Effect of lactate accumulation on translation and transcription in MDA-MB-231 breast cancer cells

Dynamic coordination of energy metabolism and protein synthesis is pivotal to cell fitness, especially in cancer cells that frequently encounter microenvironmental challenges. Yet it remains unclear whether this rapid communication depends on complex regulatory signaling pathways or can be governed by a single molecule. Here, we show that intracellular accumulation of lactate, a central product of glycolysis, is sufficient to acutely repress mRNA translation. Mechanistically, lactate is charged to the 3′ end of tRNA, a site canonically reserved for amino acids, generating translation-defective lactyl-tRNAs. This mechanism may have evolved to restrict protein synthesis during metabolic imbalance, such as when glycolytic activity exceeds lactate clearance, and is particularly relevant in highly glycolytic cancer cells, which frequently experience prolonged hypoxia and elevated lactate levels. Notably, triple-negative breast cancer (TNBC) cells evade this repression by maintaining low intracellular lactate, even under hypoxic stress. Blocking lactate export via monocarboxylate transporter (MCT) inhibition re-establishes translational repression, diminishes cancer cell fitness under metabolic stress, and impairs tumor progression. These findings uncover a unique metabolite-tRNA charging event that directly rewires translational output and reveal a metabolic vulnerability with therapeutic potential.