CCAAT/enhancer-binding protein β is involved in the breed-dependent transcriptional regulation of 3β-hydroxysteroid dehydrogenase/Δ5-Δ4-isomerase in adrenal gland of preweaning piglets

The enzyme 3β-hydroxysteroid dehydrogenase/Δ5-Δ4-isomerase (3β-HSD) catalyzes the biosynthesis of all steroid hormones. The molecular mechanisms regulating porcine adrenal 3β-HSD expression in different breeds are still poorly understood. In this study, we aimed to compare the expression of 3β-HSD between preweaning purebred Large White (LW) and Erhualian (EHL) piglets and to explore the potential factors regulating 3β-HSD transcription. EHL had significantly higher serum levels of cortisol (P < 0.01) and testosterone (P < 0.01), which were associated with significantly higher expression of 3β-HSD mRNA (P < 0.01) and protein (P < 0.05) in the adrenal gland, compared with LW piglets. The 5′ flanking region of the porcine 3β-HSD gene showed significant sequence variations between breeds, and the sequence of EHL demonstrated an elevated promoter activity (P < 0.05) in luciferase reporter gene assay. Higher adrenal expression of 3β-HSD in EHL was accompanied with higher CCAAT/enhancer binding protein β (C/EBPβ) expression (P < 0.05), enriched histone H3 acetylation (P < 0.05) and C/EBPβ binding to 3β-HSD promoter (P < 0.05). In addition, higher androgen receptor (AR) (P = 0.06) and lower glucocorticoid receptor (GR) (P < 0.05) were detected in EHL. Co-immunoprecipitation analysis revealed interactions of C/EBPβ with both AR and GR. These results indicate that the C/EBPβ binding to 3β-HSD promoter is responsible, at least in part, for the breed-dependent 3β-HSD expression in adrenal gland of piglets. The sequence variations of 3β-HSD promoter and the interactions of AR and/or GR with C/EBPβ may also participate in the regulation.