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-sen sitive sex reversal-Adrenal hypoplasia congenita critical region on the X c hromosome) dictate adrenal-specific transcriptional programs are the focus of this laboratory. SF-l-mediated transcription is upregulated by phosphory lation of serine 203 located in the hinge region of SF-1. An SF-1(S203A) mu tant attenuates SF-1 activation, while substitution of S203 with a charged aspartate (SF-1(S203D)) results in a dose dependent increase in SF-1 mediat ed transcription. Ser203 serves as a substrate for Erk2 in vitro and is cri tical for activation of SF-1 by multiple components of the MAPK pathway. Is oelectric focusing demonstrates multiple immune-reactive SF-1 species in mo use adrenal and NCI-H295A cell extracts. We propose that differential phosp horylation of SF-1 by various mitogens serves to couple extracellular signa ls to adrenal-specific transcriptional programs. Mouse studies utilizing SF -1 heterozygous mice explore the in vivo role of SF-1 levels, SF-1 phosphor ylation and SF-1 interaction with Dax-1 in adrenal steroidogenesis. SF-1 he terozygous mice exhibit a marked decrease in baseline and post-stress corti costerone with a concomitant increase in ACTH. The role of Dax-1 in these S F-1 dependent processes is explored in compound SF-1 (+/-)/Dax-1 KO mice th at exhibit an increase in basal corticosterone and a decrease in basal ACTH compared to simple SF-1 (+/-) mice. These finding are consistent with an i nhibitory role for Dax-1 in SF-1 mediated transcription. Mice that express epitope tagged SF-1 (wild type, SF-1(S203A) and SF-1(S203D)) are being used to rescue the heterozygous adrenal phenotype and to determine the in vivo role of SF-1 phosphorylation in adrenal function.