SPINOPHILIN (SPN

PPP1R9B or NEURABIN-2) is a multifunctional protein that regulates protein–protein interactions in different cell signaling pathways. SPN is also one of the regulatory subunits of protein phosphatase 1 (PP1)

implicated in the dephosphorylation of retinoblastoma protein (pRB) during cell cycle. The

SPN

gene has been described as a tumor suppressor in different human tumor contexts

in which low levels of SPN are correlated with a higher grade and worse prognosis. In addition

mutations of the SPN protein have been reported in human tumors. Recently

an oncogenic mutation of SPN

A566V

was described

which affects both the SPN–PP1 interaction and the phosphatase activity of the holoenzyme

and promotes p53-dependent tumorigenesis by increasing the cancer stem cell (CSC) pool in breast tumors. Thus

the loss or mutation of SPN could be late events that promotes tumor progression by increasing the CSC pool and

eventually

the malignant behavior of the tumor.