1. ¹Division of Biochemistry, Chiba Cancer Center Research Institute, Chiba, Japan
2. ²Department of Molecular Biology and Oncology, Chiba University Graduate School of Medicine, Chiba, Japan
3. ³Department of Pediatrics, ShengJing Hospital of China Medical University, Shenyang, People's Republic of China
4. ⁴Department of Pathology, National Center for Child Health and Development, Tokyo, Japan

Correspondence: Dr A Nakagawara, Division of Biochemistry, Chiba Cancer Center Research Institute, 666-2 Nitona, Chuoh-ku, Chiba 260-8717, Japan. E-mail: akiranak@chiba-cc.jp

⁵These authors contributed equally to this work.

Received 28 February 2008; Revised 30 April 2008; Accepted 22 May 2008; Published online 30 June 2008.

Abstract

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 knockdown 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.