Abstract LB174: REST-USP37 axis controls GLI1 levels in sonic hedgehog medulloblastoma cells

Abstract Background: Medulloblastoma (MB), the most common pediatric cerebellar tumor, has a 5-year survival rate of approximately 70-80%. About 30% of MBs are driven by Sonic Hedgehog (SHH) signaling mutations in PTCH1, SMO, and SUFU. RE1-Silencing Transcription factor (REST), a transcriptional repressor, plays a crucial role in SHH-MB progression. Previously, we have shown that elevated REST in SHH-MBs is linked to poor outcomes, and it controls SHH pathway by causing epigenetic loss of Ptch1 haploinsufficiency. This study explores REST's role in regulating SHH pathway effectors GLI1 and GLI2. Methods: Transcriptomic data was analyzed from publicly available RNA-seq and scRNA-seq datasets. Histological analysis of patient tumors and -derived xenografts, along with biochemical studies of SHH-MB cell lines, provided insights into REST-driven regulation of GLI in this MB subgroup. Summary: The scRNA-seq data of high- and low-REST SHH-MB patient tumors demonstrated an increase in cycling cerebellar granule progenitor cells (GNPs) in the context of REST elevation, which was associated with decreased GLI1 and increased GLI2 expression. Interestingly, we found that USP37-a REST target gene product and a deubiquitylase, controls GLI1 stability. USP37 decline in REST-high SHH-MBs reduces GLI1 levels, although cells are maintained in a proliferative state. GLI1 is also known to activate its own gene expression. So, we attribute the maintenance of cell proliferation under high REST conditions to the loss of stabilization of p27, a cyclin-dependent kinase inhibitor that is required for terminal cell cycle exit and initiation of terminal neurogenesis. A potential role for a compensatory increase in GLI2 levels in maintaining SHH pathway activity and cell proliferation cannot be excluded at this time. Consistent with this effect of REST on SHH signaling activity, GLI inhibitors reduce the growth of SHH-MB cells in vitro. Conclusion: In summary, our work has uncovered a novel REST-USP37-GLI1 axis in controlling SHH pathway activity in SHH-MBs. Our findings may have therapeutic implications for patients with SHH-MBs with REST elevation. Citation Format: Ashutosh Singh, Donghang Cheng, Lei Guo, Amanda Haltom, Tara Dobson, Veena Rajaram, Lin Xu, Vidya Gopalakrishnan. REST-USP37 axis controls GLI1 levels in sonic hedgehog medulloblastoma cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_2):Abstract nr LB174.