Accumulation of Fra-1 in ras-transformed cells depends on both transcriptional autoregulation and MEK-dependent posttranslational stabilization.
The AP-1 transcription factor plays an essential role in cell proliferation and tumorigenesis. It was previously shown that the fra-1 gene product is upregulated by various oncogenes and is involved in the in vitro and in vivo transformation of thyroid cells. Here we show that the ras oncogene-dependent accumulation of Fra-1 is mediated by a positive feedback mechanism which requires both transcriptional autoregulation and posttranslational stabilization of the protein. The oncogene-dependent transcriptional activation involves the cooperation between both Raf-dependent and Raf-independent pathways and is mediated by an AP-1 site within the fra-1 first intron, which becomes stably occupied by a transcriptionally active Fra-1-containing complex in ras-transformed cells. The posttranslational stabilization results in a drastic increase in the Fra-1 half-life in ras-transformed cells and is totally dependent on the activity of the MEK/ERK phosphorylation pathway. The analysis of the Fra-1 transactivation potential shows that the protein is able to stimulate a heterologous promoter in a ras-dependent manner, but the transactivating activity requires the recruitment of a heterodimeric partner. These data show that the alteration of multiple regulatory mechanisms is required for the constitutive activation of Fra-1 as a nuclear target of ras transformation.
Casalino
Laura
L
Institute of Genetics and Biophysics "A Buzzati-Traverso," Consiglio Nazionale delle Ricerche, 80125 Naples, Italy.
De Cesare
Dario
D
Verde
Pasquale
P
D000818:Animals; D015152:Blotting, Northern; D002460:Cell Line; D002461:Cell Line, Transformed; D002467:Cell Nucleus / Q000378:metabolism; D002843:Chromatin / Q000378:metabolism; D002845:Chromatography; D004247:DNA / Q000378:metabolism; D019281:Dimerization; D005786:Gene Expression Regulation; D015151:Immunoblotting; D007438:Introns; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D008954:Models, Biological; D008957:Models, Genetic; D009154:Mutation; D016133:Polymerase Chain Reaction; D011233:Precipitin Tests; D011485:Protein Binding; D011499:Protein Processing, Post-Translational; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D016760:Proto-Oncogene Proteins c-fos / Q000096:biosynthesis*; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013997:Time Factors; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D015854:Up-Regulation; D018631:ras Proteins / Q000378:metabolism*; D000099169:Fos-Related Antigen 1
D002843:Chromatin; D004247:DNA; D020928:Mitogen-Activated Protein Kinases; D017346:Protein Serine-Threonine Kinases; D016760:Proto-Oncogene Proteins c-fos; D018631:ras Proteins; D000099169:Fos-Related Antigen 1