AP3S1 encodes the sigma subunit of the adaptor protein complex 3 (AP-3), which facilitates vesicle-mediated transport from the Golgi to lysosomes and other cellular compartments. The protein functions in intracellular trafficking pathways essential for proper cellular transport processes 1. AP3S1 plays a critical role in melanocyte pigmentation, as demonstrated by zebrafish studies showing that partial knockdown of Ap3s1 sensitizes melanocytes to hypopigmentation under low-copper conditions 1. The gene shows significant disease relevance across multiple cancer types. In ovarian cancer, AP3S1 emerged as a key tumor driver gene, with knockdown experiments demonstrating its regulatory role in tumor cell migration and invasion through the TGF-β/SMAD pathway 2. AP3S1 mutations are also recurrently found in HPV-associated sinonasal squamous cell carcinoma 34. Additionally, AP3S1 variants (rs3756555) are associated with increased type 2 diabetes susceptibility in Chinese populations 5. Clinically, AP3S1 expression serves as a prognostic predictor in lung adenocarcinoma, where it promotes cell growth and migration, and is associated with immune infiltration levels 6. Notably, AP3S1 expression is frequently downregulated in cervical carcinomas, with decreased expression observed in 26% of tumors 7.