MiR-128 Is Implicated in Stress Responses by Targeting MAFG in Skeletal Muscle Cells.

Rocco Caggiano,Rosario Ammendola,Ornella Moltedo,Cinzia Perrino,Raffaella Faraonio,Giovanni Esposito,Bruno Trimarco,Fabio Cattaneo

doi:10.1155/2017/9308310

Abstract

MAFG (v-Maf avian musculoaponeurotic fibrosarcoma oncogene homolog G) is a bZIP-type transcriptional regulator that belongs to the small MAF (sMAFs) protein family. By interacting with other bZIP transcription factors, sMAFs can form homo- and heterodimers governing either repressive or activating transcriptional functions. As heterodimeric partner of Nrf2, MAFG positively influences the ARE-dependent antioxidant/xenobiotic pathways, at least in condition of a correct MAFG:Nrf2 balance. MicroRNAs (miRs) participate to different regulatory networks being involved as fine-tuning regulators of gene expression. However, the connections between cellular surveillance to stresses mediated by MAFG:Nrf2 and miR regulations are not well understood. Here, we explored the impact of miR-128 in expression of genes related to stress response. Bioinformatic predictions coupled with functional analysis revealed the presence of miR-128 binding site in the 3′UTR of MAFG. Ectopic miR-128 expression correlated with reduced expression of endogenous MAFG-dependent genes and negatively affected ARE-mediated molecular phenotype based on Nrf2 activity. Indeed, miR-128 impairs redox-dependent pathways induced in response to oxidative stress. Moreover, in condition of hypoxia, MAFG induction correlated with reduced levels of miR-128. This lead to increased mRNA levels of HMOX-1 and x-CT for blunting stress. Overall, these findings identify MAFG as novel direct target of miR-128.

Highlights

In response to oxidative and xenobiotic stresses, cells activate numerous defense systems associated with both enzymatic and not enzymatic activities
Since Nrf2 and MAFG are transcription factors and both implicated in the activation of antioxidant responsive elements (ARE)-dependent transcription [8], we performed further analyses on these genes
To determine whether MAFG downregulation through miR-128 affects the basal transcription of an array of genes that are typically regulated by the Nrf2:MAFG heterodimer [8, 11], we examined the mRNA levels of representative genes such as GCLC, GSTA-1, NQO1, x-CT, and SQSTM1 in C2C12 cells overexpressing miR-128

Summary

Introduction

In response to oxidative and xenobiotic stresses, cells activate numerous defense systems associated with both enzymatic and not enzymatic activities. The events underlying these redox-related responses are accomplished by a tight regulation of gene expression patterns involving multilayered regulatory mechanisms [1, 2]. In the form of heterodimer, the complex Nrf2:MAFG binds to and activates the transcription of antioxidant/xenobiotic genes harboring antioxidant responsive elements (ARE)/electrophile responsive elements (core ARE: TGACNNNGC), located in their transcription regulatory sequences [7, 8]. Each member of the MAF family harbors a basic-leucine zipper (b-ZIP) domain involved in DNA binding and in dimer formation, either with themselves or with different b-ZIP transcription factors, in particular Nrf2 [10, 11]. In addition to the b-ZIP domain, large Maf proteins possess an acidic transcriptional

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