Selenoprotein loss resulting from Alkbh8 deficiency engages senescence and metabolic programming and predicts poor clear cell renal cancer cell survival

Over 14,000 Americans die each year from kidney cancer with clear cell Renal Cell Carcinoma (ccRCC) being the most prevalent and malignant type. Disruptions in glutathione (GSH) metabolism have emerged as predictors of poor survival in ccRCC.  Critically important to the maintenance of the GSH redox cycle are the activities of many selenocysteine-containing GSH metabolizing enzymes whose translation is controlled by the tRNA methyltransferase alkylation repair homolog 8 (Alkbh8). Epitransciptomic marks, in the form of tRNA modifications, can regulate gene expression at the level of translation.  Our studies indicate that defective epitranscriptomic regulation and impairment in selenocysteine (SEC) incorporation, resulting from a deficiency in tRNA methytransferase Alkbh8 ( Alkbh8 -/- ), alters glutathione (GSH) metabolism (4) and triggers a gene signature that is highly predictive (Hazard Ratio 2.65, p Alkbh8 -/- gene signature drives both senescence and mitochondrial reprogramming to limit damage that results from defects in mitochondrial reactive oxygen species (ROS) detoxification.  Alkbh8 -/- mouse embryonic fibroblasts (MEFS) increase many hallmarks of senescence, including senescence associated β-galactosidase, heterocromatic foci, the cyclin dependent kinase inhibitor p16 Ink4a , mitochondrial elongation as well as the senescence associated secretory phenotype (SASP).  In addition, MEFs undergo a metabolic shift that is highlighted by a striking increase in the level of uncoupling protein 2 (UCP2) which enhances oxygen consumption to reduce mitochondrial ROS burden. Our work defines how defects in Alkbh8 and SEC utilization promote senescence and mitochondrial reprogramming and unveils new mechanistic targets for prolonging ccRCC patient survival.