AP1AR (adaptor protein complex 1 associated regulatory protein), also known as Gadkin, is a peripheral membrane protein essential for vesicular trafficking between the trans-Golgi network (TGN) and endosomes 1. AP1AR directly interacts with the gamma-1 subunit (AP1G1) of the AP-1 adaptor complex, stabilizing its membrane association and preventing premature release 1. This protein functions as a molecular linker connecting AP-1-dependent membrane trafficking with kinesin-based microtubular transport, coordinating endosomal membrane dynamics and cargo recycling 2. AP1AR plays a critical role in calcium-induced endo-lysosomal secretion, a process requiring AP-1, Gadkin, and AP-2 but not AP-3 3. Additionally, AP1AR inhibits Arp2/3 complex function, negatively regulating cell spreading and motility 4. Clinically, AP1AR has emerged as a significant biomarker in lung adenocarcinoma, showing consistent upregulation and independent association with poor overall survival 5. It is linked to cell-cycle progression, DNA replication, hypoxia, and epithelial-to-mesenchymal transition 5. Beyond cancer, AP1AR-DT, a long noncoding RNA overlapping the AP1AR locus, is implicated in bipolar disorder pathophysiology, with elevated expression reducing excitatory synaptic transmission through NEGR1 suppression 6. AP1AR also potentially links vesicle transport with pro-inflammatory responses via Toll-like receptor signaling 7.