Steroid receptor coactivator-1 interacts with serum response factor and coactivates serum response element-mediated transactivations

Steroid receptor coactivator-l (SRC-1) specifically bound to serum response factor (SRF), as demonstrated by glutathione S-transferase pull down assays, and the yeast and mammalian two hybrid tests. In mammalian cells, SRC-1 potentiated serum response element (SRE)-mediated transactivations in a dose-dependent manner. Coexpression of p300 synergistically enhanced this SRC-1-potentiated level of transactivations, consistent with the recent finding (Ramirez, S., All, S. A. S., Robin, P., Trouche, D., and Harel-Bellan, A. (1997) J. Biol. Chem. 272, 31016-31021) in which the p300 homologue CREB-binding protein was shown to be a transcription coactivator of SRF. Thus, we concluded that at least two distinct classes of coactivator molecules may cooperate to regulate SRF-dependent transactivations in vivo.