RAB15 is a small GTPase belonging to the Rab family that regulates intracellular membrane trafficking by cycling between inactive GDP-bound and active GTP-bound states to recruit effector proteins 1. As a brain-specific protein, RAB15 may act in concert with RAB3A in regulating synaptic vesicle membrane flow within nerve terminals 1. RAB15 functions in receptor recycling through the endocytic recycling compartment via its effector protein REP15, regulating transferrin receptor trafficking independently of early endosomal pathways 2. RAB15 is localized on Weibel-Palade bodies and contributes to their evoked exocytosis 3. Functionally, RAB15 inhibits lysosomal fusion of vesicles and induces autophagy, as demonstrated in bacterial pathogenesis where E. chaffeensis exploits RAB15 upregulation to evade host immune responses 4. RAB15 is regulated by DENN/MADD as a guanine nucleotide exchange factor substrate 5. Clinically, RAB15 alternative splicing patterns distinguish tumor-initiating cells from parental neuroblastoma cells, suggesting diagnostic potential 6, and RAB15 downregulation associates with age-related fertility decline in spermatozoa 7. Additionally, RAB15 variants are candidates for osteoporosis susceptibility 8.