The human adrenal cortex produces mineralocorticoids, glucocorticoids, and androgens in a species-specific, hormonally regulated, zone-specific, and developmentally characteristic fashion. Most molecular studies of adrenal steroidogenesis use human adrenocortical NCI-H295A and NCI-H295R cells as a model because appropriate animal models do not exist. NCI-H295A and NCI-H295R cells originate from the same adrenocortical carcinoma which produced predominantly androgens but also smaller amounts of mineralocorticoids and glucocorticoids. Research data obtained from either NCI-H295A or NCI-H295R cells are generally compared, although for the same experiments no direct comparison between the two cell lines has been performed. Therefore, we compared the steroid profile and the expression pattern of important genes involved in steroidogenesis in both cell lines. We found that steroidogenesis differs profoundly. NCI-H295A cells produce more mineralocorticoids, whereas NCI-H295R cells produce more androgens. Expression of the 3β-hydroxysteroid dehydrogenase (HSD3B2), cytochrome b5, and sulfonyltransferase genes is higher in NCI-H295A cells, whereas expression of the cytochrome P450c17 (CYP17), 21-hydroxylase (CYP21), and P450 oxidoreductase genes does not differ between the cell lines. We found lower 3β-hydroxysteroid dehydrogenase type 2 but higher 17,20-lyase activity in NCI-H295R cells explaining the ‘androgenic’ steroid profile for these cells and resembling the zona reticularis of the human adrenal cortex. Both cell lines were found to express the ACTH receptor at low levels consistent with low stimulation by ACTH. By contrast, both cell lines were readily stimulated by 8Br-cAMP. The angiotensin type 1 receptor was highly expressed in NCI-H295R than NCI-H295A cells and angiotensin II stimulated steroidogenesis in NCI-H295R but not NCI-H295A cells. Our data suggest that comparative studies between NCI-H295A and NCI-H295R cells may help find important regulators of mineralocorticoid or androgen biosynthesis.

Biallelic variants of steroidogenic acute regulatory protein (STAR/STARD1) may cause primary adrenal insufficiency and 46,XY disorder of sex development. STAR plays a pivotal role in transporting cholesterol into mitochondria where cholesterol serves as an essential substrate for initiating steroid biosynthesis by its conversion to pregnenolone. Generally, loss-of-function mutations of STAR cause the classic form of lipoid congenital adrenal hyperplasia (LCAH) where steroidogenesis of the adrenal cortex and the gonads is severely affected. By contrast, partial activity of STAR causes a less severe phenotype, the non-classic LCAH, which is characterized by later onset and initial manifestation with isolated adrenal insufficiency only. Disease-causing STAR variants are very rare. Numerous variants of all types have been described worldwide. Prevailing variants have been reported from Japan and Korea and in some population clusters where STAR is more common. Genotype–phenotype correlation is pretty good for STAR variants. While the exact mechanisms of cholesterol transport into mitochondria for steroidogenesis are still under investigation, the important role of STAR in this process is evident by inactivating STAR variants causing LCAH. The mechanism of disease with STAR deficiency is best described by a two-hit model: the first hit relates to impaired cholesterol import into mitochondria and thus lack of substrate for all steroid hormone biosynthesis; the second hit then relates to massive cytoplasmic lipid overload (evidenced by typically enlarged and fatty adrenal glands) leading to cell death and organ destruction. This review summarizes phenotype and genotype characteristics of human STAR variants found through the ClinVar database.

The CYP17A1 gene is the qualitative regulator of steroidogenesis. Depending on the presence or absence of CYP17 activities mineralocorticoids, glucocorticoids or adrenal androgens are produced. The expression of the CYP17A1 gene is tissue as well as species-specific. In contrast to humans, adrenals of rodents do not express the CYP17A1 gene and have therefore no P450c17 enzyme for cortisol production, but produce corticosterone. DNA methylation is involved in the tissue-specific silencing of the CYP17A1 gene in human placental JEG-3 cells. We investigated the role of DNA methylation for the tissue-specific expression of the CYP17A1 gene in rodents. Rats treated with the methyltransferase inhibitor 5-aza-deoxycytidine excreted the cortisol metabolite tetrahydrocortisol in their urine suggesting that treatment induced CYP17 expression and 17α-hydroxylase activity through demethylation. Accordingly, bisulfite modification experiments identified a methylated CpG island in the CYP17 promoter in DNA extracted from rat adrenals but not from testes. Both methyltransferase and histone deacetylase inhibitors induced the expression of the CYP17A1 gene in mouse adrenocortical Y1 cells which normally do not express CYP17, indicating that the expression of the mouse CYP17A1 gene is epigenetically controlled. The role of DNA methylation for CYP17 expression was further underlined by the finding that a reporter construct driven by the mouse −1041 bp CYP17 promoter was active in Y1 cells, thus excluding the lack of essential transcription factors for CYP17 expression in these adrenal cells.