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Insulin-like peptide 3 (INSL3) is a hormone produced by fetal and adult Leydig cells of the mammalian testis. During embryonic life INSL3 is required for testicular descent, whereas in adults it is involved in bone metabolism and male germ cell survival. Despite these important roles, the molecular mechanisms regulating INSL3 expression remain poorly understood. So far, two transcription factors have been implicated in INSL3 transcription: the nuclear receptors SF1 and NUR77. Circumstantial evidence also points to a role for androgens. Using transient transfections in MA-10 Leydig cells, we found that testosterone regulates in a time- and dose-dependent manner the human INSL3 promoter. The INSL3 promoter, however, does not contain a classical androgen-responsive element. Testosterone responsiveness was found to be mediated through an element located in the proximal INSL3 promoter, which also contains a NUR77-SF1-binding site. Furthermore, we found that posttranslational modifications, such as phosphorylation and acetylation, modulate transcription factor activity and therefore also contribute to INSL3 promoter activity in Leydig cells. All together, these data provide new insights into the molecular mechanisms regulating INSL3 expression in the mammalian testis. [ABSTRACT FROM AUTHOR]

Insulin-like 3 (INSL3) is a hormone produced by testicular Leydig cells throughout life. During embryonic life it regulates an essential step of testicular descent, whereas in adults it acts as a male germ cell survival factor. Despite the importance of INSL3 for male sex differentiation and function, very little is known regarding the molecular mechanisms that regulate its expression. So far, the nuclear receptor SF-1 is the only transcription factor known to regulate the mouse lnsl3 promoter in Leydig cells. In order to further our understanding of the transcriptional regulation of INSL3 expression, we have isolated the human INSL3 promoter and tested the effects of the nuclear receptors SF-1, LRH-1, and Nur77 on its activity in Leydig cells. In transfections assays, all three nuclear receptors activated the human INSL3 promoter but especially Nur77, which acted through a novel regulatory element. Thus, the human INSL3 promoter constitutes a novel target for the orphan nuclear receptor Nur77. [ABSTRACT FROM AUTHOR]