Ken-ichirou Morohashi

Identical origin of adrenal cortex and gonad revealed by expression profiles of Ad4BP/SF-1.

Background: Ad4BP/SF‐1 was originally identified as a steroidogenic tissue‐specific transcription factor. Recent gene disruption studies with the mammalian Ftz‐F1 gene encoding Ad4BP/SF‐1 clearly revealed the essential function of the factor for adrenal and gonadal differentiation.

Ad4BP/SF-1, a transcription factor essential for the transcription of steroidogenic cytochrome P450 genes and for the establishment of the reproductive function.

Ad4BP/SF‐l was identified as the steroidogenic tissue‐specific transcription factor regulating the expression of the steroidogenic cytochrome P450 genes. In addition to the steroidogenic endocrine tissues such as adrenal cortex, testis, and ovary, the factor was found to be expressed in the pituitary gonadotroph and the ventromedial hypothalamic nucleus. Considering the roles of the hypothalamus‐pituitary‐gonadal axis, it is reasonable to assume that Ad4BP/SF‐l is closely associated with the reproductive function of adult animals. Another fundamental role of Ad4BP/SF‐l in the fetal development was discovered by gene disruption studies. Serious structural and functional defects were observed in the Ad4BP/SF‐l‐positive tissues of the gene‐disrupted mice. Based on the sexually dimorphic expression of Ad4BP/SF‐l in the fetal gonads, the factor is also likely to be involved in the gonadal sex differentiation. Because of this functional significance during the tissue differentiation, the regulatory mechanism of the Ad4BP/SF‐ 1 gene, the mammalian Ftz‐F1 gene, has been investigated. The gene is controlled by an autore‐ gulatory mechanism in which Ad4BP/SF‐l functions as the dominant transcription factor.—Morohashi, K.‐L, and Omura, T. Ad4BP/SF‐l, a transcription factor essential for the transcription of steroidogenic cytochrome P450 genes and for the establishment of the reproductive function. FASEB J. 10, 1569‐1577 (1996)

The ontogenesis of the steroidogenic tissues

Based on the common function of steroid hormone‐producing tissues and homologous regulation by the hypothalamo‐pituitary axis, the adrenal cortex and the gonads have been suggested to have an intimate ontogenic relationship. This assumption is also supported by the findings of common transcription factors implicated in the differentiation of both types of tissue and further supported by concomitant defects in such tissues due to the disruption of a single gene. Similarly, simultaneous anomalies in those tissues are also observed in some diseases caused by mutations of the genes encoding those transcription factors. A recent immunohistochemical study with one of the transcription factors, Ad4BP/SF‐1, definitely demonstrated the presence of a particular cell population designated the ‘adreno‐genital primordium (AGP)’ which gives rise to both the adrenal cortex and the gonads. In the process of differentiation from the AGP to the mature adrenal cortex and the gonads of the two sexes, several interesting issues can be raised as to the next targets for the study. To address these issues it is important to elucidate the upstream regulatory mechanisms and downstream target genes of such transcription factors as WT1, SRY, SOX9 and DAX1, in addition to Ad4BP/SF‐1, all of which are implicated in steroidogenic tissue differentiation.

The regulation of 3β-hydroxysteroid dehydrogenase expression

3 beta-Hydroxysteroid dehydrogenasel delta 5-->4-isomerase (3 beta-HSD) catalyzes the formation of delta 4-3-ketosteroids from delta 5-3 beta-hydroxysteroids, an obligate step in the biosynthesis not only of androgens and estrogens but also of mineralocorticoids and glucocorticoids. The enzyme is expressed in the adrenal cortex and in steroidogenic cells of the gonads, consistent with this role. However, 3 beta-HSD is also expressed in many other tissues, such as the liver and kidney, where its function is not entirely clear. It is established that a family of closely related genes encode for 3 beta-HSD. The various 3 beta-HSD isoforms are expressed in a tissue-specific manner involving separate mechanisms of regulation. The human type I 3 beta-HSD is expressed at high levels in syncytial trophoblast and in sebaceous glands, and the type II isoform is almost exclusively expressed in the adrenal cortex and gonads. An important feature in liver and kidney (at least of hamster, mouse, rabbit, and rat) is the sexual dimorphic nature of 3 beta-HSD expression. We briefly review studies on the regulation of the human 3 beta-HSD I and II genes in human trophoblast and adrenal cortex and extend this to discuss the rat 3 beta-HSD I gene expressed in adrenals and gonads. The complexity of 3 beta-HSD expression through multiple signaling pathways acting on a multigene family of enzymes may contribute importantly to the diverse patterns and locations of steroid hormone biosynthesis.

Transcription factor adrenal 4 binding protein as a marker of adrenocortical malignancy.

Adrenal 4 binding protein (Ad4BP) is a transcription factor that regulates the expression of the steroidogenic enzymes and is expressed primarily in steroidogenic cells. We immunolocalized Ad4BP in adrenocortical carcinoma (eight cases) and various malignancies that histologically simulate an adrenocortical carcinoma to evaluate the value of Ad4BP as an immunohistochemical marker of adrenocortical carcinoma. These malignancies examined were renal cell carcinoma (20 cases), hepatocellular carcinoma (10 cases), malignant melanoma (eight cases), ovarian (six cases) and uterine (three cases) clear cell carcinoma, large cell carcinoma of the lung (five cases), and pheochromocytoma (three cases). Nuclear Ad4BP immunoreactivity was observed only in adrenocortical carcinoma cases but not in other tumors examined. Almost all of the adrenocortical carcinoma cells were immunohistochemically positive for Ad4BP including cells associated with bizarre nuclei. These results show that application of Ad4BP immunostain can contribute greatly to the differential diagnosis of adrenocortical carcinoma.

Transcriptional regulation of the bovine CYP17 gene by cAMP

The transcription of steroid hydroxylase genes is controlled by ACTH and cAMP in the adrenal cortex. In most instances the regulation appears to rely on transcription factors traditionally not associated with cAMP-dependent gene expression. For the non-traditional factors it remains necessary to elucidate the coupling of increases in intracellular cAMP and cAMP-dependent protein kinase (PKA) activity to the function of these proteins. The bovine CYP17 gene, which encodes the steroid 17 alpha-hydroxylase, contains two discrete DNA elements within its promoter and upstream region (CRS1 and CRS2) that individually can confer cAMP responsiveness. The CRS1 element is a target for PKA signalling and for negative regulation via the protein kinase C signal transduction pathway. The homeodomain protein Pbx1 enhances CRS1-dependent transcription, but additional CRS1-binding proteins remain to be identified. Furthermore it is not known how PKA regulates the activity of Pbx1 or its possible binding partners. Closer to the promoter, the nuclear orphan receptors SF-1 and COUP-TF have overlapping binding sites in CRS2 and they bind in a mutually exclusive manner with very similar affinities; 8 and 10 nM, respectively. SF-1 stimulates whereas COUP-TF inhibits transcription from the bovine CYP17 promoter. Together, the data suggest that cAMP-dependent control of the amounts of the activator SF-1 vs. the repressor COUP-TF could influence CRS2-dependent transcription. In addition, PKA may influence the phosphorylation of SF-1, thus increasing its activity. In vitro, PKA will elicit phosphorylation of SF-1. However, although SF-1 can be immunoprecipitated from adrenocortical cells as a phosphroprotein, we have not been able to show cAMP-dependent increase in net phosphorylation in intact cells. More careful examination of individual phosphorylation sites in SF-1 may still reveal hormone- and cAMP-induced phosphorylation of SF-1.

Follicle stimulating hormone‐β subunit gene is expressed in parallel with a transcription factor Ad4BP/SF‐1 in human pituitary adenomas

OBJECTIVES A transcription factor Ad4BP/SF‐1 is implicated in the differentiation of gonadotrophs in the pituitary gland, but it is not known whether human pituitary cells express this factor. The present study aimed to disclose (1) whether human pituitary adenomas express Ad4BP/SF‐1, and (2) if this is the case, what kinds of adenoma express the factor.