Functions as a dosage-dependent inducer in mitotic control. Tyrosine protein phosphatase required for progression of the cell cycle. When phosphorylated, highly effective in activating G2 cells into prophase. Directly dephosphorylates CDK1 and activate its kinase activity (By similarity). H2O + O-phospho-L-tyrosyl-[protein] = L-tyrosyl-[protein] + phosphate Interacts with MAPK14 and 14-3-3 proteins. When phosphorylated on Ser-130 and/or Thr-131, interacts with PLK1. Expressed predominantly in G2 phase. Phosphorylated by CHEK1 and MAPK14 at Ser-220. This phosphorylation creates a binding site for 14-3-3 protein and inhibits the phosphatase. Phosphorylated by PLK4. Phosphorylated by PLK1, leading to activate the phosphatase activity. Phosphorylation by PLK3 at Ser-192 promotes nuclear translocation. Ser-199 is a minor phosphorylation site (By similarity). Phosphorylation by CDK1 occurs at G2 and G2-M transition and leads to increased activity (By similarity). Belongs to the MPI phosphatase family.