Abstract 3668: A LIN28B-PBK Axis promotes neuroblastoma dissemination and aggression
Authors: Chen Dongdong , Cox Julie , Annam Jayabhargav , Weingart Melanie , Essien Grace , Rathi Komal , Khurana Priya , Cuya Selma M. , Schnepp Robert W. 
Published: August 2019

Abstract
LIN28B is an RNA binding protein that plays key roles in normal development and, when deregulated, oncogenesis; mechanistically, it blocks the processing of the let-7 family of tumor suppressors and binds mRNAs directly. We previously demonstrated that LIN28B induces neuroblastoma proliferation, in part by regulating the expression of RAN GTPase and Aurora kinase A (AURKA). However, given the widespread metastases seen within neuroblastoma, we speculated that LIN28B might also influence neuroblastoma dissemination. We used gain and loss of function approaches to genetically manipulate transcripts of interest in neuroblastoma cells and measured effects on self-renewal, invasion, and downstream signaling. To examine the impact of LIN28B on dissemination, we generated GFP-luciferase expressing neuroblastoma cell line models in which LIN28B levels were manipulated, injected these lines into the tail veins of NSG mice, and tracked dissemination using an IVIS Spectrum system. Results show that depletion of LIN28B significantly delayed the onset of tumor metastasis, reduced tumor burden, and extended mouse survival (104 days versus 50 days, p&lt;0.0001) compared to control cells. While LIN28B did not impact anoikis resistance, it did increase both tumorsphere number and size, linking self-renewal to metastatic dissemination. Additionally, LIN28B promoted cellular invasion. These effects were largely opposed by let-7. We next sought to understand how LIN28B promotes aggression and metastasis, specifically focusing on novel networks that are currently therapeutically targetable. Given our discovery of AURKA as a novel LIN28B target, we speculated that LIN28B might promote the expression of additional oncogenic kinases, perhaps revealing novel therapeutic possibilities to target the LIN28B network. We evaluated the TARGET dataset of neuroblastoma tumors and, focusing on the top 10 kinases most significantly and positively correlated with high LIN28B expression, nominated PBK for further study (4/10 of top correlated kinases). PBK (PDZ-binding kinase) is a Ser/Thr protein kinase expressed in normal embryonic tissues and various tumor types that plays a role in both mitosis and metastasis. Depletion of PBK mimicked the effects of LIN28B depletion, with respect to self-renewal and invasion. Depletion of LIN28B and overexpression of let-7 both reduced PBK protein expression, suggesting that PBK is a direct or indirect let-7 target. Taken together, our findings suggest that LIN28B/let-7 shapes neuroblastoma aggression, in part through influencing PBK, a kinase not previously implicated in the pathogenesis of neuroblastoma or other aggressive pediatric solid tumors. Current studies are further dissecting the functional and molecular relationships among LIN28B, let-7, and PBK in neuroblastoma.
Citation Format: Dongdong Chen, Julie Cox, Jayabhargav Annam, Melanie Weingart, Grace Essien, Komal Rathi, Priya Khurana, Selma M. Cuya, Robert W. Schnepp. A LIN28B-PBK Axis promotes neuroblastoma dissemination and aggression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3668.