Role of phosphorylation, gene dosage and Dax-1 in SF-1 mediated steroidogenesis.
The mechanisms by which SF-1 (Steroidogenic Factor-1) and Dax-1 (Dosage-sensitive sex reversal-Adrenal hypoplasia congenita critical region on the X chromosome) dictate adrenal-specific transcriptional programs are the focus of this laboratory. SF-1-mediated transcription is upregulated by phosphorylation of serine 203 located in the hinge region of SF-1. An SF-1S203A mutant attenuates SF-1 activation, while substitution of S203 with a charged aspartate (SF-1S203D) results in a dose dependent increase in SF-1 mediated transcription. Ser203 serves as a substrate for Erk2 in vitro and is critical for activation of SF-1 by multiple components of the MAPK pathway. Isoelectric focusing demonstrates multiple immuno-reactive SF-1 species in mouse adrenal and NCI-H295A cell extracts. We propose that differential phosphorylation of SF-1 by various mitogens serves to couple extracellular signals to adrenal-specific transcriptional programs. Mouse studies utilizing SF-1 heterozygous mice explore the in vivo role of SF-1 levels, SF-1 phosphorylation and SF-1 interaction with Dax-1 in adrenal steroidogenesis. SF-1 heterozygous mice exhibit a marked decrease in baseline and post-stress corticosterone with a concomitant increase in ACTH. The role of Dax-1 in these SF-1 dependent processes is explored in compound SF-1 (+/-)/Dax-1 KO mice that exhibit an increase in basal corticosterone and a decrease in basal ACTH compared to simple SF-1 (+/-) mice. These finding are consistent with an inhibitory role for Dax-1 in SF-1 mediated transcription. Mice that express epitope tagged SF-1 (wild type, SF-1S203A and SF-1S203D) are being used to rescue the heterozygous adrenal phenotype and to determine the in vivo role of SF-1 phosphorylation in adrenal function.
Babu
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PS
Internal Medicine and Physiology, University of Michigan, Ann Arbor 48109-0678, USA.
Bavers
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DL
Shah
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Hammer
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GD
D000311:Adrenal Glands / Q000378:metabolism*; D000324:Adrenocorticotropic Hormone / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D000818:Animals; D002460:Cell Line; D003345:Corticosterone / Q000096:biosynthesis*; D057137:DAX-1 Orphan Nuclear Receptor; D004268:DNA-Binding Proteins / Q000235:genetics / Q000502:physiology*; D051717:Fushi Tarazu Transcription Factors; D018628:Gene Dosage; D018398:Homeodomain Proteins; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D018345:Mice, Knockout / Q000235:genetics; D010766:Phosphorylation; D018160:Receptors, Cytoplasmic and Nuclear; D018168:Receptors, Retinoic Acid / Q000235:genetics / Q000502:physiology*; D012097:Repressor Proteins; D054339:Steroidogenic Factor 1; D014157:Transcription Factors / Q000235:genetics / Q000502:physiology*
D057137:DAX-1 Orphan Nuclear Receptor; D004268:DNA-Binding Proteins; D051717:Fushi Tarazu Transcription Factors; D018398:Homeodomain Proteins; C539966:Nr0b1 protein, mouse; D018160:Receptors, Cytoplasmic and Nuclear; D018168:Receptors, Retinoic Acid; D012097:Repressor Proteins; D054339:Steroidogenic Factor 1; D014157:Transcription Factors; C515058:steroidogenic factor 1, mouse; D000324:Adrenocorticotropic Hormone; D003345:Corticosterone