Protein phosphatase 2A inactivates Bcl2's antiapoptotic function by dephosphorylation and up-regulation of Bcl2-p53 binding Bcl2 is associated with chemoresistance and poor prognosis in patients with vari- ous hematologic malignancies. DNA damage-induced p53/Bcl2 interaction at the outer mitochondrial membrane re- sults in a Bcl2 conformational change with loss of its antiapoptotic activity in interleukin-3-dependent myeloid H7 cells. Here we find that specific disruption of protein phosphatase 2A (PP2A) activity by either expression of small t antigen or depletion of PP2A/C by RNA interference enhances Bcl2 phosphorylation and sup- presses cisplatin-stimulated p53/Bcl2 binding in association with prolonged cell survival. By contrast, treatment of cells with C2-ceramide (a potent PP2A activator) or expression of the PP2A cata- lytic subunit (PP2A/C) inhibits Bcl2 phos- phorylation, leading to increased p53/ Bcl2 binding and apoptotic cell death. Mechanistically, PP2A-mediated dephos- phorylation of Bcl2 in vitro promotes its direct interaction with p53 as well as a conformational change in Bcl2. PP2A di- rectly interacts with the BH4 domain of

内容摘要

Protein phosphatase 2A inactivates Bcl2's antiapoptotic function by dephosphorylation and up-regulation of Bcl2-p53 binding Bcl2 is associated with chemoresistance and poor prognosis in patients with vari- ous hematologic malignancies. DNA damage-induced p53/Bcl2 interaction at the outer mitochondrial membrane re- sults in a Bcl2 conformational change with loss of its antiapoptotic activity in interleukin-3-dependent myeloid H7 cells. Here we find that specific disruption of protein phosphatase 2A (PP2A) activity by either expression of small t antigen or depletion of PP2A/C by RNA interference enhances Bcl2 phosphorylation and sup- presses cisplatin-stimulated p53/Bcl2 binding in association with prolonged cell survival. By contrast, treatment of cells with C2-ceramide (a potent PP2A activator) or expression of the PP2A cata- lytic subunit (PP2A/C) inhibits Bcl2 phos- phorylation, leading to increased p53/ Bcl2 binding and apoptotic cell death. Mechanistically, PP2A-mediated dephos- phorylation of Bcl2 in vitro promotes its direct interaction with p53 as well as a conformational change in Bcl2. PP2A di- rectly interacts with the BH4 domain of