GCN2 in proteostasis: structural logic, signalling networks and disease.

Proteostasis is the finely tuned balance of protein synthesis, folding and degradation essential for cellular health. When this equilibrium is disrupted, misfolded proteins accumulate, triggering adaptive stress responses such as the unfolded protein response and the integrated stress response (ISR). Central to the ISR is the kinase GCN2, a sensor of amino acid deprivation and ribosomal stress. Upon activation, GCN2 phosphorylates eIF2α, dampening global translation while selectively enhancing the synthesis of the stress-responsive transcription factors ATF4 and CHOP. ATF4 orchestrates a broad transcriptional programme that supports amino acid metabolism, redox homeostasis, autophagy and proteasomal degradation, which are key processes for restoring proteostasis. Beyond its canonical role, GCN2 interfaces with other regulatory networks modulating mTORC1 to promote autophagic clearance of damaged proteins and organelles, facilitating stress granule formation, and integrating signals from oxidative and endoplasmic reticulum stress to rebalance the proteome. Dysregulated GCN2 activity has been implicated in diverse pathologies including neurodegeneration, cancer and pulmonary vascular disease, positioning it as a promising therapeutic target. In this review, we explore how GCN2 links nutrient sensing to translational control and metabolic adaptation, and how its central role in proteostasis may inform new strategies for treating diseases driven by protein misfolding and stress pathway imbalance.