PRG3 (proteoglycan 3) is a multifunctional protein with distinct roles in apoptosis, neuronal development, and immune regulation. As a p53-responsive gene, PRG3 encodes a 373-amino acid cytoplasmic protein that induces apoptosis through a caspase-independent mechanism similar to apoptosis-inducing factor (AIF) 1. Notably, PRG3's apoptotic function is independent of its oxidoreductase activity 1. In neuronal contexts, PRG3 promotes neuritogenesis and filopodia formation during early neuronal development through N-glycosylation-dependent mechanisms, with expression shifting from the neurite shaft to axonal plasma membranes during maturation 2. The C-terminal domain is critical for these morphological effects 3. In pathological settings, dysregulated PRG3 levels amplify Ras-driven oncogenic signaling in gliomas, enhancing proliferation and migration 4. Immunologically, PRG3 functions similarly to eosinophil major basic protein, stimulating neutrophil superoxide production and IL-8 release, and inducing histamine and leukotriene release from basophils [UniProt]. Recent evidence identifies PRG3 as a plasma pharmacodynamic biomarker for IL-5 inhibitor response in eosinophilic asthma 5, and methylation changes near PRG3 are associated with diabetic kidney disease progression in type 1 diabetes 6.