PPP1R9B (protein phosphatase 1 regulatory subunit 9B), also known as SPINOPHILIN or NEURABIN-2, functions as a multifunctional scaffold protein that regulates protein phosphatase 1 (PP1) activity and cellular signaling pathways 1. The protein targets PP1 to specific subcellular locations and modulates its phosphatase activity, particularly toward the retinoblastoma protein (pRB) during cell cycle regulation 12. PPP1R9B plays crucial roles in cytoskeletal organization by binding to F-actin and maintaining cortical actin structure, which is essential for cell adhesion and migration 3. In immune cells, it accumulates at the NK immunological synapse in a maturation-dependent manner and is required for synapse formation and maintenance 3. Functionally, PPP1R9B acts as a tumor suppressor, with its loss or mutation promoting cancer stem cell properties and tumor progression 21. Reduced PPP1R9B expression correlates with worse prognosis in breast cancer, particularly in triple-negative tumors, and increases stemness-related gene expression 2. The protein also contributes to neurodevelopmental processes, with mutations identified in patients with microcephaly and neurodevelopmental disorders 4. Additionally, PPP1R9B levels correlate with depression severity in Parkinson's disease patients, suggesting roles in neuropsychiatric pathology 5.