The small/short heterodimer partner (SHP, NR0B2) is a nuclear receptor corepressor lacking a DNA binding domain. SHP is induced by bile acid-activated farnesoid X receptor (FXR) resulting in CYP7A1 gene suppression. In contrast, Pregnane X receptor (PXR) activation by its ligands was recently suggested to inhibit SHP gene transactivation to maximize the induction of PXR target genes. However, there are also conflicting reports in literature whether PXR or rodent Pxr activation down-regulates SHP/Shp expression. Moreover, the PXR-mediated regulation of the SHP gene has been studied only at the SHP mRNA and transactivation (gene reporter assay) levels. In this study, we studied the effect of rifampicin, a prototype PXR ligand, on SHP mRNA, and protein expression in three primary human hepatocyte cultures. We found that SHP mRNA is not systematically down-regulated in hepatocyte in culture after 24 h treatment with rifampicin. Consistently, we did not observe down-regulation of SHP protein in primary human hepatocytes after 24 and 48 h of incubation with rifampicin. We can conclude that although we observed slight down-regulation of SHP mRNA and protein in several hepatocyte preparations, the phenomenon is unlikely critical for PXR-mediated induction of its target genes.

• Klíčová slova
• CYP3A4, PXR, SHP, cytochrome P450, induction,
• Publikační typ
• časopisecké články MeSH

Metformin is widely used in the treatment of type-2 diabetes. The pleotropic effects of metformin on glucose and lipid metabolism have been proposed to be mediated by the activation of AMP-activated protein kinase (AMPK) and the subsequent up-regulation of small heterodimer partner (SHP). SHP suppresses the functions of several nuclear receptors involved in the regulation of hepatic metabolism, including pregnane X receptor (PXR), which is referred to as a "master regulator" of drug/xenobiotic metabolism. In this study, we hypothesize that metformin suppresses the expression of CYP3A4, a main detoxification enzyme and a target gene of PXR, due to SHP up-regulation. We employed various gene reporter assays in cell lines and qRT-PCR in human hepatocytes and in Pxr(-/-) mice. We show that metformin dramatically suppresses PXR-mediated expression of CYP3A4 in hepatocytes. Consistently, metformin significantly suppressed the up-regulation of Cyp3a11 mRNA in the liver and intestine of wild-type mice, but not in Pxr(-/-) mice. A mechanistic investigation of the phenomenon showed that metformin does not significantly up-regulate SHP in human hepatocytes. We further demonstrate that AMPK activation is not involved in this process. We show that metformin disrupts PXR's interaction with steroid receptor coactivator-1 (SRC1) in a two-hybrid assay independently of the PXR ligand binding pocket. Metformin also inhibited vitamin D receptor-, glucocorticoid receptor- and constitutive androstane receptor (CAR)-mediated induction of CYP3A4 mRNA in human hepatocytes. We show, therefore, a suppressive effect of metformin on PXR and other ligand-activated nuclear receptors in transactivation of the main detoxification enzyme CYP3A4 in human hepatocytes.

• MeSH
• aktivace transkripce MeSH
• cytochrom P-450 CYP3A genetika   metabolismus   MeSH
• hepatocyty účinky léků   metabolismus   MeSH
• hypoglykemika farmakologie   MeSH
• koaktivátory jaderných receptorů metabolismus   MeSH
• konstitutivní androstanový receptor MeSH
• kultivované buňky MeSH
• lidé MeSH
• membránové proteiny genetika   metabolismus   MeSH
• messenger RNA metabolismus   MeSH
• metformin farmakologie   MeSH
• myši inbrední C57BL MeSH
• myši knockoutované MeSH
• myši MeSH
• polohový reflex účinky léků   MeSH
• pregnanový X receptor MeSH
• proteinkinasy aktivované AMP fyziologie   MeSH
• receptory cytoplazmatické a nukleární metabolismus   fyziologie   MeSH
• receptory glukokortikoidů fyziologie   MeSH
• receptory kalcitriolu fyziologie   MeSH
• reportérové geny MeSH
• signální transdukce MeSH
• steroidní receptory genetika   fyziologie   MeSH
• zvířata MeSH
• Check Tag
• lidé MeSH
• myši MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Research Support, N.I.H., Extramural MeSH
• Názvy látek
• Cyp3a11 protein, mouse MeSH Prohlížeč
• cytochrom P-450 CYP3A MeSH
• hypoglykemika MeSH
• koaktivátory jaderných receptorů MeSH
• konstitutivní androstanový receptor MeSH
• membránové proteiny MeSH
• messenger RNA MeSH
• metformin MeSH
• nuclear receptor subfamily 0, group B, member 2 MeSH Prohlížeč
• pregnanový X receptor MeSH
• proteinkinasy aktivované AMP MeSH
• receptory cytoplazmatické a nukleární MeSH
• receptory glukokortikoidů MeSH
• receptory kalcitriolu MeSH
• steroidní receptory MeSH