The Orphan Nuclear Receptor, Steroidogenic Factor 1, Regulates Neuronal Nitric Oxide Synthase Gene Expression in Pituitary Gonadotropes

Abstract

Steroidogenic factor 1 (SF-1), an essential nuclear receptor, plays key roles in steroidogenic cell function within the adrenal cortex and gonads. It also contributes to reproductive function at all three levels of the hypothalamic-pituitary-gonadal axis. SF-1 regulates genes in the steroidogenic pathway, such as LHbeta, FSHbeta, and steroid hydroxylase. Abundant evidence suggests that nitric oxide (NO) has an important role in the control of reproduction due to its ability to control GnRH secretion from the hypothalamus and the preovulatory LH surge in pituitary gonadotropes. Recently, we cloned and characterized the promoter of mouse neuronal NO synthase (nNOS). nNOS is localized at all three levels of the hypothalamic-pituitary-gonadal axis to generate NO. We find that its major promoter resides at exon 2 in the pituitary gonadotrope alphaT3-1 cell line and that there is a nuclear hormone receptor binding site in this region, to which SF-1 can bind and regulate nNOS transcription. Mutation of the nuclear hormone receptor binding site dramatically decreases basal promoter activity and abolishes SF-1 responsiveness. A dominant negative of SF-1, in which the transactivation (AF-2) domain of SF-1 was deleted, inhibits nNOS exon 2 promoter activity. Dosage-sensitive reversal- adrenal hypoplasia congenita critical region on the X chromosome, gene 1 (DAX-1), which colocalizes and interferes with SF-1 actions in multiple cell lineages, negatively modulates SF-1 regulation of nNOS transcription. These findings demonstrate that mouse nNOS gene expression is regulated by the SF-1 gene family in pituitary gonadotropes. nNOS, a member of the cytochrome p450 gene family, could be one of the downstream effector genes, which mediates SF-1's reproductive function and developmental patterning.