| PTEN (phosphatase and tensin homologue deleted on chromosome 10) tumor suppressor gene was the first phosphatase identified to be frequently mutated somatically in human cancers, including glioblastomas, endometrial carcinomas, mammary carcinomas, and prostate cancers. With regards to its domain organization, PTEN contains an N-terminal phosphatase domain and in vitro studies suggest that PTEN has the ability to dephosphorylate both lipid and protein substrates. PTEN's lipid substrate has been identified as phosphatidylinositol-3,4,5-trisphosphate (PtdIns(3,4,5)P3), and by this mechanism PTEN antagonizes the effects of phosphatidylinositol 3-kinase (PI3-kinase). Although the function of PTEN as a lipid phosphatase in opposing the PI3-kinase pathway has been well characterized, experimental evidence also suggests that certain biological functions of PTEN are independent of its lipid phosphatase activity, either through its protein phosphatase activities or via its interacting proteins. In order to identify novel PTEN signaling pathways we have taken two independent approaches. In the first approach, we have performed a biochemical analysis on the PTEN-associated complex. The results demonstrate that, as shown previously, PTEN is recruited to a high molecular weight complex of>650KDa and that PTEN phosphorylation status has a significant impact on complex assembly. Moreover, through 2D-DIGE followed by mass spectrometry analysis, hnRNP C was identified as a component of this complex and showed an interaction with PTEN in the nucleus, suggesting a potential role for this interaction in RNA regulation. In the second approach, using a high-throughput luciferase based protein-protein interaction screen called LUMIER we have identified 52 novel PTEN binding proteins. The interaction between PTEN and one of the hits, Dishevelled 3 (DVL3), was characterized further, and the results demonstrated that the interaction between these two proteins is mediated by the C-terminus of PTEN and the DEP domain of DVL3. In addition, through this interaction, PTEN positively regulates DVL3 activity, therefore positively regulating the Wnt/beta-Catenin signaling pathway. Overall, the work here identifies two novel PTEN signaling effects: one through hnRNP C, potentially in RNA regulation, and the second through DVL3 interaction, in positively regulating the Wnt/beta-Catenin pathway. |
