Regulated in Development and DNA Damage Responses -1 (REDD1) Protein Contributes to Insulin Signaling Pathway in Adipocytes

Claire Regazzetti,Pascal Peraldi,Karine Dumas,Yannick Le Marchand-Brustel,Jean-François Tanti,Sophie Giorgetti-Peraldi,Thierry Alquier

doi:10.1371/journal.pone.0052154

Abstract

REDD1 (Regulated in development and DNA damage response 1) is a hypoxia and stress response gene and is a negative regulator of mTORC1. Since mTORC1 is involved in the negative feedback loop of insulin signaling, we have studied the role of REDD1 on insulin signaling pathway and its regulation by insulin. In human and murine adipocytes, insulin transiently stimulates REDD1 expression through a MEK dependent pathway. In HEK-293 cells, expression of a constitutive active form of MEK stabilizes REDD1 and protects REDD1 from proteasomal degradation mediated by CUL4A-DDB1 ubiquitin ligase complex. In 3T3-L1 adipocytes, silencing of REDD1 with siRNA induces an increase of mTORC1 activity as well as an inhibition of insulin signaling pathway and lipogenesis. Rapamycin, a mTORC1 inhibitor, restores the insulin signaling after downregulation of REDD1 expression. This observation suggests that REDD1 positively regulates insulin signaling through the inhibition of mTORC1 activity. In conclusion, our results demonstrate that insulin increases REDD1 expression, and that REDD1 participates in the biological response to insulin.

Highlights

REDD1 (Regulated in development and DNA damage response 1) known as DDIT4 or RTP801 has been identified as a stressinduced protein in 2002 [1,2]
Since Mammalian target of rapamycin complex 1 (mTORC1) participates in insulin signaling pathway, we have explored the role of REDD1 in insulin signaling
Differentiated human mesenchymal stem cells differentiated in adipocytes (hMADS) and 3T3-L1 adipocytes were stimulated with insulin from 0 to 60 minutes, and REDD1 protein levels and phosphorylation of ERK1 and ERK2 were evaluated by Western blots (Figure 1)

Summary

Introduction

REDD1 (Regulated in development and DNA damage response 1) known as DDIT4 or RTP801 has been identified as a stressinduced protein in 2002 [1,2]. Its expression is induced in response to hypoxia, stress and DNA damages through the activation of distinct transcription factors. Hypoxia and CoCl2 stimulate REDD1 expression through HIF-1 (Hypoxia Inducible Factor) transcription factor [2,3], while oxidative stress and reticulum endoplasmic stress regulate REDD1 expression through ATF4-C/EBPb and DNA damages by p53/ p63 [1,4,5]. MTOR is the catalytic component of two multiproteins complexes, mTORC1 and mTORC2. Even if the two complexes are composed of mTOR, they are activated through different mechanisms and display different cellular functions. Even if the two complexes are composed of mTOR, they are activated through different mechanisms and display different cellular functions. mTORC1 regulates the rate of protein synthesis by controlling mRNA translation initiation and progression, ribosome biogenesis and autophagy, while mTORC2 regulates actin cytoskeletal organization and cell polarization [6,7]

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Results

Conclusion