SLC13A5 Is a Novel Transcriptional Target of the Pregnane X Receptor and Sensitizes Drug-Induced Steatosis in Human Liver

The solute carrier family 13 member 5 (SLC13A5) is a sodium-coupled transporter that mediates cellular uptake of citrate, which plays important roles in the synthesis of fatty acids and cholesterol. Recently, the pregnane X receptor (PXR, NR1I2), initially characterized as a xenobiotic sensor, has been functionally linked to the regulation of various physiologic processes that are associated with lipid metabolism and energy homeostasis. Here, we show that the SLC13A5 gene is a novel transcriptional target of PXR, and altered expression of SLC13A5 affects lipid accumulation in human liver cells. The prototypical PXR activator rifampicin markedly induced the mRNA and protein expression of SLC13A5 in human primary hepatocytes. Utilizing cell-based luciferase reporter assays, electrophoretic mobility shift assays, and chromatin immunoprecipitation assays, we identified and functionally characterized two enhancer modules located upstream of the SLC13A5 gene transcription start site that are associated with regulation of PXR-mediated SLC13A5 induction. Functional analysis further revealed that rifampicin can enhance lipid accumulation in human primary hepatocytes, and knockdown of SLC13A5 expression alone leads to a significant decrease of the lipid content in HepG2 cells. Overall, our results uncover SLC13A5 as a novel target gene of PXR and may contribute to drug-induced steatosis and metabolic disorders in humans.