Transcriptional regulation of human paraoxonase 1 by PXR and GR in human hepatoma cells N. Ponce-Ruiz a,b , A.E. Rojas-García a , B.S. Barrón-Vivanco a , G. Elizondo c , Y.Y. Bernal-Hernández a , A. Mejía-García c , I.M. Medina-Díaz a, ⁎ a Laboratorio de Contaminación y Toxicología, Secretaría de Investigación y Posgrado, Universidad Autónoma de Nayarit, Nayarit, Mexico b Posgrado en Ciencias Biológico Agropecuarias, Universidad Autónoma de Nayarit, Tepic, Nayarit, Mexico c Departamento de Biología Celular, Centro de Investigación y de Estudios Avanzados del IPN, México, D.F., Mexico abstract article info Article history: Received 14 April 2015 Received in revised form 15 September 2015 Accepted 30 September 2015 Available online 3 October 2015 Keywords: Paraoxonase 1 Nuclear receptors Transcription HepG2 cell Human paraoxonase 1 (PON1) is A-esterase synthesized in the liver and secreted into the plasma, where it asso- ciates with HDL. PON1 acts as an antioxidant preventing lipid oxidation and detoxifies a wide range of substrates, including organophosphate compounds. The variability of PON1 (enzyme activity/serum levels) has been attrib- uted to internal and external factors. However, the molecular mechanisms involved in the transcriptional regu- lation of PON1 have not been well-studied. The aim of this study was to evaluate and characterize the transcriptional activation of PON1 by nuclear receptors (NR) in human hepatoma cells. In silico analysis was performed on the promoter region of PON1 to determine the response elements of NR. Real-time PCR was used to evaluate the effect of specific NR ligands on the mRNA levels of genes regulated by NR and PON1. The re- sults indicated that NR response elements had 95% homology to pregnenolone (PXR), glucocorticoids (GR), retinoic acid (RXR) and peroxisomes proliferator-activated receptor alpha (PPARα). Treatments with Dexameth- asone (GR ligand), Rifampicin (PXR ligand) and TCDD (AhR ligand) increased the mRNA levels of PON1 at 24 and 48 h. We showed that the activation of GR by Dexamethasone results in PON1 gene induction accompanied by an increase in activity levels. In conclusion, these results demonstrate that GR regulates PON1 gene transcription through directly binding to NR response elements at -95 to -628 bp of the PON1 promoter. This study suggests new molecular mechanisms for the transcriptional regulation of PON1 through a process involving the activation of PXR. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction Human paraoxonase 1 (PON1, EC 3.1.8.1) is a calcium-dependent A-esterase that is synthesized in the liver and in other tissues such as the kidney, lung and brain. PON1 is secreted into the plasma where it as- sociates with high density lipoproteins (HDLs) (Mackness et al., 2010). PON1 is a member of a family of proteins, also including PON2 and PON3, that are clustered in tandem on the long arms of human chromo- some 7 (q21.22) (Primo-Parmo et al., 1996). PON1 plays an important role as an antioxidant molecule in lipid metabolism by inhibiting the oxidation of low-density lipoproteins (LDLs) and preventing the devel- opment of atherosclerosis (Ota et al., 2005; Ikeda et al., 2008; Martínez et al., 2010). Further, PON1 hydrolyzes a wide range of substrates such as organophosphate pesticides (OP), lactones, neurotoxicants (soman and sarin) and aromatic esters (phenylacetate). PON1 is the only family member that is able to hydrolyze the oxon derivatives of biotransforma- tion of OP (Mackness et al., 1991; Gouédard et al., 2003; Ticozzi et al., 2010; Costa et al., 2011). The variability of PON1 levels and the activity of serum PON1 in humans and animals have been attributed mainly to polymorphisms present in the gene, as well as pathological and physiological conditions, oxidative stress, diet, lifestyle and environmental factors (Martínez et al., 2010; Précourt et al., 2011; Costa et al., 2011). Additionally, PON1 levels in serum are significantly determined by the status of gene expression in the liver (Fuhrman, 2012). However, the molecular mechanisms involved in the regulation of the hepatic gene expression of PON1 have been little studied (Schrader and Rimbach, 2011; Fuhrman, 2012). Gouédard et al. (2003) showed that some fibrates (e.g., Fenofibrate) significantly increase the promoter activity of PON1, but some statins (e.g., Pravastatin, Simvastatin and Fluvastatin) have opposite effects (decrease in PON1 promoter activity, mRNA levels and PON1 enzyme activity) that were mediated by peroxisomes proliferator-activated Toxicology in Vitro 30 (2015) 348–354 ⁎ @Corresponding author at: Laboratorio de Contaminación y Toxicología Ambiental, Secretaría de Investigación y Posgrado, Universidad Autónoma de Nayarit, Tepic, Nayarit, Mexico. E-mail addresses: aguilas_bd@hotmail.com (N. Ponce-Ruiz), aerg81@gmail.com (A.E. Rojas-García), bravis13@hotmail.com (B.S. Barrón-Vivanco), gazuela@cinvestav.mx (G. Elizondo), yael010@hotmail.com (Y.Y. Bernal-Hernández), mejiagarciaa@gmail.com (A. Mejía-García), irmartha@hotmail.com (I.M. Medina-Díaz). http://dx.doi.org/10.1016/j.tiv.2015.09.031 0887-2333/© 2015 Elsevier Ltd. All rights reserved. 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