The family of phosphoprotein phosphatases includes enzymes that dephosphorylate serine, threonine (EC 3.1.3.16) and tyrosine (EC 3.1.3.48) residues within their substrates. Analogous to kinases, some show certain specificity towards Ser/Thr or Tyr residues, like PPM1D (EC 3.1.3.16). Phosphatases that do not show this selectivity are classified as dual-specificity phosphatases (DUSP).
Protein phosphatase magnesium-dependent 1 δ (PPM1D, also known as wip1 (wild type p53 induced protein phosphatase 1)) is a member of the PP2C family of Ser/Thr protein phosphatases, and was initially characterized as a p53-regulated phosphatase responsible for inactivation of p38-MAPK and consequent inactivation of p53. PPM1D also abrogates cell cycle checkpoints by reducing p53 and Chk1 activities through direct dephosphorylation, and it has been shown to be amplified and overexpressed in some human breast and prostate cancers, two steroid hormone-dependent cancers[1],[2].