RESUMEN
Neuroblastoma is a childhood cancer that exhibits either a favorable or an unfavorable phenotype. MYCN and MYC are oncoproteins that play crucial roles in determining the malignancy of unfavorable neuroblastoma. The Hsp90 superchaperone complex assists in the folding and function of a variety of oncogenic client proteins. Inhibition of Hsp90 by small molecule inhibitors leads to the destabilization of these oncogenic proteins and consequently suppresses tumor malignancy. Nonetheless, little is known about the effect of Hsp90 inhibition on the stability of MYCN and MYC proteins. In this study, we investigated the effect of Hsp90 inhibition on the phenotype of unfavorable neuroblastoma cells including its effect on MYCN and MYC expression. Two MYCN-amplified neuroblastoma cell lines (IMR5 and CHP134) and two non-MYCN-amplified cell lines (SY5Y and SKNAS) were used to address the effect of Hsp90 inhibition on the malignant phenotype of neuroblastoma. It was found that Hsp90 inhibition in neuroblastoma cell lines resulted in significant growth suppression, a decrease in MYCN and MYC expression, and an increase in the expression of p53. In the TP53-mutated SKNAS cell line, Hsp90 inhibition enhanced the expression of the favorable neuroblastoma genes EFNB2, MIZ-1 and NTRK1 (TrkA). In addition, Hsp90 inhibition reduced HDAC6 expression and enhanced tubulin acetylation. Together our data suggest that Hsp90 inhibition suppresses the growth of neuroblastoma through multiple cellular pathways and that MYC/MYCN destabilization is among the important consequences of Hsp90 inhibition.
Asunto(s)
Regulación Neoplásica de la Expresión Génica , Proteínas HSP90 de Choque Térmico/antagonistas & inhibidores , Neuroblastoma/genética , Neuroblastoma/metabolismo , Proteínas Nucleares/biosíntesis , Proteínas Oncogénicas/biosíntesis , Proteínas Proto-Oncogénicas c-myc/biosíntesis , Proteína p53 Supresora de Tumor/biosíntesis , Acetilación/efectos de los fármacos , Benzoquinonas , Línea Celular Tumoral , Inhibidor p21 de las Quinasas Dependientes de la Ciclina/biosíntesis , Inhibidor p21 de las Quinasas Dependientes de la Ciclina/genética , Genes myc , Genes p53 , Proteínas HSP90 de Choque Térmico/genética , Proteínas HSP90 de Choque Térmico/metabolismo , Humanos , Lactamas Macrocíclicas , Proteína Proto-Oncogénica N-Myc , Neuroblastoma/patología , Proteínas Nucleares/genética , Proteínas Oncogénicas/genética , Proteínas Proto-Oncogénicas c-akt/biosíntesis , Proteínas Proto-Oncogénicas c-akt/genética , Proteínas Proto-Oncogénicas c-myc/genética , Transfección , Tubulina (Proteína)/metabolismo , Proteína p53 Supresora de Tumor/genéticaRESUMEN
Neuroblastoma is a childhood malignancy of the sympathetic nervous system. The tumor exhibits two different phenotypes: favorable and unfavorable. MYCN amplification is associated with rapid tumor progression and the worst neuroblastoma disease outcome. We have previously reported that inhibitors of histone deacetylase (HDAC) and proteasome enhance favorable neuroblastoma gene expression in neuroblastoma cell lines and inhibit growth of these cells. In this study, we investigated the effect of trichostatin A or TSA (an HDAC inhibitor), and epoxomycin (a proteasome inhibitor) on MYCN and p53 expression in MYCN-amplified neuroblastoma cells. It was found that TSA down-regulated MYCN expression, but Epoxomycin and the TSA/Epoxomycin combination led to MYCN hyper-expression in MYCN-amplified neuroblastoma cell lines. Despite their contrasting effects on MYCN expression, TSA and Epoxomycin caused growth suppression and cell death of the MYCN-amplified cell lines examined. Consistent with these data, forced hyper-expression of MYCN in MYCN-amplified IMR5 cells via transfection resulted in growth suppression and the increased expression of several genes known to suppress growth or induce cell death. Furthermore, Epoxomycin as a single agent and its combination with TSA enhance p53 expression in the MYCN-amplified neuroblastoma cell lines. Unexpectedly, co-transfection of TP53 and MYCN in IMR5 cells resulted in high p53 expression but a reduction of MYCN expression. Together our data suggest that either down regulation or hyper-expression of MYCN results in growth inhibition and/or apoptosis of MYCN-amplified neuroblastoma cells. In addition, elevated p53 expression has a suppressive effect on MYCN expression in these cells.
