Overexpression of beta-catenin induces apoptosis independent of its transactivation function with LEF-1 or the involvement of major G1 cell cycle regulators

• Published in: Molecular biology of the cell Vol. 11; no. 10; pp. 3509 - 3523
• Main Authors: Kim, K, Pang, K M, Evans, M, Hay, E D
• Format: Journal Article
• Language: English
• Published: United States The American Society for Cell Biology 01.10.2000
• Subjects: 3T3 Cells; Animals; Apoptosis; beta Catenin; Cadherins - genetics; Cadherins - physiology; Cell Cycle - physiology; Cell Nucleus - physiology; Cell Nucleus - ultrastructure; Cytoskeletal Proteins - deficiency; Cytoskeletal Proteins - genetics; Cytoskeletal Proteins - physiology; DNA-Binding Proteins - genetics; DNA-Binding Proteins - metabolism; G1 Phase; Genes, Retinoblastoma; HeLa Cells; Humans; Kinetics; Lymphoid Enhancer-Binding Factor 1; Mice; Mice, Knockout; Recombinant Proteins - metabolism; Retinoblastoma Protein - deficiency; Retinoblastoma Protein - genetics; Retinoblastoma Protein - metabolism; Reverse Transcriptase Polymerase Chain Reaction; Trans-Activators; Transcription Factors - genetics; Transcription Factors - metabolism; Transfection; Tumor Cells, Cultured
• ISSN: 1059-1524; 1939-4586
• DOI: 10.1091/mbc.11.10.3509

beta-Catenin promotes epithelial architecture by forming cell surface complexes with E-cadherin and also interacts with TCF/LEF-1 in the nucleus to control gene expression. By DNA transfection, we overexpressed beta-catenin and/or LEF-1 in NIH 3T3 fibroblasts, corneal fibroblasts, corneal epithelia, uveal melanoma cells, and several carcinoma cell lines. In all cases (with or without LEF-1), the abundant exogenous beta-catenin localizes to the nucleus and forms distinct nuclear aggregates that are not associated with DNA. Surprisingly, we found that with time (5-8 d after transfection) cells overexpressing beta-catenin all undergo apoptosis. LEF-1 does not need to be present. Moreover, LEF-1 overexpression in the absence of exogenous beta-catenin does not induce apoptosis, even though some endogenous beta-catenin moves with the exogenous LEF-1 into the nucleus. TOPFLASH/FOPFLASH reporter assays showed that full-length beta-catenin is able to induce LEF-1-dependent transactivation, whereas Arm beta-catenin totally abolishes the transactivating function. However, Arm beta-catenin, containing deletions of known LEF-1-transactivating domains, has the same apoptotic effects as full-length beta-catenin. Overexpressed beta-catenin also induces apoptosis in cells transfected with nuclear localization signal-deleted LEF-1 that localizes only in the cytoplasm. Thus, the apoptotic effects of overexpressed exogenous beta-catenin do not rely on its transactivating function with nuclear LEF-1. Overexpressed delta-catenin, containing 10 Arm repeats, induces only minor apoptosis, suggesting that the major apoptotic effect may be due to domains specific to beta-catenin as well as to Arm repeats. The absence of p53, Rb, cyclin D1, or E2F1 does not affect the apoptotic effect of overexpressed beta-catenin, but Bcl-x(L) reduces it. We hypothesize that in vivo apoptosis of cells overexpressing beta-catenin might be a physiological mechanism to eliminate them from the population.