Ppp1r9b, also known as SPINOPHILIN or NEURABIN-2, is a multifunctional protein and one of the regulatory subunits of protein phosphatase 1 (PP1). It is involved in regulating protein - protein interactions in different cell signaling pathways, and plays a role in cell cycle regulation by participating in the dephosphorylation of retinoblastoma protein (pRB) [1,2,3,4].

Mutations in PPP1R9B, such as the SPN - A566V mutation, can affect its interaction with PP1 and phosphatase activity, promoting the tumorigenic and stemness properties of cells, especially in cells with mutant p53 [1]. Down - regulation of Ppp1r9b in breast and lung tumors increases the cancer stem cell population, correlates with a worse prognosis, and contributes to tumorigenesis [3,4].

In conclusion, Ppp1r9b is crucial for normal cell function, especially in cell cycle regulation. Its dysregulation, either through mutation or down - regulation, has significant implications in tumorigenesis, highlighting its importance as a potential target for cancer research. The study of Ppp1r9b in KO/CKO mouse models, as well as in human tumor samples, provides valuable insights into its role in cancer development and progression [1,3,4].