In the current study we test the hypothesis that liver receptor homologue-1 (LRH; designated NR5A2) is involved in the regulation of steroid hormone production. The potential role of LRH was assessed by first examining expression in human steroidogenic tissues and second by examining effects on transcription of genes encoding enzymes involved in steroidogenesis. LRH is closely related to steroidogenic factor 1 (SF1; designated NR5A1), which is expressed in most steroidogenic tissues and regulates expression of several steroid-metabolizing enzymes. LRH transcripts were expressed at high levels in the human ovary and testis. Adrenal and placenta expressed much lower levels of LRH than either ovary or liver. To examine the effects of LRH on steroidogenic capacity we used reporter constructs prepared with the 5 -flanking region of steroidogenic acute regulatory protein (StAR), cholesterol side-chain cleavage (CYP11A1), 3 hydroxysteroid dehydrogenase type II (HSD3B2), 17 hydroxylase, 17,20 lyase (CYP17), 11 hydroxylase (CYP11B1) and aldosterone synthase (CYP11B2). Co-transfection of these reporter constructs with LRH expression vector demonstrated that like SF1, LRH enhanced reporter activity driven by flanking DNA from StAR, CYP11A1, CYP17, HSD3B2, and CYP11B1. Reporter constructs driven by CYP11A1 and CYP17 were increased the most by co-transfection with LRH and SF1. Of the promoters examined only HSD3B2 was more sensitive to LRH than SF1. The high level of ovarian and testicular LRH expression make it likely that LRH plays an important role in the regulation of gonadal function.

Transcriptional induction by cAMP is mediated through the interaction of the cAMP response-element binding protein (CREB) with a cAMP response element (CRE) in the promoter of target genes. The steroidogenic acute regulatory (StAR) protein gene is regulated by cAMP-mediated signaling in steroidogenic cells even though its promoter lacks a consensus CRE. Previously, we have identified three highly conserved 5′-CRE half-sites within the -96/-67 bp region of the mouse StAR gene, and a member of the CREB family (CREB/CRE modulator (CREM)) was shown to be involved in its expression and regulation. Here we show that CREB and CREMτ (but not CREMα and CREMβ) have qualitatively similar effects on StAR promoter activity in response to (Bu) 2 cAMP. Studies on the effects of the functional integrity of the CRE half-sites on CREB-dependent (Bu) 2 cAMP-mediated StAR gene transcription demonstrated the greater importance of the CRE2 site in comparison with the CRE1 and CRE3 sites. The CRE2 sequence was also found to bind specifically to recombinant CREB protein and nuclear extract from MA-10 mouse Leydig tumor cells. The cAMP and CREB/CREM responsive region (-151/-1 bp) of the mouse StAR promoter also contains three recognition motifs for steroidogenic factor 1 (SF-1). Electrophoretic mobility shift assays and reporter gene analyses demonstrated the involvement of different SF-1 elements in StAR gene expression with the order of importance being SF-1/3>SF-1/1>SF-1/2. Specific mutations that eliminated the binding sites of CRE and SF-1 elements, either alone or in combination, resulted in an attenuation of StAR promoter activity, indicating that CREB and SF-1 can regulate StAR gene transcription in a cooperative fashion. In addition, mammalian two-hybrid assays revealed a high affinity protein-protein interaction between CREB/CREMτ and SF-1 which appeared to be dependent upon CREB protein phosphorylation. These findings further demonstrate CREB's role in StAR gene transcription and also provide evidence that the combined action of CREB/CREMτ and SF-1 results in enhanced activation of the StAR promoter.

Steroid hormones are synthesized in steroidogenic cells of the adrenal, ovary, testis, placenta and brain and are essential for normal reproductive function and bodily homeostasis. The rate-limiting and regulated step in steroid biosynthesis is the intramitochondrial transport of cholesterol, a process that is mediated by the steroidogenic acute regulatory (StAR) protein. The importance of StAR has been illustrated by analyses of patients with lipoid congenital adrenal hyperplasia (lipoid CAH), an autosomal recessive disorder that markedly disrupts the synthesis of all gonadal and adrenal steroids. Molecular and physio-pathological analyses have demonstrated that alterations in the StAR gene are the only known cause of lipoid CAH. Furthermore, StAR knockout mice have been generated and display a phenotype that is essentially identical to the human condition. Recent advances in tissue-specific and hormone-induced expression of the StAR protein provide insights into a number of human endocrinological health issues including developmental and reproductive abnormalities. Several factors and processes have been demonstrated to influence StAR expression in steroidogenic cells and there is increasing evidence that a transcription factor-binding site-rich region present in the proximal region of the StAR promoter is highly instrumental in StAR gene expression. In this review we focus on the significant findings that have been made with regards to the regulation of StAR expression and also on the clinical and endocrinological consequences of a non-functioning StAR gene.

The effects of pure FSH and/or LH preparations on the number of Leydig cells and their function in immature hypophysectomized rats have been investigated. As a result of hypophysectomy at the age of 17-18 days, the number of recognizable Leydig cells per testis decreased, as did the steroidogenic capacity in vivo and in vitro. Treatment with 64 micrograms FSH on both 22 and 23 days of age, did not affect the number of recognizable Leydig cells. In contrast, two injections of LH (10 micrograms) caused a sixfold increase in the number of Leydig cells, but had a negative effect on spermatogenesis. These stimulatory and inhibitory effects of LH diminished when FSH was added. Treatment with FSH for 7 days caused a twofold increase in the number of Leydig cells when compared with hypophysectomized controls. 3 beta-Hydroxysteroid dehydrogenase (3 beta-HSD) and esterase activity in Leydig cells also increased under the influence of FSH. The pregnenolone production per Leydig cell in the presence of 5-cholesten-3 beta,22(R)-diol (22R-hydroxycholesterol) as substrate showed a sevenfold increase. Plasma testosterone levels 2 h after injection of human chorionic gonadotrophin in intact rats and hypophysectomized FSH-treated rats were the same. Following LH treatment for 7 days, the number of Leydig cells proved to be 11 times higher, and 3 beta-HSD and esterase activity were not different from intact controls. The testicular pregnenolone production was four- to fivefold higher when compared with untreated hypophysectomized rats. However, pregnenolone production per Leydig cell in LH-treated rats was only slightly different from the hypophysectomized controls.(ABSTRACT TRUNCATED AT 250 WORDS)

In an experimental endotoxemia model utilizing mice, serum testosterone was found to be decreased 90% two h post ip injection of 200 micrograms of lipopolysaccharide (LPS). This decrease was sustained for 9 days. The early depression of serum testosterone was shown to be associated with a decrease in Steroidogenic Acute Regulatory (StAR) protein levels while the prolonged decrease corresponded to decreased protein and transcript levels of steroidogenic enzymes in Leydig cells. This acute and prolonged depression of testosterone production could lead to impaired spermatogenesis, accessory duct failure, and contribute to decreased male fertility following acute inflammation.