title: Activation of a novel c-Myc-miR27-prohibitin 1 circuitry in cholestatic liver injury inhibits glutathione synthesis in mice.
abstract: OBJECTIVE
  We showed that chronic cholestatic liver injury induced the expression of c-Myc but suppressed that of glutamate-cysteine ligase (GCL, composed of catalytic and modifier subunits GCLC and GCLM, respectively). This was associated with reduced nuclear antioxidant response element (ARE) binding by nuclear factor-erythroid 2 related factor 2 (Nrf2). Here, we examined whether c-Myc is involved in this process.
  
  
  RESULTS
  Similar to bile duct ligation (BDL), lithocholic acid (LCA) treatment in vivo induced c-Myc but suppressed GCL subunits expression at day 14. Nrf2 expression and Nrf2 ARE binding fell markedly. However, Nrf2 heterodimerization with MafG was enhanced by LCA, which prompted us to examine whether LCA treatment in vivo altered proteins that bind to ARE using biotinylated ARE in pull-down assay followed by proteomics. LCA treatment enhanced c-Myc but lowered prohibitin 1 (PHB1) binding to ARE. This was a result of c-Myc-mediated induction of microRNA 27a/b (miR27a/b), which target both PHB1 and Nrf2 to reduce their expression. Knockdown of c-Myc or miR27a/b attenuated LCA-mediated suppression of Nrf2, PHB1, and GCL subunit expression, whereas overexpression of PHB1 protected against the fall in Nrf2 and GCL subunits. Both c-Myc and PHB1 directly interact with Nrf2 but c-Myc lowers Nrf2 binding to ARE while PHB1 enhances it.
  
  
  METHODS
  This is the first work that shows how activation of this circuit in cholestatic liver injury inhibits GCL expression.
  
  
  CONCLUSIONS
  LCA feeding and BDL activate c-Myc-miR27a/b-PHB1 circuit, with the consequence of inhibiting Nrf2 expression and ARE binding, resulting in decreased reduced glutathione synthesis and antioxidant capacity.
authors.affiliation: 1 Division of Gastroenterology and Liver Diseases, Keck School of Medicine, University of Southern California , Los Angeles, California.
authors.forename: Heping
authors.initials: H
authors.lastname: Yang
authors.forename: Tony W H
authors.initials: TW
authors.lastname: Li
authors.forename: Yu
authors.initials: Y
authors.lastname: Zhou
authors.forename: Hui
authors.initials: H
authors.lastname: Peng
authors.forename: Ting
authors.initials: T
authors.lastname: Liu
authors.forename: Ebrahim
authors.initials: E
authors.lastname: Zandi
authors.forename: María Luz
authors.initials: ML
authors.lastname: Martínez-Chantar
authors.forename: José M
authors.initials: JM
authors.lastname: Mato
authors.forename: Shelly C
authors.initials: SC
authors.lastname: Lu
mesh_terms: D000818:Animals; D061745:Antioxidant Response Elements; D001483:Base Sequence; D001665:Binding Sites; D045744:Cell Line, Tumor; D002780:Cholestasis, Intrahepatic / Q000378:metabolism*; D015870:Gene Expression; D005721:Glutamate-Cysteine Ligase / Q000378:metabolism; D005978:Glutathione / Q000096:biosynthesis*; D006801:Humans; D008297:Male; D008810:Mice, Inbred C57BL; D035683:MicroRNAs / Q000235:genetics*; D051267:NF-E2-Related Factor 2 / Q000235:genetics / Q000378:metabolism; D000091402:Prohibitins; D011485:Protein Binding; D016271:Proto-Oncogene Proteins c-myc / Q000378:metabolism*; D034622:RNA Interference; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D035683:MicroRNAs; C540674:Mirn27 microRNA, mouse; C489428:Myc protein, mouse; D051267:NF-E2-Related Factor 2; C495636:Nfe2l2 protein, mouse; C000717328:PHB protein, human; D000091402:Prohibitins; D016271:Proto-Oncogene Proteins c-myc; D012097:Repressor Proteins; D005721:Glutamate-Cysteine Ligase; D005978:Glutathione