Functions as a dosage-dependent inducer in mitotic control. Tyrosine protein phosphatase required for progression of the cell cycle. Directly dephosphorylates CDK1 and activates its kinase activity. When phosphorylated, highly effective in activating G2 cells into prophase (By similarity). H2O + O-phospho-L-tyrosyl-[protein] = L-tyrosyl-[protein] + phosphate Interacts with MAPK14 and 14-3-3 proteins. When phosphorylated at Ser-122 and/or Thr-123, interacts with PLK1. Phosphorylated by CHEK1 and MAPK14 at Ser-245. This phosphorylation creates a binding site for 14-3-3 protein and inhibits the phosphatase (By similarity). Phosphorylated by PLK4. Phosphorylated by PLK1, leading to activate the phosphatase activity. Phosphorylation by PLK3 at Ser-217 promotes nuclear translocation. Ser-224 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.