TI - Protein phosphatase 4 regulates apoptosis in leukemic and primary human T cells . AB - Abstract The control of T-cell survival is of overwhelming importance for preventing leukemia and lymphoma . The present report demonstrates that the serine/threonine protein phosphatase PP4 regulates the survival of both leukemic T-cells and untransformed human peripheral blood T-cells , particularly after treatment with anti-leukemic drugs and other cytotoxic stimuli . PP4 -induced apoptosis is mediated , atleast in part , through de-PHOSphorylation of apoptosis regulator PEA-15 , previously implicated in the control of leukemic cell survival . PP4 activity significantly affects the mutation rate in leukemic T-cells , indicating that PP4 dysfunction may be important in the development and progression of leukemia .