MPP1 (membrane palmitoylated protein 1) is a heavily palmitoylated membrane protein and member of the MAGUK (membrane-associated guanylate kinase homolog) family encoded on the X chrX 1. As a scaffold protein, MPP1 localizes to plasma membrane microdomains including membrane rafts and cell-cell junctions, where it organizes signaling complexes 2. MPP1 regulates protein trafficking and stability through PDZ-domain interactions; notably, it contributes to SLC43A2 trafficking by binding phospho-degrons on substrate proteins 3. The protein functions in membrane organization and signal transduction across multiple cell types 2. In urothelial carcinoma, MPP1 inhibits immune escape by promoting CCL5 expression through binding and stabilizing USP12, thereby enhancing CD8+ T-cell chemotaxis into the tumor microenvironment 4. Low MPP1 expression in urothelial carcinoma correlates with poor immunotherapy response and survival, identifying MPP1 as a potential biomarker for guiding cancer immunotherapy 4. The MPP1 gene structure is conserved across mammals, spanning approximately 28 kb with 12 exons on Xq28, supporting its fundamental biological importance 1.