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Glioblastoma (GBM) is characterized by exceptionally high intratumoral heterogeneity. However, the molecular mechanisms underlying the origin of different GBM cell populations remain unclear. Here, we found that the compositions of ribosomes of GBM cells in the tumour core and edge differ due to alternative RNA splicing. The acidic pH in the core switches before messenger RNA splicing of the ribosomal gene RPL22L1 towards the RPL22L1b isoform. This allows cells to survive acidosis, increases stemness and correlates with worse patient outcome. Mechanistically, RPL22L1b promotes RNA splicing by interacting with lncMALAT1 in the nucleus and inducing its degradation. Contrarily, in the tumour edge region, RPL22L1a interacts with ribosomes in the cytoplasm and upregulates the translation of multiple messenger RNAs including TP53. We found that the RPL22L1 isoform switch is regulated by SRSF4 and identified a compound that inhibits this process and decreases tumour growth. These findings demonstrate how distinct GBM cell populations arise during tumour growth. Targeting this mechanism may decrease GBM heterogeneity and facilitate therapy.

AimsThe goal of this study was to determine whether NADPH oxidase (NOX)-produced reactive oxygen species enhances brain tumor growth of glioblastoma (GBM) under hypoxic conditions and during radiation treatment.ResultsExogenous ROS promoted brain tumor growth in gliomasphere cultures that expressed functional PTEN, but not in tumors that were PTEN deficient. Hypoxia induced the production of endogenous cytoplasmic ROS and tumor cell growth via activation of NOX. NOX activation resulted in oxidation of PTEN and downstream Akt activation. Radiation also promoted ROS production via NOX which, in turn, resulted in cellular protection that could be abrogated by knockdown of the key NOX component, p22. Knockdown of p22 also inhibited tumor growth and enhanced the efficacy of radiation in PTEN-expressing GBM cells.InnovationWhile other studies have implicated NOX function in GBM models, these studies demonstrate NOX activation and function under physiological hypoxia and following radiation in GBM, two conditions that are seen in patients. NOX plays an important role in a PTEN-expressing GBM model system, but not in PTEN-non-functional systems and provide a potential, patient-specific therapeutic opportunity.ConclusionsThis study provides a strong basis for pursuing NOX inhibition in PTEN-expressing GBM cells as a possible adjunct to radiation therapy.

Glioblastoma (GBM) is the most common and lethal type of brain cancer with 5-year survival of Citation Format: Alireza Sohrabi, Austin Lefebvre, Michael Condro, Harley Kornblum, Michelle Digman, Stephanie Seidlits. Microenvironmental stiffness induces metabolic reprogramming in glioblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3829.