ABSTRACT
The tumor suppressor PTEN (phosphatase and tensin homologue) negatively regulates the PI3K pathway through its lipid phosphatase activity and is one of the most commonly lost tumor suppressors in human cancers. Though the tumor suppressive function involves the lipid phosphatase-dependent and -independent activities of PTEN, the mechanism leading to the phosphatase-independent function of PTEN is understood poorly. Some PTEN mutants have lipid phosphatase activity but fail to suppress cell growth. Here, we use a cancer-associated mutant, G20E, to gain insight into the phosphatase-independent function of PTEN by investigating protein-protein interactions using MS-based stable isotope labeling by amino acids in cell culture (SILAC). A strategy named parallel affinity purification (PAP) and SILAC has been developed to prioritize interactors and to compare the interactions between wild-type and G20E PTEN. Clustering of the prioritized interactors acquired by the PAP-SILAC approach shows three distinct clusters: 1) wild-type-specific interactors, 2) interactors unique to the G20E mutant, and 3) proteins common to wild-type and mutant. These interactors are involved mainly in cell migration and apoptosis pathways. We further demonstrate that the wild-type-specific interactor, NUDTL16L1, is required for the regulatory function of wild-type PTEN in cell migration. These findings contribute to a better understanding of the mechanisms of the phosphatase-dependent and -independent functions of PTEN.
Subject(s)
Mutation, Missense , Neoplasm Proteins/metabolism , Neoplasms/enzymology , PTEN Phosphohydrolase/metabolism , Amino Acids/pharmacology , Cell Line, Tumor , Humans , Isotope Labeling/methods , Neoplasm Proteins/genetics , Neoplasms/genetics , PTEN Phosphohydrolase/geneticsABSTRACT
Transforming growth factor-beta (TGF-beta) is implicated as a tumor suppressor because it eliminates cancer cells from normal tissues by inhibiting cell growth and inducing apoptosis. Although p53 tumor suppressor is required for TGF-beta-induced p21 WAF1 expression and cell growth inhibition, its role in TGF-beta-induced apoptosis remains unclear. Here, we report that TAp73alpha, which is a member of the p53 family, binds to p53-binding sites in the promoters of proapoptotic Bax and Puma to activate their transcription, and mediates TGF-beta-induced apoptosis in gastric cancer cells. Our findings reveal a novel role of TAp73alpha in the induction of apoptosis by TGF-beta in cancer cells.
