Activation of a Novel c-Myc-miR27-Prohibitin 1 Circuitry in Cholestatic Liver Injury Inhibits Glutathione Synthesis in Mice

Abstract

Aims: 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 factorerythroid 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-Mycmediated 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. Innovation: 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. Antioxid. Redox Signal. 22,[259][260][261][262][263][264][265][266][267][268][269][270][271][272][273][274]

MicroRNA-mediated regulation of glutathione and methionine metabolism and its relevance for liver disease

“…C-Myc, which we had shown previously to be induced during BDL [54] and prohibitin 1 (PHB1), a well-known mitochondrial chaperone protein [55], also play important roles in modulating Nrf2-mediated ARE-dependent gene expression. Interestingly, c-Myc is thought to induce PHB1 at the transcriptional level but we found PHB1 expression fell despite the induction of c-Myc during cholestasis [53]. This was a result of c-Myc-mediated induction of miR27a/b, which targets both PHB1 and Nrf2 directly to reduce their expression.…”

“…Recently we described the involvement of miR-27a and miR-27b in downregulating GCLC and GCLM expression during chronic cholestatic liver injury by mechanisms that involve Nrf2 and a novel co-activator of ARE (Fig. 4) [53]. A variety of in vivo and in cellulo models, including bile duct ligation (BDL), in vivo lithocholic acid (LCA) treatment (gavage daily) and Huh-7 cells treated with LCA were employed.…”

“…These changes all work in concert to bring about down-regulation of GCLC and GCLM expression. Adapted from Yang et al [53]. …”

Oxidative stress response and Nrf2 signaling in aging

“…A very recent report from Yang and colleagues showed that Nrf2 signaling was down-regulated through a c-Myc-miR27a/b-PHB1 circuit. Lithocholic acid (LCA) induced c-Myc and reduced expression of Nrf2 and GCL in mice [370]. c-Myc promoted induction of microRNA 27a/b that targeted both PHB1 and Nrf2 to reduce their expression.…”

“…Knockdown of c-Myc or miR27a/b attenuated LCA-mediated suppression of Nrf2 and GCL expression. Furthermore, c-Myc directly interacted with Nrf2 and lowered Nrf2 binding to EpRE [370]. Indeed, c-Myc was negatively associated with expression of Nrf2-target genes in various tissues of mice [157, 371].…”