In recent years, the ketogenic diet has gained widespread attention not only as a weight-loss strategy but also as a potential adjunct therapy in cancer treatment. Among the many puzzles in the field, a key question has persisted: through which molecular pathways do ketone bodies exert their anti-cancer effects? This question is particularly critical because understanding these mechanisms could unlock new, targeted strategies that enhance therapeutic outcomes for cancer patients. The mammalian target of rapamycin complex 1 (mTORC1) pathway is a pivotal regulator of cellular growth and metabolism, highly sensitive to nutrient availability. Yet, whether and how ketone bodies influence mTORC1 activity has remained largely unclear—until now.
A groundbreaking study published in Protein & Cell has unveiled a sophisticated molecular mechanism that links ketone body signaling directly to mTORC1 regulation. Researchers have identified β-hydroxybutyrate (BHB), one of the primary ketone bodies generated during ketogenic states, as a potent inhibitor of mTORC1 activity in colorectal cancer (CRC). What sets this finding apart is the specificity: only the D-enantiomer of BHB, not its L-form or other ketone bodies, effectively suppresses mTORC1 function and tumor growth. This profound selectivity establishes a direct functional role for D-BHB in cellular metabolism and anticancer regulation, challenging previous assumptions about ketone body uniformity.
At the heart of this inhibition lies a post-translational modification known as β-hydroxybutyrylation (Kbhb), a covalent attachment of BHB to target proteins. Proteomic analysis revealed that RagC, a small GTPase critical for mTORC1 activation at the lysosomal surface, is a primary substrate undergoing Kbhb. Mass spectrometry pinpointed lysine 349 (K349) on RagC as the exact site modified by BHB. Biochemically, this modification is catalyzed by the acetyltransferase enzyme p300 and reversed by the deacetylase SIRT1, illustrating a dynamic regulatory interplay. This reversible chemical mark dramatically alters RagC’s functionality, demonstrating a novel way that metabolism can modify signaling pathways at a molecular scale.
Mechanistically, the attachment of the BHB moiety to RagC’s K349 reduces the GTP-bound active form of RagC. This altered nucleotide state prevents RagC from associating effectively with Raptor—a constituent of mTORC1—thereby disrupting the recruitment of mTORC1 to the lysosomal surface. Since lysosomal localization is essential for mTORC1 activation by nutrients and growth signals, this modification ultimately leads to the complex’s inactivation. This chain of events highlights an unprecedented mode of mTORC1 inhibition directly regulated by metabolite-driven post-translational modifications, expanding the classical concept of nutrient sensing in cellular signaling.
Genetic validation of this mechanism was elegantly demonstrated via knock-in mouse models harboring a mutation at RagC’s lysine 348 (the murine equivalent to human K349). Mice with the RagC-K348R mutation completely lost the tumor-suppressive and mTORC1-inhibitory effects observed with BHB administration and ketogenic diet interventions. This critical in vivo evidence confirms that RagC β-hydroxybutyrylation is not merely correlative but essential for mediating the anti-cancer properties of ketone bodies. The inability of these mutant mice to respond to BHB underscores the therapeutic relevance of this molecular switch.
Furthermore, clinical correlations with human colorectal cancer patient tissues underscore the translational potential of this discovery. Researchers found that tissue levels of endogenous BHB and RagC-K349bhb modification inversely correlated with tumor size, mTORC1 signaling activity—as indicated by phosphorylated S6 protein—and classic tumor markers such as CA199 and CEA. These correlations suggest that higher local abundance of ketone bodies and RagC modification is associated with suppressed tumor progression, providing insightful biomolecular markers that could guide clinical prognosis or treatment strategies.
The implications of this study extend beyond fundamental cancer biology into novel therapeutic avenues. By elucidating RagC as a sensor for ketone bodies, this work positions metabolite-driven post-translational modifications as central to nutrient sensing and signaling. Unlike canonical allosteric or competitive inhibition, covalent modifications such as Kbhb offer the possibility of sustained and fine-tuned regulation, potentially exploitable through small molecules or dietary interventions. Targeting RagC-K349bhb or its regulatory enzymes p300 and SIRT1 could inspire innovative therapies aimed at mimicking or amplifying the tumor-suppressive effects of ketogenic diets.
Moreover, this research contributes significant insights into the metabolic reprogramming often observed in cancer cells. Tumors frequently upregulate mTORC1 to promote anabolic growth, so metabolic states that inhibit this pathway can recalibrate tumor behavior. BHB’s ability to induce such modifications adds another layer of complexity to the intersection of metabolism and cell signaling, revealing how metabolic intermediates can serve as direct sensors and regulators rather than mere energy substrates.
From a broader perspective, the discovery of Kbhb modifications on RagC heralds a paradigm shift in understanding how cells integrate metabolic signals with growth regulation machinery. This metabolite-protein interaction model challenges existing paradigms that treat metabolites solely as signaling molecules in traditional endocrine or paracrine roles. Instead, it illustrates that metabolites can also enact direct, covalent modifications that translate nutritional states into specific protein functionalities, bridging cellular metabolism with gene regulation and growth control.
Future research prompted by these findings will likely explore how widespread β-hydroxybutyrylation is among other critical signaling proteins and its context-specific roles. Given that p300 and SIRT1 are widely expressed and implicated in numerous biological processes, the BHB-driven modification landscape could have ramifications beyond cancer, impacting fields such as aging, neurodegeneration, and metabolic disorders. Additionally, how other ketone bodies or metabolic intermediates interact with this modification network remains an exciting open question.
In conclusion, this study not only validates the ketogenic diet’s anti-cancer mechanisms at a molecular level but also significantly advances our understanding of nutrient sensing by mTORC1. Through the elegant demonstration that RagC senses β-hydroxybutyrate abundance via a specific lysine modification to suppress mTORC1 activity, the work unlocks new possibilities for metabolite-based therapies. This finding fosters hope for improved interventions in colorectal cancer and potentially other malignancies, leveraging the body’s intrinsic metabolic pathways to halt disease progression.
Subject of Research: Not applicable
Article Title: RagC senses β-hydroxybutyrate abundancy to suppress mTORC1
News Publication Date: 18-Mar-2026
Web References: 10.1093/procel/pwag017
Image Credits: HIGHER EDUCATION PRESS
Keywords: Cell biology, β-hydroxybutyrate, mTORC1 pathway, RagC, β-hydroxybutyrylation, ketogenic diet, colorectal cancer, post-translational modification, p300 acetyltransferase, SIRT1 deacetylase, metabolite signaling
