Testicular steroidogenesis is locally regulated by androgen via suppression of Nur77 Chin-Hee Song 1 , Eun-Yeung Gong 1 , Ji soo Park, Keesook Lee ⇑ Hormone Research Center, School of Biological Sciences and Technology, Chonnam National University, Gwangju 500-757, Republic of Korea article info Article history: Received 27 April 2012 Available online 7 May 2012 Keywords: Steroidogenesis Local regulation Androgen Nur77 AR Leydig cell abstract Steroidogenesis in the testis is regulated by a negative feedback mechanism through the hypothalamus– pituitary–testis axis. Recent studies suggest that besides this long-loop regulation, testicular steroidogen- esis is also locally regulated by androgen. However, the molecular mechanism behind this additional regulatory pathway has been poorly addressed. In the present study, we demonstrate that liganded androgen receptor (AR) suppresses the transcriptional activity of Nur77 on steroidogenic enzyme gene promoters, affecting testicular steroidogenesis. AR physically interacts and colocalizes with Nur77 in the nucleus in the presence of androgen. AR inhibits Nur77 transactivation by competing mainly with coactivators such as SRC-1 for Nur77 binding. These results suggest that androgen, through binding to AR, directly acts as a signal inhibiting the expression of steroidogenic enzyme genes in Leydig cells, even- tually resulting in decreased testicular steroidogenesis. These findings strongly support the hypothesis that androgen acts locally to regulate testicular steroidogenesis, and may provide its action mechanism. Ó 2012 Elsevier Inc. All rights reserved. 1. Introduction Androgens, which are mainly produced in testicular Leydig cells, are essential for male sexual differentiation, maintenance of spermatogenesis, and expression of male secondary sex character- istics. The biosynthesis of testosterone is dependent on both acute and chronic stimulation of Leydig cells by the pituitary luteinizing hormone (LH). Testosterone can regulate release of the hypotha- lamic gonadotropin-releasing hormone (GnRH), the signal that initially stimulates the pituitary to synthesize and release LH. This negative feedback loop is referred to as the hypothalamic–pitui- tary–gonadal (HPG) axis. Previous studies, however, have shown that testosterone represses the cAMP-induced de novo synthesis of P450c17 protein and accumulation of its mRNA in mouse Leydig cells, which occurs in an AR-dependent manner [1,2]. Steroidogenesis in Leydig cells is initiated with cholesterol transfer into the mitochondria, which is mediated by the steroido- genic acute regulatory (StAR) protein. In the mitochondria, choles- terol is converted to pregnenolone by the cholesterol side chain cleavage enzyme (P450scc). Pregnenolone is then transported to the endoplasmic reticulum and converted sequentially to proges- terone by 3b-hydroxysteroid dehydrogenase/D5ÀD4 isomerase (3b-HSD), to 17-hydoxyprogesterone, and then to androstenedione by 17a-hydroxylase/C 17–20 lyase (P450c17), and finally to testos- terone by 17-hydroxyateroid dehydrogenase. The steroidogenic-enzyme genes are generally regulated at the transcriptional level. The orphan nuclear receptor Nur77 and SF-1 are major transcription factors which are known to regulate steroi- dogenic-enzyme genes [3,4]. Nur77 family members regulate the expression of steroidogenic-enzyme genes such as steroid 21-hydroxylase, P450c17, and 20-hydroxysteroid dehydrogenase [5]. Nur77 binding regions within the gene promoter of rat P450c17 [6], Star [7], and human 3b-HSD2 have been defined [8]. In addition, LH treatment has been shown to trigger the expression of Nur77 in Leydig cells [9]. Nur77 is a member of the Nur77 gene family, which also con- tains the orphan nuclear transcription factors Nurr-1 and NOR-1. These factors have similar structural features of the conserved DNA binding domain (DBD) and ligand binding domain (LBD), but retain a variable sequence in the N-terminal AF-1 domain. Nur77 family members behave as endpoint effectors of the protein kinase A (PKA) signaling pathway acting through dimmers, and the AF-1 domain of Nur77 plays a major role in transcriptional activation, cofactor recruitment, and intra- and intermolecular interactions. Although Nur77 has been well characterized as an immediate early response gene and for its posttranslational modifications [10,11], coregulators involved in Nur77 transactiva- tion are not fully characterized. Some proteins including steroid receptor coactivator (SRC)-1, silencing mediator for retinoid and thyroid hormone receptors (SMRT) have been shown to regulate Nur77 transactivation through direct protein–protein interactions [12,13]. Androgen action is mediated by androgen receptor (AR), which is a ligand-inducible transcription factor [14]. AR consists of three 0006-291X/$ - see front matter Ó 2012 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.bbrc.2012.04.161 ⇑ Corresponding author. Fax: +82 62 530 0500. E-mail address: klee@chonnam.ac.kr (K. Lee). 1 These authors contributed equally to this work. Biochemical and Biophysical Research Communications 422 (2012) 327–332 Contents lists available at SciVerse ScienceDirect Biochemical and Biophysical Research Communications journal homepage: www.elsevier.com/locate/ybbrc