Metabolic control of tRNA-mediated translational reprogramming in glioblastoma

ABSTRACT Glioblastoma (GBM) ranks among the most lethal of human cancers. Standard-of-care therapies offer only palliation and molecularly targeted treatments have shown little benefit for patients. The failure to achieve tumor control is partly due to the presence of GBM stem cells (GSCs). These stem-like cells self-renew and differentiate into diverse cell types within the tumor, generating intratumoral heterogeneity and contribute to angiogenesis and immune escape. Although the impact of GSCs remains controversial, defining their molecular regulation may offer novel therapeutic paradigms to improve the clinical care of patients afflicted with GBMs and other brain tumors. We and others have found that GSCs are distinguished from their differentiated progeny and normal neural stem cells at multiple levels of regulation, including transcription, epigenetic, epitranscriptomics, translational, and post-translational mechanisms. In preliminary studies, GSCs display enhanced protein synthesis relative to differentiated progeny and neural stem cells, suggesting that efficient mRNA translation may contribute to tumorigenesis. During translation, tRNAs decipher genetic codes by base pairing with mRNA codons and transfer the corresponding amino acids to the growing peptide chain. Post-transcriptional tRNA modifications regulate their translational functions, which are cell-type specific and influenced by environmental cues. Aberrant modifications alter tRNAs stability, structure, and folding to restrict or expand decoding. This proposal focuses on a currently understudied area of tRNA modification in GBMs. Comparing expression profiles of disease-related tRNA-modifying enzymes, I identified differentially expressed tRNA-modifying enzymes and marks in patient-derived GBM surgical samples and cultures. As selected amino acids serve as co-factors for tRNA modifications, I hypothesize that dietary restriction of amino acids can reprogram the tRNA landscape. Indeed, in preliminary studies genetic targeting of tRNA modification enzymes or amino acid restriction reduced GSC proliferation, self-renewal, and in vivo tumor growth. tRNA modifications can specifically target a subset of tRNAs, so I also hypothesize that altered tRNA modifications change homeostasis of tRNA pools and lead to codon-biased reprogramming of translation that drive oncogenic processes in GBM. To test this hypothesis, I will use mass spectrometry to detect changes in tRNA modifications and ribosome profiling to understand downstream proteomic changes upon tRNA enzyme knockdown and diet restriction. Collectively, this proposal will provide molecular insights into roles of tRNA modifications in cancer stem cell maintenance and inform development of novel therapies for GBM.