S5A in the supplemental material), and Esrrb-ERRE2 and Esrrb-ERRE4 had enhanced reporter activities in A3-1 ES cells (see Fig. each complex. These data, together with previous findings, suggest that Dax1 functions as a negative regulator of Esrrb and Oct3/4, and these molecules form a regulatory loop for controlling the pluripotency and self-renewal capacity of ES cells. INTRODUCTION Pluripotency and self-renewal capacity are major characteristics of murine embryonic stem (ES) cells. Leukemia inhibitory factor (LIF) plays an important role for the self-renewal of ES cells, and depletion of LIF from ES cell culture medium prospects to spontaneous differentiation of cells and results in a failure of self-renewal (1, 2). A large number of transcription factors function downstream of signaling by LIF, and several transcription factors, including STAT3, Oct3/4, Sox2, and Nanog, play important tasks for pluripotency and self-renewal of Sera cells (3C5). Artificial activation of STAT3, which is definitely achieved by 4-hydroxytamoxifen A 438079 hydrochloride activation of nuclear localization of the STAT3-estrogen receptor fusion protein (STAT3ER), as well as forced manifestation of Nanog, accelerates the self-renewal inside a LIF-independent manner (6C8). gene differentiate into trophoblast cells (12). Actually, these transcription factors collaboratively regulate gene manifestation with additional factors and contribute to maintenance of pluripotency and self-renewal of Sera cells. For instance, Oct3/4 interacts with Sox2, and this complex enhances manifestation of Sera cell-specific genes, including Fgf4, Lefty1, Nanog, UTF1, and Sox2 (13). -Catenin is also a binding partner of Oct3/4, and the complex regulates manifestation of the gene (14). Nanog associates with NF-B family proteins, including RelA, RelB, and cRel. Of notice, the NF-B level raises during differentiation of Sera cells; in contrast, Nanog A 438079 hydrochloride inhibits NF-B activation and maintains pluripotency of Sera cells (15). Nanog also literally interacts with Smad1 and A 438079 hydrochloride represses the differentiation-inducing activity of Smad1 (16). Recently, high-throughput analyses exposed that a large number of proteins, including transcription factors, chromatin remodelers, epigenetic factors, rate of metabolism regulators, and cell cycle regulators, associate with Oct3/4 or Nanog, and these factors form protein interaction networks for controlling pluripotency and self-renewal of Sera cells (17C19). Previously, we recognized Dax1 (dosage-sensitive sex reversal, adrenal hypoplasia essential region, on chromosome X, gene 1; Nr0b1) as an Oct3/4-interacting protein (20). Dax1 belongs to a nuclear receptor superfamily. It consists of an N-terminal DNA-binding website (DBD) and C-terminal ligand-binding website (LBD). The DNA-binding website includes three LXXLL motifs, which perform an important part for protein-protein connection. The C-terminal ligand-binding website is similar to those of additional nuclear receptors; however, a specific ligand of Dax1 has not been identified, and thus Dax1 is definitely classified as an orphan nuclear receptor. Dax1 is specifically indicated in self-renewing Sera cells (21). Manifestation of Dax1 is definitely regulated by several transcription factors, including STAT3, Oct3/4, and A 438079 hydrochloride LRH-1, in Sera cells (21, 22). Dax1 associates with the POU-specific website of Oct3/4; as a result, transcriptional activity of Oct3/4 is definitely repressed by Dax1. Since A 438079 hydrochloride hyperactivation of Oct3/4 prospects to differentiation of Sera cells (10), Dax1 functions as a negative regulator of Oct3/4 to keep up self-renewal of Sera cells (20). To understand additional functions of Dax1 in Sera cells, we performed a candida two-hybrid screening and recognized an orphan nuclear hormone receptor, Esrrb (estrogen-related receptor beta), like a Dax1-interacting protein, and the finding is in agreement with earlier investigations (18, 23). Here, we discovered that Esrrb directly regulates the manifestation of Dax1, and Dax1 represses transcriptional activity of Esrrb. Moreover, Oct3/4, Dax1, and Esrrb have a competitive inhibition capacity for their interaction. The results of our current study, together with those WISP1 of earlier investigations, suggest that Oct3/4, Dax1, and Esrrb form a regulatory loop and cooperatively regulate the pluripotency and self-renewal capacity of Sera cells by modulating each activity. MATERIALS AND METHODS Candida two-hybrid screening. Plasmids of pGBKT7-Dax1-full length (amino acids 1 to 472), DNA-binding website (DBD; amino acids 1 to 255), ligand-binding website (LBD; amino acids 256 to 472), and Q23 region (amino acids 101 to 379) were constructed by inserting each cDNA into the pGBKT7 vector (Clontech, Mountain Look at, CA). Since full-length Dax1,.