ZC3H12D (zinc finger CCCH-type containing 12D) is an RNA-binding protein with dual roles in cell cycle regulation and immune modulation. Functionally, ZC3H12D acts as an RNase that destabilizes target mRNAs through direct binding to conserved stem-loop structures in 3'-UTRs 1. It suppresses cell cycle progression by destabilizing cyclin D1 mRNA and inhibiting G1/S transition through RB1 phosphorylation suppression 2, while in association with ZC3H12A, it enhances degradation of pro-inflammatory IL-6 mRNA in activated macrophages 3. Mechanistically, ZC3H12D negatively regulates Toll-like receptor signaling and macrophage activation by reducing mRNA stability of pro-inflammatory genes including NF-κB, TNF-α, and IL-1β 45. In immune cells, ZC3H12D binds synthetic short mRNAs and translocates to the nucleus, enhancing cytolytic activity of natural killer cells and cytotoxic T lymphocytes 6. Clinically, ZC3H12D exhibits context-dependent significance. High ZC3H12D expression in tumor-infiltrating immune cells correlates with enhanced antitumor immunity and favorable prognosis in lung adenocarcinoma and head and neck squamous cell carcinoma 78. Conversely, lower ZC3H12D expression in malignant cells associates with reduced proliferation and better outcomes 79. It serves as a tumor suppressor in certain leukemias 10.