This Article Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via HighWire Google Scholar Articles by Li, S. Articles by Branton, P. E. PubMed PubMed Citation Articles by Li, S. Articles by Branton, P. E.

 Previous Article  |  Next Article 

Journal of Virology, September 2009, p. 8340-8352, Vol. 83, No. 17
0022-538X/09/$08.00+0     doi:10.1128/JVI.00711-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

The Adenovirus E4orf4 Protein Induces G₂/M Arrest and Cell Death by Blocking Protein Phosphatase 2A Activity Regulated by the B55 Subunit

Suiyang Li,¹ Claudine Brignole,¹ Richard Marcellus,^1,4 Sara Thirlwell,¹ Olivier Binda,¹ Monica J. McQuoid,⁵ Danita Ashby,⁵ Helen Chan,⁴ Zhiying Zhang,^4,6 Marie-Joëlle Miron,¹ David C. Pallas,⁵ and Philip E. Branton^1,2,3*

Departments of Biochemistry,¹ Oncology,² Goodman Cancer Centre, McGill University, McIntyre Medical Building, 3655 Promenade Sir William Osler, Montreal, Quebec, Canada H3G 1Y6,³ GeminX Biotechnologies, Inc., P.O. Box 477-Place du Parc, Montreal, Quebec, Canada H2X 4A5,⁴ Department of Biochemistry and Winship Cancer Institute, Emory University School of Medicine, 1510 Clifton Road, Atlanta, Georgia 30322,⁵ College of Animal Science and Technology, Northwest A&F University, 22 XiNong Road, YangLing, Shaan'xi, People's Republic of China 712100⁶

Received 6 April 2009/ Accepted 5 June 2009

Human adenovirus E4orf4 protein is toxic in human tumor cells. Its interaction with the B subunit of protein phosphatase 2A (PP2A) is critical for cell killing; however, the effect of E4orf4 binding is not known. B is one of several mammalian B-type regulatory subunits that form PP2A holoenzymes with A and C subunits. Here we show that E4orf4 protein interacts uniquely with B55 family subunits and that cell killing increases with the level of E4orf4 expression. Evidence suggesting that B-specific PP2A activity, measured in vitro against phosphoprotein substrates, is reduced by E4orf4 binding was obtained, and two potential B55-specific PP2A substrates, 4E-BP1 and p70^S6K, were seen to be hypophosphorylated in vivo following expression of E4orf4. Furthermore, treatment of cells with low levels of the phosphatase inhibitor okadaic acid or coexpression of the PP2A inhibitor I₁^PP2A enhanced E4orf4-induced cell killing and G₂/M arrest significantly. These results suggested that E4orf4 toxicity results from the inhibition of B55-specific PP2A holoenzymes, an idea that was strengthened by an observed growth arrest resulting from treatment of H1299 cells with B-specific RNA interference. We believe that E4orf4 induces growth arrest resulting in cell death by reducing the global level of B55-specific PP2A activity, thus preventing the dephosphorylation of B55-specific PP2A substrates, including those involved in cell cycle progression.

---

* Corresponding author. Mailing address: CIHR Institute of Cancer Research, McGill University, 3655 Promenade Sir William Osler, Montreal, Quebec, Canada H3G 1Y6. Phone: (514) 398-7268. Fax: (514) 398-8845. E-mail: philip.branton{at}mcgill.ca

Published ahead of print on 17 June 2009.

---

Journal of Virology, September 2009, p. 8340-8352, Vol. 83, No. 17
0022-538X/09/$08.00+0     doi:10.1128/JVI.00711-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

This article has been cited by other articles:

• Castilho, P. V., Williams, B. C., Mochida, S., Zhao, Y., Goldberg, M. L. (2009). The M Phase Kinase Greatwall (Gwl) Promotes Inactivation of PP2A/B55{delta}, a Phosphatase Directed Against CDK Phosphosites. Mol. Biol. Cell 20: 4777-4789 [Abstract] [Full Text]