Phase separation of TRNAU1AP protein sustains selenoprotein translation and promotes glioblastoma tumorigenesis.

BACKGROUND: Glioblastoma (GBM) depends on selenoproteins, yet the mechanisms underlying their dysregulation remain poorly understood. The tRNA-binding protein TRNAU1AP also remains largely uncharacterized, with its mechanistic functions in in vivo tumorigenesis undefined. Additionally, while IGF2BP3 is the most dysregulated m6A reader in GBM, the pathways through which it promotes glioblastoma stem cell (GSC) self-renewal have yet to be elucidated. METHODS: TRNAU1AP expression in human GBMs and public datasets was analyzed by Western blotting, immunohistochemistry, and gene expression profiling. Functions of TRNAU1AP in GSCs were evaluated through gain- and loss-of-function assays assessing proliferation, self-renewal, and tumorigenicity. Proteomics, spatial transcriptomics, RNA immunoprecipitation, and polysome profiling were employed to investigate TRNAU1AP-mediated regulation of selenoprotein synthesis. RNA immunoprecipitation and phase-separation assays were used to characterize the TRNAU1AP-EEFSEC interaction. Multi-omics and RNA stability analyses were performed to elucidate IGF2BP3-dependent regulation of TRNAU1AP expression. RESULTS: TRNAU1AP is essential for the proliferation, stemness, and tumorigenesis of GSCs and is associated with poor patient survival. TRNAU1AP interacts with EEFSEC to form a phase-separated complex that enhances EEFSEC binding to sec-tRNAsec, thereby promoting the translation of several selenoproteins. These selenoproteins act as key effectors mediating the oncogenic functions of TRNAU1AP. Furthermore, IGF2BP3 upregulates TRNAU1AP expression through m⁶A-dependent transcript stabilization, leading to increased selenoprotein synthesis and enhanced GSC stemness and tumorigenic potential. CONCLUSION: These findings establish novel oncogenic roles of TRNAU1AP, and reveal that IGF2BP3-TRNAU1AP coupling constitutes an important mechanism for the selenoprotein synthesis and for gliomagenesis, thereby advancing the understanding of RNA-binding proteins in cancer biology.