Steroidogenic factor 1 (SF-1 or NR5A1), is a Ftz-F1 member of the nuclear receptor superfamily that plays essential roles in endocrine development, steroidogenesis, and gonad differentiation. We investigated modifications that control SF-1 function and found that SF-1 could be conjugated by SUMO-1 both in vitro and in vivo. Wild-type but not conjugation-deficient SF-1 was localized at the nuclear speckles together with SUMO-1. Thus, SUMO-1 conjugation could also target SF-1 into nuclear speckles. Collectively, these results suggest that SUMO modification at the repression domains targets SF-1 to nuclear speckles; this could be an important mechanism by which SF-1 is regulated. SF-1 was modified predominantly at

Steroid deficiencies are diseases affecting salt levels, sugar levels, and sexual differentiation. To study steroid deficiency in more detail, we used a gene-targeting technique to insert a neo gene into the first exon to disrupt Cyp11a1, the first gene in steroid biosynthetic pathways. Cyp11a1 null mice do not synthesize steroids. They die shortly after birth, but can be rescued by steroid injection. Due to the lack of feedback inhibition by glucocorticoid, their circulating ACTH levels are exceedingly high; this results in ectopic Cyp21 gene expression in the testis. Male Cyp11a1 null mice are feminized with female external genitalia and underdeveloped male accessory sex organs. Their testis, epididymis, and vas deferens are present, but undersized. In addition, their adrenals and gonads accumulate excessive amounts of lipid. The lack of steroid production, abnormal gene expression, and aberrant reproductive organ development resemble various steroid deficiency syndromes, making these mice good models for studies of steroid function and regulation.

Normal endocrine development and function require nuclear hormone receptor SF-1 (steroidogenic factor 1). To understand the molecular mechanism of SF-1 action, we have investigated its domain function by mutagenesis and functional analyses. Our mutant studies show that the putative AF2 (activation function 2) helix located at the C-terminal end is indispensable for gene activation. SF-1 does not have an N-terminal AF1 domain. Instead, it contains a unique FP region, composed of the Ftz-F1 box and the proline cluster, after the zinc finger motif. The FP region interacts with transcription factor IIB (TFIIB) in vitro. This interaction requires residues 178-201 of TFIIB, a domain capable of binding several transcription factors. The FP region also mediates physical interaction with c-Jun, and this interaction greatly enhances SF-1 activity. The putative SF-1 ligand, 25-hydroxycholesterol, has no effects on these bindings. In addition, the Ftz-F1 box contains a bipartite nuclear localization signal (NLS). Removing the basic residues at either end of the key nuclear localization sequence NLS2.2 abolishes the nuclear transport. Expression of mutants containing only the FP region or lacking the AF2 domain blocks wild-type SF-1 activity in cells. By contrast, the mutant having a truncated nuclear localization signal lacks this dominant negative effect. These results delineate the importance of the FP and AF2 regions in nuclear localization, protein-protein interaction, and transcriptional activation.

The CYP11A1 gene encodes the cholesterol side-chain cleavage enzyme, also termed cytochrome P450scc, which catalyzes the conversion of cholesterol to pregnenolone in the first step of steroid biosynthesis in mitochondria. The adrenal- and gonad-selective, hormonally and developmentally regulated expression of CYP11A1 is principally driven by its 2.3 kb promoter. Multiple trans-acting factors like SF-1, Sp1, AP-2, TReP-132, LBP-1b, LBP-9, AP-1, NF-1, and Ets control CYP11A1 transcription either through DNA-protein interaction with their specific cis-acting elements or through protein-protein interaction between each other, wherein SF-1 plays a central role in adrenals and testes. In addition to binding with its proximal and upstream motifs, SF-1 also physically interacts with TFIIB, CBP/p300, TReP-132, and c-Jun/AP-1 to specifically transmit the regulatory signals of cAMP. Other factors like Sp1 family members, AP-2, and LBP-1b/LBP-9 may be other factors that play a role in CYP11A1 transcription, particularly in placental cells. The TATA sequence could also contribute to tissue-specificity and hormonal regulation of CYP11A1 transcription. This article reviews recent studies focusing on adrenals and gonads.

During pregnancy, fetal glucocorticoid is derived from both maternal supply and fetal secretion. We have created mice with a disruption of the Cyp11a1 gene resulting in loss of fetal steroid secretion but preserving the maternal supply. Cyp11a1null embryos have appreciable although lower amounts of circulating corticosterone, the major mouse glucocorticoid, suggesting that transplacental corticosterone is a major source of corticosterone in fetal circulation. These embryos thus provide a means to examine the effect of fetal glucocorticoids. The adrenal in Cyp11a1 null embryos was disorganized with abnormal mitochondria and oil accumulation. The adrenal medullary cells did not express phenylethanolamine N-methyltransferase and synthesized no epinephrine. Cyp11a1 null embryos had decreased diencephalon Hsd11b1, increased diencephalon Crh, and increased pituitary Pomc expression, leading to higher adrenocorticotropin level in the plasma. These data indicate blunted feedback suppression despite reasonable amounts of circulating corticosterone. Thus, the corticosterone synthesized in situ by the fetus is required for negative feedback suppression of the hypothalamus-pituitary-adrenal axis and for catecholamine synthesis in adrenal medulla.

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We have investigated the structure and function of P450c21 with regard to a conserved site around Ile-172 by site-directed mutagenesis making single amino acid substitutions of residues 169 -173. Substitutions of Ile-171 and -172 resulted in production of mutant proteins with dramatic reductions in enzymatic activities, indicating the importance of these two residues in maintaining the structure and function of P450c21. The I171N protein was present at a slightly lower level, due to a decreased rate of protein synthesis. The I172N apoprotein was synthesized at the normal rate, but its hemebound P450 form was present at a much lower level. This I172N protein was tightly integrated into the membrane of endoplasmic reticulum, similar to the wild type P450c21, as shown by immunofluorescence detection, alkaline extraction, and cellular fractionation. Kinetic studies indicated that I172N had a lower V max value. In addition, the I172N protein was more sensitive to proteinase K digestion, indicating a possible alteration of conformation. This conformational change may result in the lower yield of the I172N hemoprotein and the reduced catalytic activity.

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