ENDOCRINE AND NEUROGENIC REGULATION OF THE ORPHAN NUCLEAR RECEPTORS NUR77 AND NURR-1 IN THE ADRENAL-GLANDS

nur77 and nurr-1 are growth factor-inducible members of the steroid/th yroid hormone receptor gene superfamily. In order to gain insight into the potential roles of nur77 in the living organism, we used pharmaco logic treatments to examine the expression of nur77 in the mouse adren al gland. We found that nur77 and nurr-1 are induced in the adrenal gl and upon treatment with pentylene tetrazole (Ptz; Metrazole). This ind uction is separable into distinct endocrine and neurogenic mechanisms. In situ hybridization analysis demonstrates that nur77 expression upo n Ptz treatment in the adrenal cortex is localized primarily to the in ner cortical region, the zona fasciculata-reticularis, with;minimal in duction in the zona glomerulosa. This induction is inhibitable by pret reatment with dexamethasone, indicating involvement of the hypothalami c-pituitary-adrenal axis in the activation of adrenal cortical express ion. When mice were injected with adrenocorticotrophic hormone (ACTH), nur77 expression in the adrenal gland spanned all cortical layers inc luding the zona glomerulosa, but medullary expression was not induced. Ptz also induces expression of both nur77 and nurr-1 in the adrenal m edulla. Medullary induction is likely to have a neurogenic origin, as nur77 expression was not inhibitable by dexamethasone pretreatment and induction was seen after treatment with the cholinergic neurotransmit ter nicotine. nur77 is also inducible by ACTH, forskolin, and the seco nd messenger analog dibutyryl cyclic AMP in the ACTH-responsive adrena l cortical cell line Y-1. Significantly, Nur77 isolated from ACTH-stim ulated Y-1 cells bound to its response element whereas Nur77 present i n unstimulated cells did not. Moreover, Nur77 in ACTH-treated Y-1 cell s was hypophosphorylated at serine 354 compared with that in untreated cells. These results, taken together with the previous observation th at dephosphorylation of serine 354 affects DNA binding affinity in vit ro, show for the first time that phosphorylation of Nur77 at serine 35 4 is under hormonal regulation, modulating its DNA binding affinity. T hus, ACTH regulates Nur77 in two ways: activation of its gene and post translational modification. A promoter analysis of nur77 induction in Y-1 cells indicates that the regulatory elements mediating ACTH induct ion differ from those required for induction in the adrenal medullary tumor cell line PC12 and in 3T3 fibroblasts.