RAB4B is a small GTPase belonging to the RAS oncogene family that functions as a key regulator of intracellular membrane trafficking and endosomal recycling processes 1. The protein controls early endosome sorting by interacting with the γ-subunit of the clathrin adaptor complex 1 (AP1γ), facilitating the formation of clathrin-coated vesicles for trafficking to recycling endosomes 2. RAB4B plays a critical role in glucose homeostasis by regulating GLUT4 transporter localization in adipocytes, with decreased expression observed in obese diabetic states 3. In immune regulation, RAB4B deficiency in T cells promotes adipose Th17/Treg imbalance, contributing to adipose tissue dysfunction and insulin resistance 4. The protein also serves as a cellular entry factor for viral infections, with direct interaction with Japanese encephalitis virus E protein being essential for viral internalization into early endosomes 1. Additionally, RAB4B expression shows associations with cancer prognosis and immunotherapy response across multiple cancer types 5, and genetic variants in the RAB4B-EGLN2 locus are linked to multiple sclerosis severity 6. These findings establish RAB4B as a multifunctional regulator with roles in metabolism, immunity, and disease pathogenesis.