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

Abstract

The solute carrier family 13 member 5 (SLC13A5) is a sodiumcoupled 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.

Mutations in the Na+/Citrate Cotransporter NaCT (SLC13A5) in Pediatric Patients with Epilepsy and Developmental Delay

“…A total of six NaCT mutants were prepared: four point mutations identified in this study, Y82C, G219R, T227M and L492P (Table 1 and Figure 1), and one mutation, L488P, identified previously (2). In addition, we prepared the DelG mutant of hNaCT, with a nucleotide deletion of hepatocytes, NaCT expression is correlated with lipid accumulation and triglyceride synthesis (10,11). Furthermore, inhibition of NaCT-mediated citrate transport by the liver is emerging as a therapeutic approach for the treatment of metabolic disorders, such as diabetes (11,12).…”

Arylhydrocarbon receptor-dependent mIndy (Slc13a5) induction as possible contributor to benzo[a]pyrene-induced lipid accumulation in hepatocytes

“…In vivo, all mechanisms might act in parallel. Evidence for a major contribution of mIndy in the development of hepatic steatosis was provided by showing that over-expression of mIndy in HepG2 cells increased fatty acid synthesis from citrate (Neuschäfer-Rube et al, 2014) Moreover, a previous study showed that mIndy-deficient mice are partially protected against dietinduced hepatic steatosis (Birkenfeld et al, 2011) and knockdown of mIndy in HepG2 cells reduced triglyceride accumulation (Li et al, 2015) This was attributed to a decreased uptake of extracellular citrate and incorporation of citrate into fatty acids by de novo synthesis. Notably, in this study the hepatic expression of SREBP-1c was reduced.…”

“…A very recent study showed that mIndy can be induced by activation of the pregnane X receptor (PXR) with rifampicine (Li et al, 2015) in human hepatocytes. Benzo[a]pyrene is not only a prototypic AhR activator, it also is a potential activator of PXR and it has been suggested that for example the induction of CYP3A4 is mediated via PXR activation (Luckert et al, 2013) and not via the AhR.…”

A Fibroblast Growth Factor 21–Pregnane X Receptor Pathway Downregulates Hepatic CYP3A4 in Nonalcoholic Fatty Liver Disease

“…Indeed, studies in transgenic mice have revealed involvement of PXR in hepatic lipogenesis and fatty acid oxidation (Nakamura et al, 2007;Zhou et al, 2008;He et al, 2013). Moreover, PXR was found to promote steatosis in cultured primary human hepatocytes (Bitter et al, 2015;Li et al, 2015). In addition, genetic polymorphisms in the PXR gene (NR1I2) are associated with disease severity in NAFLD (Sookoian et al, 2010).…”