Abstract 2864: Transcriptional repressor REST controls autophagy in Sonic Hedgehog medulloblastoma through the VHL-HIF1α axis

Abstract Introduction: Medulloblastoma (MB) is the most common malignant brain tumor in children. It is categorized into four molecular subgroups, each with unique genetic and epigenetic alterations, molecular signatures, and differences in clinical features and treatment responses. Targeted therapy for MB has failed in the clinic, prompting new studies of mechanisms involved in MB tumorigenesis and progression. Experimental Procedure: The transcriptomic information of the MB patients was obtained from the publicly available RNAseq datasets and was analyzed for differential expression and clustering analysis. Patient-derived orthotopic xenografts of medulloblastoma tumors with high- and low-REST expression were histologically and biochemically studied for autophagy markers. Furthermore, the SHH-MB cell lines were studied to get a mechanistic understanding of the REST-driven autophagy in this MB subgroup. Summary: Our data showed that autophagy, a process responsible for cellular recycling, and genes associated with this pathway exhibit distinctive expression patterns in human MB subgroups. Specifically, we demonstrate that autophagy is induced in one of the MB subgroups (Sonic Hedgehog-SHH) in response to elevated expression of the RE1-silencing transcription factor (REST), a transcriptional repressor and a canonical regulator of neuronal differentiation genes. REST is also a driver of SHH-MB metastasis. Pharmacological inhibition of autophagy decreases MB cell growth, suggesting it is a pro-survival pathway in REST-driven SHH MBs. In mechanistic studies, we found REST-dependent autophagy induction to involve upregulation of the hypoxia-inducible factor 1-alpha (HIF1α) due to REST-mediated silencing of the von Hippel-Lindau (VHL) gene. The VHL gene product promotes HIF1α ubiquitination and proteasomal degradation, and its loss in SHH-MBs with elevated REST expression drives HIF1α stabilization and nuclear localization to activate target autophagy-related genes. Conclusion: Our work is the first to link VHL to MB pathology. VHL loss of function in cancers has been mainly attributed to mutational events. Here, we report a novel mechanism of VHL loss, namely its epigenetic silencing by REST. Our findings provide the foundation for future pre-clinical investigations to examine the feasibility of autophagy blockade as a therapeutic strategy for REST-driven SHH MBs. Citation Format: Ashutosh Singh, Donghang Cheng, Jyothishmathi Swaminathan, Yan Zheng, Nancy Gordon, Vidya Gopalakrishnan. Transcriptional repressor REST controls autophagy in Sonic Hedgehog medulloblastoma through the VHL-HIF1α axis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2864.