and the ¶Department of Ophthalmology, Mackay Memorial Hospital, Taipei 104, Taiwan Transcriptional regulation by members of the nuclear hormone receptor superfamily is a modular process requiring the mediation of distinct subclasses of coregulators. In this study, we isolated a novel WD40 repeatcontaining gene, human nuclear receptor interaction protein (NRIP). We found NRIP interacts with either androgen or glucocorticoid receptors from in vitro and in vivo pulldown assays. Subsequently, transient transfection and luciferase activity assays suggested that NRIP was a ligand-dependent coactivator of steroid receptors (androgen and glucocorticoid) in distinct promoters. To further clarify the function of NRIP, we found an RNA interference-3-targeted NRIP gene sequence (5-GATGATACAGCACGAGAAC-3) that could efficiently and specifically knock down endogenous and exogenous NRIP gene expression and that significantly diminished cell proliferation in prostate (LNCaP) and cervical (C33A) cells. Therefore, NRIP may play a role in enhancing the transcriptional activity of nuclear receptors and may be a critical target for developing therapeutic agents against nuclear receptor-mediated progression of prostate and cervical cancers.Steroid hormone receptors, such as androgen receptor (AR), 1 estrogen receptor, progesterone receptor, and glucocorticoid receptor (GR) etc., are known as type I nuclear receptors (1). Nuclear receptor family members function as ligand-inducible transcription factors (2). The binding of growth hormone to nuclear receptor induces receptor dimerization, facilitating the ability of the nuclear receptor to bind to its cognate response element and recruit coregulators to promote the expression of target genes (3). In the past decade, several coactivators have been cloned and characterized that associate with steroid receptors and enhance their ability to transactivate target genes (4). Well studied coactivators include the p160 family proteins (SRC-1, TIF-2/GRIP-1, ACTR/-CIP) (5), the p300/cAMP response element-binding protein-binding protein family (6), Ubc9 (7), ARA70 (8), ARA55 (9), TIP60 (10), and protein arginine methyltransferases (11). Some cofactors act through functional modification of other activators or coactivators (12), resulting in efficient recruitment of coactivators by the nuclear receptor to the target gene and/or the stabilization of general initiation factors that form pre-initiation complexes on common core promoter elements (13). Some coactivators contain intrinsic histone acetyltransferase or methyltransferase activities, suggesting that they modify chromatin and integrating stimuli into an appropriate transcription response at a wide variety of promoters (14 -16). In addition, a class of coregulators serves as bridges mediating interactions between the coactivators and other general transcription factors at post-chromatin-remodeling steps (17).In this study, we isolated a novel gene named nuclear receptor interaction protein (NRIP) by using the yeast two-hybrid system. From am...

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