Reduction of beta-catenin/T-cell transcription factor signaling by aspirin and indomethacin is caused by an increased stabilization of phosphorylated beta-catenin.
Constitutive activation of the Wnt/beta-catenin pathway is thought to play a central role in colorectal carcinogenesis. A key output in this pathway is the nuclear level of beta-catenin, which determines the transcription of T-cell transcription factor (TCF)/lymphoid enhancer-binding factor-responsive target genes. In unstimulated cells, beta-catenin is continuously targeted for ubiquitin-dependent degradation, which depends on its NH(2)-terminal phosphorylation by glycogen synthase kinase-3beta (GSK-3beta) in association with a multiprotein complex. Previously, we have shown that the nonsteroidal anti-inflammatory drugs (NSAIDs) aspirin and indomethacin down-regulate beta-catenin/TCF signaling in colorectal cancer cells. Here, we demonstrate that the reduced signaling activity of beta-catenin in response to NSAIDs is a result of its enhanced phosphorylation. In SW948 and SW480 colorectal cancer cells, phosphorylation of NH(2)-terminal S/T residues time dependently increased in response to aspirin and indomethacin. In contrast, in 293 cells, NSAID treatment failed to induce detectable levels of beta-catenin phosphorylation but resulted in degradation of beta-catenin within 24 h in serum-deprived cells. The aspirin-induced beta-catenin phosphorylation in colon cancer cells preceded down-regulation of beta-catenin/TCF signaling, suggesting a causal relationship. Inhibition of this process by LiCl pointed to participation of GSK-3beta. Unexpectedly, GSK-3beta was also phosphorylated upon aspirin treatment in six colorectal cancer cell lines. We present evidence that inactivation of a phosphatase rather than stimulation of a kinase or interference with the ubiquitination machinery may be the cause of the stabilized phosphorylation. The data emphasize the importance of beta-catenin in the pathogenesis of colorectal cancer and define it as a key target for anticancer therapeutics.
Dihlmann
Susanne
S
Department of Molecular Pathology, Institute of Pathology, University of Heidelberg, D-69120 Heidelberg, Germany. susanne_dihlmann@med.uni-heidelberg.de
Klein
Simone
S
Doeberitz Mv
Magnus von Knebel
Mv
D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000494:pharmacology; D001241:Aspirin / Q000494:pharmacology*; D001665:Binding Sites; D002460:Cell Line; D045744:Cell Line, Tumor; D003598:Cytoskeletal Proteins / Q000378:metabolism*; D015536:Down-Regulation; D017930:Genes, Reporter; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism; D000071679:Glycogen Synthase Kinase 3 beta; D006801:Humans; D015151:Immunoblotting; D007213:Indomethacin / Q000494:pharmacology*; D008156:Luciferases / Q000378:metabolism; D010766:Phosphorylation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D015398:Signal Transduction / Q000187:drug effects*; D013997:Time Factors; D015534:Trans-Activators / Q000378:metabolism*; D014158:Transcription, Genetic; D014162:Transfection; D051176:beta Catenin
D000894:Anti-Inflammatory Agents, Non-Steroidal; C495270:CTNNB1 protein, human; D003598:Cytoskeletal Proteins; D015534:Trans-Activators; D051176:beta Catenin; D008156:Luciferases; C000605506:GSK3B protein, human; D000071679:Glycogen Synthase Kinase 3 beta; D038362:Glycogen Synthase Kinase 3; D001241:Aspirin; D007213:Indomethacin