During tumorigenesis, the high metabolic demand of cancer cells results in increased production of reactive oxygen species. To maintain oxidative homeostasis, tumor cells increase their antioxidant production through hyperactivation of the NRF2 pathway, which promotes tumor cell growth. Despite the extensive characterization of NRF2-driven metabolic rewiring, little is known about the metabolic liabilities generated by this reprogramming. Here, we show that activation of NRF2, in either mouse or human cancer cells, leads to increased dependency on exogenous glutamine through increased consumption of glutamate for glutathione synthesis and glutamate secretion by xc- antiporter system. Together, this limits glutamate availability for the tricarboxylic acid cycle and other biosynthetic reactions creating a metabolic bottleneck. Cancers with genetic or pharmacological activation of the NRF2 antioxidant pathway have a metabolic imbalance between supporting increased antioxidant capacity over central carbon metabolism, which can be therapeutically exploited.

Retroviruses have been invading mammalian germlines for millions of years, accumulating in the form of endogenous retroviruses (ERVs) that account for nearly one-tenth of the mouse and human genomes. ERVs are epigenetically silenced during development, yet the cellular factors recognizing ERVs in a sequence-specific manner remain elusive. Here we demonstrate that ZFP809, a member of the Kr€ uppel-associated box zinc finger protein (KRAB-ZFP) family, initiates the silencing of ERVs in a sequence-specific manner via recruitment of heterochromatin-inducing complexes. ZFP809 knockout mice display highly elevated levels of ZFP809-targeted ERVs in somatic tissues. ERV reactivation is accompanied by an epigenetic shift from repressive to active histone modifications but only slight destabilization of DNA methylation. Importantly, using conditional alleles and rescue experiments, we demonstrate that ZFP809 is required to initiate ERV silencing during embryonic development but becomes largely dispensable in somatic tissues. Finally, we show that the DNA-binding specificity of ZFP809 is evolutionarily conserved in the Muroidea superfamily of rodents and predates the endogenization of retroviruses presently targeted by ZFP809 in Mus musculus. In sum, these data provide compelling evidence that ZFP809 evolved to recognize foreign DNA and establish histone modification-based epigenetic silencing of ERVs.

Highlights d Keap1 mutations drive non-essential amino acid (NEAA) dependency in cancer d Intracellular glutamate levels dictate cellular ability to survive NEAA deprivation d Restriction of NEAA can suppress Keap1 mutant tumor growth in vivo d Limiting glutamate by glutaminase inhibition enhances response to NEAA deprivation

The unregulated proliferative capacity of many tumors is dependent on dysfunctional nutrient utilization and ROS (reactive oxygen species) signaling to sustain a deranged metabolic state. Although it is clear that cancers broadly rely on these survival and signaling pathways, how they achieve these aims varies dramatically. Mutations in the KEAP1/NRF2 pathway represent a potent cancer adaptation to exploit native cytoprotective pathways that involve both nutrient metabolism and ROS regulation. Despite activating these advantageous processes, mutations within KEAP1/ NRF2 are not universally selected for across cancers and instead appear to interact with particular tumor driver mutations and tissues of origin. Here, we highlight the relationship between the KEAP1/NRF2 signaling axis and tumor biology with a focus on genetic mutation, metabolism, immune regulation, and treatment implications and opportunities. Understanding the dysregulation of KEAP1 and NRF2 provides not only insight into a commonly mutated tumor suppressor pathway but also a window into the factors dictating the development and evolution of many cancers.