RESUMO
FOXO transcription factors are negatively regulated by the PI3K-PKB/AKT signaling pathway and have been mainly considered to be tumor suppressors due to their inhibitory effect on cancer cell growth and survival. However, FOXOs can also support tumor development and progression by maintaining cellular homeostasis, facilitating metastasis and inducing therapy resistance. In agreement with these opposing views on the role of FOXOs in cancer, studies using FOXO levels or activity as prognostic markers for cancer patient disease progression and survival came to contradicting results. While it is clear that FOXOs are involved in various aspects of cancer, it is debatable whether FOXOs function as tumor suppressors or supporters, or may be both depending on the context. In this review, we describe the role of FOXOs in signaling pathways and processes relevant to cancer and evaluate recent advances in understanding the role of FOXOs in cancer. Based on recent insights it becomes clear that FOXOs may not be classical tumor suppressors and that targeting FOXO activity might hold promise in cancer therapy.
Assuntos
Carcinogênese/genética , Fatores de Transcrição Forkhead/genética , Neoplasias/genética , Regulação Neoplásica da Expressão Gênica , Humanos , Neoplasias/patologia , Proteína Oncogênica v-akt/genética , Fosfatidilinositol 3-Quinases/genética , Transdução de Sinais/genéticaRESUMO
Loss of cellular adhesion leads to the progression of breast cancer through acquisition of anchorage independence, also known as resistance to anoikis. Although inactivation of E-cadherin is essential for acquisition of anoikis resistance, it has remained unclear how metastatic breast cancer cells counterbalance the induction of apoptosis without E-cadherin-dependent cellular adhesion. We report here that E-cadherin inactivation in breast cancer cells induces PI3K/AKT-dependent FOXO3 inhibition and identify FOXO3 as a novel and direct transcriptional activator of the pro-apoptotic protein BMF. As a result, E-cadherin-negative breast fail to upregulate BMF upon transfer to anchorage independence, leading to anoikis resistance. Conversely, expression of BMF in E-cadherin-negative metastatic breast cancer cells is sufficient to inhibit tumour growth and dissemination in mice. In conclusion, we have identified repression of BMF as a major cue that underpins anoikis resistance and tumour dissemination in E-cadherin-deficient metastatic breast cancer.