Spn, also known as SPINOPHILIN, PPP1R9B or NEURABIN-2, is a multifunctional protein. It regulates protein-protein interactions in different cell signaling pathways and is one of the regulatory subunits of protein phosphatase 1 (PP1), involved in the dephosphorylation of retinoblastoma protein (pRB) during the cell cycle. The SPN gene has been recognized as a tumor suppressor [2].

In Drosophila, the spn-A/rad51 mutant (where spn-A is related to the SPN gene in Drosophila) shows enhanced genomic damage, cell death, and low-temperature sensitivity in somatic tissues. This indicates a role for spn-A in maintaining somatic tissue during larval and pupal stages [1].

In human tumors, low levels of SPN are associated with a higher grade and worse prognosis, and an oncogenic mutation A566V has been described, which affects SPN-PP1 interaction and phosphatase activity, promoting p53-dependent tumorigenesis by increasing the cancer stem cell pool in breast tumors [2].

In conclusion, Spn plays a crucial role in regulating cell-cycle-related phosphorylation events and is involved in tumor suppression. Drosophila spn-A/rad51 mutant models and human tumor studies have revealed its significance in maintaining genomic stability in somatic tissues and its impact on tumor development, providing insights into potential disease mechanisms and treatment strategies.