Metabolic flexibility is key to survival and growth in all living organisms. In mammals, the pathways supporting cell proliferation in nutrient-limiting conditions have not been fully elucidated, although certain tumors display metabolic dependencies that can be targeted for therapy. Here, we combine metabolic tracers, nutrient supplementation, and genome-wide CRISPR-Cas9 screening to investigate the pathways mediating glutamine addiction, a hallmark of several cancers. We report that the vitamin biotin allows the bypassing of glutamine dependence by activating pyruvate carboxylase (PC), and we discover a mechanism by which the tumor suppressor FBXW7 promotes pyruvate anaplerosis. Mechanistically, we show that FBXW7 prevents c-MYC accumulation and recruitment of a cluster of transcriptional repressors, including MAX, MNT, and SIN3A, to the PC promoter, thereby maintaining PC expression and avoiding glutamine addiction. Our work sheds light on the molecular mechanisms that support metabolic flexibility and prevent glutamine addiction in cancer, with high relevance for FBXW7 -associated cancer mutations. • Nutrient-genetic screens identify mechanisms determining glutamine addiction • Biotinylation licenses anaplerosis upon glutamine depletion • FBXW7 promotes pyruvate-mediated growth of glutamine-starved cells • The MYC extended network represses PC transcription via MNT/SIN3A and deacetylation Lisci et al. present a unified model revealing how cells escape glutamine addiction, a metabolic vulnerability of several cancers. Combining systematic genetic and nutrient screens, they show that biotin and the tumor suppressor FBXW7 enable metabolic flexibility by sustaining mitochondrial pyruvate carboxylation, with FBXW7 acting upstream of MYC-mediated transcriptional regulation.
Lisci et al. (2026) studied this question.