INTERACTION OF PROTEINS WITH TRANSCRIPTIONALLY ACTIVE ESTROGEN-RECEPTORS

The ligand binding domain of the estrogen receptor contains a hormone- dependent transcriptional activation function. To investigate the mech anism by which it stimulates transcription, we have expressed fusion p roteins containing either the wild-type or a transcriptionally defecti ve form of this domain fused to glutathione-S-transferase and searched for proteins that specifically interact in vitro. By far-Western blot ting, three proteins of 160, 140, and 80 kDa expressed in different ma mmalian tells (HeLa, ZR75-1, and COS-1) were shown to associate direct ly with the wild-type receptor in the presence of estrogen. Two additi onal proteins appeared to interact indirectly with the hormone binding domain since they were detected only by a pull-down assay. All of the se interactions were abolished by antiestrogens, such as 4-hydroxytamo xifen, ICI 164384, or ICI 182780, which inhibit hormone-dependent tran scription. Moreover, they were not observed with the transcriptionally defective form of the receptor even in the presence of estrogen. Thus , since the ability of these proteins to interact with the hormone bin ding domain correlates with its transcriptional activity, one or more of them may contribute to hormone-dependent transcriptional activation by the estrogen receptor.