (ATF2), a member of the leucine zipper family of DNA binding proteins, has been implicated as a tumour suppressor in breast cancer. However, its exact role in breast cancer endocrine resistance is still unclear. We have previously shown that silencing of ATF2 leads to a loss in the growth-inhibitory effects of tamoxifen in the oestrogen receptor (ER)-positive, tamoxifen-sensitive MCF7 cell line and highlighted that this multi-faceted transcription factor is key to the effects of tamoxifen in an endocrine sensitive model. In this work, we explored further the in vitro role of ATF2 in defining the resistance to endocrine treatment. MATERIALS AND METHODS: We knocked down ATF2 in TAMR, LCC2 and LCC9 tamoxifen-resistant breast cancer cell lines as well as the parental tamoxifen sensitive MCF7 cell line and investigated the effects on growth, colony formation and cell migration. We also performed a microarray gene expression profiling (Illumina Human HT12_v4) to explore alterations in gene expression between MCF7 and TAMRs after ATF2 silencing and confirmed gene expression changes by quantitative RT-PCR. RESULTS: By silencing ATF2, we observed a significant growth reduction of TAMR, LCC2 and LCC9 with no such effect observed with the parental MCF7 cells. ATF2 silencing was also associated with a significant inhibition of TAMR, LCC2 and LCC9 cell migration and colony formation. Interestingly, knockdown of ATF2 enhanced the levels of ER and ER-regulated genes, TFF1, GREB1, NCOA3 and PGR, in TAMR cells both at RNA and protein levels. Microarray gene expression identified a number of genes known to mediate tamoxifen resistance, to be differentially regulated by ATF2 in TAMR in relation to the parental MCF7 cells. Moreover, differential pathway analysis confirmed enhanced ER activity after ATF2 knockdown in TAMR cells. CONCLUSION: These data demonstrate that ATF2 silencing may overcome endocrine resistance and highlights further the dual role of this transcription factor that can mediate endocrine sensitivity and resistance by modulating ER expression and activity.
Assuntos
Fator 2 Ativador da Transcrição/metabolismo , Antineoplásicos Hormonais/farmacologia , Neoplasias da Mama/tratamento farmacológico , Resistencia a Medicamentos Antineoplásicos/genética , Regulação Neoplásica da Expressão Gênica/genética , Fator 2 Ativador da Transcrição/genética , Antineoplásicos Hormonais/uso terapêutico , Neoplasias da Mama/genética , Neoplasias da Mama/patologia , Movimento Celular/genética , Feminino , Perfilação da Expressão Gênica , Regulação Neoplásica da Expressão Gênica/efeitos dos fármacos , Técnicas de Silenciamento de Genes , Humanos , Células MCF-7 , Análise de Sequência com Séries de Oligonucleotídeos , Receptores de Estrogênio/análise , Receptores de Estrogênio/antagonistas & inibidores , Receptores de Estrogênio/genética , Receptores de Estrogênio/metabolismo , Tamoxifeno/farmacologia , Tamoxifeno/uso terapêuticoRESUMO
Activating transcription factor-2 (ATF-2) has been implicated as a tumour suppressor in breast cancer (BC). c-JUN N-terminal kinase (JNK) and p38 MAPK phosphorylate ATF-2 within the activation domain (AD), which is required for its transcriptional activity. To date, the role of ATF-2 in determining response to endocrine therapy has not been explored. Effects of ATF-2 loss in the oestrogen receptor (ER)-positive luminal BC cell line MCF7 were explored, as well as its role in response to tamoxifen treatment. Genome-wide chromatin binding patterns of ATF-2 when phosphorylated within the AD in MCF-7 cells were determined using ChIP-seq. The expression of ATF-2 and phosphorylated ATF-2 (pATF-2-Thr71) was determined in a series of 1,650 BC patients and correlated with clinico-pathological features and clinical outcome. Loss of ATF-2 diminished the growth-inhibitory effects of tamoxifen, while tamoxifen treatment induced ATF-2 phosphorylation within the AD, to regulate the expression of a set of 227 genes for proximal phospho-ATF-2 binding, involved in cell development, assembly and survival. Low expression of both ATF-2 and pATF-2-Thr71 was significantly associated with aggressive pathological features. Furthermore, pATF-2 was associated with both p-p38 and pJNK1/2 (< 0.0001). While expression of ATF-2 is not associated with outcome, pATF-2 is associated with longer disease-free (p = 0.002) and BC-specific survival in patients exposed to tamoxifen (p = 0.01). Furthermore, multivariate analysis confirmed pATF-2-Thr71 as an independent prognostic factor. ATF-2 is important for modulating the effect of tamoxifen and phosphorylation of ATF-2 within the AD at Thr71 predicts for improved outcome for ER-positive BC receiving tamoxifen.
Assuntos
Fator 2 Ativador da Transcrição/metabolismo , Neoplasias da Mama/tratamento farmacológico , Neoplasias da Mama/metabolismo , Tamoxifeno/farmacologia , Fator 2 Ativador da Transcrição/genética , Neoplasias da Mama/genética , Proteínas de Ligação a DNA/genética , Proteínas de Ligação a DNA/metabolismo , Intervalo Livre de Doença , Feminino , Humanos , Proteínas Quinases JNK Ativadas por Mitógeno/genética , Proteínas Quinases JNK Ativadas por Mitógeno/metabolismo , Células MCF-7 , Fosforilação , Prognóstico , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismo , Proteínas Quinases p38 Ativadas por Mitógeno/genética , Proteínas Quinases p38 Ativadas por Mitógeno/metabolismoRESUMO
PURPOSE: The steroid receptor coactivator SRC3 is essential for the transcriptional activity of estrogen receptor α (ERα). SRC3 is sufficient to cause mammary tumorigenesis, and has also been implicated in endocrine resistance. SRC3 is posttranslationally modified by phosphorylation, but these events have not been investigated with regard to functionality or disease association. Here, we investigate the spatial selectivity of SRC3-pS543/DNA binding over the human genome and its expression in primary human breast cancer in relation with outcome. EXPERIMENTAL DESIGN: Chromatin immunoprecipitation, coupled with sequencing, was used to determine the chromatin binding patterns of SRC3-pS543 in the breast cancer cell line MCF7 and two untreated primary breast cancers. IHC was used to assess the expression of SRC3 and SRC3-pS543 in 1,650 primary breast cancers. The relationship between the expression of SRC3 and SRC3-pS543, disease-free survival (DFS), and breast cancer specific survival (BCSS) was assessed. RESULTS: Although total SRC3 is selectively found at enhancer regions, SRC3-pS543 is recruited to promoters of ERα responsive genes, both in the MCF7 cell line and primary breast tumor specimens. SRC3-pS543 was associated with both improved DFS (P = 0.003) and BCSS (P = 0.001) in tamoxifen untreated high-risk patients, such a correlation was not seen in tamoxifen-treated cases, the interaction was statistically significant (P = 0.001). Multivariate analysis showed SRC3-pS543 to be an independent prognostic factor. CONCLUSIONS: Phosphorylation of SRC3 at S543 affects its genomic interactions on a genome-wide level, where SRC3-pS543 is selectively recruited to promoters of ERα-responsive genes. SRC3-pS543 is a prognostic marker, and a predictive marker of response to endocrine therapy.
Assuntos
Neoplasias da Mama/metabolismo , Receptor alfa de Estrogênio/metabolismo , Coativador 3 de Receptor Nuclear/metabolismo , Fosforilação/fisiologia , Serina/metabolismo , Animais , Antineoplásicos Hormonais/farmacologia , Biomarcadores Tumorais/metabolismo , Neoplasias da Mama/tratamento farmacológico , Neoplasias da Mama/genética , Células CHO , Linhagem Celular Tumoral , Cromatina/metabolismo , Cricetulus , Intervalo Livre de Doença , Feminino , Regulação Neoplásica da Expressão Gênica/efeitos dos fármacos , Regulação Neoplásica da Expressão Gênica/genética , Humanos , Células MCF-7 , Fosforilação/efeitos dos fármacos , Prognóstico , Regiões Promotoras Genéticas/efeitos dos fármacos , Regiões Promotoras Genéticas/genética , Tamoxifeno/farmacologiaRESUMO
Members of the nuclear receptor superfamily are ligand-regulated transcription factors involved in the control of a broad range of normal physiological and disease processes. The estrogen receptor alpha (ERalpha) is a member of the steriod receptor family, which is part of the nuclear receptor superfamily. ERalpha it is important for many biological processes and plays a key role in the pathogenesis of breast cancer. Gene regulation by ERalpha requires the recruitment of a multitude of transcriptional co-regulators to the promoters of estrogen-responsive genes. There is evidence in support of the involvement of these co-regulators in breast cancer progression. We review the role of steroid receptor co-activator-3 (SRC-3), which is frequently amplified in breast cancer, and its role in breast cancer risk, outcome and response to endocrine therapy in patients with breast cancer.