A PROLINE-RICH TGF-BETA-RESPONSIVE TRANSCRIPTIONAL ACTIVATOR INTERACTS WITH HISTONE H3

The molecular mechanisms involved in the regulation of gene expression by transforming growth factor-beta (TGF-beta) have been analyzed. We show that TGF-beta specifically induces the activity of the proline-ri ch trans-activation domain of CTF-1, a member of the CTF/NP-I family o f transcription factors. A TGF-beta-responsive domain (TRD) in the pro line-rich transcriptional activation sequence of CTF-1 was shown to me diate TGF-beta induction in NIH-3T3 cells. Mutagenesis studies indicat ed that this domain is not the primary target of regulatory phosphoryl ations, suggesting that the growth factor may regulate a CTF-1-interac ting protein. A two-hybrid screening assay identified a nucleosome com ponent, histone H3, as a specific CTP-1-interacting protein in yeast. furthermore, the CTF-1 trans-activation domain was shown to interact w ith histone H3 in both transiently and stably transfected mammalian ce lls. This interaction requires the TRD, and it appears to be upregulat ed by TGF-beta in vivo. Moreover, point mutations in the TRD that inhi bit TGF-beta induction also reduce interaction with histone H3. In vit ro, the trans-activation domain of CTF-1 specifically contacts histone H3 and oligomers of histones H3 and H4, and full-length CTF-1 was sho wn to alter the interaction of reconstituted nucleosomal cores with DN A. Thus, the growth factor-regulated trans-activation domain of CTF-1 can interact with chromatin components through histone H3, These findi ngs suggest that such interactions may regulate chromatin dynamics in response to growth factor signaling.