NUCLEAR FACTOR RIP140 MODULATES TRANSCRIPTIONAL ACTIVATION BY THE ESTROGEN-RECEPTOR

A conserved region in the hormone-dependent activation domain AF2 of n uclear receptors plays an important role in transcriptional activation . We have characterized a novel nuclear protein, RIP140, that specific ally interacts in vitro with this domain of the estrogen receptor. Thi s interaction was increased by estrogen, but not by anti-estrogens and the in vitro binding capacity of mutant receptors correlates with the ir ability to stimulate transcription. RIP140 also interacts with estr ogen receptor in intact cells and modulates its transcriptional activi ty in the presence of estrogen, but not the anti-estrogen 4-hydroxytam oxifen. In view of its widespread expression in mammalian cells, RIP14 0 may interact with other members of the superfamily of nuclear recept ors and thereby act as a potential co-activator of hormone-regulated g ene transcription.