RESUMO
The antiestrogen tamoxifen has been widely used for decades as selective estrogen receptor (ER) modulator for ERalpha-positive breast tumors. Tamoxifen significantly reduces tumor recurrence by binding to the activation function-2 (AF-2) domain of the ER. Acquired resistance to tamoxifen in breast cancer patients is a serious therapeutic problem. Antiestrogen-resistant breast cancer often shows increased expression of the epidermal growth factor receptor (EGFR) family members, EGFR and ErbB2. In this report we now show that overexpression of EGFR or activated AKT-2 in MCF-7 cells leads to phosphorylation of Ser167 in the AF-1 domain of ERalpha, enhanced ER-amplified in breast cancer 1 (ER:AIB1) interaction in the presence of tamoxifen, and resistance to tamoxifen. In contrast, transfection of activated MAPK kinase, an immediate upstream activator of MAPK (ERK 1 and 2) into MCF-7 cells leads to phosphorylation of Ser118 in the AF-1 domain of ERalpha, inhibition of ER-amplified in breast cancer 1 (ER:AIB1) interaction in the presence of Tam, and maintenance of sensitivity to tamoxifen. Inhibition of AKT by short inhibitory RNA blocked Ser167 phosphorylation in ER and restored tamoxifen sensitivity. However, maximum sensitivity to tamoxifen was observed when both AKT and MAPK were inhibited. Taken together, these data demonstrate that different phosphorylation sites in the AF-1 domain of ERalpha regulate the agonistic and antagonistic actions of tamoxifen in human breast cancer cells.
Assuntos
Antineoplásicos Hormonais/agonistas , Antineoplásicos Hormonais/antagonistas & inibidores , Neoplasias da Mama/metabolismo , Receptor alfa de Estrogênio/metabolismo , Tamoxifeno/agonistas , Tamoxifeno/antagonistas & inibidores , Antineoplásicos Hormonais/uso terapêutico , Neoplasias da Mama/tratamento farmacológico , Linhagem Celular Tumoral , Resistencia a Medicamentos Antineoplásicos , Receptor alfa de Estrogênio/antagonistas & inibidores , Proteínas de Fluorescência Verde/metabolismo , Humanos , Proteína Quinase 1 Ativada por Mitógeno/genética , Proteína Quinase 1 Ativada por Mitógeno/metabolismo , Proteína Quinase 3 Ativada por Mitógeno/genética , Proteína Quinase 3 Ativada por Mitógeno/metabolismo , Proteínas Oncogênicas v-erbB/metabolismo , Fosforilação , Estrutura Terciária de Proteína , Proteínas Proto-Oncogênicas c-akt/antagonistas & inibidores , Proteínas Proto-Oncogênicas c-akt/genética , Proteínas Proto-Oncogênicas c-akt/metabolismo , RNA Interferente Pequeno/genética , RNA Interferente Pequeno/farmacologia , Serina/metabolismo , Tamoxifeno/uso terapêutico , TransfecçãoRESUMO
Activation of the mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) pathway is a frequent event in tumorigenesis. MAPKs have been implicated in cell migration, proteinase-induction, regulation of apoptosis, and angiogenesis, events that are essential for successful completion of metastasis. In this review, we discuss the potential role that MAPKs play in metastasis by regulating cell migration, proteinase-induction and apoptosis.
Assuntos
Sistema de Sinalização das MAP Quinases , Neoplasias/patologia , Apoptose , Movimento Celular , Progressão da Doença , Humanos , Modelos Biológicos , Invasividade Neoplásica , Neoplasias/enzimologia , Neovascularização Patológica , Transdução de SinaisRESUMO
The estrogen receptor alpha (ERalpha) signaling plays an essential role in breast cancer progression and endocrine therapy. Mitogen-activated protein kinase (MAPK/Erk1/2) has been implicated in ligand-independent activation of ER, resulting in the cross-talk between growth factor and ER mediated signaling. In this study, we examined the effect of the cross-talk on estradiol (E(2))-mediated signaling, tumor growth and its effect on anti-estrogen therapy. Our findings demonstrate that expression of constitutively activated mitogen activated kinase kinase (MEK1), an immediate upstream activator of MAPK in estrogen receptor positive MCF-7 breast cancer cells (MEK/MCF-7), showed an increase in ERalpha-driven transcriptional activation. In MEK/MCF-7 cells maximal transactivation levels were achieved in response to treatment with much lower E(2) concentrations (10(-10) M E(2)) when compared to MCF-7 control cells (10(-8) M E(2)). Furthermore, we have seen an increased association between ERalpha and its nuclear coactivators AIB1 or TIF-2, in MEK/MCF-7 cells relative to those seen in MCF-7 control cells. In addition, in vivo studies show that MEK/MCF-7 cell tumors are approximately threefold larger than those of MCF-7 cell, in the presence of E(2). Immunohistochemical staining demonstrates that progesterone receptor (PR) and pS2, two E(2)-regulated gene products, are significantly increased in MEK/MCF-7 cell tumors compared to those of MCF-7 control tumors, suggesting that activation of ERalpha by MAPK enhances the expression of E(2)-regulated genes and accelerates tumor growth. Remarkably, the antiestrogens tamoxifen and ICI 182,780, were shown both in vitro and in vivo studies to efficiently antagonize the stimulatory effects of E(2) on ER regulated transactivation and tumor growth in MEK/MCF-7 as well as MCF-7 cell lines. Taken together, these data suggest that MAPK/ER cross-talk enhances ERalpha-mediated signaling and accelerates E(2)-dependent tumor growth without diminishing sensitivity to the inhibitory effects of anti-estrogens.