1. ¹Laboratory of Cellular and Molecular Biology, National Institute on Aging, IRP/NIH/DHHS, 5600 Nathan Shock Drive, MSC-12, Baltimore, MD 21224, USA

Correspondence: RL Wange, E-mail: [email protected]

²Current address: 815 Abramson Research Center, Children's Hospital of Philadelphia, 34th Civic Center Blvd., Philadelphia, PA 19104, USA

Received 12 August 2004; Revised 28 December 2004; Accepted 28 December 2004; Published online 21 March 2005.

Abstract

The tumor suppressor PTEN is mutated in a high percentage of human cancers, and is implicated in pathways regulating cell growth, proliferation, survival, and migration. Despite significant advances, our understanding of its mechanisms of action remains incomplete. We have used a high-throughput proteomic immunoblotting approach to identify proteins whose expression levels are modulated by PTEN. Out of over 800 proteins screened, 22 proteins showed significant changes in expression. Five proteins that exhibited two-fold or greater changes in expression level were further characterized. AKAP121 and G3BP expression was reduced, while dihydrofolate reductase (DHFR), Rap1 and RCC1 expression was elevated in response to PTEN expression in a PTEN-null T-cell leukemia line. The phosphatase activity of PTEN was required for these effects. However, direct inhibition of PI-3 Kinase could mimic PTEN in modulating expression of DHFR, G3BP, Rap1 and RCC1, but not AKAP121. Real-time PCR showed that the effects of PTEN were primarily post-transcriptional, and would not have been revealed by mRNA-based screens. We conclude from these data that PTEN can modulate the expression level of a number of different proteins. The identified proteins have the potential to serve as previously unrecognized effectors of PTEN, and suggest the existence of additional complexity in the modes by which PTEN can regulate cellular biology.