RESUMEN
The androgen receptor (AR) signaling pathway is involved in the emergence of castration-resistant prostate cancer (CRPC). Here, we identified several androgen-regulated microRNAs (miRNAs) that may contribute to the development of CRPC. Seven miRNAs, miR-21, miR-32, miR-99a, miR-99b, miR-148a, miR-221 and miR-590-5p, were found to be differentially expressed in CRPC compared with benign prostate hyperplasia (BPH) according to microarray analyses. Significant growth advantage for LNCaP cells transfected with pre-miR-32 and pre-miR-148a was found. miR-32 was demonstrated to reduce apoptosis, whereas miR-148a enhanced proliferation. Androgen regulation of miR-32 and miR-148a was confirmed by androgen stimulation of the LNCaP cells followed by expression analyses. The AR-binding sites in proximity of these miRNAs were demonstrated with chromatin immunoprecipitation (ChIP). To identify target genes for the miRNAs, mRNA microarray analyses were performed with LNCaP cells transfected with pre-miR-32 and pre-miR-148a. Expression of BTG2 and PIK3IP1 was reduced in the cells transfected with pre-miR-32 and pre-miR-148a, respectively. Also, the protein expression was reduced according to western blot analysis. BTG2 and PIK3IP1 were confirmed to be targets by 3'UTR-luciferase assays. Finally, immunostainings showed a statistically significant (P<0.0001) reduction of BTG2 protein in CRPCs compared with untreated prostate cancer (PC). The lack of BTG2 staining was also associated (P<0.01) with a short progression-free time in patients who underwent prostatectomy. In conclusion, androgen-regulated miR-32 is overexpressed in CRPC, leading to reduced expression of BTG2. Thus, miR-32 is a potential marker for aggressive disease and is a putative drug target in PC.
Asunto(s)
Regulación Neoplásica de la Expresión Génica , Proteínas Inmediatas-Precoces/genética , MicroARNs/metabolismo , Neoplasias Hormono-Dependientes/metabolismo , Neoplasias de la Próstata/metabolismo , Proteínas Supresoras de Tumor/genética , Andrógenos/fisiología , Sitios de Unión , Estudios de Casos y Controles , Línea Celular Tumoral , Proliferación Celular , Humanos , Proteínas Inmediatas-Precoces/metabolismo , Péptidos y Proteínas de Señalización Intracelular , Masculino , Proteínas de la Membrana/genética , Proteínas de la Membrana/metabolismo , MicroARNs/genética , Neoplasias Hormono-Dependientes/genética , Análisis de Secuencia por Matrices de Oligonucleótidos , Pronóstico , Neoplasias de la Próstata/genética , Receptores Androgénicos/metabolismo , Secuencias Reguladoras de Ácidos Nucleicos , Transducción de Señal , Transcriptoma , Proteínas Supresoras de Tumor/metabolismoRESUMEN
Androgen receptor (AR) is overexpressed in the majority of castration-resistant prostate cancers (CRPCs). Our goal was to study the effect of AR overexpression on the chromatin binding of the receptor and to identify AR target genes that may be important in the emergence of CRPC. We have established two sublines of LNCaP prostate cancer (PC) cell line, one overexpressing AR 2-3-fold and the other 4-5-fold compared with the control cells. We used chromatin immunoprecipitation (ChIP) and deep-sequencing (seq) to identify AR-binding sites (ARBSs). We found that the number of ARBSs and the AR-binding strength were positively associated with the level of AR when cells were stimulated with low concentrations of androgens. In cells overexpressing AR, the chromatin binding of the receptor took place in 100-fold lower concentration of the ligand than in control cells. We confirmed the association of AR level and chromatin binding in two PC xenografts, one containing AR gene amplification with high AR expression, and the other with low expression. By combining the ChIP-seq and expression profiling, we identified AR target genes that are upregulated in PC. Of them, the expression of ZWINT, SKP2 (S-phase kinase-associated protein 2 (p45)) and FEN1 (flap structure-specific endonuclease 1) was demonstrated to be increased in CRPC, while the expression of SNAI2 was decreased in both PC and CRPC. FEN1 protein expression was also associated with poor prognosis in prostatectomy-treated patients. Finally, the knock-down of FEN1 with small interfering RNA inhibited the growth of LNCaP cells. Our data demonstrate that the overexpression of AR sensitizes the receptor binding to chromatin, thus, explaining how AR signaling pathway is reactivated in CRPC cells.
Asunto(s)
Cromatina/metabolismo , Neoplasias de la Próstata/metabolismo , Receptores Androgénicos/metabolismo , Animales , Sitios de Unión , Línea Celular Tumoral , Endonucleasas de ADN Solapado/genética , Amplificación de Genes , Perfilación de la Expresión Génica , Humanos , Péptidos y Proteínas de Señalización Intracelular/genética , Masculino , Ratones , Proteínas Nucleares/genética , Técnicas de Amplificación de Ácido Nucleico , Neoplasias de la Próstata/genética , Receptores Androgénicos/genética , Proteínas Quinasas Asociadas a Fase-S/genética , Trasplante HeterólogoRESUMEN
Transcriptional control by androgens via androgen receptor (AR) is strongly involved in prostate cancer development, but the critical target genes have remained elusive. We have characterized E twenty-six-like transcription factor 4 (ELK4) (also known as serum response factor accessory protein 1) as a novel AR target in human prostate cancer cells. In-silico screening identified three putative AR response elements (AREs) within -10 kb from the transcription start site of ELK4. Both ARE1 at -167/-153 and ARE2 at -481/-467 bound AR in vitro and mediated androgen induction as isolated elements in transcription assays in non-prostate cells. However, merely the ARE2 that cooperates with a proximal forkhead box A1-binding site was critical for the AR-dependent activation of ELK4 promoter in prostate cancer cells. Preferential loading of holo-AR onto the ARE2 and concomitant recruitment of RNA polymerase II onto the ELK4 promoter was confirmed in prostate cancer cells by chromatin immunoprecipitation. Database searches indicated that the expression of ELK4 is markedly increased in prostate cancers relative to normal prostates. Moreover, prostate cancer tissue immunostainings showed that nuclear ELK4 levels are significantly increased in androgen-refractory prostate cancers compared to untreated tumours. Reduction of the amount of ELK4 in LNCaP cells by RNAi retarded cell growth. In conclusion, ELK4 is a direct AR target in prostate cancer cells. Androgens may thus contribute to the growth of prostate cancer via influencing ELK4 levels.