N-MYC promotes cell proliferation through a direct transactivation of neuronal leucine-rich repeat protein-1(NLRR1) gene in neuroblastoma

Neuronal leucine-rich repeat protein-1(NLRR1) gene encodes a type I transmembrane protein with unknown function. We have previously described that NLRR1 gene is highly expressed in unfavorable neuroblastomas as compared with favorable tumors and its higher expression levels correlate significantly with poor clinical outcome. In this study, we have found that NLRR1 gene is one of direct target genes for N-MYC and its gene product contributes to N-MYC-dependent growth promotion in neuroblastoma. Expression levels of NLRR1 were significantly associated with those of N-MYC in various neuroblastoma cell lines as well as primary neuroblastoma tissues. Indeed, enforced expression of N-MYC resulted in a remarkable induction of the endogenous NLRR1. Consistent with these results, we have identified two functional E-boxes within the promoter region and intron 1 of NLRR1 gene. Intriguingly, c-myc also transactivated NLRR1 gene. Enforced expression of NLRR1 promoted cell proliferation and rendered cells resistant to serum deprivation. In support with these observations, small-interfering RNA-mediated knock-down of the endogenous NLRR1-reduced growth rate and sensitized cells to serum starvation. Collectively, our present findings provide a novel insight into understanding molecular mechanisms behind aggressive neuroblastoma with N-MYC amplification.