Transforming Growth Factor β-Induced Proliferative Arrest Mediated by TRIM26-Dependent TAF7 Degradation and Its Antagonism by MYC

Recognition of gene promoters by RNA polymerase II is mediated by general transcription factor IID (TFIID), which has been thought to be a static complex and to play a passive role in the regulation of gene expression under the instruction of gene-specific transcription factors. Here we show that transforming growth factor beta (TGF-beta) induced degradation of the TFIID subunit TAF7 in cultured mouse mammary epithelial cells and that this effect was required for proliferative arrest in response to TGF-beta stimulation. TGF-beta stimulated transcription of the gene for the ubiquitin ligase TRIM26, which was shown to ubiquitylate TAF7 and thereby to target it for proteasomal degradation. Sustained exposure of cells to TGF-beta resulted in recovery from proliferative arrest in association with amplification of the Myc proto-oncogene, with MYC inhibiting TRIM26 induction by TGF-beta. Our data thus show that TFIID is not simply a general mediator of transcription but contributes to the regulation of transcription in response to cell stimulation, playing a key role in the cytostatic function of TGF-beta.