Abstract LT05: METTL8-MEDIATED EPITRANSCRIPTOMIC REGULATION OF GBM CYCLING STATE IS DEPENDENT ON RTK/PI3K/AKT SIGNALING

Abstract Glioblastoma (GBM) is a lethal brain tumor with limited treatment options. Treatment failures are often attributed to the existence of glioma stem cells (GSCs), which confer intratumoral heterogeneity and therapy resistance. Contrary to common belief that cancer cells employ aerobic glycolysis (Warburg effect) to sustain their metabolic requirements, GSCs rely on oxidative phosphorylation (OXPHOS) for energy production. As a result, GSCs are uniquely sensitive to OXPHOS inhibitors (Gboxin), as well as mitochondrial translation inhibitors which disrupt OXPHOS. METTL8 is a newly discovered mitochondrial methyltransferase which catalyzes m3C32 modifications in mitochondrial tRNAsThr/Ser(UCN) (mt-tRNAs). This post-transcriptional modification ensures the optimal structure of mt-tRNAs to facilitate efficient translation of mitochondrial proteins involved in electron transport chain (ETC). Although the epitranscriptomic functions of METTL8 have been well characterized, its roles in cancers (i.e. glioblastoma) remain largely unexplored. In this study, we showed that METTL8 is overexpressed in GBM and high METTL8 expression portends poor patient prognosis. In GSC, METTL8 is under the transcriptional regulation of HIF-1α, and the chromatin accessibility at METTL8 promoter is facilitated by the deposition of histone variant H2AZ. METTL8 depletion downregulated m3C32 modifications in mt-tRNAsThr/Ser(UCN) in GSC, leading to impaired mitochondrial translation and OXPHOS defects. Phenotypically, METTL8 knockdown (KD) compromised GSCs’ self-renewal, proliferation, invasiveness and tumorigenicity. Interestingly, METTL8-KD GSC acquired a slow cycling state which is linked to reduced receptor tyrosine kinase (RTK) signaling. Consistently, METTL8-KD GSC showed lower Akt phosphorylation and exhibited increased sensitivity to mTOR/Akt inhibitors. Finally, our mechanistic findings led to the identification of a novel HIF1-α/Akt inhibitor drug combination which faithfully recapitulates the phenotypes of METTL8-KD GSCs. In conclusion, our findings provide the first in-depth study of METTL8 roles in GBM pathogenesis, and highlights a novel drug combination which could potentially be used to treat this dreadful disease. Citation Format: Bernice Woon Li Lee, You Heng Chuah, Jeehyun Yoon, Oleg V. Grinchuk, Jia Feng, Yajing Liang, Jayshree L Hirpara, Ya Ting Shen, Loo Chien Wang, Yan Ting Lim, Tianyun Zhao, Radoslaw M Sobota, Tan Boon Toh, Shazib Pervaiz, Zhewang Lin, Derrick Sek Tong Ong. METTL8-MEDIATED EPITRANSCRIPTOMIC REGULATION OF GBM CYCLING STATE IS DEPENDENT ON RTK/PI3K/AKT SIGNALING [abstract]. In: Proceedings of Frontiers in Cancer Science; 2023 Nov 6-8; Singapore. Philadelphia (PA): AACR; Cancer Res 2024;84(8_Suppl):Abstract nr LT05.