Synergistic regulation of the mouse orphan nuclear receptor SHP gene promoter by CLOCK–BMAL1 and LRH-1

Abstract Small heterodimer partner (SHP; NR0B2) is an orphan nuclear receptor and acts as a repressor for wide variety of nuclear hormone receptors. We demonstrated here that mouse SHP mRNA showed a circadian expression pattern in the liver. Transient transfection of the m SHP promoter demonstrated that CLOCK–BMAL1, core circadian clock components, bound to E-box (CACGTG), and stimulated the promoter activity by 4-fold. Liver receptor homologue-1 (LRH-1; NR5A2) stimulated the m SHP promoter, and CLOCK–BMAL1 synergistically enhanced the LRH-1-mediated transactivation. Interestingly, SHP did not affect the CLOCK–BMAL1-mediated promoter activity, but strongly repressed the synergistic activation of CLOCK–BMAL1 and LRH-1. Furthermore, in vitro pull-down assays revealed the existence of direct protein–protein interaction between LRH-1 and CLOCK. In summary, this study shows that CLOCK–BMAL1, LRH-1 and SHP coordinately regulate the m SHP gene to generate the circadian oscillation. The cyclic expression of m SHP may affect daily activity of other nuclear receptors and contribute to circadian liver functions.