RB and c-Myc activate expression of the E-cadherin gene in epithelial cells through interaction with transcription factor AP-2.
E-cadherin plays a pivotal role in the biogenesis of the first epithelium during development, and its down-regulation is associated with metastasis of carcinomas. We recently reported that inactivation of RB family proteins by simian virus 40 large T antigen (LT) in MDCK epithelial cells results in a mesenchymal conversion associated with invasiveness and a down-regulation of c-Myc. Reexpression of RB or c-Myc in such cells allows the reexpression of epithelial markers including E-cadherin. Here we show that both RB and c-Myc specifically activate transcription of the E-cadherin promoter in epithelial cells but not in NIH 3T3 mesenchymal cells. This transcriptional activity is mediated in both cases by the transcription factor AP-2. In vitro AP-2 and RB interaction involves the N-terminal domain of AP-2 and the oncoprotein binding domain and C-terminal domain of RB. In vivo physical interaction between RB and AP-2 was demonstrated in MDCK and HaCat cells. In LT-transformed MDCK cells, LT, RB, and AP-2 were all coimmunoprecipitated by each of the corresponding antibodies, and a mutation of the RB binding domain of the oncoprotein inhibited its binding to both RB and AP-2. Taken together, our results suggest that there is a tripartite complex between LT, RB, and AP-2 and that the physical and functional interactions between LT and AP-2 are mediated by RB. Moreover, they define RB and c-Myc as coactivators of AP-2 in epithelial cells and shed new light on the significance of the LT-RB complex, linking it to the dedifferentiation processes occurring during tumor progression. These data confirm the important role for RB and c-Myc in the maintenance of the epithelial phenotype and reveal a novel mechanism of gene activation by c-Myc.
Batsché
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E
CJF INSERM 94-02, Université René Descartes, 75270 Paris cedex 06, France.
Muchardt
C
C
Behrens
J
J
Hurst
H C
HC
Crémisi
C
C
D016475:3T3 Cells; D000818:Animals; D000952:Antigens, Polyomavirus Transforming / Q000235:genetics; D015820:Cadherins / Q000235:genetics*; D002460:Cell Line; D002461:Cell Line, Transformed; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004285:Dogs; D004847:Epithelial Cells / Q000378:metabolism; D005786:Gene Expression Regulation; D016259:Genes, myc; D006801:Humans; D051379:Mice; D011401:Promoter Regions, Genetic; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D016160:Retinoblastoma Protein / Q000235:genetics* / Q000378:metabolism; D050656:Transcription Factor AP-2; D014157:Transcription Factors / Q000378:metabolism*; D015533:Transcriptional Activation; D014407:Tumor Cells, Cultured
D000952:Antigens, Polyomavirus Transforming; D015820:Cadherins; D004268:DNA-Binding Proteins; D011993:Recombinant Fusion Proteins; D016160:Retinoblastoma Protein; D050656:Transcription Factor AP-2; D014157:Transcription Factors