25-HYDROXYCHOLESTEROL IS NOT A LIGAND FOR THE ORPHAN NUCLEAR RECEPTORSTEROIDOGENIC FACTOR-I (SF-1)

The orphan nuclear receptor steroidogenic factor-1 (SF-1) is involved in the transcriptional regulation of all the steroid hydroxylase genes , and also regulates the transcription of the genes for Mullerian Inhi bitory substance (MIS), alpha subunit of glycoprotein hormone, LH beta , oxytocin, GnRH receptor, ACTH receptor, prolactin receptor, DAX-1, a nd steroidogenic acute regulatory protein. Other members of the nuclea r receptor gene family, including steroid hormone, thyroid hormone, re tinoic acid, PPAR, and vitamin D receptors must bind ligand to activat e transcription, but SF-1 has been considered to be an orphan nuclear receptor because, when identified, it had no known ligand. A recent pu blication suggested that transcriptional regulation by SF-1, expressed in a non-steroidogenic CV-1 cells, could be activated by oxysterols s uggesting that these compounds could serve as natural ligands for SF-1 . We now demonstrate that 25-hydroxycholesterol, either added exogenou sly or synthesized endogenously in steroidogenic mouse Leydig MA-10 ce lls, did not act as a ligand for SF-1, as it did not increase transcri ption from six different SF-1-dependent DNA sequences. Furthermore, th e abundance of these oxysterols in MA-IO cells was much less than conc entrations needed for activation of SF-1 in CV-1 cells, indicating tha t SF-1 is not constitutively bound by ligand in MA-10 cells. Thus, in steroidogenic cells, transcriptional regulation of the steroid hydroxy lase genes by SF-1 does not depend upon the presence of 25-hydroxychol esterol, and is not modified by its presence.