Steroidogenic factor 1 (SF-1), an orphan nuclear receptor, regulates the enzymes that produce sex steroids, and disruption of the Ftz-F1 gene encoding SF-1 precludes adrenal and gonadal development. We now study the role of SF-1 at other levels of the hypothalamic/pituitary/gonadal axis. In Ftz-Fl-disrupted mice, immunohistochemical analyses with antibodies against pituitary trophic hormones showed a selective loss of gonadotrope-specific markers, supporting the role of SF-1 in gonadotrope function. In situ hybridization analyses confirmed these results; pituitaries from Ftz-Fl-disrupted mice lacked transcripts for three gonadotrope-specific markers (LH~, FSH~, and the receptor for gonadotropin-releasing hormone), whereas they exhibited decreased but detectable expression of the ~-subunit of glycoprotein hormones. SF-1 transcripts in the developing mouse pituitary, which first became detectable at embryonic day 13.5-14.5, preceded the appearance of FSH~ and LH~ transcripts. In adult rat pituitary cells, SF-1 transcripts colocalized with immunoreactivity for the gonadotrope-specific LH. Finally, SF-1 interacted with a previously defined promoter element in the glycoprotein hormone ~-subunit gene, providing a possible mechanism for the impaired gonadotropin expression in Ftz-Fl-disrupted mice. These studies establish novel roles of this orphan nuclear receptor in reproductive function.

We proposed that a cell-selective regulatory protein coordinately regulates the expression of three enzymes that are required for the biosynthesis of corticosteroids: cholesterol side chain cleavage enzyme, steroid 21-hydroxylase, and the aldosterone synthase isozyme of steroid 11 beta-hydroxylase. In this report, we identify a 53-kilodalton protein, termed steroidogenic factor 1 (SF-1), that interacts with the related promoter elements from these steroidogenic enzymes, and we isolate and characterize a cDNA that very likely encodes this protein. We first showed that nuclear extracts from bovine adrenal glands interact with the mouse steroidogenic regulatory elements, forming complexes indistinguishable from those produced by nuclear extracts from mouse Y1 adrenocortical cells. These bovine adrenal extracts were subjected to sequential ion exchange and affinity chromatography to yield a highly enriched preparation of SF-1. The predominant protein in the affinity-purified preparation comigrated with shift activity and had a mol wt of 53,000; UV cross-linking experiments demonstrated directly that this 53-kilodalton protein interacted with the steroidogenic regulatory element. Even with this marked enrichment, affinity-purified SF-1 bound six steroidogenic regulatory elements. These results support strongly the model that a steroidogenic cell-selective protein interacts with related promoter elements from three steroidogenic enzymes to regulate their coordinate expression. The recognition sequence of SF-1 closely resembles those of nuclear hormone receptor family members, suggesting that SF-1 may belong to this supergene family. By screening a Y1 cell cDNA library with the DNA-binding region of the H-2RIIBP nuclear hormone receptor cDNA, we isolated a cDNA that is selectively expressed in steroidogenic cells. When expressed as a glutathione S-transferase fusion protein in Escherichia. coli, the protein encoded by this cDNA interacts with all six related steroidogenic regulatory elements with a binding specificity indistinguishable from that of SF-1. Surprisingly, the sequence of the putative DNA-binding domain of this cDNA matches exactly the corresponding sequence of the mouse homolog of the Drosophila transcription factor fushi tarazu-factor I. The demonstration that a member of the nuclear hormone receptor family interacts with the steroidogenic regulatory elements provides intriguing insights into possible mechanisms by which these essential genes are regulated.

The orphan nuclear receptor steroidogenic factor 1 (SF-1, also called Ad4BP and officially designated NR5A1) has emerged as an essential regulator of endocrine development and function. Initially identified as a tissue-specific transcriptional regulator of the cytochrome P450 steroid hydroxylases, SF-1 has considerably broader roles, as evidenced from studies in knockout mice lacking SF-1. The SF-1-knockout mice lacked adrenal glands and gonads and therefore died from adrenal insufficiency within the first week after birth. In addition, SF-1 knockout mice exhibited male-to-female sex reversal of their internal and external genitalia, impaired expression of multiple markers of pituitary gonadotropes, and agenesis of the ventromedial hypothalamic nucleus (VMH). These studies delineated essential roles of SF-1 in regulating endocrine differentiation and function at multiple levels, particularly with respect to reproduction. This chapter will review the experiments that established SF-1 as a pivotal, global determinant of endocrine differentiation and function. We next discuss recent insights into the mechanisms controlling the expression and function of SF-1 as well as the current status of research aimed at delineating its roles in specific tissues. Finally, we highlight areas where additional studies are needed to expand our understanding of SF-1 action. I. Initial Isolation of Steroidogenic Factor 1Steroid hormones are essential for fluid and electrolyte balance, intermediary metabolism, sexual differentiation, and reproductive function. Once the pathways of steroid hormone biosynthesis were defined and shown to involve the concerted actions of several cytochrome P450 mixed-function oxidases, attention turned to elucidating the mechanisms that regulate the expression of these enzymes. With the isolation of the bovine 21-hydroxylase cDNA (White et al., 1984b), followed shortly thereafter by the cloning of cDNAs encoding the side-chain cleavage enzyme (Matteson et al., 1984;Morohashi et al., 1984) and 11␤-hydroxylase (John et al., 1984), these questions could be addressed at a molecular level.