Phosphorylation is a major post-translational modification to proteins and controls cell signaling and induction of cell proliferation, differentiation, cell death and other biological processes. Phosphatases reverse phosphorylation by removing the phosphate group added by kinases mostly to serine, threonine or tyrosine residues in a protein. Thus phosphatases have a critical role in regulating cell signaling, as generally reversal of the phosphorylation indicates a switching off of the signal. Uncontrolled or constitutive signaling by cell surface receptors may lead to increased proliferation, among other outcomes, and could lead to the pathogenesis of cancer and other diseases. Therefore, after phosphorylation and protein activation by kinases, the signal must return to the resting or inactivated state through dephosphorylation catalyzed by phosphatases.
Two important phosphatases include the serine/threonine protein phosphatase 2A (PP2A) and phosphatase and tensin homolog (PTEN). PP2A is a key phosphatase as it catalyzes dephosphorylation of many proteins, but also dephosphorylates the main protein kinases responsible for activation of major signaling pathways, including AKT, ERK MAP kinase and Protein kinase C (PKC) family members. PTEN dephosphorylates proteins, as well as the phospholipid phosphatidylinositol (3,4,5)-trisphosphate (PIP3), which induces inhibition of signaling by AKT, a critical pathway involved in cellular growth and proliferation. PTEN is a tumor suppressor frequently mutated and involved in the pathogenesis and progression of several cancers.
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