Abstract 3024: Targeting the RNA binding protein LIN28B in Group 3 medulloblastoma decreases proliferation and promotes apoptosis

Medulloblastoma (MB) is the most common pediatric malignant brain tumor and is currently divided into WNT, SHH, Group 3 and Group 4 subtypes. Even with multimodal chemotherapy, radiotherapy and surgery, many children with Group 3 MBs do not survive. While the molecular aberrations underlying WNT- and SHH-driven MBs are relatively well understood, the oncogenic drivers that lead to Group 3/4 MBs are poorly defined, limiting therapeutic progress. In addition to genetic mutations and alterations, cancers display dysregulated transcription and translation. RNA-binding proteins (RBPs) play key roles in both transcription and translation, and a subset of RBPs are differentially expressed in many different cancers. Indeed, we have previously demonstrated an oncogenic role for the RBP LIN28B in neuroblastoma and it is known to be upregulated in Wilms tumor, hepatoblastoma, germ cell tumors, leukemia among others. LIN28B is a key regulator of let-7 family miRNAs, which in turn inhibit LIN28B and other oncogenes. We hypothesize that LIN28B plays an important role in Group 3 MB and that a better understanding of LIN28B and LIN28B-driven networks will reveal novel therapeutic vulnerabilities. In support of our hypothesis we find that among the four subtypes, LIN28B levels are highest in Group 3 MB, and that overexpression is associated with significantly worse survival. Down-regulation of LIN28B results in significant reduction in cell proliferation by CellTiter-Glo and increased apoptosis by Caspase-Glo (as well as induction of cleaved PARP on immunoblots). In contrast overexpression of LIN28B increases Group 3 cell proliferation and tumor sphere formation. In addition we find that PDZ-binding kinase (PBK) a downstream target of LIN28B is downregulated when LIN28B is depleted. PBK knock down also leads to decreased proliferation of Group 3 MB cells. Finally, in order to robustly define the signaling networks downstream from LIN28B that are involved in Group 3 MB metastasis, we have performed who transcriptome RNA-seq profiling of two group 3 cell lines following LIN28B depletion and plan to interrogate a subset of these based on expression change and functional relevance to LIN28B-mediated Group 3 MB metastasis. This work will help define the role for LIN28B in Group 3 MB aggressiveness and pave the way for similar studies in other cancers. Citation Format: Shubin W. Shahab, Jo Lynne Rokita, Kyle Juraschka, Sachin Kumar, Michael Taylor, Robert W. Schnepp, Tobey J. MacDonald, Anna M. Kenney. Targeting the RNA binding protein LIN28B in Group 3 medulloblastoma decreases proliferation and promotes apoptosis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 3024.