Effect of aspirin on the Wnt/beta-catenin pathway is mediated via protein phosphatase 2A.
Nonsteroidal anti-inflammatory drugs show chemopreventive efficacy in colon cancer, but the mechanism behind this remains unclear. Elucidating this mechanism is seen as vital to the development of new chemopreventive agents. We studied the effects of aspirin on the oncogenic Wnt/beta-catenin pathway activity in colorectal cancer cell lines and observed that aspirin dose-dependently decreased the activity of this pathway, as judged by TCF-driven luciferase activity, reduced Wnt target gene expression and increased phosphorylation of beta-catenin by immunoblotting. Furthermore, the ubiquitination and cytoplasmic levels of beta-catenin were assessed by immunoblotting, and also the localization of beta-catenin was shown by green fluorescent protein-tagged beta-catenin and time-lapse fluorescent imaging. Importantly, aspirin treatment caused increased phosphorylation of protein phosphatase 2A (PP2A), an event associated with inhibition of PP2A enzymatic activity, which was confirmed by a reduction in enzymatic PP2A activity. Moreover, this inhibition of PP2A enzymatic activity was essential for the effects of aspirin on the Wnt/beta-catenin pathway as shown by transient transfection with PP2A constructs. The findings in this article provide a molecular explanation for the efficacy of aspirin in chemoprevention of colorectal cancer and shows biochemical evidence that PP2A is an important regulator of Wnt/beta-catenin pathway activity in these cells.
Bos
C L
CL
Laboratory of Experimental Oncology and Radiobiology, University of Amsterdam, The Netherlands.
Kodach
L L
LL
van den Brink
G R
GR
Diks
S H
SH
van Santen
M M
MM
Richel
D J
DJ
Peppelenbosch
M P
MP
Hardwick
J C H
JC
D064173:Anaphase-Promoting Complex-Cyclosome; D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000494:pharmacology; D001241:Aspirin / Q000494:pharmacology*; D003593:Cytoplasm / Q000378:metabolism; D015536:Down-Regulation / Q000187:drug effects; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D017930:Genes, Reporter / Q000187:drug effects; D045325:HCT116 Cells; D006801:Humans; D010749:Phosphoprotein Phosphatases / Q000378:metabolism / Q000502:physiology*; D010766:Phosphorylation / Q000187:drug effects; D054648:Protein Phosphatase 2; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D015398:Signal Transduction / Q000187:drug effects*; D051820:TCF Transcription Factors / Q000378:metabolism; D014407:Tumor Cells, Cultured; D025801:Ubiquitin / Q000378:metabolism; D043743:Ubiquitin-Protein Ligase Complexes / Q000235:genetics; D051153:Wnt Proteins / Q000378:metabolism*; D051176:beta Catenin / Q000378:metabolism*
D000894:Anti-Inflammatory Agents, Non-Steroidal; D051820:TCF Transcription Factors; D025801:Ubiquitin; D051153:Wnt Proteins; D051176:beta Catenin; D043743:Ubiquitin-Protein Ligase Complexes; D064173:Anaphase-Promoting Complex-Cyclosome; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2; D001241:Aspirin