The RNA-helicase DDX21 upregulates CEP55 expression and promotes neuroblastoma.

Approximately 25% of human neuroblastoma is caused by amplification of the MYCN oncogene, which leads to over-expression of N-Myc oncoprotein. The survival rate for this patient subtype is less than 50%. Here we show that N-Myc protein bound to the DEAD-box RNA helicase DDX21 gene promoter and upregulated DDX21 mRNA and protein expression. Genome-wide differential gene expression studies identified centrosomal protein CEP55 as one of the genes most dramatically down-regulated after DDX21 knockdown in MYCN-amplified neuroblastoma cells. Knocking down DDX21 or CEP55 reduced neuroblastoma cell cytoskeleton stability and cell proliferation and all but abolished clonogenic capacity. Importantly, DDX21 knockdown initially induced tumor regression in neuroblastoma-bearing mice and suppressed tumor progression. In human neuroblastoma tissues, a high level of DDX21 expression correlated with a high level of N-Myc expression and with CEP55 expression, and independently predicted poor patient prognosis. Taken together, our data show that DDX21 induces CEP55 expression, MYCN-amplified neuroblastoma cell proliferation and tumorigenesis, and that DDX21 and CEP55 are valid therapeutic targets for the treatment of MYCN-amplified neuroblastoma.