The nuclear-receptor interacting protein (RIP) 140 binds to the human glucocorticoid receptor and modulates hormone-dependent transactivation

The glucocorticoid receptor (CR) regulates target gene expression in respon se to corticosteroid hormones. We have investigated the mechanism of transc riptional activation by the GR by studying the role of the receptor interac ting protein RIP140. Both in vivo and in vitro protein-protein interaction assays revealed a ligand-dependent interaction between the GR and RIP140. T he ligand binding domain of the GR was sufficient for this interaction, whi le both the N- and C-terminal regions of RIP140 bound to the receptor. In a yeast transactivation assay RIP140 and SRC-1, a member of the steroid rece ptor coactivator family of proteins, both enhanced the transactivation acti vity of a GR protein (GR Delta(tau 1)) in which the potent N-terminal tau(1 ) transactivation domain has been deleted. In contrast, in COS-7 cells incr easing amounts of RIP140 significantly inhibited GR Delta(tau 1) function. In cotransfection studies in COS-7 cells, RIP140 also inhibited receptor ac tivity in presence of both SRC-1 and the coactivator protein CBP together. Thus, in yeast cells a stimulation of receptor activity was observed, while in mammalian cells RIP140 repressed GR function. Taken together, these dat a suggest that, (1) RIP140 is a target protein for the CR and (2) RIP140 ca n modulate the transactivation activity of the receptor. (C) 2000 Elsevier Science Ltd. Ail rights reserved.