PCNP (PEST proteolytic signal containing nuclear protein) is a 178-amino acid nuclear protein containing two PEST sequences that exhibits context-dependent roles in cancer biology 1. PCNP functions through multiple mechanisms including regulation of cell cycle progression, apoptosis, and key signaling pathways 2. The protein undergoes ubiquitination by NIRF E3 ligase and modulates MAPK and PI3K/AKT/mTOR signaling pathways 3. PCNP demonstrates tumor-specific effects: it acts as a tumor suppressor in thyroid cancer by promoting cell cycle arrest, activating ERK/JNK/p38 pathways, and inducing autophagy through Wnt/β-catenin pathway suppression 2. Conversely, PCNP promotes tumor progression in ovarian cancer by facilitating β-catenin nuclear translocation, activating Wnt signaling, and triggering epithelial-mesenchymal transition 4. In hepatocellular carcinoma, PCNP upregulates UHRF2 to activate ErbB3/Ras/Raf signaling pathways 5. Clinically, PCNP expression correlates with disease activity in rheumatoid arthritis and serves as a prognostic marker in multiple cancers 6. These findings establish PCNP as a versatile regulatory protein with significant therapeutic potential across various pathological conditions.