Acid Ceramidase Represses Steroidogenic Factor 1‐dependent Gene Transcription by Binding to the Receptor in the Nucleus of H295R Human Adrenocortical Cells

Abstract

Adrenocorticotropin (ACTH) regulates glucocorticoid biosynthesis primarily through the activation of a cAMP/PKA‐dependent pathway to promote the interaction of transcription factors and coactivator proteins with the promoter of steroidogenic genes. The nuclear receptor steroidogenic factor 1 (SF‐1) is essential for steroidogenic gene transcription. We have shown that sphingosine (SPH) is a ligand for SF‐1 and that suppression of acid ceramidase (ASAH1) expression, an enzyme that produces SPH, increases the transcription of multiple steroidogenic genes. Given that SF‐1 is predominantly expressed in the nucleus, we sought to define the molecular mechanisms by which ASAH1 regulates SF‐1 function. We show that ASAH1 is localized in the nuclei of H295R human adrenocortical cells and ACTH signaling promotes nuclear sphingolipid metabolism in an ASAH1‐dependent manner. Significantly, ASAH1 suppresses SF‐1 activity by directly interacting with the receptor through an LXXLL nuclear receptor‐binding motif. Furthermore, ASAH1 is recruited to the promoter of various SF‐1‐target genes and co‐localizes with the receptor on the same promoter region of the CYP17A1 and steroidogenic acute regulatory protein (StAR) genes. Taken together, we establish ASAH1 as a novel coregulatory protein that represses SF‐1 function by directly binding to the receptor on the promoter of SF‐1‐target genes.