RAB12 is a small GTPase that regulates intracellular membrane trafficking by cycling between GDP-bound (inactive) and GTP-bound (active) conformations to recruit effector proteins for vesicle formation and transport 1. RAB12 plays key roles in protein transport from recycling endosomes to lysosomes and in autophagy regulation 2. It negatively regulates osteogenic differentiation of mesenchymal stem cells through the PCBP1/GLUT1 axis, controlling glucose metabolism in the bone microenvironment 3. Mechanistically, RAB12 functions as a robust substrate of LRRK2 kinase, with phosphorylation occurring at Ser106 4. The RAB12-LRRK2 complex suppresses primary ciliogenesis and regulates centrosome homeostasis in astrocytes by enhancing Rab10 phosphorylation and recruiting RILPL1 1. RAB12 also interacts with RILP family members to regulate mast cell secretory granule transport 5. Clinically, RAB12 is relevant to Parkinson's disease, where LRRK2 mutations elevate RAB12 phosphorylation levels. Phosphorylated RAB12 (pSer106) serves as an endogenous blood biomarker of G2019S LRRK2-driven disease, correlating with motor severity and responding to LRRK2 inhibition 4. Additionally, RAB12 under-prenylation contributes to choroideremia pathology by reducing autophagy and increasing mTORC1 signaling in retinal pigment epithelium 2.