A second class of nuclear receptors for oxysterols: Regulation of RORα and RORγ activity by 24S-hydroxycholesterol (cerebrosterol)

The retinoic acid receptor-related orphan receptors α and γ (RORα [NR1F1] and RORγ [NR1F3]) are members of the nuclear hormone receptor superfamily. These 2 receptors regulate many physiological processes including development, metabolism and immunity. We recently found that certain oxysterols, namely the 7-substituted oxysterols, bound to the ligand binding domains (LBDs) of RORα and RORγ with high affinity, altered the LBD conformation and reduced coactivator binding resulting in suppression of the constitutive transcriptional activity of these two receptors. Here, we show that another oxysterol, 24S-hydroxycholesterol (24S-OHC), is also a high affinity ligand for RORα and RORγ (K_i ∼ 25 nM). 24S-OHC is also known as cerebrosterol due to its high level in the brain where it plays an essential role as an intermediate in cholesterol elimination from the CNS. 24S-OHC functions as a RORα/γ inverse agonist suppressing the constitutive transcriptional activity of these receptors in cotransfection assays. Additionally, 24S-OHC suppressed the expression of several RORα target genes including BMAL1 and REV-ERBα in a ROR-dependent manner. We also demonstrate that 24S-OHC decreases the ability of RORα to recruit the coactivator SRC-2 when bound to the BMAL1 promoter. We also noted that 24(S), 25-epoxycholesterol selectively suppressed the activity of RORγ. These data indicate that RORα and RORγ may serve as sensors of oxsterols. Thus, RORα and RORγ display an overlapping ligand preference with another class of oxysterol nuclear receptors, the liver X receptors (LXRα [NR1H3] and LXRβ [NR1H2]).