A20 regulates IL-1-induced tolerant production of CXC chemokines in human mesangial cells via inhibition of MAPK signaling.

Hongbo Luo,Ruili Sun,Jinyue Hu,Xueting Liu,Manli Jiang,Yuming Liu,Lingjuan Liao,Qian Li

doi:10.1038/srep18007

Abstract

Chemokines and chemokine receptors are involved in the resolution or progression of renal diseases. Locally secreted chemokines mediated leukocyte recruitment during the initiation and amplification phase of renal inflammation. However, the regulation of chemokine induction is not fully understood. In this study, we found that IL-1 induced a significant up-regulation of CXC chemokines CXCL1, 2, and 8 at both mRNA and protein levels in human mesangial cells. The induction of chemokines was tolerant, as the pre-treatment of HMC with IL-1 down-regulated the induction of chemokines induced by IL-1 re-stimulation. IL-1 up-regulated the ubiquintin-editing enzyme A20. A20 over-expression down-regulated IL-1-induced up-regulation of chemokines, and A20 down-regulation reversed chemokine inhibition induced by IL-1 pre-treatment, suggested that A20 played important roles in the tolerant production of chemokines. Unexpectedly, A20 over- expression inhibited the activation of ERK, JNK, and P38, but did not inhibit the activation of NF-κB. In addition, both IL-1 treatment and A20 over-expression induced the degradation of IRAK1, an important adaptor for IL-1R1 signaling, and A20 inhibition by RNA interference partly reversed the degradation of IRAK1. Taken together, IL-1-induced A20 negatively regulated chemokine production, suggesting that A20 may be an important target for the prevention and control of kidney inflammation.

Highlights

Chemokines are up-regulated by a lot of pro-inflammatory cytokines, such as TNF-α, IL-6, IFN-α, IL-1β, and IL-1α 4–10
We first detected the mesangial cell markers in human mesangial cells. Both RT-PCR and quantitative real time RT-PCR results showed that human mesangial cells expressed mesangial cell markers, including platelet-derived growth factor β - receptor (PDGFβ -R), α -smooth muscle actin (α -SMA), and Fibronectin, but did not express endothelial cell marker VE-Cadherin (Fig 1a,b)
We detected the effect of IL-1 on the expression of all CXC chemokines in human mesangeal cells, RT-PCR results showed that 20 ng/ml IL-1β or IL-1α induced up-regulation of CXCL1, 2, 3, and 8 (Fig. 1c,d). quantitative real time RT-PCR (qRT-PCR) results showed that IL-1 treatment led to an exaggerated induction of CXCL1, 2, 3, and 8 (Fig. 1e,f)

Summary

Introduction

Chemokines are up-regulated by a lot of pro-inflammatory cytokines, such as TNF-α , IL-6, IFN-α , IL-1β , and IL-1α 4–10. Toll-like receptors function to induce the production of chemokines[11,12,13,14]. By directly removing ubiquitin moieties from the signaling molecule TRAF6, A20 functions to terminate toll-like receptor-induced activity of the transcription factor NF-κ B and pro-inflammatory gene expression in macrophages[19]. The similarity of signal transduction between toll-like-receptors and IL-1 receptors, such as the equal adaptor molecules MyD88 (myeloid differentiation factor 88), IRAK (Interleukin-1 receptor activated kinase)[1, 2, 4], and TRAF6 (tumor necrosis factor receptor-associated factor 6)[20,21], suggests that A20 may function as negative regulator for chemokine production induced by IL-1. IL-1 -induced chemokines were regulated by A20 via inhibition of MAPK signaling

Methods

Results

Conclusion