Abstract 3682: Phosphorylation mediated conformational changes defines nuclear role of phosphatase and tensin homology (PTEN) in tumor suppression

Loss of function of tumor suppressor PTEN (Phosphatase and tensin homolog) causes cancer in various tissues. PTEN C-terminal phosphorylation (pPTEN) inactivates PTEN, leading to multiple malignancies with increased severity. However, little is known about the molecular mechanisms underlying such inactivation. Therefore, the objective of our work is to ascertain the molecular mechanisms by which PTEN phosphorylation drives lung cancer. PTEN C-terminal phosphorylation at a serine-threonine cluster (Ser380, Thr382, Thr383 and Ser385) conformationally inactivates PTEN, abrogating its tumor suppressor function. Replacement of these serine/threonine residues with alanine generated an artificial phosphorylation-deficient mutant of PTEN (PTEN-4A), which is constitutively active. PTEN-4A suppressed cell proliferation and migration to a greater extent as compared to PTEN-WT. PTEN-4A preferentially localized to the nucleus and suppressed the E2F-mediated transcription of cell cycle genes. The nuclear localization sequence and phosphatase activity of PTEN-4A is critical for this transcriptional suppression. Immuno-precipitation assays show that PTEN physically associates with the transcription factor E2F1, a likely mechanism for its suppressive effect on E2F1 related genes. Further, deletion analysis of PTEN-4A protein revealed that the C2 domain is indispensable for suppression of E2F-related genes. Systematic transcriptional assays identify disease-associated C2 domain mutations that lose their ability to suppress E2F-mediated transcription, supporting the concept that these mutations are oncogenic in patients. Taken together, we reveal nuclear functions of PTEN-4A in tumor suppression that can be therapeutically leveraged for developing adjunctive cancer therapies. Small molecule inhibitors that hinder PTEN phosphorylation maybe utilized to activate PTEN nuclear function in tumors. Such adjunctive therapy has a high likelihood to reduce toxic doses of chemotherapeutic agents and targeted inhibitors, including kinase inhibitors that are being used in clinical settings. Citation Format: Prerna Malaney, Jonathan Semidey-Hurtado, Jamaal Hardee, Deepal Patel, Daniel Hennessey, Kate Stanford, Emily Palumbo, Zhi Tian, Diane Allen-Gipson, Vrushank Dave. Phosphorylation mediated conformational changes defines nuclear role of phosphatase and tensin homology (PTEN) in tumor suppression. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3682.