Downregulation of E-cadherin is an essential event in activating beta-catenin/Tcf-dependent transcription and expression of its target genes in Pdcd4 knockdown cells.
We reported earlier that knockdown of tumor suppressor Pdcd4 (programed cell death 4) downregulates E-cadherin expression and activates beta-catenin/Tcf (T-cell factor)-dependent transcription in colon tumor cells. However, the underlying mechanism of these observations remains unknown. In this study, we showed that knockdown of Pdcd4 downregulates E-cadherin expression through elevated protein level of Snail. Over-expression of Pdcd4 upregulates E-cadherin expression and inhibits beta-catenin/Tcf-dependent transcription. We then showed that knockdown of E-cadherin activates beta-catenin/Tcf-dependent transcription. Conversely, over-expression of E-cadherin in Pdcd4 knockdown cells inhibits beta-catenin/Tcf-dependent transcription. In addition, Pdcd4 knockdown stimulates urokinase-type plasminogen activator receptor (u-PAR) and c-Myc expression, whereas u-PAR and c-Myc expression can be reversed by over-expressing E-cadherin in Pdcd4 knockdown cells. Using chromatin immunoprecipitation, we showed that beta-catenin/Tcf4 directly binds to the promoters of u-PAR and c-myc in Pdcd4 knockdown cells. Futhermore, knockdown of u-PAR or c-Myc inhibits invasion in Pdcd4 knockdown cells, suggesting that both u-PAR and c-Myc contribute to invasion induced by Pdcd4 knockdown. Taken together, our data showed that elevated Snail expression by Pdcd4 knockdown leads to downregulation of E-cadherin resulting in activating beta-catenin/Tcf-dependent transcription and stimulating the expression of c-Myc and u-PAR, thus providing molecular explanation of how Pdcd4 suppresses tumor invasion.
Graduate Center for Toxicology, College of Medicine, University of Kentucky, Lexington, KY 40536, USA.
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D051017:Apoptosis Regulatory Proteins / Q000235:genetics / Q000378:metabolism*; D015153:Blotting, Western; D015820:Cadherins / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D047369:Chromatin Immunoprecipitation; D015536:Down-Regulation; D015972:Gene Expression Regulation, Neoplastic; D055785:Gene Knockdown Techniques; D019073:HT29 Cells; D006801:Humans; D009154:Mutation; D011485:Protein Binding; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics / Q000378:metabolism; D034622:RNA Interference; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D055293:Receptors, Urokinase Plasminogen Activator / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D000071250:Snail Family Transcription Factors; D051820:TCF Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic; D014162:Transfection; D051176:beta Catenin / Q000235:genetics / Q000378:metabolism*
D051017:Apoptosis Regulatory Proteins; D015820:Cadherins; C489427:MYC protein, human; C114487:PDCD4 protein, human; D016271:Proto-Oncogene Proteins c-myc; D016601:RNA-Binding Proteins; D055293:Receptors, Urokinase Plasminogen Activator; D000071250:Snail Family Transcription Factors; D051820:TCF Transcription Factors; D014157:Transcription Factors; D051176:beta Catenin