Steroidogenic factor-1 and human disease

While most studies initially considered the potential effects of loss of SF-1 function on human disease, several reports have now considered what role overexpression of NR5A1 or overactivity of SF-1 might have. Various clinical conditions have been hypothesized where SF-1 might have an effect. SF-1 overexpression increases proliferation and decreases apoptosis of human adrenocortical cells and induces adrenocortical tumors in transgenic mice, so a potential role for SF-1 in adrenal tumorigenesis has been considered. 44 Initial studies from Brazil have shown a high prevalence of SF-1 overexpression in childhood adrenocortical tumors. 45 , 46 These changes have arisen following somatic copy number changes of chromosome 9q33, which contains the NR5A1 locus, and have occurred on a background of loss of heterozygosity for the tumor suppressor gene p53 ( TP53 ). More recently, studies have investigated NR5A1 transcript levels in adult adrenocortical carcinoma and shown that increased transcript levels and SF-1 expression correlate with worse prognosis in this condition. 47 Some studies have shown that SF-1 is expressed in endometriotic cells, whereas it is not usually detected in normal endometrium. 48 , 49 This aberrant expression may reflect hypomethylation of the proximal promoter. Overactivity of SF-1 has also been considered a potential cause of polycystic ovary disease in a subset of cases. A heterozygous point mutation in SF-1 (p.R365P) was reported in a single case, but the functional or clinical significance of this observation is unclear. 50

The first attempts to study the potential role of SF-1 in humans focused on individuals with features that were predicted from the in vivo and in vitro studies of Sf-1 function described above: namely 46,XY patients with female genitalia, Müllerian structures (uterus and upper vagina), complete gonadal dysgenesis, and primary adrenal failure. This is a very rare phenotype in humans and represents marked disruption of adrenal and testicular development and function. Only two patients with these features have been reported in the literature to date. In both cases, disruption of key DNA-binding motifs of SF-1 seemed to have occurred. The first individual described with this phenotype was found to have a de novo heterozygous p.G35E change in SF-1 (► Fig. 1A ). 14 This child presented in early infancy with a severe salt-losing crisis and adrenal failure. Cortisol was detected but was inappropriately low given the child’s stressed state. The child’s karyotype was 46,XY and originally a high block in steroidogenesis affecting both adrenal and testicular function (for example, P450 side-chain cleavage (CYP11A1), steroidgenic acute regulatory protein (STAR)) was suspected. However, the presence of fibrotic testes and a uterus (Müllerian structures) was consistent with gonadal dysgenesis rather than a specific block in steroidogenesis, so disruption of a common developmental regulator such as SF-1 was then hypothesized. The p.G35E change found in this patient lies within the “P-box” motif of the DNA-binding domain (► Fig. 1B ). It had been known for some time that the P-box of nuclear receptors is important in facilitating DNA-binding specificity through interactions with the DNA response elements of target genes. 15 Unlike most nuclear receptors, SF-1 is thought to bind target gene response elements primarily as a monomer rather than as a homo- or heterodimer. The P-box region supports binding of SF-1 to the major groove of DNA. In vitro studies of the p.G35E mutant SF-1 compared with wild-type showed variable loss of transcriptional activation in a range of target promoters and impaired DNA response element binding. 16 No strong dominant negative effects were seen in most assay systems, although a mild competitive effect was seen when mutant SF-1 was cotransfected with wild-type SF-1, and in some cases a mild dominant negative effect was seen in studies where a partner protein was needed for transcriptional activation. 16 , 17 However, these are relatively artificial systems compared with the true in vivo effects where SF-1 likely affects multiple target gene response elements in many different genes and at different stages of development. It is also possible that altered allelic expression or even mosaicism could have played a role in this patient or that covert disruption of the nonaffected allele because of promoter dysregulation or a deep intronic change may have occurred. Nevertheless, this “P-box” mutation was certainly highly disruptive in many assay systems and was clearly an important event in causing the phenotype in this patient. After this initial report, the aim was to find children with a similar phenotype to see whether additional alterations in SF-1 ( NR5A1 ) could be found, which, in turn, might shed further light on the underlying mechanisms of SF-1 action. In 2002, a second report was published of a homozygous p.R92Q alteration in SF-1 in an infant with a similar phenotype (primary salt-losing adrenal failure, 46,XY DSD, Müllerian structures). 18 This mutation had been inherited in a recessive manner within a consanguineous pedigree. The codon 92 change lies within the “A-box” region of SF-1 (► Fig. 1A, B ). This motif is typical of the subfamily of nuclear receptors that bind to DNA as monomers and is believed to play a supportive role in stabilizing DNA binding, through an interaction between this region and the minor groove of DNA. Again, the effects of this SF-1 disruption are likely to be complex and variable but, in several different assay systems, the mean functional activity of the p.R92Q change was found to be ~30 to 40% of wild type. 16 , 18 , 19 The fact that the condition had been inherited in a recessive manner and that the mutation was present in a homozygous state in the affected child meant that other molecular mechanisms such as dominant negative effects, mosaicism, skewed allelic expression, or even a covert second mutation were not implicated. Therefore, this report provided convincing evidence for a functional gene dosage effect of SF-1 in influencing both adrenal and gonadal development and function. It is also worth noting that—to date—no complete loss of SF-1 function has been described in humans.

Having found alterations in SF-1 in patients with adrenal and gonadal (testicular) dysgenesis, the question arose whether alterations in SF-1 might in some other cases be associated with a predominant adrenal or reproductive phenotype. As SF-1 was not thought at the time to have such a marked effect on ovary development, it was hypothesized that SF-1 mutations could be found in girls or women with primary adrenal failure or adrenal hypoplasia of unknown etiology. In such situations, where the affected child or woman has a 46,XX karyotype, a typical female appearance and presence of a uterus would be expected, so salt-losing primary adrenal failure would be the presenting feature. Such a report was published in 2000 by Biason-Lauber and Schoenle, who described a de novo heterozygous SF-1 ( NR5A1) change in a girl who had presented at 14 months of age with primary adrenal insufficiency and seizures. 20 The nucleotide change found was predicted to result in a p. R255L mutation, which affects a codon in the proximal part of the ligand-binding domain of SF-1 (► Fig. 2 ). Functional studies in this report showed that the mutant SF-1 protein was transcriptionally inactive, but without a dominant negative effect. It is also noteworthy that the child’s ovaries were detected by MRI scan and inhibin A was low normal for age, suggesting at least that early indicators of ovarian integrity were intact. This report raised the question of whether additional SF-1 ( NR5A1 ) changes could be associated with primary adrenal failure in other (46,XX) women where the cause was not known. Although data remain limited at present, attempts to find SF-1 changes in girls with adrenal dysfunction or in adult women with primary adrenal failure of unknown etiology have been unsuccessful. 21 Furthermore, although mutations and deletions of the related nuclear receptor dosage-sensitive sex reversal, adrenal hypoplasia congenita critical region, on chromosome X, gene 1 (DAX-1) ( NR0B1 ) are found in a significant proportion of phenotypic males with primary adrenal hypoplasia, no descriptions of SF-1 changes associated with adrenal failure and a male phenotype have been published. 21 Taken together, these studies suggest that alterations in SF-1 are not a common cause of primary adrenal failure in humans and—in the two cases found in 46,XY individuals to date—have always been associated with gonadal (testicular) dysgenesis or marked underandrogenization.

SF-1 continues to emerge as an important regulator of adrenal and reproductive function in humans and variations in SF-1 and in SF-1 activity have now been described in several conditions. Underactivity of SF-1 is now reported in a wide range of reproductive conditions, ranging from severe forms of gonadal dysgenesis through to male factor infertility in males, as well as a various forms of ovarian dysfunction in females. Although the adrenal phenotypes seem to be less common in this cohort of patients, it is possible that impaired adrenal function may develop with time, so it will be important to define this group of individuals well and to counsel and monitor them appropriately. Furthermore, the variable inheritance of SF-1 changes, which can occur as sex-limited dominant, recessive, or sporadic events, means that detailed genetic analysis is important in defining the condition within families and for determining whether other family members should be screened. This might be particularly important for females who could be at risk of developing infertility or men with milder SF-1 changes who might be at risk of a progressive decline in fertility. However, considerably more data are needed to define the exact time course of these conditions and the prevalence of SF-1 changes in some of the more common phenotypes, such as infertility and POI. Finally, further studies of overexpression or activation of SF-1 in reproductive dysfunction are warranted, to add to the limited data for polycystic ovary syndrome and endometriosis. SF-1 is emerging as an important mediator of adrenal tumorigenesis and may be a target for pharmacomodulation in the future, although the systemic effects of modulating SF-1 actions are unclear. 51 Newer “-omics” approaches are being used to define novel SF-1 targets, such as mediators of angiogenesis or regulators of steroid metabolism. 52 , 53 Such approaches may help to define the complex networks involved in SF-1 action during development as well as into postnatal and adult life.