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 various hematologic malignancies. DNA damage-induced p53/Bcl2 interaction at the outer mitochondrial membrane results 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 suppresses 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 catalytic subunit (PP2A/C) inhibits Bcl2 phosphorylation, leading to increased p53/Bcl2 binding and apoptotic cell death. Mechanistically, PP2A-mediated dephosphorylation of Bcl2 in vitro promotes its direct interaction with p53 as well as a conformational change in Bcl2. PP2A directly interacts with the BH4 domain of Bcl2 as a docking site to potentially "bridge" PP2A to Bcl2's flexible loop domain containing the target serine 70 phosphorylation site. Thus, PP2A may provide a dual inhibitory effect on Bcl2's survival function by both dephosphorylating Bcl2 and enhancing p53-Bcl2 binding. Activating PP2A to dephosphorylate Bcl2 and/or increase Bcl2/p53 binding may represent an efficient and novel approach for treatment of hematologic malignancies.
Deng
Xingming
X
Department of Medicine, Division of Hematology/Oncology, University of Florida Shands Cancer Center, Gainesville, FL 32610-3633, USA.
Gao
Fengqin
F
May
W Stratford
WS
D000818:Animals; D000957:Antigens, Viral, Tumor / Q000096:biosynthesis / Q000235:genetics; D017209:Apoptosis / Q000187:drug effects / Q000235:genetics; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects / Q000235:genetics; D002518:Ceramides / Q000494:pharmacology; D004249:DNA Damage / Q000187:drug effects / Q000235:genetics; D020536:Enzyme Activators / Q000494:pharmacology; D019337:Hematologic Neoplasms / Q000201:enzymology* / Q000235:genetics; D007377:Interleukin-3 / Q000235:genetics / Q000378:metabolism; D051379:Mice; D051336:Mitochondrial Membranes; D010749:Phosphoprotein Phosphatases / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects / Q000235:genetics; D011485:Protein Binding / Q000187:drug effects / Q000235:genetics; D000071636:Protein Phosphatase 2C; D017434:Protein Structure, Tertiary / Q000187:drug effects / Q000235:genetics; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2; D034622:RNA Interference; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism*
D000957:Antigens, Viral, Tumor; D002518:Ceramides; D020536:Enzyme Activators; D007377:Interleukin-3; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D016159:Tumor Suppressor Protein p53; C052617:Bcl2 protein, mouse; D010749:Phosphoprotein Phosphatases; D000071636:Protein Phosphatase 2C