167. MUTANT STEROIDOGENIC FACTOR-1 FROM PATIENTS WITH DISORDERS OF SEX DEVELOPMENT SHOW REDUCED ACTIVATION OF THE TESTIS-SPECIFIC ENHANCER OF SOX9

Abstract

The orphan nuclear hormone receptor Steroidogenic Factor 1 (SF1; NR5A1) is expressed throughout hypothalamic, pituitary, gonadal and adrenal tissues. Naturally occurring human mutations combined with mouse knockout models have revealed a critical role for SF1 as a transcription factor at multiple stages during gonadal development and during development of the adrenal. Missense mutation or truncation to SF1 in XY humans cause Disorders of Sex Development (DSD) with variable phenotypes. The precise mechanisms of SF1 action that fail in human DSD are not fully determined. This work aimed to utilise naturally occurring DSD-causing mutations in SF1 to increase our understanding of the sex determining function of SF1 in the developing male gonad. Recent work by others (1) identified SOX9 as a key target gene of SF1 during testis determination. SF1 activates Sox9 through a testis-specific enhancer element, termed TES. We tested the abilities of eleven clinical SF1 mutations to activate TES in reporter assays in HEK293T cells. Eight of the eleven SF1 mutants showed considerably reduced activation of TES compared to WT SF1. Furthermore, all mutations causing moderate to severe DSD phenotypes correlated with a more severe impairment of TES activation. In addition, all eleven of the mutants showed reduced synergistic activation of TES in co-transfection with the testis-determining co-factor SRY. Overall, this biochemical analysis of the function of mutant SF1 from DSD patients suggests that a failure of SOX9 up regulation, due to reduced activation of TES during testis development, could be the primary cause of the DSD in some patients with SF1 mutations.