Ligand-dependent and -independent regulation of human hepatic sphingomyelin phosphodiesterase acid-like 3A expression by pregnane X receptor and crosstalk with liver X receptor.

Abstract:

Pregnane X receptor (PXR) mainly regulates xenobiotic metabolism and detoxification. Additionally, it exerts pleiotropic effects on liver physiology, which in large parts depend on transrepression of other liver-enriched transcription factors. Based on the hypothesis that lower expression levels of PXR may reduce the extent of this inhibition, an exploratory genome-wide transcriptomic profiling was performed using HepG2 cell clones with different expression levels of PXR. This screen and confirmatory real-time RT-PCR identified sphingomyelin phosphodiesterase acid-like (SMPDL) 3A, a novel nucleotide phosphodiesterase and phosphoramidase, as being up-regulated by PXR-deficiency. Transient siRNA-mediated knock-down of PXR in HepG2 cells and primary human hepatocytes similarly induced mRNA up-regulation, which translated into increased intracellular and secreted extracellular protein levels. Interestingly, ligand-dependent PXR activation also induced SMPDL3A in HepG2 cells and primary human hepatocytes. Electrophoretic mobility shift assays and chromatin immunoprecipitation demonstrated binding of PXR to the previously identified liver X receptor (LXR)-binding DR4 motif as well as to an adjacent ER8 motif in intron 1 of SMPDL3A. Constitutive binding of the unliganded receptor to the intron 1 chromatin indicated ligand-independent repression of SMPDL3A by PXR. Transient transfection and reporter gene analysis confirmed the specific role of these motifs in PXR- and LXR-dependent activation of the SMPDL3A intronic enhancer. PXR inhibited LXR mainly by competition for binding sites. In conclusion, this study describes that a decrease in PXR expression levels and ligand-dependent activation of PXR and LXR increase hepatic SMPDL3A levels, which possibly connects these receptors to hepatic purinergic signaling and phospholipid metabolism and may result in drug-drug interactions with phosphoramidate pro-drugs.

SEEK ID: https://seek.lisym.org/publications/30

PubMed ID: 28414139

Projects: LiSyM Pillar I: Early Metabolic Injury (LiSyM-EMI)

Publication type: Not specified

Journal: Biochem Pharmacol

Citation: Biochem Pharmacol. 2017 Jul 15;136:122-135. doi: 10.1016/j.bcp.2017.04.013. Epub 2017 Apr 13.

Date Published: 18th Apr 2017

Registered Mode: Not specified

Authors: J. Jeske, A. Bitter, W. E. Thasler, T. S. Weiss, M. Schwab, O. Burk

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Created: 21st Jul 2017 at 11:13

Last updated: 8th Mar 2024 at 07:44

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