The Clock Protein Bmal1 Regulates Circadian Expression and Activity of Sulfotransferase 1a1 in Mice

Sulfotransferase 1a1 (Sult1a1) is a phase II enzyme that contributes extensively to metabolism and detoxification of various drugs and chemicals. Here we aimed to investigate a potential role of the clock protein Bmal1 (brain and muscle Arnt-like protein-1) in circadian regulation of Sult1a1 in mice. The regulatory effects of Bmal1 on Sult1a1 were assessed both in vivo (using Bmal1-deficient mice) and in vitro (using both normal and serum-shocked Hepa-1c1c7 cells). The relative mRNA and protein levels of Sult1a1 in the cells or mouse livers were measured by RT-qPCR and Western blotting, respectively. Sulfation activities of two Sult1a1 substrates (i.e., p-nitrophenol and galangin) were determined using mouse liver S9 fractions. Transcriptional regulation of Sult1a1 by Bmal1 was investigated using luciferase reporter, electrophoretic mobility shift (EMSA), and chromatin immunoprecipitation (ChIP) assays. We first showed that hepatic Sult1a1 was rhythmically expressed at both mRNA and protein levels (higher expressions during the night than the daytime). Consistently, the liver sulfation activities toward two Sult1a1 substrates were circadian time dependent with a higher activity at ZT14 than at ZT2. Furthermore, deletion of Bmal1 in mice blunted the circadian rhythmicity of hepatic Sult1a1 (with reduced expression levels). Likewise, Bmal1 positively regulated Sult1a1 expression in conventionally cultured Hepa-1c1c7 cells, and Bmal1 knockdown blunted expression rhythmicity of Sult1a1 in serum-shocked Hepa-1c1c7 cells. A combination of promoter analysis, EMSA and ChIP assays revealed that Bmal1 stimulated Sult1a1 transcription through its specific binding to the -571- to -554-bp region (an E-box element) in the promoter. In conclusion, Bmal1 activated the transcription of Sult1a1 and controlled circadian expression and activity of the enzyme.