The orphan nuclear receptor DAX-1 acts as a novel transcriptional corepressor of PPARc Gwang Sik Kim a,1 , Gha Young Lee c,1 , Balachandar Nedumaran a , Yun-Yong Park a , Kyung Tae Kim b , Sang Chul Park b , Young Chul Lee a , Jae Bum Kim c, * , Hueng-Sik Choi a, * a Hormone Research Center, School of Biological Science and Technology, Chonnam National University, Gwangju 500-757, Republic of Korea b Aging and Apoptosis Research Center, Seoul National University College of Medicine, Seoul 110-799, Republic of Korea c Department of Biological Sciences, Research Center for Functional Cellulomics, Seoul National University, Seoul 151-742, Republic of Korea article info Article history: Received 5 March 2008 Available online 31 March 2008 Keywords: Orphan nuclear receptor DAX-1 PPARc Corepressor PGC-1a Adipogenesis abstract DAX-1 is an atypical nuclear receptor (NR) which functions primarily as a transcriptional corepressor of other NRs via heterodimerization. Peroxisome proliferator-activated receptor (PPAR) c is a ligand-depen- dent NR which performs a key function in adipogenesis. In this study, we evaluated a novel cross-talk mechanism between DAX-1 and PPARc. Transient transfection assays demonstrated that DAX-1 inhibits the transactivity of PPARc in a dose-dependent manner. DAX-1 directly competed with the PPARc coac- tivator (PGC)-1a for binding to PPARc. Endogenous levels of DAX-1 were significantly lower in differen- tiated 3T3-L1 adipocytes as compared to preadipocytes. Using a retroviral expression system, we demonstrated that DAX-1 overexpression downregulates the expression of PPARc target genes, resulting in an attenuation of adipogenesis in 3T3-L1 cells. Our results suggest that DAX-1 acts as a corepressor of PPARc and performs a potential function in the regulation of PPARc-mediated cellular differentiation. Ó 2008 Elsevier Inc. All rights reserved. The NRs are the largest family of transcription factors, and are known to modulate gene expression in response to a variety of physiological signals, and have been determined to play pivotal roles in cellular homeostasis and development [1]. The orphan NR DAX-1 is a member of the atypical NR superfamily, and its over- all structure is quite similar to that of Small Heterodimer Partner (SHP). The ligands for DAX-1 and SHP have not been identified yet [2,3]. Mutations in the DAX-1 gene result in disorders including X-linked AHC and hypogonadotropic hypogonadism (HHG) [4]. DAX-1 has also been determined to be involved in sex determina- tion and gonadal development [5]. Previous studies have estab- lished that DAX-1 functions as a transcriptional corepressor via heterodimeric interactions with other NRs, including the androgen (AR), estrogen (ER), and progesterone receptor (PR), in addition to steroidogenic factor-1 (SF-1), liver receptor homologue-1 (LRH1), nerve growth factor-inducible gene B (NUR77), and estrogen receptor-related receptor c (ERRc) [6–12]. PPARc belongs to the type II NR superfamily, and forms hetero- dimers with retinoid X receptor (RXR) which bind to PPARc response elements (PPRE). Although RXR performs important func- tions in the functional regulation of PPARc, DAX-1 does not interact with RXRa [6]. PPARc plays a pivotal role in a host of different physiological processes, including lipid metabolism, insulin sensi- tization, inflammation, tumor susceptibility, glucose homeostasis, atherogenesis, and adipogenesis [13]. PPARc is activated by endog- enous arachidonic acid metabolites, including 15-deoxy-delta 12, 14 prostaglandin J2, and antidiabetic thiazolidinediones (TZDs), which function as insulin sensitizers and are used in the treatment of type II diabetes [14]. Adipocytes perform a critical function in energy balance. Adipo- cyte differentiation, which is also referred to as adipogenesis, is the process by which preadipocytes are converted into mature adipo- cytes. While previous studies have demonstrated the role of cofac- tors in the transcriptional regulation of PPARc [15], and a great deal is currently known regarding the coactivators of PPARc, very few corepressors have been thus far identified which repress the tran- scription activity of PPARc. Kruppel-Like Factor 2 (KLF2) harbors multiple zinc finger motifs, and is abundantly expressed in preadi- pocytes, but not in adipocytes. KLF2 overexpression in 3T3-L1 cells has been shown to inhibit adipocyte differentiation via the repres- sion of PPARc [16]. In this study, we have demonstrated that DAX-1 physically interacts with PPARc in a ligand-independent manner. We also showed that DAX-1 represses the transcriptional activity of PPARc via direct binding to the DBD/hinge region of PPARc, and competes with the PPARc coactivator, PGC-1a, for binding to PPARc. We dem- 0006-291X/$ - see front matter Ó 2008 Elsevier Inc. All rights reserved. doi:10.1016/j.bbrc.2008.03.098 * Corresponding authors. Fax: +82 62 530 0506. E-mail addresses: jaebkim@snu.ac.kr (J.B. Kim), hsc@chonnam.ac.kr (H.-S. Choi). 1 These authors contributed equally to this work. Biochemical and Biophysical Research Communications 370 (2008) 264–268 Contents lists available at ScienceDirect Biochemical and Biophysical Research Communications journal homepage: www.elsevier.com/locate/ybbrc