In addition to its role in telomere maintenance, the ribonuclear protein dyskerin is also involved in RNA processing and ribosome biogenesis, anabolic processes that are often upregulated in myc-driven cancers. Since a third of neuroblastomas show augmented N-myc or c-myc activity, we hypothesized dyskerin expression would correlate with myc activity in these neuroblastoma subtypes.
This study shows that dyskerin expression is elevated in neuroblastoma cell lines (n=15) compared to normal cells (P<0.01). We showed that the DKC1 gene is a target of both N-myc and c-myc and that the upregulation of N-myc correlates with increased DKC1 expression. Furthermore, high DKC1 expression correlated strongly with poor event-free- and overall-survival (P<0.0001) in two independent cohorts of neuroblastoma patients (n=477 and n=197, respectively).
RNAi knockdown of DKC1 in neuroblastoma cells inhibited proliferation in vitro as well as tumor growth in vivo (P<0.01). This inhibitory effect was independent of telomerase suppression since over-expression of hTR (telomerase RNA component) did not rescue the phenotype.
As dyskerin is a nucleolar protein, we hypothesized that dyskerin depletion would induce nucleolar stress resulting in cell cycle arrest. Consistent with this, dyskerin knockdown resulted the depletion of small nucleolar RNAs as well as the nuclear accumulation of ribosomal proteins, the induction of p53 and cell cycle arrest in the G1 phase. p53 mutant or silenced cells also showed cell-cycle arrest on dyskerin knockdown indicating that the contribution of p53 was not essential for proliferative arrest.
Collectively, these data suggest dyskerin may be a potential therapeutic target for myc-dependent neuroblastoma.