A role for the NGFI-B family in adrenal zonation and adrenocortical disease

The three zones of the human adrenal cortex are functionally distinct with the glomerulosa producing aldosterone, the fasciculata producing cortisol, and the reticularis producing DHEA/DHEAS. This functional zonation is largely due to the zone-specific expression of steroidogenic enzymes. Recent evidence suggests a role for the NGFI-B family of orphan nuclear receptors (particularly NURR1 and NGFI-B) in the zone-specific expression of two key steroidogenic enzymes, aldosterone synthase (CYP11B2) and 3 beta-hydroxysteroid dehydrogenase (HSD3B2). Herein we discuss the evidence that suggests a role for NURR1 (NR4A2) in the expression of CYP11B2 in the glomerulosa as well as in the dysregulation of CYP11B2 gene expression as is seen in aldosterone-producing adenoma (APA), a major cause of endocrine hypertension. NURR1 appears to be important for CYP11B2 transcription and is found at higher levels in glomerulosa and in APA. Its expression in adrenal cells is also readily increased by angiotensin II treatment. HSD3B2 is a steroid-metabolizing enzyme that is essential for adrenal production of mineralocorticoids and glucocorticoids. Thus, HSD3B2 is expressed at high levels in the glomerulosa and fasciculata where these steroids are produced but at low levels in the adrenal reticularis, which produces mainly DHEA. We recently demonstrated that NGFI-B (nur77 or NR4A1) plays an important role in the regulation of HSD3B2 transcription and may play an important role in the functional zonation of the adrenal gland. Immunohistochemistry confirmed that, within adult and fetal adrenal gland, NGFI-B expression paralleled expression of HSD3B2. Transient transfections demonstrated that NGFI-B family members enhanced HSD3B2 reporter activity but had no effect on a 17alpha-hydroxylase (CYP17) promoter construct. Taken together these results suggest that the NGFI-B family of transcription factors plays a role in establishing the functional zonation of the human adrenal by regulating CYP11B2 and HSD3B2 gene transcription.