RAB9A is a small GTPase that regulates intracellular membrane trafficking between late endosomes and the trans-Golgi network (TGN). As a Rab family member, it cycles between inactive GDP-bound and active GTP-bound forms to recruit effector proteins controlling vesicle formation and fusion 1. RAB9A specifically uses NDE1/NDEL1 effectors to interact with dynein motor complexes for retrograde trafficking of late endosomes to the TGN 1. It also recruits SGSM2 to melanosomes and is required for proper trafficking of melanogenic enzymes (TYR, TYRP1, DCT/TYRP2) to melanosomes, with functional interactions identified with BLOC-3 complex proteins during melanosome biogenesis 2. Clinically, RAB9A plays an oncogenic role in hepatocellular carcinoma by promoting cell proliferation, inhibiting apoptosis, and enhancing invasion through AKT/mTOR pathway activation 3. In melanoma, RAB9A expression is regulated by the circ_0081054/miR-637 axis, and elevated RAB9A promotes malignant behaviors including proliferation and angiogenesis 4. Notably, RAB9A exhibits noncanonical functions during human papillomavirus entry, where its GDP-bound form facilitates retromer-mediated endosomal exit, contrasting with typical cellular cargo trafficking 5. In Parkinson's disease, RAB9A expression is downregulated in G2019S LRRK2 mutation carriers, and related Rab family member phosphorylation (RAB12) serves as a biomarker for disease severity 6.