Abstract 3809: The role of LIN28B and RAN in promoting neuroblastoma tumorigenesis.
Authors: Schnepp Robert W. , Attiyeh Edward F. , Gagliardi Maria E. , Chodosh Sara , Maris John M. , Diskin Sharon J. 
Published: August 2014

Background: : Neuroblastoma is a childhood cancer of the sympathetic nervous system that accounts for approximately 10% of pediatric oncology deaths. The genetic basis of neuroblastoma has begun to be elucidated, with genome-wide association studies uncovering BARD1 and LMO1 as both predisposition genes and oncogenic drivers in a large subset of established neuroblastomas. Recently, our laboratory has shown that germline variation in LIN28B, a master regulator of the let-7 family of tumor suppressor microRNAs, promotes susceptibility to neuroblastoma. Neuroblastomas harboring the risk genotype show high LIN28B expression and this is highly associated with increased cellular proliferation, advanced stage disease and worse patient outcome (Nat. Gen., 2012).

Methods and Results: : To investigate the mechanism by which LIN28B influences the malignant phenotype, we first performed in silico analyses of several newly created and publicly available mRNA expression data sets along with SNP-array based DNA copy number data from 648 primary neuroblastomas. We observed a strong positive correlation between LIN28B and RAN expression in multiple data sets (P = 2.9 x 10−8 to 2.7 x 10−3). RAN is a member of the Ras family of GTPases that participates in mitosis and nuclear trafficking and is implicated as an oncogene in multiple malignancies. Recurrent somatic copy number gain of 12q24, where RAN is located, was observed in 15% (97/648) of neuroblastomas (p &lt; 0.0001), and this gain was associated with increased RAN expression (P = 0.0041), stage 4 (P = 0.0047), high-risk (P = 0.0005), and the MYCN non-amplified subset of high-risk in particular (P = 0.0021). Pathway analysis of the MYCN amplified subset of high-risk neuroblastoma showed that high LIN28B expression was strongly associated with increased RAN signaling (P = 7.1 x 10−8), suggesting LIN28B may regulate RAN activity. Western blotting in a panel of six neuroblastoma cell lines confirmed a tight correlation at the protein level. RNA interference targeting LIN28B resulted in depletion of RAN protein and a potent antiproliferative effect that was phenococpied by siRNA-mediated depletion of RAN.

Conclusions and Future Directions: Our data show that LIN28B expression and 12q24 gain promote the expression of RAN, suggesting two mechanisms that help to drive the malignant phenotype of neuroblastoma. We are currently determining whether LIN28B drives expression of the activated GTP-bound form of RAN. In addition, we are studying whether LIN28B regulates RAN in a let-7 dependent manner. Finally, we plan to determine whether targeting exportin1/XPO1/CRM1, which complexes with RAN in the nuclear membrane to export proteins and mRNA to the cytoplasm, will demonstrate therapeutic effect in neuroblastoma in a LIN28B- and/or RAN-dependent manner.

Citation Format: Robert W. Schnepp, Edward F. Attiyeh, Maria E. Gagliardi, Sara Chodosh, John M. Maris, Sharon J. Diskin. The role of LIN28B and RAN in promoting neuroblastoma tumorigenesis. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3809. doi:10.1158/1538-7445.AM2013-3809