RESUMO
Enhancer of zeste homolog 2 (EZH2) is the catalytic subunit of the polycomb repressive complex 2 and suppresses gene expression by catalyzing histone H3 methylation on lysine 27. EZH2 is overexpressed in metastatic prostate cancer and has been shown to promote cell proliferation and metastasis. Here we show that EZH2 also suppresses prostate cancer apoptosis by coordinating the epigenetic silencing of two proapoptotic microRNAs (miRNA), miR-205 and miR-31. We previously reported that miR-205 promotes apoptosis by targeting antiapoptotic protein Bcl-w and miR-205 is silenced in prostate cancer through promoter methylation. In this study, we found that EZH2 suppresses miR-31 expression by trimethylation of lysine 27 on histone 3 on the miR-31 promoter. SiRNA knockdown of EZH2 increased miR-31 expression and decreased the antiapoptotic protein E2F6 (E2F transcription factor 6) (a target of miR-31), resulting in the sensitization of prostate cancer cells to docetaxel-induced apoptosis. Conversely, overexpression of EZH2 blocked docetaxel-induced apoptosis. We further demonstrated that miR-205 silencing is linked to miR-31 silencing through EZH2. Suppression of miR-205 with an miRNA inhibitor caused an increase of EZH2 protein, which in turn inhibited miR-31 expression. Conversely, overexpression of miR-205 decreased EZH2 protein and increased miR-31 expression. In paired human prostate cancer specimens and adjacent normal tissues, we observed that the decrease of miR-205 expression correlated with EZH2 overexpression and miR-31 silencing. Thus, EZH2 integrates the epigenetic silencing of miR-205 and miR-31 to confer resistance to chemotherapy-induced apoptosis.
Assuntos
Apoptose , Inativação Gênica , MicroRNAs/genética , Complexo Repressor Polycomb 2/metabolismo , Apoptose/efeitos dos fármacos , Apoptose/genética , Linhagem Celular Tumoral , Docetaxel , Regulação para Baixo/efeitos dos fármacos , Regulação para Baixo/genética , Resistencia a Medicamentos Antineoplásicos/efeitos dos fármacos , Resistencia a Medicamentos Antineoplásicos/genética , Proteína Potenciadora do Homólogo 2 de Zeste , Regulação Neoplásica da Expressão Gênica/efeitos dos fármacos , Técnicas de Silenciamento de Genes , Inativação Gênica/efeitos dos fármacos , Histonas/metabolismo , Humanos , Masculino , Metilação/efeitos dos fármacos , MicroRNAs/metabolismo , Modelos Biológicos , Regiões Promotoras Genéticas/genética , Neoplasias da Próstata/genética , Neoplasias da Próstata/patologia , RNA Interferente Pequeno/metabolismo , Taxoides/farmacologiaRESUMO
Advanced prostate cancers are known to acquire not only invasive capabilities but also significant resistance to chemotherapy-induced apoptosis. To understand how microRNAs (miRNAs) may contribute to prostate cancer resistance to apoptosis, we compared microRNA expression profiles of a benign prostate cancer cell line WPE1-NA22 and a highly malignant WPE1-NB26 cell line (derived from a common lineage). We found that miR-205 and miR-31 are significantly downregulated in WPE1-NB26 cells, as well as in other cell lines representing advanced-stage prostate cancers. Antiapoptotic genes BCL2L2 (encoding Bcl-w) and E2F6 are identified as the targets of miR-205 and miR-31, respectively. By downregulating Bcl-w and E2F6, miR-205 and miR-31 promote chemotherapeutic agents-induced apoptosis in prostate cancer cells. The promoter region of the miR-205 gene was cloned and was found to be hypermethylated in cell lines derived from advanced prostate cancers, contributing to the downregulation of the gene. Treatment with DNA methylation inhibitor 5-aza-2'-deoxycytidine induced miR-205 expression, downregulated Bcl-w, and sensitized prostate cancer cells to chemotherapy-induced apoptosis. Thus, downregulation of miR-205 and miR-31 has an important role in apoptosis resistance in advanced prostate cancer.
