RAB3D is a small GTPase belonging to the RAB3 family that regulates intracellular membrane trafficking, particularly in regulated exocytosis and secretion 1. The protein localizes primarily to secretory vesicles in non-neuronal cells, including lamellar bodies in alveolar epithelial type II cells and secretory granules in various exocrine and endocrine tissues 12. RAB3D cycles between GDP-bound (inactive) and GTP-bound (active) forms to control vesicle formation, movement, and fusion processes 1. In hepatocytes, RAB3D localizes to the trans-Golgi and forms complexes with GOLGA4 and MYH10, playing a crucial role in maintaining Golgi organization and proper protein trafficking 34. The protein interacts with COPI vesiculation machinery and is essential for intra-Golgi transport 4. Clinically, RAB3D dysfunction is implicated in alcohol-associated liver disease, where ethanol-induced downregulation leads to Golgi disorganization and abnormal protein trafficking 34. Additionally, RAB3D overexpression has been associated with cancer progression, particularly in melanoma and osteosarcoma, where it promotes cell proliferation, migration, and invasion 567.