PP2A inactivation is a crucial step in triggering apoptin-induced tumor-selective cell killing
Open Access
- 5 April 2012
- journal article
- research article
- Published by Springer Science and Business Media LLC in Cell Death & Disease
- Vol. 3 (4), e291
- https://doi.org/10.1038/cddis.2012.31
Abstract
Apoptin (apoptosis-inducing protein) harbors tumor-selective characteristics making it a potential safe and effective anticancer agent. Apoptin becomes phosphorylated and induces apoptosis in a large panel of human tumor but not normal cells. Here, we used an in vitro oncogenic transformation assay to explore minimal cellular factors required for the activation of apoptin. Flag-apoptin was introduced into normal fibroblasts together with the transforming SV40 large T antigen (SV40 LT) and SV40 small t antigen (SV40 ST) antigens. We found that nuclear expression of SV40 ST in normal cells was sufficient to induce phosphorylation of apoptin. Mutational analysis showed that mutations disrupting the binding of ST to protein phosphatase 2A (PP2A) counteracted this effect. Knockdown of the ST-interacting PP2A–B56γ subunit in normal fibroblasts mimicked the effect of nuclear ST expression, resulting in induction of apoptin phosphorylation. The same effect was observed upon downregulation of the PP2A–B56δ subunit, which is targeted by protein kinase A (PKA). Apoptin interacts with the PKA-associating protein BCA3/AKIP1, and inhibition of PKA in tumor cells by treatment with H89 increased the phosphorylation of apoptin, whereas the PKA activator cAMP partially reduced it. We infer that inactivation of PP2A, in particular, of the B56γ and B56δ subunits is a crucial step in triggering apoptin-induced tumor-selective cell death.Keywords
This publication has 42 references indexed in Scilit:
- DNA Damage Response Signaling Triggers Nuclear Localization of the Chicken Anemia Virus Protein ApoptinJournal of Virology, 2011
- Formation of stable attachments between kinetochores and microtubules depends on the B56-PP2A phosphataseNature, 2011
- Hallmarks of Cancer: The Next GenerationCell, 2011
- Identification of PP2A Complexes and Pathways Involved in Cell TransformationCancer Research, 2010
- From Promiscuity to Precision: Protein Phosphatases Get a MakeoverMolecular Cell, 2009
- Family at last: highlights of the first international meeting on proteins killing tumour cellsCell Death & Differentiation, 2008
- Adenovirus E4orf4 Protein Downregulates MYC Expression through Interaction with the PP2A-B55 SubunitJournal of Virology, 2008
- The Strep-tag system for one-step purification and high-affinity detection or capturing of proteinsNature Protocols, 2007
- Protein kinase A activates protein phosphatase 2A by phosphorylation of the B56δ subunitProceedings of the National Academy of Sciences of the United States of America, 2007
- A specific PP2A regulatory subunit, B56γ, mediates DNA damage-induced dephosphorylation of p53 at Thr55The EMBO Journal, 2007